Keywords

1 Introduction

Under this section Distributed generation system, wind generation system, DFIG system, and PV system will be introduced. With the centralized facilities, large-scale generation of electricity can be achieved, and is referred to “centralized generation” which is a conventional system. Nowadays, unlike centralized generation, with small-scale generating units, the generation of electricity will be achieved, and it is known as de-centralized generation also known as distribution generation (DGs). DG refers to a variety of technologies that produce electricity at or near where it will be needed. DG can carry by a single structure, like a home or business or it can be a portion of a microgrid (MG). Meanwhile, at the same time the worldwide energy disaster, Electricity demand, and large-scale power interruptions are there so to mitigate this problem DG will play a vital role. Due to the various advantages of integrating DG, it is always a research topic. In modern years, DG has set off as a well-organized and a better substitute to the conventional energy resources and modern technologies are making DGs economically suitable [1]. DG minimizes the amount of energy loss in transmitting electricity, as the electricity is generated very near to the load where it is utilized. DG allows you to collect energy from many sources and may offer lower environmental impacts and greater reliability and stability [2, 3].

By using the power of wind, the wind turbines (WTs) will make mechanical energy and with that mechanical energy, it will drive an electric generator that generates electricity. Generally, across the blades, the wind passes over and creates lift, and produces a rotating force. The WT blades which are rotating will rotate a shaft inside the nacelle, i.e., from the blade’s swept area the WT draws kinetic energy. The gearbox here is having an important role that will maximize the rotational speed of the WT to drive the shaft of the generator. Based on Faraday’s law of magnetic induction, mechanical energy is converted to electrical energy. Generated electrical energy is then converted to desired voltage level with the help of a power transformer. The WECSs at present are the most inexpensive, available, and viable renewable energy systems which have accomplished rapid growth in modern years. Wind energy systems incorporated with DFIGs have been effectively utilized in high-power generation as they use power-electronic converters with ratings below the rating of the WT generators [4,5,6,7].

The frequently used machine nowadays is the DFIG. The induction machine can be operated either as a motor or generator. The DFIG and WTs have secured and prominence in the utilization of generators in water and wind power plants because of their efficient capability for maintaining and flexibility. In this paper, the DFIG system and its modeling have been described in brief.

A PV system utilizes solar panels to convert solar energy into usable electrical energy. It is having different segments that include the PV modules, mechanical and electrical links, mountings, and means of regulating and adapting the electrical output [8, 9]. The PV system, when hit by the sunlight, will generate DC electricity without any impact on the environment. The fundamental components of PV arrays are the solar cell and primarily it is a P–N junction that turns sunlight energy into electrical energy. The PV module’s output characteristic depends upon the temperature of the module’s cell, solar irradiation, and output voltage.

2 Microgrid (MG)

2.1 Introduction

An MG is a localized group, i.e., a small-scale power grid. It has a small-scale network of electricity consumers with a domestic origin of supply either by solar generation or by WT or by diesel generators, which is nominally coupled to a centralized national grid but it is also able to function independently i.e., islanded mode. Power systems nowadays turning into a noticeable change in the operational process mainly due to an increase in distributed energy resources (DER) and deregulation. Having microsources adjacent to the load has the benefit of mitigating transmission losses and resolving congestion in the network, nowadays it is called a microgrid [10].

From the end-user point of view, MG can give both thermal and electricity needs and with that, it improves local reliability, enhances power quality by encouraging voltage and mitigating voltage dip, and perhaps it supplies power at a lower cost. The use of distributed energy sources can bring down bids for distribution and transmission facilities from the utility point of view [11, 12].

2.2 Advantages of MG

  1. i.

    A primary advantage of MG is its capability to seamlessly attached and detach itself from the utility grid and no disruption to the loads associated with the MG during a utility-grid disturbance.

  2. ii.

    It reduces the utility grid burden in peak load periods by lowering the load on the grid.

  3. iii.

    Usage of both electricity and heat allowed by the generator's close propinquity to the user, thereby increasing the overall energy efficiency.

  4. iv.

    By generating numerous or whole of its electricity needs, MG can act to diminish the electricity costs to its users.

2.3 Disadvantages of MG

  1. i.

    Voltage, frequency, and standard of power are the key points that must be contemplated and regulated according to appropriate standards while preserving the balance of power and energy.

  2. ii.

