Inverter Compressor Boot Capacitor Charging With Low Carrier Frequency
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Solution Overview
Problem
The leakage current during boot capacitor charging operations in inverter-driven compressors is higher than during other operations, potentially triggering a leakage breaker and affecting compressor performance.
Innovation Solution
The method involves charging the boot capacitor at a carrier frequency lower than that used during normal operations, either prior to or during preparatory operations, and gradually increasing the carrier frequency to the normal operation frequency, while also performing preparatory operations like liquid discharging to reduce leakage current and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If boot capacitor charging operation is performed at normal carrier frequency, then charging is completed quickly, but leakage current becomes excessively large and may trigger leakage breaker
Solution Approach 1:
The patent applies dynamics by making the carrier frequency adjustable rather than fixed. The controller dynamically changes the carrier frequency based on the operating phase: using a first (lower) carrier frequency during boot capacitor charging to reduce leakage current, and a second (higher) carrier frequency during normal operation to improve performance. This dynamic adjustment resolves the contradiction between charging speed and leakage current reduction.
Solution Approach 2:
The patent changes the carrier frequency parameter from a constant value to a variable value that depends on the operational stage. By setting the carrier frequency to a lower value during boot capacitor charging and switching to a higher value during normal operation, the system optimizes both leakage current reduction and operational efficiency, directly addressing the technical contradiction.
2Object-affected harmful factors
If carrier frequency is reduced during boot capacitor charging, then leakage current is reduced, but preparatory operation time increases
Solution Approach 1:
The system dynamically adjusts carrier frequency based on operational phase. During boot capacitor charging, a lower carrier frequency is used to minimize leakage current. During liquid discharging and normal operation, the carrier frequency is increased to reduce preparatory time. This dynamic parameter adjustment resolves the time-leakage current tradeoff.
Solution Approach 2:
The patent performs boot capacitor charging as a preliminary action before normal operation, using a lower carrier frequency specifically for this phase to reduce leakage current. The system then transitions to higher carrier frequencies for subsequent operations, ensuring that the time penalty is minimized while still achieving leakage current reduction during the critical charging phase.
3Loss of time
If boot capacitor charging is performed before liquid discharging, then charging is completed early, but leakage current remains high throughout preparatory phase
Solution Approach 1:
The patent merges the boot capacitor charging operation with the liquid discharging operation, performing both simultaneously at the same lower carrier frequency. This integration ensures that leakage current is reduced throughout the entire preparatory phase, rather than having high leakage current during separate charging and discharging operations. The combined approach resolves the contradiction by maintaining low leakage current while completing both preparatory tasks.
Data Source
AI summary
A boot capacitor that functions as an operating power supply for a high-arm-side transistor provided in an inverter has to be charged prior to normal operation of a motor. This operation of charging the boot capacitor is performed at a carrier frequency that is lower than a carrier frequency for the normal operation.