Optimal current programming in three-phase high-power-factorrectifier based on two boost converters

Current programming in a three-phase high-power-factor rectifier based on two boost converters is discussed in this paper. It is shown that the converter currents can be expressed in terms of two mutually related auxiliary functions. The auxiliary functions are related to the input current spectrum. Optimal auxiliary functions that eliminate harmonics of the input currents are derived. A method to generate reference signals for the optimal current programming is proposed. Experimental results confirming the proposed concepts are presented     

Unified constant-frequency integration control of three-phase standard bridge boost rectifiers with power-factor correction

In this paper, a three-phase six-switch standard boost rectifier with unity-power-factor correction is investigated. A general equation is derived that relates the input phase voltages, output DC voltage, and duty ratios of the switches in continuous conduction mode. Based on one of the solutions and using one-cycle control, a unified constant-frequency integration controller for PFC is proposed. For the standard bridge boost rectifier, a unity power factor and low total harmonic distortion can be realized in all three phases with a simple circuit that is composed of one integrator with reset along with several flips-flops, comparators, and some logic and linear components. It does not require multipliers and three-phase voltage sensors, which are required in many other control approaches. In addition, it employs constant-switching-frequency modulation that is desirable for industrial applications. The proposed control approach is simple and reliable. All findings are supported by experiments.     

AC voltage and current sensorless control of three-phase PWM rectifiers

In this paper, a novel control scheme of three-phase PWM rectifiers eliminating both the AC input voltage and current sensors is proposed. The phase angle and the magnitude of the source voltage are estimated by controlling the deviation between the rectifier current and its model current to be zero. The input currents can be reconstructed from switching states of the PWM rectifier and the measured DC link currents. To eliminate the calculation time delay effect of the microprocessor, the currents ahead one sampling period are estimated by a state observer and then are used for feedback control. The proposed control scheme reduces the system cost and improves its reliability. The feasibility of the proposed AC sensorless technique for three-phase PWM rectifiers has been verified through experiments using a high performance DSP chip.     

A general three-phase PFC controller for rectifiers with a parallel-connected dual boost topology

A general constant-frequency power-factor-correction (PFC) controller is proposed for three-phase rectifiers with parallel-connected dual-boost topologies. This paper shows that unity power factor and low current distortion in all three phases can be realized by one-cycle control using one integrator with reset along with a few near and logic components. This new extension of one-cycle control provides the core PFC function to the dual-boost topologies. It does not require multipliers, as used in most other control approaches to scale the current reference according to the output power level. In each 60/spl deg/ of AC line cycle, only two switches are switched at high frequency; therefore the switching losses are significantly reduced. All switches are switched at low current, which results in reduced current ratings. This control method is simple and general. It is applicable to three-phase rectifiers that can be decoupled into parallel-connected dual-boost topologies by slight modification of the logic circuit. This control method is verified by experimental results. The proposed controller is suitable to be integrated into a three-phase PFC control chip.     

An analysis of three-phase low-harmonic rectifiers applying thethird-harmonic current injection

An analysis of the three-phase low-harmonic rectifiers applying passive third-harmonic current injection networks is presented in this paper. Optimal amplitude of the injected current to minimize the input current total-harmonic distortion (THD) is derived as a function of the injected current phase displacement. Power aspects of the third-harmonic current injection are analyzed, and it is shown that improvement in the input current THD could be obtained at the expense of the power taken by the current injection network. In the case of optimal current injection, the power taken by the current injection network is shown to be equal to 8.571% of the input power, resulting in the input current THD of 5.125%. Effects of unwanted higher order harmonics in the injected currents are studied for two previously proposed passive current injection networks. The current injection networks are compared under the constraint that volt-ampere ratings of applied components are the same. Analytically obtained results are experimentally verified     

Improving mains current quality for three-phase three-switch buck-type PWM rectifiers

Modulation schemes for three-phase three-switch buck-type pulsewidth modulation rectifiers where the switching state of one bridge leg is clamped within a /spl pi//3-wide interval of the mains period guarantee minimum switching losses as well as minimum input filter capacitor voltage ripple and minimum dc current ripple. However, as shown in this paper by a detailed analysis of the time behavior of the input filter capacitor voltages within a pulse period such modulation schemes are characterized by the occurrence of sliding intersections of the filter capacitor voltages which causes input current distortion. An advanced modulation scheme is proposed which prevents the input current distortion and allows it to maintain the optimum performance of conventional modulation schemes. The theoretical considerations are finally verified by measurements on a 5-kW hardware prototype.     

