Multi Units of Three Phase Photovoltaic using Band Pass Filter to Enhance Power Quality in Distribution Network under Variable Temperature and Solar Irradiance Level

Received Sep 6, 2017 Revised Dec 22, 2017 Accepted Dec 29, 2017 The paper proposed power quality enhancement on three phase grid of point common coupling (PCC) bus due to integration of multi units of photovoltaic (PV) to 380 volt (phase-phase) 50 Hz low voltage distribution network under variable temperature and irradiance level. The band pass filter models (single tuned and double tuned) were installed to improvement power quality on the conditions i.e. without filter, with single tuned filter, and with double tuned filter. Multi units of PV generator without filter, with single tuned, and with double tuned filter at all temperatures and irradiance levels resulted in relatively stable phase voltage (308 and 310 volt), so able to generate an unbalanced voltage of 0%. The maximum phase current for the system without filter at all temperatures and radiation levels of 9.8, 12.5, and 10 ampere respectively, resulted in an unbalanced current of 16.10% . Under the same condition, single tuned and double tuned filters were able to balance phase current to 10.45 A and 10.44 ampere respectively, resulting in an unbalanced current of 0%. Implementation of single tuned and double tuned filters was able to reduce unbalance current according to ANSI/IEEE 2411990. At constant temperature and irradiance increased, both average voltage and current harmonics also increased. Double tuned active filter was the most effective to suppress the 11th and 13th harmonics so that capable to migitate average voltage and current harmonics better than system using single tuned filter which could only reduce 5th harmonic within IEEE 519-1992. Keyword:


RESEARCH METHOD 2.1. Proposed Method
The model of a single 100 kW PV generator connected to a three phase grid is shown in Figure 1. The PV system produces output voltage become as input for the DC/DC converter. The MPPT with P and O algorithm helps single phase PV generator resulting maximum power. The low DC output voltage from PV generator is increased by DC/DC boost converter to produce output voltage by adjusting duty cycle by switching device. The DC output is further converted by a three phase DC/AC inverter circuit to an AC voltage to a three phase grid using six insulated gate bipolar transistors (IGBTs) circuit base on pulse width modulation (PWM). Figure 2 shows proposed model of three groups of PV generator linked to a 380 volt (phase-phase), 50 Hz three phase low voltage distribution network on PCC bus and a 100 MVA, 20 kV three phase grid through a 100 kVA, 20 kV/380 V three phase power transformer.
This paper performs power quality enhancement on three phase grid of PCC bus due to integration of PV generator to 220 kV 50 Hz low voltage distribution network under variable temperature and irradiance level. The research uses three group models PV generator each with 100 kW active power. The power quality parameters are voltage and current unbalance, as well as voltage and current harmonics in 12 PV generator scenarios PV connected distribution network on PCC bus. The first scenario is without filter at the irradiance level i.e. 400 W/m 2 , 600 W/m 2 , 800 W/m 2 , and 1000 W/m 2 . The second and third scenarios are with single tuned filter and double tuned filter at the same irradiance level respectively. The temperature degree of each condition are 20 0 , 25 0 , 30 0 , 35 0 , and 40 0 Celcius. So that the total scenarios are 12 different irradiantion levels (without filter, with single tuned filter, and with double tuned filter) where it has five temperatures degree.
The simulation is performed to determine voltage and current waveform of a three phase distribution network on PCC bus. The band pass filter model i.e. single tuned and double tuned is used to improve power quality performance. The single tuned filter serves to suppress 5 th single harmonic while double tuned filter expected to reduce 11 th and 13 th harmonics. A three phase phase circuit breaker (CB) is used to connect and disconnect band pass filter between a single PV generator and a three phase grid. The next process is to determine unbalance voltage and current as well as voltage and current THD in each scenario. Its results are further validated with ANSI/IEEE 241-1990 (unbalance voltage and current) and IEEE 519-1992 (voltage and current THD) as the basis for determining power quality level. Simulation and analysis of research results use Matlab/Simulink.  Table 1 shows the devices, parameters, and simulation values of proposed model.  Figure 3 shows the equivalent circuit of a solar panel. A solar panel is composed of several PV cells that have series, parallel, or series-parallel external connections [10].

Photovoltaic Model
where I PV is the photovoltaic current, I o is saturated reverse current, "a" is the ideal diode constant, V t = N S KTq -1 is the thermal voltage, N S is the number of series cells, q is the electron charge, K is the Boltzmann constant, T is the temperature of p-n junction, R S and R P are series and parallel equivalent resistance of the solar panels. I PV has a linear relation with light intensity and also varies with temperature  (2) and (3): In which I PV,n , I SC,n and V OC,n are photovoltaic current, short circuit current and open circuit voltage in standard conditions (T n = 25 C and G n = 1000 Wm -2 ) respectively. K I is the coefficient of short circuit current to temperature, ∆T = T -T n is the temperature deviation from standard temperature, G is the light intensity and K V is the ratio coefficient of open circuit voltage to temperature. Open circuit voltage, short circuit current and voltage-current corresponding to the maximum power are three important points of I-V characteristic of solar panel. These points are changed by variations of atmospheric conditions. By using (4) and (5)

