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Article

A Reduced Switch AC-AC Converter with the Application of D-STATCOM and Induction Motor Drive

1
Department of Electrical Engineering, Visvesvaraya National Institute of Technology, Nagpur 440010, India
2
Department of Electrical Engineering, Shri Ramdeobaba College of Engineering and Management, Nagpur 440013, India
*
Author to whom correspondence should be addressed.
Electronics 2018, 7(7), 110; https://doi.org/10.3390/electronics7070110
Submission received: 10 May 2018 / Revised: 3 July 2018 / Accepted: 5 July 2018 / Published: 10 July 2018
(This article belongs to the Special Issue Applications of Power Electronics)

Abstract

:
In this paper, a reduced switch AC-DC-AC converter is used as a distribution static compensator (DSTATCOM) and induction motor drive. The AC-DC-AC nine switch converter (NSC) is a reduced switch topology of conventional 12-switch back to back converter. With a 25% reduced switch count, NSC has lower losses when operated at constant frequency mode compared to twelve switch converter (TSC). The idea is to operate NSC input terminal as an active front-end rectifier to mimic synchronous generator (SG) operation. The induction motor is connected at the output of the NSC for irrigation application where no speed regulation is required. In distribution generation (DG), a large capacitor bank is used to deliver required reactive power. This may lead to over-voltage at the point of common coupling (PCC) when the load is turned off. To manage reactive power transfer at PCC, a control scheme is developed for NSC such that it can absorb or deliver reactive power with induction motor drive. Similar to SG, V-curve and inverted V-curve is plotted. The simulation and hardware results prove the feasibility of the proposed system.

1. Introduction

DG system recently getting more popular concerning gradual depletion of conventional sources. Several government policies such as subsidized solar panels and incentives on interest rebate of the windmill encourage more generation of solar and wind energy. With the increase in the connection of these renewable energy sources to the grid give rise to power quality issues [1,2,3]. It is necessary to maintain the acceptable voltage range at PCC with the varying load conditions. To keep bus voltage healthy, it is necessary to control reactive power transfer at loading and low load condition. At loading condition, sufficient reactive power must be available to avoid voltage dip at PCC. In addition, under low load condition, reactive power must be controlled to circumvent unacceptable voltage rise. To regulate reactive power transfer a FACTS device D-STATCOM has been utilized [4,5,6,7].
In this paper, in view of controlling reactive power transfer, the D-STATCOM is integrated with induction motor drive using nine switch AC-DC-AC converter. The NSC is recently introduced reduced switch topology of conventional twelve switch converter (TSC) [8,9,10,11,12,13,14,15,16]. Various AC-AC topologies are available in the literature. In matrix converter, to increase lifespan of converter the common DC-link is eliminated at the cost of an increase in the number of active switches. It requires 18 active switches for AC-AC conversion. Thus; switch associated losses and complexity increases [17]. The effort is taken to reduce the switch count of matrix converter known as sparse matrix converter. However, with reduced switch count in sparse matrix converter, power flow become unidirectional [18,19]. Retaining common DC-link capacitor, another reduced switch topology found in [20], known as the B8 converter. It is the combination of two B4 converter which is connected back to back. In the B4 converter, four active switches form two phase legs while for third phase two split capacitors midpoint is used. The drawback of this arrangement is balancing two split capacitor voltage with large DC-link voltage variation [21].
The conventional AC-DC-AC converter for induction motor drive is made up of diode bridge rectifier followed by six active switches inverter. The disadvantage of this topology is that the input grid current is non-sinusoidal and has poor power factor operation. To improve quality of input current, the diode bridge rectifier is further replaced by active six switches converter known as back to back converter. It requires twelve active switches for AC-DC-AC conversion. In the proposed AC-DC-AC induction motor drive, only nine active switches are required which gives sinusoidal input current with desired power factor. The NSC turns out to be a better alternative for AC-DC-AC with reduced switch count. Many applications of NSC are found in literature because of its two three-phase terminal connection. It is used in an uninterrupted power supply (UPS) [13]. It is used to interface solar panels, battery, and ultra-capacitor output to the grid for DG system [14]. A compact battery charging system for an electric vehicle with the six-phase motor drive is reported in [11,12]. Depending on the terminal connection of NSC, it can be operated as DC-AC-AC, AC-DC-DC, and AC-DC-AC. Of course, with the reduce switch count, there are some operating constraints of the NSC. Application criteria of the NSC reported in [15,16] clearly mentioned that the NSC when operated as AC-DC-AC with different frequency operation is not recommended as it requires double DC-link voltage when compared to TSC operation. It also states that, when NSC is operated in common AC-DC-AC frequency mode then along with reduced switch count, losses in the NSC are lesser when compared to TSC.
Considering the advantages of the NSC operated in common AC-DC-AC frequency mode, in the proposed system the three-phase induction motor is connected at the output which will run at constant speed. For irrigation application, a centrifugal pump is connected to the induction motor. In this application, there is no requirement of controlling speed. As induction motor is operated at lagging power factor, a control scheme is developed such that the NSC with induction motor can be operated as lagging, unity, and leading power factor. Operating the NSC at leading power factor can deliver reactive power to PCC. The NSC, when operated as lagging power factor, can absorb reactive power from PCC of the grid. The idea is to operate the NSC to mimic synchronous generator at the input side and induction motor drive for irrigation application at the output side.
This paper is organized as follows, Section 2 gives system description and operation of NSC. The generation of the gate signal and operating constraint is explained in Section 3. The control logic of the proposed system is given in Section 4. Simulation and experimental results are presented in Section 5 and Section 6 respectively. Finally, the conclusion is drawn in Section 7.

