IMPROVED AC-AC CONVERTER FOR INDUCTION HEATING APPLICATIONS

IMPROVED AC-AC CONVERTER FOR INDUCTION HEATING APPLICATIONS

 Electrical and Electronics Project by Ravi Devani

ABSTRACT

Induction heating applications require high frequency currents which are obtained using resonant converters viz., Series and Parallel resonant inverters. The resonance frequency in these converters will be tuned to a high value. In this paper a single-switch parallel resonant converter for induction heating is simulated. It is compared with the existing inverter topologies; half bridge and full bridge. The circuit consists of input LC-filter, bridge rectifier and one controlled power switch. The switch operates in soft commutation mode and serves as a high frequency generator. Output power is controlled via switching frequency.

Keywords — High frequency, induction heating, Resonant converters

INTRODUCTION

Induction heating is a non-contact heating process. It uses high frequency electricity to heat materials that are electrically conductive. Since it is non-contact, the heating process does not contaminate the material being heated. It is also very efficient since the heat is actually generated inside the work-piece. This can be contrasted with other heating methods where heat is generated in a flame or heating element, which is then applied to the work-piece. For these reasons Induction heating lends itself to some unique applications in industry. Static frequency converters have been extensively applied in industry as a medium –frequency power supply for induction heating and melting installations. They are applied in all branches of the military, machine-building industries, domestic heating cooking devices and other purposes. Increasing the frequency of operation of power converters is desirable, as it allows the size of circuit magnetics and capacitors to be reduced, leading to cheaper and more compact circuits. However, increasing the frequency of operation also increases switching losses and hence reduces system efficiency. One solution to this problem is to replace the "chopper" switch of a standard SMPS topology (Buck, Boost etc.) with a "resonant" switch, which uses the resonances of circuit capacitance and inductance to shape the waveform of either the current or the voltage across the switching element, such that when switching takes place, there is no current through or voltage across it, and hence no power dissipation. Because they require a substantial drive current, bipolar transistors are not generally used in resonant converters, unless the base drive is provided by the resonant circuit itself (for example in TV deflection circuits and fluorescent lamp ballasts). Power MOSFETs and IGBTs, with their effectively capacitive inputs and low drive energy requirements, are the most frequently used types. The power converter generally implemented in domestic IH appliances is a resonant inverter due to its improved efficiency and lower size, which allows developing compact appliances. Inverter topologies commonly used for IH are the full-bridge and half bridge operations some deviations of these topologies are used often to achieve multiple-output converters. The modulation strategies commonly applied to control output power are based on modifying either switching frequency or duty cycle to achieve the desired output power. Each power converter topology offers different performance features with specific requirements in terms of costs, and hardware and control complexity. The full-bridge topology can offer the higher output power (up to 5 kW) and control flexibility, and its efficiency can be significantly optimized through the proper control strategy. However, its higher cost makes it unfeasible for the mean IH appliance. The half-bridge series resonant inverter is the most used topology due to its appropriate balance between performance, complexity, and cost. It is used to design converters with up to 3.5-kW output power.

The decision has to be made considering the proper balance between cost and performance. This paper presents circuit of an AC-AC converter for induction heating .It typically includes a controlled rectifier and a frequency controlled current source or a voltage source inverter. It is a fact that the input rectifier does not ensure a sine wave input current, and is characterized by a low power. Recently many studies of high power factor rectifiers with a single switch have been made. These schemes are also characterized by a close to sine wave input current. The input circuit of the converter is constructed similarly to the input circuit in, which also ensures a high power factor. The present problem aims to minimize the cost of induction heater system by using an embedded controller.

IH TECHNOLOGY

The main blocks of an induction cooking appliance are shown in Fig. 1.

 

Fig 1. Induction cooking appliance block diagram.

The energy taken from the mains is filtered by an electromagnetic compatibility (EMC) filter, which prevents the device from inserting interferences and provides immunity to voltage transients. Then it is converted to DC using a rectifier. Then, connect this DC current to a high frequency switching circuit to administer high frequency current to the heating coil. According to Ampere’s Law, a high frequency magnetic field is created around the heated coil. A low value of filter capacitor is taken to get a high power factor, and as a consequence, a high-ripple dc bus is obtained. Then, the resonant inverter supplies variable frequency current (20–100 kHz) to the induction coil. This current produces an alternating magnetic field, which causes eddy currents and magnetic hysteresis heating up the pan. The inductor-pan system is modeled as the series connection of an equivalent resistance Req and an equivalent inductance Leq. This model shows proper results to analyze power-converter operation. At the resonance frequency, the inductive reactance and the capacitive reactance become the same, i.e. the voltage of the power source and the current in the circuit stay at the same level. The current in the circuit reaches its peak when the source frequency becomes identical to the resonance frequency. It decrements when the source frequency gets higher or lower than the resonance frequency. The current and output energy reaches its maximum value at resonance frequency.

HALF BRIDGE SERIES RESONANT INVERTER

The main power circuit employs a half-bridge series converter switching at a high frequency as shown in Fig. 2. The switching circuit consists of an IGBT.

Zero voltage/current turn-on switching is enabled by turning on the IGBT while the diode is in turn on period. The resonant circuit comprises of resonant inductance (Lr) and resonant capacitance (Cr). The capacitors, C1 and C2, are the lossless turn-off snubbers for the switches, S1 and S2. The resonant frequency fr of the converter is mainly determined by the inductance Lr and the capacitance Cr of the series capacitor. 

