Implementation and performance of automatic gain adjustment in ashunt-active filter for harmonic damping throughout a power distributionsystem

This paper discusses automatic gain adjustment in a fully-digital-controlled shunt active filter. This is the first step in cooperative control of the multiple active filters based on voltage detection for harmonic damping throughout power distribution systems. In general, the active filter should be equipped with an optimal control gain corresponding to the characteristic impedance of a distribution line. However, it is difficult to know circuit parameters of a real distribution line having various shunt capacitors and loads. Therefore, a main purpose of the gain adjustment is to make the active filter damp out harmonic propagation without considering the circuit parameters. In addition, the gain adjustment can reduce the compensating currents and losses in the active filter, and moreover it can avoid over-damping performance. Experiment results obtained from a 200-V, 20-kW laboratory system verify the effectiveness of the active filter equipped with automatic gain adjustment     

A 6.6-kV transformerless shunt hybrid active filter for installation on a power distribution system

This paper presents a fully-digital-controlled shunt hybrid filter for damping of harmonic propagation in power distribution systems. The harmonic propagation is caused by resonance between line inductances and power capacitors installed for power factor correction. A possible solution to damping out harmonic propagation is based on installation of a shunt pure active filter at the end of a feeder. This paper proposes a shunt hybrid active filter characterized by series connection of a seventh-tuned LC filter per phase and a small-rated three-phase active filter. Like the pure filter, the hybrid filter is connected to the end bus of a feeder. The capacitor of the LC filter imposes a high impedance to the fundamental frequency, so that the fundamental voltage appears across the capacitor. This unique feature allows us to directly connect the hybrid filter to the 6.6-kV power line without step-down transformers. Furthermore, the capacitor used in this hybrid filter is lighter, cheaper and smaller than the transformer used in the pure filter. Theoretical analysis, along with experimental results obtained from a 200-V, 20-kW laboratory system, verifies the viability and effectiveness of the proposed hybrid filter.     

An active power filter and unbalanced current compensator

This paper presents the synthesis and performance of a shunt active power filter based on the three-phase pulsewidth modulation (PWM) voltage converter connected to the AC mains. Current harmonics and asymmetries caused by nonlinear loads can be compensated. A decoupled system in Park's variables is achieved and so simple controllers with excellent performance can be used. The controllers are implemented directly in the Park's referential. Expressions for the controller's synthesis are derived. Experimental results from a 2 kVA IGBT prototype showing excellent dynamic and steady-state system's performances are presented. The control circuit is implemented with analog and digital electronic circuits. A considerable amount of electronic circuits are needed. The method presented in this paper can also be implemented with a digital signal processor     

A robust multilevel hybrid compensation system for 25-kV electrified railway applications

On many electrified railway systems with single-phase 25-kV industrial frequency supply, the power quality can be particularly poor when conventional thyristor based locomotives are operating, and this constrains the amount of power that can be delivered to the locomotives. This paper presents a hybrid shunt compensation system consisting of alternatively a cascaded or a reduced topology multilevel active power filter, and a low rating passive damping filter. The active power filter is controlled by a novel hysteresis current regulation strategy, and both mitigates low-order voltage harmonic distortion along the feeder and provides root mean squared voltage support. The passive filter damps harmonic resonances that are typical in such 25-kV traction systems. The results show that the filter system can significantly increase traction system power transfer capacity with only a relatively small capital investment, allowing older thyristor based locomotives and increased traffic levels to be supported without necessarily requiring a complete system upgrade. Simulation and experimental results are included showing the performance of the filter for both steady state and transient conditions.     

基于瞬时无功功率理论的APF的研究与仿真

本文介绍了并联型有源电力滤波器的工作原理和基于瞬时无功功率理论的谐波和无功电流检测方法,用Matlab SimUlink建立了带典型负载的电力有源滤波器的仿真模型,模拟实际系统,用于检验其策略和参数在实际条件下的工作情况。仿真模型的结果表明：基于瞬时无功功率理论的有源滤波器,可以很好的起到动态抑制电网谐波和补偿无功的作...     

