Research On Power Balance Coordinated Control Strategy For Double PWM Frequency Conversion

As the dual PWM converter can achieve the unit power factor output,energy bidirectional flow,the net side of the current sine,etc.It widely be used in the field of AC frequency control.From the perspective of system energy flow,based on the energy mathematical model of the PWM rectifier,the influence of energy imbalance on the system is analyzed.Based on the traditional PI control of PWM rectifier,a method of power dynamic compensation is proposed.It can restrain the fluctuation of the DC bus voltage when load power suddenly change,improve the steady-state performance of the system and reduce the harmonic of the network side current.The energy of PWM rectifier nonlinear energy storage devices such as: inductance,capacitance is periodically dynamic compensated to reduce the system non-linear error.According to the energy balance relationship of the dual PWM converter,a dynamic load power feed-forward method is proposed based on the traditional load power feed-forward method and power dynamic compensation method.It realizes the coordinated control of the rectifier side and the inverter side of the double PWM converter.According to the system transfer function to determine the compensation cycle and feed forward load power and compensation power to the rectifier side to reduce the DC side capacitor capacity,improve the system response speed,while suppressing DC bus voltage fluctuations.To simplify the system control structure and further improve the system response speed,using predictive model algorithm to replace the rectifier power inner loop PI control structure based on the power mathematical model of PWM rectifier.Building value function to reduce the error of power reference value and actual output power and introduce the power compensation algorithm to improve the overall performance of the system.Using power compensation value and the load power value as the active power command value of model prediction to improve the robustness of the system and reduce the sensitivity for system parameters.Treating inverter and three-phase asynchronous motor as one part,using rotor flux linkage oriented vector control controls motor torque current and exciting current independently.According to simulation result,system adopts power compensation arithmetic can effectively restrain DC-bus voltage fluctuation and reduce harmonic component of grid-side when motor power suddenly change.Using control method of combine model prediction algorithm with power compensation arithmetic can improve systemrespond speed and steady-state performance.System uses the both control method can realize double PWM coordination control and have some practical value in engineering application.