The switching frequency of the system is set higher than the resonance frequency, in order to avoid noise generated within the audio frequency band. The resonant load consists of the pan, the induction coil and the resonant capacitor. Induction coil and pan coupling is modeled as the series connection of an inductor and a resistor, based on its analogy with respect to a transformer. The basic circuit of a half bridge series resonant circuit is shown in Fig. 2

 

Fig 2. Half bridge series resonant inverter

By connecting the IGBT switching circuit, S1 and S2 in parallel to diodes D1 and D2, current loss is minimized. When S1 is turned-off, D2 helps S2 stay on zero voltage/current before being turned on, thereby substantially reducing current loss (the same is the case with S1). There is no reverse- recovery problem as the voltage on both sides remains zero after the diode is turned off. However, as the switching circuit is turned off at around the upper limit of voltage and current, some switching loss results on turn-off. The capacitors C1 and C2, acting as turn-off snubbers connected in parallel to S1 and S2, keep this loss to a minimum. Upon turn-on the switching circuit starts from zero voltage/current, so these turn-off snubbers operate as lossless turn-off snubbers. This has been simulated using MATLAB/ SIMULINK with the circuit diagram shown in Fig. 3.

This system does not require a big capacitor to make DC more leveled, as the primary purpose of the system is to generate heat energy. Rather, the rugged form of DC helps improve the power factor of the system. In this system, the leveling capacitor serves as a filter preventing the high frequency current from flowing toward the inverter and from entering the input part. Input current becomes the average of the inverter current, and the ripples flow to the leveling capacitor. The voltage passing the leveling capacitor is turned into a square wave in the process of high frequency switching in the inverter. The high frequency harmonics contained in the square wave are eliminated by the Lr, Cr filter. The square wave enables resonance in the resonant circuit, which in turn, creates a magnetic field around the resonant inductor affecting the load. Eddy currents are formed around the surface of the object, generating heat energy.

 

Fig 3 . SIMULINK model of Half bridge inverter

  Electrical and Electronics Project by Ravi Devani

The voltage and current waveforms of the simulated circuit are also shown below (fig. 4).

Fig. 4. (a) The voltage waveform and

(b) Current waveform

Since it is a voltage- source inverter voltage waveform is having square pulses and the current waveform is oscillatory as is seen in figure 4(a),(b).

SIMULATION PARAMETERS:

Lr=52.7uH and Cr=0.8uF, resonant

frequency=24.5kHz

FULL BRIDGE HYBRID RESONANT INVERTER

Another commonly used inverter topology with 4 semiconductor switches is described in this section. This high frequency full bridge hybrid resonant inverter supplies more power when compared to half bridge series resonant inverter. One hybrid resonant inverter consists of four semiconductor switches (IGBT’s) for each heat in grange. The switching frequency lies between 25 to 35 kHz. It can be considered as a combination of both series and parallel resonant circuits where the switching is made at zero current cross over (ZCS). An advantage of the series circuit is that both zero current and zero voltage switching are possible. Different diameters of induction coils can be chosen for different diameters of flat bed pans. For getting maximum efficiency (with induction system, about 88%) of the system, the coil diameter and the diameter of the utensils must be equal. The full resonant current passes through the switches resulting in ON losses. Depending on the converter design there will be reactive power consumption or more complexity. In a parallel load, there would be low ON losses in the switches but turn-on / turn-off losses would be more as the switching takes place at high voltage and current. So, a hybrid inverter, (i.e. by using combined series and parallel circuit) can be used to reduce the losses in the switches. Fig. 5 shows a resonant inverter system for one cooking zone. Here the energy is transferred from the series resonant circuit to the parallel resonant circuit. By turning on one of the switch pairs S1, S4 or S2, S3 a resonant current starts flowing through L1 to CR and when this current is zero, the switches are turned off. After that the series resonant circuit is disconnected and the energy transferred to resonant capacitor is dissipated as heat in RL by the current flowing through the parallel resonant circuit. RL is the equivalent resistance for the magnetic loss in the induction heating system.

Fig. 5 Full bridge Hybrid resonant inverter system for one cooking zone

This is simulated and the SIMULINK block is shown in Fig. 6 and the corresponding voltage waveform is shown in Fig.7

 

Fig. 6 SIMULINK model of hybrid resonant inverter using IGBT

 

Fig. 7 voltage waveform of hybrid resonant inverter

TABLE1: INPUT PARAMETERS OF SIMULATION

 

AC TO AC CONVERTER

In the proposed scheme of the AC-AC converter there are two main advantages: It is having a high power factor and a sine wave input current. Also the inverter circuit is composed with only a single controlled switch, which serves as a high-frequency generator for induction heating. Fig.8 shows the circuit diagram.

 

Fig. 8 Circuit diagram of AC- AC converter

The operating principles of the circuit are illustrated by Fig. 9

 

Fig.9a. Mode 1 (to-t1)

 

Fig.9b. Mode 1I (t1-t2)

 

Fig.9c. Mode 1II (t2-t3)

Fig.9 Equivalent Circuits

Interval 1: t0<t<t1

The equivalent circuit is shown in Fig.9a. Four diodes D1-D4 and the switch S are off. In this interval the capacitor C charges up linearly at a rate and a polarity corresponding to the instantaneous input voltage Vin.

