Varistor-Protected Switch for Grid-Adaptive Power Electronic Devices
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Solution Overview
Problem
Power electronic devices, such as frequency converters, face challenges in protecting against surge voltages across different grid configurations, leading to increased costs due to the need for capacitor banks to withstand the highest surge voltage rating, which is not efficient for all grid types.
Innovation Solution
A power electronic device is designed with a varistor connected in parallel to a switch, allowing the device to adapt to different grid types by controlling the surge voltage rating. The varistor becomes conductive before exceeding an allowable voltage, forming a voltage divider with the capacitor bank to limit the voltage applied to it, thus reducing the required surge rating of the capacitor bank.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the capacitor bank is designed to withstand the highest surge voltage rating for all grid configurations, then the device can operate in any grid type (star-coupled or delta-coupled), but the cost of the power electronic device increases
Solution Approach 1:
The patent introduces a dynamically reconfigurable circuit topology using a switch that can change the connection state of the capacitor bank based on grid type detection. In star-coupled grids, the switch connects the capacitor bank to ground, reducing its surge voltage exposure. In delta-coupled grids, the switch disconnects it, allowing the capacitor bank to withstand higher surge voltages. This dynamic reconfiguration enables cost-effective design by adapting the capacitor bank's surge rating requirements to the actual grid configuration rather than designing for the worst-case scenario in all situations
Solution Approach 2:
The patent changes the electrical parameters (surge voltage rating requirements) of the capacitor bank based on the grid configuration. By detecting the grid type and switching the capacitor bank's connection state, the effective surge voltage rating parameter is adjusted to match the actual operational requirements, thereby reducing costs while maintaining compatibility across different grid types
2Reliability
If the switch is opened to increase surge rating in delta or IT grids, then the capacitor bank surge rating requirement increases, but the risk of overvoltage damage to the switch increases
Solution Approach 1:
The patent introduces a varistor as an intermediary protective element connected in parallel with the switch. When high surge voltages occur in delta or IT grids, the varistor activates and limits the voltage across the switch, preventing overvoltage damage while allowing the switch to remain in the appropriate state for surge protection. The varistor acts as a voltage-clamping device that protects the switch from harmful overvoltages
Solution Approach 2:
The varistor is pre-positioned in parallel with the switch to provide beforehand protection against overvoltage damage. This protective measure is in place before any surge event occurs, cushioning the switch from potential damage by absorbing or limiting excessive voltage stress during surge events
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 solution enables the power electronic device to operate in various grid configurations while minimizing the risk of switch damage from overvoltage and reducing the surge voltage load on the capacitor bank, thereby optimizing component design and cost-effectiveness.
Implementation Method 1
the varistor in the conducting state and the capacitor bank form a voltage divider, wherein the varistor limits a voltage over the capacitor bank to an allowable level
Implementation Method 2
the varistor is dimensioned such that it becomes conductive before a voltage over the varistor exceeds an allowable voltage over the switch
Data Source
AI summary
A power electronic device comprising a grid side (L1, L2, L3) connected to a capacitor bank (2) is described, the capacitor bank (2) being connected to ground via a switch. Such power electronic device should be used in different types of grid with low costs. To this end a varistor (5) is connected in parallel to the switch.