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Held on February 5, 2012 – Updated Slides can be downloaded here

Abstract:

Brushless permanent magnet (PM) motors are preferable choice in many applications due to low weight and volume, high torque and power density, excellent controllability and reliability, simplicity and ruggedness, high efficiency and low maintenance. They have superior advantages in variable speed and load applications compared with induction, switched- and variable-reluctance motors. In recent years, poly-phase PM motors of 3-, 4-, 5-, 6- and 7-phase configurations have been investigated. Some of these motor configurations have shown promise to improve performance over three-phase configurations.

Extensive research has been carried out in radial, axial, transverse and Halbach array flux architectures. The radial flux motors (RFM) has been widely used in the industry due to relative ease in manufacturing. Axial flux motors (AFM) have been difficult to manufacture due to the high expense of fabricating lamination stacks. Axial flux motors have shown superior performance over radial flux motors under a narrow set of circumstances and additionally where length of the motor is less than 30% of the diameter (length/diameter<0.3). Transverse flux motors (TFM) are more difficult to design and manufacture. Halbach array motors have shown promise for operations requiring significantly higher speed and are not considered suitable for low speed, high torque operations.

Several control methods exist today for control of PM machines. Trapezoidal control injects trapezoidal current waveforms into the motor windings. Sinusoidal control injects sinusoidal current. Field oriented control (FOC) converts poly-phase motor currents into a Cartesian coordinate system which rotates with the motor’s synchronous speed. This results in direct control of air gap flux and hence torque. FOC has been known to improve a motor’s dynamic performance substantially. Space vector control is known to increase DC bus voltage utilization by as much as 15% by clever application of the available bus voltage.

Studies of 3-, 5- and 7-phase inverters for low voltage applications have been conducted. The study stated that the 5- and 7-phase inverters resulted in lower current per phase and leg resulting in higher reliability, better DC bus voltage utilization resulting in more output power, and better utilization of harmonics resulting in more torque. The study showed significant improvement in performance of 5-phase inverters over 3-phase inverters. The performance of 7-phase inverters was marginal over the 5-phase inverters.

Substantial innovations have taken place in the field of power electronics in the last decade. These innovations have continually churned out better semiconductor devices, thermal management systems, and materials. These breakthroughs have allowed smaller and more efficient inverters. Some tougher and space constrained applications have demanded a tight integration between motors and inverters. We will briefly discuss such innovations and their applications.

This workshop will cover simulation, algorithm and software development methodology and tools for brushless permanent magnet motor systems. Under algorithm development, we will cover the principles of FOC (field oriented control, or vector control), followed by various advanced implementation techniques for high performance and energy efficiency including predictive current control, decoupling control, space vector modulation, field weakening operation, as well as modeling and simulation This section will also cover control system analysis and compensation – open loop transfer function, stability criteria, Type 1, 2 and 3 Amplifiers, and K factor technique for stability analysis if time permits.

In this section we would briefly discuss use of such tools as dSPACE™, VISSIM™ etc. This section will also provide Software development examples based on Agile Software Development Model. Under hardware development, we will focus on MCU/DSP selection criteria, FPGA based designs, power stage design and achieving the desired performance from PM machines when integrated with an Inverter. This section will cover selection of power devices, PCB layout, safety, EMI/EMC, environmental and reliability considerations, thermal analysis, mechanical and manufacturing considerations.

Speaker Bio:
Rakesh Dhawan is a twenty-two years veteran of motors and motor drive Industry. He has developed critical understanding and published on a wide range of motors, motor drives, high frequency electromagnetic components, electric vehicles and switch mode power systems. He has co-authored over 25 publications in various refereed journals and conference proceedings and is an inventor on 7 issued or pending US patents. He has served on the Technical committee of the Applied Power Electronics Conference (APEC). He received the B. Tech (Electrical Engineering) degree from Indian Institute of Technology (IIT), Kharagpur, India. He received his MS degrees from University of Minnesota under the tutelage of Power Electronics pioneer Prof. Ned Mohan. He received his MBA from Old Dominion University.

He has been directly responsible for over twenty five successful product launches in his career many of them involving brushless permanent magnet motor systems. Rakesh has conducted several workshops in the recent past in the field of motors and motor drives. His interests include brushless permanent magnet motor systems, light electric vehicles, electric bicycles, switch mode power supplies, solar inverters, simulation, statistics, project management and new and ultra-fast product development methodologies. Rakesh is a high energy individual with a difference; he combines technology excellence, leadership and professional management skills with his inborn entrepreneurial instincts.

