Extended smart meters-based remote detection method for illegal electricity usage

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1&

Published in IET Generation, Transmission & DistributionReceived on 5th June 2012Revised on 3rd January 2013Accepted on 22nd January 2013doi: 10.1049/iet-gtd.2012.0287

332The Institution of Engineering and Technology 2013

ISSN 1751-8687

Extended smart meters-based remote detectionmethod for illegal electricity usageByambasuren Bat-Erdene1, Bumjoo Lee2, Min-Young Kim3, Tae Hong Ahn4, Donghan Kim1

1Department of Electrical Engineering, Kyung Hee University, Korea2Department of Electrical Engineering, Myongji University, Yongin, Korea3School of Electrical Engineering and Computer Science, Kyungpook National University, Korea4Department of Game Development, Chunnam Techno University, Korea

E-mail: [email protected]

Abstract: Power delivery systems that use power lines can communicate with other electrical systems, monitor the quality ofelectrical energy and provide an economical solution for automatic meter reading (AMR). Energy meters can be connected toa low-voltage power system by power line carriers for all consumers. Illegal electricity usage in the power delivery systemcan be easily detected if AMR is installed in the system, which consists of a terminal smart meter (TSM) and a gatewaysmart meter (GSM). This study proposes a novel remote detection method for illegal electricity usage that uses both TSM andGSM, where the TSM and the GSM are installed on the power system of each consumer and on the node of the powersystem feeder, respectively. TSM and GSM simultaneously disconnect an electrical source for a very short period of time.After this, the proposed detection method sends a low-voltage signal with a high frequency from the TSM to the GSM duringthe time of disconnection. Once the signal has passed, the proposed detection method detects illegal electricity usage bymeasuring the amount of time it was disconnected. This study presents the structure of the proposed detection method as wellas the mathematical model, proof, simulation and experimental results.

1 Introduction

Information can be transmitted economically throughelectrical power transmission lines by using a power linecarrier (PLC) communication system with no extra wiring[1–9]. PLC communication can also be used for many otherpurposes such as to communicate with other electricaldevices, to monitor the power quality, to control theoptimal flow of electrical current and to implement anautomatic meter reading (AMR) system. Remote monitoringof electrical consumption of every user is possible if theAMR system is implemented within the power deliverysystem [10–15].There is already an emerging technology of monitoring the

electricity consumption of customers through the use of AMRsystem based not only on PLC communication but also onbroadband over power lines (BPL) [16]. AMR systems canbe remotely used in the power delivery system to detect anyillegal consumption of electricity. Illegal electricity usage isa major problem for electricity distribution companies. Forexample, the Minister of Energy and Natural Resources inTurkey has stated that the illegal usage of electricityconstitutes 19% of the total electricity consumption inTurkey [17]. The same problem exists in Iran [18], andeven Mongolia is now seeking an optimal solution forremote detection of illegal electricity usage [19–21].Detecting illegal electricity usage in real time is impossible

through methods that involve statistical data, which are

derived from a time-domain reflectometer in the mainpower cable [22–25]. To detect a fault in the power line aswell as the location of an illegal connection, manycompanies or countries use detection methods based on thetime-domain reflectometer in the power cable of consumers.However, these methods are unsuitable for remote real-timedetection of illegal electricity consumption. Thus, a moreoptimal method is required to detect illegal electricityconsumption.

2 Research background

The structure of a power delivery system that transmitselectrical energy is shown in Fig. 1. According to Fig. 1,electrical voltage supported from the electrical source isdecreased because of the power transformer and istransmitted by the low-voltage transmission line to each ofthe subsystems.The subsystem then transmits electricity from a node to

local users. Illegal electricity usage may exist on the userside of the subsystems, on the outside of nodes or on thelow-voltage transmission line. However, illegal electricityusage mostly occurs on the customer side of the subsystems.In 2004, H. Cavdar suggested a new AMR-based method

of detecting illegal electricity consumption [17]. Heassumed that electricity could be used illegally in the fourways shown in Fig. 2: switching of energy cables at the

IET Gener. Transm. Distrib., 2013, Vol. 7, Iss. 11, pp. 1332–1343doi: 10.1049/iet-gtd.2012.0287

