Showing papers on "PWM rectifier published in 1995"

VSI-PWM rectifier/inverter system with a reduced switch count

Abstract: A current-controlled VSI-PWM rectifier and inverter with capacitor DC link is regarded as one of the most important structures for three-phase to three-phase power conversion. This type of power converter normally requires twelve switches for the rectifier and an inverter composed of self turnoff switch such as a bipolar transistor or an IGBT with an anti-parallel diode. In this paper, a new three-phase to three-phase AC/AC power converter for AC motor drives is proposed. The proposed power converter employs only eight switches and has the capability of delivering sinusoidal input currents with unity power factor and bidirectional power flow. This paper describes the feasibility and the operational limitations of the proposed structure. A mathematical model of the system is derived using the generalized modulation theory and experimental results for steady-state and dynamic behavior are presented to verify the developed model.

Performance investigation of a current-controlled voltage-regulated PWM rectifier in rotating and stationary frames

Abstract: Active front-end rectifiers with reduced input current harmonics and high input power factor will be required in the near future for utility interfaced applications. In order to meet the new and more stringent regulations with force-commutated switches, the voltage source inverter approach is superior to the conventional current source approach, in terms of number of components and control options. However, the straightforward power angle control of the rectifier is characterized by a slow response and potential stability problems. This paper proposes a current-controlled PWM rectifier as an alternative. It provides near sinusoidal input currents with unity power factor and a low output voltage ripple. Moreover, it produces a well-defined input current harmonic spectrum, exhibits fast transient response to load voltage variations, and is capable of regenerative operation. PWM pattern generation is based on a carrier technique and the current controller is implemented in the: (a) stationary (abc) frame; and (b) rotating (dqo) frame. The design and the performance of the two controller options are investigated and compared. >

A zero-voltage switched, three-phase isolated PWM buck rectifier

Abstract: A novel three-phase, single-stage, isolated PWM rectifier is proposed, which is capable of achieving unity power factor, and low harmonic distortion of input currents, and at the same time realizing zero-voltage switching for all power semiconductor devices. Operation of the proposed circuit is thoroughly analyzed. Design equations and trade-offs are provided. The performance of the proposed circuit is demonstrated through a 2 kW, 100 kHz, digital signal processor controlled prototype. The conversion efficiency is around 93%. >

A current-type PWM rectifier with active damping function

Abstract: A new control method for current-type pulse-width modulation (PWM) rectifiers which can provide active damping function is presented. This damping function is effective only on the harmonic components of AC input current selectively. Thus steady-state waveform distortion and transient oscillation of the input current are reduced by the active damping effects. The active damping function can be realized by feedback control of an LC filter connected to the AC side of the rectifier, and it does not require any additional components in the main circuits, permitting a simple circuit configuration. The control system of the proposed PWM rectifier is analyzed by using a simple block diagram developed in the present paper. From the analytical results, the influence of the circuit parameters and control delay on the active damping effects and the stability of the operation are clarified to establish the design method. To confirm the effectiveness of the active damping function, some results of basic experiments are included. As an example of application of the active damping function, the proposed rectifier is applied to reduce the harmonic currents generated by conventional rectifiers operating in parallel with the proposed rectifier. Some experimental results in this application are also included.

Space vector based analysis of the variation and control of the neutral point potential of hysteresis current controlled three-phase/switch/level PWM rectifier systems

Abstract: This paper treats the control of the the capacitive output voltage center point of a unidirectional three-phase three-level PWM rectifier system. It is shown that, for hysteresis control of the input phase currents and resistive fundamental mains behavior, the center point potential can be controlled by an offset of the phase current reference values. Based on the results of a digital simulation, the transfer function is determined which describes the dynamic behavior of the system part to be controlled. Furthermore, the dimensioning of the center point voltage control is discussed. There, the considerations are related to an application of the PWM rectifier system for supplying the DC link of an uninterruptible power supply (8 kW rated power). Finally, the control behavior for stationary operation and for a step change of the load of the output voltage center point is examined for verifying the controller dimensioning. >

Transformerless four-wire PWM rectifier and its application in AC-DC-AC converters

Abstract: The paper introduces a transformerless four-wire power-factor-corrected boost rectifier which does not draw low-order harmonic currents from the supply neutral. The four-wire rectifier topology and control is described. The main application of such a rectifier is a new transformerless, four-wire AC-DC-AC converter for uninterruptible power supplies. Simulation results show the steady-state and dynamic response of the four-wire rectifier and the four-wire AC-DC-AC converter.

A novel three-phase three-switch three-level unity power factor boost-type pwm rectifier

Abstract: Based on the combination of a three-phase diode bridge and a DC/DC boost converter a new three-phase three-switch three-level PWM rectifier system is developed. It can be characterized by sinusoidal mains current consumption, controlled output voltage and low blocking voltage stress on the power transistors. The application could be, e.g., for feeding the DC link of a telecommunications power supply module. The stationary operational behavior, the control of the mains currents and of the output voltage are analyzed. Finally, the stresses on the system components are determined by digital simulation and compared to the stresses in a conventional PWM rectifier system.

