 Open Access
 Authors : Maharo Rakotoarimanana, Harlin Andriatsihoarana, Fanjanirina Razafison, Georgette Ramanantsizehena
 Paper ID : IJERTV12IS120019
 Volume & Issue : Volume 12, Issue 12 (December 2023)
 Published (First Online): 13122023
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
A New Model of ThreePhase Dimmer for DeltaConnected Inductive Loads
Maharo RAKOTOARIMANANA
School of Industrial Engineering Higher Institute of Technology of Antananarivo
Antananarivo, Madagascar
Fanjanirina RAZAFISON
School of Industrial Engineering Higher Institute of Technology of Antananarivo
Antananarivo, Madagascar
Harlin ANDRIATSIHOARANA
Higher Polytechnic School of Antananarivo, University of Antananarivo Antananarivo, Madagascar
Georgette RAMANANTSIZEHENA Physics and applications doctoral school, University
of Antananarivo Antananarivo, Madagascar
Abstract – This work consists of the design and simulation of a new model of ACAC electronic converter or dimmer, in terms of power arrangement and control strategy, for the variablepower supply of a threephase deltamounted inductive load. The power circuit uses two bidirectional electronic switches, one in series to supply the load, and the other in parallel to freewheel the load current. The two switches are complementary controlled. Each switch consists of two transistors and two power diodes. The "Pulse Width Modulation with fixed frequency and variable duty cycle" control strategy is adopted to chop the supply voltage and vary the power supplied to the load. Simulation in Matlab Simulink enables the new model dimmer to be implemented and its performance to be compared with that of the conventional six thyristor dimmer. The simulation shows that the new dimmer design is efficient and outperforms the ancient model by a wide margin, ensuring : (i) better energy efficiency, (ii) increased load life and stability, with lower voltage and current Harmonic Distortion Rates, and (iii) reduced disturbance to the supply network. The development and implementation of the new model dimmer will enable more effective and efficient variable power supply and regulation of starmounted industrial three phase loads such as furnaces and electric motors..
Keyword: threephase delta dimmer, simulation, harmonics, power factor, efficiency.

INTRODUCTION
Control and power electronics enable industries to (i) regulate actuator output quantities by varying the power supply, and (ii) control the form of electrical energy. Dimmers enable the electrical power supplied to an AC load to be varied from a sinusoidal voltage source, and its behavior to be controlled [1], [2] (speed of an induction motor, thermal power of a heating resistor, etc.). These loads are the main electrical actuators used in industry, and are connected in star or delta configuration. Conventional thyristor dimmers are widely used for their variation, but have the disadvantage of :
(a) disturbing the supply network with input current harmonics and low power factors (b) affecting the durability and stability of equipment supplied with output voltage and current harmonics [3][5].
The aim of this work is to improve the performance of dimmers for deltamounted inductive loads [6]. The methodology adopted is to design a new threephase dimmer model for star loads, in terms of control and power assembly, and to compare its performance with that of conventional dimmers, through simulation in Matlab Simulink.
The control strategy consists of fixedfrequency, variable duty cycle chopping, or Pulse Width Modulation[2], [7], of the supply voltage. The power circuit uses two bidirectional electronic switches, with transistors, for each load branch, one connected in series for the power supply and the other in parallel to freewheel the inductor currents [7][9].
The result is a new model of threephase dimmer, for deltamounted loads, with high performance in terms of efficiency, Total Harmonic Distortion (THD) and power factor.

MATERIALS AND METHODS

Classic dimmer

Singlephase circuit
Two headtotail thyristors are used as bidirectional switches. Current pulses from the gates close the switch, while current cancellation opens it. To vary the output voltage, the current is allowed to flow for only part of the halfperiod for each halfwave. We then wait for an Alpha angle of less than 180Â° before pulsing the thyristor gates to command them. Current cancellation after each halfperiod naturally reopens the thyristor switch.
Fig. 1. Singlephase 2 thyristor dimmer power circuit, output voltage and gate pulse curves for alpha = 45Â°, R load
The alpha delay alters the sinusoidal shape of the supply voltage, causing voltage and current harmonics. It also increases the phase shift between mains voltage and load current, thus reducing the power factor value.

