Tutorial - Boost PFC Converter Control Loop Design

Boost PFC Converter Control Loop Design

SmartCtrl Tutorial Boost PFC Converter Control Loop Design

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Powersim Inc. www.powersimtech.com

Boost PFC Converter Control Loop Design SmartCtrl1 is a general purpose controller design software specifically for power electronics applications. This tutorial is intended to guide you, step by step, to design the control loops of a PFC (power factor correction) boost converter with the SmartCtrl Software. ‐

The example used in this tutorial is the PFC boost converter circuit that comes with the PSIM example set (the PSIM file is “UC3854_PFC.sch” under the folder “examples\PWM IC”). The PSIM schematic is shown below: Lm Iin

Lf

15

300u Vin

V

1mH

A

324Vpk 50Hz

Vo

Do

Cf 1u

Rcs 0.25 Rpk2 1.8k

1

R1 30k

Co 450uF

Q

Rci 10k

Rmo 3.9k

Rload 592

V v_io

Rs Cpk 100pF

Rcz 6.66432K

Rpk1 10k

100

V Vcc

Ccz 1.59211n

Current regulator RVAC 620k RB1

Vvea

RFF2 91k RFF3 20k

UC3854 1

16

2

15

3

14

4

13

5

12

6

11

7

10

8

9

CFF2 0.47uF

RVF

CVF

14.2082K

356.753n

Voltage regulator

C1 100u

CT 1.2n Css 1n Rset

150k RFF1 910k

CFF1 0.1uF

C2 1u

10k

RENA 22k

10k

RVI 26.1667K

RVD 0.5k

C3 1uF

The circuit includes the inner current loop and the outer voltage loop. The current loop regulator parameters are the resistance Rcz and the capacitance Ccz, and the voltage regulator parameters are the resistance RVF and the capacitance CVF, highlighted in the red dotted boxes above. Let’s assume that these values are unknown. The objective is to design the current/voltage regulators using the SmartCtrl software. The design procedure is described below. , or from the Data menu, select To begin the design process, in SmartCtrl, click on the icon Predefined topologies > AC/DC converters > PFC Boost converter. ‐

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The dialog window will appear as follows.

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SmartCtrl is copyright in 2010 by Carlos III University of Madrid, GSEP Power Electronics Systems Group, Spain

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The PFC boost converter is controlled by a double loop control scheme. The inner loop is a current loop, and the outer loop is a voltage loop. Note that the PFC boost converter design must be carried out sequentially. The SmartCtrl program will guide you through this process.

Inner Loop Design 1. Define the converter Select the plant as Boost (LCS_VMC) PFC for boost PFC converter with the current loop and the voltage loop. Complete the parameters in the corresponding input data window. Note that the input voltage is the peak value. When finished, click OK to continue.

2. Select the current sensor Select the current sensor among the available types. In this example, select Current sensor, and set the gain to 0.25 based on the circuit (this value is equivalent to the sense resistor value).

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3. Select the current regulator From the inner loop regulator drop down menu, select PI as the current regulator type. ‐

4. Select the crossover frequency and the phase margin SmartCtrl provides a guideline and an easy way of selecting the crossover frequency and the phase margin through the Solution Map. Click on the Set button, and the Solution Map will be shown as below. In the Solution Map, each point within the white area corresponds to a combination of the crossover frequency and the phase margin that leads to a stable solution. In addition, when a point is selected, the attenuation given by the sensor and the regulator at the switching frequency is provided. To carry out the selection, left click a point within the white area, or enter the crossover frequency and the phase margin manually.

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Once the crossover frequency and the phase margin are selected, the Solution Map will be shown on the right side of the converter input window. If, at any time, one needs to change the crossover frequency or the phase margin, click on the white area of the Solution Map, as shown in the figure below.

Once the inner loop design is completed, one can move on to the outer loop design.

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Outer Loop Design The procedure of designing the outer loop is similar to that of the inner loop design. It includes the following: 1. Select the voltage sensor

When using a voltage divider, one must enter the reference voltage, and the program will automatically calculate the sensor gain. In this example, the reference voltage is 7.5V. The sensor input data window is shown below.

Reference voltage

Then press on “Calculate Vref/Vo from Vref” button to set the attenuation of the voltage divider.

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Boost PFC Converter Control Loop Design 2. Select the outer loop regulator In this example, select PI as the regulator type, and enter the regulator parameters as below.

3. Determine the crossover frequency and the phase margin Similar to the inner loop design, the crossover frequency and the phase margin of the outer loop must be selected. A Solution Map is also provided to help select a stable solution. Press the Solution map (outer loop) button and the solution map will appear.

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Then select a point by clicking within the white area, and click OK to continue.

Once the crossover frequency and the phase margin are selected, the Solution Map will appear on the right side of the converter input window. If, at any time, these two parameters need to be changed, click in the white area of the Solution Map, as shown in the figure below.

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Accept the selected design by clicking on OK. The program will automatically show the control system performance by means of the Bode plots, the Nyquist plot, phase margin, etc. SmartCtrl provides the regulator component values needed to implement the regulators, as well as the voltage divider resistors. Since there are two control loops, one must select which one to display.

Displayinner loop Displayouter loop

Display outer loop solutionsmap Display inner loop solutionsmap

At this point, the control loop design of the converter will be completed. We will validate the design by means of time domain simulation. ‐

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Design Verification through Simulation In order to validate the design from SmartCtrl, time domain simulation is carried out in PSIM. ‐

We will compare the performance of the converter with two different designs.

Design #1 Inner loop: f cross=3 kHz Phase Margin=45º

Design #2

Outer loop: f cross=30 Hz

Inner loop: f cross=15 kHz Phase Margin=45º

Output voltage

Outer loop: f cross=30 Hz

Output voltage

Input voltage

Input voltage

Input current*50

Input current*50

It can be observed that Design #2 shows a much less waveform distortion that Design #1, and that the waveform distortion can be greatly reduced by increasing the crossover frequency of the inner loop. This example illustrates that SmartCtrl in combination with PSIM provide a fast and powerful platform for the design and validation of converter control for power factor correction applications.

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Tutorial - Boost PFC Converter Control Loop Design

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