抑制恒压恒频逆变器输出电压谐波的改进前馈策略

Improved Feedforward Strategy for Constant-Voltage Constant-Frequency Inverter for Suppressing Output Voltage Distortion

前馈控制能够预测输出随扰动变化的规律,使输出偏差产生之前即被纠正,将其应用于恒压恒频逆变器可以抑制负载电流对输出电压的影响。比例微分前馈能够完全补偿基于模拟电路控制的逆变器负载电流扰动,使之获得良好的输出电压波形,然而,在基于数字电路控制的恒压恒频逆变器中,比例微分前馈不能纠正负载电流谐波通过控制延时环节产生的输出电压谐波,甚至放大该谐波,恶化输出电能质量。以单相LC滤波的恒压恒频逆变器为研究对象,建立了数字电路控制的逆变器s域模型,揭示了逆变器带非线性负载输出电压总谐波畸变率升高的机理,从阻抗模型的角度分析了比例微分前馈控制造成谐波放大的原因,据此提出了基于多谐振控制器的前馈策略,并给出前馈环节参数设计方法。实验结果验证了所提改进前馈策略的可行性,以及在抑制输出电压谐波方面的优越性。

Feedforward control can predict output tendency under disturbance, so that the output deviation is corrected before generated. Applying it to a constant-voltage constant-frequency inverter can suppress influence of load current on output voltage. Proportional and differential feedforward can fully compensate load current disturbance of the inverter controlled with analog circuit to obtain a good output voltage waveform. However, in the constant-voltage constant-frequency inverter based on digital circuit control, proportional and differential feedforward cannot suppress harmonics in output voltage caused by load current harmonics over digital control delay, and may even amplify the harmonics and deteriorate output power quality. Taking single-phase LC-filtered constant-voltage constant-frequency inverter as research object, an s-domain model of the inverter controlled with digital circuit was established, and the mechanism of the higher harmonic distortion in output voltage of the inverter with nonlinear load was revealed. From the perspective of impedance model, the reasons for harmonic amplification caused by proportional differential feedforward control were analyzed. Based on this, a feedforward strategy based on a multi-resonant controller is proposed, and the design method of the feedforward link parameters is given. Experimental results verify feasibility of the proposed feedforward strategy and its superiority in suppressing output voltage harmonics.