Wound Induction Machine Control System for DC Voltage Management
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Solution Overview
Problem
In wound induction machines, during power system breakdowns, the 'current zero-missing' phenomenon can occur, leading to increased direct current voltage that may damage switching elements, and high reactive power excitation results in high breakdown currents, necessitating high-power consumption resistors to suppress voltage increases, thereby increasing device size and cost.
Innovation Solution
A control system comprising a chopper, short-circuit unit, voltage detector circuit, and controller that reduces direct current voltage between the converter and inverter, and shorts wires to manage direct current components, preventing zero missing and suppressing voltage increases by strategically operating the chopper and inverter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high reactive power excitation is used in the leading direction, then strong excitation occurs in the leading direction, but high breakdown current occurs upon breakdown of the electric power system
Solution Approach 1:
The control device detects voltage drops indicating impending breakdown and preemptively switches the inverter from normal alternating current output to direct current output before the breakdown occurs. This preliminary action prevents the high breakdown current from occurring when the breakdown actually happens, while maintaining the strong leading excitation during normal operation
2Reliability
If the off period of the switching element is extended to suppress voltage increase, then the direct current voltage increase is suppressed, but the size and cost of the device increase due to requiring high power consumption resistor
Solution Approach 1:
The invention extracts and removes the resistor component from the system entirely. Instead of using a resistor to dissipate energy and suppress voltage, the system uses the inverter to actively generate direct current output that counteracts voltage increases, eliminating the need for power-consuming resistors while protecting switching elements
3Reliability
If the inverter switches to irregular operation mode due to current zero-missing phenomenon, then the circuit breaker separates the wound induction machine from the electric power system, but a direct current component is superimposed on the alternating current output
Solution Approach 1:
The control device detects voltage drops that indicate the electric power system is approaching breakdown before it actually occurs. It preemptively switches the inverter to direct current output mode, eliminating the alternating current with direct current component that would otherwise be generated when the circuit breaker separates the system after breakdown occurs
Data Source
AI summary
According to one embodiment, a control system includes a chopper, a short-circuit unit, a voltage detector circuit, and a controller. The chopper reduces a direct current voltage between a converter connected to a stator in a wound induction machine and an inverter connected to a rotor in the wound induction machine. The short-circuit unit shorts a wire used for connection between the rotor and the inverter and the voltage detector circuit is to detect the direct current voltage. The controller causes driving the chopper and, at the same time, outputting from the inverter an alternating current over which a direct current component is superimposed when a voltage value exceeds a first predetermined value, and causes driving the short-circuit unit and, at the same time, halting the inverter when the voltage value exceeds a second predetermined value.