2015 IEEE Power, Communication and Information Technology Conference (PCITC) Siksha ‘O’ Anusandhan University, Bhubaneswar, India.
Enhancement of Voltage profile of Wind Connected System by Power Filter Compensation Scheme Mohit Kumar Jain
Prof. Ratna Dahiya
Department of Electrical Engineering National Institute of Technology Kurukshetra, Haryana
[email protected]
Department of Electrical Engineering National Institute of Technology Kurukshetra, Haryana
[email protected]
Abstract— Wind energy has become increasingly popular in last two-three decades. Renewable energy source using wind energy supply power in remote sectors or it can be use to fed power to the grid connected power systems. Changing in load or wind speed can cause power quality issues. Present paper represent a FACTS based PFC (power filter compensator) controlled by tri-loop controller which improves voltage profile of wind energy system. The proposed power filter compensator is driven by tri-loop controller and error fed to PI or PID controller which gives output to PWM generator for generating signals and it operates IGBT switch for capacitor bank to compensate reactive power and improves voltage profile of the power system. To demonstrate the working of technique a simulation model is developed for several operations in MATLAB/SIMULINK software environment.
causes major power quality issues like variation in voltage, current, harmonics, poor power factor etc. [3,4]
Keywords- FACTS; power filter compensator; wind energy; PID controller;PI controller; Tri loop controller
I.
INTRODUCTION
Energy demand increases rapidly from last two or three decades as fossil fuel is drawn in the world. When fossil fuels will be burned toxic gases cause the pollution in the environment and responsible in global warming. Wind energy has become the most popular renewable source of energy in this scenario. Wind system produced energy by several generator schemes like a doubly fed induction generator (DFIG), squirrel cage induction generator (SCIG) and direct drive synchronous generator [1-2] but SCIG is the most preferable generator scheme for wind energy system because it is standalone and constant speed operated system. Fluctuation in power and voltage due to variable load is the main problem in the standalone wind generating system so the system becomes unstable and it can be reason for equipment failure in the system. A power filter compensation scheme is employed to enhance the voltage profile of the system against dynamic load and varying wind speed. In modern grid systems sudden change of loads is a common issue and these loads are basically non-linear loads such as drives, telecommunication load and home appliances which have highly non- linear characteristics, it
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The WECS is connected to grid system or it can also be used as a standalone system for supplying power in remote areas. However a change in wind speed can affect quality of power in grid systems. Dynamic load variation and velocity of wind cause a change in prime mover, energy and corresponding injected electrical power into grid connected system [5]. Different methods have been suggested for improvement of voltage profile for such network. Some of the methods proposed through controlling the excitation of generator and some methods through FACTS devices by using STATCOM, UPFC and fuzzy controllers [6,7]. FACTS devices are very costly and increased installation cost of system. This paper presents FACTS based power filter compensation scheme (PFC) to stabilize voltage of the wind connected energy system. The proposed method based on a tri loop controller driven FACTS device which calculate total error (et) from its all three loops and fed to PWM through PID or PI controller in the form of pulses so it operate IGBT switches for capacitor bank which improves the voltage profile by supplying reactive power to the system. A single line diagram of proposed method is shown in fig: 1. A wind turbine is connected to self-excited induction machine of rating 11 KV and 3.6 MVA, generated power is supplied to the load through a 30 km transmission. Two transformers are used in system, where first transformer step up the voltage and another is distribution transformer for step down the voltage. The proposed PFC scheme is connected at load bus and a hybrid load (linear and nonlinear load) is connected at the end.. The wind turbine model is developed on the basis of steady-state power characteristic of the turbine C
⎛C ⎞ 3 CP ( λ , β ) = C1 ⎜ 2 − C3 β − C4 ⎟ e λi + C6 λ λ ⎝ i ⎠
(1)
2015 IEEE Power, Communication and Information Technology Conference (PCITC) Siksha ‘O’ Anusandhan University, Bhubaneswar, India. Where S is the area swept by the rotor blades, ρ is the air density and v is the wind speed. Cp is the fraction of the wind captured by a wind turbine is known as the power coefficient factor. The pitch angle β of rotor blades and λ is tip speed ratio. 1
λi
=
1
λ + 0.08β
−
0.035
1
β 3 + 1 λi
=
1
λ + 0.08β
−
0.035 β 3 +1
(2)
The based wind speed is selected at 12m/s and the base rotational speed is set at 1.2 times of the generator synchronous speed.
Fig. 2.
