Pwm Based Sensorless Direct Torque Control for Bldc
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 1 (2017) © Research India Publications. http://www.ripublication.com
PWM BASED SENSORLESS DIRECT TORQUE CONTROL FOR BLDC MOTOR TEJA SREENU TADIVAKA1, M ANANTH SRINIVAS GUPTHA 2, SUDHA VENKATA GIRISH3 1Assistant Professor, Electrical Department, KL University, Guntur, India 2, 3 Student, Electrical Department, KL University, Guntur, India
Abstract: Generally, duo to higher efficiency, motors are the better choice in present days. Usually high power density, easy maintenance and control, BLDC motor is accounted as high pursuance motor and high torque to inertia ratio these Brushless dc which is efficient in generating more amounts of motors are one of the growing electrical drives in torque over wide speed ranges. BLDC motors are present scenario. This paper proposes a concept of inside-out of common dc motors and they exhibit the sensor less PWM based direct torque and indirect same torque-speed characteristics [14]. The main flux control of BLDC has been investigated. There difference lies in usage of brushes. Like DC motor are several methods that are projected for BLDC to brushless dc motor do not have brushes so that they gain better torque and current control i.e with are electronically commutated. Commutation is minimum torque and current pulsations. Most of the nothing but changing the motor phase currents at proposed techniques are complex and they does not desired time to create rotational torque. The take stator flux control in to account, so that high commutation sequences are desired by the rotor speed operations are not possible. The proposed position and the rotor position is detected either by sensorless method is similar to the usual Direct using position sensors or by sensor less techniques Torque control method which is utilized for For Brushless DC [1] motors with trapezoidal sinusoidal Alternating Current motors so that it back emf [1] obtaining low frequency ripple free controls toque directly and stator flux indirectly by torque, and instantaneous torque and flux are major varying direct axis current. And the electric rotor considerations. There are different methods are stated position can be found by using winding inductance for controlling the brushless dc motor and generally and stationary reference frame stator fluxes and there are: 1) Measurement of back EMF, 2) Back currents. The validity of the projected sensorless EMF integration method, 3) Flux estimation method three phase conduction Direct Torque Control of and 4) Freewheeling current detection method. The BLDC motor drive method is established in the merits and de-merits for this above stated methods MATLAB/SIMULINK and results are observed. are based on their own operation. And this paper
Keywords— Brushless dc(BLDC) Motor, Direct presents a basic ssensorless direct torque and indirect Torque Control(DTC), stator flux control, Space Vector flux control of BLDC motor, the current , torque and Modulation(SVM) flux signals used in this DTC technique are sinusoidal [1] in nature as like normal DTC I. INTRODUCTION For applications like high accuracy, high controller. This method provides advantages of efficiency and high power density [1] Brushless DC conventional DTC such as fast torque response
584 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 1 (2017) © Research India Publications. http://www.ripublication.com
compared to vector control, and position-sensorless Stator Coils drive. The electrical rotor position is known by Hall effect calculating winding inductance and stationary Sensors Rotor permanent reference frame stator flux linkages and currents [1]. Magnet S
The basic property of Direct Torque Control is that to select the voltage vector in relation with the error Driving Shaft Rotor permanent between reference and calculated torque and flux Magnet N linkage values. In the proposed scheme, the main Driving End Shaft control moto is to keep the motor’s torque and amplitude of the stator flux within particular limits.
The inverter is triggered by SVM controllers to Hall effect Sensor Magnets switch whenever these limits are exceeded.
II. Modelling of Brushless DC Motor Fig 1: Cross sectional view of BLDC Motor
BLDC motors is one of the classifications in And the schematic diagram for Brushless DC motor permanent magnet synchronous motors [1]. As its is shown in below figure 2. name indicates as synchronous motor , the magnetic The mathematical modeling for BLDC drive is field created by both the stator and rotor rotates with obtained by considering the following considerations the same frequency. So BLDC motors do not such as, experience any “slip”. BLDC motor is built with a permanent magnet rotor and wire wound stator poles.
