pfc buck-boost converter based voltage controlled adjustable speed pmbldcm drive for...

EUROPEAN TRANSACTIONS ON ELECTRICAL POWEREuro. Trans. Electr. Power 2011; 21:424–438Published online 26 April 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/etep.452

PFC buck-boost converter based voltage controlled adjustablespeed PMBLDCM drive for air-conditioning

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Sanjeev Singh*,y and Bhim Singh

Department of Electrical Engineering, Indian Institute of Technology, Delhi, New Delhi 110016, India

SUMMARY

In this paper a power factor correction (PFC) buck-boost converter based adjustable speed voltage controlledvoltage source inverter (VSI) fed permanent magnet brushless DC motor (PMBLDCM) drive is employedfor an air-conditioning system for the improved energy efficiency. A single-phase single-switch AC–DCconverter topology based on the buck-boost converter is employed for PFC which ensures near unity powerfactor in wide speed range. The speed control scheme has a new concept of DC link voltage controlproportional to the desired speed of the PMBLDC motor. Moreover, the control of VSI is used only forelectronic commutation of PMBLDCM. Therefore, the number of sensors is reduced as compared toconventional PMBLDCM drive. The proposed control scheme with a PFC converter based PMBLDCMdrive is designed, modelled and simulated in Matlab–Simulink environment for an air conditionercompressor. The results obtained are presented to validate the effectiveness of the proposed speed controlschemewith PFC feature in wide range of the speed and an input AC mains voltage. Copyright# 2010 JohnWiley & Sons, Ltd.

key words: PFC; PMBLDCM; air conditioner; buck-boost converter; voltage control; VSI

1. INTRODUCTION

An air-conditioner load constitutes a substantial part of total electrical power demand in domestic

sector. Single-phase induction motors are mostly used to drive the compressor of these air conditioners.

The temperature in the air conditioned zone is regulated through a hysteresis band by ‘on/off’ control.

The motor, therefore, operates either at full load (compressor ‘on’) or very light load (compressor ‘off’)

at nearly constant speed [1]. The motor with constant speed compressor achieves maximum efficiency

near rated load only. Therefore, most of the existing air-conditioners are not energy efficient and

thereby, provide scope for energy conservation. Innovations in solid state controllers, electric motor

industry and system designs [2] have improved the efficiency marginally but the variable speed

operation of the air conditioner improves the system efficiency significantly. Because, the compressor

driven by a motor with speed control delivers desired cooling capacity and maintains the room

temperature efficiently.

For an air-conditioner compressor, a permanent magnet brushless DCmotor (PMBLDCM) is a good

option due to its wide speed range, high efficiency, rugged construction, ease of control and low

maintenance requirements. The PMBLDCM motor is a kind of three phase synchronous motor with

trapezoidal back EMF waveform, having permanent magnets (PMs) on the rotor, replacing the

mechanical commutator and a brush gear. The commutation is accomplished by electronic switches,

which supply the current to the motor windings as a function of the rotor position [3–7].

A diode bridge rectifier (DBR) fed from single-phase AC supply followed by a smoothening DC link

capacitor and a voltage source inverter (VSI) are mostly used in a conventional PMBLDCM drive. The

orrespondence to: Sanjeev Singh, Department of Electrical Engineering, Indian Institute of Technology, Delhi, New

lhi 110016, India.

mail: [email protected]

pyright # 2010 John Wiley & Sons, Ltd.

PMBLDCM DRIVE FOR AIR-CONDITIONING 425

PMBLDCM is supplied by three-phase rectangular current blocks of 1208 duration, in phase with the

constant part of the back emf waveform timed to coincide with the intervals of constant phase current.

These motors need rotor-position information only at the commutation points, for example, every

608electrical in the three-phase, therefore, comparatively simple controller is required for its

commutation [3–7].

An application of PMBLDCM for air conditioners is reported in the literature for vehicular [8] and

domestic [9] applications. For air-conditioning system, a PMBLDC motor is operated at constant

torque (i.e. rated torque) and variable speed to achieve energy conservation [8]. In a PMBLDCM,

constant torque is achieved by a stable winding current and the speed can be varied by varying the

terminal voltage of the motor, as the back emf is proportional to the motor speed and the developed

torque is proportional to the phase current [3–6]. In this work, the speed of PMBLDC motor is

controlled by controlling the terminal voltage of the motor. The control of VSI is based on the rotor

position signals and used only for electronic commutation of the PMBLDC motor. This results in

reduction of sensors used for the speed control of the PMBLDCM drive.

