The impact on the stability of power systems is rising as the penetration level of renewable energy with sporadic natures rises rapidly on the grid. However, the impact of different types of renewable energy sources (wind, solar) and their combination on system stability varies even with the same penetration level. This paper concentrates mainly on the stability analysis of multi-machine systems connected to various types of renewable energy sources. The study presents a simple and novel control technique named automatic reactive power support (ARS) for both single and combinations of renewable sources by injecting the available reactive power into the system during fault through converters to enhance system stability. The permanent magnet synchronous generator (PMSG) and doubly fed induction generator (DFIG) are both considered as wind generators in this paper for comparison. In addition, transient stability enhancement is carried out by improving critical clearing time of a three-phase fault in the power system. With the creation of a 3-phase fault at various buses, stability analysis is carried out on the 9-bus WSCC test bus system and also on the 68-bus IEEE test system. Comparative analysis of six test case conditions is provided and the considered cases are without renewable source, with DFIG as a wind generator, PMSG as a wind generator, solar PV farm, wind farm with DFIG and solar PV in combination and the combination of wind farm with PMSG and solar PV. Moreover, the improvement in critical clearing time of the system is compared using conventional and proposed controls with all the aforementioned renewable sources. Comparative results show that the proposed control technique improves system stability and also that the combination of renewable energy sources ought to enhance the critical clearing time of system.

Integrating wind power generators, whose frequency varies in a wide range due to varying wind speeds, into a grid is a formidable problem. At present, the use of permanent magnet synchronous generators (PMSG) and doubly fed induction generators (DFIG) as wind generators with suitable control is the best possible solution. However, a dual-field excited synchronous generator (DESG), which has two windings on the rotor, can also be used for the same purpose with appropriate control. A new control strategy, which essentially employs the d-axis and q-axis components of the alternator terminal voltage, is suggested here. This strategy essentially results in exciting the two field windings with a slip frequency. This eventually holds the stator frequency constant, irrespective of the rotor speed of the wind generator. The difference between the required frequency and the natural frequency, analogous to the rotor speed of the wind power generator, is the slip frequency. The ring modulator automatically adjusts the slip frequency depending on the actual speed of the generator’s rotor. This paper uses the ANSYS MAXWELL 2022 R1 software to design a DESG and uses a ring modulator as the control function generator for feedback with ANSYS TWIN BUILDER 2022 R1. Simulations are carried out using transient–transient co-simulation by combining both of these software tools for cases of both a constant-speed input and of a variable-speed input to the rotor of the machine. Moreover, a mathematical model of the DESG as a wind generator with the proposed controlled strategy is used to perform the stability analysis of a nine-bus three-machine system, and the results are compared with those of conventional wind generators.

Wind power generation is considered to be the significant dispatchable source in the integrated grid. Integration of wind firms impose serious frequency fluctuations in the grid due to intermittent wind speed variations. Doubly-fed induction generator (DFIG) and permanent magnet synchronous generator (PMSG) based wind power generation with suitable control strategy has become popular for solving frequency related issues in the grid. In this paper, constructional features of dual excited synchronous generator (DESG) are investigated for regulating the frequency fluctuations in the grid. DESG has two field windings one is on the d-axis and the other is on q-axis. Since, the construction of field windings on both the axes abide lot of efforts, two different ways of constructing field windings (DESG-1 and DESG-2) are suggested in this paper. In DESG-1, the two field windings are arranged with some angular deflection and in DESG-2, the two field windings are separated by 90°. The two windings in both DESG-1 and DESG-2 must be excited as per their arrangement to get the synchronous frequency at the stator terminals. The performance of aforementioned DESGs with different speeds is investigated in MAXWELL software.

Most of the power electronic components act as non-linear loads because they draw non- sinusoidal current from the power supply. Due to these non-linear loads, current harmonics are injected in the power network. For normal operation, any power network is equipped with provisions to keep the harmonics level to a minimum value. Whenever a fault occurs in the distribution system, the primary goal is to re-energize the healthy part of the network which got interrupted. It can be done by changing the topology of the network. This method is called as Service Restoration (SR). In this paper, a service restoration strategy is proposed when non-linear loads are present in the radial distribution system. Service restoration problem is formulated as a multi-objective, constrained optimization problem. Three new objectives are included to address the problem of harmonics injection by non-linear loads. Multi-Objective Particle Swarm Optimization (MOPSO) and Non-Dominated Sorting Genetic Algorithm-II (NSGA-II) are used to find the optimal switching sequence for restoration. To test the effectiveness of the proposed methodology, IEEE 33 bus and IEEE 69 bus test systems are taken.

A dual excited synchronous generator (DESG) is basically having two windings on rotor which are 90 degree apart electrically. Keeping two windings on rotor gives the advantage of control of rotor angle and voltage independently. Most of the work presented till now covers the stability analysis of DESG using mathematical model. However, this paper presents, the finite element method (FEM) analysis of DESG and its constructional design in which both the field windings are placed neither on d-axis nor on q-axis. Magnetic field flux distribution and a simple transient analysis of conventional synchronous generator (CSG) and DESG connected to a 3-phase R-L load with a step change in both field excitations at different instants of time is studied and results are presented here.