Modular Power Converter PWM Timing for DC Injection Mitigation
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Solution Overview
Problem
Power flow control systems in power transmission lines suffer from direct current (DC) injection without transformer isolation, necessitating effective methods to measure and remove DC components using modular converters.
Innovation Solution
A modular power converter system with a coupling capacitor, pulsed square-wave generator, and control circuit to measure and adjust pulse timing to counterbalance the average injected DC component, utilizing Fourier transformation and phase-locked loop circuits for precise timing adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If modular converters are used for power flow control in transmission lines, then reactive power injection capability is improved, but DC component injection occurs causing system instability
Solution Approach 1:
The patent extracts and removes the harmful DC component from the converter output by introducing a dedicated DC measurement and correction mechanism. The system measures the DC component separately and applies a correction angle specifically targeting DC elimination, thereby separating the DC mitigation function from the overall power control system.
Solution Approach 2:
The patent implements a feedback control mechanism where the DC component is continuously measured and fed back to the control system. Based on this feedback, a correction angle is dynamically adjusted and applied to the pulse timing, creating a closed-loop system that automatically compensates for DC injection and maintains system stability.
2Object-affected harmful factors
If pulse timing is adjusted to counterbalance DC injection, then DC component is reduced, but control system complexity increases
Solution Approach 1:
The patent changes the timing parameter of the converter pulses by introducing a correction angle that shifts the pulse positions. This parameter adjustment is achieved through Fourier transformation of the DC component and applying a phase shift, which modifies the pulse timing to counterbalance the DC injection without requiring complex hardware modifications.
3Measurement precision
If Fourier transformation and phase-locked loop circuits are used for precise timing adjustments, then DC injection mitigation precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces mechanical or analog measurement methods with Fourier transformation and digital signal processing techniques. The DC component is measured by transforming the current signal into the frequency domain, allowing precise identification and measurement of the DC component through mathematical analysis rather than complex hardware circuits.
Data Source
AI summary
A modular power converter is operable to mitigate a DC component of injection onto a power transmission line. The modular power converter includes a pulse width modulation (PWM)-controlled generator, a voltage emulator, and a control circuit. The PWM-controlled generator includes drivers and a coupling capacitor. The PWM-controlled generator is to store voltage on the coupling capacitor and inject a voltage of the converter, which includes the DC component of injection, onto the power transmission line. The voltage emulator is to determine a DC measurement emulating the voltage of the converter, as a time-varying average value that is based on summing generator driver-state weighted values of the voltage on the coupling capacitor. The control circuit is to generate PWM pulses to operate the PWM-controlled generator and adjust timing of the PWM pulses, based at least on the DC measurement from the voltage emulator to counter-balance the DC component of injection.