Under Frequency Load Shedding Scheme — Simulation & Power Modeling

Abstract — Under Frequency Load Shedding Scheme

Under Frequency Load Shedding Scheme: Power Electronics, MATLAB/Simulink & Circuit Modeling Integrated Analysis: MATLAB/Simulink · MOSFET/IGBT Gate Drivers · SPWM/SVPWM · THD Spectrum · ~9268 Words Chapter 1: Power Electronics Overview, System Specifications & Topology Modeling The source files for paper: OPF-based Under Frequency Load Shedding Tracking the Dynamic Frequency Trajectory Under-frequency load shedding (UFLS) prevents system collapse during large disturbances. Increased penetration of distributed energy resources (DERs) and reduced system inertia makes it challenging to design a static UFLS scheme, which relies on preset frequency thresholds and load shed fractions to meet design criteria across all possible operating conditions.

Analytical & State-Space Control Methodology

Due to non-linearity and traceability issues, previous adaptive UFLS schemes use simplified tractable frequency models that overlook AC network effects such as voltage-dependent load/generation. This paper leverages model order reduction techniques to obtain a higher fidelity low-order model of system frequency dynamics that captures AC network effects while incorporating turbine governor action and their associated limits. The model is then used in a new AC-aware predictive optimization framework to adapt UFLS setpoints periodically based on current operating conditions while minimizing load shed. Validated on a 1,648-bus system with PSS/E simulations, the proposed method meets design criteria under various operating conditions and disturbance scenarios. Furthermore, the framework outperforms conventional static UFLS schemes and adaptive UFLS schemes based on simplified dynamic models.

Simulink Waveforms & Power Quality Findings

The transition of the power grid towards renewable energy resources (RES) has significantly reshaped the operation and has displaced traditional synchronous generators, leading to a reduction in system inertia traditionally provided by synchronous generators . Reduced inertia levels lead to larger frequency sensitivity to power imbalances, impacting grid reliability and stability. Under-frequency load shedding (UFLS) is used as the power grid’s emergency brake and sheds load during large contingencies to help restore the balance between load and generation, halt frequency decline, and help prevent overall system collapse. Conventional UFLS schemes are static and rely on several UFLS relays in the network with preset frequency thresholds. The UFLS relays are designed such that when they trip a predetermined percentage of load is shed when the frequency at the relay drops below a preset threshold . Typically, UFLS schemes consist of multiple stages each with a corresponding frequency threshold and load shed amount. The amount of load shed and the frequency thresholds are designed to meet certain performance criteria laid out by the North American Electric Reliability Corporation (NERC) for contingencies with an imbalance of up to 25% between load and generation . However, with the increased prevalence of distributed energy resources (DERs), load patterns behind the UFLS relays have become more erratic with larger variations . Furthermore, generation from DERs such as residential solar PV can exceed local demand leading to reversed power flow (backfeeding). Static UFLS schemes do not adapt to changing operating conditions, fluctuating load patterns, reduced system inertia, and bi-directional power flows. As a result, static UFLS schemes may fail to restore frequency to within safe limits.

Scope & Practical Applications

• High-efficiency DC-DC converters and isolated resonant topologies (LLC / DAB)
• Sinusoidal and Space Vector PWM inverters for grid integration & industrial motor drives
• MOSFET / IGBT gate driver optimization with active Miller-clamp shoot-through protection
• Power quality conditioning with Total Harmonic Distortion (THD) strictly compliant with IEEE 519
• Complete Simscape .SLX model files, parameter calculation scripts, and IEEE dissertation reports