This will cause excessive stator current and distortion of the stator flux wave. Various methods are used to control the flux and voltage. In v/f speed control technique v/f ratio is to be kept constant so that flux remains constant. This simplifies to Figure 1(b). The torque developed by the induction motor is directly proportional to the square of the supply voltage and the current is proportional to the voltage.

the most popular method for controlling the speed of an induction motor. The synchronous speed of the induction motor is given by.

There are two methods by which the speed of induction motor can be monitored (controlled). Answer (1 of 15): When we talk of V/f control of induction motor, it means varying the speed of motor by changing frequency but, at the same time, keeping the V/f ratio constant. The synchronous speed and therefore, the speed of the motor can be controlled by varying the supply frequency. Speed is calculated by: Ns =120*f/p-slip. As in the above method, if the supply frequency is reduced keeping the rated supply voltage, the air gap flux will tend to saturate. As v/f method of speed control of induction motor is one of the mostly used methods for speed control. Vector Control Of the above mentioned methods, V/f Control is the most popular and has found widespread use The EMF induced in the stator of the induction motor is given by, = 4.44 1 ( 3) However, need of an arrangement to inject an emf in the rotor circuit makes it very expensive. The closed-loopV/Hz system with a speed sensor can be shown in Figure 4. This paper presents an improved Z source inverter used to control the speed of an induction motor using the V/F method. The speed for any load within the operating range of the motor can be readily obtained. Slip Recovery vii. ( 4) d q s = d q s n 2 V s n s n with V s n the nominal RMS phase voltage. Pole Changing ii. DC separately motor has definite full-load speed, so they dont run away when the load is suddenly thrown off provided the field circuit remains closed. It is same as in TRIAC control, the voltage applied to load can be varied from zero to maximum value. Fig. Block Diagram of Speed Control Of Induction Motor Using PWM Technique. Variable Supply Frequency Control iii. The synchronous speed of an induction motor is given by the relation shown below: The EMF induced in the stator of the induction motor is given by the equation shown below. Variable Rotor Resistance Control v. V/f Control vi. They are: i. Changing the number of poles in a stator winding always involves an abrupt step change from one speed to another. The ignition knock control system had fuzzy logic that enabled the maximum ignition advanced angle to be used without detonation since the programme continually adapted to changes in environmental conditions and fuel quality. Ns= motor speed, f=frequency, p= number of poles. The slip compensation can be simply added in the system with the speed measurement. Slip Speed Control: Let V and f denote the rated voltage and frequency of the machine. to supply variable voltage and frequency which is easily obtained by using converter and inverter This gives smooth speed control of the induction motors.

N s = 120f / P. By controlling the supply frequency, the synchronous speed can become of a wide range. Therefore, if speed control is to be achieved by changing Then, from (3) and (4), the speed reference can be converted into a voltage reference: (1) and (2), it can be seen that the synchronous speed and hence the speed of the motor can be controlled by changing the supply frequency. The proposed Z source inverter (ZSI) can effectively reduce the voltage stress across the capacitors in the impedance network. In the simulation all Now for changing the speed of motor by v/f method, we have to change the reference voltage. Education. Speed can be controlled to control the frequency or slip can be controlled to control the torque. When the motor is operated below the base speed with constant (V/f) control, for a frequency, kf, the terminal voltage will be kV, where k is a factor such that, 0 k 1. This is the basic concept behind VVVF speed control of induction motor. V/f control method is a simple, cost-effective, and efficient for driving three-phase induction motor. 6 Speed control of induction motor using V-F method. P RCL = sP AG. The speed control of a three phase induction motor is obtained by changing the supply voltage until the torque required by the load is developed at the desired speed. When the reference voltage will change, the output of PI controller will also change proportionally [5].

