A dual two-level inverter scheme with common mode voltage elimination for an induction motor drive

Pulse-width modulated (PWM) inverters are known to generate common mode voltages which cause motor bearing currents in the induction motor drives. They also result in leakage currents which act as sources of conducted electromagnetic interference in the drive system. The common mode voltage generated by a conventional three-level inverter can be eliminated by switching only the voltage space vectors which do not produce the common mode voltage. This paper presents a PWM switching strategy to eliminate common mode voltage using the open-end winding configuration for the induction motor. The switching strategy presented in this paper, does not generate any alternating common mode voltages in the drive system and hence the electrostatic coupling of the common mode voltage, which results in the bearing currents and the leakage currents, is avoided. The proposed scheme is devoid of neutral point voltage fluctuations and does not require neutral point clamping diodes, when compared to the common mode elimination scheme based on the conventional three-level inverter topology. Also, the present scheme uses a single dc-link with half the voltage compared to the conventional three-level inverter based scheme.     

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.     

Reduced Switch Count DC-Link AC–AC Five-Leg Converter

This paper investigates a reduced switch count dc-link ac–ac five-leg converter for three-phase power conversion. The converter provides both an input rectifier and an output inverter by sharing a leg in order to reduce the number of power switches. Scalar and vector pulsewidth modulation techniques are presented and the concepts of local and global apportioning factors are introduced. A control technique that aims at maximizing the utilization of the dc-link voltage is proposed. A hysteresis current controller that allows operating with one leg being shared by the load and grid sides is developed. In addition, several relevant characteristics of the converter are addressed, such as voltage capability, harmonic distortion, shared-leg and capacitor currents, and power rating. The features of such a converter are compared to those of the six-leg and four-leg converters. Selected experimental results are presented.     

Experimental evaluation of direct torque-controlled 3-phase induction motor under inverter faults

ABSTRACT

In this paper, analysis and design of fault-tolerant converter topology for direct torque-controlled (DTC) induction motor (IM) drive suitable for low, medium and high power applications is proposed. The proposed converter topology can restore normal operation of the drive after the occurrence of open-circuit or short-circuit of power switches in the inverter. It consists of a current-controlled three-level boost converter (TLBC) to boost the dc-link voltage at input terminals of an inverter during post-fault, balance the voltages at dc-link capacitors and retains all the advantages of the conventional IM drive. Simulation and experimental results are presented for pre- and post-fault operation. The results are compared with conventional fault-tolerant DTC of the drive to highlight the merits of proposed converter.     

Long-Lifetime Power Inverter for Photovoltaic AC Modules

This paper presents a power inverter tailored for low-power photovoltaic (PV) systems. The inverter features high reliability, thanks to a circuit topology that obviates aluminum electrolytic capacitors from the circuit. Moreover, all components, including logic and control, have been designed to exhibit high reliability at high temperatures. Three conversion stages form the power topology. First, a full bridge connected to a high-frequency transformer and a full-bridge rectifier amplifies the voltage of the PV panel to approximately 475 V. This stage is controlled by using a phase-shift pulsewidth-modulation controller that permits zero-voltage switching, thereby minimizing losses. Second, a buck converter is connected in series with the rectifier and is controlled by using current mode in order to shape the current injection into a rectified sine wave. Last, a full bridge is operated at line frequency to unfold the current injection. The amplification stage has a proportional compensator that maintains the voltage at the PV terminals constant. The current injection stage has a proportional-derivative compensator that controls the amplitude of the grid current so that the dc-link average voltage is maintained constant. Experimental results show that the peak efficiency of the system is 89%, and the total current harmonic distortion is below 5%. Finally, analyses show a designed lifetime of approximately ten years.     

