AN EFFICIENT HYBRID ACTIVE POWER FILTER (H-APF) FOR HARMONIC MITIGATION USING COMPENSATION TECHNIQUES

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INTRODUCTION
The growth and economy of the country depend on the power generation and its usage.
Due to recent advancement in technology, people demand high-quality power to their daily need. The problem occurred in power system due to voltage, current, frequency variation like swell, transient, harmonics, and spikes in electrical and electronic equipment's. The usage of the new power electronic devices starts from small non-linear load in the home to extensive industrial applications. The power quality problems are resolved in recent years by incorporating new techniques in power systems (Ahsan, Pan, & Li, 2018;Diab et al., 2018). The voltage and current harmonics in power systems are solved by using filtering methods. The harmonics are occurred by electromagnetic interference and voltage/ current distortion. The Reactors, transformations-K-factor, Pulse and Phase shifting solutions, Tuned, low-pass filters, active and hybrid-Harmonic filters are the different harmonics mitigation techniques to compensate the current from the loads (Schwanz, Bollen, & Larsson, 2016).
The Passive Filters (PF's) are used to mitigate the current harmonics, but facing problems with parallel resonance. The APF's are used to reduce the drawbacks of PF's and mitigate the harmonics. The APF mainly performs the harmonics detection, reference current signal calculation and gate pulses generation. In general, APF is classification is processed on Topology, Converter, and Number of phases. The converter base includes voltage and current source inverter. The Topology type includes Unified Power Quality-Conditioner (UPQC), Series, Shunt, and Hybrid APF. The phases include single-phase, 2-Wire and 3-phase, 3 or 4 -wire. The Hybrid-APF are classified based on the topology includes Shunt APF with Series APF, Shunt APF with Shunt PF, APF in Series along with Shunt PF and Series APF with Shunt PF. The control strategies are used to compensate the current in APF, which includes proper signal conditioning, reference signal generation based on time and frequency domain, DC Link controlling using PI Controller, sliding mode, and Fuzzy and finally firing signal generation using HCC, PWM and other Techniques (Demirdelen et al., 2013).
Most of the existing research done is on active filters or passive filters individually. The active filters classify as the shunt filter, which is costly and not convinced for higher energy 3C Tecnología. Glosas de innovación aplicadas a la pyme. ISSN: 2254-4143 Edición Especial Special Issue Noviembre 2021 systems and series filters to isolate the harmonics, but not to a great extent. Similarly, passive filters eliminate particular harmonics but cause parallel resonance. The hybrid filter offers efficient and cost-effective solutions with harmonic elimination with better power quality improvements. In the proposed design Hybrid-APF is designed, is the integration of S-PF connected in Series with S-APF. The Hybrid-APF overcomes the drawbacks of the APF.
The Hybrid-APF is designed using controlling strategies, which includes reference signal generation with time-domain using PQ -method and DQ-Method, DC-Link controlling using PI Controller, firing signal generation using HCC.
The proposed method has hybrid combination of Passive and Shunt active power filter, using current compensation techniques like PQ-Theory and Hysteresis current controller.
The switching losses are controlled by PI controller and improve the APF computations.
The proposed approach is improved version of conventional methods in terms of THD and reactive power. The proposed model is easily reconfigurable by replacing PQ-method with DQ-method and vice versa. In future, by replacing the PI controller with artificial neural network (ANN) based controller to improve the THD and power. Section 3 explains the simulation results of the Hybrid-APF. Section 4 discuss the other filtering methods with THD and reactive power comparison with improvements and also concludes the overall work with improvements. Nandankar and More (2017) present transformer-less H-APF using different inverter topologies, which includes Six-switch Two-leg, Nine-Switch and Voltage-Source Inverters.