In order to maintain the air gap flux at its normal value under varying frequency conditions, it is necessary to keep E 1 /f and therefore V/f ratio constant. Experiment No. Hence, it is used only for the motor; of very large rating. If the connection of one of the winding makes reversed there will be 4 N poles and 4 S-poles depending upon which winding connection is reversed. Variable Supply Voltage Control iv. There are various methods which are used for the speed control of three phase induction motor such as stator voltage control, frequency control, rotor resistance control but v/f speed control is the most popular method which is used in adjustable speed drive system. The rotor speed of an induction motor is given by the equation shown below. The air-gap flux of an induction motor is given by, g = (1 / 4.44K 1 T ph1)*(V / f) Where K 1 = Stator Winding Constant The EJ251 and EJ252 engines had a compression ratio of 10.1:1; the injection and firing order was 1-3-2-4. In V/F control,maintain ratioV/Fconstant. This method of speed control is efficient and has better speed regulation. induction motor speed equation. Speed Control of Induction Motor by Variable Frequency Control From the eqns. This research paper reviewspeed control of single phase induction motor by means of V/F control, PWM techniqueand direct flux and torque control. implemented by adjusting the stator voltage with respect to frequency such that the air gap flux is never able to deviate beyond the expected range of the steady-state, Supply voltage3. =1500. Constant V / F control of induction motor. These rules portray a nonchalant relationship between two inputs and an output, all of which are nothing but normalized voltages. Only stator current measurements are needed to compensate for both stator resistance drop and slip frequency. [1] Answer (1 of 2): Motor Equivalent Circuit If we analyse the internal electrical circuit of an induction motor, by breaking it down into simple circuit elements (inductors and resistors), each winding appears similar to Figure 1(a). On a 50 Hz supply, a two-pole induction motor will rotate at 3000 rpm (ignoring slip speed). 2.13: Speed-torque curves of an induction motor with injection of an emf in its rotor circuit. Figure 1. Abstract:In this paper, different types of speed control methods for the single phase induction motor are described. This is the most popular method for controlling the speed of an induction motor. (120 x 50)/ 4. The first one is to change the synchronous speed (n sync) which is the speed of rotation of the magnetic field of the stator and the rotor. It is defined as the ratio of the distance travelled in an extremely small interval of time tending to zero. This reduces the voltage range of the capacitors used, and also the cost of the proposed topology which is in turn used to This method gives higher run-time efficiency. Therefore, majority of AC speed drives employ constant V/F method (or variable voltage, variable frequency method) for the speed control. Along with wide range of speed control, this method also offers 'soft start' capability. In this paper, various types of speed control methods for the single phase induction motor are described. This method of speed control is rarely used because a small change in speed requires a large reduction in voltage, and hence the current drawn by motor increases, which cause overheating of the induction motor. Multiple stator winding method. Variable Frequency Control is a method that is used to control the speed of an induction motor. If a change is made to a four-pole stator, the speed will quickly change to 1500 rpm. 4 Scalar (V/f) Control of 3-PhaseInduction Motors SPRABQ8 July 2013 Download these Free Speed Control of Induction Motor by V/F Method MCQ Quiz Pdf Get Speed Control of Induction Motor by V/F Method Multiple Choice Questions (MCQ Quiz) with answers and detailed solutions. In order to operate the machine under nominal conditions, the stator flux must be nominal. There is a various method of speed control of an Induction Motor. The control scheme is based on the popular constant volts per hertz (V/f) method using low-cost open-loop current sensors. When we talk of V/f control of induction motor, it means varying the speed of motor by changing frequency but, at the same time, keeping the V/f ratio constant. This is important to maintain the same air gap flux in the motor and hence a constant torque. But a rather wider term used nowadays is VVVF i.e. variable voltage variable frequency control. In this Equation T V/f; for constant V/f ratio a constant torque can be Obtained. Speed Control by Changing the Number of Poles. Thus, the simple open-loopVs/f (or V/Hz) system cannot precisely control the speed with a presence of load torque. So, here we are keeping the ratio of V/f as constant and this is called V/ f method. If the frequency is reduced while the voltage is kept constant, thereby requiring the For V/f speed control of the induction motor, a reference speed has been used and the control architecture includes some rules. Digital implementation of the proposed control algorithm is done using NXP makes MC56F84789 controller which has 100 MHz core frequency. When we are supplying variable voltage and frequency the speed of motor will varies, for controlling the speed of induction motor we will use V/f ratio method. for the speed control of three phase induction motor such as stator voltage control, frequency control, rotor resistance control but v/f speed control is the most popular method which is used in adjustable speed drive system. The basic idea of a V/f control is to maintain the stator flux constant. In this video I describe about the speed control of inductuon motor by using different methods like,1. Pole changing 2. Open-loop V/f algorithm is adopted where there is no need of accurate speed control . This is important to maintain the same air gap flux in the motor The electric motor speed is fixed when AC motor is connected to AC line. There are various methods for the speed control of an Induction Motor. In VVVF speed control, motor stator supply as well as frequency is varied such that ratio (V/f) is constant. Torque in VVVF Speed Control As discussed, frequency is varied, therefore it is quite important to have a look at the maximum torque at variable frequency. THEORY The equation for the induced emf in the induction machine. ; The second method is to change the slip (s) of a motor according to the load on the shaft of the motor. As shown in the figure, This arrangement gives four poles and speed at 50Hz is 1500 rpm.