Bridgeless PFC Cuk Derived Converter Fed BLDC Motor with PID and Fuzzy Logic Controller 1 J. Pearly Catherine, 2 R. Balamurugan Department of Power Electronics and Drives, K.S.Rangasamy College of Technology (Autonomous) K.S.R Kalvi Nagar, Tiruchengode, Namakkal, Tamilnadu, India, Ph./Fax: 04288 274741-44/04288 274860 1 J. Pearly Catherine, R. Balamurugan, email: 1 pearlykpm@gmail.com, 2 nrbals@gmail.com Abstract A bridgeless single phase ac-dc rectifier based Cuk derived converter topology fed BLDC motor is proposed to improvepower factor at the AC mains near to the unity with low THD for PFC applications. It utilizes one control signal over the whole line cycle. In addition, the proposed converter exhibits low inrush current and low magnetic emissions as classical Cuk topology. The partial elimination of s in DBR in the bridgeless topology results in lower conduction losses as compared with conventional Cuk converter. The proposed method is simulated in MATLAB/Simulink with PID and fuzzy logic controller for precise speed control. Simulation results are presented along with the theoretical analysis. Keywords Power Factor Correction(PFC), Total Harmonic Distortion (THD), Diode Bridge Rectifier(DBR), Cuk Derived Converter, Fuzzy Logic Control (FLC) Introduction BLDC motors are most popular in household appliances over the last few decades [1-3]. As the name indicates, it has no brushes for commutation thus eliminates the disadvantages of wear and tear in conventional DC motors. The es are electronically commutated with the help of rotor position detected using hall sensors. Hence the BLDC motor is also known as electronically commutated motor [4-5]. Power quality problems have become important issues in these motors due to the recommended limits of harmonics in supply current by various international power quality standards such as the International Electro technical Commission (IEC) 61000-3-2 [6]. Combination of motor with inverter is the BLDC motor setup.bldc motor is powered with two level inverter.the two level inverter composed of 6 es. Based on rotor position obtained from hall sensors/optical encoders/resolvers, the power electronic es are commutated. A BLDC motor when fed by a bridge rectifier (DBR) has higher conduction losses. The high conduction loss caused by the high forward voltage drop of the bridge begins to degrade the overall system efficiency.the heat generated within the bridge rectifier may destroy the individual s. Hence, it becomes necessary to utilize a bridge rectifier with higher current handling capability or heat dissipating characteristics. This increases the size and cost of the power supply, which is unacceptable for an efficient design. Bridgeless topologies seems to be the best solution for reducing the conduction and ing losses of the converter. Several bridgeless topologies are introduced. Bridgeless boost converter requires an additional converter or an isolation transformer to step down the voltage [10-11].Bridgeless buck converter is limited for step down applications [12-13]. Bridgeless SEPIC converter has large number of semiconductor devices in the current conduction path during each ing cycle and has discontinuous output current resulting in a relatively high output ripple.bridgeless buckboost converter operates with high peak current in power components and poor transient response that makes it less efficient [15-16]. This paper presents a BL Cuk converter-fed BLDC motor drive with constant dc link voltage of VSI for improved power quality at ac mains with reduced components. Section II deals with Cuk derived converter topologies, Section III deals with simulation analysis of the proposed method with PID Controller, Section IV deals with simulation analysis of the proposed method with FLC, Section VI deals with conclusion and future scope of the paper. CUK DERIVED CONVERTER TOPOLOGIES Bridgeless Cuk converter has the following advantages because of its features: 1. Easy implementation of transformer isolation. 2. Natural protection against inrush current occurring at start up or overload current, lower input current ripple. 3. Less electromagnetic interference associated with discontinuous conduction mode (DCM) topology. 4. Cuk converter has both input and output currents with a low current ripple. 5. Can achieve power factor near to the unity. For applications, which require a low current ripple at the input and output ports of the converter, the Cuk converter seems to be a potential candidate in the basic converter topologies. The three new Cuk derived topologies are derived from the conventional PFC Cuk rectifiers [17-19]. The bridgeless Cuk derived converter is a combination of two dc-dc converters. One for each half line period (T/2) of the input voltage. There are one or two semiconductor es in the current flowing path. Current stresses in the active and passive es are further reduced. Circuit efficiency is improved as compared to conventional Cuk rectifier. They do not suffer from high common mode noise problem and common mode emission performance is similar to the conventional PFC topologies.. Power Factor Correction rectifiers are used to improve the rectifier power density and to reduce noise emissions via soft ing techniques or coupled magnetic topologies [7-9]. 57 ISSN 2348-7852 (Print) ISSN 2348-7860 (Online)
