 Open Access
 Total Downloads : 552
 Authors : Pratibha Thakur, Sanjeev Gupta
 Paper ID : IJERTV3IS10836
 Volume & Issue : Volume 03, Issue 01 (January 2014)
 Published (First Online): 27012014
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Simulation of SoftSwitched ThreePhase Inverter for RL and Induction Motor Load
Pratibha Thakur
PG Scholar
Department of Electrical Engineering Samrat Ashok Technological Institute Vidisha, (M.P) India
Sanjeev Gupta
Associate Professor Department of Electrical Engineering Samrat Ashok Technological Institute
Vidisha, (M.P) India
Abstract
In this paper a new QuasiResonant topology is proposed for softswitching of all three phase inverter switches for both positive and negative DC link current. This softswitched threephase inverter is proposed for a frequency of 400 Hz. The topology consists of four switches, two resonant inductors, and a capacitor. It will provide zero voltage switching condition for obtaining soft switching in all inverter switches when the switching frequency is exceeding the limit. The softswitching operation of inverter is explained in terms of modes for both positive and negative DC link current. A simulation model of softswitched threephase inverter for RL and induction motor load is developed using MATLAB software.
Keywords: MATLAB, ZVS, SoftSwitching, Three phase, Inverter, MOSFET

Introduction
Inverter is a device which convert DC power into AC power at desired output voltage and frequency by using power electronic devices. When the power switches of conventional pulse width modulated (PWM) inverter operate in switch mode so that due to hard switching during turn on and turn off process, the power electronic device has to withstand high current and voltage simultaneously resulting high stress and switching power losses, These switching losses is proportional to switching frequency of PWM inverter, thus limiting the switching frequency of conventional PWM inverter. When switching power losses are increases the efficiency of inverter is reduce and also large amount of heat produce inside the inverter, which forces to use larger heat sink for industrial personnel which causes volume and weight
of the system is increased and also system suffer from EMI.
Today softswitching technique is very important in modern technology. In this technique zero voltage and zero current switching were used which improved the performance as compared to hardswitched PWM Inverter [1]. Soft switching technique developed from load resonant to quasi resonant reported in [25]. In quasiresonant technique resonant network is activated during resonant interval to enable softswitching [5]. Quasi resonant DC link for voltage source inverter have been reported in [510].
A two switch resonant link inverter is reported for operates with unity power factor load [5]. A two switch quasiresonant topology having displacement factor equal to 0.88 legging can be handle passive load [7]. A resonant snubber based topology in [8] is proposed for active and passive load. The modify topology of quasiresonant technique [9], this modify topology has a limitation which restrict high power factor load operation. A current controlled softswitching inverter which provides good sinusoidal waveform of current for induction machine in [10].
All above reported topology of the quasi resonant link inverter have some limitation so that in this paper presented a new versatile quasiresonant topology which provide softswitching of all three phase inverter switches for both positive DC link current and negative DC link current and also overcome the limitation of the above discussed topologies. This topology can handle low as well as high power factor active and passive load. The complete quasiresonant softswitched three phase inverter for RL and Induction motor load is simulated using a MATLAB simulator. Typical simulation result of RL load and Induction motor load is presented in this paper.

Proposed Topology
The proposed quasiresonant topology for three phase inverter of 400 Hz or 50 Hz is shown in Fig.1 which provides soft switching at the high range switching frequency. The resonant tank as shown in Fig.1 consist of main switch (SWM), auxiliary switch (SWA), two shunt switch ((SW1SH) and (SW2SH)), two resonant inductor (Lr and LSH) and resonant capacitor Cr. So this resonant network is activated during resonant interval to enable softswitching transition. This softswitching transition is implemented by using zerovoltage transition. The circulating energy associated with softswitching transition due to resonance is quite small. The resonant components which are used in this topology involved with load current only during the resonant interval and out of operation during nonresonant interval. The DC link voltage is always clamped to the source voltage in this topology. Since the resonant component are involved only during a small interval of switching cycle. The size and VA rating of these resonant components become quite small. This topology provide softswitching operation when the link current is positive it means DC link current flow from resonant tank to inverter and also provide soft switching operation when the DC link current is negative it means DC link current flow from inverter to resonant tank. In this topology the DC link current is denoted by lLink. In a switching cycle this DC link current is assumed to be ripple free.
Figure 1. Proposed QuasiResonant soft switched three phase inverter

