Regenerative braking system

Details Regenerative braking system Regenerative braking system

1999-09-15

2001-04-24

Donels, Jeffrey (Department: 2837)

Electricity: motive power systems

Braking

Dynamic braking

C180S065310

Reexamination Certificate

active

06222334

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a regenerative braking system for controlling a current flowing through the armature of an electric motor thereby to control a regenerative torque generated in the electric motor upon regenerative braking of a hybrid vehicle.
2. Description of the Related Art
Hybrid vehicles have an internal combustion engine and an electric motor for assisting in the output drive power of the internal combustion engine as propulsive power units for the vehicles. When such a hybrid vehicle is accelerated, the drive power of the internal combustion engine and also the drive power of the electric motor are applied to the drive wheels of the hybrid vehicle. In this manner, the output drive power of the internal combustion engine is reduced, the consumption of the fuel by the engine is lowered, and the exhaust performance of the engine is increased while at the same time the vehicle achieves a necessary acceleration capability.
The electric motor also operates as an electric generator. When the hybrid vehicle is decelerated, the kinetic energy of the vehicle is imparted from the drive wheels to the electric motor, which then operates as the electric generator. When the electric generator generates electric energy, it produces a regenerative torque which is applied to brake the vehicle (regenerative braking). The generated electric energy is retrieved to charge a power supply of the electric motor, e.g., a battery, an electric double-layer capacitor, or the like for effective energy utilization.
The regenerative torque generated in the electric motor is generally controlled by detecting a current flowing through the armature of the electric motor (hereinafter referred to as an “armature current”), and controlling the armature current in a feedback control loop so that the detected armature current will be equalized to a target current according to a given torque command. Specifically, a PWM (Pulse Width Modulation) control process is carried out to vary the pulse duration of a generated voltage outputted from the armature depending on the difference between the detected armature current and the target current for thereby regulating the armature current. With the armature current thus regulated to control the regenerative torque generated in the electric motor, if variations of the power supply voltage are relatively small as when a battery is used as the power supply of the electric motor, then since the ability of the actual current to follow the target current is constant, the regenerative torque generated in the electric motor can well be controlled. However, when a power supply whose output voltage is largely variable, such as an electric double-layer capacitor, is used as the power supply of the electric motor, the controllability of the regenerative torque generated in the electric motor is reduced as the ability of the armature current flowing from the armature to the power supply changes due to variations in the power supply voltage.
The above drawback may be eliminated by a software-implemented servo control process for inputting a detected power supply voltage, a detected armature current, a detected rotational speed of the electric motor, etc. as control parameters, and controlling the armature current depending on these control parameters.
In order to carry out the software-implemented servo control process, however, it is necessary to hold a large amount of data in advance for determining manipulative quantities to control an armature current from the values of the various control parameters, and also to perform complicated calculations for determining the manipulative quantities based on the large amount of data thus held. The complicated calculations need to be carried out at high speed so as not to cause a delay in the control of the electric motor. Consequently, the software-implemented servo control process requires, for its execution, a high-performance CPU and DSP capable of high-speed complex calculations. As a result, the system for effecting the regenerative braking is complex in structure and high in cost.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a regenerative braking system for recovering electric energy generated by regenerative operation of an electric motor to charge a power supply of the electric motor for effecting regenerative braking to generate a regenerative torque depending on a predetermined torque command in the electric motor, comprising current detecting means for detecting an armature current flowing through an armature of the electric motor, a voltage detecting means for detecting a voltage of the power supply of the electric motor, rotational speed detecting means for detecting a rotational speed of the electric motor, target generated power calculating means for calculating a target generated power to be outputted from the armature to the power supply, from the voltage of the power supply detected by the voltage detecting means, the rotational speed of the electric motor detected by the rotational speed detecting means, and the torque command, actual generated power calculating means for calculating an actual generated power actually outputted from the armature, from the armature current of the electric motor detected by the current detecting means and the voltage of the power supply detected by the voltage detecting means, manipulative quantity calculating means for calculating a manipulative quantity to eliminate a difference between the target generated power and the actual generated power, from the difference, and regenerative control means for controlling the armature current of the electric motor depending on the manipulative quantity upon regenerative braking.
The regenerative control means controls the armature current of the electric motor depending on the manipulative quantity calculated by the manipulative quantity calculating means to eliminate the difference between the target generated power and the actual generated power. Stated otherwise, the regenerative control means controls the armature current of the electric motor in order to eliminate the difference between the target generated power and the actual generated power for thereby causing the regenerative torque generated in the electric motor to follow the torque command. Thus, even when the voltage of the power supply suffers large variations, the regenerative control means controls the armature current of the electric motor to suppress the effect of variations of the voltage of the power supply, so that the regenerative torque generated in the electric motor can follow the torque command with high accuracy.
If the voltage of the power supply of the electric motor increases by retrieving the electric energy generated by the electric motor, then since the difference between the voltage of the electric motor and the voltage of the power supply is reduced, the armature current flowing from the electric motor to the power supply is reduced. When the armature current is reduced, the regenerative torque generated in the electric motor may become smaller than the torque command. In such a case, the actual generated power is reduced, resulting in an increase in the difference between the target generated power and the actual generated power, so that the manipulative quantity calculated by the manipulative quantity calculating means increases. The regenerative control means increases the armature current of the electric motor depending on the manipulative quantity, i.e., to increase the actual generated power to eliminate the difference between the actual generated power and the target generated power. Therefore, even if the voltage of the power supply increases, the armature current of the electric motor is prevented from being reduced, allowing the regenerative torque generated in the electric motor to follow the torque command.
Because the manipulative quantity can be calculated by a simple calculating process, e.g., a PI (proportional plus integral) process, it is no

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