Biomedical

Communication

Biosci. Biotech. Res. Comm. 11(2): 270-276 (2018)

On the use of brushless digital DC motor and fuzzy logic

controller for hearts left ventricular assist device (VAD)

Donya Nias

, Mohammad H. Fatehi

and Hassan Masoumii

Department of Electronic Engineering, Kazerun Branch, Islamic Azad University, Kazerun, Fars, Iran

Department of Electronic Engineering, Faculty of Engineering, Kazerun Branch, Islamic Azad University,

Kazerun, Fars, Iran

ABSTRACT

The developments of technology and increase in clinical requirements have caused creation of a novel type of blood

pump. The present study has been conducted using controlled brushless DC motor and fuzzy logic for hearts left

ventricular assist device. We have used a fuzzy logic system based on a mathematical one that analyzes analog input

values in terms of logic variables which can take on continuous values between 0 and 1 in contrast to classical or

digital logic. This system operates on discrete values of either 1 or 0. The clinical system includes a blood pump, a

centrifugal pump, a brushless DC motor, a solenoid, power supply and control. In order to control the ventricular

blood pressure and the blood volume (cardiac output), a fuzzy logic controller has been used. The method applied

in this research provides conditions for the designer to describe the status in a few words clearly to make control

decision based on linguistics structures. The structures and rules could be developed or changed by the physician for

personal use. Permanent magnet brushless direct current motor (BLDC) has been the main element in majority of ven-

tricular assist devices (VAD) development. To this end, an Implantable Centrifugal Blood Pump has been developed at

the Institute Dante Pazzanese of Cardiology (IDPC) to assist patients with cardiovascular diseases. In order to make a

high quality controller, it is important to use reliable virtual BLDC model. Permanent Magnet Synchronous Machine

(PMSM) has implemented the differential equations for this motor using a state-space model. This could be the main

contribution of this study. The results obtained from this study could be applied by further studies in order to enhance

the motor model. Therefore, the results could lead to reliable simulations for the proposed controller.

KEY WORDS: LEFT VENTRICULAR ASSIST DEVICE, BRUSHLESS DC MOTOR, FUZZY LOGIC, CARDIOVASCULAR DISEASE

270

ARTICLE INFORMATION:

Received 16

March, 2018

Accepted after revision 19

June, 2018

BBRC Print ISSN: 0974-6455

Online ISSN: 2321-4007 CODEN: USA BBRCBA

Thomson Reuters ISI ESC / Clarivate Analytics USA and

Crossref Indexed Journal

NAAS Journal Score 2018: 4.31 SJIF 2017: 4.196

Online Contents Available at: http//www.bbrc.in/

DOI: 10.21786/bbrc/11.1/12

Donya Nias et al.

INTRODUCTION

The brushless motors (BLDC) have been the main com-

ponent of propulsion in the creation of majority of the

Ventricular Assist Devices (VAD). Among the features

used in implantable pumps, no brush is existed and this

could avoid the wear observed in other electrical motors

and implantable systems. The operation at high rota-

tional speeds and small size are also factors that support

this use (Fonseca 2003, Bock et al., 2008, Leao et al.,

2012, Viswajith et al., 2017).

The three-phase brushless electric motor has a syn-

chronous permanent magnet on the rotor and coils on

the stator located, usually star connected with inverter

control for bridge-type H (Bock et al., 2008; Fonseca

2003; Hsieh & Liao 2010). The operation of a BLDC is

accomplished through strategic switching of the coils, as

well as in a stepper motor. The switching is performed

by a circuit that supplies current to the motor coils as a

function of rotor position. The phase current of a BLDC,

usually rectangular, is synchronized with the Back Elec-

tromotive Force (BEMF) to produce maximum torque

and constant speed, with the trapezoidal BEMF as the

main feature of control (Shao 2003; Shao et al., 2003

Leao et al., 2012).

The MATLAB/Simulink software was employed as

virtual environment for simulation, since it allows data

and results integration with other software including

Comsol Multiphisycs to model ICBP. The dynamic model

is required to study transients of the motor drive sys-

tem and steady state. The immediate currents are cru-

cial for power computation and electromagnetic torque

is underlying for drive system performance evaluation.

These features become a signi cant factor in uses such

as VAD and are different from industrial appliances that

may not be underlying (Krishnan, 2010).

