03-04-2010, 09:20 PM
microcontroller based power monitoring for 600KVA BATTERY BACK UP
1.INTRODUCTION
The microcontroller-based power monitoring system is an electronic device used to continuously monitor the parameters of power such as voltage, current, frequency, etc at the various points of an electric or electronics devices. The entire system is controlled by the microcontroller (80C31) and it is the real time monitoring of various parameters. Thus the name REAL TIME MONITORING OF HIGH CAPACITY (400KVA-600KVA) BATTERY BACK UP SYSTEM. This system is an 8-channel device, which accepts 8 analog input signals and consist of analog multiplexer, A/D converter, ROM, RAM, buffer etc. The different channels are selected by simple switch operation. From the UPS the channels and alarms are given to the microcontroller and it will process and control the parameters.
Fig 1.1 UPS MONITORING SYSTEM
The above system can be utilized for remote monitoring of electrical system and process plant. This power monitoring system has been designed for heavy industrial locations, which is equipped with latest technology to provide complete power analysis of power consumption, power disturbances, harmonics, and flickering in a single system.
2.POWER MONITORING SYSTEM
Fig 3.1 Block Diagram of PMS
2.1 BLOCK DIAGRAM DESCRIPTION:
The block diagram consist of power supply, multiplexer, A/D converter, microcontroller, EPROM, RAM and display unit. 80C31 microcontroller is the main component of the power monitoring system. The function of microcontroller is that it processes the signal and controls the operation of the system using fixed program that is stored in ROM and that does not change over the lifetime of the system. The microcontroller accepts the data, process it and display the output using a switch able display system.
The 8 analog signal is fed to the multiplexer unit then the microcontroller sends three MUX selection signals (A, B, C) to the multiplexer to select one signal from the 8 input signals. From the 3 input signals there occurs 8 combinations. Then the signal from the MUX is fed to the A/D converter. There it converts the analog signal into digital Random access memory (RAM) is apart of microcontroller (80C31). The program execution occurs using RAM. The EPROM is another important block in PMS circuitry. It is a storage device that is used to store the program for the monitoring system.
The next block is the display unit here we use liquid crystal display (LCD) for displaying the output of power monitoring system. LCD is driven from the ac supply using special circuitry. They are more expensive than LED displays.
2.1.1. POWER SUPPLY:
A 5v power supply is given to VCC pin of the entire IC chip and the microcontroller.
Fig 3.2 power supply
The power supply is used to provide 5V DC. It consists of a step down transformer that step down 230V to 9V AC.I t followed by a bridge rectifier that converts AC to DC. A capacitive type is used to smoothens the dc waveform. A regulator IC 7805 is used to provide a constant 5V dc irrespective of load fluctuations.
2.1.2 MICROCONTROLLER
Fig 2.3 Block Diagram of microcontroller
Microcontroller is a single chip computer. A microcontroller has a CPU (microprocessor), ROM, RAM, I/O Port and Timer all on a single chip. The prime use of microcontroller is to control the operation of a machine using fixed program that is stored in ROM. The microcontroller design uses a set of single and double byte instructions that are used to move code and data from internal memory to ALU.
2.1.3 ADC
ADC is used to convert analog signals to digital signals. Microcontroller operates on digital mode. The different type of ADC is successive approximation, dual slope, flash type and sigma delta type.
Here we are using ADC 0808 “it is an 8 bit chip compactable ADC with 8 channel multiplexer. The ADC 0808 data acquisition component is a monolithic CMOS device with an 8-bit A/D converter, 8- channel multiplexer & microprocessor compactable control logic. The ADC uses successive approximation method for conversion. The converter features a high impedance chopper stabilized comparator, a 256 R voltage divider with analog switch tree and a successive approximation register. The 8 channels multiplexer can directly access any of 8 single ended analog signals.
The device eliminates the need for external zero and full-scale adjustment. Easy interfacing to microcontroller provided by the latched and decoded multiplexer address input and TTL Tristate outputs.
The ADC 0808 offers high speed, high accuracy, minimal temperature dependence, repeatability and consume minimum power.
