Hardware-in-the-loop Simulation Of Half-bridge Zero-current Switching Isolated DC-DC Converter

The fact that the topology of power electronic circuits(PEC)is becoming more and more complex,the number of switching devices and the working states are increasing bring challenges to the modelling work.The ideal switch model is commonly used,which treats the on-switch as zero resistance and the off-switch as zero conductance.The on-switch with zero resistance merges two points into one point,and the off-switch with zero conductance completes the opposite process,which contribute to a system matrix with variable structure and variable parameters.With the number of switching devices increasing,the method of ideal switch modelling becomes inefficient,and it is very difficult to solve the inverse of a large matrix in FPGA.So,modelling of the complex PEC which is applied to real-time simulation is the focus of this paper.As the switching frequency of PEC is getting higher,the required simulation step is becoming smaller.The simulation step of the real time emulator based on CPU is difficult to further reduce.In recent years,with the rapid development of FPGA,it is able to realize smaller simulation step,and has been widely used in real-time simulation.Firstly,this paper introduces the assiociated discrete circuit(ADC)method,derives the equivalent admittance Gs and the parallel current source,establishes the state machine to updates the switch state,and points out the defect of the ADC method.Taking the Buck circuit as an example,the switching process of ADC method is analyzed in detail.It is concluded that the current error is proportional to the equivalent admittance Gs,and the voltage error is inversely proportional to Gs.Secondly,this paper analyzes the relationship between switch loss(because of the modelling method)and equivalent admittance Gs,and gives the method of how to select the optimal Gs.The correctness of the optimal Gs selection is proved through the simulation of Buck circuit.By adding the damping resistance,the oscillation of the current and voltage is suppressed.The calculation method of the damping resistance under the optimal Gs is derived.Then,taking the zero-current switching isolated DC-DC converter as an example,the working principle of the converter has been analyzed,and the equivalent mathematical model of the converter based on ADC has been derived.The off-line simulation of the circuit and the simulation based on Sim Power System(SPS)have been completed,and the relative error of two groups of simulation has been shown,which means that this method is feasible.Finally,in dSPACE real-time simulation platform,the mathematical model of DC-DC converter based on FPGA is implemented.MCode module of System Generator is used to accelerate the implementation process of FPGA,and hardware in the loop(HIL)simulation is completed.The results of the HIL simulation are in agreement with the results of physical experiment,and the correctness of the ADC modelling and the effectiveness of FPGA implementation are further proved.