Fig. 1 Power delivery system

a Overall structureb Subsystem that transmits electricity from single node to local users

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meter box (Case 1), use of external phase before the meterterminals (Case 2), use of fixed magnet (Case 3) and use ofmechanical objects (Case 4).Note that Cases 3 and 4 only occur for mechanical energy

meters, and do not occur for digital energy meters.H. Cavdar’s basic method involves the use of two electrical

meters: one on the user side and the other placed outside theuser’s residence. Any variation in measurements between twoenergy meters confirms illegal electricity usage. H. Cavdar’smethod can detect any illegal consumption of electricitybetween any two points when the energy meter and themain energy meter are installed. However, in manycountries, illegal consumption is rife through a street-levelconnection from the main power line without any energymeter. Thus, H. Cavdar’s method requires extra number ofenergy meters and it can be only used on a singlelow-voltage grid.In 2007, A. Pasdar and S. Mirzakuchaki suggested that

illegal electricity usage could be detected through a remotemethod based on a smart meter [18]. The smart meterdisconnects all users to transmit a low-voltage signal with ahigh-frequency through the main power line. Their methoddetects illegal electricity usage by measuring andcomparing the impedance value with that of a normal

Fig. 2 Four cases of illegal electricity usage

a Case 1: shunt connectionb Case 2: branched connectionc Case 3: magnetic disturbanced Case 4: mechanical locking


regime. However, the main drawback of their method is thatthe power delivery system of all users must bedisconnected. Thus, this paper presents a novel approachthat enables detecting illegal electricity usage remotelywithout any disconnections.

3 Novel method for detecting illegalelectricity usage

In the proposed remote detection method for illegal electricityusage, two extended smart meters – terminal smart meter(TSM) and gateway smart meter (GSM) – are used. TSM isinstalled on every user side, where GSM is installed on thenodes, as shown in Fig. 3a. Since GSM is installed on thestarting section of the node, it can connect and disconnectthe node on the user side. The roles of TSM are to detectand measure illegal electricity usage. Block diagrams ofGSM and TSM are shown in Fig. 3b and c.To detect illegal electricity usage, the process of the

proposed detection method includes two cases. The firstcase is to check whether a shunt connection exists on thecurrent coil of the energy meter by using TSM. The illegalway of either mechanical locking or magnetic disturbance

1333& The Institution of Engineering and Technology 2013

Fig. 3 Block diagrams of two proposed smart meters

a Place of proposed smart metersb GSMc TSM

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cannot occur in this case because a digital energy meter isused. The second case is to check whether an electricalenergy exists from the phase of energy meter on the TSMof each user. A detailed procedure of two cases is describedin the following sections.

3.1 Detection scheme for illegal shunt connection

The proposed detection method checks for illegal electricityusage on the node of each user because it could exist in anynode of the power delivery system on the user side. TSM isused to check this type of illegal electricity usage, where anAC/AC regulator and EM2 energy meter are used as well asthe input switch SWmk as shown in Fig. 3c. To check forshunt connections, the proposed detection method changesthe input voltage of the energy meter to a low value byusing an AC/AC regulator. After this, EM2 measures thevariation in output voltage.If there is no shunt connection, the output voltage is

switched to low amplitude for a short period of time, andthen returned to the previous normal value according to thecontrol command given from the control block. In contrast,the output voltage cannot be controlled according to thecontrol command if the energy meter has shuntconnections. In this case, there is no variation on the outputvoltage and its value would equal to the input voltage.When a shunt resistance is connected, the shunt resistance

is approximately equal to zero (Zshunt≃ 0). The resistance ofthe AC/AC regulator is greater than the shunt resistance(Zac/acregulator≫ Zshunt). Thus, the current is passed to thebranch with the minimum resistance according to Ohm’slaw as follows

Vsource ≃ Vout, Ishunt ≃ Iuser (1)

where Vsource is the power source voltage, Vout is the outputvoltage of TSM, Ishunt is the shunt branch current and Iuseristhe user current. This way, the output voltage does notchange according to the control command of the AC/ACregulator in TSM and illegal electricity usage can be detected.


