A Novel Multi-Functional DSTATCOM with Distribution Generation using FRC Controller

Distribution Generation plays a significant role in remote areas where the utility grid is affected and initializing by renewable energy sources to acquire the sufficient power demand. In distribution system, it is very exigent consumer related concern which is confronted due to mis-operation of massive non-linear load apparatus. A multi-functional distributed static compensator incorporates the best choice for enhancing the power quality features with effective control scheme under rambled non-linear loads. Conventional control schemes are more adversed with greater switching losses due to extreme harmonic frequencies in a refernce current component. This paper proposes, a novel multi-objective fundamental reference current control scheme based multi-functional DSTATCOM furnishes the current harmonic compensation at PCC, reactive power compensation, power factor correction, active power exchanging, minimizing the switching losses, incredible efficiency and power factor correction. The validation of proposed multi-functional DSTATCOM with proposed control strategy under rated capacity of distribution generation is evaluated by using Matlab/Simulink platform and simulation results are presented

A new supervisory energy managmement control strategy of a modified D-STATCOM configuration and dual DC source in distribution grids.

A microgrid is a state-of-the-art, next generation of electric distribution grid that provides a fundamental paradigm shift from passive grid networks to active networks. Power electronic technologies play a vital role in enabling microgrids to meet their system level requirements of power quality, reliability and demand response capability. A conventional distribution static compensator (D-STATCOM) is a power electronic converter which acts as a reactive power compensator and voltage controller at the point of common coupling in a grid system. However, these devices have limited ability to mitigate voltage fluctuations caused by active power disturbances. By integrating energy storage into the DC link of a D-STATCOM, controllable active power from the storage device can result in enhanced voltage compensating capability. The active and reactive power control between the D-STATCOM and AC power point is achieved by suitable tuning of the phase and magnitude of the output voltage of the D-STATCOM’s converter. Recent advances and innovations in energy storage systems such as super-capacitors and batteries allow the combination of battery-supercapacitor hybrid energy storage systems to act as an effective solution for energy management in smart grid operation. However, the concept and control of the hybridisation of energy storage are relatively new, and there are great challenges to the development of control management systems, for example, reduce battery current stresses. This study presents a novel approach in applying a fuzzy-PI controller to a D-STATCOM based energy storage unit to provide enhanced power quality and voltage stability in distribution grids. Full information is provided concerning the implementation of the system, and the dynamic controls devised during the research programme. A second novel approach is the use of sugeno fuzzy logic controller based decision making for power management of the D-STATCOM based HESS to achieve a robust and superior performance for voltage regulation. Recent developments in this field have tended to converge on intelligent control as the best approach to achieve an effective strategy for power sharing with HESSs by using a high-power storage unit (supercapacitor) and high energy storage unit (battery) in combination with the D-STATCOM to avoid the drawbacks of a single storage unit. This development is considered one of the main ways to upgrade energy storage technology, with gains of faster voltage regulation and decreased battery current peak value. Verification of the control designs has been achieved through simulation using MATLAB/SIMULINK based on the derived analytical model in state-space form. Comprehensive simulation results show that the proposed fuzzy controller demonstrates significant improvements over conventional controllers in supporting voltage stability in distribution networksPhD in Energy and Powe

