Implementation of dSPACE Controlled CSVPWM Based Induction Motor Drive

Implementation of dSPACE Controlled CSVPWM Based Induction Motor Drive

1Y.Chintu Sagar. 2Dr.K.Sri Gowri and 3G.Kumaraswamy

1PG Student, Electrical and Electronics, RGMCET NANDYAL, A.P, INDIA,

2 Professor, Electrical and Electronics, RGMCET NANDYAL, A.P, INDIA,

3Assistant Professor, Electrical and Electronics, RGMCET NANDYAL, A.P, INDIA,

Abstract The paper presents dSPACE controlled Induction motor drive fed through conventional space vector pulse width modulation (CSVPWM) algorithm based voltage source inverter. Two important performance measuring factors harmonic distortion in line current and dc bus utilization of the inverter can be improved with space vector approach in comparison with the popular sinusoidal PWM approach; the paper contemplates on the implementation of SVPWM algorithm for pulse generation which in turn are fed to intelligent power module that feeds the motor drive through DS1104 PPC603e / 250 MHz control desk . The results conclude the successful implementation of dSPACE Controlled induction motor drive. To validate the proposed work, numerical simulation including the experimental results is presented.

Index Terms CSVPWM, dSPACE , RTI, Space Vector approach

tested at different modulation indices ranging from low,

1. INTRODUCTION

   With the inventions of fast switching power semiconductor devices and motor control algorithms, emerging interest instituted among researchers in the area of PWM techniques. During the past decade several PWM algorithms have been studied extensively. Various PWM methods have been developed to achieve wide modulation range, less switching loss, improved total harmonic distortion (THD) with ease in digital implementation with less computation burden on the controller. A large variety of algorithms for PWM exist, and a survey of these was done in [1]. There are two popular approaches for the implementation of PWM algorithms, namely triangular comparison (TC) approach and space vector (SV) approach. For a long period, TC approach based PWM methods were widely used in most applications. The earliest modulation signals for TC approach are sinusoidal. But, the addition of the zero sequence signals to the sinusoidal signals results in several non-sinusoidal signals. Compared with sinusoidal PWM (SPWM) algorithm, non-sinusoidal PWM algorithms can extend the linear modulation range for line-to-line voltages. Different zero-sequence signals lead to different non sinusoidal PWM modulators [2]. In this paper pulse generation through dSPACE control desk is done for CSVPWM algorithm, which in turn generates the required ac voltage by means of intelligent inverter module (PEC16DSM01). The performance of the motor is

   medium to high. Simulation and experimental results of pulse pattern for a-phase, modulating waves of phase a, b are also presented.

   With the development of digital signal processors, SVPWM has become one of the most popular PWM methods for three-phase inverters [3]-[4]. It uses the space vector approach to compute the duty cycle of the switches. The main features of this PWM algorithm are easy digital implementation and wide linear modulation range for output line-to-line voltages. The equivalence between TC and SV approaches were elaborated in [5] and concluded that SV approach offers more degrees of freedom compared to TC approach.

   While, SVPWM gives superior performance, switching losses in the inverter are more as it generates continuous pulses (modulating signal). Hence, to reduce the switching losses of the inverter, discontinuous PWM (DPWM) methods are considered. The generation of these DPWM algorithms [6]-[8] can also be considered. However, this paper presents the results of CSVPWM algorithms for induction motor using the conventional notion of sector selection.

2. CONVENTIONAL SVPWM ALGORITHM

   The main purpose of the voltage source inverter (VSI) is to generate a three-phase voltage with controllable amplitude, and frequency. A conventional 2- level, 3-phase VSI feeding a three-phase induction motor is shown in Fig 1.

   From Fig.1, it can be observed that the two switching devices on the same leg cannot be turned on and cannot be turned off at the same time, as this condition will result in short circuit/open circuit to the connected phase. Thus the nature of the two switches on the same leg is complementary. The switching-on and switching-off sequences of a switching device are represented by an existence function, which has a value of unity when it is turned on and becomes zero when it is turned off. The existence function of a VSI comprising of switching devices Ti is represented by Si, i = 1, 2, . . . 6. Hence, S1, S4 which take values of zero or unity respectively, are the existence functions of the top device (T1) and bottom device (T4) of the inverter leg connected to phase a.