The conventional PMBLDC motor drive fed from single-phase AC supply through DBR–VSI, has a

pulsed current waveform at AC mains featuring a peak value higher than the amplitude of the

fundamental input current, due to uncontrolled charging of the DC link capacitor. It results in power

quality (PQ) problems at input AC mains such as poor power factor (PF), increased total harmonic

distortion (THD) in ACmains current and its high crest factor (CF). The use of power factor correction

(PFC) converter topologies [9–12] is, therefore, mostly recommended for such drives. For the drives in

low power range (current less than 16A), a standard IEC 61000-3-2 [13] is recommended for

regulating the PQ.

A single stage PFC topology uses a DC–DC converter between the VSI and DBR fed from single-

phase AC supply [11,12]. The DC–DC converter provides controlled DC voltage to the VSI from an

uncontrolled DC output of DBR, while improving the PF at AC mains through high frequency

switching of the converter device. There are manyDC–DC converter topologies available such as buck,

boost, buck-boost, Cuk, SEPIC and Zeta, amongst which buck-boost topology is the simplest one with

wide control of the output voltage.

This paper presents the buck-boost PFC converter [14] fed PMBLDCM drive for an air conditioner,

which has high efficiency thereby reduced energy consumption with desired speed control. Some of the

additional features are such as speed control by DC link voltage control, PFC at input AC mains,

reduced THD of AC mains current and reduced complexity of the controller. A detailed design and

performance evaluation of the proposed speed control scheme with a PFC converter are presented for

an air conditioner compressor driven from a PMBLDC motor of 1.5 kW, 400V rating. The paper is

organized in six main parts, namely introduction, proposed control scheme of PMBLDCM for air-

conditioning, their design, modelling of the proposed PMBLDCM drive, performance evaluation and

conclusion.

2. PROPOSED SPEED CONTROL SCHEME OF PMBLDC MOTOR

The proposed speed control scheme is shown in Figure 1 with the control loop for commutation control

in VSI and a speed control (i.e. voltage control) with PFC in a DC–DC converter. It replaces the

conventional control of the motor speed and the stator current involving various sensors for voltage and

current signals by controlling the reference DC link voltage as an equivalent reference speed. As in a

PMBLDCM, the torque is controlled by the winding current and the speed can be varied by varying the

terminal voltage of the motor, as the back emf is proportional to the motor speed and the developed

torque is proportional to the phase current.

A rate limiter is introduced in the reference voltage to ensure the stator current of the PMBLDCM

within the specified limits. The rate limiter maintains the voltage error (Ve) at DC link nearly constant

during transient states so that the current rise in the motor is controlled by DIav¼ (Ve)/Req, where Req is

the equivalent resistance of the PMBLDC motor appearing at DC link, thereby limiting the current to

desired value. Moreover, the design of the rate limiter is mainly governed by the mechanical time

Copyright # 2010 John Wiley & Sons, Ltd. Euro. Trans. Electr. Power 2011; 21:424–438DOI: 10.1002/etep

Figure 1. Control schematic of proposed buck-boost PFC converter fed PMBLDCM drive.

426 S. SINGH AND B. SINGH

constant of the PMBLDC motor, as the Req of the motor appearing at DC link, varies according to the

back emf of the motor.

The rotor position signals are used to generate the switching sequence for the VSI which performs

only as an electronic commutator of the PMBLDC motor. The rotor position of PMBLDCM is sensed

using Hall effect sensors and converted to required signals for commutation using Table I. Based on

these signals switching sequence is generated for the VSI using Table II.

The voltage at DC link is controlled using a buck-boost DC–DC converter along with PFC action.

The duty ratio (D) of the buck-boost DC–DC converter decides the output DC voltage, however, the

switching frequency ( fs) is decided by the switching device used, operating voltage and power level

and switching losses of the device. For high fs in the PFC converter, a metal oxide field effect transistor

(MOSFET) is used as the switching device in this work. However, insulated gate bipolar transistors

(IGBTs) are used in VSI bridge, to reduce the switching stress and EMI filtering issues, as it operates at

lower frequency compared to PFC switch.

Table I. Back emf signals based on the Hall effect sensor signals.

