IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 07, 2014 | ISSN (online): 2321-0613 All rights reserved by www.ijsrd.com 437 Digital Signal Controller Based Four Switch Three Phase Inverter Fed BLDC Motor Control M. S. Aspalli 1 Farhat Mubeen. M Munshi 2 1 Professor 2 M.Tech Student 1,2 Department of Electrical Engineering 1,2 PDA College of Engineering, Gulbarga, Karnataka Abstract— Brushless Direct Current Motors (BLDC) are used in many applications for their low cost, high performance , ease of control, less maintenance because of absence of commutators and brushes and high efficiency. These advantages of BLDC motors have led to their wide spread use in variable speed drives. The main objective of this paper is to develop a drive system for BLDC motor with reduced switches and minimum hardware. The proposed work is based on, the dsPIC controlled four switch three phase inverter fed BLDC motor drive. The advantage of this inverter that uses four switches instead of conventional six switches is lesser switching losses, lower electromagnetic interference (EMI), less complexity and reduced interference circuit. dsPIC30F4011 digital controller is used to generate the switching pulses for Four Switch Three Phase Inverter consists of MOSFET Switches to drive the BLDC motor. Simulation and experimental work are carried out and results are presented. A simulation is carried out using MATLAB/SIMULINK and in the experimental work a prototype model is constructed to verify the simulation results. Key words: BLDC Motor, Four Switch Three Phase Inverter, dsPIC30F4011 Digital Signal Controller. I. INTRODUCTION Brushless Direct Current (BLDC) motors are one of the motor types rapidly gaining popularity in recent years. An electronic controller using solid states is used for motor commutation instead of the brushed commutation used in the brushed DC motors. Compared to induction machines, they have lower inertia, allowing for faster dynamic response to reference commands. In addition, they are more efficient due to the permanent magnets, which results in significantly lower rotor losses. Power semiconductor devices are the heart of the power electronics converters that are being extensively used in as on-off switches. The switches are not ideal and they have conduction, turn-on and turn-off switching losses which reduces the efficiency of overall system. One way to increase the efficiency of the drive is by reducing the losses at possible places such as, in the converter used along with BLDC motor. It may also be improved by reducing the number of circuit elements as the number of devices reduces the associated amount of switching loss reduces. Conventionally, BLDC motors are excited by a six- switch inverter. However, cost-effective design is becoming one of the most important concerns for the modern motor control research. Researchers are always conscious about their cost and are always exploring methods to bring in cost minimization. Cost effectiveness can be achieved either by reducing the number of power switches used in the inverter circuit, or by using high performance processors, and proper designing the algorithms and their implemented in conjunction with a reduced component inverter to produce the desired torque characteristics [9]. The motor commutation in BLDC motors is implemented by an electronic controller and, to determine the rotor position and to know when to commutate, either Hall sensors (sensored commutation) or the back EMF generated in the stator windings of the motor (sensor less commutation) are used. Advantages of Hall sensor based controllers are simpler to implement compared to the sensor less control and are used in applications that require good starting torque that minimizes erratic startup behavior. Under sudden load increase, the information of commutation angle is not in jeopardy of becoming lost. This paper presents a low cost BLDC motor drive which uses four switch three phase inverter and High performance Digital signal Controller which is a single-chip, embedded controller that seamlessly integrates the control attributes of a Microcontroller (MCU) with the computation and throughput capabilities of a Digital Signal Processor (DSP) in a single core. II. FOUR SWITCH THREE PHASE INVERTER Power circuit of the FSTPI fed BLDC motor is shown in Fig 1. The power inverter has 4 MOSFET switches, S1, S2, S3 and S4 and a split capacitor. The two phases A and B are connected to the two legs of the inverter, while the third phase C is connected to the centre point of dc link capacitors, C1 and C2. The value of the capacitances C1 and C2 are equal. Vc1 and Vc2 are the voltages across the DC link capacitors (Vc1=Vc2). Vdc is the voltage across the capacitor C1 and C2 (Vdc =Vc1+Vc2). A BLDC motor needs quasi square current waveforms [11] which are synchronized with the back-EMF to generate constant output torque and have 120 conduction and 60 non conducting regions. Also, at every instant only two phases are conducting and the other phase is inactive [2]. Fig. 1: Four switch three phase inverter However, in the four-switch converter, one phase of the motor is always connected to the midpoint of the dc- link capacitors, so that current is flowing even at the zero- vectors. The BLDC motor has a trapezoidal back EMF, and rectangular stator currents are needed to produce a constant electric torque. Hence the voltage PWM scheme for FSTPI must have six commutations and the six commutations are (X,0), (1,0), (1,X), (X,1), (0,1) and (0,X).