3.2 Detection scheme for illegal branchedconnection

The proposed detection method checks for an illegal branchedconnection of the energy meter. In this case, GSM, EM1,SWmk, testing voltage generator (TVG), AC/AC regulatorand EM2 of TSM shown in Fig. 3 are used. To detectbranched connection, the switch SWmn of TSM installedon the node of each user and the switch SWnode_m ofGSM installed on the starting section of the node must beinstantly and repetitively connected and disconnected at thesame time for a very short period. Normal voltage isprovided to the nodes on the user side by using an AC/ACregulator of TSM during repetition period. Then, theproposed detection method checks for illegal electricityusage of each user by using TSM.As an example, consider the kth user on the mth node.

To check for illegal electricity usage on the outside phaseof user k, the proposed detection method uses TVG withthe low-voltage source with a high frequency in TSM. Thelow-voltage source with a high frequency is connectedthrough the switch SWmk when the switch SWnode_m ofGSM is disconnected.If SWnode_m is connected and SWmk is connected to an

AC/AC regulator, the signal is sinusoidal with the lowfrequency. However, if SWnode_m is disconnected andSWmk is connected to TVG, the signal is also sinusoidal,but its amplitude is low and frequency is high.GSM measures the important parameters when SWmk is

connected to TVG. In this case, the impedance of Line kbetween the starting section of the node and the user k canbe calculated by using the measured parameters. If the linehas no illegal connection, the calculated impedance shouldequal to the original impedance of the line. However, if ithas an illegal connection, the calculated impedance will bedifferent compared to the original impedance of the line. Todetect illegal electricity usage for all users, this operationshould be executed for each user in order.When the power delivery system has no illegal electricity

consumption, the circuit is disconnected by GSM and onlyTSM is installed on the user side, which is expressed as theequivalent circuit in Fig. 4.


Fig. 4 Equivalent circuit of the proposed detection method

Fig. 5 Illegal electricity usage on the branch of node

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TVG is either connected or disconnected by TSMaccording to the control command of AMR system. In thiscase, TVG is transmitted through line impedance of thisbranch and then it is measured on the detecting node. As anexample, it is assumed that Node 1 in Fig. 4 is checked andTSMs connect and disconnect with a low voltage signalwith a high frequency in order. If n number of TSM isinstalled on this node, the ‘node voltage vector’ isexpressed as follows

V node 1 = [V 11 V 12, . . . , V 1n]T (2)

where V11 indicates the measured voltage from the sourceVTVG when the switch SW11 is connected, whereas all theother switches are disconnected. In other words, thosevoltages are the values on the node when the low-voltagesource with a high frequency is connected by the controlcommand without any overlap.The important parameters mentioned above are the ‘node

current vector’ and the ‘node impedance vector’, which areexpressed as follows

inode 1 = [i11 i12, . . . , i1n]T (3)

Znode 1 = [Z11 Z12, . . . , Z1n]T

with Z1j = R1j + jX1j = R1j + j(2pfTVGL1j)

j = 1, 2, . . . , n

(4)

The frequency fTVG in (4) is the frequency of low-voltagesource in TSM installed on the detection method.If the substation of the power delivery system has m

number of nodes and n number of TSMs in each node, thevoltage, current and impedance are expressed as matrices asfollows

V =

V 11 V 21 · · · Vm1V 12 V 22 . . . Vm2

..

. ... . .

. ...

V 1n V 2n . . . Vmn

⎡⎢⎢⎢⎣

⎤⎥⎥⎥⎦ (5)


Fig. 6 Simulation models of the detection method

a Simulation model for shunt connectionb Simulation model for branched connectionc Simulation model for voltage compensation

Fig. 7 Simulation results for shunt connection

a Vnode–AC input voltageb Vout–AC output voltage in the normal casec Vout rns–RMS output voltage in the normal cased Vout rns–RMS output voltage when the shunt resistance Zshunt is connected

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1336 IET Gener. Transm. Distrib., 2013, Vol. 7, Iss. 11, pp. 1332–1343& The Institution of Engineering and Technology 2013 doi: 10.1049/iet-gtd.2012.0287

Fig. 8 Simulation results for branched connection when the system is normal

a Vgate – AC node voltageb Vout – AC output voltagec Ihigh.fr – current of low voltage source with high-frequency on TSMd Vdiff – output voltage of detection model

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i =

i11 i21 · · · im1i12 i22 . . . im2

..