To achieve proper commutation permanent magnet S1 S3 S5
DC motors use mechanical commutators and brushes. D1 D3 D5
But in case of BLDC motor it uses Hall Effect R L Ia sensors [15] in place of mechanical commutators and DC Vdc Ib Ic brushes. So BLDC is said to be electronically S4 S6 S2 commutated. Brushless DC motor is just inside-out of D4 D6 D2 DC motor. The stator of BLDC motor contains [15] winding coils and the rotor with permanent magnets. Fig 2: Basic schematic diagram for BLDC. The stator develops the magnetic field to makes the 1. It has three symmetrical windings. rotor to rotate. The Hall Effect sensors which are 2. Has no magnetic saturation. placed 120 electrical degrees apart detects the rotor 3. Neglecting hysteresis and eddy current position so as to make proper commutation sequence. losses. Therefore, BLDC motors replaces the coils with 4. Ignorance of mutual inductance. permanent magnets in armature so it does not require 5. And neglecting armature reaction. any brushes and commutators as shown in figure 1.
585 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 1 (2017) © Research India Publications. http://www.ripublication.com
The mathematical modelling is obtained by considering the KVL equations for figure 2. The measured values of direct axis and quadrature di axis currents are obtained by the following matrix, V i r L a e a a a dt a i sin( 30) sin( 30) i di d 2 b Vb ibrb L eb i dt iq 3 cos( 30) cos( 30) di V i r L c e These obtained measured are compared with c c c dt c reference direct and quadrature axis currents for For solving these equations, in this paper we have obtaining error tolerance. The reference current used a concept of line-to-line park’s transformation signals are obtained by the electromagnetic torque. technique. This line-to-line parks transformation From the definition of newton’s law of motion, the converts the three phase voltages to two phase total applied torque is equal to sum of all individual coordinators expressed as, torques across each element.
1 1 dw Va T T J m Bw Vab 3 3 e m dt m Vb Vca 3 3 Vc The electromagnetic torque generated by a brushless 3 3 dc motor is expressed as The matrix coordinates obtained from the above line to line park’s transformation are transformed to eaia ebib ecic Te orthogonal matrix coordinates (α, β). wm
Similarly, same like as voltage, the three phase Assuming the three phase windings are symmetrical, currents also transformed to two phase orthogonal so that the magnitudes of back emfs and currents matrix. These two phase currents (Iα, Iβ) and voltage should be equal for three phases. From the above two
(Vα, Vβ) are used for calculating the flux linkages equations, the electromagnetic torque can be
(ψα, ψβ) from the expression described as, developed by a BLDC motor at any instant is
1 2epip (V i ra ) Te L wm
1 (V i r ) Where ep is called phase back emf and ip is a non- L a zero phase current. And from this equation the phase angle is calculated The back EMF for a BLDC motor is given as as,
ep kwm j 1 tan ( / )
586 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 1 (2017) © Research India Publications. http://www.ripublication.com
The error difference is obtained from comparison of IV. Principle of Operation of PWM-DTC Scheme the currents is given to SVM controller for obtaining for BLDC Drive the gate pulses to the three phase inverter. The basic control block diagram shows the III. MODULATION TECHNIQUE: implementation of the Direct Torque [1] Control In this section a simple modulation based PWM technique [16] is as shown in figure 4. technique is described to control the new NPC With this proposed control technique, first the values converter for a three phase system. The modulation is for estimated torque and flux linkages are determined based on that described in [16], but in our case, the from the actual three phase component currents and new technique called space vector modulation is used the three phase stator voltages. For doing these instead of the carrier-based PWM. A sixth part of the calculation we are considered the two phase vector diagram for a five-level converter is shown in rotational orthogonal matrix vectors. And after Figure 3, where (−V, 0, V) voltage levels are denoted determination of estimated torque and flux linkages, as 2, 1 and 0 respectively. then these estimated values are used for generating triggering sequences. Two proportional integral controllers are used to regulate the current errors. The gate switching signals for the inverter is obtained from the voltage vectors which are obtained from controlling and comparison of actual phase values of voltage and current vectors. The complete block diagram for the PWM based DTC controller is shown in figure 4.
