Real Time Simulation of Direct Torque Control of BLDC Motor Drive using Opal-RT Simulator

This paper presents real time simulation of direct torque control of Brushless DC motor drive using Opal-RT simulator. The BLDC motor which is not having brushes has minimum losses which can be largely used in industries. The control of BLDC based upon various conventional methods which are used to control of ac machines. In this paper the mathematical model of BLDC Motor and torque control method used is based upon position of rotor which gives proper orientation of rotor, this signal is gives to controller which again gives to selecting switching table, again by proper selection of switching the signal is send to 3 phase inverter which then rotates the motor and torque control can be achieved. Also the real time simulation can be achieved by using Opal-RT simulator OP-4501 the simulation results and real time results are obtained by using FPGA card and at time step.


I. INTRODUCTION
In recent years, variable speed drives equipped with BLDC motors are extensively integrated into various applications ranging from servos to traction drives. Compared to BLAC it is relatively low cost. Since it has shorter end windings and does not require precision position sensor encoders. Therefore, in general, BLDC Drives are relatively low cost, the main advantages of the BLDC motors can be listed as follows: Low Noise, Low inertia High efficiency, High power density, more starting torque, Large speed ranges, speed, and torque characteristics are linear, They operate in any condition and having minimum maintenance. In between the control strategies that exhibit a high torque dynamic, the DTC method is mostly used for induction motor drives. The direct control is achieved by inverter switching pattern for control of electromagnetic torque and stator flux. Conventionally speed control of BLDC drive is doing hysteresis controller. But recently DTC has been employed for the BLDC drive. In DTC relationship is established between the torque responses. It gets better dynamic performance than conventional control methods that are less sensitive to parameter variations and simpler to implement. Electric vehicles have recently received many attentions from researchers due to their advantages over the conventional use of non-renewable sources. Electric Vehicle reduces the pollution that subsidies to climate change and smog, improving public health and reducing ecological damage. The block diagram for DTC control of BLDC motor Drive is as shown in Figure1. From the BLDC motor flux and torque reference is taken, that is compared with estimated value of torque and flux depending upon this hysteresis controller applied the parameter for voltage space vectors that are applied to BLDC motor with the help of inverter and estimated flux here voltage space vectors that are being applied to BLDC motor. By selection of voltage vectors flux trajectory i.e. circle or hexagon is produced. (In this technique conditions of intensity switches are resolved straightforwardly by the determined and reference torque and transition signals. This is accomplished by utilizing exchanging table. The contribution of which are torque, stator motion blunder and stator transition determined mistake which is isolated into six parts of 60 degrees) The switching table output is applied to inverter which is depends on the error signals. For energy saving in industry there is increase in use of variable speed drives. Initially direct current machines are control by decoupled nature of flux and torque then field oriented control and DTC methods are developed. Also these methods then used for control of ac machines. In field oriented control method current controller and ability to know just sector in which stator flux linkage space vector is varied rather exact position of vectors. In DTC the current controller

II. BLOCK DIAGRAM OF TOPOLOGY
There are a few special features of DTC control that can be summarized as follows: • No feedback current control • No traditional PWMalgorithm is applied • No vector transformation as in vector control • Feedback signal processing is somewhat similar to stator flux-oriented vector control • Hysteresis-band control generates flux and torque ripple and switching frequency is not constant (like hysteresis-band current control)

A. Simulation of Direct Torque control of BLDC motor drive
The simulation model for DTC of BLDC motor drive is shown in figure. The overall system consists of two loops for torque and stator flux. The stator flux and torque thai is reference value is compared with actual value taken from motor stationary reference frame model and from this errors are calculated for analysis. The errors then given to hysteresis current controller, depending upon this from current controller results are combining with position of stator flux and it making switching selection table.   Here, Figure 6 shows that the torque is estimated from reference speed and actual speed which is calculated as shown in simulation model ( Figure 6)  Where ea,eb and ec are back emf"s which is simulated in model as, From back emf the abc reference coordinate is converted into alpha-beta reference frame for calculation of alpha from given i.e. rotor angle Figure 9 again speed is calculated to torque estimation then pulses are generated which is fed to inverter. Figure 9 abc reference frame to alpha-beta reference frame conversion.
Following Figure 10 Figure 13 shows the no load spe information about the speed control of the BLDC motor for various applications.

B. REAL TIME SIMULATION
Digital simulators are evolved from analog simulator as simulation tools in past decades. It is carried out by using modern computer technologies it requires less cost and increases the performance. Now a day, the digital simulators are used widely in a number of industries because of it can be used virtually and there is no need for hardware prototype. The results are calculated before applying to real hardware model. In the real-time simulation, it depends on automatic code generation. Which played a very important role in many engineering field and applications, such as industrial motor drive design, power grid statistical protection tests and complex robotic controller design? From the last three decades' real-time simulators are used in power system and electrical drives. Simulation has major role in development of layout of power system transmission to motor drive optimization and plays critical role for large number of application. As the power system is a highly complex system also it is highly nonlinear in nature. By using a sophisticated controller, it is very complicated to run the system. So that the real-time simulation gives many advantages. The advantages of using real-time simulation are as:

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The OPAL-RT used in following Field, Electrical Power Systems, Electrical Power Electronics, Aerospace &Defence, Automotive, Academic & Research.

C.REAL TIME IMPLEMENTATION FOR DIRECT TORQUE CONTROL OF BLDC MOTOR DRIVE I. Software Synchronization
The MATLAB simulation diagram for DTC of BLDC motor drive is shown in Figure 15 to run this simulation model into  SC_Console subsystem consist of user interface blocks like scope, display, etc as shown in Figure 17 Console subsystem is available for the user while the simulation model is running. In the subsystem OpComm block is used for the communication purpose between master subsystem and console subsystem. The RT-Lab generated SC_Console block is shown in Figure  18 below it is running in RT-Lab simulator which is generated after the following through execution steps.SC Console consists of various scopes. The motor generates back emf shows inFigure 20 which is used for calculation of estimated speed. The back emfea is seen on graph with respect to time. The switching pattern generated by hysteresis controller by referring value of torque, phase currents and position of rotor is seen in graph as shown in Figure21, the switching pattern shown is only for phase-a i.e. for one leg of inverter, which is then runs the BLDC motor. The electromechanical torque of BLDC motor is shown in Figure 22.The Figure 23 Shows common mode voltage, which is calculated as,   IV. CONCLUSION In DTC method, between estimated and actual values of flux and torque has error, for reducing the torque and speed errors we have to control different state of inverter is possible. With comparison with other conventional methods, this method minimizes steady stateerrors by controlling estimated torque of highperformance motor drive. Also the real time simulation is performed using OPAL-RT Figure.30 Back-emf (ea) Figure31 Electromagnetic TorqueOP4510 first we analyzed the results using software synchronized method and the results also analyzedon digital oscilloscope using hardware synchronized method.
Due to DTC method errors between estimated and actual values of flux and torque, it is possible to control directly different state of inverter to reduce torque and flux errors. The simulated results help to determined precise control of estimated torque and hence it leads to reduction in less steady state errors compared with other conventional methods of high performance motor drives. Also the real time simulation is performed using OPAL-RT. OP4510 first we analyzed the results using software synchronized method, and the results also analyzed on digital oscilloscope using hardware synchronized method.