Motor drive device having overvoltage protection circuit
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Solution Overview
Problem
Existing overvoltage protection circuits for synchronous motors require temperature sensors to monitor semiconductor switches, which increase costs and can fail to accurately recognize the suitable timing for redriving the motor, leading to potential failures.
Innovation Solution
A motor drive device with an overvoltage protection circuit that uses a temperature estimation unit to calculate the temperature of a semiconductor switch by employing motor and semiconductor switch constants, eliminating the need for a temperature sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a temperature sensor is provided to monitor the semiconductor switch temperature, then the temperature monitoring accuracy is improved, but the device cost and complexity increase
Solution Approach 1:
The patent replaces the physical temperature sensor with an electrical measurement system. Instead of using a temperature sensor to directly measure the semiconductor switch temperature, the system measures the on-resistance of the switch, which correlates with temperature, and calculates the temperature from this electrical parameter. This substitution eliminates the need for additional temperature sensing hardware while achieving accurate temperature monitoring.
Solution Approach 2:
The patent introduces on-resistance as an intermediary parameter between the semiconductor switch and the temperature measurement system. Rather than directly measuring temperature, the system measures the on-resistance (which changes with temperature) and uses this intermediate electrical parameter to infer the temperature. This intermediary approach allows temperature monitoring through existing electrical measurement circuits without requiring separate temperature sensing hardware.
2Loss of information
If a temperature sensor is provided to monitor the semiconductor switch, then the temperature recognition capability is improved, but the reliability decreases due to potential sensor failure
Solution Approach 1:
The patent replaces the temperature sensor with an electrical measurement system that monitors on-resistance. This substitution eliminates the reliability issues associated with temperature sensors while maintaining the ability to recognize temperature changes. The on-resistance measurement uses existing electrical circuits that are already part of the motor drive system, thereby improving overall system reliability.
Solution Approach 2:
The semiconductor switch itself provides the temperature information through its on-resistance characteristic. Instead of requiring an external temperature sensor, the switch's own electrical property (on-resistance) is used to indicate its temperature state. This self-service approach eliminates the need for separate sensing hardware and improves reliability by using the component's inherent characteristics.
3Reliability
If the motor drive device waits for the semiconductor switch to cool down before redrive, then the safety is improved, but the productivity decreases due to idle time
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors the on-resistance of the semiconductor switch and uses this information to determine when the switch has cooled down sufficiently for safe redrive. The control unit receives the on-resistance value, compares it against predetermined thresholds, and automatically permits or prohibits redrive based on the temperature status. This feedback-based approach optimizes the cooling wait time, ensuring safety while minimizing unnecessary idle time.
Solution Approach 2:
The patent performs preliminary temperature assessment by measuring the on-resistance immediately after the overvoltage protection operation. Based on this preliminary measurement, the control unit can quickly determine whether the semiconductor switch has already cooled down to a safe temperature level, allowing for immediate redrive permission without requiring a fixed waiting period. This preliminary action approach reduces idle time while maintaining safety.
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
Accurately recognizes the temperature of the semiconductor switch at low cost, ensuring safe and efficient operation by preventing redrive until the temperature falls below a predetermined threshold.
Implementation Method 1
a temperature estimation unit configured to calculate an estimated temperature value of the semiconductor switch that rises and then falls by turning on the semiconductor switch
Implementation Method 2
semiconductor switch constants including on-resistance, thermal resistance, and a thermal time constant that are related to the semiconductor switch
Data Source
AI summary
This motor drive device comprises: a motor drive circuit that drives a synchronous motor by supplying AC power to the synchronous motor via power lines; an overvoltage protection circuit that short-circuits between the phases of the power lines by turning on a semiconductor switch when driving of the synchronous motor by the motor drive circuit is stopped and prevents the occurrence of overvoltage due to a back electromotive force between the terminals of the synchronous motor; and a temperature estimation unit that calculates a temperature estimation value of the semiconductor switch by using a motor constant and a semiconductor switch constant, said motor constant including at least one of the inertia and back electromotive force constants of the synchronous motor, said semiconductor switch constant including the on-resistance, thermal resistance, and thermal time constant of the semiconductor switch.