WIRELESS LOAD CONTROL DEVICE USING GSM MODULE

WIRELESS LOAD CONTROL DEVICE USING GSM MODULE

ABSTRACT

This paper presents Wireless Load Control Device (WLCD) using GSM module. The WLCD consists of PIC18F4550, GSM Module, relay circuit, keypad, and LCD. PIC18F4550 is used as a microcontroller to process the received data and then the output signal is sent for on/off relay switch. The users can on/off load in two ways, either keypad or short message service (SMS). The WLCD can control three loads and the current status of each load is displayed on the LCD. A working prototype of WLCD was built to demonstrate the effectiveness and efficiency of on/off load control through the GSM network.

Keywords: wireless load control device, PIC microcontroller, 18F4550, GSM module, SIM900B

INTRODUCTION

Nowadays, the innovative technologies have become an integral part of human life. Various load control method and technology such as power line carrier (PLC), telephone modem, internet, WIFI, Bluetooth, and

ZigBee were established and developed to facilitate comfortable for humans. There are many researches about load control method and technology until now. For example, in 2000, R. C. Luo et al. presented intelligent autonomous mobile robot control through the Internet. In 2010, X. Liu and W. Wang introduced a control system of indoor intelligent Lighting which is based on power line carrier communication. The power line is used to transmit the analogue or digital signals with high speed. Not only power line technology but also wireless remote control and GSM network are used to combine for remote the indoor intelligent lighting and controlling the sensing. Architecture for power monitoring system using the wireless sensor network technology is proposed in 2011. In 2013, V. Bhatia and P. Whig present the modeling and simulation of electrical load control system using RF technology. Moreover, V. Bhatia and P.

Whig designed and simulated the smart elevator control system with Security based on Dual Tone Multi Frequency. R. Makwana et al. tried to study the comparative of different wireless protocol between ZigBee (over IEEE 802.15.4) and Bluetooth (over IEEE 802.15.1).

In addition, the microcontrollers are playing a very important role in the development of the smart systems. The microcontroller is basically a single chip microprocessor suited for machine controlling and system processing because it carries out autonomous operations and takes smart decisions. Moreover, the devices such as air conditioners, power tools, toys, office machines employ microcontrollers for its operation.

This paper designs and develops the control of electrical loads using GSM module. PIC18F4550 is used for processing and controlling of the WLCD. By pressing the keypad on the WLCD, the controllability of the electrical load can be achieved. Moreover, the users can send the command to remote control the electrical load and receive the current status of the load by GSM module.

MATERIAL AND METHOD

The complete system of WLCD can be shown in Fig. 1, consists of four major parts: (1) input command, (2) microcontroller, (3) output display, and (4) electrical load driver.

 

Fig. 1: Block diagram of the WLCD

Hardware Implement

Input Command

WLCD can receive the input command in two ways (i.e. keypad or SMS). 3x4 keypad switches are connected to the microcontroller for sending the input command to control each electrical load. In the other way, the user can interface with the WLCD by sending the SMS from the mobile phone to its. The GSM module (SIM900B) is used to receive that SMS from the user via GSM network and send the data to the microcontroller via RS232 serial port.

Microcontroller

A microcontroller (PIC18F4550) is used as an interface device (input command, LCD and the electrical load driver). It is a 40-pin dip, low power consumption and high speed FLASH/EEPROM technology. It consists of 256 bytes EEPROM memory, 35 Input/output, two external clock modes (up to 48MHz), 13 channels of 10-bit analog to digital converter, and a capture/compare/PWM functions. 7805 voltage regulators are used to convert 12Vdc to 5Vdc and the output is then given to the microcontroller and GSM module. The electrical load driver, keypad and LCD are connected with microcontroller at port A, B and D, respectively.

Output of the WLCD

16X2 LCD is used in the system to display the current status of the WLCD. Besides the LCD, the user can receive the current status of electrical load by sending SMS to the WLCD.

Electrical load driver

The electrical load driver includes the opto-isolator and the relay circuit. The opto-isolator has the function to transmit the output signal from the microcontroller to the relay circuit. The relay circuit is an interrupting device designed for shutting on/off the power supply. The relay switch is designed for the electrical load at 220Vac and 10A. When the WLCD receives the command, the microcontroller will control the relay switch to on/off the electric power supply via the opto-isolator. The prototype of hardware implementation was done as shown in Fig.2.