2. System Description and Operation of NSC

Figure 1 shows the overall single-line diagram of the three-phase power system connection. The NSC is connected at PCC with interfacing source inductance (Ls). Along with the NSC, a different rating of reactive loads are also connected at the PCC. The Vs is the grid phase voltage at PCC. The is, il, and ia are the source, reactive load, and NSC currents respectively. The aim is to maintain the unity power factor at PCC such that no reactive power exchange at the PCC. To achieve this, the NSC is controlled so that, when the inductive load is connected, NSC will deliver reactive power and when the capacitive load is connected, NSC will absorb reactive power. Figure 2 shows phasor representation of the operation of the NSC. In Figure 2a, at PCC along with the NSC, an inductive load is connected. Thus NSC is operated at leading power factor (ia leads Vs) such that Vs is in phase with is. Similarly when the capacitive load is connected at the PCC, the NSC is operated at lagging power factor (ia lags Vs) resulting in-phase operation of Vs and is. As shown in Figure 1, a different rating of reactive load is connected at PCC to test the operation of NSC as DSTATCOM.
Figure 3 shows the arrangement of NSC operated as DSTATCOM and induction motor drive. The terminal a, b, and c are the input points and the terminals x, y, and z are the output points of the NSC. For simplicity it is assumed that upper six switches (S1, S2, S4, S5, S7, S8) act as a DSTATCOM and lower six switches (S2, S3, S5, S6, S8, S9) act as a inverter to drive induction motor which is coupled to the centrifugal pump. The Vcom and Vinv are the input and output terminal voltage of the NSC. The Vcom is the function of DC-link voltage (Vd). The reactive power transfer depends on the difference between a magnitude of Vs and Vcom. The voltage Vs is constant, thus by varying Vcom, reactive power transfer can be altered. As Vcom is a function of Vd, to charge DC-link capacitor (Cd) active power from PCC to NSC is transferred by varying power angle ‘ δ ’ between Vs and Vcom. As the input terminal of the NSC is operated as active front end converter, to synchronize NSC at PCC, instantaneous angle ‘ θ ’ of the PCC voltage is tracked. To measure this angle ‘ θ ’, three-phase voltage is sensed by using voltage sensor. Synchronous reference frame phase lock loop (SRF-PLL) is implemented in the logic controller to extract angle ‘ θ ’ [22]. In practical, to interface voltage sensor signal and logic controller, signal conditioning circuit is required. Along with sensing voltage, a current sensor is required to calculate the active and reactive power of the converter. Another voltage sensor is required to measure DC-link capacitor voltage. As Vinv is the output of the NSC, which is the function of DC-link voltage. To keep Vinv magnitude constant, the modulation index of an inverter is changed according to the variation in DC-link voltage. To get desired gate pulses of the NSC, logic is developed in a logic controller. The controller ePWM (enhance pulse width modulation) pulses of the controller are processed by buffer circuit, an isolation circuit, and gate driver circuit to operated active power switches.

