Neutral-Point EV Charging Control for Sensor Fault Current Limiting
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Solution Overview
Problem
During external charging of a vehicle using the neutral point charging method, a sticking abnormality in one of the current sensors can cause a circulating current between phases, leading to a large current concentration and increased temperature of the switching elements.
Innovation Solution
A vehicle power supply device with a control device that sets an upper limit value for each phase current based on the maximum input current and limits the currents to prevent exceeding this value, while also switching to a lower overcurrent threshold during charging to prevent overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback control is performed to control each phase current during external charging, then the input current from external power supply and output current to battery can be made equal, but a circulating current is generated when current sensor abnormality occurs, causing large current concentration and temperature rise of switching elements
Solution Approach 1:
The control device sets upper limit values for phase currents before external charging begins. These predetermined limits are established based on expected charging conditions, preventing harmful circulating currents from causing damage even if current sensor abnormalities occur during charging operation.
Solution Approach 2:
The control device dynamically adjusts current limits by switching between a first current limit during normal charging and a second, lower current limit during voltage rise periods. This parameter change prevents circulating currents from causing temperature rise while maintaining efficient charging operation under normal conditions.
2Power
If a high current limit is used during traveling, then the electric motor can deliver maximum power, but using the same current limit during charging allows circulating current to cause overheating
Solution Approach 1:
The control device dynamically adjusts current limits based on operating mode (traveling vs. charging) and charging conditions (voltage rise detection). During traveling, high current limits enable maximum motor power. During charging, the device switches to lower current limits to prevent overheating from circulating currents, and further adjusts limits when voltage rise is detected.
3Productivity
If feedback control continuously adjusts switching elements to maintain current equality, then charging efficiency is improved, but current sensor abnormalities cause circulating current that concentrates in specific phases
Solution Approach 1:
Upper limit values for phase currents are set in advance before charging begins. These predetermined limits serve as safety constraints that prevent circulating currents from causing harmful effects, while the feedback control continues to operate efficiently within these bounds to maintain good charging performance.
Solution Approach 2:
The control device uses feedback control to adjust switching elements for efficient charging while simultaneously monitoring phase currents against predetermined upper limits. When currents approach these limits, the feedback mechanism prevents further increase, thereby suppressing circulating currents while maintaining efficient charging operation.
Data Source
AI summary
A vehicle power supply device applied to a vehicle including an electric motor including coils for a plurality of phases. The vehicle power supply device includes: a battery; a power conversion device including, for each of phases of the electric motor, a switching element and a current sensor; and a control device configured to control the power conversion device such that electric power supplied via a neutral point of the electric motor is stepped up and then supplied to the battery, execute a feedback control to control currents of the respective phases such that an input current from the external power supply and an output current to the battery are equal, set an upper limit of the currents of the respective phases based on a maximum value of the input current, and limit the currents of the respective phases so as not to exceed the set upper limit value.