Sensorless Motor Drive Vector Control with Filter Capacitor Current Compensation
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Solution Overview
Problem
Existing motor drive control systems face challenges in accurately controlling motor voltages and currents due to the presence of output filters and transformers, which complicates sensorless speed control and stability, especially in applications like electric submersible pumps and permanent magnet synchronous motors, leading to oscillations and difficulties in starting motors at low speeds.
Innovation Solution
The implementation of a power conversion system with an inverter controller that computes and compensates for filter capacitor currents based on damping resistance values, allowing for sensorless vector control and stable speed regulation without the need for additional sensors, using a processor to adjust inverter switching signals and compensate for filter capacitor currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If output filters and transformers are used in motor drive systems, then voltage and current control accuracy is improved, but sensorless speed control stability deteriorates causing oscillations
Solution Approach 1:
The patent implements feedback compensation by calculating the filter capacitor current based on the measured inverter output current and filter parameters, then using this calculated current to compensate the motor current reference in the vector control system. This closed-loop feedback approach stabilizes sensorless speed control by accounting for the filter's impact on current distortion and oscillations.
Solution Approach 2:
The patent introduces an intermediary calculation step that models the filter capacitor current as a separate entity. By calculating this intermediate current component and subtracting it from the inverter output current, the system obtains a more accurate representation of the actual motor current, thereby improving sensorless control stability.
2Stability of the object's composition
If filter capacitor current compensation is implemented, then motor speed control stability is improved, but control system complexity increases
Solution Approach 1:
The patent replaces physical sensors and additional hardware components with a computational model that calculates filter capacitor current based on electrical parameters and filter characteristics. This substitution of mechanical/physical measurement systems with mathematical modeling reduces hardware complexity while achieving the desired compensation effect.
Solution Approach 2:
The control system performs self-compensation by using its own measured inverter output current and known filter parameters to calculate the filter capacitor current. The system serves itself by generating the compensation signal internally without requiring external sensors or additional measurement devices.
3Device complexity
If sensorless vector control is used, then the number of sensors is reduced, but control precision at low speeds deteriorates causing starting difficulties
Solution Approach 1:
The patent changes the control parameters by introducing filter compensation calculations that are particularly effective at low speeds. By dynamically calculating and compensating for filter capacitor current using the measured inverter current and filter parameters, the system maintains accurate motor current estimation even at low speeds where sensorless control typically struggles.
Data Source
AI summary
Disclosed examples include motor drive power conversion systems with an inverter, as well as a controller methods to drive a motor in which output filter capacitor currents are computed and used to compensate the motor control in consideration of damping resistance values of an output filter.