Pmbldc Motor With Pwr Fctr Cntrller

2012 International Conference on Computing, Electronics and Electrical Technologies [ICCEET]

PMBLDC Motor Drive with Power Factor

Correction Controller

Gishin Jacob George, Rakesh R, N.Arun

Abstract--This paper presents a boost converter

configuration, control scheme and design of single phase

power factor controller for permanent magnet brushless

DC motor (PMBLDCM) drive. PMBLDC motors are the

latest choice of researchers, due to the high efficiency,

silent operation, compact size, high reliability, and low

maintenance requirements. The proposed Power Factor

Controller topology improves power quality by improving

performance of PMBLDCM drive, such as reduction of

AC main current harmonics, near unity power factor.

PFC converter forces the drive to draw sinusoidal supply

current in phase with supply voltage. It uses a boost

converter to obtain unity power factor with improved

performance. The system includes a speed controller for

PMBLDC drive and a voltage controller for boost

converter .. The voltage or speed controllers can be realized

using proportional integral (PI) controller. Simulations

are done using MA TLABI SIMULINK software.

Index Terms-PMBLDC Motor, Power factor

correction, Voltage Controller, Speed Controller, VSI,

Boost Converter.

I. INTRODUCTION BLDC motors are widely used in industries

such as Appliances, Consumer, Automotive, Medical, Aerospace, Industrial Automation Equipment and Instrumentation. Usually, the low-power adjustable speed drives (AS Os) are powered from single-phase AC mains through a diode bridge rectifier (OBR) with smoothening DC capacitor and voltage source inverter (VSI). Fig. 1 shows the OBR-VSI fed PMBLOCM drive with DC link capacitor. The AC mains current waveform, as shown in Fig. 2 and Fig.3 is far from sinusoidal, because of the fact that, the DBR does not draw any current from the AC network when the AC voltage is less than the DC link voltage, as the diodes are reverse biased during that period; however, it draws a peaky current when the AC voltage is higher than the DC link voltage. This result in a pulsed input current waveform featuring a peak value higher than the peak of the fundamental input current [13], thereby, 71.97% total harmonic distortion (THO) in the input current.

The PMBL motors belong to three-phase synchronous motor family and can be categorised as permanent magnet synchronous motor (PMSM) and

Gishin Jacob George is with School of Electrical Engineering. VIT University, Vellore, India. (Email: [email protected]) Rakesh R. is with School of Electrical Engineering, VIT University, Vel\ore, India. (Email: -rakeshramachandran.k!algmail.com) N.Arun, Asst.Professor (Sr.), School of Electrical Engineering, VIT University, Vel\ore, India.(Email:[email protected]).

978-1-4673-0210-4112/$31.00 ©2012 IEEE 63

VOLTAGE =�f-----j

�MOTOR

Fig. I : Conventional OBR-VSI fed PMBLOCM drive topology

10

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.1 0 L...-_-'-....liI.-'-_-'-� ........ _ ........ _:':""O __ L...-""""--l 0.2 0 . .21 0.22 0.23 Q.24 0.25 0'.26 (1.21

70

'i' 60 � 50 i 40 " ... "30

Time s Fig.2: Input current waveform

F'UIId':lmentoil tSOHzj " 6 719 • TIiD" 71.97%

� 20 i 10

O �o ��-4I�I��--� S 10 1 5 20 H�lmll">ic order

Fig.3: THD for conventional DBR-VSI fed PMBLDCM drive. PMBLDCM [14]. The PMSM uses continuous rotorposition feedback for supplying sinusoidal voltages and currents to the motor with sinusoidal back EMF, so that the interaction with sinusoidal currents produces constant torque with very low ripple. However, the PMBLOCM is supplied by three-phase rectangular current blocks of 120° electrical duration, in which the back EMF is trapezoidal, with the constant part of the waveform timed to coincide with the intervals of constant phase current. Therefore PMBLDC motors need rotor-position information only at the commutation points, for example, every 60° electrical in the three phases [1]. PMBL machines are best suited for position control and medium size industrial drive because of their excellent dynamic capability, reduced losses and high torquelweight ratio. The applications of PMBL motors have been reported in diverse fields such


