Coordinate Control of Power/Current for Grid-Connected Inverter Based on PCI Controller under Unbalanced Grid Conditions

Chencong Zhao,Zhouhua Xie,Jun Liu,Feihang Zhou

doi:10.1155/2019/5968984

Chencong Zhao, Zhouhua Xie + Show 2 more

Open Access

https://doi.org/10.1155/2019/5968984

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Abstract

The oscillations on output power and distortion of the inverter currents will occur in the case of unbalanced grid voltage faults. Constant output power and good current quality cannot be achieved simultaneously. Aiming at these problems, a coordinate control strategy for suppressing power fluctuations and current harmonics is proposed by analyzing instantaneous power control and current balance control. The proposed control is achieved by adjusting the weight coefficient of current reference values to change the current harmonic contents based on proportional complex integral (PCI) controller and proportional multiple complex integral (PMCI) controller. The control strategy with a simple control structure neither needs to detect harmonic components of the inverter currents, nor needs to separate the positive and negative components of voltage and current, which is easy to be realized. The feasibility and effectiveness of the proposed control are verified by the comparison and analysis of simulation.

Highlights

With the problem of global climate increasingly serious and nonrenewable resources being largely consumed, the development of renewable energy has attracted much attention
The traditional control strategy is the dual current vector control in the positive and negative sequence reference frames, and this method is applied in [9,10,11], by controlling the positive and negative components of voltage and current to eliminate oscillations on the active power. The realization of this control objective is based on the injection of negative sequence currents, which will inevitably result in harmonics distortion in three-phase inverter currents, and the oscillations on reactive power have not been eliminated
It can be seen that the total harmonic current distortion (THD) is large in the three cases (i.e., 10.31%, 11.39%, and 23.65%, respectively), which does not meet the THD standard of less than 5% stipulated by the IEEE Std

Summary

Introduction

With the problem of global climate increasingly serious and nonrenewable resources being largely consumed, the development of renewable energy has attracted much attention. The realization of this control objective is based on the injection of negative sequence currents, which will inevitably result in harmonics distortion in three-phase inverter currents, and the oscillations on reactive power have not been eliminated. In order to obtain constant output active and reactive powers, a control scheme is proposed which utilizes the resonance compensation method without considering the distortion of inverter currents [12,13,14]. Current reference values to reduce the imbalance of grid voltage This method mainly aims at current quality; the problem of power oscillations has not been solved under unbalanced grid voltage. Weight coefficient is introduced in current references to change the harmonic contents in inverter currents, and the coordinate control of power fluctuations suppression and current balance is realized.

Model of Grid-Connected Inverter

Conventional Control Strategies

Simulation Results

R104 P

Conclusion