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Current Directional Protection of Series Compensated Line Using Intelligent Classifier

Current Directional Protection of Series Compensated Line Using Intelligent Classifier

To overcome the current based directional protection problems, an effective intelligent classifier is proposed in this paper. The SVM classifier is introduced for fault di- rection classification of the series compensated lines. In this method, one cycle current samples including the half cycle of pre and post fault current samples at the relaying end are used as input data to the classifier for distinguish- ing the backward faults from the forward faults. In order to verify the proposed method, different faults simulations have been performed upon a typical 400-kv, 325-km power system using PSCAD/EMTDC [14]. Simulated backward and forward faults include different system sce- narios such as variation in fault location, fault inception angle and fault resistance at both of the pre-fault power flow directions for all fault types. The performance of the proposed protection schematic are evaluated under current inversion condition, fault type, high fault resistance, close in fault, air gap breaker operation. Also, the proposed cur- rent directional relaying is perfectly robust for the voltage and current inversion problems.

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A Unity Power Factor Bridgeless Buck-Boost Converter Fed BLDC Motor Drive

A Unity Power Factor Bridgeless Buck-Boost Converter Fed BLDC Motor Drive

For a complete switching cycle of the proposed converter, there are three modes of operation in the positive half cycle of the supply voltage. In first mode of operation, the switch Sw1 conducts to charge the inductor Li1 and this increases the inductor current iLi1 as shown in Fig. 2(a). Diode Dp completes the input side circuitry, and the dc link capacitor Cd is discharged by the VSI-fed BLDC motor. In second mode of operation, switch Sw1 is turned off, and the transfer of stored energy in inductor Li1 takes place to dc link capacitor Cd until the inductor is completely discharged. The current in inductor Li1 decreases till it reaches zero. In third mode, no energy is left in the inductor Li1 and hence, it enters discontinuous conduction, i.e. current of Li1 becomes zero for the rest of the switching period. At this time, as shown in Fig. 2(c), both switch and diode are not conducting, and energy is supplied to the load via dc link capacitor Cd; hence, voltage Vdc across dc link capacitor Cd starts to decrease. The operation is repeated when switch Sw1 is turned on again after a complete switching cycle. Similarly, during the negative half cycle of the supply voltage, switch Sw2, inductor Li2, and diodes Dn and D2 operate for voltage control and PFC operation.

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A Novel Control Technique Using Seven Level Converter Topology For Single-Phase Transformerless Pv Systems

A Novel Control Technique Using Seven Level Converter Topology For Single-Phase Transformerless Pv Systems

cause the capacitor to discharge can be discarded in favor of those states which result in the charging of the capacitor. As such, during the positive half cycle, the switching state +E with switches 1,2,7,8 on is chosen as it causes the capacitor to charge. Also, in the negative half cycle, the switching state – E with switches 1,3,7,8 on, which again causes charging of the capacitor is chosen. With this choice, the capacitor discharges only when the switches 1,2,5,6 are on for the switching state 3E; whereas it is either floating or charging during all the other switching states. This choice of switching states helps in maintaining the capacitor voltage at its desired value (to the one that it has been charged initially). If the capacitor still continues to lose charge, a slight negative offset can be provided in the modulating wave. This will cause the discharging time of the capacitor on account of the switching state 3E to decrease, with a corresponding increase in the charging time. This will further help in maintaining the capacitor voltage constant. It must be mentioned here that these techniques will keep the capacitor voltage constant only in case of light loads, i.e. loads that do not draw a significant amount of current. If the load current has a large value, then these techniques will not be sufficient in maintaining the capacitor voltage constant.

