Power Control Device Duty Command Phase Shift Compensation
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Solution Overview
Problem
The existing power control methods for AC-driven loads, such as motors, face accuracy issues due to the duty command value calculation time exceeding the sampling cycle, leading to incomplete PWM signal generation and reduced load control accuracy, especially when the sampling cycle becomes shorter than the calculation time.
Innovation Solution
A power control method that corrects the duty command value based on the phase shift of the PWM voltage, using a compensation amount adjusted according to the carrier signal cycle, to ensure accurate PWM signal generation and improve load control accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sampling cycle is shortened to improve PWM control accuracy, then the load control accuracy improves, but the duty command value calculation cannot be completed within the sampling cycle
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values for the duty command value in a lookup table before operation. During runtime, the controller simply retrieves the pre-computed correction value based on the carrier wave state, avoiding time-consuming calculations during the sampling cycle. This allows the system to use shorter sampling cycles while maintaining accurate PWM control through the pre-prepared correction data.
2Reliability
If dead time is added to prevent simultaneous switching of paired switching elements, then switching safety improves, but the phase of the PWM signal is delayed
Solution Approach 1:
The patent applies preliminary anti-action by calculating and applying a correction value to the duty command value that compensates for the phase delay caused by dead time addition. The correction value is computed based on the state of the carrier wave (increasing or decreasing) and is added to the original duty command value before PWM generation. This preliminary correction counteracts the phase delay effect, maintaining accurate PWM signal timing while preserving the necessary dead time for safe switching operation.
3Reliability
If spread spectrum modulation or frequency switching is used for temperature protection, then element protection improves, but the sampling cycle may become shorter than calculation time
Solution Approach 1:
The patent applies preliminary action by pre-computing correction values for various carrier wave states and storing them in advance. This allows the system to rapidly switch between different carrier frequencies (as in spread spectrum modulation or temperature protection schemes) without performing complex calculations during each switching event. The pre-prepared correction values ensure that load control accuracy is maintained even when the sampling cycle becomes shorter than the calculation time due to frequent frequency changes.
Data Source
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AI summary
A power control method for calculating a duty command value to be used for a PWM control, generating a PWM signal corresponding to a comparison result between the duty command value and a carrier signal, and applying a PWM voltage to a load by driving an inverter based on the PWM signal. The power control method comprises obtaining a compensation amount according to a phase shift generated in the PWM voltage so as to compensate for the shift, correcting the compensation amount according to a cycle of the carrier signal, and correcting the duty command value depending on whether a strength of the carrier signal is increasing or decreasing using the corrected compensation amount.