Novel unity power factor circuits using zero-vector control forsingle-phase input systems

This paper proposes two novel circuits which realize a unity input power factor single-phase to three-phase converter with a motor load. The power supply is connected to the neutral point of the motor, and the three-phase inverter is controlled to act also as a virtual AC/DC power converter leg. This virtual leg is controlled by zero vectors of the three-phase inverter. The main features of these circuits are as follows: no inductive components are required; a reduction in the number of switching devices compared with conventional topologies; and motor current increases because converter input current also flows through the motor windings. A full-bridge converter can be built using the same number of switching devices as the conventional half bridge and with no need for a capacitive leg with an accessible neutral point. In this paper, the proposed full-bridge-type circuit is experimentally tested using a 750-W induction motor as load     

A novel three-phase AC/DC converter without front-end filter basedon adjustable triangular-wave PWM technique

This paper proposes a novel three-phase AC/DC converter without a front-end filter. Because an adjustable triangular-wave pulsewidth modulation (PWM) (ATPWM) technique is adopted, not only is a front-end filter located after the three-phase rectifier is omitted, but also the size of the input AC filter and the output DC filter are reduced. In addition, this AC/DC converter has many advantages such as simpler structure, higher reliability, and better output waveform. The principle of operation, harmonics elimination, and feedback control of the novel AC/DC topology are elaborated. A thorough analysis on its performance under an unbalanced system is presented. Finally, the theoretical analysis is proved to be correct by simulations and experiments     

Direct frequency convertor with sinusoidal line currents forspeed-variable AC motors

A novel concept for a static three-phase to three-phase power converter for an AC drive with a unity power factor and reduced harmonics on the line side is presented. The power circuit comprises two back-to-back connected six-pulse bridges having no energy storage elements in the DC link. This permits pulse-width modulation (PWM) control in both bridges while requiring active turn-off semiconductor switches in only one bridge. The line-side harmonics are suppressed by a three-phase second-order filter. The method of predictive optimization is used for the control of the power converter. The complex control structure of the system is based on an online prediction of space vector trajectories. The steady-state operation of the system is exemplified by simulation results     

Characterization of single-stage three-phasepower-factor-correction circuit using modular single-phase PWM DC-to-DCconverters

The complete DC characteristics of three-phase modular power-factor-correction (PFC) converters using single-phase pulsewidth modulation (PWM) DC-to-DC converter modules for high-power applications are studied. Using circuit averaging, the converter input and output quantities are determined numerically. Both the continuous and discontinuous output current modes of operation (CCM and DCM) are studied in detail. Near-unity power factor can be achieved with the converter modules operating in the DCM. An averaged model was used to study and determine the boundaries between DCM and CCM over the full period of the three-phase input voltage. It is found that high power factor is inherent in the converter system provided that the converters are operated in the DCM and the voltage conversion ratio is selected properly. The criteria for obtaining high power factor are analyzed and the optimal circuit parameters are determined to obtain the best achievable power factor. Both simulations and experimental results from a 1.5-kW prototype using full-bridge converter modules have confirmed the analysis     

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     

Three-Dimensional Feedforward Space Vector Modulation Applied to Multilevel Diode-Clamped Converters

Simplified space vector modulation (SVM) techniques for multilevel converters are being developed to improve factors such as the computational cost, number of commutations, and voltage distortion. The feedforward SVM presented in this paper takes into account the actual DC capacitor voltage unbalance of the multilevel power converter. The resulting technique is a low-cost generalized feedforward 3-D SVM method and is particularized for three-phase multilevel diode-clamped converters. This new modulation technique can be applied to topologies where the gamma component may not be zero. The computational cost of the proposed method is similar to those of comparable methods, and it is independent of the number of levels of the power converter. Experimental results using a three-level diode-clamped converter are presented to validate the proposed modulation technique.     

A Line-Interactive Single-Phase to Three-Phase Converter System

This paper describes a line-interactive single-phase to three-phase converter. A typical application is in rural areas supplied by a single-wire with earth return system. The traditional objective of feeding a three-phase induction motor is not anymore the main concern for such conversion. Due to the evolution of the farm technology, some of the local loads (as electronic power converters, computers, communication equipments, etc) require high power quality that is intended as sinusoidal, symmetrical, and balanced three-phase voltage. Additionally, to maximize the power from the feeder, the system provides a unity power factor to the grid. A three-phase voltage source inverter-pulsewidth modulation converter is used for this purpose. The power converter processes a fraction of the load power and the energy necessary to regulate the dc link voltage. As it does not need to supply active power, it is not necessary to have a source at the dc side. However, if island mode operation is needed, a dc source must be available at the dc link to supply the load. The control strategy, design criteria, and experimental results are presented     