    The storage of electrical energy in battery banks is required in an MG therefore there is a need for space as well as maintenance.

  3. iii.

    It is difficult to resynchronize with the main grid.

  4. iv.

    MG protection faces the most difficult challenge.

  5. v.

    Issues related to stand-by charges and net metering may impede MG.

2.4 Configuration of the Hybrid Microgrid (HMG)

Figure 1 deliberates the configuration of an HMG system that is consisting of AC and DC grids. These grids are having compatible sources, loads, power supplies, and a three-phase converter. The transformer and breaker are used to connect the AC bus to the main utility grid. In the proposed system, the PV array is linked to a DC bus to mimic DC sources with a boost converter. To mimic AC sources DFIG system is connected to an AC bus. To mimic the load which was connected in common to the grid and both the DFIG and solar PV system will deliver power to the load under different operating conditions.

Fig. 1
A diagram of hybrid A C and D C grids. The grids consist of compatible sources, loads, power supplies, and a three-phase converter.

A hybrid AC/DC MG system

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3 Control and Modeling

3.1 DFIG

A comprehensive model of DFIG is described in Fig. 2. In the rotor circuit, two reverse transformers have been used. The main motivation of the machine side converter is that it can manage the real by handling the current units of the DC motor, while the grid-sided converter manages the DC-link voltage and make sure the operation of the unit's power factor supply and keeps reactive power “Q” of the power system at zero. The simulated DGID model is shown in Fig. 3. In this DFIG Model, the performance of the DFIG system is analyzed under different values of wind speed. A load of 2 MW was connected at the load end and results of different parameters under varying wind speed have been observed.

Fig. 2
A model diagram of the doubly fed induction generator system. It has an encoder, 3 phase supply, machine side vector control, grid side vector control, and other necessary connections.

Overall DFIG system

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Fig. 3
A simulated D F I G model has the system subjected to varying wind speeds. Different parameters are measured while a load of 2 megawatts is at the load end.

DFIG model diagram

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3.2 The Solar PV Array System

A comprehensive schematic diagram and model diagram of the solar PV array is represented in Figs. 4 and 5, respectively. The performance validation of the PV array system had been carried out with variations in temperature and irradiance values. Here Max.PPT technique is used to track the maximum power peak point at which the panel has the peak energy. As from Fig. 4, the DC power obtained from the solar panel is converted into AC by using a 3-level bridge inverter after that the output level of the inverter will be converted to the desired level by using a transformer. The obtained AC supply is integrated into an already existed MG which is linked with DFIG to serve the resistive load of 2 MW which is connected at the end, and it can have been analyzed different parameters under variations in temperature and solar irradiance which is discussed in the result section.

Fig. 4
A schematic diagram of the solar P V array. It depicts D C power converted into A C through a 3-level bridge inverter, a transformer is then used to reach the desired level. The diagram also elaborates on other necessary connections in the system.

Schematic diagram of Solar PV array system

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Fig. 5
A model diagram of solar P V array. The system analyzes different parameters under varied temperatures and solar irradiance. It also elaborates on other necessary connections between the components in the system.

Solar PV array model diagram

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4 Results

An MG that is linked with a solar PV system and DFIG wind generation system is simulated using the MATLAB environment. The grid-connected mode has been considered for performance validation. The performance analysis is carried out with the HMG, DFIG, and PV Systems. With variation in the solar irradiation, the temperature of the cell, and the speed of the wind, a rigorous analysis of the MG has been done under MATLAB/Simulink environment.

4.1 PV Array Simulation

The only PV system is considered with the MG and corresponding simulated results are observed and discussed here. Figure 6 represents the output voltage (Va) of the solar system, the output voltage taken at the secondary side of the boost transformer.

Fig. 6
A graph of voltage in volts from negative 2 to 2 versus time in seconds from 0 to 0.1. The graph depicts a curve with a steady rise and fall with peaks at 2 volts.

PV array output voltage

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Figure 7 represents the output current (Ia) of the solar system, and it has been taken at the secondary side of the transformer.

Fig. 7
A graph of current in Ampere from negative 20 to 20 versus time in seconds from 0 to 1. The graph depicts a minimal fluctuating curve between negative 10 and 10.

PV array output current

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Figure 8 depicts the output real power (P) which is produced by the solar PV system and here it produces slightly lesser than rated power of the PV system, i.e. 100 kW at steady state. The mean real power (P) produced by the solar system is 92.88 kW.

