Power Factor Correction for Chopper Fed BLDC Motor

Transcription

1 ISSN No: Power Factor Correction for Chopper Fed BLDC Motor S.Dhamodharan, D.Dharini, S.Esakki Raja, S.Steffy Minerva *Corresponding Author: S.Dhamodharan Department of EEE, Info Institute of Engineering, Coimbatore. Received: 05/01/2017, Revised: 08/02/2017 and Accepted: 27/03/2017 Abstract Power factor correction (PFC) based Cuk converter fed brushless DC motor (BLDC) drive as a cost effective solution for low power applications. The speed of the BLDC motor is controlled by varying the DC bus voltage of voltage source inverter (VSI) which uses a low frequency switching of VSI (electronic commutation of BLDC motor) for low switching losses. A diode bridge rectifier (DBR) followed by a Cuk converter working in discontinuous conduction mode (DCM) is used for control of DC link voltage with unity power factor at AC mains. A bridgeless-single ended primary inductance converter (BL-SEPIC) fed brushless DC (BLDC) motor drive for low power household applications. The speed of the BLDC motor is controlled by adjusting the DC link voltage of the VSI feeding a BLDC motor. The VSI feeding BLDC motor is used for achieving an electronic commutation of the BLDC motor and operates in a low frequency switching for reduced switching losses in it. A bridgeless configuration of SEPIC is proposed which offers lower conduction losses due to the elimination of diode bridge rectifier (DBR) at the front end. A new configuration of a Luo converter with high frequency isolation for feeding brushless DC (BLDC) motor drive with power quality improvements at AC mains. In this work, a low frequency switching of the voltage source inverter (VSI) is used for reducing the switching losses associated with the six solid-state switches of VSI (Voltage Source Inverter). This is achieved by electronic commutation of BLDC motor and adjusting the DC bus voltage of the VSI for speed control. Keywords: Brushless DC motor, Discontinuous Inductor Current Mode, Isolated-Luo Converter, Power Factor Correction, Improved Power Quality, Voltage Source Inverter, cuk converter, sepic converter. 1. Introduction Nowadays efficiency and cost are the major concerns in designing and developing low-power applications like home application, industrial application and research application etc. Due to the several advantages of brushless direct current motors (BLDC), it has a continuous growth and number of applications has been noticed during the 37

2 past years. The features of BLDC motor are high efficiency, high flux density per unit volume, low electromagnetic interference, silent operation and low maintenance requirements. However, the use of BLDC motors is not limited to domestic applications. They are also used in medical equipment, motion control, transportation or many other industrial tools. As energy consumption is important to all over the world, in order to fulfil the enormous demand, strict regulations have been announced by worldwide organizations like International Electrotechnical Commission (IEC) regarding the power quality of applications. Therefore, more advanced supply friendly and efficiency applications need to be developed by manufacturers under the standard IEC As a consequence of this requirement, different kind of power quality correction techniques are available today for applications using BLDC motor drives, but the most common is the Power Factor Correction (PFC) converter. PFC improves the power quality at ac mains as it reduces the total harmonic distortion (THD) in the supply current. The aim of our project is to investigate a bridgeless PFC converter topology suitable for low-power BLDC motor applications. The proposed converter should be able to reduce the switching losses compared to other PFC topologies by minimizing the conducting elements during a cycle, therefore improving the efficiency and the industry standards. The bridgeless PFC converters transfer energy from the DC mains to the voltage source inverter (VSI), which controls the electronic commutation of the BLDC motor. The speed control of the motor is achieved by controlling the input power of the VSI. It greatly decreases the switching loss as the required switching frequency of the converter equals to the electrical frequency of the BLDC. Real power (P) is what the system actually consumes as electric power. This is transformed into different form of powers used for heating, lighting or moving. Reactive power (R) is responsible for creating and maintaining the electromagnetic field, closely related to an inductive load. S, or apparent power consists of the two previous. It is the product of the rms values of voltage and current of the load. Apparent power should be considered when designing an electric device, as I current flow through the electric circuit, therefore the heat loss is I2 R. The relation between electrical power components is illustrated. 2. Block diagram and simulation: 38

3 3 Simulation: 3.1 Cuk converter: Cuk converter fed bldc motor drive as a cost effective solution for low power application. The speed of the bldc motor is controlled by varying the dc bus voltage of voltage source inverter which uses a low frequency switching of VSI for low switching losses. A diode bridge rectifier followed by cuk converter working in a discontinuous conduction mode is used for controlling the dc link voltage with unity power factor. 3.2 Sepic converter: Modelling of a particular converter is done by either Circuit Averaging method or State Space Averaging method. Analytical and circuit based models that become complicated for fourth order and some second order systems. The simplest approach is to use the state space analytical method. Mathematical model determines the voltage, current and signal transfer function of the switching converter. 39

4 3.3 LUO converter: This converter is widely used in dc-dc conversion as it exhibits good voltage regulation over a wide range of voltage fluctuations and possess high light load efficiency.it can also operate as an excellent power factor preregulator. This bridgeless configuration offer reduced conduction losses in the frontend converter due to complete and partial elimination of diode bridge rectifier 4 Simulation result: 4.1 Cuk converter: OFF condition: When the switch is OFF, the inductor currents iɩ₁ and iɩ₂ flow through the diode.the circuit is shown Capacitor C₁ is charged through the diode by energy from both the input and L₁. Current iɩ₁, decreases, because Vc₁ is larger than Vd.Energy stored in L₂ feed the output. Therefore, Il2 also decreases. 40

