Increasing Flux Density Analysis in Sensor-Less Brushless Dc Motor for Artificial Heart Pumping System 1

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Increasing Flux Density Analysis in Sensor-Less Brushless Dc Motor for Artificial Heart Pumping System

1

Archana R*

²

Kannaian T

1

Assistant Professor, Department of Electronics and communication System Nehru Arts and Science College, Coimbatore, Tamilnadu, India

2

Secretary, PSG College of Arts and Science, Coimbatore, Tamilnadu, India

1

Now-a-days the electromechanical energy conversion is playing a vital role to convert mechanical energy into useful work. The development of life saving medical equipment’s with special electrical machines is tremendously increasing such as heart pumping pace maker, inter organ blood replacement devices, dialysis machines etc., Out of which the heart disease is the major problem faced by all the humans. For severe heart issues the best solution is to replace pace maker device for heart pumping system. In this case pace maker is an electro mechanical device that is driven by Sensorless Brushless DC Motor along with the power supply unit. The performance of motor can be improved by controlling the parameters such as flux density, torque, speed and any of the mechanical parameters like air gap length and number of phase windings. In proposed work the flux density of the machine can be increased by increasing the air gap between the stator and rotor. By increasing the air gap the flux density generation at rotor because of excitation can be increased ultimately the efficiency of the motor also increased. The efficiency of the motor is well defined by controlling the back EMF at different phases of BLDC motor. At full load operation the torque can be increased by means of load increasing at motor shaft. But in the proposed technology by increasing the air gap between the stator and rotor the speed of the machine can be maintain at rated speed without losing their efficiency. The entire system performance is analysed by developing a model of Sensor less Brushless DC Motor in MATLAB Simulink environment. The efficiency of BLDC motor can be investigated by various torque and speed operation.

Keywords: Heart Pumping System, Brushless DC motor, MMF analysis

1. Introduction

In general any important component of a system is the heart of the system.

Similarly the heart is a primary organ in our body to circulate the blood in all parts of our body. Also it controls the nutrients and tissues by supplying the oxygen by means to removing the carbon dioxide. According to the year 2003 survey the 3 out of 10 adults are suffering by severe heart diseases. The major risk factors for heart diseases are stroke, kidney failure and heart failure [1]. In order to save human lives from heart failures the development of artificial heart pumping system is an important one. The driving arrangement is a main competent work to achieve the efficient heart pumping system. In general, the artificial heart assembly replaces the entire system like Ventricular Assist Device (VAD) or else to adjoin the external blood pumping for heart[2].

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1.1 Structure of Heart Pumping System

The structure of the Artificial Heart Pump (AHP) arrangement consists of axially feed stator, rotor, permanent magnet and front back vanes. In normal operating conditions the blood flow pumped through levitated arrangement of the stator terminal.The direction of the rotation is decided by the power supply polarity from the battery in pumping system. In static state the flow is controlled by the driving motor which is located at the centre of pump. The rotor has the impeller, which rotates to inject the blood forward to the internal vessels of heart [3].

1.2 Sensorless Brushless DC Motor

Brushless DC Motor is one of the specialized motor in special electrical machines family, because of the absence of commutator and brush arrangements. It offers high reliability, compact size, less weight and more life span than the other types of special motors. BLDC motors are classified as sensor based and sensor less BLDC motor. In sensor based BLDC motor the position of rotor is identified by Hall Effect sensors[4]. The maximum amount of flux density can be achieved, when both stator and rotor position is in aligned condition. Identifying the rotor position of BLDC motor plays a vital role in its operation. The maximum torque and wide speed ranges can be controlled by the position of stator and rotor. Normally the Hall Effect sensor detects the position and transfer the signal to microcontroller unit to generate the control signal of BLDC motor[5].

The operation of Sensorless BLDC motor is entirely different from Sensor based operation. The parameter involved in Sensorless operation is back Electro Motive Force (EMF) of stator winding. The rotor position is identified by the back EMF of each stator phase winding of BLDC motor[6]. It also helps to determine the speed of the same. The control signal generation of sensor less BLDC motor is generated by digital signal processor (or) microcontroller unit from back EMF signal. The schematic diagram of BLDC motor arrangement with microcontroller is shown in Figure 1.

Figure 1. Schematic Structure of BLDC Motor with Microcontroller

2. Estimation of Rotor Position and Flux Density in Sensorless BLDC Motor

The modelling of BLDC motor to estimate the flux density for sensor less operation is developed suitably [7]. The stator phase voltages, phase currents, electromagnetic torque, rotor speed and flux linkages are estimated from the following modelling equations.