3. Generation of Gate Signal and Operating Constraints of the NSC

The AC-DC-AC NSC is operated as rectifier and inverter simultaneously. For rectifier and inverter operation two modulating references, Refrec and Refinv respectively is compared with a single carrier signal (Vc). For front-end rectification operation, Refrec must be synchronized to the PCC. Thus; SRF-PLL is implemented to track instantaneous angle ‘ θ ’ of the grid. Also, to control active power transfer between PCC and NSC, the reference Refrec is shifted by an angle ‘ δ ’ with respect to the PCC voltage. Figure 4 shows the PCC voltage and phase shifted references by an angle ‘ δ ’. The Three-phase modulating references of the NSC are given by-
R e f rec _ a = m r s i n ( θ + δ ) + V dc _ offset R e f rec _ b = m r s i n ( θ 120 + δ ) + V dc _ offset R e f rec _ c = m r s i n ( θ + 120 + δ ) + V dc _ offset R e f inv _ x = m i s i n ( θ + δ ) V dc _ offset R e f inv _ y = m i s i n ( θ 120 + δ ) V dc _ offset R e f inv _ z = m i s i n ( θ + 120 + δ ) V dc _ offset
where mr and mi are the modulation indices of Refrec and Refinv. The angle ’ θ ’ is an instantaneous angle of the PCC voltage tracked by SRF-PLL. The angle ’ δ ’ is a phase shift angle. To understand the generation of the gate signal of the NSC, one leg of the NSC is considered. There are eight possible switching states. Table 1 shows switching states and associated pole voltages. Among that eight switching states only three valid states are possible for the operation of the NSC. From Table 1, it is observed that pole voltage VaN is always greater than or equal to VxN. Hence; modulating reference Refrec is always kept above Refinv. Thus; to achieve switching constraint a small DC-offset is added and subtracted from Refrec and Refinv. The switching constraint is applied to avoid short circuit of a DC-link capacitor or open circuit condition of the inductive load. Figure 5 shows the generation of gate pulses and pole voltage. When Refrec is greater than the Vc, gate signal for S1 is generated. When Refinv is lower than the Vc, gate signal for S3 is generated. Applying XOR logic to the gate signal of S1 and S3, gate signal for S2 is obtained.

