0 Introduction Today, the power systems of various countries in the world are developing more and more, and the operation of power systems is also becoming more and more complicated. It is more and more difficult for accidents to be predicted by traditional analysis methods. In China, with the construction of the Three Gorges Power Station, the implementation of the West-to-East Electricity Transmission Project, and the advancement of the nationwide networking project, a large-scale nationwide interconnected power grid will form in the early part of this century in China’s mainland. AC lines, and DC lines, also include power electronic devices such as reactive power compensators and FACTS devices, making the safe and stable operation of the power grid complicated. In order to improve the safe and stable operation of the power grid, higher requirements have been put forward for power system simulation technology. This article discusses the status and development trends of existing digital simulation software and systems for power systems.
1 off-line power system simulation technology off-line power system simulation is a digital computer for the physical process of the power system to establish a mathematical model, using mathematical methods to solve the process of simulation research, the simulation speed and the actual system of dynamic processes ranging.
According to the purpose of simulation, the mathematical model used by the power system simulation software can be linear or nonlinear, steady or time-varying, continuous or discrete, lumped or distributed parameters, deterministic or random, etc. Ignoring some minor factors is often a simplified model.
At present, power system offline simulation software uses different simulation methods for different dynamic processes. There are mainly three kinds of electromagnetic transient process simulation, electromechanical transient process simulation and mid-to-long term dynamic process simulation.
1.1 Electromagnetic transient process simulation The electromagnetic transient process digital simulation is a numerical simulation method to simulate the electromagnetic transient process from several microseconds to several seconds in the power system. The electromagnetic transient process simulation must take into account the characteristics of the transmission line distribution parameters and the frequency characteristics of the parameters, the electromagnetic and electromechanical transient processes of the generator, and the nonlinear characteristics of a series of components (lightning arrestors, transformers, reactors, etc.). Therefore, mathematical models for electromagnetic transient simulation must establish algebraic or differential, partial differential equations for these components and systems. The commonly used numerical integration method is the implicit integration method.
Because the electromagnetic transient simulation requires not only the detailed nonlinear model of the dynamic components of the power system, but also the transient process of the network, it also needs to describe using differential equations, which makes the simulation scale of the electromagnetic transient simulation program limited. In the general electromagnetic transient simulation, the power system must be simplistic.
Electromagnetic transient programs (EMTPs) are commonly used in electromagnetic transient simulation programs. Since 1987, EMTP revisions have continued to develop on the basis of multinational cooperation. China Electric Power Research Institute ) EMTPE was developed based on EMTP. Programs with similar functions to those of EMTP include EMTDC (PSCAD) from the Manitoba DC Research Center in Canada, MicroTran from Columbia University in Canada, and NETOMAC from Siemens in Germany.
1.2 Simulation of Electromechanical Transient Process Simulation The electromechanical transient process simulation mainly focuses on the transient stability of a power system subjected to large disturbances and the static stability of a power system subjected to small disturbances. The transient stability analysis is the study of the power system's dynamic behavior and the ability to maintain synchronous and stable operation under the influence of large disturbances such as short-circuit faults, cut off lines, generators, loads, generators lose excitation or impact loads.
The algorithm of electromechanical transient simulation for power systems is to solve the differential equations and algebraic equations of power systems simultaneously to obtain the time domain solution of physical quantities. The methods for solving differential equations include implicit trapezoidal integration, improved Euler's method, Runge-Kutta method, etc. Among them, the implicit trapezoidal integral method has been used more and more due to its good numerical stability. The method of solving algebraic equations mainly adopts Newton method suitable for solving nonlinear algebraic equations. According to the order of solving differential equations and algebraic equations, it can be divided into alternating solutions and simultaneous solutions.
At present, the commonly used electromechanical transient simulation programs in China are the Power System Synthesis Program (PSASP) [1] and the Chinese version of the BPA power system analysis program. Commonly used internationally are PTS/E of PTI Corporation of USA, ETMSP [2] of EPRI of the United States, and programs developed by International Electric Industry Company such as ABB's SYMPOW program [3] and Germany's Siemens's NETOMAC[4] also organic electrical transients. Simulation function.
1.3 Mid-term and long-term dynamic process simulation The long-term dynamic process simulation of power system is a long-term dynamic simulation of the power system after disturbance. It is necessary to count the long process and slow dynamics of the power system that are not considered in the simulation of the general transient stability process. Characteristics, including the dynamic response of power plant thermal and hydraulic systems and nuclear reaction systems, and the dynamic behavior of relay protection systems and automatic control systems. The long-period dynamic stability calculation can range from tens of seconds to tens of minutes, or even hours. Mainly used to analyze the dynamic characteristics of the power system for a long time.