Ha Hb Hc Ea Eb Ec

0 0 0 0 0 00 0 1 0 �1 þ10 1 0 �1 þ1 00 1 1 �1 0 þ11 0 0 þ1 0 �11 0 1 þ1 �1 01 1 0 0 þ1 �11 1 1 0 0 0

Table II. VSI switching sequence based on the back emf signals.

Ea Eb Ec S1 S2 S3 S4 S5 S6

0 0 0 0 0 0 0 0 00 �1 þ1 0 0 0 1 1 0�1 þ1 0 0 1 1 0 0 0�1 0 þ1 0 1 0 0 1 0þ1 0 �1 1 0 0 0 0 1þ1 �1 0 1 0 0 1 0 00 þ1 �1 0 0 1 0 0 10 0 0 0 0 0 0 0 0



The PFC control scheme uses outer loop for voltage control equivalent to the speed control and inner

loop for the current control using a current multiplier approach. It employs an average current control

scheme for the continuous conduction mode (CCM) of the PFC converter. The control action begins

with the DC link voltage sensing which is compared with a reference voltage equivalent to the

reference speed. The resultant Ve is passed through a voltage PI controller to give the modulating

current signal. This signal is multiplied with a unit template of input AC voltage and compared with the

DC current sensed after the DBR. This current error is amplified and compared with a saw-tooth carrier

wave of fixed frequency ( fs) to generate the PWM pulses for the DC–DC converter. The complete

control strategy consists of selection of sensors, design of control algorithm and PWM controller for

the drive.

3. DESIGN OF BUCK-BOOST PFC CONVERTER BASED PMBLDCM DRIVE FOR AIR

CONDITIONING SYSTEM

The design of PFC buck-boost converter is carried out for a PMBLDCM drive having DBR at front end.

The parameters of this PFC converter are selected on the basis of PQ constraints at ACmains and allowable

ripple in DC-link voltage. The output voltage (Vdc) of the PFC buck-boost converter is given by as:

Vdc ¼DVin

1� D(1)

A ripple filter is also designed for rated output of the converter to reduce the ripples introduced due to

high fs of the buck-boost converter. The inductance (Lo) of output ripple filter restricts the inductor peak

to peak current ripple (DILo) within specified value for the given fs, whereas, the capacitance (Co) is

calculated for a specified ripple in output voltage (DVdcr) and average output current (Iav). The

governing design equations for the output filter inductor and a capacitor are given as:

Lo ¼ð1� DÞVdc

ffsðDILoÞg; (2)

Co ¼Iav

2vDVdcr

(3)

The PMBLDCM considered in this work is rated at 1.5 kW, 1500 rpm. Therefore, the PFC converter

is designed for a base DC link voltage of Vdc¼400Vat Vin¼ 198 V for Vs¼ 220Vrms. Other design data

are fs¼ 40 kHz, Iav¼ 4A, DVdcr¼ 5V (1.25% of Vdc), DILo¼ 4.0A. The design parameters are

calculated as Lo¼ 0.5mH, Co¼ 1600mF.

Since the Req of the PMBLDCmotor appearing at DC link varies according to the back emf developed

in the motor which is 6.6V (inclusive of ON resistance of switches) at starting and reaches around 100V

at rated speed and rated current, the rate limiter is designed to maintain the same slope for the DC link

voltage and to limit the current at double the rated value, that is 8A. This results in a voltage rise rate of

{400V� (6.6V� 8A)}/0.38 s� 910V/seconds, where 0.38 s is the mechanical time constant of the

PMBLDC motor. The value of reference voltage rate limiter is considered as 800V/seconds so that the

motor current remains always less than the maximum allowed value (i.e. 8A), therefore, the value ofVe at

DC link is set as 80mV/switching cycle during transient states which results in a current rise (DIav) of

12mA/switching cycle in themotor. As a result of this the PMBLDCM reaches its rated speed within one

mechanical time constant of the motor and draws its rated current during steady state.

4. MODELLING OF THE PROPOSED PMBLDCM DRIVE

The modelling of proposed PMBLDCM drive involves modelling of the PFC converter and

PMBLDCM. These components are modelled by mathematical equations and complete drive is

represented as a combination of these models.



4.1. PFC converter

The PFC converter consists of a DBR at front end and a buck-boost converter with an output ripple

filter. The modelling of PFC converter consists of the modelling of a voltage controller, a reference

current generator and a PWM controller as given below.

