Inverter Control with Sinewave Filter Capacitor Current Compensation
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Solution Overview
Problem
Conventional sensorless motor drive control methods are unsuitable for low-speed operations with output filters and transformers, particularly in applications like electric submersible pumps and permanent magnet synchronous motors, due to unstable motor speed oscillations and difficulties in accurate voltage and current control.
Innovation Solution
A power conversion system and method that uses a controller to compute speed error and torque reference values, compensating motor current references based on output filter transfer functions to achieve sensorless speed control, thereby mitigating oscillations and enabling stable motor operation without direct motor load feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional sensorless motor drive control methods are used, then device complexity is reduced, but motor speed stability deteriorates due to oscillations at low speeds
Solution Approach 1:
The patent implements a feedback mechanism where the controller computes speed error based on speed reference and feedback values, and uses this feedback to adjust control parameters. The system continuously monitors motor operation and adjusts the inverter control based on computed speed error and torque reference, creating a closed-loop control system that maintains stability without requiring additional physical sensors
Solution Approach 2:
The patent dynamically changes control parameters including speed reference values, torque reference values, and motor current reference values based on operating conditions. The controller adjusts these parameters in real-time to compensate for filter capacitor currents and maintain stable motor operation across different speed ranges, particularly at low speeds where oscillations occur
2Object-affected harmful factors
If output filter is added to reduce high frequency content, then electromagnetic compatibility is improved, but current control accuracy deteriorates due to filter capacitor current
Solution Approach 1:
The patent extracts and separates the filter capacitor current component from the total current measurement. The controller identifies and computes the capacitor current portion independently, then compensates for it in the control algorithm, allowing accurate motor current control despite the presence of the output filter
Solution Approach 2:
The patent introduces an intermediary computational layer that models the filter transfer function and capacitor current behavior. This intermediary model allows the controller to predict and compensate for filter effects without requiring direct measurement of motor current, bridging the gap between inverter output and motor load
3Adaptability or versatility
If transformer is added to extend cable length, then adaptability to long cable applications is improved, but voltage and current control difficulty increases
Solution Approach 1:
The patent creates a universal control algorithm that handles multiple functions including compensation for output filters, transformers, and long cable effects through a single integrated approach. The controller uses the same transfer function-based methodology regardless of whether a filter, transformer, or both are present, simplifying the control system while maintaining accuracy across different configurations
Data Source
AI summary
Disclosed examples include power conversion systems, methods and computer readable mediums to operate an inverter to drive a motor load through an intervening filter, by computing a speed error value according to a speed reference value and a speed feedback value, computing a torque reference value according to the speed error value, computing a motor current reference value according to the torque reference value, compensating the motor current reference value according to capacitor currents of the output filter using a transfer function representing an output current to input current amplitude vs. frequency behavior of the output filter and the motor load, and controlling the inverter according to the inverter output current reference value.