Application of Gate Turn-Off Thyristors in 460-V 7.5-250-hp AC Motor Drives

A 7.5-250-hp range of variable-frequency ac motor drives has been under development at the Westinghouse R & D Center since early in 1981. Design and performance details for prototype equipment rated for 10, 20, and 50 hp will be discussed. The drive system comprises a three-phase thyristor controlled ac/dc converter in conjunction with a dc/ac adjustable-frequency inverter using gate turn-off thyristors (GTO's). The output of the inverter is a six-step voltage wave in the range of 6-120 Hz, suitable for driving three-phase ac induction or synchronous motors. Details of the inverter design, including means to protect the gate turn-off thyristors from output line-to-line or line-to-ground short circuits, will be given special attention.     

Fault-tolerant switched capacitor–based boost multilevel inverter

This paper proposes a fault-tolerant switched capacitor (SC)–based boost multilevel inverter. The proposed inverter is able to convert a low-level dc voltage into a desired ac output voltage in single-stage power conversion. It can accomplish a high voltage gain by using multiple SC cells arrangement at reduced voltage stresses on the switching devices and passive circuit elements in the boost network. The principle of operation and steady-state analysis of the proposed topology are presented to formulate the mathematical relationship between input dc and output ac voltage. In addition to that, the proposed inverter can also provide reliable electrical power supply at prescribed ac output voltage in the event of open-circuit failure of power switches. The fault tolerability is realized by reconfiguring the pulse width modulation (PWM) control scheme, whereas the reduction in output voltage is compensated by the boosting characteristic of the inverter. The effectiveness of the proposed inverter has been compared with other impedance source multilevel inverters in terms of voltage gain, boosting capability, and voltage stresses. A laboratory prototype of the proposed inverter is developed for experimentation, and its operation is validated by simulation and experimental results.     

DSP-based real time output waveform synthesis for three-phase PWM inverter

A new digital control technique is proposed to synthesize an arbitrary three-phase PWM inverter output. Sensing two line-to-line voltages, the required pulse patterns for deadbeat response are computed in a real time manner based on the predicted voltage by an observer at 18-kHz sampling frequency. When used for the uninterruptible power supply, this closed-loop voltage control inherently results in a very low THD and a very quick transient response with less filter capacity. Also, with the repetitive compensator, the proposed scheme has advantages in improving the output waveform for nonlinear load. This paper describes the modeling technique, theoretical analysis, simulations and experimental results.     

A New Current Source GTO Inverter with Sinusoidal Output Voltage and Current

A new current source inverter with sinusoidal output voltage and current is presented. Gate turn-off thyristors (GTO's) and pulsewidth modulation (PWM) control techniques are used in the current source inverter to produce the sinusoidal output voltage and current. Three capacitors are connected to the ac output terminals to absorb overvoltages which occur when the GTO current is cut off and to provide a filter function for reducing harmonics in the output current. Voltage spikes, which have been a serious problem in the practical application of this inverter, are suppressed by adding gate pulses which force the inverter into a state of shoot-through. Moreover, this inverter permits the capacitance of an ac output terminal capacitor for absorbing overvoltages to be reduced to one-tenth or less of that of a commutating capacitor in a conventional thyristor type current source inverter. A 3.7-kW induction motor is driven by the inverter. The motor efficiency and noise level are measured and compared with those obtained when the motor is driven by a conventional voltage source PWM inverter. An operating efficiency five or six percent higher and noise level 10 dB lower are obtained for the former. Therefore, this current source GTO inverter is very suitable for ac motor variable speed drives.     