4. Control Logic of the Proposed System

To control NSC, sinusoidal pulse width modulation technique is incorporated. A common DC-link is shared for both the rectifier and inverter operation. The rectifier input and inverter output voltage is a function of DC-link voltage and it is given by
V c o m = R e f r e c V d / 2
V i n v = R e f i n v V d / 2
In the proposed system, NSC is connected to PCC with the source inductance. Figure 6 shows the single line diagram of the connection of the NSC to PCC with Ls which have its internal resistance Rs. The PCC voltage Vs0 is a reference voltage while Vcom∠δ is a variable voltage as it depends on the dc-link voltage of the NSC. The reactive power flow depends on the voltage magnitude of |Vs| and |Vcom| and the active power flow depends on power angle between Vs and Vcom. From Figure 6, rectifier input voltage Vcom is given by
V c o m = V s ( R s + j X s ) i a
Resolving ia in d-q plane,
i a = i a d * + j i a q *
where iad-active component, iaq-reactive component. By controlling iad and iaq current component of the NSC active and reactive power flow of the NSC is controlled. From (5) and (4)
V c o m = ( V s R s i a d * + X s i a q * ) j ( R s i a q * + X s i a d * )
The magnitude and angle of Vcom is given by
V c o m = | V c o m | δ
where
| V c o m | = ( V s R s i a d * + X s i a q * ) 2 + ( R s i a q * + X s i a d * ) 2
δ = t a n 1 ( R s i a q * + X s i a d * ) ( V s R s i a d * + X s i a q * )
To calculate i*aq current reference, reactive power of the PCC is continuously monitored. In addition, to calculate i*ad reference output power of the NSC is measured. The active and reactive power in d-q reference is given by
P ( t ) = 3 2 [ V d ( t ) i d ( t ) + V q ( t ) i q ( t ) ]
Q ( t ) = 3 2 [ V d ( t ) i q ( t ) + V q ( t ) i d ( t ) ]
Aligning the d-axis of the input and out voltage of the NSC with the d-axis of the synchronous reference frame.
For input side of the NSC
V d = V c o m d
For output side of the NSC
V d = V i n v d
As the q-axis is orthogonal to the reference axis
V q = 0
By using Equations (10)–(14), active power of NSC input and output is given by
P i n = 3 2 [ V c o m d i a d ]
Bu using Equations (6), (10), and (11), real power at the inverter output side is given by:
P o u t = 3 2 [ V i n v d i L d ]
where iLd is a d-axis component of the load current. Assuming NSC to be lossless converter and applying power balance criteria,
P i n = P o u t
3 2 [ V c o m i a d ] = 3 2 [ V i n v d i L d ]
As the same dc-link is shared by the rectifier and inverter, Vcomd and Vinvd is given by:
V c o m d = R e f r e c V d / 2
V i n v d = R e f i n v V d / 2
The mr and mi are the only variable in Refrec and Refinv, Thus; by using Equations (18)–(20)
i a d = [ m i m r ] i L d
Equation (21), gives relation between source current and load current in terms of modulation index of rectifier and inverter reference. The iLd is active component of the load current. Thus;
i a d = [ m i m r ] i L c o s ϕ o
where ϕo is load phase angle. The iLcosϕo is calculated from measured output power. Thus; i*ad reference is generated. To calculate i*aq, reactive current component (issinϕ) of the PCC current is measured. The aim is to maintain zero reactive power at PCC. Thus, the issinϕ is compared with zero reference so as get desired i*aq. Figure 7 shows the proposed control diagram. The calculated i*ad and i*aq is fed to the phase shift generator block which generates desired phase shift to control active power or to charge DC-link capacitor at desired voltage level. The extracted PLL angle θ and angle δ is used to generate desired gate pulses for the operation of NSC.

