Due to the disparity of power modules, asymmetry of driving pulses and measurement errors of sensors, dc currents may be injected to grid-connected photovoltaic (PV) inverters. The dc current injection may cause magnetic saturation of the power transformers. To solve this issue, this article thus proposes an effective current control strategy and compensation method, which does not require any extra sensor and hardware circuit. First, the root-cause of dc current injection is comprehensively analyzed. Subsequently, a proportional-integral-resonant (PIR) controller is proposed to eliminate the dc component caused by disparity of power modules, asymmetry of driving pulses and measurement errors of grid voltage. The injected dc current caused by grid current measurement error is estimated from the line-frequency ripple of the dc-link voltage, and then it is suppressed by a feedback compensation controller. In addition, the dc current rejection capability is evaluated, and the proposed method is benchmarked with the virtual capacitor-based method. Finally, experimental tests are performed on a 1.2-kW single-phase PV inverter to verify the effectiveness of the proposal.

中文翻译：

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单相并网光伏逆变器的经济有效的直流电流抑制

由于电源模块的差异，驱动脉冲的不对称性以及传感器的测量误差，直流电流可能会注入到并网光伏（PV）逆变器中。直流电流注入可能导致电源变压器的磁饱和。为了解决这个问题，本文提出了一种有效的电流控制策略和补偿方法，不需要任何额外的传感器和硬件电路。首先，全面分析了直流电流注入的根本原因。随后，提出了一种比例积分谐振（PIR）控制器，以消除由功率模块的不均匀性，驱动脉冲的不对称性和电网电压的测量误差引起的直流分量。由电网电流测量误差引起的注入直流电流是根据直流母线电压的线路频率纹波估算的，然后由反馈补偿控制器将其抑制。此外，评估了直流电流抑制能力，并以基于虚拟电容器的方法为基准对所提出的方法进行了基准测试。最后，在1.2 kW单相光伏逆变器上进行了实验测试，以验证该建议的有效性。