A zero crossing detector detects the transition of a various signal waveform from positive and negative and gives a narrow pulse that exactly coincides with the zero voltage condition. At high frequencies it will be quite difficult process. (Rod Elliott, 2005)
Zero crossing detector is useful in many applications in power electronics. At a specific frequency zero crossing detector can be used and operates without delay at predictive finite impulse response [FIR] and filters like band pass filters with negative phase delay. (Polla, 2011)
The application of Zero cross family of optically isolated triac drivers are less cost, easy to operate and effective solution for interface applications between low current dc control circuit such as logic gates and microprocessor and ac power loads(120,240 or 380 volt single or 3-phase). These isolated triac drivers provides enough gate trigger current for high current, high voltage thyristors between the line and the control circuitry with 7.5KV dielectric withstand voltage and also it will not intended for such devices as solid state relays. It will include various resistors and capacitor combinations such as Full Wave Rectifier Bridge, discrete transistor, trigger SCRs.
In the three phase power system, the developing demand for solid state switching of AC power heating controls and other industrial applications has resulted in the use of the triac circuits in the control of three phase power. http://www.fairchildsemi.com/an/AN/AN-3004.pdf
http://www.fairchildsemi.com/sitesearch/fsc.jsp?command=text&attr1=Appications+of+Zero+Voltage+Crossing+Optically+Isolated+Triac+Drivers&attr2=undefined&v0=Applications+of+Zero+Voltage+Crossing+Optically+Isolated+Triac+Dr&vid=%24__visitId__%24&g=sitemap+taxonomy&i=sitemap+id&qid=%24__queryId__%24&s1=sitemap+id%2F%2F1&s0=iphrase+relevance%2F%2F0&tq=1&q=20&as=1&qtid=%24__queryId__%24&t=0&ia=1&c0=i%3A1%3B770%3Bsitemap+content+metadata+description%2Csitemap+content+metadata+keyword%2Csitemap+name%2Csitemap+taxonomy%2Csitemap+text%3BApplications%2CZero%2CVoltage%2CCrossing%2COptically%2CIsolated%2CTriac%2CDr%2Cof%3B%3Aapplication%2C%3Azero%2C%3Avoltag%2C%3Across%2C%3Aopticalli%2C%3Aisolat%2C%3Atriac%2C%3Adr%2Ciphrase+stopword%3B1%2C1%2C3%2C1%2C4%2C1%2C5%2C1%2C6%2C1%2C7%2C1%2C8%2C1%2C9%2C1%2C2%2C1%3B%2B0+%2B1+%2B2+%2B3+%2B4+%2B5+%2B6+%2B7&qt=1303230794&text=
In other words, the circuit provides the positive and negative voltage, when the positive voltage is input voltage and the negative voltage is output voltage. In that zero crossing detector is using the AC voltage and generated by VSC to the system Ac voltage and it provides the zero crossing of the system AC sin wave in the form of square wave and it have to used this wave form as reference to generate the AC voltage . (Javed, 2006)
The circuit is shown below:
FIGURE 5.29: ZERO CROSSING DETECTOR (H.Nouri Notes)
FIGURE 5.30: OUTPUT OF ZERO CROSSING DETECTOR (H.Nouri Notes)
ANALYSIS OF DRIVER CIRCUIT:
One of the electronic circuits is Gate Driver. The purpose of gate driver are apply exact power levels to Insulated Gate Bipolar Transistor[IGBTs] and it gives as isolation amplifiers and frequently provide short circuit protection. Based on the insulated gates, IGBTs provide a continuous gate circuit in order to obtain the gate current. Basically, they are four types of gate drivers. For positive supply, the high side gate drivers are used to generate IGBTs and it will not be connected at ground reference, and for negative supply, low side gate drivers are used to generate the IGBTs. Gate drivers includes some specifications are supply voltage, peak output current, propagation delay, rise time, fall time and power dissipation and operating temperature and switching frequency. The schematic diagram of driver circuit is: (Javed, 2006)
FIGURE 5.31: IGBT DRIVER CIRCUIT (H.Nouri Notes)
Pathak and ochi (2003) explained about reducing the total losses and higher operating efficiency for some subsystems, achieving compact design and calculating the weight of resultant systems.