As with the transient stability calculation of power systems, long-term process stability calculations for power systems are also the simultaneous solving of differential equation sets describing the dynamic element pairs of the system and algebraic equations describing the network characteristics of the system to obtain a time-domain solution of the long-term dynamic stability of the power system. . However, the response time constant of the long process dynamics of the power system is from tens of milliseconds to more than 100 seconds. It is a typical rigid system and requires an implicit integration algorithm. In order to avoid long calculation time, automatic variable step length calculation technology must also be adopted.
At present, the main international long-term dynamic stability calculation programs include [5]: EUROSTAG program developed by French Electric Power Company [6], LTSP program of American Electric Power Research Institute [7], General Electric Company of the United States and Tokyo Electric Power Company of Japan. The jointly developed EXTAB program [8]; In addition, the US PTI PSS/E program [9] and Czech Power's MODES program also have long-term dynamic stability calculations.
2 Power System Real-time Simulation Technology Real-time power system simulation can be divided into digital simulation, physical simulation and digital-analog hybrid simulation. The simulation speed is exactly the same as the actual system dynamic process.
2.1 Development Process of Power System Real-time Simulation Technology The power system real-time simulation system has probably gone through the following three historical stages, mainly the following three types:
a. Based on the similarity theory, the dynamic simulation system of power system represented by the actual rotary motor is the earliest real-time simulation tool for power system research. The hardware of the power system simulation laboratory is usually composed of a number of scaled down motors, a number of redundant line models, power supplies, loads, switch models, and corresponding monitoring and control systems. It is commonly used to perform real-time simulation studies of electromechanical transients and dynamic processes in power systems. The main advantages of these devices are straightforward and clear physical meaning. The disadvantages are that the equipment is expensive, the area is large, the scale of the simulatable power system is limited by the scale of the device itself and the physical characteristics of the components, the scalability and compatibility of the device are poor, and it is difficult to promote in large quantities. They have played an important role in the development of the power system and will continue to play a role in the future.
b. The digital-analog hybrid real-time simulation system of the digital-analog hybrid real-time simulation system, except that the rotating elements such as the motor and the dynamic load are simulated with digital components, the rest of the components are basically the same as the components used in the movable mold. The flexibility of its use and the research scope of the power system have been greatly improved. The real-time simulation scope of the power system can already cover the whole process of the power system disturbance, ie the electromagnetic transient process, electromechanical transient process and dynamics can be simulated. The entire process of power system disturbances. The greatest advantage of the digital-analog hybrid real-time simulation system is its good numerical stability, and the scale of the simulation depends on the hardware scale. In the digital-analog hybrid simulation system, since components such as lines and transformers are analog components, digital components such as a generator are completely decoupled from each other through these analog components. Therefore, as long as the digital components such as a generator do not have numerical instability, The entire simulation system will not produce numerical oscillation problems.
Since the main part is still a physical model based on similarity theory, the digital-analog hybrid real-time simulation device also has the shortcomings of the above physical model, namely, the equipment is expensive, the land area is large, and the scale of the simulatable power system is limited by the scale of the device itself. The physical characteristics of the components, the device's scalability and compatibility are poor, and it is difficult to promote them in large quantities.
c. All-digital real-time simulation system Despite the fact that the power system dynamic simulation system and the digital-analog hybrid power system real-time simulation system play an important role in the real-time research of the power system, due to its long modeling cycle and poor repeatability, the laboratory Due to the large floor space and other reasons, people have not given up on the exploration of the all-digital real-time simulation system.
In the early 1990s, with the advent of commercial high-speed digital signal processors (DSPs), RTDS, the Manitoba DC Research Center of Canada, took the lead in introducing the world's first all-digital real-time simulation system (RTDS) for power systems. Following the RTDS company, the French Electric Power Company (EDF) and TEQSIM of the Quebec Hydropower Research Institute in Canada also carried out the development and research of the all-digital real-time simulation system.
All digital real-time simulation systems, regardless of their hardware platform, are based on multi-CPU parallel processing technology. The software downloaded to the CPU during system simulation determines which power system components the CPU simulates. In the case that the time step and the bandwidth of the I/O device satisfy the requirements, the system's primary component model depends only on the software and has nothing to do with the hardware. This remarkable feature provides users with sufficient room for future simulation of new components.
However, it should be noted that in all-digital power system real-time simulation systems, due to the influence of various factors such as communication, data exchange, and model algorithms between parallel processors, the problem of numerical instability becomes an important issue that limits the scale of simulation.