Interval 2: t1<t<t2

The equivalent circuit is shown in Fig.9b. Two diodes D1, D3 and the switch S are on. In this interval the capacitor C is discharging via the circuit C-D1-S-Lrload- D3. This interval ends when the capacitor voltage reduces to zero.

Interval 3: t2<t<t3

The equivalent circuit is shown in Fig.9c. All the diodes and the switch S are on. In this interval the current through switch S flows via two parallel bridge branches. This interval ends when this switch current decreases to zero. At this moment the switch turns off and the process starts from the beginning. The theoretical waveforms are shown in fig.10

 

Fig.10 Ideal Switching Waveforms

Before the analysis it is assumed that all the circuit components are ideal. The analytical calculations are based on two more assumptions: the switch current can be assumed as semi sinusoidal, and the load power is determined by the first harmonic of the load voltage. Evaluation of the relationship between input and output voltages 

Mg = Vo/Vin 

The AC to AC converter fed induction heater is simulated using Matlab/Simulink and their results are presented here. The SIMULINK model of AC-AC converter is shown in Fig 11 and its corresponding waveform is also shown ( fig. 12)

 

Fig.11 SIMULINK model of AC-AC converter

 

Fig.12 Voltage Waveform of AC- AC converter

TABLE 2: SIMULATION PARAMETERS

 

CONCLUSION

Different inverter topologies are used in induction heating applications. Of that the basic half- bridge and full bridge inverter topologies have been compared. A new topology have been proposed. The AC-AC converter circuit for induction heating has been simulated. Its power factor is close to unity. The circuit topology is very simple since includes only one power switch. This switch operates in a soft commutation mode. The converter provides a wide range power control. This converter has advantages like reduced hardware, reduced stresses and high power density.

REFERENCES

[1] J.Acero, J. M. Burdio, L.A. Barragan, D. Navarro, R.Alonso, J. R. Garcia, F. Monterde, P. Hernandez, S. Llorente, and I. Garde, “Domestic induction appliances,” IEEE Ind. Appl. Mag., vol. 16, no. 2, pp. 39–47, Mar./Apr. 2010.

[2] I. Mill´an, J. M. Burd´ıo, J. Acero, O. Luc´ıa, and S. Llorente, “Series resonant inverter with selective harmonic operation applied to all-metal domestic induction heating,” IET Power Electron., vol. 4, pp. 587–592, May 2011.

[3] R. L. Steigerwald, “A comparison of half-bridge resonant converter topologies,” IEEE Trans. Power Electron., vol. 3, no. 2, pp. 174–182, Apr. 1988

[4] H. W. Koertzen, J. D. van Wyk, and J. A. Ferreira, “Design of the halfbridge series resonant converters for induction cooking,” Proc. IEEE Power Electron. Spec. Conf. Records, 1995, pp. 729–735

[5] Nitai Pal, Pradip Kumar Sadhu, Dola Sinha and Atanu Bandyopadhyay,” Selection of Power Semiconductor Switches – a Tool to Reduce Switching & Conduction Losses of High Frequency Hybrid Resonant Inverter fed Induction Cooker”, International Journal of Computer and Electrical Engineering, Vol. 3, No. 2, April, 2011 1793-8163

[6] P. K. Sadhu, N. Jana, R. Chakrabarti, and D. K. Mittra “A Unique Induction Heated Cooking Appliances Range Using Hybrid Resonant Converter” – Int. J. of Circuits, Systems and Computers, World Scientific, Volume 14, Number 3, June

2005, pp. 619-630

[7] Bayindir, N.S.; Kukrer, O.; Yakup, M (May 2003).: “DSP based PLL controlled 50–100 kHz 20 kW high-frequency induction heating system for surface hardening and welding applications”. IEE Proc.-Electr. Power Appl., Vol. 150, No.3, pp. 365-371.

[8] Mollov, S.V.; Theodoridis, M.; Forsyth, A.J. (January 2004): “High frequency voltage-fed inverter with phase-shiftcontrol for induction heating”, IEE Proc.-Electr. Power Appl., Vol. 151, No. 1, pp. 12-18.

[9] J. M. Burdío, L. A. Barragán, F. Monterde, D. Navarro, and J. Acero, “Asymmetrical voltage-cancelation control for fullbridge series resonant inverters,” IEEE Trans. Power Electron., vol. 19, no. 2, pp. 461–469, Mar. 2004.

[10] I. Millán, D. Puyal, J. M. Burdío, C. Bemal, and J. Acero, “Improved performance of half-bridge series resonant inverter for induction heating with discontinuous mode control,” in Proc. IEEE Appl. Power Electron. Conf. Expo.,

2007, pp. 1293–1298.

[11] F. P. Dawson and P. Jain, “A comparison of load commutated inverter systems for induction heating and melting applications,” IEEE Trans. Power Electron., vol. 6, no. 3, pp. 430–441, Jul. 1991.

[12] O. Lucía, J. M. Burdío, I. Millán, J. Acero, and D. Puyal, “Load-adaptive control algorithm of half-bridge series resonant inverter for domestic induction heating,” IEEE Trans. Ind. Electron., vol. 56, no. 8, pp. 3106– 3116, Aug. 2009.

[13] N. J. Park, D. Y. Lee, and D. S. Hyun, “A power-control scheme with constant switching frequency in class-D inverter for induction-heating jar application,” IEEE Trans. Ind. Electron., vol. 54, no. 3, pp. 1252–1260, Jun. 2007.

