Rapid transaction to load variations of active filter supplied by PV system

Abstract

This paper deals with the analysis and control of a photovoltaic (PV) system connected to the main supply through a Boost converter and shunt active filter supplied by a PV system providing continuous supply of nonlinear load in variation. A robust control of a PV system connected to the grid while feeding a variable nonlinear load is developed and highlighted. This development is based on the control of the Boost converter to extract the maximum power from the PV system using the Perturb and Observe (P and O) algorithm in the presence of temperature and illumination. The proposed modeling and control strategy provide power to the variable nonlinear load and facilitates the transfer of power from solar panel to the grid while improving the quality of energy (harmonic currents compensation, power factor compensation and dc bus voltage regulation). Validation of the developed model and control strategy is conducted using power system simulator Sim-Power System Blockset Matlab/Simulink. To demonstrate the effectiveness of the shunt active filter to load changes, the method of instantaneous power (pq theory) is used to identify harmonic currents. The obtained results show an accurate extraction of harmonic currents and perfect compensation of both reactive power and harmonic currents with a lower THD and in accordance with the IEEE-519 standard.

Keywords

solar panels / maximum power point tracking (MPPT) / DC/DC converter (Boost) / shunt active filter / instantaneous power control / power quality / harmonics / imbalances / reactive energy

Introduction

High power demand and climate changes have led to the research in the area of renewable energies [1]. Introduction, integration and control of renewable energy in electric power systems [2] have become an important issue. Hence, the design of smart power grid renewable energy systems has attracted many researchers in recent years [3].

The photovoltaic (PV) solar energy is an attractive choice, but its application is limited and not widely used [4]. The PV generator which converts light into electrical exhibits a nonlinear characteristic in terms of power output as a function of solar illumination and temperature. In this case, the connection between the source and the variable nonlinear load indicates a significant gap between the potential and the transferred powers. Because of its simplicity in operation and environmental impact, this system is not competitive when the demand for electricity increases. A study must be conducted in order to maximize the power from PV generators; therefore, system performance and lower cost of installation are important factors [5]. To extract optimum power at any time to supply continuously the load, a converter must be introduced to maximize the power produced by the PV panels. This device is a very effective interface between the PV system, the load and the power supply. The main objective of a DC/DC (Boost) converter is to extract the maximum point of the power using perturb and observe (P and O) algorithm. This converter links the maximum power point tracking (MPPT) Bridge [6,7] and DC/AC converter (shunt active filter) to provide a continuous supply to a variable nonlinear load. Most previously reported works have taken into consideration only the illumination of a PV panel supplying a variable nonlinear load. In contrast, in the present paper the P and O algorithm is developed, taking into account both the temperature and illumination. The overall structure of the studied system composed of a PV panel, a power interface, nonlinear load and main supply is presented. Then, the model of each element of the system is developed and validated by computer program performed in a Matlab environment. The obtained results have demonstrated the effectiveness of the proposed structure.

System descriptions

The studied system consisting of a PV panel connected to the main source ensuring continuous supply of the nonlinear load through two converters DC/DC (Boost) and DC/AC (parallel active filter) is shown in Fig.1.

Modeling of PV system

The equivalent circuit of PV cell most known and reported in the literature [8–10] is characterized by a source of current I_sc which models the conversion of luminous flux (G: irradiation) into electrical energy, a shunt resistor R_p which represents the state along the surface periphery of the cell, a series resistor R_s as various resistors of contact and connection and a diode D in parallel (equivalent to the PN junction). The equivalent circuit of PV cell is illustrated in Fig. 2.

The diode current is expressed as

(1)i_{\mathrm{D}}=I_{\mathrm{0}}\left({\mathrm{e}}^{V_{\mathrm{D}}/V_{\mathrm{T}}}-\mathrm{1}\right),

where V_T=KT/\mathrm{e} is the thermal voltage, V_T = 26 mV at T = 300 K; I_{\mathrm{0}} is the saturation current; e is the electron charge (e = 1.6 × 10^-19 C); K is Boltzmann’s constant (K = 1.38 × 10^-23 J/K); and V_D is the diode terminal voltage.

The total voltage is

(2)V_{\mathrm{P}\mathrm{V}}=V_{\mathrm{D}}-R_{\mathrm{S}}{I}_{\mathrm{P}\mathrm{V}},

where I_{\mathrm{P}\mathrm{V}} is the total current.

