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Sensor Fault Detection and Isolation of a Single
Phase PWM Rectifier for Electric Railway
Traction Using Pole Placement Technique
K.Kavinelavu
PG Student
Department of Electrical and Electronics Engineering
Sri Manakula Vinayagar Engineering College, Puducherry ,India.
e-mail:[email protected]
Abstract-Modern railway traction power systems are
fed by 2×25 kv/50 Hz single phase ac current sources
or by 1500 vdc voltage from electric railway substations.
This paper presents an easy and a robust sensor fault
detection and isolation (FDI) of a single phase PWM
rectifier for electric railway traction application. PR
controller is used to regulate ac currents in single phase
system, in order to obtain both zero magnitude and
phase errors. Catenary current sensor and dc link
voltage sensor failures of the single phase PWM
rectifier are considered. Fault detection and isolation
method is mainly depend on pole placement based
observed values and threshold values. This method
allows a good detection and isolation of the sensor fault.
Simulation results are presented to illustrate the
effective performance of the fault detection and
isolation.
Fig. 1. Electrical railway traction system.
in electric railway traction system and explain the use
of this converter in modern locomotives [4],[15].
In mostly, the interest on the single phase PWM
rectifier for electric railway power systems has
greatly increased. For the line side converter, control
strategies, dc voltage ripple reduction, power quality,
and harmonic analysis are the most treated problems
in the literature [6]-[10].
In electric railway traction system, the motor side
converter and induction motor performances are
mostly depend on the availability of the grid side
converter. The GsC utilizes a closed loop control to
regulate the dc link voltage as well as the input
current. The control loop requires one current sensor,
a dc-link voltage sensor, and a grid voltage sensor.
Therefore, invalid measurement, due to sensor
failures, perturbs seriously the performance of the
GsC and may cause system shutdown. In this
circumstance, sensor fault detection and isolation
(FDI) should be achieved to improve the rectifier
availability.
Fault detection and isolation, and fault tolerant
control for the three phase drive systems have been
Index terms-Electric traction, fault detection and
isolation (FDI), pole placement, sensor fault, single
phase pwm rectifier.
I.
INTRODUCTION
N
owadays electric railway traction power
systems are fed by 2×25 kv/50 Hz single phase
ac current sources or by 1500 Vdc voltage from
electric railway substations [1]-[3]. This traction
system consists of a typical ac/dc/ac power system is
shown in Fig. 1. The grid side converter (GsC) is a
single phase PWM boost rectifier.
Commonly, the use of a single phase PWM
rectifier allows a sinusoidal absorption of the inverter
input current, power factor increase, and the dc link
voltage control [4]-[5]. These advantages are required
1
largely reported in the literature; however, very few
works have dealt with a single phase PWM rectifier
especially for electric traction. In [11], the authors
have focused on single phase rectifier static switch
failures in railway traction and in [12], the authors
have investigated speed sensor FDI for induction
motor drives used in electric traction.
FDI model-based methods like parity space
method or observer based methods have been
attractive during recent years. Parity space method
has been used for FDI in WECS [13]-[15] and
electrical drives, but cannot lead to reconfiguration
control. Observer – based methods are preferred
when reconfiguration is aimed. The proposed method
does not require the single phase rectifier model but
only the switch control signal value. Therefore, this
model overcomes the problem related to power
converter’s model described in [16].
The structure of this paper is as follows: In section
II, the system description and its control strategy are
presented. Section III deals with the PWM rectifier
state space model to estimate the catenary current
and the dc bus link voltage using observer. Section
IV describes the FDI method. Section V concerned
with simulation results. Section VI cocerned with
conclusion.
external vdc control loop using a proportional
integrator (PI) controller maintains the dc link
voltage equal to its reference vdc*, when current load
or voltage grid varies. An inner loop controls the
input current rectifier using a proportional-resonant
(PR) controller in order to ensure unity power factor
operation and sinusoidal current absorption with a
zero phase and zero steady-state errors. The control
principle is illustrated in Fig. 2.
Fig. 2. Control strategy of single phase grid side
converter.
Grid synchronization is performed using a second
order generalized integrator (SOGI)-frequency look
up loop (FLL) [17]-[19]. In order to increase
robustness against grid faults, voltage grid is shared
in positive and negative sequences using a
quadrature-signal generation (QSG).