as computers, automobiles, transportation, aerospace equipment, power tools, toys, vision and sound equipment and healthcare equipments ranging from microwatt to megawatts. Advanced control algorithms and ultra-fast processors have made PMBL motors suitable for position control in machine tools, robotics and high precision servos, speed control and torque control in various industrial drives and process control application. A PFC converter forces the drive to draw sinusoidal supply current in phase with the supply voltage. It uses a DC-DC converter topology, boost converter, to obtain unity PF with improved performance, such as reduction of AC mains current harmonics, reduction of acoustic noise minimum number of components, maximum efficiency, etc.

II. STATE OF THE ART PMBLDC motors are generally powered by a

conventional three-phase voltage source inverter (VSI) or current source inverter (CSI) which is controlled using rotor position. The rotor position can be sensed using Hall sensors, resolvers, or optical encoders. These position sensors increase cost, size and complexity of control thereby reducing the reliability and acceptability of these drives. Due to the high cost of the motor and controller, very few commercial applications of PMBLDC motors have been reported. Recently some additional applications of PMBLDC motors have been reported in electric vehicles (EVs) and hybrid electric vehicles (HEVs) due to environmental concerns of vehicular emissions. PMBLDC motors have been found more suitable for EVs/HEVs and other low power applications, due to high power density, reduced volume, high torque, high efficiency, easy to control, simple hardware and software and low maintenance. Due to ease of control in PMBLDC motors, they are preferred for numerous applications in low power and variable speed drives.

III. REVIEW OF BOOST CONVERTER The topology of boost converter is shown in

Figure 4. The diode bridge rectifies the AC line voltage, and the power switch S, the inductor L and the output diode do operate as a boost converter. The ripple in the output voltage is reduced by using the capacitor C. The load is assumed to be purely resistive (R).

L "I

I D��

I Ga1ePulses RJoad

r JUl�� Vo

Figure 4: Boost converter

64

The input line filter reduces the high-frequency components in the input current. The power switch is operated at a constant switching frequency, and the output voltage is varied by varying the duty cycle. It is assumed that the boost converter operates at CCM and the switching frequency is much higher than the line frequency. Hence, the input voltage can be assumed as a constant during one switching cycle.

IV. MODELLING OF PMBLDC MOTOR The modelling of PMBLDC motor drive

includes the modelling of a speed controller, reference current generator, current controller and modelling of PMBLDC motor [13] as shown in Fig. 5. Each of the above components of PMBLDCM drive can be modelled by mathematical equations and combination of such models represent complete PMBLDCM drive [7]. The modelling of a speed controller is of prime importance as the performance of the system depends on this controller. Assuming that at tlh instant of time,

�. (t) is the actual rotor speed, OJ; (t) is the reference

speed, then the speed error OJe (t) can be calculated

as [7]:

OJe (t) = OJ: (t) - OJr (t) A speed controller is used to process this speed error to

obtain desired control signal.

A. Speed Controller The PI controller is used as the speed

controller. The PI controller output at tlh instant T(t) is given as[7]

T(t) =T(t-l) +kp{Ul(t)-alCt-1)}+lsUl(t) where Kp and KJ are the proportional and integral gains of the PI controller respectively.

Let 1*= T(t)/Kb , where Kb is the back-emf constant of the PMBLDCM.