   By maintaining the volt-second balance, a combination of switching states can be utilized to generate a given sample in an average sense during

   Fig -2. Voltage space vectors produced by a voltage source inverter

   a sub cycle. The voltage vector Vref

   in Fig.2 represents

   Fig -1. 2-level, 3-phase voltage source inverter feeding induction motor

   S1 S4 1; S3 S6 1; S5 S2 1

   (1)

   the reference voltage space vector or sample, corresponding to the desired value of the fundamental components of the output phase voltages. But, there is no direct way to generate the sample and hence the sample can be reproduced in the average sense. The reference vector is sampled at equal intervals of time, Ts referred to as sampling time period. Different voltage vectors that can be produced by the inverter are applied over different durations with in a sampling time period such that the average vector produced over the sub cycle is equal to the

   As seen from Fig 1, there are totally six switching devices and only three of them are independent. The combination of these three switching states gives out eight possible voltage vectors. At any

   time, the inverter has to operate one of these voltage vectors. Out of eight voltage vectors, two are zero voltage vectors (V0 and V7) and remaining six (V1 to V6) are active voltage vectors. In the space vector plane, all

   sampled value of the reference vector, both in terms of magnitude and angle. As all the six sectors are symmetrical, here the discussion is limited to sector-I only. Let T1 and T2 be the durations for which the active states 1 and 2 are to be applied respectively in a given sampling time period Ts . Let Tz be the total duration for which the zero states are to be applied. From the principle

   of volt-time balance T1 , T2 and Tz can be calculated as:

   the voltage vectors can be represented as shown in Fig 2.

   For a given set of inverter phase voltages (V the space vector can be constructed as

   an, V

   bn, V

   cn),

   T1 2 3 M Sin(60o )Ts

   (4)

   2

   4

   T2 2

   3 M Sin( )Ts

   (5)

   Vs 2 Van

   3

   j

   • Vbn e 3

     j

   • Vcne 3

   (2)

   TZ Ts T1 T2

   (6)

   From (2), it is easily shown that the active voltage vectors can be represented as

   in (7).

   Where M is the modulation index and is given

   Vk

   2 Vdc e

   3

   j(k 1)

   3

   where k 1,2,…,6

   (3)

   M 2vref

   3Vdc

   (7)

   In the SVPWM algorithm, the limit for modulation index is 0.866 [1]. In the SVPWM srategy, the total zero voltage vector time is equally distributed between V0 and V7. Further, in this method, the zero voltage vector time is distributed symmetrically at the start and end of the sub cycle in a symmetrical manner. Moreover, to minimize the switching actions of the inverter, it is desirable that switching should take place in one phase of the inverter should take place only for a transition from one state to another. Thus, SVPWM uses 0127-7210 in first sector, 0327-7230 in second sector and so on. Table-1 depicts the switching sequence for all the sectors.

   TABLE I

   SWITCHING SEQUENCES IN ALL SECTORS FOR SVPWM

   Sector number	On- sequence	Off-sequence
   1	0-1-2-7	7-2-1-0
   2	0-3-2-7	7-2-3-0
   3	0-3-4-7	7-4-3-0
   4	0-5-4-7	7-4-5-0
   5	0-5-6-7	7-6-5-0
   6	0-1-6-7	7-6-1-0

   Also, with the SVPWM algorithm, the linear modulation range and dc bus utilization compared with traditional SPWM can be increased [1].

3. SIMULATION RESULTS AND

   DISCUSSIONS

   To validate the proposed PWM algorithms, numerical simulation is performed using Matlab- Simulink. To maintain constant average switching frequency, the switching frequency of SVPWM algorithm is taken as f s .For the simulation, the average switching frequency of the inverter is taken as 10 kHz and the dc link voltage is taken as 600 V. The simulation results of the conventional SVPWM algorithm is shown in Fig.3 Fig4

   Here , modulating waveforms and pole voltages of the inverter have shown. From the results it is concluded that SVPWM algorithm generates continuous modulating

   wave andhence continuous pulses to the inverter and hence gives more switching losses in the inverter.

   Fig-3. Simulation Results Of Proposed SVPWM Algorithm modulating waves

   Fig- 4. Simulation Results Of Proposed SVPWM Algorithm Pulses

4. HARDWARE IMPLEMENTATION RESULTS AND DISCUSSIONS

   The experimental setup of the proposed control system is shown in Fig.5. The proposed algorithm has been implemented using the rapid prototyping and real time interface system dSPACE with DS1104 control card. DS1104 controller card is built by a German company called dSPACE. It is a powerful system which provides rapid control prototyping and Hardware-In-Loop (HIL) simulations which can be used for many different applications.The obvious advantages of using hardware- in-loop simulations is that performance of systems can be compared both practically and theoretically. DS1104 Controller Board comes with software packages called Real Time Workshop and Control Desk. DS1104 control card includes the PowerPC 603e/250 MHz main

   processor and Texas instruments TMS320F240 sub processor.DS1104 control cards allows the user to construt the system in MATLAB/Simulink and then to convert the model files to real-time codes using the Real- Time interface(RTI) of the control. The software packages used in the process of implementing, experimenting, and testing control systems of the dSPACE are listed below:

   Use of Simulink software in MATLAB:

   Simulink is an interactive environment integrated in MATLAB which is used for the purposes of modelling, analysing and simulating the whole systems. This is usually the first step in designing systems where the user can test the model offlizne by analyzing the theoretical version of the model. It provides designers a graphical user interface for constructing block diagrams.

