Efficient Voltage-Controlled PFC Cuk Converter for Air Conditioners

1. A Voltage-Controlled PFC Cuk Converter-Based PMBLDCM Drive for Air-Conditioners

2. CONTENTS • INTRODUCTION • PMBLDCM DRIVE • CUK CONVERTER • AIR CONDITIONER CONCEPT AND PRINCIPLE OF OPERATION • MODELLING OF PFC CUK CONVERTER BASED PMBLDCMD • MATLAB AND SIMULINK RESULTS

3. INTRODUCTION • A permanent magnet brushless DC motor (PMBLDCM) is a kind of three-phase synchronous motor having permanent magnets on the rotor. It is regarded as a rugged and efficient machine for variety of applications. • To mitigate PQ and associated problems several international standards have come up in the recent past which is specially meant for low power drives. Therefore, the drive system having inherent power factor correction (PFC) are more in demand and PFC converters have become preferred feature of new drives. Since the PMBLDCM drives have to be operated from the utility supply, therefore they should conform to the international PQ standards

4. Brushless DC Motor • No Commutators • Position of Coils with respect to the magnetic field is sensed electronically. • Current is commutated through electronic switches to appropriate phases.

5. PMBLDCM DRIVE • Brushless DC (BLDC) motors are synchronous motors with permanent magnets on the rotor and armature windings on the stator, Hence, from a construction point of view, they are the inside-out version of DC motors, which have permanent magnets or field windings on the stator and armature windings on the rotor.

7. How It Works • When electric current passes through a coil in a magnetic field, the magnetic force produces a torque which turns the motor. • Force in Motor: F=ILB F = Force B = Magnetic Field L = Length of Conductor I = Current in Conductor • Torque in Motor: T = IBA sin θ A = LW L = Length of Winding W = Width of Winding

8. ADVANTAGES • BLDC motors obtain life-long field excitation from permanent magnets mounted on the rotor surface. • Permanent magnet brushless DC motors (PMBLDCMs) are considered as better option in various low power (less than 5 kW) applications due to their energy efficiency and ease of control. • As the demand for efficiency, precise speed and torque control, reliability and ruggedness increases..

9. CUK CONVERTER • The Cuk converter (pronounced Chook, sometimes incorrectly spelled Cuk) is a type of DC-DC converter that has an output voltage magnitude that is either greater than or less than the input voltage magnitude. • As with other converters (buck converter, boost converter, buck-boost converter) the Cuk converter can either operate in continuous or discontinuous current mode. • However, unlike these converters, it can also operate in discontinuous voltage mode (i.e., the voltage across the capacitor drops to zero during the commutation cycle).

10. NON-ISOLATED CUK CONVERTER • The non-isolated Cuk converter can only have opposite polarity between input and output. It uses a capacitor as its main energy-storage component, unlike most other types of converters which use an inductor. • It is named after Slobodan Cuk of the California Institute of Technology, who first presented the design. • The Cuk converter enables the energy flow bi-directionally, by adding a diode and a switch.

11. CIRCUIT DIAGRAM OF NON-ISOLATEDCUK-CONVERTER

12. AIR CONDITIONER • In the broadest sense air conditioning can refer to any form of cooling, heating, ventilation or disinfection that modifies the condition of air, typically for thermal comfort. • The more common use of air conditioning is to mean cooling and often dehumidification of indoor air, typically via refrigeration. • The process whereby the condition of air, as defined by its temperature and moisture content, is changed.

13. PROPOSED SPEED CONTROL SCHEME OF PMBLDC MOTOR FOR AIR-CONDITIONER • The proposed speed control scheme which is based on the control of the dc link voltage reference as an equivalent to the reference Speed. However, the rotor position signals acquired by Hall-effect sensors are used by an electronic commutator to generate switching sequence for the VSI feeding the PMBLDC motor, and therefore, rotor position is requiredonly at the commutation points.

14. The Cuk dc–dc converter controls the dc link voltage using capacitive energy transfer which results in non-pulsating input and output currents. • The proposed PFC converter is operated at a high switching frequency for fast and effective control with additional advantage of a small size filter. For the control of current to PMBLDCM through VSI during the step change of the reference voltage due to the change in the reference speed, a rate limiter is introduced, which limits the • Stator current of the PMBLDCM within the specified value which is considered as double the rated current in this work.

