PMSM Speed Fluctuation Suppression via D-Q Axis Feedforward Compensation
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Solution Overview
Problem
Permanent magnet synchronous motors experience significant speed fluctuations during abrupt load changes, leading to vibrations and potential out-of-step conditions, which existing control methods struggle to effectively suppress, especially in applications like compressor systems where stability and comfort are critical.
Innovation Solution
A method involving feedforward compensation on d-axis and q-axis currents is implemented, using PI control to adjust voltages and currents, thereby stabilizing motor speed and reducing vibrations by superposing compensation currents with reference currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bandwidth of the speed loop is increased to suppress speed fluctuation and prevent out-of-step under abrupt load changes, then the motor response speed and stability improve, but speed ripple increases, speed overshoot becomes more likely, and no single bandwidth setting is suitable for all frequency bands and load conditions
Solution Approach 1:
The patent divides the speed control into multiple frequency bands using a notch filter to identify and separate the periodic load frequency component from the overall speed signal. This segmentation allows different control strategies to be applied to different frequency components, resolving the contradiction between overall stability and localized speed ripple.
Solution Approach 2:
The patent dynamically adjusts the bandwidth parameter of the speed loop based on operating conditions and identified periodic load frequencies. By changing the bandwidth parameter adaptively rather than using a fixed value, the system maintains stability across different frequency bands and load conditions while minimizing speed ripple and overshoot in each specific operating range.
2Speed
If the bandwidth of the speed loop is kept low to maintain smooth speed control, then speed ripple and overshoot are reduced, but the motor becomes prone to out-of-step conditions under abrupt load changes and takes longer to stabilize speed
Solution Approach 1:
The patent performs preliminary identification of periodic load frequencies using a notch filter before applying the speed control. By detecting and compensating for periodic load components in advance, the system prepares the control parameters proactively, enabling the low bandwidth to maintain smooth speed control while still responding effectively to abrupt load changes through pre-adjusted compensation.
Solution Approach 2:
The patent implements a feedback mechanism where the identified periodic load frequency information is fed back into the speed control loop. This feedback allows the system to continuously adjust the bandwidth and compensation parameters based on actual operating conditions, ensuring both speed smoothness and reliability under varying load conditions.
3Device complexity
If conventional PI control is used without feedforward compensation, then the control system remains simple, but speed fluctuation under periodic load cannot be effectively suppressed, leading to vibration and potential quality issues
Solution Approach 1:
The patent applies feedforward compensation by calculating the required compensation current in advance based on the identified periodic load frequency and amplitude. This preliminary calculation of compensation parameters allows the system to proactively counteract periodic load effects before they cause significant speed fluctuations, effectively suppressing vibration while maintaining relatively simple control structure.
Solution Approach 2:
The patent introduces a notch filter as an intermediary component that specifically targets and filters the periodic load frequency component from the speed signal. This intermediary element enables the control system to isolate and compensate for periodic disturbances without requiring complete redesign of the entire control architecture, thus maintaining simplicity while improving reliability.
Data Source
AI summary
A method for suppressing a speed fluctuation of a permanent magnet synchronous motor is provided in the present disclosure, including: obtaining a target speed ω_<sup2>ref</sup2>, a feedback speed, a fluctuation speed Δω, a q-axis inductance Lq and a permanent magnet flux linkage φf of the permanent magnet synchronous motor; performing a PI adjusting on Δω to obtain a q-axis reference current Iq_ref, and obtaining a q-axis target voltage U*q according to Iq_ref, ω_<sup2>ref</sup2>, Δω and φf; performing a PI control on a q-axis actual voltage according to U*q to obtain a q-axis compensation current Iq_add; obtaining a d-axis target voltage U*d according to Iq_ref, Iq_add, ω_<sup2>ref</sup2>, Δω and Lq; performing a PI control on a d-axis actual voltage according to U*d to obtain a d-axis compensation current Id_add; superposing Iq_add and Iq_ref to perform a feedforward compensation on a q-axis current and superposing Id_add and the d-axis reference current to perform a feedforward compensation on a d-axis current.