In hard-wired electronic circuits they are different ways of MOSEFET/IGBTs and also there are some advantages of IC Drivers.
Firstly, the compactness is one of the advantages. In some designs, the usage of IC Drivers results is smaller sized circuits and those subsystems are applicable in multiple drivers design there are some features like UV, OV, OL and DESAT can be construct in some control logic and generates IC Drivers of MOSFET/IGBT.
Shorter Propagation Delays are used at IC Drivers. This is used at geometry; it provides the results into the smaller distances and it pass through by signals.
According to geometry and Shorter conduction paths, the IC Drivers outputs are developing from lower rise and fall times for available capacitive loads.
Repeatability and Predictability are one more advantage; it cannot be provide exact results at hard wired driver.
There are some important parameters that are generalised in an IC Drivers, developers are need not to go for time consuming steps for explaining, developing and testing circuits to generate ICs of MOSFET/IGBTs which save the time and capital and gradually decrease the “time to market†for complete products.
In half bridge and 3-phase bridge configurations, low side drivers are using for driving phase leg, the upper side of MOSFET/IGBT driver are modify to electrically isolation. There are some floating high side drivers with boot-strap power supply along with a low side driver and it has different useful features are:
To protect negative voltage transients.
To balance the latchup above entire operating range.
Rise time and fall time will be corresponding in nature.
Propagation delay should be co-ordinating for required outputs.
5.6 TEST PLAN OF MICROCONTROLLER:
Basically, the switching techniques are implemented in PIC Microcontroller PIC16F877. Presently, we are implementing the switching techniques with applications of fibre optics communication. (Javed, 2006)
The Microcontroller PIC16F877 is designed from Harvard architecture microcontroller and developed by Microchip Technology. It is used to implement the different switching techniques. It contains so many characteristics like less cost, larger user base, broad availability, general collection of applications and it consists of 40 pins. (Javed, 2006)
FIGURE 5.32: MICROCONTROLLER PIC16F877 (Javed, 2006)
In that, there are some core features and peripheral features for Microcontroller PIC16F877.
5.6.1 CORE FEATURES OF PIC16F877:
A. While doing the experiment with 8-bit CMOS Flash Microcontroller it required 28/40 pin. In that there is one advantage is to erase the data and it can enter the data for many times. (Javed, 2006)
B. The performance of RISC is high priority.
C. Single cycle executions are followed by all instructions for branches which are two cycles.
D. In that, there are some specifications to operate the microcontroller like the maximum operating speed is 20MHz clock input i.e. every instruction cycle is of 200ns. It will be operate at 4MHz or 16MHz etc.
E. Up to 8K*14 words of FLASH programme memory.
F. Up to 368*8 bytes of data memory [RAM].
G. Up to 256*8 bytes of EEPROM data memory.
H. Interrupt capability [up to 14 sources].
I. In that, there are different types of addressing modes like direct, indirect and relative.
J. For reset purpose we can operate Power on reset [POR].
K. Power up timer [PWRT] and oscillator start up timer [OST].
L. Watch dog timer [WDT] with its own on chip RC oscillator.
M. The operating voltage range: 2V to 5.5V.
N. Low power consumption.
5.6.2 PERIPHERAL FEATURES OF PIC16F877:
Timer0: 8-bit timer/counter with 8-bit prescaler.
Timer1: 16-bit timer/counter with prescaler can be incremented during SLEEP via external Crystal /clock.
Timer2: 8-bit timer/counter with 8-bit period register, prescaler and postscaler.
Capture, compare, PWM modules
Capture is 16-bit, max. resolution is 12.5ns.
Compare is 16-bit, max.resolution is 200ns.
PWM max. resolution is 10-bit.
