Motor Drive Control System Voltage Limiting for Switching Loss Reduction
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Solution Overview
Problem
Existing motor drive control systems face challenges in suppressing heat generation in switching devices during motor lock conditions, leading to potential thermal breakdown and increased noise, while also incurring higher costs and size due to decreased switching frequency and additional drive circuits.
Innovation Solution
A motor drive control system that sets the DC voltage command value to a limit voltage or lower when a motor lock is detected, reducing switching loss and temperature increase without deteriorating control performance or generating audible noise, and includes features like power generation ensuring means to maintain electric power supply during locked states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the carrier frequency of PWM signal is changed from normal frequency (10 kHz) to a low frequency (1.25 kHz) to lower the switching frequency of switching device, then switching loss is reduced and sudden heat generation is avoided, but control response deteriorates and audible noise increases
Solution Approach 1:
The patent dynamically changes the DC voltage command value parameter based on motor operating conditions. When motor lock is detected, the DC voltage command value is set to a limit voltage or lower, which changes the operating parameters of the switching devices and reduces switching loss without requiring frequency changes that cause audible noise
2Loss of energy
If additional drive circuits are provided in parallel for each switching device to quickly render the switching device on and off in locked state, then switching loss is reduced and heat generation is reduced, but device complexity and cost increase
Solution Approach 1:
The patent extracts and addresses the root cause of excessive switching loss by limiting the DC voltage command value to a limit voltage or lower during motor lock conditions. This eliminates the need for additional drive circuits by fundamentally changing the voltage control strategy rather than adding hardware complexity
3Temperature
If the DC voltage command value is set to a limit voltage or lower when motor lock is detected, then switching loss is reduced and temperature increase is suppressed, but power output capability may be limited
Solution Approach 1:
The patent implements dynamic voltage control where the DC voltage command value is adjusted based on real-time motor operating conditions. During motor lock, the voltage is limited to prevent overheating, while under normal conditions the voltage can be increased to maintain power output capability, creating a dynamic balance between temperature control and power delivery
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
Effectively suppresses temperature increase in switching devices, allowing for extended operation in locked states without performance degradation, reduced size and cost of switching devices, and improved vehicle performance by maintaining torque output and power supply.
Implementation Method 1
a converter configured to be able to step up an output voltage of a DC (Direct Current) power supply
Implementation Method 2
the DC voltage which is variably controlled by the converter is converted into an AC voltage by an inverter to drive and control an AC motor
Implementation Method 3
The electric power converter such as inverter converts the power through switching at a high frequency and with a high power. Therefore, the electric converter has to be configured to avoid heat generation of a switching device
Data Source
Figure 1
Figure 2
Figure 3~5(c)
AI summary
In a motor drive control system configured to include a converter capable of stepping up the voltage, when the locked state of MG2 operating as an electric motor does not occur (NO in S 130), a voltage command value VHref for the converter output voltage is set according to respective required voltages of MG1 operating as an electric generator and MG2 (S 140). In contrast, when the locked state ofMG 2 occurs (YES in S 130), the voltage command value VHref is set to a limit voltage Vlmt or less for limiting the voltage step-up by the converter (S 150, S 180). When the locked state occurs, the converter output voltage is decreased and accordingly the DC voltage switched by the inverter is lowered, so that a switching loss at the switching device forming a part of the inverter is reduced and the temperature increase due to the heat generation can be suppressed.