Power quality improvement in a PV distribution system by using D-STATCOM

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Power quality improvement in a PV

distribution system by using D-STATCOM

P S V SUBRAHMANYAM

Electrical & Electronics department,JNTU Kakinada,BVC engineering college Odalarevu,Andhrapradesh,India

pechettisurya@gmail.com

Prof.S.SRIKANTH

Professor,EEE,BVC Engineering college,Odalarevu, JNTU Kakinada,Andhrapradesh,India

Sambana.srikanth@gmail.com

Abstract:

In this paper one of the FACTS devices ie D-statcom is proposed to compensate the reactive power and unbalancing caused due to linear and non-linear loads in distribution system. It is very useful to rectify the power quality problems and to improve the voltage regulation and making system stable. When there is an integration of PV cell power to low voltage distribution grid, the voltage and frequency does not match each other in the network due to non linear loads. This paper presents modified instantaneous reactive power theory (IRP) for calculation of instantaneous active and reactive power by transforming the 3-phase quantities to 2-phase quantities. The above scheme are analyzed under various operating conditions and the model performance is evaluate using MATLAB/SIMULINK software. These results are evaluated and the system effectiveness is established.

Keywords: D-Statcom, power quality, PV cell, active and reactive power. 1. INTRODUCTION:

In recent years a number of changes takes place in electrical power network to increasing the share of distributed energy resources (DER) in total energy production. Cost and efficiency are the main factor influencing the common applications of DERs. Today we are using different types of DG technologies. They can be grouped as fuel applied micro turbines, fuel cells or gas based reciprocating engines or renewable energy sources like PV, wind, & hydro etc. optimization of DG sources efficiency requires interconnection to the electrical power network, converting energy present at that moment and transmitting it in to grid and it can be granted that the integration of considerable number of DERs in to the grid. This may cause difficulties with maintaining the required power quality. Disturbances such as voltage variations & harmonics may occur by using DERs. If the loads are installed in the grid, it may heighten the problems in the grid. In today’s scenario power quality maintenance in a power system is very essential because of the increase in different types of loads that pollute power systems. Induction loads like induction motor, induction generator etc require reactive power for their magnetization. A voltage dip will occur, if the reactive power is consumed from the grid, this affects other sensitive loads which are connected to the grid. Hence compensation is necessary for these types of loads for requiring reactive power.

2. POWER INJECTION PRINCIPLE:

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Figure 1: Line diagram of generating distribution network.

For small line resistance, R< < X. The active & reactive power components are

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From the above approximate power components, it can be seen that the power flow is dependent on above four controlling variables Vs, Vr, X and s-R. We can increase both the active & reactive component of the injected power in the transmission line by employing a shunt compensation at midpoint.

The injected power at midpoint is given by

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(4) 3. D-STATCOM :

For distribution network D-Statcom is the most important controllers it is widely used to regulate system voltage, reduce voltage harmonics, improve voltage profile, reduce transient voltage disturbances and load compensation. Rather than using fast switches combined with conventional capacitors and inductor. If D-Statcom synthesizes the reactive power output and it controls using pulse with modulation (PWM) or other voltage / current shaping techniques. Compare with Statcom, D-Statcom have lower rated power and inconsequence, faster power electronic switching.

3.1. Operation :

D-Statcom controllers can be designed based on both voltage source inverter (VSI) and current source inverter (CSI) topology shown in fig. 2. Nevertheless of topology, A controller is a compound of an array of semiconductor devices with turn off capability (i.e. IGBT, IGCT,GTO etc) connected to the feeder via a relative small reactive filter. The VSI is connected to feeder via reactorLFand has a voltage source (capacitor CD) on

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The voltage source inverter for D-Statcom are constructed based on multi-level topologies, with or without use of a transformer. These type of solutions will provide support for operation with a high level of terminal voltage. For operation of D-Statcom converter it is possible to represent its PWM-controlled VSI with an instantaneous voltage source. The generating principle of instantaneous active & reactive power by D-Statcom a shown in Figure 3.In this, the currents and voltages are represented with instantaneous space vectors obtained using a power –in variant Clarke transform three cases are presented in figure 3: general one, for reactive power equal to zero and the active power equal to zero.

