Integrated Starter-Alternator Control System for Automotive - IEEE Xplore

CINTI 2013 • 14th IEEE International Symposium on Computational Intelligence and Informatics • 19–21 November, 2013 • Budapest, Hungary

Integrated Starter-Alternator Control System for Automotive Gheorghe-Daniel Andreescu, Senior Member, IEEE, Cristina-Elena Coman Dept. of Automation and Applied Informatics, “Politehnica” University of Timisoara, 2 Vasile Parvan Blvd., Romania E-mail: [email protected], [email protected] starting torque performances. Furthermore, design improvements for IPM machines are made in [10]. The biaxial excitation generator for automobiles (BEGA) used for ISA in HEVs is proposed and is validated by experimental results in [11]. A sensorless control strategy for BEGA based on the active-flux is applied in [12] in wide speed range. This paper proposes an ISA control system employing a PMSM with voltage source inverter, with field oriented control. The motor / generator mode is given by the torque reference selecting an external torque (for motor mode) or a torque delivered by a dc voltage loop to charge the battery up to 42 V (for generator mode), managed by using the ISA active power. The proposed simulation scenarios resume the physical operating modes and load conditions of the vehicle with good dynamic responses.

Abstract—This paper develops a control system for an Integrated Starter Alternator (ISA) used in hybrid electric vehicles. ISA employs a permanent magnet synchronous machine with voltage source inverter, using field oriented vector control with torque reference. The motor / generator mode is given by the torque reference selecting with a switch an external torque (for motor mode) or a torque delivered by a dc voltage loop to charge the battery (for generator mode). The internal combustion engine is simulated by a DC motor with speed control, and the battery is managed by using the ISA active power. The simulation results, based on real scenarios, prove the ability of the proposed ISA control system to work in motor and generator modes with smooth transition between them. The scenarios include the motor mode with starting and added demanded mechanical torque, and the generator mode to charge the battery up to 42 V, with good dynamic responses.

II.

I. INTRODUCTION Hybrid and electric vehicles are developed in order to reduce pollution, especially in city areas, and to increase energetic efficiency. The electric vehicles (EV) have relative short autonomy per battery charge, and therefore hybrid electric vehicles (HEV) are more suitable. For high electric power demand, the battery dc bus has increased from 14 V to 42 V. A solution for cost reduction is to substitute the starter and alternator machines with a single integrated starter-alternator (ISA) that can work in both motor and generator mode. Studies to determine the best topology and control strategy of the ISA are made in [1]. One choice for ISA in automotive industry is the induction machine (IM). In [2] is presented a topology for integrated starter generator (ISG) with IM using direct torque control (DTC) on 42 V bus. Other studies [3], [4] employ IM for ISA driven by a direct rotor flux oriented control (DFOC) connected to the 42 V bus, with the advantage of predicting ISA regulated dc voltage developed during load dump and sudden speed change. The PM-assisted reluctance synchronous machines (PM-RSM) prove to have high peak tangential force densities, moderate saturation level, 90% efficiency for high speed (over 2000 rpm) and the advantage that the PM does not demagnetize at peak torque [5]. Direct torque and flux control with space vector modulation (DTFC-SVM) strategy is used for an experimental PM-RSM sensorless control in [6] proving effectiveness for low to high speed. Another recently prototype for ISA is the permanent magnet synchronous motor (PMSM) [7]. In [8] a PMSM with fractional-slot winding prototype is built and tested, and the results show high torque and satisfactory fluxweakening operating region. Segmented PMSM prototype is studied in [9], with reduced cogging torque and high

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ISA MODELING AND CONTROL

A. ISA Model In this paper a PMSM is used for ISA, with the model in dq rotor reference frame given by the equations: dλ (1) vd = Rs id + d - ωr λ q dt d λq vq = Rs iq + + ωr λ d (2) dt λ d = Ld id + λ PM ; λ q = Lq iq (3)

Te =

3 ⎡ p λ PM + Ld − Lq id ⎤ iq ⎦ 2 ⎣

(

)

(4)

dω m ω (5) = Te − TL − Bω m , ω m = r dt p where vd, vq and id, iq are the stator d,q voltage and current components, respectively, Rs is the stator resistance, Ld and Lq are dq axis inductances, ωr is the electrical rotor speed, ωm is the mechanical rotor speed, p is the number of pole pairs, λPM is the PM flux, Te is the electromagnetic torque, J is the equivalent inertia, B is the viscous friction coefficient, and TL is the load torque. The PMSM parameters are given in Table I. J