Regenerative medium-voltage AC drive based on a multicell arrangement with reduced energy storage requirements

Multicell power circuit topologies have proved to be an effective alternative to medium-voltage ac drives. The main advantage is the improved power quality at both the ac system and the motor sides. However, several drawbacks are present in these configurations, such as a lack of sustained regenerative operating mode, uncontrolled input reactive power, and a large second current harmonic that is injected by the load into the dc link of each cell, which leads to a bulky electrolytic capacitor. This paper proposes to replace the input diode-based front-end rectifier with an active front-end rectifier in all cells of the topology and a novel control strategy in order to overcome the aforementioned drawbacks. In fact, the active front-end rectifier allows the topology to regenerate and the control strategy handles the reactive input power and reduces the large second current harmonic from the dc-link capacitor, thus reducing its size. These features are achieved without any penalties in the quality of both the ac input current and the motor voltage waveforms. Experimental results confirm the theoretical considerations.     

Control of the single-phase three-leg AC/AC converter

This paper investigates the control of a single-phase three-leg ac/ac reversible converter in which a leg is shared by both the grid and the load side. Pulsewidth-modulation (PWM) techniques based on scalar and vector approaches are developed, introducing the concept of local and general apportioning factor and, also, a complete equivalence between scalar and space vector PWM. A hysteresis current controller capable of taking into account the shared leg is developed and a zero current error linear controller is presented. Furthermore, a control strategy to obtain maximum utilization of the dc-bus voltage is proposed. In addition, several relevant characteristics of the converter are addressed, such as voltage rating, harmonic distortion, shared leg and capacitor currents, and power rating. The converter is compared to four-leg and two-leg converters. Experimental results are presented.     

A space vector-based rectifier regulator for AC/DC/AC converters

A voltage-sourced rectifier control scheme for use with AC/DC/AC variable speed drives is presented. A control scheme is derived that directly calculates the duration of time spent on the zero state and on each switching state adjacent to the reference vector, over a constant switching interval, in order to drive the line current vector to the reference vector. In addition, under transient conditions, when deadbeat control is not possible, a control scheme is presented that ensures that the line current vector is driven in the direction of the reference current vector. The current reference for the rectifier controller is derived from the bus voltage error and a feedforward term based on the estimated converter output power. The proposed space vector-based rectifier regulator is shown to exhibit improved harmonic and transient performance over existing per-phase duty cycle prediction methods, especially at modulation indices near unity. The deadbeat control of the rectifier input current is accomplished every half-cycle with constant switching frequency while still symmetrically distributing the zero state within the half-cycle period     

A novel instantaneous power control strategy and analytic model forintegrated rectifier/inverter systems

This paper is concerned with the design and implementation of an integrated pulse width modulation (PWM) rectifier/inverter for three-phase induction motor drives. Two identical PWM converters are used to serve as power regulator with unity power factor and servo motor drive using field-oriented control, respectively. A new input-output instantaneous power balancing approach is proposed to improve the dynamic response of input power regulation during output load change in order to minimize the DC-link capacitance. By using the synchronous rotating-frame current regulators, both the input and output currents of the integrated system are characterized with fast current response and low harmonic distortion. The effects of the dynamic response using different input power control methods are compared and the systematic design and analysis of the proposed method are also presented. Theoretical results of the analysis are verified experimentally     

PWM AC／DC功率双向变流器建模方法的研究（一）

基于脉宽调制（PWM）的AC/DC功率双向变流器作为主要功率变换电路，在许多实际应用的电力电子系统中得到广泛应用，如统一电能质量调节器中的有源电力滤波器系统，交-直-交变频调速系统中的整流或逆变部分，电源系统的逆变器，再生能源并网发电系统中的逆变器以及灵活交流输电系统中的统一潮流控制器等等。在各种应用系统中，人们建立其数学模型进行系统分析和控制设计以满足系统目标。PWM整流器数学模型的研究是PWM整流器及其控制技术研究的基础，本文研究介绍了目前较为流行的四种建模方法，并分别分析其特点及应用。     

Three-phase power quality compensator under the unbalanced sources and nonlinear loads

A three-phase voltage-source inverter for a power quality compensator under the unbalanced mains and nonlinear loads is proposed to provide balanced three-phase source current and improve input power factor. The proposed converter is based on the conventional three-phase voltage-source inverter with three additional ac power switches to achieve three-level pulsewidth modulation. The voltage stress of three ac power switches is clamped to half the dc-link voltage. The balanced reference mains currents are estimated using the dc-bus voltage and load currents. A proportional-integral voltage controller is used in the outer loop to compensate the switching losses of the voltage-source inverter. To perform the integrated power quality compensation, a hysteresis current control scheme is adopted to track the balanced line current command in phase with mains voltage. Three voltage levels are generated on the ac terminal of the proposed inverter. Computer simulation and experimental results are provided to verify the effectiveness of the proposed control scheme.     

