Shunt Active Power Filter Based on P-Q Theory with Multilevel Inverters for Harmonic Current Compensation

A shunt active power filter based on P-Q theory combined with high pass filters (HPFs) for harmonic-current compensation was proposed in this paper. A dual level H-bridge inverter (DLHI) and clamp diode multilevel inverter (CDMI) as inverters was used. The proposed active power filter was applied to 3-phase power system with 220V voltage and 50Hz frequency. the simulation model was constructed by using Simulink MATLAB. The results show that the proposed active power filter with CDMI produces lower total harmonic distortion (THD) than the active power filters with DLHI. Additionally, the proposed shunt active power filter has lower THD compared with other types of active power filters.

1633 Q theory is flexible in designing shunt active power filters combined with a multilevel inverter for harmonic-current compensation. The design methodology is detailed in the following sections. Section 1 describes the state of the art solutions. Section 2 describes the P-Q theory instantaneous power. Furthermore, the performance of the proposed shunt active power filter is reported in Section 3. Finally, Section 4 concludes this research.

Research Method
As shown in Figure 1, we propose a shunt active power filter based on P-Q theory combined with high pass filters (HPFs) for harmonic-current compensation. We applied the proposed active power filter to 3-phase power system with a voltage of 220 V and frequency of 50 Hz. A flow chart for calculation of compensating current shown in Figure 2. A system wih nonlinear load was constructed using Simulink MATLAB.  According to IEEE-519 standard, the total harmonic distortion (THD) is given by [14]: where is the effective value of fundamental current and is the effective value of harmonic current. Filter is not only reduce interference but also reduce harmonics power [15], [16][17][18]. To reduce the THD, this study was used the P-Q theory. The P-Q instantaneous power theory was introduced by Akagi, et al [13,14]. The P-Q theory consists of Clark Transformation as shown in Figure 2. The three-phase current of and voltage in R-S-T coordinates transform to - coordinates using Equation (2) and (3) [14].
After the Clarke transformation of current and voltage. It's followed by instaneous power calculation. Real power and reactive powers are calculated with (4): Thus: ̅ ̃ ̅ ̃ where ̅ =instantaneous real power P due to the fundamental component; ̃= instantaneous harmonic real power P due to the harmonic component; ̅ =instantaneous reactive power Q due to the fundamental component; ̃= instantaneous harmonic reactive power Q due to the harmonic component; In this paper, a high pass filter (HPF) was used. The real power is set to zero and an instantaneous reactive power is set into opposite vectors in order to cancel the reactive component of the line current. The compensator will only compensate the instantaneous reactive power.
To get the reference current harmonics, the harmonic currents in the bi-phase system to be transformed by Inverse Clarke Transformation of α-β, which is given by Equation (6) [13,14] The controller is used for generating pulses as the input of the inverter by comparing the value of the reference current and the current measured.

Result and Analysis
The performances of the proposed shunt active power were explained in this section. Section 3.1 shows the performance of three-phase power system with nonlinear load without an active filter. Furthermore, section 3.2 and section 3.3 was explained shunt active power filter with dual level H-bridge inverter (DLHI) and clamp diode multilevel inverter (CDMI), respectively.

Performance the three phase power system with nonlinear load
A system with nonlinear load as shown in Figure 3, and the THD before the shunt active filter operation has 28.41 %, 27.08 %, and 28.35 % for phase R, phase S, and phase T, respectively. It is shown that a nonlinear load was effected to increase the THD value. Figure 5a. shows a three phases of current in transient condition and steady state condition. At the steady state condition, the Fourier Series approximations of I R current is shown in Figure 6  The FFT analysis shows that the three phases system has large a total harmonic distortion (THD) and the time domain plot also agrees with Fourier Series approximations. The Fourier Series approximations shows that the three phases system has a lot of harmonic frequency. This paper was proposed a shunt active power filter based on P-Q theory. As an inverter, a dual level H-bridge inverter (DLHI) and clamp diode multilevel inverter (CDMI) was used in this research.

Performance Shunt Active Filter with dual level H-bridge inverter (DLHI)
The performance shunt active filter with dual level H-bridge inverter (DLHI) is shown in Figure 7. It is shown that before the shunt active filter operation, the source of current is highly rich in harmonics. After the shunt active filter starts the compensation process, the source is sinusoidal with phase 0 , 120 , and 240 . A Powergui FFT Analysis Tools on Powergui Matlab Simulink is used to get the value of THD. The THD before the shunt active filter operation has 28.41 %, 27.08 %, and 28.35 %. The THD after the shunt active filter with dual level H-bridge inverter (DLHI) has 3.73 %, 3.72 %, and 4.53 %. The THD value has conformity with the standard IEEE recommendations (THD <=5%).

Performance Shunt Active Filter with clamp diode multilevel inverter (CDMI)
The performance shunt active filter with a clamp diode multilevel inverter (CDMI) is shown in Figure 8. It is shown that before the shunt active filter operation, the source of current is highly rich in harmonics. After the shunt active filter starts the compensation process, the source is sinusoidal with phase 0 , 120 , and 240 . The THD after the shunt active filter with clamp diode multilevel inverter (CDMI) has 1.91 %, 1.93 %, and 1.91 %. The THD value has conformity with the standard IEEE recommendations (THD <=5%). The result showed that active power filter with CDMI produced lower total harmonic distortion (THD) than active power filter with DLHI. The THD with DLHI and CDMI is lower than limits of IEEE harmonics standards. It is also shown that the proposed shunt active power filter has lower THD compared to another type of active power filter as shown in Table 4.

Conclusion
A shunt active power filter based on P-Q theory with dual level H-bridge inverter (DLHI) and clamp diode multilevel inverter (CDMI) was design, modified, and analyzed. This shunt active power filter was applied to 3 phase power system with a voltage of 220 V and frequency of 50 Hz. The simulation model was constructed using Simulink MATLAB. The simulation result showed that active power filter with CDMI produced lower total harmonic distortion (THD) than active power filter with DLHI. The two cases studied in conformity with the standard IEEE recommendations (THD <=5%). It is also shown that the proposed shunt active power filter has lower THD compared to another type of active power filter.