 

fig 2. The WLCD prototype

Software Implement

According to the hardware circuit design features, WLCD controlling program flowchart is introduced as shown in Fig. 3. First, the system initializes each module, and then turns off all electrical loads. Then, WLCD started already, the microcontroller sends the command of AT + CMGD = 2 for clearing the second data storage space in the SIM card of GSM module. When the user sends the short messages to WLCD, GSM module will send that command to the microcontroller. After that the microcontroller will turn on/off load according to the received command and show the current status on the LCD. The microcontroller sends a command (such as AT+CMGS="+66868273639" and “SW1-ON SW2-ON SW3-OFF”) to the GSM module for informing the current status to the user. In the other way, when the received command is sent from the keypad, the WLCD will operate to on/off the electrical load and show the current status of each electrical load on the LCD module.

 

Fig. 3: Flow diagram of WLCD controlling program

Table 1 shows the control command to control the electrical loads of WLCD. For example, when the user need to on only SW2, the command is “*010#”.

Table 1: WLCD control commands

 

RESULTS

Electrical loads such as fans, bulbs, and computer etc. are tested and controlled wirelessly by the WLCD. When starting up the program, the LCD will show as Fig. 4(a). Then, three electrical loads can be controlled at a time in the present system. For example, when the user enters “*000#” to the WLCD using keypad, all of electrical loads will turn off and the LCD will show the current status as shown in Fig. 4 (b). Next, the user sends the SMS command (“*111#”) to the WLCD, the LCD will show the phone number of a user as shown in Fig. 4 (c). Then, all loads are switched on and the LCD will show the current status of electrical load as shown in Fig. 4 (d). After that, the microcontroller will send the current status to the user via SMS as shown in Fig. 4 (e).

 

(a) Start up the program

 

(b) Off all electrical load

 

(c) the number of user who send the command to the WLCD

 

(d) On all electrical load

 

 (e) SMS send and receive from WLCD

Fig. 4: the result of WLCD

CONCLUSION

To control the electrical load by wireless communication using GSM module, the WLCD was constructed. The WLCD is designed to provide three loads (rated of each load at 220Vac 10A). The electrical loads can be turned on/off by keypad on WLCD or SMS via GSM network as the command shown in Table 1. The user can know the current load status by LCD on WLCD or the SMS from WLCD.

The advantage of WLCD can be stated as follows:

- wireless control from remote places,

- ease of operation by using any mobile possible to on/off electrical load,

- the users will get a convenient, and

- time saving.

In addition, this WLCD can be applied to the other systems such as controlling the pump, motor, etc. In the future work, we will add the electrical measuring system which can read and send the electrical measuring value such as power and energy to the user. The system will be designed to increase the current load more than 10A by using the higher size of the relay. Moreover, the WLCD can be extended to the desired number of loads by adding the relay circuits and changing the control commands.

REFERENCES

[1] R.C. Luo, T.M. Chen, and C.C. Yih. Intelligent Autonomous Mobile Robot Control through the Internet. IEEE International Symposium ISIE. 2000, 1: 6-11.

[2] X. Liu and W. Wang. Indoor Intelligent Lighting Control System Based on Power Line Carrier Design. 2010 Second WRI Global Congress on Intelligent Systems (GCIS), 2010, 1: 408-411.

[3] R. V. P. Yerra et al. WSN based power monitoring in smart grids. Seventh International Conference on Intelligent Sensors, Sensor Networks and Information Processing (ISSNIP), 2011, 401-406.

[4] V. Bhatia and P. Whig. Modelling and Simulation of Electrical Load Control System using RF Technology. International Journal of Multidisciplinary Science and Engineering, 2013, 4(9): 44-47.

[5] V. Bhatia and P. Whig. A Secured Dual Tone Multi Frequency based Smart Elevator Control System. International Journal of Research in Engineering & Advanced Technology. 2013, 1(4): 1-5.