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Design and Implementation of Transformerless Mosfet Inverter for a Grid Connected Single Phase Photovoltaic System

Design and Implementation of Transformerless Mosfet Inverter for a Grid Connected Single Phase Photovoltaic System

HERIC: Topology of inverter with MOSFET switches highly proficient and dependable inverter in which it has two switches on Alternative Current part in full bridge for the purpose of decoupling photovoltaic section from grid for the time of freewheeling period [1]. There will be a common mode voltage during this period so clamping should be done at input voltage side of Direct Current midpoint [5]. HB-ZVR: H bridge zero voltage rectifier replaced HERIC topology. The switches are made up of MOSFET. Two freewheeling switches are replaced in this topology with one bidirectional switch and four diodes. Another diode D5 is added for elimination of leakage current. Only the one directional clamping is done in this topology when (VAN – VBN) is upper than DC link midpoint voltage. There is also a common mode voltage oscillation occurs in reverse condition but it is comparatively less than HERIC. Conduction losses are less in both the topologies as the grid current flows from beginning to end the switches during complete grid period H5: Switches are made by the combination of MOSFET and IGBT. An additional switch added on DC part of the full bride inverter which is MOSFET. In the period of half cycle of the positive, freewheeling current flows all the way through body diode of switch S3 and switch S1. During the half cycle of negative freewheeling current flows from beginning to end switch body diode of switch S1and S3. In the freewheeling of current no implemented with MOSFET because it has low reverse recovery problem in its body diode. Higher conduction losses are there since output current flows from end to end three switches in the active approach of full grid cycle. Common mode fluctuation is also seen due to no clamping by the side of the mid-point of DC link side. oH5: This topology made up of switches with the combination of MOSFET and IGBT. An additional switch S6 is supplementary for the clamping purpose which is IGBT [5]. Since using IGBT the dead time to be added between S5 and S6 switches to stay away from input split capacitor short circuit. Common mode fluctuation is obtained during dead time. High conduction losses are seen since grid current flows in the course of switches in active mode. H6: The topology made up of IGBT switches with two diodes on Direct Current side of full bridge inverter. Common mode voltage fluctuation is better than the other topologies as there is bidirectional clamping branch. Diode D1 or D2 conduct (VAN – VBN) is higher or lower than the link voltage of half of the DC. Higher conduction losses will be obtained when flow of grid current through four switches [3]. 2. PROPOSED TOPOLOGY

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Design and Implementation of Transformerless Mosfet Inverter for a Grid Connected Single Phase Photovoltaic System

Design and Implementation of Transformerless Mosfet Inverter for a Grid Connected Single Phase Photovoltaic System

HERIC: Topology of inverter with MOSFET switches highly proficient and dependable inverter in which it has two switches on Alternative Current part in full bridge for the purpose of decoupling photovoltaic section from grid for the time of freewheeling period [1]. There will be a common mode voltage during this period so clamping should be done at input voltage side of Direct Current midpoint [5]. HB-ZVR: H bridge zero voltage rectifier replaced HERIC topology. The switches are made up of MOSFET. Two freewheeling switches are replaced in this topology with one bidirectional switch and four diodes. Another diode D5 is added for elimination of leakage current. Only the one directional clamping is done in this topology when (VAN – VBN) is upper than DC link midpoint voltage. There is also a common mode voltage oscillation occurs in reverse condition but it is comparatively less than HERIC. Conduction losses are less in both the topologies as the grid current flows from beginning to end the switches during complete grid period H5: Switches are made by the combination of MOSFET and IGBT. An additional switch added on DC part of the full bride inverter which is MOSFET. In the period of half cycle of the positive, freewheeling current flows all the way through body diode of switch S3 and switch S1. During the half cycle of negative freewheeling current flows from beginning to end switch body diode of switch S1and S3. In the freewheeling of current no implemented with MOSFET because it has low reverse recovery problem in its body diode. Higher conduction losses are there since output current flows from end to end three switches in the active approach of full grid cycle. Common mode fluctuation is also seen due to no clamping by the side of the mid-point of DC link side. oH5: This topology made up of switches with the combination of MOSFET and IGBT. An additional switch S6 is supplementary for the clamping purpose which is IGBT [5]. Since using IGBT the dead time to be added between S5 and S6 switches to stay away from input split capacitor short circuit. Common mode fluctuation is obtained during dead time. High conduction losses are seen since grid current flows in the course of switches in active mode. H6: The topology made up of IGBT switches with two diodes on Direct Current side of full bridge inverter. Common mode voltage fluctuation is better than the other topologies as there is bidirectional clamping branch. Diode D1 or D2 conduct (VAN – VBN) is higher or lower than the link voltage of half of the DC. Higher conduction losses will be obtained when flow of grid current through four switches [3]. 2. PROPOSED TOPOLOGY