4.1.1. Voltage controller. The voltage controller is the most important component of this control

scheme and it closely follows the voltage reference equivalent to a reference speed. Avoltage gradient

of 800V/seconds is introduced in the voltage reference for the rate limit of DC link voltage during step

change to ensure the stator current of the PMBLDCM within the specified limits.

A proportional integral (PI) controller is used for DC link voltage control. If at kth instant of time,

V�dc(k) is reference DC link voltage, Vdc(k) is sensed DC link voltage then the voltage error Ve(k) is

calculated as:

VeðkÞ ¼ V�dcðkÞ � VdcðkÞ (4)

The voltage (PI) controller gives a desired control signal after processing this Ve. The output of the

controller Ic(k) at kth instant is given as:

IcðkÞ ¼ Icðk � 1Þ þ KpvfVeðkÞ � Veðk � 1Þg þ KivVeðkÞ; (5)

where Kpv and Kiv are the proportional and integral gains of the voltage controller.

4.1.2. Reference current generator. The reference input current of the buck-boost converter is

denoted by i�dc and given as:

i�dc ¼ IcðkÞuvs; (6)

where uvi is the unit template of the voltage at input AC mains, calculated as:

uvs ¼vin

Vsm

; vin ¼ vsj j; vs ¼ Vsm sinvt; (7)

where Vsm is the amplitude of input AC voltage and v is frequency in rad/seconds at input AC mains.

4.1.3. PWM controller. The reference input current of the buck-boost converter (i�dc) is compared

with its sensed current (idc) to generate the current error Didc¼ (i�dc � idc). This current error is

amplified by gain kdc and compared with fixed frequency ( fs) saw-tooth carrier waveform md(t) to get

the switching signals for the MOSFET of the buck-boost PFC converter as:

If kdcDidc > mdðtÞ then S ¼ 1 ; (8)

If kdcDidc � mdðtÞ then S ¼ 0 ; (9)

where S is the switching function representing ‘on’ position of MOSFET of the PFC converter with

S¼ 1 and its ‘off’ position with S¼ 0.

4.2. PMBLDCM drive

The PMBLDCM drive considered in this work consists of an electronic commutator, a VSI and a

PMBLDC motor.

4.2.1. Electronic commutator. The electronic commutator uses signals from Hall effect sensors to

generate required signals for electronic commutation as shown in Table I and the switching sequence

for the VSI is generated based on the logic given in Table II.



4.2.2. Voltage source inverter. Figure 2 shows an equivalent circuit of a VSI fed PMBLDCM. The

output of VSI to be fed to phase ‘a’ of the PMBLDC motor is given as:

vao ¼ Vdc

2for S1 ¼ 1 ; (10)

vao ¼ �Vdc

2for S2 ¼ 1 ; (11)

vao ¼ 0 for S1 ¼ 0; and S2 ¼ 0; (12)

van ¼ vao � vno; (13)

where 1 and 0 represent ‘on’ and ‘off’ position of respective IGBT switch of the VSI and considered in

a similar way for other IGBT switches of VSI, that is S3–S6.

Using similar logic vbo, vco, vbn, vcn are generated for other two phases of the VSI feeding PMBLDC

motor, where vao, vbo, vco and vno are voltages of three-phases and neutral terminal (n) with respect to

virtual mid-point of the DC bus shown as ‘o’ in Figure 2. The voltages van, vbn, vcn are voltages of three-

phases with respect to neutral and Vdc is the DC link voltage.

4.2.3. PMBLDC motor. The PMBLDCM is modelled in the form of a set of differential equations

given as:

van ¼ Ria þ pla þ ean; (14)

vbn ¼ Rib þ plb þ ebn; (15)

vcn ¼ Ric þ plc þ ecn (16)

In these equations, p represents differential operator (d/dt), ia, ib, ic are current, la, lb, lc are flux

linkages and ean, ebn, ecn are phase to neutral back emf of PMBLDCM, in respective phases, R is

resistance of motor windings/phase.

Moreover, the flux linkages can be represented as:

la ¼ Lsia �Mðib þ icÞ; (17)

lb ¼ Lsib �Mðia þ icÞ; (18)

lc ¼ Lsic �Mðib þ iaÞ; (19)

where Ls is self-inductance/phase, M is mutual inductance of motor winding/phase.

Since the PMBLDCM has no neutral connection, therefore:

ia þ ib þ ic ¼ 0 (20)

From Equations (13–20) the voltage between the neutral and mid-point of DC bus is given as:

vno ¼fvao þ vbo þ vco � ðean þ ebn þ ecnÞg

3(21)

Figure 2. Equivalent circuit of a VSI fed PMBLDCM drive.



