AC Motor Drive Torque Control via DC Line Current Estimation
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Solution Overview
Problem
Conventional AC motor driving apparatuses face challenges in reducing the number of current sensors to minimize cost and space while achieving precise torque control, especially during low-speed and high-speed rotations, as existing methods require multiple current detections per PWM carrier cycle, which is difficult and inefficient.
Innovation Solution
An AC motor driving apparatus that uses a minimal number of current sensors, including a current sensor on the DC line or a particular phase, to detect rotor position and estimate three-phase motor currents, allowing for precise torque control without relying on PWM pulse patterns, and includes redundancy for error handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple current sensors are used to detect motor current in each phase, then torque control precision is improved, but apparatus cost and space requirements increase
Solution Approach 1:
The patent extracts the current detection function from three separate phase current sensors and consolidates it into a single DC line current sensor. By detecting only the DC line current and using mathematical relationships with inverter switching patterns, the system achieves equivalent torque control precision without requiring multiple sensors, thereby reducing apparatus cost and space requirements.
Solution Approach 2:
The patent introduces the inverter switching pattern as an intermediary element that connects the single DC line current detection to the three-phase motor current estimation. The switching pattern information serves as a mediator that enables the calculation of individual phase currents from the aggregated DC line current measurement, resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If current is detected twice per PWM carrier cycle at high speed, then torque control precision is improved, but detection difficulty increases due to small PWM pulse width at low speed
Solution Approach 1:
The patent changes the detection dimension from time-domain sampling (detecting current at specific moments within PWM carrier cycle) to a more flexible approach where current detection timing is adapted based on rotational speed. By using the rotation sensor information and adjusting detection strategy according to speed conditions, the system maintains measurement precision across varying speeds without being constrained by fixed PWM carrier cycle requirements.
Solution Approach 2:
The patent implements dynamic adaptation of current detection strategy based on motor rotational speed. At low speeds where PWM pulse width is small, the system adjusts detection timing and methodology to accommodate the reduced pulse duration. This dynamic approach allows the system to maintain adequate current detection precision across the entire speed range, from zero speed to high-speed rotation.
3Use of energy by moving object
If one-pulse mode is used for high-speed rotation efficiency, then voltage utilization is improved, but current detection becomes difficult
Solution Approach 1:
The patent uses the inverter switching pattern information as an intermediary to bridge the gap between one-pulse mode operation and current detection. By combining the known switching pattern with the DC line current sensor output, the system can calculate phase currents even during one-pulse mode operation, thereby maintaining both voltage utilization efficiency and current detection capability.
Solution Approach 2:
The patent incorporates feedback from the rotation sensor that detects rotor position and rotational speed. This feedback information is used to determine the appropriate detection mode and timing, allowing the system to maintain accurate current detection whether operating in PWM mode or one-pulse mode. The feedback mechanism enables the control unit to adapt its detection strategy to the current operating conditions.
Data Source
AI summary
The AC motor driving apparatus comprises an inverter for supplying power to an AC motor, current sensors for detecting current that flows in the motor or inverter, a rotation sensor for detecting the rotation of the rotor in the motor, and a control unit for controlling the driving of the inverter. A current detection value detected by the current sensor and a rotor rotational position are used to estimate three-phase motor current values. The estimated motor current values are used to control the inverter. Thereby, an inexpensive, space-saving AC motor driving apparatus as well as an AC motor controller, electric actuator, or vehicle that can perform highly precise torque control from zero speed to high-speed rotation without depending on the PWM pulse pattern are provided.