International Journal of Applied Engineering Research ISSN 0973-4562 Volume 9, Number 22 (2014) pp. 13027-13045 © Research India Publications http://www.ripublication.com
Implementation of V/F Control for Variable Speed Drive of a 3- Inverter Fed Induction Motor K. Subramanian1, V. Kavitha2and R. Saravanakumar3 1
2
Power Electronics and Drives Division, School of Electrical Engineering M. Tech Student, Power Electronics and Drives, School of Electrical Engineering 3 Robotics and Control Division, School of Electrical Engineering VIT University, Vellore, Tamil Nadu, India, 632014
[email protected];
[email protected];
[email protected]
Abstract Induction machine are widely used in most of the industries and house hold appliances etc. in motoring operation or else it is working as a generator in variable wind speed power generation scheme, cage rotor induction machines are suitable for motor and generator operation because of its rugged rotor construction, simple in control, easy to maintenances. Different techniques are implemented to control the speed; V/F control is predominant to others in particular for variable speed drive applications. Attempted to implement the V/F control of a 3-Ф, 1kW, 415V, 2.2A, and 1440 rpm delta connected machine is presented in this paper. The machine parameters are estimated on line by using Lab VIEW. It is normalized and substituted in computer simulation study. A separate sine PWM and space vector PWM controller developed in MATLAB/SIMULINK software for open loop control. Power circuit of two-level inverter with induction motor is configured using the built in libraries of power system toolbox. Simulation completed by selecting the Ode23tb solver for computing the simulation circuit in open loop. In experimental study, digital signal processor TMS320F407 controller based IPM-inverter fed Induction motor is considered for V/F control with a step load change. Simulated and experimental results are presented and discussed. Key Words: V/F control, Sine PWM, Space Vector PWM, variable speed drive, simulation
I. Introduction At present most of the electric drives comprises with solid state semiconductor power
Paper Code: 25459 - IJAER
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K. Subramanian
switches which may optimizes the size of the drive is shown in Fig.1 compared with earlier drives. Maximum efficiency of the drives can be achieved by introducing efficient control mechanisms [1]-[3].
Fig.1 block diagram PWM inverter fed induction motor drive
The control parameters are identified from the modified single-phase equivalent circuit of a three-phase induction motor is shown in Fig.2. It is referred to the stator side.
Implementation of V/F Control for Variable Speed Drive
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Fig.2 Stator referred single-phase equivalent circuit
From Fig.2, the rotor current, power, and torque developed by the motor is written as [2]: ′
=
(1)
′
=
+
+
−
= 3
′
+ ′
′
1−
(2)
=
(3)
Substituting the equations (1) and (2) and rearrange the term the torque equation (3) becomes ⎡ 3 ⎢ = ⎢ ⎢ ⎣
′
′
+
+
′
+
Where, V is the applied voltage, Rs and
Rr ' s
⎤ ⎥ ⎥ ⎥ ⎦
(4)
is the stator and stator referred rot
resistance, Xs andXr ' are the stator and stator referred reactance, s is the slip,Pm ,Pg and Pcu are the mechanical, air-gap and actual powers, T is the torque produce by the motor and ωm angular speed of the rotating m.m.f. From equation (4) we will consider different control parameters of the given induction motor [3]. Implementation of V/F control in open loop is main objective of this work. Therefore, voltage and frequency is considered for the control parameter of this study.
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K. Subramanian
II. V/F Control Scheme In order to understand the V/F control the equation (4) modified with variable frequency and the maximum torque developed by the motor is [3]: =
(5)
⁄
±
+4
+
′
Where, K is the constant; f is the supply frequency; Ls +Lr ' are the stator and stator referred inductance. Positive sign for motoring and negative sign for braking operation of the motor indicates in the numerator term of eqn, (5). If the frequency is R not low, fs