Rakesh is a member of IEEE and the Entrepreneur’s Organization (Washington-DC Chapter) and is very keen on nurturing innovation and entrepreneurial talent in the field of technology development and management.

Integration of PSpice Simulation and Statistics. This video covers review of basic simulation strategy, understanding simulation objectives, product development cycle, simulation technique based on the product development cycle, Use of Statistics, Integration of Statistics and Manufacturing data into PSpice Simulation.

Assuming a motor has been designed with a certain number of poles and slots. Further, let us assume that we wish to change the number of turns to see if the design can be optimized with respect to copper losses.

As you begin to change the number of turns, the following relationships hold true:

Torque α N*I                                      [1]

Resistance α N²                                   [2]

BackEMF α N                                     [3]

BaseSpeed α (Vbus/2 – I*R)/Ke        [4]

In the above equations, we have assumed Ldi/dt = 0 at peak values. Ke is the BackEMF constant in V/rad/s. Vbus is the bus voltage of the inverter. All the above values can be assumed to be peak.

Now, the question is as follows:

Q: Can one reduce copper losses in the motor at a specified torque level by changing the number of turns? One is not allowed to change the number of poles or slots or motor diameter or lamination stack height.

Now if one were to compute copper losses at a specified copper level, we arrive at the following :

Torque = Constant (as we wish to calculate at a specified torque level);

Hence, NI = Constant

Therefore, as N goes up, I goes down. As N goes up, R goes up. Let us look at the following equations:

N₁I₁ = N₂I₂                              [5]

N₁²R₁ = N₂²R₂                         [6]

Calculating, I₂²R₂, substituting for I₂ and R₂ below

I₂²R₂= (N₁I₁/ N₂)²*( N₂/ N₁)²* R₁ = I₁²R₁       [7]         

As can be seen in [7] above, the copper losses can be increased or decreased for a specified torque level.

Check Out Our Upcoming Workshop:
http://www.strategictechgroup.com/workshop-brushless-permanent-magnet-motors-motor-drives/index.html

1. Introduction:

Brushless Direct Current (BLDC) motor drives are widely used in Automobiles, Aerospace, Consumer, Automation equipment, Instrumentation etc. The development of advanced magnetic materials, power electronics and digital control systems make the Permanent Magnet (PM) BLDC motors an effective solution for wide rage of inverter fed variable speed drives. BLDC use in electric vehicles has increased substantially in the recent years due to its high power and torque density and ease in controllability.

A Brushless DC motor has a permanent magnet rotor and a wound stator. The windings are connected to an inverter. The inverter energizes the windings in a pattern which rotates the magnetic field around the stator. The energized stator winding causes the PM rotor to rotate in a synchronous fashion around the stator. So it is important to know the perfect sequence to energize the stator windings. In this paper we have shown the simulation results and step by step procedure to simulate  a BLDC motor control system.

Keywords: Motor Control, Permanent Magnet Motors, BLDC motor, Back EMF, Inverter, Simulation, Spice, PSpice, Brushless, Motor Drive, Torque Control, PWM Motor Control

2. Permanent Magnet BLDC Motor Control: Concepts, Operation and Modeling:

The first experiment involving rotation of electromagnetic components was conducted in early 1900s.The development of first practically useful PM motor started with the invention demonstrated by Edison around 1900. The improvements were mainly driven by the development of better magnetic materials. However, in the last decade the interest has increased due to the advancement of power electronics, semiconductor materials, and digital control.

2A. Magnet Materials:

The magnetic phenomenon was discovered more than 2500 years ago. For the longest time, the only known magnetic material was lodestone (Fe3O4). The most significant early use of Permanent Magnet was the compass. The relation between magnetism and electricity was first discovered by Orsted, Sturgeon and Faraday in the 19^th century. The development of commercially available PM materials began in the 20^th century with production of magnetic steel. In 1930s the first PM aluminum-nickel-cobalt alloy (AlNiCo) was developed for electro mechanical systems. However it had a very limited use due to its low coercive force.

[Definition of Coercive Force - The amount of reverse magnetic field which must be applied to a magnetic material to make the magnetic flux return to zero. It is the value of H at point c on the hysteresis curve.]

In 1950s the low cost ferrite permanent magnets with high coercive force were developed. Until today this remains the most useful PM because of its superior price-performance ratio.

