A novel PWM scheme for single-phase three-levelpower-factor-correction circuit

This paper presents a control scheme for a single-phase AC-to-DC power converter with three-level pulsewidth modulation. A single-phase power-factor-correction circuit is proposed to improve the power quality. The hysteresis current control technique for a diode bridge, with two power switches is adopted to achieve a high power factor and low harmonic distortion. A control scheme is presented where the line current is driven to follow the reference sinusoidal current which is derived from the DC-link voltage regulator, the capacitor voltage balance compensator and the output power estimator. The blocking voltage of each power device is clamped to half of the DC-link voltage. The high power factor and low current total harmonic distortion are verified by computer simulations and hardware tests     

Three-phase series VAr compensation based on a voltage-controlledcurrent source inverter with supplemental modulation index control

Shunt-type static VAr compensators have been shown to be an effective means of increasing the transmission capability of power systems and of increasing the power factor of industrial loads. This paper presents an alternative to the shunt connection consisting of a series-connected transformer-coupled pulsewidth modulation (PWM) inverter. The scheme consists of a current source inverter (CSI) fed from a self-controlled DC current bus and presents the following features: (1) instantaneous series injected voltage control through online PWM of the DC link current; and (2) steady-state modulation index of the PWM pattern near unity through DC link current minimization. The first feature results in fast dynamic response, while the second feature ensures low and fixed injected voltage harmonic distortion and reduced steady-state compensator losses. Operation of the compensator and of the two-loop control scheme are presented. Simulation and experimental results on a 2 kVA laboratory prototype unit confirm the feasibility of the proposed VAr compensator structure     

Single-phase integrated power quality compensator based oncapacitor-clamped configuration

A control scheme of an integrated power quality compensator, which employs an active rectifier to work simultaneously as an active power filter (APF) to decrease current harmonics, is proposed. The employed rectifier is based on a capacitor-clamped configuration to produce multilevel pulsewidth modulation waveforms which result in low voltage stress and low conduction loss on the power switches. The proposed active rectifier is controlled to track the supply current to be a sinusoidal wave with low current harmonics. The advantages of the proposed control scheme are high power factor, low current harmonics, no complicated calculations for current harmonics elimination, and no dedicated APF needed for harmonic elimination. The experimental results are used to verify the validity and effectiveness of the proposed control scheme     

Power factor correction based on diode clamped rectifier

Multilevel converters are recent alternative ways of implementing high power medium voltage applications compared with two-level converters. This paper presents a three-level pulse-width modulation scheme based on the diode clamped rectifier for power factor correction. Eight power switches are employed in the adopted switching mode rectifier. The voltage stress of each power switch is only half of the dc-link voltage. This advantage allows the low voltage stress semiconductor to be used in the high voltage applications. The control scheme is based on a look-up table to achieve high power factor and low current harmonics to meet the harmonic limits of International Electrotechnical Commission standard 1000-3-2. The neutral point voltage balance problem is overcome by using a voltage compensator to reduce the voltage variation under the unbalanced load condition. The proposed control technique illustrates its validity and effectiveness through simulations and experiments.     

Grid current regulation of a three-phase voltage source inverter with an LCL input filter

Many grid connected power electronic systems, such as STATCOMs, UPFCs, and distributed generation system interfaces, use a voltage source inverter (VSI) connected to the supply network through a filter. This filter, typically a series inductance, acts to reduce the switching harmonics entering the distribution network. An alternative filter is a LCL network, which can achieve reduced levels of harmonic distortion at lower switching frequencies and with less inductance, and therefore has potential benefits for higher power applications. However, systems incorporating LCL filters require more complex control strategies and are not commonly presented in literature. This paper proposes a robust strategy for regulating the grid current entering a distribution network from a three-phase VSI system connected via a LCL filter. The strategy integrates an outer loop grid current regulator with inner capacitor current regulation to stabilize the system. A synchronous frame PI current regulation strategy is used for the outer grid current control loop. Linear analysis, simulation, and experimental results are used to verify the stability of the control algorithm across a range of operating conditions. Finally, expressions for ""harmonic impedance" of the system are derived to study the effects of supply voltage distortion on the harmonic performance of the system.     

