This paper proposes a repetitive-based controller for active power filters, which compensates selected current harmonics produced by distorting loads. The approach is based on the measurement of line currents and performs the compensation of selected harmonics using a closed-loop repetitive-based control scheme based on a finite-impulse response digital filter. Compared to conventional solutions based on stationary-frame current control, this approach allows full compensation of selected frequencies, even if the active filter has limited bandwidth. Compared to synchronous-frame harmonic regulations on line currents, the complexity of the proposed algorithm is independent of the number of compensated harmonics. Moreover, it is more appropriate for digital signal processor implementation and less sensitive to rounding and quantization errors when finite word length or fixed-point implementation is considered. Experimental results on a 5-kVA prototype confirm the theoretical expectations.

This paper proposes an effective technique to control the power flow among different phases of a three-phase four-wire distribution power system by means of single-phase converters arbitrarily connected among the phases. The aim is to enhance the power quality at the point-of-common-coupling of a microgrid, improve voltage profile through the lines, and reduce the overall distribution losses. The technique is based on a master/slave organization where the distributed single-phase converters act as slave units driven by a centralized master controller. Active, reactive, and unbalance power terms are processed by the master controller and shared proportionally among distributed energy resources to achieve the compensation target at the point-of-common-coupling. The proposed control technique is evaluated in simulation considering the model of a real urban power distribution grid under non-sinusoidal and asymmetrical voltage conditions. The main results, concerning both steady-state and transient conditions, are finally reported and discussed

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This paper investigates three different control techniques for controlling shunt active compensators for harmonic, reactive power and unbalance compensation. The considered methods were the instantaneous real and imaginary power theory (PQ), the Conservative Power Theory (CPT) and the synchronous reference frame method (DQ). So, the major goal is to explore the main similarities and differences in terms of steady state performance, dynamic response and computational complexity of each compensation method. Additionally, the paper also discusses how to achieve selective compensation by means of every technique, by means of suitable power and current decompositions. A three-phase grid with unbalanced non-linear load and non-negligible line impedance was used for comparing the approaches under ideal and deteriorated voltage conditions. I.978-1-4799-5776-7/14/$31.00 ©2014 IEEE

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A multifunctional control strategy for a singlephase Asymmetrical Cascaded H-Bridge Multilevel Inverter (ACHMI), suitable for microgrid systems with nonlinear loads, is presented. The primary advantage of ACHMI is to produce a staircase output voltage with low harmonic content utilizing unequal DC voltages on the individual H-bridge cells. In gridconnected mode of operation, the control strategy of the ACHMI is based on the Conservative Power Theory (CPT), providing selective disturbing current compensation besides injecting its available energy. In autonomous mode of operation, two different control methods along with a damping resistor in the filter circuit are developed for regulation of the ACHMI instantaneous output voltage in a variety of load conditions. The first method is a single-loop voltage control scheme without the need of any current measurement. The second one is multi-loop voltage control scheme with a load current feed-forward compensation strategy and preservation of the grid-connected current control scheme. The steady state response and stability of both voltage control schemes are analyzed, and based on the application requirement, the control schemes are implemented individually. The effectiveness of each control strategy is experimentally verified using a hardware-in-the-loop (HIL) setup with the control algorithm implemented in the TMSF28335 DSP microcontroller.

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