2.2 Application and Development of China's Power System Real-time Simulation The development history of China's power system real-time simulation has basically tracked the latest technologies in different stages of the development of real-time power system simulation in the world. The basic situation is as follows: In the early 1960s, assistance from the former Soviet Union The Institute of Electrical Engineering has built China's largest dynamic simulation laboratory for power systems; in the early 1980s, in order to analyze and study the electromagnetic transients of the 500 kV transmission system under construction in China, the Institute of Electrical Engineering and Wuhan Institute of High Voltage Research have come from PTI. TNA equipment was introduced separately; in the mid-1980s, in order to cooperate with the system debugging of Geshang DC project and the investigation and analysis of accidents after the project was put into operation and training of operating personnel, the early numbers were introduced from the original Swiss BBC company (now ABB). Model-combined HVDC simulation equipment; In 1996, in order to carry out real-time simulation studies on the transmission and distribution projects of the Three Gorges Project under construction in China, the Institute of Electrical Engineering introduced advanced digital-analog hybrid simulation system from TEQSIM of Canada; In the medium term, in order to track the trend of international real-time power system simulation technology development and 500k V. The need for on-site commissioning of relay protection and routine inspections. A small number of power companies and institutes of electricity, National Electric Power Research Institute of Electric Power Automation and some universities have introduced a small amount of RTDS devices; currently, the Institute of Electric Power is working to develop all-digital Real-time simulation system.
2.3 Typical all-digital real-time simulation system As far as all-digital real-time simulation equipment is concerned, there are currently three major international products: RTDS of the RTDS Division of the Manitoba DC Research Center in Canada, ARENE of the French Electricity Company (EDF), Hypersoft, Quebec TEQSIM, Canada.
2.3.1 RTDS System RTDS is the first all-digital real-time simulation device developed in the world, and its technology is mainly based on the Manitoba DC Research Center in Canada.
RTDS's parallel processor uses NEC's high-speed signal processor and AD's SHARCAD21062 high-speed signal processor. The processor's main board and software are developed in-house. The advantage of this approach is that it can make full use of the DSP's hardware resources, but today's rapid development of computer chip technology, this development model is not conducive to upgrading the hardware.
The software core of RTDS is EMTDC and the graphical interface is PSCAD.
2.3.2 HyperSim System The technology of TEQSIM, Quebec, Canada, is based on the Québec Institute for Hydropower (1REQ). IREQ has established the world's largest digital-analog hybrid real-time simulation system. Based on its digital-analog hybrid real-time simulation technology, TEQSIM has recently developed a fully digital power system real-time simulation system (HYPERSIM) in order to adapt to the development trend of real-time power system simulation technology.
Hypersil hardware uses a shared memory-based multi-CPU super-parallel processing computer such as the SGl2000 or multi-CPU Alpha workstation for parallel computing. Mainly used for electromagnetic transient simulation of power systems, the scale of simulation can be quite large, and can also be used for device testing. Among them, HYPERSIM based on SGl3200 server can also be used to simulate the dynamic characteristics of DC systems.
The software core of HYPERSIM is the EMTP program.
2.3.3 ARENE System ARENE is an all-digital real-time simulation system researched and developed by the French Electric Power Company (EDF). The system's hardware platform is a multi-processor HP-CONVEX parallel processing computer produced by HP. So far, the maximum number of CPUs for this parallel-processing computer has reached 64.
The hardware of ANENE system adopts standard components (such as HP's parallel processing computer and I/O interface board) that are available on the market. EDF only researches algorithms and related software for real-time simulation of power systems. At the same time, the real-time simulation system also provides user-defined functions based on the C language. With this function, users can define new component models themselves.
ARENE's software core is also an EMTP program.
2.3.4 Real-time Simulation System Based on PC Platform [10]
At present, the mature hardware equipment of all-digital real-time simulation system for power systems adopts DSP or workstations and servers based on RISC technology, and hardware equipment costs are relatively large. In order to save hardware equipment costs, the Institute of Electrical Engineering, Japan's Mitsubishi Electric Corporation, Columbia University, Canada and other units are using commercial computer (PC) as a hardware platform to develop a digital real-time simulation system for power systems.
The system consists of multiple high-end microcomputers that implement parallel processing of cluster computers through high-speed network connections. Its advantages are low price and good scalability, but the technology is relatively complicated. Currently, all of them are in the research stage and have not yet formed a product. However, this technology is a development direction of all-digital real-time simulation in the future.
3 Development trend of power system simulation technology With the development of power systems, higher requirements have been put forward for the safety and reliability of power systems; at the same time, with the application of a large number of advanced control devices for power systems, such as FACTS and power electronic devices, DC Transmission systems, relay protection devices, safety and stability monitoring devices, etc. put forward new requirements for power system simulation technology.
3.1 Hybrid Simulation of Electromagnetic and Electromechanical Transients The electromechanical transient simulation program of power systems based on fundamental wave, single-phase and phasor simulation technology cannot simulate the fast transient characteristics of power electronic devices such as HVDC and FACTS, and nonlinearity such as MOV. Waveform distortion caused by components. The current simulation program uses a quasi-steady state model for the simulation of HVDC and FACTS.
The electromagnetic transient simulation program is limited by the model and algorithm, and its simulation scale is not large. In the general electromagnetic transient simulation, the power system should be equivalenced and simplified.
