Inverter Voltage Compensation for DC Offset Suppression
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Solution Overview
Problem
Power conversion devices connected to loads and grid interconnection devices face issues with suppressing DC components and frequency changes in output voltages, leading to premature disconnection of grid interconnection devices due to active isolated operation detection functions, especially during transient load changes.
Innovation Solution
A power conversion device with an inverter, filter, detector, feedback controller, and PWM controller that continuously detects DC components and adjusts the inverter voltage command to suppress DC components by superimposing a compensation amount, synchronized with the AC voltage command, to maintain zero or offset error values, thereby controlling frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pulse signal modulator changes the pulse signal per half period to cancel DC components (PTL 1), then the DC component can be suppressed, but it takes time to suppress the DC component and frequency change, especially when the DC component varies transiently
Solution Approach 1:
The feedback controller continuously calculates the DC component amount in advance and determines the inverter voltage command with superimposed compensation before the DC component causes frequency changes. This preliminary calculation and continuous adjustment approach allows the system to proactively suppress DC components rather than reactively correcting them after they manifest, thereby reducing response time especially during transient load changes
Solution Approach 2:
The system employs a feedback controller that continuously detects the DC component amount in the output voltage and uses this feedback information to dynamically adjust the inverter voltage command. The compensation amount is calculated based on the detected DC component, creating a closed-loop control system that rapidly responds to transient variations in DC components, thereby improving both suppression effectiveness and response time
2Reliability
If reactive power is injected by the active isolated operation detection function to promote frequency change detection, then isolated operation can be detected, but the frequency change promotes disconnection of the grid interconnection device
Solution Approach 1:
The feedback controller applies preliminary anti-action by continuously suppressing DC components and their associated frequency changes before they reach levels that would trigger disconnection. By maintaining the output voltage frequency within acceptable ranges through proactive DC component compensation, the system prevents the frequency changes that would otherwise cause the grid interconnection device to disconnect, thereby ensuring continuous operation while still allowing isolated operation detection to function
Data Source
AI summary
A power conversion device includes an inverter that generates an inverter voltage, a filter that receives the inverter voltage and outputs an output voltage, a detector that detects a DC component of the output voltage, a feedback controller that receives an AC voltage command and the DC component and determines an inverter voltage command such that the DC component is equal to a target value which is zero or a value corresponding to an offset error of the detector, and a PWM controller that receives the inverter voltage command and performs pulse width modulation control of the inverter. The feedback controller computes a compensation amount for compensating for the DC component and determines, as the inverter voltage command, the AC voltage command on which a product of an absolute value of a sine wave synchronized with a period of the AC voltage command and the compensation amount is superimposed.