Simple Switching Strategy for High-Torque Control Performance utilizing Neutral Point Clamped Multilevel Inverter

<p>Three-level Neutral Point Clamped (NPC) inverter allows the configuration of switching devices to operate at high voltage and produce lower current/voltage harmonics. It is known that, DTC of induction machine which employs hysteresis controller has major drawbacks namely larger torque ripple and variable switching frequency. This paper aims to propose a suitable voltage vector selection to provide better torque regulation and lower switching frequency by employing DTC with 3-level NPC multilevel inverter. A simple switching strategy was formulated using 7-level torque hysteresis and 2-level flux hysteresis controllers to give more options in selecting an appropriate voltage vector, inherently, according the motor operation conditions. The improvements offered were verified through simulations.</p

Performance Analysis of Direct Torque Control of Induction Machines

This paper presents the study of effects of hysteresis controllers on performance of Direct Torque Control (DTC) of induction machines. By analyzing the DTC performances through simulations, it can provide useful information for the beginner researchers to identify the root of problems and hence chooses the appropriate hysteresis bandwidths for any operating conditions to achieve high DTC performances. It should be noted that the DTC drive has gained widely acceptance for many industrial applications due to its simplicity. However, the DTC which is based on hysteresis comparators has two major drawbacks, namely variable switching frequency and larger torque ripple. It can be shown that the DTC performance may deteriorate if the inappropriate flux and torque bandwidths are chosen. This research is aimed to analyze DTC performances in terms of total harmonic distortion (THD), torque ripple and switching frequency for variations of controller hysteresis bandwidths and operating conditions. The problems which are mainly associated in hysteresis controllers were identified by simulating the DTC of induction machine at different applications of hysteresis bandwidth, sampling frequency and operating conditions (e.g. different of load torque or speed levels). This study provides the consideration for the designer in choosing appropriate bandwidth to have high performance of DTC drives

Improved Performance of Direct Torque Control of Induction Machine with 3-Level Neutral Point Clamped Multilevel Inverter

A 3-Level Neutral Point Clamped (NPC)Multilevel Inverter was implemented to improve the performance of Direct Torque Control (DTC) of Induction Machine. Larger torque ripple and variable switching frequencies are known as the major problems in DTC of induction machine. This paper aims to propose a suitable voltage vector selection to provide better torque regulation and switching frequency which consequently minimize the major problems. A simple switching strategy was proposed using 7-level torque hysteresis and 2-level flux hysteresis controllers to give more options in selecting an appropriate voltage vector, inherently, according the motor operating conditions. The improvements offered were verified through simulations

Current Control of BLDC Drives for EV Application

This paper presents a current blocking strategy of brushless DC (BLDC) motor drive to prolong the capacity voltage of batteries per charge in electric vehicle applications. The BLDC motor employs a simple torque hysteresis control (THC) that can offer a robust control and quick torque dynamic performance. At first, a mathematical modeling of BLDC motor and principle of torque hysteresis control will be described, so that the benefit offered by the proposed current blocking strategy can be highlighted. It can be shown that the current control method naturally provides current limitation, in which the current error (or ripple) is restricted within the pre-defined band-gap furthermore provide current protection. The benefit of proposed current blocking strategy will be highlighted such that it can prevent the current drained from the batteries when the torque demand is released to set to 0 Nm. The control scheme is validated and verified by the simulation and experimental results