Renewable Plant Inverter Control for Primary Frequency Response
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Solution Overview
Problem
Existing control systems for renewable energy plants struggle to provide immediate real power response to sustained underfrequency deviations, leading to potential frequency excursions and plant curtailment, which do not comply with regulatory requirements.
Innovation Solution
A method and system that utilize a renewable energy plant control system to measure frequency and power output, generate error signals, and apply control signals to the inverter while limiting outputs to predetermined power limits, thereby preventing inverter shutdown and integral windup during frequency events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter operates below the low power limit, then the inverter shuts down to protect itself, but the plant cannot provide immediate primary frequency response required by FERC regulations
Solution Approach 1:
The control system preemptively limits the power command to stay above the inverter's low power threshold before the inverter can shut down. By continuously monitoring the power command and comparing it to the known low power limit, the system adjusts the command in advance to prevent shutdown conditions, ensuring both inverter protection and continuous frequency response capability.
2Reliability
If the inverter is commanded to produce power below its low power limit, then the inverter shuts down, but this causes integral windup in the PI controller and power spikes upon restart
Solution Approach 1:
The control system implements feedback by continuously monitoring the actual power output and comparing it to the commanded power. When the commanded power approaches the low power limit, the system detects this condition and adjusts the command accordingly. This feedback mechanism prevents integral windup by ensuring the controller operates within valid ranges and avoids the instability that would occur upon inverter restart.
Data Source
AI summary
A method for providing primary frequency response for a renewable energy plant coupled to an electric power grid, the renewable energy plant having an intermittent energy source coupled thereto by an inverter, the method comprising: using a renewable energy plant control system, measuring frequency and determining a first difference signal between the measured frequency and a frequency reference; measuring power output from the renewable energy plant and determining a second difference signal between the measured power output and a power reference; generating an error signal from a sum of the first and second difference signals; generating a control signal by applying the error signal to a controller; limiting the control signal output from the controller to between predetermined minimum and maximum power limits for the inverter; while the control signal is limited by the predetermined minimum power limit for the inverter, disabling an integral function of the controller; and, applying the control signal to the inverter to control the power output from the intermittent energy source.