II. SYSTEM DESCRIPTION AND CONTROL
STRATEGY
The system under study is modeled using the
following state equations, where, S is the binary
switching control signal, and where the dead time is
neglected
𝑣𝑔 = −𝑟𝑖𝑐 − 𝐿
𝑖𝑐𝑓 = 𝑐𝑓
𝑑𝑖𝑐
𝑑𝑡
A. PR Current Control
The PR controller is generally used to regulate ac
currents in three phase system [20]-[24], as well as
single phase system, in order to obtain both zero
magnitude and phase errors. The transfer function of
single and three phase PR controllers and filters can
be derived using internal model control, modified
state transformation or frequency domain approach.
The grid current controller is implemented using
the proportional resonant PR controller which is
defined as
+ 𝑣𝑖𝑛
𝑑𝑣𝑑𝑐
𝑑𝑡
𝑖𝑑𝑐 = 𝑖𝑐𝑓 + 𝑖𝑙𝑑
(1)
where, as reported in Fig. 2, ic is the catenary inverse
current, 𝑖𝑐𝑓 is the current in the capacitor, and 𝑖𝑙𝑑 is
the load current. 𝑣𝑔 is the grid voltage and vdc is the
dc-link voltage. The output current converter current
𝑖𝑑𝑐 and the input rectifier voltage Vin are expressed as
𝑣𝑖𝑛 = (2𝑆 − 1)𝑣𝑑𝑐
𝑖𝑑𝑐 = −(2𝑆 − 1)𝑖𝑐 .
(2)
𝐺𝑐 (𝑠) = 𝐾𝑝 + 𝐾𝑖
The goal of the system is to ensure unity power
factor operation and dc link voltage regulation. An
𝑆
𝑆 2 +𝜔𝑜2
(3)
where the coefficients 𝐾𝑖 and 𝐾𝑝 are the resonant
control and the proportional gain, respectively.
2
The system desired dynamic has been tuned
through a proportional gain in terms of phase, gain
margins, and bandwidth. The PR controller transfer
function is expressed by (3), where the second term
of the right side represents the generalized integrator
block (GI). This is characterized by an infinite gain at
all resonance frequency and a null gain at all other
frequencies. Therefore, the PR is able to track a
sinusoidal current reference without a steady state
error.
Fig. 3 illustrates the structure of SOGI-QSG-FLL,
where 𝜔𝑓𝑓 = 314 rad/sec and k are the fixed
frequency and gain. The 𝛾 is a negative gain used to
eliminate the error in the dc component by varying 𝜔
of the SOGI until to the input frequency [17].
III. STATE SPACE MODEL FOR A PWM
RECTIFIER
By using equations (1) and (2), the state space
model of the rectifier is given by
𝑥̇ = 𝐴𝑥 + 𝐵𝑢 + 𝐷𝑣
𝑦 = 𝐶𝑥
(7)
where A is the system matrix
B. Reference Current for PR Current Control
Measuring the current references in terms of
phase, frequency, and amplitude is very important
when the power flow between the grid and loads
directly depend on it. Therefore, the reference current
ic* is giyen by
𝑖𝑐 ∗ = 𝐼𝑐 √2sin(𝜃𝑔 )
−
A
𝑟
2𝑆−1
𝐿
=[−2𝑆+1
𝐿
0
𝑐𝑓
AS= 0 =[
𝑟
−1
𝐿
𝐿
1
𝑐𝑓
̂𝑦= C𝑥̂
To obtain unity power factor, the fundamental
phase angle 𝜃 of 𝑖𝑐 should be equal to the
fundamental phase angle of 𝜃𝑔 of 𝑣𝑔 . The SOGIQSG is used to generate 𝑣𝑔+ , 𝑣𝑔− of the supply
voltage 𝑣𝑔 . Their transfer functions are expressed as
+
Q(s)
=
𝑣𝑔
−
𝑣𝑔
𝑣𝑔
𝑘𝑤′𝑠
(s) = 𝑠2+𝑘𝑠+𝜔′2
𝑘𝑤′2
(s) = 𝑠2+𝑘𝑠+𝑤′
(9)
0
𝑟
1
𝐿
AS= 1 =[ −1
𝐿
−
],
𝑐𝑓
0
].
