A PI-type dead-time compensation method for vector-controlled GTOinverters

In the case of voltage-source gate-turn-off thyristor (GTO) inverters, the conventional dead-time compensation methods do not work well, since the terminal voltage of an inverter leg is not constant during the dead-time period, due to the presence of the snubber circuit. We propose a closed-loop dead-time compensation method that regulates the voltage error by a proportional-integral (PI)-type compensator. We show its superior performance by the reduction in current ripple and in the sixth harmonic component of the motor current in the synchronous frame     

异步电机矢量控制中死区补偿的仿真研究

为了研究异步电机矢量控制中的死区补偿问题,详细分析了逆变器中死区的产生和对输出电压、电流的影响,结合矢量控制中死区时间补偿方法,提出了在异步电机转子磁场定向控制上应用一种基于前馈补偿的死区补偿方法,并对系统应用Matlab／SIMULINK进行了仿真研究。仿真结果表明,该死区补偿策略在矢量控制中取得了良好的补偿效果。     

Regenerative converter for PWM AC drives

Since the PWM induction motor drive has become the industrial drive of choice, applications involving four-quadrant operation for AC drives have become more common. To satisfy such applications, a regenerative AC/DC converter that is robust is needed to allow bidirectional power flow between the load and power distribution system. A robust technology that is well understood is the 6 SCR converter operating in the inverting mode. However, the typical 6 SCR converter will either limit the maximum DC bus voltage or require a step-up transformer. The proposed regenerative converter allows the SCR power structure to operate as a synchronous line commutator, while a two-transistor series/shunt chopper, with a power resistor, controls the regenerative power flow, and offers an emergency braking capability. In addition, SCR commutation is accomplished by the line voltage and diversion of bus current. Both simulation and experimental results are given     

EMI emissions of modern PWM AC drives

Electromagnetic interference (EMI) noise is defined as an unwanted electrical signal that produces undesirable effects in a control system, such as communication errors, degraded equipment performance and malfunction or nonoperation. This article provides a common understanding of the EMI issues and provides simple pre-installation and post-installation guidelines useful for all interested parries involved in the industry application of adjustable speed PWM invertor-fed AC motor drives     

Cable design for PWM variable-speed AC drives

The advent of pulsewidth modulation (PWM) drives utilizing insulated gate bipolar transistor (IGBT) technology has made the selection of the interconnecting power cable between the drive and load an important decision. Motor bearing currents, reflected voltage wave, and electromagnetic interference shielding have become areas of concern in the PWM drive system. Based on the previous literature, a cable with a high conductivity and continuously welded and corrugated aluminum sheath is most advantageous. This paper emphasizes the worthiness of this type of armored cable     

Application issues for PWM adjustable speed AC motor drives

In this article, some application issues for adjustable speed AC motor drives have been investigated. The effects of high PWM frequency, or high dv/dt on the motor terminal voltages and bearing currents have been addressed and explained. Mitigation techniques have been shown to significantly reduce the transient peak voltage and dv/dt at the motor terminals, as well as within the motor windings. This reduction contributes to improved reliability of PWM motor drive systems     

级联SVG控制策略及死区补偿技术研究

针对应用在中高压大功率领域的级联H桥静止无功发生器(static var generator,SVG)进行了深入研究,提出一种新的控制策略及死区补偿技术.该控制策略通过建立SVG多回路占空比平均值数学模型,计算各相平均导通时间,并通过相移控制及直流母线电压平衡补偿控制,实现级联SVG输出.考虑实际设备运行中器件开关死区引起的输出电压偏差,在计算得到的占空比信号基础上,通过合理增减开关占空比时间,以补偿死区负面效应.所提出的控制策略及死区补偿方法,提高了系统动态响应能力,降低了输出电流畸变,仿真和实验结果均表明所提策略的有效性.     

Evaluation of motor power cables for PWM AC drives

Three-phase power cables installed between the inverter and motor of AC motor drive systems have been mostly ignored in the years since AC drives have become widely accepted in industrial applications. However, power cable characteristics have become quite critical with the advent of faster inverter switching times, which have decreased by a factor of perhaps 20:1 in the last ten years. This paper describes the present areas of concern with regard to power cabling, as well as a test program to quantitatively evaluate power cable-related remedies for these problematic areas. A relative ranking of test results is developed comparing the eight power cable types tested. Cable connector considerations are examined, together with interconnection of the cable shield, or sheath, and the NEC ground circuits are discussed in light of the test results and recommendations presented. Power cable voltage ratings are discussed and recommendations made. A final cable total performance comparison, including installation factors, summarizes the paper     