As power electronic devices and other non-linear components such as HVDC and FACTS are widely used in power systems, the waveform distortion caused by these components and their rapid transient process have an increasing impact on the electromechanical transient process of the system. System electromagnetic transient simulation programs and electromechanical transient simulation programs have been difficult to adapt to modern power system simulation requirements. Therefore, it is necessary to develop power system simulation software that can simulate the electromagnetic transient process and electromechanical transient process.
There are two trends in the development of mixed simulation of electromagnetic transients and electromechanical transients: one is the development of a mature electromagnetic transient program in the direction of electromechanical transients, so that the electromagnetic transient program has both mathematical models and simulation capabilities for electromechanical transient processes. To overcome the shortage of electromagnetic transient program simulation small scale. The main idea is to divide large-scale power systems into subsystems that require electromagnetic transient simulation and subsystems that only perform electromechanical transient simulation, and perform electromagnetic transient simulation and electromechanical transient simulation separately at the boundary of each subsystem. Electromagnetic transient simulation and electromechanical transient simulation transfer [11-12]. Another trend is the development of a mature electromechanical transient program in the direction of electromagnetic transients. The main idea is the rapid transient process and nonlinear characteristics that have important influence on the electromechanical transient process in components such as power electronics in the electromechanical transient process. Conduct electromagnetic transient simulation to improve the simulation accuracy of electromechanical transient programs.
3.2 Dynamic simulation of the whole process In the situation that the long-distance transmission capacity of the power system is increasing and the overload problem of the transmission network is increasingly prominent, the transient stability and the long-term dynamic stability (including voltage stability) of the power system after transient stability are included. Problems will gradually become the main issue of the safe and stable operation of the power system, threatening the safe and stable operation of the power system. Analyze the long-term dynamic stability of the power system to avoid large-scale blackouts (such as the two large-scale power outages in the Western United States in 1996), and study effective measures to prevent accidents (ie, the third line) It is bound to become an important part of the calculation and analysis of the power system. Therefore, the development of a long process simulation program for power systems is very necessary.
Early power system long process simulation software generally ignores the electromechanical transient process at the beginning of the disturbance, assuming that the electromechanical oscillation of the entire network has subsided and the system frequency is consistent. However, the dynamic process of the power system (from the electromechanical transient process to the long process dynamics) is a continuous process and is not totally separated. The electromechanical transient process has an impact on the medium and long-term processes, and the medium- and long-term processes also have a role in the subsequent new transient process. Therefore, in the long process simulation, the electromechanical transient process must be simulated. Therefore, it is required to develop a practical whole-process dynamic simulation software for a power system.
The whole process of dynamic simulation of power system is to integrate the electromechanical transient process, medium-term process and long-term process of the power system. Its characteristic is to realize the fast electromechanical transient process and the slow middle-long-term dynamic process unified simulation. This is a typical rigid system that requires a rigid numerical integration method with an automatic variable step size technique.
3.3 Large-scale real-time simulation system A large number of advanced control and measurement devices for power systems, such as FACTS control devices, DC transmission control devices, relay protection devices, safety and stability monitoring devices (including wide-area measurement devices, etc. State and electromechanical transient real-time simulation devices are tested and verified before they can be put into practical use. Therefore, the development of digital or analog-digital hybrid power system real-time simulation devices is a must.
However, the simulation scale of current real-time simulation devices (including all-digital and digital-analog hybrid) is not large. In large-scale power grid simulation tests, large-scale equivalent simplifications are needed to make the application of real-time simulation devices special. It is a large-scale simulation study on the electromechanical transient and dynamic characteristics of large power grids. Therefore, there is a need to develop large-scale power system real-time simulation devices.
Due to the limitations of laboratory scale and physical equipment, the simulation scale of real-time simulation equipment of digital-analog hybrid power systems cannot be expanded indefinitely. However, with the rapid development of computer software and hardware technology, continuous improvement of computing technology, and increasingly perfect simulation technology, the all-digital power system real-time simulation device is expected to have the ability to perform real-time simulation of large-scale power systems.
4 Conclusion For the current technical level, the power system real-time simulation system is characterized by the simulation of real-time power system process, can be a unified simulation of the power system's electromagnetic transient process, electromechanical transient process and the follow-up dynamic process, can take people to the actual The physical device performs simulation tests; however, due to the requirements of real-time simulation and the limitations of the hardware scale of the simulation system, the scale of the power system that the general real-time simulation system can simulate is always limited. Real-time digital simulation is mainly applicable to the detailed study of the transient and dynamic processes of the backbone network and local systems of large power systems, as well as the experimental research of physical devices.
The scale of power system off-line simulation is basically unlimited, and it can simulate a large-scale power system more completely. It is suitable for studying the complex transient and dynamic processes of large-scale power systems. But the offline calculation program can not be connected to the actual physical device for simulation. For the simulation of the new power system physical device, an accurate mathematical model is needed. In addition to the theoretical analysis, the mathematical model needs to be verified by simulation test. Therefore, the power system real-time digital simulation system and off-line calculation program are complementary, and the two cannot replace each other.
