Development of a novel commutation method that sharply reduces commutation failure of matrix converters

This paper proposes the safest novel commutation method for a matrix converter. There are two conventional commutation methods which depend on the polarity of the input line voltage (it is called “voltage commutation”) and depend on the polarity of the output current (it is called “current commutation”). However, problem of the voltage commutation is that commutation failure occurs around zero of the input line voltage. It is difficult to detect its polarity due to depending on offset and delay of the sensor. Similarly, the current commutation failure occurs around zero of the load current. A cause of these detection errors are a detection delay and an offset of a sensor. The proposed commutation method combines the input voltage commutation and the load current commutation. Therefore, the proposed commutation method can decrease the commutation failure without high accuracy sensor. In addition, a voltage error compensation based on the proposed commutation method is proposed in this paper. The proposed method can simply compensate for the commutation error of the output voltage and the input current at the same time. The effects of the proposed method are confirmed by experimental results with a 750 W induction motor and a R‐L load. Those results confirm that the proposed commutation can decrease commutation failure. Moreover, the total harmonics distortion of the input current and the output current are 2.6 point and 0.9 point lower than that of the condition without the compensation at 100% output power. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(4): 49–57, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20826     

Stability-margin adjustment on the basis of trials for PWM converters

For a pulsed dc drive, the influence of hysteresis in adjustment of the stability margin to compensate for uncontrollable drift of the bifurcation boundary is considered. Search adaptation is employed, in combination with the symbolic prediction of PWM converter dynamics.     

Quasi-dual modulation of three-phase PWM converters

The possibility of transferring the modulation method developed for a pulse width modulated (PWM) power converter with a DC voltage link (VLC) to a PWM converter with a DC current link (CLC) based on the inverse current and voltage behavior of these two systems is evaluated. The duality between VLC and CLC, which has been intuitively clear, is treated here in a scientific approach. It is shown that the nonplanar property of three-phase bridge circuits leads to a quasi-dual relation of the switching states of the VLC and CLC systems. The code conversion of the binary switching functions of a VLC into control signals of the power electronic devices of a CLC is given. The remaining degree of freedom of the correspondence is set by the requirement of minimum switching frequency of the converter     

PWM开关功率变换器闭环系统数值仿真的一种方法

提出了ＰＷＭ开关功率变换器闭环系统分阶段数值仿真的一种方法。将主电路及控制电路作为一个统一的整体,建立闭环系统各子拓扑的线性状态微分方程,使各拓扑切换时刻的确定变得非常简单且提高了仿真效率。     

A novel PWM strategy to minimize the surge voltage forcurrent-source converters

This paper presents a novel technique of pulsewidth modulation (PWM) wave control to minimize the surge voltage at the turn-off of switching devices. Two kinds of sawtooth carriers with different hypotenuses are employed to obtain a PWM waveform with minimum surge voltage, where each sawtooth carrier appears alternately at every 60° interval relative to the sinusoidal wave cycle. It is difficult to analyze the output waveforms because they are complicated. In order to obtain the analytical result, a frequency analysis approach using a switching function is proposed the results of which are verified experimentally     

PWM开关功率变换器分析与仿真方法简述

对开关功率变换器解析建模、数值仿真及符号分析方法的一些新进展及基本结果作了较为全面的叙述。着重说明符号分析法－等效小参量法的优越性,并指出了符数混合分析法是今后开关功率变换器分析方法发展的一个方向。     

A new PWM control method for AC to DC converters withhigh-frequency transformer isolation

A PWM control method for a switch-mode rectifier (SMR) based on the idea of coordinate transformation is presented. This method realizes sinusoidal input current waveforms, a controllable input displacement factor, and an arbitrary output voltage waveform. This method is advantageous for reducing higher and fractional harmonic components of the input waveforms and is suitable for real-time control. Simulations and experiments are carried out to confirm the feasibility of the proposed method     

A general procedure for investigation of electromagnetic processes of a valve engine under the full commutation

Features of physical processes in the electromechanical energy converter of a valve engine are described, and a general procedure of studying the electromagnetic processes in normal and emergency operational modes is developed that is based on them. As a result, the energy parameters and instantaneous values of output engine coordinates are obtained for these modes.     

State feedback control of current-type PWM AC-to-DC converters

A control method for current-type PWM AC-to-DC converters that realizes a sinusoidal AC input current and unity power factor is discussed in detail. In such converters, an LC filter placed on the AC side may cause a resonant problem, especially in the transient condition. To overcome this problem, state feedback control is introduced, and a control strategy suitable for DC-output current control as well as AC-side current control is proposed. Circuit parameters and feedback coefficients in the AC-side current control system are optimized on the basis of an analysis in which the system is treated as a sampled-data system. A method of investigating parameters in the DC-side current control system is shown. To confirm the effectiveness of the control strategy and the validity of the analytical results, an experimental investigation of the basic characteristics of the system is made. As an example, this system is applied to controlling the current waveform in the reactor. The experimental results for this application are also included     

New aspects of inspecting commutation angles of high-voltage direct current systems

Contents The conventional method of calculating high-voltage direct current (HVDC) converter commutation angles can result in very inaccurate results if the ripple of the DC is fairly high, or the HVDC link consists of capacitor commutated converters (CCC). For conventional line-commutated current source converters with a high DC ripple new analytical equations are presented for determining the commutation angles and the instantaneous values of DC DCside current at the firing instants. An iterative method for the calculation of commutation angles of CCC was also developed. The results are confirmed by digital simulation. Received: 30 April 2001 / Accepted: 8 June 2001     