The current of one cell is

(3)I_{\mathrm{S}\mathrm{C}}=i_{\mathrm{D}}+{\displaystyle \frac{V_{\mathrm{D}}}{R_{\mathrm{P}}}}+I_{\mathrm{P}\mathrm{V}},

(4)i_{\mathrm{D}}={\displaystyle \frac{V_{\mathrm{P}\mathrm{V}}}{R_{\mathrm{P}}}}+{\displaystyle \frac{R_{\mathrm{s}}}{R_{\mathrm{P}}}}{I}_{\mathrm{P}\mathrm{V}}.

For one cell, there are the following equations:

(5)I_{\mathrm{P}\mathrm{V}}=I_{\mathrm{S}\mathrm{C}}-I_{\mathrm{0}}\left({\mathrm{e}}^{V_{\mathrm{D}}/V_{\mathrm{T}}}-\mathrm{1}\right)-{\displaystyle \frac{V_{\mathrm{D}}}{R_{\mathrm{P}}}},

(6)V_{\mathrm{D}}=V_{\mathrm{P}\mathrm{V}}+R_{\mathrm{s}}{I}_{\mathrm{P}\mathrm{V}}.

For the PV panel, the diode terminal voltage is expressed as

(7)V_{\mathrm{D}}={\displaystyle \frac{V_{\mathrm{P}\mathrm{V}}}{N_{\mathrm{s}}}}+{\displaystyle \frac{R_{\mathrm{s}}}{N_{\mathrm{P}}}}{I}_{\mathrm{P}\mathrm{V}},

where N_s and N_p are the cell number in series and in parallel, respectively.

(8)I_{\mathrm{P}\mathrm{V}}=N_{\mathrm{P}}{I}_{\mathrm{S}\mathrm{C}}-N_{\mathrm{p}}{I}_0\left(e^{\frac{V_{\mathrm{P}\mathrm{V}}/N_{\mathrm{s}}+R_{\mathrm{s}}{I}_{\mathrm{P}\mathrm{V}}/N_{\mathrm{p}}}{V_{\mathrm{T}}}}-\mathrm{1}\right)-{\displaystyle \frac{V_{\mathrm{P}\mathrm{V}}}{R_{\mathrm{p}}}}-{\displaystyle \frac{R_{\mathrm{s}}{I}_{\mathrm{P}\mathrm{V}}}{R_{\mathrm{p}}}}.

Taking into account the temperature T, the current I_{\mathrm{PV}}becomes

(9)I_{\mathrm{P}\mathrm{V}}=N_{\mathrm{P}}{I}_{\mathrm{S}\mathrm{C}\mathrm{T}}-N_{\mathrm{p}}{I}_{\mathrm{o}\mathrm{s}}\left(e^{\frac{V_{\mathrm{P}\mathrm{V}}/N_{\mathrm{s}}+R_{\mathrm{s}}{I}_{\mathrm{P}\mathrm{V}}/N_{\mathrm{p}}}{V_{\mathrm{T}}}}-\mathrm{1}\right)-{\displaystyle \frac{V_{\mathrm{P}\mathrm{V}}}{R_{\mathrm{P}}}}-{\displaystyle \frac{R_{\mathrm{s}}{I}_{\mathrm{P}\mathrm{V}}}{R_{\mathrm{P}}}},

(10)I_{\mathrm{o}\mathrm{s}}=I_{\mathrm{o}\mathrm{r}}{\left({\displaystyle \frac{T}{T_{\mathrm{r}}}}\right)}^{\mathrm{3}}-e^{\frac{q{E}_{\mathrm{G}\mathrm{0}}}{\beta k}\left(\frac{\mathrm{1}}{T_{\mathrm{r}}}-\frac{\mathrm{1}}{T}\right)}-\mathrm{1},

(11)I_{\mathrm{S}\mathrm{C}\mathrm{T}}=\left[I_{\mathrm{S}\mathrm{C}}+K_{\mathrm{I}}\left(T-\mathrm{298.15}\right)\right]{\displaystyle \frac{G}{\mathrm{1000}}},

with G irradiation, T the temperature, T_r is the temperature of reference, which is equal to 25°C and E_G0 is the gap for crystalline silicon, which is equal to 1.12 eV.

Maximum power point tracking (MPPT)

The P and O algorithm is employed for the MPPT controller, because of its simple structure and requirement of less measured parameters. The DC-bus controller is used to regulate the DC-bus voltage during the absence of solar irradiance (no PV power injection). The P and O algorithm [11–14] is based on the perturbation of the PV system by increasing or decreasing the reference voltage V_ref or by acting directly on the duty cycle of the Boost converter and observation of the effect on output power of the PV panel. If the actual power P(K) of the panel is greater than the previous value P(K-1), the same direction of previous disturbance is kept, otherwise the disturbance of the previous cycle is reversed. The flowchart of the P and O algorithm tracking the maximum power point of the PV panel is demonstrated in Fig. 3.