Finally, it should be pointed out that the correct selection of power system mathematical models and parameters is the basis of power system simulation. A large number of power system engineering studies and accident simulations have shown that models and parameters have a significant impact on power system simulation accuracy and reliability [13]. Therefore, the study of power system model and parameters is an important foundation in the development of power system simulation technology and should be studied in depth.
1 off-line power system simulation technology off-line power system simulation is a digital computer for the physical process of the power system to establish a mathematical model, using mathematical methods to solve the process of simulation research, the simulation speed and the actual system of dynamic processes ranging.
According to the purpose of simulation, the mathematical model used by the power system simulation software can be linear or nonlinear, steady or time-varying, continuous or discrete, lumped or distributed parameters, deterministic or random, etc. Ignoring some minor factors is often a simplified model.
At present, power system offline simulation software uses different simulation methods for different dynamic processes. There are mainly three kinds of electromagnetic transient process simulation, electromechanical transient process simulation and mid-to-long term dynamic process simulation.
1.1 Electromagnetic transient process simulation The electromagnetic transient process digital simulation is a numerical simulation method to simulate the electromagnetic transient process from several microseconds to several seconds in the power system. The electromagnetic transient process simulation must take into account the characteristics of the transmission line distribution parameters and the frequency characteristics of the parameters, the electromagnetic and electromechanical transient processes of the generator, and the nonlinear characteristics of a series of components (lightning arrestors, transformers, reactors, etc.). Therefore, mathematical models for electromagnetic transient simulation must establish algebraic or differential, partial differential equations for these components and systems. The commonly used numerical integration method is the implicit integration method.
Because the electromagnetic transient simulation requires not only the detailed nonlinear model of the dynamic components of the power system, but also the transient process of the network, it also needs to describe using differential equations, which makes the simulation scale of the electromagnetic transient simulation program limited. In the general electromagnetic transient simulation, the power system must be simplistic.
Electromagnetic transient programs (EMTPs) are commonly used in electromagnetic transient simulation programs. Since 1987, EMTP revisions have continued to develop on the basis of multinational cooperation. China Electric Power Research Institute ) EMTPE was developed based on EMTP. Programs with similar functions to those of EMTP include EMTDC (PSCAD) from the Manitoba DC Research Center in Canada, MicroTran from Columbia University in Canada, and NETOMAC from Siemens in Germany.
1.2 Simulation of Electromechanical Transient Process Simulation The electromechanical transient process simulation mainly focuses on the transient stability of a power system subjected to large disturbances and the static stability of a power system subjected to small disturbances. The transient stability analysis is the study of the power system's dynamic behavior and the ability to maintain synchronous and stable operation under the influence of large disturbances such as short-circuit faults, cut off lines, generators, loads, generators lose excitation or impact loads.
The algorithm of electromechanical transient simulation for power systems is to solve the differential equations and algebraic equations of power systems simultaneously to obtain the time domain solution of physical quantities. The methods for solving differential equations include implicit trapezoidal integration, improved Euler's method, Runge-Kutta method, etc. Among them, the implicit trapezoidal integral method has been used more and more due to its good numerical stability. The method of solving algebraic equations mainly adopts Newton method suitable for solving nonlinear algebraic equations. According to the order of solving differential equations and algebraic equations, it can be divided into alternating solutions and simultaneous solutions.
At present, the commonly used electromechanical transient simulation programs in China are the Power System Synthesis Program (PSASP) [1] and the Chinese version of the BPA power system analysis program. Commonly used internationally are PTS/E of PTI Corporation of USA, ETMSP [2] of EPRI of the United States, and programs developed by International Electric Industry Company such as ABB's SYMPOW program [3] and Germany's Siemens's NETOMAC[4] also organic electrical transients. Simulation function.
1.3 Mid-term and long-term dynamic process simulation The long-term dynamic process simulation of power system is a long-term dynamic simulation of the power system after disturbance. It is necessary to count the long process and slow dynamics of the power system that are not considered in the simulation of the general transient stability process. Characteristics, including the dynamic response of power plant thermal and hydraulic systems and nuclear reaction systems, and the dynamic behavior of relay protection systems and automatic control systems. The long-period dynamic stability calculation can range from tens of seconds to tens of minutes, or even hours. Mainly used to analyze the dynamic characteristics of the power system for a long time.
As with the transient stability calculation of power systems, long-term process stability calculations for power systems are also the simultaneous solving of differential equation sets describing the dynamic element pairs of the system and algebraic equations describing the network characteristics of the system to obtain a time-domain solution of the long-term dynamic stability of the power system. . However, the response time constant of the long process dynamics of the power system is from tens of milliseconds to more than 100 seconds. It is a typical rigid system and requires an implicit integration algorithm. In order to avoid long calculation time, automatic variable step length calculation technology must also be adopted.
