Active Inverter Part Research Articles

An auxiliary unit with selective harmonic suppression and inherent reactive power compensation for civil distribution networks

In view of the fact that there are usually two dominant harmonic currents and large amounts of inductive loads in residential distribution networks and low voltage distribution networks (called civil distribution networks in the paper), an auxiliary unit with selective harmonic suppression and inherent reactive power compensation for civil distribution networks is proposed in this paper. The proposed auxiliary unit consists of a passive part and an active inverter part. The passive part is composed of a compensation capacitor and two series resonance circuits tuned at the frequencies of the two dominant current harmonics. The passive part is used to compensate reactive power with a constant capacity and reduces capacity requirements of the active inverter part as well as voltage ratings of active inverter part. Owing to the low-impedance of the series resonance circuits, the vast majority of compensation currents generated by the active inverter part are injected to grid. These characteristics have been verified by experiment results. It is indicated that the proposed auxiliary unit is a preferred topology for improving power quality in civil distribution networks.

Design and Analysis of Adaptive Impedance Structure for Cophase Railway Traction Supply Power Quality Conditioner

The electrical locomotives are treated as single-phase nonlinear loads, which can cause the low power factor, high contents of harmonic currents, and negative-sequence current. The power quality conditioners are widely used for solving the power quality issues in the railway power system. In power quality conditioners, the coupled impedance can affect the operation voltage, compensation range, and performance. Therefore, this article discusses the effect of different coupled impedances in conditioners, including fixed inductive impedance, fixed capacitive impedance, and adaptive impedance. Moreover, an adaptive impedance-coupled hybrid power quality conditioner (AI-HPQC) is proposed in comparison with inductive-coupled railway power quality compensator (RPC) and capacitive-coupled hybrid power quality conditioner (HPQC). Furthermore, a control method for the AI-HPQC is proposed for the coordination control of the adaptive impedance part and the active inverter part. The validities of the RPC, HPQC, and the proposed AI-HPQC are verified by both simulation and experimental results.

Multifunctional Hybrid Structure of SVC and Capacitive Grid-Connected Inverter (SVC//CGCI) for Active Power Injection and Nonactive Power Compensation

In this paper, the structure, coordinate control method, and parameter design of a hybrid system are proposed for active power injection and nonactive power (reactive, harmonic, and unbalance power) compensation. The proposed hybrid system consists of a static var compensator (SVC) in parallel with a capacitive-coupling grid-connected inverter (CGCI) (SVC//CGCI). In SVC//CGCI, the SVC part is used to dynamic compensate the reactive power and unbalance power, while the low rating CGCI part is used to inject active power, provide harmonic power and a fixed amount of capacitive reactive power. Compared with conventional inductive-coupling grid-connected inverter (IGCI), the CGCI can provide active, reactive and harmonic power with low rating of active inverter part. The cost of the SVC part is much lower than that of active inverter part, thus the reduction of inverter rating can lead to a decrease in the total cost of the SVC//CGCI. Therefore, the SVC//CGCI can be a cost effective solution for active power injection and nonactive power compensation. Finally, simulation and experimental results are provided to show the advantages and validity of the proposed SVC//CGCI in compared with the conventional IGCI and SVC//IGCI.

Minimizing Inverter Capacity Design and Comparative Performance Evaluation of SVC-Coupling Hybrid Active Power Filters

In this study, a minimizing inverter capacity design is proposed, and the characteristics and performance of static VAR compensator (SVC) coupling hybrid active power filters (SVC-HAPFs) are analyzed. The cost of the SVC part is much lower than that of the active inverter part, and thus, the reduction of inverter part capacity can lead to a decrease in the total cost of SVC-HAPF. To demonstrate the advantages of the proposed minimizing inverter capacity design of SVC-HAPF, comparisons are given between the conventional and the proposed SVC-HAPF designs. Comparisons are also provided among active power filters (APFs), HAPFs, and the proposed SVC-HAPF in terms of dc-link voltage, compensation range, and performance. Finally, simulation and laboratory-scale experimental results are given to validate the minimizing inverter capacity design, and to verify the characteristics and compensation performances of APF, HAPF, and the proposed SVC-HAPF.

