Electric Vehicle Motor Control for Regenerative Braking Overcharge Prevention
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Solution Overview
Problem
Electrically powered vehicles face challenges in controlling traction motors during accelerator pedal release to prevent overcharge of power storage devices, particularly due to errors in rotation angle sensors leading to unintentional deceleration torque and excessive regenerative power generation.
Innovation Solution
The vehicle incorporates a motor control unit that includes a DC offset generation unit to superimpose a DC current component on the AC current of the motor generator, a charge/discharge monitoring unit to set a charge power upper limit, and a vehicle control unit to determine and limit regenerative power, ensuring deceleration torque is generated within safe limits while preventing overcharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If regenerative power generation is increased to improve energy efficiency, then energy efficiency is improved, but overcharge of the power storage device occurs
Solution Approach 1:
The patent changes the control parameter from pure regenerative braking to a composite braking mode that includes both regenerative power generation and motor power consumption. By adjusting the duty cycle of the inverter switching elements, the system dynamically controls the balance between regenerative power and motor power consumption, preventing overcharge while maintaining energy efficiency.
Solution Approach 2:
The motor generator acts as an intermediary between the power storage device and the braking system. Instead of directly charging the power storage device during regenerative braking, the system uses the motor generator to convert kinetic energy to electrical energy, then uses inverter control to manage the power flow, preventing excessive charging by dissipating excess energy through controlled motor power consumption.
2Loss of energy
If d-axis current is increased to suppress regenerative power, then regenerative power is suppressed, but unintentional deceleration torque occurs due to rotation angle sensor errors
Solution Approach 1:
The patent extracts the harmful effect of rotation angle sensor errors by eliminating the need for precise angle detection in the power consumption control mode. By controlling the inverter switching elements directly based on detected regenerative power levels rather than through d-q axis conversion, the system removes the dependency on accurate rotation angle data, preventing unintentional deceleration torque.
Solution Approach 2:
The patent replaces the mechanical/electromagnetic control mechanism (d-q axis conversion based on rotation angle) with an electrical control mechanism (direct inverter switching control based on power detection). This substitution eliminates the need for precise mechanical angle measurement while achieving the same power suppression effect.
3Force
If deceleration torque is generated to provide engine braking effect, then braking performance is improved, but regenerative power generation increases causing overcharge
Solution Approach 1:
The patent implements dynamic control of the inverter switching elements to continuously adjust the balance between regenerative power generation and motor power consumption. The duty cycle is dynamically modified based on real-time detection of regenerative power levels and vehicle deceleration requirements, allowing the system to maintain appropriate deceleration torque while preventing overcharge of the power storage device.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively controls the traction motor to prevent overcharge of the power storage device by managing deceleration torque and regenerative power, enhancing the reliability of electrically powered vehicles by reducing the dependency on accurate rotation angle sensor data.
Implementation Method 1
an inverter configured to perform bidirectional DC/AC power conversion between the DC power supply and the motor generator
Implementation Method 2
the motor generator generates vehicle driving force at the time of acceleration while carrying out regenerative power generation for converting the kinetic energy of the vehicle into electrical energy at the time of deceleration such as braking
Implementation Method 3
controlling the inverter to superimpose a DC current component on AC currents of respective phases in the motor generator
Data Source
AI summary
An electrically powered vehicle includes a motor generator configured to be capable of transmitting and receiving torque to and from a driving shaft coupled to a driving wheel; a DC power supply including a power storage device; and an inverter for performing bidirectional DC/AC power conversion between the DC power supply and the motor generator. The MG-ECU controls a plurality of power semiconductor switching elements to be turned on/off in accordance with a torque command value and a state value of the motor generator. When an accelerator pedal is released, the MG-ECU controls the inverter to superimpose a DC current component on an AC current of each phase in the motor generator in accordance with the state of charge of the power storage device.