[6] R. Makwana et al. Wireless Based Load Control and Power Monitoring System. International Conference on Energy Efficient Technologies for Sustainability (ICEETS), 2013, 1207 – 1211.

WIRELESS DATA ACQUISITION FOR PHOTOVOLTAIC POWER SYSTEM

WIRELESS DATA ACQUISITION FOR PHOTOVOLTAIC POWER SYSTEM

ABSTRACT

This paper presents a wireless system for monitoring the input and output of the array in a photovoltaic generation plant. The system comprises of sensors, data acquisition system, wireless access point and user computer that enable the users to access the array parameter wirelessly. Description and function of set up equipment are presented as well as the application program that supports the system.

INTRODUCTION

Recently, the number of energy in the world is reaching to concern state. This is caused by the need of energy is growing very fast. Due to concerns regarding global warming and air pollution, there has been an international movement in the promotion of renewable energy technologies for electricity generation, green energy is one among proposed solutions for these issues.

Solar energy is converted to electricity in a photovoltaic generation plant that contains photovoltaic array as solar electricity conversion equipment, electrical power converter, power storage and other supporting equipment. According to operation mode, photovoltaic generation plants are met in isolation mode, grid interconnected mode and plant that can operate in both modes. For all of these modes, there are needs to acquire the input and output parameter of the photovoltaic array as the generation equipment. The acquired parameters are used for control action information, generation planning, energy forecasting, and performance observation or documentation need. Some of the parameters are irradiance, temperature and array's electrical output. A satisfied data acquisition system is required for this need.

Related to acquisition system for photovoltaic performance, Benghanem et ai. have accomplished a research in which, several instruments are used to detect, integrate, and record solar energy measurement using both conventional electronics as well as microprocessor data acquisition system . Further, Machacek et aI., developed a system for measuring, collecting, analyzing, and displaying data for 100 W solar energy converter, data acquisition is formed by NI-6023E plug-in card and feed the rough data to the control program built in a MATLAB script.

Data from acquisition system module are needed to produce useful information. The speed of the process is the important parameter. To accommodate this requirement, during the past decade, digital control has been widely used. Digital control, which is determined by application of microprocessors, makes the sampling and computing process are faster than before. Implementation of such a system has been done on a dc voltage monitoring and control system for a wind turbine inverter.

Fig 1. Simplified diagram of the Wireless data acquisition for photovoltaic system.

Regarding with data transmission, Chen, et.al, have studied carrying the acquired signal from data acquisition module using internet. Java language is used for designing a dynamic webpage to graphically display various real time waveforms of the controlled system for multi-user at the same time. The system is implemented on a small scale wind power generation system equipped with an EZDSP 2812 controller. An FPGA ECIO is implemented as a bidirectional communication interface for coordinating the asynchronous data transmission modes. In this paper, we present a photovoltaic generation monitoring system for a 5 kWp laboratory scale photovoltaic generation. Temperature, irradiance, voltage, and current of the array are acquired, processed and then transmitted such that can be used for reviewing the performance of the generation plant. Acquired data is transmitted by wireless method using Wi-Fi signal (IEEE 802.11 standard), while microcontroller of PIC 16F877A is used to control the acquisition system process and a Delphi application program is built to graphically display the acquired data. Figure 1 show the simplified diagram of such system.

PV GENERATIONCHARACTERISTIC FORMONITORING SYSTEM

The acquisition system is aimed to detect and collect the parameters that indicate the electrical characteristic of the array and the factors influencing them.

Fig. 2. V- I characteristic of PV module, 

(a) characteristics on various irradiance at a constant temperature, 

(b) Characteristic on various temperature at a constant irradiance

As shown in Figure 2, photovoltaic array characteristic (V-I curve) shows the dependency of cell current and voltage to irradiance and temperature. Irradiance contributes to the cell current, the higher irradiance the higher current draw by array photovoltaic, while the temperature effects to the cell voltage, the higher temperature the lower voltage appears on the cell terminal. In Figure 2a, it is shown a set of photovoltaic cell 1-curve under varying irradiance at a constant temperature, meanwhile figure 2(b) shows the one at the same irradiance values, but under varying temperature. Both figures are also show the point where the multiplication of PV array voltage and current reaches the maximum value: maximum power point (MPP), at which condition that the array operates with maximum efficiency and produces maximum output power. Variation of irradiance and temperature in photovoltaic module is characterized as short time fluctuation; follows the behavior of atmospheric condition around plant during time. The effect of this variation is the unpredictable variation of power output, current and voltage of the plant. An acquisition system for this condition should consider the phenomenon.