THE BACKGROUND
The nine-switch Two-leg inverter-based HPF achieves better THD and reactive power. Babu, Kar, and Halder (2016) and Kar and Halder (2016) analyze the H-APF using HCC for power quality, which includes PQ-Theory, HCC for current compensation, along with Fryze compensation theory. The PQ method is better THD than Fryze compensation method. Balasubramanian and Palani (2016) present Shunt H-APF using PQ Theory with current source and voltage source type non-linear load.
The APF is designed using six Transistors are connected parallel and acts as an inverter with DC voltage capacitance along with HCC and PQ method. Thuyen (2018)

PROPOSED METHOD
In this section, the proposed Hybrid-APF is designed for Power quality improvements and to mitigate the harmonics. The Hybrid-APF is an integration of S-PF connected serially with S-APF. The primary model includes Three-Phase AC Source, RL components followed by Non-linear Load along with S-PF and S-APF.
Hybrid-APF architecture is represented in Figure1 The Non-linear load includes the 3-phase RL load, followed by six-diodes connected in parallel and an unbalanced load. The unbalanced load has three resistors 2Ω,4Ω and 6Ω in parallel. The Shunt PF is wired in series with IGBT (Universal Bridge) based Shunt-

PQ METHOD
There are so many methods that are used to compensate the currents, in that PQ-method is a commonly used method in power system to improve the power quality. The instantaneous I and V waveform values are expressed by three-phase instantaneous space vectors (αβ0).
These current and voltage values of the 3-phase system are converted to αβ0 values with the difference of 2π/3 on each phase. The mathematical equations are expressed in a matrix using Clark's Transformation for current and voltage conversion is below. (1) The three-phase instantaneous space vectors are generated using equations (1) and (2) (1) and (2) are removed from the 3-phase systems, so V 0 and I 0 are not considered for further analysis.
The p and q values are generated using below equations (3) and equation (4) are expressed in matrix form. (3) The p and q values are compensated using average and oscillator values are expressed in the below equation (5).
(5) The p ac and q ac are oscillatory values and p dc and q dc are average values. The compensating power of p and q is expressed in equation (6).
The compensating current reference generator (CCRG) of αβ is expressed in the below equation (7).
The CCRG of αβ values are converted back to abc values using Inverse Clark's transformation and are expressed in equation (8).  The current compensation using PQ-Method is represented in Figure 2. The 3Ф Main's voltage (V sabc ) and load current (I labc ) from the 3-phase main power supply are given as input to the abc to αβ0 transformation block (eq (1-2)) followed by instantaneous PQ calculation using (eq (3-4)). The reference compensated current is generated by CCRG using equations (5-7). Finally, the conversion of the αβ to ABC transformation is achieved by equation (8).
The DC link voltage is used to improve the APF computations. PI Controller achieves the generation of the switching losses of the converters. The Hybrid-APF switching losses are balanced by using the DC link voltage as constant.

DQ-METHOD
The DQ-Method is similar to PQ-Method and it is represented in Figure 3. The 3-phase source voltage (V sabc ) is applied to Phase-Locked Loop (PLL) which is used to synchronize the different frequencies and voltage signals based on gains. The PLL output (k) is used to synchronize the DQ and CCRG. The load current (I labc ) is converted to αβ0 values with the difference of 2π/3 using equation (2). The DQ calculation is achieved using park conversion below equation (9).
The rotating reference frame (RRF) -dq occurred based on DC components and harmonic values are frequency shifted by 'k'. The DC values are extracted by using LPF with margin at the line frequency.
The CCRG generates the αβ0 values using inverse park conversion in below equation (10).
Apply the inverse Clarke transformation using equation (8) to generate the final compensated current I cabc values and these values are processed in HCC.

