Digitally controlled high power switch-mode rectifier

High power switch-mode rectifiers offer advantages over conventionally used line-commutated thyristor rectifiers in terms of size and cost. This paper describes operation of the high power switch-mode rectifier based on an original control strategy which is digitally implemented. The rectifier is operated in a constant output current mode. The control strategy provides a fast transient response to disturbances and achieves equal current sharing between the buck converter modules which are paralleled within the switch-mode rectifier. Equal current sharing is maintained in steady-state as well as in transient operation. The paper demonstrates that the transient response to load disturbances achievable with the proposed control strategy is superior to the response obtained with the conventional control strategy in terms of the output current overshoot and the settling time. The control algorithm is digitally implemented on a DSP/FPGA based digital control platform and its performance is verified on a 2 kW scaled-down experimental setup of the switch-mode rectifier.     

A new space-vector-modulated control for a unidirectionalthree-phase switch-mode rectifier

A unidirectional three-phase switch-mode rectifier that delivers sinusoidal input currents in phase with the corresponding input phase voltages is proposed and analyzed in this paper. In the proposed topology, three AC switches are placed before the bridge rectifier and, respectively, across two power lines. A simple control scheme combing space-vector modulation and hysteresis current control is presented. Sinusoidal input line currents are observed in experimental results     

A digitally controlled switch mode power supply based on matrix converter

High power telecommunication power supply systems consist of a three-phase switch mode rectifier followed by a dc/dc converter to supply loads at -48 V dc. These rectifiers draw significant harmonic currents from the utility, resulting in poor input power factor with high total harmonic distortion (THD). In this paper, a digitally controlled three-phase switch mode power supply based on a matrix converter is proposed for telecommunication applications. In the proposed approach, the matrix converter directly converts the low frequency (50/60Hz, three-phase) input to a high frequency (10/20kHz, one-phase) ac output without a dc-link. The output of the matrix converter is then processed via a high frequency isolation transformer to produce -48V dc. Digital control of the system ensures that the output voltage is regulated and the input currents are of high quality under varying load conditions. Due to the absence of dc-link electrolytic capacitors, power density of the proposed rectifier is expected to be higher. Analysis, design example and experimental results are presented from a three-phase 208-V, 1.5-kW laboratory prototype converter.     

A fuzzy-controlled active front-end rectifier with current harmonicfiltering characteristics and minimum sensing variables

A control strategy which allows conventional voltage-source current-controlled (VSCC) pulsewidth modulation (PWM) rectifiers to work simultaneously as active power filters is presented. The proposed control strategy also allows compensating the system power factor and compensating unbalanced loads. The measurement and/or calculation of the harmonics and reactive power are not required, making the proposed control scheme very simple. The active front-end rectifier acts directly on the mains line currents, forcing them to be sinusoidal and in phase with the mains voltage supply. To improve the dynamic of the system, the amplitude of the current is controlled by a fuzzy system, which adjusts the DC-link voltage of the PWM rectifier. The strategy is based on connecting all the polluting loads between the PWM rectifier and their input current sensors. The main advantages of this approach are the following: (1) there is no need to install a specially dedicated active power filter; (2) it also works simultaneously as a power factor compensator; and (3) no special and complicated calculations are required for harmonic elimination. The viability of the proposed active front-end rectifier is proved by simulation and with experimental results obtained from a 2 kVA PWM prototype     

A constant output current three-phase diode bridge rectifier employing a novel "Electronic Smoothing Inductor"

This paper presents an improvement of the well-known conventional three-phase diode bridge rectifier with dc output capacitor. The proposed circuit increases the power factor (PF) at the ac input and reduces the ripple current stress on the smoothing capacitor. The basic concept is the arrangement of an active voltage source between the output of the diode bridge and the smoothing capacitor which is controlled in a way that it emulates an ideal smoothing inductor. With this the input currents of the diode bridge which usually show high peak amplitudes are converted into a 120/spl deg/ rectangular shape which ideally results in a total PF of 0.955. The active voltage source mentioned before is realized by a low-voltage switch-mode converter stage of small power rating as compared to the output power of the rectifier. Starting with a brief discussion of basic three-phase rectifier techniques and of the drawbacks of three-phase diode bridge rectifiers with capacitive smoothing, the concept of the proposed active smoothing is described and the stationary operation is analyzed. Furthermore, control concepts as well as design considerations and analyses of the dynamic systems behavior are given. Finally, measurements taken from a laboratory model are presented.     

