AC Motor Inertia Calculation via Delay Compensation
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Solution Overview
Problem
Conventional control devices for AC rotating machines without speed or position sensors experience estimation delays, leading to errors in calculating the moment of inertia, which affects the accuracy of controlling the machine.
Innovation Solution
A control device for AC rotating machines that includes a command generation unit, current detection unit, speed estimation unit, and inertia moment computing unit, where the output torque is corrected to account for estimation delays, allowing for accurate calculation of moment of inertia using estimated speed and corrected output torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If speed estimation is performed using PI control without sensors, then sensorless operation is achieved, but estimation delay occurs leading to inaccurate moment of inertia calculation
Solution Approach 1:
The patent applies preliminary action by pre-calculating the delay characteristic of the speed estimation and compensating for it in advance. The delay characteristic calculation unit computes the expected delay based on system parameters before the actual moment of inertia calculation, allowing the system to compensate for the estimation delay proactively rather than reactively. This enables accurate moment of inertia calculation despite the inherent delay in sensorless speed estimation.
2Ease of operation
If conventional speed estimation is used, then sensorless control is implemented, but delay occurs until estimated speed converges
Solution Approach 1:
The patent implements feedback by continuously monitoring the convergence status of the estimated speed and using this information to adjust the moment of inertia calculation timing. The system feeds back the estimation delay characteristic to the moment of inertia calculation unit, which then compensates for the delay. This feedback mechanism reduces the effective loss of time by accounting for the convergence delay rather than waiting passively for it to expire.
3Device complexity
If estimated speed is used directly for moment of inertia calculation, then calculation is simplified, but error occurs due to estimation delay
Solution Approach 1:
The patent introduces an intermediary element - the delay characteristic calculation unit - that mediates between the speed estimation unit and the moment of inertia calculation unit. This intermediary computes the delay characteristic based on the estimated speed and system parameters, then uses this delay information to correct the moment of inertia calculation. This intermediary approach maintains relative simplicity while significantly improving calculation accuracy by accounting for the estimation delay.
Data Source
AI summary
A control device for an AC rotating machine includes: a current detection unit; a command generation unit for generating a voltage command, using a moment of inertia J; a speed estimation unit for calculating an estimated speed ω0 on the basis of the voltage command and detected current; an output torque computing unit for calculating output torque on the basis of the detected current; and an inertia moment computing unit for calculating the moment of inertia J. The output torque computing unit gives a delay characteristic corresponding to an estimation delay of the estimated speed ω0, to the output torque, and the inertia moment computing unit calculates the moment of inertia J on the basis of the estimated speed ω0 and the output torque having the delay characteristic.