含负载前馈补偿的电流型PWM整流器改进无差拍控制

Improved Deadbeat Control of Current-Source PWM Rectifiers with Load Feed-Forward Compensation

针对三相电流源型PWM整流器直流侧电压-直流侧电流双闭环控制策略中动态响应速度较慢、参数整定复杂的问题,该文提出一种无差拍预测电流控制与负载功率前馈补偿相结合的改进控制策略。首先,分析三相电流源型PWM整流器在两相静止坐标系中的网侧离散化数学模型,在此基础上,电流内环采用无差拍控制跟踪网侧电流,但由于电感参数与控制延时的影响,将导致网侧电流控制精度及波形质量下降。针对此问题,该文采用改进型无差拍控制策略,并利用根轨迹法对电流内环稳定性能进行分析。在环路设计中,通过在外环上加入负载功率前馈等效电流,加快了系统动态响应,解决了负载突变时直流侧电压超调问题。最后,对传统方案和改进方案进行了对比仿真测试和样机实验,验证了所提控制策略的正确性。

In a three-phase current source PWM rectifier(CSR),it is necessary to maintain good dynamic performance and supply constant DC output voltage.However,the DC-side voltage and DC-side current double closed-loop control strategy has a slow dynamic response and is prone to an output voltage of DC-side overshoot during load sudden changes.Therefore,this paper proposes an improved control strategy scheme combined with deadbeat predictive current control and load power feedforward compensation.Firstly,based on the power conservation theory,the power relationship between the input side and the output side of the rectifier is analyzed,and the feedforward current is obtained as the reference current of the inner loop current by feedforward compensation of the DC side power.Secondly,the discrete mathematical model of a three-phase current source PWM rectifier in a two-phase static coordinate system is analyzed.The equation relationship between grid-side current&voltage and AC-side voltage is deduced from the mathematical model according to that the internal loop current is tracked by deadbeat control.However,due to the influence of inductance parameters and control delay,the grid-side current’s control accuracy and waveform quality will be degraded.Accordingly,an improved deadbeat control strategy is adopted.The control algorithm is predicted to the time k+2,and the current at the time k+1 is eliminated by the arithmetic iteration process.It can avoid the deepening of the assumption approximation,make the current at the time k directly related to the current at the time k+2,and simplify the calculation process.The results show that this method improves the control accuracy of grid-side current and reduces the current harmonic content.Finally,the root locus method is used to analyze the stability of the current inner loop.The comparative simulation and experimental results show that the improved scheme is superior to the conventional scheme in steady and dynamic conditions.Under steady-state conditions,the grid-side voltage and the grid-side current are in the same phase,and the grid-side current is sinusoidal at half-load and full-load operation.Its total harmonic distortion rate(THD)is 2.08%and 2.48%,respectively.The DC-side output voltage keeps stable output at a given value without voltage fluctuations.Under dynamic conditions,the output voltage of the DC side can quickly restore stability,regardless of the sudden increase or decrease of system load,and its fluctuation amplitude is less than 15V.The following conclusions can be drawn from the simulation and experimental analysis:(1)The proposed control strategy enables the CSR system to have good performance.Under different power loads,unit power factor operation can be realized.The current THD values are below the limits,the output voltage is stable,and the transient system response is rapid.(2)The dynamic response of the system can be effectively improved by introducing load power feedforward into the outer loop.When the load suddenly increases or decreases,the DC output voltage can be quickly restored to a given value,and the overshoot and undershoot voltages are effectively suppressed.