Power Filter compensator structure
III. SIMULATION OF TRI LOOP CONTROLLER Fig. 1.
Single Line diagram of wind connected AC system
II. POWER FILTER COMPENSATOR (PFC) Power filter compensator is a low cost compensator with series and shunt filters, filters provide additional reactive compensation to the system for improvement in voltage profile. PID and PI controller based tri loop controller calculate errors in form of pulses for pulse width modulation (PWM) in on-off timing sequence, these switching pulses are fed to PWM [8-9]. Power filter compensator is connected with capacitor bank and a universal bridge (uncontrolled rectifier) is connected after capacitor bank. Two IGBT switches are employed in the circuit as shown in Fig. 2, when one switch to another will be off and that time resistor and inductor is working as a low - pass filter and when first switch goes off second switch turn on that resistor and inductor will be out of circuit and capacitor bank feed reactive power by capacitive admittance to the grid. These switches are controlled by tri loop controller. Power filter compensator takes values of load voltage and load current from load bus and analyse error in tri loop controller as shown in Fig. 2.
Tri loop controller has fed error signal to PI or PID controller, it has basically three loops, first loop is for voltage stabilization that mean root mean square (RMS) value of voltage error of load bus tracked by this loop and try to kept voltage near at 1 p.u. Second loop is for load current of bus that is current error tracking loop, in case of load excursions and change in velocity of wind, variations are compensated by loop and third loop maintain maximum energy utilization under varying wind conditions and load as shown in Fig. 3 [10]. Total error of these three loops is fed to PI or PID controller, output signal processed by PI or PID controller send to PWM generator, PWM operate switches through these signals for compensation. IGBT switches are controlled by the output of PWM pulses so total admittance of control circuit changes in different conditions, it happens due to switching operation of the IGBT. PWM get these signals from PID controller with the proportion of gain 1 to 10. The Tri loop controller makes system economic and efficient compared to other FACTS compensation scheme, total error of tri loop controller calculated by changing in voltage at load bus, current at load bus and power at load bus.
2015 IEEE Power, Communication and Information Technology Conference (PCITC) Siksha ‘O’ Anusandhan University, Bhubaneswar, India. t
y (t ) = K P .e(t ) + ∫ K I .e(τ ).dτ + K D . 0
dy dx
(6)
V. SIMULATION AC SYSTEM MODEL The AC system for proposed method is shown in Fig. 4. An induction generator driven by a wind turbine generates the power. This generation system is connected to load through a transmission line of 30 k.m. these loads are linear and non-linear in nature. PWM controller with tri loop controller is connected at load bus for improving the results, a fixed capacitor bank is also connected on load bus in the system.
Fig. 3.
Tri loop controller structure
IV. PI AND PID CONTROLLER A PID and PI controller entails added design resilience, since it involves three promptly adjustable terms. This form of controller is used in industrial process widely for control applications. In many cases, the nominal plant transfer function G(s) is unknown, and the PID design is based on a step response analysis of the process, the proportional gain of PID are KP, the time integral TI, and the derivative time TD, tuned on-line or manually adjusted to obtain the best work and in PI controller only TI and KP are adjusted. The transfer function HPID(s) of the PID controller in sdomain are below,
H PID ( s ) = K P +
KI Y ( s) + KDs = P + I + D = s E ( s)
(4)
Or,
H PID ( s ) = K P (1 +
1 + TD s ) TI s
K K Where, TI = P and TD = D KI KP Here Y(s) is the output signal of the controller And E(s) is error signal. PID controller output in time domain is.
Fig. 4.
(5)
Simulated wind energy AC system
VI. SIMULATION RESULTS The results are obtain for proposed PFC scheme under PI and PID controller using of MATLAB Simulink software. Case a) PWM based PFC controller without compensation The dynamic response of voltage and current in per unit rms value at sending end bus is shown in Fig. 5 and 6, these waveforms are trace without using compensation scheme and found fluctuation in voltage and current after load excursion at time 0.16 sec.
2015 IEEE Power, Communication and Information Technology Conference (PCITC) Siksha ‘O’ Anusandhan University, Bhubaneswar, India. Voltage and current in per unit rms value at load bus is shown in Fig. 7 and 8, fluctuation of load voltage and current are high when compensation scheme is not used.
3
2.5
1.02
Load current in pu
✳❅■❄❉ ■❇❅■❄ ✶❏● ▼ ❁❇❅ ❉ ■❐◆
1.01 1 0.99 0.98 0.97
2
1.5
1
0.96
0.5
0.95 0.94
0
0.93 0.92
0
0.05
0.1
0.15
0.2 Time in Sec
0.25
0.3
0.35
0
Variation of sending end voltage v/s time without any compensation
1.2
0.25
0.3
0.35
0.4
Variation of Load end current v/s time without any compensation
Fig. 11 and 12 are showing voltage and current waveform of load bus with PFC controller using PI and it observe that voltage profile of load bus is better now and current waveform is smooth, load voltage approaches toward 1 p.u.
1 0.8 0.6 0.4
1.02
0.2
1.01
0
0.05
0.1
0.15
0.2 Time in Sec
0.25
0.3
0.35
1
0.4
Sending end voltage in pu
✳❅■❄❉ ■❇❅■❄ ❃◆❒ ❒❅■▼❉ ■❐◆
1.4
Fig. 6.
