This study examines two distinct configurations of hybrid energy-storage systems for electric vehicles. The first configuration integrates a battery and a supercapacitor in parallel, while the second configuration combines a battery with a photovoltaic (PV) system in parallel. Subsequent sections elucidate the performance of these two configurations.
5.1. Combination of Supercapacitor and Battery Linked in Parallel
In this configuration, the battery and supercapacitor are connected in parallel, as illustrated in
Figure 9a,b. During the starting mode, both the battery and supercapacitor are assumed to be fully charged. Initially, the voltages across the battery and supercapacitor are 40 V and 20 V, respectively, as depicted in
Figure 11. As the drive system starts its operations, the motor draws current from the available voltage sources (i.e., the battery and supercapacitor), causing their voltages to increase, as shown in
Figure 11. Specifically, at 0.03 s, the battery voltage reaches 52 V, and at 0.02 s, the supercapacitor voltage reaches 24 V. Subsequently, the motor speed stabilizes, indicating a constant operating condition.
A boost converter is employed to increase the voltage level.
Figure 9a,b portrays that two boost converters are connected across the energy storage devices and a motor.
Figure 11 represents the battery and supercapacitor voltages with and without boost converter. In starting mode, both sources provide voltage to drive the system. In this mode, the supercapacitor voltage is greater than the battery voltage because, initially, it is assumed that the supercapacitor is in a fully charged condition. In the presence of the inductor in the boost converter, the voltages increase linearly up to 0.02 s. After 0.02 s, the capacitor is discharged so that the voltage across the supercapacitor decreases as compared to the battery voltage. The maximum flux is developed in the boost converter’s inductor to provide constant voltage to the motor. The drive system runs continuously at constant supply from 120 V to 135 V.
When the motor is connected to both supply voltages, current flows through the windings and flux is established within them. Initially, both sources are assumed to be fully charged. The supercapacitor initially delivers a very high current of 9 A as shown in
Figure 12a. As the supercapacitor discharges, its voltage gradually decreases, resulting in a reduction in current, as illustrated in
Figure 12a, up to 0.03 s. Simultaneously, the battery supplies voltage and thus, causing the current to rise to 3.8 A due to the motor’s characteristics or behavior as shown in
Figure 12b. When the battery provides voltage, the maximum flux is established in the motor’s winding. Subsequently, the motor operates at a constant current, gradually decreasing to 0.2 A, as depicted in
Figure 12b.
Figure 13 depicts the variations in power output of both the battery and supercapacitor. Initially, the supercapacitor is fully charged, delivering a higher power output of approximately 450 W. As the supercapacitor discharges, its power output gradually decreases to 280 W within 0.03 s. Concurrently, the battery supplies the voltage necessary for the motor operation, resulting in increased power consumption by the motor due to its inherent characteristics.
When the motor reaches maximum flux development, it operates at a constant power level. As illustrated in
Figure 13, the motor power output increases to 420 W and subsequently decreases to 40 W under no-load conditions. Beyond 0.06 s, the motor maintains a steady power output to drive the system.
Figure 14 represents the BLDC motor current when the battery and supercapacitor are connected in parallel. In the BLDC motor for the generation of rotating magnetic field, hall sensors are used. In
Figure 14, Phase ‘A’ is represented in yellow color, Phase ‘B’ is represented in blue color and Phase ‘C ‘ is represented in orange color. Each coil in the BLDC motor is placed at 120° of phase displacement. Initially, no flux is present in the motor winding. Therefore, motor takes a higher current at the initial stage. When all the fluxes are developed in the motor according to requirements, the motor takes a normal current, as represented in
Figure 14.
Figure 15 illustrates the dynamic profile of the motor speed for the battery–supercapacitor configuration. When the supply is connected, the motor’s shaft initiates acceleration, gradually increasing speed from zero. The motor speed exhibits linear growth increment until it reaches 600 rpm. During discharging mode, the supercapacitor supplies a lower voltage than the battery, causing the motor speed to rise linearly till 0.05 s. Subsequently, upon establishing maximum flux in the motor, a constant supply voltage is delivered, leading to a stabilized motor speed of 1500 rpm.
