Photovoltaic based distribution static compensator for power quality improvement

This paper deals with a model of photovoltaic (PV) array or battery operated DC/DC boost converter fed three-leg VSC (Voltage Source converter) with star delta transformer for power quality improvement. A synchronous reference frame theory is proposed for three-phase four-wire DSTATCOM (Distribution Static Compensator) which includes voltage source converter and a dc link capacitor. The proposed DSTATCOM provides reactive power compensation, source harmonic reduction and neutral current compensation at the point of common coupling (PCC). The PV array or battery operated boost converter is used to step up the voltage to match the DC link requirement of the three-leg VSC. The main advantage of this proposed approach is that, it will provide continuous compensation for the whole day. The star/delta transformer provides isolation to the VSC and path to the zero sequence fundamental as well as harmonics neutral current. To derive the reference current in order to generate the firing pulse to the VSC, the overall system is designed, developed and validated by using MATLAB–SIMULINK environment.     

An improved control algorithm of DSTATCOM for power quality improvement

This paper presents the modeling and implementation of a three-phase DSTATCOM (Distribution Static Compensator) using STF (Self Tuning Filter) based IRPT (Instantaneous Reactive Power Theory) control algorithm for power quality improvement. It is used for harmonics elimination, load balancing and reactive power compensation at distorted PCC (Point of Common Coupling) voltages under nonlinear loads. An adaptive fuzzy logic controller is used to control the dc bus voltage of VSC (Voltage Source Converter) based DSTATCOM to improve the response and to reduce the overshoot and undershoot of traditional PI (Proportional-Integral) controller under unbalanced loading conditions and supply voltage fluctuations. The effectiveness of the proposed control algorithm is demonstrated through simulation using MATLAB SIMULINK and real time implementation of DSTATCOM conducted using a DSP (Digital Signal Processor dSPACE 1104).     

Implementation of Differential Equation of Single-Phase Source-Load System Based Control Algorithm for Three-Phase DSTATCOM under Stiff Source

This paper focuses on implementation of differential equation of the single-phase source-load system based control algorithm for three-phase distribution static compensator (DSTATCOM) in a power distribution system with a stiff source. The DSTATCOM has been adopted to alleviate the power quality issues such as load unbalancing, reactive power, and current harmonics, which are caused by solid-state equipment and devices. The proposed control algorithm is employed for extraction of fundamental active and reactive current components of polluted load currents, which are used for estimation of reference source currents. The control algorithm carries out computations by using a sliding sampling window that has a width of half of the fundamental cycle. The primary advantages of this control algorithm are immune to noise, not influenced from DC component that may exist in load current, and being less affected from frequency deviations. A prototype of voltage source converter (VSC)-based DSTATCOM is developed using a field programmable gate array (FPGA) processor to validate the proposed control algorithm and its performance is analyzed under steady-state and dynamic conditions. Experimental results demonstrate satisfactory performance of the DSTATCOM with the proposed control algorithm under linear and non-linear loads.     

Prototype hardware realization of the DSTATCOM for reactive power compensation

This paper presents the hardware prototype implementation of a hysteresis current controller (HCC) based DSTATCOM for reactive power compensation. To compensate the desired amount of reactive power, the amount of current to be injected is calculated using the instantaneous reactive power theory. The reactive component of load current is set as the reference current. The VSC is operated in the closed-loop to supply the reference current. If the VSC supplies this reference current, the DSTATCOM is said to supply the required reactive power when connected to the grid. The performance of the DSTATCOM for reactive power compensation is studied in the prototype hardware using the field programmable gate array (FPGA) controller. The issues associated with the implementation of hardware prototype are discussed and the experimental setup is found to compensate the reactive power. The Spartan-3A DSP FPGA controller is programmed using the system generator feature in the MATLAB.     

Load compensation using DSTATCOM in three-phase,three-wire distribution system under various source voltage and delta connected load conditions

This paper deals with a Distribution STATic COMpensator (DSTATCOM) for balancing of source currents, power factor correction and harmonic mitigation in three-phase, three-wire distribution system supplying delta connected load under various source voltage conditions. The control strategy applied to the DSTATCOM play a major role in its performance. A novel approach based on an improved instantaneous active and reactive current component (IARCC) theory is proposed for generation of three-phase reference currents for DSTATCOM. A three-phase voltage source converter with a dc bus capacitor is employed as DSTACOM which will track the reference currents in a hysteresis band scheme. The performance of DSTATCOM is evaluated under sinusoidal, unbalanced sinusoidal and unbalanced distorted source voltage conditions. Variation in load current, variation in magnitude and harmonic content in source voltage has been considered. Delta connected linear as well as non-linear load conditions have been considered. The performance of the DSTATCOM using the proposed control strategy is demonstrated using simulation results in MATLAB/SIMULINK software. Simulation results demonstrate the feasibility of proposed scheme for the control of DSTACOM.     