The next introduction of PM was sintered rare-earth cobalt magnets developed around 1970. These are also known as Samarium Cobalt alloy (SmCo). These magnets have higher performance and coercive force than the ferrite magnets. There have been recent introductions of other PMs with better performance. In 1980s Neodymium-Iron-Boron (NdFeB) was invented with higher performance and less cost than SmCo. However, NdFeB is not always superior due to its lower thermal stability. There is a significant research activity in the area of metallurgy to invent new and powerful PM. Today the high performance rare-earth magnets are widely used in small motors like hard disk drive and servo drives etc. Great care is needed at all times to handle the permanent magnet materials because of their brittle nature.

2B. Basic Operating Principle, BLDC Motor Control:

Brushless DC motors are also known as Magnet Synchronous motors. The question is whether BLDC can be classified as an AC or a DC motor. Though the supply is DC and does not directly operate the motor. BLDC is a PM synchronous motor that uses position sensor to detect the position of the rotor and an inverter to control the armature currents. BLDC motors can also be configured as an inside-out motor for direct-drive electric vehicle applications when armature can be located in the center of the motor and the magnets are on the outside.

[Definition of Trapezoidal Motor: In a trapezoidal motor the back-EMF induced in the stator windings has a trapezoidal shape and its phases must be supplied with quasi-square currents for ripple free torque operation.]

In BLDC motor the armature does not rotate, instead the PMs rotate. In brushed DC motor, windings are in the rotor. So it becomes difficult to transfer the current to the moving rotor.

In a three phase BLDC six step commutation is the simplest method to drive the motor. One set of sequence represents a full electrical rotation. Number of electrical cycle is equal to the number of pole pairs. Increase in pole pairs may decrease the torque ripple. The speed and torque of the motor depend on the strength of PMs and in certain instances the magnetic field generated by energized winding. Also it is necessary to know the exact position of the rotor magnet to start the motor. The two main objectives are to control the speed and torque of the BLDC motor. In figure 2 it shows the closed loop representation of the BLDC motor for speed and torque control.

Brushless DC Motor Control

Rotation

Figure 2 shows a basic block diagram of BLDC motor control system. A flux is generated by an energized stator which interacts with the rotor magnet flux. Maximum flux is generated when the angle between the stator and rotor flux is close to 90 degree. It is necessary to know the proper position of the rotor magnet to ensure alignment of the stator flux close to this angle. Generally in low cost systems, three hall sensors are placed on the stator with 60 or 120 electrical degree phase shift to provide the position feedback. Six step commutation requires that the windings be switched every 60 electrical degrees. Three hall sensors read the rotor position every 60 electrical degrees of rotation. So in one complete electrical rotation hall sensors provide six unique position values. Table 1 shows hall sensor table for a three-phase BLDC motor with six unique values along with active phase voltages and switches.

Hall Sensor Values (H3,H2,H1) Phases Switches 100 Va-Vb AT-BB 101 Va-Vc AT-CB 001 Vb-Vc BT-CB 011 Vb-Va BT-AB 010 Vc-Va CT-AB 110 Vc-Vb CT-BB

Table 1: Commutation sequence from Hall sensor

Generally the hall table is provided by the motor manufacturer. Depending on the current hall value, firing signal is given to the corresponding switches of the inverter as per Table 1.

[Definition of BACK EMF: Back-EMF is a voltage that occurs in electric motors when there is a relative motion between the armature of the motor and the external magnetic field].

Speed Control:

Speed of a BLDC motor is proportional to the applied voltage across its windings. A precise speed can be controlled using a conventional PI controller. A well designed PI controller generates a duty cycle command based on the difference between the actual and commanded speed. Depending on the duty cycle command, PWM pulses are generated that vary the gate drive of the inverter switches to get the required speed.

Torque Control:

Torque is directly proportional to the motor current. In this mode of control, a current reference proportional to the desired torque is generated. Current feedback is compared with this reference and the error is fed to a PI. A duty cycle is generated proportional to the output of the PI amplifier.

3. Mathematical Modeling of BLDC Motors:

The three phase star connected BLDC motor can be described by the following basic equations. These are per phase modeled equation. A per phase model is also shows in figure 3.

Where V, I and e are the voltage, current and  back-emfs of phase A, B and C. R and L are the resistance and inductance of each phase respectively. T_e and T_L are electrical torque and load torque, j is the rotor inertia, K_f is the friction constant and ω_m is the rotor speed.

