Adaptive SVM to compensate DC-link voltage ripple for four-switchthree-phase voltage-source inverters

An adaptive space vector modulation (SVM) approach to compensate the DC-link voltage ripple in a B4 inverter is proposed and examined in detail. The theory, design, and performance of this pulsewidth modulation (PWM) method are presented, and the method effectiveness is demonstrated by extensive simulations and experiments. High-quality output currents are guaranteed by this approach even with substantial DC-voltage variations that might be caused by an unbalanced AC supply system, the diode rectification of the line voltages, and circulation of one output phase current through the split capacitor bank. The application of this approach to induction machine drives is also discussed. It is concluded that the DC-voltage ripple effect on the B4 inverter output can be minimized by an adaptive SVM algorithm with the advantage of improving the response of the DC-link filter and the output quality of the inverter becoming high     

Z源逆变器中SVPWM技术实现的研究

在传统SVPWM调制方法里,通过在零矢量中插入直通状态（逆变器同一桥臂同时开通）,使其应用在Z源逆变器（ZSI）中。Z源逆变器在实现交流输出的同时,实现了对直流侧电压任意倍数的升压。文章具体阐述了基于ZSI的SVPWM调制方法,并给出开关信号调制图,说明了直通调制比D、升压因子B与参考电压幅度间的约束关系。仿真结果证实了该调制方法的正确性和有效性。     

New feedforward space-vector PWM method to obtain balanced AC output voltages in a three-level neutral-point-clamped converter

In three-level neutral-point-clamped voltage-source inverters, proper modulation allows the average voltages of the DC-link capacitors to be kept at one-half the level of the DC-link voltage. However, in some operating conditions, a low-frequency ripple appears in the neutral-point potential and its frequency is three times that of the output voltages. As a result, the output voltages also have low-frequency distortion, which includes even and odd multiples of the fundamental. In this paper, a new space-vector pulsewidth-modulation strategy is presented to avoid that low-frequency output voltage distortion. This modulation method tries to balance the voltages of the capacitors by using only three vectors per modulation cycle. The duty ratios are directly calculated from the space-vector diagram, even when balance is not achieved. For all cases, the result is a balanced set of three AC output voltages. Some simulated and experimental results are given to validate the method.     

基于dsPIC的PV逆变器的一种改进结构及其实现

针对目前PV光伏并网发电系统的核心逆变器的现状、结构和控制方法进行了详细的分析,从电网、PV系统及用户的需求出发,指出传统的单级全桥逆变器普遍具有不能处理较宽的输入PV电压,且需要重型工频升压变压器等缺点。在此基础上,本文创新设计并实现了一种基于单级全桥逆变器的并联耦合改进结构。实测证明这种并联耦合反激结构可以有效地减小通过大容量输入电解电容的纹波电流的RMS,从而延长电容的寿命;还可减小输出电流的纹波,从而降低输出电流的THD（谐波失真）;还可适应较宽的输入电压,减小交流纹波,减小磁芯,同时可以提供较高的额定输出电流等优点。     

A source voltage-clamped resonant link inverter for a PMSM using apredictive current control technique

A simple source voltage-clamped resonant link (SVCRL) inverter is proposed to clamp the DC-link voltage to the input source voltage and reduce the current rating of a resonant inductor. The current control of a permanent magnet synchronous motor (PMSM) employing a predictive current control technique (PCCT) for the SVCRL, inverter is also investigated to overcome the disadvantage of the current-regulated delta modulation (CRDM) control technique. By employing the PCCT based on the discrete model of a PMSM and estimation of back electromotive force (EMF), the minimized current ripple with a small number of switchings can be obtained. Finally, the comparative computer simulation and experimental results are given to show the usefulness of the proposed technique     

Design and analysis of power-CMOS-gate-based switched-capacitor boost DC-AC inverter