5. Simulation Result

The MATLAB simulation is carried out considering different load conditions at PCC. The simulation parameters are given in Table 2. To maintain unity power factor operation at PCC, the reference current i*qREF is kept as 0. Referring to Figure 1, to test the dynamic performance of the proposed control technique different reactive loads are connected for different time duration. The time duration of different load connection is given in Table 2. The switching frequency (Fsw) of the NSC is 9 kHz. The modulation index of a rectifier is kept constant at 0.8, whereas modulation index of an inverter is varying to keep Vinv constant. To satisfy switching constraint a small dc-offset of 0.1 pu is added only in rectifier references. The NSC input and output line voltages are shown in Figure 8.
Figure 9 shows the exchange of the three-phase reactive power transfer under varying load conditions. During 0–1 s, 3100 VAR reactive power (Qload) is absorbed by the R-L load. Thus; to maintain zero reactive power (Qref) transfer at PCC, NSC delivers −3100 VAR (QNSC) so that actual reactive power (Qact) is equals to Qref. Similarly, during 1–2 s, 1550 VAR is absorbed by an R-L load, thus NSC provided −1550 VAR to the PCC. During 2–3 s, no load is connected parallel to the NSC, thus there is no exchange of reactive power at PCC. During 3–4 s, an R-C load is connected which delivers −1400 VAR reactive power, thus NSC absorbs 1400 VAR from PCC. Similarly, for 4–5 s, R-C load delivers −2450 VAR, thus NSC absorbs 2450 VAR from PCC to maintain zero reactive power at PCC.
Figure 10 and Figure 11 show the effect of varying load conditions on the NSC phase current (ia) and power factor of the NSC respectively. Figure 10a shows, during 0–1 s the NSC is operated at 0.8 leading power factor (ia leads Vs). After the change in load, NSC changed its operation to 0.93 leading power factor. When there is no load connected parallel to the NSC at 2 s, the NSC switched its operation from 0.93 lead to 0.999 unity power factor (ia in-phase to Vs) as shown in Figure 10b. Figure 10c shows at 3 s when an R-C load is connected at PCC, the NSC is operated at 0.95 lagging power factor (ia lags Vs). At 4 s when an R-C load is changed, the NSC shifted its operation from 0.95 lagging power factor to 0.86 lagging power factor as shown in Figure 10d.
Figure 12 and Figure 13 show a change in DC-link capacitor voltage and the angle δ respectively. As earlier discussed, the reactive power transfer from NSC to PCC depends on voltage magnitude of Vs and Vcom. As Vcom depends on DC-link voltage, with the changed in DC-link voltage Vcom varies and thus reactive power transfer varies. In a simulation, at first, NSC delivered reactive power thus at that instant required DC-link is more. With the change in load, NSC changed its operation from delivering to absorbing reacting power. Thus, according to a required magnitude of Vcom, DC-link voltage is varied as shown in Figure 12. To charge or discharge the DC-link capacitor the angle δ is varied as per desired DC-link voltage requirement and finally, it settled down. As a common DC-link is shared for rectifier and inverter function of the NSC, with the change in DC-link voltage Vinv also changes. To maintain Vinv constant, mi is varied to keep NSC output voltage constant. Figure 14 show change in modulation index of the inverter. Figure 15 and Figure 16 show induction motor three-phase current and speed under dynamic load variations at PCC.
The simulation results are summarized in Table 3. It is observed that the input rectifier operation of the NSC mimics the operating principle of the synchronous generator. The synchronous generator delivers reactive power when its field is over-excited and absorbs reactive power when its field is under-excited. The V-curve and inverted V-curve is obtained by varying field excitation of the synchronous motor. A Similar phenomenon is observed in case of the NSC. By controlling DC-link voltage of the NSC reactive power transfer can be controlled. From simulation results shown in Table 3, V-curve and inverted V-curve is plotted in Figure 17.

6. Experimental Setup and Result

The experimental setup of the NSC with induction motor connected to the source through the source inductance is shown in Figure 18. The experimental parameters are given in Table 4. The Hioki 3197 power quality analyzer is used to measure various system parameters. The source voltage is kept constant at 110 V. Three LV20-P voltage sensors are used to measure source voltage to track instantaneous source angle ( θ ) for the rectifier operation of the NSC. The NSC input (Vab) and output (Vxy) line voltages are shown in Figure 19.
To demonstrate reactive power transfer between source and NSC, i*qREF reference is varied. The operation of NSC is tested for different power factor conditions.

6.1. NSC Operated at Unity Power Factor Condition

To operate NSC with induction motor drive at unity power factor, reference i*qREF is kept as 0 pu. The phase angle between Vs and ia is 4.5 as shown in Figure 20a. Ideally, as i*qREF is 0, the angle between Vs and ia must be equal to zero. However, due to the presence of harmonics in the system, a small reactive power is consumed by the harmonics present in pulsating nature of the input and output voltages. Figure 20b shows various parameters of the system. It is observed that a small reactive power of 16 VAR is absorbed by the NSC. The power factor is almost unity i.e., 0.974 PF. Figure 20c shows the phase voltage and phase current are in phase. The DC-link voltage is 380 V. The NSC phase current is 0.64 A.

6.2. NSC Operated at Lagging Power Factor Condition

The lagging power factor operation of the NSC is tested for two conditions; i*qREF = 0.7 pu, and i*qREF = 0.3 pu. As shown in Figure 21a, when i*qREF is 0.7 pu, 81 VAR reactive power is absorb by the NSC. The phase angle between Vs and ia is 43.4 (lag) i.e., 0.701 PF. The amplitude of phase current ia increased to 1.05 A as compared to the unity power factor operation. The DC-link voltage is droped to 369 V. As shown in Figure 22b, when i*qREF is 0.3 pu, 33 VAR reactive power is absorb by the NSC. The phase angle between Vs and ia is 22.2 lag i.e., 0.896 PF. The amplitude of ia and DC-link voltage is 0.70 A and 371 V respectively.