4. Back EMF modeling:

Fig 4 shows the back EMF model in PSpice. The model have parameters like frequency (F_req), rise time (T_r), fall time (T_f), pulse width (P_w), amplitude (A), motor inductance (L_mot) and motor resistance (R_mot).

Fig 5 shows simulated trapezoidal back emf from the model in fig 4.

5. BLDC Motor: Basic Model

In our simulation technique we have modeled a BLDC motor similar to BN-23 from Moog (http://www.moog.com). Some of the key specifications are listed below:

Frequency	133.33 Hz
Back EMF (A)	6.3V
Back EMF constant	3.15V/1000rpm
Motor/Terminal resistance(R_mot)	0.181 ohm
Motor/Terminal Inductance(L_mot)	242 uH

The complete motor model is showing in figure 6.

Figure 6: A BN-23 motor model

Every parameter of interest has been defined in this simulation example. In our simulation technique we generate a parameter text file. The importance of the text file is that it includes all the parameters of interest. It is a convenient way to change parameters and re-run analysis. The parameter file is shown in appendix A.

Fig. 6 shows the 3-phase BLDC model. Fig. 7 shows the three phase trapezoidal BackEMF waveforms from the model shown in figure 6.

6. The Inverter:

An inverter is used for energizing the stator winding based on the rotor position. The current in any two energized phases can be turned ON and OFF anytime during every 60 electrical degrees. The inverter and motor model are shown in Fig 8.

In the above model we assume that switch and diode are ideal in nature. It is important to use ideal components at the beginning of any simulation activity to reduce unnecessary complexity and build any system model one step at a time.

The sub-circuits used for the switch and diode are shown in appendix B and C respectively.

Fig 9  shows PSpice model related to the gate drive circuits. AT is connected to the gate of the top switch of leg A. AB is connected to the gate of the bottom switch of leg A. Similarly BT,BB,CT,CB are connected to the gates of leg B-top switch, leg B-bottom switch, leg C- top switch and leg B-bottom switch respectively.

A phase current that is being turned OFF will flow through its complementary freewheeling diode while the current in the phase which is turned ON will start rising from zero. We have implemented six step firing of the stator winding current in this simulation example. It is important to know the current flow in the system at every instance of time and how the off phase winding current flows through the complementary freewheeling diode when a switch is turned off in a particular interval. In this paper we have shown the simulation results of BLDC motor control system without any PWM to highlight the simulation technique and the basics of the firing sequence.

7. Analysis of Current Flow in BLDC Motors:

When switch AT and switch BB are on, current flows through the coils A and B. This is shown in fig. 10. It is clear from the simulation results that when switch AT is on, current flows through coil A and it is positive whereas current through coil B is negative while flowing through switch BB. When Switch AT is on and BB is off, we start to energize the coil C by switching ON the switch CB and switching OFF the switch BB. Consequently, there will be no further current flow through coil B. However, the current in phase B can not come to zero instantly. It has to flow through the complementary diode D3. Current in Phase A once again starts to increase as the switch CB starts conducting soon after the current in Coil B finishes through Diode D3.

There are 18 different states of current flow in the 3-phase BLDC motor in a 360 degree electrical cycle. The different steps are illustrated here with a brief discussion and simulation results.

Step 1: AT and BB are ON (0 degree)à Current starts to increase in coil A (+ve) and comes out from coil B (-ve)

Step 2:  AT and BB are ON (0-60 degree)à Current still flows in coil A (+ve) and B (-ve).

Step 3: AT is ON and BB is OFF (60 degree)à Current flows in coil A (+ve) and energy stored in coil B flows through the freewheeling diode D3. There is a slight drop in the phase current.

Step 4:  AT and  CB is ON(60 degree)àCurrent  flows in coil A(+ve) and once again starts to increase and comes out from Coil C(-ve)

Step 5:  AT and CB are ON (60-120 degree)à Current flows in coil A (+ve) and C (-ve).

Step 6: AT is  OFF and  CB is ON(120 degree)à Energy stored in coil A flows through the freewheeling diode D2 and current  flows through coil C(-ve)

Step 7: BT is just ON and Switch CB is ON (120 degree)à Current starts to increase through coil B (+ve) while flowing through in coil C (-ve)

Step 8: BT and CB are ON (120-180 degree)à Current flows in coil B (+ve) and C (-ve).

Step 9: BT is ON and CB is OFF (180 degree)à Current still flows in coil B (+ve) and energy stored in coil C flows through the freewheeling diode D5.

Step 10:  BT and AB are ON (180 degree)à Current still flows in coil B(+ve) and A(-ve).

