EMS of Electric Vehicles using LQG Optimal Control

EMS of Electric Vehicles using LQG Optimal Control, PG Student of EEE Dept, HoD of Department of EEE, JNTU College of Engineering & Technology, JNTU College of Engineering & Technology, Ananthapuramu Ananthapuramu Abstract This paper proposes a strategy of a frequency separation-based coordinating power sources within offgrid applications. One of the application is an electric vehicle equipped with two power sources that is ultracapacitor (UC) and a battery, the interaction problem between can be formulated and solved as a linear quadratic Gaussian (LQG) optimal control problem. The two power sources that is battery and ultracapacitor are controlled according to their respective frequency range of specialization to share the stochastically variable load therefore the main source battery supplies the required power for low-frequency variations, whereas ultracapacitor supplies power for high-frequency. The system chosen for applications should be bilinear; the system can be modelled as linear parameter varying system. The entire operating range is designed and coupled with a gain-scheduling structure based on LQG optimal control structure this is done by using MATLAB simulation. Index Terms-- Energy management system (EMS), Electric vehicles (EVs), gain scheduling. I. INTRODUCTION Now a days pollution is main problem as well as lack of electricity is major issues in india. Especially Indian capital city New delhi is facing so much pollution problem. Renewable energy sources are the energy sources for building a sustainable development and environment friendly energy. Among all the renewable energy sources, the solar energy is most considered one of the best promising renewable power generation technologies. However, seasonal climatic conditions and the geographic can affect the solar energy output [1]. Where as in order overcome pollution problem electrical vehicles are best solution and if it is zero emission vehicles then it is very best solution to reduce air pollution.[2] Power supply systems onboard of all electric vehicles are working on base of various 141 technologies, for example battery packs. The reliability and lifetime of battery packs depends on technology and operating regimes. so replacement of battery leads to ecological and economic problems. UCs is other approach for the power flow within various electrical system application, that is renewable energy generation systems, portable power supplies, uninterruptible hybrid and electric transportation. The benefits of a ultracapacitor system are having more capacity as well as energy management control. in order to achieve optimization of battery and ultracapacitor energy storage system[3],[4] For wide operating temperature range, fast charging and for long life cycle, relatively high-specific power and able to support high-frequency variations of power demand. From above characteristics UC treated as a high power-density supplies used for the supplement main high energy density sources, as fuel cells or a lead-acid batteries, which are used to supply for the low-frequency variations for the power demand [5] This paper deals with a power supply structure having a battery as main source (MS) and an UC pack as a secondary source, which is used for smoothing power delivered by the battery. In urban areas the EVs on road experiencing variable and random load current in response because of unsteady traffic i.e., frequent up hill, or downhill runs, acceleration, deceleration. Their PSS should have control structure that implements power sharing strategy between battery and UC packs to reduce the variations of battery current therefore the lifetime of system is more. This process is done with the help of MATLAB Simulink. A general strategy for the power source coordination is designed to a certain power flow

configuration that corresponds to a two-source off - grid applications. For a battery and UC system a linear quadratic Gaussian (LQG) is the solution for designing an energy management system. This improves the battery exploitation and increases its lifetime. This paper consists of following sections: Section II presents the features of PSS configuration which are considered in this paper, And a proposed general approach of energy management design. Section III presents the architecture of the EV PSS based on two sources, a battery and an UC. Section IV the basic structure of the proposed optimal energy management system (EMS) is done. Section V presents the PSS modelling and the details on control design. Section VI discusses the simulation results obtained on a. Finally, the conclusion is discussed in Section VII. II. GENERAL APPROACH FOR ENERGY MANAGEMENT SYSTEM DESIGN Fig. 1 shows the General power flow configuration and EMS for a two-dc DC sources (PSS) which are used for off-grid applications. It is about a two- DC DC-source system consists of the main source (MS) and the auxiliary source (AS) coupled to a DC bus with the help of bidirectional DC DC converters which supplies a reversible load. This configuration can be found easily in a large palette of applications which includes renewable energy conversion systems [6]. Assumption is DC bus voltage is supposed constant which is regulated by the MS. By each source have the same output voltage they can work as current sources that is power flow is managed with the controlling current injected into the DC bus by each source.. Fig.1 General power flow configuration and EMS for a two-dc DC-source PSS and DE 142