E. For Analog-to- Digital Converter 10-bit multi-channel is used.
F. Synchronous Serial Port [SSP] with SPI [Master mode] and I2C [Master/Slave].
G. Universal Synchronous Asynchronous Receiver Transmitter [USART/SCI] with 9-bit address Detection.
H. Parallel Slave Port [PSP] 8-bits wide, with external RD, WR and CS control [40/44 pins]. (Javed, 2006)
The board unit of Microcontroller PIC16F877 is to design the different switching techniques with using 40 pin microcontroller chip 14-pin AND gate [P0048SB] and 14-pin inverter [74VHC148]. For the different switching techniques the wiring and connections are slightly different. (Javed, 2006)
FIGURE 5.33: PIC MICROCONTROLLER (H.Nouri Notes)
For developing the Zero crossing Detector, PWM Inverter and Fundamental pulses purposes we are using the Microcontroller PIC16F877. It is basically three phase system with one level Statcom. Actually, we are executing the outputs with applications of fiber optics.
5.7 APPLICATIONS OF MICROCONTROLLER:
In the microchip technology PIC is one of the families of Harvard Architecture microcontroller. Basically it was developed by general instruments of micro electronics division. The full form of PIC is Programmable Interface Controller. We consider a single chip; in that micro controller is a computer control system. In that, manufactures build many electronic circuits, that can be decode and it implement as algorithm and finally convert them to electrical signals. In microcontroller we use number of logic gates instead of hard wiring and it performs some logic function that is used for gates electronically [3]. The combination of the instructions needed to the microcontroller that is called program. (D.W.SMITH, 2002)
Tsai and Ke (2009) explained about PIC16F877 at high-voltage high-frequency pulse power supply is to verified for a long time and also it examine for various industrial fields of semiconductor manufacturing, packing, PCB and LCD panel manufacturing and also for industrial pipeline systems they are using for chemical processing of water and exhausted smoke, and disinfection at particular distances and it has one more advantage, silent-discharge is developed for large scale applications at industrial pipeline systems. In that, a high-voltage high-frequency pulse power supply is used at plasma applications. This plasma applications used at different field like gas discharge, dielectric discharge (silent discharge) and corona discharge and also it is mainly used in industrial large-scale ozone-generation system and also practically generate ozone gas is at silent-discharge. This is finally used for gas clean system. The PFC rectifier and a voltage-source full-bridge inverter are for future extension of high-voltage and high-frequency pulse power supply. The function of inverter out is wiring to load during high-voltage high frequency transformer. For controlling the out of the inverter, they considered Pulse Width Modulation [PWM] and Pulse-density Modulation [PDM]. This Plasma application has different stages at control unit. There are PFC stage and Inverter stage. (Tsai and Ke ,2009)
In the PFC stage, the microcontroller UC3854 is an average mode and it have to complete the experiment with help of fixed frequency current control with stability and low distortion. (Tsai and Ke ,2009)
FIGURE 5.34: CIRCUIT OF PFC STAGE . (Tsai and Ke ,2009)
In the Inverter stage, it has five statuses and also including active and passive statuses to resolve with power switching elements of the two legs. In the active status the two diagonally opposite power switches are executing and for passive status the two power switches is at same voltage levels. In inverter there is leading leg and trailing leg. For leading leg the power moves from active to passive statuses. For trailing leg the power moves form passive to active statuses. In the RLC series circuit, the inverter switching frequency is high when compared to load resonant frequency.
FIGURE 5.35: CIRCUIT OF INVERTER STAGE. (Tsai and Ke ,2009)
There is another microcontroller application which is called as laser based smart displacement sensor. This application is very important for different types of the system. There are some characteristics of contactless and ruggedness, optical systems that are based on optical detectors. While doing this experiment it gives some drawback. To avoid these drawbacks we have to choose different light emitters and light detectors, displacement-measuring systems then we will get poor resolution or high sensitivity at the geometrical settings and environment light. This application is generalised at direct laser illumination of two light detectors. The laser source, detectors data acquisition, data neutral processing and data communication are to be controlling and executing at 8-bit RISC microcontroller and that indicates as the “Brain†of the smart laser sensor. (Postolache, Pereira, Girao, 2001)
FIGURE 5.36: THE CIRCUIT DIAGRAM OF THE SMART DISPLACEMENT SENSOR (Postolache, Pereira, Girao, 2001)