A novel approach of reference current generation for power quality improvement in three-phase, three-wire distribution system using DSTATCOM

This paper presents a novel approach based on an improved instantaneous active and reactive current component theory for generating reference currents for distribution static compensator (DSTATCOM). Three-phase reference current waveforms generated by proposed scheme are tracked by the three-phase voltage source converter in a hysteresis band control scheme. The performance of the DSTATCOM using the proposed control strategy has been evaluated under various source and load conditions. The performance of the proposed control strategy has been evaluated in terms of load balancing, reactive power compensation, compensator rating and harmonic mitigation. A three-phase, three-wire distribution system supplying star connected linear as well as non-linear unbalanced load is considered for simulation study. The detailed simulation results using MATLAB/SIMULINK software are presented to support the feasibility of proposed control strategy.     

配电系统大功率交流电弧炉电能质量问题及方案治理研究

根据典型参数搭建电弧炉供配电系统，采用电弧炉现场录波数据作为负荷模型，以此为平台对电弧炉运行时给系统带来的电能质量问题进行详细分析，包括负荷谐波、不平衡以及母线电压波动等。以电能质量治理为目标，综合设计补偿方案：无源电力滤波器用于滤除负荷谐波电流，降低连接母线电压的总谐波畸变(total harmonic distortion, THD)，而变压器隔离的链式DSTATCOM配合瞬时电流分相控制方法，能够分相快速对负荷相电流进行控制，补偿负荷不平PSCAD/EMTDC中构建仿真系统，对基于现场数据模型的衡、抑制母线电压波动和闪变现象的产生。在电弧炉系统和补偿方案进行研究，最后给出了仿真结果用以表明所提治理方案的有效性。     

Fuel-efficient Induction Generator Based Diesel Generator Set for Stand-alone Supply Systems

This article proposes a fuel-efficient, diesel engine driven, self-excited induction generator based diesel generator set for stand-alone supply systems. The system uses a static compensator along with a battery energy storage system. The static compensator with a battery energy storage system provides the voltage control, load compensation, harmonics elimination, load balancing, and reactive power compensation. The fuel efficiency of the generator is improved by loading the generator continuously between 80% and 100% of its rated capacity. The battery energy storage system takes the power from the generator during light load periods and supplies the power to the load during overloads. In addition, a continuous loading of the generator eliminates the problem of frequency variation of the induction generator under varying loads. The proposed system is designed to feed both three-phase as well as single-phase loads. A zigzag transformer is used for neutral current compensation. A power balance theory based control algorithm has been used to estimate the reference source currents.     

Design and control of LCL filter interfaced grid connected solar photovoltaic (SPV) system using power balance theory

In this paper solar photovoltaic (SPV) system connected to the utility grid is designed and simulated. The utility grid and SPV system are coupled with current controlled voltage source converter (VSC) and LCL filter. The design of LCL filter, MPPT algorithm and power quality improvements are discussed and simulation results are shown for the performance analysis of grid-coupled PV system under different load condition. The system is controlled through power balance theory method. The principle behind the control implementation is to evacuate the solar power generated during the daytime and the reactive power demand for the load should be supplied by the PV. The grid coupled system consists of SPV system, dc–dc boost converter, maximum power point tracking (MPPT), voltage source converter (VSC), LCL filter, different loads and three phase utility grid. This system is capable of eliminating harmonic and load balancing by supplying unbalanced current from the PV as a compensator. The system is simulated with 10 kW SPV array using indirect current control scheme.     

