Overcurrent Protection Matlab

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Overcurrent Protection for Gyrotrons in EAST ECRH System Weiye Xu 1*, Handong Xu 1, Jianqiang Feng 1**, Yong Yang 1, Huaichuan Hu 1,Fukun Liu 1, Yunying Tang 1 1 Institute of Plasma Physics, Chinese Academy of Sciences, 350 Shushanhu Rd., Hefei, Anhui, China Abstract: In this paper, an overcurrent protection system is designed to ensure the safety of the gyrotrons in the EAST ECRH system. Two overcurrent protection systems were established, a fast one and a slow one. The fast one uses the current transformers as the current sensors. The models of the current transformers and the superconducting magnet were built to analyze the effect of the environmental magnetic field on the current transformers using FI method. The analysis results show that the magnetic induction at the position near the current transformers must less than 0.002 T, i.e., the current transformers should be placed at a distance greater than 2.2 meters from the magnet center to ensure its normal work. The slow one uses the shunt to monitor the currents. An anti-fuse FPGA and a timer is used to realize the signal processing in the fast protection circuit and the slow protection circuit respectively. The response time of the fast protection circuit is less than 100 ns, and the response time of the slow protection circuit is less than 31 μs.

Tokamak Is One Of The Most Promising Methods To

achieve the magnetic confinement nuclear fusion. A 140GHz/4MW/100s ECRH (electron cyclotron resonance

Heating) System For East (Experimental Advanced

Superconducting Tokamak) is being built in ASIPP (Institute of Plasma Physics, Chinese Academy of Sciences). The ECRH system includes four gyrotrons which are capable of producing 900~1000 kW of RF output power.

In EAST ECRH system, the overcurrent protection is one of the most important parts of the supervisory control and protection system. The gyrotrons are electric vacuum devices, they are very fragile, and must be operate very carefully. In the case of internal breakdown or bad electron beam focusing, the cathode current, the anode current will exceed the normal value. In that case, the high voltage power supplies of the gyrotrons must be shut off immediately to protect the gyrotrons from broken. Therefore, a reliable control and protection system, especially the overcurrent protection system must be established to ensure the safety of the gyrotrons.

In this paper, an overcurrent system is designed. Some EMC problems for overcurrent protection are discussed. The details are discussed in the following sections. In Section 2, the architecture of the supervisory control and protection system are given. In Section 3, the design and the analysis of the overcurrent protection system is given. Then, in Section 4, we give the conclusions.

Ecrh

In order to ensure the safety and the reliable operation of the gyrotrons, a supervisory control and protection system has been developed. It can be decomposed into nine subsystems, namely: central control system, state monitoring and the interlock system (use PLC), video monitoring system, overcurrent protection system, arc protection system, polarization control system, data acquisition system, power measurement and control system, data management and publishing system. Where the central control system is used to control the timing of the gyrotron operation; the state monitoring and the interlock system implements the interlock of all the subsystems; the video monitoring system is used for video recording of the heating device room where the gyrotrons are placed in order to monitor the status of the heating device room; the overcurrent protection system is one of the most important protection systems to protect the gyrotrons from broken, and it is the focus of this paper. The arc protection system monitors the arc signals of the MOU, the output window, and the miter bends to prevent these devices from being damaged by the arc; the polarization control system is used to control the polarization of the millimeter wave so that the electron cyclotron wave can be mostly absorbed by the plasma; The data acquisition system is used to acquire and record the relevant data of the gyrotrons.

The power measurement and control system is responsible for measuring and control the output power of the gyrotrons. The data management and distribution system is used to store the relevant data and provide a convenient way to access data.

The Architecture Of The Supervisory Control And

protection system are shown in Fig. 1. Whenever the current exceeds the threshold value, the overcurrent protection system will send the protect signals to the cathode power supply, the anode power supply, the PLC for interlock, and the center control system to shut off the power supplies and interlock the whole system. The cathode power supply and the anode power supply can be shut off within 10 μs.

3. Overcurrent Protection System For Gyrotrons

In the case of internal breakdown or bad electron beam focusing, the arc may happen in the gyrotrons while the cathode current, the anode current will exceed the normal value. It is very dangerous for gyrotrons because they may be damaged by arc. So, the high voltage power supplies of the gyrotrons must be shut off immediately whenever the current exceeds the threshold value to protect the gyrotrons from broken. Therefore, a reliable overcurrent protection system has to be established to ensure the safety of the gyrotrons.

According to the safety requirements of the gyrotrons, the overcurrent protection must ensure that the high-voltage output is cut off within 10 μs when the overcurrent happens.