(11)
A. Design of Observer
Luenberger state observer [25],[26] is used for the
estimation of the dc link voltage 𝑣𝑑𝑐 and catenary
current 𝑖𝑐 . This observer can be expressed by
̂𝑥̇ = A𝑥̂ + Bu +Dv + 𝐿𝑜𝑏 (𝑦 − 𝑦̂)
Fig. 3. SOGI-FLL structure.
𝑣𝑔
(8)
Now, the state vector is defined by the catenary
current 𝑖𝑐 and the dc bus voltage 𝑣𝑑𝑐
𝑥 = [𝑖𝑐 𝑣𝑑𝑐 ]
𝑢 = 𝑣𝑔 and 𝑣 = 𝑖𝑙𝑑
(10)
S is the switching control signal. It can take two
values 1 or 0.
−
=
0].
The input matrices B and D are
1
0
−
𝐵 = 𝐿 , 𝐷 = −1
𝑐𝑓
0
𝐼𝑐 √2 = 𝑖𝑙𝑑 + 𝑖𝑃𝐼
(4)
where 𝑖𝑃𝐼 is the output of the dc bus voltage of PI
controller and 𝜃𝑔 is the phase angle obtained using
the SOGI-QSG-FLL.
D(s)
] , 𝐶 = [1
(12)
A state correction factor 𝐿𝑜𝑏 (𝑦 − 𝑦̂) is defined as
the difference between the measurement and observer
quantity, where L is matrix gain is to chosen to define
the observer dynamic.
Pole placement based poles should be proportional
to system poles. Therefore, pole placement is a
method employed to place the closed loop poles of a
plant in pre-determined locations. Placing poles is
desirable because the location of the poles
corresponds directly to the eigenvalues of the system,
(5)
(6)
3
which control the characteristics of the response of
the system.
V. SIMULATION RESULTS
IV. FDI METHOD
To illustrate the FDI method development,
different performance conditions are examined by
using simulation in Matlab/Simulink software.
System parameters are given in Table II. Simulation
model of the single phase PWM rectifier is shown in
below Fig. 4.
The single phase PWM rectifier control requires
accurate dc bus voltage and line current
measurements. If any sensor fault occur in the
converter, it will degrade the performances of the
converter and will cause the system shutdown.
Therefore, to ensure the operation continuity and
prevent from system shutdown,a fast FDI method
should be performed. Faults that can affect current or
voltage sensor are presented in Table I, where 𝑋𝑟 and
𝑋𝑚 are the real and sensor output quantities,
respectively. During the system operation, only one
sensor fault is considered. In this paper, gain fault is
considered during operation.
Fig. 4. Simulink model of single phase PWM rectifier
with FDI.
TABLE I
ELECTRIC SENSOR FAULT
Fault type
Measured signal
Gain fault
Xm = (1+G) Xr
Offset
Xm = Xr + Xoffset
Noise
Xm = Xr + n(t)
Simulink model for control strategy of the single
phase PWM rectifier is shown in Fig. 5.
A. Threshold establishment
The FDI method is based on comparison of
observed values to a defined threshold value. The
threshold value is carefully chosen to minimize the
false alarm rate due to system parameter variations,
operating points variation [27] and [28]. If the
threshold value is low, fault detection increases. If
the threshold value is high, fault detection decreases
and the fault may not be detected. The threshold
values for dc link voltage is 𝑇𝑣 = 0.1 and the
threshold value for catenary current 𝑇𝑖 = 0.05.
Fig. 5. Model for control strategy of single phase
PWM rectifier.
For simulations, the dc link voltage sensor fault
occurs at 0.6s to 0.8s is shown in Fig. 6.
B. FDI
FDI is based on the comparison of observed
values and threshold values 𝑇𝑣 and 𝑇𝑖 . Therefore, this
comparison block is used to generate Boolean error is
in the form of square waveforms. Therefore, fault
detection is achieved by using Boolean error. The
Boolean error is set to 1 or 0. If it is set to 1, the dc
link voltage sensor may be faulty. If it is set to 0, the
current sensor may be faulty.
Fig. 6. DC link voltage sensor Fault detection at 0.6s
to 0.8s.
4
VI. CONCLUSION
An easy and fast pole placement based sensor
fault detection and isolation of a single phase PWM
rectifier has been developed and simulated. A
proportional-resonant (PR) controller is used to
ensure unity power factor operation and sinusoidal
current absorption with zero phase and zero steadystate errors. The FDI method is based on observed
values and threshold values. Simulation results shows
the effectiveness of the FDI method.
