EEET2669 POWER ELECTRONICS CONVERTERS LECTORIAL #5

1.   A 3.36kVA 240V 50Hz grid connected single phase  H-Bridge voltage-source inverter has a DC link voltage of 400V, and is controlled using a two-level hysteresis current controller. The maximum instantaneous switching rate that the converter can tolerate is 8kHz, and the permissible current error is ±1.5A. Calculate:

a.  The  minimum  filter inductance  required to achieve the converter performance criteria.

b.  The minimum switching rate that will be achieved with the inductance determined in part (a).

c.  The average switching rate that will be achieved with the inductance determined in part (a).

2.    For the converter described in question 1 above, it is proposed to replace the two-level hysteresis regulator with a three-level hysteresis controller. Calculate:

a.  The  minimum  filter inductance  required to achieve the converter performance criteria defined in question 1.

b.  The average switching rate that will be achieved with the inductance determined in part (a).

3.    For the converter described in question 1 above, it is required to operate at a constant switching frequency of 5kHz. A two-level variable band hysteresis regulator is to be employed. Calculate:

a.  The  inductance  required  to  achieve  this  switching frequency while  complying with the performance requirements in question 1.

b.  The excursion range for the hysteresis band-width.

c.  Sketch the variation in hysteresis band-width that would ensure regulation of the converter switching frequency.

4.   A DC-DC buck converter is required to produce a 5V output from an input voltage that varies over the range 10 – 20V. A hysteresis current controller is used to control the converter, for a minimum load of 5W at a maximum switching frequency of 50kHz.

a.  Calculate the minimum  inductance required for the converter to operate in continuous conduction mode for the entire input voltage range and load range while complying with the switching rate constraint.

b.  Identify the operating condition that gives rise to the minimum  switching frequency, and calculate the minimum switching frequency that occurs with this inductance value.

5.   A  DC-DC boost converter is required to produce a 24V output from an input voltage that varies over the range 8 – 12V. A hysteresis current controller is used to control the converter, for a minimum load of 5W at a maximum switching frequency of 20kHz.

a.  Calculate the  minimum  inductance and  hysteresis  bandwidth  required for the converter to operate in continuous conduction mode for the entire input voltage range and load range while complying with the switching rate constraint.

b.  Identify the operating condition that gives rise to the minimum switching frequency, and calculate the minimum switching frequency that occurs with this inductance value.