Direct Torque Control: Stator Flux Regulation Improvement at Low Speed

A simple method to improve stator flux regulation of a direct torque control (DTC) of induction motor drive is presented. By using this method, the simple control structure of DTC is retained and no modification to the voltage vectors look-up table is required. To implement this technique, the index to the look-up table is modified so that the reverse voltage vectors are selected (instead of zero-voltage vectors) whenever the stator flux regulation fails. To study the viability and the effectiveness of this simple method in improving the flux regulation at low speed, experiments are conducted to a ¼ hp induction motor with DTC technique. The control algorithm is implemented using a DS1104 controller board with Xilinx FPGA.

High Performance Direct Torque Control of Induction Motor Drives: Problems and Improvements

This paper presents some of the main problems, as well as their root causes, of Direct Torque Control (DTC) 3-phase induction motor drive. The high torque ripple in DTC drive due to the hysteresis controller inevitably becomes worst with the discrete implementation of the drive system. The hysteresis controller also causes variable switching frequency that depends on operating conditions, especially the speed. The simplification used in stator flux expression for voltage vectors selection in flux control results in a poor flux regulation at low speed. To overcome these problems, techniques that have been implemented at UTM- PROTON Future Drive Laboratory (UPFDL) are presented and described. Some experimental results obtained from the previous works are also presented and discussed.

High-Speed Computation using FPGA for Excellent Performance of Direct Torque Control of Induction Machines

The major problems in hysteresis-based DTC are high torque ripple and variable switching frequency. In order to minimize the torque ripple, high sampling time and fast digital realization should be applied. The high sampling and fast digital realization time can be achieved by utilizing high-speed processor where the operation of the discrete hysteresis regulator is becoming similar to the operation of analog-based comparator. This can be achieved by utilizing field programmable gate array (FPGA) which can perform a sampling at a very high speed, compared to the fact that developing an ASIC chip is expensive and laborious

A New Fixed Switching Frequency Direct Torque Controlled PMSM Drives with Low Ripple in Flux and Torque

Direct Torque Control (DTC) has gained popularity for development of  advanced  motor  control  due  to  its  simplicity  and  offers  fast  instantaneous torque  and  flux  controls.  However,  the  conventional  DTC  which  is  based  on hysteresis  controller  has  major  drawbacks,  namely  high  torque  ripple  and variable  inverter  switching  frequency.  This  paper  presents  an  improved switching strategy for reducing flux and torque ripples in DTC of PMSM drives; wherein  the  torque  hysteresis  controller  and  the  look-up  table  used  in  the conventional  DTC  are  replaced  with  a  constant  frequency  torque  controller (CFTC)  and  an  optimized  look-up  table,  respectively.  It  can  be  shown  that  a constant switching frequency is established due to the use of the CFTC while the reduction of torque and flux ripples is achieved mainly because of the selection of optimized  voltage  vector (i.e.  with an optimized  look-up  table).  This paper also  will  explain  the  construction  of  DTC  schemes  implemented  using MATLAB-Simulink  blocks.  Simulation  results  were  shown  that  a  significant reduction of flux and torque ripples which is about 90% can be achieved through the proposed DTC scheme.

Overview on Strategies and Approaches for FPGA Programming

This paper presents an overview of strategies and approaches for FPGA programming. At first, design entry methods are briefly introduced. Then, the concepts of FPGA programming in some perspective viewpoints, such as: execution perspective, modelling perspective, programming style perspective, construction methodology perspective and synthesis perspective will be explained. Finally, the principle of VHDL programming use synchronization-evolution-action approach is introduced

A New Fixed Switching Frequency Direct Torque Controlled PMSM Drives with Low Ripple in Flux and Torque