Fig 2: EV Power chain consists of the PSS and the DE The EMS is designed by assuming that MS current is controlled to ensure that of DC bus voltage regulation by means of a two-loop control structure, outer closed loop represents the plant for the subsequent control design approach for Fig1. This loop is modelled as a linear system in which variations around the operating point. The main source current inner closed-loop dynamics are neglected as they are much faster than outer loop dynamics; for the linear system, is obtain from high-pass filters (HPFs) represented in transfer function By using AS we have benefits for example in order to protect MS, HF acts as backup source, and also supplies a fast-variable current to enhance the fast variations of load current of dc link because the LF which has slowly variable load current. The HF variations of load current of Fig 1 act as a disturbance to DC-link voltage and it can be rejected by using an AS. It is the implementation of the frequency separation of the two sources.. III. POWER SYSTEM SUPPLY CONFIGURATION AND PROBLEM FORMULATION PSS is shown in left side of Fig. 1 which consists of MS and AS. The main source that is battery provides constant voltage which is denoted by E, 143 secondary source is nothing but UC. Both MS and AS are bidirectional which is obtained by using two quadrant DC-DC converters to which they supply to common DC link. And their output currents arei L1 for battery and i L2 for UC, and they are injected into common DC link to balance the i L load current. The above converters are Insulated Gate Bipolar Transistors (IGBTs) which are based upon pulse width modulation control. IGBTs provides the bidirectional characteristics i.e., power flows from source to load as well as load to source that is discharging mode and charging mode respectively. Therefore v DC. is balanced between supply and load section. In driver s environment (DE) which is shown in right of Fig 1, due to driving conditions and vehicle speed reference variation, the vehicle dynamics and its electromechanical drive are given to external perturbations. Fig 3 represents the simulation drivers environment. The motor which we used here is PMSM i.e., permanent-magnet synchronous motor. PMSM can be used as a motor as well as generator. In accelerating period the PMSM can be used as motor, while in decelerating period the PMSM can be used as generator. By using charging of power sources PMSM supplies the power to DC link. The speed of the vehicle will be set as a set point with the help of speed controller. The torque

of PMSM is controlled with the help of 3-phase VSI (voltage source inverter) which is coupled with DC link. 144 Fig 3: Drivers environment (DE) Fig 2 represents a control structure that implemented the current or torque given by the vehicle driver. The speed corresponding to driving condition is given in the form of current drawn from DC link which is treated as load for PSS. The PSS, DE interacts with each other by draining power from DC link. Fig 4 Proposed EMS. Actual motion of vehicle of drivers action is translated into current injected by the electromechanical drive from the DC link and viceversa. The PMSM current is limited by using vector control as shown in Fig 2 energy flowing to load has to ensure correctly with the help of EMS by using of two converters that is battery as well as ultracapacitor irrespective of driving conditions. DC link allows a constant value of voltage, with drive having good dynamic performance and with natural operation of permanent magnetic synchronous motor inverter with the help of internal currents limitation, and the maximum voltage at UC terminals. Therefore, EMS has to be designed based upon the optimal frequency-separation based control strategy detailed as in Section II. LF variations of i L are drawn from battery, whereas HF variations are drawn from UC by using gain scheduling. In this way the exploitation of battery is improved. IV.PROPOSED OPTIMAL ENERGY MANAGEMENT SYSTEM FOR ELECTRIC VEHICLE Generally the system is a nonlinear model and is subjected to a stochastic perturbation that is load current, i L. Linearization of operating points will gives us to set of linear systems. In simulation we used the linear system those parameters depend on operating point. A performance index allows to obtain control input as the solution for the LQG control problem which is represented in the form of transfer function. Fig. 4 shows the control diagram of EMS. Consider our system is to be linear, in that the load current i L is always to be constant therefore the two sources closed loop has to maintain the constant DC link voltage that v DC and gradually v UC as a ultracapacitor voltage, because of this closed loop dyanamics becomes very slow, therefore UC voltage is allowed to vary within a range. Therefore the system has to operate at steady state, it implies the battery is only providing the whole current where as the UC controller does not provide anything (that is it provides zero current ( i uc 0). If we neglect the battery current of a closed-loop dynamics with respect to the outer DC-link that is voltage loop dynamics, then i bat remains same. The linear system contains, battery current variation and DC-link voltage variation as states of the linear system. Therefore, variations of the two currents has now become a state performance maximization and minimization. V. CONTROL DESIGN In this section, we deal to obtain the linear model of the DC-link voltage control loop. This modelling will allow to presented the stated control problem into the formalism of LQG. Fig 5 GAIN SCHEDULING

