Phase-Shifted Inverter Control for DC Bus Ripple Reduction

Solution Overview

Problem

Existing vehicle systems experience current ripple on direct current buses due to fluctuations in direct current, leading to errors in controlling rotary electric machines, and current solutions involving larger capacitor banks increase vehicle weight and cost.

Innovation Solution

A system that controls rotary electric machines by using a first inverter to provide alternating currents with a reference phase and a second inverter to provide phase-shifted alternating currents, with a phase offset determined by the output signals of the first inverter, to reduce current ripple on the direct current bus, thereby minimizing the size and weight of capacitor banks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If larger capacitor banks are used to filter current ripple on the direct current bus, then current ripple is reduced, but vehicle weight and cost increase

Engineering Contradiction:

Improvecurrent rippleVSAvoidvehicle weight

Core Design Contradiction:

Object-generated harmful factorsVSWeight of moving object

Solution Approach 1:

The patent changes the operating parameters of the inverters by introducing phase shifts between them. By adjusting the phase relationship of the alternating current outputs from multiple inverters, the patent modifies how current ripple is generated and superimposed on the DC bus, thereby reducing the ripple amplitude without requiring larger capacitor banks.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potentially harmful effect of multiple inverters drawing current from the same DC bus into a beneficial effect. By carefully controlling the phase relationships between inverters, the individual current ripple components from each inverter combine in a way that reduces the total ripple on the DC bus, transforming what could be an aggravating factor into a solution.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Object-generated harmful factors

If larger capacitor banks are used to filter current ripple on the direct current bus, then current ripple is reduced, but vehicle cost increases

Engineering Contradiction:

Improvecurrent rippleVSAvoidvehicle cost

Core Design Contradiction:

Object-generated harmful factorsVSEase of manufacture

Solution Approach 1:

The patent changes the operating parameters of the inverters by introducing phase shifts between them. By adjusting the phase relationship of the alternating current outputs from multiple inverters, the patent modifies how current ripple is generated and superimposed on the DC bus, thereby reducing the ripple amplitude without requiring larger capacitor banks.

Inventive Principle:

Principle #35Parameter changes

3Object-generated harmful factors

If greater capacitive filtering is used on the direct current bus, then current ripple is reduced, but fuel economy deteriorates

Engineering Contradiction:

Improvecurrent rippleVSAvoidfuel economy

Core Design Contradiction:

Object-generated harmful factorsVSLoss of energy

Solution Approach 1:

The patent changes the operating parameters of the inverters by introducing phase shifts between them. By adjusting the phase relationship of the alternating current outputs from multiple inverters, the patent modifies how current ripple is generated and superimposed on the DC bus, thereby reducing the ripple amplitude without requiring larger capacitor banks.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potentially harmful effect of multiple inverters drawing current from the same DC bus into a beneficial effect. By carefully controlling the phase relationships between inverters, the individual current ripple components from each inverter combine in a way that reduces the total ripple on the DC bus, transforming what could be an aggravating factor into a solution.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 system effectively reduces current ripple on the direct current bus, allowing for more efficient control of rotary electric machines while decreasing the size and weight of capacitor banks, thus improving fuel economy and reducing costs.

Implementation Method 1

The second inverter is configured to provide a second group of alternating currents with a phase shift with respect to the reference phase, such that the phase shift is effective to reduce the direct current ripple on the direct current bus

Methodology Applied

Scientific EffectPhase shift:

Data Source

PatentEP2686950B1System for controlling rotary electric machines to reduce current ripple on direct current bus

Publication Date: 2021.06.09 DEERE & CO

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AI summary

The system (11) comprises a first' motor (26) for applying rotational energy to a respective first wheel (30) of the vehicle. A second motor (28) is arranged for applying rotational energy to a respective second wheel (32) of the vehicle. A first inverter (22) is coupled to the first motor (28), where the first inverter (22) is capable of receiving direct current electrical energy from the direct current bus (12). The first Inverter (22) is configured to provide a first group of alternating currents with a corresponding reference phase. A second inverter (24) is coupled to the second motor (28). The second Inverter (24) Is capable of receiving direct current electrical energy from the direct current bus (12). The second inverter (24) is configured to provide a second group of alternating currents with a phase shift with respect to the reference phase, such that the phase shift is effective to reduce the direct current ripple on the direct current bus (12).