. ... . .

. ...

i1n i2n . . . imn

⎡⎢⎢⎢⎣

⎤⎥⎥⎥⎦ (6)

Z =

Z11 Z12 · · · Z1n

Z21 Z22 . . . Z2n

..

. ... . .

. ...

Zm1 Zm2 . . . Zmn

⎡⎢⎢⎢⎣

⎤⎥⎥⎥⎦ (7)

Using this, the ‘node voltage matrix’ in the overall system canbe described as follows according to Ohm’s law

V = VTVG − i × Z (8)

where VTVG is the low-voltage matrix with a high frequencyin TSM. When the power delivery system has no illegalelectricity consumption, the following equality is satisfied

V calc − Vmeas = 0 (9)

where Vcalc and Vmeas are the voltage matrices of the overallsystem obtained from the computational method andmeasurements from GSM, respectively.An abnormal condition is described when the power

delivery system has illegal electricity usage. To detect this


condition, a branch of the node must be considered, asshown in Fig. 5.If the branch has no illegal electricity usage, this condition

must be satisfied as follows

V node = VTVG = i × Z (10)

However, in the abnormal condition, (10) is modified as follows

V node = VTVG − (i × Z2 + iline × Z1) (11)

where i = iline + iillegal. In addition, illegal electricity usage maydirectly occur to user’s bus. In this case, Z2 becomes zero andthe node voltage is simplified as follows

V node = VTVG − iline × Z (12)

When illegal electricity usage exists on the branch of nodes inthe overall system, (10) is not valid and it can be expressed asfollows

V calc − Vmeas = 0 (13)

In other words, if (13) is valid, illegal electricity usage on theoutside phase of the energy meter exists on the overall powerdelivery system.Input voltage must be disconnected and connected when

the system checks for the branched connection. During thistransition, voltage drop is generated. The AC/AC regulatorof TSM is used to compensate for this voltage drop. In the


Fig. 9 Simulation results for branched connection when the Zillegal1 is connected

a Vout – AC output voltageb Inode – AC current of branch on usersc Ihigh.fr – current of low-voltage source with high-frequency on TSMd Vdiff – output voltage of detection model

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process of compensation, the output voltage is regulated bythe AC/AC regulator, which is controlled by the signal inthe control block of TSM. Note that this signal isconfigured according to the control command of AMR system.In the two cases of the detection schemes, an AC/AC

regulator is used for different purposes. In the case of shuntconnection, the purpose of the AC/AC regulator is tochange the output voltage of TSM to a very low value in ashort period, where this changed output voltage is passed tothe user. However, in the case of branched connection, thepurpose of the AC/AC regulator is to regulate the outputvoltage drop which is generated by the interruption becauseof connection and disconnection of the input voltage. Thus,the AC/AC regulator has an important role in the detectionmethod of illegal electricity usage.Many types of AC/AC regulators are used in electrical

power systems, which are classified as follows: voltageconversion, output voltage response, automatic controlsystem of AC/AC regulator and harmonic influence on thepower system [26–35]. Furthermore, various types ofcommutation strategies are also used in AC/AC regulators[36–37]. In the proposed method, a buck–boost choppertype AC/AC regulator is used because it has a goodresponse and regulation of output voltage.

4 Simulation results

To show the feasibility of the proposed detection method,simulation models of the detection method were


implemented by using MATLAB/Simulink software. Thesimulation models of the detection method consist of threesubsections: simulation model for shunt connection,simulation model for branch connection and simulationmodel for voltage compensation, which is caused byconnection and disconnection of the input voltage for ashort period of time. Three subsections of simulationmodels are shown in Fig. 6.

