Soft switching space vector PWM inverter using a new quasi-parallelresonant DC link

A soft switching quasi-parallel resonant DC-link (QPRDCL) inverter with improved PWM capability has been recently presented. The circuit has the minimum voltage stress of the devices and provides the flexibility of selecting the on/off instants of the resonant link, resulting in improved PWM capability. In this paper, the operational principles and the detailed analysis of the QPRDCL inverter are presented for the resonant components design and the inverter control. An SVPWM with optimal vector sequence suitable for the QPRDCL inverter is also presented through the comparisons among five different modified space vector PWM (SVPWM) techniques classified by the voltage vector sequences. The performance of the selected optimal SVPWM is verified by the experimental results     

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.     

一种新型软开关DC-DC PWM升压变换器设计

为提高转换效率并降低电源开关的电流应力,提出一种基于新型有源缓冲电路的PWM DC-DC升压变换器。该有源缓冲电路使用ZVT—ZCT软开关技术,分别提供了总开关ZVT开启及ZCT闭合、辅助开关ZCS开启及ZCT闭合。消除了总开关额外的电流及电压应力,消除了辅助开关电压应力,且有源缓冲电路的耦合电感降低了电流应力。另外,通过连续将二极管添加到辅助开关电路,防止来自共振电路的输入电流应力进入总开关。实验结果表明,相比传统的PWM变换器,新的DC-DC PWM升压变换器在满负荷时电流应力降低且总体效率能达到98.7%。     

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     

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。     

Extension of operation of space vector PWM strategies with low switching frequencies using different overmodulation algorithms

This paper investigates the operation of four space vector-based synchronized pulse-width modulation (PWM) strategies in the overmodulation zone using three different overmodulation algorithms. It is shown that the symmetries in the PWM waveforms generated can be preserved in the overmodulation zone also. With any given overmodulation algorithm, the voltage control characteristics (i.e., fundamental voltage versus control variable) are found to vary with PWM strategy, pulse number and type of clamping. The inverse of the appropriate voltage control curve is used during premodulation to maintain the modulator gain constant. The differences in the nature of the voltage control characteristics with the different overmodulation algorithms are brought out. These characteristics are compared and contrasted against those at high switching frequencies. The harmonic distortion in the different cases is evaluated and compared. It is shown that the bus clamping strategies perform better than the conventional strategy with any given overmodulation algorithm employed. These strategies, which exploit the flexibilities in the space vector approach, are useful in high power drives on account of their superior waveform quality at low switching frequencies and high DC bus utilization.     

A rugged soft commutated PWM inverter for AC drives

A novel DC-DC power converter for variable-speed AC power drives using the zero-voltage switching technique is described. This converter combines the advantages of soft commutated inverters and those of conventional pulsewidth modulated (PWM) inverters. In the proposed scheme, the soft commutation reduces the constraints on the switches, and the PWM enables simple and efficient regulation of the power flow. Furthermore, the zero-voltage switching technique makes operation safe, and the switching of bipolar transistors at 20 kHz is easily achieved without compromising the efficiency of the system     

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.     

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.     

Advanced bus-clamping PWM TechniquesBased on space vector approach

Conventional space vector pulsewidth modulation (CSVPWM) employs conventional switching sequence, which divides the zero vector time equally between the two zero states in every subcycle. Existing bus-clamping PWM (BCPWM) techniques employ clamping sequences, which use only one zero state in a subcycle. This paper deals with a special type of switching sequences, termed here as "double-switching clamping sequences," which use only one zero state and apply an active vector twice in a subcycle. The present work brings out a class of bus-clamping PWM techniques, which employ such sequences. It is shown analytically as well as experimentally that the proposed BCPWM techniques result in reduced harmonic distortion in the line currents over CSVPWM as well as existing BCPWM techniques at high modulation indices for a given average switching frequency of F/sub SW/. At high modulation indices, the dominant harmonic components in the line voltages are around 2F/sub SW/ with the proposed BCPWM techniques, while the dominant components are around F/sub SW/ and 1.5F/sub SW/, respectively, with CSVPWM and existing BCPWM techniques. The proposed techniques also reduce the inverter switching losses at high power factors over CSVPWM and existing BCPWM techniques.     