PV GENERATION MONITORING SYSTEM

The PV generation and monitoring system shown in Figure 1, is a diagram of a laboratory scale system that contains three units photovoltaic array produces three de voltages of 0 - 150 range. These de voltages is then fed to three single phase PV inverter respectively to be inverted to ac power before sending to the utility. Maximum current for each array are lOA de. Array power input in form of temperature and irradiance and the de output of array are picked up as data acquired for the monitoring system. Three ACS754 current sensors with maximum current 50A and sensitivity of 37.8 mV/A are connected to de output of each solar array, while irradiance and temperature sensor placed around the array. For voltage acquisition, 1k.o.-1M.o. voltage divider was used, which means 10mV for every one volt de solar panel output. LM35 temperature sensor which sensitivity of 10mV/oC is used for measure the ambient temperature of solar panel. The irradiance is sensed using LDR. Data acquisition diagram is shown in Figure 3. In order to determine the analog signal from the sensor to be passed to ADC, which contains eight analog signal from sensors (3 for de current, 3 for de voltage, one for irradiance and the remaining for temperature) dual eight-channels analog multiplexer DG407B are used. The analog multiplexer was controlled using microcontroller and passing the multiplexing signal with their own voltage references. In the ADC block, each analog signal from multiplexer is digitalized to eight bits digital signal. Eight-bit signal is used caused by the condition that communication between microcontroller and serial to Ethernet module uses eight bit data. Thus, voltage reference for ADC is Vrej = resolution x 28 , where the resolution is equal to sensitivity of each sensor. ADC operation is also controlled by the microcontroller. In this system, the microcontroller is employed to run the following function: controlling the multiplexer for determining the analog signal from the sensor to be passed; controlling the operation of ADC, and as communication protocol between Ethernet and the acquisition system. To accommodate these functions, the low-power consumption PIC 16F877A microcontroller is used. This unit is built within eight channels 10 bit ADC and an UART connection for serial communication. Microcontroller serial connection is connected to Wiznet EGSR7150 in order to convert format data from serial to Ethernet data, conversion process is reversal. Further, the acquainted data is sent to the access point to be sent in form of Wi-Fi signal to connected user computer. To accommodate communication between computer and acquisition system and to display the result, a computer application program is required.

Fig. 3. Data acquisition system diagram

For this need, an application program, written in Delphi language is developed. This program is built to allow the user can interact and control the process steps in these two subsystems (microcontroller in acquisition system and displaying process in computer). Communication between computer and acquisition system is done wirelessly. Communication process involves two application programs, one is in the computer side and the other is in microcontroller side. Flowchart of communication between these two applications programs is shown in Figure 4, which shows two main blocks, indicates the process flow in each side. First of all, the programs will self-initialize when they are activated. User can decide whether to acquire data or not. If acquisition data will be done, program will send a query command to the acquisition program on microcontroller contains which data to be acquired. Microcontroller in acquisition system -based on the command query- orders the multiplexer to by-pass the intended analog signal from the sensors and digitalized them. Analog signal from the sensors contains high noise, which can degrade the measurement accuracy. To avoid this, analog signal is picked up and converted three times; their average is computed and become data to be sent back as acquisition data to user computer. In user computer, acquisition data is received by Ethernet port. Application program then processes the data to be displayed and to be saved in the virtual memory. The displaying application program is shown in Figure 5.

There are 5 charts that show the measured and calculated parameters. Voltage, current, and calculated PV array power of whole channel is displayed in one chart respectively. Each PV array power output is obtained by multiplying the voltage and current of respective array. The array temperature and irradiance are displayed separately in others charts. Nominal values of these parameters are also displayed. To start data acquisition, user must connect the application to acquisition module pressing the "Connect to network" button. Timer setting button is provided to determine measurement interval of the acquisition data. Prototype ofthe photovoltaic acquisition system is shown in Figure 6. The left side picture shows layer for power supply, voltage divider and current sensor, this layer is placed in the bottom of acquisition compartment. The right side pictures shows layer for the microcontroller, multiplexer, Vref board and data converter.