B. Reference Current Generation The reference phase currents of the motor

windings are la *, Ib * and Ie * for phases a, b, c, respectively. For duration of 0-60° the reference currents can be given as

la*= 1 *, Ib* =1 * and le*= 0 Similarly, the reference currents for the other duration can be generated, which will follow the trapezoidal voltage of respective phases. These reference currents are compared with sensed phase currents for error current generation as

�Ia =( la *- la), Mb = (Ib * - Ib), Me= (Ie *- Ie)·

C. Current Controller The switching sequence for the VSI is

generated by the current controller, after comparing the current error of each phase with fixed frequency carrier waveform. The current errors �I., �Ib, �Ie are amplified by gain kl before comparing with carrier waveform met). The switching sequence is obtained based on the logic given for phase 'a' as


If k1 �Ia > met) then Sa = 1 If k1 Ma:S met) then Sa = 0

Similarly the switching sequences Sb and Sc are generated.

V. PROPOSED PFC TOPOLOGY In the proposed PFC Topology a boost

converter is used to boost the input voltage which is fed to a voltage source inverter (VSI), the PMBLDC motor is given its supply from this VSI. A Speed Controller and a Voltage Controller is used in the motor side and the input side respectively. Both Controllers are realised using Proportional Integral (PI) controller.

The control loop of VSI-based topology, employed to execute PFC operation involves inner current loop and outer voltage loop. The complete control scheme block diagram is shown in Fig.S with a DBR connected to single-phase AC mains, followed by a Boost Converter and output ripple filters.

L1 Li

� I.,

IlJ,Jl£MOTOR

BRIDGE -(I _ VOLTAGE

0 RECfIFIER SOURCE

I. � T � ��n1ER

l\:,l

Fig.S : Proposed DBR-VSI fed PMBLDCM drive topology

For the Voltage Controller, the DC linl<voltage is sensed and compared with the reference DC link voltage. The error voltage is passed through a PI Controller, and multiplied with a unit template of absolute input voltage so as to generate the reference current signal. This signal is compared with sensed converter current which gives the modulating wave for the PWM. This current error is the modulating signal and a triangular wave is taken as the carrier signal so as to generate the PWM gate pulses for turning on/off the Boost converter switch. The flowchart for Voltage Controller is shown in Fig: 6.

The control of PMBLDC motors can be accomplished by control algorithms using conventional six pulse inverters which can be either VSI or CSI. The control of these inverters for PMBLDCM needs rotorposition information only at the commutation points, for example, every 60° electrical in the three phases; therefore comparatively simple controller is required for commutation and control. The rotor position is sensed using Hall Effect sensors. The speed of the motor is measured and is compared with the reference speed. The error signal is passed through a PI controller to give

6S

a reference signal. This reference signal is compared with the Boost converter output current so as to give modulating signal for PWM. This signal is compared with triangular carrier signal to generate the PWM pulses for turning on/off the VSI switches. The flowchart for Speed Controller is given in Fig:7.

Obtain the Dc link Volrage,Rectifier Output Current & AC Source Voltage

YES

IREF generation using PI Coniroller & multiply with absolute AC Source Voltage

PWM Generation for Boost Converter S"itch

Fig: 6 Control Flowchart for Voltage Controller

Obtain the Actual Motor Speed,Dc link CUrrent & Hall Sensor Signals

Fig : 7 Flowchart for Speed Controller


VI. SIMULA nON RESULTS The proposed PFC topologies of PMBLDCM

drive are modelled in the MATLAB/Simulink environment for a YS[ fed PM BLOC motor. The P[ controller is utilized for voltage as well as speed control and PWM signals are generated for YS[ using 40 kHz triangular carrier waves. The YS[ fed PMBLOC motor is started at no load for stabilising of DC link voltage. The power quality is monitored through FFT analysis of source current (i.e. current at AC mains) under steadystate condition. Boost PFC topology is evaluated for a dc linl( voltage of 400Y to drive PMBLDC motor at 1100 rpm with rated load torque. Boost PFC converter shows very good response with input AC mains current THD of l. 51 %, along with PF ofO.99l.

