AC motors used more than a DC motor for AC currents can be generated and distributed with less cost than the DC current. In addition, the DC motor has advantages in terms of cost, size, weight, and require less maintenance than DC motors.Squirrel cage induction motor, AC motor is the type most widely used in industry. This motor can be operated in a place where there are a lot of gas and dust or on a very humid conditions and will operate very well with little attention. This motor has no brushes and commutator, and construction is strong, so able to withstand the large inrush current, and easy to repair and maintenance. Synchronous speed of induction motors (ns) formulated with ns = 120 f / p so that arrangements can be done by adjusting the speed of the input voltage frequency (f) or by changing the number of poles (p). The speed by changing the number of poles is done by designing the stator windings in such a way so that with simple changes in the relationship coil, the number of poles can be changed by ratio of 2:1. This method is not practical and can only generate a little speed variation. While speed control with frequency settings, performed with an inverter, can produce changes in the discrete and continuous speed with a wide range of settings, smooth speed changes, and rapid response arrangements. Previously, preferably a DC motor to be operated at varying speeds for easy control and quick response. However, after developing the use of inverters for AC motor speed varies even become popular. Some important applications of induction motor speed control is on the fan speed control, compressors, pumps and blowers.
In the PLC, PID controller implementation for
induction motor speed is set as follows:
(* Determine the time base *)
% M0: =% S5;
(* Enable internal counter *)
IF THEN SET%% S13 Q0.11; END_IF;
(* Calculate the speed of motor *)
IF RE% M0 THEN
% MD8: = (% ID0.11-% MD2) * 3;
% MD2: =% ID0.11; (* md8 is the speed of motor *)
(* Calculates the average velocity *)
ROL_ARW (1,% MW40: 10);% MW40: =% MD8;
END_IF;
% MW60: = (% MW40 +% MW41 +% MW42 +% MW43 +% MW44
+% MW45 +% MW46 +% +% MW47 MW49 MW48 +%) / 10;
(* Compute the error signal *)
% MD10: =% MD14,% MW60; (* signal error * = sp-pv)
% MF12: = DINT_TO_REAL (% MD10);
(* Integral *)
IF RE% M0 THEN
% MF16: = (% MF16 MF12 +%) *% MF20; END_IF;
IF% MF16> = 25000.0 THEN% MF16: = 25000.0; END_IF;
(* Derivative *)
FE IF% M0 THEN% MF32: = (% MF12 MF18-%) *% MF20;
% MF18: =% MF12; END_IF;
(* Output control *)
(* Mf22 = KP Mf24 = RIC Mf26 = KD *)
% MF30: =% MF22 * (% +% MF16 MF12 MF24 +% *% *% MF26 MF32);
% MD28: = REAL_TO_DINT (% MF30);
(* Output limits *)
IF% MD28> = 5000 THEN% MD28: = 5000; END_IF;
IF% MD28 <= 0 THEN% MD28: = 0; END_IF;
% QW4.1: =% MD28;
(* Data acquisition *)
IF RE% M0 THEN
ROL_ARW (1,% MW300: 40);% MW300: =% MD10;
ROL_ARW (1,% MW340: 40);% MW340: =% MW329;
ROL_ARW (1,% MW380: 40);% MW380: =% MW379;
ROL_ARW (1,% MW420: 40);% MW420: =% MW419;
ROL_ARW (1,% MW250: 40);% MW250: =% QW4.1; END_IF;
Description:
1. Time base used is an internal system object on the PLC, it is% S5 with a period of 100 ms that is stored in the memory bit% M0.
2. Internal counter that is activated by a direct enable a value in% Q0.11, and here is used internally% S13 system object that will begin when the value of a PLC in RUN.
3. Ongoing enumeration values in the internal counter is at address% ID0.11 then stored in% MD2. The motor speed is calculated by counting the number of incoming pulses at a specific time interval, ie 100ms long. If the motor rotates with a speed of 1500 rpm, it will produce 500 pulses so as to obtain the motor speed in rpm, the number of pulses multiplied by three. Because of the speed calculation is not accurate, to obtain
more precise motor speed then calculated the average velocity.
4. Error signal (error) is calculated by subtracting the setpoint with an average speed (considered as present value). Then also calculated the error signal integration and derivation. % MF20 is used to enable or disable mode padasaat integral and derivative tuning, then after tuning is completed,% MF20 can be removed only.
5. Limits on the integrals necessary to enable the integration of the error signal does not swell up too big so that if any reduction in value, then the system
can respond more quickly. 25000.0 Figures obtained by calculating the maximum output value and the value of Ki.
6. To run this control program operators need to enter a setpoint and PID constants.
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