HYSTERESIS CURRENT CONTROLLER (HCC)
The HCC is used to obtain the pulse width modulation (PWM) signals for Hybrid-APF. The HCC is working based on the feedback mechanism. The switching gate signals are given, when the error limitation crosses the given tolerance value in H-APF. The architecture of the HCC is represented in Figure4.
The PQ/DQ Method generates the compensated reference three-phase current (I cabc ) and measured current (I mabc ) from the mains are inputs to the HCC model. The relation operator (>=) acts as a switch to compare the three-phase reference and measured current.
If (I ca >= I ma ) then g 1 will be activated (Switch ON) otherwise g 4 will be activated. Similarly, if (I cb >= I mb ) then g 2 else g 5 gate pulses and If (I cc >= I mc ), g 3 else g 6 gate pulse is generated.
The switching control of the Hybrid-APF using HCC is achieved to generates the gate pulses and input to the Universal Bridge (IGBT Inverter). Modelling parameters considered as a specification for different filtering techniques are represented in Table 1. The Schematic of Hybrid-Active Power Filter (H-APF) using Simulink Tool is represented in Figure 5. The 3Ф-AC source voltage 400V with a frequency of 50Hz is selected for different filtering techniques for harmonics reduction reactive power improvements. To compare with Hybrid-APF, other filtering techniques are designed and analyzed in this section. The S-PF is wired to 3-phase mains, which includes three-phase RL, which is connected in parallel. Harmonic Filter is designed separately, which includes two 5 th & 7 th order, 11 th & 13 th order are connected in parallel. Shunt-APF is connected with 3-phase mains, which includes Universal Bride, PI Controller, followed by HCC and DQ/PQ-

Method.
The experimental setup is conducted for non-linear Load, Passive Filter with Load, harmonic filter with Load, Shunt-APF with Load, and proposed Hybrid-APF with load to generate the THD and reactive power results. The Hybrid-APF generates the three-phase V s , I s , V load and I load waveforms, after PQ method and HCC compensation technique and it is represented in Figure 6. The Hybrid-APF has performed the current compensation using PQ method and HCC with the Load. After compensation, the DC Link V and I waveforms are represented in Figure 7 and 8, respectively.  The FFT analysis of percentage THD results are obtained after simulating the different filtering technique models with Load is represented in Figure 9. The Three-Ф source with only non-linear load results the 10.33 % THD for I s before filtering technique introduced in Figure 9(a).The Shunt Passive filter with Load obtains 9.24% THD, the Harmonic Filter with Load obtains 8.54% THD, shunt-APF obtains the 2.43% THD, Hybrid-APF using THD for source current are represented in Figure 9(b-f)respectively.

DISCUSSION
The THD is a central part of the electrical modules to eliminate the harmonics in main power systems as per IEEE 519 standards. The THD calculation for H-APF using PQ-Method for different Harmonics and Nonlinear loads are tabulated in Table 2 and Table   3 respectively.   The percentage of reactive power is generated for Load, and different Filtering Techniques is tabulated in  The Shunt-APF uses less reactive power than Hybrid-APF, but it utilizes more THD and affects for harmonics mitigation. Hybrid-APF achieves the three-Phase Current compensation for Non-linear loads.
The comparison of proposed model with similar work of Balasubramanian and Palani (2016) of same parameters with THD improvements of 34% are tabulated in Table 6.

CONCLUSIONS
This article presents the Hybrid-APF with modeling and simulation. The Hybrid-APF is an integration of Shunt-PF and Shunt-APF along with 3-Phase AC Source, RL Components and Non-linear Load. The S-APF will compensate for the voltage and currents using PQ Method and HCC. The Hybrid-APF simulation results for Source current and voltage, load current and voltage is presented. The Hybrid-APF is compared with other filtering techniques like Passive Filter, Active Harmonic Filter and Shunt-APF. The Proposed Hybrid -APF achieves better THD than other Filtering techniques. The Hybrid-APF achieves 2.29 %THD using PQ-Method which is better than DQ-Method THD-7.52%. The Hybrid-APF using PQ Method THD improvement over Shunt-APF is 5.76%. The Hybrid-APF utilizes less reactive power (KVAR) around 5.05%, which is quite useful for power system networks. In the future, improve the THD and reactive power of Hybrid-APF by using Artificial-Neuro-Fuzzy Logic Controller as a current compensation method.