Figure 3: Controlling principle of D-Statcom instantaneous active & reactive power

By this fig. it is clear that by generating an appropriate AC voltage it is possible to generate arbitrary instantaneous vectors of both active power and reactive power the equivalent series resistance modeling losses on AC side is related to the real component of current. Therefore the D-Statcom are limited the possible active and reactive powers that can be generated or absorbed and the limitation is related to the maximum ratings of circuit parameter and VSI components. In Figure 3 is presented an exemplary limit for AC voltage which depends on VSI, DC voltage VDC , This limit, together with terminal voltage VT and filter inductance LF , defines the operating region of D-Statcom. The operating region of two level VSI based controller is presented in figure 4. In this Y denotes the modules of admittance on the AC side of VSI. In practice the operating region does not limit the maximum ratings of VSI semiconductors that’s why the static V-I characteristics of D-Statcom reactive power is symmetrical shown in Figure 5.

Figure.4: Operating region of a two level VSI based D-statcom

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The consumed active power in the D-Statcom only to cover internal losses. Assuming lossless operation the averaged active power has to be zero. There is no similar limitation for reactive power because it is only exchanged between phases but not conversion.

4. GRID CONNECTED PHOTOVOLTAIC SYSTEM:

The photovoltaic(PV) power generation systems are renewable energy sources that expected to play a vital role in fulfilling the future requirements of electricity. This PV systems classified into grid connected , stand –alone or hybrid systems the grid current generally shaped by the grid connected PV system. This follow a predetermined sinusoidal reference using hysteresis band current controller which has the advantage of inherent peak current limiting and fast dynamic performance. The schematic diagram of grid connector PV system as shown in figure 6. it consists of mainly two parts , the PV array and the power conditioning unit (PCU) this PCU includes:

 A (MPPT) maximum power tracking circuit. It allows the maximum output power of the PV array  A power factor control unit, which tracks the phase of the utility voltage and provides inverter current

reference synchronized with the utility voltage .

 A converter which can consist of DC/DC converter to increase the voltage and a DC/AC inverter stage.

Figure 6 : Schematic diagram of Grid connected photovoltaic system

4.1. PV array modeling:

To obtaining high power numerous PV cells are connected in series and parallel circuits on a panel, which is a power module. A group of several modules electrically connected in series-parallel combinations to generate the required current and voltage is called as PV array. The building block of PV arrays is the solar cell. It is basically a P-N semiconductor junction that directly converts solar radiation in to DC current due to the effect of photovoltaic . The equivalent circuit of a solar cell as shown in fig 7.

Figure 7: circuit diagram of PV cell

In the circuit, the series resistance Rs represents the internal loss, shunt resistance Rsh in parallel with diode, This corresponds to the leakage current to the ground. Today’s the most important application of PV system is the grid integration of RES application based on PV system gaining interest over traditional stand alone systems. This trend increases due to the benefits of using RES in distributed generation power systems.

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5. MATLAB MODELLING AND SIMULATION RESULTS

The grid connected Photovoltaic system is shown in figure8, power transmission voltage 415V feed for distribution level to the consumer. The PV power system has been designed and penetrates the power to the grid at near distribution of consumer. Here simulation is carried out in different cases,

Case 1: proposed grid connected D-Statcom based PV system with un balanced nonlinear load condition.

Figure 8: MATLAB/SIMULINK model of proposed grid connected PV system with D-Statcomunder unbalanced nonlinear loading condition

The above figure.8 shows the MATLAB/SIMULINK model of proposed grid connected PV system with D-Statcom under unbalanced nonlinear load condition.

Figure 9: simulation results of source voltage,source current,load current of D-statcom under unbalanced nonlinear load condition

Figure 9 shows simulation results of source voltage, source current and load current of power system obtained due to unbalanced nonlinear load with D-statcom ,the load current is unbalanced and the source current becomes compensated and parameters are sinusoidal nature.

Figure 10: simulation showing unity powerfactor by using D-statcom

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Figure 11: FFT analysis of source current (Is)

Figure.11 shows the FFT analysis of source current obtained from the grid connected PV system by using D-statcom we get 4.11%

Case 2: proposed grid connected PV system without D-Statcom under un balanced nonlinear load condition.

Figure 12: SIMULINK model of proposed grid connected PV system without D-Statcomunder unbalanced nonlinear load condition

Figure.12 shows the MATLAB/SIMULINK model of proposed grid connected PV system without D-Statcom under unbalanced nonlinear load condition.

Figure 13: simulation results of source voltage,source current,load current with out D-statcom under unbalanced nonlinear load condition

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Figure 14: simulation showing powerfactor with out D-statcom

Figure 14 shows the power factor of unbalanced nonlinear load without using D-statcom

Figure 15: FFT analysis of source current(Is) without using D-statcom

Figure 15 shows the FFT analysis of source current obtained from the grid connected PV system without D-statcom we get 14.19%

6. CONCLUSION

In this paper we have modeled and analyzed the PV (photovoltaic) power system is being integrated with D-Statcom to low voltage power distribution grid at consumer end to compensate the harmonics coming from grid side inverter and other side we have different loads in that, most of the unbalanced nonlinear loads injects harmonic currents to source side and effects the source current. By using D-Statcom, the source current does not effect. In this, we have studied and analyzed the operation and performance of D-statcom at unbalanced non linear load condition and also gives the comparison by using with and without D-statcom. This proposed model is implemented using MATLAB SIMULINK software and the obtained resultant waveforms are evaluated and system stability effectiveness and power system performance have been established.