Novel four quadrant DC-link soft switching inverter generating sinusoidal waveforms

A novel high frequency resonant link inverter using zero-voltage switching (except for one device where zero-current switching is used) operable in four quadrants is proposed. It provides several excellent advantages over the conventional resonant link inverters, such as low VA ratings, low acoustic noise and low harmonic distortion.<>     

A new active common-mode EMI filter for PWM inverter

This paper presents a new active common-mode electromagnetic interference (EMI) filter for the pulse-width modulation (PWM) inverter application. The proposed filter is based on the current sensing and compensation circuit and it utilizes a fast transistor amplifier for the current compensation. The amplifier utilizes an isolated low-voltage DC power supply for its biasing and it is possible to construct the active filter independent of the source voltage of the equipment. Thus the proposed active filter can be used in any application regardless of its working voltage. The effectiveness of the proposed circuit has been verified by experimental results.     

The nearest three virtual space vector PWM - a modulation for the comprehensive neutral-point balancing in the three-level NPC inverter

This letter presents a new modulation approach for the complete control of the neutral-point voltage in the three-level three-phase neutral-point-clamped voltage source inverter. The new modulation approach, based on the virtual space vector concept, guarantees the balancing of the neutral-point voltage for any load (linear or nonlinear) over the full range of converter output voltage and for all load power factors, the only requirement being that the addition of the output three-phase currents equals zero. The implementation of the proposed modulation is simple according to the phase duty-ratio expressions presented. These expressions are only dependent on the modulation index and reference vector angle. The performance of this modulation approach and its benefits over other previously proposed solutions are verified experimentally.     

Optimized space vector switching sequences for multilevel inverters

Previous work has shown that space vector modulation and carrier modulation for two-level inverters achieve the same phase leg switching sequences when appropriate zero sequence offsets are added to the reference waveforms for carrier modulation. This paper presents a similar equivalence between the phase disposition (PD) carrier and space vector modulation strategies applied to diode clamped, cascaded N-level or hybrid multilevel inverters. By analysis of the time integral trajectory of the converter voltage, the paper shows that the optimal harmonic profile for a space vector modulator occurs when the two middle space vectors are centered in each switching cycle. The required zero sequence offset to achieve this centring for an equivalent carrier based modulator is then determined. The results can be applied to any multilevel converter topology without differentiation. Discontinuous behavior is also examined, with the space vector and carrier based modulation methods shown to similarly produce identical performance. Both simulation and experimental results are presented.     

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     

A new soft recovery PWM quasi-resonant converter with a foldingsnubber network

A new soft recovery (SR) quasi-resonant converter (QRC) having a multiple-order folding snubber network (MFSN) is introduced. It is obtained by combining a normal QRC with a folding snubber network of which the surrounding components are composed of passive devices only (diodes and capacitors). The reverse recovery loss of the main rectifier diode is eliminated by this method utilizing multiple resonance with a multiple-order folding snubber network. By realizing soft switching conditions, the proposed converter has pulsewidth modulation capability with high efficiency and is suitable for high-voltage and high-power DC to DC converter applications     

A new single-phase five-level PWM inverter employing a deadbeat control scheme

A single-phase five-level PWM inverter is presented to alleviate harmonic components of the output voltage and the load current. Operational principles with switching functions are analyzed. To keep the output voltage sinusoidal and to have the high dynamic performances even in the cases of load variations and the partial magnetization in filter inductor, the deadbeat controller is designed and implemented on a prototype. The validity of the proposed inverter is verified through simulation and experiments. To assess the proposed inverter, it is compared with the conventional single-phase three-level PWM inverter under the conditions of identical supply DC voltage and switching frequency. In addition, it is compared with the five-level cascaded PWM inverter.     

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.<>     

A self-balancing space vector switching modulator for three-level motor drives

This paper describes how to formulate a self-balancing space vector modulator for the three-level neutral point clamp topology typically used for high power induction motor drives. Besides space vector modulation principle is used to calculate pattern times within one control update cycle, several other techniques are proposed in order to obtain a production quality modulator. These include a pivot point concept to be used for pattern selections in order to achieve minimum switching losses, techniques for neutral point voltage balancing, power device minimum on/off time guarantee, adjacent state switching, and sine triangular equivalent etc. Lab test results are given for effectiveness of the modulator.