RESONANT FILTER FOR PHOTOVOLTAIC APPLICATIONS · synchronous reference frame voltage control for single phaseinverters ´ IEEE Trans Industr ial Electron 2013; Vol. 61(1), pp. 258

RESONANT FILTER FOR PHOTOVOLTAIC APPLICATIONS

Baldwin Immanuel T, Suresh A, Rashmi M R Assistant Professor, Department of Electrical and Electronics Engineering (Marine), AMET University,

Chennai Professor, Department of Electrical and Electronics Engineering, S.A. Engineering College, Chennai

Associate Professor, Department of Electrical and Electronics Engineering, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Bengaluru, India

Abstract:

Inorder to integrate solar power to AC grid, it has to be converted into alternating pure

sinusoidal voltage of power frequency. The inverter converts dc output from photovoltaic(PV)

panel to AC. The output of the inverter is not a smooth AC. To get smooth AC before injecting

to grid, A LCL filter is proposed in this paper. Power balance algorithm is applied to generate the

pulses for inverter. The behavior of the circuit is analyzed for both linear and non-linear loads.

Keywords:Power Balance Theory, LCL Filter, PV System, Voltage Source Inverter

I. Introduction

Modern energy systems are becoming smarter and reliable. The renewable energy

sources are helping the grid to be resilient and more reliable. Since solar power is free from

carbon emission, its utility is hyperbolically increasing [1]. To inject solar power to existing grid,

it has to be converted to alternating voltage using inverters [2]. Hence one must design compact,

energy efficient inverter, filter and have proper control [3].Roof top solar power can be used for

home appliances and excess energy can be injected to the grid to meet peak hour demand [4]. If

the generation of consumer is not self sufficient, the required power can be drawn from the

utility grid. All this process to happen smoothly, the converters should to controlled

automatically and they should have better dynamic response.

Voltage Source Inverters (VSI) are very widely used for converting DC to AC both for

standalone applications and grid interface.The output from VSI is not sinusoidal. For grid

interface one should inject pure sinusoidal AC. Therefore a filter is essential to eliminate

harmonics in inverter output. Various passive filters were suggested in the literature which

comprises Inductor (L) filter, Capacitor (C) filter and series/parallel combination of these basic L

and C filters [5-8].The combination of L-C-L filter reduces the ripples in output current. Since it

will be designed for high frequency, the filter size will be small and filter is cost effective. The

device ratings will also be less because of less di/dt and dv/dt stress [9].In order to synchronise

PV power to the grid, the controller is must. Many control algorithms were proposed in the

literature [10] in order to ensure proper synchronization. Many researchers

recommendedSynchronousReference Frame (SRF) theory for control algorithm because of its

International Journal of Pure and Applied MathematicsVolume 119 No. 7 2018, 393-405ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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simplicity [11-12]. A Phase Locked Loop (PLL) in used in SRF theory which derives angle θ

from grid supply line is used for synchronizing the inverter output to the grid[13-14]. There were

some approaches which did not use PLL for synchronization. Those algorithms were based on

instantaneous power balance theory [15-16]. Therefore this paper presents LCL resonant filter

for photovoltaic system for grid connection using power balance theory.

II. Description of the system

The VSI with L-C-L filter for photovoltaic system is showedin Figure 1. The

configurations consisted of PV module,VSI, L-C-L filter, grid module and loads.The solar

irradiation is converted to voltage using photovoltaic cells. Since the voltage varies with solar

insolation, the supply voltage ripple is minimized using capacitor. The DC voltage is converted

to alternating voltage of grid frequency and injected to the grid or can supply the load. The L-C-

L filter design depends on the attenuation of ripple in the current to be injected to the

grid.Instantaneous power balance control approach is used to generate PWM pulses for the

inverter switches.With proper control both real and reactive powers can be controlled.

The filter inductance is given by 𝐿𝑓 =𝑉𝑠

2 6𝑓𝑠𝑖𝑟𝑖𝑝𝑝𝑙𝑒 (1)

Where𝑉𝑠- grid supply voltage

𝑓𝑠- inverter switching frequency and

𝑖𝑟𝑖𝑝𝑝𝑙𝑒 =15% of the rated output current

Figure 1. System Configuration

The filter capacitor is given by 𝐶𝑓 =0.05

𝜔𝑛𝑍𝑏𝑎𝑠𝑒(2)

Where 𝑍𝑏𝑎𝑠𝑒 =𝑉𝑠

2

𝑃𝑛 (3)

𝜔𝑛 is the operating frequency

𝑃𝑛 is the inverter rated power.

International Journal of Pure and Applied Mathematics Special Issue

394

III. Simulation Results

The simulation had been carried out in Matlab/ simulink environment. The

simulation circuit is showed in Figure 2 where the linear load is considered. PV cell

model is shown in Figure 3.

Figure 2. Simulation Model for Linear Load

Figure 3. PV Cell Model

Figure 4 shows the simulation circuit to implement power balance theory. The load voltage is

shown in Figure 5 and load current in Figure 6. The real and reactive powers consumed by load

are shown in Figure 7.The grid voltages are shown in Figure 8.


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Figure 4. Simulation Circuit for Power Balance Algorithm

Figure5. Load Voltage


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Figure6.Load Current

Figure 7. Real and Reactive Power Drawn by the Load

Figure 8. Grid Voltages

Real Power-watts

Reactive Power-VAR


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The grid currents during load increase are shown in Figure 9. The frequency spectra of load

voltage and load currents are shown in Figure 10 and 11 respectively.

Figure 9. Grid Currents

Figure 10. Load current FFT spectra


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Figure 11. FFT Analysis of Load Voltage

The current THD is found to be 1.41& and voltage THD is 1.36%. Thus the proposed

algorithm reduces the harmonic distortion compared to the existing algorithms. The simulation

circuit for rectifier fed RL load which is nonlinear load is shown in Figure 12for linear load

Figure 13 and 14 gives load voltage and load current traces respectively. The real and reactive

powers drawn by the load are shown in Figure 15.

Figure 12. The simulation circuit for rectifier fed RL load


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Figure13. Load Voltage

Figure14. Load Currents


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Figure 15.Load Real and Reactive Powers

The utility grid voltage and currents are shown in Figure 16 and 17 respectively. The FFT

analysis is carried out and FFT spectra of load current and load voltages are given in Figure 18

and 19 respectively.

Figure 16. Grid Voltage

Real Power-watts

Reactive Power-VAR


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Figure 17. Grid Currents

Figure 18. Load current FFT spectra


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Figure 19. Load voltage FFT spectra

The harmonic distortion in load current was found to be 31.48% and the load voltage THD is

4.04%.

IV. Conclusion

A resonant L-C-L filter for interfacing solar photovoltaic system with the grid

was designed and simulated. Power balance algorithm was used to provide reactive power

compensation both for linear and nonlinear loads. Further the working can be extended to reduce

load current THD by harmonic current injection for nonlinear loads.

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RESONANT FILTER FOR PHOTOVOLTAIC APPLICATIONS · synchronous reference frame voltage control for single phaseinverters ´ IEEE Trans Industr ial Electron 2013; Vol. 61(1), pp. 258