Fig. 8
A graph of power in kilowatts from 0 to 120 versus time in seconds from 0 to 3. It plots a curve that has notable drops at 0.3 and 1 second and is almost stable after 1.5 seconds.

Solar PV system output active power

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Figure 9 represents the output reactive power (Q)—as a purely resistive load has been taken, Q drawn by the load is 0 VAR. With a 2 MW load connected through a 5 km feeder, results of P and Q have been recorded. The temperature is kept at 50 °C and the solar irradiance at 1000 W/m2 and P drawn by the load is 1.98 MW and the Q drawn by the load is 0 VAR—as the load is purely resistive.

Fig. 9
A graph of Q in kilovolt ampere reactive from negative 80 to 100 versus time in seconds from 0 to 3. A curve fluctuates from 0 to 0.4 seconds and then plateaus thereafter.

Solar PV system output reactive power

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In this simulation, Fig. 10 is showing the solar irradiance with variation in time. A signal builder has been taken such that the solar irradiance will vary from 0 s to 0.5 s it is 1000 W/m2 and from 0.5 s it will bring down to 500 W/m2 at 1 s and it raises from that point to 1000 W/m2 and it continues to them till 3 s.

Fig. 10
A graph of irradiance in watts per meter squared from 200 to 1200 versus time in seconds from 0 to 3. It has a stable line from (0, 1000) to (0.5, 1000), drops at (1, 500), then rises, and plateaus from (1.5, 1000). All values are estimated.

Variation of irradiance considered

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It can be seen from Fig. 11 that different values of the solar cell temperature have been considered. The temperature varies such that from 0 to 2 s it is at 40 °C and from that point, it increases to 50 °C and it continues to there till 3 s.

Fig. 11
A graph of temperature in degrees Celsius from 35 to 55 versus time in seconds from 0 to 3. It starts with a stable line at 40 degrees Celsius for 2 seconds, then rises, and plateaus at 50 degrees Celsius.

Variation of solar cell temperature considered

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4.2 DFIG Simulation

Here only the WGS with MG has been considered for performance evaluation. A DFIG WGS is connected to the main grid of 25 kV. In this model, the variation of wind speed considered is shown in Fig. 12. Initially, the wind speed is kept at 4 m/s after 2 s the wind speed increases to 40 m/s. The response of the wind speed is shown in Fig. 12.

Fig. 12
A graph of wind speed in meters per second from 0 to 50 versus time in seconds from 0 to 3. It has a straight line from (0, 5) to (2, 5), rises, and plateaus at 40 meters per second thereafter.

Varying wind speed considered

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In Fig. 13 the output voltage sampled at the output side of the WT was represented. Actually, in Fig. 13 the output voltage is represented per unit (P.U), the actual value of the output voltage which was generated by the DFIG WT is 575 V.

Fig. 13
A graph of V subscript a b c B 575 from negative 1.5 to 1.5 versus time in seconds from 0 to 0.2. Three waveforms of output voltages are plotted with peaks and troughs between negative 1 and 1.

DFIG 3-ϕ output voltage

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In Fig. 14 the output current sampled at the output side of the WT is represented. Actually, in Fig. 14 the output current is represented in the P.U system.

Fig. 14
A graph of I subscript a b c B 575 from negative 4 to 4 versus time in seconds from 0 to 0.2. Three waveforms of output currents are plotted with peaks and troughs from high to low amplitude.

DFIG 3- ϕ output current

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In Figs. 15 and 16, the output real power (P) and reactive power (Q) of the DFIG WGS are shown respectively. The P generated by the WGS at a steady state is nearly 8 MW and the Q is 0 VAR.

Fig. 15
A graph of P in megawatts from negative 10 to 20 versus time in seconds from 0 to 0.2. A curve begins from the origin, falls, then rises at 0.04 with minor fluctuations and stabilizes from there.

DFIG output active power

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Fig. 16
A graph of Q in megavolts ampere reactive from negative 20 to 5 versus time in seconds from 0 to 0.2. A curve begins from the origin, falls at 0.02, then rises with minor fluctuations and stabilizes from there.