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Solar Panel Using Active Stacked NPC Multi Level Converter

Solar Panel Using Active Stacked NPC Multi Level Converter

The load current paths during the dead time ( S2 and S2 care turned off) .The voltage and current waveforms of S2on a cycle are shown in Fig. 13. It is observed that S2commutes at fs won a half cycle when Sr> 0. On the second half cycle (Sr< 0), the load current does not pass through S2. Due to the symmetry of this topology, switch S2c has a similar operation. Through the commutation N →O − 1 , the load current is commutated to the lower current path (S4 −S 3c ).First, S4c is turned off, and S 4is turned on after a dead time. For the commutation O 1 →N, switch S 4 is turned off first, and then, (after a dead time) S 4c is turned on. The paths of the load current during the dead time ( S4 and S 4c are turned off) . During the commutation N →O −2, the load current is commutated to the middle current path(S2c −S 3 ). S 3c has to be turned off, and then, (after a dead time) S3 is turned on. In the case of commutation O − 2 →N, S 3 is turned off, and S 3c is turned on after a dead time. Fig. 12(d) shows the load current paths during the dead time (S 3 and S 3c are turned off). In conclusion, each power device of the proposed structure operates at f sw only on a half cycle, and the average switching frequency on the entire cycle is equal to half of the switching frequency (f av = f sw /2) . In the same time, the apparent switching frequency of the output voltage is twice the switching frequency (fap =2f Sw ). This advantage leads to a better balancing of the total losses in power devices.

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SSC  FSFE Physics Paper 1 2012-QP.pdf

SSC FSFE Physics Paper 1 2012-QP.pdf

25. Consider the following statements about the reflected waves from A and from B: I. The light reflected at point A undergoes a change of phase of half a cycle. II. The light reflected at point B undergoes a change of phase of half a cycle. III. At point B there is a half cycle phase difference between the reflected and

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A pilot study to prevent a thin endometrium in patients undergoing clomiphene citrate treatment

A pilot study to prevent a thin endometrium in patients undergoing clomiphene citrate treatment

We often see patients with a thin endometrium as a result of standard CC treatment, which is the most common adverse effect of CC treatment. In fact, our preliminary study showed that 41 out of 100 women had a thin endometrium during a standard CC treatment cycle. Since a thin endometrium is a critical factor of implantation failure, we have to go to the next-step therapy such as gonadotropin therapy. Gonadotropin therapy not only burdens the patient with stress and medical expense but also can cause multiple pregnancy and OHSS. Therefore, preventing CC-induced thinning of the endometrium is important.

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Radially polarized, half-cycle, attosecond pulses from laser wakefields through coherent synchrotron radiation

Radially polarized, half-cycle, attosecond pulses from laser wakefields through coherent synchrotron radiation

The required experimental conditions for RHA generation are within current technical capabilities. Petawatt lasers, presently coming up, will provide sufficiently high power for the high intensities and relatively broad focal spots preferable here. The sample simulation case shown above used a single 350 TW driving pulse delivering 6.5 J in ∼ 20 fs. These parameters are well within the ELI-facility capabilities [29] and are also becoming available commercially. The conical angle of the RHA beam is typically less than 10 ◦ , thereby al- lowing refocusing even at half-meter distance by a concentric mirroring tube with diameter less than 16 cm; such tech- niques have already been implemented in the measurement of wakefield-based electro-optic shocks [30]. The RHA pulse should also be easily distinguished from other sources due to its radial polarization and hollow pattern.

