Parallel Inverter AC Filter Circuit for Resonance Damping
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Solution Overview
Problem
The AC filter circuit in power conversion systems faces challenges in achieving both size reduction and resonant current suppression due to the need for a large AC filter reactor to allow fundamental wave current flow, which complicates the design when multiple power conversion devices are connected in parallel.
Innovation Solution
Incorporating a second filter reactor in series with the AC filter capacitor and a resistance in the AC filter circuit, forming an RLC series circuit, which allows a smaller reactor to handle fundamental wave currents and suppresses resonant currents by acting as a damping element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an AC filter reactor is provided on the downstream side of an AC filter capacitor to suppress resonant current, then resonant current suppression is improved, but the reactor size increases making size reduction difficult
Solution Approach 1:
The patent divides the AC filter reactor into two separate components: a first filter reactor connected in series with the power conversion circuit, and a second filter reactor connected in series with the AC filter capacitor. This segmentation allows each reactor to be smaller in size while collectively achieving the required resonant current suppression performance.
Solution Approach 2:
The patent introduces a damping resistor as an intermediary element connected in series with the second filter reactor and AC filter capacitor. This damping resistor suppresses resonant current without requiring the second filter reactor to be large in size, thereby enabling size reduction of the AC filter circuit while maintaining reliability.
2Volume of stationary object
If the AC filter reactor size is reduced, then size reduction is achieved, but resonant current suppression performance deteriorates
Solution Approach 1:
The damping resistor serves as an intermediary that compensates for the reduced size of the filter reactors. By introducing this resistor in series with the second filter reactor, the system achieves resonant current suppression without requiring large reactor sizes.
Solution Approach 2:
The patent creates a composite filtering structure combining two filter reactors of smaller individual sizes with a damping resistor. This composite configuration achieves the same or better resonant current suppression performance as a single large reactor would provide.
3Reliability
If a T-type LC low-pass filter configuration is used with the AC filter reactor on the downstream side, then resonant current suppression is improved, but the fundamental wave current must flow through the reactor requiring larger size
Solution Approach 1:
The patent segments the filter configuration so that the first filter reactor handles the fundamental wave current from the power conversion circuit, while the second filter reactor (which can be smaller) handles only the ripple current along with the AC filter capacitor. This segmentation allows the second reactor to be smaller since it doesn't need to carry the full fundamental wave current.
Solution Approach 2:
The patent applies different functional requirements to different parts of the filter circuit. The first filter reactor is designed for fundamental wave current filtering, while the second filter reactor is optimized specifically for ripple current filtering in conjunction with the AC filter capacitor, allowing each component to be sized appropriately for its specific function.
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 enables a reduction in the size of the AC filter circuit components while maintaining required performance, effectively suppressing resonant currents and reducing costs by using smaller components.
Implementation Method 1
a resistance constructing a series circuit together with the AC filter capacitor and the second filter reactor
Implementation Method 2
the resistance provided to the AC filter circuit acts as a damping element
Implementation Method 3
a second filter reactor connected in series to the AC filter capacitor
Implementation Method 4
an AC filter capacitor connected to an output side of the power conversion circuit
Data Source
AI summary
A power conversion system including a plurality of power conversion devices connected in parallel. Each of the plurality of power conversion devices includes: a power conversion circuit configured to convert DC to AC; and an AC filter circuit connected to an output side of the power conversion circuit. The AC filter circuit is an LC low-pass filter including a first filter reactor and an AC filter capacitor connected in an L shape. The AC filter circuit further includes a second filter reactor connected in series to the AC filter capacitor, and a resistance constructing a series circuit together with the AC filter capacitor and the second filter reactor.