   Real-Time Workshop:

   Real-Time Workshop software builds the Real-Time code (C-code) from the models built in Simulink. The user can also manually program the algorithm using C programming language and this is possible by using the Microtech PowerPC C compiler which is available in the CD-rom provided by dSPACE. This is accessed from MATLAB which is an add-on software package that comes separate with MATLAB. This package comes along with the DS1104 Controller Board.

   Real-Time Interface(RTI):

   This software acts as an interface between Simulink software package and DS1104 hardware. This software package comes along with the DS1104 board. As stated earlier, Real-Time Workshop builds the real-time C-code from the models built in Simulink. That real-time code is then compiled which is downloaded automatically into the target DSP system (DS1104 Controller Board) which is then executed.

   Control Desk:

   This is another software package that comes along with DS1104 board. Control Desk is an integrated tool that allows the designer to control and monitor the operation of the overall systems It allows the designers to look at the variables, display their behaviour and modify the simulation parameters by interacting directly with the dSPACE board. By controlling the variables through control desk, there is no need to waste time in re- compiling the whole model. As the variables are changed along, the designer can observe these changes straight away on control desk. If these modifications were to be done in Simulink, repetitive compilation will be required to execute the changes that have been made to the algorithm. It is similar to a digital oscilloscope where the user can observe any changes that occur, thus, helping in designing a better systems..A control desk software, which is dSPACE experiment software which provides and make the development of controllers more effective.

   The CSVPWM algorithm has been implemented using a dSPACE board with TMS320F240. The dSPACE works on Matlab/Simulink platform which is a common engineering software and easy to understand. Another feature of the dSPACE is the control desk which allows the graphical user interface, Through the control desk the user can observe the response of the system, give command to the system through this interface. Real time interface is needed for the dSPACE to work. RTI is the link between dSPACEs real-time systems and the development software. MATLAB/ Simulink from the Math Works. Power circuit for the drive consist a Semikron IGBT based voltage source inverter with opto- isolation and gate driver circuit SKHI22A. The dc voltage for the VSI is achieved through a three-phase diode bridge rectifier module. A capacitive filter is used at the dc link of this module to reduce the voltage ripples. The motor used in this experimental investigation is a three phases, 3KW, 4 pole squirrel cage induction machine,

   The CSVPWM Pulses are first designed in MATLAB/SIMULINK environment and relevant coding are written to generate the pulses and by using dSPACE software conversion tool the M-files are converted in to the C coding. Thus, the triggering pulses are given to the inverter and the induction motor is driven by Voltage Source Inverter (VSI). From the test done, control of induction motor was successfully implemented using dSPACE .

   Fig -5. Real Time Implementation

   Engg And Tech, Andhra Pradesh, India for sanctioning fund to carry out this work under RPS scheme and providing necessary facilities to carry this work.

   REFERENCES

   Fig -6. Real Time Implementation Results

   Fig -7. Real Time Implementation Results

5. CONCLUSION

The proposed CSVPWM algorithm has been developed, simulation and hard ware results are presented in this paper. The proposed conventional space vector pulse width modulation algorithm uses the concept of sector selection. Moreover, the proposed algorithm uses sector and angle calculations .It requires the angle and sector calculations and hence increases the complexity involved in the algorithm. From the test done, control of induction motor was successfully implemented using dSPACE which means this process is feasible. Speed of the Inducton motor is controlled successfully by varying the frequency or voltage by declaring these two as control parameters in the dSPACE control desk with out disturbing the hard ware setup which is already running.

ACKNOWLEDGMENT

The authors are thankful to the AICTE and Management of Rajeev Gandhi Memorial College of

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BIOGRAPHIES

1Y.Chintu Sagar is born in 1989 in India .He is graduated from RGM College of Engineering and Technology, Nandyal in 2010.Presently he is doing post graduation in Power Electronics and Electrical drives Specialization at RGM College

of Engineering and Technology, Nandyal. His main areas of interest include Induction motor drives, Electrical machines, power Electronic converters and Power Electronic Drives.

2Dr. K.Sri Gowri received the B.Tech degree from SVU college of Engineering, Tirupati in 1997, the M.Tech degree from RGM College of Engineering and Technology, Nandyal and has been awarded Ph.D in the area of Power Electronic Control

of Electric Drives from JNTU Kakinada in 2010. She is currently Professor in the Department of EEE in RGMCET, Nandyal, A.P. Her areas of interest include Power Electronics, Pulse Width Modulation Techniques, Drives and Control, Renewable Sources of Energy.

3G. Kumaraswamy is born in 1983 in India. He is graduated from JNTU University in 2005 and pursued Post graduation from the same university. He is currently working as a Assistant professor in the department of electrical and electronics

engineering R.G.M college of engineering and technology, Nandyal, Andhra Pradesh, India. He has eight years of teaching experience. He has attended several National workshops. His main areas of research include Photovoltaic cells, multilevel inverters.