University of Leicester, United Kingdom
7. Discussion and conclusion
The starter-generator has been tested in the generating mode at different loads as well as at different speeds with the diesel engine serving as the prime mover. The same
battery pack of 300V (nominal) was used as the DC source, and a resistance bank was used as the load. Figure 4.19 shows the phase current and DC bus charging current at 30Nm torque command, for which the speed and charging voltage were 3200rpm and 365V, respectively. The average peak of phase current reaches 116A (corresponding torque is 29Nm) with a 3.33% error in torque/current regulation. The DC bus charging
Time (40ms/Div)
Figure 4.18. Ch1: DC bus current, and Ch2: Phase current (250ms).
Current: Ch1 (20A/Div), Ch2 (100A/Div) 20A/Div
100A/Div Engine cranking
Engine cranking
Time (2ms/Div)
Current: Ch1 (20A/Div), Ch2 (50A/Div)
20A/Div
50A/Div
Figure 4.19. Ch1: DC bus current, and Ch2: Phase current (generation).
Current: Ch1 (20A/Div), Ch2 (100A/Div)
Time (2ms/Div)
20A/Div
100A/Div
Figure 4.20. Ch1: DC bus current, and Ch2: Phase current (generation).
current reaches 23.6A. In this experiment, the input power to the PM BLDC is 9.717kW
( 9.717kW
60 3200
29 2× × =
×
=
=Tω π
Pin ), and the output power delivered to the DC bus
is 8.614kW (Pout =VdcIdc =365×23.6=8.614kW), which corresponds to 88.64%
efficiency for the PM starter-generator system. Figure 4.20 shows the phase current and DC bus charging current at a 36Nm torque command where the speed and charging voltage were 3000rpm and 385V, respectively. The average peak of the phase current reaches 140A (corresponding torque is 35Nm) with a tracking error of 2.77%, and the DC bus charging current reaches 26A. In this experiment, the input power to the PM BLDC
is 11kW ( 11kW
60 3000
35 2× × ≈
×
=
=Tω π
Pin ), and the output power delivered to the
DC bus is 10.01kW (Pout =VdcIdc =385×26=10.01kW) with an efficiency of 91%.
Torque in Nm
Current in amp
Figure 4.21. Average peak of phase current for different torque commands at 4200rpm.
The average peaks of phase currents maintain the linear relationship with torque commands at a constant speed of 4200rpm, as shown in Figure 4.21. Figure 4.22 shows the DC bus charging current vs. speed profiles in the generating mode for different torque commands. From this figure, it can be observed that the DC bus charging current for a certain torque command increases at higher rate with increase in speed of the generator, indicating better efficiencies near the corner speed of 4,750rpm. Table 4.3 shows the
2250 2750 3250 3750 4250
16.25 Nm 13.5 Nm
10.5 Nm 8.5 Nm
DC bus charging current in amp
Generator speed in rpm
Figure 4.22. DC bus charging current vs. speed at different torque commands.
Table 4.3. Efficiency, inputs and outputs at different load conditions
input and output power, and efficiencies at different load conditions in generating mode.
The efficiency increases as the output power increases towards the rated power.
4.5 CONCLUSION
This chapter is dedicated to the advanced controller and hardware design, simulation, and experimentation of the PM BLDC starter-generator subsystem.
Simulations in both motoring and generating modes have been carried out to design the controller and inverter. From the simulation results, it was proven that the selected PM BLDC starter-generator components have enough power and torque production capability to start the 1.9L diesel engine. The simulation also helped in tuning the controller parameters as well as selecting proper inverter rating for the starter-generator drive.
The controller for the high power starter-generator has been implemented in hardware successfully using a 32-bit fixed point digital signal processor (TI DSP TMS320F2812). The experimental results demonstrate the performance of the generator subsystem in different operating modes. The high power density of the starter-generator and a well-designed torque controller enabled the 1.9L diesel engine to start in 250ms, which helps to reduce the tailpipe emissions and engine torque ripple. The current drawn at starting is also minimized. The quick start-stop feature of the engine helps improve fuel economy by reducing unburnt fuel during starting and turning the engine off instead of idling in a vehicle stop situation. The starter-generator was also operated at its highest efficiency point for power generation. The experimental results in the generating mode show that the new high-resolution current sensing board enables excellent current regulation in the controller.
CHAPTER V
INDUCTION MOTOR DRIVE FOR EFFICIENT PROPULSION SYSTEM
The propulsion motor is a key component of the hybrid electric vehicle. In this research, an induction motor drive has been considered for the propulsion system.
Induction motors exhibit high dynamic and static performance in traction applications as well as in HEV applications. Induction motors are cheap, reliable, robust, and have instant power and torque capability as well as wide speed operation range while maintaining a good efficiency. However, the controller needs accurate knowledge of the machine parameters to achieve high performance. Parameter mismatch between controller and the motor detunes the controller, and deteriorates the performance of the motor drive. Therefore, for efficient use of induction motor, an on-line parameter estimation and adaptation technique is necessary. This technique must be simple, reliable, and robust in the event of disturbance and internal noise. The adaptation technique must also be sufficiently simple computationally to be done in real time on a processor. From the modeling of induction motor and control equations, it has been found that rotor resistance is the dominant parameter in the controller. In addition, stator resistance information helps to know the machine temperature that is essential for thermal management. A novel observer based adaptation method for tracking and adapting the rotor and stator resistance in real time is presented in this chapter.
5.1 IMPACT OF PARAMETER VARIATION ON INDUCTION MOTOR