2.1.4 MEMORY
In this circuit two types of memory are used. They are RAM and EPROM. Program is burned in EPROM and RAM is used for temporary storage of data during the execution.
EPROM
Using an EPROM we can program and erase the memory chip thousands of time. It is a storage device for real time monitoring system. Ultraviolet radiation is mainly used to erase the program. Here we use Intel 27C256 EPROM.
RAM
RAM is a volatile memory. RAM can be also referred as read and write memory. There are mainly two types of RAM. Static and Dynamic RAM. Here we use SRAM.
2.1.5 LIQUID CRYSTAL DISPLAY :
LCD are used as numerical indicator especially in digital watches were there is much smaller current needs than LED display. It has prolonged battery life. Liquid crystals are organic compounds, which exhibit both solid and liquid properties. A Ëœcellâ„¢ with transparent metallic conductors, called electrodes on opposite faces containing a liquid crystal and on which light falls goes dark, when a voltage is applied across the electrodes. The effect is due to molecular rearrangement within the liquid crystal.
The pattern of the conducting electrodes on a seven-segment LCD decimal display for producing the numbers from 0 to 9. Only the Liquid crystal under those electrodes to which the voltage is applied goes dark. The display has a silvered background which reflects back incident light and it is against this continuously visible background that the numbers shown up as a dark segment.
3.CIRCUIT DESCRIPTION:
The figure shown before illustrates the circuit used for the realization of the THE REAL TIME MONITORING OF HIGH CAPACITY (400KVA-600KVA) BATTERY BACK UP SYSTEM, circuit consists of nine different type of ICâ„¢s including the microcontroller 8031. A liquid crystal display (LCD) has also been provided for the visualization of the various parameters monitored by the system.
A crystal oscillator of 11.057 MHz has been connected to the appropriate oscillator pins of microcontroller for providing the frequency and timing to the various machine and instruction cycles involved with its operation. The analog signals to be monitored are made to be available as inputs to the A/D converter ADC0808 at the 8 different channels. A corresponding binary signal at the A, B and C inputs of the microcontroller selects the respective channel. The binary input is varied by pressing the push button switch (PB) accordingly. The address data bus of the microcontroller has been connected to the appropriate pins of latch 744C373, external RAM-6264, external EPROM-27C256, buffer IC-74LS244.
The decoder IC 74HC138 when enabled selects the buffer (1 & 2 ICâ„¢s-74LS244) either for accepting digitally converted and buffered analog inputs or providing buffer data lines respectively.
IC4060 is a 14-stage ripple carry binary counter activated by a crystal of frequency 5MHz provides the necessary oscillations required for the operation of the A/D converter0808.
Liquid crystal display (LCD) ODM 16116-2SL capable of displaying all kinds of alphanumeric characters, is used. Apart from the above-mentioned ICâ„¢s NOT gate IC7414 has been used for the selection of certain other ICâ„¢s during process. The entire PMS has been provided a constant uninterrupted supply of 5V for the operation of the various ICâ„¢s used in the system.
4. MICROCONTROLLER
Microcontrollers are general purpose digital computers. A microcontroller is a true computer on a chip. The design incorporates all the features found in a microprocessor CPU, ALU, SP, PC and registers.
It also has added features like ROM, RAM, parallel I/O port, serial I/O counter and a clock circuit. Microcontroller is a general-purpose device, but one that is meant to read data perform limited calculations on that data and control its environment based on that calculations. The prime use of microcontroller is to control the operation of a machine using a fixed program that is stored in ROM and that does not change over the lifetime of the system.
The microcontroller design uses a much-limited set of single and double byte instruction that are used to move code and data from internal memory to the ALU. Many instructions are couple with pins on the integrated circuit package; the pins are programmable, that is having several different functions depending on the wishes of the programmer. The micro controller is concerned with getting data from and to its own pins; the architecture and the instruction set optimized to handle data in byte size.
Microcontroller will have many types of bit handling instructions. They have one or two operational codes for moving data from internal memory to CPU. They are concerned with the rapid movement of bits within the chip. The microcontroller can function as a computer with the addition of no external digital parts.
