Link Capacitor Control for Converter Weight Reduction
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Solution Overview
Problem
Conventional three-phase power converters require large capacitors to maintain a stiff DC link voltage, leading to significant weight and volume issues due to the need for storing multiple cycles of AC energy, which is inefficient and cumbersome.
Innovation Solution
A power conversion system that uses a link capacitor with a capacitance significantly less than traditional designs, controlled by a conversion controller to manage charge and discharge intervals within each switching period, allowing for efficient energy transfer and reduced capacitor size through precise control of switch vectors and duty ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a large capacitor is used to maintain stiff DC link voltage for multiple AC cycles, then the voltage stability is improved, but the weight and volume of the converter increase significantly
Solution Approach 1:
The patent implements periodic charge and discharge cycles of the link capacitor within each switching period. The controller alternates between charging the capacitor during a first time interval and discharging during a second time interval, creating a rhythmic energy transfer pattern that maintains voltage stability without requiring large capacitor capacity. This periodic action allows the system to 'borrow' energy temporarily and repay it cyclically, eliminating the need for large bulk capacitors that would otherwise be required to smooth voltage over multiple AC cycles.
Solution Approach 2:
The patent transitions from a static voltage maintenance approach (requiring large capacitors) to a dynamic control approach. The controller actively manages the capacitor's charge and discharge states by adjusting switch vectors and duty ratios in real-time. This dynamic control allows the system to adapt the capacitor's energy storage level continuously, maintaining voltage stability with a much smaller capacitor by actively balancing charge and discharge within each switching period.
2Use of energy by moving object
If a large capacitor is used to store enough energy for multiple AC cycles, then the energy storage capacity is improved, but the volume of the converter increases
Solution Approach 1:
The system uses periodic charge-discharge cycles within each switching period to achieve the necessary energy transfer. Instead of storing energy statically for multiple AC cycles, the capacitor dynamically exchanges energy with the DC sources and AC loads in rhythmic intervals. This periodic energy exchange allows the system to maintain effective energy storage capacity while using a much smaller capacitor volume, as the energy is cycled rapidly rather than being held in reserve.
Solution Approach 2:
The patent changes the operational parameters of the capacitor from static long-term storage to dynamic short-term cycling. By adjusting the switching frequency and duty ratios, the system transforms the capacitor's role from a large energy reservoir to a high-frequency energy buffer. This parameter change allows the same energy transfer function to be achieved with a smaller capacitor by increasing the rate of charge-discharge cycles rather than the total stored energy.
3Manufacturing precision
If conventional pulse width modulation with stiff voltage is used, then the sinusoidal output synthesis is achieved, but the capacitor size dominates the converter
Solution Approach 1:
The patent replaces the conventional continuous stiff voltage approach with periodic charge-discharge cycling. The controller implements alternating intervals where the capacitor is charged during a first time interval and discharged during a second time interval within each switching period. This periodic action maintains the voltage levels needed for precise sinusoidal output synthesis while dramatically reducing the capacitor quantity required, as the energy is replenished cyclically rather than requiring large continuous storage.
Solution Approach 2:
The system transitions from a static stiff voltage maintenance method to a dynamic voltage control method. The controller actively adjusts the capacitor's charge state in real-time, creating a dynamically balanced voltage profile that achieves the same sinusoidal synthesis precision as conventional methods. This dynamic approach allows the system to use minimal capacitor material by actively managing energy flow rather than relying on large passive energy storage.
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 achieves efficient energy transfer and reduced hardware requirements by dynamically controlling the link capacitor's charge and discharge cycles, synthesizing sinusoidal output waveforms while minimizing the size and weight of capacitors needed.
Implementation Method 1
a link capacitor (110) connected in parallel with the converter
Data Source
AI summary
A controller selects a first switch vector based on a current, voltage, or power of a multi-phase load or power source. The first switch vector identifies a first state for each of a plurality of half-bridges of a converter as on or as off during a first interval. A second switch vector is selected based on the current, voltage, or power of the multi-phase load or power source. The second switch vector identifies a second state for each of the half-bridges as on or as off during a second interval. The first interval is computed based on the selected first switch vector. The second interval is computed based on the selected second switch vector. Each of the plurality of half-bridges is controlled as on or as off during the first interval based on the selected first switch vector and during the second interval based on the selected second switch vector.