The permissible arc energy for the gyrotron gun is 10 J. Two sets of overcurrent protection systems who work in parallel were designed. The current detection principle is shown in Fig. 2.

A shunt whose resistance value is 500 mΩ is used to measure the anode current for slow overcurrent protection. A shunt whose resistance value is 1 mΩ is used to measure the cathode current for slow overcurrent protection. Four current transformers (two current transformers whose model is Pearson 2100 are used to sense the cathode current, and two current transformers whose model is Pearson 110 are used to sense the anode current) are used for fast overcurrent protection. The two sets of protection systems will be described separately in the following sections.

Fig. 2. The principle of current detection. Two shunts are used to measure the cathode current and the anode current for slow overcurrent protection. Two current transformers are used for fast overcurrent protection.

3.1. Fast Overcurrent Protection

The functional block diagram of the fast protection

System Is Shown In Fig. 3. The High-Speed Current

transformers are used in the fast protection system to monitor the anode current and the cathode current. The cathode current and anode current are sensed by Pearson 110 and Pearson 2100 respectively. The output signals of the current transformers are sent to the rapid protection circuit through attenuators (×1 attenuation for anode current, ×10 attenuation for cathode current). When the signal amplitude exceeds the preset threshold, the rapid protection circuit will send out the protection signals to shut off the high voltage Fig. 1. Architecture of the supervisory control and protection system. The green cables indicate the connections between the devices and the PLC device, the red cables represent the protection signals from the devices to the high voltage power supply, the black cables indicate the network cables, and the blue cable indicates the connections between the devices and the center console.

3

power supplies. In order to achieve the isolation between

Improve

electromagnetic compatibility, the protection signals are converted to optical signals which can be transmitted by fiber. The fast protection circuit has the functions such as self-test, latch, reset, and so on. The threshold can be set remotely by the control room host computer through the communication interface.

Fig. 3. The functional block diagram of the fast protection system. The fast switching diode is used to clamp the input voltage signal as the signal conditioning circuit. The response time of the comparator is 7ns and the output signal is TTL level. The signal processing circuit uses an anti-fuse FPGA.

The FPGA can latch the comparator and can control the latch time. During the period of the comparator latch, the comparator will always output a high level signal. All of the input and output signals to FPGA are isolated by the high- speed optocoupler with a typical response time of 50 ns. The FPGA is programmed with a watchdog function. Electro- optical conversion circuit, i.e. the optical drive circuit is implemented by using a fiber-optic transmitter. It can drive optical transmission distance of 1.25 km in the ideal case when the drive current is 30 mA. Under normal conditions, there is light output, and if there is no light, it means that the protection is occurring.

The PCB of the fast protection circuit uses four-layers. The top and bottom layer is the signal layers. The middle two layers is the power layer and ground layer respectively. The power plane was divided into two parts: 5V digital power supply and 5V analog power supply. The ground floor is also divided into two parts: digital ground and analog ground.

The fast protection circuit has been tested. The test results of the input–output logic is shown in Fig. 4 (a) and the test results of the response time is shown in Fig. 4 (b). In Fig.

4, the signal 3 is the input signal and the signal 4 is the protection output signal. As we can see, when the input voltage exceeds the threshold, the fast protection circuit will output high-level voltage; when the input voltage turns to low-level, the fast protection circuit will turn the output voltage to low-level. The response time is less than 100 ns.

B

Fig. 4. The test results of the fast protection circuit. (a) The input-output logic of the fast protection circuit. (b) The response time of the fast protection circuit.

As Shown In Fig. 3. The High-Speed Current

transformers are used in the fast protection system to monitor the anode current and the cathode current. The cathode current and anode current are sensed by Pearson 110 and Pearson 2100 respectively. Both the current transformers are single shielded. The transformers have insulated mounting brackets and the only grounding is through the cable braid.

The parameters of the Pearson current transformer we used (in the case of one turn) is shown in table 1. The useable rise time of the current transformers is 20 ns. If the rise time (the interval from 10% to 90% of the transition) of the input current pulse is less than the useable rise time, there will be an overshoot or ringing, and the amplitude of the overshoot or ring will be more than 10% of the transition.

The principle of measuring current using the current transformer is shown in Fig. 5. The secondary winding is wound on the core. The number of secondary windings is 50 for Pearson 2100, and the number of secondary windings is 500 for Pearson 110. The value of the output resistor R is 50 Ω for both two kinds of transformers. Because of the use of ferromagnetic core materials, and the current transformers are placed close to the superconducting magnet for gyrotron. The ferromagnetic cores can become saturated by the magnetic field. We analyze whether the magnetic field influences the normal use of current transformers in the followings.