[14] J. M. Burdío, F. Monterde, J. R. García, L. A. Barragán, and A. Martínez, “A two-output series-resonant inverter for induction-heating cooking appliances,” IEEE Trans. Power Electron., vol. 20, no. 4, pp. 815–822, Jul. 2005.

 Electrical and Electronics Project by Ravi Devani

DATA LOGGER AND REMOTE MONITORING SYSTEM FOR MULTIPLE PARAMETER MEASUREMENT APPLICATIONS

DATA LOGGER AND REMOTE MONITORING SYSTEM FOR MULTIPLE PARAMETER MEASUREMENT APPLICATIONS

Electrical and Electronics Project by Ravi Devani

ABSTRACT

The present article portrays a design and implementation of microcontroller based embedded system for data logging and remote monitoring of environmental parameters with simplicity to users. The main task of monitoring parameters viz. temperature (T) and humidity (H) along with transmission of this information in the form short message service (SMS) to user’s mobile phone is done by the system. Also weather monitor system provides data-logging facility. The logged data can be then transferred to a personal computer (PC) having a graphical user interface program for further analysis or printing the measurements. The observed data is comparable with the actually measured data using conventional mercury thermometer and masons hygrometer for measurement of temperature and humidity, respectively.

Keywords: - microcontroller, data logger, AVR, SMS

INTRODUCTION

Remotely monitoring of environmental parameters is important in various applications and industrial processes. In earlier period weather monitoring systems are generally based on mechanical, electromechanical instruments which suffer from the drawbacks like poor rigidity, need of human intervention, associated parallax errors and durability. With the inclusion of electronics the instruments were made compact and cheaper. However, these systems lack flexibility of remote monitoring and data logging.

Kang and Park have developed monitoring systems, using sensors for indoor climate and environment based on the parameters mentioned in 2000. Combination of these sensors with data acquisition system has proved to be a better approach for temperature and relative humidity monitoring in 2005. Vlassov in 1993 introduces the usage of surface acoustic waves devices as temperature sensor.These systems, however, are quite complex in nature as some of them require the use of on-chip transmitter circuit and involve fabrication process. This demand the development of a microcontroller based embedded system for weather monitoring. Such a system should monitor and provide data for remote examine. A device for weather monitoring systems has been developed and implemented as described in this paper is capable to data logging and remote examine. The device is simple to use, requires no additional hardware and allows the flexible selection of data-size and the time intervals between the readouts through a simple keypad (two keys only). The collected data by weather monitoring system can easily be exported to a PC via a serial port to make subsequent data analysis or graphic and digital storage thus automatic data collection is possible without giving up PC resources.

MATERIALS AND METHODS

The design of weather monitoring system involves various steeps, viz selection of proper sensor to sense physical parameter, design of signal conditioning circuit which support digital logic device, selection of Central Processing Unit (CPU) and Display unit.

 

Fig.1: Block diagram of weather remote monitoring device.

The functional block diagram of weather remote monitoring device is shown in Fig. 1.The system shown in block diagram is designed around the ATMEL AVR microcontroller. As shown in the Fig.1.the microcontroller’s on-chip peripherals like ADC, UART, EEPROM, POR, and Timer are being used to lower the cost and to increase the efficiency and reliability. This makes AVR microcontroller a better choice for such embedded systems. Sensors sense the physical parameters, in this case the humidity, temperature, the analog output of sensor are given to on-chip Analog to Digital Converter. ADC converts analog voltage into corresponding digital word which is processed to get the actual physical parameter and then displayed onto the LCD module interfaced to the ports of microcontroller. The device also acts as a data logger, with the help of RTC (Real Time Clock) and MMC (Multi Media memory Card) interfaced to microcontroller. The current time for data-logging purposes is provided by the time-base circuit while nonvolatile storage is provided by MMC. The stored records then can be transmitted using serial (RS-232) links to PC for permanent storage in the data files using graphical user interface program (GUI).

1. The sensor circuit

For temperature sensing, an integrated circuit temperature sensor LM35 is used, which has an analog output voltage. The output voltage of sensor is linearly proportional to temperature with a gradient of 10mV/ºC and able to operate in the range -55ºC to +150ºC with an accuracy of ± 0.5ºC. These make LM35 good choice for ambient temperature monitoring. Relative humidity measurement is performed by calibrated humidity sensor module SY-HS-220 which minimizes the system complexity by reducing component count. The humidity sensor module converts relative humidity to voltage with an accuracy of ± 5% RH. The characteristics curve of relative humidity (% RH) vs. output voltage (mV) is shown in the Fig.2.

 

Fig. 2: Humidity sensor characteristics plot.

Using equation of straight line,

                                (1)

Herein, Y is % relative humidity, m is slope and c is offset.

Slope is calculated by using Humidity sensor characteristics plot as,

                                     

The characteristic is a straight line and the slope is constant along the line. Thus multiplying measured voltage from sensor by calculated slope gives Relative Humidity. In addition, the output voltages from both the sensors are sufficiently large in magnitude so, there is no need of separate signal conditioning circuitry, which improves reliability of the system.

2. Central processing unit (CPU)

The main component here is the Atmega32 microcontroller which works as CPU. This microcontroller not only controls the system but also synchronizes all the module operations. The CPU use calibrated 8 MHz internal RC oscillator. Atmega32 provides eight channels ADC (Analog to Digital Convertor) which can be used in 10-bit mode.