From Equations (17–20), the flux linkages are given as:

la ¼ ðLs þMÞia; lb ¼ ðLs þMÞib; lc ¼ ðLs þMÞic (22)

From Equations (14–16 and 22), the current derivatives in generalized state space form are given as:

pix ¼vxn � ixR� exn

Ls þM; (23)

where x represents phase a, b or c.

The developed electromagnetic torque Te in the PMBLDCM is given as:

Te ¼eania þ ebnib þ ecnic

vr

; (24)

where vr is motor speed in rad/seconds.

The back emfs may be expressed as a function of rotor position (u) as:

exn ¼ KbfxðuÞvr; (25)

where x can be phase a, b or c and accordingly fx(u) represents function of rotor position with a

maximum value �1, identical to trapezoidal induced emf given as:

faðuÞ ¼ 1 for 0 < u � 120; (26)

faðuÞ ¼6

p

� �ðp� uÞ

� �� 1 for 120 < u � 180; (27)

faðuÞ ¼ �1 for 180 < u � 300; (28)

faðuÞ ¼6

p

� �ðu � 2pÞ

� �þ1 for 300 < u � 360 (29)

The functions fb(u) and fc(u) are similar to fa(u) with a phase difference of 120 and 2408, respectively.Therefore, the electromagnetic torque expressed as:

Te ¼ KbffaðuÞia þ fbðuÞib þ fcðuÞicg (30)

The mechanical equation of motion in speed derivative form is given as:

pvr ¼P

2

Te � Tl � Bvr

J(31)

Moreover the derivative of the rotor position angle (u) is given as:

pu ¼ vr (32)

where P is number of poles, Tl is load torque in Nm, J is moment of inertia in kg-m2 and B is friction

coefficient in Nms/rad.

These Equations (14–32) represent the dynamic model of the PMBLDC motor.

5. PERFORMANCE EVALUATION OF PROPOSED PMBLDCM DRIVE

The proposed PMBLDCM drive is modelled in Matlab–Simulink environment and a detailed

performance evaluation is carried out for an air conditioning compressor load. The compressor

behaves as a constant torque load equal to the rated torque with the speed variation to match air

conditioning system requirement. The PMBLDCM of 1.5 kW, 400 V, 4 A rating is used to drive a

compressor load of air conditioner rated at 1440 rpm and 9.95 Nm torque. The detailed data of the



motor and simulation parameters are given in Appendix. The speed of the motor is controlled

by controlling the DC link voltage. The performance evaluation of the proposed converter

topology is carried out on the basis of various parameters such as THDi and CF of current at

input AC mains, displacement power factor (DPF), PF and efficiency of the complete drive (hdrive)at different speeds of the motor. Moreover, these parameters are also evaluated for variable input

AC voltage at constant DC link voltage of 400 V which is equivalent to 1362 rpm reference speed

of the PMBLDCM. The results are shown in Figures 3–9 and Tables III–V to demonstrate the

effective speed control of the proposed PMBLDCM drive in a wide range of speed and an input

AC voltage.

5.1. Performance during starting

The performance of the proposed PMBLDCM drive fed from 220V AC mains during starting at

rated torque and 1000 rpm speed is shown in Figure 3a. A voltage rate limiter less than 800 V/

seconds is introduced in the reference voltage to limit the starting current of the motor as well as the

charging current of the DC link capacitor. Therefore, the voltage controller closely tracks the

Figure 3. Performance of the PMBLDCM drive under speed variation at 220VAC input. (a) Startingperformance of the PMBLDCM drive at 1000 rpm. (b) Performance of the PMBLDCM drive under speed

variation from 700 to 300 rpm.


Figure 4. Performance of the PMBLDCM drive under steady state condition at 220VAC input. (a)Performance of the PMBLDCM drive at 300 rpm speed. (b) Performance of the PMBLDCM drive at

rated speed (1440 rpm).

Figure 5. DC link voltage variation under speed control for the proposed PMBLDCM drive at rated torqueand 220VAC input.



Figure 6. PQ parameters of PMBLDCM drive under speed control at rated torque and 220VAC input. (a)Variation of DF, DPF, PF; (b) Variation of current at AC mains and its THD.