Implementation of a Three-Phase Capacitor-Clamped Active Power Filter Under Unbalanced Condition

A capacitor-clamped voltage-source inverter for active power filter operation under balanced and unbalanced conditions is proposed to suppress current harmonics and compensate the reactive power generated from the nonlinear loads. The adopted voltage-source inverter is based on a three-level capacitor-clamped topology to reduce the voltage stress of power semiconductors. Two control loops are used in the control scheme to achieve harmonic and reactive currents compensation and to regulate the inverter dc side voltage. In the adopted inverter, the neutral point voltage is compensated by a voltage compensator to obtain the balanced capacitor voltages on the dc side. In order to control the flying capacitor voltages, two redundant states in each inverter leg can be selected to compensate the flying capacitor to obtain a better voltage waveform with low harmonic contents on the ac terminals. The balanced and sinusoidal line currents are drawn from the ac source under the balanced and unbalanced conditions. The feasibility of the proposed scheme is confirmed through experimental results     

基于GTO的静止无功补偿装置研究

基于大功率全控型电力电子器件GTO的静止无功补偿装置具有自关断特性,在以DSP控制技术的支持下,通过实时检测电网无功功率的变化,自动发出GTO通/断控制脉冲,快速投切电容器,实现对供电线路无功功率的跟踪调节。该装置比普通晶闸管补偿装置（TSC）的可靠性高。在实现三相共补与分相补偿时,具有响应速度快、控制简单、噪音和损耗小、可靠性高、结构简练等优点。     

An AC VRM topology for high frequency AC power distribution systems

In this paper, a series resonant converter with pulse-width modulation (PWM) control is presented as an ac voltage regulator module (VRM) for high frequency ac power distribution systems. The proposed topology has close-to-unity rated power factor, low total harmonic distortion in input current, zero voltage switching under all load conditions, low voltage stress of the active switch and high overall efficiency. Simulation and experimental results are presented to prove the performance of the proposed ac VRM converter.     

A new control scheme for single-phase PWM multilevel rectifier withpower-factor correction

A new control scheme for a single-phase bridge rectifier with three-level pulsewidth modulation is proposed to achieve high power factor and low current distortion. The main circuit consists of a diode-bridge rectifier, a boost inductor, two AC power switches, and two capacitors. According to the proposed control scheme based on a voltage comparator and hysteresis current control technique, the output capacitor voltages are balanced and the line current will follow the supply current command. The supply current command is derived from a DC-link voltage regulator and an output power estimator. The major advantage of using a three-level rectifier is that the blocking voltage of each AC power device is clamping to half of the DC-link voltage and the generated harmonics of the three-level rectifier are less than those of the conventional two-level rectifier. There are five voltage levels (0, ±V_DC/2, ±V_DC) on the AC side of the diode rectifier. The high power factor and low harmonic currents at the input of the rectifier are verified by software simulations and experimental tests     

Long-Lifetime Power Inverter for Photovoltaic AC Modules

This paper presents a power inverter tailored for low-power photovoltaic (PV) systems. The inverter features high reliability, thanks to a circuit topology that obviates aluminum electrolytic capacitors from the circuit. Moreover, all components, including logic and control, have been designed to exhibit high reliability at high temperatures. Three conversion stages form the power topology. First, a full bridge connected to a high-frequency transformer and a full-bridge rectifier amplifies the voltage of the PV panel to approximately 475 V. This stage is controlled by using a phase-shift pulsewidth-modulation controller that permits zero-voltage switching, thereby minimizing losses. Second, a buck converter is connected in series with the rectifier and is controlled by using current mode in order to shape the current injection into a rectified sine wave. Last, a full bridge is operated at line frequency to unfold the current injection. The amplification stage has a proportional compensator that maintains the voltage at the PV terminals constant. The current injection stage has a proportional-derivative compensator that controls the amplitude of the grid current so that the dc-link average voltage is maintained constant. Experimental results show that the peak efficiency of the system is 89%, and the total current harmonic distortion is below 5%. Finally, analyses show a designed lifetime of approximately ten years.     