At present, the main international long-term dynamic stability calculation programs include [5]: EUROSTAG program developed by French Electric Power Company [6], LTSP program of American Electric Power Research Institute [7], General Electric Company of the United States and Tokyo Electric Power Company of Japan. The jointly developed EXTAB program [8]; In addition, the US PTI PSS/E program [9] and Czech Power's MODES program also have long-term dynamic stability calculations.
2 Power System Real-time Simulation Technology Real-time power system simulation can be divided into digital simulation, physical simulation and digital-analog hybrid simulation. The simulation speed is exactly the same as the actual system dynamic process.
2.1 Development Process of Power System Real-time Simulation Technology The power system real-time simulation system has probably gone through the following three historical stages, mainly the following three types:
a. Based on the similarity theory, the dynamic simulation system of power system represented by the actual rotary motor is the earliest real-time simulation tool for power system research. The hardware of the power system simulation laboratory is usually composed of a number of scaled down motors, a number of redundant line models, power supplies, loads, switch models, and corresponding monitoring and control systems. It is commonly used to perform real-time simulation studies of electromechanical transients and dynamic processes in power systems. The main advantages of these devices are straightforward and clear physical meaning. The disadvantages are that the equipment is expensive, the area is large, the scale of the simulatable power system is limited by the scale of the device itself and the physical characteristics of the components, the scalability and compatibility of the device are poor, and it is difficult to promote in large quantities. They have played an important role in the development of the power system and will continue to play a role in the future.
b. The digital-analog hybrid real-time simulation system of the digital-analog hybrid real-time simulation system, except that the rotating elements such as the motor and the dynamic load are simulated with digital components, the rest of the components are basically the same as the components used in the movable mold. The flexibility of its use and the research scope of the power system have been greatly improved. The real-time simulation scope of the power system can already cover the whole process of the power system disturbance, ie the electromagnetic transient process, electromechanical transient process and dynamics can be simulated. The entire process of power system disturbances. The greatest advantage of the digital-analog hybrid real-time simulation system is its good numerical stability, and the scale of the simulation depends on the hardware scale. In the digital-analog hybrid simulation system, since components such as lines and transformers are analog components, digital components such as a generator are completely decoupled from each other through these analog components. Therefore, as long as the digital components such as a generator do not have numerical instability, The entire simulation system will not produce numerical oscillation problems.
Since the main part is still a physical model based on similarity theory, the digital-analog hybrid real-time simulation device also has the shortcomings of the above physical model, namely, the equipment is expensive, the land area is large, and the scale of the simulatable power system is limited by the scale of the device itself. The physical characteristics of the components, the device's scalability and compatibility are poor, and it is difficult to promote them in large quantities.
c. All-digital real-time simulation system Despite the fact that the power system dynamic simulation system and the digital-analog hybrid power system real-time simulation system play an important role in the real-time research of the power system, due to its long modeling cycle and poor repeatability, the laboratory Due to the large floor space and other reasons, people have not given up on the exploration of the all-digital real-time simulation system.
In the early 1990s, with the advent of commercial high-speed digital signal processors (DSPs), RTDS, the Manitoba DC Research Center of Canada, took the lead in introducing the world's first all-digital real-time simulation system (RTDS) for power systems. Following the RTDS company, the French Electric Power Company (EDF) and TEQSIM of the Quebec Hydropower Research Institute in Canada also carried out the development and research of the all-digital real-time simulation system.
All digital real-time simulation systems, regardless of their hardware platform, are based on multi-CPU parallel processing technology. The software downloaded to the CPU during system simulation determines which power system components the CPU simulates. In the case that the time step and the bandwidth of the I/O device satisfy the requirements, the system's primary component model depends only on the software and has nothing to do with the hardware. This remarkable feature provides users with sufficient room for future simulation of new components.
However, it should be noted that in all-digital power system real-time simulation systems, due to the influence of various factors such as communication, data exchange, and model algorithms between parallel processors, the problem of numerical instability becomes an important issue that limits the scale of simulation.
2.2 Application and Development of China's Power System Real-time Simulation The development history of China's power system real-time simulation has basically tracked the latest technologies in different stages of the development of real-time power system simulation in the world. The basic situation is as follows: In the early 1960s, assistance from the former Soviet Union The Institute of Electrical Engineering has built China's largest dynamic simulation laboratory for power systems; in the early 1980s, in order to analyze and study the electromagnetic transients of the 500 kV transmission system under construction in China, the Institute of Electrical Engineering and Wuhan Institute of High Voltage Research have come from PTI. TNA equipment was introduced separately; in the mid-1980s, in order to cooperate with the system debugging of Geshang DC project and the investigation and analysis of accidents after the project was put into operation and training of operating personnel, the early numbers were introduced from the original Swiss BBC company (now ABB). Model-combined HVDC simulation equipment; In 1996, in order to carry out real-time simulation studies on the transmission and distribution projects of the Three Gorges Project under construction in China, the Institute of Electrical Engineering introduced advanced digital-analog hybrid simulation system from TEQSIM of Canada; In the medium term, in order to track the trend of international real-time power system simulation technology development and 500k V. The need for on-site commissioning of relay protection and routine inspections. A small number of power companies and institutes of electricity, National Electric Power Research Institute of Electric Power Automation and some universities have introduced a small amount of RTDS devices; currently, the Institute of Electric Power is working to develop all-digital Real-time simulation system.
