Sensorless AC Motor Drive Transition Scheme
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Solution Overview
Problem
Conventional sensorless motor drives face challenges in low-speed operation, particularly with unstable motor speed oscillations and difficulty in starting from a stopped condition, especially in applications with transformers and sine wave filters, such as electric submersible pumps and permanent magnet synchronous motors.
Innovation Solution
The implementation of dual-mode motor drive control techniques that transition from low-speed open loop current regulated control to high-speed EMF-based position estimation control, allowing for smooth transitions without the need for tuning, and employing hysteresis to manage mode changes, thereby minimizing undesirable transients and facilitating stable speed regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional sensorless field-oriented control or open loop speed control techniques are used, then the motor drive system is simpler to implement, but the system becomes unsuitable for low-speed operation with transformers and sine wave filters
Solution Approach 1:
The control system is segmented into two distinct modes: open-loop current-regulated control for low-speed operation and EMF-based sensorless control for higher-speed operation. This segmentation allows each mode to be optimized independently, with the open-loop mode ensuring reliable startup and low-speed performance, and the EMF-based mode providing accurate speed control at higher velocities. The system transitions between these segments based on speed thresholds, resolving the contradiction between simplicity and low-speed reliability.
Solution Approach 2:
The control system dynamically switches between open-loop and closed-loop modes based on operating conditions, particularly motor speed. The transition is managed through a speed threshold detection mechanism that activates the appropriate control mode. This dynamic adaptation allows the system to maintain reliability across the full speed range while keeping the control architecture relatively simple, as each mode uses control techniques appropriate to its operating regime.
2Device complexity
If sensorless voltage-frequency control techniques are used, then the system avoids position and speed sensors, but motor speed oscillations occur following load transitions or speed setpoint adjustments
Solution Approach 1:
The system performs preliminary action by using open-loop current-regulated control during the startup phase and low-speed operation to establish stable motor operation before transitioning to EMF-based sensorless control. This preliminary control phase prepares the motor for smooth transition to sensorless mode, preventing speed oscillations that would occur if sensorless control were applied directly from standstill. The open-loop mode acts as a preparatory stage that ensures stable operating conditions before the more sophisticated EMF-based control takes over.
Solution Approach 2:
The open-loop current-regulated control mode serves as an intermediary between the power converter and the EMF-based sensorless control system. During the transition phase, this intermediary mode bridges the gap by providing stable current regulation that prevents speed oscillations. The intermediary mode ensures smooth handoff between control strategies, maintaining speed stability during the transition from standstill to sensorless operation and during load transitions.
3Adaptability or versatility
If multiple transitions between current-frequency and active flux sensorless control are implemented, then the system can handle various operating conditions, but the system requires tuned first-order lag compensators with zero input
Solution Approach 1:
The invention extracts and removes the need for complex tuned first-order lag compensators with zero input that plague multi-mode transition systems. By using a straightforward speed-threshold-based transition mechanism between open-loop and EMF-based control modes, the system achieves operating condition adaptability without requiring additional complex compensating elements. The solution takes out the unnecessary complexity of multiple transition modes, retaining only the essential two-mode structure that provides sufficient adaptability while eliminating the need for intricate parameter tuning.
Data Source
AI summary
Motor drive control apparatus and methods are presented for sensorless control of a driven motor using open loop current regulated control during low-speed operation and an EMF-based position observer for position estimation during higher speed operation, with zero feedback speed during low-speed open-loop operation and feedback speed estimated by the EMF-based observer during high-speed operation and with velocity mode control over the full speed range and mode control hysteresis for smooth transitions between open loop and EMF-based observer control.