Classic threephase deltamounted load connection The power circuit uses one bidirectional electronic switches, with thyristors, for each load branch.
Fig. 2. Classic threephase dimmer power circuit for delta loads


New model dimmer

Newmodel singlephase dimmer
The new pulsewidthmodulated dimmer chops the supply voltage and therefore only supplies the load with power at portions of each halfwave [1], [2], [7], [10], [11]. Two bidirectional switches are used:
one in series with the load, to connect it to the source;
the other is connected in parallel to allow the current to pass in freewheeling mode.
Each switch consists of two transistors and two diodes.
These switches, controlled in complementary, are closed and opened at regular intervals, but with varying durations. This is the variable duty cycle pulse width modulation strategy. The control frequency must be carefully chosen: a too high value will ensure a quasisinusoidal output voltage, but will impact on the efficiency due to switching loss of the power transistors [12], [13].
Fig. 3. Power circuit and control strategy for new singlephase dimmer model
During positive halfwave of the supply voltage, from [0; T/2], with T the period, T1D1 and T1pD1p conduct successively.
During negative halfwave of the supply voltage, from [T/2;T], T2D2 and T2pD2p conduct successively.
If T1D1 or T2D2 are conducting, the dimmer is said to be in the supply phase. If T1pD1p or T2pD2p conduct, the dimmer is said to be in freewheel phase.
The pulsewidth modulation control strategy, with fixed period and variable Alpha duty cycle, is adopted to supply the load only at portions of each halfwave.

Newmodel threephase dimmer for deltamounted loads
As with the classic dimmer, the newstyle dimmer for three phase delta loads involves the use of three singlephase circuits. The circuit therefore comprises six bidirectional switches (twelve transistors and twelve power diodes).
Fig. 4. Power circuits of a new model dimmer for star load.


Simulation in Matlab Simulink
The Matlab Simulink software is used to simulate the operation of the converters in order to highlight their performance and make comparisons.
The dimmers will be powered by a threephase sinusoidal voltage generator V_in = 220V RMS between phase and neutral, 380V between phases, 50Hz, and feeding a RL type load (cosfi power factor = 0.8 at 50Hz), mounted in delta configuration.
Load: RL series R=17.6 R= 42.017mH IGBTs will be used as transistors:

Internal resistance 0.001

Voltage drop during conduction 0.6V For diodes

Internal resistance 0.0001

Voltage drop during conduction of 0.6V
Voltage, current and power measurements will be made to analyze the input and output behavior of each circuit. These measurements will be ade for RMS values of the fundamental output voltage V_out equal to :

0.25 x V_in RMS = 55V

0.5 x V_in RMS = 110V
– 0.75 x V_in RMS = 165V


Quantities to be measured
For three values of RMS output voltage, the quantities to be measured are :

Input and output RMS voltage and current

Input and output active and reactive power

Active power efficiency

Harmonic Distortion Rate or THD of output voltage, output current and input current.


RESULTS

Variation of the RMS value of the fundamental output voltage
For conventional dimmers, the variation is obtained by acting on the value of the Alpha firing angle; for newmodel dimmers, by acting on the value of the Alpha duty cycle.
Fig. 5. Variation of fundamental output voltage
The output voltage varies linearly with Alpha for the new model dimmer.

