3-Level Inverter ON Voltage Error Correction
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Solution Overview
Problem
Conventional methods for correcting ON voltage drop in 2-level inverters are not applicable to 3-level inverters, leading to instability and distortion in sensorless vector control due to differences in circuit configuration and PWM control methods.
Innovation Solution
A 3-level power conversion device with a control section that calculates and corrects ON voltage errors using time ratios of three potentials and current values, adjusting the voltage command to compensate for ON voltage drops in semiconductor switching elements and flyback diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 2-level inverter correction method is applied to a 3-level inverter, then the device complexity is reduced, but the manufacturing precision of voltage command is deteriorated due to differences in circuit configuration and PWM control methods
Solution Approach 1:
The patent applies local quality by recognizing that the 3-level inverter requires a specialized correction method tailored to its specific circuit configuration and PWM control characteristics, rather than using a generic 2-level inverter approach. The correction calculation is locally adapted to account for the unique properties of the 3-level topology including its twelve switching elements and two carrier PWM control mechanism.
Solution Approach 2:
The patent implements parameter changes by modifying the voltage command value based on calculated ON voltage errors specific to the 3-level inverter configuration. The correction amount is dynamically adjusted according to the actual operating parameters of the 3-level circuit, including the specific conduction states of its switching elements and diodes, thereby achieving accurate voltage compensation tailored to this topology.
2Device complexity
If ON voltage drop correction is not performed, then the device complexity is reduced, but the stability of sensorless vector control is deteriorated due to voltage errors causing distortion in output current or torque
Solution Approach 1:
The patent implements feedback by calculating the ON voltage errors based on the actual conduction states of the switching elements and diodes in the 3-level inverter, and using this calculated error information to correct the voltage command. This closed-loop approach ensures that the voltage applied to the motor accurately reflects the intended voltage command, thereby maintaining the stability and precision of sensorless vector control.
Solution Approach 2:
The patent applies preliminary action by pre-calculating the ON voltage errors before they affect the motor control performance. The correction amount is computed in advance based on the known characteristics of the switching elements and diodes, and this pre-calculated correction is then applied to the voltage command to prevent voltage errors from causing distortion in the output current or torque.
Data Source
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Figure 3(A)~3(D)
AI summary
A control section (9) for controlling a 3-level power conversion circuit (1) is provided. The control section (9) calculates ON voltage error based on time ratios of three potentials in a predetermined certain period and a current value from a current detection section (7) for detecting current output from the 3-level power conversion circuit (1), corrects a voltage command value based on a voltage correction amount for correcting the ON voltage error, and performs ON/OFF control for semiconductor switching elements of the 3-level power conversion circuit (1) based on the corrected voltage command value.