电压源型PWM逆变器死区效应补偿策略研究

针对电压源型PWM逆变器的死区效应,提出了一种减小零电流钳位和寄生电容影响的死区补偿方法。分析了因死区时间和开关器件的非理想特性引起的误差电压,对因零电流钳位造成的电流极性检测不准进行了校正,并根据功率开关器件寄生电容引起的导通和关断延时,对补偿电压大小进行了调整。仿真结果证明,该补偿方法有效改善了电机的电流波形,提高了逆变器的输出性能。     

并网逆变器死区效应消去补偿方法研究

针对并网逆变器死区效应问题,在充分分析并网逆变器工作特点及零电流箝位现象的基础上,提出了一种新颖的逆变器死区效应消去补偿方法。该方法在非过零区域依据并网电流的方向选择有效开关管,屏蔽无效开关,在过零区域根据并网电流的大小进行前馈补偿。与传统死区消去和补偿方法相比,该方法充分考虑了零电流箝位现象,能够更好地抑制电流过零处逆变器输出电压波形畸变,有效消除了死区效应的影响,降低输出电压谐波含量,从而改善并网电流质量。利用Matlab/Simulink仿真软件进行了仿真验证,仿真结果证明了逆变器死区效应消去补偿方法的有效性和正确性。     

Sixth torque harmonic in PWM inverter-fed induction drives and its compensation

The sixth-order torque ripple harmonic in induction motors under field-oriented control with voltage space phasor modulation is investigated by means of a simulation model. It is shown that the main reason for its appearance lies in the pulsewidth modulation. Measurements on a 220-kW asynchronous drive confirm the simulation results. A compensation strategy is proposed.     

Analysis and compensation of current measurement error invector-controlled AC motor drives

Recently, as the higher performance of torque control is required, current measurement error inherent in all kinds of AC drives becomes significant. In this paper, the effects of current measurement error, classified as offset error and scaling error, are analyzed. It is demonstrated that the offset error causes the torque of a motor to oscillate at the stator electrical frequency and that the scaling error causes the torque of a motor to oscillate at twice the stator electrical frequency. These torque ripples deteriorate the performance of speed control, because they act as disturbance loads. In order to obtain precise torque control and eliminate speed ripples, a compensation method is proposed. The simulation and experimental results show that the analysis is correct and the compensation method improves the performance of torque control by eliminating torque ripples effectively     

A fully digital control strategy for synchronous reluctance motorservo drives

For existing electric drives, the controller implementation is either totally analog or hybrid analog/digital, and the control algorithm broadly falls into two categories, average torque control (ATC) and instantaneous torque control (InsTC). In this paper, a fully digital-implementation oriented control strategy-incremental torque control (IncTC)-is proposed and verified with digital simulation. A TMS320C30 DSP-based implementation of the proposed IncTC is developed and tested. Experimental results given in the paper indicate that the proposed IncTC is valid and holds a great promise for reluctance motor digital control     

Optimal common-mode voltage reduction PWM technique for inverter control with consideration of the dead-time effects-part II: applications to IM drives with diode front end

The main theme of this paper is to demonstrate the applications of the newly developed common-mode voltage reduction pulsewidth-modulation (PWM) technique, which restricts the common-mode voltage to one-third of DC-link voltage, to vector-controlled induction motor drives. As compared to previous common-mode voltage reduction techniques, the presented technique can be applied to the inverter with diode front end and has no adverse effect on the linear modulation range. Therefore, vector-controlled drives using the developed technique for inverter control have a wide speed range. Moreover, the effects of the common-mode voltage reduction PWM technique on speed response for vector-controlled induction motor drives will be fully investigated in this paper. It will be demonstrated by intensive experimental results that speed performance does not deteriorate significantly within the rated speed range.     

A three-phase PWM strategy using a stepped reference waveform[invertor drives]

The theoretical derivation of a carrier-based three phase pulse-width-modulated (PWM) technique for invertor drives using a stepped reference waveform is presented. The reference waveform is divided into 30° intervals, with each interval being controlled individually to control the magnitude of the fundamental harmonic. This process contrasts with the commonly used approach of amplitude modulating the entire reference waveform to control the fundamental harmonic. The resultant PWM technique is shown to be similar to a square-wave strategy but with a lower current distortion being obtained at high fundamental magnitudes and high carrier frequencies. The practical realization of the PWM technique is described using performance criteria such as minimum pulse widths, peak carrier frequencies, and the current distortion     