Energy efficiency improvements to electric locomotives using PWM rectifier technology

Abstract: This paper explores the benefits and feasibility of retrofitting existing phase controlled DC motor drives in the Queensland Rail coal transport system with PWM rectifier technology. The major benefits of this would be the replacement of the dynamic brake with a regenerative system and unity power factor operation with a high quality input current waveshape. Test results indicate that very significant energy savings are possible if regenerative braking is introduced. The paper also surveys standard PWM rectifier topologies suitable for this service.

Energy savings through regenerative braking using retrofit converters

Abstract: This paper explores the benefits and feasibility of retrofitting existing phase controlled DC motor drives in the Queensland Rail coal transport system with PWM rectifier technology. The major benefits of this would be, the replacement of the dynamic brake with a regenerative system and unity power factor operation with a high quality input current waveshape. Test results indicate that very significant energy savings are possible if regenerative braking is introduced. The paper also surveys two standard PWM rectifier topologies suitable for this service. These two topologies are modelled and simulated using the dynamic systems simulation package "SIMULINK". >

Fish method based on-line optimal control for PWM rectifiers

Abstract: A control strategy for hard switching high power PWM rectifiers, based on carrierless volt-second (flux) control is presented. Insights from the fish method yield switching rules in the synchronous frame such that, even during major setpoint changes, none of the switches ever violates a pre-determined minimum pulse width. The control method realizes outstanding transient behaviour at low switching frequencies and allows a small DC-link capacitance, low inductance loads as well as nonequal dwell-times. Experimental data of a small DSP-controlled 1 kW IGBT PWM rectifier is presented. >

A novel PWM scheme for harmonic reduction in power converters

Abstract: The harmonic content in the output of the rectifier can be reduced by employing pulse-width modulation. Sinusoidal pulse-width modulation (SPWM) is commonly used to reduce the harmonic content in the output and to vary the average voltage. However, the SPWM technique gives a large second harmonic component in the output and a low fundamental output voltage. The paper describes a novel PWM scheme called inverted-sine PWM (ISPWM) which uses a sinusoidal reference signal and an inverted-sine carrier. The ISPWM has a better spectral quality and a higher average voltage compared to the SPWM. The paper computes the harmonic content of the ISPWM output for different values of modulation index and compares them with the results obtained for a conventional SPWM. The complete control circuit for generating the ISPWM control signal for a PWM rectifier is developed. Experimental waveforms of voltages and currents and their frequency spectra are presented. >

A current controlled near unity power factor three-phase PWM buck rectifier without passive damping requirements

Abstract: Three-phase current source PWM rectifier (also known as three-phase buck rectifier) is often used as the front-end in utility interfaced systems. An input LC filter is required to suppress the current harmonics injected into AC mains. The input filter affects the input displacement factor (IDF) of the system, which varies with the rectifier operating point and may result in unacceptable low values. In this paper, closed-loop control of the input line currents is proposed to achieve near unity IDF independent of the load conditions. The current reference template is generated from the filter capacitor voltages, the need for damping resistors is eliminated and efficiency is increased. The output DC current is regulated by varying the amplitudes of the current references. The proposed scheme features good steady state results, fast transient response and higher efficiency. The paper includes analysis, a design example and simulation results for steady state and transient conditions.

Real time digital control of uninterruptible power supply system

Abstract: This paper describes a real time digital control scheme of the Uninterruptible Power Supply UPS) system using Digital signal Processor (DSP). The rating of the UPS is 5kVA of 220V three phase input and 220V single phase output. The power switching devices of the PWM rectifier and inverter are Insulate Gate Bipolar-Junction Transistor (IGBT's) working at switching frequency of 10kHz. The real time digital control of input current and output voltage results in sinusoidal waveforms. And also, a full software based Digital Phase-Locked Loop(DPLL) technique is used for the synchronization of frequency and phase to suppress the transient problems in the output voltage at the instant of power transfer between inverter output and bypass line.

A current-source inverter fed inductio~n motor drive system

Abstract: Standard low and medium induction power motor drives are based on the PWM voltage source inverter (VSI) fed from a diode rectifier. The dual topology, based on the current source inverterhectifier structure is used in medium and high power applications. This paper addresses some of the drawbacks of this approach compared to the voltage source approach. The proposed drive features: (a) an on-line operated PWM inverter, using instantaneous output capacitor voltage control based on space vector modulation; (b) a line- synchronized PWM rectifier, with dc bus current control; (c) an additional inverter modulation index control loop, ensuring a constant inverter modulation index. The resulting advantages include: (a) ruggedness and inherent continuous regeneration capability; (b) near unity global input power factor; (c) reduced motor voltage distortion; (d) reduced dc bus inductor and switch conduction losses; (e) fast motor dynamic response; (f) elimination of motor circuit resonances. Simulated and experimental results based on a DSP implementation are given. improper gating, particularly under fast transients, which reduces tlhe converter reliability.