Microcontroller models vary in data size from 4 to 32 bits. Four bits units are produced in high volume for very simple applications, and 8 bits units are the most versatile and16 bits are used in high-speed controller and signal processing applications. Many models feature programmable pins that allows external memory to be added..
4.1.1 FEATURES
¢ 8051 Central Processing Unit
- 128.8 RAM (80C31)
- 256.8 RAM (80C32)
- Three 16-bit counter/timers
- Boolean processor
- Full static operation
- Low voltage (2.7V to 5.5V @ 16 MHz) operation
¢ Memory addressing capability
- 64k ROM and 64k RAM
¢ Power control modes
- Clock can be stopped and resumed
- Idle mode
- Power-down mode
¢ CMOS and TTL compatible
¢ Two speed ranges at VCC=5V
Fig 5.2 Logic symbol of microcontroller
4.1.2 PIN DESCRIPTIONS
POWER SUPPLY: VCC
This is the power supply voltage for normal, idle, and power-down operation. 80c51 operates a power supply of 5V.
GROUND: VSS
0V reference is used as the ground.
PORT 0: P0.0-0.7
Port 0 is an open-drainer, bi-directional I/O port with Schmitt trigger inputs. Port 0 pins that have 1s written to them float and can be used as high-impedance inputs. Port 0 is also the multiplexed low-order address and data bus during accesses to external program and data memory. In this application, it uses strong internal pull-ups when emitting 1s.
PORT 1: P1.0-P1.7
Port 1 is an 8-bit bi-directional I/O port with internal pull-ups and Schmitt trigger inputs. Port 1 pins that have 1s written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs, port1 pins that are externally pulled low will source current because of the internal pull-ups. Alternate functions for port 1 include:
T2 (P1.0): Timer/Counter 2 external count input/clockout
T2EX (P1.1) Timer/Counter 2 Reload/Capture/Direction control
PORT 2
2.0-P2.7Port 2 is an 8-bit bi-directional I/O port with internal pull-ups and Schmitt trigger inputs. Port 2 pins that have 1s written to them are pulled high by the internal pull-ups and can be use as inputs.
As inputs, port 2 pins that are externally being pulled low will source current because of internal pull-ups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that uses 16-bit addresses (movx@DPTR). In this application, it uses strong internal pull-ups when emitting 1s.During accesses to external data memory that uses 8-bit data addresses (MOV@Ri), port 2 emits the contents of the P2 special function register.
PORT 3
3.0-P3.7 Port 3 is an 8-bit bi-directional I/O port with internal with internal pull-ups and Schmitt trigger inputs. Port 3 pins that have 1s written to them are pulled high by the internal pull-ups and can be use as inputs. As inputs, port 3 pins that are externally being pulled low will source current because of internal pull-ups. Port 3 also serves the special features of the 80C51 family, as listed below.
RxD (P3.0) Serial input port
TxD (P3.1) Serial output port
INTO (P3.2) External interrupt
INTI (P3.3) External interrupt
TO (P3.4) Timer 0 external input
T1 (P3.5) Timer 0 external input
WR (P3.6) External data memory write strobe
RD (P3.7) External data memory read strobe
RESET: RST
A high on this pin for two machine cycles while the oscillator is running, resets the device. An internal diffused resistor to VSS permits a power-on reset using only an external capacitor to VCC.
ADDRESS LATCH ENABLE: ALE
Output pulse for latching the low byte of the address during an access to external memory. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency, and can be used for external timing or clocking. ALE can be displayed by setting SFR auxiliary .0. With this bit set, ALE will be active during a MOVX instruction.
PROGRAM STORE ENABLE: PSEN
The read store is used for external program memory. When the 80C31/32 is executing code from the external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory. PSEN is not activated during fetches from internal program memory.
EXTERNAL ACCESS ENABLE / PROGRAMMING SUPPLY VOLTAGE: EA/VPP
EA must be externally held low to enable the device to fetch code from external program memory locations 0000H to 0FFFH.
CRYSTAL 1: XTAL1 Input to the inverting oscillator amplifier and input to the internal clock generator circuits.
