Network-Friendly Low-Switching-Frequency Multipulse High-Power Three-Level PWM Rectifier

ABSTRACTThree-phase converters using diode or silicon-controlled rectifier (SCR) are widely employed to convert the commercial AC supply to DC. Such converters inject harmonics into the power supply system and thereby distort supply system voltage waveform. A simple input current wave-shape improvement technique using a shunt-connected harmonic current compensator is presented in this work, intended to reduce the total harmonic distortion (THD) of input current of three-phase diode and SCR phase-controlled rectifiers operating with inductive loads, by matching them to the specific converter as a combined package. The compensator proposed here comprises of a three-limb voltage source converter using insulated-gate bipolar transistor, working on instantaneous current and voltage measurements of the compensator only and not of the load. The technique uses a simple feedforward control for AC source current harmonic compensation of rectifiers without monitoring the AC line currents, i.e. use of online computation. The proposed system is simulated and tested on a laboratory prototype. The measured input current THD values without additional line filters are found to be below 8.3%, which is within acceptable limits, proving that the new technique is capable of compensating predetermined current harmonics of diode or SCRs.

In conventional Two-Level Voltage Source Converters (2L-VSCs), connecting between high/medium dc voltage and medium/low ac voltage requires semiconductor devices rated at the high/medium dc-voltage, which negatively affects the converter cost. Alternatively, the Capacitor-Tapped Multi-module VSC (CT-MC) can be used, where it has a good bucking capability. The CT-MC consists of three (or multiple of three) Half-Bridge Inverter (HBI) modules, where the dc terminals of these modules are connected in series across the high/medium dc-link voltage, i.e. semiconductor devices with a lower voltage rating can be employed. The ac outputs of the involved HBIs are integrated to the ac gird through proper transformer(s). In this paper, the performance of the CT-MC is investigated, when Selective Harmonic Elimination (SHE) method is employed for dc-ac conversion to reduce the converter switching losses, while keeping the Total Harmonic Distortion (THD) of the ac currents within the recommended range. Simulation results are presented to show the performance of CT-MC when SHE is applied.

In the given work has been analysed work single-phase three-zone AC-DC voltage converter. It is shown, that application multizone converters essentially improves quality of output voltage, and also an input current of the converter. Analytical expressions for total harmonic distortion of output voltage, input current, adjusting and external characteristics, and also a power factor are presented. Systems of pulse-phase regulation of new converters are created. The graphics illustrating results of computer modelling which visually show comparability of theoretical results and the spent experiments are resulted.

In this work the new single-phase three-zone AC-DC voltage converter is compared with the existing scheme of the four-zone rectifier used in electric locomotives. It is shown, that in the new scheme of the three-zone (n-zone in general) rectifier essentially decrease reverse voltage on thyristors. Analytical expressions for total harmonic distortion of output voltage, input current, control and external characteristics, as well as power factor are presented. The diagrams illustrating results of computer modelling are given. Total comparison shows essential reduction of expenses by power semiconductor devices.

A new passive 28-step current shaper for three-phase rectification is proposed in this paper. With a phase-shifting transformer on the AC side and six interphase transformers on the DC side, per-phase input current can be shaped into a 28-step sinusoidal waveform. The total harmonic distortion of AC input currents obtained is 6.53%, lower than one-half of that in a conventional 12-pulse converter. The transformer voltampere rating is also lowered down to one-fifth of that in a 12-pulse converter. A 2 kW experiment is performed to verify the proposed circuit.

This paper provides a brief comparison between two different modulation methods for direct matrix converter (DMC). The power semiconductors are modelled as ideal bidirectional switches and the DMC is controlled using Venturini method, optimized Venturini and space vector modulation respectively. These methods are compared and analysed in some aspects such as total harmonic distortion and harmonic spectrum analysis of output voltage and input current. A simple model of DMC is proposed to represent the power circuit, including the input filter and a three-phase Y-connected RL load. Simulated input and output parameters of DMC are presented using PSIM software for both modulation strategies.

This paper proposed an electronic ballast that uses an input current shaper to reduce the total harmonic distortion of the line input current, that only process a small part of the total power. Base on the minimum value of the conduction angle to satisfy the requirements of the IEC 61000-3-2 Class-C standard, the conduction loss of the ICS stage can be reduced. The input current shaper is achieved by using a bridge rectifier which acts as the Class-DE resonant rectifier. By using this topology the conduction angle of the diode can be increased to high enough for satisfy the IEC 61000-3-2 Class-C standard requirements. The proposed electronic ballast is designed for 36-W fluorescent lamp and operated at a line rms voltage of 220 V, a line frequency of 50 Hz with the switching frequency fixed at about 76 kHz. The experimental results show that the total harmonic distortion is 29.5%, the power factor is 0.96, a lamp-current crest factor is 1.42, and 95.2% efficiency at full power.

To reduce the conduction loss, a novel three-phase current source rectifier, named Delta-type Current Source Rectifier (DCSR), has been proposed in previous research. This rectifier has delta-type connection on its input side, and its dc-link current can be shared by multiple devices at a time to reduce up to 20% conduction loss. A high-efficiency modulation scheme for DCSR has been proposed, where the conduction states involve more switches to share the dc-link current. However, it causes current distortion when the input voltages have intersections. In this paper, the phenomenon is analyzed in detail. The clamped voltage on the diode bridge will fluctuate at the voltage intersections, resulting in false current pulse and distortion. An improved modulation scheme is then proposed for DCSR to reduce the input current distortion without sacrificing much efficiency. Through experiment in a 7.5 kW prototype, its effectiveness is verified and the total harmonic distortion (THD) of the input current is reduced dramatically.

