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1 Hybrid Electrical Vehicle Driven By BQZSI Fed Induction Motor Drive N.Vinay Vardhan 1, P. Ram Kishore Kumar Reddy 2 1 PG Student [PEED], Dept. of EEE, MGIT, Hyderabad, Telangana, India 2 Associate Professor and Head, Dept. of EEE, MGIT, Hyderabad, Telangana, India Abstract: With the increase in oil price and global warming, automobile manufacturers are producing more hybrid electric vehicles (HEV) and electrical vehicles (EV). Many research efforts have been focused on developing efficient, reliable, and low cost power conversion techniques for the future new energy vehicles. This paper proposes a new closed loop speed control of an induction motor fed by a bidirectional quasi Z source inverter (BQZSI), the speed control is based on the indirect field oriented control (IFOC) strategy. The IFOC is implemented based on a voltage pulse width modulation (PWM) with voltage decoupling compensation to insert the shoot through (ST) state within the switching signals. The proposed speed control method, with reduced DC input voltage compared with the standard adjustable speed drives (ASD) using voltage source inverter (VSI), are able to change the motor speed from zero to the rated speed with the rated load torque. The performance of the proposed speed control methods is verified by MATLAB simulation of a 15 kw induction motor fed by a BQZSI. The simulation results during different operation modes verify the validity of the proposed closed loop speed control method. Keywords: Hybrid Electrical Vehicle, BQZSI, IFOC, Induction Motor, Shoot Through. 1. INTRODUCTION The traditional ASD system is based on a VSI, which consists of a diode rectifier frond end, dc link capacitor, and inverter bridge. It suffers from some common limitations and problems, such as: the obtainable output voltage is limited far below the input line voltage, voltage drops can interrupt an ASD system and shut down critical loads and processes, and the performance and reliability are compromised by the VSI structure from mis-gating, dead time, common mode voltage. A recently developed Z-source inverter (ZSI) has a niche for ASD systems to overcome the above problems. It can produce any desired output ac voltage, even greater than the line voltage, provide ride-through during voltage droops without any additional circuits, improve the power factor and reduce harmonic current and common-mode voltage. The ZSI, as shown in Fig. 1-a, can utilize the ST state to boost the input voltage, which improves the inverter reliability and enlarge its application field [1]. In comparison with other power electronics converters, it provides an attractive single stage dc-ac conversion with buck-boost capability, reduced cost, reduced volume and higher efficiency due to a lower component number [2]. The basic ZSI topology has some significant drawbacks, namely that the input current is discontinuous in the boost mode and the Z-network capacitors must sustain a high voltage [3]. Discontinuous input current is prohibited for many sources and requires large input filters. To a great extent this shortcoming is avoided in the quasi-z-source inverter (QZSI), as shown Fig. 1-b, by the presence of an input coil in the QZSI buffers the source current [4]. Moreover, voltage on one of the Z-network capacitors is lower than in case of the basic ZSI topology. In addition, it is also possible to develop joint earthing of the input power source and the dc link bus, which reduce the common-mode noise. Hence, the QZSI topology has no disadvantages when compared to the traditional ZSI topology. The QZSItopology therefore can be used in any application in which the basic ZSI topology would be used. (a) (b) Figure 1: (a) Basic ZSI Topology (b) Quasi ZSI Topology In this paper, the IFOC strategy is presented in detail for controlling the speed of an induction motor fed by the BQZSI during motoring and regenerative braking operations. Using the BQZSI with the proposed control strategy as a single stage converter achieves the following advantages: reduced cost and higher efficiency due to fewer components, and reduced volume and easier control implementation compared to traditional or boosted VSI. 2. OPERATION MODES AND MODELING OF THE BQZSI The BQZSI can be obtained by replacing the input diode, D, by a bidirectional switch, S7, to allow bidirectional power flow [5,6]. S7 operates during the regenerative Page 4

2 braking mode and its gate signal is the complement of the ST signal. A third order model, with state variables: capacitor voltage v c, inductor current it, and load current if, of the BQZSI can be illustrated by simplifying the ac side circuit to an equivalent dc RL load in parallel with a switch S2 and the bidirectional switch S7 is represented by a switch S1, as shown in Fig. 2. The two basic operation of the BQZSI are shown in Fig. 3. In mode 1, the energy transferred from the source to the load is zero because the load side and the source side are decoupled by the ST state. In mode 2, real energy transfer between the source and the load occurs. [7] field current and the torque current can be controlled independently. Fig. 4 shows a block diagram of the IFOC technique for an induction motor. Proportional