Voltage unbalance and harmonics compensation in AC microgrid using add‐on repetitive controller

Abstract

Summary Voltage unbalance and harmonics are the major power quality issues in inverter‐based low voltage microgrids (MGs). In the presence of nonlinear load, the interconnecting inverters in the MG may not be able to compute the amount of reactive power and harmonics to be compensated independently without violating their respective ratings. This may result in disproportionate sharing of power by the individual inverters, and consequently resulting in the overloading of some of the inverters. Therefore, in the proposed work, a repetitive controller (RC) in addition to an existing controller has been developed and added in the outer most. This RC can control the individual inverters to compensate voltage unbalance and nonlinear loading through proportionate effort sharing by individual inverters in the MG. This technique has been successfully implemented on three‐phase voltage source inverter which is controlled to maintain perfect three‐phase balanced set of voltages under unbalance nonlinear loading conditions. The proposed strategy has shown an effective compensation even under highest degree of unbalance and nonlinear loading in MG. The proposed controller is designed and simulated with MATLAB/Simpower system. Field programmable gate array‐based hardware prototype has been developed to validate the control approach experimentally.

The optimal design of repetitive controllers based on inverse frequency response

“…Now, I(e i𝜔 j T ) can be separated into the numerator 𝛽(𝜔 j ) = 𝛽 p e ip𝜔 j T + 𝛽 p−1 e i(p−1)𝜔 j T + • • • + 𝛽 0 and the denominator 𝛾(𝜔 j ) = 𝛾 q e iq𝜔 j T + 𝛾 q−1 e i(q−1)𝜔 j T + • • • + 𝛾 0 . In parallel with (6), the cost function in (15) can be rewritten as…”

“…Based on the previous tracking error and the control input signal, the RC scheme repeatedly changes the control input signal to achieve tracking error convergence. Most recent applications of RC involve power electronics, such as active power filters, 1,2 uninterruptible power supply (UPS), 3 magnetically suspended rotors, 4 and microgrids 5‐7 . Other RC applications include rehabilitation robots 8,9 and manufacturing 10,11 …”

“…Most recent applications of RC involve power electronics, such as active power filters, 1,2 uninterruptible power supply (UPS), 3 magnetically suspended rotors, 4 and microgrids. [5][6][7] Other RC applications include rehabilitation robots 8,9 and manufacturing. 10,11 Performance tracking of the RC system relies directly on the effectiveness of the repetitive controller.…”

An improved power control strategy for grid‐connected hybrid microgrid without park transformation and phase‐locked loop system

“…Due to the fact that most of the DGs generate DC power and increased utilization of DC loads in recent years, the DC MG concept was emanated afterwards. Efficiency is the major precedence of DC MG, other vital supremacies include no reactive power demand, and elimination of the exigency for AC‐DC or DC‐AC conversion stages 3 . However, the AC MG are still presiding, since the existing distribution networks are set off at AC, and AC‐based distributed energy sources (DERs) and loads are still eminent in power system networks.…”