Modeling DC/DC (Boost) converters

The DC/DC (Boost) converter [15–17] is composed of an inductance (L), a diode (D), a capacitor (C), and a switch (S_a), as depicted in Fig. 4.

The modeling Boost converter depends on the state of the switch S_a.

First case: S_a is closed (ON): 0<t<αT.

In matrix form, the state model can be written as

(12)\left[\begin{array}{c}\hfill {\displaystyle \frac{\mathrm{d}{i}_{\mathrm{L}}}{\mathrm{d}t}}\hfill \\ \hfill {\displaystyle \frac{\mathrm{d}{v}_{\mathrm{0}}}{\mathrm{d}t}}\hfill \end{array}\right]=\left[\begin{array}{cc}\hfill \mathrm{0}\hfill & \hfill \mathrm{0}\hfill \\ \hfill \mathrm{0}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{RC}}\hfill \end{array}\right]\left[\begin{array}{c}\hfill i_{\mathrm{L}}\hfill \\ \hfill v_{\mathrm{0}}\hfill \end{array}\right]+\left[\begin{array}{c}\hfill {\displaystyle \frac{\mathrm{1}}{L}}\hfill \\ \hfill \mathrm{0}\hfill \end{array}\right]v_i,

\dot{x}=A_{\mathrm{1}}x+B_{\mathrm{1}}{v}_i,

A_{\mathrm{1}}=\left[\begin{array}{cc}\hfill \mathrm{0}\hfill & \hfill \mathrm{0}\hfill \\ \hfill \mathrm{0}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{RC}}\hfill \end{array}\right],B_{\mathrm{1}}=\left[\begin{array}{c}\hfill {\displaystyle \frac{\mathrm{1}}{L}}\hfill \\ \hfill \mathrm{0}\hfill \end{array}\right].

Second case: S_a is open (OFF): αT<t<T.

In matrix form, this state model can be expressed as

(13)\left[\begin{array}{c}\hfill {\displaystyle \frac{\mathrm{d}{i}_L}{\mathrm{d}t}}\hfill \\ \hfill {\displaystyle \frac{\mathrm{d}{v}_{\mathrm{0}}}{\mathrm{d}t}}\hfill \end{array}\right]=\left[\begin{array}{cc}\hfill \mathrm{0}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{L}}\hfill \\ \hfill {\displaystyle \frac{\mathrm{1}}{C}}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{RC}}\hfill \end{array}\right]\left[\begin{array}{c}\hfill i_{\mathrm{L}}\hfill \\ \hfill v_{\mathrm{0}}\hfill \end{array}\right]+\left[\begin{array}{c}\hfill {\displaystyle \frac{\mathrm{1}}{L}}\hfill \\ \hfill \mathrm{0}\hfill \end{array}\right]v_i,

\dot{x}=A_{\mathrm{2}}x+B_{\mathrm{2}}{v}_i,

A_{\mathrm{2}}=\left[\begin{array}{cc}\hfill \mathrm{0}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{L}}\hfill \\ \hfill {\displaystyle \frac{\mathrm{1}}{C}}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{RC}}\hfill \end{array}\right],B_{\mathrm{2}}=\left[\begin{array}{c}\hfill {\displaystyle \frac{\mathrm{1}}{L}}\hfill \\ \hfill \mathrm{0}\hfill \end{array}\right].

To link these two cases of Boost operation, the following average model is used:

\dot{x}=Ax+B{v}_i,

\{\begin{array}{c}\hfill A=A_{\mathrm{1}}d+A_{\mathrm{2}}\left(\mathrm{1}-d\right),\hfill \\ \hfill B=B_{\mathrm{1}}d+B_{\mathrm{2}}\left(\mathrm{1}-d\right),\hfill \end{array}