B. DC Motor Model The internal combustion engine (ICE) is modeled using a DC motor with the model given by: di va = Ra ia + La a + kV ωm (6) dt TE = kT ia (7) where va, ia is the armature voltage and current,

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G.-D. Andreescu and C.-E. Coman • Integrated Starter-Alternator Control System for Automotive

respectively, Ra, La is the armature resistance and inductance, respectively, ωm is the mechanical rotor speed, kV is the back-EMF constant, TE is the electrical torque and kT is the torque constant. The eq. (5) is added. The DC motor parameters are given in Table II. C. Proposed Control System The proposed control system is shown in Fig. 1, where ISA and ICE are mechanical coupled. FOC is the PMSM field oriented control (Fig. 2) with the electromagnetic torque Te* as the control reference, VSI is the voltage source inverter, R-VDC is the PI regulator for battery dc voltage, R-ω is the PI speed regulator of ICE (DC motor), and R-ia is the PI armature current regulator. The ISA (PMSM) motor / generator mode is selected by a switch that gives to the FOC torque reference Te*: i) an external torque TeM* (motor mode), or ii) a torque TeG* delivered by the dc voltage loop for battery charge (generator mode). The ICE (DC motor) has a speed control loop (R-ω) with cascaded current control (R-ia). The mechanical coupled model of ISA (PMSM) and ICE (DC motor) is presented in Fig. 3, highlighting that the total electromagnetic torque TeΣ applied to the mechanical model (5) is the sum between the ICE (DC motor) torque TE and the ISA (PMSM) torque TeMG, which is positive in motor mode and negative in generator mode. At startup, PMSM works as motor with the maximum reference torque TeM needed to power the ICE. After establishing the desired mechanical rotor speed, the PMSM switches to generator mode with the TeG as reference torque given by R-VDC. If there is a requirement for an added mechanical motor torque to ICE for faster acceleration, then ISA switches in motor mode.

Figure 3. Mechanical coupled model of ISA and ICE

Figure 4. Battery model with auxiliary loads R1 and R2

The battery model [13], given in Fig. 4, [13]has the parameters given in Table III: V0, R0, R and C, and with auxiliary loads R1 and R2. To obtain 42 V battery, three 14 V batteries are connected in series. The chosen command variable is the battery current ibatt computed by using the PMSM active power P (8) given by the reference stator voltages vα*, vβ*, and the measured stator currents iα, iβ (Fig. 2).

(

P = 3 / 2 v*αi α + v*βiβ

III. SIMULATION RESULTS Simulation tests are performed to prove the performance of the ISA proposed control system presented in Fig. 1, with details specified in Figs. 2-4. The simulation environment is MATLAB/ Simulink®, with a 100 µs sampling rate. The PMSM and DC motor models given by eqs. (1-7), and the associated mechanical coupled model from Fig. 3 are used. In order to show the performances of the proposed solution, two case scenarios are developed: The first scenario is created to simulate the real events for ISA, and to show the performance of the proposed ISA control system in motor/generator modes: startup, cruising, acceleration with added mechanical torque, and again cruising. The imposed speed profile contains the following phases: acceleration only with ISA in motor mode until 50 rad/s; starting ICE and cruising at 50 rad/s with ISA switched in generator mode; acceleration until 100 rad/s as generator, then acceleration until 150 rad/s as motor, and finally cruising at 150 rad/s as generator. In this scenario, Fig. 5 shows the dynamic responses for the mechanical speed ωmec, ISA torque Te, ICE torque TE, the ISA active power P and the dc voltage VDC. At startup, i.e., acceleration to 50 rad/s in 2.5 s, ISA operates as motor with positive maximum torque TeM = 19 Nm, and ICE is not started (TE = 0). The dc voltage drops because the current ibatt flows out of the battery. When 50 rad/s is reached, ICE starts and a 50 rad/s cruising speed is regulated by ICE speed controller. ISA is

- VDC ibat

R-VDC

TeG*

Te*

vs *

FOC

TeM*

vs VSI

ISA (PMSM)

is

is

θ ω ia ω*

ω -

ia* R-ω

ia -

ua* R-ia

(8)

The ibatt flows in/out the battery for charging/ discharging, respectively, depending on the P sign. ibatt = P / V0 (9)

battery

VDC*

)

ICE (DC Motor)