PWM型开关变换器闭环系统时域分析的精细积分法

为了探讨开关变换器的拓扑结构计算方法,将精细积分法应用于开关变换器闭环系统的时域分析,利用递推的方法求解指数矩阵,将分段线性开关网络转化为离散时域方程,并用二次插值算法求解开关切换的时刻。实例仿真表明,该方法使得方程的求解精确度高且仿真时间短,各拓扑切换时刻的确定简单而高效。     

基于无源性理论的双馈风力发电机双PWM变换器协调控制

交流励磁双馈风力发电系统在实现最大风能跟踪过程中,转子侧功率变化频繁,使得双PWM变换器中的直流母线电压波动剧烈.基于无源性理论提出了一种双PWM变换器的协调控制方案,对双PWM变换器的转子侧和电网侧分别进行直接功率控制,使其具有相同的动态响应特性;在电容电压反馈控制的基础上引入功率前馈控制,使电容两侧功率流动动态平衡,以减少电容电压的波动.建立了双PWM变换器励磁的双馈风力发电系统的仿真模型,仿真结果表明该协调控制策略极大地改善了直流母线电压的动态特性,实现了最大风能跟踪,并且降低了变换器中电容容量要求,提高了风电系统的电能质量.     

双端口多功能交-直流双PWM变流器控制策略

针对传统中大功率密度的交-直流PWM变流器存在输出直流电压降压困难、电路设计复杂的问题,提出一种以三相交-直流变换和三重化直-直流变换为核心的交-直流双PWM变流器电路拓扑.在分析其工作原理,建立数学模型的基础上,综合运用软件锁相技术,瞬时无功理论,正序、负序、零序分解理论,自动限流及均流控制.同时采用交流电网和(或)直流电网双端口供电方式,实现交直流能量的双向流动.在理论分析和仿真研究的基础上,完成了380kW原理样机的研制.样机实验结果表明:采用该控制策略的双PWM变流器具备了充电器、不间断电源、无功补偿器等多种功能,同时输出直流电压调节范围宽、电路设计简洁且具有扩展性.     

Effect of DC ripple and commutation on the line harmonics ofcurrent-controlled AC/DC converters

Line harmonics are usually predetermined under the simplified assumption that the DC current is sufficiently smoothed. But in practical operation of controlled converters, e.g., feeding medium-sized DC drives, DC ripple often cannot be neglected. For the predetermination of line harmonics, this means that the operating point is specified by the EMF and the mean value of the DC current, i.e., the associated control and commutation angles are unknown. The consideration of the basic effects of commutation and DC ripple leads to line current harmonics that are separated into positive and negative sequence systems. Selected results of systematic evaluations show the amplitude and phase as functions of DC reactance as well as of the EMF and mean DC current in the range of usual low- and medium-voltage supply networks. In comparison with the conventional precalculations assuming sufficient DC smoothing, significant deviations occur in the case of higher DC ripple     

A new simple analytical method for calculating the optimum inverter size in grid-connected PV plants

A new simple analytical method for the calculation of the optimum inverter size in grid-connected PV plants in any location is presented. The derived analytical expressions contain only four unknown parameters, three of which are related to the inverter and one is related to the location and to the nominal power of the PV plant. All four parameters can be easily estimated from data provided by the inverter manufacturer and from freely available climate data. Additionally, analytical expressions for the calculation of the annual energy injected into the ac grid for a given PV plant with given inverter, are also provided. Moreover, an expression for the effective annual efficiency of an inverter is given. The analytical method presented here can be a valuable tool to design engineers for comparing different inverters without having to perform multiple simulations, as is the present situation. The validity of the proposed analytical model was tested through comparison with results obtained by detailed simulations and with measured data.     

A control method to realize sinusoidal input and output current waveforms for matrix converters based on PWM

A matrix converter (MC) is a three‐phase AC‐to‐AC direct converter without any energy storage requirement. It is expected to be a next‐generation converter by reason of possibilities of small size and high efficiency. At present, there are some problems preventing it from being used practically. One of the problems is the distortion in the input current. The control methods proposed so far have not realized sufficient reduction of the input current harmonics compared with conventional PWM rectifiers. As a solution to these problems, many approaches have been proposed. In the present paper, an improved PWM method that can achieve both sinusoidal input and output currents simultaneously is considered. In this method, the MC is treated as a controlled voltage source viewed from the load side. On the other hand, it is treated as a controlled current source viewed from the line side. The proposed control method is based on the mathematical expression of the function of the PWM operation of MC. To improve the input current waveform, two line‐to‐line voltages of the three‐phase line are used to control the output current. The output duty ratio of the two line‐to‐line voltages is utilized to improve the input current waveform without affecting the controllability of the output current. In addition, the compensation of the variations in the line voltage and the output current are introduced. In this way, the proposed method can realize the sinusoidal input and output currents. The effectiveness of the proposed control method is confirmed by some experimental results employing a laboratory prototype. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(1): 66–76, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20242     

Direct space vector PWM strategy for matrix converters with reduced number of switching transitions

This paper proposes a novel “Direct Space Vector PWM (Direct SVPWM)” strategy based on the direct AC/AC conversion approach for three‐phase to three‐phase matrix converters. This method allows the sinusoidal input and output waveforms as a major premise, and gives top priority to the improvement of output control performance in motor drive applications, such as providing maximum riding comfort in elevators, etc. Output voltage harmonics, switching losses, and common‐mode voltages can be reduced across the entire voltage region. In addition, the switching count can be reduced even further by fully utilizing the output current detection value. Direct space vectors are first defined, and the method of selecting space vectors is described. Next, the PWM duty calculation technique is explained. Finally, the validity of the proposed method is demonstrated by comparison with the conventional virtual indirect method based on experimental and analytical results. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 172(3): 52–63, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20953