A=\left[\begin{array}{cc}\hfill \mathrm{0}\hfill & \hfill \mathrm{0}\hfill \\ \hfill \mathrm{0}\hfill & \hfill -{\displaystyle \frac{d}{RC}}\hfill \end{array}\right]+\left[\begin{array}{cc}\hfill \mathrm{0}\hfill & \hfill -{\displaystyle \frac{\left(\mathrm{1}-d\right)}{L}}\hfill \\ \hfill {\displaystyle \frac{\left(\mathrm{1}-d\right)}{C}}\hfill & \hfill -{\displaystyle \frac{\left(\mathrm{1}-d\right)}{RC}}\hfill \end{array}\right]=\left[\begin{array}{cc}\hfill \mathrm{0}\hfill & \hfill -{\displaystyle \frac{\left(\mathrm{1}-d\right)}{L}}\hfill \\ \hfill {\displaystyle \frac{\left(\mathrm{1}-d\right)}{C}}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{RC}}\hfill \end{array}\right],

B=\left[\begin{array}{c}\hfill {\displaystyle \frac{d}{L}}\hfill \\ \hfill \mathrm{0}\hfill \end{array}\right]+\left[\begin{array}{c}\hfill {\displaystyle \frac{\left(\mathrm{1}-d\right)}{L}}\hfill \\ \hfill \mathrm{0}\hfill \end{array}\right]=\left[\begin{array}{c}\hfill {\displaystyle \frac{\mathrm{1}}{L}}\hfill \\ \hfill \mathrm{0}\hfill \end{array}\right].

Thus, the state model controlling the operation of the Boost converter is

(14)\left[\begin{array}{c}\hfill {\displaystyle \frac{\mathrm{d}{i}_L}{\mathrm{d}t}}\hfill \\ \hfill {\displaystyle \frac{\mathrm{d}{v}_{\mathrm{0}}}{\mathrm{d}t}}\hfill \end{array}\right]=\left[\begin{array}{cc}\hfill \mathrm{0}\hfill & \hfill -{\displaystyle \frac{\left(\mathrm{1}-d\right)}{L}}\hfill \\ \hfill {\displaystyle \frac{\mathrm{1}-d}{C}}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{RC}}\hfill \end{array}\right]\left[\begin{array}{c}\hfill i_{\mathrm{L}}\hfill \\ \hfill v_{\mathrm{0}}\hfill \end{array}\right]+\left[\begin{array}{c}\hfill {\displaystyle \frac{\mathrm{1}}{L}}\hfill \\ \hfill \mathrm{0}\hfill \end{array}\right]v_i,

where L{\displaystyle \frac{\mathrm{d}{i}_{\mathrm{L}}}{\mathrm{d}t}}=V_i-\left(\mathrm{1}-d\right)v_{\mathrm{0}} and C{\displaystyle \frac{\mathrm{d}{v}_{\mathrm{0}}}{\mathrm{d}t}}=\left(\mathrm{1}-d\right)i_{\mathrm{L}}-{\displaystyle \frac{v_{\mathrm{0}}}{R}}.

The dynamics of the current i_L crossing the inductor L is given by the differential equation

L{\displaystyle \frac{\mathrm{d}{i}_{\mathrm{L}}}{\mathrm{d}t}}=V_i-\left(\mathrm{1}-d\right)v_{\mathrm{0}}=u_i.

From which, the control algorithm (d) of the Boost converter is extracted:

(15)d=\mathrm{1}-{\displaystyle \frac{V_i-u_i}{V_{\mathrm{0}}}}=\mathrm{1}-{\displaystyle \frac{V_{\mathrm{PV}}-u_i}{V_{\mathrm{dc}}}}.

The block diagram of the Boost control algorithm is displayed in Fig. 5.

Three phase shunt active filter control

The method of active and reactive power is a compensation technique widely used and applied to three-phase shunt active filter control [18–21]. This method, the so-called instantaneous power (pq theory), operates according to Concordia transformation \alpha -\betato obtain active (real) and reactive (imaginary) powers.

Note that (v_sα, v_sβ) and (i_Lα, i_Lβ) are the orthogonal components of Concordia respectively associated with supply voltages v_sk (k = a, b​​, c) and currents drawn by the polluting load I_LK. From Concordia transformation, voltages and currents can be expressed as