(a) Type I (b) Type II (c) TypeIII Figure 1. CUK Derived Converter Topologies The three new Cuk rectifiers are compared based on components count, mode of operation in DCM and driver circuit complexity as tabulated in Table 1. The bridgeless PFC Cuk rectifiers of Fig. 1 utilize two power es (Q1 and Q2). However, the two power es can be driven by the same control signal, which significantly simplifies the control circuitry. TABLE I. CUK CONVERTERTOPOLOGIES IN DCM MODE Item Conv. Cuk Type-I Type- II Type- III Diode 4 slow+1 fast 2 slow+3 2 fast 2 slow+2 Switch fast 1 2(with unidirec tional current capabili ties) fast 2 2 Current Conducti on Path when S W on Current Conducti on Path when S W on Current Conducti on Path in DCM Compone nt Count Number of Capacito rs Driver circuit Complexi ty 2 slow s 3 s ( 2 slow fast) 2 slow s 1 slow with series 2 s ( 1 slow fast) 1 slow 1 body 1 fast 1 slow 2 s( 1 slow fast) - 1 slow 10 11 11 13 2 3 4 3 1 nonfloating 2 nonfloating 1 floatin g + 1 nonfloatin g 2 nonfloatin g Operation of bl cuk converters The choice of mode of operation of a PFC converter is a critical issue because it directly affects the cost and rating of the components used in the PFC converter [20] - [22]. Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM) are widely used in practice. In CCM or DCM, the inductor s current or the voltage across intermediate capacitor in a PFC converter remains continuous or discontinuous in a ing period respectively. To operate a PFC converter in CCM, one requires three sensors (two voltage, one current) while a DCM operation can be achieved using a single voltage sensor. The stresses on PFC converter operating in DCM are comparatively higher as compared with its operation in CCM.By operating the rectifier in DCM, several advantages can be gained such as: 1. Natural near-unity power factor. 2. The power es are turned ON at zero current and the output s are turned OFF at zero current. (a) 58 ISSN 2348-7852 (Print) ISSN 2348-7860 (Online)
(b) Figure 2. Circuits of Type I Cuk rectifier (a)during positive half cycle. (b)during negative half cycle. The mode of operation is an application dependent. CCM is suitable for high power applications and DCM for low power applications. Thus, the losses due to the turn-on ing and the reverse recovery of the output s are considerably reduced. Conversely, DCM operation significantly increases the conduction losses due to the increased current stress through circuit components. As a result, this leads to one disadvantage of the DCM operation, which limits its use to low-power applications (less than 300 W). Hence, DCM is preferred for low-power applications. (a) (b) Figure 4. Circuits of Type III Cuk rectifier (a)during positive half cycle. (b)during negative half cycle. (a) IV. SIMULATION OF CUK CONVERTER FED BLDC MOTOR DRIVE USING PID CONTROLLER A computer simulation model for PFC Cuk converter fed BLDC motor drive is developed using the MATLAB/SIMULINK software is shown in figure. 5. The ing pulse for Cuk converter is generated with the help of PID controller. Single phase ac voltage is given as input to the Cuk rectifier. The voltage source inverter boost the DC voltage of the rectifier and is fed to the BLDC Motor. (b) Figure 3. Circuits of Type II Cuk rectifier (a)during positive half cycle. (b)during negative half cycle. 59 ISSN 2348-7852 (Print) ISSN 2348-7860 (Online)
Figure 5. Simulink Model Using PID Controller The speed control can be achieved by varying the DC link voltage of the inverter. The power factor calculation block is shown in figure 6. Figure 6. Power Factor Calculation Block The power factor of AC mains is 0.88, which is not good. Hence the power quality gets affected. Figure 7. Sub Block for Power Factor Calculation The sub block of power factor calculation is shown in figure 7.The line side voltage and current is taken as input and it is converted into corresponding real and reactive power and the power factor is calculated with the help of math operator blocks. Figure 10. Stator Back EMF with PID Controller The trapezoidal shape back EMF waveform was shown in figure 10. The back EMF waveform is departed from its ideal shape at the time of starting. Later then it regains its original form. V. SIMULATION OF CUK CONVERTER FED BLDC MOTOR DRIVE USING PID CONTROLLER A computer simulation model for PFC Cuk converter fed BLDC motor drive is developed using the MATLAB/SIMULINK software is shown in figure 11. The ing pulse for Cuk converter is generated with the help of hall signals obtained from hall sensors. The speed of the motor is controlled by controlling the DC link voltage of the inverter with the help of fuzzy logic controller. Single phase ac voltage is given as input to the Cuk rectifier. The voltage source inverter boost the DC voltage of the rectifier and is fed to the BLDC Motor. Figure 