Third Harmonic Injection Feedback to Input Technique for Input

Ali Saadon Al-

Ogaili

1’*

;

Ishak bin Aris

1

;

Mohammad

Reza Maghami

1

;

Mohammad

Lutfi b.

Othman

1

;

Norhafiz B.

Azis

1

J. Electrical Systems “ Special issue AMPE2015”

Selected paper

Third Harmonic Injection Feedback to

Input Technique for Input Current

Improvement in Phase Bridge

Rectifier

J E S

This paper schemed a circuit which applying active harmonic injection current with star connection of capacitors bank. The proposed circuit has a controller that regulates the synchronization of phase and injected appropriate harmonic waveform to reduce the harmonic components that appears in the three phase system. The aspirations of this paper were to propose and construct a three-phase rectifier with third harmonic injection current with regard to obtain an input current of three phase bridge rectifier of sinusoidal waveforms and produce low total harmonic distortion (THD). Consequently, the prototype of the three phase rectifier of the harmonic injection current is designed and fabricated. In this paper, in order to develop the method to obtain sinusoidal waveforms for input current, new method of harmonic injection in current is suggested. Experimental and simulation results have been compared. As a result, satisfactory similarities have been found in both experiments and simulations. As a remarkable achievement, it has been proven that the suggested method is accurate.

Keywords: Three-phase convertor; input current; Total harmonic distortion; sinusoidal waveform .

1.

Introduction

Smart grid and power electronic are two topics which is need to focus more on that. The ever increasing demand for smart technologies, protocols, and smart grid systems [1, 2] has been coupled with the advancement of power electronics. Power Electronics is beginning to engage a critical role in multiple applications that cover switch-mode power supplies in computers and consumer electronics, uninterruptable power supplies, adjustable speed motor drives for energy conservation and factory automation, and many other systems for the industry interface[3]. Within systems of such almost invariably, the 60-Hz input voltage is at beginning rectified into DC voltage, which is subsequently adopted into the voltages and currents of the suitable magnitude, frequency, and phase in order to meet the load requirement[4].

The most popular and common three-phased interface includes a diode rectifier bridge as shown in Figure 2.1 where the rectifier is hooked up with a big filter capacitor at its output to supply a smooth DC. An interface that is traditional as such, suffers from two serious setbacks: firstly the current pulled from the utility is exceedingly distorted and, secondly the DC voltage is unregulated, which in the case, its average value varies depend on the magnitude of the utility voltage input and the output load[5] .

Generally the power electronic products with high power density, high efficiency, low current distortion and simple control scheme are strongly recommended for the industrial applications. Conventional diode bridge rectifiers or phase-controlled rectifiers have properties of simple structure and low THD. Meanwhile, the drawbacks of these circuits are uncontrolled DC bus voltage, high current harmonics in the AC mains and disturbance in the nearby systems [5-10].

* Corresponding author: Ali Saadon Al-Ogaili

Department of Electrical Engineering, Faculty of Engineering ,Universiti Putra Malaysia ,43400 Serdang,

Selangor, Malaysia

J. Electrical Systems “ Special issue AMPE2015 ”

Passive filters with diode bridge rectifier are adopted to increase the input power factor and decrease the current harmonics. However, the disadvantages of passive filters are uncontrolled DC-link voltage, large volume and heavy weight of passive elements, and series and parallel resonance with system impedance. To reduce the current harmonics, several circuit topologies of the AC-DC converters have been proposed in the past twenty years.

Figure 1. Three-phase diode bridge rectifier

These circuit configurations are based on the boost-buck-boost, half-bridge, and full bridge converters. One active switch is used in this rectifier to perform DC bus voltage regulation.

The sinusoidal line current with low current distortion is drawn from the AC source. The drawback of this topology is that only single switch is active in the rectifier[10, 11] [12].

The third harmonic current injection is an approach to minimize input current harmonics of three-phase rectifiers. The method is suitable for high power applications, and circuits of low complexity. In comparison with the multi-pulse rectifiers that dominate the applications area, smooth waveforms of the input currents are obtained. The method is a three-phase rectifier applying active current injection. To compensate for the drawbacks and to minimize the harmonic distortion of the input current, more than one technique are proposed; one of this technique is the circuit topology for a three-phase rectifier using a harmonics current injection method that will be discussed in this paper.