Improved Modification of the Closed-Loop-Controlled AC-AC Resonant Converter for Induction Heating

A single-switch parallel resonant converter for induction heating is implemented. The circuit consists of an input LC-filter, a bridge rectifier, and a controlled power switch. The switch operates in soft commutation mode and serves as a high frequency generator. The output power is controlled via the switching frequency. A steady state analysis of the converter operation is presented. A closed-loop circuit model is also presented, and the experimental results are compared with the simulation results.     

An improvement technique for the efficiency of high-frequencyswitch-mode rectifiers

A new technique for improving the efficiency of single-phase high-frequency switch-mode boost rectifiers is proposed. This rectifier includes an additional boost converter that follows the main high-frequency switching device. The additional converter, which is controlled at lower frequencies, bypasses almost all the current in the main switch and the high frequency switching loss is greatly reduced accordingly. Both switching devices are controlled by a simple method; each controller consists of a one-shot multivibrator, a comparator and an AND gate, and the maximum switching frequency can be limited without any clock generator. The rectifier works cooperatively in high efficiency and acts as though it were a conventional high-frequency switch-mode rectifier with one switching device. The proposed method is verified by experiment. This paper describes the rectifier configuration and design, and discusses the steady-state performance concerning the switching loss reduction and efficiency improvement. Transient performance is also included     

Master/Slave Control of Input-Series- and Output-Parallel-Connected Converters: Concept for Low-Cost High-Voltage Auxiliary Power Supplies

This paper deals with low-cost high input voltage auxiliary power supplies. The objective of the paper is to give an overview of the existing solutions, and then present a new, efficient, and cost-effective solution. The proposed solution is based on input-series- and output-parallel (ISOP)-connected converters topology and simple decoupled master/slave control strategy. The main output voltage is controlled by the master converter, while the input voltages and output currents are controlled and balanced by the slave converter. The ISOP topology has two important advantages, namely the use of two series-connected rated for lower voltage converters gives a significant reduction of the switch-mode power supply overall cost and size, and lossfree balancing of the voltages of the input serially connected filter capacitors. The proposed solution is theoretically analyzed and experimentally verified on a laboratory setup. The experimental results are presented and discussed.      

Digital interval modeling and hybrid control of uncertain systems

This paper addresses two issues: (1) converting a continuous-time uncertain system to an equivalent discrete-time interval model; and (2) constructing a robust digital control law from a robust analogue control law for hybrid control of sampled-data uncertain systems. The system matrices characterizing the state-space representation of the original continuous-time uncertain systems are assumed to be interval matrices. The Pade approximation method together with a geometric-series approximation method is employed to obtain the generalized enclosing discrete-time interval models. The generalized enclosing interval models are able to tightly enclose the exact discrete-time uncertain model, and can be utilized for digital simulation and digital design of continuous-time uncertain systems. A new family of digitally redesigned interval controllers is constructed from a continuous-time robust controller for robust digital control of continuous-time uncertain systems. Using the newly digitally redesigned interval controllers, the dynamic states of the digitally controlled sampled-data uncertain systems are able to closely match those of the original analogously controlled continuous-time uncertain systems for a relatively longer sampling period     

Limit-Cycle Oscillations Based Auto-Tuning System for Digitally Controlled DC–DC Power Supplies

This paper introduces a new method and system for parameter extraction and automated controller adjustment, suitable for low power digitally controlled DC-DC switch-mode power supplies (SMPS). The system allows closed-loop calibration throughout regular converter operation. During a short-lasting test phase, SMPS parameters, such as output capacitance and load, are estimated by examining the amplitude and frequency of intentionally introduced limit cycle oscillations in duty ratio control variable as well as from its steady state value. Accordingly, a digital compensator is automatically constructed to provide fast dynamic response and good output voltage regulation. In addition, the load estimation data are used for improving efficiency of a converter having segmented transistors. It is performed through a selection of driving sequence resulting in minimized sum of switching and conduction losses. The effectiveness of the system is demonstrated on an experimental 400 kHz, 9 V-to-3.3 V, 10 W, digitally controlled synchronous buck converter.     

