- Original Research
- Open Access
A novel controllable crowbar based on fault type protection technique for DFIG wind energy conversion system using adaptive neuro-fuzzy inference system
© The Author(s) 2018
- Received: 6 August 2018
- Accepted: 18 September 2018
- Published: 16 October 2018
This paper proposes a novel controllable crowbar based on fault type (CBFT) protection technique for doubly fed induction generator (DFIG) wind energy conversion system connected to grid. The studied system consists of six DFIG wind turbines with a capacity of 1.5 MW for each of them. The operation mechanism of proposed technique is used to connect a set of crowbar resistors in different connection ways via activation of controllable circuit breakers (CBs) depending on the detected fault type. For each phase of DFIG, a crowbar resistor is connected in parallel with a controllable CB and all of them are connected in series to grid terminals. The adaptive neuro-fuzzy inference system (ANFIS) networks are designed to detect the fault occurrence, classify the fault type, activate the CBs for crowbar resistors associated with faulted phases during fault period, and deactivate them after fault clearance. The effectiveness of proposed CBFT protection technique is investigated for different fault types such as symmetrical and unsymmetrical faults taking into account the single-phase to ground fault is the most frequently fault type that occurs in power systems. Also, a comparison between the behaviours of studied system in cases of using traditional parallel rotor crowbar, classical outer crowbar, and proposed CBFT protection techniques is studied. The fluctuations of DC-link voltage, active power, and reactive power for studied system equipped with different protection techniques are investigated. Moreover, the impacts of different crowbar resistance values on the accuracy of proposed technique are studied. The simulation results show that, the proposed technique enhances the stability of studied wind turbine generators and contributes in protection of their components during faults.
- ANFIS networks
- Power electronic converters
- DFIG wind turbines
- Fault types
In the last few decades, Energy problems are increased rapidly due to fast depletion of the fossil fuel and its highly cost, thus renewable energy plays an alternative way in order to overcome the expected power crisis. Wind energy is one of the renewable energy sources, where it is clean, plentiful, environmentally friendly, and widely distributed. Also, it reduces the toxic atmospheric and not producing greenhouse gas emissions . Wind energy conversion system converts the wind energy into mechanical energy based on the principle of aerodynamic through the turbine, then the mechanical energy is converted into electrical energy based on the principle of electromagnetic induction through the generator [2, 3]. The usage of DFIG is receiving high attention regarding wind turbines connected to electrical grid. The DFIG is an induction machine with a wound rotor, where the stator windings are connected to grid and the rotor windings are connected to bidirectional converters, thus the stator and rotor windings are connected to grid bus, hence the derived term of ‘doubly fed’ [4, 5]. The DFIG is sensitive to voltage dips during grid fault, subsequently the high current is passing through the power electronic converters . This situation needs special attention to block converters and disconnect DFIG from the grid to avoid any risks [7–9]. The fault ride through (FRT) or low voltage ride through (LVRT) is a term that refers to the wind turbines must be remain connected to grid during faults . Also, all requisites for safe operation of DFIG components is required, because of rotor current will become very large during grid faults . Therefore, DFIG requires a protection system called crowbar techniques that usually adopted for limiting the high currents in order to improve the fault handling capacity and protection requirements . The crowbar protection technique is necessary to avoid a disconnecting of DFIG wind turbines during grid faults. Many researches introduce different crowbar protection techniques such as series crowbar resistors connected with stator windings, parallel crowbar resistors connected with rotor windings, and outer crowbar resistors connected between the DFIG terminals and electrical grid [10–18]. Traditionally, the parallel crowbar is engaged to rotor windings, where the converters are disabled and the DFIG is converted to a singly fed induction generator. Therefore, the usage of traditional parallel rotor crowbar technique is unsatisfactory for LVRT grid requirements. Recently, this problem is solved by using the outer crowbar technique that designed in [14, 15]. Typically, only 5% of the faults occurrences in power systems are a three-phase fault with or without ground. Regarding the unbalanced faults, 80% are single-phase to ground fault