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𝑉_𝑎 = 𝑅𝐼_𝑎+ 𝐿^𝑑𝐼^𝑎

𝑑𝑡 + 𝐸_𝑎 (1)

𝑉_𝑏= 𝑅𝐼_𝑏+ 𝐿^𝑑𝐼^𝑏

𝑑𝑡 + 𝐸_𝑏 (2)

𝑉_𝑐 = 𝑅𝐼_𝑐+ 𝐿^𝑑𝐼^𝑐

𝑑𝑡 + 𝐸_𝑐 (3)

In case of balanced circuits the phase currents are equal

𝐼_𝑎+ 𝐼_𝑏+ 𝐼_𝑐= 0 (4)

𝐼_𝑎 = −(𝐼_𝑏+ 𝐼_𝑐) (5)

Torque 𝑇_𝑒/𝑃ℎ = 𝐾_𝑡[𝑓 ∅_𝑏 𝐼_𝑏] (6) Rotor speed 𝜔_𝑟 =^𝑇^𝑒^−𝑇^𝑙

𝑗𝑆 +𝐵 (7)

Back EMF E= 𝐾𝑏𝜔 (8)

Flux linkage ∅ = 𝐸_𝑏 (9)

The detection of back EMF to control the speed in BLDC motor is done by direct back EMF method and indirect back EMF method[8]. The direct back EMF method detects the EMF of phase windings at unpowered condition of stator voltage compared with neutral point voltage. Indirect back EMF is detected by zero crossing of isolated back EMF phase detection[9]. In flux estimation the flux linkage values are determined by integrating the magnitude of voltage and current throughout the complete rotation. The flux linkage based method works on speed independent variable which gives rotor position consistently [10]. For initial starting of the BLDC drive DC kick start method is used.

Once the two phases are aligned, the drive continues with the flux linkage based switching sequence framed by the following equations and algorithms.

𝐸 ∝^𝑑∅

𝑑𝑡 (10)

𝐸 = 𝑉 − 𝐼𝑎𝑅𝑎− 𝐿^𝑑𝐼_𝑑𝑡^𝑎 (11)

𝑑∅

𝑑𝑡 = 𝑉 − 𝐼_𝑎𝑅_𝑎− 𝐿^𝑑𝐼_𝑑𝑡^𝑎 (12)

∅ = (𝑉 − 𝐼_𝑎𝑅_𝑎 − 𝐿^𝑑𝐼^𝑎

𝑑𝑡) (13)

Table 1. Switch Sequences of Stator Phase Winding

ψa Ψb ψc S1 S2 S3 S4 S5 S6

+Ve -Ve +Ve 1 0 0 0 0 1

+Ve -Ve -Ve 0 0 1 0 0 1

+Ve +Ve -Ve 0 1 1 0 0 0

-Ve +Ve -Ve 0 1 0 0 1 0

-Ve +Ve +Ve 0 0 1 1 0 0

-Ve -Ve +Ve 1 0 0 1 0 0

The above table 1 consists sequences are involved to estimate the phase voltages of stator phase windings in sensor less operation of BLDC motor [11].

3. Results and Discussions

In the proposed model the control circuit along with the BLDC motor modelling is modelled in MATLAB simulink environment shown in Figure 2. A simple PI controller is used and the reference signal is compared with the actual flux of BLDC motor. The error which is generated from the controller generates the triggering pulse of converter circuit.

The maximum flux density obtained by controlling the back emf of BLDC motor. The

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Sensorless operation will gives the maximum flux density at maximum torque drawn by motor during heart pumping. The EMF generator will trigger the motor by each phase voltage of motor. It gives the maximum torque with standing capacity at maximum flux density by means of controlled back EMF. Hence the efficiency of BLDC motor has increased with controlled speed and back EMF.

Figure 2. Simulink Model of BLDC Motor Control Circuitry 3.1 Analysis of Sensorless BLDC Motor With Uncontrolled Back EMF

The BLDC motor is excited by the battery source with 28VDC at different phase sequences. The proposed motor is 3 phase BLDC with each phase having equal phase differences. The motor is driven by the controller in sequential manner. The voltages of each phase are shown in Figure 3 (a), (b), (c).

(a)

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(b)

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Figure 3. Phase Voltages Va, Vb, Vc of BLDC Motor at Ideal State

The generated back EMF of three phases is shown in Figure 4. The average flux density is less during the uncontrolled phase voltage conditions. The generated back emf is mainly based on the phase voltages of BLDC motor. At Sensorless operation the back emf is less compared with sensor operation. The generation of back EMF is 5Volt at uncontrolled condition of each phase.

(a)

(b)

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Figure 4. Back EMF of Three Phases Ea, Eb, Ec of BLDC Motor

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The torque value of BLDC motor at uncontrolled condition is oscillatory. In the proposed system,1Nm torque value is taken for analysis. The torque is not in a steady state condition rather than the conditional one. The un-steady state torque waveform is shown in Figure 5.

The speed of the BLDC motor at uncontrolled condition is shown in Figure 6. The speed control of BLDC motor is essential in heart pumping applications since the speed should be maintained constant at different torque conditions.