多电平高压变频中的波形调制方法

本文从调制波变换方法和载波调制技术两个方面介绍了高压变频中常用的一些波形调制方法。同时提出了一种新的波形变换方式——波形连续变换技术（continuous Waveform Modulation，CWM），最后给出了实际高压变频装置采用CWM技术的输出相电压波形。     

一种混合9电平电压源逆变器及其变频脉宽调制

介绍了一种应用于中高压变频调速装置的9电平输出电压源逆变器，逆变器的主电路由2种不同拓扑结构的逆变电路组成，分别使用不同参数的开关器件实现，可以综合利用阻断电压高的器件和开关速度快的器件的优点。分析了逆变器主电路的拓扑结构及特点，研究了主电路的开关模式后提出了一种基于载波调制的适合于任意电平数目混合逆变器的PWM(脉宽调制)算法，最后仿真研究了混合9电平逆变器在变速驱动场合中的应用，并验证了算法的有效性。对线电压的频谱分析表明，混合9电平逆变器有很好的输出波形，输出谐波含量少，在高频段输出线电压的总谐波畸变率小于5％，输出电压的dv／dt小，可用于驱动大容量的中高压异步电动机。     

A vector control system using a neutral-point-clamped voltage-source pwm inverter

This paper describes a vector control system of an induction machine using a neutral-point-clamped voltage-source inverter (NPC-VSI) that is one of the double series-connected inverters. The NPC-VSI is able to output five-level step-shaped line-to-line voltage without output transformers or reactors, and it may reduce harmonic currents corresponding to torque ripples. However, the NPC-VSI has a problem in that excessive high voltage is applied to switching devices when a neutral point of two dc capacitors of the NPC-VSI varies from the center of the dc link voltage, because the neutral point is floating. This paper proposes also a current controller to which the space vector theory is applied. This can reduce harmonic currents to one-fourth those of a conventional voltage-source inverter using six switching devices, and regulate the neutral point potential within a preset range. To simplify the current controller, information about voltage space vectors is given from the vector controller to the current controller. The validity of the current controller is confirmed by a prototype using an induction machine of 2.2 kW.     

DC–AC Cascaded H-Bridge Multilevel Boost Inverter With No Inductors for Electric/Hybrid Electric Vehicle Applications

This paper presents a cascaded H-bridge multilevel boost inverter for electric vehicle (EV) and hybrid EV (HEV) applications implemented without the use of inductors. Currently available power inverter systems for HEVs use a dc–dc boost converter to boost the battery voltage for a traditional three-phase inverter. The present HEV traction drive inverters have low power density, are expensive, and have low efficiency because they need a bulky inductor. A cascaded H-bridge multilevel boost inverter design for EV and HEV applications implemented without the use of inductors is proposed in this paper. Traditionally, each H-bridge needs a dc power supply. The proposed design uses a standard three-leg inverter (one leg for each phase) and an H-bridge in series with each inverter leg which uses a capacitor as the dc power source. A fundamental switching scheme is used to do modulation control and to produce a five-level phase voltage. Experiments show that the proposed dc–ac cascaded H-bridge multilevel boost inverter can output a boosted ac voltage without the use of inductors.      

基于特定谐波消除PWM的三电平有源中点钳位逆变器共模电压抑制方法

带电机负载的逆变系统中,降低逆变器输出共模电压的幅值对预防定子绕组绝缘击穿、延长轴承寿命和减小电磁干扰等具有重要意义。以三相三电平有源中点钳位型逆变器为研究对象,分析了三相特定谐波消除脉宽调制(SHEPWM)输出开关状态产生的共模电压幅值及其对中点电压的影响,研究了SHEPWM方法的中点电压自平衡特性,提出了一种改进的SHEPWM控制策略。该控制策略在不影响消除线电压特定谐波及保持中点电压自平衡特性的前提下,能有效降低逆变器输出的共模电压幅值。最后搭建了三电平有源中点钳位型逆变器仿真和实验平台,并对提出的控制策略进行验证,实验结果证明了控制策略的有效性。     