and 15% are double-phase faults with or without ground, where these faults often can be deteriorated to three-phase fault [19, 20]. It is clear that, the single-phase to ground fault is most frequently fault type that occurs in electrical power system. Most researchers concentrate on the studying of DFIG wind turbine behaviours in case of three-phase to ground fault [9–18]. This paper proposes a novel controllable CBFT protection technique driven by ANFIS for studied DFIG wind turbines. The ANFIS is a type of artificial intelligent algorithms that involves the two algorithms of fuzzy logic system and neural network system [21–23]. Moreover, the ANFIS can be designed and employed to get the benefits of both fuzzy logic and neural structure in one scheme [24, 25]. The proposed protection technique is structured as a combination of three crowbar resistors that connected to wind turbine generator terminals. The combination resistors are connected in different ways which they are controlled by ANFIS networks. The accuracy of proposed CBFT protection technique is studied for different fault types of symmetrical and unsymmetrical faults such as single-phase, double-phase, and three-phase to ground faults. In addition, the behaviours of studied DFIG wind turbines equipped with classical outer crowbar and proposed ANFIS CBFT protection techniques during different fault types are investigated. Also, a comparison with traditional parallel rotor crowbar protection technique as introduced in [10–14] is added to demonstrate the effectiveness of the proposed technique. Moreover, the impacts of different crowbar resistor values on the accuracy of proposed protection technique equipped with studied system are investigated. The rest of this paper is organized as follows: Section 2 presents the description of DFIG wind energy conversion system. Section 3 describes the structure of ANFIS network. Section 4 introduces the Methods, where the methodology of classical outer crowbar and proposed CBFT protection techniques are driven by ANFIS networks. In Section 5, the simulation results are demonstrated to show the effectiveness of proposed technique. Finally, the paper is concluded in Section 6.
2.1 Wind turbine model
where Tm is the mechanical torque, and ωt is the turbine rotor speed.
2.2 DFIG model
2.3 AC/DC/AC converters
The AC/DC/AC converters equipped with bidirectional IGBTs are connected between rotor windings and grid bus. The power that transmitted via converters is typically about 25–30% of generator nominal power . The rotor side converter (RSC) and grid side converter (GSC) are voltage sourced converters that use forced commutated power electronic components to synthesize AC voltage from DC voltage source. The shunt capacitor that connected to DC side works as a DC voltage source. The controllers of converters are divided into two main parts such as RSC controller and GSC controller, where the RSC is used to control active power and reactive power (or voltage level), while the GSC is used to control DC-link voltage and reactive power.
Parameters of each ANFIS structure
Input membership function number
Input membership function shape
Output membership function shape
Error of testing
4.1 The methodology of classical outer crowbar protection technique driven by ANFIS
4.2 The methodology of proposed controllable CBFT protection technique driven by ANFIS
Grid fault type codes
Phase a to ground
Phase b to ground
Phase c to ground
Phases a and b to ground
Phases b and c to ground
Phases c and a to ground
Phases a, b, and c to ground
1a, b, c
Parameters of studied system
The parameters of DFIG
Rated voltage (V)
Rated power (MW)
Rated frequency (Hz)
Rotor resistance (pu)
Stator resistance (pu)
Mutual inductance (pu)
Rotor leakage inductance (pu)
Stator leakage inductance (pu)
The parameters of transmission line
Zero sequence resistance (Ω/km)
Positive sequence resistance (Ω /km)
Zero sequence capacitance (F/km)
Positive sequence capacitance (F/km)
Zero sequence inductance (H/km)
Positive sequence inductance (H/km)
The parameters of transformer (T1)
575 V/25 kV
0.0017 + j0.05
The parameters of transformer (T2)
25 kV/220 kV
0.00534 + j0.16
The parameters of grid
0.0004 + j0.004
5.1 Impacts of different fault types
The comparison between performance of DFIG wind turbine generators in case of using the classical outer crowbar and in case of using the proposed ANFIS CBFT protection techniques during different fault types is studied and illustrated in the following subsections. Also, a comparison with traditional parallel rotor crowbar protection technique is investigated to demonstrate the effectiveness of the proposed technique. It is worth to be mentioned that, the operation mechanism of traditional parallel rotor crowbar protection technique as described in [10–14] is designed to deactivate the RSC during fault occurrence and the rotor windings are connected to the crowbar resistors instead of the converters.