An improved control algorithm of shunt active filter for voltageregulation, harmonic elimination, power-factor correction, and balancingof nonlinear loads

This paper deals with an implementation of a new control algorithm for a three-phase shunt active filter to regulate load terminal voltage, eliminate harmonics, correct supply power-factor, and balance the nonlinear unbalanced loads. A three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source inverter (CC-VSI) with a DC bus capacitor is used as an active filter (AF). The control algorithm of the AF uses two closed loop PI controllers. The DC bus voltage of the AF and three-phase supply voltages are used as feedback signals in the PI controllers. The control algorithm of the AF provides three-phase reference supply currents. A carrier wave pulse width modulation (PWM) current controller is employed over the reference and sensed supply currents to generate gating pulses of IGBTs of the AF. Test results are presented and discussed to demonstrate the voltage regulation, harmonic elimination, power-factor correction and load balancing capabilities of the AF system     

Discrete Frequency Tuning Active Filter for Power System Harmonics

Severe voltage distortion, due to power system harmonic resonance, has been reported in recent years. This issue becomes more significant in high penetration of a photovoltaic (PV) network. A conventional voltage detection active filter operates as similar conductance for all harmonic frequencies to resolve this problem whether in a fixed conductance command or in an automatic gain adjustment control. However, its filtering capability is impeded by the mismatch between the active filter and the radial line, and the voltage distortion may still be significant. This paper proposes a discrete frequency tuning active filter to suppress power system harmonics. The active filter operates as variable conductance for each individual harmonic frequency. Each harmonic conductance is dynamically adjusted according to the corresponding harmonic voltage distortion of the active filter installation point in response to increase or decrease of nonlinear loads, or variation of resonant frequency in the power system. The mismatching problem between the feeder impedance and the active filter can be avoided effectively. Therefore, harmonic voltage distortion can be maintained at an allowable level throughout the feeder with lower peak current and lower rms current of the active filter, and loads installed at various locations of the power system receive more uniform voltage waveform.     

应用并联型有源滤波器抑制雷达电源的谐波

针对雷达电源工作时产生的谐波电流对电网污染严重的情况，提出了采用并联型有源电力滤波器来抑制雷达电源工作时产生的谐波电流。首先分析了并联型有源电力滤波器的工作原理和基于傅里叶变换理论的谐波电流检测算法；然后介绍了采用二重化方案设计的主电路以及相应控制电路，最后给出了实验结果。实验证明，无论雷达电源工作在稳态还是脉动方式，并联型有源电力滤波器能有效抑制其工作时产生的谐波。     

基于UPF的谐波电流检测方法的研究

将功率因数的概念引入有源滤波器的控制中,建立了基于单位功率因数(UPF)的谐波及无功电流检测的数学模型.给出了检测电路中低通滤波器的设计方案,分析了滤波器的类型、阶数及截止频率对检测精度和检测系统响应过程的影响.最后利用MATLAB/SIMULINK对检测方法进行仿真,并通过基于DSP的并联有源滤波器实验装置验证了该检测方法的可行性和有效性.     

An instantaneous active and reactive current component method foractive filters

A shunt active filter based on the instantaneous active and reactive current component i_d-i_q method is proposed. This new control method aims to compensate harmonics and first harmonic unbalance. To evaluate its relative performance, it is compared with the instantaneous active and reactive power p-q method under various mains voltage conditions and for different harmonic injection high-pass filters. Both methods are completely frequency-independent, however under distorted mains voltages the proposed method presents a better harmonic compensation performance. The system synthesis and implementation are performed. Simulation and experimental results are presented     

新型三相三线制并联有源滤波器的滑模控制方法

为了提高有源滤波器的谐波补偿效果,设计了一种新型滑模控制器,用于三相三线制并联有源滤波器的参考电流跟踪控制.谐波电流检测方法采用基于瞬时无功功率理论的谐波电流检测方法,能快速、准确的检测出负载电流中的谐波分量.直流侧电压控制方法采用PI控制方法实现.Simulink仿真结果显示,与传统的滞环比较控制方法相比,所设计的新型滑模控制方法能够有效的降低跟踪误差,提高有源滤波器的谐波补偿效果.     

