电网不平衡时的三相PWM整流器控制策略

三相电网不平衡时,电压会存在负序分量。此时,如果对三相电压型PWM整流器采用普通的控制策略进行控制,会使其网侧电流含有大量的谐波,从而无法得到正弦输入电流。文章通过对三相电压型PWM整流器在电网不平衡情况下的建模,分析了网侧电流谐波产生的原因。在此基础上,采用了一种能使其网侧电流正弦化的控制策略,并进行了仿真验证。研究表明,该控制策略有良好的控制能力,可以使得交流侧电流达到正弦。     

电网不平衡条件下三相电压型PWM整流器非线性控制研究

本文提出了一种电网不平衡条件下三相电压型PWM整流器的控制方法。首先,建立了三相电压型PWM整流器的数学模型,基于网侧单位功率因数及负载电压恒定的控制目标,建立了网侧电流给定方程组。其次,基于“三相不平衡abc静止坐标系”与“不平衡坐标变换”建立的dq解耦模型,采用输入-输出线性化的电流控制策略,实现了有功电流与无功电流的独立控制。仿真实验结果表明：文中所提出的控制策略是有效的。     

基于SVPWM的航空高功率因数整流器设计

为了消除电网谐波污染、提高整流器的功率因数,对具有输出电压稳定、能够获得单位功率因数特点的三相电压型PWM整流器的控制策略进行了研究.介绍了空间矢量PWM(SVPWM)控制技术,并将该技术应用于航空整流器的设计;完成数字控制电路中网侧电压调理电路和直流侧输出电压调理电路以及相关软件的设计.实验结果表明,采用SVPWM电流控制技术能够使网侧电压与电流同相位,实现单位功率因数整流.     

电网不平衡条件下PWM整流控制策略的研究

通常情况下由于各种原因三相电网电压是不完全平衡的.这就使得常规的PWM整流器整流效率较低,为了提高电网不平衡条件下PWM整流器的整流效率,本文讨论了一种在电网不平衡条件下PWM整流的控制方法,在分析不平衡电网数学模型的基础上,建立了正、负序双电流控制策略的数学模型,利用Simplorer7.0对系统进行了仿真,通过对不平衡条件下常规的PWM整流器和不平衡条件下正、负序双电流控制的仿真结果进行对比,表明正、负序双电流控制可以提高网侧功率因数,改善系统的动态性能,同时得到较平稳的整流输出电压,有利于提高系统整体的运行效率。     

光伏阵列三相并网仿真模型

根据光伏太阳池板的内部结构和输出伏安特性建立光伏阵列的Matlab仿真模型,采用增量电导法跟踪光伏阵列的最大功率,利用三相电压型PWM整流器结构并网逆变器,对直流侧电压和交流侧电流实行双闭环控制,该模型可用于先伏发电系统的动态仿真研究.仿真实验证明直流侧的输出电压在给定值600 V附近波动,而交流侧的电流成正弦且谐波小.在此控制策略下光伏阵列的功率稳定,能够很好的跟随太阳辐射强度和环境温度的变化.     

基于改进滑模控制的动车组网侧PWM整流器

本文针对传统线性比例积分(proportional integral,PI)控制方式下的动车组网侧PWM整流器响应速度慢,直流侧电压波动较大的问题,考虑将滑模控制策略应用到整流器控制环节当中。针对滑模控制本身的抖振问题,本文采用连续的Sigmoid函数来代替滑动模态当中的不连续的Signum切换函数函数,以此来降低滑模控制固有的抖振问题。针对网侧电流谐波畸变的问题,本文将具有特定次谐波抑制能力的陷波器加入到了直流侧电压控制的反馈环节,以此来抑制网侧电流谐波,降低网侧电流谐波畸变率。最后在MATLAB/simulink平台搭建基于滑模控制的PWM整流器仿真模型,通过与传统PI控制下的整流器进行对比分析,验证本文所提方法的有效性。     

三电平整流器控制策略优化

CRH2型动车组采用三电平NPC结构的PWM整流器,本文介绍动车组三电平整流器控制策略适应性创新工作,控制策略从预测电流控制法和中点平衡控制两方面介绍了优化方法,表明我们在引进动车组技术的基础上优化的电流预测控制策略的动态和静态性能良好,能够有效平衡直流侧谐波的中点电位滞环控制方法可行.     