A General PWM Strategy for Four-Switch Three-Phase Inverters

A general pulsewidth modulation (PWM) method for control of four-switch three-phase inverters is presented. The proposed vector PWM offers a simple method to select three or four vectors that effectively synthesize the desired output voltage, even in presence of voltage oscillations across the two dc-link capacitors. The method utilizes the so called space vector modulation, and includes its scalar version. Different vector combinations are compared. The effect of Wye and delta motor winding connections over the pulse width modulator is also considered. The common mode voltage generated by the four-switch three-phase converter is evaluated and compared to that provided by the standard six-switch three-phase inverter. Simulation and experimental results are presented to demonstrate the feasibility of the proposed approach     

矩阵变换器空间矢量脉宽调制控制算法及仿真研究

本文选择最有代表性的三相输入、三相输出交一交矩阵变换器为研究对象,在分析三相-三相矩阵变换器数学模型的基础上,给出了基于常用空间矢量脉宽调制策略的矩阵变换器调制模型和调制策略,并用Matlab Simulink建立了空间矢量调制的矩阵变换器的仿真模型,给出了仿真实验结果。实验结果证实了所提出的空间矢量脉宽调制控制算法的正确性和可实现性。     

A three-phase ZVS PWM DC/DC converter with asymmetrical duty cycle associated with a three-phase version of the hybridge rectifier

This paper proposes the use of a three-phase version of the hybridge rectifier in the three-phase zero-voltage switch (ZVS) DC/DC converter with asymmetrical duty cycle. The use of this new rectifier improves the efficiency of the converter because only three diodes are responsible for the conduction losses in the secondary side. The current in the secondary side of the transformer is half the output current. In addition to this, all the advantages of the three-phase DC/DC converter, i.e., the increased frequency of the output and input currents, the improved distribution of the losses, as well as the soft commutation for a wide load range, are preserved. Therefore, the resulting topology is capable of achieving high efficiency and high power density at high power levels. The theoretical analysis, simulation, and experimental results obtained from a 6-kW prototype, and also a comparison of the efficiency of this converter with the full-bridge rectifier are presented.     

Current Source Optimization in AC-DC GTO Thyristor Converters

A digital interface for a three-phase PWM ac-dc GTO converter is described, and a microprocessor-based firing scheme for the PWM control system is proposed. Two modulation strategies, equal pulsewidth modulation (EPWM) and sinusoidal pulsewidth modulation (SPWM), are implemented and their efficiencies of operation considered. Applied as the inner current loop in a dc motor controller with constant-gain proportional-plus-integral (PI) control, a fast response to step reference input changes is obtained. The theoretical responses using an approximate z-transform analysis are used to obtain optimum operational parameters.     

Series resonant AC-power interface with an optimal power factor andenhanced conversion ratio

A method of power pulse modulation with internal frequencies of tens of kHz which is also suitable for multikilowatt power levels is applied to a series-resonant converter system for generating synthesized multiphase bipolar waveforms with reversible power flow. The power circuitry of the converter is provided with one single high-frequency resonant link in the direct energy path. Natural current commutation of the thyristors is obtained by the use of a series-resonant circuit for power transfer and control. Consequently, switching losses can be reduced to a minimum without compromising the reliability of the solid-state components. Test results of a converter system generating three-phase sinusoidal waveforms demonstrate the significant aspects of this improved series-resonant power processor and indicate the possibilities of fast-acting DC and AC converter systems with reversible power flow     

Current Reconstruction Techniques for Survivable Three-Phase PWM Converters

In high-performance three-phase pulsewidth-modulated (PWM) converter systems used in generator and motor drives, failure of current sensors will directly interrupt the system performance, and will even cause disastrous consequences. Redundancy in design is one of the popular choices to overcome this issue. However, this usually leads to an undesirable increase in size and cost. This letter presents two novel model-independent current reconstruction methods for three-phase PWM converter systems based on space vector modulation. Using the proposed sensor placement and software algorithm, phase currents within a three-phase converter can be reconstructed to an acceptable level of accuracy under single-survived-sensor ($S^3$) scenario. A hardware prototype is built and fault tolerant algorithm is implemented using a DSP (TMS320F2812). Experiments are conducted under worst-case scenario to verify the flexibility of sensor placement/converter layout and software algorithm.      

