Simulation and Hardware Implementation on Performance Improvement of BLDC Motor using Interleaved Buck Converter

Brushless DC motors (BLDC) are widely used motors for many of the industrial applications, automobile applications etc. The motor is powered by a DC electric source (with help of a converter) and an integrated inverter power supply which provides sequence of pulses to the motor. The performance of the converter mainly contribute to the performance of the motor. The cuk converter used for supplying the inverter produces high output power ripples, which in turn affect the output of the inverter circuit and there by affecting the motor performance. Hence the motor operation is degraded. In this paper the BLDC motor is powered by an interleaved buck converter, whose output power has much less ripples, which in turn upgrade the motor performance. The simulation of the proposed model was done in MATLAB/SIMULINK. And performance improvement achieved was verified by hardware implementation and testing. Keywords— Brushless DC motor, Power ripple, Interleaved buck converter.

INTRODUCTION Due to the improved performances such as high efficiency, high torque, high power factor, simple control and lower maintenance compared to other types of motors, brushless DC motors are widely used. These motors are mainly used in applications such as electric vehicles, actuators, robotics etc. These motors are also known as electronically commutated motors, which are powered by a DC electric source via an integrated inverter power supply. This integrated inverter power supply produces AC electric power to drive the motor. Unlike DC motors they do not have brushes or commutator segments. So these motors have very low wear and tear, thus requiring less maintenance. Internal or external position sensors are used by BLDC motors in order to sense the position of the rotor. According to the position of rotor the windings in the stator are excited with the help of voltage source inverter.
The switch mode regulation is provided by the DC-DC converter used for supplying the voltage source inverter. The unregulated DC voltage is converted to regulated DC voltage with the help of this converter and thus the speed of the motor is controlled. The performance of the DC-DC converter plays an important role in The performance of the motor. By replacing Cuk converter, which produces high output power ripple with an interleaved buck converter improves the performance of the motor. The parallel combination of two buck converters forms the interleaved buck converter, in which the discontinuous mode of operation of one converter is replaced by the other. The output ripple is actually the small unwanted residual periodic variation of the direct current output of a power supply, which has been derived from alternating current source. This paper describes simulation study of Brushless DC motor fed by Cuk converter and Interleaved Buck converter. It is done for same supply voltage and reference speed. The simulation work is done in MATLAB/SIMULINK environment.
The hardware implementation of the simulation work on BLDC motor fed by interleaved buck converter is done. Control and monitoring of the system has been achieved by AT89S8253 processor.

II.
CUK CONVERTER It is a DC -DC converter whose output voltage magnitude can be varied by varying the duty ratio. For duty ratio less than 0.5 the cuk converter act as buck converter and for duty ratio greater than 0.5 the converter act as boost converter. It is actually a boost converter followed by a buck converter with a capacitor to couple energy.
The Cuk converter is studied in four different modes of operation, continuous conduction mode (CCM) and in discontinuous conduction mode (DCM). In continuous conduction mode the current in inductors L1 and L2 are Interleaved buck converter is the parallel combination of two buck converter as shown in the figure above. The circuit constituting switch S1, inductor L1 and diode D1 forms the first buck converter and the circuit constituting switch S2, inductor L2 and diode D2 forms the second buck converter.
The two converters here are operated alternatively such that the first buck converter is operated by turning ON the switch S1 and the time at which the output voltage of first converter becomes zero, the second converter is turned ON by turning ON the switch S2 . Similarly when the output voltage of second converter becomes zero, the first converter is turned ON thus the operation continues. This mode of operation of the circuit produces a continuous output voltage there by reducing the voltage ripples which in turn reduces output power ripple.  Figure 3. The system is supplied with single phase AC supply .The AC supply is converted to DC using a diode bridge rectifier and is filtered by using a filter. Then the filtered DC is passed through a DC-DC converter (Interleaved buck converter) so that the output power ripple produced by the circuit is reduced. Then the filtered continuous DC is supplied to a voltage source inverter in order to produce excitation signals to the motor. Here the converter is operated according to the duty ratio provided. Proportional Integral controller is used to achieve closed loop operation and AT89S8253 processor is used to get switching signals for the inverter.  The simulation time was 10 seconds. The circuit input voltage was 50V. The simulation diagrams are shown below.    Fig.7, it can be inferred that the power ripple generated by interleaved buck converter is only about 4.5 watt. The voltage ripple produced by the circuit is only 2.2 volt and the current fluctuation is about 0.11 ampere. (Fig 8). From Fig.8, for the set speed of 1000rpm, the motor attains its rated speed within 4 seconds and the operation of motor is much smoother than that of the motor fed by cuk converter.
Transient response of motor set at 1000 rpm is shown in Fig 9. From the figure it can be inferred that for a rise in supply voltage from 50 volt to 100 volt there is not much deviation from its current running speed and when the supply voltage is increased to about 250 volt, the motor speed increases to about 1350 rpm and settles to 1000 rpm in 0.45sec. Thus the motor speed increases according to the hike in voltage and settles to the normal operating condition within small time. Similarly the motor speed is decreased slightly according to the dip in voltage and settles to the normal operating condition.

VI. HARDWARE IMPLEMENTATION OF INTERLEAVED BUCK CONVERTER FED BLDC MOTOR
This project aims to develop a circuit, which reduces the ripples in the power fed to BLDC motor than that of ripples produced by the cuk converter.  The tacho pulses (voltage pulses) obtained from the motor for the set speed of 1080 rpm is shown in Fig.14. Number of voltage pulses in 100 milliseconds multiplied by sixty gives the speed of motor in rpm. As the speed of the motor increases the number of voltage pulses in a second increases.
Here from the figure there are nine voltage pulses in fifty milliseconds. Thus in hundred milliseconds there are eighteen voltage pulses. Thus 18 × 60 = 1080 rpm.
VIII. CONCLUSION The operation of Brushless DC motor fed by Cuk converter and Interleaved buck converter is modeled in MATLAB/SIMULINK and the waveforms were observed in various operating conditions. From the simulation waveforms it can be observed that the output power ripple of BLDC motor fed by interleaved buck converter is reduced to about 75% than that of BLDC motor fed by cuk converter. Performance improvement achieved was verified by hardware implementation and testing. Through hardware implementation and testing it is understood that the output voltage ripple produced by interleaved buck converter is very less than that of cuk converter. Total harmonic distortion of voltage and current at motor input is found to be 32.33 % .