Output filters for PWM drives with induction motors

When an induction motor is energized from a pulse width modulated (PWM) inverter, through long connecting cables, its insulation system can be severely stressed. The high dv/dt voltage pulses at the output of the inverter cause traveling waves in the connecting cable between the inverter and the motor. When the traveling wave reaches the motor, a large impedance mismatch is present which leads to a reflected voltage wave that, when added to the incoming incident wave, can reach two times the inverter output voltage. The resulting overvoltage at the motor terminals stresses the insulation system and can lead to reduced motor life. Various output filter arrangements can be used to condition the inverter output voltage before it is applied to the cable. The advantage of adding output filtering is that the dielectric stress on the motor insulation and the inverter cable charging current can both be reduced. The major disadvantages of adding filtering is that they represent extra cost, they require extra mounting space, and they introduce extra losses in the system. The most commonly used types of inverter output filters are: simple output line inductors; output limit filter; sine wave output filter; and motor termination filter. These filters are discussed     

交流电流直接控制的单相PWM整流器非线性控制策略

由于单相电压型PWM整流器比较难以实现交流电流的直接控制,为了使得系统控制达到期望的效果,根据反步法在多变量非线性系统的控制方面的诸多优点,设计了基于反步法的非线性控制算法。详细介绍了单相电压型PWM整流器的数学模型,根据电感电容的能量关系分别构造了电压、电流环的Lyapunov函数,通过Lyapunov函数导数的负定,推断出系统的稳定性。且进行了基于PSIM的电路仿真,并构建采用IGBT全控型开关管的单相H桥的整流电路进行了验证。实验结果显示该方案下能够保证跟踪误差渐近收敛,说明系统设计是正确有效的。     

Unity-power-factor PWM converter with DC ripple compensation

The generation of harmonics and their subsequent propagation into power lines is a topic of increasing concern to power-supply authorities. To prevent obstacles in the power system, a unity-power-factor PWM converter will be applied at ac-dc power conversion plants. However, the PWM converter, especially at single-phase circuit, has some serious defects, including low-frequency ripple current that flows into the dc line and gives rise to a low-frequency ripple voltage that appears on the dc output. In usual cases, it is necessary to connect a very large capacitor or a passive L-C resonant circuit to the dc line for reduction of low-frequency ripple voltage. However, when batteries are connected to the dc output, most of the dc ripple current flows into the battery even if the above circuits are used, because the impedance of the battery is very low compared to that of the circuits. The low-frequency ripple current causes power loss on the battery and the temperature rises. It is well known that the life of a battery is deeply influenced by the temperature. The ripple current, therefore, should be reduced as low as possible. To accomplish reduction of the low-frequency ripple current, a novel topology for the PWM rectifier is presented in this paper. The main circuit is constituted by adding only a pair of switching devices to the conventional PWM converter circuit. With a simple control technique, the ripple energy on the dc line is converted into stored energy on the input ac capacitors through additional switches. The theoretical characteristics are obtained by using the state-space averaging method. The effect of ripple reduction is confirmed by experiments using a breadboard setup. © 1998 Scripta Technica, Electr Eng Jpn, 123(1): 51–62, 1998     

MRAS-based speed sensorless control scheme with stator resistance identification function for vector-controlled induction motor drives

This paper describes a new scheme for the speed sensorless control of the vector-controlled induction motor drive. Based on the model reference adaptive system (MRAS) theory, the rotor speed of the induction machine is estimated with a full-order adaptive observer. The estimated speed then is used as the signal for the vector control and the speed control. To accurately estimate the speed at the lower speed range, the value of the stator resistance also is identified at the same time and then is used to modify the resistance value set in the observer. The resulting system is verified to be hyperstable with Popov's criterion. As a result, this drive can operate stably in a wide range of speed even at zero speed. Also, it is shown theoretically that neither speed nor resistance of the rotor can be identified at the same time because these two parameters are dependent on each other. Simulation results and experiments also show that the scheme is effective.     

Controlled AC drives with ride-through capability at powerinterruption

General purpose PWM inverter drives are equipped with an undervoltage protection mechanism, causing the system to shut down within a few milliseconds after a power interruption in the mains. This may entail loss or damage of material in such critical applications as the production of textile fibers, paper, or with extruder drives. The proposed solution to this problem is to recover some of the mechanical energy stored in the rotating masses. When a power interruption occurs, a sequence of fast feedforward commands is applied to force an immediate transition into the regeneration mode. During the interrupt interval, the drive system continues to operate at almost zero torque, just regenerating a minor amount of power to cover the electrical losses in the inverter. The method is implemented in an additional software package to be used with general-purpose inverter drives of limited dynamic performance. Experimental results are presented