基于DSTATCOM的点焊机无功功率补偿研究

为了更好地解决点焊机负荷引起三相负荷不平衡、系统功率因数低等电能质量问题,提出了基于静止同步补偿器（DSTATCOM）的无功功率补偿方法。首先给出了配电静止同步补偿器的主电路结构,然后利用改进的基于瞬时无功理论的电流检测方法检测出谐波和无功电流,分析了配电静止同步补偿器平衡三相不平衡负荷的原理。最后根据点焊机在实际工作中的情况,通过Matlab/Simulink仿真验证了采用的补偿方法可以平衡三相电流,提高系统功率因数和缓解电压跌落。该研究表明用于不平衡负荷的配电静止同步补偿器具有良好的动态性能和静态补偿效果。     

一种高性价比并联混合有源电力滤波器

分析了传统的并联混合型有源电力滤波器的优缺点，在此基础上提出一种新型的并联混合有源电力滤波器，其有源部分不承受基波电压和不流过基波无功电流，进一步减小了有源滤波部分的容量和逆变器直流侧电压，并兼具较大容量的无功静补偿能力。同时提出一种新的控制方法和控制器结构，控制系统由5个控制环组成。在控制电路中，5个反馈信号，即负载电流、电源电流、逆变器输出电流、电源电压和直流母线电压，计算逆变器的参考电压信号。为了证明提出的有源滤波器的性能，利用PSCAD/EMTDC进行了仿真验证，仿真和实验结果表明该装置滤波和无功补偿效果较好，而且这种混合有源电力滤波器的性能价格比较高，因而具有良好的工程推广应用价值。     

Nonlinear modeling and control of a photovoltaic fed improved hybrid DSTATCOM for power quality improvement

This paper proposes a low rating photovoltaic fed improved hybrid distributed static compensator (DSTATCOM) for the compensation of harmonics and reactive power. The proposed system satisfies the load active power demand with reduced power rating of the photovoltaic source for same load rating as compared to the standard L or LCL filters. The system is modeled and controlled by considering the non-linearity of the system. A dc voltage droop regulator is used to control the power flow from solar system and to maintain dc link voltage. To make the system robust, switching pulses for inverter is generated using sliding mode controller. The efficacy of proposed model with sliding mode controller over linearly controlled system is validated through simulation results. The proposed system prototype is developed and operated in real time to show the effectiveness of the system.     

Active power filter based on three-phase two-leg switch-clamped inverter

A novel three-phase two-leg switch-clamped inverter is presented to achieve multilevel pulse-width modulation (PWM) operation, harmonics elimination, reactive power compensation and dc-link voltage regulation. Four active switches with voltage stress of dc-link and two ac switches with voltage stress of half dc-link are used in the proposed inverter. In this paper, the proposed inverter is operated as a controllable current source to supply the necessary active power for the compensation of inverter losses, to suppress current harmonics, and to compensate the reactive power drawn from the non-linear loads. Therefore, the balanced and sinusoidal line currents are drawn from the ac source. Two control loops are used in the adopted control scheme to maintain the constant dc-link voltage (outer loop with low-bandwidth control) and to achieve the line current command tracking (inner 1oop with high-bandwidth control). The mathematical model of the proposed converter for the operation active power filter is derived and the control scheme is provided. Computer simulations and experimental results based on a laboratory scale-down prototype are presented to verify the effectiveness of the proposed control scheme.     

基于单周控制的三电平三相四线制有源电力滤波器

针对电力工业三相四线制系统的零线电流、谐波、无功功率和三相不平衡问题,以及高电压、大容量有源电力滤波器APF(Active Power Filter)控制方案复杂的问题,提出一种单周控制的三电平三相四线制APF,其产生的补偿电流与负载的有害电流分量大小相等、方向相反,从而使得经该APF补偿后,电源电流只含有负载电流的基波有功分量。主电路采用三相三桥臂结构的三电平二极管箝位变换器,既无需升、降压变压器,也无需动态均压电路;控制策略采用单周控制,其兼有调制和控制的双重性,控制器结构简单,具有控制精度高、补偿效果好,滤波器工作于恒定开关频率的特点,适合推广到工业应用。在建立数学模型的基础上进行了仿真研究,仿真结果证明其能有效地补偿系统谐波、零序和无功电流,从而提高输电线功率因数和传输效率。     

一种基于电压源型多端直流输电的供电系统

针对目前单个电压源型FACTS装置只能抑制和消除某一种特定的电能质量问题,提出了一种能综合控制电能质量的新供电方案,其核心是将电压源型多端直流输电系统应用于向重要负荷供电的方案设计。介绍了该供电方案的系统结构,并设计了相关的控制器。一电压源型五端供电系统在几种典型异常运行工况下对重要负荷供电影响的数字仿真表明,电压源型多端直流输电系统是实现电能质量综合控制的有效供电方案。     

