| Power hardware in the loop(PHIL)simulation,combining advantages of digital simulation and physical experiments,can effectively analyze the steadystate characteristics of large-scale power grids and accurately simulate the dynamic characteristics of power electronic devices.It brings great flexibility to the theoretical research and engineering design of the flexible DC transmission.In the PHIL simulation of flexible DC transmission,the interface power amplifier needs to convert the digital side signal into the power signal to drive the active load on the physical side.On the one hand,the power output capability of the power amplifier is required to match the load on the physical side,on the other hand,the power amplifier is required to realize bidirectional power transmission.In addition,the bandwidth and delay of power amplifier will affect the accuracy and stability of simulation.However,it is difficult for the existing power amplifiers to meet the requirements of dynamic performance and power level at the same time.Firstly,this paper analyzes the influence of the delay and bandwidth of the power amplifier on the system.On this basis,the bandwidth and delay requirements of the power amplifier in the PHIL simulation of the flexible DC transmission are given.In view of the above requirements,a hybrid power amplifier topology is proposed,which is composed of switching amplifier and linear amplifier in series.Based on the detailed analysis of the topological working principle,it is proved that the topology combines the advantages of switching amplifier and linear amplifier,thus meeting the demand of dynamic performance and power level of the power amplifier in the digital physical hybrid simulation of flexible DC transmission.In order to achieve the expected performance of hybrid power amplifier topology,the paper further analyzes the influence of parameters on the key performance of hybrid power amplifier.According to the above influence,the design basis of the parameters in hybrid power amplifier is given.In addition,the control scheme of the hybrid power amplifier is designed in detail.The control of the switching power amplifier is mainly to ensure the balance of the capacitor voltage of the internal sub module and suppress the low-frequency harmonic of the switching power amplifier,so as to ensure the stability and output accuracy of the switching power amplifier.The linear power amplifier control is to make the linear power amplifier accurately compensate the error between the reference and the output of the switching power amplifier.After the above control design is completed,the closed-loop transfer function of the hybrid power amplifier is derived through simplification,and the analysis of the transfer function proves that the designed control scheme makes the hybrid power amplifier have higher small signal bandwidth.Finally,the hybrid power amplifier prototype is built,and the parameter design and control strategy of the hybrid power amplifier are verified in detail on the prototype. |
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