4.1 Detecting illegal shunt connection

The simulation model for shunt connection is shown inFig. 6a. The parameters used in this model are as follows:Vnode = 220 V, fline = 50 Hz, Li = 200 µH, Ci = 10 µF, L = 4mH, C1, C2 = 0.1 µF of snubber circuit, R1 = R2 = 10 kΩ ofsnubber circuit, Co = 20 µF, Zload = 100 Ω, Fpwm = 10 kHz,Zshunt = 1 µΩ, Kp = 2, KI = 40. To check for shuntconnections, the simulation model changes the magnitudeof output voltage by a small value for a short period of timeaccording to the proportional-integral-derivative (PID)controller command using buck–boost AC/AC converter. Inother words, the process is to change the output voltage toverify the existence of shunt resistance.The first simulation was to disconnect the shunt resistance,

Zshunt, when the system was normal. The simulation wascarried out in three steps.In the first step, the value of desired regulation voltage,

Uref, was changed to 155.5 V and the simulation continuedfor 0.361 s. In the second step, the value of Uref was


Fig. 10 Simulation results for voltage compensation

a Vgate – AC node voltageb Vuser – AC output voltage on userc Vuser rms – RMS of output voltage on user

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changed to 141.4 V and the simulation was carried out from0.361 to 0.6 s. In the final step, the value of Uref wasreturned to 155.5 V and the simulation was carried out from0.6 to 0.8 s. The corresponding results of simulation modelare shown in Fig. 7. When the system was normal, theoutput voltage of the system had been regulated to thedesired regulation voltage according to the PID controller.Note that the output voltage was stabilised to the desiredregulation voltage within 0.1 s.Fig. 7d shows the simulation results when Zshunt was

connected and the system had the shunt connection on thecurrent coil of the energy meter. Similar to the previouscase, three steps were also carried out for the shuntconnection. In the first step, the value of Uref was regulatedto 155.5 V for 0.2 s. In the second step, the value of Uref

was changed to 141.4 V from 0.2 to 0.5 s. In the final step,the value of Uref was returned to 155.5 V from 0.5 to 0.8 s.The results showed that the output voltage had not been

regulated to the desired regulation voltage and it was equalto the input voltage when Zshunt was connected. Thus, thesimulation results confirmed that the shunt connection onthe current coil of the energy meter could be alwaysdetected through the proposed method.

4.2 Detecting illegal branched connection

The simulation model for branched connection is shown inFig. 6b. This model checks for illegal electricity usage onthe outside phase of the energy meter, where the parametersused in this model are as follows: Vnode = 220 V, fline = 50 Hz,


Zload = 100 Ω, Zline1 = Zline2 = 1 Ω, Zillegal1 = Zillegal2 = 100 Ω,Fpwm = 250 Hz, duty ratio D = 0.5, Vtest = 20 V, Ftest = 1.5 kHz.Both control switches of GSM and TSM in the model were

connected and disconnected at the same time. If the controlswitch of GSM was disconnected, the control switch ofTSM was disconnected from the user and then it wasconnected to Vtest. During this time, Vgate is measured andcompared to the computational voltage of gate, where it isused to calculate the voltage difference as follows

V diff = V gate.meas − (V test − iterminal × Z) (14)

where Vdiff is the difference between the measured andcalculated voltage on this node and Vtest is the voltage witha high frequency, which is used on the TSM. iterminal is thebranch current and Z is the total line impedance on the branch.The simulation for branch connection consisted of three

steps. The first step was to implement the model when therewas no illegal electricity usage and the system was normal.In the second step, the simulation model was modified byconnecting the illegal usage, Zillegal1, as shown in Fig. 6b.In the final step, the simulation experiment was changed byconnecting the illegal usage, Zillegal2, as shown in Fig. 6b.Fig. 8 shows the simulation results when the illegal

electricity usage was disconnected. When the system wasnormal, the current of a low voltage with a high frequencyon TSM was unable to pass to the branch, which is shownin the detection point in Fig. 8d. Particularly, the outputvoltage of detection model, Vdiff, was zero. According to(9), the value of Vdiff should be zero when illegal electricity


Fig. 11 Experimental model for branched connection

a Schematicb Layout

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usage on the outside phase of the energy meter does not exist.Fig. 9 shows the simulation results when Zillegal1 wasconnected to the outside phase of the energy meter.

Fig. 12 Snapshot of experimental model for branched connection

a Controller moduleb Gate driver modulec Power switch moduled Measurement modulee Power line module


As shown in Fig. 9, the currents of a low voltage with ahigh frequency were different compared to the normal case.When the low voltage with a high frequency in TSM wasconnected to the proposed detection method, the currentpassed to the branch. In addition, the output voltage ofdetection model was not zero as shown in Fig. 9d.According to (14), the voltage difference between thecalculated and measured voltages on the node was not zerowhen the illegal electricity usage was connected to theoutside phase of the energy meter. Since the simulationresults were consistent to the computational model, theillegal electricity usage because of branched connectioncould be easily detected through the proposed method.