Step 11: BT and AB are ON (180-240 degree)à Current flows in coil B (+ve) and A (-ve).

Step 12: BT is OFF and  AB is ON(240 degree)à Energy stored in coil B  flows through the freewheeling diode D4 and it also flows through coil A(-ve)

Step 13: Switch CT  and Switch AB are ON(240 degree)à Current starts to increase in coil C (+ve) and it also flows through coil A(-ve)

Step 14: CT and AB are ON (240-300 degree)à  Current flows in coil C (+ve) and A (-ve).

Step 15: CT is ON and AB is OFF (300 degree)à Current flows in coil C (+ve) and energy stored in coil A flows through the freewheeling diode D1.

Step 16: CT and BB are ON (300 degree)à Current flows through coil C (+ve) and Coil B (-ve)

Step 17: CT and BB are ON (300-360 degree)à Current flows through coil C (+ve) and coil B (-ve).

Step 18:  CT and BB are ON (360 degree)à Energy stored in coil C flows through the freewheeling diode D6 and coil B (-ve)

Concluding Remarks:

Understanding the BLDC motor operation and firing the proper stator winding are important in simulation and development of any BLDC motor control system. This article lays down the basic foundation of a BLDC motor control model which will be used to analyze torque and speed control along with advanced PWM techniques in the subsequent articles. In the future articles, we will also explore various control strategies such as High Side PWM, High and Low Side PWM, High and Low Side PWM with two active inverter legs, High and Low Side PWM with 180o phase shift, PWM activation of all inverter legs at all times. These strategies impact performance, cost, efficiency and volume of a motor control system.

Appendix A: Parameter Text File

******* Modeling Moog Brushless Motor BN23  ****** .Param Freq=133.33 .Param A = 6.3 * A = Back EMF Voltage .PARAM Tr= {1/Freq/12} .PARAM Tf= {1/Freq/12} .PARAM Pw= {1/Freq/3} .PARAM R_MOT =0.181 .PARAM L_MOT =242u .PARAM GATE_Tr =10uS .PARAM GATE_Tf = 10uS .PARAM 180_DEGREE = {1/Freq/2} .PARAM 120_DEGREE = {1/Freq/3} .PARAM 240_DEGREE = {2/Freq/3} .PARAM 30_DEGREE = {1/FREQ/12} .PARAM OFFSET = 0 *PARAM DLY1 = {1/FREQ/12} .PARAM DLY1 = 0 *DLY1 = 30 Degrees .PARAM DLY2 = {DLY1+1/Freq/2} *DLY2 = DLY1+180 Degrees .PARAM DLY3 = {DLY1+ 1/Freq/3} *DLY3 = DLY1+ 120 Degrees .PARAM DLY4 = {DLY1+ 1/Freq/3+1/Freq/2} *DLY4 = DLY3+180 Degrees .PARAM DLY5 = {DLY1+2/Freq/3} *DLY5 = DLY1+240 Degrees .PARAM DLY6 = {DLY1+2/Freq/3+1/Freq/2} *DLY6 = DLY5+180 Degrees *** Gate Drive Voltage .PARAM GATE_DRV_V = 5 **END**

Appendix B: Switch Sub-Circuit

****  Idle Switch  Spice subckt***** *********** CONNECTIONS: ****               DRAIN ****                |                                  SOURCE ****                |   |                              GATE ****                |   |   |                          GATE GND ****                |   |   |  | ****                |   |   |  | .SUBCKT SWITCH      D   S   G  GG Switch_Idle D S G GG IDLE_SWITCH .MODEL IDLE_SWITCH VSWITCH (RON=0.005) .ENDS SWITCH *** End of sub-circuit definition. *** Adapted from Power Electronics: Computer Simulation, Analysis and Education using PSpice by Ned Mohan

Text File:

Appendix C: Diode Implementation with Snubber :

Text File: Ideal Switch Diode

****  Idle Switch  Diode Spice sub-ckt *** *********** CONNECTIONS: ****                                                          Anode ****                           |                           Cathode ****                           |   | ****                           |   | ****                           |   | ****                           |   | .SUBCKT SW_DIODE_WITH_SNUB     A   K DX A K POWER_DIODE RX K KK 10 CX KK A 100nF .MODEL POWER_DIODE D(CJO=0.01fF, IS=2e-6, RS=0.01) .ENDS SW_DIODE_WITH_SNUB *** End of sub circuit definition. *** Adapted from Power Electronics: Computer Simulation, Analysis and Education using PSpice by Ned Mohan