250 mV Supply Voltage Digital Low‐Dropout Regulator Using Fast Current Tracking Scheme

This paper proposes a 250 mV supply voltage digital low‐dropout (LDO) regulator. The proposed LDO regulator reduces the supply voltage to 250 mV by implementing with all digital circuits in a 0.11 μm CMOS process. The fast current tracking scheme achieves the fast settling time of the output voltage by eliminating the ringing problem. The over‐voltage and under‐voltage detection circuits decrease the overshoot and undershoot voltages by changing the switch array current rapidly. The switch bias circuit reduces the size of the current switch array to 1/3, which applies a forward body bias voltage at low supply voltage. The fabricated LDO regulator worked at 0.25 V to 1.2 V supply voltage. It achieved 250 mV supply voltage and 220 mV output voltage with 99.5% current efficiency and 8 mV ripple voltage at 20 μA to 200 μA load current.     

Suppression of line voltage related distortion in current controlled grid connected inverters

The influence of selected control strategies on the level of low-order current harmonic distortion generated by an inverter connected to a distorted grid is investigated through a combination of theoretical and experimental studies. A detailed theoretical analysis, based on the concept of harmonic impedance, establishes the suitability of inductor current feedback versus output current feedback with respect to inverter power quality. Experimental results, obtained from a purpose-built 500-W, three-level, half-bridge inverter with an L-C-L output filter, verify the efficacy of inductor current as the feedback variable, yielding an output current total harmonic distortion (THD) some 29% lower than that achieved using output current feedback. A feed-forward grid voltage disturbance rejection scheme is proposed as a means to further reduce the level of low-order current harmonic distortion. Results obtained from an inverter with inductor current feedback and optimized feed-forward disturbance rejection show a THD of just 3% at full-load, representing an improvement of some 53% on the same inverter with output current feedback and no feed-forward compensation. Significant improvements in THD were also achieved across the entire load range. It is concluded that the use of inductor current feedback and feed-forward voltage disturbance rejection represent cost-effect mechanisms for achieving improved output current quality.     

Single-phase high power factor pre-regulator with three-level modulation scheme

A control scheme for the single-phase three-level pulse-width modulation active rectifier is proposed. A hysteresis current control scheme is used to draw the sinusoidal line current in phase with the mains voltage. The line current command is derived from a voltage controller and a phase-locked loop circuit. The blocking voltage of each power device is clamped to half of the DC-link voltage in the proposed active rectifier. In order to generate the three-level voltage pattern on the DC side of the active rectifier, the region detector of the line voltage, capacitor voltage compensator and hysteresis current comparator are employed in the adopted control algorithm to achieve high input power factor and low current distortion. To investigate the proposed control algorithm, the adopted rectifier is simulated and experimental tests from a laboratory prototype undertaken.     

单相光伏逆变器的改进型并网控制方法

单相光伏并网逆变器通常采用双闭环控制和电网电压前馈控制的策略,其中双闭环的外电压环为采用PI恒压控制逆变前直流侧电压,分析比较了准比例谐振调节和PI调节两种电流内环的输出外特性,通过对电流内环采用准比例谐振控制的控制系统进行分析建模,建立了逆变器的单相并网仿真模型。仿真结果显示电流内环采用准比例谐振控制能实现并网电流的无静态误差控制,并减小电网频率偏移对并网电流的影响。仿真及实验得到的输出正弦电流波形良好,基于该并网控制策略的光伏逆变器能以高功率因数向电网发电,动态响应快、鲁棒性强、跟踪精度高、并网电流的THD明显优于传统方法,从而验证了改进后模型的可行性和实用性。     

单周期控制三相VIENNA整流器

电网谐波污染已经引起世界各国的高度重视,功率因数校正（PFC）是治理谐波的一种有效方法。文章对基于单周期控制的三相VIENNA整流器进行了研究,推导了单周期控制三相VIENNA整流器的控制规律,与其它控制方案相比不需要乘法器,不需对电源电压进行检测,控制逻辑比较简单并且以恒定开关频率工作,能够实现单位功率因数校正和低电流畸变。仿真结果验证了理论分析的正确性。     

A simple input current wave-shaping technique for three-phase diode and SCR converters