基于DSP的UPF谐波电流检测系统误差研究

从谐波电流检测原理、交流采样方法和硬件实现方案等方面,研究了基于DSP的UPF谐波电流检测系统的误差,分析了各项主要误差的产生原因及量级大小,并提出了相应的减小或修正误差的改进方法,以提高谐波电流的检测精度.这些方法已在基于DSP的并联型有源电力滤波器实验装置上得以应用.结论亦可为它类有源电力滤波器的设计提供参考.     

Real-Time Estimation of Fundamental Frequency and Harmonics for Active Shunt Power Filters in Aircraft Electrical Systems

A novel algorithm for fundamental frequency and harmonic components detection is presented in this paper. The technique is based on a real-time implementation of discrete Fourier transform, and it allows fast and accurate estimation of fundamental frequency and harmonics of a distorted signal with variable fundamental frequency. It is suitable for active shunt filter applications, when fast and accurate tracking of the reference signal is required to achieve a good control performance. The main application for the algorithm is aircraft ac power systems, where the fundamental frequency can be either fixed on 400 Hz and its actual value fluctuates around the nominal value, or variable in the range 360–900 Hz. Hence, a real-time estimation of fundamental frequency is essential for active filter control. The proposed algorithm has been at first implemented in Matlab/Simulink for computer simulation, and it has been compared with a Phase Locked Loop (PLL) algorithm for frequency detection and the synchronous $dq$ reference method for harmonic detection. Experimental tests have been carried out in order to validate the simulation results. The distorted current absorbed by a nonlinear load is analyzed and processed by means of a digital implementation of the algorithm running on the active shunt power filter control DSP, in order to calculate the active filter compensating current.      

APF中数字低通滤波器的设计及仿真实现

文中介绍了基于瞬时无功功率理论的ip-iq谐波检测方法及对低通滤波器的要求,分析了数字低通滤波器的类型、阶数及截止频率对有源电力滤波器谐波检测效果的影响。利用MATLAB仿真软件设计了二阶巴特沃思（Butter—worth）数字低通滤波器,对ip-iq谐波检测算法进行了仿真研究,仿真结果证明所选择的数字低通滤波器的正确性。     

A New Control Technique for Three-Phase Shunt Hybrid Power Filter

This paper presents a nonlinear control technique for a three-phase shunt hybrid power filter (SHPF) to enhance its dynamic response when it is used to compensate for harmonic currents and reactive power. The dynamic model of the SHPF system is first elaborated in the stationary “abc” reference frame and then transformed into the synchronous orthogonal “dq” reference frame. The “dq” frame model is divided into two separate loops, namely, the two current dynamic inner loops and the dc-voltage dynamic outer loop. Proportional–integral (PI) controllers are utilized to control the SHPF input currents and dc-bus voltage. The currents track closely their references so that the SHPF behaves as a quasi-ideal current source connected in parallel with the load. It provides the reactive power and harmonic currents required by the nonlinear load, thereby achieving sinusoidal supply currents in phase with supply voltages under dynamic and steady-state conditions. The SHPF consists of a small-rating voltage-source inverter (VSI) in series with a fifth-harmonic tuned $LC$ passive filter. The rating of the VSI in the SHPF system is much smaller than that in the conventional shunt active power filter because the passive filter takes care of the major burden of compensation. The effectiveness of the control technique is demonstrated through simulation and experimentation under steady-state and dynamic operating conditions.      

Odd-harmonic digital repetitive control of a single-phase current active filter

Shunt active power filters have been proved as useful elements to correct distorted currents caused by nonlinear loads in power distribution systems. This work presents an all-digital approach, based on the repetitive control technique, for their control. In particular, a special digital repetitive plug-in controller for odd-harmonic discrete-time periodic references and disturbances is used. This approach does not introduce high gain at those frequencies for which it is not needed, and thus it improves robustness. Additionally, the necessary data memory capacity is lower than in traditional repetitive controllers. The design is performed for the particular case of single-phase shunt active filter with a full-bridge boost topology. Several experimental results are also presented to show the good behavior of the closed-loop system.     