integral (PI) controllers regulate the stator voltages, v ds * and v qs * ' to achieve the reference stator currents, i ds * and i qs *. The required voltage is then synthesized by the inverter using PWM. During motor operation the actual rotor resistance and inductance can vary. The resulting errors between the values used and the actual parameters cause an incomplete decoupling between the torque and the flux. In order to compensate for this incomplete decoupling, the values of compensation voltages are added to the output of the current controllers. This voltage compensation can improve the performance of the current control loops. [12] Fig. 2: A Simplified equivalent of BQZSI Figure 4: IFOC Block Diagram Current controllers are based on PI control technique, these controller blocks calculate the liner component of direct and quadrature axis voltages V ds&v qs respectively. The current PI controllers are designed based on the following equations. Kp=2R 1 T 1 ζω n R 1 (1) Ki=R 1 T 1 ω 2 n(2ζ 2 1) (2) Figure 3: The basic two equivalent operation modes for the BQZSI: (a) shoot through state. (b) Non shoot-through state 3. INDIRECT FIELD ORIENTED CONTROL TECHNIQUE In order to achieve high dynamic performance in an induction motor drive application, vector control is often applied. The principal aim of vector control is to independently control the flux and torque in the induction motor, in a similar way to the control of a separately excited DC motor [8,9]. In the IFOC method, the rotating reference frame is rotating at synchronous angular velocity, ω e [10, 11]. This reference frame allows the three phase currents to be viewed as two dc quantities under steady state conditions. The q-axis component is responsible for the torque producing current, i qs, and the d-axis is responsible for the field producing current, i ds. These two vectors are orthogonal to each other so that the 4. SHOOT THROUGH CONTROL The simple ST boost control method, uses two straight lines equal to or greater than the peak value of the three phase references to control the shoot-through duty ratio in a traditional sinusoidal PWM, as shown in Fig.5. Figure 5: Simple ST boost control method waveforms When the triangular waveform is greater than the upper line, Vp, or lower than the bottom line, Vn, the circuit Page 5

3 turns into ST state. Otherwise it operates just as traditional carrier based PWM. A carrier triangular wave with frequency of 5 KHz and modulation signals from IFOC are inputs for the simple ST boost control. This control method inserts shoot through signal in the pulses and are given to inverter switches. The carrier wave frequency is chosen as 5 KHz such that switching frequency will be 10 KHz. To insert the ST correctly, the switching frequency of the inverter should be constant. That is the reason for not using the hysteresis current controlled FOC scheme because it has a variable switching frequency operation [13]. 5. SIMULATION AND RESULTS In order to verify the proposed closed loop speed control and capacitor voltage control strategies, simulations were carried out using MATLAB Simulink for a 15 kw Induction Motor using the parameters in Table 1. is given to IFOC block. The IFOC block estimates torque, flux from the given inputs and calculates the reference stator currents i*ds &i*qs. These are used to calculate the Stator reference voltages V*ds & V*qs by voltage decoupling method. The stator reference voltages are converted to abc axis and are fed to PWM block which uses these signal as modulation signals to generate switching pulses with inserted shoot through signal. These pulses are fed to inverter and the complement of ST signal is given to bidirectional switch which operates during regenerative mode. Fig. 6 shows the entire closed loop system containing: the input battery, the BQZSI, PWM control and the IFOC speed control, the IFOC generates the modulation index according to the operating conditions & PWM (Simple ST Boost Control) generate the switches pulses. Figure 7: Motor Speed Figure 6: Closed Loop control of BQZSI Fed Induction Motor Table 1: Simulation Specifications Then the vehicle was decelerated (Regenerative braking) to two third of the rated speed during the time interval sec, from the motor was run at constant speed. Then the motor again decelerated (Regenerative braking) to standstill speed i.e. zero speed during the time interval and the motor was operated at standstill in the period sec. Fig. 7 shows the comparison of actual rotor speed (Green) with reference speed (Blue), the result is accurate as the actual speed followed the reference speed. This MATLAB results validate that the operation of Induction Motor at different conditions using the proposed control method is satisfactory. The Bidirectional Quasi Z-Source Inverter fed Induction Motor will be controlled by indirect field oriented control or feed forward vector control method as discussed earlier. The speed feedback & stator currents from motor Figure 8: Motor Torque Page 6