 

Fig. 3: Full working schematic of weather remote monitoring device.

 Electrical and Electronics Project by Ravi Devani

3. The display circuit

The device uses LCD module for local real-time display. The module has onboard display controller, which relieves the main microcontroller from manually generating dot-matrix character display. The display unit is composed of 16x2 dot matrix alphanumeric LCD. The LCD is configured in 4-bit mode with read-write control (WR) pin grounded. This configuration requires less number of I/O pins of microcontroller, typically 6 only. The circuit diagram shown in Fig. 3. reveals actual pin connections of the device.

4. Data logging & remote monitoring circuitry

The device allows the selection of amount of data and the time intervals between them through a simple keyboard (two keys only). The current time for data-logging purposes is provided by the time-keeping circuit typically from 30sec to 99min. Memory card (MicroSD) with 1GB capacity from SanDisk [7] is connected to the microcontroller for storing the sensors readings to store more than 100 days reading (for 30-second sampling interval). MicroSD cards are available very cheap nowadays, a great option for having a huge memory in any embedded system project. The interface of the MMC and the microcontroller is based on the SPI bus which is shown in Fig. 3. Fig. 4 shows the SD card pin-out & the bread-board adapter design by soldering 7-pins of a breakout header on the microSD. Interfacing of the microSD to Atmega32 is shown in the Main Circuit diagram of system.

 

Fig.4: Bread-board adapter design by soldering 7-pins of a breakout header on the microSD adapter

The microcontroller sends current monitored parameters through SMS in the time interval specified by user. In present system Nokia-3310 mobile phone is interfaced to microcontroller, using Nokia F-Bus Protocol [6]. A typical SMS sent by the system is shown in the Fig.5b.

5. The Time-Base Circuit

A real-time clock (RTC) chip-DS1307 is used for Time-Base purpose. Communication between the RTC and the microcontroller is achieved via a simple serial interface bus protocol. A separate battery source supplies the power required by the chip, hence enables RTC operation kept without interruption in the event of main power source failure.

6. The interfacing circuit and GUI

Data stored in MMC can be accessed directly with the personal computer (PC) through serial port connection .The GUI software allows the user to download the data from MMC, the data can also redirect to Excel. The graphical user interface (GUI) is developed using Visual Basic language. The screen shot of GUI is shown in Fig.5a.

(5a)

(5b)

Fig.5: Screen shot of GUI program run on PC and typical SMS view on user mobile phone

SOFTWARE DESCRIPTION OF DEVICE

The firmware for the CPU is written in embedded–C language. Fig.6. shows the flow chart of the device software. The programmed behavior of the device is as follows:

When the device is powered-up, the initialization part of the device software configures various on-chip peripherals such as timers, interrupts, ADC etc. and initializes the externally interfaced LCD, RTC, and MMC. This initialization sequence puts these resources into a known state. Once initialize, device display parameter and setup user data using keys (sw1, sw2).At regular time interval specified by user setup, device store parameter & send it through SMS to user mobile phone. Device checks request to send stored record through serial port as shown in device software flow chart.

 

Fig.6: Flow chart of the weather remote monitoring device software.

RESULT

The accuracy of proposed device has been tested through extensive experiments. Present device can measure temperature from 0oC to 100oC with 0.5oC resolution and relative humidity from 30%RH to 90%RH with resolution of 1%RH. Although final accuracy of weather remote monitoring system depends on sensor accuracy. The observed data is comparable with the actually measured data using conventional mercury thermometer and Masons Hygrometer. The results obtained are summarized in Table-1, Table- 2.

Table 1: Comparison of temperature measurements.

 

From Table-1, it can be observed that the temperature sensor shows a good level of stability as well as accuracy. The average error of 0.60C is observed due to ±0.50C error by the sensor and ±0.250C introduced by ADC. The humidity sensor of proposed device also show very good accuracy as shown in Table-2.an error of 2% is observed mainly due to the hysteresis effects of the sensor. This device is very useful in Green house, as data logger and remote monitoring where temperature and humidity plays vital role, hence it is necessary to monitor and control this parameter. The readout storage capacity of device can be easily increased by adding external memory such as Multimedia or Flash memory card.

Table 2 : Comparison of Humidity measurements.

 

(7a)

(7b)

Fig.7: Graph of humidity and temperature compared with Hygrometer and mercury thermometer respectively

CONCLUSION

From the graphs of Humidity and temperature it is clear that there is very close agreement between the data collected by our system and that measured by already available and calibrated systems, which validates the measurements made by our system. The presented system can be useful for studding behavior of Industrial and Home processes application having multiple parameters. Though the system employs SMS technology which is a point-to-point communication technology with the limitations of small bandwidth; it imposes no need of PC or web server for remote monitoring and thus saves the cost. With slightly modifying the firmware current monitored parameters can be sent to many users through SMS.

REFERENCES

[1] Kang. J. and Park S. “Integrated comfort sensing system on indoor climate” Sensors and Actuators. 2000. 302-307.

[2] Moghavvemi M. and Tan. S. “A reliable and economically feasible remote sensing system for temperature and relative humidity measurement”. Sensors and Actuators. 2005. 181-185.

[3] Vlassov Y.N. and Kozlov A.S. “Precision SAW pressure sensors” IEEE proceeding of 47th frequency control symposium. 1993. 665-669.