Analysis and Design of a Modular Three-Phase AC-to-DC Converter Using CUK Rectifier Module With Nearly Unity Power Factor and Fast Dynamic Response

In this paper, the analysis and design of a modular three-phase ac-to-dc converter using single-phase isolated CUK rectifier modules is discussed based on power balance control technique. This paper analyzes the operation of a modular converter as continuous-conduction-mode power factor correction (CCM-PFC). Design equations, as well as an average small-signal model of the proposed system to aid the control loop design are derived. It is used to obtain the inductor current compensator, thus the output impedance and audio susceptibility become zero, and therefore, the output voltage of the converter presented in this paper is independent of the variations of the dc load current and the utility voltage. The control strategy consists of a single output voltage loop and three-inductor current calculator. The main objective of the proposed system is to reduce the number of stages and improve dynamic response of dc bus voltage for distributed power system. The proposed scheme offers simple control strategy, flexibility in three-phase delta or star-connected, simpler design, fast transient response, good inductor current sharing, and power factor closed to unity. Both simulation and experimental results are presented. They are in agreement with the theoretical analysis and experimental work.      

基于数字控制方式的DC—DC转换器系统设计

文章给出了应用于高频数字控制DC—DC系统设计的两种方法。基于功率级的S域平均模型,采用传统的Redesign方法,得到数字PID控制的系统离散模型。针对数字PID控制的DC-DC系统的负载调节能力,提出了一种采用Direct—Digital方法实现的三阶数字控制器。基于Matlab／Simulink的系统仿真结果表明,当负载电流在500mA到1A跳变时,提出的三阶补偿系统的最大过;中电压160mV,稳定时间为30μs,相比二阶PID补偿系统竹过冲为450mV,稳定时间为110μs,负载调节性能得到很大的改善;同时,当输入电压在1μs内从3V跳变到5V时,三阶补偿系统的过;中电压和稳定时间分别为450mV和45μs,相比二阶补偿系统的过冲为610mV,稳定时间115μs,线性调节能力也得到较大改善。     

三相PWM整流器的前馈解耦控制与仿真研究

基于前馈解耦控制策略,研究了三相电压型PWM整流器的建模与控制问题。首先,在d-q旋转坐标系下建立了三相电压型PWM整流器的数学模型,给出了三相电压型PWM整流器的双闭环控制结构,按此方法确定了电压、电流PI调节器的设计方法。仿真结果表明该方法能使所设计的PWM整流器运行于单位功率因数,输出的直流电压稳定在期望值且具有快速的动态响应,满足了设计要求。     

Discretization of cascaded continuous-time controllers and uncertain systems

This paper presents a new method for the digital modeling of a continuous-time uncertain system and a new method for the digital redesign of a sampled-data uncertain system. The system matrices characterizing the state-space representation of the original uncertain system are assumed to be interval matrices. The Chebyshev quadrature formula together with the interval arithmetic are used for the digital interval modeling, and a dual concept of digital interval modeling is utilized to discretize a predesigned cascaded analog controller for robust digital control of a continuous-time uncertain system. Using the newly developed digital interval models and digitally redesigned controllers, the resulting dynamic states of the digitally controlled sampled-data uncertain systemsare able to closely match those of the originally analogously controlled continuous-time uncertain systems for a relatively longer sampling period.This work was supported inpart by the U.S. Army Research Office under Grant DAAG-55-98-1-0198.     

Modeling and control of a synchronous generator with an active DCload

The design and analysis of a system consisting of a variable-speed synchronous generator that supplies an active DC load (inverter) through a three-phase diode rectifier requires adequate modeling in both time- and frequency-domains. As an example, the system's control-loops are difficult to design without an accurate small-signal model; at the same time, the system protection design requires large-signal transient modeling. A particularity of the described system is strong nonideal operation of the diode rectifier, a consequence of the large value of the generator's synchronous impedance. This nonideal behavior influences both steady-state and transient performance. This paper presents an average model of the system that accounts, in a detailed manner for the dynamics of the power source and the load, and for the effects of the nonideal operation of the diode rectifier. The model is nonlinear, but time-continuous, and can be used for large- and small-signal analysis. The developed model was verified on a 105 kW generator-set with inverter output, whose DC-link voltage control-loop design was successfully carried out based on the average model. It is shown that a high bandwidth is needed for this control-loop in order to achieve the proper impedance matching between the power source and the active electronic load     

