Motor Drive System DC-Link Capacitor Size Reduction
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Solution Overview
Problem
Existing motor drive systems with non-paralleled source inverters sharing a common DC-link face challenges in minimizing DC-link capacitance due to uncontrolled current ripple, which affects size, weight, cost, and complexity, particularly in applications like 'more electric aircraft' where reducing the DC-link capacitor size is desirable.
Innovation Solution
The solution involves synchronizing the modulation carriers of source converters with a pre-selected phase shift to achieve interleaving, thereby minimizing DC-link current harmonics, which can be achieved through internal or external communication between controllers, optimizing the phase difference between carriers to reduce ripple and thus the required DC-link capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple source converters share a common DC-link without carrier synchronization, then system complexity is reduced and ease of operation is improved, but DC-link current ripple increases requiring larger DC-link capacitor size
Solution Approach 1:
The patent applies periodic action by interleaving the modulation carriers of multiple source converters with a phase shift. This creates periodic current ripple patterns that are out of phase, allowing the ripples to cancel each other out when summed, thereby reducing the overall DC-link current ripple and enabling smaller DC-link capacitor sizes.
Solution Approach 2:
The patent changes the phase parameter of the modulation carriers between different source converters. By introducing a pre-selected phase shift (e.g., 180 degrees for two converters) between the carriers, the current ripple characteristics are modified to achieve cancellation effects, reducing the required DC-link capacitance.
2Weight of stationary object
If DC-link capacitor size is reduced to decrease weight and cost, then system weight and cost are improved, but DC-link current ripple increases affecting power dissipation and EMI
Solution Approach 1:
The interleaved periodic modulation carriers create current ripple patterns that are phase-shifted. When these ripples are combined at the DC-link, they partially or fully cancel each other, reducing the harmful current ripple effects while allowing for smaller, lighter DC-link capacitor design.
Solution Approach 2:
The patent converts the potentially harmful effect of multiple independent current ripples into a beneficial cancellation effect. By deliberately introducing phase shifts between converters, the harmful ripples are transformed into a mechanism that reduces overall ripple, allowing lighter components while maintaining performance.
3Volume of stationary object
If modulation carriers are synchronized with phase shift to reduce DC-link current ripple, then DC-link capacitor size is reduced, but control system complexity increases
Solution Approach 1:
The control system implements periodic interleaving of modulation carriers with fixed phase shifts. This periodic structure simplifies the synchronization requirement compared to continuous adjustment, as the phase relationship is predetermined and maintained, reducing the actual control complexity while achieving ripple reduction.
Solution Approach 2:
The phase shift between modulation carriers is predetermined and configured in advance during system design or initialization. This preliminary setup eliminates the need for complex real-time synchronization adjustments, reducing control system complexity while maintaining the ripple cancellation benefit.
Data Source
AI summary
A power converter system comprising a power source; a plurality of voltage source converters for driving respective loads; the plurality of voltage converters connected to the power source via a common DC-link, control means (10a, 10b) for driving the voltage source converters by means of respective control signals modulated onto respective modulation carriers; and means for synchronizing the control means such that the respective modulation carriers are interleaved with a selected phase shift therebetween.