6.3. NSC Operated at Leading Power Factor Condition

The leading power factor operation of the NSC is also tested for two conditions; i*qREF= −0.4 pu, and i*qREF= −0.6 pu. As shown in Figure 22a, when i*qREF is −0.4 pu, 44 VAR reactive power is delivered by the NSC. The phase angle between Vs and ia is 29.6 (lead) i.e., 0.857 PF. The amplitude of phase current ia increased to 0.88 A as compared to the unity power factor operation. The DC-link voltage is increases to 401 V. As shown in Figure 22b, when i*qREF is 0.6 pu, 65 VAR reactive power is delivered by the NSC. The phase angle between Vs and ia is 40.6 (lead) i.e., 0.751 PF. The amplitude of ia and DC-link voltage is 0.88 A and 408 V respectively.
The positive reactive power shown in Figure 21 states that reactive is absorb by the NSC. The negative reactive power shown in Figure 22 states that the reactive power is delivered by NSC. Thus, the NSC with induction motor drive can be operated to absorb or to deliver reactive power to the connected source. Figure 23 show induction motor phase current on half load. The V-curve and inverter V-curve is plotted from experimental results is shown in Figure 24.
Comparing V-curve of simulation and experimental showed in Figure 17a and Figure 24a, it is observed that the amplitude of the NSC phase current (ia) is minimum near unity power factor. The amplitude of ia increased as the power factor lowered on both the lagging as well as leading side. Referring to Figure 6, the power factor at the PCC depends on the voltage magnitude of Vs and Vcom. The PCC voltage Vs is constant and the magnitude of the Vcom is directly depends on DC-link voltage (Vd) as per (2). Thus; controlling Vd, power factor at the PCC is controlled. Comparing inverted V-curve of simulation and experimental results showed in Figure 17b and Figure 24b, as the DC-link voltage increases power factor shifted from lagging to leading. Ideally, when the magnitude of the Vs and Vcom is equal, the power factor at PCC must become zero. However, practically, there is a small voltage drop across the internal resistance of the source inductance. This drop varies with the amplitude of the current flowing through it. Thus; for different loading conditions, values of V-curve and inverter V-curve are different but nature of curve remain same. In experimental results switching and conduction losses are present whereas in simulation switches are ideal. Thus, there is a slight difference in the shape of V-curve and inverter V-curve of the NSC for simulation and experimental results.

7. Conclusions

In this paper, the compact AC-DC-AC NSC is used as DSTATCOM and induction motor drive application. The switch count is reduced by 25% as compared to the conventional TSC. The control scheme is developed to operate NSC so as to mimic the operation of SG. The NSC can absorb or deliver reactive power at the PCC with induction motor drive. The NSC with induction motor drive is operated at desired power factor of the PCC. To verify simulation results, an experimental prototype is developed in the laboratory. The V-curve and inverted V-curve is obtained from simulation and experimental results are found similar in nature. Due to the presence of internal resistance of the source inductance and the switching losses in the experimental results, there is a slight difference in the shape of V-curve and inverted V- curve of the simulation and experimental results. The experimental results proved the practicability of the proposed control scheme to operate NSC as DSTATCOM and induction motor drive.

Author Contributions

C.J., M.C. and M.R. developed the concept: C.J. designed and performed the experiments: C.J. and M.C. wrote the paper; M.R. analyzed the data. These authors contributed equally to this work.

Funding

This research received no external funding.

Acknowledgments

Authors acknowledges the VNIT, Nagpur for providing infrastructure support.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

