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| An FPGA-Based General Solver for Electromagnetic Transient Real-Time Simulation of Power Electronic Systems |
| Zhou Bin, Wang Guangsen, Li Weichao, Wang Zhiwei, Jie Guisheng |
| National Key Laboratory for Vessel Integrated Power System Technology Naval University of Engineering Wuhan 430033 China |
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Abstract As the frequency of power electronic switches increases, the traditional electromagnetic transient (EMT) real-time simulation based on CPUs fails to describe the high-frequency characteristics of switches accurately. It has become a trend to take FPGAs as the hardware platforms for real-time simulation. However, the following challenges exist: (1) the high programming threshold and long development cycle make it difficult to conduct a real-time simulation based on FPGAs; (2) it is hard to ensure the real-time performance of simulation while completing high complexity and large-scale iterative calculation. Therefore, this paper proposes a real-time EMT simulation universal solver for power electronic systems based on FPGAs.
Firstly, a method that the node equation is reorganized into the form of a state space equation is proposed, and only the state quantity and measurement quantity in the simulation model are considered. As a result, the calculation quantity is reduced, and the calculation parallelism is increased. Secondly, the general framework of the FPGA real-time simulation solver is designed. The solver regards the fixed admittance matrix nodal method (FAMNM) as the switch modeling and circuit analysis method, and takes the multiply accumulator (MAC) for the basic computing unit. Its framework includes two parts, namely offline preprocessing and online calculation. The offline program of the solver can automatically obtain the parameters of the simulation models and generate the calculation data. A new organization method of FPGA ROM initialization data considering multiple simulation conditions is applied to improve the utilization of storage resources when generating calculation data, which splices and writes multiple data into the same initialization file. As the core of the online program, the matrix-vector multiplication (MVM) computing architecture can not only automatically configures computing resources and control logic according to parameters, but also automatically configure the reuse degree of resources by users. Finally, an implementation method of low-delay single-cycle floating-point accumulation is proposed. Rather than through a unidirectional shift, the alignment of the float-pointing accumulator is finished by a bidirectional shift, moving the shift alignment step out of the critical path of floating-point accumulation and realizing high-speed accumulation. The performance of the proposed solver is analyzed from two aspects of simulation speed and simulation scale: it can achieve a running speed of 400 MHz and a simulation step of 100 ns. Compared with the eHS solver from OPAL-RT under the same conditions, its simulation speed is doubled, and its simulation scale increases by 29.69 %~79.17 %. A two-level bridge converter and a three-level NPC converter are taken as test examples separately to verify the correctness and generality of the proposed solver. The real-time simulation at a high switching frequency is compared with the eHS solver based on an OP5700 simulator and the offline simulation based on Matlab. The results show that the maximum simulation errors of the proposed solver for the two examples are 3.47 % and 3.08 %, respectively.
The following conclusions can be drawn from the theoretical analysis and simulations. The proposed general solver based on FPGAs, with high-speed MAC as the basic computing unit, can achieve a running speed of 400 MHz, a simulation step of 100ns, and maintain a high simulation accuracy. It has the characteristics of strong versatility, high automation, and flexible configuration. Under the same hardware conditions, its simulation speed, simulation scale, resource utilization, and use flexibility are all superior to the eHS solver of OPAL-RT.
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Received: 26 May 2022
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2023, Vol. 38 
