Electrical energy is generated centrally in bulk amount and transmitted economically with the use of high voltage transmission over a long distance to the consumption point. To maximize the reliability of electrical supply, to maintain security level of power system and because of some other factors like environment, economic etc., interconnection of transmission systems in various geopolitical and geographic areas is a common practice. This makes the transmission system very large and complex electrical network, consisting of generation and consumption areas in hundreds and transmission lines in thousands.
For a complex circuit like transmission system, controlling of power flow through the transmission lines is a complicated problem, next important issue with that complex system is to control the voltage at each bus with other performance parameters of the system. Due to the rapid depletion of fossil fuel and environment pollution people were now attracted towards non-conventional energy sources like PV, wind, hydro etc. Solar and wind energy resources were abundantly available all over the world.
Literature Survey
Micro-grids: An overview of ongoing research, development and demonstration projects was presented by Asano. The penetration of distributed generation (DG) at medium and low voltages (MV and LV), both in utility networks and downstream of the meter, was increasing in developed countries worldwide. Wind/PV/Diesel Micro Grid System implemented in remote islands in the Republic of Maldives was suggested by Nayar. This work presented an innovative wind/PV/diesel hybrid system implemented in three remote islands in the Republic of Maldives. Micro-grid Dynamic Performance Improvement Using a Doubly Fed Induction Wind Generator was given by Nabayi. The micro-grid system was assumed to be a portion of a medium voltage distribution feeder and was supplied by two Distributed Generation (DG) units, i.e., a gas-turbine synchronous generator and a variable-speed wind turbine with DFIG.
Joint optimization of hybrid energy storage and generation capacity with renewable energy was presented by Yang. In an isolated power grid or a micro-grid with a small carbon footprint, the penetration of renewable energy was usually high. In such power grids, energy storage was important to guarantee an uninterrupted and stable power supply for end users. Joint investment and operation of micro-grid was suggested by Huang. Renewable energy generations in Hong Kong were first studied, and identified the potential benefit of mixed deployment of solar and wind energy generations. Cooperative planning of renewable generations for interconnected micro-grids was given by Wang. To efficiently explore and utilize the diverse renewable energy generations, a theoretical framework for the cooperative planning of renewable generations in a system of interconnected micro-grids were proposed.
Power converters allow connection of independent equipment and components on a common system. DGs technologies require specific converters and power electronic interfaces that are used to convert the generated energy to suitable power types directly supplied to a grid or to consumers. The development of an Advanced Power Electronic Interface (APEI) helps meet various power demands with lower cost compared to DER systems since power converters provide similar functions. Smart grid integration of micro hybrid power system using 6-switched 3-level inverter is suggested by Alper. Reliability evaluation of grid-connected micro-grid considering demand response is proposed by Zhou. On the use of real lime simulators for the test and validation of protection and control systems of micro grids and smart grids is presented by Simon.
Micro grid is a combination of micro generators, energy storage systems and loads. Control strategy of micro grids is an important issue to make micro grids as a controllable unit. The control strategies of micro grids are realized by the control of converters. The control strategies of converters are different from AC micro grids to DC micro grids. A review on control strategies of AC/DC micro grid is suggested by Chen. Micro-grid Grid Outage Management Using Multi-Agent Systems is given by Morais. Modeling and analysis of the AC/DC hybrid micro-grid with bidirectional power flow controller is presented by Zheng. Based on MPPT controller includes two stages, the first stage is the well-known Incremental Conductance algorithm and the second stage is based on the predictive hysteresis controller. Techno-economic feasibility of hybrid diesel/PV/wind/battery electricity generation systems for non-residential large electricity consumers under southern Iran climate conditions is presented by Baneshi. Performance comparison of hysteresis and resonant current controllers for a Multifunctional Grid Connected Inverter is presented by Preetha.
Research Gap
The above literature does not deal with the Power quality improvement of four Bus System using closed loop Hysteresis – Controller. Hence the proposed work compares the responses of HC, PR and FOPID Controllers for MGS under closed loop conditions. Simulation results of the above-mentioned controllers for MGS are included along with the time domain parameters.
