Motor Control Device Regenerative Power Management
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Solution Overview
Problem
Existing motor control systems for electric vehicles face challenges in managing regenerative power during disconnection from the DC power supply, leading to increased inter-terminal voltage of capacitors and phase currents, which can cause damage to the inverter circuit and motor.
Innovation Solution
A motor control device with a power conversion circuit and a switching control unit that determines abnormality conditions and selects between three-phase short circuit processing and six-switch opening processing based on motor operating conditions to manage regenerative power, preventing excessive voltage and current levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If six-switch opening processing is executed to stop inverter operation when disconnected from DC power supply, then inverter operation is stopped, but inter-terminal voltage of capacitor increases rapidly causing potential damage
Solution Approach 1:
The patent converts the harmful regenerative power that would otherwise cause capacitor overvoltage into a beneficial braking force. By detecting regenerative operation state and controlling switching elements to connect motor terminals together, the system transforms the harmful electrical energy into mechanical braking torque, protecting the capacitor while utilizing the energy for vehicle deceleration.
Solution Approach 2:
The patent introduces an intermediary control mechanism between the motor and capacitor. The switching control unit acts as a mediator, detecting the regenerative operation state and intervening by connecting motor terminals together through switching elements, thereby preventing direct energy flow to the capacitor and eliminating the overvoltage problem.
2Reliability
If capacitor capacitance and voltage resistance are increased to cope with voltage increase, then capacitor can withstand higher voltage, but inverter circuit size increases
Solution Approach 1:
Instead of increasing capacitor specifications to handle the harmful regenerative power, the patent converts this harmful energy into useful braking force. By controlling switching elements to connect motor terminals during regenerative operation, the system prevents energy from reaching the capacitor, eliminating the need for larger, more expensive capacitor components.
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
The solution effectively suppresses the increase in inter-terminal voltage and phase currents, preventing damage to the inverter circuit and motor, while maintaining a compact and cost-effective design without the need for additional discharge circuits.
Implementation Method 1
three-phase short circuit processing, in which all of the upper stage side switching elements or all of the lower stage side switching elements are switched ON
Implementation Method 2
six-switch opening processing, in which all of the switching elements of the power conversion circuit are switched OFF
Implementation Method 3
a capacitor that smooths a DC side voltage of the power conversion circuit
Implementation Method 4
power stored in a stator coil of the motor is charged to the capacitor via freewheel diodes (FWD) connected in reverse parallel to the switching elements
Data Source
AI summary
A switching control unit that ON/OFF-controls switching elements of a power conversion circuit includes a power supply side abnormality determination unit, and a regeneration abnormality response processing selection unit that selects either three-phase short circuit processing, in which all upper stage side switching elements or all lower stage side switching elements are switched ON, or six-switch opening processing, in which all of the switching elements of the power conversion circuit are switched OFF, as processing to be executed when the power supply side abnormality determination unit determines that a power supply side abnormality has occurred, the three-phase short circuit processing and the six-switch opening processing being selected in accordance with a motor operating condition of the AC motor at the time of the determination.