Fig. 4. PC and microcontroller software flowchart

Fig.5. Application program appearance

Fig. 6. Prototype of the photovoltaic acquisition system, (a) upper layer, (b) lower layer IV.

CONCLUSION

A wireless data acquisition system for photovoltaic generation system that uses PICI6F877A microcontroller as the main control has been presented. Implementation of the EGSR7150 Ethernet to serial module and the access point as Wi-Fi communication tool between acquisition equipment and user computer for graphically displaying the acquired parameter has work properly as intended. Implementation of such a system on a laboratory scale photovoltaic generation shows the practical simplicity, efficient and low cost.

REFERENCES

[I] Po-Yen Chen; Se-Kang Ho; Wei-Jen Lee; Chia-Chi Chu; Ching-Tsa Pan, "An Internet Based Embedded Network Monitoring System for Renewable Energy Systems",proc. The 7th nternational Conference on Power Electronics, pp.225-228 , October 22-26,2007.

[2] M.Benghanem; A. Maafi, "Data Acquisition System for Photovoltaic Systems Performance Monitoring", IEEE t rans. On nstrumentation and Measurement, Vo1.47, No.1, pp.30-33, February 2008.

[3] J. Machacek; z. Prochazka; j. Drapela, "System for Measuring and Collecting Data from Solar-cell Systems", Proc.9th International Conference Electrical Power Quality and Utilization, Barcelona, 9-11 October 2007.

[4] Z. Wang; L. Chang, "A DC voltage Monitoring and Control Method for Three Phase Grid-Connected Wind Turbine Inverters", IEEE Trans. On Power Electronics, Vol. 23, No.3, pp. 1118-1125, May 2008.

[5] T. Yuki; h. Yoshikiro; K. Kosuke, "Temperature and Irradiance Dependence of the I-V Curves of Various Kinds of Solar Cells" International Photovoltaic Science & Engineering Conference, Shanghai, China 2005

[6] A. Moein, M. Pouladian, "WIH-Based IEEE 802.11 ECG Monitoring Implementation", Proceedings of the 29th Annual International Conference of the IEEE EMBS Cite Internationale, Lyon, France August 23-26,2007.

[7] h. Zhao, X. Chen, K.H. Chon, "A Portable, Low-cost, Battery-powered Wireless Monitoring System for Obtaining Varying Physiologic Parameters from Multiple Subjects" , Proceedings of the 28th IEEE EMBS Annual International Conference, New York City, USA, Aug 30Sept 3, 2006

[8] A. Perujo; r. Kaiser; D.U Sauer; H. Wenzl; I. Baring-Gould; N.Wilmot; F. Mattera; S. Tselepis; F [9] h. Zhiqiang; Z. Wenxian; L. Jianke, "Research on High-Speed Data Acquisition and Processing Technique", The Eighth International Conference on Electronic Measurement and Instruments, ICEMI'2007

SIMULATION AND COMPARISON OF SPWM AND SVPWM CONTROL FOR THREE PHASE INVERTER

SIMULATION AND COMPARISON OF SPWM AND SVPWM CONTROL FOR THREE PHASE INVERTER

ABSTRACT

A voltage source inverter is commonly used to supply a three-phase induction motor with variable frequency and variable voltage for variable speed applications. A suitable pulse width modulation (PWM) technique is employed to obtain the required output voltage in the line side of the inverter. The different methods for PWM generation can be broadly classified into Triangle comparison based PWM (TCPWM) and Space Vector based PWM (SVPWM). In TCPWM methods such as sine-triangle PWM, three phase reference modulating signals are compared against a common triangular carrier to generate the PWM signals for the three phases. In SVPWM methods, a revolving reference voltage vector is provided as voltage reference instead of three phase modulating waves. The magnitude and frequency of the fundamental component in the line side are controlled by the magnitude and frequency, respectively, of the reference vector. The highest possible peak phase fundamental is very less in sine triangle PWM when compared with space vector PWM. Space Vector Modulation (SVM) Technique has become the important PWM technique for three phase Voltage Source Inverters for the control of AC Induction, Brushless DC, Switched Reluctance and Permanent Magnet Synchronous Motors. The study of space vector modulation technique reveals that space vector modulation technique utilizes DC bus voltage more efficiently and generates less harmonic distortion when compared with Sinusoidal PWM (SPWM) technique. In this paper first a model for Space vector PWM is made and simulated using MATLAB/SIMULINK software and its performance is compared with Sinusoidal PWM. The simulation study reveals that Space vector PWM utilizes dc bus voltage more effectively and generates less THD when compared with sine PWM.