[4] Jan Cimo and Bernard Siska, “Design and realization of monitoring system for measuring air temperature and humidity, wind direction and speed”. Journal of Environmental Engineering and Landscape Management. 2006. 14(3).127 -134.

[5] K.Gowardhan, “Control anything from a cell phone Tiny Planet” Smart Materials Structures and Conference on Systems International.2005. Bangalore. India.

[6] Wayne Peacock. “Nokia F-Bus Protocol”.2004. online website www.Embedtronics.com

[7] SanDisk Corporation. SanDisk SD card product manual. Version-2.2.2004. www.sandisk.com .

Electrical and Electronics Project by Ravi Devani

IMPLEMENTATION OF PLC BASED ELEVATOR CONTROL SYSTEM

IMPLEMENTATION OF PLC BASED ELEVATOR CONTROL SYSTEM

 Electrical and Electronics Project by Ravi Devani

ABSTRACT

This paper describes programmable logic controller based elevator control system. An elevator is one of the important aspects in electronics control module in automotive application. Nowadays, Myanmar is a developing country and there is enormous increase in high-rise building in Myanmar. This paper mainly focuses on using programmable logic controller to control the circuit and building the elevator model. Hall Effect sensor is used for the elevator position. DC Motor is used to control the up and down movement of the elevator car. Push buttons are used to call the elevator car. The elevator position is described by using the display unit. In this paper, Auto Station Software ladder logic program is used for four floors control system.

Keywords –WPLC, Elevator Design, Hall Effect sensor, DC motor, Ladder logic

INTRODUCTION

For most people residing in urban cities, elevators have become an integral part of their daily life. Simply stated, an elevator is a hoisting or lowering mechanism, designed to carry passengers or freight, and is equipped with a car and platform that typically moves in fixed guides and serves two or more landings. Hydraulic and roped elevators are the two types of elevators in use today. The main design considerations for choosing either electric traction drive or hydraulic for a particular project are the number of floors, the height of the building, the number of people to be transported, desired passenger waiting times and frequency of use.

This project is to design and construct an elevator using a programmable logic controller. Hall Effect sensor is used to know the elevator position. Hydraulic and roped elevators are the two types of elevators in use today. Elevators are prevalent throughout many multi-level structures.

RELATEDWORK

In [9], the author explained that an approximate small-scale elevator model with PLC is adopted for the controller design which uses the Ladder Language based on the GE FANUC Versamax PLC. The ladder logic has implemented by using VersaPro. 2.02. In this control design technique, the Light Dependent Resistor (LDR) is used to sense the elevator floor.GE FANUC Versamax PLC is having a configurable memory of 64kbyte. The author provided to improve the quality in elevator systems, develop and drives the used setting and increase the reliability of elevator. The author also mentioned to achieve high speed nine-phase Permanent Magnet Synchronous Motor Control System.

In [10], the author mentioned that making of wireless module to realize the transmission of user information, PLC control system are adopted, the serial communication mode between the PLC and the wireless module was adopted. SI4432 Transceiver, Single-Chip computer and PLC are used to modify the control system of construction elevator. The control system of the construction elevator was made up of PLC, wireless calling device and wireless host transceiver. Elevator control system can determine the next travel direction based on the call information and the current operation automatically, realizes unattended operation.

In [11], the author described the application of sate chart to the modeling, design and implementation of an elevator system, whose system behavior involves aggregating complexity of state descriptions, and imposition of underlying control policy. Based on the operational flow of an elevator, they derive the associated state chart model by looking into the inherent hierarchical structure of the elevator. This research was supported in part by the grant NSC90-2213-E-011-020 and NSC90-2212-E-014-023 by the National Science Council, Taiwan, R.O.C.

PROGRAMMABLE LOGIC CONTROLLER

The first Programmable Logic Controller, PLC was developed by a group of engineers at General Motors in 1968. It was developed when that company was looking for an alternative to replace complex relay control system. The term ‘programmable logic controller’ is defined by EN 61131-1 as a digitally operating electronic system which uses a programmable memory for the internal storage of user-oriented instructions for implementing specific functions such as logic, sequencing, timing, counting and arithmetic to control through digital or analogue inputs and outputs, various machines or process.

A. Ladder Programming algorithm

There are many types of programming languages in Programmable Logic Controller, PLC. Languages are typically fixed to Ladder Logic (LD), Sequential Function Block (SFC), Function Block Diagram (FBD) and Structure Text (ST). The common program language of PLC is ladder diagram.

B. Ladder Logic

Ladder diagram is an automatic control diagram language that developed during World War II. Ladder logic is the primary programming language of programmable logic controllers. Since the PLC was developed to replace relay logic control systems, it was only natural that the initial language closely resembles the diagrams used to document the relay logic. By using this approach, the engineers and technicians using the early PLCs did not need retraining to understand the program. To introduce ladder logic programming simple switch circuits are converted to relay logic and then to PLC ladder logic. Any control task modifications are done by changing the program. This is why the use of the PLC is preferred to the traditional hard wired circuits in industrial controls.

 

Figure1. PLC Architecture

 

Figure2. Ladder diagram algorithm

In the chart of traditional ladder diagram, if X0, X1, X4 and X6 are in ON condition and the others are in OFF condition, output point Y0 will be in ON condition as shown as dotted line in the figure 2.

Implementation of PLC Based Elevator Control System

C. Ladder Software Package

The Auto Station installation package issued by Invt Auto-Control Technology is an executable program. The main interfaces include 7 sections: Menu, Tool bar, Project Manager Window, Instruction Tree window, Information window, Status bar and Operation area.