Predictive transient-following control of shunt and series activepower filters

A novel technique is presented for generation of a contemporary estimate of the fundamental component of the distorted input current or voltage to an uncontrolled three-phase bridge rectifier with a DC link smoothing filter. This allows for accurate calculation of cancellation references for series and shunt active power filters (APF) operating under steady-state and transient conditions. Improved transient performance allows for reduction of the power rating and control system bandwidth of an APF. An artificial neural network (ANN) predictor has been used to directly calculate the mean dq-axis input to the rectifier without filtering. This is a critical stage in separating harmonic distortion from fundamental current or voltage. The technique is developed using simulation data for both series and shunt APFs and validated with experimental results. The predictive harmonic identifier shows good steady-state performance and excellent transient performance that far exceeds that of a conventional identifier using time-domain or frequency-domain filtering     

A DSP-based implementation of a nonlinear model reference adaptive control for a three-phase three-level NPC boost rectifier prototype

In this paper, the design and the implementation of a model reference adaptive control (MRAC) applied to a three-phase three-level neutral-point-clamped (NPC) boost rectifier are presented. This control strategy is developed with a view to regulate dc output and neutral point voltages and to reduce the influence of parameter variations while maintaining unity power factor. A nonlinear multiple-input multiple-output (MIMO) state space model of the rectifier is then developed in dq0 reference frame. The proposed controller is based on the use of a feedback linearization technique followed by a robust MRAC scheme allowing the design of a suitable controller applied to the plant. The control law is designed in Simulink/Matlab and applied to the converter via a 1920-Hz pulse width modulator both executed in real time using the DS1104 DSP of dSPACE. A 1.25 kW laboratory prototype is developed for validation. The experimental results are given for different operating conditions: nominal power operation, balanced and unbalanced dc load steps, boost inductor variation, and reactive power control. The proposed control law performs perfectly in a wide operation range giving low output voltage ripple, low line-current THD, a small overshoot and a fast settling time under system parameters variation.     

Brushless permanent magnet (BPM) motor drive system usingload-commutated inverter

The goal of this work is to develop a brushless permanent magnet (BPM) motor drive system with low total system cost, high reliability and adequate performance for high-volume production and application to commercial appliances. The power converter used is a low-cost thyristor-based load-commutated inverter (LCI). Although LCIs have been used to supply sinusoidally excited permanent magnet motors, their application to BPM motors is a key contribution of this work. A detailed digital computer model capable of predicting the steady state as well as the transient performance of a BPM motor driven by an LCI has been developed. The utility-side phase-controlled rectifier, as well as the motor-side inverter-including the DC-link inductor, are modeled. A load-commutated inverter specifically designed to supply the BPM motor has been fabricated in the laboratory. The developed control strategy has been implemented on an INTEL 80C196KD microcontroller board. Simulation and experimental results to support the use of an LCI to drive a BPM motor are included in the paper     

A Simple Method to Improve the Dynamic Response of Single-Phase PWM Rectifiers

A single-phase boost rectifier system with conventional low-bandwidth voltage loop exhibits poor dynamic response. A simple method is presented to improve the dynamic response of the rectifier without affecting its steady-state performance. A fast voltage controller is used to improve the dynamic response of the rectifier. The increased low-frequency ripple at the output of the voltage controller is filtered out using a new filter. Design methodology for the voltage loop is presented. The filter is simple enough for analog and digital implementations. Low input current distortion, fast voltage-loop response, and improved dynamic response against line and load disturbances are demonstrated experimentally on a 300-W digitally controlled boost rectifier operating at a switching frequency of 100 kHz.      

基于虚拟电网磁链定向的三电平PWM整流器矢量控制研究

为实现无网侧电压传感器的三电平PWM整流器控制,在分析三电平PWM整流器数学模型的基础上,采用一种新颖的虚拟磁链观测器,提出了基于虚拟电网磁链定向的三电平PWM整流器矢量控制策略,在双三电平变频器系统中对其进行了实验研究。实验结果表明,该控制系统可提高整流器功率因数,并具有良好的动静态特性。