Output signal patterns
The three output voltages between phases, and currents per phase, are read on an oscilloscope and displayed over 1 period.
TABLE I. DIMMER OUTPUT VOLTAGE AND CURRENT CURVES
Ratio V_out H1 RMS / Vin RMS
Threephase dimmer for Ymounted load models
Classical with thyristors
Newmodel
0.25
Alpha firing angle = 6.8ms
Alpha duty cycle = 0.255
0.50
Alpha firing angle = 5.57 ms
Alpha duty cycle = 0.5
0.75
Alpha firing angle = 4.06 ms
Alpha duty cycle = 0.745
Fig. 6. Dimmer output voltage and current curves in Matlab Simulink
For the classic dimmer, the thyristors start to conduct after the control pulses, and open after the current is canceled. For the new model dimmer, the supply voltage is effectively chopped.

Harmonic Distortion Rate THD

THD of output voltage
For the three values of the fundamental output voltage between phase and neutral, the THD values are shown in Fig. 7.
Fig. 7. THD of output voltage
The THD of the output phasetoneutral voltage varies from 49.86% to 139.10% for the classic dimmer, and from 2.78% to 3.44% for the new model dimmer.

THD of input and output current
For the three values of the fundamental output voltage between phase and neutral, the THD values are shown in Fig. 8.
Fig. 8. input and output phasecurrent THD
The THD of the output current from one phase to one over varies from 8.38% to 17.90% for the classic dimmer and from 0.50% to 0.63% for the new model dimmer.
The THD of the current per input phase varies from 8.38% to 17.90% for the classic dimmer and from 0.26% to 0.28% for the new model dimmer.


Power factors
For the three values of the fundamental output voltage between phase and neutral, the values of the input and output power factors are shown in Fig. 9.
Fig. 9. Input and output power factors
The output power factor varies from 0.3927 to 0.3928 for the classic dimmer and from 0.7943 to 0.8065 for the new model dimmer.
Input power factor ranges from 0.2839 to 0.6301 for the classic dimmer and from 0.804 to 0.8116 for the new model dimmer.

Active power efficiency
For the three values of the fundamental output voltage between phase and neutral, the values of the input and output power factors are shown in Fig. 10.
Fig. 10. Active power efficiency
Active power efficiency ranges from 59.95% to 81.03% for the conventional dimmer, and from 97.21% to 99.23% for newmodel one.


DISCUSSIONS

The voltage and current output curves are consistent with theory. The output voltages and currents of the new model dimmer have quasisinusoidal curves.

The variation in output voltage, supplied to the load, is obtained for both assemblies, and is quasilinear for the new model dimmer, for alpha from 0 to 100%. This makes the converter ideal for industrial control applications.

THD values for output voltage and output currents are much lower for the new model dimmer than for the conventional one. This ensures longer life and greater energy efficiency for loads such as electric motors.

Input current THD values are very low for the new model dimmer compared to the classic one. The new model dimmer will therefore pollute the electrical network only slightly.

The high value of the power factor ensures high active power while reducing disturbance to the distribution network (also reducing the cost of reactive power compensation).

For all these reasons, the active power efficiency of the new model dimmer is much better than that of the conventional dimmer.

Generation of the pulsewidth modulated (PWM) control signals for the new model dimmer is simpler and less costly than for the conventional dimmer. Power assembly costs are, however, higher for the newmodel dimmer.


CONCLUSION
In summary, a new model of pulsewidth modulation dimmer for threephase deltamounted loads is proposed in this work. Simulation in Matlab Simulink has enabled to compare the performance of this dimmer with that of a conventional dimmer for supplying a threephase, balanced, starconnected RL load. The new dimmer model is efficient and outperforms the conventional one in terms of energy efficiency, input and output harmonic distortion rate (voltage and current), power factor and RMS voltage variation. In addition, the control circuit is easier to implement, especially for control applications.
However, the cost of the power assembly is higher. In practice, the dimmer can be realized and used to supply variable power to industrial inductive loads. In the long term, the realization and largescale use of this dimmer will contribute to the development of industrial automation and thus to the achievement of the ninth and twelfth Sustainable Development Goals, namely industry, innovation and infrastructure, and responsible consumption and production.

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