Hybrid Structure of Static Var Compensator and Hybrid Active Power Filter (SVC//HAPF) for Medium-Voltage Heavy Loads Compensation

In this paper, the structure, modeling, parameter design, and control method are proposed for a new hybrid structure of a static var compensator in parallel with a hybrid active power filter (SVC//HAPF). The SVC part of the SVC//HAPF is used to dynamically compensate the reactive power. And, the HAPF part is used to provide harmonic power and small amount of reactive power compensation. Due to the large fundamental voltage drop on coupling the LC part, the active inverter part of the SVC//HAPF has low voltage rating. Meanwhile, the parallel-connected SVC acts as a current divider to reduce the active inverter current. Therefore, the proposed SVC//HAPF shows the great promise in compensating harmonic current and wide-range reactive power with a low (both) voltage and current rating active inverter part. To show the advantages of the proposed SVC//HAPF, simulation comparisons among the active power filter (APF), HAPF, SVC in series with HAPF (SVC−HAPF), and the proposed SVC//HAPF are provided. Finally, experimental results based on the laboratory-scaled hardware prototype are given to show the validity of the SVC//HAPF.

Adaptive Thyristor-Controlled LC-Hybrid Active Power Filter for Reactive Power and Current Harmonics Compensation With Switching Loss Reduction

In this paper, an adaptive dc-link voltage controlled thyristor-controlled LC-coupling hybrid active power filter (TCLC-HAPF) is proposed for reducing switching loss, switching noise, and enhancing the compensating performance. Unfortunately, the TCLC-HAPF has both controllable active TCLC part and active inverter part; thus, the conventional minimum dc-link voltage calculation methods for active power filter (APF) and LC-coupling hybrid APF (LC-HAPF) cannot be directly applied to the TCLC-HAPF. Moreover, the aforementioned dc-link voltage calculation methods were developed based on the fast Fourier transform (FFT), which makes the calculation complex. This paper also presents a simplified minimum dc-link voltage calculation method for TCLC-HAPF reactive power and current harmonics compensation, which can significantly reduce the large amount of the calculation steps by using the FFT method. After that, an adaptive dc-link voltage controller for the TCLC-HAPF is developed to dynamically keep its operating at its minimum dc-link voltage level to reduce its switching loss and switching noise. Finally, representative simulation and experimental results are given to verify the proposed simplified dc-link voltage calculation method and the adaptive dc-link voltage control method of TCLC-HAPF.

Unbalanced Control Strategy for A Thyristor-Controlled LC-Coupling Hybrid Active Power Filter in Three-Phase Three-Wire Systems

This paper proposes a control strategy for a three-phase three-wire thyristor-controlled LC -coupling hybrid active power filter (TCLC-HAPF), which can balance active power and compensate reactive power and harmonic currents under unbalanced loading. Compared with TCLC-HAPF with conventional control strategy, active power filters and hybrid active power filters which either fail to perform satisfactory compensation or require high-rating active inverter part for unbalanced compensation, a control strategy was proposed for TCLC-HAPF to operate with a small rating active inverter part for a variety of loads with satisfactory performance. The control idea is to provide different firing angles for each phase of the thyristor-controlled LC -coupling part (TCLC) to balance active power and compensate reactive power, while the active inverter part aims to compensate harmonic currents. First, the required different TCLC impedances are deduced. Then, independent firing angles referenced to the phase angle of voltage across TCLC are calculated. After angle transformations, final firing angles referenced to phase angle of load voltages are obtained. In this paper, a novel controller for TCLC-HAPF under unbalanced loading is proposed. Simulation and experimental results are provided to verify the effectiveness of the proposed controller in comparison with a state-of-the-art controller.