Harmonic filtering of high-power 12-pulse rectifier loads with aselective hybrid filter system

Current distortion of 12-pulse rectifier loads is significantly lower compared to six-pulse rectifier loads. However, in passive filtering of the lowest and dominant characteristic 11th and 13th harmonics, the use of 5th and 7th filters is often required in order to prevent possible parallel and series resonance between the passive filter and source impedance which can be excited by source background distortion or by load current residual noncharacteristic harmonics at the 5th and 7th harmonic frequencies. In hybrid filter systems, an active filter (AF) can be added in series with the passive filter in order to isolate the source and load. In most proposed hybrid filter systems, AF control is based on the detection of total current distortion and high-frequency inverters. With a selective AF control system and voltage-controlled inverter, the AF can be controlled to isolate the load at the critical frequencies only while at all other frequencies the passive filter function is preserved so that lower switching frequency and AF rating is required. In this paper, the authors present a selective AF filter control system and simple hybrid filter topology suitable for the compensation of high-power 12-pulse rectifier loads. Harmonic current controllers based on the second-order infinite-impulse response digital resonant filters are used, as they can be considered as simple digital algorithms for more complex double cascaded synchronous-reference-frame-based proportional plus integral controllers. They are centered to the targeted harmonic frequencies by using an adaptive fundamental frequency tracking filter. This approach gives good results, even if the reference waveform (in our case, a load voltage) is highly distorted or unbalanced and no separate phaselocked loop is required. Test results for a laboratory model of this system and stability analysis are presented and the importance of delay-time compensation is discussed     

A passive series, active shunt filter for high power applications

This paper presents a hybrid series passive/shunt active power filter system for high power nonlinear loads. This work is motivated by the fact that the ability of a converter to perform effectively as an active filter is limited by the power and the frequency distribution of the distortion for which it must compensate. This system is comprised of a three-phase shunt active filter and series AC line smoothing reactance installed in front of the target load. The proposed system significantly reduces the required shunt active filter bandwidth. The space-vector pulse width modulation (PWM) controller is based on a dead-beat control model. It is implemented digitally using a single 16-bit microcontroller. This controller requires only the supply current to be monitored, an approach different from conventional methods. The paper provides background on the operation of the filter, the details of the power circuit, the details of the control design, representative waveforms, and spectral performance for a filter which supports a 15 kVA phase controlled rectifier load. Experimental data indicate that the active filter typically consumes 2% or less of the average load power, suggesting that a parallel filter is an efficient compensation approach. The spectral performance shows that the active filter brings the system into compliance with IEEE519-1992 up to the 33rd harmonic for an AC line smoothing reactance of 0.13 p.u     

An Optimization-Based Algorithm for Shunt Active Filter Under Distorted Supply Voltages

In this paper, an optimization-based control algorithm for the compensation of steady-state load under distorted supply voltages is presented. For balanced and sinusoidal supply voltages, load compensation using shunt active filter produces perfect harmonic cancellation (PHC) and unity power factor (UPF) source currents. However, when the supply voltages are distorted, compensation for PHC will not provide UPF, as the harmonics in the supply voltages are not utilized for delivering the average power. In the same way, to achieve UPF source currents, the compensated source currents should have the same harmonics, unbalance, shape, and be in phase with the respective supply voltages, thereby violating the perfect harmonic cancellation objective. Hence, there should be an optimal operation between these two important compensation characteristics. The optimization-based control algorithm presented in this paper gives the best power factor while satisfying the constraints such as total harmonic distortion limits and average power balance of source currents. It is also flexible to adopt different compensation characteristics based upon the supply voltage conditions. Matlab and its optimization toolbox are used for simulation studies and solving the nonlinear optimization problem, respectively. The algorithm is validated by using a prototype of digital signal processor (TMS320F2812PGFA)-based shunt active power filter. Detailed experimental results are presented.     

FPGA-based fully digital controller for three-phase shunt active filters

This article presents a fully digital controller for a three-phase shunt active filter. The harmonic isolator and the current controller both have been implemented in only one Field Programmable Gate Array (FPGA). This article discusses the design and implementation of digital hybrid modulated hysteresis current controller and multi-variable filters for shunt active filter controlling. Simulation and experimental results based on ‘FPGA in the loop’ prototyping demonstrate the effectiveness of the proposed fully digital controller.