Keywords: PWM, SVPWM, three phase inverter, total harmonic distortion.

INTRODUCTION

AC drives are more predominant than dc drives. Ac drives requires high power variable voltage variable frequency supply. The research in Pulse width modulation schemes has been intensive in the last couple of decades. PWM techniques have been used to achieve variable voltage and variable frequency in ac-dc and dc-ac converters. PWM techniques are widely used in different applications such as variable speed drives (VSD), static frequency changers (SFC), un-interruptible power supplies (UPS) etc. The main problems faced by the power electronic design engineers are about the reduction of harmonic content in inverter circuits. The classical square wave inverter used in low or medium power applications suffers from a serious disadvantage such as lower order harmonics in the output voltage. One of the solutions to enhance the harmonic free environment in high power converters is to use PWM control techniques. The objective of PWM techniques was to fabricate a sinusoidal AC output whose magnitude and frequency could both be restricted.

PWM switching strategies not only addresses the primary issues viz, less THD, effective dc bus utilization etc but also take care of secondary issues like EMI reduction , switching loss, better spreading of Harmonics over the spectrum. Real-time method of PWM generation can be broadly classified into Triangle comparison based PWM (TCPWM) and Space Vector based PWM (SVPWM).

In TCPWM methods such as sine-triangle PWM, three phase reference modulating signals are compared against a common triangular carrier to generate PWM pulses for the three phases. The frequency of the carrier signal is very high compared to the modulating signal. The magnitude and frequencies of the fundamental component in the line side are controlled by changing the magnitude and frequency of the modulating signal. It is simple and linear between 0% and 78.5% of six step voltage values, which results in poor voltage utilization. Voltage range has to be extended and harmonics has to be reduced.

In SVPWM methods, the voltage reference is provided using a revolving reference vector. In this case magnitude and frequency of the fundamental component in the line side are controlled by the magnitude and frequency, respectively, of the reference voltage vector. Space vector modulation utilizes dc bus voltage more efficiently and generates less harmonic distortion in a three phase voltage source inverter.

SPACE VECTOR PULSE WIDTH MODULATION

Space Vector Modulation (SVM) was originally developed as vector approach to Pulse Width Modulation (PWM) for three phase inverters. It is a more sophisticated technique for generating sine wave that provides a higher voltage to the motor with lower total harmonic distortion. The main aim of any modulation technique is to obtain variable output having a maximum fundamental component with minimum harmonics. Space Vector PWM (SVPWM) method is an advanced; computation intensive PWM method and possibly the best techniques for variable frequency drive application.

A space vector PWM

The circuit model of a typical three-phase voltage source PWM inverter is shown in Figure-1. S₁ to S₆ are the six power switches that shape the output, which are controlled by the switching variables a, a’, b, b’, c and c’. When an upper switch is switched on, i.e., when a, b or c is 1, the corresponding lower transistor is switched off, i.e., the corresponding a’, b’ or c’ is 0. Therefore, the on and off states of the upper switch S₁, S₃ and S₅ can be used to determine the output voltage. SVPWM is a different approach from PWM modulation, based on space vector representation of the voltages in the α-β plane. The α-β components are found by Clark’s transformation. Space Vector PWM (SVPWM) refers to a special switching sequence of the upper three power transistors of a three-phase power inverter. It has been shown to generate less harmonic distortion in the output voltages and/or currents applied to the phases of an AC motor and to provide more efficient use of dc input voltage. Because of its superior performance characteristics, it has been finding widespread application in recent years.