Figure 1. Proposed ISA control structure with simulated ICE

2 3 pλ PM

Figure 2. FOC strategy with id*=0 and torque reference as input

340

VDC [V]

TE [Nm]

Te [Nm]

wmec [rad/s]


Figure 5. Dynamic responses of the proposed ISA control system for the first scenario in motor/generator modes: mechanical speed ωmec, ISA torque Te, ICE torque TE, ISA active power P, battery dc voltage VDC

Figure 6. Dynamic responses of the proposed ISA control system for the second scenario with R2 load resistance switch off and switch on: mechanical speed ωmec, ISA torque Te, ICE torque TE, ISA active power P, battery dc voltage VDC

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G.-D. Andreescu and C.-E. Coman • Integrated Starter-Alternator Control System for Automotive

TABLE I.

switched to generator mode with the negative torque reference Te given by the dc voltage regulation loop for battery charge, while ICE develops a positive torque TE. In this period the DC voltage increases to the 42 V reference, ibatt current flows in the battery for charging. At time 10 s, ICE accelerates with maxim torque TE = 60 Nm until 100 rad/s (time 11 s), when ISA is switched to motor mode to obtain an added torque of Te = 19 Nm for better acceleration. At 150 rad/s ISA is switched to generator mode and a 150 rad/s cruising speed is regulated by ICE speed controller. The second scenario is created to show the performance to reject load disturbance of the dc voltage regulation loop for battery charge in ISA generator mode, with dynamic responses presented in Fig. 6. At startup until 100 rad/s, ISA operates in motor mode with maximum torque TeM = 19 Nm, and ICE is not started (TE = 0). When the speed reaches 100 rad/s, ICE starts to run with 100 rad/s cruising speed regulated by ICE speed controller, and ISA is switched to generator mode. After the dc voltage reaches steady state of 42 V, the resistance R2 = 5 Ω is switched off at 20 s, and back on after 2 s. In the R1 and R2 parallel connection, if R2 is interrupted then the load resistance increases, and thus the ISA torque Te, the ICE torque TE and the ISA active power P decreases. The simulation results from Fig. 6 prove good load disturbance rejection of ISA control system.

PMSM (ISA) PARAMETERS

Rated power (Pn) Rated torque (Te) Rated mechanical speed (ωrn) Number of pole pairs (p) Stator resistance (Rs) d-axis inductance (Ld) q-axis inductance (Lq) Permanent magnet flux (λPM) Equivalent inertia (J)

3.3 kW 19 Nm 157 rad/s 2 0.01 Ω 0.5 mH 0.5 mH 0.06 Wb 1 kgm2

TABLE II. DC MOTOR (ICE) PARAMETERS Rated power (Pn) Rated torque (TE) Rated mechanical speed (ωrn) Armature resistance (Ra) Armature inductance (La) Torque constant (kT) Back-EMF constant (kV)

10 kW 60 Nm 157 rad/s 0.4 Ω 0.02 H 1.5 Nm/A 1.5 V/rad/s

TABLE III. BATTERY PARAMETERS Internal resistance (R0) Load resistance (R1) Load resistance (R2) Resistance (R) Capacitor (C) Voltage source (V0)

0.024 Ω 5Ω 5Ω 0.06 Ω 20 F 42 V

REFERENCES [1]

IV. CONCLUSION This paper develops an ISA control system for automotive applications. ISA employs a PMSM with field oriented vector control (FOC) having the electromagnetic torque as control reference, and a voltage source inverter supplied by 42 V battery. The internal combustion engine (ICE) is simulated using a DC motor with speed control. The main paper contributions are the following: • The ISA motor / generator mode is selected by a switch that gives to the FOC torque reference an external torque (motor mode), or a torque delivered by a dc voltage loop to charge the battery to 42 V (generator mode). • The battery is managed in simulation by using the ISA active power. • The simulation test results, based on real scenarios, prove good performance of the proposed ISA control system in motor / generator mode, and with good load disturbance rejection. The scenarios include the motor mode: starting, and added mechanical torque to ICE at request, and the generator mode to regulate the battery voltage to 42 V, with good dynamic responses.

[2]

[3]

[4]

[5]

[6]

[7]

ACKNOWLEDGMENT This work was partially supported by the strategic grant POSDRU/107/1.5/S/77265 (2010) within the Sectoral Operational Program for Human Resources Development 2007-2013, Romania, co-financed by the European Social Fund - Investing in people.

[8]

[9]

APPENDIX

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