最小共模电压SVPWH调制算法电压源整流器的研究（下）

摘要：本文在基于三相VSR一般数学模型的基础上推导了直流侧共模电压的表达式,分析了理想情况下无死区时和实际情况下有死区时传统SVPWM算法的零矢量和非零矢量对共模电压幅值和谐波分布的影响,并在此基础上提出了一种采用非零矢量等效合成零矢量作用的最小共模电压SVPWM调制算法和共模电压不受死区影响的死区时间设置方法。以上分析得到了MATLAB／SIMULINK仿真分析和变频空调样机的定性验证。结果表明：相比传统采用零矢量的SVPWM算法．最小共模电压SVPWM算法使共模电压的幅值和变化率降低66％,减轻了共模电压干扰。     

Common-Mode Ripple Current Estimator for Parallel Three-Phase Inverters

For the three-phase parallel voltage source inverter systems with common dc link, several control methods were developed to suppress the common-mode circulating current. The common-mode ripple current is the main disturbance source of the common-mode circulating current control system that forms part of the parallel discontinuous pulsewidth modulation (PWM) inverter system. In this paper, a real-time analysis method for the common-mode ripple voltage of the three-phase discontinuous PWM inverter is proposed, whereby the amplitude of the common-mode ripple current can be estimated correctly, the hysteresis width of the circulating current controller can be adjusted to be as small as possible, and consequently, the rms circulating current is minimized as well. The simulation and experimental results are presented to confirm the theoretical analysis method of the common-mode ripple current and the performance of the proposed common-mode ripple current estimator.      

A Single-Stage PV Module Integrated Converter Based on a Low-Power Current-Source Inverter

This paper presents a transformerless three-phase inverter designed for the integration into a special type of a photovoltaic (PV) module, which is capable of providing an output voltage of several hundred volts. The chosen topology, a current-source inverter, features a single-stage power conversion system that directly feeds into the grid. The principle operation and control is described, and a modified modulation strategy is proposed to attenuate common-mode currents. A robust and highly efficient laboratory prototype of a 250-W module integrated converter has been implemented and tested. Its compact and flat design allows the direct attachment to the PV module.     

一种低漏电流七开关无变压器型光伏并网逆变器拓扑

无变压器型光伏逆变系统中的漏电流高于300mA时规定必须在0.3s内从电网中切除。为解决系统中脉动共模电压引起的漏电流问题,提出新型七开关逆变拓扑(H7),该拓扑在直流输入端引入两个高频开关管,续流阶段确保直交两侧完全解耦,维持共模电压的恒定。在调制方法上,还可以实现倍频SPWM策略,降低电流纹波。在任意模态中开关管始终交错工作,有助于热应力均衡。最后,通过2kW的样机平台验证了抑制后漏电流峰值仅为60mA,相对于传统拓扑性能更优越,提高了系统的安全裕度。     

DC Link Capacitor Voltage Balancing in a Three-Phase Diode Clamped Inverter Controlled by a Direct Space Vector of Line-to-Line Voltages

In this paper, the direct modulation strategy of a three-level inverter with self stabilization of the dc link voltage is extended to a five-level inverter. Therefore, a new modeling and control strategy of a five-level three-phase diode-clamped inverter (DCI) is presented. The obtained modeling shows that modulated multilevel voltages are obtained by combination of eight different three-level functions, which are called modulation functions. Therefore, a space-vector scheme without using a Park transform is explained. Based on this algorithm, the location of the reference voltage vector can be easily determined. Then, the voltage vectors are selected to generate corresponding levels and simultaneously their durations are calculated. More over, the redundancies of different switch configurations for the generation of intermediate voltages are used to limit the deviation of capacitor voltages. Experimental results are given to illustrate the proposed control strategy of the three-phase three-level diode clamped inverter. Then, obtained results for a five-level three-phase DCI with the extended version of the control strategy are presented to show the good performances of the proposed balancing modulation.     

PWM变频器谐波及其抑制策略综述

随着PWM变频器的广泛使用,它所带来的问题不可忽视。本文主要介绍了变频器使用过程中带来的共模电压和过电压问题。分别介绍了共模电压和过电压的产生机理,在此基础上介绍了过电压和共模电压的几种抑制策略,包括抑制过电压的几种滤波器以及共模电压滤波器和PWM调制策略的优化,并对这几种抑制策略进行了分析比较。     

死区对PWM逆变器共模电压的影响及其抑制方法

变频器采用的空间矢量脉宽调制(SVPWM)会产生共模电压,后者对变频器和电机产生危害。改进的空间矢量脉宽调制法有利于降低共模电压,但由于没有考虑死区的影响,实际效果受到较大影响。文章详细研究了死区对PWM逆变器共模电压的影响,并提出了一种消除死区的方法来抑制死区影响并对共模电压起到一定的抑制作用,使改进的空间矢量脉宽调制法能够真正达到预想的效果。最后通过Matlab仿真实验,验证了该方法的有效性。     

An active circuit for cancellation of common-mode voltage generatedby a PWM inverter