 

Figure-1. Three phase voltage source inverter.

SPACE VECTOR CONCEPT

The space vector concept, which is derived from the rotating field of induction motor, is used for modulating the inverter output voltage. In this modulation technique the three phase quantities can be transformed to their equivalent two-phase quantity either in synchronously rotating frame (or) stationary frame. From these two-phase components, the reference vector magnitude can be found and used for modulating the inverter output. The process of obtaining the rotating space vector is explained in the following section, considering the stationary reference frame. Considering the stationary reference frame let the three-phase sinusoidal voltage component be,

V_a = V_mSinωt                  (1)

V_b = V_mSin(ωt-2π/3)       (2)

V_c = V_mSin(ωt-4π/3)       (3)

When this three-phase voltage is applied to the AC machine it produces a rotating flux in the air gap of the AC machine. This rotating resultant flux can be represented as single rotating voltage vector. The magnitude and angle of the rotating vector can be found by means of Clark’s Transformation as explained below in the stationary reference frame. To implement the space vector PWM, the voltage equations in the abc reference frame can be transformed into the stationary dq reference frame that consists of the horizontal (d) and vertical (q) axes as depicted in Figure-2. From Figure-2, the relation between these two reference frames is below =

          (4)

Figure-2. The relationship of abc reference frame and stationary dq reference frame.

 

and f denotes either a voltage or a current variable.

As described in Figure-2. This transformation is equivalent to an orthogonal projection of [a b c]^t onto the two-dimensional perpendicular to the vector [1 1 1]^t (the equivalent d-q plane) in a three-dimensional coordinate system. As a result, six non-zero vectors and two zero vectors are possible. Six non-zero vectors (V₁-V₆) shape the axes of a hexagonal as depicted in Figure-3, and supplies power to the load. The angle between any adjacent two non-zero vectors is 60 degrees. Meanwhile, two zero vectors (V₀ and V₇) and are at the origin and apply zero voltage to the load. The eight vectors are called the basic space vectors and are denoted by (V₀, V₁, V₂, V₃, V₄, V₅, V₆, V₇). The same transformation can be applied to the desired output voltage to get the desired reference voltage vector,V_ref in the d-q plane. The objective of SVPWM technique is to approximate the reference voltage vector V_ref using the eight switching patterns. One simple method of approximation is to generate the average output of the inverter in a small period T to be the same as that of V_ref in the same period

 

Figure-3. Basic switching, vectors and sectors.

SWITCHING STATES

Table-1. Switching patterns and output vectors.

 

For 180° mode of operation, there exist six switching states and additionally two more states, which make all three switches of either upper arms or lower arms ON. To code these eight states in binary (one-zero representation), it is required to have three bits (2³ = 8). And also, as always upper and lower switches are commutated in complementary fashion, it is enough to represent the status of either upper or lower arm switches. In the following discussion, status of the upper bridge switches will be represented and the lower switches will it’s complementary. Let "1" denote the switch is ON and "0" denote the switch in OFF. Table-1 gives the details of different phase and line voltages for the eight states.

SOFTWARE IMPLEMENTATION OF SVPWM

Space vector PWM can be implemented by the following steps:

Step-1: Determine,,and angle(dVqVrefVα).

Step-2: Determine the time duration,, and 1T2T0T

Step-3: Determine the switching time of each transistor (1S to6S).

Step-1: Determine Vd,Vq,Vref and angle(a)

From Figure-4,Vd,Vq,Vref  and angle (α) can determined as follows:

          (6)

           (7)

           (8)

                            (9)

, where f = fundamental frequency.

 

Figure-4 Voltage space vector and its components in (d,q).

Step-2: Determine the time durationT1,T2 and T0

From Figure-5 the switching time duration can be calculated as follows:

Switching time at sector-1

           (10)

              (11)

                      (12)

           (13)

           (14)

                              (15)

           (16)

               (17)

            (18)

            (19)

            (20)

 

Figure-5. Reference vector as a combination of adjacent vectors at sector-1.

Step-3: Determine the switching time of each transistor

(S1 TO S6)

(a) Sector 1

(b) Sector 2

(c) Sector 3

(d) Sector 4

(e) Sector 5

(f) Sector 6

Figure-6. Switching pulse pattern for the three phases in the 6 different sectors.