• Harmonic Measurement of the Fifth and the Seventh Order

Looking at a three-phase diode bridge rectifier as given in Figure 1 D 1 to D 6 are the components of the three-phase diode bridge rectifier. This rectifier’ s input current contains harmonic distortion currents of many orders but for this case of a three-phase bridge rectifier, the fifth and seventh orders are the main target[12, 13].

2. Methodology

2.1 Current Injection

The current injection network is described by two current points of supply in the circuit diagram of Figure 2. The use of the current injection device is to split the current provided from the current injection network into three balanced components, and to place them back to the supply lines.

129

International Conference on Advanced Mechanics, Power and Energy 2015 (AMPE2015), 5-6 December 2015, Kuala Lumpur, Malaysia

Figure 2: Flow of the third-harmonic currents

2.2 Principles of the Current Injection Method

The need for this method is to reduce the distortion level of the harmonics in input currents or if possible to eliminates it. Waveforms of different harmonics are rectified and modified by an active network so that these harmonics will be reduced. This modification is achieved by injecting equal-but-opposite compensating harmonic current into the line [14].

2.3

Choosing of the Parameters

2.3.1 Source

The source which is used in this project was a three-phase 240 V rms with the maximum of 10 A current supply capacities. This supply passes through auto transformer in order to control the value of input voltage. In the simulations, a variable sinusoidal voltage power supply has been used with the values which were mentioned earlier[15, 16].

2.3.2

The output Filter

The three inductors are connected in series with three-phase input lines as passive low pass filters with cutoff frequency of the first harmonic. The value of L is calculated by using the impedance equation. In the experimental circuit, the value of the fabricated L was obtained with tolerance of 3% in comparison with the calculated value. The circuit reduces the harmonic component of the switching frequency by an LC filter.

The LC filter, containing an inductor and a capacitor in parallel, is connected to the output side of the diode bridge. Phase shift of harmonic current and harmonic component of the switching frequency are the two factors that influence the input current in the LC filter design. The phase shift in the LC filter causes distortion, so the higher the phase shifting, the higher distortion. Therefore, THD can be reduced by increasing the impedance of the filter because the filter current is the major cause of phase shifting. The maximum current

130

J. Electrical Systems “ Special issue AMPE2015 ” which is passed through each IGBT is 10 A. To purchase suitable diodes that could be able to suffer even more current in an expected condition of experiment, 1.5 times more than this value was used.

•

Load

Indeed, there has been no calculation to choose the value of the load, but the value of the load that is used in the simulation and experiment has important effect on calculations of the other parts for circuit’ s voltage and current.

•

Switching Control Pulse

The two IGBTS are switched at the frequency of 250Hz and duty cycle of 50%. To produce this value, PIC microcontroller with manufacturing number of microchip

PIC16F876A-I/SP has been used.

2.4 control circuit

2.4.1 Design of Current Injection Network

The circuit that has been proposed contains two switch devices (IGBT Transistors) within the Current Injection Network. The use of the IGBT in this circuit is mainly for its high efficiency and swift switching, since it is designed to quickly turn on and off. While the input current for the three phase Diode Bridge rectifier has a fifth order harmonic within it, this leads to cause both high THD and a non-sinusoidal waveform in the input current. Thus it is required to reduce harmonic in the fifth order which leads to an improvement THD and a sinusoidal waveform in the input current. Within the Current Injection Network, two switches exist at its core. When the switches are programmed at 250Hz, it leads to reducing the THD and enhancing the sine wave of the input current.

2.4.2 Dual Circuit

The two switches are contained within the current injection network, work in different consistency. This means each switch turns ON and OFF but at opposite directions. For instance, Switch 1 or (S1) at the time it is ON, Switch 2 or (S2) must be switched OFF and vice versa. This is done to avoid short circuit. Accordingly, Figure 3 shows the form of dual circuit gate driver. The gate driver used at this dual circuit is IR2110, which is suitable for medium and high voltage applications in power system. The Pins 10 and 12 which are contained within the gate driver (IR2110) are connected to the PIC, while Pins 1 and Pin 7 of the gate driver (IR2110) are connected to the gates of the two switches.

131


Figure 3: The dual circuit of two IGBTS in the control circuit

2.4.3PIC of the control strategy

Microcontrollers can do anything that is programmed into their data memory and registers.

PIC is basically called programmable integrated circuits because it has a register data that can be written into, read, and or both. PIC microcontrollers are programmed to generate pulse for triggering switches in power electronics with adjustable period and pulse width.