DFIG output reactive power

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In this model also a 2 MW load has been taken, which is connected at the end of a 5 km long feeder to the microgrid. The samples of P and Q have been used for analysis. The simulation runs for 3 s and at 3 s the P drawn by the load is 1.99 MW which is very much closer to the rated load and obviously, the reactive power drawn by the load is 0 VAR. The main utility grid taking 7.11 MW of P and 6.56 MVAR of Q and the load drawing P of 1.99 MW and the Q drawn is 0.7 kVAR which is the reactive VAR drawn by the feeder as the load is purely resistive. By observing these results, it is clear that the system is well balanced.

4.3 MG Simulation

In this Model, the PV array and the DFIG WT generation sources both are interconnected to a common utility grid and it is finally coupled to the main power grid like Grid-tied mode and a load of 2 MW is connected at the end of a 5 km feeder as same as in the PV array model and DFIG WT model. In Fig. 17 Solar PV system generated real power (Ppv) sample which is taken at the output end side of the solar PV system is shown. Here the solar PV system generates 92.70 kW of Ppv which is shown in the figure. In Fig. 18 Solar PV system generated reactive power (Qpv) sample which is taken at the output end side of the solar PV system is shown. Here the solar PV system generates 0.68 kVAR and which is giving to the main grid. In Fig. 19, the real power (Pdfig) generated by the DFIG WT is shown. Here at time 3 s the Pdfig generated is 9.66 MW.

Fig. 17
A graph of the active power of solar, P V in watts from negative 3 to 2 versus time from 0 to 3. A curve starts with steep fluctuations, then fluctuates mildly before it stabilizes at (1.7, 1).

Solar PV array real power

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Fig. 18
A graph of the reactive power of solar, P V in volts ampere reactive from negative 25 to 5 versus time from 0 to 3. A curve starts with steep fluctuations before it stabilizes at (0.5, 0).

Solar PV array’s reactive power

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Fig. 19
A graph of the active power of D F I G in watts from negative 3 to 4 versus time from 0 to 3. A curve starts with steep fluctuations until 0.25 seconds, then somehow stabilizes after.

DFIG real power

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In Fig. 20, the Reactive power (Qdfig) generated by the DFIG WT is shown. Here at time 3 s the Qdfig generated is 8.26 MVAR. In Fig. 21 the real/active power (Pload) drawn by the load which is connected commonly to the MG is shown. Here the load drawing 1.99 MW of Pload from the grid at time 3 s.

Fig. 20
A graph of the reactive power of D F I G in volts ampere reactive from negative 4 to 2 versus time from 0 to 3. A curve starts with steep fluctuations up to 0.25 seconds, then has a minor upward trend.

DFIG reactive power

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Fig. 21
A graph of the active power of load in watts from 0 to 2 versus time in seconds from 0 to 3. A line remains constant at 2 on the y axis.

Active power is drawn by the load

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In Fig. 22 the reactive power (Qload) drawn by the load which is connected commonly to the MG is shown. Here the load drawing 0 VAR of Qload from the grid at time 3 s but as we connected the load through a 5 km feeder so the feeder consuming some amount of reactive Vars which is 0.7 kVAR.

Fig. 22
A graph of the reactive power of load in volts ampere reactive from negative 1000 to 0 versus time in seconds from 0 to 3. A line remains constant at negative 700 on the y axis.

Reactive power is drawn by the load

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In this MG model, the P contributed by the DFIG WT generator is 9.66 MW, and the Q contributed by the DFIG WT generator is 8.26 MVAR, the P contributed by the PV array model is 92.7 kW and the Q contributed by the PV array is 676 VAR. Here it is observed that the power is received by the load at the starting of the feeder. The samples of P and Q are taken, those values are 1.99 MW and −0.7 kVAR. Here the main power grid taking P of 3.54 MW and the Q taking by the main power grid is 3.83 MVAR. With a load of 2 MW and the load is drawing P of 1.99 MW, as it is a resistive load so the Q drawn by the load is 0 VAR.

5 Conclusion

A fully renewable-energy-dependent MG has been designed and the model was simulated for a particular chosen load and the simulation results are analyzed. From the simulation results, it was observed that the designed MG is successfully meeting the required load demand as a connected load of 2 MW, and the MG conveniently serving the load with 1.99 MW as the connected load is resistive so the reactive power at the load end is zero. It is found that from this analysis, modeling of renewable energy-dependent MG was found to be feasible and functional for the desired load.