Fig. 7. DC link voltage sensor fault isolation at 0.6s
to 0.8s.
REFERENCES
[1] M. Brenna and F. Foiadelli, “Analysis of the
filters installed in the interconnection points between
different railway supply systems,” IEEE Trans. Smart
Grid, vol. 3, no. 1, pp. 551–558, Mar. 2012.
[2] M. Brenna, A. Capasso, M. C. Falvo, F. Foiadelli,
R. Lamedica, and D. Zaninelli, “Investigation of
resonance phenomena in high speed railway supply
systems: Theoretical and experimental analysis,”
Elect. Power Syst. Res., vol. 81, no. 10, pp. 1915–
1923, 2011.
[3] C. Bae, D. Jang, Y. Kim, S. Chang, and J. Mok,
“Calculation of regenerative energy in DC 1500 V
electric railway substations,” presented at the 7th Int.
Conf. Power Electronics, Daego, Korea, Oct. 2007.
[4] O. Stihi and B. T. Ooi, “A single phase controlled
current PWM rectifier,” IEEE Trans. Power
Electron., vol. 3, no. 4, pp. 453–459, Oct. 1988.
[5] D. Dong, T. Thacker, I. Cvetkovic, R. Burgos, D.
Boroyevich, F. Wang, and G. Skutt, “Modes of
operation and system-level control of singlephase
bidirectional PWM converter for microgrid systems,”
IEEE Trans. Smart Grid, vol. 3, no. 1, pp. 93–104,
Mar. 2012.
[6] M. Brenna, F. Foiadelli, and D. Zaninelli, “New
stability analysis for tuning PI controller of power
converters in railway application,” IEEE Trans. Ind.
Electron., vol. 58, no. 2, pp. 533–543, Feb. 2011.
[7] Z. Shu, S. Xie, and Q. Li, “Single-phase back-toback converter for active power balancing, reactive
power compensation, and harmonic filtering in
traction power system,” IEEE Trans. Power
Electron., vol. 26, no. 2, pp. 334–342, Feb. 2011.
[8] H. Li, K. Zhang, H. Zhao, S. Fan, and J. Xiong,
“Active power decoupling for high-power singlephase PWM rectifiers,” IEEE Trans. Power
Electron., vol. 28, no. 3, pp. 1308–1319, Mar. 2013.
Fault is created between dc link capacitor and the
load at the time period of 0.6s to 0.8s. This fault can
be isolated using PR controller is shown in Fig. 7. In
this PR controller the transfer function is mainly
based on pole placement.
Fig. 8. Simulation results for sensor fault detection
and isolation of dc link voltage.
FDI method is based on the comparison between
observed values and threshold values. Here, the
threshold value for dc link voltage is 𝑇𝑣 =0.1.
Therefore the simulation results for sensor fault
detection and isolation of dc link voltage is shown in
Fig. 8.
TABLE II
SYSTEM PARAMETERS
Parameter
Value
220V
RMS voltage supply 𝑣𝑔
Line inductance Ln
DC link voltage 𝑣𝑑𝑐
DC link capacitor 𝑐𝑓
1mH
400V
3300µf
5
[9] W. Song, X. Feng, and K. Ma Smedley, “A
carried-based PWM strategy with the offset voltage
injection for single phase three-level neutralpointclamped converters,” IEEE Trans. Power Electron.,
vol. 28, no. 3, pp. 1083–1095, Mar. 2013.
[10] B. Bahrani and A. Rufer, “Optimization-based
voltage support in traction networks using active lineside converters,” IEEE Trans. Power Electron., vol.
28, no. 2, pp. 673–685, Feb. 2013.
[11] A. M. S. Mendes, R. F. Rocha, and A. J.Marques
Cardoso, “Analysis of a railway power system based
on four quadrant converters operating under faulty
conditions,” in Proc. IEEE Int. Elect. Mach. Drives
Conf., Niagara Falls, Canada, 2011, pp. 1019–1024.
[12] H. Abu-Rub, M. Diguet, Z. Krzeminski, and A.
Lawicki, “Speed and load torque observer application
in high-speed train electric drive,” IEEE Trans. Ind.
Electron., vol. 57, no. 2, pp. 565–574, Feb. 2010.
[13] B. Tabbache, M. Benbouzid,AKheloui, and J-M.
