Variable Speed Drive Input Filter for High Frequency Distortion
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Solution Overview
Problem
Variable speed drives (VSDs) for HVAC&R applications face issues with high frequency distortion in line to ground voltages, leading to voltage transients that can exceed the rated voltage of input devices, potentially causing failure, and existing solutions like galvanically isolated disconnects increase cost, size, and complexity, or require higher voltage-rated devices that reduce efficiency.
Innovation Solution
A circuit with a three-phase Pulse Width Modulated (PWM) VSD incorporating an active converter topology, featuring a three-phase input capacitor bank and a grounding capacitor, along with a three-phase inductor with center taps, to filter line to ground voltages and reduce high frequency distortion, and a bypass contactor for efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a galvanically isolated disconnect is provided to isolate input devices from high frequency distortion, then device reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces an input filter as an intermediary component between the AC power source and the converter stage. This filter includes capacitors connected between each input line and neutral, and between each input line and ground, along with inductors in series with each input line. The filter mediates the high frequency distortion by providing alternative paths for noise currents while maintaining normal power transmission, thus protecting input devices without requiring galvanic isolation.
2Reliability
If input devices are rated at higher voltage to withstand transients, then device reliability is improved, but cost increases and efficiency decreases
Solution Approach 1:
The patent applies preliminary action by placing the input filter before the converter stage to preemptively attenuate high frequency distortion and voltage transients. The filter's capacitors and inductors are configured to block noise currents and voltage spikes before they reach the input devices, allowing these devices to operate at their rated voltage without requiring higher voltage ratings, thus maintaining efficiency while ensuring reliability.
3Object-affected harmful factors
If traditional filtering solutions are implemented, then high frequency distortion is reduced, but device size and cost increase
Solution Approach 1:
The patent employs parameter changes by optimizing the values of capacitors and inductors in the input filter to achieve effective noise filtering with minimal component sizes. The capacitors are configured with specific capacitance values and the inductors with specific inductance values to target the frequency range of the distortion, allowing the filter to be compact while maintaining effectiveness in reducing high frequency distortion.
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
The solution effectively reduces common mode and differential mode currents, provides ground fault protection, improves cooling, reduces size, weight, and cost, and enables efficient operation by eliminating losses during maximum frequency operation.
Implementation Method 1
The three-phase input capacitor bank is configured to filter line to ground voltages to reduce or substantially eliminate high frequency distortion across the converter stage
Implementation Method 2
A three-phase inductor with three windings, wherein each winding of the three-phase inductor further includes a center tap
Data Source
AI summary
Systems and methods for improved VSDs are provided. One embodiment relates to an apparatus for common mode and differential mode filtering for motor or compressor bearing protection when operating with VSDs, including conducted EMI/RFI input power mains mitigation. Another embodiment relates to a method to extend the synchronous operation of an Active Converter to the AC mains voltage during complete line dropout. Another embodiment relates to an Active Converter-based Variable Speed Drive system with Improved Full Speed Efficiency.