The PIC that is used in the experimental work of this project is a PIC16F877A and is programmed using C programming language figure 4 shows the signal that control the two

IGBTs switches. It has internal memory; RAM and ROM, CPU and input/output (I/O) parts. All of these parts are embedded into a chip. The PIC has few KB of ROM, less than

256 bytes of RAM, 256 bytes of Electrically Erasable Programmable Read Only Memory

(EEPROM) and several analogue and digital (IO/ms)[16].

132

Figure 4. The signal of the injection current


2.4.4Synchronization Circuit

The circuit shown in Figure 5 explains the synchronization between the input current phase a and the current from two switches, where it consists of transformer, Zener Diode, three resistors fix, one variable resistor, one capacitor and 74121IC. The supply DC voltage +5v for PIC transistor is provided by the output from synchronization circuit. The need for synchronization is to align the phase of the injection current and the supply current. The phase of injection current generated cannot be assumed to be the same with that of the supplied current. Therefore, there is a need for synchronization of phase to allow zero crossing. This is the major contribution of this topology to the current injected method of reducing THD. As shown in the circuit, the transformer steps down the AC supply from

240 V to 12 V, and the 12 volts is used to power the synchronization circuit [17-20].

Figure 5: The dual circuit

3. Simulation and Experimental Results

The three phase bridge rectifier with injection harmonic current has been studied on using both simulation model and experiment prototype as figure 6 to demonstrate the validity of the proposed approach and the system achievement.

133


Figure 6: The simulation circuit of the proposed system

134

Figure 7: The input current for phase A experimental and simulation with injection

Z=240 Ω



Z=244 Ω


Z=270 Ω

135



Z=340 Ω

136

Figure 11: The input current for phase A experimental and simulation with injection without filter

Z=

270

Ω


Figure 12: The input current for phase A experimental and simulation with injection without filter

Z=

340

Ω

Figure 13: The input current for phase A experimental and simulation without injection with filter Z= 270

Ω

Figure 7 through Figure 13 show the input current for phase A , comparing both the simulation and experimental results with an injection harmonic current and

LC filter with different load impedances of Z= 240,244,270 and 340 Ω while load impedances of Z= 270

Ω

and

340 Ω

with an injection harmonic current but no

LC filter connected in the circuit as

137

International Conference on Advanced Mechanics, Power and Energy 2015 (AMPE2015), 5-6 December 2015, Kuala Lumpur, Malaysia in the proposed circuit. And lastly, Figure 4.45 also shows an input current for the phase A, which compares both simulation and experimental result where no injection harmonic current but only LC filter were connected in the proposed circuit. Consequently the output waveforms were the same with a slight variation in waveforms, but yet follow the pattern of sinusoidal shape.

As a summary, in these results of this work as a new method for reduction of harmonic of three phase bridge rectifier using harmonic current injection method has been demonstrated. These outcomes include the simulation and experimental results. The results are based on the problem statement and objectives of this thesis. Furthermore, the results are also based on suggested method of this thesis, which are reduction of harmonic of three phase bridge rectifier with injection, without injection, with filter and without filter, which are successfully illustrated. All of the results are explained by comparing between simulations and experiments.

4.

Conclusion

The objectives of this project were to design and construct a three-phase rectifier with harmonic injection current in order to obtain an input current of sinusoidal waveforms and achieve low input current THD. Hence, the prototype of the three-phase rectifier of the harmonic injection current is designed and fabricated. In order to develop the method to obtain sinusoidal waveforms for input current, new method of harmonic injection in current is suggested. As a result, low input current THD has been achieved.

Experimental and simulation results have been compared. As a result, satisfactory similarities have been found in both experiments and simulations. As a remarkable achievement, it has been proven that the suggested method is accurate. To design simple topology in three phase bridge rectifier with harmonic injection current and required, only two active switches of IGBT have been studied for power application. In this project the synchronization between the injection signals and the input signal was achieved.

Fifth, seventh and other orders of harmonics have been eliminated and THD value has been reduced. On the other hand, the sinusoidal waveforms for the input currents have been obtained according to simulation result from MATLAB software as well as measurement results. The fifth order harmonic is reduced from 22.8% to 0.52% .This reduction’ s effects on subsequent harmonics have been shown in the experiments and simulations. Also the

THD value is reduced from 32% to 5.5%.

Acknowledgment

The authors grateful acknowledge the financial support for this study by the Universiti

Putra Malaysia.

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