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Radially polarized, half-cycle, attosecond pulses from laser wakefields through coherent synchrotronlike radiation

Radially polarized, half-cycle, attosecond pulses from laser wakefields through coherent synchrotronlike radiation

ily met even for γ ∼ 100. As a result, the coherency is well preserved at the initial contraction phase, during which the trapped sheet electrons are only accelerated up moderate en- ergies (less than 50MeV in the present case). After that the sheet electrons are confined within a small radius and shall emit normal betatron x-rays which are incoherent and orders of magnitude weaker in intensity. Third, due to axial sym- metry and inward acceleration of disk electrons, radially po- larized half-cycle electromagnetic pulses are produced during the contraction. Here, owing to the ultrarelativistic feature of sheet electrons, the dephasing time arising from velocity mis- match between the coherent radiation and the electron sheet is much longer than the contraction period (i.e., from injection to focused to the laser axis), which is typically a few tens of laser periods as shown in Fig. 1(a). Therefore, the radiated pulse is almost overlapped with the sheet profile during the contraction phase and naturally has an attosecond duration. It is interest- ing to mention that radially polarized half-cycle pulses have also been recently demonstrated from thin photoconductors, where a sequence of annulus microelectrodes are fabricated on a wafer surface to induce radial currents [25]. However, due to the static wafer plane, only pulses of picosecond dura- tion are generated, determined by the lifetime of the radiating currents.

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High-field half-cycle terahertz radiation from relativistic laser interaction with thin solid targets

High-field half-cycle terahertz radiation from relativistic laser interaction with thin solid targets

forward-moving electrons dominate inside the target, as shown for t=35fs and 61fs. At the rear half duration of the laser, backward-moving electrons increase. At t=104fs when the laser leaves the target, there are both backward and forward electrons near and inside the target. Less hot electrons are pulled back by sheath fields near the target surfaces, some of which are confined by the quasi-static fields in a long time oscillating in and out of the target while drifting towards the ends of the target, as shown for t=227fs. Spatial and phase plots of hot electrons also show the evolution of electron bunches. In the beginning, both forward and backward hot electrons are found at the front surface of the target [Fig.4(c) and 4(g)]. Subsequently, forward ones cross the rear side [Fig.4(d)and 4(h)] producing the first forward THz pulse, and most of them are pulled back by the static field near the rear surface and traverse the front surface [Fig.4(e) and 4(j)] producing the second backward THz pulse. Then, the majority of those electrons are dragged back by the static field near the front surface [Fig.4 (f) and 4(j)] generating the second forward THz pulse.

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Apparatus and method for on line barkhausen measurement

Apparatus and method for on-line barkhausen measurement

Apparatus and method for measuring the Barkhausen signal of a moving magnetic film, ribbon or fiber wherein first and second stationary electromagnet coils are arranged and separated by a distance, d, along the path of movement of the film, ribbon or fiber. The first and second coils are energized in a manner to generate first and second opposing DC magnetic fields through which the moving film, ribbon or fiber passes along its path of movement. As the film, ribbon or fiber moves through the first and second opposing magnetic fields at a velocity, v, it experiences one complete cycle of magnetization in a period of time equal to d/v. A stationary third signal pick-up coil is disposed between the first and second coils to detect the Barkhausen signal from the moving film, ribbon or fiber. The pick-up coil typically is disposed midway between the first and second coils where the Barkhausen signal will be approximately maximum.

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HIGH VOLTAGE DC UP TO 2 KV FROM AC BY USING CAPACITORS AND DIODES IN LADDER NETWORK..

HIGH VOLTAGE DC UP TO 2 KV FROM AC BY USING CAPACITORS AND DIODES IN LADDER NETWORK..

With some other types of semiconductor device such as the insulated-gate bipolar transistor (IGBT), both turn- on and turn-off can be controlled, giving a second degree of freedom. As a result, they can be used to make self- commutated converters. In such converters, the polarity of DC voltage is usually fixed and the DC voltage, being smoothed by a large capacitance, can be considered constant. For this reason, an HVDC converter using IGBTs is usually referred to as a voltage sourced converter. The additional controllability gives many advantages, notably the ability to switch the IGBTs on and off many times per cycle in order to improve the harmonic performance. Being self-commutated, the converter no longer relies on synchronous machines in the AC system for its operation. A voltage sourced converter can therefore feed power to an AC network consisting only of passive loads, something which is impossible with LCC HVDC.