References:

1. Tang Jiaheng; Guan Shouping; “Estimating rotor state of PMSM variable-speed system,” TENCON ’93. Proceedings. Computer, Communication, Control and Power Engineering. 1993 IEEE Region 10 Conference on, vol., no.0, pp.575-579 vol.5, 19-21 Oct 1993
2. Lovelace, E.C.; Keim, T.; Lang, J.H.; Wentzloff, D.D.; Jahns, T.M.; Wai, J.; McCleer, P.J.; “Design and experimental verification of a direct-drive interior PM synchronous machine using a saturable lumped-parameter model,” Industry Applications Conference, 2002. 37th IAS Annual Meeting. Conference Record of the, vol.4, no., pp. 2486- 2492 vol.4, 2002
3. Young-Kyoun Kim; Jeong-Jong Lee; Jung-Pyo Hong; Yoon Hur; “Analysis of cogging torque considering tolerance of axial displacement on BLDC motor by using a stochastic simulation coupled with 3-D EMCN,” Magnetics, IEEE Transactions on, vol.40, no.2, pp. 1244- 1247, March 2004
4. Kemao Peng; Guoyang Cheng; Chen, B.M.; Lee, T.H.; “Improvement on a hard disk drive servo system using friction and disturbance compensation,” Advanced Intelligent Mechatronics, 2003. AIM 2003. Proceedings. 2003 IEEE/ASME International Conference on, vol.2, no., pp. 1160- 1165 vol.2, 20-24 July 2003.
5. Lovelace, E.C.; Jahns, T.M.; Lang, J.H.; “Impact of saturation and inverter cost on interior PM synchronous machine drive optimization,” Industry Applications, IEEE Transactions on, vol.36, no.3, pp.723-729, May/Jun 2000
6. Ned Mohan, Tore Undeland, William Robbins, “ Power Electronics, Converters, Application, and Design” 2ndedition, John Wiley & Sons, New York, 1995
7. Rakesh K Dhawan, “Workshop on Advanced Power Electronics and Motor Drives Simulation Techniques using PSpice” Pune 2010.
8. John Keown, “OrCAD PSpice and Circuit Analysis,” Prentice-Hall Inc., New Jersey, 2001

Our Innovation workshop scheduled in Bangalore for Dec 10 and 11 is a collection of lessons learnt in the past twenty five years in launching innovative and high tech products in the US, Europe and India. It has been an extraordinary learning experience with great successes and a few failures. This workshop ties theory and practice in New Product Development, Technology Feasibility, Project Management, Theory of Constraints and Statistics in extraordinary set of principles to provide an integral view of these disciplines for Innovation and Technology Management.

Our second day is dedicated to simulation, design and analysis of complex Power Electronic Systems such as Electric Vehicles, Brushless Permanent Magnet Motors Drives, Induction Motor Drives, Switch Mode Power Supplies etc.

These are valuable lessons and if you are an engineering professional, you must attend. This sort of training is not available in books or schools. These are the lessons from the trenches. We rarely repeat the same material in our workshops.

Do Not Miss It If You are Serious about Your Career

Details of the Workshop are shown below:

A Workshop on
Unleashing Innovation
Tools and Techniques for Ultra-Fast Product Launch Cycles
& Exceptional Product Performance
Direct Application to Electric Vehicles, Motor Drives ,
Switch Mode Power Systems & Embedded Systems
Dec 10 & 11

At The Pride Hotel, Bangalore

For More Details Visit: http://www.strategictechgroup.com/india/

This workshop is about

Developing ultra-fast innovative technology products with specific application to Electric Vehicles, Motor Drives, Power Electronics, Switch Mode Power Systems & Embedded Systems:

Both days recommended for Managers who are also hardcore Engineers:

• For Manager and Future Managers: First day of the workshop is dedicated to tools and techniques for New Product Development, Product Feasibility, Product Development Cycle, Project Management, Statistics, and Theory of constraints.
• For Hardcore Engineers: Second day of the workshop is dedicated to Design and Simulation of Electric Vehicles, Brushless and Induction Motor Drives, and Switch Mode Power Supplies using Spice.

Workshop Advantages

• Leverage significant opportunities through the use of correct methods and tools;
• Learn to compete globally by launching innovative products with reduced cost;
• Dramatically cut development time;
• Innovate with new Topologies;
• Improve Manufacturability;
• Add State of the Art Techniques to your bag;
• Improve Quality and Reliability;
• India’s market is emerging rapidly and her appetite for technology has increased significantly in the past few years.