Direct Torque Control (DTC) has gained popularity for development of advanced motor control due to its simplicity and offers fast instantaneous torque and flux controls. However, the conventional DTC which is based on hysteresis controller has major drawbacks, namely high torque ripple and variable inverter switching frequency. This paper presents an improved switching strategy for reducing flux and torque ripples in DTC of PMSM drives; wherein the torque hysteresis controller and the look-up table used in the conventional DTC are replaced with a constant frequency torque controller (CFTC) and an optimized look-up table, respectively. It can be shown that a constant switching frequency is established due to the use of the CFTC while the reduction of torque and flux ripples is achieved mainly because of the selection of optimized voltage vector (i.e. with an optimized look-up table). This paper also will explain the construction of DTC schemes implemented using MATLAB-Simulink blocks. Simulation results were shown that a significant reduction of flux and torque ripples which is about 90% can be achieved through the proposed DTC scheme

Improved Output Voltage Quality using Space Vector Modulation for Multilevel Inverters

Space vector modulation (SVM) has received wide acceptance due to many benefits over other techniques such as higher output voltages, lower total harmonic distortion (THD), high-efficiency and flexible to be implemented in vector control systems. In digital implementation, the SVM equations can be optimally computed by eliminate the use of complex forms. In this paper, the simple SVM based on two-level inverter is employed for higher levels of inverters. This is to retain the simplicity of SVM computation for three-level and five-level cascaded H-bridge multilevel inverter (CHMI). Moreover, the proposed method utilizes two controller boards to perform high computational workloads and to eliminate glitch and error problems. Experiment results show that the THD of output voltage in five-level CHMI gives the smallest value among the results obtained from other levels

A Simple Approach of Space-vector Pulse Width Modulation Realization Based on Field Programmable Gate Array

Employing a field programmable gate array to realize space-vector pulse width modulation is a solution to boost system performance. Although there is much literature in the application of three-phase space-vector pulse width modulation based on field programmable gate arrays, most is on conventional space-vector pulse width modulation with designs that are complicated. This article will present a simple approach to realize five-segment discontinuous space-vector pulse width modulation based on a field programmable gate array, in which the judging of sectors and the calculation of the firing time are simpler with fewer switching losses. The proposed space-vector pulse width modulation has been successfully designed and implemented to drive on a three-phase inverter system that is loaded by an induction machine of 1.5 kW using the APEX20KE Altera field programmable gate array (Altera Corporation, San Jose, California, USA)

Strategies for FPGA Implementation of Non-Restoring Square Root Algorithm

This paper presents three strategies to implement non restoring square root algorithm based on FPGA. A new basic building block is called controlled subtract-multiplex (CSM) is introduced in first strategy which use gate level abstraction. The main principle of the method is similar with conventional non-restoring algorithm, but it only uses subtract operation and append 01, while add operation and append 11 is not used. Second strategy presents the first strategy in register transfer level (RTL) abstraction. In third strategy, a modification for the implementation of conventional non-restoring algorithm is presented which also use RTL abstraction. The all above strategies is implemented in VHDL programming and adopt fully pipelined architecture. The strategies have conducted to implement successfully in FPGA hardware, and each of the strategies is offer an efficient in hardware resource. In generally, the third strategy is superior.DOI:http://dx.doi.org/10.11591/ijece.v4i4.600

A Parallel Energy-Sharing Control Strategy for Fuel Cell Hybrid Vehicle

This paper presents a parallel energy-sharing control strategy for the application of fuel cell hybrid vehicles (FCHVs). The hybrid source discussed consists of a fuel cells (FCs) generator and energy storage units (ESUs) which composed by the battery and ultracapacitor (UC) modules. A direct current (DC) bus is used to interface between the energy sources and the electric vehicles (EV) propulsion system (loads). Energy sources are connected to the DC bus using of power electronics converters. A total of six control loops are designed in the supervisory system in order to regulate the DC bus voltage, control of current flow and to monitor the state of charge (SOC) of each energy storage device at the same time. Proportional plus integral (PI) controllers are employed to regulate the output from each control loop referring to their reference signals. The proposed energy control system is simulated in MATLAB/Simulink environment. Results indicated that the proposed parallel energy-sharing control system is capable to provide a practical hybrid vehicle in respond to the vehicle traction response and avoids the FC and battery from overstressed at the same time.