speed control of pmdc motor using interleaved buck converter · 2015-12-23 · speed control of...

International Conf. on Electrical, Electronics, Mechanical & Computer Engineering, 06th July-2014, Cochin, India, ISBN: 978-93-84209-34-6

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SPEED CONTROL OF PMDC MOTOR USING INTERLEAVED BUCK CONVERTER

1LIJI.I.V, 2RABIYA RASHEED

1,2Student, Assistant Professor

Abstract- This paper proposes a new interleaved buck converter (IBC) having low switching losses and improved step-down conversion ratio, which is suitable for the speed control of PMDC motor. Armature controlled methods are used for the speed control. The armature voltage across the dc motor depends on the converters output voltage which further depends on the duty cycle. Since the speed of the dc motor is directly proportional to the armature voltage, speed can be controlled by varying duty cycle. Also by varying the motor load torque, the armature current developed in the motor and hence its speed can be adjusted. The controller used for the speed control is PI controller. The proposed converter is similar to the conventional IBC, but two active switches are connected in series and a coupling capacitor is employed in the power path. The proposed IBC the voltage stress across all the active switches is half of the input voltage before turn-on or after turn-off when the operating duty is below 50% and there by the capacitive discharging and switching losses can be reduced considerably. There by the proposed converter to have higher efficiency and operate with higher switching frequency. By using the interleaved topology the output ripple can be reduced effectively. The features, operation principles, and relevant analysis results of the proposed IBC are presented in this paper.

Index Terms- Buck, Interleaved, Low Switching Loss, PMDC Motor.

I. INTRODUCTION BUCK-TYPE dc–dc converters are widely employed in the power electronics industry. Buck converters are most widely used dc–dc converters in the world because no other topology is as simple. Their applications range from low-power regulators to very high power step-down converters, which are characterized by a low number of components, low control complexity, and no insulation. To achieve a high step-down voltage ratio and high current density, but without needs of isolation; an interleaved buck converter (IBC) is usually the first choice. The advantages of the interleaving technique include the reduced output current ripple and the increased output current ripple frequency. Therefore, to obtain these advantages, the interleaving technique is employed in the continuous conduction mode (CCM) buck-based current source. The interleaved structure is used in many large current and high-power applications due to its advantages of power distribution, current ripple cancellation, fast transient response, and passive components size reduction the reduced output current ripple and the increased output current ripple frequency. DC motors are widely used in systems with high control requirements. Generally, to control the speed, adjustment of the armature voltage of the motor is used ; while, applying PWM signals with respect to the motor input voltage is one of the methods most

employed to drive a DC motor. However, the hard switching strategy causes an unsatisfactory dynamic behavior, producing abrupt variations in the voltage and current of the motor. These problems can be resolved by using DC-DC power converters, which allow the smooth start of a DC motor by applying the required voltage in accordance with controlling the speed. In particular, the DC-DC Buck power converter has two energy storing elements (an inductor and a capacitor) that generate smooth DC output voltages and currents with a small current ripple, reducing the noisy shape caused by the hard switching of the PWM. By using an interleaved buck converter reduced output current ripple and there by effective speed control is achieved. II. LITERATURE SURVEY Buck converters are widely used as step-down dc-dc converters. To reduce size and weight of the converters, operate them at high switching frequencies. However, as the switching frequencies increase, switching loss, noise, and stress associated with turn-on and turn-off transitions also increase. These drawbacks reduce power conversion efficiency and powering capability, which in turn seriously deteriorate in system performance. To alleviate the problems described above, several kinds of soft-switching converters, such as quasi-resonant converters (QRCs)][2], and multi resonant converters (MRCs)[3] have been used as step-down converters .These converters achieve soft