A multistage power CMOS-transmission-gate-based (CMOS-TG) quasi-switched-capacitor (QSC) boost DC-AC inverter is proposed and integrated with a boost DC-DC converter for a step-up application with AC or DC load. In this paper, using CMOS-TG as a bidirectional switch, the various topologies can be integrated in the same configuration for achieving two functions: boosting and alternating; boosting for getting a sinusoidal output in which the peak is the result of a many times step-up of the input; alternating to realize the positive/negative half sinusoidal of the output. The inverter does not require any inductive elements as inductor and transformer, so integrated circuit (IC) fabrication will be promising for realization. By using the state-space averaging technique, the large-signal state-space model of the inverter is proposed, and then both the static analysis and dynamic small-signal analysis are derived to form a unified formulation for inverter/converter. Based on this formulation, there are presented for theoretical analysis/control design, including steady-state power, conversion efficiency, voltage conversion ratio, output ripple percentage, capacitance selection, closed-loop control and stability, and total harmonic distortion (THD), etc. Finally, a six-stage QSC boost DC-AC inverter is simulated by PSPICE, and the simulations are discussed for some cases, including: 1) steady-state AC output, ripple percentage, and power efficiency; 2) transient response of the regulated inverter for load variation; 3) a practical capacitive load: electromagnetic luminescent (EL) lamp, and 4) efficiency, ripple percentage, and THD for different loads. The results are illustrated to show the efficacy of the proposed inverter.     

A novel control scheme for the multilevel rectifier/inverter

A novel three-level pulsewidth modulation (PWM) rectifier/inverter is proposed: this single-phase three-level rectifier with power factor correction and current harmonic reduction is proposed to improve power quality. A three-phase three-level neutral point clamped (NPC) inverter is adopted to reduce the harmonic content of the inverter output voltages and currents. In the adopted rectifier, a switching mode rectifier with two AC power switches is adopted to draw a sinusoidal line current in phase with mains voltage. The switching functions of the power switches are based on a look-up table. To achieve a balanced DC-link capacitor voltage, a capacitor voltage compensator is employed. In the NPC inverter, the three-level PWM techniques based on the sine-triangle PWM and space vector modulation are used to reduce the voltage harmonics and to drive an induction motor. The advantages of the adopted th-ree-level rectifier/inverter are (1) the blocking voltage of power devices (T1, T2, S_a1-S_c4) is clamped to half of the DC-link voltage, (2) low conduction loss with low conduction resistance due to low voltage stress, (3) low electromagnetic interference, and (4) low voltage harmonics in the inverter output. Based on the proposed control strategy, the rectifier can draw a high power factor line current and achieve two balance capacitor voltages. The current harmonics generated from the adopted rectifier can meet the international requirements. Finally, the proposed control algorithm is illustrated through experimental results based on the laboratory prototype.     

A new phase-controlled parallel resonant converter

A phase-controlled resonant converter was obtained by connecting in parallel the AC loads of two identical parallel resonant inverters. A phase shift between the drive signals of the two inverters controls the amplitude of the output voltage of the new inverter. A voltage-driven rectifier is used as an AC load of the inverter, which results in a phase-controlled parallel resonant DC-DC converter. A frequency-domain analysis is performed for the steady-state operation of the inverter, and two types of voltage-driven rectifiers and design equations are derived. The converter can be operated at a constant switching frequency, which reduces EMI problems. It is found that for switching frequencies higher than the resonant frequency by a factor of 1.07, the load of each switching leg is inductive. The converter is capable of regulating the output voltage in the range of load resistance from full-load to no-load. Experimental results are presented for a prototype of the phase-controlled parallel resonant converter with a center-taped rectifier tested at an output power of 50 W and a switching frequency of 116 kHz     

箝位二极管承受低电压的有源箝位谐振直流环节逆变器

为解决无源箝位谐振直流环节逆变器辅助电路中采用耦合电感辅助换流（即抽头电感法）所引起的箝位二极管两端承受的电压应力过大问题,提出一种箝位二极管承受低电压的有源箝位谐振直流环节逆变器,该逆变器采用有源箝位的方法可使箝位二极管两端承受的最大反向电压不超过直流母线电压的最大值.且该逆变器的辅助谐振电路中只有一个辅助开关器件,箝位电路中无需设置箝位开关,控制简单且硬件成本较低.此外,在箝位电路的作用下可将逆变器的直流母线电压箝位在输入直流电压的1.1~1.3倍,有效地降低了电压应力.以各个阶段下的等效电路为基础,对电路的工作过程进行了分析,并进行了实验验证,实验结果表明开关器件实现了软开关,且在额定功率3kW条件下,逆变器的效率达到96.5%.因此,该拓扑结构能够有效地提高工作效率.     