CRYSTAL 2: XTAL2 Output from 6the inverting oscillator amplifier.
OSCILLATOR CHARACTERISTICS
XTAL 1 and XTAL 2 are the input and the output respectively, of an inverting amplifier. The pins can be configured for use a on-chip oscillator, as shown in the logic symbol.
To drive the device from an external clock source XTAL 1 should be driven while XTAL 2 is left unconnected. There are no requirements on the duty cycle of the external clock signal, because the input to the internal clock circuitry is through a divide-by-two flip-flop. However, minimum and maximum high and low times specified in data sheet must be observed.
RESET
A reset is accomplished by holding the RST pin high for at least two machine cycles (24 oscillator periods), while the oscillator is running. To ensure a good power-up reset, the RST pin must be high long enough to allow the oscillator time to start up (normally a few milliseconds) plus two machine cycles.
4.2 STOP CLOCK MODE
The static design enables the clock speed to be reduced down to 0 MHz (stopped). When the oscillator is stopped, the RAM and the Special Function Register retain their values. This mode allows step-by-step utilization and permits reduced system power consumption by lowering the clock frequency down to any value. For lowest power consumption the power mode is suggested.
4.3 IDLE MODE
In idle mode (see Table 2), the CPU puts itself to sleep while all of the on-chip peripherals stay active. The instruction to invoke the idle mode is the last instruction executed in the normal operating mode before the idle mode is activated. The CPU contents, the on-chip RAM, and all of the special function registers remain intact during this mode. The idle mode can be terminated either by any enabled interrupt (at which time the process is picked up at the interrupt service routine and continued), or by a hardware reset which starts the processor in the same manner as a power-on reset.
DESIGN CONSIDERATION
When the idle mode is terminated by a hard ware reset, the device normally resumes program execution, from where it left off, up to two machine cycles before the internal rest algorithm takes control. On-chip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write when Idle is terminated by reset, the instruction following the one that invokes Idle should not be one that writes to a port pin or to external memory.
5. IC DESCRIPTION
The ICâ„¢s used in this circuit diagram are
¢ ADC- 0808M
¢ RAM- HM6264A
¢ EPROM- FM 27C256
¢ DECODER- 74 LS 138
¢ BUFFER- DM74LS244
¢ LATCH- DM74LS373
¢ COUNTER- CD4060B
¢ Voltage Regulators“ LM7805
¢ INVERTER- DM74LS14
¢ NAND GATE- DM74LS20
5.1 ADC0808M
The ADC0808M is a monolithic CMOS device with a 8-channel multiplexer, 8-bit analog- to-digital (A/D) converter, and microprocessor-compatible control logic. The 8-channel multiplexer can be controlled by a microprocessor through a three-bit address decoder with address load to select anyone of eight single-ended analog switches connected directly to the comparator.
The 8-bit A/D converter use3s the successive approximation conversion technique featuring a high impedance threshold detector, a switched capacitor array, a sampled-and-hold, and a successive approximation register (SAR). Detailed information on interfacing to the most popularly microprocessor is readily available from the factory. The comparison and converting methods used eliminate the possibility of missing codes, nonmonotonicity, and the need for zero and full-scale adjustment. Also featured are latched three state outputs from SAR and latched inputs to the multiplexer address decoder. The single 5V supply and low power requirements make the ADC0808M especially useful for a wide variety of applications.
5.1.1 FEATURES
¢ Total unadjusted error¦ + 0.75 LSB Max
¢ Resolution of 8-bits
¢ 100 ms conversion time
¢ Ratio metric conversion
¢ Monotonous over the entire A/D conversion range
¢ No missing codes
¢ Easy interface with microprocessor
¢ Latched three state outputs
¢ Latched address inputs
Fig 6.1 Pin diagram of ADC 0808
5.1.2PRINCIPLE OF OPERATION
The ADC0808M consists of an analog signal multiplexer, an 8-bit successive-approximation converter, and related control and output circuitry.
