Pulse Width Modulation Inverter Control Research Articles

Close-Loop Current Control With Current-Sensing Resistor for Electromagnet Driven by Full-Bridge PWM Inverter

The full-bridge pulse-width-modulation (PWM) inverter is wildly applied to drive the electromagnet and enables advanced technologies, such as the active magnetic bearing (AMB) and the permanent-electro magnetic suspension (PEMS). However, the characteristic relationship between the current through the electromagnet and the duty cycle of the PWM signal has strong nonlinearity around the zero current. Moreover, the electromagnet possesses the induction that results in the time constant and significantly hinders the change of the current. Hence, the open-loop control of the full-bridge PWM inverter cannot accurately or timely tune the current through the electromagnet, especially around the zero current. This work proposes a closed-loop current control approach by three steps: (1) inserting a current-sensing resistor into the middle of the electromagnet, (2) obtaining the current signal with an analog signal-processing circuit, and (3) generating the PWM signal with the bang-bang control circuit. The proposed approach innovatively arranges the current-sensing resistor to take advantage of the symmetry and to minimize the influence from the high-frequency switching of the inverter, so that the measured current signal is comparable to the hall-effect current sensor. The experimental results demonstrate the effectiveness and efficiency of the proposed closed-loop current control approach, though the weak charging capability of the full-bridge PWM inverter still hinders its performance.

Grid-Connected Photovoltaic Generation System

This study addresses a grid-connected photovoltaic (PV) generation system. In order to make the PV generation system more flexible and expandable, the backstage power circuit is composed of a high step-up converter and a pulsewidth-modulation (PWM) inverter. In the dc-dc power conversion, the high step-up converter is introduced to improve the conversion efficiency of conventional boost converters and to allow the parallel operation of low-voltage PV modules. Moreover, an adaptive total sliding-mode control system is designed for the current control of the PWM inverter to maintain the output current with a higher power factor and less variation under load changes. In addition, an adaptive step-perturbation method is proposed to achieve the objective of maximum power point tracking, and an active sun tracking scheme without any light sensors is investigated to make PV plates face the sun directly in order to capture maximum irradiation and enhance system efficiency. Experimental results are given to verify the validity of the high step-up converter, the PWM inverter control, the ASP method, and the active sun tracker for a grid-connected PV generation system.

High-Performance Stand-Alone Photovoltaic Generation System

This study develops a high-performance stand-alone photovoltaic (PV) generation system. To make the PV generation system more flexible and expandable, the backstage power circuit is composed of a high step-up converter and a pulsewidth-modulation (PWM) inverter. In the dc-dc power conversion, the high step-up converter is introduced to improve the conversion efficiency in conventional boost converters to allow the parallel operation of low-voltage PV arrays, and to decouple and simplify the control design of the PWM inverter. Moreover, an adaptive total sliding-mode control system is designed for the voltage control of the PWM inverter to maintain a sinusoidal output voltage with lower total harmonic distortion and less variation under various output loads. In addition, an active sun tracking scheme without any light sensors is investigated to make the PV modules face the sun directly for capturing the maximum irradiation and promoting system efficiency. Experimental results are given to verify the validity and reliability of the high step-up converter, the PWM inverter control, and the active sun tracker for the high-performance stand-alone PV generation system.

Design and implementation of an FPGA-based control IC for AC-voltage regulation

This paper presents a field-programmable gate army (FPGA)-based control integrated circuit (IC) for controlling the pulsewidth modulation (PWM) inverters used in power conditioning systems for AC-voltage regulation. We also propose a multiple-loop control scheme for this PWM inverter control IC to achieve sinusoidal voltage regulation under large load variations. The control scheme is simple in architecture and thus facilitates realization of the proposed digital controller for the PWM inverter using the FPGA-based circuit design approach. Bit-length effect of the digital PWM inverter controller has also been examined in this paper. The designed PWM inverter control IC has been realized using a single FPGA XC4005 from Xilinx Inc., which can be used as a coprocessor with a general-purpose microprocessor in application of AC-voltage regulation. Owing to the high-speed nature of FPGA, the sampling frequency of the constructed IC can be raised up to the range that cannot be reached using a conventional digital controller based merely on microcontrollers or a digital signal processor (DSP). Experimental results show the designed PWM inverter control IC using the proposed control scheme can achieve good voltage regulation against large load variations.

Fuzzy-tuning current-vector control of a three-phase PWM inverter for high-performance AC drives

This paper proposes a new discrete fuzzy-tuning current-vector control (FTC) scheme for three-phase pulsewidth modulation (PWM) inverters. The proposed current control scheme can achieve fast transient responses and, at the same time, have very low total harmonic distortion in output current during steady-state operation. The proposed FTC scheme generates quasi-optimum PWM patterns by using a closed-loop control technique with instantaneous current feedback. The proposed FTC scheme has been realized using a single-chip digital signal processor (TMS320C14) from Texas Instruments. Experimental results are given to verify the proposed fuzzy-tuning current control strategy for three-phase PWM inverters.

Two management strategies to deal with PWM inverter's control variable saturation

Conventional PM (permanent magnet) synchronous motor drives are supplied by PWM (pulse width modulation) inverters. The limitation of the inverter's control variables has two important consequences: a reduction of the average torque; and important current and voltage ripples. In this paper, two strategies are proposed to deal with this problem for a two-current loop structure. The first one allows the use of the maximum available voltage without current distortions in case of successive limitations. The second one is an attempt to maintain a set of balanced voltages at the machine terminals to reduce the torque ripples in case of double limitations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Deadbeat control of PWM inverter with modified pulse patterns for uninterruptible power supply

A modified algorithm of pulse-width-modulation (PWM) inverter deadbeat control suitable for uninterruptible-power-supply (UPS) systems is presented. Two state variables are measured at each sampling interval, then, using the data, the pulse width is computed in real time in order to force the output voltage equal to the reference at each sampling instant which is called the deadbeat control. Two kinds of PWM pulse patterns are used to increase the fundamental component of the output voltage, considering the microprocessor computation time. Experimentation and simulation has verified that the proposed control scheme increased the output-voltage amplitude, providing an excellent transient response and accurate phase positioning for various load conditions. This algorithm is suitable for applications of high-power UPS systems, in which the switching frequency is in the range of a few kHz and the precise control of power flow is required. >

Dynamically Optimal Switching Patterns for PWM Inverter Drives (for Minimization of the Torque and Speed Ripples)

Several optimization criteria exist for pulsewidth modulation (PWM) inverter control as applied to ac motor drives. Drive dynamics, i.e., torque and speed ripples, are analyzed and optimized. As a representative example, the PWM inverter control is assumed to have three and five degrees of freedom. These degrees of freedom are realized by so-called switching angles which determine the inverter output voltage waveshape. This voltage is applied to an induction motor. Analysis is executed for a steady-state approximation (using Fourier analysis) as well as for the rigorous fifth-order dynamic equations. The results are compared. The optimal solution for the switching angles as a function of the voltage fundamental is shown. The location of the optima is compared with the efficiency optimal control presented in an earlier paper. A means is provided to compare results for different optimization criteria in order to reach an overall optimum as the best compromise between the results gained from the different optimization methods.