EE4524 Assignment Questions 

Please read the following CAREFULLY before you submit the design report.

• Weightage of the design report: 50% of the total mark.
• Submit the PLECS simulation and design report to our course mailbox (EE4524A@gmail.com).
• Use your NTU email but not a private one (in case sent to the spam box).
• Submission deadline: Week 9, 11:59pm, 20 March 2026.
• Email subject line: EE4524 – Tutorial Group – Name, e.g., EE4524 – F11 – Wu Yang.
• Format of the report: PDF, name the file as EE4524 – Tutorial Group – Name; font style

Times New Roman; font size 12; max 5 pages; file size < 5 MB.

Question 1

A small wind turbine is connected to a permanent magnet synchronous generator that produces 30 kW power. This wind generator is operated at the unity power factor and connected to the grid through a three-phase back-to-back AC/DC/AC power converter. The generator output frequency is 35 Hz and the voltage is 200 V (phase rms). The grid frequency is 50 Hz and the voltage is 230 V (phase rms). The DC capacitance has a value of 5 mF, and the DC bus voltage V_dc is controlled at 800 V. The filter inductor has a value of 5 mH, and its internal equivalent series resistance (ESR) is 10 times the inductance value. The converter switching frequency is 20 kHz.

• Briefly discuss the functionality of the AC/DC/AC power converter in this wind generation system and the key components of this power converter. (20 Marks)
• Design a PI controller for current regulation in the dq rotating frame such that the time constant of the current loop is 1 ms. Briefly explain why abc to dq transformation is needed for inverter control. (10 Marks)
• Design another PI controller for DC voltage regulation such that the time constant of the voltage loop is 100 ms. Briefly explain why DC voltage control only determines the reference for i_d but not i_q. (10 Marks)
• Build the PLECS simulation model that consists of the above power converter. (20 Marks)

Question 2

DC-DC converters are widely applied in data centers. Design a DC-DC converter for a data center server rack with input voltage V_in of 380 V and an output resistive load of 20 Ω. The filter inductor/capacitor you use will have an ESR of 10 times the inductor/capacitor value. The switching frequency is 50 kHz. The desired output voltage V_out range shall be 300-450 V (for students with even last digit in their matric no.), and250-500 V (for students with odd last digit in their matric no.).

• Choose a suitable topology and describe its operating principle. Derive the voltage gain (V_out / V_in) analytically using inductor voltage-second balance. (20 Marks)
• Build the PLECS simulation model that consists of the above power converter. Use cascaded PI controllers for voltage and current control loops. Present the waveform in

the report for tracking performance when the output voltage reference changes from its minimal value to its maximum value. (20 Marks)

[1] The output voltage could be inversed.

[2] Rigorous analysis is not required.