基于DSP的正弦波逆变电源瞬时值反馈优化控制方法

正弦波逆变电源输出受到瞬时值反馈不及时的影响,导致电源输出均衡性较差。为了提高正弦波逆变电源的稳态控制能力,提出基于数字信号处理DSP（digital signal processing）的正弦波逆变电源瞬时值反馈优化控制方法,建立逆变电源系统基本结构,构建三相级联H桥控制电路,并完成控制电路的构建及电源电路的设计。在零序电压的反馈调节下,实现电源电压的平衡控制和电压自均衡耦合调节,利用电压自均衡耦合控制器对正弦波逆变电源的输出功率进行补偿抑制;利用DSP技术对电源输出信号进行反馈处理,得到瞬时值反馈的控制优化算法;对逆变电源控制系统的软件及硬件进行优化设计,完成基于DSP的正弦波逆变电源瞬时值反馈优化控制。测试结果表明,使用该方法进行正弦波逆变电源控制的输出增益较高、控制稳定性较好、对电源输出的电流纹波抑制能力较强,提高了电源的输出质量。     

线电压脉宽调制逆变器供电异步电机性能仿真

介绍了一种线电压脉宽调制技术(LVPWM),分析了其调制原理。与传统的SPWM技术不同,这种新型的脉宽调制技术是以线电压为参考波形的。讨论了采用LVPWM方法三相桥式电压型逆变器的电压输出能力。建立了仿真模型对LVPWM进行了仿真研究。研究表明,从线电压出发控制逆变器是可行的。仿真结果证明了这种脉宽调制方法的有效性。     

Dynamic performance and control of a static VAr generator usingcascade multilevel inverters

A cascade multilevel inverter is proposed for static VAr compensation/generation applications. The new cascade M-level inverter consists of (M-1)/2 single-phase full bridges in which each bridge has its own separate DC source. This inverter can generate almost sinusoidal waveform voltage with only one time switching per cycle. It can eliminate the need for transformers in multipulse inverters. A prototype static VAr generator (SVG) system using 11-level cascade inverter (21-level line-to-line voltage waveform) has been built. The output voltage waveform is equivalent to that of a 60-pulse inverter. This paper focuses on dynamic performance of the cascade-inverter-based SVG system. Control schemes are proposed to achieve a fast response which is impossible for a conventional static VAr compensator (SVC). Analytical, simulated, and experimental results show the superiority of the proposed SVG system     

一种改进的矩阵变换器双电压合成控制策略

在低电压输出时,传统双电压合成控制策略将产生大量窄脉冲,从而引起换流失败及输出波形畸变.针对这种情况,在分析传统的矩阵变换器双电压合成控制策略的特点及窄脉冲引起的换流失败机理后,提出了一种改进的双电压合成控制策略.采用在一个采样周期内,期望输出线电压由一中间输入线电压和一最小输入线电压合成策略,在低电压输出时窄脉冲的数量大约减少80%.改进策略减少了因PWM脉宽小于开关换流所需时间而弓I起的电压误差,使输出电压和输入电流的谐波减少,进而改善了矩阵变换器低电压输出时的控制性能.通过仿真和实验验证了所提出的矩阵变换器改进双电压合成控制的正确性和有效性.     

A sinusoidal PAM-PWM inverter

A new strategy, using both PAM (pulse amplitude modulation) and PWM (pulsewidth modulation) in combination for a power inverter is described. The output waveforms in the proposed PAM-PWM inverter are investigated both theoretically and experimentally. The line-to-line voltage waveform includes the fundamental component and the sidebands of the carrier frequency. Lower-order harmonics are not included in the output waveform. The amplitude of the fundamental component increases 15 percent more than that of a conventional sine-wave inverter. Since each inverter arm does not operate during two-thirds of the period, the heat generated in the devices is reduced, i.e., the size of the inverter system can be minimized because of the reduction in the heat dissipating equipment.     

An Inverter for Traction Applications

An inverter configuration with an auxiliary shutoff circuit designed for traction applications is described. The auxiliary shutoff energy adds to the main shutoff energy providing the necessary shutoff capability at stall and low motor speeds where maximum traction is required. The auxiliary shutoff is automatically programmed so that its effect diminishes gradually as the motor speed increases. Such programming results in a reliable inverter where the volt-ampere rating of thyristors are best utilized to provide active power and safety margin. The inverter can be used in conjunction with a chopper, providing variable dc voltage, to convert a fixed dc voltage source to a variable frequency and amplitude ac source. The inverter can also be used in conjunction with a controlled rectifier, providing variable dc voltage, to convert the 60-Hz fixed frequency and voltage commercial supply to a variable voltage and frequency ac supply.     