Operating principal
Paper proposed quasiresonant topology which provide softswitching of all three phase inverter switches and also provide softswitching operation in independent direction of DC link current
so that there are two operation one in which DC link current is positive (i.e. resonant tank to inverter) and other operation where DC link current is negative (i.e. inverter to resonant tank).
Figure 2. Initial condition under positive DC link current
Figure 3. Switching waveform under positive DC link current

Case I: The DC Link Current is Positive
The DC link current is positive it means that link current flow from resonant tank to inverter and load. Fig.2 shows the initial condition under positive link current at this condition resonant capacitor clamped to source voltage and only main switch was conduct. For obtaining softswitching of threephase inverter switches the circuit goes through various modes of operation, shows in Fig. 3 various modes of operation switching waveform.
MODE I (tot1)
This mode is started when the gate signal to main switch SWM is withdrawal at to. During small interval of this mode resonant capacitor discharges to zero, because of zerovoltage diode which is anti parallel across the inverter switches get forward biased. At the instant of ZVS, switching status of inverter is changed. End of this mode at t1 gate pulse to auxiliary switch is released. The circuit topology of this mode is shown in Fig. 4(a).
MODE II (t1 – t2)
At starting of this mode auxiliary switch is turnon. Current increases linearly from zero when flowing through the resonant inductor Lr, while the current which is flowing through diode in the inverter decreasing. At the end of this mode resonant inductor current is equal to link current and also the current becomes zero which is flowing through the anti parallel diodes of inverter switches. The circuit topology of this mode is shown in Fig. 4(b).
MODE III (t2 – t3)
This mode starts at t2 with charging capacitor Cr because resonance of Lr and Cr and the. Voltage across the DC link / resonant capacitor Cr gradually increases from zero to source voltage VDC
.The resonant inductor current is equal to the sum of the link current and charging current of capacitor Cr. Due to resonance of Lr and Cr link voltage is further increases causes diode Dp to be forwardbiased. End of this mode at t3 main switch is turned on and auxiliary switch is turned off. The circuit topology of this mode is shown in Fig. 4(c).
MODE IV (t3 – t4)
This mode starts at t3 with turned on with main switch and turned off with auxiliary switch. When current in the resonant inductor grater then the DC link current, the excess current which is more than the link current is flowing through the diode Dp. At the end of this mode at t4current in the resonant inductor is equal to load current. The circuit topology of this mode is shown in fig. 4(d).
MODE V (t4 – t5)
This mode starts at t4 with turned off of diode Dp and main switch SWM at the same time stats conducting. Now current in the Link is a some of the main switch current and current in the resonant inductor Lr. End of this mode at t5 main switch SWM conducts total link current and energy which is stored in resonant inductor is recovered. The circuit topology of this mode is shown in Fig. 4(e) which is changes in to initial state and same mode is repeated.

MODE I

MODE II

MODE III

MODE IV

MODE V

Figure 4. Modes under positive DC link current
(a) Mode I (b) Mode II (c) Mode III (d) Mode IV
(e) Mode V
3.1 Case II: The DC Link Current is Negative
When the DC link current is negative under these condition link current is flowing from inverter to resonant tank (i.e. negative). For negative DC link current during softswitching of inverter switches circuit goes through various modes of operation. The switching waveform of gate pulse to shunt switches, resonant capacitor voltage and shunt inductor current are shown in the Fig. 5. The circuit topology of initial condition under negative link current is shown in fig