A Three-Phase Soft-Switched Isolated AC/DC Converter Without Auxiliary Circuit

This paper describes an ac/dc converter system consisting of a voltage-source converter (VSC) with purely capacitive snubbers and a two-phase by three-phase cycloconverter, connected via a medium-frequency (MF) transformer. By alternately commutating the two converters, it is possible to achieve beneficial switching conditions for all semiconductor devices. A commutation and modulation algorithm is described, which allows for pulsewidth-modulation control of the output voltage while maintaining soft switching. Low-load operation of the converter is a potential difficulty because the load current may be insufficient for recharging the snubber capacitors of the VSC. However, if the cycloconverter is used to momentarily short circuit the transformer, a quasi-resonant commutation mode of the VSC can be achieved, making a fast and soft commutation of the VSC down to zero load possible, without an auxiliary circuit. Furthermore, the design and operation of a 40-kVA prototype converter system are described. The experimental results from the prototype clearly show the practical feasibility of the studied concept.     

i_p-i_q检测法的单周控制三电平有源电力滤波器

并联型有源电力滤波器APF可以有效补偿由非线性负载产生的谐波和无功功率电流。为了实现单独对谐波分量、无功功率分量进行补偿,或者对谐波和无功功率分量同时进行补偿这些不同的补偿目标,同时为了满足大功率、高电压和输出电流波形畸变小的需要,提出了将中点箝位变换器和ip-iq电流检测法应用于单周控制有源电力滤波器的方法。采用ip-iq电流检测算法可分离出负载电流中的谐波分量、无功功率分量,且电网电压波形畸变不影响检测结果,故可提供不同补偿目标的参考信号。理论推导和仿真结果表明,该法能分别单独补偿谐波分量、无功功率分量,或者同时补偿谐波和无功功率分量,而且电网电压波形畸变不影响补偿效果。通过将ip-iq电流检测法运用于单周控制三电平有源电力滤波器,既实现多种补偿目标,又具有电网电压波形畸变不影响补偿效果、单周控制策略简单、三电平变换器输出电流波形畸变小的优点。     

基于单相STATCOM的不平衡负荷平衡化补偿的仿真研究

单相STATCOM由于具有输出无功电流谐波含量低、响应速度快等优点而适合于不平衡负荷的平衡化补偿。文中给出了采用单相STATCOM实现平衡化补偿的两种主电路结构及电压-无功综合控制方法。三相补偿电流相量采用对称分量法通过矢量变换获得，单相无功功率采用单相瞬时无功功率算法得到，单相逆变器采用特定谐波消除PWM算法(SHE-PWM)，以保证输出无功电流的谐波总畸变率小于5％，同时保证直流侧电容电压的稳定。对所给出的补偿方法进行了仿真研究，结果验证了单相STATCOM进行快速平衡化补偿的能力比较强。     

Active power flow control in a distribution system using discontinuous voltage controller

This paper proposes a hybrid discontinuous control methodology for a voltage source converter (VSC), which is used in an uninterrupted power supply (UPS) application. The UPS controls the voltage at the point of common coupling (PCC). An LC filter is connected at the output of the VSC to bypass switching harmonics. With the help of both filter inductor current and filter capacitor voltage control, the voltage across the filter capacitor is controlled. Based on the voltage error, the control is switched between current and voltage control modes. In this scheme, an extra diode state is used that makes the VSC output current discontinuous. This diode state reduces the switching losses. The UPS controls the active power it supplies to a three-phase, four-wire distribution system. This gives a full flexibility to the grid to buy power from the UPS system depending on its cost and load requirement at any given time. The scheme is validated through simulation using PSCAD.     

多端电压源型直流输电系统的控制策略

以提高多端电压源型直流输电系统的运行可靠性为目的,提出了基于直流电压 — 有功功率调节特性的多端直流输电系统控制策略。在系统负荷发生突变或任一换流站故障退出后,所有具备功率调节能力的换流站根据给定的调制方式在一定程度上分担系统功率的缺额,这样既维持了系统内的功率平衡,又避免了单个换流站承担功率过大的情况。最后通过数字仿真验证了所提出的控制策略设计的正确性和可行性。