Fig. 5. The schematic diagram of measuring current with the current transformer. The primary winding is in one turn.

As Shown In Table 1, The Maximum Dc Current Is

0.78A for both of the model 110 and the model 2100. The core in model 110 and the core in model 2100 are made out of the same material, that is supermalloy, a magnetically soft material. Unfortunately, we do not know the magnetization curve of the core. But we can estimate the magnetization curve of the core according to the parameters of the Pearson current transformers which are shown in table 1.

Firstly, We Should Need To Model The Current

transformers. According to the parameters of the Pearson current transformers which are shown in table 1, we know that the size of model 110 and model 2100 are exactly the same. The only structure difference between model 110 and model 2100 is the number of secondary windings. The number of secondary windings can be calculated by this

(1)

where S is sensitivity; R is the value of the output resistor which is 50 Ω for both two kinds of transformers. So, the number of secondary windings is 50 for Pearson 2100, and the number of secondary windings is 500 for Pearson 110.

The model we built are shown in Fig. 6. The primary winding is a solid coil with one turn. The secondary winding is a stranded coil whose turn is 50 for model 2100, and is 500 for model 110. The core is a nonlinear material. The FI[6, 7] (finite integration) method is used for the electromagnetic simulation. The S-Parameters obtained in the electromagnetic simulations is introduced into the circuit file to run the EM/circuit co-simulation. The co-simulation circuit model is shown in Fig. 6 (b).

Set the primary current as 0.78A, the simulation result shown in Fig. 7 (a) shows that the magnetic field strength on the core is H≈4 A/m. The relationship between magnetic

B

Fig. 6. The simulation model of the current transformer we built. (a) The model of the current transformer. (b) The schematic of the circuit model. Coil 2 represents the primary winding, and coil 1 represents the secondary winding.

Bringing H≈4 and μ0 into (2), we can got the relationship between the maximum relative permeability μrmax and the

(4)

Because this formula is got by assuming the relative permeability μr is a constant which is equal to the maximum relative permeability μrmax, the calculated saturation magnetic induction Bmax is larger than the real saturation magnetic induction Bs.

Because the core in model 110 and the core in model 2100 are made out of the same material. We estimated the magnetization curve of the core by analyzing the droop rate of model 2100. The droop rate is the downward slope of the Table 1 The parameters of the Pearson current transformer we used (in the case of one turn).

Deployment In Out-Of-Position Situations

D. Bendjaballah1, A. Bouchoucha1, M. L. Sahli1,2* and J-C. Gelin2

Abstract

Side-impact collisions represent the second greatest cause of fatality in motor vehicle accidents. Side-impact airbags have been installed in recent model year vehicle due to its effectiveness in reducing passengers’ injuries and fatality rates. In meeting these requirements, simulations of folding and deploying airbags are very useful and are widely used. The paper presents a simulation method for the deploying airbags using three materials in different working conditions. Finite element analysis is primarily used to evaluate this concept. In these simulations, the gas flow is described by the conservation laws of mass, momentum, and energy. The numerical results indicate that the FE method in this paper is capable of capturing airbag deploying process accurately.

Keywords: Airbag simulations, Out-of-position, Crash, Modeling, Out-of-position

Background

The passive safety of cars has become a very high prior- ity issue for the automotive industry. Today, there are not only one or two airbags in a car; certain models have ten times more than that. With the increasing usage of airbags, the number of accidents where the airbag itself can cause an injury to the occupant also increases

(Augenstein Et Al. 2003; Gabauer And Gabler 2010;

Audrey et al. 2011). As is well known, safety belts are also now devices designed to provide protection to the users of vehicles during crash events, minimizing the loads necessary to adapt their movement to the move- ment of the car (Freesmeier and Butler 1999; Schmitt et al. 1997). In general, the seat belt is designed to restrain the occupant in the vehicle and prevent the

Occupant From Having Harsh Contacts With Interior

surfaces of the vehicles. The airbag acts to cushion any impact with vehicle structure and has positive internal pressure, which can exert distributed restraining forces over the head and face. As a safety component of auto- mobile, an airbag decreases occupants’ injury likelihood effectively in case of an accident (Ruff et al. 2007). These safety elements can reduce the death rates on the roads, and its protection effects have been widely approved (Crandall et al. 2001; Teru and Ishikawa 2003). With computational tools such as finite element methods designed for dynamic contact problems, crashworthiness simulations can now be used with reliable accuracy to evaluate occupant protection in various collision condi- tions with safety metric/parameters such as acceleration, head injury criteria, intrusion distance, intrusion vel- ocity, and neck forces (neck injury risk or whiplash).

