A PFC-Based BLDC Motor Drive Using aCanonical Switching Cell Converter

Vashist Bist, Student Member, IEEE, and Bhim Singh, Fellow, IEEE

AbstractThis paper presents a power factor correction (PFC)-based canonical switching cell (CSC) converter-fed brushless dcmotor (BLDCM) drive for low-power household applications. Thespeed of BLDCM is controlled by varying the dc-bus voltage ofvoltage source inverter (VSI). The BLDCM is electronically com-mutated for reduced switching losses in VSI due to low-frequencyswitching. A front-end CSC converter operating in discontinuousinductor current mode (DICM) is used for dc-bus voltage controlwith unity power factor at ac mains. A single sensor for dc-busvoltage sensing is used for the development of the proposed drive,whichmakes it a cost-effective solution. A prototype of the proposedconguration is developed, and its performance is validated withtest results for the control of speed over a wide range with a unitypower factor at universal ac mains.

Index TermsBrushless dc motor (BLDCM), canonicalswitching cell (CSC) converter, discontinuous inductor currentmode (DICM), power factor correction (PFC), power quality.

I. INTRODUCTION

A MONG NUMEROUS motors, brushless dc motor(BLDCM) is preferred in many low and medium powerapplications including household appliances, industrial tools,heating ventilation and air conditioning (HVAC), medical equip-ments, and precise motion control systems [1][7]. BLDCM ispreferred because of its high torque/inertia ratio, high efciency,ruggedness, and low-electro-magnetic interference (EMI) pro-blems [1], [2]. The stator of the BLDCM consists of three-phaseconcentrated windings and rotor has permanent magnets [1], [2].It is also known as an electronically commutated motor (ECM)since an electronic commutation based on rotor position viaa three-phase voltage source inverter (VSI) is used [8], [9].Therefore, the problems associated with brushes, such as spark-ing, and wear and tear of the commutator assembly areeliminated.Fig. 1 shows a conventional scheme of BLDCM drive fed by

an uncontrolled rectier and a dc-link capacitor followed by athree-phase pulse width modulation (PWM)-based VSI is usedfor feeding the BLDCM [10]. This type of scheme draws peaky,harmonic rich current from the supply and leads to a high valueof total harmonic distortion (THD) of supply current andvery low power factor at ac mains as shown in Fig. 2 [11]. Avery high THD of supply current of 65.3% and a very poor

power factor of 0.72 is achieved which is not acceptable byInternational Electro-technical Commission (IEC) 61000-3-2[12].A front-end power factor correction (PFC) converter is used

after the diode bridge rectier (DBR) for improving the qualityof power and achieving a near unity power factor at ac mains[13], [14]. The mode of operation of the PFC converter is acritical issue as it directly affects the cost of overall system.The continuous inductor current mode (CICM) and the dis-continuous inductor current mode (DICM) are the two basicmodes of operation of a PFC converter [13], [14]. A control ofcurrent multiplier is normally used for PFC converter operatingin CICM and requires three sensors (2-V, 1-C) for the opera-tion which is not cost-effective for low-power applications,whereas, a PFC converter operating in DICM uses a voltagefollower control which requires sensing of dc-link voltagefor voltage control and inherent PFC is achieved at acmains [13], [14].Many topologies of a PFC-based BLDCM drives have been

reported in the literature [10], [15][23]. A boost PFC converterhas been the most popular conguration for feeding BLDCMdrive as shown in Fig. 3 [16][18]. A constant dc-link voltage ismaintained at the dc-link capacitor and a PWM-basedVSI is usedfor the speed control. Hence, the switching losses in VSI are veryhigh due to high switching PWM signals and require hugeamount of sensing for its operation. Cheng [19] has proposedan active rectier-based BLDC motor drive fed which requirescomplex control and is suitable for higher power applications.Lee et al. [20] have explored various reduced parts congura-tions for PFC operation which also uses a PWM-based VSI andhave high switching losses in it. A buck chopper operating as afront-end converter for feeding a BLDC motor drive has beenproposed by Barkley et al. [21]. It also has higher switchinglosses associated with it due to high-frequency switching.Madani et al. [22] have proposed a boost half bridge PFC-basedBLDCM drive using four switch VSI. This also requires anecessary PWM operation of VSI and PFC half bridge boostconverter, which introduces high switching losses in the overallsystem.These switching losses are reduced by using a concept of

variable dc-link voltage for speed control of BLDC motor [24].This utilizes the VSI to operate in low-frequency switchingrequired for electronic commutation of BLDC motor, hencereduces the switching losses associated with it. The front-endSEPIC and Cuk converter feeding a BLDC motor using avariable voltage control have been proposed in [10] and [23],

Manuscript received September 07, 2013; revised December 20, 2013;accepted January 28, 2014. Date of publication February 11, 2014; date ofcurrent version May 02, 2014. Paper no. TII-13-0613.