References:

[1] Furuhashi.T, S.Okuma, Y. Uchikawa, “a study on the theory of instantaneous reactive power”, IEEE Trans. Industrial Electronics, vol.37, No. 1, pp. 86-90, 1990.99

[2] Ghosh A., G..Ledwich, “Load compensating DSTATCOM in weak ACsystem”, IEEE Trans. Power Delivery, vol.18, No. 4,pp. 1302-1309,2003.

[3] Hingorani NG, Gyugyi L. Understanding FACTS. Concepts and Technology of Flexible AC Transmision Systems. NewYork: IEEE Press, 19

[4] H Akagi . Active Filters and Energy Storage Systems for Power Conditioning in Japan. Proc. of First International Conference on Power Electronics Systems and Application, 2004; 80–88.

[5] J. Solanki and B. Singh , "A Comparison of Control Algorithms for dstatcom" ieee t ransactions on industrial electronics, VOL. 56, NO.7, mL Y 2009.

[6] Ledwich.G , A.Ghosh,. “Power Quality Enhancement Using CustomPower Devices”, Kluwer Academic Publisher, 2002.

[7] Papic I, Blazic B,. Improved D-STATCOM Control for Operation with UnbalancedCurrents and Voltages. IEEE Trans.Power Delivery, Vol. 21, No. 1, 2006; 225–233.

Figure

Figure 2:  VSI & CSI based D-statcom General topology

Figure 2:

VSI & CSI based D-statcom General topology p.2
Figure 1: Line diagram of generating distribution network.

Figure 1:

Line diagram of generating distribution network. p.2
Figure.4: Operating region of a two level VSI based D-statcom
Figure.4: Operating region of a two level VSI based D-statcom p.3
Figure 3: Controlling principle of D-Statcom instantaneous active & reactive power

Figure 3:

Controlling principle of D-Statcom instantaneous active & reactive power p.3
Figure 5: D-statcom V-I characterstics

Figure 5:

D-statcom V-I characterstics p.3
Figure 6 : Schematic diagram of Grid connected photovoltaic system

Figure 6 :

Schematic diagram of Grid connected photovoltaic system p.4
Figure 7: circuit diagram of PV cell

Figure 7:

circuit diagram of PV cell p.4
Figure 9 shows simulation results of source voltage, source current and load current of power system obtained due to unbalanced nonlinear load with D-statcom ,the load current is unbalanced and the source current becomes compensated and parameters are sinu

Figure 9

shows simulation results of source voltage, source current and load current of power system obtained due to unbalanced nonlinear load with D-statcom ,the load current is unbalanced and the source current becomes compensated and parameters are sinu p.5
Figure 8:  MATLAB/SIMULINK model of proposed grid connected PV system with D-Statcom under unbalanced nonlinear loading condition

Figure 8:

MATLAB/SIMULINK model of proposed grid connected PV system with D-Statcom under unbalanced nonlinear loading condition p.5
Figure 9: simulation results of source voltage,source current,load current of D-statcom under unbalanced nonlinear load condition

Figure 9:

simulation results of source voltage,source current,load current of D-statcom under unbalanced nonlinear load condition p.5
Figure 11: FFT analysis of  source current (Is)

Figure 11:

FFT analysis of source current (Is) p.6
Figure.12 shows the MATLAB/SIMULINK model of proposed grid connected PV system without  D-Statcom under unbalanced nonlinear load condition
Figure.12 shows the MATLAB/SIMULINK model of proposed grid connected PV system without D-Statcom under unbalanced nonlinear load condition p.6
Figure.11 shows the FFT analysis of source current obtained from the grid connected PV system by using D-statcom we get 4.11%
Figure.11 shows the FFT analysis of source current obtained from the grid connected PV system by using D-statcom we get 4.11% p.6
Figure 14:  simulation showing  powerfactor  with out  D-statcom

Figure 14:

simulation showing powerfactor with out D-statcom p.7
Figure 14 shows the  power factor of unbalanced nonlinear load without using D-statcom

Figure 14

shows the power factor of unbalanced nonlinear load without using D-statcom p.7

References