Motor Drive DC Bus Capacitor with Current Limiting Reactor
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Solution Overview
Problem
Electric motors driving devices prone to back-driving at high speed and/or torque during power disturbances, such as submersible pumps, face challenges in maintaining rotation direction due to insufficient capacitance in power storage arrangements, leading to production losses and harmonic issues.
Innovation Solution
A second power storage arrangement with a larger capacitor and rate limiting circuit is connected across the DC bus, allowing increased capacitance without inrush current problems, and a controller reduces motor speed with bus voltage drops to extend power supply during interruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the capacitance in the power storage arrangement is increased to sustain motor operation during power interruptions, then the duration of action is improved, but harmful factors increase due to inrush current destroying the rectifier section
Solution Approach 1:
A current limiting reactor (inductor) is introduced as an intermediary component between the capacitor arrangement and the rectifier section. This inductor limits the rate of current change (di/dt), preventing excessive inrush current from damaging the rectifier when power is restored, while still allowing the capacitor to provide sufficient energy storage to maintain motor operation during power interruptions.
Solution Approach 2:
The invention changes the electrical parameters of the power storage circuit by adding inductance in series with the capacitance. This creates an LC circuit that modifies the current waveform characteristics, limiting peak current while maintaining voltage storage capability, thus resolving the contradiction between energy storage duration and inrush current protection.
2Stability of the object's composition
If the capacitance in the power storage arrangement is increased to prevent motor back-driving, then the stability of the object's composition is improved, but harmful factors increase due to harmonic distortion causing utility surcharges
Solution Approach 1:
The current limiting reactor serves as an intermediary that filters harmonic currents generated by the rectifier-capacitor circuit. The inductor's impedance to high-frequency harmonic currents reduces the amplitude of distorted waveforms fed back to the utility grid, thereby reducing harmonic distortion while maintaining the capacitor's ability to stabilize motor operation.
Solution Approach 2:
By adding series inductance, the circuit parameters change from a purely capacitive load to an LC combination. This modifies the current waveform shape and reduces peak harmonic content, lowering total harmonic distortion (THD) to acceptable levels while preserving the voltage support function during interruptions.
3Duration of action of moving object
If a large capacitor arrangement is added to maintain motor operation during power interruptions, then the duration of action is improved, but device complexity increases
Solution Approach 1:
The power storage arrangement is segmented into two functional parts: a capacitor arrangement for energy storage and a current limiting reactor for current control. This segmentation allows each component to be optimized for its specific function while working together to achieve extended motor operation without requiring an excessively large capacitor alone.
Solution Approach 2:
The current limiting reactor serves multiple functions simultaneously: it limits inrush current, filters harmonic distortion, and provides ballast for the capacitor charging current. This multi-functionality reduces the need for additional separate components, thereby managing device complexity while achieving the desired extension of motor operation duration.
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 maintains motor rotation direction during power interruptions, reduces harmonic distortion, and prolongs operation time by managing capacitance and motor speed, avoiding component damage and utility surcharges.
Implementation Method 1
The power storage arrangement typically includes a capacitor arrangement, and is configured to be charged and discharged by current flowing into the bus from the input rectifier section and out of the bus to the inverter section
Implementation Method 2
A second power storage arrangement with a larger capacitor and rate limiting circuit is connected across the DC bus
Data Source
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AI summary
An apparatus is provided for controlling operation of an electric motor through use of an additional power storage arrangement connected across the DC busses of a motor drive and controlling the speed of the motor. The additional power storage arrangement includes an additional capacitor arrangement and a rate limiting arrangement in a series circuit relationship with one another.