This paper proposes an active common-noise canceler (ACC) that is capable of eliminating the common-mode voltage produced by a pulsewidth modulation (PWM) inverter. An emitter follower using complementary transistors and a common-mode transformer are incorporated into the ACC, the design method of which is also presented in detail. Experiments using a prototype ACC, whose design and construction are discussed in this paper, verify its viability and effectiveness in eliminating common-mode voltage in a 3.7 kW induction motor drive using an insulated gate bipolar transistor (IGBT) inverter. Some experimental results show that the ACC makes significant contributions to reducing a ground current and a conducted electromagnetic interference (EMI). In addition, the ACC can prevent an electric shock on a nongrounded motor frame and can suppress motor shaft voltage     

Application of a three-level NPC inverter as a three-phase four-wire power quality compensator by generalized 3DSVM

A two-level four-leg inverter has been developed for the three-phase four-wire power quality compensators. When it is applied to medium and large capacity compensators, the voltage stress across each switch is so high that the corresponding dv/dt causes large electromagnetic interference. The multilevel voltage source inverter topologies are good substitutes, since they can reduce voltage stress and improves output harmonic contents. The existing three-level neutral point clamped (NPC) inverter in three-phase three-wire systems can be used in three-phase four-wire systems also, because the split dc capacitors provide a neutral connection. This paper presents a comparison study between the three-level four-leg NPC inverter and the three-level NPC inverter. A fast and generalized applicable three-dimensional space vector modulation (3DSVM) is proposed for controlling a three-level NPC inverter in a three-phase four-wire system. The zero-sequence component of each vector is considered in order to implement the neutral current compensation. Both simulation and experimental results are given to show the effectiveness of the proposed 3DSVM control strategy. Comparisons between the 3DSVM and the 3-D hysteresis control strategy are also achieved.     

General Modulation Strategy for Seven-Phase Inverters With Independent Control of Multiple Voltage Space Vectors

This paper focuses on the analysis of a seven-phase voltage-source inverter for high-performance motor drives. The problem of the modulation strategy of the inverter is solved by combining the multiple space vector representation with traditional carrier-based pulsewidth modulation. This approach leads to the definition of a general modulation strategy that can be usefully utilized in multimotor drives, as well as in multiphase motor drives for improving the torque density. The inverter output voltage capability is investigated, showing that the proposed modulation strategy is able to fully exploit the dc input voltage either in sinusoidal or nonsinusoidal operating conditions. The results obtained in the analytical investigation are confirmed by experimental tests.     

基于升降压斩波电路的三相DC/AC逆变器研究

为了解决常用的逆变器所带来的问题,我们提出一种新型的带升降压功能的三相DC/AC变换器拓扑,并介绍了其工作原理。借助于PSIM仿真软件,对单相和三相电路进行了仿真研究,提出了由单相组成三相电压输出的构成方法。在列出仿真参数的前提下,给出了负载电压,负载电流以及调制给定电压和逆变器输出电压的仿真结果。仿真结果表明三相DC/AC逆变器可以实现50 kHz高频功率变换下宽输入电压范围工频逆变输出,证明了理论分析的正确性。     

三相电压源逆变器三种方波调制算法的仿真分析(上)

根据桥臂中点目标电压波形的不同,三相电压源逆变器具有多种调制方式,如方波调制、梯形波调制、SPWM调制和SVPWM调制等。本文从学习的角度,采用仿真方法分析了三相电压源逆变器采用方波调制时120°、150°和180°导电方式的工作原理,并进行了简单的比较分析。     

Trinary Hybrid 81-Level Multilevel Inverter for Motor Drive With Zero Common-Mode Voltage

This paper proposes a trinary hybrid 81-level multilevel inverter for motor drive. Benefiting from the trinary hybrid topology of the inverter, 81-level voltages per phase can be synthesized with the fewest components. Bidirectional DC-DC converters are used not only to inject power to the DC links of the inverter but also to absorb power from some DC links in cases with a lower modulation index. The higher bandwidth of DC-DC converters alleviates the ripples of DC-link voltages caused by the load current. The space vector modulation used here, which selects voltage vectors that generate a zero common-mode voltage in the load, works at a low switching frequency. With up to 81-level voltages per phase, the total harmonic distortion is small, and the relationship between the fundamental load voltage and the modulation index is precisely linear. A vector controller is used to control an induction motor, which results in a high dynamic response for speeds or torques. The performance of the proposed inverter for the motor drive is confirmed by simulation and experiment.     

Four-wire dynamic voltage restorer based on a three-dimensional voltage space vector PWM algorithm

A modified voltage space vector pulse-width modulated (PWM) algorithm for a four-wire dynamic voltage restorer (DVR) is described. The switching strategy based on a three-dimensional (3-D) /spl alpha//spl beta/O voltage space is applicable to the control of three-phase four-wire inverter systems such as the split-capacitor PWM inverter and the four-leg PWM inverter. In contrast to the conventional voltage space vector PWM method, it controls positive, negative and zero sequence components of the terminal voltages instantaneously. Three 3-D modulation schemes are analyzed with respect to total harmonic distortion (THD), weighted total harmonic distortion (WTHD), neutral line ripple and switching loss over the whole range of the modulation index when the DVR experiences both balanced and unbalanced sags with phase angle jumps. Experimental results from a 9 kW DVR system using a split-capacitor PWM inverter are presented to validate the simulation results.     