Figure 5. Torque at Uncontrolled Back EMF

Figure 6. Speed of the BLDC Motor Without Steady State Condition 3.2 Analysis of Proposed Back EMF Controlled Sensor less BLDC Motor

The generation of back EMF by controlling the flux density in sensor less operation is derived by the equations (6), (7), (8). The back EMF at 1Nm torque condition is increased by adjusting the flux density of BLDC motor. The controlled back EMF of each phase is shown in Figure 8 (a), (b), (c).

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(b)

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Figure 7. Controlled back EMF of BLDC motor i.e., Va, Vb, Vc

By controlling the back EMF of Sensorless BLDC motor the torque is regulated from an unsteady state to steady state condition as shown in Figure 8. Similarly the speed of BLDC motor is controlled by proposed back EMF control method and the waveform is shown in Figure 9.

Figure 8. Torque at Controlled Back EMF Condition

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Figure 9. Speed at controlled back EMF condition

4. Conclusion

The artificial heart pumping system by ventricular assistance is very essential for heart patients. Normally DC motor is used for pumping applications because of its size and low voltage applications. But the speed control of DC motor with respect to speed and torque is very difficult because of its construction. To overcome this drawback the proposed system is preferred with Sensorless based BLDC for artificial heart pumping applications.

In general the phase voltages and back EMF of BLDC motor is based on the excitation voltage from source. The efficiency of the device is analysed by controlling the speed and torque with respect to maximum flux density. In proposed system the flux density controls the back EMF by changing the air gap between the BLDC motor stator and rotor poles. The back EMF of each phase windings is increased by stationary control of flux and the maximum back EMF is extracted in each phase windings and verified with simulated wave forms. Hence by controlling the flux density the proposed system has increased the back EMF and speed-torque values (torque at 1Nm condition, constant speed is maintained at 1000rpm) are verified at both controlled and uncontrolled conditions. Therefore the performance of BLDC motor for heart pumping applications is improved by proposed back EMF control system.

5. References

[1]. Hoshi H., Shinshi T., Takatani S “Third-generation blood pumps with mechanical noncontact magnetic bearings. Journal of Artificial Organs, 2006, 30(5): 324-338.

[2]. Yang Sheng, Study on Drive Motor for Axial -flow Magnetic-levitation Artificial Heart Pump [D]. Shandong University, 2010.

[3]. ShenJian-xin, Fei Wei-zhong, Chen Li-gen. Influence of Air gap Field Distribution and Surface PM Magnetization in Brushless DC Motors”, Journal of Small & Special Electrical Machines, 2006, 34(6):7-9.

[4]. Y. Ramachandra, M. Akhileshwar, A. Pandian, Rajesh Nalli, K. Subbarao, “Analysis of Recent developments in Brushless DC motors controlling techniques”

International Journal of Innovative Technology and Exploring Engineering (IJITEE), ISSN: 2278-3075, Volume-8 Issue-5 March, 2019.

[5]. Kim.T,Lee .H..M, position sensor-less brushless DC drives: audit and future patterns, IET Electrical. Power Applications, volume. 1 no. 4, July 2007, pp. 557 – 564.

[6]. SitapatiKartik, “ Performance Assessments of Radial and Axial Field, Permanent- Magnet, Brushless Machines” IEEE Trans., vol. 37, no. 5, 2001.

[7]. Minoru , Kondo, (2007), constraint Quantities for PM synchronous Motor, IEEE Transactions on Electrical And Electronic Engineering, 2: 109-117.

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[8]. J. C. Gamazo, E. V. Sanchez and J. G. Gil, "Position and Speed Control of Brushless DC Motors Using Sensorless Techniques and Application Trends ", Sensors, pp.

6901-6947,2010.

[10]. Ahmet FENERC_IO _GLU, “Design and analysis of a magnetically levitated axial flux BLDC motor for a ventricular assist device”, Turkish Journal of Electrical Engineering & Computer Sciences, (2016) 24: 2881 – 2892, doi:10.3906/elk-1405- 139.

[11]. Varshney G, Katiyar VK, Kumar S. Effect of magnetic field on the blood in artery having multiple stenos is a numerical study”, International Journal of Engineering, Science and Technology, 2010; 2: 67-82.

[12]. Asama J, Hamasaki Y, Oiwa T, Chiba A. “Proposal and analysis of a novel single- drive bearing less motor. IEEE Transaction on Industrial Electronics, 2013; 60: 129- 138.

Authors

Dr.T.Kannaian, holds a Ph.D. in Information and Engineering

from PSG College of Technology, Anna University and has an M.Tech from the Indian Institute of Science (IISc), Bangalore with specialization in Electronics Design Technology. Prior to his M.Tech he completed M.Sc. in physics from Christian College,Marthandam. He has 33 years of teaching and Research experience in Electronics.His area of research is in Electronics and wearable sensors. He has published more than 20 publication in reputed journals and has H- index of 10. He has been an advisor to a number of small and medium scale electronics Industries in and around Coimbatore.

Increasing Flux Density Analysis in Sensor-Less Brushless Dc Motor for Artificial Heart Pumping System 1