单相三电平PWM整流器3次谐波改善方法

由于三电平整流器功率器件承受电压应力小、输入电流谐波少、正弦度好。因此,文中选取单相三电平PWM整流器为研究对象。分析了各个工作状态下的开关组合及整流器的工作原理,同时选取瞬态直接电流控制作为电流内环控制方法对系统进行了仿真。同时分析了单相PWM整流器网侧电流的3次谐波产生原因,且采用了一种新型谐波抑制方法来消除此3次谐波。通过仿真验证了该新型控制算法对抑制网侧电流3次谐波的有效性,并降低了网侧电流的总谐波畸变率     

三相电流型整流器空间矢量调制仿真研究

相对于传统的电压型PWM整流器而言,电流型PWM整流器用于电机驱动具有动态响应快,便于实现再生制动和四象限运行,限流能力强,短路保护可靠性高,能在宽范围内精确控制转矩和速度等优点,在小、中等功率得到广泛的应用。利用三相电压型整流器（VSR）的电压空间矢量调制技术（SVM）实现三相电流型整流器（CSR）的三逻辑空间矢量调制,对其数学模型进行了推导,并利用Matlab建立了系统的仿真模型。仿真结果证明了该方法的有效性,实现了电流型整流器交流侧的单位功率因数和直流侧电流的平稳运行,对电力无功补偿和谐波抑制具有很好的效果。     

三相电压型PWM整流器的双闭环控制研究

传统三相PWM整流方式采用传统二极管或相控可控硅实现,但这种整流方式电压利用率低、损耗大,同时也会对电网引入大量谐波分量。因此建立三相电压型PWM整流器的数学模型,利用Park变换将静止坐标系转换为同步旋转坐标系,并对d、q轴分量进行电压前馈解耦,对解耦后的电压电流分量采用双闭环的控制策略。同时推导和分析了工程化典型Ⅱ型系统的电流内环PI参数设计,研究结果表明：采用典型Ⅱ型系统设计,直流侧输出电流的动态响应速度快、抗扰动能力强。然后利用仿真软件MATLAB进行原理性验证,比较不同类型系统设计的电流波形,验证了设计和分析的正确性。     

A novel control method for input output harmonic elimination of thePWM boost type rectifier under unbalanced operating conditions

This paper presents a new control strategy to improve the performance of the PWM boost type rectifier when operating under an unbalanced supply. An analytical solution for harmonic elimination under unbalanced input voltages is obtained resulting in a smooth (constant) power flow from AC to DC side in spite of the unbalanced voltage condition. Based on the analysis of the open loop configuration, a closed loop control solution is proposed. Simulation results show excellent response and stable operation of the new rectifier control algorithm. A laboratory prototype has been designed to verify the discussions and analyses done in this paper. Theoretical and experimental results show excellent agreement. Elimination of the possibility of low order AC and DC side harmonics due to unbalance is expected to materially affect the cost of DC link capacitor and AC side filter. The proposed method is particularly useful in applications where the large second harmonic at the DC link may have a severe impact on system stability of multiply connected converters on a common link     

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     

Regulation of a PWM rectifier in the unbalanced network state usinga generalized model

This study concerns the modeling and control of a pulse-width-modulated (PWM) rectifier in the case of network variations. The aim is to limit and stabilize variations of DC output voltage and line currents in such circumstances. Network variations can result in costly damage to power converters and their loads but a power converter such as the PWM rectifier, using cascade digital control, offers many capabilities to stabilize the system with optimized control. A generalized model of the PWM rectifier is first presented using the Clarke notation in order to separate the positive and negative sequences. The model is also extended to the harmonics. The cases of harmonic disturbance and an unbalanced network are then analyzed and an optimized regulation is presented for the latter case, validating the generalized model. Experimental results are proposed. The line current compensation loop method coupled with identification of network parameters offers a good solution to stabilize the PWM rectifier in an unbalanced network     

New control scheme of three-phase PWM AC/DC converter without phase angle detection under the unbalanced input voltage conditions

In general, three-phase PWM AC/DC power converters have been implemented in the synchronous frame model to eliminate steady state errors effectively and to obtain fast transient response characteristics. However, controllers designed in such way would have input current harmonics and DC-link voltage ripples under the unbalanced input voltage conditions due to the assumption of the balanced input voltage conditions. This paper describes a new control scheme to minimize harmonic distortions of the input current and DC-link voltage in the converter under the unbalanced input voltage. conditions. The synchronous frame input voltage, which is considered as the input side back-EMF component, is regulated pertinently according to the input voltage conditions. The current command is selected to eliminate the reactive power and the second order harmonic component of active power. In this case, the analysis of the input voltage is implemented in the synchronous frame without detecting the phase angle and magnitude of each phase voltage. The proposed control scheme is simple and effectively minimizing the harmonic distortions in the input and output system under the unbalanced input voltage conditions.     

