Inverter Controller for DER Integration and Grid Stability
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Solution Overview
Problem
The integration of distributed energy resources (DERs) into dynamic distribution systems faces challenges in smooth transition between isolation and grid modes, especially due to the inertialess nature of microsources, which requires a method to effectively utilize power and energy storage resources without relying on complex centralized command and control systems.
Innovation Solution
A controller system that calculates and adjusts the operating frequency of an inverter based on local information such as voltage, current, and frequency to manage the charge and discharge of energy storage devices, ensuring seamless transitions and efficient energy distribution within the DER system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If distributed energy resources are integrated into the distribution system, then energy efficiency and reliability are improved, but system stability deteriorates due to the inertialess nature of microsources
Solution Approach 1:
The patent introduces a controller as an intermediary device that manages the connection and operation of inertialess microsources in the distribution system. The controller monitors system conditions and regulates power flow from microsources, ensuring stable operation despite their lack of inherent inertia. This mediator enables reliable integration of DERs while maintaining system stability through active control.
2Reliability
If complex centralized command and control systems are used to manage DER transitions, then transition smoothness is improved, but system complexity increases
Solution Approach 1:
The patent implements a self-service control approach where the controller at each DER site autonomously manages transitions between grid-connected and islanded modes using local measurements and predefined control logic. The controller detects grid conditions and automatically executes transition sequences without requiring complex centralized coordination, thereby achieving smooth transitions while minimizing system complexity.
3Reliability
If energy storage devices are used to support microsource operation, then power quality and reliability are improved, but device complexity and cost increase
Solution Approach 1:
The patent designs the controller to manage multiple functions including power quality regulation, energy storage coordination, and mode transition control. The energy storage devices serve multiple purposes: stabilizing voltage and frequency, providing inertial support during transitions, and enabling islanded operation. This multi-functional approach improves power quality and reliability while avoiding the need for separate dedicated devices for each function.
Data Source
AI summary
A microsource is provided, which includes an inverter, an energy storage device, and a controller. The controller calculates a maximum frequency change for the inverter based on a first comparison between a first power set point and a measured power from the inverter. The first power set point is defined based on a charge level of the energy storage device. A minimum frequency change for the inverter is calculated based on a second comparison between a second power set point and the measured power from the inverter. An operating frequency for the inverter is calculated based on a third comparison between a power set point and a measured power flow. A requested frequency for the inverter is calculated by combining the maximum frequency change, the minimum frequency change, and the operating frequency. The requested frequency is integrated to determine a phase angle of a voltage of the inverter to control a frequency of an output power of the inverter.