Power Quality improvement in ZETA Converters for Brush-less DC Motors (BLDC)

Power quality improvements in a ZETA Converter for

Brushless DC Motor Drives (BLDC)

Hello!I am Rehan YounasI am here to talk a bit about TECHNOLOGYYou may contact me at rehanyounas980@yahoo.com

What is a Converter?A converter is a device used for conversion of AC/DC quantities from one form to other. But in most cases this term is reserved for converting AC voltages into DC The purpose is accomplished with the help of Diodes, IGBTS,Thyristors and many other components.

Why Convert AC/DC at all??Conversion is done to meet the demand of electrical machinary with the goal of providing continous, harmonicless source of energy.

IEC Standard 61000-3-2It is a standard that limits the total harmonic distortion (THD) of supply current and power factor (PF) at ac mains. And every electric machinery must meet this limit for standardization.

Brushless DC Motor Brushless DC (BLDC) motor is an ideal motor for low and medium power applications because of its high efficiency, high energy density, high torque/inertia ratio, low maintenance requirement and a wide range of speed control. It finds applications in a wide range of household appliances, industrial tools, heating, ventilation and air conditioning and many others. Failure of Conventional Converters…..

In a conventional scheme of diode bridge rectifier (DBR) with high value of dc-link capacitor fed BLDC motor drive, a high amount of harmonics current is drawn at ac mains. This combination draws peaky current and leads to a very highly distorted supply current and very low PF at AC

mains. So there is a need for improved power factor converters which are less expensive and reliable.

ZETA ConverterThe improved power factor demand for a DBR fed Brushless DC Motor Derive entails to use a more sophisticated converter where ZETA comes to assist……. The family of converters is growing larger day by day with the advancement in ever changing scientific era where machine demands better quality operation keeping the resources in mind. Zeta converter is a recent addition to it acting as an inherent PF corrector. The main feature of its distinction is its wide range operation with Discontinuous Current Mode operation.

Historical BackgroundLet’s talk about the need for ZETA Converters

“ The conventional scheme of DBR fed BLDC failed

to meet the IEC standards. Ammount of distortion at AC mains, THD, low PF

quality issues were significant. Conventional converters were inefficacious and

expensive.

Less efficient Expensive Unreliable

Techniques for PFC

Two stages PFC ConvertersEfficiency is increased but It requires higher number of components and thus has higher losses associated with it..

Single stage PFC ConvertersIt require a single converter for performing both tasks of voltage control as well as PFC operation but is less efficient…

PFC Boost Converters A constant dc-link voltage is maintained at the dc-link capacitor of the voltage source inverter (VSI) feeding the BLDC motor thus requires more sensors…

BASIC operationThe PFC zeta converter is designed to operate

in DICM, such that the current in input side inductor becomes discontinuous, whereas the current in output side inductor and the voltage across intermediate capacitor remain in continuous conduction for a complete switching cycle.

Performance Parameters

DC Link Capacitance Constraint (Cdc)The maximum value of dc-link capacitor should achieve at minimum value of dc-link voltage with K taken as 2% of Vdcmin.

Input Inductance Constraint (Lin)To achieve a discontinuous conduction at the worst-case scenario of maximum dc-link voltage (i.e.Lic200), the value of input inductor Lin, must be selected lower than Lic200.

Output Inductance Constraint (Lo)The maximum current ripple in an inductor occurs at the maximum power and for minimum value of supply voltage.

Power Factor Crest Factor THD

11.4

5.00%

0.74

2.6

65%

Comparison of Diode Bridge Rectifier and ZETA Converter

1) ZETA Converter2) DBR

ConclusionsExperimental verification, dynamic performance and comparative analysis of proposed ZETA converter for BLDC derive resemble with the predicted simulation results. A smooth control of dc-link voltage with limited

inrush in supply and stator current is obtained. Voltage and current stresses on the PFC

converter switch are reduced. The improved power quality indices have been

observed within the recommended limits of IEC 61000-3-2.

CreditsDr. Bhim SinghVashist Bist Indian Institute of Technology Delhi, India

Origional authors of the paper “Power quality improvement in a ZETA

converter for saperately excited Brushless DC motor drives”

References◇ Power quality improvements in a zeta converter for brushless

DC motor drives by Bhim Singh, Vishist Basu Department of Electrical Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India.

◇ Gopalarathnam, T., Toliyat, H.A.: ‘A new topology for unipolar brushless DC motor drive with high power factor’, IEEE Trans. Power Electron., 2003, 18, (6), pp. 1397–1404

◇ Sokira, T.J., Jaffe, W.: ‘Brushless DC motors: electronic commutation and control’ (Tab Books, USA, 1989)

◇ Handershot, J.R., Miller, T.J.E.: ‘Design of brushless permanent magnet motors’ (Clarendon Press, Oxford, 2010)

Thanks!Any questions?You can find me at:

◇ REHAN YOUNAS◇ rehanyounas980@yahoo.com