DC-Bus Capacitor Ripple Current Reduction via Converter Switching Sequencing

Solution Overview

Problem

High DC bus ripple current in power conversion systems increases component temperature and electromagnetic interference, degrades component operation and durability, and requires large, expensive capacitors for filtering, necessitating a reduction in ripple current to minimize component size and cost.

Innovation Solution

A system and method for controlling power converter systems by determining and sequencing the switching states of multiple converters connected to a DC-bus capacitor to minimize the difference in current sums between adjacent time intervals, thereby reducing ripple current through the capacitor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If larger capacitors are used to filter ripple current, then the ripple current filtering capability is improved, but the cost, weight, size, and volume of the power conversion system increase

Engineering Contradiction:

Improveripple current filtering capabilityVSAvoidcapacitor weight

Core Design Contradiction:

Object-affected harmful factorsVSWeight of stationary object

Solution Approach 1:

The patent changes the timing parameters of converter switching operations. By adjusting when each converter switches relative to others, the system modifies the temporal distribution of ripple currents, causing them to partially cancel each other out. This parameter change allows achieving the same filtering effect with smaller capacitance values.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs periodic switching actions of multiple converters with coordinated timing. Each converter operates in a periodic cycle, and by synchronizing these cycles with specific phase relationships, the system creates a periodic cancellation pattern of ripple currents that reduces the overall ripple magnitude without requiring larger capacitors.

Inventive Principle:

Principle #19Periodic action

2Object-affected harmful factors

If larger capacitors are used to filter ripple current, then the ripple current filtering capability is improved, but the cost of the power conversion system increases

Engineering Contradiction:

Improveripple current filtering capabilityVSAvoidsystem cost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The patent changes the timing parameters of converter switching operations. By adjusting when each converter switches relative to others, the system modifies the temporal distribution of ripple currents, causing them to partially cancel each other out. This parameter change allows achieving the same filtering effect with smaller capacitance values.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces expensive large-capacitance filtering components with a control strategy that uses inexpensive switching timing adjustments. The 'disposable' nature refers to using control complexity rather than physical component size to achieve the filtering function, effectively substituting software/control logic for expensive hardware.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Power

If higher ripple current flows through the DC bus, then the power conversion capability is improved, but the temperature of components increases and durability decreases

Engineering Contradiction:

Improvepower conversion capabilityVSAvoidcomponent temperature

Core Design Contradiction:

PowerVSTemperature

Solution Approach 1:

The patent employs periodic switching actions of multiple converters with coordinated timing. Each converter operates in a periodic cycle, and by synchronizing these cycles with specific phase relationships, the system creates a periodic cancellation pattern of ripple currents that reduces the overall ripple magnitude without requiring larger capacitors.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent converts the harmful effect of individual converter ripple currents into a beneficial cancellation effect. By carefully timing the switching of multiple converters, the ripple currents that would normally be harmful are made to oppose and cancel each other, transforming the harmful individual effects into a beneficial overall reduction in ripple and component heating.

Inventive Principle:

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

Data Source

PatentUS8717788B2Method and system for controlling a power converter system connected to a DC-bus capacitor

Publication Date: 2014.05.06 FORD GLOBAL TECH LLC

AI summary

A method and system for controlling a power converter system with a direct current (DC)-bus capacitor connected to at least a first converter and a second converter. The first converter is with associated first current and the second converter is with associated second current. Switching states of the first and second converters are determined. The switching states of the second converter are sequenced relative to the first converter to reduce a difference of sums of the associated first and second currents between adjacent time intervals.