A New Unbalanced Voltage Compensation Method Based on HOPF Oscillator for Three-Phase DC/AC Inverters With Unbalanced Loads

Abstract

In islanded microgrids, distributed generators (DGs) are employed as distributed compensators to improve the power quality on the load side. Due to the access of unbalanced loads, the low-voltage microgrid will naturally exhibit three-phase unbalance, which may cause additional power losses and deteriorate power quality. Therefore, this paper proposes a novel unbalanced-voltage compensation control method based on the Hopf oscillator, which introduces the negative-sequence voltage and current into the traditional Hopf oscillator to achieve the negative sequence voltage droop characteristics. It can not only realize the negative sequence droop control of a single inverter, but it is also capable to support the reactive power automatic distribution between multi-parallel grid-forming inverters. Compared with the traditional unbalanced voltage compensation method based on filtered negative sequence reactive power, the proposed unbalanced voltage compensation method can slightly improve the dynamic response. Experimental results verify the effectiveness of the proposed control strategy.

A control strategy of microgrid voltage source inverter based on self‐learning sliding mode control

“…At 0.1S, the phase‐to‐phase resistance is connected to phase A and phase C, and at 0.2S, the control strategy is switched to the scheme proposed in the paper. In this paper, the voltage unbalance index [9] is defined as follows: $$$$\begin{equation}VUF = \frac{{V_{RMS}^ - }}{{V_{RMS}^ + }}*100,\end{equation}$$$$where $$V_{RMS}^ - $$ and $$V_{RMS}^ + $$ are the amplitudes of negative sequence voltage and positive sequence voltage, respectively.…”

“…At 0.1S, the phase-to-phase resistance is connected to phase A and phase C, and at 0.2S, the control strategy is switched to the scheme proposed in the paper. In this paper, the voltage unbalance index [9] is defined as follows:…”

“…As the strategies based on communication would still be affected under extreme circumstances, Luo Siyi proposed an unbalanced voltage compensation control method based on Hopf oscillator, which introduced negative sequence voltage and current into the traditional Hopf oscillator to achieve negative sequence voltage drop characteristics. It could not only realize the negative sequence drop control of a single inverter, but also support the automatic reactive power distribution between multi-parallel grid inverters [9]. Mohsen Hamzeh separated the positive and negative sequences of the output voltage through a negative sequence impedance controller, which could effectively compensate the negative sequence components of the unbalanced load [21].…”

“…), various power quality problems will occur in the system, such as voltage deviation, negative sequence and waveform distortion [5][6][7][8]. These problems will cause damage to interconnected electrical equipment, increase the probability of failure and affect the stable operation of the whole system [9][10]. Therefore, the International Electrotechnical Commission has defined the above power quality issues [11].…”