The following abbreviations and symbols are used in this manuscript:
DGDistribution generation
NSCNine switch converter
DSTATCOMDistribution static compensator
TSCTwelve switch converter
SGSynchronous generator
PCCPoint of common coupling
FACTSFlexible Alternating Current Transmission System
VsPhase voltage of grid
isPhase current of grid
i1Phase current of reactive load connected across NSC
iaPhase current of NSC
VcomNSC input phase voltage
VinvNSC output phase voltage
iLNSC output phase current
ϕ aAngle between Vs and ia
ϕ 1Angle between Vs and i1
ϕ 0Angle between Vinv and iL
VdDC-link voltage
θ Instantaneous angle of the grid
δ Power angle between Vs and Vcom
RefrecModulation references for rectifier operation
RefinvModulation reference for inverter operation
VcCarrier reference
mrModulation index of Refrec and Refinv respectively
LsSource inductance
RsInternal resistance of the source inductor
a,b,cInput terminals of the NSC
x,y,zOutput terminals of NSC
NCommon point of negative dc-link voltage
VaNPole voltage between terminal a and N
VxNPole voltage between terminal x and N
Id*Generated active current reference
QrecReactive power at PCC
QNSCReactive power of NSC
QloadReactive power of other load connected across NSC
QrefDesired reactive power at PCC
Vab1Fundamental component of the NSC input line voltage
Vxy1Fundamental component of NSC output line voltage

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Figure 1. Single-line diagram of three-phase power system connection.
Figure 1. Single-line diagram of three-phase power system connection.
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Figure 2. Phasor representation of operation of NSC. (a) NSC operated at leading power factor; (b) NSC operated at lagging power factor.
Figure 2. Phasor representation of operation of NSC. (a) NSC operated at leading power factor; (b) NSC operated at lagging power factor.
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Figure 3. Arrangement of NSC operated as DSTATCOM and induction motor drive.
Figure 3. Arrangement of NSC operated as DSTATCOM and induction motor drive.
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Figure 4. PCC voltage and phase shifted references by an angle ‘ δ ’.
Figure 4. PCC voltage and phase shifted references by an angle ‘ δ ’.
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Figure 5. Generation of gate pulses.
Figure 5. Generation of gate pulses.
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Figure 6. Single line diagram of the connection of the NSC to PCC.
Figure 6. Single line diagram of the connection of the NSC to PCC.
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Figure 7. Control scheme.
Figure 7. Control scheme.
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Figure 8. NSC input and output line voltages: Vab, Vxy (500 V/div, 10 ms/div).
Figure 8. NSC input and output line voltages: Vab, Vxy (500 V/div, 10 ms/div).
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Figure 9. Exchange of three-phase reactive power at PCC: Q (2000 VAR/div, 0.5 s/div).
Figure 9. Exchange of three-phase reactive power at PCC: Q (2000 VAR/div, 0.5 s/div).
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Figure 10. Phase voltage and NSC phase current under various load conditions: Vs, 15 * ia (200 V/div, 200 A/div, 50 ms/div).
Figure 10. Phase voltage and NSC phase current under various load conditions: Vs, 15 * ia (200 V/div, 200 A/div, 50 ms/div).
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Figure 11. NSC operated at different power factor: (0.2 pu/div, 0.5 s/div).
Figure 11. NSC operated at different power factor: (0.2 pu/div, 0.5 s/div).
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Figure 12. DC-Link capacitor voltage: ( 200 V/div, 0.5 s/div).
Figure 12. DC-Link capacitor voltage: ( 200 V/div, 0.5 s/div).
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Figure 13. Change in angle delta ( δ ): (2 deg/div, 0.5 s/div).
Figure 13. Change in angle delta ( δ ): (2 deg/div, 0.5 s/div).
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Figure 14. Change in modulation index of inverter: mi (0.1 pu/div, 0.5 s/div).