A new control scheme for single-phase PWM multilevel rectifier withpower-factor correction

A new control scheme for a single-phase bridge rectifier with three-level pulsewidth modulation is proposed to achieve high power factor and low current distortion. The main circuit consists of a diode-bridge rectifier, a boost inductor, two AC power switches, and two capacitors. According to the proposed control scheme based on a voltage comparator and hysteresis current control technique, the output capacitor voltages are balanced and the line current will follow the supply current command. The supply current command is derived from a DC-link voltage regulator and an output power estimator. The major advantage of using a three-level rectifier is that the blocking voltage of each AC power device is clamping to half of the DC-link voltage and the generated harmonics of the three-level rectifier are less than those of the conventional two-level rectifier. There are five voltage levels (0, ±V_DC/2, ±V_DC) on the AC side of the diode rectifier. The high power factor and low harmonic currents at the input of the rectifier are verified by software simulations and experimental tests     

Three-Level Inverter Scheme With Common Mode Voltage Elimination and DC Link Capacitor Voltage Balancing for an Open-End Winding Induction Motor Drive

A dc link capacitor voltage balancing scheme along with common mode voltage elimination is proposed for an induction motor drive, with open-end winding structure. The motor is fed from both the ends with three-level inverters generating a five level output voltage space phasor structure. If switching combinations, with zero common mode voltage in the pole voltage, are used, then the resultant voltage space vector combinations are equivalent to that of a three-level inverter. The proposed inverter vector locations exhibit greater multiplicity in the inverter switching combinations which is suitably exploited to arrive at a capacitor voltage balancing scheme. This allows the use of a single dc link power supply for the combined inverter structure. The simultaneous task of common mode voltage elimination with dc link capacitor voltage balancing, using only the switching state redundancies, is experimentally verified on a 1.5-kW induction motor drive     

Improved modulation techniques for PWM-VSI drives

PWM-VSI based AC motor drives have two main problems. The inverter is nonlinear which causes instability problems in some specific working points of the AC machine and it emits acoustic noise due to the switching frequency. Nonlinearities like dead-time in the inverter, load dependent DC-link voltage ripple and the voltage drop across the switches are modeled and compensated by improved modulation techniques in order to obtain an almost ideal inverter. Different feedback and feedforward techniques are proposed. The acoustic noise is reduced by using a random modulation strategy. Measurements show a significant improvement by using feedforward and feedback techniques for linearizing the inverter. An improvement in reduction of the acoustic noise emission is also achieved by using random modulation. It is concluded that a combination of a random modulation strategy and feedforward/feedback techniques gives an almost ideal AC motor drive system     

A novel high-performance utility-interactive photovoltaic inverter system

This paper presents a novel photovoltaic inverter that cannot only synchronize a sinusoidal AC output current with a utility line voltage, but also control the power generation of each photovoltaic module in an array. The proposed inverter system is composed of a half-bridge inverter at the utility interface and a novel generation control circuit which compensates for reductions in the output power of the system that are attributable to variations in the generation conditions of respective photovoltaic modules. The generation control circuit allows each photovoltaic module to operate independently at peak capacity, simply by detecting the output power of the system. Furthermore, the generation control circuit attenuates low-frequency ripple voltage, which is caused by the half-bridge inverter, across the photovoltaic modules. Consequently, the output power of the system is increased due to the increase in average power generated by the photovoltaic modules. The effectiveness of the proposed inverter system is confirmed experimentally and by means of simulation.     