Interleaved three-phase boost rectifiers operated in thediscontinuous conduction mode: analysis, design considerations andexperimentation

Interleaved discontinuous conduction mode (DCM) three-phase boost rectifiers provide current ripple cancellation and increase the effective frequency of the input current ripple. As a result, the size and cost of the differential mode (DM) input filter is reduced. This work presents a detailed analysis of the input current ripple of interleaved three-phase DCM boost rectifiers. The design curves derived from the analysis are used to determine the DM input filter parameters. The experimental results are shown for two interleaved three-phase DCM boost rectifiers rated at 8 kW of total power and operated at 40 kHz with IGBTs as the main power switches. The results show that the interleaved rectifiers comply with the IEC 61000-3-2 Class A harmonic standard for this power level     

Techniques for minimizing the input current distortion ofcurrent-controlled single-phase boost rectifiers

Techniques for minimizing the input current distortion of current-controlled single-phase boost rectifiers are described. The switching patterns of several boost rectifiers are examined to identify the nature of their input current waveforms. This analysis is used to examine the low-frequency current distortion levels, and hence the power quality, associated with the rectifiers. A PWM (pulse width modulation) strategy that selectively switches between positive unipolar PWM and negative unipolar PWM, called phase-adjusted unipolar PWM, is shown to produce the lowest current distortion levels. A novel two-switch asymmetrical half-bridge rectifier is presented that draws an input current at a unity fundamental power factor and with the same low distortion as obtained with the four-switch H-bridge rectifier. The operation of the various rectifiers is examined with reference to theoretical predictions, circuit simulations, and experimental results. This analysis is used to compare the performances of the various rectifier switching patterns     

Continuous and discrete variable-structure controls for parallel three-phase boost rectifier

We describe three nonlinear control schemes for a parallel three-phase boost rectifier consisting of two modules. The basic idea, however, can be extended to a system with N modules. All of the control schemes are developed in a synchronous frame. Moreover, each of the closed-loop power-converter modules operates asynchronously without any communication with the other module. Based on the dynamical equations of the parallel converter, we find that independent control of both of the modules on the DQ axes is not necessary and possible. Consequently, we develop control schemes that stabilize the dq axes and limit the zero-axis disturbance by preventing the flow of the pure zero-sequence current. One of the control schemes is developed purely in the discrete domain. It combines the space-vector modulation scheme with a variable-structure control, thereby keeping the switching frequency constant and achieving satisfactory dynamic performance. The performances of the other control schemes are also satisfactory.     

Line current characteristics of three-phase uncontrolled rectifiers under line voltage unbalance condition

Three-phase uncontrolled rectifiers with capacitive filters are highly sensitive to line voltage unbalance, drawing significantly unbalanced line current even under slightly unbalanced voltage condition. This paper presents an analysis of this "unbalance amplification effect" for an ideal rectifier circuit without AC- and DC-side inductors. A novel way of modeling the voltage unbalance is established by introducing a deviation voltage superimposed on balanced three-phase line voltages, which allows simplified analysis of the rectifier operation. With proper approximations, closed-form expressions for symmetrical components of the fundamental line current and correspondingly the current unbalance factor are derived in terms of the voltage unbalance factor, filter reactance, and load current. The equivalent RMS value of the third harmonic current is also derived. The analysis clearly shows high sensitivity of the current unbalance to the voltage unbalance, and provides a basic guideline for rectifier circuit design. The validity of the analysis is confirmed by simulation.     

A novel control method for three-phase PWM rectifiers using asingle current sensor

This paper proposes a control method for three-phase voltage-source PWM rectifiers using only a single current sensor in the DC-link. A PWM modulation strategy for reconstructing three phase currents from the DC-link current is given. When 3φ input currents cannot be reconstructed, a method for modifying the switching state of the PWM rectifier and a method for the predictive state observer is proposed. Compensation of the 2 sampling delays is also included, and this method is combined with all of the experiments. Performance differences between the two methods in a typical voltage source PWM rectifier are investigated experimentally     

Robust model predictive current control strategy for three-phase voltage source PWM rectifiers

Traditional model predictive control (MPC) strategy is highly dependent on the model and has poor robustness. To solve the problems, this paper proposes a robust model predictive current control strategy based on a disturbance observer. According to the current predictive model of three-phase voltage source PWM rectifiers (VSR), voltage vectors were selected by minimizing current errors in a fixed time interval. The operating procedure of the MPC scheme and the cause of errors were analysed when errors existed in the model. A disturbance observer was employed to eliminate the disturbance generated by model parameters mismatch via feed-forward compensation, which strengthened the robustness of the control system. To solve the problem caused by filter delay in MPC control, an improved compensation algorithm for the observer was presented. Simulation and experimental results indicate that the proposed robust model predictive current control scheme presents a better dynamic response and has stronger robustness compared with the traditional MPC.     