Three-phase converters using diode or silicon-controlled rectifier (SCR) are widely employed to convert the commercial AC supply to DC. Such converters inject harmonics into the power supply system and thereby distort supply system voltage waveform. A simple input current wave-shape improvement technique using a shunt-connected harmonic current compensator is presented in this work, intended to reduce the total harmonic distortion (THD) of input current of three-phase diode and SCR phase-controlled rectifiers operating with inductive loads, by matching them to the specific converter as a combined package. The compensator proposed here comprises of a three-limb voltage source converter using insulated-gate bipolar transistor, working on instantaneous current and voltage measurements of the compensator only and not of the load. The technique uses a simple feedforward control for AC source current harmonic compensation of rectifiers without monitoring the AC line currents, i.e. use of online computation. The proposed system is simulated and tested on a laboratory prototype. The measured input current THD values without additional line filters are found to be below 8.3%, which is within acceptable limits, proving that the new technique is capable of compensating predetermined current harmonics of diode or SCRs.     

A multimodule parallelable series-connected PWM voltage regulator

This paper presents the analysis and design of a single-phase voltage regulator (VR) and its multinodule parallel control. The VR employs the pulsewidth modulation three-arm rectifier-inverter topology. The inverter side adjusts the load voltage with the series regulating structure aiming to minimize converter capacity and attain higher efficiency. The rectifier side regenerates the load power and executes the active power filter function to achieve unity power factor. Based on such high-performance VR, a resistive droop method combined with the P-V droop and Q-δ shift scheme is then proposed to control the current sharing such that multiple VRs can be paralleled directly without any control interconnection. The proposed parallel control technique possesses the features of fast response, precise voltage regulation, equal fundamental and harmonic current sharing, tolerance for parameter mismatch, and so on. Two prototype 1 KVA VRs are implemented, and the effectiveness is demonstrated by some simulation and experimental results     

Natural Harmonic Elimination of Square-Wave Inverter for Medium-Voltage Application

In this paper, a low-frequency square-wave inverter with a series-connected pulsewidth modulation (PWM) inverter is investigated for high-power applications. The series compensators produce only the desired harmonic voltages to make the net output voltage sinusoidal with small PWM switching harmonics only. An open-loop control strategy for the series compensator is proposed in this paper. This strategy indirectly sets the compensator DC bus voltage to the desired level. No external DC source or active power at fundamental frequency is required to control this dc bus voltage. Different variations of this basic strategy are presented in this paper for medium-voltage applications. Theoretical analysis of this strategy is presented in this paper with simulation and experimental results.     

High-performance programmable AC power source with low harmonicdistortion using DSP-based repetitive control technique

This paper proposes a new control scheme based on a two-layer control structure to improve both the transient and steady-state responses of a closed-loop regulated pulse-width-modulated (PWM) inverter for high-quality sinusoidal AC voltage regulation. The proposed two-layer controller consists of a tracking controller and a repetitive controller. Pole assignment with state feedback has been employed in designing the tracking controller for transient response improvement, and a repetitive control scheme was developed in synthesizing the repetitive controller for steady-state response improvement. A design procedure is given for synthesizing the repetitive controller for PWM inverters to minimize periodic errors induced by rectifier-type nonlinear loads. The proposed control scheme has been realized using a single-chip digital signal processor (DSP) TMS320C14 from Texas Instruments. A 2-kVA PWM inverter has been constructed to verify the proposed control scheme. Total harmonic distortion (THD) below 1.4% for a 60-Hz output voltage under a bridge-rectifier RC load with a current crest factor of 3 has been obtained. Simulation and experimental results show that the DSP-based fully digital-controlled PWM inverter can achieve both good dynamic response and low harmonics distortion     

低压电网的谐波与治理

本文介绍了对谐波的特殊性,各种谐波源设备产生的谐波电流大小的估算,低压网络中谐波电流（电压也一样）的合成,谐波的危害,工业（包括实业等）私用电网的谐波电压标准,谐波治理措施（包括对谐波设备本身的,对配电变压器的,以及不得不采用滤波器等）,无源和有源滤波器的工作原理和优缺点比较,工程设计如何应对谐波的考虑,以及谐波对中性线电流大小的影响。均作了介绍,限于篇幅,不可能详细。欲知其详,请见《电气工程应用》2005年全年4期杂志。