Thus, new types of airbag products are being developed to handle different collision scenarios.

Become Standard Equipment On Most New Passenger

vehicles (Braver and Kyrychenko 2004; Teng et al. 2007; Yoganandan et al. 2007). The airbag cushion is com- posed of a woven fabric which is rapidly inflated during a car crash. The airbag dissipates the passenger’s kinetic energy thereby reducing injury through biaxial stretching of the fabric bag and escaping gas through vents. There- fore, the performance of the airbag is greatly influenced by the mechanical properties of the fabric. Generally, air bags are designed to deploy in a crash that is equivalent to a vehicle crashing into a solid wall at 8 to 14 mph.

Air bags most often deploy when a vehicle collides with another vehicle or with a solid object like a tree. There are various types of airbags: frontal, side-impact, and curtain airbags. In general, the passenger side airbags are usually larger than the driver airbags (see Fig. 1).

Besançon, France

© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Bendjaballah et al. International Journal of Mechanical

Doi 10.1186/S40712-016-0070-2

Extensive studies have shown that the airbag deploy- ment in load cases consists of two occupant loading phases: a punch-out effect where the airbag bursts out of its container with the airbag and airbag module cover accelerating towards the occupant and a second loading phase during which the airbag is taking on its deployed shape and volume (membrane-loading effect). Bankdak et al. (2002) developed an experimental airbag test system to study airbag-occupant interactions during close proximity deployment. The results provided insight for simulating the effect of inflation energy and mass flow on target response. Bedard et al. (2002) found that while left-side (driver-side) impacts accounted for only 13.5% of all crashes, the fatality rate among these

Crashes Was 68.3% In Comparison To Front Impact

(48.3%), right-side impact (31.3%), and rear impact (38.4%). These studies underscore the importance of oc- cupant safety during side-impact collisions. In the last years, the current market requested to reduce the time and cost airbag development. In order to achieve this result, virtual simulations play an important role since they allow to minimize the number of experimental tests (Pei et al. 2013; Cao et al. 2014). Several simulation models of airbag were established (Wang et al. 2007). It is feasible to optimize the parameters of airbag deploy- ment using simulation technology. Experimental and numerical studies have quantified injury risks to close- proximity occupants from deploying side airbags. These studies have focused on the prevention of the most ad- verse effects of airbag deployment (Duma et al. 2003).

Other studies have proposed airbag characteristics to minimize particular biomechanical responses (Haland and Pipkorn 1996). In a more recent study, Marklund and Nilsson (2003) compared deformation patterns with experimental data as well as the computational costs associated with three different airbag deployment simu- lation methods; they concluded that the SPH method is relatively inexpensive and produces incremental deform- ation patterns that compare most closely to the experi- mental results. The process of inflation of an airbag is one of the determining factors in saving lives. The duration from the initial impact of the crash to the full inflation of an airbag is about 40 ms, and during this time, the airbag goes from being in a folded state to a fully inflated state, with a high internal pressure. After achieving this state, the airbag begins to deflate, thus providing a nice cushion for the body impacting it.

Ideally, the person in the crash should come into contact with the airbag at this time. In the present study, a large volume passenger side airbag model is developed to handle different collision scenarios. The main aim is evaluate the performance of deploying of passenger side airbag using finite element methods (FEM).

Materials

The tensile specimens were made in different airbags (P: Peugeot, R: Renault, and VW: Volkswagen) with a length of 200 mm long and a width of 40 mm. Table 1 shows the mechanical properties of the airbag.

Tensile Tests

To determine the mechanical properties of the material of airbag used in the test pieces, tensile tests were performed on Lloyd EZ20 universal testing machine in Constantine. These tests were conducted using rect- angular samples. The axial force and axial displacement acquired during a test are converted into stress and the strain in order to be used for the fabric material model.

The continuous recording of the stress-strain data was performed during both the load and unload phases. A minimum of five samples were made in order to check the repeatability of the measurements. All the data was collected by using a PC-based data acquisition system and analyzed by commercial software. The picture frame test device that is made for this study is shown in Fig. 2.