Major Opportunity in the Field of Power Electronics, Motor Drives & Embedded Systems:

Power Electronics and Motor Drives remain vital and critical for industry and infrastructure development in India. These fields continue to play a key role in renewable energy converters, hybrid vehicles, automobiles with fuel cells and home and office use distributed power systems. The pace of innovation in Power Electronics Technology is expected to increase exponentially in the years to come. Major strides continue to be made in topologies, components, control algorithms, simulation and analysis.
STG’s Unique and Proven Approach:
What does it take to unleash innovation? What does it take to compete at the global level with American, European and Japanese companies? IT has been India’s forte as a service provider. However, we have been unable in developing innovative technologies in the IT industry. Now is the time to think differently. The world is our playing field. Many Indian companies have resources and knowledge to play at the global level through the development of innovative technologies. Let us take advantage of this golden moment before it is too late. Learn about our Unique and Proven Approach for guaranteed product innovation and market introductions.

About the Presenters

Rakesh Dhawan is a twenty years veteran of High Technology Industry. Rakesh has BTech in Electrical Engineering from IIT, Kharagpur, India, Masters’ (MSEE) from University of Minnesota, USA, and MBA from Old Dominion University, USA. Rakesh has been an entrepreneur who has built several high quality technology businesses in the past. Rakesh has six approved and filed patents and twenty five conference and journal publications to his credit. His interests include light electric vehicles, brushless and induction motor drives, switch mode power supplies, solar inverters, simulation, statistics, project management and new and ultra-fast product development. Rakesh has built and managed several high tech product development teams in his career. He has been directly responsible for over twenty five successful product launches in his career.. Rakesh has conducted several workshops in the US, in the recent past. He feels that Indian industry is fast moving up the value chain, and is poised to benefit from such events/workshops. This is the second workshop in a series of such events, the first being in Pune.

Bhuvanesh Sharda is a sustainability practitioner who believes that Industrial and Business sustainability is interwoven with the sustainability of  the environment and nature. Bhuvanesh is a mechanical Engineer with Automobile specialization. Bhuvanesh has an experience of twenty five years in the Automobile , White Goods and Engineering Industry. Bhuvanesh has been deeply involved in setting up green/brown field projects for well known organizations like Hindustan Isuzu at Halol (now known as General Motors), Eicher Tractors at Alwar, Ashok Leyland , IFB Dish washer and Microwave, Merloni TermoSanitari Chakan Tata Yazaki , Minda and Tenneco. Bhuvanesh has developed in depth understanding of the philosophies like TQM, Lean ,TPM , TPS, TBEM and TOC. Bhuvanesh has worked in the large cross sections of industry, products and technologies and cultures within India and abroad. Bhuvanesh is a hands on person and  has had  experience of all the functions in organizations.

Strategic Technology Group (STG)  has developed extensive expertise in the field of embedded software.  We have always focused on simplifying the whole process and sticking to the fundamentals. Some of the fundamentals we have followed rigorously are outlined below (Integration and Testing will be discussed at a later stage) :

1. Develop high level requirements (Customer Requirements) – This is very critical and customers must sign off on these;
2. Concept Development/Develop basic flow chart – This is a semi-technical flow chart, translating customer requirements into feasible technical (software-related) steps;
3. Match concept to three layers (Application Code layer , Application Peripheral Interface (API) layer, Hardware layer. We will discuss these three layers in detail in a later post;
4. Develop and Modularize the pseudo code into the above three layers;
5. Develop code related to each of the modules;
6. Release and control the modules with a revision control for later use.

The above approach has greatly accelerated our development resulting in very stable and reliable code.  We will describe in detail the above steps in the future blog postings.

Fuzzy logic imitates human thinking more closely when we think about desired device (such as a washing machine etc.) behavior. It has significant advantages in developing control algorithms for industrial as well as commercial devices or appliances.  An example of a Fuzzy rule for motor speed control is given below:

IF motor temperature is high
THEN reduce phase current to a lower value

or

IF speed control is active and speed oscillations are high
THEN slightly reduce the proportional gain

Fuzzy Logic implementations are relatively simple in DSPs (Digital Signal Processors) or Micro-controllers. It has several advantages in simplifying the overall understanding of the desired behavior of the device. For those who like to think in terms of programming languages such as C, C++, assembly etc. Fuzzy logic is more like C++ in terms of understanding and implementing control algorithms whereas Binary logic is more like assembly programming language. However, most engineers are trained in thinking using Binary logic.