Micro Grid System
A micro-grid is a small-local-grid with control capability, which means it can disconnect from the large- grid and operate independently. The grid connects homes, businesses and other buildings to central power sources, which allow us to use appliances, heating/cooling systems and electronics. But this interconnectedness means that when part of the grid needs to be repaired, everyone is affected. A micro-grid generally operates while connected to the grid, but importantly, it can break off and operate on its own using local energy generation during storms or power outages, or for other reasons. A microgrid can be powered by distributed generators, batteries, and/or renewable resources like solar panels. Depending on how it’s fueled and how its requirements are managed, a micro-grid might run indefinitely.
System Description
Block diagram of a micro-grid system with FOPID/PR/H controller is shown in figure 1. Output of PV is stepped up using QBC. Blockdiagram of 4-bus system is shown in figure 2. The output of QBC is in viewed and it is applied to the load. Load voltage is sensed and it is compared with reference voltage.
For boost converter
Real power flow in
Reactive power flow in
Output of rectifier is
Simulation Results and Discussion
Open loop 4-bus micro grid with load disturbance
Detailed simulation studies and of 4-bus micro grid with load disturbance with using different controllers are carried out on MATLAB/ Simulink platform and the results obtained for various operating conditions are presented in this section. Values of parameters used in the model for simulation are shown accordingly. Circuit diagram of 4-bus system with UPFC-4-bus micro grid with load disturbance is shown in figure 3.
Voltage at bus-3 in four bus system is shown in figures(s) 4 a) to f) and its value is 0.5*104 Volts. RMS Voltage at bus-3 in four bus system shown and its value is approximately 4000 Volts. There is a fall in the voltage, real and reactive power due to load disturbance. Current at bus-3 in 4-bus system is appeared shown and its value is 54 Amp and RMS Current at bus-3 in 4-bus system is shown and its value is 38 Amp. Real power at bus-3 in 4-bus system with load disturbance is given and its value is 2*105 Watts. Reactive power at bus-3 in 4-bus system is shown and its value is 0.35*105 VAR. Hence, it is suggested to go for closed loop FB-MGS improve
voltage regulation.
Closed loop FOPID controlled 4-bus micro grid system
Circuit diagram of closed loop FOPID control four bus micro grid system with HPFC is appeared in figure 5. Voltage at bus 3 is measured and rectified to get analog signal. It is compared with reference voltage to get VE for FOPID1. Output of FOPID 1 is reference current and it is compared with actual current to get current error. This is applied to FOPID 2. Output of FOPID 2 is used to update PW of BC. Voltage at bus-3 in closed loop FOPID control four bus micro grid system is shown in figure(s) 6 a) to f) and its value is 6000 Volts. RMS Voltage at bus-3 in four bus system is shown and its value is 0.49*104 Volts.
Current at bus-3 in closed loop FOPID control four bus micro grid system is appeared to 50 Amp and RMS Current at bus-3 in 4-bus system is appeared to be 40 Amp. Real power at bus-3 in 4-bus system with load disturbance is appeared to be a value of 0.18*105 Watts. Reactive power at bus-3 in 4-bus system is of value 0.45*105 VAR. They all settle at 0.65sec and voltage, current, real power and reactive power are stable. In order to improve the time response, PR controller may use for FBS.
bus-3 with FOPID e) Real power at bus-3 with FOPID f) Reactive power at bus-3 with FOPID
Closed loop PR controlled 4-bus micro grid system
Circuit diagram of closed loop PR control four bus micro grid system with HPFC is appeared in figure 7. Voltage at bus-3 in closed loop PR control four bus micro grid system is shown in figure(s) 8 a) to f) and its value is 0.5*104 Volts. RMS Voltage at bus-3 in four bus system is shown and its value is 4100 Volts. Current at bus-3 in closed loop FOPID control four bus micro grid system is shown and its value is 50 Amp and RMS Current at bus-3 in 4-bus system is of 38 Amp. Real power at bus-3 in 4-bus system with load disturbance is appeared to be 1.4*105 Watts. Reactive power at bus-3 in 4-bus system is 0.47*104 VAR.
Comparison results of Time domain FOPID/PR controlled 4-bus micro grid system voltage at bus-3 parameters
Comparison of closed loop four bus micro grid system with HPFC time domain parameters of voltage at bus – 3 using FOPID and PR controllers are given in table-1. By using PR controlled 4-bus micro grid system voltage at bus-3 rise-time is reduced from 0.29Sec to 0.27Sec; the peak-time is reduced from 0.45Sec to 0.38Sec; the settling-time is reduced from 0.65Sec to 0.46Sec; the steady-state-error is reduced from 2.3 volts to 1.7 volts.