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Experimental Study of Synthetic Jets

Experimental Study of Synthetic Jets

Crook and Wood [28] also studied the effect of cavity and orifice geometry on synthetic jet formation. In order to facilitate changing the cavity height and orifice diameter, they constructed a shaker driven modular set up where different circular orifice plates can be interchanged. Smoke particles were used for visualization. The oscillator was set at 50.1 Hz. Reynolds number was computed with the hot-wire anemometry measurement of maximum centerline velocity during the ejection phase of the cycle. A vortex ring is formed when maximum value of circulation is reached. The excess circulation flow or vorticity that could not reach the maximum value will shape a tail behind the ring. The “tail” forms due to insufficient Reynolds number which causes the vortex ring not to roll up. Smith et al [29] also observed the tail behind a ring in their experiment. Figure 3 [4] shows the two dimensional images of the smoke seeded flow field as a function of Reynolds number and height to diameter aspect ratio. The white vertical line shows the approximate location of the orifice the white horizontal bars represent the approximate diameter of the orifice. The “tail” is shown in the figure with white arrows. The Reynolds number decreases from top to bottom and increases from left to right.

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1.
													 synthesis and characterization of aluminum metal matrix composites

1. synthesis and characterization of aluminum metal matrix composites

Other die components include cores and slides. Cores are components that usually produce holes or opening, but they can be used to create other details as well. There are three types of cores: fixed, movable, and loose. Fixed cores are ones that are oriented parallel to the pull direction of the dies (i.e. the direction the dies open), therefore they are fixed, or permanently attached to the die. Movable cores are ones that are oriented in any other way than parallel to the pull direction. These cores must be removed from the die cavity after the shot solidifies, but before the dies open, using a separate mechanism. Slides are similar to movable cores, except they are used to form undercut surfaces. The use of movable cores and slides greatly increases the cost of the dies. Loose cores, also called pick-outs, are used to cast intricate features, such as threaded holes. These loose cores are inserted into the die by hand before each cycle and then ejected with the part at the end of the cycle. The core then must be removed by hand. Loose cores are the most expensive type of core, because of the extra labor and increased cycle time. Other features in the dies include water-cooling passages and vents along the parting lines. These vents are usually wide and thin (approximately 0.13 mm or 0.005 in) so that when the molten metal starts filling them the metal quickly solidifies and minimizes scrap. No risers are used because the high pressure ensures a continuous feed of metal from the gate.

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Creating Entrepreneurship in Skill based Educational Institutes in Western Maharashtra

Creating Entrepreneurship in Skill based Educational Institutes in Western Maharashtra

