Sensorless PWM AC Motor Drive With Commutation Noise Rejection
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Solution Overview
Problem
Existing sensorless variable speed drives for AC motors face challenges in accurately estimating motor state variables due to noise from PWM commutations, particularly at low velocities, and require additional sensors or offline prefiltering, which increases complexity and cost.
Innovation Solution
A PWM-based sensorless variable speed drive that discards corrupted time segments of the drive current signal corresponding to power inverter commutations, using a state variable estimation module to improve noise rejection and enable real-time control without external sensors or signal injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external high-frequency probing signal is injected to improve state variable estimation at low velocity, then measurement precision is improved, but acoustic noise and harmful dynamics are generated
Solution Approach 1:
The patent converts the harmful PWM commutation noise into a useful probing signal. By treating the PWM switching artifacts as the excitation source instead of injecting an external high-frequency signal, the system achieves state variable estimation at low velocities without generating additional acoustic noise or exciting unmodeled dynamics.
Solution Approach 2:
The PWM inverter's own commutation noise serves as the probing signal for sensorless control. The system uses its inherent switching artifacts rather than requiring an external signal injection mechanism, thereby simplifying the control architecture and eliminating the harmful effects of external signal injection.
2Measurement precision
If an external high-frequency probing signal is injected to improve state variable estimation at low velocity, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent eliminates the need for external signal injection hardware and processing by converting the PWM commutation noise into the probing signal. This approach simplifies the control system architecture while maintaining the ability to perform accurate state variable estimation at low velocities.
3Productivity
If PWM frequency is increased to allow higher probing signal frequency, then productivity is improved, but acoustic noise and harmful factors increase
Solution Approach 1:
The patent converts the PWM commutation noise into a useful probing signal, allowing the system to benefit from high PWM frequencies for productivity without suffering from the associated acoustic noise. The same switching artifacts that would normally be harmful are instead utilized as the excitation source for sensorless control.
4Measurement precision
If offline prefiltering is used to remove PWM noise from measured current, then measurement precision is improved, but loss of time occurs
Solution Approach 1:
The patent performs noise filtering and state variable estimation in real-time during normal operation rather than requiring offline processing. By using the PWM commutation times to identify and exclude corrupted current measurement segments during ongoing control, the system achieves accurate state variable estimation without processing delays.
Data Source
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AI summary
A variable speed drive (200) comprising: - an output terminal (210) for delivering a drive voltage (upwm); - a power inverter (220) for generating the drive voltage (upwm); - a drive controller (230) for controlling the generation of the drive voltage (upwm); and - a current sensor (240) for providing a drive current intensity signal (is) to the drive controller (230), wherein the drive controller (230) includes: - a PWM generator (232); - a control law module (234); and - a state variable estimator (236) estimating a state variable (z) of the controlled AC electric motor (300), wherein the control law module (234) computes a target voltage signal (us) and outputs the target voltage signal to the PWM generator (232), wherein the PWM generator (232): - approximates the target voltage signal (us) with a pulse-width modulated inverter control signal (M); - controls the power inverter (220) using the inverter control signal (M), thereby obtaining the drive voltage (upwm); - computes, based on the deviation between the inverter control signal (M) and the target voltage signal (us), a state variable estimation support signal (s1); - extracts, from the inverter control signal (M), a time sequence (R) of the next commutations of the power inverter's solid-state switches (T1, T2); and - outputs the state variable estimation support signal (si) and the commutation time sequence (R) to the state variable estimator (236), and wherein the state variable estimator (236): - estimates a state variable (z) based on the state variable estimation support signal (s1) and the drive current intensity signal (is), wherein those time segments of the drive current intensity signal (is), which, according to the commutation time sequence (R), correspond to the commutation of one of the power inverter's solid-state switches (T1, T2), are discarded in the state variable estimation as corrupted time segments; and - outputs the state variable estimate (z) to the control law module (234).