15. Laboratory tests with leading AC manufacturers have shown around 35% and 50% energy savings for the BLDC units. • The logic for the speed selection with respect to temperature and load as well as the motor speed variation is done entirely by software based controls resulting in a compact and reliable control unit which easily fits into the appliance. • For split units there is a communication interface between indoor and outdoor units.

16. The DC-DC converter used in the second stage is usually a flyback or forward converter for low power applications and a full-bridge converter for higher power applications. • However, these two stage PFC converters have high cost and complexity in implementing two separate switch-mode converters, therefore a single stage converter combining the PFC and voltage regulation at DC link is more in demand. • The single-stage PFC converters operate with only one controller to regulate the DC link voltage along with the power factor correction. • The absence of a second controller has a greater impact on the performance of single-stage PFC converters and requires a design to operate over a much wider range of operating conditions

18. Halls Sensors sense the position of the coils • The Decoder Circuit turns appropriate switches on and off • The voltage through the specific coils turns the motor

19. Fuzzy logic controller makes the PMBLDC drive more robust to load variations. The key feature of this scheme is to compensate the oscillations and harmonics in the response of the PMBLDC motor • The theory of brushless dc motors was proposed in 1962 by T.G. Wilson and P. H. Trickey.But the limitations in magnet and power switching have prevented them to bring into real life. • In 1980,Powertec.. Industrial Corporation started manufacturing them.

20. MATLAB • Matlab is a high-performance language for technical computing. It integrates computation, visualization, and programming in an easy-to-use environment where problems and solutions are expressed in familiar mathematical notation. • Typical uses include Math and computation Algorithm development Data acquisition Modeling, simulation, and prototyping Data analysis, exploration, and visualization Scientific and engineering graphics Application development, including graphical user interface building.

21. Matlab is an interactive system whose basic data element is an array that does not require dimensioning. • This allows you to solve many technical computing problems, especially those with matrix and vector formulations, in a fraction of the time it would take to write a program in a scalar no interactive language such as C or Fortran. • The name matlab stands for matrix laboratory. Matlab was originally written to provide easy access to matrix software developed by the linpack and eispack projects. • Today, matlab engines incorporate the lapack and blas libraries, embedding the state of the art in software for matrix computation.

22. SIMULINK • Simulink is a tool used to visually program a dynamic system (those governed by Differential equations) and look at results. • Any logic circuit, or control system for a dynamic system can be built by using standard building blocks available in Simulink Libraries. • Various toolboxes for different techniques, such as Fuzzy Logic, Neural Networks, dsp, Statistics etc. are available with Simulink, which enhance the processing power of the tool. • The main advantage is the availability of templates / building blocks, which avoid the necessity of typing code for small mathematical processes.

25. ADVANTAGES • Increased Reliablilty & Efficiency • Longer Life • Elimination of Sparks from Commutator • Reduced Friction • Faster Rate of Voltage & Current • Precision Voltage & Current Applied to Field Coils

26. Applications • Low Power • Consumer Electronics • Medical Field • High Power • Industrial Machinery • Vehicles • Airplanes

27. Disadvantages • Requires Complex Drive Circuitry • Requires additional Sensors • Higher Cost • Some designs require manual labor (Hand wound Stator Coils)

28. CONCLUSION • A new speed control strategy for a PMBLDCMD using the reference speed as an equivalent voltage at dc link has been simulated for an air-conditioner employing a Cuk PFC converter and experimentally validated on a developed controller. • The speed of PMBLDCM has been found to be proportional to the dc link voltage; thereby, a smooth speed control is observed while controlling the dc link voltage. • The PFC Cuk converter has ensured near unity PF in a wide range of the speed and the input ac voltage. Moreover, PQ indices of the proposed PFC drive are in conformity to the International Standard.

29. FUTURE SCOPE • The proposed PMBLDCM has been found as a promising variable speed drive for the Air-Con system. • Moreover, it may also be used in the fans with PMBLDC motor drives on the trains recently introduced in Indian Railways.

30. Useful Links • http://en.wikipedia.org/wiki/Electric_motor • http://electronics.howstuffworks.com/motor3.htm • http://www.hernonmfg.com/electricmotor.htm • http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html • http://www.servomag.com/flash/2-pole/2pole-bldc-motor.html • http://www.engineersedge.com/motors/brushless_dc_motor.htm • http://www.freescale.com/webapp/sps/site/application.jsp?nodeId=02nQXGrrlPY7r803B5