The harmonic spectrum shows 7 [.97% THO in the AC mains current at rated torque for conventional YSI. The THO of AC mains current is reduced to [. 51 % with the boost PFC topology at same load on the motor. The PQ performance analysis of proposed PFC topology shows that the THO of AC mains current always remains within the limit imposed by IEC 61000-3-2 and other international PQ standards [5, 6].

FA wfndow: 4 of 25 cycles or se!ecl,ed signal

0.3 0.�1 0.32 0.33 0.34 0.35 0.36 0.31 Tim& {s}

Hanoonic cedeI Fig.S : Current at AC mains and its harmonic spectra of Boost PFC converter Feeding YS[ based PMBLOCM drive.

[t is observed that source current is always in phase with the source voltage and results in close to unity PF operation of PFC converter during load perturbation as well as during steady-state operation. Moreover, the PMBLDCM drive shows an improved performance in terms of reduced current and torque ripples during steady state as well as transient conditions.

� s; ;}l

66

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1200

,_

BOa

GQ;iI

·00

�

0

-Q � 1 �:> 11., a,4 O� �6 �1

F

,�

Fig. [3 : Torque

�. 0<,


Above figures shows source voltage, source current, motor speed, stator current and torque for proposed VSI based topology fed PMBLDCM drives in steady state condition. Fig. 9 and fig. 1 0 shows that the source voltage and current is in phase with each other at steady state. From Fig 11 shows the speed of the motor following the reference with minimum ripples. The performance of the PMBLDCM drive is improved with boost PFC topology in terms of low torque ripples, smooth speed variation and unity power factor at AC mains.

The PMBLDCM drives use either uncontrolled rectifier (i.e. Diode Bridge) or controlled PWM rectifier (i.e. PWMVSC). The PWM-VSC is used only if bidirectional power flow or regeneration is required, otherwise DBR is most commonly used front end converter for PFC topology. Boost PFC topology is the best option for most of the drives as their rated DC voltage is higher than the single-phase supply RMS voltage. The non-isolated boost PFC topology does not have any protection to load over current or short-circuit conditions. For low-power drives, for example computer peripherals, robotics and many such applications, the PMBLDCM drives are generally preferred at low voltages.

VII. PERFORMANCE ANALYSIS OF SPEED & VOLTAGE CONTROLLER

The efficient working of the Speed Controller & Voltage Controller can be analysed by giving disturbances by changing reference values and observing the machine to follow the given reference values of the control parameters. The Speed reference is varied at different time instants Speed variations at time, t=l.205 sec (Nref = 1000), t=l.605 sec (Nref = 1500), t=3.704sec (Nref = 2000). Fig 14 shows that the motor speed follows the reference given, the red line is the reference speed and the blue line actual motor speed.

llmeinsl'{

Fig 14 : Speed Variations with Reference Speed

67

Fig 15:DC link Voltage Variations with Reference Voltage

The DC link Voltage reference is varied at different time instants Speed variations at time D t=2.004 sec (Vref=300V),t = 2.471sec (Vref=400V),t = 4.623 sec (Vref=500V). It can be observed that the DC link voltage is affected by variations in Speed and Torque. Fig.14 and Fig. 15 shows that the actual values of the control parameters follow the reference values.

VIII. APPLICATIONS PMBLDC motors are best suited for low

power appliances in commercial and domestic applications. Majority of them use single-phase AC induction motors with capacitor or split phase starting. These motors operate at constant speed directly from AC mains irrespective of efficiency; however, PMBLDC motors can offer low-energy consumption, improved performance, reduced acoustic noise and many more convenience features. Therefore household appliances are expected to be one of largest end product market for PMBLDC motors, over the next few years. The major household appliances include fans, blowers, washing machines, room air-conditioners, refrigerators, food processors etc. The rotor-position sensors (Hall effect sensors, resolvers or optical encoders) increase the cost and the size of the motor. special mechanical arrangement is also required for mounting the sensors. The system reliability also reduces because of the additional components and wiring. The sensor less control of PMBLDC motors reduces the drive cost up to some extent, while little increased control complexity. Owing to the features of high-power density, less volume, high torque, high efficiency, easy to control and low maintenance, the applications of PMBLDC motors have been reported in EVs and HEVs, vehicular air conditioner, aerospace application, traction, robotics, tread mills, washers, wheelchair,]computer hard disc drives, compressors of household air conditioner, and commercial freezers, fans and pumps [12].