(16)\left[\begin{array}{c}\hfill i_{\alpha }\hfill \\ \hfill i_{\beta }\hfill \end{array}\right]=C_{\mathrm{23}}\left[\begin{array}{c}\hfill i_a\hfill \\ \hfill i_b\hfill \\ \hfill i_c\hfill \end{array}\right]\mathrm{a}\mathrm{n}\mathrm{d}\left[\begin{array}{c}\hfill i_a\hfill \\ \hfill i_b\hfill \\ \hfill i_c\hfill \end{array}\right]=C_{\mathrm{32}}\left[\begin{array}{c}\hfill i_{\alpha }\hfill \\ \hfill i_{\beta }\hfill \end{array}\right]

with

C_{\mathrm{23}}=\sqrt{{\displaystyle \frac{\mathrm{2}}{\mathrm{3}}}}\left[\begin{array}{ccc}\hfill \mathrm{1}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{\mathrm{2}}}\hfill & \hfill -{\displaystyle \frac{\mathrm{1}}{\mathrm{2}}}\hfill \\ \hfill \mathrm{0}\hfill & \hfill {\displaystyle \frac{\sqrt{\mathrm{3}}}{\mathrm{2}}}\hfill & \hfill -{\displaystyle \frac{\sqrt{\mathrm{3}}}{\mathrm{2}}}\hfill \end{array}\right]

and

(17)C_{32}={\displaystyle \frac{\mathrm{1}}{\sqrt{\mathrm{3}}}}\left[\begin{array}{cc}\hfill \sqrt{\mathrm{2}}\hfill & \hfill \mathrm{0}\hfill \\ \hfill -{\displaystyle \frac{\mathrm{1}}{\sqrt{\mathrm{2}}}}\hfill & \hfill \sqrt{{\displaystyle \frac{\mathrm{3}}{\mathrm{2}}}}\hfill \\ \hfill -{\displaystyle \frac{\mathrm{1}}{\sqrt{\mathrm{2}}}}\hfill & \hfill -\sqrt{{\displaystyle \frac{\mathrm{3}}{\mathrm{2}}}}\hfill \end{array}\right].

The real and imaginary instantaneous powers of the load, denoted as p and q respectively are defined by

(18)\left[\begin{array}{c}\hfill p\hfill \\ \hfill q\hfill \end{array}\right]=\left[\begin{array}{cc}\hfill v_{\mathrm{s}\alpha }\hfill & \hfill v_{\mathrm{s}\beta }\hfill \\ \hfill -v_{\mathrm{s}\beta }\hfill & \hfill v_{\mathrm{s}\alpha }\hfill \end{array}\right]\left[\begin{array}{c}\hfill i_{\mathrm{L}\alpha }\hfill \\ \hfill i_{\mathrm{L}\beta }\hfill \end{array}\right].

Substituting the diphase voltages and currents by three phase, the equations of active and reactive power are obtained.

p=v_{\mathrm{s}\alpha }{i}_{\mathrm{L}\alpha }+v_{\mathrm{s}\beta }{i}_{\mathrm{L}\beta },

q=v_{\mathrm{s}\alpha }{i}_{\mathrm{L}\beta }-v_{\mathrm{s}\beta }{i}_{\mathrm{L}\alpha }.

From the power matrix expression, the currents equation can be deduced.

(19)\left[\begin{array}{c}\hfill i_{\mathrm{L}\alpha }\hfill \\ \hfill i_{\mathrm{L}\beta }\hfill \end{array}\right]={\displaystyle \frac{\mathrm{1}}{v_{\mathrm{s}\alpha }^{\mathrm{2}}+v_{\mathrm{s}\beta }^{\mathrm{2}}}}\left[\begin{array}{cc}\hfill v_{\mathrm{s}\alpha }\hfill & \hfill -v_{\mathrm{s}\beta }\hfill \\ \hfill v_{\mathrm{s}\beta }\hfill & \hfill v_{\mathrm{s}\alpha }\hfill \end{array}\right]\left[\begin{array}{c}\hfill p\hfill \\ \hfill q\hfill \end{array}\right].

In the case of sinusoidal voltages supplying a nonlinear load, the instantaneous power p and q are expressed as

(20)\{\begin{array}{l}p=\overline{p}+\tilde{p}\hfill \\ q=\overline{q}+\tilde{q}\hfill \end{array}.

The powers p and q each contains a direct part and an alternative part:

\overline{p} is a DC power related to the active fundamental component of the current.

\overline{q} is a DC power related to the reactive fundamental component of the current.

\tilde{p}and \tilde{q} are alternative (AC) powers related to the harmonic components of the current.

The active filter must compensate only reactive q power and the AC component of the active power \tilde{p}.

