Random space vector modulation technique for high switchingfrequency inverter control

A new random space vector modulation (RSVM) technique is presented, which dramatically reduces both the number of calculations required for high switching frequency inverter control in real time and the annoying noise by randomising the harmonic spectrum     

Novel switching method for single-phase NPC three-level inverter with neutral-point voltage control

This paper proposes a novel switching method with the neutral-point voltage control in a single-phase neutral-point-clamped three-level inverter (SP-NPCI) used in photovoltaic systems. A proposed novel switching method for the SP-NPCI improves the efficiency. The main concept is to fix the switching state of one leg. As a result, the switching loss decreases and the total efficiency is improved. In addition, it enables the maximum power-point-tracking operation to be performed by applying the proposed neutral-point voltage control algorithm. This control is implemented by modifying the reference signal. Simulation and experimental results provide verification of the performance of a novel switching method with the neutral-point voltage control.     

Random modulation techniques with fixed switching frequency forthree-phase power converters

This paper proposes a new family of random modulation techniques for three-phase power converters which operate with a fixed switching frequency. The techniques are based on adjusting the duration of the zero-vectors or adjusting the three pulse positions in a switching period. Three methods are selected for experimental tests because they preserve the fixed switching frequency known from standard PWM techniques. The new methods are also compared with random switching frequency modulation and with fixed switching frequency modulation. Voltage, current and acoustic noise spectra are used for comparison and it is concluded that two of the techniques are especially useful at lower fundamental frequencies. The techniques can substitute classic random modulation techniques with variable switching frequency in some applications     

Torque and current control of induction motor drives for inverter switching frequency reduction

In this paper, an indirect field-oriented control (FOC) induction motor (IM) drive with instantaneous current and torque control is presented. This proposed control scheme employs hysteresis current and torque controllers to regulate the stator currents. The torque controller is proposed to serve the current controller so that full advantage of the zero voltage vector can be taken to reduce the switching frequency of the inverter. As a result, the actual stator currents can follow the current references as closely as possible, and the current ripple and torque ripple can be greatly decreased compared with the conventional adaptive pulsewidth modulation control method. To verify the feasibility of the proposed scheme, computer simulations and experiment results demonstrate that the proposed method can obtain a high-performance IM drive system.     

Zero-voltage switching for three-level capacitor clamping inverter

A zero-voltage switching (ZVS) scheme for a three-level capacitor clamping inverter based on the true pulsewidth modulation (PWM) pole is proposed in this paper. With this scheme, the main switches work with ZVS through the assistance of a small rating zero current switching (ZCS) lossless auxiliary circuitry without imposing any voltage/current spikes on the main devices or any extra control complexities. Consequently, a three-level capacitor clamping inverter system can operate at a promoted switching frequency and becomes more eligible to be considered for high-power advanced applications, for example, in high-speed drives or power active filter areas. In this paper, the main circuit operation issues as regards the clamping voltage stability, damping capacitor stress, and output voltage spectrum are shortly reviewed first, after which the commutation principle, auxiliary circuitry stress analysis, and auxiliary circuitry designing methodology are presented in detail. Experimental results from a 700 V supply 3 kW half-bridge three-level capacitor clamping inverter are demonstrated which conform well to the proposal     

微网逆变器并网/孤岛无缝切换控制研究

微网并网运行与离网孤岛运行之间的切换会引起电压电流的暂态冲击,从而威胁系统的可靠运行。研究微网离并网运行时的恒压恒频与恒功率控制策略,并提出基于滞环缓冲环节的并网/孤岛无缝切换策略,抑制并网/孤岛切换过程中产生的暂态冲击。最后建立系统的Matlab/Simulink仿真模型,分别仿真分析了传统控制策略和新型控制策略。仿真结果表明,提出的新型切换控制策略可有效抑制切换过程中的暂态冲击,实现微网的平滑切换。     

