Variable Speed Drive Precharge Circuit with Dual Semiconductor Switches
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Variable speed drives face challenges in safely managing inrush currents during precharge operations and protecting against short circuit or fault events due to the use of auxiliary semiconductor devices with lower maximum current ratings.
Innovation Solution
A converter module with a plurality of switching modules, where one semiconductor switch is connected in anti-parallel or series with another, allowing the second switch to be controlled during precharge to limit inrush currents, and applying an auxiliary gate to emitter voltage greater than standard to ensure safe operation during precharge and fault events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the second semiconductor switch is controllably switched during precharge operation to limit inrush current, then inrush current is reduced, but the switch may not be able to handle high currents during fault events
Solution Approach 1:
The converter module contains multiple switching modules with different semiconductor switches. The second switch in each module is dedicated to precharge current limiting, while the modular structure ensures that fault currents can be managed by other switching modules or through the collective capability of all modules, preventing any single switch from being overwhelmed.
Solution Approach 2:
The second semiconductor switch is designed to handle precharge current limiting with a lower current rating, which is sufficient for the partial function of precharge operation. During fault conditions, the system relies on the combined capability of multiple switching modules rather than requiring any single switch to handle excessive fault currents alone.
2Reliability
If multiple switching modules are used in the converter, then system reliability and current handling capability are improved, but device complexity increases
Solution Approach 1:
The converter is segmented into multiple identical or similar switching modules, each with standardized semiconductor switches. This modular segmentation improves reliability through redundancy and distributed current handling, while the standardized nature of each module keeps individual module complexity manageable.
Solution Approach 2:
Each switching module is designed with universal functionality to handle both precharge operation and fault conditions. The semiconductor switches can be controllably switched for precharge current limiting and also contribute to fault current management, making each module multi-functional and reducing overall system complexity compared to having separate dedicated components for each 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 solution effectively limits inrush currents and enhances the reliability of variable speed drives during precharge and fault conditions by ensuring the semiconductor switches can handle higher currents, reducing the risk of damage and improving safe turn-off probabilities.
Implementation Method 1
The conduction of the semiconductor devices, such as insulated gate bipolar transistors (IGBTs) or other types of power switches or transistors used for rectifying the AC line voltage, is controlled so as to let only small pulses of inrush current flow during precharge operation of the VSD
Implementation Method 2
controlling the second semiconductor switch by applying an auxiliary gate to emitter voltage that is greater than a standard gate to emitter voltage applied to the first semiconductor switch
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A converter module for a variable speed drive having a semiconductor device for precharge is described. The precharge circuit includes switching modules, one switching module with a first semiconductor switch connected in parallel or series with a second semiconductor switch. The second semiconductor switch is switched on and off during the precharge operation in order to limit the inrush current into the DC Link. After the precharge operation, the second semiconductor switch is turned on all the time and acts like a diode. The second semiconductor device may have a lower maximum current rating than the main semiconductor devices. The lower current rated semiconductor device experience the same short circuit current as the higher current rated semiconductor device. The lower current rated semiconductor device can be supplied with a larger gate to emitter voltage than the higher current rated semiconductor device to equalize current between semiconductor devices.