LC-coupling Hybrid Active Power Filter Research Articles

Improved model predictive control based on Luenberger state observer for LC‐coupling hybrid active power filter

AbstractAn improved model predictive control (MPC) with Luenberger state observer is proposed in this article for LC‐coupling hybrid active power filter (LC‐HAPF). Traditionally, the implementation of MPC for LC‐HAPF requires additional sensors to measure coupling capacitor voltage, thereby increases the system cost and reduces reliability. The existence of one‐step sampling delay in practice will also affect the final compensation performance. To relax these problems, both continuous and discrete models are deduced first. Then, the Luenberger observer is utilized based on the discrete model to mitigate the steady‐state error without additional sensors. In addition, the sampling delay compensation is provided by improving the prediction horizon. Finally, the effectiveness of the improved MPC for LC‐HAPF is verified by experiment results, indicating that the proposed method has fast dynamic response and low steady‐state error.

Robust fault‐tolerant design for LC‐coupling hybrid active power filter

AbstractIn this paper, an open‐circuit fault‐tolerant topology of LC‐coupling hybrid active power filter (LC‐HAPF) and its control strategy are proposed at the switch level, which can greatly improve the reliability of the system. The proposed structure has a contactor between the midpoint of each bridge arm and the negative bus of the dc‐link capacitor. When a single‐phase fault occurs, the proposed LC‐HAPF can be reconstructed into a three‐phase four‐switch system to compensate for the harmonic and reactive power, while the power quality compensation effect is hardly affected. When a two‐phase fault occurs, the operation of the normal bridge arm is not affected, and the two faulty bridge arms can suppress harmonic current and compensate for a fixed reactive power through the passive filters. When the bridge arms all fail, the whole device acts as a passive filter to suppress the harmonic current of the load and to compensate for reactive power as well. Finally, the effectiveness of the proposed topology and its control strategy is verified by simulation and experiment results.

Linear Quadratic Regulator Optimal Control with Integral Action (LQRIC) for LC-Coupling Hybrid Active Power Filter

Renewable energy generation and nonlinear load devices will generate harmonics and reactive power to power grids, resulting in current distortion and low power factors. To solve the power quality problems, the LC-coupling hybrid active power filter (LC-HAPF) is proposed, with lower DC-link voltage and lower cost compared with conventional active power filters (APFs). The LC-HAPF requires a controller to operate, therefore, hysteresis current control (HCC) and proportional current control (PCC) were proposed. However, they both result in significant steady-state error. Hence, linear quadratic regulator control (LQRC) with integral action (LQRIC) is proposed for the LC-HAPF in this paper to mitigate the steady-state error. The d-q-0 coordinate state-space model of the LQRIC-controlled LC-HAPF is derived, and a detailed design guideline of the weighting matrices Q and R of LQRIC is given. By the state-space model and weighting matrices, the gain matrix K of LQRIC can be acquired by MATLAB, thus a good steady-state performance can be ensured. Finally, the simulation results of different controllers for the LC-HAPF under 40V and 50V DC-link voltages are given to verify the effectiveness of the proposed LQRIC. The experimental results of LQRIC-controlled LC-HAPF are also given to verify the feasibility of the proposed LQRIC.

Hybrid Active Power Filter for Power Quality Improvement

A Deadbeat current controller for an LC-coupling hybrid active power filter is proposed, which can track with the reference compensation current with low steady- state error and fast dynamic response. Moreover, it can lead Hybrid Active power Filter to be operating at a fixed switching frequency with low output current ripples, thus reducing the size of the filtering circuit. The stability issue and parameter design of the proposed deadbeat current controller are analyzed and discussed. Finally, the compensating performance of the deadbeat current controller for the Hybrid Active Power Filter (LC-HAPF) is verified by simulation compared with the conventional hysteresis bandwidth modulation control, the proportional-integral (PI) control, and the proportional multi-resonant control for the LC-HAPF, which shows its effectiveness and superior compensating performances.

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.

Adaptive DC-Link Voltage-Controlled Hybrid Active Power Filters for Reactive Power Compensation

This paper presents a novel adaptive dc-link voltage-controlled LC coupling hybrid active power filter (LC-HAPF) for reducing switching loss and switching noise under reactive power compensation. First, the mathematical relationship between LC-HAPF dc-link voltage and reactive power compensation range is deduced and presented. Based on the compensation range analysis, the required minimum dc-link voltage with respect to different loading reactive power is deduced. Then, an adaptive dc-link voltage controller for the three-phase four-wire LC-HAPF is proposed, in which the dc-link voltage as well as the reactive power compensation range can be adaptively changed according to different inductive loading situations. Therefore, the compensation range, switching loss, and switching noise of the LC-HAPF can be determined and reduced correspondingly. In this paper, the reference dc-link voltage is classified into certain levels for selection in order to alleviate the problem of dc voltage fluctuation caused by its reference frequent variation, and hence reducing the fluctuation impact on the compensation performances. Finally, representative simulation and experimental results of a three-phase four-wire center-split LC -HAPF are presented to verify the validity and effectiveness of the proposed adaptive dc-link voltage-controlled LC-HAPF in dynamic reactive power compensation.