Fuzzy logic is often defined as being able to deal with vagueness or fuzziness. It should be thought more as providing precise definition of human thoughts. Let us look at two sentences below:

It is dark outside (binary statement).
It is very dark outside (fuzzy statement).
It is slightly dark outside (fuzzy statement).

Now, one can characterize ”darkness” by a continuous linear function (called membership function in Fuzzy language)  from o to 1 symbolizing low darkness to high darkness. Now we have infinite values to deal with in darkness. That is not really the case with a binary statement. Therefore, Fuzzy logic can be precise in depicting human thought.

It is easy to develop an N-dimensional(with N factors interacting with each other) fuzzy inferencing engine. This inferencing technique is illustrated in Fig. 1 of Fuzzy Logic based Inductor Program. For each variable, there are the following four main steps:

1. Fuzzification (processing each variable through a membership function)
2. Formation of Fuzzy rules (which are mostly in terms of IF-THEN statements)
3. Fuzzy Inferencing (This is where the variables are processed through the Fuzzy rules. Here boolean operators are used to convert IF-THEN statements into boolean statements)
4. Defuzzification (This is where a single value on a scale of 0 to 1 is obtained for the desired output. A final form of the membership function is determined and by using an averaging method such as COG (center of gravity), a single value for the output is obtained.)

The above four steps can be repeated several times based on the system complexity.

Now let us look at a brushless motor controller with Fuzzy logic. Below is a block diagram of a brushless motor controller with six-step control:

The above conventional controller is modified as shown below:

In the above block diagram we have replaced the conventional PI regulator with a fuzzy controller. We have also added a differentiator to sense the rate of change and direction of the error signal (E). The rate of change and direction indicator is denoted by CE. The fuzzy controller decides its output based on the pattern of the speed loop error signal.

Now a fuzzy rule can be established as follows:

RULE 1:
IF Error (E) is almost zero (AZ) AND rate of change of E (CE) is slightly positive (SP)
THEN the output of the Fuzzy controller (OP) should be set to slightly negative (SN)

Obviously, with the above statement, you are trying to correct the overshoot in speed.  Here  E and CE are our fuzzy input variables and the OP is the output fuzzy variable.  And characterizations such as almost zero (AZ), slightly positive (SP) and slightly negative (SN) would need to be processed through corresponding membership functions defined for E and CE. And now let us define another rule:

RULE 2:
IF Error (E) is slightly positive (AZ) AND rate of change of E (CE) is slightly negative (SN)
THEN the output of the Fuzzy controller (OP) should be set to  almost zero (AZ)

With the above rule, we know that the system has almost reached steady state, hence there is no need to increase the output of the fuzzy controller.

Now, let us define our membership function for E and CE. We would assume that the membership functions of triangular type as shown below:

Now the membership function collating slightly negative (SN), almost zero (AZ) and slightly positive (SP) are shown below:

Compare these membership functions with those in Fig. 5 of Fuzzy Logic based Inductor Program. Now let us observe the following:

SN has a range of -4 to 0. When SN is -2, it is assigned a value of 1.0.
AZ has a range of -2 to +2. When AZ is 0, it is assigned a value of 1.0.
SP has a range of 0 to +4. When SP is +2, it is assigned a value of 1.0.

Now there is no reason to use the triangular membership functions. We can use other membership functions as well. In control applications, triangular membership functions provide most stable and predictable results. Other membership functions can work well, however, analysis and simulation are required to verify their usefulness and stability.

Now, considering the value of E to be -1 and CE to be +1.8, let us see what happens:

For E = -1.0, looking at the membership functions above: SN=0.5, AZ=0.5, SP=0
FOR CE=+1.0,  SN=0, AZ=0.5, SP=0.5

with Rule 1: OP = AZ (E) AND SP(CE) = 0.5 AND 0.5 =0.5
with Rule 2: OP – AZ(E) AND SN(CE) =  0.5 AND 0 = 0

with above rules, OP is assigned a value of 0.5. Thereafter, we use COG method to obtain a crisp value of the OP as shown below:

Now using COG method, OP = 3.5/8 = 0.4375. By using Fuzzy logic, we have obviated the need for PI, PID, and type 1, 2 and 3 compensators. Is that not cool? This is where a clever digital technique can pretty much obliterate an age old analog technique.