A comparison of fuzzy self‐tuning (FST), sliding mode control (SMC) and conventional proportional–integral (PI) control methods is performed under unbalanced grid conditions using a bridgeless power factor correction (PFC) converter. The bridgeless PFC converter operates the correction of AC line current to obtain a DC output voltage without full bridge rectifier based on these control methods. These control methods generate the duty cycles to provide higher unity power factor and lower total harmonic distortion of input current, even if AC line voltage is distorted. This study focuses on the performance analysis of FST and SMC methods adaptation to the input current for the bridgeless PFC converter and comparing with the conventional PI controller. Although the SMC method is only used in the current control loop, the FST method is used in both current and voltage control loops for eliminating harmonics of input current and regulating of output voltage. The performance of control methods is evaluated with a TMS320F2812 digital signal processor. The simulation and experimental results are compatible with the limits for harmonic current emissions, IEC 61000‐3‐2 and show that the FST and SMC are better than the conventional PI control method and FST is superior to the SMC.

Considering the development of the hybrid wind and solar photovoltaic generation and smart grid, Active Front-End (AFE) converters for high-power applications are facing significant opportunities and challenges related to power quality and efficiency. The Pre-programmed Pulse-Width Modulation (PPWM) techniques can strictly control the harmonic spectrum of a specified voltage or current waveform generated by a high-power AFE converters, and have been extensively applied to reduce or even eliminate the harmonic distortion with low switching losses for high-power converters in order to deal with these issues aforementioned. For the PPWM techniques with low switching frequency, Selective Harmonic Elimination (SHE) and Selective Harmonic Mitigation (SHM) have been the prevailing solutions and gain widespread popularity, among which SHM can provide further control of the harmonic spectrum in cases of similar switching losses to SHE. Over the past several decades, the applications of SHE and SHM have been extended to high-power AFE converters. Thus, the aim of this study is to provide a comprehensive literature review regarding their various formulations, solving algorithms, and existing problems to high-power AFE converters. In addition, the suggestions for future applications of PPWM in high-power AFE converters are also discussed.

Offline pulse width modulation (PWM) techniques are employed to reduce the line current distortion in induction motor (IM) drives where the switching frequency is highly constrained. An optimal PWM technique is proposed here for a neutral point clamped (NPC) inverter fed IM drive to minimize the motor current distortion, subject to constraints on number of switching instants per quarter cycle. Two types of pole voltage waveforms of the NPC inverter are considered, namely type-I and type-II. This paper reports optimal switching angles for both type-I and type-II waveforms to minimize the resulting total harmonic distortion (THD) in motor current. In general optimal type-II is found to result in lower THD than optimal type-I PWM. The optimal type-II PWM offers superior performance in terms of motor current distortion than synchronized sine-triangle PWM and selective harmonic elimination PWM, as shown by simulation and experimental results on an NPC inverter fed 3.7 kW induction motor drive.

From the aspect of the isolated transformer for 18-pulse rectifier, a new topology of the 18-pluse autotransformer-rectifier with the advantages of small equivalent capacity, low harmonics and outstanding symmetrical structure is proposed, which is superior to the existing American patents. The relationship between the input and output currents, the distortion of input current, the relationship between the voltage of each branches and the phase shift angle and the equivalent capacity of the autotransformer are derived by using the potential vector diagram and the balance principle of the magnet potential. The phase shift angle of the proposed novel 18-pulse autotransformer is 20° that is exactly the same with the isolated transformer, which verifies the potential vector of the two is coincident. The input current distortion rate of this autotransformer is 10.05%, which reduces the harmonics of the rectifier to the power grid. The equivalent capacity is only 17.76% of the output power, which greatly reduces the volume and weight of the system. Finally, a prototype is made, which validates the correctness of the theoretical deduction and simulation, and provides a theoretical guide for future design.

This paper describes the operation of an AC-DC converter employing sixth-order harmonic injected PWM. The boost converter operating on the rectified output uses a constant switching frequency PWM and discontinuous current mode to reduce the total harmonic distortion in the input current. The implementation and the characteristics of the converter are presented.

This paper proposes a current ripple cancelation method in DC side for an isolated AC-DC converter with a matrix converter. In this system, input currents are distorted by an error between a reference and actual input current caused by a ripple component at a dc current in the output side when the smoothing inductor in the output side is minimized. The proposed ripple cancellation method combines current slopes during positive with negative cycles of a high-frequency current. In addition, dead-time-induced voltage error is also reduced by the extension of a minimum pulse width of each switch in the matrix converter with the proposed method. It is demonstrated that the input current total harmonic distortion (THD) is improved by eliminating the ripple components regardless of the amplitude of the ripple component. From the experimental results with the 10-kW prototype, the input current THD is reduced from 8.2% to 5.3% at the 0.2 p.u..

In this paper, a hybrid pulsewidth modulation (PWM) scheme is proposed to suppress the LC resonance for the high-power current-source inverter (CSI) fed drives with low switching frequency. In CSI drive systems, the selective harmonic elimination (SHE) is selected due to the better performance of harmonics, but the LC resonance cannot be effectively damped due to the lack of control flexibility of SHE. In this paper, SHE is only used for the steady-state operation. The modulation scheme is then switched to space vector modulation with dynamic capacitor voltage control when the transient event occurs. The smoothed transitions between different modulation schemes are proposed. The proposed hybrid method effectively solves the resonant issues in CSI drives, while maintaining the power quality. Both simulation and experiments verify the performance of the proposed hybrid PWM scheme.