Varistor-Protected EC Motor Intermediate Circuit
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Solution Overview
Problem
Existing intermediate circuits for EC motors face challenges in complying with the low voltage guideline during capacitor failure simulations, as short-circuit tests can lead to capacitor bursting and electrolyte dispersion, which complicates high-voltage testing and increases costs due to the need for additional fuses or encapsulation.
Innovation Solution
Incorporating varistors in parallel with each series-connected capacitor, where all varistors are similarly designed with threshold voltages below the breakdown voltage of the capacitors, ensuring that in case of failure, the sum of threshold voltages of remaining varistors is equal to or less than the nominal voltage, preventing capacitor bursting by reducing resistance and applying a protective short-circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional fuses are connected in series before the capacitor to prevent bursting, then the capacitor is protected against excessive current, but the device complexity and installation space increase
Solution Approach 1:
A varistor is introduced as an intermediary protective component connected in parallel with the capacitor. The varistor acts as a mediator that clamps voltage spikes and limits excessive voltage across the capacitor, preventing bursting without requiring series fuses. This resolves the contradiction by providing protection through a different mechanism that adds less complexity to the circuit.
Solution Approach 2:
The varistor is pre-positioned in parallel with the capacitor to cushion against voltage surges before they can cause capacitor bursting. The varistor's non-linear resistance characteristic allows it to automatically conduct when voltage exceeds a threshold, providing beforehand protection against overvoltage conditions that would otherwise damage the capacitor.
2Reliability
If fuses are used to protect against capacitor bursting, then the capacitor is protected, but the cost and installation space increase due to large fuse requirements for high DC voltages
Solution Approach 1:
The varistor serves as a compact intermediary device that replaces bulky high-voltage fuses. By connecting the varistor in parallel with the capacitor, it provides voltage clamping protection without requiring the large physical dimensions associated with high-voltage series fuses, thus reducing both cost and installation space.
3Object-affected harmful factors
If capacitor encapsulation is used to prevent electrolyte dispersion, then the capacitor is protected against bursting effects, but the device complexity and cost increase
Solution Approach 1:
The varistor provides beforehand protection by clamping voltage spikes before they can cause capacitor bursting and electrolyte dispersion. This preventive approach eliminates the need for encapsulation structures, as the voltage limiting action occurs upstream of the failure mode, thereby reducing device complexity and cost.
4Volume of moving object
If series-connected capacitors are used for space and cost reasons, then the intermediate circuit is more compact and economical, but the risk of capacitor bursting and tracking increases during failure simulation
Solution Approach 1:
The intermediate circuit uses segmented series-connected capacitors instead of a single large capacitor, which reduces size and cost. The varistor added in parallel with each capacitor segment provides individual protection, preventing catastrophic failure and electrolyte tracking even though the capacitors are connected in series for compactness.
Solution Approach 2:
Varistors are introduced as intermediary protective elements in parallel with each series-connected capacitor. These varistors clamp voltage spikes that occur during failure conditions, preventing capacitor bursting and the subsequent electrolyte tracking problem, thereby enabling the use of compact series-connected capacitor configurations without the associated risks.
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 ensures reliable protection against capacitor bursting while maintaining normal operation, reducing costs and installation space compared to traditional fuses or encapsulations, and allows for successful high-voltage testing compliance.
Implementation Method 1
a varistor is connected in each case in parallel with each series-connected capacitor, wherein all the varistors are designed similarly, and the capacitors and the varistors are dimensioned so that the threshold voltage of the varistors is below the breakdown voltage of the respective parallel-connected capacitor
Data Source
AI summary
The present disclosure relates to an intermediate circuit for an EC motor, comprising at least two similar series-connected capacitors for the connection of an electronic commutation device of an EC motor for nominal operation at a nominal voltage. In each case, a varistor is connected in parallel to each series-connected capacitor, wherein all the varistors are designed similarly. The capacitors and the varistors are dimensioned so that the threshold voltage of the varistors is less than the breakdown voltage of the respective parallel-connected capacitor, and, in the case of the failure of a capacitor or of a varistor, the sum of the threshold voltages of the remaining varistors is smaller than/equal to the nominal voltage of the intermediate circuit, and the sum of the threshold voltages of the series-connected varistors is greater than the nominal voltage of the intermediate circuit.