Sensorless Motor Drive Control with Sine Wave Filter
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Solution Overview
Problem
Conventional sensorless motor drive control systems, particularly those using voltage-frequency control, face issues with uncontrolled drive current, transformer saturation, and starting problems, especially when combined with sine wave filters, and are not effective for driving permanent magnet motors.
Innovation Solution
The implementation of current regulation and reduced bandwidth control methods, including a current-frequency control component and a proportional-integral (PI) controller, allows for open-loop power converter control, mitigating these issues and enabling effective sensorless position control in systems with sine wave output filters and step-up transformers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If voltage-frequency control is used for sensorless motor drive, then system simplicity is improved, but control precision and reliability deteriorate due to uncontrolled drive current and transformer saturation
Solution Approach 1:
The patent transforms the control approach by changing the controlled parameter from voltage-frequency relationship to current-frequency relationship. The controller regulates inverter output current based on frequency or speed setpoint, and the current setpoint is determined according to frequency with zero current corresponding to zero frequency. This parameter transformation eliminates transformer saturation and uncontrolled current issues while maintaining sensorless operation.
Solution Approach 2:
The patent implements feedback control by using a proportional-integral (PI) controller with bandwidth below the resonant frequency of the output filter. The controller receives feedback signals representing inverter output current and regulates the current to match the current setpoint value. This feedback mechanism improves control reliability by continuously adjusting the output based on actual system state.
2Ease of operation
If sine wave output filter is added to the motor drive system, then output waveform quality is improved, but inrush current and resonant instability issues arise
Solution Approach 1:
The patent applies preliminary anti-action by implementing rate limiting on the frequency or speed setpoint before it reaches the current-frequency control component. The rate limiter prevents abrupt changes in frequency commands that would cause inrush current through the output filter. By pre-limiting the rate of change of the setpoint, the system avoids exciting the resonant frequency of the filter and prevents inrush current conditions.
Solution Approach 2:
The patent makes the control system dynamic by implementing a PI controller with bandwidth specifically designed to be below the resonant frequency of the output filter. This dynamic control approach allows the system to respond to frequency changes while automatically filtering out components that would excite the filter resonance, thereby eliminating oscillations and stabilizing the system.
3Power
If step-up transformer is used to boost motor drive output voltage, then voltage capability is improved, but transformer saturation and I2R losses increase
Solution Approach 1:
The patent changes the control parameter from voltage-based to current-based control. By regulating the inverter output current directly according to frequency setpoint, the system optimizes the current waveform and magnitude to prevent transformer saturation. The current-frequency relationship with zero current at zero frequency ensures proper transformer operation, reducing core losses and improving overall efficiency while maintaining the voltage boosting capability.
4Stability of the object's composition
If current regulation with reduced bandwidth control is implemented, then control stability is improved, but response speed decreases
Solution Approach 1:
The patent optimizes the controller bandwidth parameter to achieve the optimal balance between stability and response speed. The PI controller bandwidth is specifically set below the resonant frequency of the output filter, which provides sufficient stability margin while maintaining adequate response speed for motor drive applications. This parameter optimization allows the system to be stable without excessive response delay.
Data Source
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AI summary
A power converter (10), control apparatus (20) and methods (100) are presented for driving a permanent magnet motor or other load (6) through a sine wave filter (16) and a transformer (18), in which inverter output current (IA, IB, IC) is controlled using a current-frequency relationship (24) to convert a desired frequency or speed value (21, 31) to a current setpoint (32), and the inverter output current (IA, IB, IC) is regulated using a control algorithm (26) with a bandwidth below the resonant frequency of the sine wave filter (16).