Design of AC Mains Monitor Based on MSP430*

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1 NAME OF STUDENTS:- Abstract:- An AC Mains quality monitoring system based on MSP430 is proposed in this paper. The monitoring system can monitor RMS voltage and AC Mains frequency. It is showed that the monitoring system is not only an accurate mete of electrical energy, but also to accurately detect the abnormality and record it. Also the purpose of this project is to practice DSP algorithm on MSP430 microcontroller. measuring True RMS voltage and frequency is part of that project, alongside of spectrum the LCD screen will display True RMS Voltage and frequency of AC mains line. most of the normal AC mains voltage meter measure average/peak voltage and then adjust the voltage a little considering sine wave input waveform. average measurement technique works well till input is pure sine wave but as soon as you input other waveform like square wave from backup UPS, normal meter will not read them correctly. so if you want real effective voltage level you have to calculate true RMS voltage. but calculating true RMS is not very easy it need a decent amount of calculation to be performed. small microcontroller are not generally meant for these calculation but MSP430 is mixed signal microcontroller, it has few very advanced peripherals to support some light weight DSP WCE,SANGLI Page 1

2 operations. we will see in a minute how to calculate True RMS of a signal and what are the challenges doing this on a small microcontroller. True RMS The term RMS stands for Root-Mean-Squared. Most books define this as the amount of AC power that produces the same heating effect as an equivalent DC power, or something similar along these lines, but an RMS value is more than just that. The RMS value is the square root of the mean (average) value of the squared function of the instantaneous values. The symbols used for defining an RMS value are VRMS or IRMS. In practical you have to take few samples of the input wave at a fixed interval,square each sample result, add all of the result, calculate mean of the results and then finally to get final RMS value calculate square root of the mean. graphically how to calculate true RMS is as shown in the figure below. WCE,SANGLI Page 2

3 One of the problems faced by industry is fluctuation in AC supply. Problem:- Proposed Solution:- Mains In this paper,to measuree the true RMS value of voltage and frequency of AC Mains,we have used Mixed signal processor and designed an AC Mains Monitor based on MSP430 microcontroller.this paper is devided into two sections from here onwards 1.Hardware design 2.Software design WCE,SANGLI Page 3

4 1.Hardware design :- Hardware of this miniproject contains 1.AC Mains supply 2.Voltage control Integrated circuit 3.MSP430 launchpad 4.16x2 Liquid crystal display 1.AC Mains supply:-this supply contains live wire and neutral wire whose electrical parameters are measured during this miniproject 2. Voltage control Integrated circuit:-as AC Mains supply is bipolar signal,but we need unipolar signal for Mixed signal processing.so we have to add some DC offset voltage to original signal and for the same purpose we are using this IC. 3.MSP430 launchpad:-actually we are using 3 blocks from this launchpad. WCE,SANGLI Page 4

5 1.10 bit ADC Module:-Output from Voltage control IC is given as input to pin no.p1.0(analog channel input) to convert the signal into digital signal so that it can be processed by microcontroller 2.Actual MSP430 IC:-To process on the digital signal send by ADC Module to calculate the True RMS Voltage of AC mains. 3.Analog Comparator Module:-This Analog Comparator Module is used to convert the sine wave into square wave so that we can measure the frequency of signal.frequency of square wave and sine wave are same.sine wave is given to the non-inverting terminal of comparator and reference voltage is given to inverting terminal of an Op-amp.Now if Sine wave exceeds the reference voltage,output voltage goes high and if it is less than the reference voltage,output voltage goes low to create a square wave on COUT pin. WCE,SANGLI Page 5

6 4. 16x2 Liquid crystal display:-this LCD is used to display the value of RMS voltage and Frequency of AC Mains supply.data pins(8 in number) of LCD are connected to port pins of MSP430.RW pin is grounded.potentiometer is used to control brightness of LCD. 2.SOFTWARE DESIGN:- Software development environment used for our project is Code Composer Studio. WCE,SANGLI Page 6

7 Actual C code written in Code Composer Studio mainly contains three parts: bit ADC interfacing with MSP430 microcontroller which is available on MSP430 Value Line series launchpad,to convert analog signal to digital and measure the avg voltage that is RMS voltage by averaging the value 100 samples. 2. Analog Comparator which is also available on MSP430 Value Line series launchpad is used for converting input sin wave into square wave, which is then given as an input to counter to measure the time period of given square wave,so that we can estimate the freq of AC Mains X2 LCD is interfaced with MSP430 to display the rms voltage and freq of AC Mains. Block Diagram:- WCE,SANGLI Page 7

8 Circuit Diagram:- 16X2 LCD LM016L VSS VDD VEE RS RW E D0 D1 D2 D3 D4 D5 D6 D CONTROLLER IC P1.0/TACLK P2.0/ACLK P1.1/TA0 P2.1/INCLK P1.2/TA1 P2.2/CAOUT/TA0 P1.3/TA2 P2.3/CA0/TA1 P1.4/SMCLK/TCK P2.4/CA1/TA2 P1.5/TA0/TMS P2.5/ROSC P1.6/TA1/TDI/TCLK P1.7/TA2/TDO/TDI AC MAINS SUPPLY 6 5 XIN XOUT MSP430C1101 RST/NMI TEST 7 1 WCE,SANGLI Page 8

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