Speed Control of PMDC Motor Using Interleaved Buck Converter


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switching without an auxiliary switch.The major drawback of QRC is the capacitive turn on switching losses and the switching frequency range is wide, which makes it difficult to optimize the magnetic components and MRC is the increased circulating energy caused by a continues resonance of the multi element resonant circuit, increased conduction losses and increased frequency dependent losses.. Most recent development in high frequency converters is those with a soft-switching PWM converters. They can relieve the drawbacks described previously. The converters are usually classified into two groups: passive soft-switching converters and active soft-switching converters. A converter with passive soft-switching feature is more attractive to low power applications. In [4] a single passive soft-switching converter is introduced. the buck converter is equipped with a lossless turn-off snubber to reduce turn-off loss and is operated at boundary of discontinuous conduction mode and continuous conduction mode to reduce turn-on loss But the disadvantage of this paper is high ripple current and low power level. In [6], an IBC with a single-capacitor turnoff snubber is introduced. Its advantages are that the switching loss associated with turn-off transition can be reduced, and single coupled inductor implements the converter as two output inductors. However, since it operates at discontinuous conduction mode , all elements suffer from high-current stress, resulting in high conduction and core losses. In addition, the voltages across all semiconductor devices are still the input voltage. In [7], an IBC with active-clamp circuits is introduced. In the converter, all active switches are turned ON with zero-voltage switching .In addition, a high step-down conversion ratio can be obtained and the voltage stress across the freewheeling diodes can be reduced. However, in order to obtain the mentioned advantages, it requires additional passive elements and active switches, which increases the cost significantly at low or middle levels of power applications. In [8], an IBC with zero-current transition is introduced to reduce diode reverse recovery losses. The ZCT is implemented by only adding an inductor into the conventional IBC. However, in spite of these advantages, the converter suffers from high current stress, because the output current flows through each module in a complementary way. To overcome these drawbacks propose a new technique. In the proposed technique, a new IBC, which is suitable for the applications where the input voltage is high and the operating duty is below 50 %, is proposed[1]. III. PROPOSED TOPOLOGY In this paper, a new IBC, which is suitable for the speed control of PMDC motor is proposed. The two active switches are driven with the phase shift angle of

180 and the output voltage is regulated by adjusting the duty cycle at a fixed switching frequency. The proposed Converter also operates at CCM so the current stress is low. During the steady state, the voltage stress across all active switches before turn-on or after turn-off is half of the input voltage. There by the capacitive discharging and switching losses can be reduced considerably. The voltage stress of the freewheeling diodes is also lower than that of the conventional IBC [10] so that the reverse-recovery and conduction losses on the freewheeling diodes can be improved by employing schottky diodes. The conversion ratio and output current ripple are lower than those of the conventional IBC. Here the load is used as a PMDC motor. By using this interleaved buck converter, which have an advantage of reducing the ripple current at the output, speed control of the motor is very effective. Figure 1 shows the circuit configuration of the proposed IBC. The load used here is a PMDC motor. Figure3 show the key operating waveforms of the proposed IBC in the steady state. Referring to the figure, it can be seen that switches Q1 and Q2 are driven with the phase shift angle of 180. Each switching period is divided into four modes, whose operating circuits are shows in figure 2.

Fig1: Circuit configuration of the proposed IBC

Mode 1 [ t0-t1 ]: Mode 1 begins when Q1 is turned on at t0. Then, the current of L1 , iL1 (t), flows through Q1 , CB , and L1 and the voltage of the coupling capacitor VCB is charged. The current of L2 , iL2 (t), freewheels through D2 . During this mode, the voltage across L1 , VL1(t), is the difference of the input voltage VS , the voltage of the coupling capacitor VCB, and the output voltage V0 , and its level is positive. Hence, iL1(t) increases linearly from the initial value. The voltage across L2 , VL2(t), is the negative output voltage, and hence, iL2(t) decreases linearly from the initial value. The voltage across Q2, VQ2(t), becomes the input voltage and the voltage across D1 , VD1(t), is equal to the difference of VS and VCB. The voltages and currents can be expressed as follows:

01 )( VVVtV CBSL (1)

02 )( VtVL (2)