Figure 14. Change in modulation index of inverter: mi (0.1 pu/div, 0.5 s/div).
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Figure 15. Three-phase induction motor current: iL (10 A/div, 0.5 s/div).
Figure 15. Three-phase induction motor current: iL (10 A/div, 0.5 s/div).
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Figure 16. Induction motor speed: (500 RPM/div, 0.5 s/div).
Figure 16. Induction motor speed: (500 RPM/div, 0.5 s/div).
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Figure 17. V-curve and inverted V-curve of the NSC.
Figure 17. V-curve and inverted V-curve of the NSC.
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Figure 18. Experimental setup.
Figure 18. Experimental setup.
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Figure 19. NSC input and output voltages: Vab, Vxy (200 V/div, 5 ms/div).
Figure 19. NSC input and output voltages: Vab, Vxy (200 V/div, 5 ms/div).
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Figure 20. Unity power factor operation of the NSC i*qREF = 0 pu: Vd, Vs, ia ( 100 V/div, 100 V/div, 2 A/div, 10 ms/div).
Figure 20. Unity power factor operation of the NSC i*qREF = 0 pu: Vd, Vs, ia ( 100 V/div, 100 V/div, 2 A/div, 10 ms/div).
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Figure 21. Lagging power factor operation of the NSC: Vd, Vs, ia (100 V/div, 100 V/div, 2 A/div, 10 ms/div).
Figure 21. Lagging power factor operation of the NSC: Vd, Vs, ia (100 V/div, 100 V/div, 2 A/div, 10 ms/div).
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Figure 22. Leading power factor operation of the NSC: Vd, Vs, ia (100 V/div, 100 V/div, 2 A/div, 10 ms/div).
Figure 22. Leading power factor operation of the NSC: Vd, Vs, ia (100 V/div, 100 V/div, 2 A/div, 10 ms/div).
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Figure 23. Induction motor current: iL (1 A/div, 10 ms/div).
Figure 23. Induction motor current: iL (1 A/div, 10 ms/div).
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Figure 24. Experimental V-curve and inverted V-curve of the NSC.
Figure 24. Experimental V-curve and inverted V-curve of the NSC.
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Table 1. Switching states.
Table 1. Switching states.
Switching States (SS)S1S2S3VaNVxN
Valid states
1110VdVd
2101Vd0
301100
Forbidden states
411100
500000
6100Vd0
701000
800100
Table 2. Simulation parameter.
Table 2. Simulation parameter.
Vs3-Phase, 400 V, 50 Hz
Induction Motor5.4 hp, 4 pole, 400 V, 50 Hz
Ls, Rs, mr, Fsw10 mH, 1.63 Ω , 0.8, 9 kHz
Load at PCC parallel to NSC drive
1-R-L25 Ω , 0.1 H [0–1 s]
2-R-L25 Ω , 0.3 H [1–2 s]
No-load[2–3 s]
3-R-C25 Ω , 30 μ F [3–4 s]
4-R-C25 Ω , 60 μ F [4–5 s]
Table 3. Simulation results.
Table 3. Simulation results.
[Vs = 230 V/phase, mr = 0.8]
ia (A)
% THD
cos ϕ aVab1 (V)
% THD
Vd (V)QNSC (VAR)Vxy1 (V)
% THD
iL (V)
% THD
① 0–1 s7.80.8424.2854−31004007.8
4.5%lead32.10%32.24%4.9
② 1–2 s6.720.93412.3830−15504007.8
4.9%lead32.16%32.24%4.8
No-load 2–3 s6.3180.99940080504007.8
4.93%unity32.16%31.91%3.8
③ 3–4 s6.670.95388.978314204007.8
4.58%lag32.01%31.7%4.0
④ 4–5 s7.320.86380.776724504007.8
4.36%lag31.97%31.56%4.89
Table 4. Parameter of Experimental Setup.
Table 4. Parameter of Experimental Setup.
ItemSpecification
AC Source0–110 V
Source Inductance10 mH
IGBTKGT25N120NDH
Gate driver ICMIC4425
DSPdsPIC33EP512MU810
SoftwareMPLAB X IDE v2.10
SensorsLV-20P, LA-25P
Induction Motor1 hp, 4 Pole,110 V, 50 Hz

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Jibhakate, C.; Chaudhari, M.; Renge, M. A Reduced Switch AC-AC Converter with the Application of D-STATCOM and Induction Motor Drive. Electronics 2018, 7, 110. https://doi.org/10.3390/electronics7070110

AMA Style

Jibhakate C, Chaudhari M, Renge M. A Reduced Switch AC-AC Converter with the Application of D-STATCOM and Induction Motor Drive. Electronics. 2018; 7(7):110. https://doi.org/10.3390/electronics7070110

Chicago/Turabian Style

Jibhakate, Chaitanya, Madhuri Chaudhari, and Mohan Renge. 2018. "A Reduced Switch AC-AC Converter with the Application of D-STATCOM and Induction Motor Drive" Electronics 7, no. 7: 110. https://doi.org/10.3390/electronics7070110

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