This study has been divided into two main parts: the

 rst part consist of mathematical modeling that Simulink

block uses to represent BLDC motor and the second part

describes the virtual implementation with help of Matlab

/ Simulink blocks diagram to represent the electrome-

chanical actuator. Moreover, the main objective of this

study is to apply the block Permanent Magnet Synchro-

nous Machine (PMSM) to present the actuator from ICBP

to begin researches current and speed control (Paraspour

& Hanitsch 1994; Guyton C, 1986).

The dynamics of the aortic valve plays a critical role

in the understanding of heart failure and its treatment

using the continuous  ow left ventricular assist device

(LVAD). Maintaining proper and active dynamics of the

aortic valve is important when the LVAD is used as a

bridge-to-recovery treatment. This treatment requires

that the LVAD pump control must be adjusted so that a

proper balance between the volume of blood contributed

through the aortic valve and that contributed though

the pump must be maintained. That is, the pump control

must be adjusted so that the pump does not take over the

entire pumping function in the circulatory system but

instead must share with the left ventricle in ejecting the

total amount of blood needed by the circulatory system

(Viswajith et al., 2017).

VENTRICULAR ASSIST DEVICE (VAD)

A ventricular assist device (VAD) is mechanical pump

supporting heart function and blood  ow in people with

heart insuf ciency. The devices could support the func-

tion of the left, right, or both heart ventricles. Ventri-

cles are the lower chambers of human heart. The VAD

includes tubes to carry blood out of heart and send it

to blood vessels, a power source, and a control unit to

FIGURE 1. The block diagram BLDC

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS ON THE USE OF BRUSHLESS DIGITAL DC MOTOR AND FUZZY LOGIC CONTROLLER 271

Donya Nias et al.

FIGURE 2. Outputs of waveform; (a) Stator Current & Electromotive force; (b) DC bus Voltage;

monitor device function. The device may be used to sup-

port the heart until it recovers, to support the heart while

waiting for a heart transplant, or to help heart work bet-

ter in case of being eligible for a heart transplant (Para-

spour & Hanitsch 1994, Goldowsky 2004,Patel 2005, Gill

et al 2006).

Surgery is required to connect the VAD to heart. The

surgery will be performed in a hospital. Patients will

have general anesthesia and will not be awake or feel

pain during the surgery. The patients will receive anti-

clotting medicine through an intravenous (IV) line in

arm. A breathing tube connected to a ventilator will help

patients’ breath. A surgeon will open the chest and con-

nect heart’s arteries and veins to a heart-lung bypass

machine. The surgeon will place the pump in the upper

part of belly wall and connect the pump to heart using a

tube. Another tube will connect the pump to one of the

major arteries. The VAD will be connected to the con-

trol unit and power source outside the body. When the

heart-lung machine is switched off, the VAD will sup-

port blood  ow and take over heart’s pumping function,

(Libre etal.,2011; Nicolaescu 2012).

BRUSHLESS DC MOTOR (MOTOR DESIGN)

The brushless motors (BLDC) could be the main compo-

nent of propulsion in the development of majority of the

Ventricular Assist Devices (VAD). Among the features

272 ON THE USE OF BRUSHLESS DIGITAL DC MOTOR AND FUZZY LOGIC CONTROLLER BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

Donya Nias et al.

used in implantable pumps, no brush is existed and this

could avoid the wear observed in other electrical motors

and implantable systems. The operation at high rota-

tional speeds and small size are also factors that support

this use .The three-phase brushless electric motor has a

synchronous permanent magnet on the rotor and coils

embedded on the stator, usually star connected with

inverter control for bridge-type H.

The BLDC operation is accomplished through strate-

gic switching of the coils, as well as in a stepper motor.

The switching is performed by a circuit that supplies

current to the motor coils as a function of rotor position.

The phase current of a BLDC, usually rectangular, is syn-

chronized with the Back Electromotive Force (BEMF) to

produce maximum torque and constant speed using the

trapezoidal BEMF as the main feature of control . The

sensor less control was used as redundant position rotor

control in absence of other position sensors as source of

failures and should be avoided in implantable devices.

Lack of using others sensors could reduce the number of

wires for motor control and this is the fact that is associ-

ated with the surgical practice and could reduce post-

operative complications, ( Andrade et al., 2008 Andrade

2010).