5.1.1 Impact of single-phase to ground fault
5.1.2 Impact of double-phase to ground fault
5.1.3 Impact of three-phase to ground fault
As indicated in Fig. 11(c), the reactive power is increased to 5.9 MVAR and decreased to − 0.59 MVAR during fault period, while it is fluctuated between − 2 and 3.5 MVAR after fault clearance in case of using traditional parallel rotor crowbar protection technique. Otherwise, in cases of classical outer crowbar and proposed CBFT protection techniques, the reactive power variation is fluctuated between 6.08 and 2.35 MVAR after fault occurrence, while during the rest time of fault period, the magnitude of it equals 0.56 MVAR nearly. Also, it is fluctuated between 2.35 and − 2 MVAR after fault clearance.
Finally, the operation of DFIG wind turbines in case of using the proposed ANFIS CBFT protection technique is more stable, where it can return to steady state conditions in a short time after fault clearance comparing with the traditional parallel rotor crowbar and classical outer crowbar protection techniques. The studied system is staying to deliver stable active power with proposed CBFT protection technique during fault period. Moreover, the variations of DC-link voltage, active power, and reactive power are decreased by using the proposed ANFIS CBFT crowbar protection technique. The proposed technique is more accurate in case of single-phase to ground fault considering this fault is the most frequently fault type that occurs in power system. The operation mechanism of proposed technique is designed based on fault type, where this fault is detected and classified using ANFIS networks. Also, the proposed technique inserts a specified crowbar resistor for faulted phases only to enhance the studied system stability.
5.2 Impacts of crowbar resistance values
This paper presents a novel ANFIS controllable CBFT protection technique to protect the DFIG wind turbines grid connected during different faults. The studied system has a total capacity of 9 MW, where it consists of six wind turbine generators with a capacity of 1.5 MW for each of them. The proposed protection technique consists of three crowbar resistors, where each resistor is connected in parallel with a controllable single-phase CB and both of them are connected between the terminals of DFIG wind turbine and electrical grid. The ANFIS networks are used to detect and classify the fault types, then it sends a control signal to activate the specified CBs of faulted phases to protect the DFIG, DC-link capacitor, and converters from dangerous effects. The accuracy of proposed protection technique is investigated during different fault types such as single-phase to ground fault, double-phase to ground fault, and three-phase to ground fault. The variations of DC-link voltage, active power, and reactive power during occurrence of different fault types are investigated when the studied system is equipped with proposed protection technique and when it is equipped with classical outer crowbar protection technique. Also, a comparison with traditional parallel rotor crowbar protection technique is investigated to demonstrate the effectiveness of proposed technique. The simulation results show that, the variations of measured DC-link voltage, active power, and reactive power during fault periods are more stable and have little fluctuations when the wind turbine generators are equipped with proposed CBFT protection technique. The reduction of fluctuations when the studied system is equipped with proposed CBFT protection technique is more obvious in case of single-phase to ground fault considering this fault is the most frequently fault type that occurs in power systems. Also, the impacts of different crowbar resistance values on the behaviour of studied system and the accuracy of proposed protection technique are investigated. Finally, the results show that the proposed CBFT protection technique based on ANFIS has obvious effect for enhancing the stability of studied system.
Availability of data and materials
Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.
ON suggested the idea of the proposed protection technique. ON carried out the MATLAB model for studied wind energy conversion system. ON and IH carried out the ANFIS protection technique algorithms. ON and IH participated in result analysis and discussion. Both authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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