Inverter Over Current Protection via Capacitor AC Sampling
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Solution Overview
Problem
Conventional over current protection circuits in inverters suffer from high latency and high loss due to the use of Hall sensors, which fail to enable immediate protection when over current occurs, especially when connected to pure capacitive loads, leading to significant surge currents.
Innovation Solution
An over current protection circuit that detects AC current on a filtering capacitor, using a current transformer and rectifier to generate a sampled current signal, and a comparator to determine if the over current protection mechanism should be enabled, allowing for timely intervention to restrain power conversion operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Hall sensor is used for current sampling in the over current protection circuit, then the circuit can detect current, but the protection mechanism cannot be enabled immediately due to high latency and high loss
Solution Approach 1:
The patent extracts the DC current component from the current sampling by using a capacitor to bypass DC current, allowing only AC current components to be sampled. This eliminates the need for Hall sensors and enables faster detection of over current conditions through the AC coupling path, directly resolving the latency issue.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element in the current sampling path. This capacitor acts as a mediator that blocks DC current while allowing AC current components to pass through to the sampling circuit, enabling rapid detection without the latency associated with Hall sensors.
2Adaptability or versatility
If the inverter is connected to a pure capacitive load, then the inverter can operate, but a serious inverse drop occurs causing surge current and significant current increase through the inductor
Solution Approach 1:
The patent implements preliminary detection of AC current changes on the capacitor before the surge current fully develops. By monitoring the capacitor current in advance and comparing it against reference values, the system can trigger protection mechanisms proactively, preventing the harmful surge current from occurring in the first place.
Solution Approach 2:
The patent establishes a feedback loop that continuously monitors the AC current through the capacitor and compares it with reference values. When the monitored current exceeds the reference threshold, the system immediately responds by enabling over current protection, creating a closed-loop control that prevents surge current damage.
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
Enables rapid over current protection in inverters, preventing damage from surge currents by detecting current changes ahead of voltage changes, thus enhancing the stability of power conversion operations.
Implementation Method 1
The over current protection circuit detects an AC current on the filtering capacitor
Implementation Method 2
The current sampling unit samples the AC current and rectifies the sampled AC current to generate a sampled current signal
Data Source
AI summary
An inverter and an over current protection method thereof are provided. The inverter includes an inverting circuit, a filtering capacitor and an over current protection circuit. The inverting circuit is configured to convert a DC input voltage into an AC output voltage and provide the AC output voltage to a load. The filtering capacitor is coupled to the inverting circuit and the load in parallel. The over current protection circuit is coupled to the inverting circuit and the filtering capacitor and configured to provide an over current protection mechanism. The over current protection circuit detects an AC current on the filtering capacitor and determines whether to enable the over current protection mechanism according to the AC current in order to restrain the power conversion operation of the inverting circuit.