Microgrid Inverter Control via Non-Linear Frequency Response
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Solution Overview
Problem
Microgrid applications face challenges in maintaining stable power frequency and voltage due to volatile renewable energy sources and sluggish generator responses, as traditional Statcom systems lack capacity for long-duration grid support, and energy storage systems require advanced management for charge maintenance and protection.
Innovation Solution
A system incorporating a DC link, energy storage system (ESS), and bidirectional DC-to-AC inverters with non-linear power-frequency control, along with a DC-to-DC converter and controller, manages power transfer by sensing grid frequency, determining power flow, and adjusting output frequency and current magnitude to support grid stability and ESS charging/discharging modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Statcom systems are used to provide reactive power compensation and transient voltage support, then voltage stability is improved, but operational duration is limited to seconds
Solution Approach 1:
The patent combines Statcom systems with energy storage systems (ESS) to create a hybrid configuration. The Statcom provides fast voltage support while the ESS extends operational duration, allowing the system to maintain voltage stability for prolonged periods during microgrid transitions or utility disconnections.
Solution Approach 2:
The hybrid system performs multiple functions: the Statcom component provides reactive power compensation and transient voltage support, while the ESS component provides extended energy storage and prolonged operational capability, creating a multi-functional system that addresses both short-term and long-term voltage stability requirements.
2Duration of action of moving object
If energy storage systems are used to provide supplemental power for long-duration grid support, then operational duration is improved, but system complexity increases due to charge maintenance and component protection requirements
Solution Approach 1:
The patent introduces a controller as an intermediary device that manages the ESS operations. The controller handles charge maintenance, monitors system state, and coordinates between the ESS and grid, thereby reducing the operational complexity and protecting ESS components while enabling long-duration support.
Solution Approach 2:
The system implements feedback control mechanisms where the controller continuously monitors ESS charge state, grid conditions, and system performance, automatically adjusting operations to maintain optimal charge levels and protect components, thereby simplifying management of the complex ESS integration.
3Measurement precision
If non-linear power-frequency curves are used to adjust output frequency, then frequency control precision is improved, but control complexity increases
Solution Approach 1:
The patent employs dynamic non-linear power-frequency curves that adapt to different operating conditions rather than using fixed linear relationships. This allows precise frequency control across varying load and generation scenarios, with the control characteristics changing dynamically to match system needs.
Solution Approach 2:
The system changes control parameters by selecting different non-linear power-frequency curves based on operating conditions. The controller adjusts frequency setpoints using these curves, transforming the control approach from static linear to dynamic non-linear parameter relationships for improved precision.
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 system effectively supports microgrid stability by providing reactive power, managing frequency and voltage, and protecting ESS components from power surges, enabling comprehensive operation across various conditions, including undervoltage and overvoltage correction, and up to 100% power replacement during grid source unavailability.
Implementation Method 1
a bidirectional DC-to-AC inverter with non-linear power-frequency control
Implementation Method 2
a DC-to-DC converter coupled between the DC bus and the energy storage system
Data Source
AI summary
A system that manages a supplemental energy source connected to a power grid uses a two stage control strategy to manage power transfers in and out of the power grid as well as in and out of an energy storage system, such as a battery bank. One stage uses a non-linear transfer function to control an output frequency of a DC-to-AC inverter to limit undesired effects of power transients that occur on the grid. A second stage uses control strategy for transferring energy between the energy storage system and an internal DC link based on a relationship between a voltage on a DC link connecting the first and second stages and a DC link reference voltage, the voltage on the DC link, and a voltage at the energy storage system. The control strategy includes rapid charging, over-charging protection, and grid transient stabilization.