 

Figure3. Auto Station main interface

PROPOSED SYSTEM

In order to design a control circuit, it is divided into several units or modules for its particular task or control which first can be tested or implemented independently and then combined together. The basis of PLC based elevator control can be classified into three main groups. The first is the floor, the second is the PLC controller and the last is the Elevator. The block diagram of PLC Based Elevator Control System is described in Figure 4 to accomplish the PLC based control system, the design uses six major components: PLC controller, DC motor driver, push button, level sensor, display unit and Elevator. Level sensors are used to know the elevator position and push buttons are used to be input by the user request. The display unit will display the number of floor. The PLC compares the user request and the push button to drive the elevator motor Up or Down. When the user request is greater than the sensor value, the motor will go up and it is less than the sensor value, it will go down. When the two values are equal, the motor must stop.

 

Figure4. Block diagram of PLC based elevator control system

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This design can be divided into several units or modules. They are sensor unit, processing unit and power unit. There are some devices and components used in the in the design to implement each unit. These devices used in this system are as follows;

Ø Power Supply Unit

Ø Hall Effect sensor

Ø IVC1 1410MAT PLC controller

Ø H-bridge DC motor

Ø Push Button

Ø Display Unit

Ø Elevator

A. Power Supply Unit

The DC power supply unit is vital component in modern electronic devices as they need a wide range of DC voltages for their operations. The purpose of a power supply is to provide the required amount of power specified voltage from primary source.

B. Description of Hall Effect Sensor

A Hall Effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall Effect sensors are used for proximity, positioning, speed detection and current sensing applications. In its simplest form, the sensor operates as an analogue transducer, directly returning a voltage. A Hall Effect sensor can be used to measure the current without interrupting the circuit. Frequently, it is combined with circuitry that allows the device to act in a digital (on/off) mode and may be called a switch. It is commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. It consists basically of a thin piece of rectangular p-type semiconductor materials. A typical Hall Effect sensor has three wires or terminals; one for ground, one for supply or reference voltage and one for output. To produce an output signal, it must be supplied with a voltage from 5 to 12 V. There are many different types of magnet movements, such as Head-on, Sideways, Push-pull, and Push-push detections.

Implementation of PLC Based Elevator Control System

 

Figure5. (a) Heard on detection

 

(b) How Hall Effect works

C. Features of IVC1 1410MA TPLC Controller

The programmable controller PLC that is used in this research is IVC1 As shown in Figure 6, PORT0 and PORT1 are for communication. PORT0 is RS232, and use socket Mini DIN8, while PORT1 is RS485 or RS232. The bus socket is for connecting extension modules. The mode selector switch can be set to ON or OFF.

 

Figure6. Structure of IVCI series basic module

D. H-bridge DC Motor

Bidirectional control of a DC motor requires a circuit called an H-bridge, named for its schematic appearance, is able to move current in either direction through the motor winding. H-bridge topology was chosen in this system. An H-Bridge configuration using BJTs is shown in Fig 3.11. It is called an “H-bridge”, because it looks like an H letter. An H-bridge is an electronic circuit which enables electric motors to be run forward or backward action. It is mostly used in motor control of elevator. It is available as integrated circuits or can be built from separate components for specific design. In this system, the DC motor with H-bridge driver circuit advance the elevator car to the next position. The motor can provide for both directions: clockwise (CW) direction and counterclockwise (CCW) direction. This circuit uses four transistors for forward and reverse directions. Its operation is as follows. To rotate the DC motor four transistors are used. When the transistor Q1 and Q4 are ON and the other transistors are OFF, a positive voltage will be applied across the motor and the motor will rotate clockwise direction. When the transistor Q2 and Q3 are ON and the other transistors are OFF, the voltage across the motor will be negative, allowing counterclockwise operation of the motor. In DC motor, clockwise direction for Upcondition and counter clockwise direction is for Down-condition.

 

Figure7. H-bridge DC-motor Circuit

The motor used here is a H-bridge DC motor. Base on the design specification the output power and the output torque of the motor are calculated by a simple calculation. The power and torque calculation are mentioned as follow.

Weight of empty cabin = 100 kg

Counter weight = 100 kg

8persons with 65kg = 520 kg

For constant speed operation of 1m/s = 60m/1min

The power, work and force and torque are calculated using the equations (1 ), ( 2 ), (3 ), (4) and (5 ).

Power = work / time                   (1)

Work = Force x distance            (2)

Force, F = mg                             (3)

Power = Force x distance / time

So, Power = Force x velocity     (4)

F = 520 x 9.8 = 5096 N

P = 5096 x 1m/s = 5096 W

1hp = 745 W

5096 W = 6.84 hp (approximately 7hp or 5215W)

Rotational Speed _= 1500rpm

The torque of the motor can be calculated by using the equation(5)

Torque of motor (Nm) = 

                                                                     (5)

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SIMULATION RESULTS

The simulation of elevator position control is carried out with the Auto Station in order to know the performance of the controller. Auto Station software platform is use to perform the experiment. The PLC for experiment is equipped withIVC1-1410MAT programmable logic controller.

In this system, the ladder program must be run in the PLC controller by downloading ladder software.

