Motor Control Device Using Single Current Sensor and Estimation
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Solution Overview
Problem
Existing motor control systems require multiple current sensors to perform vector control, increasing costs and facing challenges in accurately detecting phase currents when two phase voltages are equal, which hinders efficient motor control.
Innovation Solution
A motor control device that detects phase current of one phase using a current sensor and estimates other phase currents using a current estimator, generating specified current values based on motor speed and rotor position to control the motor via an inverter, allowing for single sensor operation and accurate current estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two current sensors are used to detect current values of two phases, then measurement precision of phase currents is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts only one current sensor from the traditional two-sensor configuration and uses mathematical estimation to derive the other phase currents. The current sensor detects only one phase current, and the controller estimates the remaining two phase currents based on the detected current and voltage relationships, thereby reducing sensor quantity while maintaining control accuracy.
Solution Approach 2:
The patent introduces voltage detection and mathematical estimation as intermediary means between direct current measurement and motor control. By detecting voltage values and using the relationship between voltage and current in each phase, the system indirectly obtains phase current information without requiring direct measurement of all three phases, thus reducing hardware complexity.
2Device complexity
If single shunt current detecting method is used to reduce sensor quantity, then device complexity is reduced, but measurement precision deteriorates when two phase voltages are equal
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors voltage values of all three phases and adjusts the current estimation strategy accordingly. When two phase voltages are equal, the system detects this condition and switches to an alternative estimation method or uses past current information, ensuring accurate current detection under all operating conditions through continuous feedback and adaptation.
Solution Approach 2:
The patent makes the current detection method dynamic by switching between different detection and estimation strategies based on real-time voltage conditions. When voltage differences between phases are sufficient, direct estimation is used; when voltages are equal or nearly equal, the system dynamically transitions to using historical current data or alternative calculation methods, adapting to changing operational states to maintain precision.
3Measurement precision
If carrier frequency of PWM is decreased to handle small voltage differences, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The patent dynamically adjusts the PWM carrier frequency based on the voltage difference between phases. When voltage differences are small, the carrier frequency is temporarily reduced to ensure accurate current detection. When voltage differences are sufficient, the carrier frequency returns to its normal higher value to maintain high control response speed and productivity, thus adapting to real-time conditions.
Solution Approach 2:
The patent changes the PWM carrier frequency parameter adaptively rather than using a fixed frequency. By monitoring voltage differences and adjusting the carrier frequency accordingly, the system optimizes the balance between measurement precision and control speed, ensuring accurate current detection when needed while maintaining high productivity during normal operation.
Data Source
AI summary
A motor control device includes a current detecting portion that detects phase current of one phase among three phase currents supplied from an inverter to a motor, and a current estimator that estimates phase current of phases other than the detected phase current by using a specified current value indicating current to be supplied to the motor, and derives control current corresponding to the specified current value from the estimated phase current and the phase current of one phase. The motor control device controls the motor via the inverter so that the control current follows the specified current value.