As we implemented the EMS as shown in Fig 4 as discussed in section IV, we use gain scheduling which is represented in Fig 5. This is done by using math functions along with gain controllers in simulation. After the implementation of EMS Fig 4 it is equipped with power systems of system as shown in Fig 2. To that the DE Fig 3 is coupled to the Dc link as shown in Fig 2. The Drivers environment is designed as shown in Fig 3, in that we set the reference speed and convert it speed in terms of rps. Linearization of the system allows to use a PI controller for the DC-link voltage Control. Where the PI (Proportional integral) having transfer function is Kp(1 + 1/(Ti s)). We use the current converter to convert two phase current to three phase current. We used PWM inverter to convert the three phase current into three single phase voltages. And this three single phase voltages are given to the PMSM model, and the output of PMSM model are in terms of speed, torque as well as currents..vi.simulation RESULTS 1. EMS OUTPUT The battery and ultra capacitor voltages are represent above with respect to time in milli seconds. 2. The speed, torque and current of a PMSM The Permanent magnet synchronous motor is torque control by using three phase voltage source inverter coupled with DC link. The speed, torque and current characteristics of a PMSM are given above. 3. Output voltage of a DC link VII. CONCLUSION This paper deals with a power source coordination for a electric vehicle, to which frequency separation- based energy management system is proposed. battery used as a main power source where as an UC bank is treated as auxiliary source and used controlled to support sudden variations of power demand in the system. The PSS configuration is used to a larger class of systems: it indicates upon the parallel connection of two sources to a common DC link, and then connected to the load. Power is supplied to motor by regulating DC-link voltage. An LQG control approach with the gain scheduling scheme is used for optimally size the trade off between battery and UC current variations further UC has been modelled as actuator element. In such a way UC prevents HF disturbances coming from load at DC-link voltage level. In such a battery exploitation is improved and the lifetime of battery is preserved. The proposed energy management system approach is general because it can be used for a large consideration of power supply. Future work may be used to design of source coordination strategies to the configurations having more than two sources. LQG control technique cannot applicable for configurations having more than two sources in such case H techniques is used for operation of each source with a distinct frequencies for a linear parameter varying techniques REFERENCES [1] E. M. Natsheh, A. R. Natsheh, and A. Albarbar, Intelligent controller for managing power flow 145

within standalone hybrid power systems, IET Sci., Meas. Technol., vol. 7, no. 4, pp. 191 200, 2013. [2] A. Florescu, I. Munteanu, A. I. Bratcu, and S. Bacha, Frequency separation based energy management control strategy of power flows within electric vehicles using ultracapacitors, in Proc. 38th Annu. Conf. IEEE Ind. Electron. Soc. (IECON), Montréal, QC, Canada, Oct. 2012, pp. 2957 2964. [3] E. Ozatay, B. Zile, J. Anstrom, and S. Brennan, Power distribution control coordinating ultracapacitors and batteries for electric vehicles, in Proc. Amer. Control Conf. (ACC), vol. 5. Boston, MA, USA, Jun./Jul. 2004, pp. 4716 4721. [4] E. Faggioli, P. Rena, V. Danel, X. Andrieu, R. Mallant, H. Kahlen, Supercapacitors for the energy management of electric vehicles, J. Power Sour., vol. 84, no. 2, pp. 261 269, 1999. [5] P. Thounthong, S. Raël, and B. Davat, Control strategy of fuel cell and supercapacitors association for a distributed generation system, IEEE Trans. Ind. Electron., vol. 54, no. 6, pp. 3225 3233, Dec. 2007. [6] M. H. Nehrir et al., A review of hybrid renewable/alternative energy systems for electric power generation: Configurations, control, and applications, IEEE Trans. Sustain. Energy, vol. 2, no. 4, pp. 392 403, Oct. 2011. V.ANUHYA is pursuing her M.Tech in Control Systems at JNTU College of Engineering & Technology, Ananthapuramu, Andhra Pradesh, India. Dr R.Kiranmayi is presently working as HOD in Department of EEE, JNTU College of Engineering & Technology, Ananthapuramu, Andhra Pradesh, India. Her research areas are Electrical Power Systems, Photo Voltaic Systems. Her publications include 14 International Journals, 5 International conferences and 4 National Conferences. R.Kiranamayi is Life Member in Indian Society for Technical Education and The Institute of Engineers. 146