Voltage/Current and Unbalance Harmonics
Power quality means quality of voltage and current. Power quality is determined based on the voltage and current value or the tolerance limit of equipment used. In general, current and voltage wave form of pure sinusoidal waves. One problem that occurs is non sinusoida or distorted current and voltage waves generated by harmonics in the power system [11]. Harmonic is distorted periodic steady state wave caused by the interaction between the shape of a sine wave at the fundamental frequency system with another wave component which is an integer multiples frequency of fundamental frequency. The most common harmonic index, which relates to the voltage waveform, is THD, which is defined as the root mean square (rms) of the harmonics expressed as a percentage of the fundamental component as showed in (12). For most applications, it is sufficient to consider the harmonic range from the 2 nd to 25 th , but most standards specify up to the 50 th . Second harmonic index is current THD means the ratio of rms harmonic current value to rms fundamental current which expressed in (7) [11].
Where V n and I n (the rms voltage and current at harmonic n), V 1 and I 1 (the fundamental rms voltage and current), N (the maximum harmonic order to be considered). The allowable maximum THD value for each country is different depending on the standard used. THD standards most often used in electric power system is IEEE 519-1992. There are two criteria used in the analysis of harmonic distortion that voltage distortion limit and current distortion limit [13]. There are several standards that can be used to determine level of voltage unbalance in three phase systems, e.g. IEC, NEMA, and IEEE. In this study, value of unbalance voltage use Equation 8 is based ANSI/IEEE 241-1990 Standard [14] (8), value of unbalance voltage expressed in percent (%) and is defined as follows; V avarage is the average value of maximum voltage on phase a, b, c, (volt), V a,b,c min is minimum voltage on phase a, b, c, (volt), V a,b,c max is maximum voltage on phase a, b, c (volt ). By using the same equation, then percentage of unbalance current can be calculated by replacing voltage magnitude into current magnitude.

Band Pass Filter
The shunt passive filters always considered as good solution to solve harmonics current problems. Shunt passive filters can be classified into three basic catagories as follows (a) Band pass filters (of single or double tuned), (b) High pass filters (of first, second, third-order or C-type), and (c) Composite filters as shown in Figure 4 [7]. There are two models of band pass filter, i.e. single tuned filter and double tuned filter. A single tuned filter consisting of inductor L, capacitor C and small damping resistor R are connected in parallel with non-linear loads to provide low impedance paths for specific harmonic frequencies, thus resulting in absorbing the dominant harmonic currents flowing out of the load. Furthermore it also compensates reactive power at system operating frequency [15]. Single tuned passive filters are used to suppress harmonic at a single frequency e.g. 5 th , 7 th , 9 th , 11 th , or 13 th harmonic. Whereas double tuned passive filter is used to eliminate harmonics at two frequencies such as the 5 th and 7 th harmonics or the 11 th and 13 th harmonics [16]. In this paper a single tuned filter and double tuned filter model are used to reduce 5 th harmonics as well as 11 th and 13 th harmonics respectively.