2.3 Typical all-digital real-time simulation system As far as all-digital real-time simulation equipment is concerned, there are currently three major international products: RTDS of the RTDS Division of the Manitoba DC Research Center in Canada, ARENE of the French Electricity Company (EDF), Hypersoft, Quebec TEQSIM, Canada.
2.3.1 RTDS System RTDS is the first all-digital real-time simulation device developed in the world, and its technology is mainly based on the Manitoba DC Research Center in Canada.
RTDS's parallel processor uses NEC's high-speed signal processor and AD's SHARCAD21062 high-speed signal processor. The processor's main board and software are developed in-house. The advantage of this approach is that it can make full use of the DSP's hardware resources, but today's rapid development of computer chip technology, this development model is not conducive to upgrading the hardware.
The software core of RTDS is EMTDC and the graphical interface is PSCAD.
2.3.2 HyperSim System The technology of TEQSIM, Quebec, Canada, is based on the Québec Institute for Hydropower (1REQ). IREQ has established the world's largest digital-analog hybrid real-time simulation system. Based on its digital-analog hybrid real-time simulation technology, TEQSIM has recently developed a fully digital power system real-time simulation system (HYPERSIM) in order to adapt to the development trend of real-time power system simulation technology.
Hypersil hardware uses a shared memory-based multi-CPU super-parallel processing computer such as the SGl2000 or multi-CPU Alpha workstation for parallel computing. Mainly used for electromagnetic transient simulation of power systems, the scale of simulation can be quite large, and can also be used for device testing. Among them, HYPERSIM based on SGl3200 server can also be used to simulate the dynamic characteristics of DC systems.
The software core of HYPERSIM is the EMTP program.
2.3.3 ARENE System ARENE is an all-digital real-time simulation system researched and developed by the French Electric Power Company (EDF). The system's hardware platform is a multi-processor HP-CONVEX parallel processing computer produced by HP. So far, the maximum number of CPUs for this parallel-processing computer has reached 64.
The hardware of ANENE system adopts standard components (such as HP's parallel processing computer and I/O interface board) that are available on the market. EDF only researches algorithms and related software for real-time simulation of power systems. At the same time, the real-time simulation system also provides user-defined functions based on the C language. With this function, users can define new component models themselves.
ARENE's software core is also an EMTP program.
2.3.4 Real-time Simulation System Based on PC Platform [10]
At present, the mature hardware equipment of all-digital real-time simulation system for power systems adopts DSP or workstations and servers based on RISC technology, and hardware equipment costs are relatively large. In order to save hardware equipment costs, the Institute of Electrical Engineering, Japan's Mitsubishi Electric Corporation, Columbia University, Canada and other units are using commercial computer (PC) as a hardware platform to develop a digital real-time simulation system for power systems.
The system consists of multiple high-end microcomputers that implement parallel processing of cluster computers through high-speed network connections. Its advantages are low price and good scalability, but the technology is relatively complicated. Currently, all of them are in the research stage and have not yet formed a product. However, this technology is a development direction of all-digital real-time simulation in the future.
3 Development trend of power system simulation technology With the development of power systems, higher requirements have been put forward for the safety and reliability of power systems; at the same time, with the application of a large number of advanced control devices for power systems, such as FACTS and power electronic devices, DC Transmission systems, relay protection devices, safety and stability monitoring devices, etc. put forward new requirements for power system simulation technology.
3.1 Hybrid Simulation of Electromagnetic and Electromechanical Transients The electromechanical transient simulation program of power systems based on fundamental wave, single-phase and phasor simulation technology cannot simulate the fast transient characteristics of power electronic devices such as HVDC and FACTS, and nonlinearity such as MOV. Waveform distortion caused by components. The current simulation program uses a quasi-steady state model for the simulation of HVDC and FACTS.
The electromagnetic transient simulation program is limited by the model and algorithm, and its simulation scale is not large. In the general electromagnetic transient simulation, the power system should be equivalenced and simplified.
As power electronic devices and other non-linear components such as HVDC and FACTS are widely used in power systems, the waveform distortion caused by these components and their rapid transient process have an increasing impact on the electromechanical transient process of the system. System electromagnetic transient simulation programs and electromechanical transient simulation programs have been difficult to adapt to modern power system simulation requirements. Therefore, it is necessary to develop power system simulation software that can simulate the electromagnetic transient process and electromechanical transient process.
