Inverter Capacitance Estimation via Regeneration Mode
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Solution Overview
Problem
Existing methods for estimating the capacitance of DC-link capacitors in motor drive systems require additional hardware or offline measurements, which are inconvenient and lack reliability, especially during normal operation.
Innovation Solution
An inverter vector driving system that estimates capacitance using software by operating the induction motor in a regeneration mode, generating d-axis and q-axis voltage commands, and applying a recursive least square algorithm to calculate capacitance from DC-link voltage and current, without requiring additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offline measurement technique is used to identify capacitance, then measurement accuracy is improved, but system operation is interrupted and capacitor must be separated
Solution Approach 1:
The patent replaces the mechanical/physical offline measurement system with a software-based online estimation system. The capacitance value is estimated through computational algorithms using voltage and current signals already present in the motor drive system, eliminating the need for physical capacitor separation and RLC meter measurement.
Solution Approach 2:
The system uses its own operating signals (voltage and current during motor operation) to estimate capacitance without requiring external measurement equipment. The capacitance estimation is performed using the system's own operational data, allowing continuous operation while monitoring capacitor health.
2Reliability
If additional current sensor is added to measure ripple components, then capacitance estimation reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the existing current sensor serve multiple functions: it measures both motor control currents and the ripple components needed for capacitance estimation. The same sensor hardware is utilized for both motor drive control and capacitor health monitoring, eliminating the need for additional sensing equipment.
Solution Approach 2:
The system extracts capacitance estimation information from signals already present in the system during normal operation. By analyzing the ripple components in the existing current and voltage signals, the system performs self-diagnosis without requiring external measurement devices or additional sensors.
3Speed
If capacitance calculation is performed only once during estimation process, then calculation speed is improved, but estimation reliability decreases
Solution Approach 1:
The patent performs capacitance estimation continuously during motor operation rather than as a single calculation. The estimation process runs continuously using ongoing voltage and current measurements, providing updated capacitance values that reflect the capacitor's actual state during operation, thereby improving reliability while maintaining calculation speed.
Data Source
AI summary
The present invention relates to an inverter vector driving system and a method for estimating capacitance using the same. The present invention provides a method for estimating capacitance in an inverter vector driving system including a capacitor to which a rectified DC voltage of a three-phase power supply is charged, and a PWM inverter configured to transform the DC voltage into a three-phase AC voltage to be applied to a motor of an induction motor, including: operating the motor of the IM in a regeneration mode; generating a d-axis voltage command and a q-axis voltage command for the motor; adjusting a pulse of the PWM inverter by using the d-axis voltage command and the q-axis voltage command; and estimating capacitance of the capacitor by using a DC-link voltage and a DC-link current that are generated at the capacitor due to the inclusion of the AC component.