Comparison results of Time domain FOPID/PR controlled 4-bus micro grid system current at bus-3 parameters
Comparison of closed loop four bus micro grid system with HPFC time domain parameters of current at bus – 3 using FOPID and PR controllers are given in table-2. By using PR controlled 4-bus micro grid HPFC systemcurrent at bus-3 rise-time is reduced from 0.30Sec to 0.28Sec; the peak-time is reduced from 0.47Sec to 0.37Sec; the settling-time is reduced from 0.66Sec to 0.44Sec; the steady-state-error is reduced from 0.7amps to 0.6amps.
Closed loop -Hysteresis- controlled 4-bus micro grid system
Circuit diagram of closed loop HC control four bus micro grid system with HPFC is appeared in figure 9 and Circuit diagram of four bus micro grid system QBC with inverter is appeared in figure 10. Voltage at bus-3 in closed loop HC control four bus micro grid system is shown in figure(s) 11 a) to f) and its value is 0.6*104 Volts. RMS Voltage at bus-3 in four bus system is shown and its value is 4150 Volts. Current at bus-3 in closed loop HC control four bus micro grid system is appeared to be value is 50 Amp and RMS Current at bus-3 in 4-bus system is appeared to be 40 Amp. Real power at bus-3 in 4-bus system with load disturbance is appeared to be 1.8*105 Watts. Reactive power at bus-3 in 4-bus system is shown and its value is 1.2*104 VAR.
Comparison results of Time domain PR/H controlled 4-bus micro grid system voltage at bus-3 parameters
Comparison of closed loop four bus micro grid system with HPFC time domain parameters of voltage at bus – 3 using PR and H controllers are given in table-3. By using HCcontrolled 4-bus micro grid system voltage at bus-3 rise-time is reduced from 0.27Sec to 0.26Sec; the peak-time is reduced from 0.38Sec to 0.35Sec; the settling-time is reduced from 0.46Sec to 0.40Sec; the steady-state-error is reduced from 1.7 volts to 1.1 volts. Bar-Chart comparison of four bus micro grid system with HPFC PR and HC are shown in figure 12.
Comparison results of Time domain FOPID/PR controlled 4-bus micro grid system current at bus-3 parameters
Comparison of closed loop four bus micro grid system with HPFC time domain parameters of current at bus – 3 using PR and H controllers are given in table-4. By using HCcontrolled 4-bus micro grid HPFC system current at bus-3rise-time is reduced from 0.28Sec to 0.26Sec; the peak-time is reduced from 0.37Sec to 0.35Sec; the settling-time is reduced from 0.44Sec to 0.39Sec; the steady-state-error is reduced from 0.60 amps to 0.41 amps. Bar-Chart comparison of four bus micro grid system with HPFC of PR and HC are shown in figure 13.
Conclusion
Closed loop controlled 4 bus system using FOPID, PR and Hysteresis- controller system are simulated. Simulation is done and the outcomes are compared in terms of voltage, current, Real Power and Reactive Power at bus-3. By using HC control 4-bus micro grid system voltage at bus-3 settling-time is reduced from 0.65Sec to 0.40Sec; the steady-state-error is reduced from 2.3 volts to 1.1 volts and using H- controlled 4-bus micro grid HPFC system current at bus-3 settling-time is reduced from 0.47Sec to 0.39Sec& the steady-state-error is reduced from 0.37 amps to 0.41 amps. Hence, the closed-loop-H- controlled-4-bus micro grid-systemis superior to closed-loop-FOPID and PR- controlled-4-bus micro grid – system. The advantages of Hysteresis controlled 4-bus micro grid -system is improved-time domain-response and reduced steady-state-speed-error of voltage and current at bus-3.
Arjuna Rao is M.Tech. (Power Systems) NIT, Trichy, M.B.A from Bangalore University and PGDEEMEA from Annamalai University. Currently, he is holding the post of Joint Director CPRI. His areas of interest include Power System Analysis, LV switchgear and Distribution Transformers. He is also a Fellow of the Institution of Engineers (FIE) and an IEEE Professional Member in Power & Energy Society. He has eighteen publications in the area of Power systems, DTRs, ITRs & Switchgear. Rao is currently pursuing his Ph.D. in the area of Microgrid.
Dr. H. R. Ramesh is currently a Professor & Chairman of Department of Electrical Engineering, UVCE, Bangalore.