5 ON condition: When the switch is ON, Vc₁ reverse biases the diode.the inductor currents iɩ₁, and iɩ₂ flow through the switch.since Vc₁ >Vₒ.C₁ discharges through the switch, transferring energy to the output and L₂.Therefore, increases. The input feed energy to L₁ and L₂ over one time period to zero yields. 4.2 Sepic converter : Duty cycle calculation: The amount that the SEPIC converters step up or down the voltage depends primarily on the on the Duty Cycle and the parasitic elements in the circuit. The output of an ideal SEPIC converter is given by Inductor selection: For determining the inductance is to allow the peak-to-peak ripple current to be approximately 40% of the maximum input current at the minimum input voltage. The ripple current flowing in equal inductors L1 and L2 is given by 4.3 LUO CONVERTER: ON condition: When switch is turned-on, the inductor L1 is charged by the supply voltage V1. At the same time the inductor L2 observe the energy from the source and capacitor C1. The load is supplied by the capacitor C2. 41

6 OFF condition: When switch is turned-off, and hence the current is drawn from the source become zero. The current il1 flows through the freewheeling diode to charge the capacitor C1. Current il2 flow through C2-R circuit and the freewheeling diode D to keep itself continuous. 5.Conclusion: A Hardware implementation of phase advanced method drive of BLDC motors was presented in this paper. In contrast to the classical software implementation of the phase advanced driving, this hardware implemented method requires significantly reduced computational power while maintaining the advanced angle accuracy even better than most of the existing software algorithms can perform. In addition the price difference of these rotary encoders for BLDC motor applications compared to the three separate hall sensor solution is insignificant or even cheaper. A disadvantage of the current encored technology is that there is no possible to change the phase advance during the motor operation, because the encoder has to be set into configuration mode which disables the position signal generation. Nevertheless the future version of this encoder type (already under development) will be able to change the offset of the zero angle position during the motor operation. A current control strategy using common DC signal for brushless DC machines. In electric traction and most industrial applications, a wide range of speed and torque control of the BLDC motor is required. This current control strategy is based on the generation of quasi-square currents using only one current controller for the three phases. This control strategy uses a triangular carrier for the power transistors which is simpler and more accurate than any other options. The advantages of this strategy are a) control scheme is very simple b) phase currents are kept balanced c) current is controlled through a DC component, and hence phase over currents are eliminated by controlling the torque and speed can be adjusted for a wide range. This proposed control strategy has been compared with conventional techniques to show the excellent characteristic of this modulation technique. A specially designed transformer fed Resonant DC link inverter dedicated for BLDC motor drive system. By deriving the soft switching technique, the optimal control of the resonant operation is achieved. It was confirmed that all the switched devices are operated in the soft switching stat when the switches are turned ON and OFF through the simulation and experimental results. The following observations were made through the proposed resonant DC link inverter. All the high switching frequency switches work under soft switching condition. Voltage stress on all the switches is very low it is not greater than the DC supply voltage. The normal operation of the inverter is entirely the same as that of the hard switching inverter. This arrangement is a simple auxiliare switches control scheme for inverter. Freewheeling diodes were turned off under zero current condition and this greatly reduced the reverse recovery problem of the diodes. As the switching frequency is as high as 25 khz, the switching acoustic noise can be eliminated. Only one DC link voltage notch is needed during one PWM cycle and the switching frequency of the auxiliary switches would not be 42

7 higher than PWM frequency. These analysis have been successfully verified with the simulation results using Multisim Software and Hardware result using MYDAQ. 6.Scope for future work: To develop a simulation and hardware implementation of New cost Effective Four Switch Inverter for BLDC motor, Digital control of BLDC motor drive and also sensor less speed control of BLDC motor drive can be implemented using the PI controller with better performance. The proposed work can be implemented for a wireless control of three phase BLDC motor using a Zigbee protocol. Zigbee is a low cost, low power, wireless mesh networking standard based on IEEE Conventional PI controller was considered in this research work. A fuzzy logic or adaptive control procedure may be used to get improved performance characteristics. References [1] ECEN 5807: Modelling and Control of Power Electronics Systems. Supplementary Notes and Materials. Chapter 16. Harmonics in Power Systems. [2] Huai Wei. Issa Batarseh: Comparison of Basic Converter Topologies for Power Factor Correction. Southeastcon '98. Proceedings. IEEE. pp April ISBN: [3] B. Singh, Recent advances in permanent magnet brushless DC motors, Sadhana, Vol. 22, Part 6, pp , Dec [4] B. Singh, B. N. Singh, A. Chandra, K. Al-Haddad, A. Pandey and D.P. Kothari, A review of single-phase improved power quality AC-DC converters, IEEE Trans. Ind. Elect., vol.50, no. 5, pp , Oct [5] Vashist Bist. Bhim Singh: An adjustable-speed PFC Bridgeless Buck-Boost Converter-Fed BLDC Motor Drive. IEEE Transactions on Industrial Electronics. vol. 61. no. 6. pp June [6] E. H. Ismail, Bridgeless SEPIC Rectifier With Unity Power Factor and Reduced Conduction Losses, IEEE Trans. Ind. Electron., vol.56, no.4, pp , April Components, 16 (1994)