UPS Forced Commutation Control for Magnetic Flux Compensation
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Solution Overview
Problem
Conventional uninterruptible power apparatuses face issues with magnetic flux imbalance during forced commutation, leading to inrush currents and triggering of overcurrent protection mechanisms due to the switching characteristics of thyristors.
Innovation Solution
An uninterruptible power apparatus with a control module that calculates and compensates for magnetic flux offsets by injecting a second voltage during the forced commutation period, using a DC/AC conversion circuit to adjust the output voltage and maintain magnetic flux balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a reverse voltage is applied to quickly turn off the thyristors during forced commutation, then the switching speed is improved, but magnetic flux imbalance occurs in the transformer which generates inrush current
Solution Approach 1:
The control module calculates the magnetic flux offset amount before the forced commutation is complete and provides a compensation command to the DC/AC conversion circuit. This preliminary compensation action counteracts the magnetic flux imbalance that will be caused by the reverse voltage, preventing the inrush current from occurring in the first place
Solution Approach 2:
The DC/AC conversion circuit acts as an intermediary between the reverse voltage injection and the transformer. It generates a compensation voltage based on the calculated magnetic flux offset, which mediates the magnetic flux balance and prevents the harmful inrush current while allowing the thyristors to be turned off quickly
2Device complexity
If the switch unit is used to transfer power from grid to load, then the device complexity is reduced, but the overcurrent protection mechanism is triggered due to inrush current
Solution Approach 1:
The control module performs preliminary calculation of the magnetic flux offset amount and generates the compensation command before the forced commutation period ends. This preliminary action ensures that the DC/AC conversion circuit is ready to provide compensation voltage, preventing the inrush current that would trigger the overcurrent protection mechanism
Solution Approach 2:
The control module continuously monitors the voltage at the load terminal and calculates the magnetic flux offset amount based on the error between the actual voltage and the voltage command. This feedback mechanism ensures that the compensation voltage is accurately adjusted to maintain magnetic flux balance and prevent overcurrent protection triggers
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses inrush currents and maintains magnetic flux balance, preventing overcurrent protection triggers and ensuring stable power supply to the load.
Implementation Method 1
The control module turns off the first thyristor and the second thyristor by injecting a second voltage into the load terminal during a forced commutation period
Implementation Method 2
The control module controls the DC/AC conversion circuit to provide a third voltage to the load terminal based on the compensation command and the voltage command
Data Source
AI summary
An uninterruptible power apparatus (100, 100', 100A) is coupled between a power grid (200) and a load (300). The uninterruptible power apparatus (100, 100', 100A) includes a bypass path (1, 1'), a power conversion module (2), and a control module (3, 3'). The bypass path (1, 1') is coupled to the power grid (200) through a grid terminal (100-1), and coupled to the load (300) through a load terminal (100-2). The control module (3, 3') turns off a first thyristor (122) and a second thyristor (124) by injecting a second voltage (V2, V2a-V2c) into the load terminal (100-2) during a forced commutation period (FC). The control module (3, 3') calculates a magnetic flux offset amount (Vx, Va-Vc) based on an error amount (Er, Era-Erc) between the second voltage (V2, V2a-V2c) and a voltage command (Vx, cmd, Va, cmd-Vc, cmd), and provides a compensation command (Vcmd) in response to the magnetic flux offset amount (Vx, Va-Vc). The control module (3, 3') controls the DC/AC conversion circuit (26, 26') to provide a third voltage (V3) to the load terminal (100-2) based on the compensation command (Vcmd) and the voltage command (Vx, cmd, Va, cmd-Vc, cmd).