Inverter Synchronization via Diode Current Measurement
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Solution Overview
Problem
Inverters often fail to synchronize effectively with alternating voltage sources, particularly when connected to rotating machines or networks, leading to inaccuracies and risks of overcurrents, especially in field weakening regions where rotational speed-generated voltage equals the DC bus voltage, causing difficulties in determining phase angle and angular velocity.
Innovation Solution
Measuring current through diodes of the inverter to determine phase angle and angular velocity, using phase locked loops and Fourier analysis to synchronize the inverter with the alternating voltage source, enabling accurate modulation initiation without overcurrent risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If zero-current control is used for synchronization, then synchronization accuracy is improved, but current controller speed requirement increases leading to potential overcurrent pulses
Solution Approach 1:
The patent performs preliminary determination of phase angle and angular velocity using measured currents before initiating inverter modulation. This preliminary synchronization action allows the system to establish accurate phase information in advance, eliminating the need for high-speed current controllers during the synchronization process and preventing overcurrent pulses.
2Device complexity
If short circuit pulse method is used for synchronization, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent uses measured currents through diodes as an intermediary to determine phase angle and angular velocity. Instead of directly applying complex synchronization algorithms or simple but inaccurate pulse methods, the system measures the natural current flow through diodes during field weakening, which provides accurate phase information without requiring complex control circuitry or test pulses.
3Speed
If operation in field weakening region is performed, then rotational speed range is extended, but synchronization accuracy deteriorates due to low DC bus voltage
Solution Approach 1:
The patent converts the harmful effect of low DC bus voltage in field weakening region into a beneficial measurement opportunity. Instead of trying to maintain high voltage levels, the system exploits the natural current flow through diodes that occurs during field weakening operation. This current contains the necessary phase information and can be accurately measured even at low voltages, thereby achieving precise synchronization exactly where conventional methods fail.
Data Source
AI summary
A method and device are disclosed for synchronizing an inverter with an alternating voltage source. The method includes measuring a current generated by the alternating voltage source and flowing through diodes of the inverter, determining a phase angle and angular velocity relating to the alternating voltage source from the measured current for enabling synchronization between the inverter and the alternating voltage source, and starting modulation of the inverter according to the obtained phase angle and angular velocity.