This paper applies finite control set model predictive control (FCS-MPC) for dynamic reactive power compensation using a hybrid active power filter (HAPF). The FCS-MPC uses a model based on LCL-filter equations to predict the system behavior and optimize the control action. In fact, the application of FCS-MPC in grid-connected converters with LCL-Filter is quite recent. This algorithm is a very promising control technique for power electronics converters and its use for reactive power control of hybrid filter has not been reported in the literature yet. This paper uses the FCS-MPC in a multivariable structure along with an adaptive notch filter to damp resonance. The main purpose is to improve the dynamic response of the HAPF. Simulation as well as practical results prove the feasibility of FCS-MPC application in HAPF reactive power control. The dynamic response of the equipment was significantly improved and represents the main contribution of this paper. As a result, the FCS-MPC allows tracking fluctuations and abrupt changes in load reactive power.

Smart impedance is a new way to look at hybrid active power filters. As originally proposed in the literature, hybrid active filters were presented to improve the physical limitation of tuned passive filters. A new conditioner named smart impedance is proposed to eliminate the need of passive filter tuning procedure, the whole tuning process is performed electronically. The proposed topology is able to manipulate the displacement power factor and perform multiple frequency harmonic current mitigation at the same time. In weak systems, where the source impedance is not negligible, like in smart grids, smart impedance guaranties the voltage regulation and stability. The smart impedance control strategy uses proportional resonant controller, which allows phase-locked loop-less power system synchronization. Smart impedance system is composed of an active converter, a coupling transformer, and a capacitive unit, arranged as three phase or single phase equipment.

Canonical switching cell is known as the basic building block of dc-dc buck, boost, buck-boost, Ćuk converters, voltage/current source inverters as well as multilevel converters. This paper reveals the existence of another basic switching cell as a singular structure of the canonical switching cell. The proposed new basic cell can constitute SEPIC, Zeta converters, and Z-source converters. Each of the basic switching cells has the simplest form with two complementary switches, one inductor and one capacitor. An approach to construct a dc-dc converter by connecting source/load to the basic switching cells’ terminals is demonstrated. Some existing topologies of dc-dc converters are correlated following the proposed approach. Further, this paper reviews Z-source/ quasi-Z-source converters, universal converters, and multiple-source converters to uncover some general approaches for topology manipulating. Z-source/quasi-Z-source converters and the emerging classes of universal converters are used as examples to demonstrate the incorporation of their switches. Multiple source converters are fabricated by combining basic switching cells, in both the voltage source and current source form, using the duality principle. With the ever-increasing research efforts on converter topologies, it is hoped that this paper will improve the understanding of the existing converter relationships and inspire insights for new topological developments and applications.

In this paper, the concept of grid-connected inverter without interfacing filters is proposed. Conventional grid-side voltage sensors and traditional phase-locked loop (PLL) are removed. Only the grid current is feedback to implement grid synchronization and decoupled P/Q control. 60-Hz sinusoidal output current is achieved relying on grid-side impedance only. The controller employs virtual impedance to couple with a wide range of grid-side impedance variations. With the proposed controller, the grid-connected inverter is capable of 1) decoupling the output real and reactive power; 2) synchronizing with a grid frequency fluctuation, and 3) tolerating the grid impedance variation. This paper addresses the principle of the proposed method. Multiple simulation results are provided for validation.

Isolated microgrids, due to the high values of the output converter impedances, suffer power quality problems, such as harmonic distortion and resonances. These impedances are normally the LCL output filter needed to suppress the switching ripple of the converters. As complex impedances, they are dependent on the frequency, therefore very sensitive to harmonic content of load current. This leads to a significant microgrid voltage distortion which results in undesirable power quality levels. Hybrid active power filters are a reasonable choice for harmonic compensation allowing good filtering performance at reduced cost. This paper describes the use of Smart Impedance, which is a new application of a hybrid active power filter, to change the microgrid bus impedance forcing it to behave as a quasi-infinite bus, without increasing active power capacity of the microgrid. The implementation can improve microgrid power quality by mitigating harmonic currents and harmonic voltage resonance. It allows connecting more nonlinear load in the bus keeping the microgrid voltage quality. Experimental results are presented to demonstrate the effectiveness of the proposed approach.

This paper proposes a synchronization scheme for grid-connected Voltage Source Inverters (VSI) without physical interface inductors, voltage sensing or conventional PLL algorithms. Especially, issues with converters connected trough long cables are addressed. These cables present non-negligible LC characteristics that can lead to resonance peaks degrading current or voltage waveforms. A virtual impedance is used as grid coupling element, providing a virtualized synchronization point within software using only already available current-sensor information. Also, virtual resistance is used to actively dampen resonance peaks caused by cable characteristics. Theoretical analysis and simulation results are presented to verify the proposed strategy.