Implementation of a three-level rectifier for power factorcorrection

In this paper, a new single-phase switching mode rectifier (SMR) for three-level pulse width modulation (PWM) is proposed to achieve high input power factor, low current harmonics, low total harmonic distortion (THD) and simple control scheme. The mains circuit of the proposed SMR consists of six power switches, one boost inductor, and two DC capacitors. The control algorithm is based on a look-up table. There are five control signals in the input of the look-up table. These control signals are used to control the power flow of the adopted rectifier, compensate the capacitor voltages for the balance problem, draw a sinusoidal line current with nearly unity power factor, and generate a three-level PWM pattern on the AC side of adopted rectifier. The advantages of using three-level PWM scheme compared with two-level PWM scheme are using low voltage stress of power switches, decreasing input current harmonics, and reducing the conduction losses. The performances of the proposed multilevel SMR are measured and shown in this paper. The high power factor and low harmonic currents at the input of the rectifier are verified by software simulations and experimental results from a laboratory prototype     

AC voltage and current sensorless control of three-phase PWM rectifiers

In this paper, a novel control scheme of three-phase PWM rectifiers eliminating both the AC input voltage and current sensors is proposed. The phase angle and the magnitude of the source voltage are estimated by controlling the deviation between the rectifier current and its model current to be zero. The input currents can be reconstructed from switching states of the PWM rectifier and the measured DC link currents. To eliminate the calculation time delay effect of the microprocessor, the currents ahead one sampling period are estimated by a state observer and then are used for feedback control. The proposed control scheme reduces the system cost and improves its reliability. The feasibility of the proposed AC sensorless technique for three-phase PWM rectifiers has been verified through experiments using a high performance DSP chip.     

A New Control Method for Input–Output Harmonic Elimination of the PWM Boost-Type Rectifier Under Extreme Unbalanced Operating Conditions

Under severe fault conditions in the distribution system, not only input voltages but also input impedances must be considered as unbalanced. This paper presents a new control method for input–output harmonic elimination of the pulsewidth-modulation (PWM) boost-type rectifier under conditions of both unbalanced input voltages and unbalanced input impedances. The range of imbalance in both input voltages and input impedances, for which the proposed method is valid, is analyzed in detail. An analytical approach for complete harmonic elimination shows that PWM boost-type rectifier can operate at unity power factor under extremely unbalanced operating conditions resulting in a smooth (constant) power flow from ac to dc side. Based on the analyses in open-loop configuration, a feedforward control method is proposed. Elimination of harmonics at ac and dc side of the converter affects the cost of dc link capacitor and ac side filter. The proposed method is very useful when the PWM boost-type rectifier is subject to extreme imbalance due to severe fault conditions in the power system. In addition, by using the proposed method, the PWM boost-type rectifier can be operated from the single-phase supply in cases where three-phase source is not available. Simulation results show excellent response and stable operation of the PWM boost-type rectifier under the proposed control algorithm. Experimental and simulation results are in excellent agreement.      

A new control strategy to improve the performance of a PWM AC to DCconverter under unbalanced operating conditions

Abnormal harmonics of significant magnitude are generated at the output and input terminals of a PWM (pulse-width-modulated) AC-to-DC power converter under unbalanced operating conditions. A new control strategy is presented to selectively cancel the generated lower-order abnormal harmonics at the output and input terminals and thereby to preserve the high-performance features of a PWM AC-to-DC power converter. The proposed technique essentially involves computing the sequence components of the unbalanced input supply and suitably counter-unbalances the PWM gating signals of the power converter switches to cancel the generated abnormal harmonics. The technique is essentially a feedforward approach and is suitable for higher-power GTO (gate turn-off thyristor) type PWM AC-to-DC power converters. A procedure for implementing this technique in real time is discussed. Selected results are verified experimentally on a prototype PWM AC-to-DC power converter     

A fuzzy-controlled active front-end rectifier with current harmonicfiltering characteristics and minimum sensing variables

A control strategy which allows conventional voltage-source current-controlled (VSCC) pulsewidth modulation (PWM) rectifiers to work simultaneously as active power filters is presented. The proposed control strategy also allows compensating the system power factor and compensating unbalanced loads. The measurement and/or calculation of the harmonics and reactive power are not required, making the proposed control scheme very simple. The active front-end rectifier acts directly on the mains line currents, forcing them to be sinusoidal and in phase with the mains voltage supply. To improve the dynamic of the system, the amplitude of the current is controlled by a fuzzy system, which adjusts the DC-link voltage of the PWM rectifier. The strategy is based on connecting all the polluting loads between the PWM rectifier and their input current sensors. The main advantages of this approach are the following: (1) there is no need to install a specially dedicated active power filter; (2) it also works simultaneously as a power factor compensator; and (3) no special and complicated calculations are required for harmonic elimination. The viability of the proposed active front-end rectifier is proved by simulation and with experimental results obtained from a 2 kVA PWM prototype