Fig. 1 a Frontal and side airbags. b Oblique view of facet occupant model in sitting posture following airbag deployment (Lim et al. 2014)

0.150

Bendjaballah et al. International Journal of Mechanical and Materials Engineering (2017) 12:12

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Figure 3 shows the stress-strain relationship of the airbag sample under axial tensile loads. The results are showing a linear increase in extension with the increas- ing stresses. This is an expected output and it confirms with the theoretical behavior of a sample subjected to tensile stress. The rupture strain values for different airbags (R/P/VW) were 0.322, 0.441, and 0.472, respect- ively. The measured elastic parameters (i.e., Young’s modulus E and initial yield strength) and Poisson’s ratio are summarized in Table 2. The tensile tests of the woven fabrics can show differences on mechanical prop- erties because woven fabrics can resist in-plane shear loads once the yarn lock-up angle has been reached. The differences of material property on material direction can affect the shape of fully deployed bag (see Fig. 3b).

Theoretical Background

Numerical simulations of airbags use very complex and techniques such as an orthotropic model to identify the mechanical behaviors during the airbag inflation and the fluid mechanics (gas flow) to describe the inflator gas flow (pressure gradient) and improve the representation of the pressures within the airbag. To model the airbag as an orthotropic model, three material constants have to be provided. Assuming a plane stress condition, the

Ð1Þ

where σ is the normal stress and τ is the shear stress, the subscript refers to the principal material directions, i.e., the fill and warp directions. Also, ε and γ are the strain components. The material elastic constants Qij are

Ð2Þ

where E1 and E2 are the Young’s modulus in the fill and wrap directions and G12 is the shear modulus of the fabric material. νij is the Poisson ratio of the material.

The gas exerts a pressure load on the airbag causing it to expand. This expansion puts the airbag under tensile stress lowering the expansion rate. In this study, heat conduction and heat transfer is not taken into account.

Fig. 2 A photograph of Lloyd EZ20 universal testing Fig. 3 Stress versus strain using Lloyd EZ20 machine for a three different airbags at 0° and 90° and b VW airbag test specimens at

Different Angles

Table 2 Physical and mechanical properties of the airbag

Page 3 Of 9

In the deployment of an airbag, an inflator supplies high velocity gas into an airbag causing it to expand rapidly. The gas inside the airbag is assumed to be ideal, to be of constant entropy, and to satisfy the equation of state:

Ð3Þ

Here p, ρ, and e are respectively the pressure, density, and specific internal energy, and γ is the ratio of the heat capacities of the gas. The gas flow is described by the conservation laws for mass, momentum, and energy that

Ð4Þ

here, V is a volume, A is the boundary of this volume,

N Is The Normal Vector Along The Surface A, And U

denotes the velocity vector in the volume. Applying Bernoulli’s equation in the case of an ideal gas with

Ð5Þ

Here, the subscript ex denotes quantities at the throat of the tube. Furthermore u, p, and ρ denote the quan- tities inside that part of the tube that is supplying mass.

Materials And Boundary Conditions

The airbag system mainly consists of three parts: the airbag itself, the inflator unit, and the crash sensor or diagnostic unit. Thus, to study the behavior of the airbag using FE simulations, we need to have an FE model of the airbag in the folded position. A FE model of the airbag was used to simulate the test condition as shown in Fig. 5. LS-DYNA® material model FABRIC (MAT_34) is used to simulate the airbag material. It is a variation of the layered orthotropic material model. Additionally, in the LS-DYNA® material model, fabric leakage can be accounted for. However, for this CAB material, the leak- age is almost negligible and therefore no leakage is specified. The mechanical properties can be determined from the physical test. Typical material properties for airbag fabrics are taken as given in Chawla et al. (2004a) (Table 3). These properties are used to simulate inflation process of airbag (see Table 1). The car dashboard is modeled as the rectangular thin plate using a MAT_RI-

Gid Material, And The Degrees Of Freedom Are Con-

strained in all the directions. The similar properties of thermoplastic polymer are assigned for contact purposes. The porosity of the fabric is assumed zero. The nitro- gen gas is taken for inflating the airbag. Properties of nitrogen gas and initial bag conditions are shown in Table 4. The example on which we perform the study is a typical passenger side airbag. The geometric de- tails have been measured from a commercially avail- able airbag. The initial state of the airbag is a closed rectangular whose sides are to be finished to 482 × 635 mm2 and is shown in Fig. 4.

Table 3 Material properties of airbag and rigid plate used in FE

–

Table 4 Initial values used for FE simulation of the swelling of

3.33 × 10−4

Fig. 4 The initial airbag geometry in the form of a rectangular Bendjaballah et al. International Journal of Mechanical and Materials Engineering (2017) 12:12

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