A random switching method for HPWM full-bridge inverter

To overcome the problem of unequal switching loss in power switches, in conventional hybrid pulse width modulation (HPWM) full-bridge inverters, a random switching method for HPWM full-bridge inverters is proposed. The proposed method equalizes switching losses of the four switches, while also providing good output performance     

Enhanced inverter switching for fast response direct torque control[of induction motor drives]

In classical direct torque control (DTC), an inverter switching event can occur once in each control update period. Because the nature of the inverter switching event is unconstrained, it is essential to limit the inverter switching frequency, and hence the control update period, to ensure that under no circumstances is the allowable switching frequency of any individual power device exceeded. Consequently the switching capability of individual power devices is generally under-utilized, and the control scheme produces high levels of ripple in the motor current and torque. This paper describes a new strategy for device switching and voltage vector selection in DTC. The basis of the strategy is an increase in the control update frequency, while limiting the switching rate of each inverter leg. Although the rate at which device switching events may occur is unchanged, the higher control update frequency leads to higher resolution timing of switching events. The advantages of the strategy, demonstrated by experimental results on a 3 kW induction motor drive, are a significant reduction in the steady-state torque ripple as well as a faster transient response     

Zero-voltage switching for the neutral-point-clamped (NPC) inverter

This paper proposes a transformer-assisted pulsewidth-modulation zero-voltage-switching neutral-point-clamped (NPC) inverter. With the assistance of a transformer-assisted small-rating lossless auxiliary circuit, the main switches work with zero-voltage switching without suffering from any voltage/current spikes, under simple explicit control. The technique allows for higher operating frequency and better device utilization of the NPC inverter. Operation, analysis, design, as well as testing results from a 7-kW prototype are presented in detail.     

A switching control strategy based on output regulation subspaces for the control of induction motors using a three-level inverter

In this work we present the design of a new switching control strategy for a three-level converter aimed to improve the performance of a direct torque control (DTC) for induction machines, special attention is given to the reduction of torque ripple. As in classical DTC, the proposed technique is aimed to directly regulate the outputs: torque and flux amplitude. We show that classical DTC can be considered as a particular case of the proposed control strategy. The proposed criterion to design the switching control sequence is based on a quadratic criterion of the output errors plus a prediction in one-step ahead, and an interesting partition of the input state space generated by the output regulation subspaces (ORS) to facilitate the selection of the control vector for reducing the computational load. As a result, a control vector is selected without the requirement of an auxiliary space vector or any other modulation technique. Simulations results using the proposed control technique confirm the validity of this approach.     

Direct torque control with imposed switching frequency in an 11-level cascaded inverter

This paper presents the application of direct torque control in an induction motor, using a multilevel cascaded inverter with separated DC sources. The control strategy operates with imposed switching frequency, improving torque behavior. The paper studies the theoretical concepts related to this method, like vector selection, state variables estimation, and commutation time calculation. In addition, this paper presents results for a three- and eleven-level inverter-fed drives, from which it can be appreciated that the increase of levels of the load voltage reduces the torque ripple.     

光突发交换网络的拥塞控制技术研究(本期优秀论文)

光突发交换(OBS)技术能很好地支持突发业务,有希望应用于Internet核心交换.但是,OBS网络的单向预约信令方式容易造成网络拥塞和大量的突发丢失.文章在深入研究现有的OBS网络拥塞控制策略的基础上,提出了一种新的基于速率的OBS拥塞控制策略.边缘源结点向宿结点周期性地发送和接收资源管理分组(RMP),边缘源结点根据RMP中的拥塞反馈指示了解网络中的拥塞状况,并改变突发发送速率,从而解除拥塞.     

