Determine Controller in closed loop System in Labview

·  PID

• The PID acts as the controller of the system. The steady state (Ess) error gives response to PID to correct the error. A PID controller calculates an "error" value as the difference between a measured process variable (actual value) and a desired set point. The controller attempts to minimize the error by adjusting the process control inputs.

• The PID controller calculation (algorithm) involves three separate constant parameters, and is accordingly sometimes called three term control: the proportional, integral and derivative values, denoted P, I, and D.

• Proportional Gain kp produces an output value that is proportional to the current error value. This kp will adjusting the time response which reducing the rise time (Tr). However, high proportional gain kp will results the system become unstable which is increasing overshoot of the system.

• Integral Gain ki produces a contribution to both the magnitude of the error and the duration of the error. The Integral Gain ki accelerates the movement of the process towards set point and eliminates the steady state error that occurs to the controller. However, it also can cause the present value to overshoot the setpoint value of the system.

• Derivative Gain kd slows the rate of change of the controller output. kd used to reduce the magnitude of the overshoot produced by the proportional and integral component and improve the combined controller-process stability. However, the derivative term slows the transient response of the controller.

• For the stability of this DC motor speed control system process, the gain of Kp, Ki and Kd is tuned by using manual tuning method. This method is first by setting set ki and kd values to zero. Increase the kp until the output of the loop oscillates, then kp should be set to approximately half of that value for a "quarter amplitude decay" type response. Then increase ki until any offset is corrected in sufficient time for the process. However, too much ki will cause instability. Finally, increase kd, if required, until the loop is acceptably quick to reach its reference after a load disturbance. However, too much kd will cause excessive response and overshoot. A fast PID loop tuning usually overshoots slightly to reach the setpoint more quickly.

• In this process control, the output of the PID controller (algorithm) gives the range of output 0-100 duty cycle for the input of the PWM

· MOTOR

• Refer to the graph above; the speed of the motor is proportional to the duty cycle. In this system, the range speed of the motor is 0-2600 RPM and the voltage supply to the motor is 0-5V depends on the duty cycle (0-100%) of the PWM.

• The Motor Voltage (Vm) that supplied to the motor from the PWM and MOSFET give variable speed to the motor depending on the variable voltage supplied.

• The desire speed that set at the setpoint input for example 2000 RPM needs at a range of 4.2V. Thus the PWM must inject at least 80% - 90% duty cycle to supply the motor input for producing 2000 RPM.

Output From Sensor(osiloscope)

Output from sensor

Result Test Sensor (RE08A kit)

No	Volt	Frequency (Hz)	RPM
1	0.5Volt	184.5Hz	1383.75
2	1.0Volt	191.9Hz	1432.5
3	1.5Volt	287.9Hz	2159.25
4	2.0Volt	557.4Hz	4180.5
5	2.5Volt	617.8Hz	4633.5
6	3.0Volt	790.5Hz	5928.75
7	3.5Volt	946.4Hz	7098
8	4.0Volt	1.154kHz	8655
9	4.5Volt	1.269kHz	9517.5
10	5.0Volt	1.446kHz	1084.5

Interfacing Between Hardware and Software

Do connection between function generator and hardware. Where the trainer will provide 5V supply to the hardware

Do a connection between function generation, hardware and DAQ.

Produce signal from sensor

Output signal from sensor which produce pulse will send to the oscilloscope when the motor start rotate

Simulate PWM Using Labview Softwere

PWM

• Pulse Width Modulation (PWM) used in this process to control the speed of the motor by varying the duty cycle of the PWM. In this system, 0% duty cycle produce 0V of output voltage which means the PWM is in fully-off state while 100% duty cycle produces 5V of output voltage which means the PWM is in fully-on state.
  

• The variable output voltage which denoted here as Controlled Voltage (Vc) is used for variable input voltage to the motor which give variable speed to the motor which depends on the input voltage.

Pulse width modulation ( Final Control Element)

• Pulse width modulation (PWM) is a technique to control the DC motor speed which is a series of digital pulses is used to control an analog circuit. The length and frequency of these pulses determines the total power delivered to the circuit.  The digital pulse train that makes up a PWM signal has a fixed frequency and varies the pulse width to alter the average power of the signal. The ratio of the pulse width to the period is referred to as the duty cycle of the signal.  Figure below is the waveform of PWM in 40% until 100% of duty cycle.

Labview program

LABVIEW SOFTWARE (one of SCADA system which can monitor and controlling)

Design a circuit and program in labview

Features need to be added on the labview software:

• SET POINT (knob which control the voltage)
• DAQ ASSIST 1(acquired and transmit signal from output sensor)
• DAQ ASSIST 2 (generate voltage from DAQ card to the hardware)
• SIMULATE SIGNAL (PWM)
• WAVEFORM SENSOR
• WAVEFORM PWM
• CALCULATION
• PID (Compare and calculating the error continuously)
• CONSTANT(create value for PWM duty cycle)
• MEAN BLOCK (get the average result in order to get precise value)
• WIRING AND CONNECTION

Installation of Hardware

Step 1

Street board has been used for installing the mosfet circuit.

 

Step 2

Mosfet circuit is attached to the prospect

Step 3

Installation of dc motor 6V and Iron 88 stainless steel is used to hold the motor.

Step 4
Wiring installation for signal output from the sensor

Step 5

Sensor RE08A included with slotted disc is connected together with motor

Step 6

Complete circuit Hardware

Interface Between The DC Motor and Sensor RE08A

• Optical encoder (Speed Sensor)

Speed sensor is used to measure the speed of the DC motor. This sensor is placed at the rotation of the shaft. The connection of this sensor is shown in Figure below.

• There are plenty of speed sensors that available at the current market. For this project, Rotary Encoder Kit RE08A has been chosen because easy to use, easy to understand. This kit is made to sense the rotation of the DC motor by generating the pulses. These pulses can be translated into the speed of the DC motor by applying a simple mathematical formula which will be added into the programming part. The pulses generated by this RE08A are shown in Figure below and the formula to calculate the speed is shown in Equation below

• Figure above shows that +5 pin is connected to the +5V source. The Gnd pin is connected to the ground. The Signal pin which gives the pulses as output is connected to the counter pin at DAQ through interrupt approach. 
  

• These pulses represent the rotation of the DC motor. We have to count these pulses in one minute to get the speed in rpm. The LabView will measure the time period of the pulse signal. Then, we use the mathematical method to find frequency. 

• Frequency is multiply with 60 because 60 is assume as a 60 second or 1 minute. Then, Divide by 8 because one full rotation has 8 blades.

• Figure below shows the interface between the DC motor and the RE08A. Slotted disc has been installed at the end of DC motor shaft. The wire from DC motor is connected to the power source. In order to control the speed, an adjustable resistor has been connected to the power source which is seeks to adjust the desired speed. The value of speed will appear at the computer screen

Interface between the DC motor and RE08A

    Installation of sensor

• 
  There are 3 terminal of sensor which is 5V, ground, and signal.5V terminal is generated by function generator in the lab and the ground of sensor is connected to the DAQ ground terminal. Signal that produce from this sensor is connected to the DAQ assist means that DAQ required signal from sensor.