The document discusses stability and control of power grids, outlining various stability categories such as rotor angle, frequency, voltage, converter-driven, and resonance stability. Each category is defined, with types, modeling approaches, and challenges in developing control strategies highlighted. Additionally, it addresses traditional and modern methods for frequency and voltage control in power systems alongside ongoing research initiatives for improving stability and management in the presence of converter-interfaced generators.

1. Stability and Control of Power Grids

2. Stability
Theory of
Power Grids
 Categories:
• Rotor Angle Stability
• Frequency Stability
• Voltage Stability
• Converter-Driven Stability
• Resonance Stability
IEEE classifications of power system stability (Year: 2004 and 2020)

3. Rotor Angle
Stability
 Definition:
• Ability of synchronous machines to remain in synchronism
after a disturbance.
 Types:
• Small-Disturbance Angle Stability
• Transient Stability

4. Voltage
Stability
 Definition:
• Ability to maintain steady
voltages at all buses after a
disturbance.
 Types:
• Short-Term Voltage Stability
• Long-Term Voltage Stability
 Modelling:
• Complex differential-
algebraic equations for
short-term,
• Simplified steady-state
models for long-term.

5. Frequency
Stability
 Definition:
• Ability to maintain a
steady frequency
following a severe
disturbance.
 Types:
• Short-Term Frequency
Stability
• Long-Term Frequency
Stability
 Modelling:
• Typically employs linear
models.

6. Converter-Driven Stability
 Definition:
• refers to the stability issues in power systems influenced by converter-
interfaced generators (CIGs.
 Dynamics and Timescales:
• Fast-Interaction Instability: Driven by rapid dynamic interactions between
CIGs and other fast-response components. Occurs at frequencies up to
several kilohertz.
• Slow-Interaction Instability: Involves slower dynamic interactions
between CIGs and the electromechanical dynamics of synchronous
generators.
 Modelling Challenges:
• Developing accurate models for CIGs (Converter-Interfaced Generators) is
difficult, which makes it challenging to create reliable stability guidelines.
 Control Strategies:
• Droop Control: Emulating droop characteristics of synchronous generators.
• Virtual Synchronous Machines: Configuring converters to mimic inertia and
damping characteristics of synchronous machines.
• Enhanced Protection Schemes: Designing schemes that respond to rapid
changes and high-frequency oscillations caused by CIGs.
 Research and Development:
• Ongoing research aims to develop better models and control strategies for
stable grid operation with high CIG penetration.

7. Resonance Stability
 Definition:
• refers to stability issues in power systems that arise when energy exchange takes place
periodically in an oscillatory manner.
 Types of Resonance:
o Torsional Resonance:
• Involves interactions between series compensated lines and the turbine-generator
mechanical shaft, leading to poorly damped, undamped, or negatively damped
oscillations.
o Electrical Resonance:
• Known as Induction Generator Effect (IGE), occurs due to interactions between series
compensation and the electrical characteristics of the generator, resulting in large
current and voltage oscillations.
 Dynamics and Timescales:
• Sub-Synchronous Resonance (SSR): Can manifest as resonance between series
compensation and the mechanical torsional frequencies of the turbine-generator shaft,
or between series compensation and the electrical characteristics of the generator.
 Modelling Challenges:
• Standard models for SSR and electrical resonance involving electromagnetics are still
evolving, making it challenging to establish comprehensive stability criteria.
 Control Strategies:
• Supplemental Controllers: Devices like HVDC lines, SVCs, STATCOM, and PSS can
interact with torsional mechanical modes, sometimes improving damping.
• Active Damping Strategies: Employed to prevent or mitigate high-frequency
oscillations, including harmonic instability and multi-resonance issues.
 Research and Development:
• Ongoing research aims to better understand and mitigate resonance stability issues,
particularly in systems with high penetration of converter-interfaced generators (CIGs).

8. Control of
Power Grids
 Frequency Control:
 Traditional:
o Primary,
o Secondary,
o Tertiary.
 New Challenges:
o Variability, Reduced
Inertia.
 New Methods:
o Advanced Control,
o Energy Storage,
o Demand-Side
Management.

9. Voltage
Control
 Traditional:
• Preventive and corrective
measures, hierarchical
structure.
 New Challenges:
• Voltage Fluctuations,
• Reverse Power Flow.
 New Methods:
• Coordination of DERs,
• Coordinated Control
Frameworks,
• Network Reconfiguration.

10. Single Machine
Connected to
Infinite Bus
 Focus Areas:
 Voltage Control, Frequency
Control.
 Importance:
 Preventing voltage collapse,
 balancing power supply and
demand.
 Secondary Focus:
 Rotor Angle Stability,
 Active and Reactive Power
Control.

11. Multi-
Machine
Power
Systems
 Key Variables:
• Frequency,
• Voltage,
• Rotor Angle,
• Active Power,
• Reactive Power,
• Power Flow.
 Control Mechanisms:
• AGC, AVRs, SVCs, Economic Dispatch, OPF, PSS, etc.
 Advanced Strategies:
• AI, Machine Learning, Real-Time Monitoring.

12. Thank you for your
attention!