RESULTS AND DISCUSSIONS

The main aim of any modulation technique is to obtain variable output having maximum fundamental component with minimum harmonics. The objective of Pulse Width Modulation techniques is enhancement of fundamental output voltage and reduction of harmonic content in Three Phase Voltage Source Inverters. In this paper different PWM techniques are compared in terms of Total Harmonic Distortion (THD). Simulink Models has been developed for Sinusoidal PWM (SPWM), Space vector PWM (SVPWM), and Space vector PWM switching Patterns. Simulation work is carried in MATLAB 7.0/Simulink.

The simulation parameters used are:

Fundamental frequency 50 Hz

Switching frequency 10 kHz

DC voltage 600 Volt

ODE Solver ode23tb

Simulation of SPWM

In Sinusoidal PWM three phase reference modulating signals are compared against a common triangular carrier to generate the PWM signals for the three phases. It is simple and linear between 0% and 78.5% of six step voltage values, which results in poor voltage utilization. Frequency in conventional SPWM output waves owing to their fixed switching frequencies. Simulation has been carried out by varying the modulation index between 0 and 1.Finally performance of chaos based SPWM has been compared with SPWM. The block diagram for Sinusoidal pulse width modulated inverter fed induction motor is shown in Figure-7. The line voltage and line current are shown in Figures 8 and 9, respectively.

 

Figure-7. Block diagram of SPWM inverter fed induction motor.

 

Figure-8a. Response of line voltage in SPWM.

 

Figure-8. Response of line voltage in SPWM.

 

Figure-9a. Response of line current in SPWM.

 

Figure-9b. Response of line current in SPWM.

 

Figure-10. Response of rotor speed in SPWM.

 

Figure-11. Response of torque in SPWM.

Simulation of SVPWM

Space vector PWM is an advanced technique used for variable frequency drive applications. It utilizes dc bus voltage more effectively and generates less THD in the Three Phase Voltage Source Inverter. SVPWM utilize a chaotic changing switching frequency to spread the harmonics continuously to a wide band area so that the peak harmonics can be reduced greatly. Simulation has been carried out by varying the modulation index between 0 and 1. Finally performance of SVPWM has been compared with conventional Sine PWM.

The Block Diagram of Space Vector Pulse width modulated inverter fed Induction Motor is shown in Figure-12. The line voltage and line current are shown in Figures 13 and 14, respectively.

 

Figure-12. Simulink block diagram of space vector PWM.

 

Figure-13. Response of line voltage in SVPWM.

 

Figure-14. Response of line current in SVPWM.

 

Figure-15. Response of rotor speed in SVPWM.

 

Figure-16. Response of torque in SVPWM.

Simulation results of SPWM and SVPWM

MODULATION INDEX = 0.4:

 

(A) SPWM           (B) SVPWM

MODULATION INDEX = 0.6:

 

(A) SPWM       (B) SVPWM

MODULATION INDEX = 0.8:

 

(A) SPWM       (B) SVPWM

MODULATION INDEX = 1:

 

(A) SPWM       (B) SVPWM

Table-2. Comparisons between SPWM and SVPWM by varying modulation index.

CONCLUSIONS

Space vector Modulation Technique has become the most popular and important PWM technique for Three Phase Voltage Source Inverters for the control of AC Induction, Brushless DC, Switched Reluctance and Permanent Magnet Synchronous Motors. In this paper first comparative analysis of Space Vector PWM with conventional SPWM for a two level Inverter is carried out. The Simulation study reveals that SVPWM gives 15% enhanced fundamental output with better quality i.e. lesser THD compared to SPWM.

PWM strategies viz. SPWM and SVPWM are implemented in MATLAB/SIMULINK software and its performance is compared with conventional PWM techniques. Owing to their fixed carrier frequencies cfin conventional PWM strategies, there are cluster harmonics around the multiples of carrier frequency. PWM strategies viz. Sinusoidal PWM and SVPWM utilize a changing carrier frequency to spread the harmonics continuously to a wideband area so that the peak harmonics are reduced greatly.

REFERENCES

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