Semiconductor Precharge Control for Inrush-Limited Inverter Power

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Solution Overview

Problem

The existing relay units in motor-driven vehicles, such as hybrid and electric cars, face challenges in reducing the size and weight due to the need for a current limiting resistor to manage inrush currents, which consumes power and increases the size of the relay unit.

Innovation Solution

A semiconductor unit is introduced between the motor and the inverter circuit, comprising a transistor and a controller that controls the power supply from the battery to the inverter circuit, eliminating the need for a current limiting resistor by intermittently operating the transistor at a lower control voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a current limiting resistor is used to limit inrush current from the battery to the inverter circuit, then the inrush current is limited, but the relay unit size and weight increase

Engineering Contradiction:

Improveinrush current limitationVSAvoidrelay unit weight

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The patent replaces the mechanical contact type relay and current limiting resistor with a semiconductor transistor (IGBT) controlled by a gate drive circuit. The transistor electronically limits inrush current through controlled conduction, eliminating the need for bulky mechanical relays and high-power resistors, thereby reducing relay unit weight and size.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the control parameter by applying a specific gate voltage (Vge) to the transistor that is lower than the voltage required for full activation. This partial activation allows the transistor to limit current effectively while maintaining a smaller, more compact design compared to fully activated mechanical relay systems.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If a current limiting resistor with large resistance value is used to limit inrush current, then the inrush current is limited, but the resistor size increases due to power consumption

Engineering Contradiction:

Improveinrush current limitationVSAvoidresistor size

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent substitutes the passive current limiting resistor with an active semiconductor transistor controlled by a gate circuit. The transistor dynamically controls current flow through its conduction characteristics, eliminating the need for large-power resistors and reducing the overall component area in the relay unit.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent employs intermittent operation of the transistor during the pre-charging phase, controlling the gate voltage to allow periodic current flow that limits inrush current while reducing continuous power dissipation, thereby minimizing the size requirements for current-limiting components.

Inventive Principle:

Principle #19Periodic action

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

This configuration reduces the size and weight of the relay unit by effectively managing inrush currents without the need for a current limiting resistor, enhancing the efficiency and compactness of the vehicle's electrical system.

Implementation Method 1

The transistor is configured to control supply of power from the battery to the inverter circuit. The controller controls a control voltage that is a voltage applied to a control terminal of the transistor.

Methodology Applied

Scientific EffectTransistor conduction control:

Data Source

PatentUS12128772B2Semiconductor unit, battery unit, and vehicle

Publication Date: 2024.10.29 ROHM CO LTD

AI summary

A semiconductor unit is arranged between a motor and an inverter circuit that controls the motor. The semiconductor unit includes a transistor and a controller. The transistor is arranged between the inverter circuit and a positive electrode of a battery that supplies power to the inverter circuit, and controls supplying of power from the battery to the inverter circuit. The controller is connected to a control terminal of the transistor, and controls a control voltage that is a voltage applied to the control terminal. When power starts to be supplied from the battery to the inverter circuit, the controller controls the control voltage to intermittently operate the transistor and also decreases the control voltage, which is applied to the control terminal of the transistor, to be lower than the control voltage at which the transistor is fully activated.