SUMMARY

This report is about a simulation study of modeling classical control technique of dc motor drive with improvement in proportional-integral (PI) control which is used closed-loop operation to control speed of motor. The speed regulator uses a PI controller in order to obtain the electromagnetic torque needed to reach the desired speed. Current controller controls the armature current by computing the appropriate thyristor firing angle or by using the firing gate angle. This generates the rectifier output voltage needed to obtain the desired armature current and thus the desired electromagnetic torque. This report also includes the work already completed and work planned for the next semester.

Figure1: Proportional Integral control (PI)

INTRODUCTION

Figure 2: main idea of PI controller

The control schematic of PI control dc motor converter-controlled separately-excited dc motor drive is shown above. The motor drive shown is a speed-controlled system. The thyristor bridge converter gets its ac supply through single-phase transformer thus the dc output is fed to the armature of the dc motor. The field is separately excited, and the field supply can be kept constant or regulated. The dc motor has a tachogenerator whose output is utilized for closing the speed loop. The output of the tachogenerator is filtered to remove the ripples to provide the signal, ωmr. The speed command ωr* is compared to the Speed signal to produce a speed error signal. This signal is processed through a Proportional-integral (PI) controller to determine the torque command. The torque command is limited, to keep it within the safe current limits, and the current command is obtained by proper scaling. The armature current command ia* is compared to the actual armature current ia to have a zero current error. Since there is an error, PI current controller processes it to alter the control signal vc. The control signal modifies the triggering angle α to be sent to the converter for implementation.

The inner current loop assures a fast current response and also limits the current to a safe preset level. This inner current loop makes the converter a linear current amplifier. The outer speed loop ensures that the actual speed is always equal to the commanded speed and any transient is overcome within the shortest feasible time without exceeding the motor and converter capability. The operation of the closed-loop speed controlled drive, the speed can be maintained constant by adjusting the motor terminal voltage as the load torque changes. A speed from zero to rated value commanded, and the motor is assumed to be at standstill. This will generate a large speed error and a torque command. The armature current will generate the triggering angle to supply a preset maximum dc voltage across the motor terminals. The inner current loop will maintain the current at the level permitted by its commanded value, producing a corresponding torque. As the motor start running, the torque and current are maintained at their maximum level, thus accelerating the motor rapidly. When the rotor attains the commanded value, the torque command will settle down to a value equal to the sum of the load torque and other motor losses to keep the motor in steady-state.

INITIALIZATION

Meet with supervisor discussing about final year degree project. Learn and study more detailed about ac/dc motor, induction motor and its modeling. Some researchers are made on the internet about MATLAB software and its applications. Articles from IEEE website are read about the dc motor. This project use dc motor drive as load. Decisions are made to study about controller of DC motor by comparing between Proportional-Integral (PI) controller and Fuzzy Logic Controller. Supervisor given idea to produce block set by using continues block...