Uninterruptible Power Supply for Critical AC Loads?A New Approach

An uninterruptible ac supply system consisting of two power sources (static inverter and ac line) and a thyristor switch is presented. The thyristor switch is operated in such a way that the equalization current flow between the sources is prevented. Consequently continuous parallel operation of the sources may be applied. Faults in one of the sources do not affect the voltage supplied to the load. In order to obtain these features the trigger mode of the switch must meet certain requirements. The analysis of these requirements is given and an implementation of the system is presented. Test results are illustrated by oscillograms. The advantages of the system are that 1) load transfer is performed in an instantaneous and smooth way, 2) the system is able to deliver large inrush currents required by the load and to blow fuses in branch circuits of the load, and 3) no voltage monitors are required.     

A New and Simple Three-Phase Thyristor Inverter for Variable Frequency Operation

A new three-phase inverter circuit is described and analyzed for the condition of an inductive load. The circuit does not require an auxiliary supply or any auxiliary thyristors to assist commutation. All commutation capacitors are placed across the dc side but are used in the same way as capacitors that are normally used for ac side commutation. The output voltage of the inverter is a quasi sine wave controlled by a simple firing circuit. The author was a visiting Research Fellow with the Department of Electrical Engineering and Electronics, the University of Manchester Institute of Science and Technology, Manchester, England.     

An Economical Auxiliary Commutated Thyristor Three-Phase Inverter Suitable for Pulse Frequency Modulation

A new economical auxiliary impulse commutated thyristor inverter is described that is capable of providing a wide range of output ac voltage and output frequency which is useful in variable speed ac drive applications. Output voltage control is provided by a pulse frequency modulation technique, and input dc voltage to the inverter is constant and can be provided by a diode rectifier bridge. The parameters for the various circuit elements, such as commutating inductances and capacitances, di/dt limiting series thyristor inductances, and dv/dt limiting RC snubber circuits are all calculated from a dynamic simulation of a single-phase version of the inverter circuit using a software named ATOSEC I developed at the Universitédu Québec for a CDC 6400/IBM-370 computer. Experimental results obtained on a practical single-phase inverter are compared with those predicted from computer simulation and performance characteristics obtained in the case of a practical three-phase pulse frequency modulated inverter providing variable output voltage and variable output frequency are reported.     

Modeling and simulation of ac–dc buck-boost converter fed dc motor with uniform PWM technique

PWM controlled rectifiers can efficiently and economically be employed in low and medium power applications of dc drives and in front-end converters of rectifier–inverter systems while maintaining the advantages of design simplicity and operation reliability of naturally commutated schemes. Due to the high dc voltage that is produced which is greater than the peak voltage of the utility supply, the ac–dc buck-boost converter is especially suited as a front-end power source in variable-speed drive systems to convert the utility supply voltage into a variable dc link voltage where a single-phase or a three-phase utilities power supply is available. In this paper, the dynamic model and steady state equivalent circuit of a single-phase ac–dc buck-boost converter fed dc motor with uniform PWM control is presented. The waveforms of voltage and current, the input and output characteristics of the converter are discussed and verified. Measured, computed and simulated results are shown to be very close and the model is proved to be efficient and accurate.     

A Sinusoidal PWM Method With Voltage Balancing Capability for Diode-Clamped Five-Level Converters

This paper presents a novel sinusoidal pulsewidth modulation control method with voltage balancing capability for the diode-clamped five-level rectifier/inverter system. A complete analysis of the voltage balance theory is given. The voltage balancing effects of the third harmonic offset injection to all three-phase voltages are discussed. The proposed control utilizes the offset voltage to regulate the average currents flowing into and out of the inner junction without affecting output line-to-line voltage. The voltage balancing was achieved by selecting proper offset voltages for both sides. A five-level experimental system is built up and used to prove the theory.