)()()( 0100

1 tittL

VVVti LCBS

L



7

)()(1 titi CBQ (3)

)()()()( 20200

2 titittLVti DLL

(4)

SQ VV 2 (5)

CBSD VVV 1 (6)

)(2

)( 00

0 ttCItVV

BCBCB (7)

Mode 2 [t1 - t2 ]: Mode 2 begins when Q1 is turned OFF at t1. Then, iL1(t) and iL2(t) freewheel through D1 and D2, respectively. Both VL1(t) and VL2(t) become the negative V0 , and hence, iL1(t) and iL2(t) decrease linearly. During this mode, the voltage across Q1, VQ1(t), is equal to the difference of VS and VCB and VQ2(t) becomes VCB. The voltages and currents can be expressed as follows:

021 )()( VtVtV LL (8)

)()()()( 110

111 tittL

Vtiti DLL (9)

)()()()( 210

122 tittL

Vtiti DLL (10)

CBSQ VVtV )(1 (11)

CBQ VtV )(2 (12)

Mode 3 [t2 - t3 ]: Mode 3 begins when Q2 is turned ON at t2. At the same time, D2 is turned OFF. Then, iL1(t) freewheels through D1 and iL2(t) flows through D1 , CB , Q2 , and L2 . Thus,VCB is discharged. During this mode, VL2(t) is equal to the difference of VCB and V0 and its level is positive. Hence, iL2(t) increases linearly. VL1(t) is the negative V0, and hence, iL1(t) decreases linearly. The voltages and currents can be expressed as follows:

01 )( VtVL (13)

01 )( VVtV CBL (14)

)()()( 2120

1 tittLVti LL

(15)

)()()( 2220

1 tittL

VVti LCB

L

)()(2 titi CBQ (16)

)()()( 211 tititi LLD (17)

CBSQ VVV 1 (18)

CBQ VV 1 (19)

)(2

)( 00

0 ttCItVV

BCBCB (20)

Mode 4 [t3 - t4]: Mode 4 begins when Q2 is turned OFF at t3, and its operation is the same with that of mode 2. The steady-state operation of the proposed IBC operating with the duty cycle of D < 0.5 has been described. From the operation principles, it is known that the voltage stress of all Semiconductor devices except Q2 is not the input voltage, but is determined by the voltage of coupling capacitor VCB. The maximum voltage of Q2 is the input voltage, but the voltage before turn-on or after turn-off is equal to VCB. As these results, the capacitive discharging and switching losses on Q1 and Q2 can be reduced considerably. In addition, since diodes with good characteristics such as schottky can be used for D1 and D2, the reverse-recovery and conduction losses can be also improved.

Figure 2: Operating modes when D < 0.5

Figure 3: Key operating waveforms



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IV. ANALYSIS RESULT

A. DC Converssion Ratio: The dc conversion ratio of the proposed IBC can be derived using the principle of inductor volt- second-balance(VSB). The following equations can be obtained from the VSB of L1 and L2 , respectively.

SSCBS TDVDTVVV )1()( 00 (21)

SSCB TDVDTVV )1()( 00 (22) The voltage of the coupling capacitor can be obtained by substituting (22) into (21) and is equal to half of the input voltage as follows:

2S

CBVV (23)

Then, the dc conversion ratio M can be obtained from (21) and (23)

2D

VVM

S

O (24)

B. Inductor Current Ripple:

Figure 4: voltage and current waveform of the output inductor

Figure 4 shows the voltage and current waveforms of the output inductor of the buck converter. From the figure, the current ripple can be expressed as follows:

Skk

ripple TDK

Vi 1 (25)

C. Coupling Capacitor

The ripple voltage of the coupling capacitor can be obtained from figure 3 as follows:

1

02

)(1 t

t SB

OCB

BCB fC

DIdttiC

V (26)

where

)(5.022

)( 000 tt

LVViIti Sripple

CB

0100 ),(

5.0 tDTtttL

VVi SS

ripple

D. PMDC motor As the magnetic field strength of a permanent magnet is fixed it cannot be controlled externally, field control of this type of dc motor cannot be possible. Thus permanent magnet dc motor is used where there is no need of speed control of motor by means of controlling its field. Armature control method is used for the

modeling of PMDC motor. Transfer function of motor is given by

SKKBRSBLJRSJLK

sEs

Tbaaaa

T

a )()()()()(

23

(27)

figure 5 Block diagram of the armature controlled DC motor V. SIMULATION RESULTS Software used is MATLAB/SIMULINK.Input voltage of 100-200 V is applied and constant output voltage of 24 V is obtained with a duty ratio less than 0.5.Load is used as a PMDC motor. Speed control of PMDC motor is done by using a PI controller. simulink model of proposed converter shown in figure 6.Load torque of 20 N-m and power of 210 w PMDC motor is used. The parameters are Ra=0.5Ω ,La=0.01H ,KT=1.8N.m/A, J=0.02215kgm2, Bm=0.00295.

Figure 6: Simulink model.

In figureg7 shows the gate pulses. Here we can see that the gate pulse 1 and 2 having 1800 phase shift. Voltage across inductor 1 and 2 are also shown in this figure. current through the inductors and voltage and current through coupling capacitor shon in figure 8.current and voltages in diodes are shown in figure 9.current and voltages in Q1 and Q2 shown in figure 10.half of the supply voltages are in Q1. Output voltage 24 v with an input of 200v is in figure11.Input current and output current shown in figure 12.in this fig. we can see that ripple current is reduced due to interleaved technology. Torque of PMDC motor is in figure 13 and speed in figure14.



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. Figure 7: (a) gate pulse of mosfet1 (b) gate pulse of mosfet2 (c)

voltage across L1 (d) voltage across L2.

Figure8: (a) Current owing through L1 (b)Current flowing through L2 (c) Current owing through CB (d) voltage CB.

Figure 9: (a) Current owing through iD1 (b) voltage across iD1

(c) Current owing through iD2 (d) voltage across iD2.

Figure 10: (a) Current owing through Q1 (b) Current flowing

through Q2 (c) voltage across Q1 (d) voltage across Q2.

Figure 11: output voltage.

Figure 12: (a) Current flowing through Iin (b) Current flowing

through Ia .

Figure 13: output torque

Figur14: speed.

CONCLUSION Speed control of PMDC motor is done by using proposed interleaved converter. Interleaved means there is an 180 degree phase shift between two switches. The main advantage of the proposed IBC is that since the voltage stress across active switches is half of the input voltage before turn-on or after turn-off when the operating duty is below 50%, the capacitive discharging and switching losses can be reduced considerably. These are verified with the experimental results. Moreover, it is confirmed that the proposed IBC has a higher step-down conversion ratio and a smaller inductor current ripple. Therefore the speed control is very effective. Here armature control methods are used. And the controller used for speed control is PI controller. Effective speed control is done by using the proposed converter since low ripple current at the output. ACKNOWLEDGMENT Initially, I would like to thank, the God Almighty for showing his blessings on me for successful completion of this work. Also I would like to thanks teachers friends and parents. ABBREVIATIONS IBC - interleaved buck converter MRC - multi resonant converter PMDC - permanent magnet dc motor PWM - pulse width modulation QRC - quasi resonant converter REFERENCES

[1] Il-OunLee,Shin-Young Cho,andGun- WooMoon, "Interleaved Buck Converter Having Low Switching Losses and Improved Step-Down Conversion Ratio"IEEE transactions on power electronics, vol. 27, no. 8, august 2012



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[2] Zheng, T., Chen, D-Y.,and Lee, F-C. (1986) "Variations of Qusai-resonant dc-dc converter topologies" IEEE power electronics specialists conference record,pp.381-392.

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speed control of pmdc motor using interleaved buck converter · 2015-12-23 · speed control of...

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