Electric Motor Drive Overvoltage Protection via Phase Short-Circuit Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional electric motor drive devices face challenges in reliably suppressing voltage increases in smoothing capacitors during abnormal conditions, such as load dumps, which can lead to overvoltage and require larger components, and are not suitable for applications without braking resistors like those in electric vehicles.
Innovation Solution
An electric motor drive device with an overvoltage protection unit that includes a discharge circuit with a discharge resistor and IGBT, and a phase short-circuit control unit, which controls the inverter to bring the motor into a phase short-circuited state, effectively managing regenerative power and reducing capacitor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the capacitance of the smoothing capacitor is reduced for size reduction, then the device size is reduced, but voltage increase due to absorption of regenerative power becomes great, leading to overvoltage
Solution Approach 1:
The patent divides the overvoltage protection function into two independent parts: a discharge circuit with discharge resistor for absorbing regenerative power, and a phase short-circuit control function for stopping regenerative power flow. This segmentation allows the smoothing capacitor to be downsized while maintaining reliable overvoltage protection through coordinated operation of both functions.
Solution Approach 2:
The discharge circuit is activated in advance to absorb regenerative power before the smoothing capacitor voltage reaches dangerous overvoltage levels. By preliminarily processing the regenerative power through the discharge resistor, the system prevents voltage buildup that would otherwise require a larger capacitor to handle.
2Reliability
If a bypass resistance circuit is used for overvoltage protection, then overvoltage is suppressed, but the rated power capacity of the bypass resistance circuit increases, causing the size of the overvoltage protection device to increase
Solution Approach 1:
The patent merges the overvoltage protection function with the existing phase short-circuit control function already present in the inverter. By utilizing the existing IGBTs and control circuitry for dual purposes (overvoltage protection and regenerative power management), the system achieves effective overvoltage suppression without adding separate bypass resistance circuits, thereby avoiding size increase.
Solution Approach 2:
The inverter's switching elements and control circuit are designed to perform multiple functions: normal motor control, regenerative power processing, and overvoltage protection. This multi-functionality eliminates the need for dedicated overvoltage protection components, keeping the overall device size compact while maintaining reliable protection.
3Volume of moving object
If a resistor for discharging regenerative power is used also as a braking resistor, then size reduction is promoted, but the solution is not applicable to cases without braking resistors such as electric motor drive devices for automobiles
Solution Approach 1:
The patent extracts the overvoltage protection function from the braking resistor system. By using the discharge circuit with discharge resistor specifically for overvoltage protection during regenerative operation, and the phase short-circuit control to stop regenerative power flow, the system provides effective protection without requiring a separate braking resistor, thereby enabling application in vehicles like automobiles that do not have braking resistors.
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 reliably suppresses voltage increases in smoothing capacitors, enabling size reduction and simplification of the device configuration, while ensuring reliable operation even in the absence of braking resistors.
Implementation Method 1
a discharge circuit 10 having a discharge resistor 7 and a fuse 8 connected in series; and a first determination circuit 11 for performing determination as to voltage of the smoothing capacitor 4, wherein the discharge circuit 10 is connected between both terminals of the smoothing capacitor 4, and conduction of the IGBT 9 is controlled on the basis of an output signal from the first determination circuit 11
Implementation Method 2
the discharge circuit 10 in which the discharge resistor 7, the fuse 8, and an IGBT 9 as a semiconductor switching element are connected in series
Implementation Method 3
the discharge circuit 10 having a discharge resistor 7 and a fuse 8 connected in series
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The electric motor drive device (100) includes a smoothing capacitor (4) and an inverter (1), and further includes an overvoltage protection unit (6) for overvoltage protection for the smoothing capacitor (4), and a phase short-circuit control unit (12). The overvoltage protection unit (6) includes: a discharge circuit (20) having a discharge resistor (7) and an IGBT (9) connected in series; and a first determination circuit (21) which determines, with determination delay, that smoothing capacitor voltage exceeds first set voltage, and turns on the IGBT (9). The phase short-circuit control unit (12) is provided in a control device (5) for drive-controlling the inverter (1) and includes a second determination circuit (13) which determines, with a determination period longer than the determination delay of the first determination circuit (21), that smoothing capacitor voltage exceeds second set voltage lower than the first set voltage, to perform phase short-circuit control for the inverter (1).