Basic requirements are also needed;

Ø PLC

Ø Programming Device ( personal computer )

Ø Connector Cable

Ø Programming Software

A. Specification of PLC controller

IVC1 1410MAT programmable logic controller with Auto Station software has been chosen for developing and ladder logic was downloaded into the PLC. For the working model of an elevator various logics for different operations have to be developed and it is discussed in the following.

Table -1 SPECIFICATIONS OF IVC1 1410MAT DEVICE

 

B. Ladder logic for motor operation and to get signal from the floor sensors

The next step of receiving the input signal is to make the motor to operate either up or down direction and the logic has been developed correspondingly. Figure 8 shows the snap shot of the logic for the motor operation in both up and down direction. The motor operation is purely based on the input that the PLC gets from the push buttons. Based on the desired input and corresponding floor, the PLC wil make the motor to stop.

Outputs used for motor operation

1) Up motoring - O:4/1

2) Down motoring- O:4/1

 

Figure8. Ladder logic for motor Up and Down operation

C. Ladder logic for floor scan

As an initial move the ladder logic has to be developed for receiving the input signal from the push buttons and the same is used with the program to get the corresponding output based on this output.

Figure 9 describes the logic that has been developed to get the inputs from the call buttons present at every floor. When a particulars switch from the corresponding floor has been pressed the program in the PLC gets activated and the relevant bit will be activated.

Figure9. Ladder logic for scan floor

Implementation of PLC Based Elevator Control System

C. Ladder logic for close and move operation

The process of door closing has to start once the door has been fully opened so a sensor is placed at the end of door opening and when the sensor is cut a signal will be sent to the PLC. Figure 10illustrates the operation of door closing once the door opening operation comes to end that is when the sensor present at end for door opening has been cut. At the end of door closing the sensor will give a signal to the PLC will stop the door motor.

 

Figure10. Ladder logic for close and move operation

E. Ladder logic for tracking elevator car movement

Once the operation of the elevator motor ceases the logic has to be developed in such a way that it facilitates to track the elevator car movement. Based on the input from the floor sensors, the program downloaded in the PLC to track the movement. Figure 11 describes the operation of tracking movement. According to the input, the output O:2/12, O:2/13, O:2/14 and O:2/15 will be activated.

 

Figure11. Ladder logic for tracking movement operation

F. Ladder logic for stop and open door operation

The next step receiving the input signal is to stop the motor and then to open the door. After stopping the condition of motor, the door operation will activate at once. At the end of motor stopping the elevator car, the sensor will give a signal to the PLC. And then this will open the door motor. Figure12 express the operation of stop and open door according to the PLC controller.

 

Figure12. Ladder logic for stop and open door operation\

Figure13. GUI result of the complete fourth floors Elevator Control System

CONCLUSION

Although some calibrations and requirements may have, the modeling PLC based on elevator control system is done. The traditionally used relays and IC boards have been replaced by PLC for easy and cheap controlling of machines used in this elevator. By developing this proposed system, the result of elevator control system can be applied in the real world. By using PLC based elevator control system, the desired position can be forecasted. The simulation results of the four floors system have been discussed. As a future work, IVC1 1410MAT PLC based elevator model is intended to construct and tested to be applicable in the real world.

REFERENCE

[0] www.silicontechnolabs.in

[1] Yaing Sun, “Teaching Module Design of Elevator Controlled by PLC”, MICROCOMPUTER APPLICATIONS, 2013, pp.63-67, 31(5).

[2] Jie Zhang, “Application of PLC in elevator control system”, Journeel of Liaoning Normal University(Natural Science Edition), 2009, pp.318-320,32(3).

[3] Darshil, Sagar, Rajiv, Pangaokar and S.A. Sharma “Development of a PLC Based Elevator System with Colour Sensing Capabilities for

Material Handling in Industrial Plant”, Jiont International Conference on Power System Technology and IEEE Power India Conference, 2008,pp.1-7

[4]Jayawardana.H.P.A.P., Amarasekara.H.W.K.M., Peelikumura.P.T.S., Jayathilaka.W.A.K.C., Abeyaratne.S.G. and Dewasurendra.S.D. “Design and implenentation of astatechart based reconfigureurable elevator controller”, 6th IEEE International Industrial and Information Systems, IEEE Conference Publications, pp. 352-357

[5] Pillay, P., and Krishnan, Modeling of DC Motor Drives. IEEE Trans. Industry Applications, 1988, pp. 537-541, Vol. 35. no.4. IEEE database.

[6] Zhang Yajun, Chen Long, Fan Lingyan, “A Design of Elevator Positioning Control System Model,” IEEE Int. Conference Networks & Signal Processing, Zhenjiang, China, June 8-10. 2008, pp. 535-538.

[7] Hongqun Li, Yue Zhou, PLC Control and Real-time Monitoring of a Sightseeing Lift.Techniques of Automation & Applications, 2008,Vol.27 No.11.

[8] Xiaojuan Liu, Development of Elevator Monitor System Based on the Fieldbus, February 2008, Vol.30 No.1. Journal of EEE.

[9] S.B. Ron Carter, “Design and Implementation of PLC based Elevator”, April 2013, Volume 68_ No.7.

[10] Caiqiao Wei“Design of Control System of Construction Elevator Based on PLC”, 2014 4th Electronic System_ Integration Technology Conference.

[11] Yi-Sheng Huang, Sheng-Luen Chung, and Mu-Der Jeng “Modeling and Control of Elevator by State Chart”, June 2014, pp. 242-252,Asian Journal of Control, Vol. 6, No. 2.

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