Initially due to conduction of diode Dp DC link voltage is clamped to source voltage and all the switching devices are off state in the resonant tank.
Figure 5. Switching waveform under negative DC link current
Figure 6. Initial condition under negative DC link current
Now explain each mode which shows how switching status of inverter devices is changed when DC link current is negative.
MODE I (t0 – t1)
This mode starts at t0 with release of gate pulse to shunt switches ( SW1SH , SW2SH ). In this mode dclink voltage is clamped to the source voltage. Shunt inductor current iLsh linearly starts increasing from zero. In this mode DC Link is the sum of current in shunt inductor iLsh and current in diode Dp. At the end of this mode shunt inductor current equal to load current and diode Dp turnoff. The circuit topology of this mode is shown in Fig. 7(a).
MODE II (t1 – t2)
This mode starts at t1 with turn off of diode Dp and discharging of resonant capacitor Cr. current in the shunt inductor is sum of the discharging capacitor current and dclink current. At the end of this mode t2 the resonant capacitor Cr discharges to zero voltage. The circuit topology of this mode is shown in Fig. 7(b).
MODE III (t2 – t3)
This mode starts at t2 with discharging of resonant capacitor to zero voltage, at this instant switching status of inverter devices is changed under ZVS and diode D1SH get forwardbiased through SWISH because of energy in the shunt inductor Lsh. The current which is flowing through diode D1SH is the difference between dc link current and shunt

MODE I

MODE II
inductor current. Shunt inductor current iLsh is conducted by the switch SW2SH. End of this mode at t3 gate pulse from shunt switch is released SW1SH and SW2SH is released. The circuit topology of this mode is shown in Fig. 7(c).
MODE IV (t3 – t4)
This mode starts at t3 with withdrawal of gate pulse from the shunt switches SW1SH , SW2SH. Shunt inductor energy recovered to source through diode D1SH and D2SH so that conduction of diode D1SH and D2SH.The shunt inductor current decay to zero simultaneously resonant capacitor charged with dc link current. End of the mode at t4 resonant capacitor voltage equal to source voltage. The circuit topology of this mode is shown in Fig. 7(d). Diode Dp conduct full DC link current when becomes forward biased.

MODE III

MODE IV

Figure 7. Modes under negative dc link current (a) Mode I (b) Mode II (c) Mode III (d) Mode IV

Simulation Result
The Proposed softswitched three phase inverter has been simulated for RL and induction motor load using MATLAB. Fundamental frequency of 400 Hz, switching frequency of link is 40 KHz and modulation index of 0.9 are used. In QuasiResonant topology resonant parameters of small size and weight are used Lr = 1ÂµH, Lsh = 0.5ÂµH, Cr = 50nF. The source voltage is 150 V DC. Due to high frequency and low power operating capability MOSFET is selected as power switch in proposed softswitched inverter.
Gate pulse for main and auxiliary switch is given from two pulse generator and these pulses are given such that when main switch is on auxiliary switch is off. Gate pulse for two shunt switches are given from one pulse generator because these two shunt switches are on at same time. Gate pulse for threephase inverter switches is given from discrete PWM generator. Voltage across the resonant capacitor providing zero voltage switching, when zero voltage condition is obtained across resonant capacitor switching status of inverter device is changed.
Figure 8. Voltage across the resonant capacitor
The proposed quasiresonant topology provide zerovoltage switching condition across the resonant capacitor for obtaining softswitching in all inverter switches so now shown in Fig.8 zero voltage switching waveform across the resonant capacitor Cr.
4.1 For RL load
For RL load R=5, L= 5mH and source voltage of 150V DC is taken. Fundamental frequency, switching frequency, and modulation index were 400 Hz, 40 KHz and 0.9 taken respectively. Fig 9 shown simulation model of soft switched threephase inverter for RL load and three phase current and voltage wave form shown in Fig.10 when RL load is used.

Simulation circuit
Switeching Voltage
[G3_2] [G1_2] [G2_2]Discrete,
= 1.5e005
s
pow ergui
[SM]g m
D S
main switch
g
D
[SH] [G1_2] [G5_2] [G3_2] [G4_2] [G5_2]
[SA] gS
D
g
D
S
shunt switcp
g
D
S5 S3
g
S
D
S
S1
[G6_2]S
auxilary switch
A Va bc Ia bc
v
B
a
+
–
b
C c
v
+
–
Vin
[SH] [G2_2] [G6_2]g
g
D
[G4_2]
ThreePhase
A B C
VI Measurement
ThreePhase Series RL Branch
g
D
D
g
D
A B C
S4 S6 S2
S
S
S
S
shunt switcp
Main switch Pulse Generator
[SM] [SA] [SM] [SH]Shunt switch Pulse Generator
[SH]Auxilary switch Pulse Generator
NOT
Logical Operator
[SA] [G1_2] [G2_2] [G3_2] [G4_2] [G5_2] [G6_2]Unit Delay
1
z
Pulses
Discrete PWM Generator
6 pulses
Figure 9. Simulation model of softswitched threephase inverter for RL load