All-optical inverter with one picojoule switching energy

An ultrafast inverter based on soliton dragging in optical fibres with a switching energy of only 1 pJ, which is the lowest switching energy of any all-optical device, is demonstrated. The inverter consists of a 30 m length of moderately birefringent fibre followed by a 2 km length of a polarisation-maintaining fibre. The switching energy is lowered by separating the soliton dragging mechanisms in two different fibres and optimising the parameters in a time domain chirp switch that is based on time shift keying logic.<>     

Some system design considerations for a high switching frequency PWM inverter

A sinusoidal PWM inverter is required to faithfully reproduce the control waveforms at the output with minimum distortion. This paper presents some design considerations for such an inverter. The choice of switching frequency is the main criterion which affects the output voltage harmonic distortion at high switching frequencies. This paper shows that there exists an optimum switching frequency above which the output harmonic distortion becomes more visible. The dead time generator circuit for a low cost inverter and effect of driver circuits on the output waveform are discussed. Experimental results from laboratory models are presented.     

新型电流源型三相逆变器的软开关拓扑设计

针对硬开关损耗大的缺陷,提出一种新型的应用于电流源型三相逆变器的软开关拓扑及其控制方法。对电流源型三相逆变器进行了系统的研究,包括数学模型的建立与分析,电流空间矢量控制技术,电流双向流动拓扑与控制,新型的软开关拓扑及其控制方法。提出了一种新型的应用于电流源型三相逆变器中的软开关拓扑,明确了其控制逻辑,分析其各个模态的电压电流特征和工作波形图。最后使用Matlab仿真软件在电流空间矢量控制下进行总体仿真,验证了拓扑及其控制方法的可行性和有效性,实现了开关的软化,降低了开关应力,并提高了效率。     

Two-level switching pattern deadbeat DSP controlled PWM inverter

A two-level switching algorithm of the deadbeat controlled PWM inverter is presented. Two levels, instead of three levels, are used in the pulse pattern. This scheme allows the use of higher switching frequency for a given computation time delay, which results in lower total harmonic distortion (THD) at the output. Control algorithms are derived. The proposed control scheme is implemented using a TI TMS320C14 DSP controlling an inverter to produce a very low THD sinusoidal output voltage. Simulation and experimental results are presented to verify the performance     

Novel switching techniques for reducing the speed ripple of AC drives with direct torque control

The main theme of this paper is to present novel switching techniques, which insert zero-voltage vectors and/or more nonzero-voltage vectors to the conventional switching table, for AC drives with direct torque control. For the same sampling frequency of a drive controller, the proposed techniques are quite effective in reducing the torque pulsation and the speed ripples of the motors, as demonstrated in several experimental results. Moreover, the experimental confirmations have been made not only on an induction machine but also on a permanent-magnet synchronous machine.     

A simplified functional simulation model for three-phasevoltage-source inverter using switching function concept

In this paper, a functional simulation model for the voltage-source inverter (VSI) using the switching function concept is studied and the actual implementation of the model is proposed with the help of Matlab Simulink. Also, this concept is extended to the voltage-doubler-type pulse width-modulated (PWM) AC-DC rectifier and the PWM AC-DC-AC converter. With the developed functional model, the simplification of the static power circuits can be achieved so that the convergence and long run-time problems can be solved. Also, in the functional model, the design parameters, such as voltage and current ratings of the power semiconductor switches and load current, can be easily calculated. The general switching function concept is reviewed in brief and the proposed functional models for the VSI, voltage-doubler rectifier, and PWM AC-DC-AC converter and their implementations using Matlab Simulink are explained in detail. Also, several informative simulation results verify the validity of the proposed models     

A new quasi-resonant DC-link PWM inverter using single switch for soft switching

This paper presents a new quasi-resonant DC-link (QRDCL) inverter. Only one switching device is used to create zero voltage instants under all load conditions. The maximum voltage across the inverter devices is maintained at around (1.01-1.1) times the input source voltage. The circuit has the flexibility of selecting switching instants of the resonant link in synchronism with any PWM technique. Control technique does not require the help of inverter switches to create the zero voltage instants in the DC-link, and voltage and current sensors are eliminated from the control circuit. In this paper, the principle of operation and detailed analysis of the proposed QRDCL inverter are presented and design considerations for achieving soft switching are obtained. Detailed PSPICE simulation studies are carried out to study the feasibility of the proposed topology under various load conditions. The experimental results of the proposed QRDCL PWM inverter feeding a three phase induction motor are given.