Motor Controller Minimizing Inverter Loss via Dynamic Switching

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Solution Overview

Problem

The high-withstand-voltage switching elements used in electric vehicle power conversion devices experience excessive inverter loss at higher switching frequencies, leading to increased size, weight, and cost of coolers, making it difficult to configure a small, lightweight, and cost-effective power conversion device.

Innovation Solution

A controller for the motor that generates pulse-width modulation signals and current commands to minimize inverter loss, using a voltage-command generating unit and current-command generating unit to optimize torque generation and reduce inverter loss, while maintaining symmetry in the inverter output voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a high-withstand-voltage switching element is used in an inverter for electric vehicle power conversion, then the inverter can operate at high voltage (1500-3000V), but the switching loss and conduction loss increase significantly, resulting in inverter loss of several kilowatts to 10-odd kilowatts

Engineering Contradiction:

Improveinverter operating voltageVSAvoidinverter loss

Core Design Contradiction:

PowerVSLoss of energy

Solution Approach 1:

The patent dynamically adjusts the switching frequency of the inverter based on operating conditions. The control unit monitors the inverter output frequency and switching frequency relationship, and when the pulse number becomes too small (causing voltage symmetry collapse), it reduces the switching frequency to restore symmetry. This dynamic adjustment allows the system to maintain efficient operation across different operating points while minimizing inverter losses.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the switching frequency parameter adaptively. When operating at high inverter output frequencies (around 400Hz for 8-pole motors), the switching frequency is reduced from the typical 750Hz to maintain a pulse number of at least 3, preventing voltage symmetry collapse and minimizing switching losses. This parameter change optimizes the trade-off between power conversion efficiency and loss reduction.

Inventive Principle:

Principle #35Parameter changes

2Speed

If the switching frequency is increased to improve power conversion performance, then the inverter can respond faster and reduce current oscillation, but the inverter loss increases and the cooler size must be increased

Engineering Contradiction:

Improveswitching frequency responseVSAvoidinverter loss

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The system dynamically adjusts switching frequency based on real-time operating conditions. The control unit calculates the pulse number (carrier frequency divided by inverter output frequency) and when it falls below the threshold of 3, it reduces the switching frequency. This dynamic response maintains adequate switching performance while preventing excessive loss generation, allowing fast response when needed but reducing frequency when it would cause excessive losses.

Inventive Principle:

Principle #15Dynamics

3Weight of moving object

If an 8-pole permanent-magnet synchronous motor is used to reduce motor size and weight, then the motor dimensions are reduced, but the inverter output frequency increases to about 400Hz, causing pulse number to become too small and voltage symmetry to collapse

Engineering Contradiction:

Improvemotor weightVSAvoidvoltage symmetry

Core Design Contradiction:

Weight of moving objectVSStability of the object's composition

Solution Approach 1:

The control unit continuously monitors the relationship between inverter output frequency and switching frequency, calculating the resulting pulse number. When the pulse number approaches the critical threshold of 3, the system provides feedback by reducing the switching frequency to restore voltage symmetry. This closed-loop feedback mechanism ensures stable operation of the high-speed 8-pole motor without voltage symmetry collapse.

Inventive Principle:

Principle #23Feedback

4Speed

If the pulse number in the inverter output voltage becomes too small, then the inverter can operate at high frequencies, but positive-and-negative symmetry of the voltage collapses, generating current oscillation and torque pulsation

Engineering Contradiction:

Improveinverter output frequencyVSAvoidvoltage symmetry

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The control unit continuously monitors the pulse number (switching frequency divided by inverter output frequency) and provides feedback when it approaches the critical value of 3. Upon detecting this condition, the system automatically reduces the switching frequency to maintain voltage symmetry. This feedback mechanism prevents the collapse of positive-negative voltage symmetry that would otherwise occur at high frequencies, eliminating current oscillation and torque pulsation.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8278855B2Controller of motor preventing an increase in inverter loss

Publication Date: 2012.10.02 NEXGEN CONTROL SYSTEMS LLC

AI summary

In configuring a power conversion device to drive an alternating-current motor for an electric vehicle, the device is configured in a small size, light weight, and at a low cost, while avoiding size increase of a cooler. A current-command generating unit provided in a controller to control the alternating-current motor is adjusted not to increase a loss of an inverter in a state that the inverter as a main circuit within the power conversion device is outputting a maximum voltage that can be generated at an output voltage of a direct-current power source and when a torque command is reduced, and outputs a current command to cause the alternating-current motor to generate a torque based on the torque command.