Variation of sending end current v/s time without any compensation
1.4
1.2
✬❏❁❄ ❖❏● ▼ ❁❇❅ ❉ ■❐◆
0.2 Time in sec
Voltage and current waveform shown in Fig. 9 and 10 are response of sending voltage and current when PFC controller is used in the system, fluctuation in voltage and current become in PI controller.
1.6
1
0.99 0.98 0.97 0.96 0.95 0.94 0.93
0.8
0.92 0.6
0
0.4
Fig. 9.
0.2
0
0.15
Case b) PWM based PFC controller with PI controller compensation
1.8
0
0.1
0.4
Fig. 8. Fig. 5.
0.05
0
Fig. 7.
0.05
0.1
0.15
0.2 Time in Sec
0.25
0.3
0.35
Variation of Load end voltge v/s time without any compensation
0.4
0.05
0.1
0.15
0.2 Time in Sec
0.25
0.3
0.35
0.4
Variation of sending end voltage v/s time with PI controller
2015 IEEE Power, Communication and Information Technology Conference (PCITC) Siksha ‘O’ Anusandhan University, Bhubaneswar, India. Waveforms in Fig. 15 and 16 are dynamic response of load voltage and current in p.u., voltage profile is better and stabilize than other two observations, response of current waveform is also better than two other cases.
2.5
1.02 1.01
1.5
✳❅■❄❉ ■❇❅■❄ ✶❏● ▼ ❁❇❅ ❉ ■❐◆
Sending end Current in pu
2
1
0.5
0
0
Fig. 10.
0.05
0.1
0.15
0.2 Time in Sec
0.25
0.3
0.35
0.98 0.97 0.96 0.95 0.94 0.93
0.4
0.92
Variation of sending end current v/s time with PI controller
1.5
1 0.99
0
Fig. 13.
0.05
0.1
0.15
0.2 Time in Sec
0.25
0.3
0.35
0.4
Variation of sending end voltage v/s time with PID controller
1
0.3
✳❅■❄❉■❇ ✣◆❒❒❅■▼❉■ ❐◆
Load Voltage in pu
0.35
0.5
0.25
0.2
0.15 0
0
Fig. 11.
0.05
0.1
0.15
0.2 Time in Sec
0.25
0.3
0.35
0.4
0.1
Variation of Loadend voltage v/s time with PI controller
0
Fig. 14.
0.05
0.1
0.15
0.2 Time in Sec
0.25
0.3
0.35
0.4
Variation of sending end current v/s time with PID controller
1.4
1.4 1.2
1.2
✬❏❁❄ ✶❏● ▼ ❁❇❅ ❉ ■❐◆
Load current in pu
1
0.8
0.6
0.4
1
0.8
0.6
0.4 0.2
0.2 0
0
Fig. 12.
0.05
0.1
0.15
0.2 Time in Sec
0.25
0.3
0.35
0.4
Variation of Load end current v/s time with PI controller
Case c) PWM based PFC with PID controller compensation Waveforms of sending end voltage and current are shown in Fig. 13 and 14 observed with PFC using PID controller, dynamic response of voltage in fast and current become smoother.
0
0
Fig. 15.
0.05
0.1
0.15
0.2 Time in sec
0.25
0.3
0.35
0.4
Variation of Load end voltage v/s time with PID controller
2015 IEEE Power, Communication and Information Technology Conference (PCITC) Siksha ‘O’ Anusandhan University, Bhubaneswar, India. [9]
T. A. Seoud, A. M. Sharaf, “A novel modulated power filtercompensator scheme for standalone wind energy utilizationsystems”, Canadian Conference on Electrical and ComputerEngineering (CCECE’09), pp. 390-393, 2009. [10] A. M. Sharaf, W. Wang, I. H. Altas, “A novel modulated powerfilter compensator for renewable dispersed wind energy interface”,International Conference on Clean Electrical Power (ICCEP’07),21-23 May, pp. 549-555, 2007.
0.45 0.4
✬❏❁❄ ❃◆❒❒❅■▼❉ ■❐◆
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0
0
Fig. 16.
0.05
0.1
0.15
0.2 Time in sec
0.25
0.3
0.35
0.4
Variation of Load end Current v/s time with PID controller
VII. CONCLUSION This paper presents FACTS based power filter compensation scheme (PFC) with PI and PID controller for voltage stabilization enhancement in gird connected wind energy system. The power filter compensator using PWM is based on complementary switching process of capacitor bank connected to IGBT switch. The switching process done with help of tri loop controller and pulse width modulation (PWM). This scheme is fully validated for voltage stability enhancement. It is observed that PID controller based scheme gives better results than PI based controller as shown above. Results of proposed scheme are obtained in MATLAB Simulink environment. The proposed scheme can be extended other power quality issues like power factor, total harmonic distortion. REFERENCES [1]
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