RESULTS AND ANALYSIS
The results analysis is began from determination of maximum and minimum grid voltages in each phase, to compute unbalanced voltage using Equation 8, as well as voltage THD of three phase grid on PCC bus without, with single tuned filter, and with double tuned filter respectively. By using the same procedure and equation, then obtained unbalance current and current THD. Table 2 represents unbalanced voltage and average voltage harmonics (THD V ) in three PV generator integration model to a three phase grid and four levels of irradiance with five different temperature levels. Table 3 shows the unbalanced current and average harmonic current (THD I ) on the PCC bus under the same condition.   Figure 5 shows a grid voltage waveform of PV generator model connected three phase grid on two levels of solar irradiance (600 W/m 2 and 1000 W/m 2 ) on PCC bus without filter, with single tuned filter, and double tuned filter. Figure 6 shows harmonics spectra of grid voltage of PV generator model connected three phase grid on two levels of solar irradiance (600 W/m 2 and 1000 W/m 2 ) on PCC bus without filter, with single tuned filter, and with double tuned filter. Figure 7 shows performance of voltage and current average harmonics in three PV generator model connected three phase grids on PCC bus at four levels of irradiance (temperature 25 0 C), without filter, with single tuned filter, and with double tuned filter. Table 3 shows that maximum voltages (phase A, B, and C), the system without filter for all irradiance levels (400 to 1000 W/m 2 ) and temperatures (20 to 40 0 C) are stable at 308 and 310 volt, so it generates an unbalanced voltage of 0%. The maximum phase voltage of system using a single tuned filter for all irradiance levels and temperatures (20 0 C, 25 0 C, and 30 0 C) is equal to 308 volt and at temperatures (35 0 C and 40 0 C), the value increases to 310 volt, resulting in same an unbalance voltage of 0%. The same value using a double tuned filter at all radiation levels (400 to 1000 W/m 2 ) and temperature (20 0 C to 40 0 C) is equal to 307.8 volt, resulting in same an unbalanced voltage of 0%. Under the condition without filter, irradiance level remains, and temperature increases, average voltage harmonics (THD V ) is relatively the same. While for the condition without filter and fixed temperature, but irradiance level increases, then average voltage harmonics also increases. The lowest average voltage harmonics is generated at irradiance of 400 W/m 2 and temperature of 25 0 C as 2.58%, while the highest occurs at irradiance of 800 W/m 2 and temperature of 25 0 C as 4.18%. Under the condition of using single tuned filter, irradiance remains, and temperature increases, then average voltage harmonics is relative same. Under the condition of without filter, fixed temperature, but irradiance increase, then average voltage harmonics also increases. The lowest average voltage harmonics is generated at irradiance 400 W/m 2 and temperature 20 0 C as 0.22%, while the highest harmonics occurs at irradiance of 800 W/m 2 and temperature of 25 0 C as 0.43%. Application of double tuned filter at fixed irradiance and increased temperature produces relatively same average voltage harmonics. On the other hand, at constant temperature and irradiance, so that average voltage harmonics increases. The lowest average voltage harmonics is generated at irradiance of 400 W/m 2 and temperature of 20 0 C as 0.09%, while the highest occurs at irradiance of 1000 W/m 2 and temperature of 25 0 C as 0.18%. The use of double tuned filter can suppress 11 th and 13 th harmonics so as significantly reduce average voltage harmonics, compared to single tuned filter that only reduce 5 th harmonics.   Figure 6. Voltage harmonics spectra on phase A at two levels of solar irradiance with temperature of 25 0 C Table 3 shows that maximum currents in phase A, B, and C, for system without filter for all irradiance levels (400 to1000 W/m 2 ) and temperatures (20 to 40 0 C) are different e.i. 12.5, 9.8, and 10 A respectively, resulting in an unbalanced current of 16.10%. In the same condition, single tuned filter is able to balance phase currents of 10.45 ampere each, resulting in an unbalanced current equal to 0%. Under without filter conditions, irradiance remains, and temperature increases (20 0 C to 40 0 C), average current harmonics (THD I ) is relatively same. While the conditions without filter and temperature remains, but irradiance increases, then average current also increases. The lowest average current harmonics generated at irradiance of 40 0 W/m 2 and temperature of 300C as 1.653%, while the highest occurs at irradiance of 1000 W/m 2 and temperature of 20 0 C as 1.957%. Under condition of with single tuned filter, fixed irradiance, and temperature increases, then average current harmonics is relatively same. Under same filter condition and fixed temperature, but irradiance increases, so average current harmonics value also increases. The lowest average current harmonics is generated at 400 W/m 2 irradiance and temperature (20 0 C to 40 0 C) as 0.09%, while the highest happens at irradiance of 800 W/m 2 and temperature (20 0 C to 35 0 C) as 0.17%. The application of double tuned filter at fixed irradiation and temperature increase produces a relatively constant current harmonics. Otherwise, on fixed temperature and irradiance increases, then average current harmonics also increases. The lowest average current harmonics is generated at irradiation of 400 W/m 2 and temperature (20 0 C to 40 0 C) as 0.03%, while the highest harmonics hanppen at irradiance of 800 W/m 2 and temperature (20 0 C to 40 0 C) as 0.05%. Implementation of double tuned filter on three phase PV generator can decrease average current harmonics better than single tuned filters. Figure 7(a) shows that at increasing irradiance level (400 W/m 2 to 1000 W/m 2 ) and fixed temperature (25 0 C), average voltage harmonics also increases. Double tuned filter can significantly reduce average voltage harmonics of system compared to single tuned filter and without filter. Figure 7(b) also shows that at increasing irradiance level (400 W/m 2 to 1000 W/m 2 ) and fixed temperature (25 0 C), average current harmonics also increases. Double tuned filter is mostly effective to suppress 11 th and 13 th harmonics so it can migitate both average voltage harmonics and average current harmonics, better than system with single tuned filter which can only decrease 5 th harmonics.

CONCLUSION
Multi units of PV generator connected to a three phase distribution network, without filter, with single tuned, and with double tuned filter at all temperatures and irradiance levels results in relatively stable phase voltage (308 volt and 310 volt), so able to generate an unbalanced voltage of 0%. The maximum phase current for the system without filter at all temperatures and radiation levels of 12.5, 9.8, and 10 A, respectively, resulting in an unbalanced current of 16.10%. Under the same condition, single tuned and double tuned filters are able to balance phase current to 10.45 A and 10.44 ampere respectively, resulting in an unbalanced current of 0%. Implementation of single tuned and double tuned filters able to reduce unbalance current according to ANSI/IEEE 241-1990. At constant temperature and irradiance increases, both average voltage and current harmonics also increase. Double tuned active filter is the most effective to suppress the 11 th and 13 th harmonics so capable to migitate average voltage and current harmonics better than system using single tuned filter which can only reduce 5 th harmonic within IEEE 519-1992.