A single-stage three-phase boost-buck AC/DC converter based ongeneralized zero-space vectors

In this paper, first a set of generalized zero-space vectors is proposed. Based on this concept, a novel single-stage three-phase pulsewidth modulation (PWM) boost-buck AC/DC converter is then proposed to achieve clean sinusoidal input current, unity power factor, adjustable DC voltage and fixed switching frequency and to be insensitive to input voltage distortion as well as simplify the control of all switches. By choosing proper switching sequences such that the largest magnitude line current is conducted through the antiparallel diodes without switching action, the switching loss and thermal stress can be reduced greatly. Finally, a prototype is constructed, and experimental results are given to validate the proposed converter     

一种低成本单相-三相周波变换器的研究

本文提出一种适用于异步电机传动的单相-三相周波变换器。应用一种基于开环恒压频比控制的离散跳频起动策略,实现了电机的良好起动特性,同时保证了低频阶段降低起动电流而保持足够大的起动力矩的目标。由于仅采用7个晶闸管,该周波变换器-电机传动系统具有造价低,结构简单的特点。仿真及实验结果表明了该控制策略的有效性以及系统方案的可行性。     

Modeling and analysis of static and dynamic characteristics forbuck-type three-phase PWM rectifier by circuit DQ transformation

The static and dynamic characteristics of buck-type three-phase pulse width modulation (PWM) rectifier are fully analyzed based on the DC and AC circuit models developed by the circuit DQ transformation. Various static power converter characteristics such as gain, real and reactive power, power factor and unity power factor conditions are completely analyzed. Transition characteristics are also analyzed by both exact small-signal models with full set of equations and simplified output models in explicit form. The usefulness of the models is verified through computer simulations and experiments with good agreement shown     

A carrier-based PWM method for three-phase four-leg voltage source converters

In this paper a voltage modulation method based on a triangular carrier wave for the three-phase four-leg voltage source converter is described. The four-leg converter can produce three output voltages independently with one additional leg. The proposed modulation method for the four-leg converter can be implemented with a single carrier by a simple but useful "offset voltage" concept. The method is equivalent to the so called three-dimensional space vector PWM method, but its implementation is much easier. The maximum magnitude of the balanced three-phase voltage and the maximum magnitude of zero sequence voltage, which can be synthesized simultaneously, are derived. The feasibility of the proposed modulation technique is verified by computer simulation and experimental results. These results show that a proposed carrier-based pulsewidth modulation (PWM) technique can be easily implemented without conventional computational burden.     

Bidirectional Switch Commutation for a Matrix Converter Supplying a Series Resonant Load

This paper describes a bidirectional switch commutation strategy for a three-phase to two-phase matrix converter supplying a series resonant load. Classical modulation techniques are not applicable because of the needed high output frequencies. This fact, together with the different topology compared to classical three-phase to three-phase matrix converters, makes a new investigation of commutation principles necessary. The paper shows that the three-phase to two-phase resonant matrix converter can be compared with the full-bridge series-resonant converter. Thus, the commutation of the full-bridge series-resonant converter gives the conditions for the bidirectional switch commutation at the matrix converter. One of the main benefits of the derived strategy is the minimization of commutation steps independent of the load current sign.     

矩阵变换器实现感应电机矢量控制系统方法研究

论述了空间矢量调制矩阵变换器的基本原理,给出了矩阵变换器-异步电动机调速系统组合控制模型,分析了空间矢量调制策略,并且在MATLAB/SIMULINK平台上,针对矩阵变换器-异步电机矢量控制系统的电机起动运行进行了仿真,仿真结果验证了矩阵变换器空间矢量调制策略的可行性和正确性,表明其策略方法具有良好的起动调速性能,具有很大的应用前景。     

Voltage Balancing Control of Diode-Clamped Multilevel Converters With Passive Front-Ends

In the previous literature, it has been reported that it is not possible to guarantee the balance of the dc-link capacitor voltages of multilevel three-phase diode-clamped dc–ac converters with passive front-ends for high modulation indices, especially for more than three levels. This paper proposes a novel closed-loop control approach capable of guaranteeing such balance for all operating conditions of the converters without the need for additional hardware. Three different phase duty-ratio perturbation schemes are proposed. They are compared through simulation for the case of a four-level three-phase diode-clamped dc–ac converter operated with a virtual-vector-based modulation. The most simple and effective perturbation scheme, only requiring the sensing of all dc-link capacitor voltages, is tested experimentally in the same four-level converter. The results demonstrate the feasibility of guaranteeing the dc-link capacitor voltage balance for all converter operating conditions.