There are two trends in the development of mixed simulation of electromagnetic transients and electromechanical transients: one is the development of a mature electromagnetic transient program in the direction of electromechanical transients, so that the electromagnetic transient program has both mathematical models and simulation capabilities for electromechanical transient processes. To overcome the shortage of electromagnetic transient program simulation small scale. The main idea is to divide large-scale power systems into subsystems that require electromagnetic transient simulation and subsystems that only perform electromechanical transient simulation, and perform electromagnetic transient simulation and electromechanical transient simulation separately at the boundary of each subsystem. Electromagnetic transient simulation and electromechanical transient simulation transfer [11-12]. Another trend is the development of a mature electromechanical transient program in the direction of electromagnetic transients. The main idea is the rapid transient process and nonlinear characteristics that have important influence on the electromechanical transient process in components such as power electronics in the electromechanical transient process. Conduct electromagnetic transient simulation to improve the simulation accuracy of electromechanical transient programs.
3.2 Dynamic simulation of the whole process In the situation that the long-distance transmission capacity of the power system is increasing and the overload problem of the transmission network is increasingly prominent, the transient stability and the long-term dynamic stability (including voltage stability) of the power system after transient stability are included. Problems will gradually become the main issue of the safe and stable operation of the power system, threatening the safe and stable operation of the power system. Analyze the long-term dynamic stability of the power system to avoid large-scale blackouts (such as the two large-scale power outages in the Western United States in 1996), and study effective measures to prevent accidents (ie, the third line) It is bound to become an important part of the calculation and analysis of the power system. Therefore, the development of a long process simulation program for power systems is very necessary.
Early power system long process simulation software generally ignores the electromechanical transient process at the beginning of the disturbance, assuming that the electromechanical oscillation of the entire network has subsided and the system frequency is consistent. However, the dynamic process of the power system (from the electromechanical transient process to the long process dynamics) is a continuous process and is not totally separated. The electromechanical transient process has an impact on the medium and long-term processes, and the medium- and long-term processes also have a role in the subsequent new transient process. Therefore, in the long process simulation, the electromechanical transient process must be simulated. Therefore, it is required to develop a practical whole-process dynamic simulation software for a power system.
The whole process of dynamic simulation of power system is to integrate the electromechanical transient process, medium-term process and long-term process of the power system. Its characteristic is to realize the fast electromechanical transient process and the slow middle-long-term dynamic process unified simulation. This is a typical rigid system that requires a rigid numerical integration method with an automatic variable step size technique.
3.3 Large-scale real-time simulation system A large number of advanced control and measurement devices for power systems, such as FACTS control devices, DC transmission control devices, relay protection devices, safety and stability monitoring devices (including wide-area measurement devices, etc. State and electromechanical transient real-time simulation devices are tested and verified before they can be put into practical use. Therefore, the development of digital or analog-digital hybrid power system real-time simulation devices is a must.
However, the simulation scale of current real-time simulation devices (including all-digital and digital-analog hybrid) is not large. In large-scale power grid simulation tests, large-scale equivalent simplifications are needed to make the application of real-time simulation devices special. It is a large-scale simulation study on the electromechanical transient and dynamic characteristics of large power grids. Therefore, there is a need to develop large-scale power system real-time simulation devices.
Due to the limitations of laboratory scale and physical equipment, the simulation scale of real-time simulation equipment of digital-analog hybrid power systems cannot be expanded indefinitely. However, with the rapid development of computer software and hardware technology, continuous improvement of computing technology, and increasingly perfect simulation technology, the all-digital power system real-time simulation device is expected to have the ability to perform real-time simulation of large-scale power systems.
4 Conclusion For the current technical level, the power system real-time simulation system is characterized by the simulation of real-time power system process, can be a unified simulation of the power system's electromagnetic transient process, electromechanical transient process and the follow-up dynamic process, can take people to the actual The physical device performs simulation tests; however, due to the requirements of real-time simulation and the limitations of the hardware scale of the simulation system, the scale of the power system that the general real-time simulation system can simulate is always limited. Real-time digital simulation is mainly applicable to the detailed study of the transient and dynamic processes of the backbone network and local systems of large power systems, as well as the experimental research of physical devices.
The scale of power system off-line simulation is basically unlimited, and it can simulate a large-scale power system more completely. It is suitable for studying the complex transient and dynamic processes of large-scale power systems. But the offline calculation program can not be connected to the actual physical device for simulation. For the simulation of the new power system physical device, an accurate mathematical model is needed. In addition to the theoretical analysis, the mathematical model needs to be verified by simulation test. Therefore, the power system real-time digital simulation system and off-line calculation program are complementary, and the two cannot replace each other.
Finally, it should be pointed out that the correct selection of power system mathematical models and parameters is the basis of power system simulation. A large number of power system engineering studies and accident simulations have shown that models and parameters have a significant impact on power system simulation accuracy and reliability [13]. Therefore, the study of power system model and parameters is an important foundation in the development of power system simulation technology and should be studied in depth.
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