High-power CSI-fed induction motor drive with optimal power distribution based control

In this article, a current source inverter (CSI) fed induction motor drive with an optimal power distribution control is proposed for high-power applications. The CSI-fed drive is configured with a six-step CSI along with a pulsewidth modulated voltage source inverter (PWM–VSI) and capacitors. Due to the PWM–VSI and the capacitor, sinusoidal motor currents and voltages with high quality as well as natural commutation of the six-step CSI can be obtained. Since this CSI-fed drive can deliver required output power through both the six-step CSI and PWM–VSI, this article shows that the kVA ratings of both the inverters can be reduced by proper real power distribution. The optimal power distribution under load requirements, based on power flow modelling of the CSI-fed drive, is proposed to not only minimise the PWM–VSI rating but also reduce the six-step CSI rating. The dc-link current control of the six-step CSI is developed to realise the optimal power distribution. Furthermore, a vector controlled drive for high-power induction motors is proposed based on the optimal power distribution. Experimental results verify the high-power CSI-fed drive with the optimal power distribution control.     

High-Performance Transformerless Online UPS

In this paper, a high-performance single-phase transformerless online uninterruptible power supply (UPS) is proposed. The proposed UPS is composed of a four-leg-type converter, which operates as a rectifier, a battery charger/discharger, and an inverter. The rectifier has the capability of power-factor collection and regulates a constant dc-link voltage. The battery charger/discharger eliminates the need for the transformer and the increase of the number of battery and supplies the power demanded by the load to the dc-link capacitor in the event of the input-power failure or abrupt decrease of the input voltage. The inverter provides a regulated sinusoidal output voltage to the load and limits the output current under an impulsive load. The control of the dc-link voltage enhances the transient response of the output voltage and the utilization of the input power. By utilizing the battery charger/discharger, the overall efficiency of the system is improved, and the size, weight, and cost of the system are significantly reduced. Experimental results obtained with a 3-kVA prototype show a normal efficiency of over 95.6% and an input power factor of over 99.7%.      

A common mode voltage reduction in boost rectifier/inverter systemby shifting active voltage vector in a control period

This paper proposes a new space-vector pulse width modulation (SVPWM) strategy that can reduce the number of common mode voltage pulses in a three-phase boost rectifier/inverter system using a synchronized switching sequence. In the proposed SVPWM strategy, it is possible to eliminate one common mode voltage pulse in every control period by shifting the active voltage vectors of the inverter to align to those of the boost rectifier. Thus, a reduction in the total number of common mode voltage pulses and RMS motor leakage current can be obtained without extra hardware. Since the proposed SVPWM strategy can be simply implemented in software, it is widely applicable regardless of the power capacity of the converter and results in no increment of converter volume, weight and price. Moreover, because the proposed SVPWM strategy maintains the magnitude of the active voltage vector required for motor control and simply changes the distribution of the zero, voltage vector, it does not effect the control performance of the power converter     

A novel approach to practical matrix converter motor drive system with reverse blocking IGBT

This paper proposes a novel control strategy and a protection circuit and shows the advantage of utilizing a newly developed reverse blocking insulated gate bipolar transistor (RB-IGBT), to solve several practical problems of the matrix converter. The proposed control strategy is based on a virtual indirect control method with a virtual rectifier and a virtual inverter. Pulse-width modulated (PWM) pulses for the matrix converter are obtained by combining PWM pulses for the virtual rectifier and inverter. As a result, the control part of the input current and output voltage can be clearly separated. Thus, the conventional inverter control algorithms can be applied to the virtual inverter control. The advantage of this method is confirmed by experimental results with a 22-kW induction motor drive system. Good sinusoidal waveforms are obtained for the input and output currents, and the total harmonic distortion (THD) of the input and output current are 5.1% and 1.4%, respectively. The conduction loss of the RB-IGBT is decreased to about two-thirds of the conventional ac switch with series connection diode. Thus, the converter loss is about a half to the conventional PWM rectifier-inverter system with the same capacity. Furthermore, the protection problem is solved by a dynamic clamp method without an electrolytic capacitor. This protection circuit directly dissipates reactive load energy by dynamic clamp operation of an IGBT.     