4.3 Voltage compensation

The simulation model for voltage compensation is shown inFig. 6c, which is caused by connection and disconnectionof the node voltage. The purpose of this model is toregulate an output voltage drop that is caused by theinterruption of input voltage when the detection method is


Fig. 13 Experiment results for branched connection

a Power switch signals: CH1 for S1, S2 and S3, CH2 for S4b Voltage measurements: CH1 for AC node (V1), CH2 for TVG (V2)c Voltage measurement of load Z1 (V3)d Current measurement of TVG (I1)

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checking a branched connection. In addition, this modelchecks the influence on the users and node voltage. Bothswitches of GSM and TSM in Fig. 6c create a voltage drop,which can be regulated by using an AC/AC regulator inTSM. The parameters used in this model are as follows:Vnode = 220 V, fline = 50 Hz, Zline1 = 1 Ω, Fswitches = 2 kHz,duty ratio of switches D = 0.5, Vtest = 20 V, Ftest = 30 kHz,Li = 200 µH, Ci = 10 µF, L = 4 mH, C1, C2 = 0.1 µF ofsnubber circuit, R1 = R2 = 10 kΩ of snubber circuit, Co = 20µF, Zload = 100 Ω, Fpwm = 15 kHz, Kp = 2, KI = 40Fig. 10 shows the simulation results for voltage

compensation when Uref was set to 155.5 V. Note that thedesired regulation voltage was equivalent to the input ofPID controller in buck–boost AC/AC converter. The outputvoltages Vuser and Vuser rms–were regulated to the desiredregulation voltage within 0.2 s as shown in Fig. 10b and c.Thus, the voltage drop caused by the interruption of nodevoltage could be regulated when the detection methodchecks for illegal electricity usage on the outside phase ofthe energy meter. In addition, the proposed detectionmethod does not depend on other users.

5 Experimental results

The experiment was carried out on the branched connectionmodel because branched connection is very important part


of our proposed remote detection algorithm of illegalelectricity usage. This experiment model checks for illegalelectricity usage on the outside phase of the energy meter.Fig. 11 shows the experimental model including theschematic and layout for branched connection. As shown inFig. 11, the experimental model included two branches,where the load impedances of first and second user wererepresented as Z1 and Z2, respectively. A test signal couldbe transmitted by the first user’s bus line. The switch‘SW1’ could be either connected or disconnected as anillegal electricity usage, which is controlled by operator.The power switches S1, S2, S3 and S4 were controlled by‘control block’, where both users could be connectedthrough ‘Line 1’, ‘Line 2’ and ‘Line 3’.Fig. 12 shows the snapshot of experimental model, which

consists of a controller module, gate driver module, powerswitch module, measurement module and power linemodule. AVR controller and Toshiba’s photo-couplerTLP250 were used as the control block and gate driver,respectively. Power MOSFETs AQV204 were used for S1,S2 and S3, whereas solid-state relay PDA1-203Z was usedfor S4. LEM’s LV25-P and HAIS 50-P were used as thevoltage and current transducers, respectively.The parameters used in the model are as follows: source

voltage was 110 V AC at 60 Hz; test signal was 10 V AC at2 kHz; switching frequency was 250 Hz; duty ratio of S1,


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S2, and S3 D = 0.5; duty ratio of S4 D = 0.25; Z1 = 100 W; Z3= 60 W; Zillegal = 30 W; Lines 1 and 2 were 3m cable line at600 V with 5 A; Line 3 was 5 m cable line at 600 V with 5 A.Fig. 13 shows the experimental results. Fig. 13a shows the
control signals of power switches, where CH1 signalrepresents the control signals of S1, S2 and S3. In Fig. 13a,CH2 signal represents the control signal of S4, which couldeither connect or disconnect a test signal. CH1 signal ofFig. 13b represents the voltage measurement of V1 on thenode of branches and CH2 signal represents the voltagemeasurement of V2, which was equivalent to test signal.The result showed that the measurement signal wassuccessfully combined with the test signal according to theproposed algorithm. Fig. 13c shows the voltagemeasurement of V3 on the bus line of user. It showed thatthe test signal was not passed into user side. Fig. 13dshows the current measurement of I1 on TVG branch whenillegal electricity usage was connected through the switchSW1. As shown in Fig. 13d, the current was generatedwhen the illegal electricity usage existed on the branch.Thus, the proposed algorithm was able to detect the illegalelectricity usage on the outside phase of energy meter.