基于Buck-Boost逆变器的离散滑模控制仿真研究

为了获得比较理想的正弦输出电压，优化逆变器的动态性能，文中基于Buck—Boost逆变器．采用了离散滑模变结构的控制策略。Buck—Boost逆变器可以获得比直流输入电源高或低的交流输出电压，文中阐述了其工作原理．并结合状态方程，推导出滑模面的存在条件、到达条件和稳定条件，然后对电路参数、控制系数以及控制算法进行了设计。仿真结果表明采用离散滑模控制的Buck—Boost逆变器对系统扰动和负载变化具有很强的鲁棒性，系统具有良好的动态响应。     

Parallel-connections of pulsewidth modulated inverters usingcurrent sharing reactors

A technique of parallel connection of power devices by using current sharing reactors for pulsewidth modulated (PWM) inverters is reported in this paper. The proposed technique not only increases the current capacity but also decreases the output harmonic contents. The output voltage waveforms of the proposed inverter have certain voltage levels during their half cycles, thus it is anticipated that it will be difficult to analyze the output waveforms. For such waveforms, a frequency analysis approach is described, whose results are verified by experiments     

Torque ripple reduction in DTC of induction motor driven bythree-level inverter with low switching frequency

A torque ripple reduction technique of direct torque control (DTC) for high power induction motors driven by three-level inverters with the inverter switching frequency limited around 0.5-1 kHz level is presented. It is noted that conventional two-level DTC algorithms to reduce torque ripple are devised for applications with relatively high switching frequency above 2-3 kHz and cannot accomplish satisfactory torque ripple reduction for three-level inverter systems with such lower switching frequencies. A new DTC algorithm, especially for low switching frequency inverter system, illustrates quite reduced torque ripple characteristics all over the operating speed region. Simulation and experimental results show effectiveness of the proposed control algorithm     

三态DPM电流滞环控制零电压开关逆变器的分析与设计

文中分析了三态DPM电流滞环控制技术在逆变器中的应用。基于高频脉冲直流环节单向电压源逆变技术设计了三态电流滞环控制零电压开关逆变器,克服了依靠谐振电路实现软开关所带来的结构复杂和控制难度大的缺陷,在工程应用中效果良好。     

Switching Characterization of Cascaded Multilevel-Inverter-Controlled Systems

In this paper, the method of triangular carrier switching control of two-level inverters is extended to cascaded multilevel inverters using phase-shifted multicarrier unipolar pulsewidth modulation (PWM). The condition for smooth modulation is obtained using the Bessel's function representation of the PWM output and the switching condition of the multilevel-inverter-controlled system. A method is proposed for the determination of the minimum amplitude of the triangular carrier for smooth modulation at fixed switching frequency. It is shown that the multilevel modulation based on the phase-shifted carriers significantly reduces the ripple magnitude in the switching function and allows the use of a smaller carrier amplitude under closed loop. This increases the forward gain and, hence, improves the tracking characteristics. The proposed cascaded multilevel inverter control is implemented for the operation of a distribution static compensator (DSTATCOM) in the voltage control mode. The experimental verification of the theoretical and simulation results is provided through a field-programmable gate array (FPGA) based control of a laboratory model of a single-phase DSTATCOM.     

Solar power generation system for reducing leakage current

This paper proposes a transformer-less multi-level solar power generation system. This solar power generation system is composed of a solar cell array, a boost power converter, an isolation switch set and a full-bridge inverter. A unipolar pulse-width modulation (PWM) strategy is used in the full-bridge inverter to attenuate the output ripple current. Circuit isolation is accomplished by integrating the isolation switch set between the solar cell array and the utility, to suppress the leakage current. The isolation switch set also determines the DC bus voltage for the full-bridge inverter connecting to the solar cell array or the output of the boost power converter. Accordingly, the proposed transformer-less multi-level solar power generation system generates a five-level voltage, and the partial power of the solar cell array is also converted to AC power using only the full-bridge inverter, so the power efficiency is increased. A prototype is developed to validate the performance of the proposed transformer-less multi-level solar power generation system.