Power factor-corrected transformerless three-phase PWM converter for UPS applications

This thesis describes the research of a new transformerless three phase PWM converter for uninterruptible power supplies (UPS) applications. The removal of the bulky three phase transformer in larger power UPS can provide a significant saving in weight and cost of the overall system. The converter consists of a new four-wire rectifier coupled with a four-wire inverter via a dc bus. The supply and load neutral may be connected together without any neutral current flowing into the utility regardless of the load on the inverter. This allows the load to be at the same potential as the utility. The rectifier, inverter and complete UPS and control system are described in detail and simulation results are used extensively to back up the theory. An experimental prototype of the four-wire rectifier provides further confirmation of the principles. A further proposal to digitize the system is given. This would reduce the size of the required control circuit and simplify the hardware requirements

A Single-Input Single-Output Approach by using Minor-Loop Voltage Feedback Compensation with Modified SPWM Technique for Three-Phase AC–DC Buck Converter

The modified sinusoidal pulse-width modulation (SPWM) is one of the PWM techniques used in three-phase AC–DC buck converters. The modified SPWM works without the current sensor (the converter is current sensorless), improves production of sinusoidal AC current, enables obtainment of near-unity power factor, and controls output voltage through modulation gain (ranging from 0 to 1). The main problem of the modified SPWM is the huge starting current and voltage (during transient) that results from a large step change from the reference voltage. When the load changes, the output voltage significantly drops (through switching losses and non-ideal converter elements). The single-input single-output (SISO) approach with minor-loop voltage feedback controller presented here overcomes this problem. This approach is created on a theoretical linear model and verified by discrete-model simulation on MATLAB/Simulink. The capability and effectiveness of the SISO approach in compensating start-up current/voltage and in achieving zero steady-state error were tested for transient cases with step-changed load and step-changed reference voltage for linear and non-linear loads. Tests were done to analyze the transient performance against various controller gains. An experiment prototype was also developed for verification

A Model-Based Direct Power Control for Three-Phase Power Converters

Direct Power Control (DPC) technique has been widely used as control strategy for three-phase power rectifiers due to its simplicity and good performance. The DPC uses the instantaneous active and reactive power to control the power converter, the controller design has been proposed as a direct control with a look up table (LUT), and in recent works, as an indirect control with an inner control loop with proportional plus integral controllers for the instantaneous active and reactive power errors. In this paper a model-based DPC for three-phase power converters is designed, obtaining expressions for the input control signal which allow to design an adaptive control law minimizing the errors introduced by the parameters uncertainties as the smoothing inductor value or the grid frequency. Controller design process, stability study of the system and experimental results for a synchronous three-phase power rectifier prototype are presented to validate the proposed controller

SENSORLESS DIRECT POWER CONTROL FOR THREE-PHASE GRID SIDE CONVERTER INTEGRATED INTO WIND TURBINE SYSTEM UNDER DISTURBED GRID VOLTAGES

Wind turbines with permanent magnet synchronous generator (PMSG) are widely used as sources of energy connected to a grid. The studied system is composed of a wind turbine based on PMSG, a bridge rectifier, a boost converter, and a controlled inverter to eliminate low-order harmonics in grid currents under disturbances of grid voltage. Traditionally, the grid side converter is controlled by using the control VFOC (Virtual Flux Oriented Control), which decouple the three-phase currents indirect components (id) and in quadratic (iq) and regulate them separately. However, the VFOC approach is dependent on the parameters of the system. This paper illustrates a new scheme for the grid-connected converter controller. Voltage imbalance and harmonic contents in the three-phase voltage system cause current distortions. Hence, the synchronization with the network is an important feature of controlling the voltage converter. Thus, a robust control method is necessary to maintain the adequate injection of the power during faults and/or a highly distorted grid voltage. The proposed new control strategy is to use the direct power control based virtual flux to eliminate side effects induced by mains disturbances. This control technique lowers remarkably the fluctuations of the active and reactive power and the harmonic distortion rate. The estimated powers used in the proposed control approach is calculated directly by the positive, negative, and harmonic items of the estimated flux and the measured current without line sensor voltage.Ветряные турбины с синхронным генератором на постоянных магнитах (PMSG) широко используются в качестве источников энергии, подключенных к сети. Исследуемая система состоит из ветряной турбины на основе PMSG, мостового выпрямителя, повышающего преобразователя и управляемого инвертора для устранения гармоник низкого порядка в токах сетки при возмущениях напряжения сети. Традиционно преобразователь на стороне сети управляется с помощью виртуального потокоориентированного управления VFOC (Virtual Flux Oriented Control), который разделяет трехфазные токи на косвенные компоненты (id) и на квадратичные компоннеты (iq) и регулирует их отдельно. Однако подход VFOC зависит от параметров системы. Данная статья иллюстрирует новую схему для контроллера преобразователя, подключенного к сети. Дисбаланс напряжения и содержание гармоник в трехфазной системе напряжения вызывают искажения тока. Следовательно, синхронизация с сетью является важной особенностью управления преобразователем напряжения. Таким образом, надежный метод управления необходим для поддержания адекватной подачи энергии во время неисправностей и/или значительно искаженного напряжения сети. Предложенная новая стратегия управления заключается в использовании виртуального потока на основе прямого управления мощностью для устранения побочных эффектов, вызванных помехами в сети. Этот метод управления значительно снижает колебания активной и реактивной мощности и уровень гармонических искажений. Оценочные мощности, используемые в предлагаемом подходе к управлению, рассчитываются непосредственно по положительным, отрицательным и гармоническим элементам оцененного потока и измеренного тока без напряжения линейного датчика

High performance control of a three-phase PWM rectifier

Ph.DDOCTOR OF PHILOSOPH

Sliding Mode Controller For 3-Phase Boost Rectifier Circuit

Feedback control is the elementary mechanism through which many systems, like electrical, mechanical, or biological system maintain their equilibrium. Feedback control may be defined as the use of various signals that are determined by comparing the actual values of the system variables to their desired values, as a means of a control system. At the present, boost type three phase rectifiers are increasingly used for industrial applications such as uninterruptible power supplies (UPS), battery chargers, motor drives. Also, such as MOSFET, IGBT are commonly used by semiconductors, operate in high frequency switching devices which are free to switch at frequencies much higher than the main frequency, allowing the controller whose dynamic response is very high. The efficient conversion of power is a problem in the modern world. The power factor, one of the most vital characteristics in the AC/DC power conversion, describes the efficiency and superiority of such process. The unity-value power factor converter does not introduce any alteration to the energy source and exploits performance of the power conversion. Many schemes and solutions that are available in the field of power factor correction (PFC) are presented in the work. The thesis shows a power factor correction for a class of three-phase boost rectifier. Here a full-bridge boost converter has been studied for power factor control, using output sliding mode control. The sliding mode control drives the output voltage to the preferred dc level in the existence of external disturbances and internal parameter uncertainties providing a value of power factor close to unity. The controlled converters is simulated and studied for the effectiveness of the proposed control algorithms and good consistency is achieved