6 Conclusions

In this paper, a novel remote detection method was proposedto measure the amount of illegal electricity usage. Theexperiment and simulation results of the proposed methodwere consistent with the theoretical descriptions. When theproposed GSM and TSM were installed in the remotedetection method, illegal usage of electricity could bedetected in real time.

7 Acknowledgments

This work was supported by a grant from the Basic ScienceResearch Programme through the National ResearchFoundation of Korea (NRF) funded by the Ministry ofEducation, Science and Technology (2012R1A1A2043822)and the Technology Innovation Programme of theKnowledge economy (no. 10041834) funded by theMinistry of Knowledge Economy (MKE, Korea).

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Fig. 15 Steady-state equivalent circuit of buck–boost chopper-typeAC/AC converter

Fig. 14 Circuit configuration of buck–boost chopper type AC/ACvoltage regulator

Fig. 16 Structure of automatic control system of AC/AC regulator

www.ietdl.org
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9 Appendix: AC/AC converter and controlsystem

A buck–boost chopper-type AC/AC regulator is used in thispaper. The circuit configuration of buck–boost chopper-typeAC/AC voltage regulator is shown in Fig. 14 [26].This circuit is used in one-phase system, which allowed

regulating the swell and the sag of output voltage. Theinductor, Li, and the capacitor, Ci, are used as an input filterto absorb high harmonics of current. Two switches S1 andS2 are bidirectional, which represents the insulated gatebipolar transistor (IGBT). The inductor, L, stores energyand transfers to the output side. S1 connects anddisconnects the power source, which is used to regulate theenergy transmission of L. S2 provides the stored energyfrom L to the output side when S1 is disconnected. TheseIGBT switches are controlled by pulse-width modulationsignals with a constant duty ratio. The capacitor of outputfilter, Co, reduces the output voltage ripple.Considering the transfer function of the converter, the

average inductor voltage during one switching period isdefined as follows [26]

uL(t) = Dui(t)− (1− D)uo(t) (15)

where D is the duty ratio, and ui(t) and uo(t) are the averageAC input voltage and the output voltage during theswitching period, respectively.The equivalent circuit of the converter in steady-state mode

is shown in Fig. 15. Note that Zo is the equivalent resistance ofload.Based on the equivalent circuit, the total impedance can be

expressed as follows

Z = Zo + jvL

D(1− D) (16)

where Z is the total impedance and ω is the angular frequencyof line voltage. According to Kirchhoff’s law, the inputcurrent of the circuit is given by

I i =DUi

(1− D)Z (17)

In addition, the output voltage of the circuit is given by

Uo = − DZo

(1− D)Z U i (18)

According to the transfer function of AC/AC converter, theimplementation of automatic control system is possible. PIDautomatic controller can be used in the AC/AC regulator ofthis system to detect illegal electricity usage.The corresponding structure of automatic control system is

shown in Fig. 16. The automatic control system measures therms value of AC voltage on the load resistance. Then, itcompares to the reference voltage, which is the desiredregulation output voltage of AC/AC regulator. The controlsystem transmits the compared result to the input of PID


controller, where the voltage error, ue, is expressed as follows

ue = uref − umeas (19)

where uref is the rms value of desired regulation voltage andumeas is the rms value of measured voltage on the loadresistance. Note that the output value of the controller is theduty ratio, D. The overall transfer function of the controlleris given as follows

Fcontroller = Kp +KI

KS+ KDs (20)

where Kp, KI and KD are the proportional, integral andderivative gains, respectively. The output of the controller isexpressed as follows

D = Kpue(t)+ KI

∫ue(t)dt + KD

due(t)

dt(21)

Thus, the AC/AC regulator model and the automatic controlsystem in the proposed detection method can beimplemented according to the PID automatic controller.


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