The reference currents in \alpha \beta frame are given as

(21)\left[\begin{array}{c}\hfill i_{\mathrm{L}\alpha }^{*}\hfill \\ \hfill i_{\mathrm{L}\beta }^{*}\hfill \end{array}\right]={\displaystyle \frac{\mathrm{1}}{v_{\mathrm{s}\alpha }^{\mathrm{2}}+v_{\mathrm{s}\beta }^{\mathrm{2}}}}\left[\begin{array}{c}\hfill v_{\mathrm{s}\alpha }-v_{\mathrm{s}\beta }\hfill \\ \hfill v_{\mathrm{s}\beta }{v}_{\mathrm{s}\alpha }\hfill \end{array}\right]\left[\begin{array}{c}\hfill p^{*}\hfill \\ \hfill q^{*}\hfill \end{array}\right].

By subjecting these references into inverse Concordia transform, the reference current of the filter in the three-phase frame is obtained.

(22)\left[\begin{array}{c}\hfill i_{\mathrm{L}a}^{*}\hfill \\ \hfill i_{\mathrm{L}b}^{*}\hfill \\ \hfill i_{\mathrm{L}c}^{*}\hfill \end{array}\right]=C_{\mathrm{32}}\left[\begin{array}{c}\hfill i_{\mathrm{L}\alpha }^{*}\hfill \\ \hfill i_{\mathrm{L}\beta }^{*}\hfill \end{array}\right].

The extraction of filter references currents enables the filter to provide reactive power and AC power source. The AC power source will deliver only the active power (average value). The control block of the active filter is as illustrated in Fig. 6.

Computer simulation and results

The simulation of the proposed system is conducted in a Matlab/Simulink environment with parameters listed in Table 1. Changes in the characteristic of currents and powers according to PV panels (I = f (V) and P = f (V)) are simulated taking into consideration brutal change of irradiation G and the temperature T (G = 500 W/m² and T = 27°C, G = 650 W/m² and T = 29°C, G = 850 W/m² and T = 32°C and G = 1000 W/m² and T = 35°C).

The obtained results using MPPT algorithm are illustrated in Fig. 7 showing PV panel current and power characteristic according to voltage(I=f (V) and P=f (V)), respectively.

Figure 8 illustrates the system dynamic response when solar panel supplies continuously variable nonlinear load through the DC/DC Boost converter and the DC/AC inverter (active filter). The source voltages, source currents, variable nonlinear load currents, three phase active filter currents, DC voltage V_dc and Boost current are presented.

It can be observed that the Boost current provided by the PV panel is increased simultaneously with irradiation G and temperature T (From t = 0 s to t = 0.05 s when G = 500 W/m² and T = 27°C, from t = 0.05 s to t = 0.15 s for G = 650 W/m² and T = 29°C, t = 0.15 s to t = 0.25 for G = 850 W/m² and T = 32°C and from t = 0.25 s to t = 0.35 when irradiation and temperature reach their maximum values 1000 W/m² and T = 35°C).

Simulation results show a perfect harmonic currents and reactive power compensation. The inverter (active filter) DC voltage is maintained constant (ripples free) around 500V throughout the operation of electrical energy produced by the PV panel, proving the high performances of the inverter control using the instantaneous powers (pq theory) technique.

Figure 9 presents the system power flow, it can be noted that from t = 0 s to t = 0.35 s the PV panel supplies continuously the changing load and the excess of produced energy is fed to the main supply.

Figure 10 shows the source current total harmonic distortion (THD) of phase a for FFT of three cycles corresponding to 2.92% which is well below IEEE-519 recommendations.

Conclusions

In this work, the control of PV system using a Boost converter to extract the maximum power point (MPP) from the PV system using the P and O algorithm and the inverter control to supply power to a variable nonlinear load in order to improve power quality was developed and tested. The computer simulation has confirmed that the developed control algorithm is efficient and is able to track the MPP produced by the PV panel. The proposed grid side converter control algorithm has improved voltage and current waveform of the main source (harmonic currents and reactive power compensation, load balancing, and DC bus voltage regulation) and made easier the transfer of solar panel produced power to the main grid. In this paper performances of the PV system connected to the main supply (grid) have been presented and analyzed. The system is designed to supply power continuously to the load by injecting the power excess to the grid and when the panel is unable to provide enough power required by the load, the grid feeds back the energy to the system.

From the characteristics (I = f (V) and P = f(V)), it can be observed that the Boost control algorithm is effective in extracting PV panel MPP according to the signal produced by the P and O algorithm. The effectiveness of the DC/DC converter, the active filter with the pq theory as a control strategy has proved its auto-adaptivity to compensate simultaneously harmonic currents generated by a changing nonlinear load and reactive power and maintain, at the same time, the DC bus voltage constant around its reference value. The obtained source currents THD is well below IEEE-519 recommendations.

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