Power Systems and Energy Storage 

Part A. DC motor control with H-bridge switching mode controller (100 marks)

MATLAB Simulink model ‘DC_motor_drive’ is simulating a variable speed control of certain separately-excited wound- rotor DC motor. The load torque is constant and independent of speed (hoist type of load). Your individual operating parameters are generated using your student ID number. The required motor load torque is calculated by using the last three digits (NNN) of you ID number: load _torque_(N*m) = 0.2*NNN. The required motor speed is calculated as: motor_speed_(rpm) = 1.750*NNN.

You are required to use the model to complete the following tasks.

1. Set the required load torque value by amending the relevant model input parameter. Adjust the control (carrier waveform) duty cycle value to achieve the motor operation at the required speed (with ±5% accuracy). Do not change any motor or power supply parameters (voltages, resistance and inductances). Plot time dependences of the motor speed, armature current and torque values for the time period sufficient to reach a steady motor speed. Explain your settings and describe your results. Indicate the motor current discontinuity periods if they appear in your results. (30 marks)
2. Amend the model to collect data for the time dependence of current via all IGBTs and diodes together with their gate signals and the carrier waveform (in a similar way as it is shown for one (Q3/D3) IGBT-diode pair). Explain the H-bridge controller operation using these waveforms. Additionally, indicate current pass on the circuit diagram for all operation steps of the controller. (20 marks)
3. Modify the model to calculate the average armature voltage and current values at the steady operating condition (when the motor speed is stabilised). You can do this by passing the desired signal

via the Mean filter added to the model. Alternately, you can collect the data and process it elsewhere (using MATLAB script or Excel). Explain in details what you have modified and how your modification/processing does work, show the details. Compare the obtained results with the theoretically expected values. Comment on any differences. (20 marks)

4. Modify the model to induce the motor speed reversal via control signal modification – explain in details what modifications you have made and how they work, show the evidence of operation at the reversed speed. (15 marks)
5. Answer the question: Is the drive model capable to support the regenerative braking mode? If yes, explain and demonstrate this mode of operation. If not, explain what modifications to the model are required and amend the model. (15 marks)

Part B. Variable speed drive for Induction motor (100 marks)

MATLAB Simulink model ‘Induction_motor_Drive’ can be used for simulating the V/f=const type of speed control of certain Induction (Asynchronous) motor. The load torque is proportional to the square of the speed (fan/pump type of load). Your individual motor speed parameter is generated using your student ID number. The required motor speed is calculated by using the last three digits (NNN) of you ID number: motor_speed_(rpm) = 1.750*NNN.

You are required to use the model to complete the following tasks:

1. Explore the model which is originally set for the motor operation at rated voltage (460 Vrms) and frequency (60 Hz) driving fan type load at rated speed (1750 rpm). Explore the reference sinewave settings. Analyse and describe the power converter design. Plot and discuss the motor speed and torque variation with time. (5 marks)
2. Amend the model to collect the line voltage and line current waveforms for all 3 phases of the motor. Collect this data together with PMW carrier/reference and commutation waveforms. Present the collected data showing their correlation in time, with full labeling of all parameters. Describe the meaning of the obtained waveforms. Explain the PWM converter operation using these waveforms and circuit diagram. (20 marks)