Simulation result for RL load
Figure 10. Three phase current and voltage wavefom for RL load

For Induction motor load
For Induction motor load source voltage of 150V DC is taken. Fundamental frequency (400Hz) and switching frequency (40 Khz) at modulation index 0.9 are considered. Fig11 showed simulation model of softswitched three phase inverter for

Simulation circuit
induction motor load and three phases current and voltage waveform in Fig.12 when Induction motor load is used. The current waveform is found sinusoidal.
[G1_2]
[SM] [SA] g Dg m
D S
main switch
S
[SH]g
D
shunt switcp
[G1_2]D
S1
[G5_2]g
g
S
D
S5
[G3_2]g
S
D
S3
S
[G2_2] [G3_2] [G4_2] [G5_2] [G6_2]
s
Discrete,
= 1.5e005
pow ergui
S
auxilary switch
+
A Va bc
1
Ia bc Tm
v
+
–
Vin
[SH]– v
[G2_2] [G6_2]g
D
[G4_2]

a Constant
b A m

c B
C
g
D
g
D
g
D
S4 S6 S2
S
S
S
S
shunt switcp
[G1_2]
Main switch Pulse Generator
[SM] [SA] [SM] [SH]Shunt switch Pulse Generator
[SH]Auxilary switch Pulse Generator
NOT
Logical Operator
[SA] [G2_2] [G3_2] [G4_2] [G5_2] [G6_2]1
Pulses
z
Discrete PWM Generator
6 pulses
Figure 11. Simulation model of softswitched threephase inverter for induction motor load


Simulation result for Induction motor load

Figure 12. Three phase current and voltage waveform for Induction motor load


Conclusion
In this paper a softswitched threephase inverter is simulated in MATLAB for RL and Induction motor loads. The switching sequence of various switches in the resonant link is allowed soft switching of switches in the threephase inverter. This softswitching is ensured independent of DC link current direction by the quasiresonant topology and its control strategy. The proposed quasiresonant topology is attractive over other topology as it can work for both RL and induction motor loads.These softswitched threephase inverter is operated at high frequency and resonant component of small size and weight are used which is attractive for airborne power supplies.

References

D. M. Divan, A resonant dclink converter a new concept in static power conversion ", IEEE Trans. Ind. Appl., 1989, 25, (2), pp.317325.

Mohan, N., T. Undeland, and W. Robbins, Power electronics converters, applications and design (John Wiley and sons, Singapore. 1995).

M. D. Bellar, T. Wu, A. Tchamdjou, J. Madhabi, and M Ehsani, A review of soft
switched dcac converters, IEEE Trans. Ind. Appl.,1998, 34, (4), pp.847860.

V. V. Deshpande and S. R. Doradla, A new topology for parallel resonant dclink with reduced peak voltage, IEEE Trans. Ind. Appl., 1996, 32, (2), pp.301 307.

K. Wang, Y. Jiang. S. Dubovsky, G. Hua. D. Boroyevich, and F. C. Lee, Novel dcrail softswitched threephase voltage source inverters, IEEE Trans .Ind. Appl.,1997, 33, (2), pp.509517.

J. Sung and K. Nam, A simple dcrail soft switched voltage source Inverter, IEEE PESC Conf Rec.,1998, pp.491496.

B. J. C Filho and T. A. Lipo, Spacevector analysis and modulation issues of passively clamped quasiresonant inverters, IEEE Trans. Ind . Appl., 1998, 34, (4), pp.861868

J. S. Lai, Resonant snubberbased soft switching inverters for electric propulsion drives, IEEE Trans. Ind. Appl., 1997.44, (1) pp.7180.

S. Behera, S .P. Das, and S. R. Doradla, Design, simulation and Implementation of a quasiresonant dcac converter with improved performance. IEEE PEDS Conf Rec, 2001, pp.663668.

D. Andrade, R. M. F Neto, L. C. Freitas, J.

B. Vieira, and V. J. Farias, A softswitched currentcontrolled converter for induction machine drives, IEEE Trans. Power Electron., 2001, 16, (1), pp.6371.