Fig. 5(a) shows the control block diagram for the seven-level inverter. The control object of the seven-level inverter is its output current, which should be sinusoidal and in phase with the utility voltage. The utility voltage is detected by a voltage detector, and then sent to a phase- lock loop (PLL) circuit in order to generate a sinusoidal signal with unity amplitude. The voltage of capacitor C2 is detected and setting voltage given to fuzzy logic controller. Then, the outputs of the PLL circuit and the fuzzy logic controller are sent to a multiplier to produce the reference signal, while the output current of the seven- level inverter is detected by a current detector. The reference signal and the detected output current are sent to absolute circuits and then sent to a fuzzy logic controller. The detected utility voltage is also sent to an absolute circuit and then sent to a comparator circuit, where the absolute utility voltage is compared with both half and whole of the detected voltage of capacitor C2 , in order to determine the range of the operating voltage. The comparator circuit has three output signals, which correspond to the operation voltage ranges, (0, Vdc/3), (Vdc/3, 2Vdc/3), and (2Vdc/3, Vdc). The feed-forward control eliminates the disturbances of the utility voltage, Vdc/3 and 2Vdc/3,. The absolute value of the utility voltage and the outputs of the compared circuit are sent to a feed-forward controller to generate the feed-forward signal. Then, the output of the fuzzy logic controller and the feed-forward signal are summed and sent to a PWM circuit to produce the PWM signal. The detected utility voltage is also compared with zero, in order to obtain a square signal that is synchronized with the utility voltage. Finally, the PWM signal, the square signal, and the outputs of the compared circuit are sent to the switching signal processing circuit to generate the control signals for the power electronic switches of the seven-level inverter, according to Table I. The fuzzy logic controller controls the output current of the seven level inverter, which is a sinusoidal signal of 60 Hz. Since the feed-forward control is used in the control circuit, the fuzzy logic controller can be a simple amplifier, which gives good tracking performance, the gain of the fuzzy logic controller determines the bandwidth and the steady state error. The gain of the fuzzy logic controller must be as large as possible in order to ensure a fast response and a low steady-state error. But the gain of the fuzzy logic controller is limited because the bandwidth of the power converter is limited by the switching frequency.

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Intelligent Controller Based Feed Forward Control for AC to DC Converter PWM strategy With Reduced Switching Loss

Intelligent Controller Based Feed Forward Control for AC to DC Converter PWM strategy With Reduced Switching Loss

Consider the single-phase system shown in Fig. 1 and assume the ac grid system internal impedance is highly inductive and, therefore, represented by L. The equivalent series resistance of L is neglected. Consider the converter is operated in the rectifier mode. While ac grid voltage source is operating in the positive half- cycle vs > 0, the operating circuits of Statuses A and B listed in Table I of the proposed simplified PWM are shown in Fig. 2(a) and (b), respectively. Using Kirchhoff’s voltage law in the circuit operation shown in Fig. 2(a) and (b), the voltage relationship can be obtained as follows:

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AC to AC Step Down Cycloconverter

AC to AC Step Down Cycloconverter

By controlling the switching period of thyristors, time periods of both positive and negative half cycles are changed and hence the frequency. This frequency of fundamental output voltage can be easily reduced in steps, i.e., 1/2, 1/3, 1/4 and so on.

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A Novel Pfc Circuit For Reduced Switching Loss Bidirectional Ac/Dc Converter Pwm Strategy With Feedforward Control For Grid-Tied Microgrid Systems

A Novel Pfc Circuit For Reduced Switching Loss Bidirectional Ac/Dc Converter Pwm Strategy With Feedforward Control For Grid-Tied Microgrid Systems

Abstract- In this paper, a buck half-bridge DC-DC converter is used as a single-stage power factor correction (PFC) converter for feeding a bidirectional AC/DC converter. A simplified pulse width modulation (PWM) strategy is used for the bidirectional ac/dc single phase converter in a microgrid system. Then, the operation mechanism of the novel simplified PWM is clearly explained. The number of switchings of the simplified PWM strategy is one fourth that of the unipolar PWM and bipolar PWM. Based on the novel simplified PWM strategy, a feasible feedforward control scheme is developed to achieve better rectifier mode and inverter mode performance compared with the conventional dual- loop control scheme. The simplified PWM strategy with the feedforward control scheme has lower total harmonic distortion than the bipolar PWM and higher efficiency than both unipolar and bipolar PWMs. Furthermore, the simplified PWM operated in the inverter mode also has larger available fundamental output voltage V AB than both the

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A Single-Phase Ac-Dc Converter with Improved Efficiency Using Atmega 8 Microcontroller

A Single-Phase Ac-Dc Converter with Improved Efficiency Using Atmega 8 Microcontroller

The proposed topology uses two slow diodes (Da and Db) to connect the ground of the PFC to the input line. The current does not return through these diodes, so their related conduction losses are low. The gating signals for MOSFETs are 180° out of phase. To evaluate the circuit operation, the input line cycle has been divided into the positive and negative half-cycles. The full circuit operation depends on the duty cycle.

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