孤岛微电网电流同步U-I下垂控制方法

采用电压-电流(U-I)下垂控制的孤岛微电网系统始终运行于工频频率,避免了传统下垂控制存在的频率偏差及频率越限问题,但电源间易产生环流,功率分配精度差。为此,提出电流同步U-I下垂控制方法,该方法由电流同步控制及U-I幅值下垂控制两部分构成。前者通过调节输出电压相角使各电源输出电流相角一致,以抑制电源间环流；后者依据输出电流的幅值调节输出电压的幅值,使各电源出力依据自身容量分配。在此基础上,建立双端系统的小信号模型,分析电流同步控制环路中控制参数对系统稳定性的影响,为参数设计提供依据。仿真及实验结果表明,相比U-I下垂控制,所提方法的系统环流减小50%以上,电压畸变率改善近10%,电源间功率分配精度及系统电能质量均得到明显提升。

Synchronous Current U-I Droop Control Strategy for Islanded Microgrids

The constant-frequency synchronous current phasor control method for island microgrid has many advantages, such as the effect of power sharing between inverters, less affected by system parameters, strong resistance to voltage disturbance and simple implementation method. However, when it is applied to the microgrid with nonlinear unbalanced loads, there is the problem of voltage distortion and voltage unbalance. Therefore, a virtual harmonic resistance based constant-frequency synchronous current phasor control method was proposed. By introducing virtual harmonic resistors, the output impedance of the inverter in the low harmonic frequency domain was reduced, and the voltage distortion and voltage unbalance was suppressed. In the meantime, the harmonic current was evenly distributed among parallel inverters. The output impedance model of the inverter was established. According to the model analysis, it was found that the virtual harmonic resistance would cause resonance and amplify the high-order voltage harmonics. Therefore, active damping control is used to suppress resonance generation. The simulation and experimental results show that the proposed control method can effectively improve the voltage waveform quality and realize the reasonable averaging of harmonic current.