IX. CONCLUSION The PFC converter topology for Power quality

improvement in PMBLDC motor drives is designed and their performance is simulated to provide in depth understanding on various aspects of these drives. The performance of this topology has been evaluated through simulation for validation of their designs. Boost PFC topology is used as this is the best option for applications having rated DC voltage higher than single phase supply RMS voltage. The PMBLDCM drives incorporating PFC converter can be a milestone towards the widespread application of these drives.

X. REFERENCES [1]. MILLER T.lE. : 'Brushless permanent magnet and reluctance motor drive' (Clarendon Press, Oxford, 1989 [2]. DUBEY G.K. : 'Power semiconductor controlled drives' (Prentice Hall, New Jersey, 1989) [3]. KRISHNAN R. : 'Electric motor drives: modelling, analysis and control' (Pearson Education, India, 2003) [4]. RASHID M.H. : 'Power electronics: circuits, devices and applications' (Pearson Education, India, 2004) [5]. IEC 555-2: 'Harmonics, equipment for connection to the public low voltage supply system', 1990 [6]. IEEE 1159: 'Recommended practice for monitoring electric power quality', 1995 [7]. B.SINGH, S.SINGH. :'Single-phase power factor controller topologies for permanent magnet brush less DC motor drives', lET Power Electron., 2010, Vol. 3, Iss. 2, pp. 147-175 [8]. ANAND SATHY AN. :' Digital PWM Control of Brushless DC (BLDC) Motor Drives', PhD thesis, lIT, Chicago, Illinois,2008 [9]. NED MOHAN, TORE M. UNDELAND, WILLIAM P. ROBBINS: 'Power Electronics', Third Edition, John Wiley and Sons, New Delhi. [10]. H.S. ATHAB, D.D.C. LU: 'Simple Controller for single phase power factor correction rectifier' ,I ET Power Electron., 2010, Vol. 3(4), pp. 590-600. [II]. KATSUHIKO OGATA: 'Modem Control Engineering', Fourth Edition, Prentice Hall, India. [12]. BHIM SINGH , SANJEEV SINGH. :'State of the Art on Permanent Magnet Brushless DC Motor Drives', Journal of Power Electronics, Vol. 9, No. 1, January 2009 [13]. Sanjeev Singh, 'An adjustable speed PMBLDCM drive for air conditioner using PFC Zeta converter', International Journal of Power Electronics, 2011 [14]. Padmaraja Yedamale, 'Brushless DC (BLOC) Motor Fundamentals', Microchip Technology Inc., 2003. [15]. Vladimir Blasko,' A Novel Method for Selective Harmonic Elimination in Power Electronic Equipment', IEEE transactions on Power Electronics, vol. 22, January 2007

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VII. BIOGRAPHIES

Gishin Jacob George was born in India in 1987.He graduated from M. G. University and currently doing his post -graduation at VIT University. His areas of interests are Power Electronics applications in power system, power factor correction, boost converters, EMI/EMC etc.

Rakesh R. was born in India in 1987. He graduated from Kerala University and doing his post-graduation at VIT University. His employment experience includes Lecturer at MEA Engineering College, Kerala and Project Trainee at LRDE, DRDO, Bangalore. His areas of interests are Power Electronics applications in power system, power factor correction, boost converters, etc.

N.Arun. is currently working as an Assistant Professor (Sf.), VIT University. He received M.Tech in Power Electronics & Drives from Pondicherry College of Engineering. His area of research is non-linear controller design for drives.

Pmbldc Motor With Pwr Fctr Cntrller

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