Design and performance of a passive EMI filter for use with a voltage-source PWM inverter having sinusoidal output voltage and zero common-mode voltage

This paper deals with integrating a small-sized passive electromagnetic interference (EMI) filter with a voltage-source pulse-width modulated (PWM) inverter. The purpose of the filter is to eliminate both high-frequency common-mode and normal-mode voltages from the three-phase output voltages of the inverter. A laboratory system consisting of a 5-kVA inverter, a 3.7-kW induction motor, and a specially-designed passive EMI filter was constructed to verify the viability and effectiveness of the filter. As a result, both line-to-line and line-to-neutral output voltages look purely sinusoidal as if the inverter were an ideal three-phase variable-voltage, variable-frequency power supply when viewed from the motor terminals. This results in a complete solution to serious EMI issues related to high-frequency common-mode and normal-mode voltages produced by the PWM inverter.     

A dual-bridge inverter approach to eliminating common-mode voltagesand bearing and leakage currents

This paper presents a dual-bridge inverter approach to eliminate the motor common-mode voltage and resulting bearing and leakage currents. The novel dual-bridge inverter is controlled to generate balanced excitation of the induction motor under pulsewidth modulation (PWM) inverter operation. Theoretical analysis, simulation results, and experimental results are presented to verify this concept     

Selective Harmonic Elimination PWM Control Scheme on a Three-Phase Four-Leg Voltage Source Inverter

A selective harmonic elimination (SHE) control strategy on a three-phase four-leg inverter is reported in this paper. The control signals of the four legs are calculated as follows: 1) control signals of three legs are mathematically expressed using Fourier-based equations on line-to-line basis as conventional SHE technology, which eliminates lower order nontriplen harmonics, and 2) the fourth leg produces the harmonics that are equal to the lower triplen harmonics produced by the other legs. The inverter has almost symmetric three-phase output voltage with unbalanced load because the fourth leg provides a low-impedance path for the triplen harmonics. The switching-to-fundamental frequency ratio is only 13 and 27 (per unit) p.u. for the three legs and the fourth leg in the proposed prototype, which is with the total harmonic distortion of output voltage lower than 4%. Selected solutions for the switching angles are presented and verified by simulation and experimentation in order to confirm the effectiveness of the proposed scheme.     

A common mode voltage reduction in boost rectifier/inverter systemby shifting active voltage vector in a control period

This paper proposes a new space-vector pulse width modulation (SVPWM) strategy that can reduce the number of common mode voltage pulses in a three-phase boost rectifier/inverter system using a synchronized switching sequence. In the proposed SVPWM strategy, it is possible to eliminate one common mode voltage pulse in every control period by shifting the active voltage vectors of the inverter to align to those of the boost rectifier. Thus, a reduction in the total number of common mode voltage pulses and RMS motor leakage current can be obtained without extra hardware. Since the proposed SVPWM strategy can be simply implemented in software, it is widely applicable regardless of the power capacity of the converter and results in no increment of converter volume, weight and price. Moreover, because the proposed SVPWM strategy maintains the magnitude of the active voltage vector required for motor control and simply changes the distribution of the zero, voltage vector, it does not effect the control performance of the power converter     

Induction-generator-based system providing regulated voltage withconstant frequency

The electrical characteristics of an isolated induction-generator-based system are improved through the association with a voltage-source pulsewidth modulation (PWM) inverter. The electronic converter allows the achievement of a better system behavior in many aspects: voltage regulation, frequency stabilization, and reactive power compensation. The system operation strategy consists of maintaining constant synchronous frequency at the induction generator via an association with a PWM inverter. The system power balance and the generator voltage regulation may be accomplished by two different means: through the rotor speed regulation, or by sending part of the energy stored in the inverter DC side to the grid through a single-phase line, in case the rotor speed is not regulated and a single-phase grid connection is available. The obtained results demonstrated the system is stable, robust, and an effective source of regulated three-phase voltages     

Voltage-Balance Compensator for a Carrier-Based Modulation in the Neutral-Point-Clamped Converter

This paper presents an optimal voltage-balancing compensator for a specific modulation technique applied to a neutral-point-clamped converter. The technique uses two modulation signals per phase, and it is called double-signal pulsewidth modulation. It completely eliminates low-frequency oscillations in the neutral-point voltage. However, it does not provide natural voltage balancing; therefore, a compensation loop is required. The proposed control generates a feedback compensation signal that correctly modifies the three-phase modulation signals. The optimal compensation signal is calculated by a dynamic limiter according to the intrinsic limitations of the system related to the variability range of the modulation signals. It significantly improves the voltage balancing under all operating conditions of the converter. In addition, this compensation strategy does not increase the switching frequencies of the power devices. The algorithm is tested and verified using both simulation and experimentation.