4 Figs. 7 9 show the BQZSI fed Induction Motor response during the motoring and regenerative braking operation modes. The system is operated in different operation modes, as shown in Fig.7: the acceleration mode with the rated torque during the time interval sec, the steady state operation mode with the rated torque and the rated speed during the time interval sec. Figs show state if charge (SOC), current and voltage of the input battery and their variations during the previous mentioned operation modes. The initial state of charge of the battery was taken as 100%. The state of charge (SOC) of battery during the period 0 1 sec is constantly decreasing as the motor is accelerated and running in forward motoring condition during this period. After 1 second the state of charge (SOC) of the battery starts rising as the motor is subjected to regenerative braking during this period. Later the SOC again starts decreasing as motor ran at constant speed during Figure 9: Stator Current Figure 13: DC Link Voltage Figure 10: Battery State of Charge Figure 11: Battery Current Figure 12: Battery Voltage 6. CONCLUSION This paper proposes a new control strategy for the speed control of an Induction Motor fed by a BQZSI as ASD system. This control strategy utilizes the IFOC technique to control the Induction Motor speed during motoring and regenerative braking operation modes. In this control strategy, Simple ST Boost control is used to generate switching pulses. The control strategy is tested during standard (acceleration, steady state, regenerative braking and standstill) and transient (overload, deceleration and light load) operation modes. MATLAB simulations results verify the validity of the proposed control strategy. The application of a BQZSI for ASD system can improve efficiency as it is a one stage converter with a reduced volume and easier control implementation and reduce production cost due to a fewer components. REFERENCES [1] Swapnil N. Rahangdale, Vasant M. Jape Comparative Analysis of ZSI Fed IM Drive And VSI Fed IM Drive With Variable Torque, International Journal of Engineering and Technical Research (IJETR) ISSN: , Volume-2, Issue-3, March [2] Fang Zheng Peng, Senior Member, IEEE "Z- Source Inverter", IEEE Transactions on Industry Applications, Vol. 39, No. 2, March/April [3] Fang Zheng Peng, Alan Joseph, Jin Wang, Miaosen Shen, Lihua Chen, Zhiguo Pan, Eduardo Ortiz-Rivera, and Yi Huang, Z-Source Inverter Page 7

5 for Motor Drives, IEEE Transactions on Power Electronics, Vol. 20, No. 4, July [4] Anderson J, Peng F, Four quasi-z-source inverters, Power Electronics Specialists Conference, PESC IEEE. [5] Omar Ellabban, Joeri Van Mierlo and Philippe Lataire Control of a Bidirectional Z-Source Inverter for Electric Vehicle Applications in Different Operation Modes Journal of Power Electronics, Vol. 11, No. 2, March [6] Haitham Abu-Rub, Atif Iqbal, SkMoin, Fang Z Peng, Yuan Li, Ge Baoming "Quasi-Z-Source Inverter-Based Photovoltaic Generation System With Maximum Power Tracking Control Using ANFIS" IEEE Transactions on Sustainable Energy, Volume 4, No 1, January [7] Omar Ellabban, Joeri Van Mierlo, Philippe Lataire, Control of a Bidirectional Z-Source Inverter for Hybrid Electric Vehicles in Motoring, Regenerative Braking and Grid Interface Operations, Electric Power and Energy Conference (EPEC), 2010 IEEE. [8] Zeraoulia, Diallo D Electric Motor Drive Selection Issues for HEV Propulsion Systems: A Comparative Study Vehicular Technology, IEEE Transactions on (Volume:55, Issue: 6). [9] Technical University Darmstadt's K. Hasse and Siemens' F. Blaschke Method for controlling asynchronous machines US patent No - US A. [10] Fengchen Sun, Jian Li, Liqing Sun, Li Zhai, and Fen Cguo, "Modeling and simulation of vector control AC motor used by electric vehicle", Journal of Asian Vehicles, vol. 3, no. 1, June 2005, pp [11] Mannan, M.A.Murata, T.Tamura, TJ.Tsuchiya, "Indirect field oriented control for high performance induction motor drives using space vector modulation with consideration of core loss," IEEE 34th Annual Conference on Power Electronics Specialist, Vol. 3, pp [12] Abdesselam Chikhi, Mohamed Djarallah, Khaled Chikhi, A Comparative Study of Field-Oriented Control and Direct-Torque Control of Induction Motors Using An Adaptive Flux Observer, Serbian Journal Of Electrical Engineering Vol. 7, No. 1, May 2010, [13] Omar Ellabban, Joeri Van Mierlo and Philippe Lataire, "Experimental study of the shootthrough boost control methods for the Z-source inverter", EPE Journal, Vol. 21, No. 2, pp , Jun BIOGRAPHY N. VINAY VARDHAN received his B.Tech degree in Electrical and Electronics Engineering from KSR Institute of Engineering and Technology, JNTU Hyderabad, Telangana, India in He is currently working towards his M. Tech degree in Power Electronics and Electrical Drives (PE&ED) in Mahatma Gandhi Institute of Technology, Hyderabad, Telangana, India. His interested areas are in the field of Power Electronics, Electrical Drives and also Control Systems. Dr. P. RAMKISHORE KUMAR REDDY received M. Tech from Jawaharlal Nehru technological University, Hyderabad, in the year 2003 and Ph.D from Jawaharlal Nehru technological University, Ananthapur, India in the year He is presently Associate Professor and Head of the Electrical and Electronics Engineering Department, MGIT, Hyderabad. He presented 7 research papers in various national and international conferences and journals. His research areas include Power Systems and control systems. Page 8