Figure 7. Current waveform at input AC mains and its harmonic spectra of the PMBLDCM drive understeady state condition at rated torque and 220VAC input. (a) Is and THD at 300 rpm speed; (b) Is and THD at

700 rpm speed; (c) Is and THD at 1000 rpm speed; (d) Is and THD at rated speed (1440 rpm).


reference voltage ramp and the motor attains the reference speed smoothly within 0.4 s while

keeping the stator current within permissible value. The current (is) waveform at input AC mains is

in phase with the supply voltage (vs), that is PFC buck-boost converter maintains good PF during

starting period.


Figure 8. PQ parameters with input AC voltage at 400V DC link voltage (equivalent to 1362 rpm speed).(a) Variation of current at AC mains and its THD; (b) Variation of DF, DPF and PF.


5.2. Performance under speed control

Figures 3–5 show the performance of the proposed PMBLDCM drive under the speed control at

constant rated torque (9.95Nm) and 220VAC mains supply voltage. These results are categorized as

performance during transient and steady state conditions.

5.2.1. Transient condition. Figure 3b shows speed control of the compressor from 700 rpm,

that is near half the rated load of the compressor to 300 rpm, that is light load of the compressor.

It is observed from Figure 3a and b that the speed control is fast and smooth in either

direction, that is acceleration or retardation. Moreover, the stator current of PMBLDCM is

within the allowed limit (twice the rated current) due to the introduction of rate limiter in

reference voltage. The PFC buck-boost converter ensures near unity PF during the transient

condition.

5.2.2. Steady state condition. An exhaustive performance evaluation of the proposed PMBLDCM

drive is carried out for the speed control of the compressor under steady state condition and the results

are shown in Figures 4 and 5 and Table III for comparison. Figure 4a and b shows the voltage (vs) and

current (is) waveforms at AC mains, DC link voltage (Vdc), the speed of the motor in rpm (N),

developed electromagnetic torque of the motor (Te), stator current of the PMBLDCmotor for phase ‘a’

(Ia) and shaft power output (Po) at 300 and 1440 rpm speeds. Figure 5 shows linear relation between

motor speed and DC link voltage. Since the reference speed is decided by the reference voltage at DC

link, it is observed that the variation of the reference DC link voltage effectively changes the speed of

the motor.

5.3. PQ performance

The performance of the proposed PMBLDCM drive in terms of various PQ parameters such as

THDi, CF, DPF, PF is summarized in Table IVand shown in Figures 6 and 7. Near unity PF and reduced

THD of AC mains current are observed in wide range of motor speed as shown in Figure 6a and b. The

THD of AC mains current remains within 5% along with near unity PF in wide range of the speed

as well as load as shown in Table IV and Figure 7a–d.

5.4. Performance under varying Input AC voltage

To provide a complete evaluation of the proposed PMBLDCM drive for air conditioning system,

performance of the PMBLDCM drive under variation of AC mains voltage at rated torque and

1362 rpm speed (i.e. equivalent to 400V at DC link) are summarized in Table V.

Figure 8a and b shows variation of input current and its THD at AC mains, DF, DPF and PF with an

input AC voltage. The THD of input current at AC mains is within specified limits of international


Figure 9. Steady state and transient performance of proposed PFC Drive. (a) Variation of sourcevoltage (Vs): 500 V/div, source current (Is): 10 A/div, DC link voltage (Vdc): 200 V/div and speed (N):800 rpm/div, time: 2.0 s/div. (b) Variation of source voltage (Vs): 500 V/div, source current (Is): 2.5 A/div, DC link voltage (Vdc): 200 V/div and motor current (Ia): 2.5 A/div, time: 1.0 s/div; (c) Variation ofsource voltage (Vs): 500 V/div, source current (Is): 5 A/div, DC link voltage (Vdc): 500 V/div and motorcurrent (Ia): 2.5 A/div, time: 50 ms/div at steady state of 1200 rpm speed. (d) Current THD at AC mains

at steady state of 1200 rpm speed.



Figure 9. Continued


norms [13] along with near unity PF in wide range of AC input voltage. However, at low AC input

voltage the performance of the drive becomes sluggish and the motor takes little longer time to reach

the steady state condition.

