AC Motor Star Point Switching for Overvoltage Protection
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Solution Overview
Problem
The existing drive devices for motor vehicles with three-phase motors and DC voltage sources face issues of undesirable braking torque and overvoltage due to power section failures in the field weakening range, leading to potential damage and inefficiencies, and current solutions like Voltage Protection Modules require additional components and effort.
Innovation Solution
A drive device with a monitoring system that automatically detects malfunctions and controls a switching element to connect the star point of the three-phase motor to either terminal of the DC voltage source, preventing feedback into the battery unless safe conditions are met, thereby preventing dangerous braking torque and overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the field weakening range is reduced to avoid braking torque and overvoltage problems, then reliability improves, but power density and efficiency deteriorate
Solution Approach 1:
A switching element is introduced as an intermediary component connected between the star point of the three-phase motor and the negative terminal of the DC voltage source. This switching element acts as a mediator to provide a controlled path for feedback current, preventing uncontrolled braking torque while allowing the field weakening range to be maintained for optimal power density and efficiency.
2Reliability
If a Voltage Protection Module with thyristor and six diodes is used to prevent braking torque and overvoltage, then reliability improves, but device complexity increases
Solution Approach 1:
The invention extracts and eliminates the unnecessary diodes from the traditional Voltage Protection Module. Instead of using a thyristor with six diodes, only a single switching element connected to the star point is required. This extraction of redundant components significantly reduces device complexity while maintaining the protective function against braking torque and overvoltage.
3Object-affected harmful factors
If the power transistors are switched off due to driver supply interruption, then safety improves, but harmful feedback torque into the battery occurs
Solution Approach 1:
The invention converts the potentially harmful feedback braking torque into a beneficial controlled process. By providing a switching element that creates a defined current path from the motor phases through the star point to the negative terminal, the harmful regenerative braking energy is redirected through a controlled route, preventing damage while utilizing the energy feedback mechanism safely.
4Object-affected harmful factors
If the battery contactor opens to prevent feedback, then overvoltage protection improves, but component damage risk increases due to uncontrolled energy feedback
Solution Approach 1:
The switching element is positioned and configured in advance to provide a pre-established safe path for feedback current. Before any overvoltage or damage can occur, the switching element is ready to immediately channel the feedback energy through the star point to the negative terminal, preventing uncontrolled energy feedback and component damage while maintaining overvoltage protection.
Data Source
AI summary
The drive device has a high voltage battery (1) that is connected to a three-phase alternating current (AC) motor (4) through a direct current (DC) converter (9). Three terminals (5-7) of AC motor are connected together to form a star point (8) that is connected to a negative terminal (2) or a positive terminal (3) of high voltage battery via a switching element (10) e.g. thyristor or transistor so that the neutral point is switched to potential of one of terminal. An independent claim is included for method for operating drive device.