8. Speed Response The speed response of the BLDC motor is shown in figure 8. Depending upon the loading condition, the PID controller controls the DC link voltage to obtain the constant speed response. Initially the speed is gradually increased and settled to reference value. Figure 11. Simulink block of BLDC motor drive with Fuzzy logic controller The simulation block for AC mains power factor calculation block is shown in figure 12. The display shows the AC mains power factor which could be affected when the motor is connected to the mains. With the help of cuk converter with fuzzy logic ing pulse, the power factor has been improved to 0.98 which is nearer to unity. Figure 9. Electromagnetic Torque with PID Controller The electromagnetic torque waveform is shown in figure 9. It contains more amount of ripple content in its waveform which degrade the performance of the motor. At the time of starting the acceleration of the motor is high because of high starting torque. Figure 12. Power Factor Calculation Block The sub block of power factor calculation is shown in figure 13.The line side voltage and current is taken as input and it is converted into corresponding real and reactive power using real and reactive power Simulink 60 ISSN 2348-7852 (Print) ISSN 2348-7860 (Online)
block. The speed should be linearly varied and settled at 0.07ms. Compared to other controllers, the settling time of the artificial intelligent controllers is minimum. The electromagnetic torque waveform is shown in figure 15. At a time of starting, the torque should be maximum and reduced to nominal value after the motor settled to reference speed. Figure 13. Sub block for power factor calculation The two inputs are taken as speed error and change in speed error for fuzzy logic controller. Thus the decision making rules for FLC for obtaining controlled signal comprises of 11x3 matrices. Based upon these rules the ing pulse for cuk converter is generated corresponding to speed variation. The cuk converter regulates the supply given to the inverter, so that the speed should be maintained at the reference value. TABLE II. RULES TABLE FOR FLC Figure 15. Electromagnetic Torque waveform Due to commutation of inverter, the generated electromagnetic torque contains significant amount of ripple in its waveform. This causes acoustic noise in the motor and performance of the motor gets degraded. As said earlier compared to other bridgeless converters, the type III cuk converter effectively regulates the inverter supply and improves the power factor at AC mains near to unity. The ac-dc bridgeless converter thus reduces the conduction losses and the use of PWM inverter makes it possible to operate at the fundamental ing frequency. The artificial intelligent fuzzy logic controller generates the ing pulses for the Cuk converter. The speed is controlled effectively by controlling the DC link voltage. For the performance evaluation of the proposed drive under input ac voltage variation, the DC link voltage is kept constant as shown in figure 14. Figure 16. Back EMF Waveform The trapezoidal shape back EMF waveform is shown in figure 16. The shape of the back EMF waveform gets collapsed at the time of starting. After the motor settles to the reference value, the non-linearity in the back EMF waveform gets reduced. Figure 14. Speed Response Figure 17. Total Harmonic Distortion The Total Harmonic Distortion (THD) is achieved as 5.46% is represented in figure 17. For any type of load the harmonic level is almost constant. VI. CONCLUSION A comparative analysis of different types of converter topologies for power factor correction in BLDC motors has been discussed. A suitable Type III Cuk Converter seems to be a potential candidate for PFC.The bridgeless Cuk 61 ISSN 2348-7852 (Print) ISSN 2348-7860 (Online)
converter fed BLDC motor drive improves the power factor at the AC mains near to the unity with precise speed control of fuzzy logic controller with low THD. The suitable controller for PFC operation of BLDC motor drives has been analysed. FLC seems to be the best controller in performance improvement of BLDC motor drives for attaining the power factor near to unity.hence the overall system can be implemented in Air-conditioning System.In the future work, renewable energy like Solar, Fuel cell can be used as the source for the system which is useful to reduce the demand of electricity. It also reduces the pollution and greenhouse effect. Controller performance may further improved by using other intelligent control algorithms like genetic-fuzzy and neuro-genetic. As far as the environment aspects are concerned, this kind of hybrid systems have to be wide spread in order to cover the energy demands and in the way to help reduce the greenhouse gases and the pollution of the environment. 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R, An Approach of Power Factor Correction in BLDC Motor Drives Using Cuk Derived Converters TELKOMNIKA Indonesian Journal of Electrical Engineering, vol. 12, Issue 12, pp.8092-8097, December 2014. 62 ISSN 2348-7852 (Print) ISSN 2348-7860 (Online)