Modeling of the high-power-factor discontinuous boost rectifiers

This paper presents a modeling approach to obtain a small-signal model for a single-switch single-phase and three-phase discontinuous boost high-power-factor rectifiers. Such converters present nonlinear characteristics, and an approximation of them is used to derive the models. The most important result obtained is that the small-signal output impedance is not equal to the load impedance. The analysis is validated by experimental results     

Fast current controller in three-phase AC/DC boost converter usingd-q axis crosscoupling

In this paper, a new simple current controller with both satisfactory steady-state characteristics and fast transient response is proposed. In this scheme, a reference modification part is incorporated with the generally used synchronous-frame proportional-integral (PI) controller for the fast transient response. Simulation and experimental results are presented and show the effectiveness of the proposed current controller. In the simulation and experimental results, both the current controller and DC-link regulator show conspicuous performance improvement. It is also observed in the simulation and experiment that the proposed current controller has a similar characteristic as the synchronous-frame PI controller in the steady state and as the minimum-time current controller in the transient state     

An analysis of three-phase rectifiers with near-sinusoidal input currents

An analysis of a three-phase low-harmonic diode rectifier equipped with inductors, capacitors, and diodes is presented. Inductors and capacitors are used in conjunction with the three-phase diode rectifier bridge to improve the waveform of the currents drawn from the utility grid. The operation of the proposed converter is analyzed and, on this basis, design considerations are commented upon. The converter characteristics are determined as a function of the load current. Comparisons between the studied converter and other rectifiers (classical rectifiers, with passive or active filters, and three-phase low-harmonic rectifiers applying the third-harmonic current injection) are also presented. Several possible applications of the three-phase rectifiers with near-sinusoidal input currents are mentioned. Analytically obtained results are experimentally verified.     

Implementation of single-phase boost power-factor-correctioncircuits in three-phase applications

A three-phase rectifier employing three single-phase boost power-factor-correction circuits is analyzed. Each converter operates in the continuous conduction mode (CCM), which allows a high power factor and a small EMI filter. Current sharing is ensured by a common voltage loop driving the individual current loops of the three converters. A suitable circuit arrangement is devised to limit phase interaction. The zero-voltage-transition technique (ZVT) is successfully applied to each converter, in order to obtain zero turn on losses and soft turnoff of the freewheeling diodes. Results of a 1800-W 100-kHz experimental prototype are reported, which confirm the theoretical forecasts     

A modified boost rectifier for elimination of circulating current in power factor correction applications

This paper develops a modified AC/DC boost rectifier for power factor correction applications. The developed rectifier topology uses fewer devices compared to semi-bridgeless type boost rectifiers, and the overall efficiency is increased due to the elimination of the circulating current provided by the inductors. Moreover, it achieves a higher power factor and better total harmonic distortion (THD) in high load conditions. The performance of the developed topology was evaluated and verified by means of simulation and hardware experimental results.     

A new class of low-cost three-phase high-quality rectifiers withzero-voltage switching

Several new schemes for constructing three-phase low-harmonic rectifiers are introduced here. These three-phase AC-DC topologies are derived from parent DC-DC power converter topologies. With a single active switch featuring the zero-voltage switching (ZVS) property in addition to the diode-rectifier bridge, the rectifiers are capable of naturally drawing approximately sinusoidal input-current waveforms at nearly unity power factor. Thus, a family of low-cost high-efficiency three-phase high-power-factor rectifiers is obtained. A second power switch can be introduced to improve the current waveshape further. Simulation results are supplied for each of the proposed schemes to demonstrate the validity of the proposed power converters     

A three-phase to three-phase series-resonant power converter withoptimal input current waveforms. I. Control strategy

A control strategy for multiphase-input multiphase-output AC to AC series-resonant (SR) power converters is presented. After reviewing some basics in SR power converters, a hierarchy of control mechanisms is presented, together with their respective theoretical backgrounds and practical limitations. The respective controllers are then presented in a simulation context. The control scheme fully exploits the capabilities of high-frequency power converters and facilitates the extraction of currents at a unity power factor from the supply side, even under transient conditions. The control scheme takes into account losses and inaccuracies in the control electronics without deteriorating the intended waveforms. Through computer simulation, it has been shown that, in particular, the input current wave-shapes are greatly improved compared to the best-available operating data     

A novel discrete control strategy for independent stabilization of parallel three-phase boost converters by combining space-vector modulation with variable-structure control

We propose a discrete nonlinear controller, developed in a synchronous frame, for a parallel three-phase boost converter consisting of two modules. The basic idea, however, can be extended to a system with N modules. Each of the closed-loop power-converter modules operates asynchronously without any communication with the other modules. The controller stabilizes the currents on the dq-axes and limits the flow of the pure-zero sequence current. It combines the space-vector modulation scheme with a variable-structure control, thereby keeping the switching frequency constant and achieving satisfactory dynamic performance.