The authors arewith theDepartment of Electrical Engineering, Indian Instituteof TechnologyDelhi, New Delhi 110016, India (e-mail: vashist.bist@gmail.com; bsingh@ee.iitd.ac.in).

Digital Object Identier 10.1109/TII.2014.2305620

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1551-3203 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

but at the cost of two current sensors. This paper presents thedevelopment of a reduced sensor-based BLDC motor drive forlow-power application.

II. PROPOSED BLDCM DRIVE USING CSC CONVERTER

Fig. 4 shows the proposed BLDCM drive with a front-endPFC-based canonical switching cell (CSC) converter. A CSCconverter operating in DICM acts as an inherent power factorpre-regulator for attaining a unity power factor at ac mains. Avariable dc-bus voltage of the VSI is used for controlling thespeed of the BLDCM. This operates the VSI in low-frequencyswitching by electronically commutating the BLDCM for reduc-ing the switching losses in six insulated gate bipolar transistors(IGBTs) of VSI which share the major portion of overall lossesin the BLDCM drive. The front-end CSC converter is designed

and its parameters are selected to operate in aDICM for obtaininga high-power factor at wide range of speed control. A prototypeof proposed drive is developed to experimentally demonstrate itsperformance for control of speed over a wide range with a unitypower factor at universal ac mains (90265 V).

III. OPERATING PRINCIPLE OF PFC-BASED CSC CONVERTER

The proposed BLDCM drive uses a CSC converter operatinginDICM [25][28]. InDICM, the current in inductor becomesdiscontinuous in a switching period ( ). Three states of CSCconverter are shown in Fig. 5(a)(c). Waveforms of inductorcurrent and intermediate capacitors voltage for a com-plete cycle of line frequency are shown in Fig. 6(a), whereasFig. 6(b) shows the variation in different variables of CSCconverter such as switch gate voltage ( ), inductor current( ), intermediate capacitors voltage ( ), and dc-link voltage( ) in a complete switching period. Three modes of operationare described as follows.

Mode I: As shown in Fig. 5(a), when switch is turned ON,the energy from the supply and stored energy in the intermediatecapacitor are transferred to inductor . In this process, thevoltage across the intermediate capacitor reduces, whileinductor current and dc-link voltage are increased asshown in Fig. 6(b). The designed value of intermediate capacitoris large enough to hold enough energy such that the voltageacross it does not become discontinuous.

Mode II: The switch is turned OFF in this mode of operation asshown in Fig. 5(b). The intermediate capacitor is chargedthrough the supply current while inductor starts discharginghence voltage starts increasing, while current decreases inthis mode of operation as shown in Fig. 6(b). Moreover, thevoltage across the dc-link capacitor continues to increase dueto discharging of inductor .

Mode III: This is the discontinuous conduction mode ofoperation as inductor is completely discharged and current

becomes zero as shown in Fig. 5(c). The voltage acrossintermediate capacitor continues to increase, while dc-linkcapacitor supplies the required energy to the load, hencestarts decreasing as shown in Fig. 6(b).

IV. DESIGN OF A PFC-BASED CSC CONVERTER

The proposedBLDCMdrive uses a PFC-based CSC converteroperating in DICM. The front-end PFC-based CSC converter of

is designed for a 314-W BLDCM. (Full specica-tions are given in the Appendix.) The dc-link voltage has to becontrolled from 50 V ( ) to 200 V ( ) with a nominalvoltage of 120 V ( ). For the supply voltage ( ) of 220 V, thevoltage appearing after the DBR is given as [11]

A nominal duty ratio ( ) corresponding to is as [11]

Fig. 1. Conventional DBR-fed BLDCM drive.

Fig. 2. MeasuredPQ indices of the conventionalDBR-fedBLDCMdrive at ratedload on BLDCM with supply voltage as 220 V showing (a) supply voltage andsupply current; (b) active, reactive, and apparent power, PF, and DPF; and(c) THD of supply current at ac mains.

Fig. 3. Conventional PFC converter-fed BLDCM drive.

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The design of a CSC converter is very similar to a nonisolatedCuk converterwith a single inductor and a switching cell which isa combination of a switch , diode , and an intermediatecapacitor [14]. The critical value of inductance to operateat boundary condition is given as [14]

where is inductor, ( ) current, and is switching frequency.

Now to operate this converter for PFC even at very low dutyratio, the value of inductor is taken around 1/10th of the criticalvalue [29]. Hence, it is