DC Source Current I Id* Iq* Id* + e1 Vd S1 a - PI Controller d S2 Id Voltage Vabc Space Vector Pulses S3 b BLDC + e2 Controller Vq q Vabc Modulation S4 Motor PI Controller S5 c Iq* - S6 3-ph VSI q I V-I Measurement
α Vαβ Vba Vba Vca β Vabc dq Transformation of Vca αβ Vαβ and Iαβ Iαβ Clark’s Iba Transformation Ica Vαβ Iαβ Iabc Calculation of Flux
ϴs=tan-1(Ψβ/Ψα) Linkages Ψα=ʃ(Vα-Rs iα)dt Ψβ =ʃ(Vβ-Rs iβ)dt
iα
(Ψsβ-Lsisβ) ϴre=tan-1 iβ 2 Js (Ψsα -Lsisα ) I Te + Ψα 1/2k + Ψβ Tm
Fig 3: SPWM technique for output voltages Fig 4: Control Diagram of DTC-SVM Technique
587 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 1 (2017) © Research India Publications. http://www.ripublication.com
V. Selection of Electric Rotor Position 14
13.5 The electric rotor position θre which is required in 13 torque estimation, can be found using the equation. 12.5
12
11.5 1 s Ls is tan 11 re s Ls is Electromagnetic Torque 10.5 10
9.5 The electric rotor position is found by using winding 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Time(sec) inductance and stationary reference frame stator flux 6: Simulation Result for Electromagnetic linkages and currents [1]. And the value of θre is Torque at Tm=10.5 N-m used in calculation of electromagnetic torque Te.
600 VI. Simulation Diagram and Results 500
The experimental setup for DTC- SVM based 400 BLDC drive is done in Matlab/Simulink model. 300 Switching pulses for the three phase inverter are speed Wr (rpm)speed 200 obtained from the switching table which decides the 100 pulses from the error signals of stator currents. The 0 absolute value of current is estimated from the 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Time(sec) estimated torque which is derived from the Fig 7: Simulation Result for Speed mechanical modelling and motor parameters such as phase voltage and phase currents. The complete 15 simulation model of the system is shown in figure 5. 10
5
0
Current (Amps) -5
-10
-15 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Time (sec) Fig 8: Simulation Result for Stator Currents
Fig 5: Simulation Diagram for BLDC Drive.
588 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 1 (2017) © Research India Publications. http://www.ripublication.com
classified into two types: i.e. one is hysteresis-based switching table DTC, and another one is constant switching frequency pattern operating with space vector modulation technique. Out of these two controllers we considered a Constant switching frequency DTC based PWM technique as it has the capability to improve performance of drive by reducing the disturbances in the torque and stator flux
linkages. Therefore, finally, it conclude that the PWM-DTC based technique is an excellent solution Fig 9: Simulated indirectly controlled Flux linkage when Ids is zero under 10.5 N-m load torque for controlling Brushless DC motor drive. Finally it conclude that the Torque control principle will play a strategic role in the improvement of high performance drives.
VII REFERENCE
1) Salih Baris Ozturk, Member, IEEE, and Hamid A. Toliyat, Fellow, “Direct Torque and Indirect Flux Control of Brushless DC Motor” in IEEE/ASME Fig 10: Simulation Result for Stator Direct Axis Current TRANSACTIONS ON MECHATRONICS, VOL. 16, NO. 2, APRIL 2011
2) Atef Saleh Othman Al-Mashak- beh “Proportional Integral and Derivative Control of Brushless DC Motor” European Journal of Scientific esearchVol.35 No.2 (2009), pp.198- 203
3) Microchip Technology, “Brushless DC (BLDC) motor fundamentals”, application Note, AN885, 2003. Fig 11: Simulation Result for Quadrature Axis Current 4) Gwo-Rueyyu and Rey-Chue Hwang “Optimal PID Speed Control of Brushless DC Motors Using VI. CONCLUSION LQR approach” IEEE International Conference on This paper has presented a concept of PWM systems, Man and Cybernetics, 2004, pp.473-478. technique based direct torque controller for brushless 5) C.Gencer and M.Gedikpinar “Modelling and dc drive system. The DTC control strategy is an Simulation of BLDCM using Mat lab/Simulink” alternative method to Field Oriented Control. For Journal of Applied Sciences 6(3):688-691, 2006. controlling an AC drives the basic DTC strategies are
589 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 1 (2017) © Research India Publications. http://www.ripublication.com
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