Bourgeot, “Sensor faulttolerant control of an
inductionmotor based electric vehicle,” in Proc. 14th
Conf. Power Electron. Appl., Aug./Sep. 2011, pp. 1–
8.
[14] H. Berriri,W. Naouar, and I. Slama-Belkhodja,
“Easy and fast sensor fault detection and isolation
algorithm for electrical drives,” IEEE Trans. Power
Electron., vol. 27, no. 2, pp. 490–499, Feb. 2012.
[15] C. W. Chan, S. Hua, and Z. Hong-Yue,
“Application of fully decoupled parity equation in
fault detection and identification of DC motors,”
IEEE Trans. Ind. Electron., vol. 53, no. 4, pp. 1277–
1284, Jun. 2006.
[16] S. Karimi, A. Gaillard, P. Poure, and S. Saadate,
“FPGA-based real time power converter failure
diagnosis for wind energy conversion systems,” IEEE
Trans. Ind. Electron., vol. 55, no. 12, pp. 4299–4308,
Dec. 2008.
[17] P. Rodr´ıguez, A. Luna, R. S. Mu˜noz-Aguilar,
I. Etxeberria-Otadui, R. Teodorescu, and F.
Blaabjerg, “A stationary reference frame grid
synchronization system for three-phase gridconnected power converters under adverse grid
conditions,” IEEE Trans. Power Electron, vol. 27,
no. 1, pp. 99–112, Jan. 2012.
[18] P. Rodriguez, A. Luna, I. Candela, R.
Teodorescu, and F. Blaabjerg, “Grid synchronization
of power converters using multiple second order
generalized integrators,” presented at the IEEE
34thAnnu. Conf. Industrial Electronics Society,
Orlando, FL, USA, Nov. 2008.
[19] M. Bejaoui, I. Slama-Belkhodja, E. Monmasson,
B. Marinescu, and L. Charaabi, “FPGA design of a
robust phase locked loop algorithm for a three phase
PWM grid connected converter,” presented at the
13th Eur. Conf. Power Electron. Appl., Barcelona,
Spain, pp. 8–10, Sep. 2009.
[20] A. Hasanzadeh, O. C. Onar, H. Mokhtari, and A.
Khaligh, “A proportional-resonant controller-based
wireless control strategy with a reduced number of
sensors for parallel-operated UPSs,” IEEE Trans.
Power Delivery, vol. 25, no. 1, pp. 468–478, Jan.
2010.
[21] Y. Shuitao, L.Qin, F. Z. Peng, andQ. Zhaoming,
“A robust control scheme for grid-connected voltagesource inverters,” IEEE Trans. Power Electron., vol.
58, no. 1, pp. 202–212, Jan. 2011.
[22] Z. Wei, D. D.-C. Lu, and V. G. Agelidis,
“Current control of gridconnected boost inverter with
zero steady-state Error,” IEEE Trans. Power
Electron., vol. 26, no. 10, pp. 2825–2834, Oct. 2011.
[23] R. Teodorescu, F. Blaabjerg, M. Liserre, P.C.
Loh, “Proportional-resonant controllers and filters for
grid-connected voltage-source converters,” IEE proc.
Electric power Appl., vol. 153, no. 5, pp. 750-762,
sep. 2006.
[24] M. Ciobotaru, T. Kerekes, R. Teodorescu, A.
Bouscayrol, “PV inverter simulation using
MATLAB/Simulink graphical environment and
PLECS blockset,” IEEE trans. Ind. Electron., pp.
5313-5318, Mar. 2006.
[25] D. G. Luenberger, “An Introduction to
observers,” IEEE Trans. Autom. Control, vol. AC16,
no. 6, pp. 596–602, Dec. 1971.
[26] G. Ellis, Observers in Control Systems: A
practical Guide. NewYork, NY, USA: Academic,
2002.
[27] L. Massimiliano, A. Ferrara, A. F. De Loza, and
L. M. Fridman, “Manipulator fault diagnosis via
higher order sliding-mode observers,” IEEE Trans.
Ind. Electron., vol. 59, no. 10, pp. 3979–3986, Oct.
2012.
[28] A. Emami-Naeini, M. M. Akhter, and S. M.
Rock, “Effect of model uncertainty on fault
detection: The threshold selector,” IEEE Trans.
Autom. Control, vol. 33, no. 12, pp. 1106–1115, Dec.
1998.
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