Control and Stability of Residential Microgrid with Grid-Forming Prosumers

The rise of the prosumers (producers-consumers), residential customers equipped with behind-the-meter distributed energy resources (DER), such as battery storage and rooftop solar PV, offers an opportunity to use prosumer-owned DER innovatively. The thesis rests on the premise that prosumers equipped with grid-forming inverters can not only provide inertia to improve the frequency performance of the bulk grid but also support islanded operation of residential microgrids (low-voltage distribution feeder operated in an islanded mode), which can improve distribution grids’ resilience and reliability without purposely designing low-voltage (LV) distribution feeders as microgrids. Today, grid-following control is predominantly used to control prosumer DER, by which the prosumers behave as controlled current sources. These grid-following prosumers deliver active and reactive power by staying synchronized with the existing grid. However, they cannot operate if disconnected from the main grid due to the lack of voltage reference. This gives rise to the increasing interest in the use of grid-forming power converters, by which the prosumers behave as voltage sources. Grid-forming converters regulate their output voltage according to the reference of their own and exhibit load sharing with other prosumers even in islanded operation. Making use of grid-forming prosumers opens up opportunities to improve distribution grids’ resilience and enhance the genuine inertia of highly renewable-penetrated power systems. Firstly, electricity networks in many regional communities are prone to frequent power outages. Instead of purposely designing the community as a microgrid with dedicated grid-forming equipment, the LV feeder can be turned into a residential microgrid with multiple paralleled grid-forming prosumers. In this case, the LV feeder can operate in both grid-connected and islanded modes. Secondly, gridforming prosumers in the residential microgrid behave as voltage sources that respond naturally to the varying loads in the system. This is much like synchronous machines extracting kinetic energy from rotating masses. “Genuine” system inertia is thus enhanced, which is fundamentally different from the “emulated” inertia by fast frequency response (FFR) from grid-following converters. Against this backdrop, this thesis mainly focuses on two aspects. The first is the small-signal stability of such residential microgrids. In particular, the impact of the increasing number of grid-forming prosumers is studied based on the linearised model. The impact of the various dynamic response of primary sources is also investigated. The second is the control of the grid-forming prosumers aiming to provide sufficient inertia for the system. The control is focused on both the inverters and the DC-stage converters. Specifically, the thesis proposes an advanced controller for the DC-stage converters based on active disturbance rejection control (ADRC), which observes and rejects the “total disturbance” of the system, thereby enhancing the inertial response provided by prosumer DER. In addition, to make better use of the energy from prosumer-owned DER, an adaptive droop controller based on a piecewise power function is proposed, which ensures that residential ESS provide little power in the steady state while supplying sufficient power to cater for the demand variation during the transient state. Proposed strategies are verified by time-domain simulations

Power quality improvement in low voltage distribution network utilizing improved unified power quality conditioner.

Doctoral Degree. University of KwaZulu-Natal, Durban.The upgrade of the power system, network, and as it attained some complexity level, the voltage related problems and power loss has become frequently pronounced. The power quality challenges load at extreme end of the feeder like voltage sag and swell, and power loss at load centre due to peak load as not received adequate attention. Therefore, this research proposes a Power Angle Control PAC approach for enhancing voltage profile and mitigating voltage sag, voltage swell, and reduced power loss in low voltage radial distribution system (RDS). The amelioration of voltage sag, voltage swell, weak voltage profile, and power loss with a capable power electronics-based power controller device known as Improve Unified Power Quality Conditioner I-UPQC was conceived. Also, the same controller was optimally implemented using hybrid of genetic algorithm and improved particle swarm optimization GA-IPSO in RDS to mitigate the voltage issues, and power loss experienced at peak loading. A new control design-model of Power Angle Control (PAC) of the UPQC has been designed and established using direct, quadrature, and zero components dq0 and proportional integral (PI) controller method. The simulation was implemented in MATLAB/Simulink environment. The results obtained at steady-state condition and when the new I-UPQC was connected show that series inverter can participate actively in ameliorating in the process of mitigating sag and swell by maintaining a PAC of 25% improvement. It was observed that power loss reduced from 1.7% to 1.5% and the feeder is within the standard limit of ±5%. Furthermore, the interconnection of I-UPQC with photovoltaic solar power through the DC link shows a better voltage profile while the load voltage within the allowable range of ±5% all through the disturbance and power loss reduction is 1.3%. Lastly, results obtained by optimal allocation of I-UPQC in RDS using analytical and GA-IPSO show that reactive power injection improved the voltage related issues from 0.952 to 0.9989 p.u., and power loss was further reduced to 1.2% from 3.4%. Also, the minimum bus voltage profile, voltage sag, and power loss are within statutory limits of ±5 % and less than 2 %, respectively. The major contributions of this research are the reduction of sag impact and power loss on the sensitive load in RDS feeder.Publications on page iii