基于电驱动钻机的交流电子负载的研究

基于现代电力电子技术,深入研究能量回馈式的交流电子负载的主电路结构和控制策略。主电路采用AC／DC／AC拓扑,并选用电压型PWM整流器构成其输入、输出变流器。提出了一种基于DSP的交流电子负载的控制策略。     

Practical Control Implementation of a Three- to Single-Phase Online UPS

A high-performance three- to single-phase online uninterruptible power supply (UPS) is proposed. The proposed UPS is composed of a rectifier, a battery charger/discharger, and an inverter. The rectifier has the capability of power-factor correction and regulates a dc-link voltage. When the rectifier becomes unavailable or when the current required by the load exceeds the output rating of the rectifier, the charger/discharger supplies the power demanded by the load to a dc-link capacitor. The inverter provides a regulated sinusoidal output voltage and limits an output current under an impulsive load. New control algorithms of the rectifier, the charger/discharger, and the inverter are proposed. The proposed algorithms of the rectifier and the charger/discharger improve dynamic performance at step load change. To improve the transient response of the output voltage at outage of an input source, a mode change method of the charger/discharger is also proposed. Additionally, the proposed current-limit algorithm of the inverter can be implemented without additional hardware, and it increases the reliability of the UPS.      

High efficiency, unity power factor VVVF drive system of aninduction motor

A high-efficiency, unity-power-factor VVVF (variable voltage, variable frequency) drive scheme for an induction motor is presented. A unity-power-factor PWM (pulsewidth modulated) converter regulates DC voltage. An inverter circuit with the magnetic flux control PWM method generates VVVF PWM waveforms. The modulation factor of the inverter PWM control with controllable DC link DC voltage is studied. As a result, the distortion factor and the switching frequency are reduced by over-modulation with low DC link voltage. A high-efficiency and unity-power-factor VVVF induction motor drive has been achieved using the control strategy     

ESR and capacitance monitoring of a dc-link capacitor used in a three-phase PWM inverter with a front-end diode rectifier

Condition monitoring plays an important role in estimating health condition of capacitors because the ageing of the capacitors is usually accompanied by an increase in equivalent series resistance (ESR) and a decrease in capacitance. Either capacitance or ESR cannot be a unique indicator of the lifetime of capacitors in some cases. This paper presents a condition monitoring method of a dc-link capacitor used in a three-phase PWM inverter with a front-end diode rectifier intended for motor drives. The monitoring method extracts both the ESR and capacitance of a capacitor under test from the actual ripple current and voltage without disconnecting the capacitor nor injecting an additional current. The monitoring method, therefore, can be implemented online. Experimental results verify that the monitoring method independently obtains the ESR and capacitance changes of the capacitor under test. This contributes to accurate lifetime estimation of dc-link capacitors.     

A hybrid structure using phase-controlled rectifiers andhigh-frequency converters for magnet-load power supplies

Thyristor rectifiers are still the preferred choice for large magnet power supplies. However, large harmonic voltages, resulting in large current ripple, and slow dynamic response are major drawbacks of these converters. This paper presents a topology and a control technique for hybrid large-power high-precision magnet power supplies. The system consists of a phase controlled rectifier connected in series with a high-frequency PWM converter. The rectifier is designed to handle the main output power and the PWM converter is used only for harmonics cancellation and error compensation. A feedforward control scheme is proposed to ensure that the desired power sharing is maintained during both the steady state and transient operations. The operating principles of the proposed structure are discussed in the paper, and the results from a 1 kVA experimental setup are provided to validate the proposed topology