5.2. Combination of Battery and Photovoltaic Module Connected in Parallel
In this configuration, the battery and PV module are connected in parallel, as depicted in
Figure 10. The dynamic voltage profiles of both the battery and photovoltaic (PV) system are illustrated in
Figure 16. Initially, the battery voltage exhibits a linear increase from 48 V to 52 V within the first 0.03 s. Concurrently, owing to fluctuations in solar irradiance levels, the generated voltage by the PV module does not remain constant. To maintain a consistent voltage output, Maximum Power Point Tracking (MPPT) is implemented with the PV module, resulting in a stabilized voltage output of 28 V, as depicted in
Figure 16. Meanwhile, the battery supplies a steady voltage to the motor for operation, and thus, enabling the establishment of maximum flux within the motor winding starting from 0.03 s. Minor deviations in PV voltage occur in response to changes in solar irradiance levels.
Figure 17 illustrates the temporal variations of boosted voltages of the photovoltaic (PV) module and the battery.
Figure 10 depicts the configuration in which two boost converters are connected across the energy storage unit and a motor. The voltages supplied by the battery and PV module alone are insufficient to power the system adequately, and thus, necessitating a voltage boost. The voltage levels are elevated to meet operational requirements using the boost converters. During the initial phase, the PV voltage surpasses that of the battery. Between 0.01 and 0.03 s, both voltages exhibit linear increments. At 0.03 s, the PV voltage exceeds the battery voltage due to the presence of an inductor in the boost converter. Subsequently, the converter stabilizes the voltage across the battery and PV terminals at 0.05 s, enabling the PV system to generate a voltage of 138 V consistently.
The variations in the currents drawn by the battery and PV module are depicted in
Figure 18 and
Figure 19, respectively. Initially, the voltage generated by the PV module exceeds that of the battery, resulting in the motor drawing a higher current from the PV module. Between 0.02 and 0.05 s, both sources exhibit linear behavior. At 0.03 s, the battery voltage surpasses the PV module’s voltage, leading to the battery supplying a higher current until 0.05 s. Subsequently, from 0.05 s onward, the PV voltage exceeds the battery voltage, and all current is sourced from the PV module. Under no-load conditions, the system module consistently provides approximately 2 A of current to the system.
Figure 20 represents the BLDC motor current when the battery and PV module are connected in parallel. Phase ‘A’, ‘B’ and ‘C’ currents are represented in blue, red and yellow colors, respectively. Each coil in the BLDC motor is placed at 120° of phase displacement. At the starting condition, there is no flux available in the winding of the motor and therefore the motor initially takes a higher current from the PV module. When all the fluxes are developed in the motor according to requirements, the motor takes a normal current, as represented in
Figure 20.
The variations in battery and PV module power are depicted in
Figure 21. Initially, the voltage of the PV module exceeds that of the battery, leading to the PV module supplying higher power to the motor to drive the system. Initially, the motor consumes 650 W of power, consistent with its operational characteristics, which demand higher power at the outset. As the motor windings reach maximum flux, the power consumption decreases to 550 W. Simultaneously, the battery voltage surpasses the PV voltage, prompting the motor to draw additional power, extracting 500 W from the battery, which diminishes to 150 W within 0.05 s. Subsequently, the motor consistently draws 250 W of power from the supply at a constant voltage.
The variation of motor speed over time is depicted in
Figure 22. Upon connection to the supply system, the motor’s shaft starts accelerating, initiating from zero speed. The motor’s speed increases linearly up to 700 rpm. When slight fluctuations occur in the PV voltage due to variations in the solar irradiation, resulting in a decrease in PV voltage relative to the battery, the motor’s speed resumes in linear increments until 0.05 s. Upon establishing maximum flux in the motor, a constant voltage is supplied, enabling the motor to maintain a steady speed of 1500 rpm.
A comparison of different parameters of both battery–supercapacitor and battery–PV system configurations is presented in
Table 6.