6. HARDWARE IMPLEMENTATION

The proposed PFC based drive is implemented on a laboratory prototype of 0.75 kW rating, 300V,

PMBLDC motor using a microchip dsPIC 30F6010 while running the motor under speed control at no

load. The speed control (acceleration and deceleration) is demonstrated with DC link voltage variation

in Figure 9a and b. Similar variation is shown in Figure 9c with stator phase current of the PMBLDCM

while maintaining in phase current to the AC mains voltage. Figure 9d shows the AC mains current

THD while PF is maintained at near unity value. The presented hardware results validate the


Table III. Performance of drive under speed control at 220V input AC voltage (VAC).

Speed(rpm)

VDC

(V)hdrive(%)

Load(%)

200 93.0 54.9 13.9300 119.3 64.0 20.8400 145.5 69.9 27.8500 171.7 74.4 34.7600 198.2 77.5 41.7700 224.5 79.8 48.6800 251.0 81.6 55.6900 277.3 82.9 62.51000 303.7 84.2 69.41100 330.2 85.3 76.41200 356.8 86.0 83.31300 383.5 86.7 90.31400 409.8 87.2 97.21440 420.2 87.5 100.0

Table IV. PQ parameters under speed control at 220V input AC voltage (VAC).

Speed(rpm)

THDi

(%)DPF PF CF

200 2.30 0.9998 0.9995 1.42300 2.00 0.9998 0.9996 1.42400 1.93 0.9999 0.9997 1.41500 1.98 0.9999 0.9997 1.41600 2.08 0.9998 0.9996 1.41700 2.19 0.9998 0.9996 1.41800 2.29 0.9999 0.9996 1.41900 2.46 0.9999 0.9996 1.411000 2.69 0.9999 0.9995 1.411100 2.92 0.9998 0.9994 1.411200 3.22 0.9998 0.9993 1.411300 3.52 0.9997 0.9991 1.411400 3.81 0.9997 0.9990 1.411440 3.92 0.9998 0.9990 1.41

Table V. Variation of PQ parameters with input AC voltage (VAC) at 1362 rpm (400Vdc).

VAC(V)

THDi

(%)DPF PF CF Is (A) hdrive

(%)

170 6.97 0.999 0.997 1.41 9.64 86.9180 6.06 0.999 0.998 1.41 9.09 86.9190 5.31 1.000 0.998 1.41 8.61 86.9200 4.67 1.000 0.999 1.41 8.17 87.0210 4.15 1.000 0.999 1.41 7.78 86.9220 3.72 1.000 0.999 1.41 7.43 86.9230 3.37 1.000 0.999 1.41 7.10 87.0240 3.09 1.000 0.999 1.41 6.81 86.9250 2.82 1.000 0.999 1.41 6.54 86.9260 2.58 1.000 1.000 1.41 6.28 86.9270 2.37 1.000 1.000 1.41 6.05 86.9




implementation of the proposed concepts for speed control and PQ improvement at AC mains while

maintaining near unity PF.

7. CONCLUSION

A new speed control strategy of a PMBLDCM drive using reference DC link voltage equivalent to

reference speed has been designed, modelled and implemented for a compressor load of an air-

conditioner. The speed control has been achieved directly proportional to the voltage control at DC

link. The rate limiter introduced in the reference voltage at DC link of the PMBLDC motor effectively

limits the motor current during transients (starting and speed control). The addition of PFC feature to

the proposed drive has ensured near unity PF in wide range of speed and input AC voltage. Moreover,

PQ parameters of the proposed PMBLDCM drive have been found in conformity to the international

standard IEC 61000-3-2 [13]. The performance of the drive has been found very good and energy

efficient as an adjustable speed drive in the wide range of input AC voltage.

8. LIST OF SYMBOLS ABBREVIATIONS

AC A

Copyrig

lternating Current

DC D
irect Current
APPENDIX

Rated power: 1.5 kW, Rated voltage: 400 VDC, Rated speed: 1500 rpm, Rated current: 4.0 A, Rated

torque: 9.95Nm, No of poles: 4, Resistance: 2.8V/ph, Inductance (L+ M): 0.00521H/ph, Back EMF

constant: 1.23Vs/rad, Moment of inertia¼ 0.013Kg/m2. Source impedance (2pfLs): 0.03 pu,

Switching frequency of PFC switch¼ 10 kHz.

REFERENCES

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61000-3-2, 2000.

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ht # 2010 John Wiley & Sons, Ltd. Euro. Trans. Electr. Power 2011; 21:424–438DOI: 10.1002/etep

pfc buck-boost converter based voltage controlled adjustable speed pmbldcm drive for...

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