ANALYSIS OF THE SIMULINK MODEL

The model performed in MATLAB/SIMULINK used

blocks of the Sim Power Systems toolbox. The BLDC was

simulated using a block of Permanent Magnet Synchro-

nous Machine (PMSM) with a trapezoidal back electro-

motive force (BEMF) signal (Leão et al., 2009). The BLDC

is connected to an inverter and is supplied by a variable

source of Direct Current (DC). The source is adjusted by

a Proportional Integral (PI) control with feedback of the

FIGURE 2. (Continued)

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS ON THE USE OF BRUSHLESS DIGITAL DC MOTOR AND FUZZY LOGIC CONTROLLER 273

Donya Nias et al.

motor speed. The rotor position information is toggled

between hall signal and sensor less estimator in 0.5sec

of the simulation time. Hence, the behavior of redundant

system could be simulated, if the information of rotor

position is given by the hall sensor to stop operation.

Figure 1 has illustrated block diagram to study the

dynamic of the actuator electromechanical of ICBP. The

LPF was adjusted to 500Hz of cut-off frequency for the

speed of 2000rpm and 300Hz of cut-off frequency for

the speed of 1500rpm.

Figure 2 has presented the output waveform of the

simulated model.

ANALYSIS OF FUZZY CONTROLLER

A heart assist device coupled with the natural heart

forms a complicated system. In fact, there are two con-

trol strategies. The heart assist system pumps either

synchrony to the heart rhythm or asynchrony. In both

cases, the systolic pressure and the blood volume  ow

(cardiac output) are considered as controlling parame-

ters. The controlling parameters are the motor speed and

the switching frequency of the solenoid. In the diastolic

phase, the motor active length will be reduced due to the

axial rotor movement. The speed and the motor current

are increased and the losses are decreased. An additional

speed control during this time improves the motor ef -

ciency. The synchrony pumping is relatively simple to

control, but the heart assistance is not fully effective

and the mobility of the patient is restricted (Paraspour &

Hanitsch 1994; Guyton 1986, Zadeh 1987, Zadeh L. A.,

1978, Zadeh 1987, Pedrycz 1989).

The fuzzy controller has two input variables including

blood pressure and cardiac output. The output variables

are set speed of the actuator. For purpose of fuzzi cation

of variables in each case,  ve linguistic terms (very low,

low, medium, high and very high) are de ned in Figure

3. The membership function of the heart parameters is

shown in Figure 4.

Figure 5 illustrates the block diagram to analyze the

dynamics of Block diagram BLDC when using fuzzy

block.

CONCLUSION

The present study has presented and analyzed an elec-

tromechanical left ventricular heart assist device driven

by a brushless D.C motor and controlled by the fuzzy set

theory. For an implantable device, various restrictions

should be considered such as  xed low voltage, constant

magnetic  ux, and upper limit of current density to avoid

signi cant temperature increase and low volume require-

ments. According to the equations of the electromechani-

cal system and the above mentioned restrictions, an opti-

mization method has been developed in this study.

The optimization method has been used to design

and make prototype drive and its electronic control. In

combination with the blood circulation, the heart assist

device is a nonlinear and multivariable system. In this

study, the linguistic description of the system, the opti-

mization of the fuzzy sets and the development of the

control rule basis have been realized with regard to the

physiological parameters. The fuzzy control algorithm

has been proved by an off-line simulation enhanced by

the on-line and interactive optimization. The use of the

fuzzy logic provides higher robustness and reliability for

the medical device, since a fuzzy controller tolerates a

certain imprecision in dealing with the controlling prob-

lem.

The electromotive and mechanical parameters associ-

ated with BLDC motor have provided simulation results

according to the literature. Current values are consist-

ent with the data given by the manufacturer in its cata-

log. At the same time, the real time loads of the model

show power values compatible with the application of

a ventricular assist device (VAD). The PMSM block was

appropriate to present the actuator ICBP and allowed

Very HighHighMediumLowVery lowCardiac

output

Negetive SmallNegetive SmallNegetive SmallNegetive SmallNegetive BigVery low

ZeroZeroZeroNegetive SmallNegetive SmallLow

Posetive SmallPosetive SmallZeroZeroNegetive SmallMediume

Positive BigPosetive SmallPosetive SmallZeroNegetive SmallHigh

Positive BigPositive BigPosetive SmallZeroNegetive SmallVery High

FIGURE 3. Basis of fuzzy logic

274 ON THE USE OF BRUSHLESS DIGITAL DC MOTOR AND FUZZY LOGIC CONTROLLER BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

Donya Nias et al.

FIGURE 4. (a),(b) heart parameters membership function

FIGURE 5. The block diagram BLDC

development of a controller. Further studies should be

conducted to enhance and improve the dynamic model

of control for better power values. Moreover, motor

dynamometer tests should be applied for purpose of

validating the model dynamic.

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