TKR COLLEGE OF ENGINEERING & TECHNOLOGY

AN AUTONOMOUS INSTITUTION
Accredited by NBA and NAAC with ‘A+’ Grade.
Sponsored by TKR Educational Society, Approved by AICTE,
Affiliated to JNTUH
Medbowli , Meerpet , Balapur, Hyderabad, Telangana - 500097
Department of Electrical & Electronics Engineering
Major Project Phase -1
Grid Forming Inverter Power Control Stability Analysis
Using MATLAB/SIMULINK

BY BATCH : 07
K.SHIVA KUMAR (22K95A0238)
M.RAHUL (22K95A0249)
PROJECT GUIDE:
DR.S.NARASHIMHA
D.SAI KRISHNA (22K95A0223)
(PROFESSOR) Y.ABHINAY (22K95A0281)
Abstract
The trend of transforming the supply structure of renewable energy is gradually increasing. Renewable energy sources based on
power electronic equipment are rapidly replacing existing synchronous generators (SGs). Renewable energy sources, including wind
turbine, solar photovoltaics (PV), and energy storage system (ESS), are also called inverter-based resources (IBRs), and these
resources are already being used in our daily lives to cover a considerable proportion of electricity demand. Researchers are trying
to make the power grid more stable by using new devices called grid- forming inverters (GFMs), which act like traditional power
generators. These GFMs help stabilize the grid and handle faults, but they can become unstable when the grid’s short circuit ratio
(SCR) is high.

In this project, the researchers created a mathematical model of a GFM and its interaction with the grid’s SCR. Will design and
develop a new control method for GFMs to keep the grid stable during small and large disturbances. This may compare with existing
methods .The simulations result will carried out in MATLAB /simulation.
Problem Statement
Grid-forming inverters (GFIs) are critical components in modern power systems, serving as voltage sources to maintain grid
stability. Their effective control is essential for ensuring grid synchronization, power sharing, and overall system reliability.
This project aims to analyze the stability of GFI power control systems using MATLAB/Simulink, addressing challenges
related to nonlinear dynamics, grid disturbances, and parameter variations.

Challenge Solution Objective

Voltage and Frequency Stability: As MATLAB/Simulink is a powerful tool Develop Control Strategies:
GFIs operate in a decentralized for modeling and simulating complex Investigate and propose advanced
manner, maintaining voltage and power systems. It offers a graphical control algorithms that enhance the
frequency stability is critical. interface, a vast library of pre-built stability and performance of GFIs in
Instabilities can arise from sudden blocks, and built-in solvers, making it varying operational scenarios.
load changes, generation fluctuations, ideal for this task.
or communication delays among
inverters.
Objectives
The project aims to achieve specific objectives to understand and
address the stability challenges posed by grid-forming inverters.

Model Development: Stability Analysis:

Employ small-signal linearization
Create a detailed MATLAB/Simulink model of the
techniques to analyze system stability
GFI system, including the inverter, control
around an operating point. Calculate
circuitry, and grid representation.
eigenvalues and eigenvectors to determine system
stability margins.

Control Design: Sensitivity Analysis:

Develop and implement appropriate control Study the sensitivity of GFI stability to
strategies, such as proportional-integral- parameter variations and grid disturbances.
derivative (PID) or model predictive control dentify critical parameters that significantly
(MPC), to ensure GFI stability and affect stability and develop strategies to
performance. mitigate their impact.
Model Development:
1. Define System Components
• Grid-Forming Inverter Model: Start by modeling the inverter. Grid-forming inverters operate in voltage-source mode,
where they control both voltage and frequency.
• Control Strategies: Implement power control algorithms, such as droop control (P-f and Q-V droop), virtual synchronous
machine (VSM) control, or other techniques that emulate the behavior of synchronous generators.
• Grid Representation: Model the grid or microgrid that the inverter will interact with. Include parameters for grid
impedance, load, and fault conditions.

2. Inverter Control Design

• Droop Control: Implement active power-frequency (P-f) and reactive power-voltage (Q-V) droop control to manage power
sharing among inverters. These functions are crucial for stability as they enable the inverter to respond to frequency and
voltage changes.
• Virtual Inertia: Introduce virtual inertia control if you want to emulate the behavior of a traditional synchronous
generator and enhance frequency stability.
• Inner Control Loops: Include inner voltage and current control loops, using a proportional-integral (PI) or proportional-
resonant (PR) controller, to maintain desired output waveforms.
Stablility Analysis:
Step 1: Define the Inverter Model
1. Define the Dynamic Model: Create a dynamic model of the inverter that includes key components like:
2. Linearize the System: Linearize the inverter model around a steady-state operating point. MATLAB's linearize() function can
be helpful here if you are using Simulink, or you can use analytical methods to derive the linearized model equations.
Step 2: Set Up the Transfer Functions
1.Transfer Functions: Develop transfer functions for the inverter’s active and reactive power controllers. For a basic grid-
forming inverter, these typically involve
2. State-Space Representation: If your system has multiple states, consider using a state-space representation (ss in MATLAB)
to capture all the dynamics
Step 3: Perform Stability Analysis
1.Bode Plots: Use bode() to plot the frequency response of each control loop. This helps assess the gain and phase margins,
which are indicators of stability.
2. Nyquist Plots: Nyquist plots (nyquist() in MATLAB) are useful for checking the closed-loop stability, especially in systems
that might have right-half plane poles or zeros.
3. Root Locus: Root locus analysis (rlocus()) allows you to study how the poles of the system change with varying control
gains, which is helpful for tuning purposes.
Step 4: Analyze and Interpret Results
1.Stability Margins: From the Bode and Nyquist plots, calculate the gain and phase margins to quantify the stability
2. Time-Domain Simulation: Simulate the inverter in Simulink or MATLAB to observe time-domain responses for setpoint
changes or disturbances. Use step() and impulse() functions for response analysis.
Block Diagram
 Block Diagram Description
This block diagram represents a control system typically used in grid-connected power systems,
particularly for grid-forming converters. Here’s a breakdown of the components and their functions:

1. Power Control BlockInputs: The power control block takes in two primary inputs, and , which
represent the voltage and current at the point of common coupling (PCC). It also receives reference
values , and , which are desired or set points for voltage magnitude, frequency, active power, and
reactive power, respectively . Function: This block manages the power flow to the grid by adjusting
the voltage magnitude () and phase () based on the reference values. The goal is to match the set
points for power and frequency with the grid’s requirements.
2. Voltage Control BlockInputs and Outputs: The outputs and from the power control block are fed
into the voltage control block, where it modulates the voltage waveform for synchronization with the
grid.Impedance : The voltage control block includes an impedance
In an inverter system, PCC stands for the Point of Common Coupling. This is the point where the
inverter, which is typically generating AC power from a DC source (like solar panels or batteries),
connects to the grid or to a larger electrical network. The PCC serves as a boundary or interface
between the power generated by the inverter and the existing power grid or the electrical system of
a facility.
1. Voltage Synchronization: The inverter needs to synchronize its output voltage, frequency, and
phase with those of the grid at the PCC. This ensures smooth power transfer and avoids issues
like harmonics or voltage instability.
2. Power Quality Measurement: Power quality parameters (such as voltage, current, frequency,
and harmonics) are often measured at the PCC. This helps in monitoring and ensuring that the
inverter is delivering clean, stable power to the grid.
3. Fault Detection: The PCC is also a critical point for detecting any abnormalities, like faults, that
could affect either the grid or the inverter. This can include overvoltage, undervoltage, or
frequency deviations, prompting safety mechanisms to protect both the inverter and the grid.
4. Grid Compliance: Most utilities have regulations that specify requirements for inverters at the
PCC, especially in grid-tied systems. These requirements often include the ability to disconnect
automatically if grid conditions fall outside certain limits.
In an inverter, voltage magnitude and phase are crucial aspects of its output that determine how
effectively it supplies power to a load or connects with the grid. Here’s a brief breakdown of these
two parameters:
1.Voltage Magnitude:
Definition: This is the absolute value of the output voltage of the inverter.
Control: By adjusting the modulation index (usually in a Pulse Width Modulation or PWM control
strategy), the inverter can control the magnitude of the output AC voltage.
Relevance: Accurate control of voltage magnitude is essential for maintaining voltage stability, which
is critical in applications like grid-connected systems, where the inverter must match the grid voltage
level to prevent disruptions.
2. Voltage Phase:
Definition: The phase angle of the inverter output voltage represents the shift between the
inverter’s voltage waveform and a reference, usually the grid’s voltage waveform.
Control: Phase control is often managed by adjusting the switching signals to maintain
synchronization with the grid.
Relevance: Proper phase alignment (especially in grid-tied applications) ensures that power flows
efficiently and reduces the risk of instability or power loss. Leading or lagging phase angles can also
control reactive power flow, which is vital for power factor correction.Together, voltage magnitude
and phase are adjusted to achieve the desired power flow and stability in applications, particularly
when operating in parallel with the utility grid.
Expected Results
• Power Flow Control: The Power Control block will regulate
the active and reactive power flow to the grid based on the
reference values. This ensures that the desired amount of
power is delivered to the grid while maintaining grid stability.

• Voltage Regulation: The Voltage Control block will adjust the

voltage magnitude and phase at the PCC to match the reference
values. This maintains the grid voltage within acceptable limits
and prevents voltage fluctuations.

• Grid Stability: By controlling the power flow and voltage, the

system contributes to the overall stability of the grid. It helps to
prevent voltage sags, swells, and frequency deviations.
.
Conclusion
Grid-forming inverters play a crucial role in the evolving
power grid, particularly in scenarios with high levels of
renewable energy integration. Their ability to provide voltage
and frequency support ensures grid stability, but their control
dynamics introduce new challenges in terms of stability,
especially in weak grid environments. Advanced control
techniques, along with robust stability analysis methods, are key
to ensuring that these inverters can operate reliably and safely
under various grid conditions.
 References
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THANK YOU