MULTIPLEXER
The analog multiplexer selects1 of 8 single-ended input channels as determined by the address decoder. Address load control loads the address codes into the decoder on a low-high transition. The output latch is reset by the positive going edge of the start pulse. Sampling also starts with the positive going edge of the start pulse and last for 32-clock period. The conversion process may understand by a new start pulse before the end of 64 clock periods. The previous data will be lost if a new start of conversion occurs before the 64th clock pulse.
Continuous conversion may be accomplished by connecting the end of conversion output to the start input. If used in this mode an external pulse should be applied after power up to assure start up.
CONVERTER
The CMOS threshold detector in the successive approximation conversion system determines each bit by examining the charge on a series of binary weighted capacitors (fig.2). In the first phase of conversion process, the analog input is sampled by the closing switch SC and all ST switches, and by simultaneously charging all the capacitors to the input voltage.
In the next phase of the conversion process, all SC and ST switches are open and the threshold detector begins identifying bits by identifying the charge (voltage) on each capacitor relative to the reference voltage. In the switching sequence, all 8 capacitors are examined separately until all 8 bits are identified, and then the charge convert sequence is repeated. In the first step of the conversion phase, the threshold detector looks at the first capacitor (weight = 128). Node 128 of this capacitor is switched to the reference voltage and equivalent nodes of all the other capacitors on the ladder are switched to REF-. If the voltage at the summing node is greater than the trip-point of the threshold detector (approximately one-half the VCC voltage), a bit is placed in the output register, and the 128-weight capacitor is switched to REF-. If the voltage at the summing node is less than the trip point of the threshold detector, this 128-weight capacitor remains connected to REF+ through the remainder of the capacitor-sampling (bit-counting) process.
With each step of the capacitor-sampling process, the initial charge is redistributed among the capacitor. The conversion process is successive approximation, but relies on charge redistribution rather than successive approximation register (and reference DAC) to count and weigh the bits from MSB to LSB.
5.2 LM7805
The LM78XX series of three terminal regulators is available with several fixed output voltages making them useful in a wide range of applications. One of these is local on card regulation, eliminating the distribution problems associated with single point regulation. The voltages available allow these regulators to be used in logic systems, nstrumentation, HiFi, and other solid state electronic equipment. Although designed primarily as fixed voltage regulators these devices can be used with external components to obtain adjustable voltages and currents.
The LM78XX series is available in an aluminum TO-3 package which will allow over 1.0A load current if adequate heat sinking is provided. Current limiting is included to limit the peak output current to a safe value. Safe area protection for the output transistor is provided to limit internal power dissipation. If internal power dissipation becomes too high for the heat sinking provided, the thermal shutdown circuit takes over preventing the IC from overheating.
6. FLOWCHART
fig 8.1 flowchart
7. CONCLUSION AND FUTURESCOPE
The A.C. power supplies are commonly used as stand by so uses for critical loads and in applications where normal A.C supplies are not available. The stand by power supplies is also known as uninterruptible power supply (UPS) system. The load in the configuration is normally supplied from the ac main supply and the rectifier, maintains the full charge of the battery. If the supply fails, the load is switched to the output of the inverter, which then takes over the main supply. The inverter runs only during the time when the supply failure occurs. The inverter can be used to condition the supply to the load, to protect the load from the transients in the main supply, and to maintain the load frequency at the desired value. The UPS consist of a battery, an inverter and a static switch. In case of power failure, the battery supplies the back up system. When the main power supply on, the UPS operates as rectifier and charge battery.
Nuclear power plants will be powered AC power supply .Any fault in power supply cause hazard effect in nuclear power plant. So opt for an additional back up system. PMS system monitors 8 different channels, I/P AC voltage, DC voltage, DC current, AC O/P voltage, current. It has an additional facility of monitor 8 alarms like over temperature, burning of fuses etc. These conditions are dangerous to nuclear power plant. This system checks alarm condition at any time. This system keeps the back-up power supply ready to support the plant when necessary.
11. REFERENCES
¢ Microcontroller 8051- Programming & Architecture Kenneth J Ayala
¢ The 8051 Microcontroller and Embeded system
Muhammed Ali Mazidi
¢ Linear Integrated circuit-Roy Chaudary
