Time-Synchronized Injection Modules for Low-Harmonic Power Flow Control
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Solution Overview
Problem
Current power grid control systems, reliant on substation-based static synchronous series compensators, generate high-voltage square waves that cause harmonic oscillations, leading to expensive and maintenance-intensive high-speed, high-voltage switching circuits, while distributed impedance injection modules struggle with harmonic oscillations due to additive impedance injections.
Innovation Solution
Implementing transformer-less flexible alternating current (AC) transmission systems (TL-FACTS) based impedance injection modules with synchronized clocks and high-speed communication links to generate pseudo-sinusoidal waveforms by coordinating impedance injections from multiple distributed modules, reducing harmonic oscillations and eliminating the need for high-speed switching circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If substation-based static synchronous series compensators generate high-voltage square waves for line balancing, then power flow control capability is improved, but harmonic oscillations are caused and system cost increases
Solution Approach 1:
The patent divides the single substation-based compensator into multiple distributed impedance injection modules along the transmission line. Each module independently generates lower-voltage square waves that are phase-shifted and combined to create an effective pseudo-sinusoidal waveform, achieving the same power flow control capability without the harmful high-voltage square wave injections from a single point.
Solution Approach 2:
The patent converts the harmful harmonic oscillations caused by square wave injection into a beneficial effect by using the transmission line's own impedance to smooth the combined waveform. The distributed modules' square waves, when combined with proper phase shifting, are naturally filtered by the line impedance to produce the desired pseudo-sinusoidal waveform for effective power flow control.
2Manufacturing precision
If high-speed high-voltage switches are used to generate pseudo-sine waves, then waveform quality is improved, but device complexity and maintenance cost increase
Solution Approach 1:
The patent segments the waveform generation function across multiple distributed modules, each using simpler switching circuits to generate square waves. The complex pseudo-sinusoidal waveform is achieved through the combination of these simpler square waves with different phase shifts, eliminating the need for complex high-speed high-voltage switches in a single location.
Solution Approach 2:
The patent uses periodic square wave injections from distributed modules with specific phase relationships. By controlling the timing and phase of these periodic square wave injections, the system synthesizes the desired pseudo-sinusoidal waveform through constructive interference, achieving waveform quality without complex switching hardware.
3Speed
If distributed impedance injection modules are used for local control, then responsiveness to disturbances is improved, but harmonic oscillations occur due to additive impedance injections
Solution Approach 1:
The patent introduces asymmetric phase shifts between the square wave injections from different distributed modules. This asymmetric timing arrangement ensures that the square waves do not add constructively at harmonic frequencies, but instead combine to form the desired pseudo-sinusoidal waveform with reduced harmonic content, maintaining fast local response while eliminating harmful additive effects.
Data Source
AI summary
In prior art grid systems, power-line control is done by substation based large systems that use high-voltage (HV) circuits to get injectable impedance waveforms that can create oscillations on the HV power lines. Intelligent impedance injection modules (IIMs) are currently being proposed for interactive power line control and line balancing. These IIMs distributed over the high-voltage lines or installed on mobile platforms and connected to the HV power lines locally generate and inject waveforms in an intelligent fashion to provide interactive response capability to commands from utility for power line control. These IIMs typically comprise a plurality of impedance-injection units (IIUs) that are transformer-less flexible alternating current transmission systems interconnected in a series-parallel connection and output pulses that are additive and time synchronized to generate appropriate waveforms that when injected into HV transmission lines are able to accomplish the desired response and provide interactive power flow control.