power igbt and the boost converter

EE Power Electronics 04/26/2015

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EE Power Electronics From: Mario Augusto Junior

Partner: Ryan Selby

To: Kaung Thu

Date: Performed: 04-24-2015;

Subject: Power IGBT and the Boost Converter

Abstract: In this lab, basically the operation of a boost converter was analyzed. A boost converter stands for increasing the input voltage. In other words the boost converter has the output larger than its input in value. For that, the frequency and the inductor value have to be taken into account to get the desired output voltage.

Introduction:

Switching power supplies, DC/DC converters and other power circuits using different technologies to change an input voltage and thus get a different value of output voltage with maximum stability and efficiency. In figure 1 we have the typical circuit of a boost converter:

Figure 1 - Boost Converter Circuit


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As it can be seen, the basic element of this step is a channel power field effect transistor C, which are the main switching the load current and the inductor. Other components may be used, for example, P-channel MOSFETs or bipolar. However, the preference for the N-channel MOSFET is in its lowest resistance between the drain and the source when conduction (Rds (on)), which allows controlling more intense currents with, lower heat dissipation. In operation, the transistor Q1 is continuously switched on and off by the control circuit action. This action causes a pulsating current is created through the diode and diode CR1. Despite the inductor being connected to the capacitor C only when the diode conducts, a filter L / C is obtained effectively. The function of this filter is to filter the pulse train thus obtaining a continuous load voltage (Vo). Operating Modes In the continuous conduction mode the output voltage depends on the duty cycle and input voltage. In this circuit the input voltage, output load current and duty cycle must not change. In this mode of operation, the voltage raising stage (boost) assumes two states in each cycle of the switching signal. These cycles are shown in Figure 2.

Figure 2 - ON and OFF modes of operation of a Boost Converter

ON mode, the transistor Q1 conducts and CR1 is off. In the OFF mode the transistor is cut and CR1 leading. A simplified representation of Figure 2 allows the current view of the two modes. It is important to note the waveforms in the various elements of this circuit in this operating mode. These waveforms are shown in Figure 3.


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Figure 3 – Operation Mode of the Boost Converter Circuit

See that there is always a current flowing through the inductor. In batch mode, observing the waveforms shown in Figure 4.

Figure 4 - The current that flows in the inductor

For this we consider what happens when the load current decreases and the driving mode changes from continuous to discontinuous. When the load current falls below a certain value during a switching cycle of the current through the inductor is zero. The current will remain zero until the beginning of the next cycle. A power rating of a converter "boost" operating in this mode will have three different states in each control signal cycle, unlike only two states continuously.


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Pre lab part 1, 2 and 3:

Part 1) 1) The gate threshold voltage VGS for IRG4BC10U power MOSFET.

The circuit in the figure 1 was built in PSpice. Then, was performed a parametric sweep on the applied voltage source to obtain the VGE(th). To determine the value with better accuracy the Increment parameter was set close to 0.1V.

Figure 5 - Simple Bias Circuit to find the VGE_THRESHOLD of IRG4BC10U

Figure 6 - Curve of VGS and Current of IRG4BC10U

According to the graphic on figure 2, the threshold VGS for IRG4BC10U power MOSFET obtained was 5.18 Volts at 1.11mA. According to datasheet of the device the threshold voltage is in between 3 – 6 Volts. Therefore, 5.18 volts is a good value obtained. But the current obtained in the experiment was considerable larger than the one provided by datasheet, datasheet says that it should be around 250uA. The simulated device on the PSpice software and the physical device present the difference because of limitations of the software. Perhaps, the software was designed with no accuracy for the current, which is different of the datasheet to the physical device. Part 2) Static test of the Boost Converter To test the static of Boost Converter, the circuit on figure 3 and 4 was build on PSpice. The inductor from PSpice is ideal, so the internal resistance was set as 24 Ohm for 1mH. 1 kOhm for the load. The simulation was done with the standard diode, 1N4001 and repeated with fast recovery diode, MR852RL.

V_V1

0V 1V 2V 3V 4V 5V 6V 7V 8V 9V 10V 11V 12V 13V 14V 15V 16V 17V 18V 19V 20VV(Z1:G)

0V

2.0V

4.0V

6.0V

SEL>>

(5.1820,5.0704)

I ( Z 1 : C )0 A

5 0 m A

1 0 0 m A

1 5 0 m A

(5.1820,1.1161m)


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Figure 7 - Circuit for static test of the Boost Converter with the standard diode 1N4001

Figure 8 - Circuit for static test of the Boost Converter with the standard diode MR852

Figure 9 - Measurement of load, diode, inductor, and transistor voltages for 1N4001


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Figure 10 - Measurement of load, diode, inductor, and transistor voltages for MR852

The table 1 compares the load, inductor, transistor, and diode measurement of the circuit with two different diodes:

Table 1 - Measurement of components for MR582 and 1N4001 diodes

1N4001 MR852 Load 2.32V 2.37V

Inductor 55.86mV 56.93mV Transistor 2.94V 2.9V

Diode 616.545m 570.6mV

Comparing both MR582 and 1N4001 diodes is possible to note that they have close values each other for the components measured as shown in table 1. It happens because there is no switching going on between both transistors. Then, the time recovery is not an issue. Part 3) Now, the function generator was connected to drive the gat of the IGBT as shown in he figure 7 and 8. The operation of the circuit is shown in table 2 with the duty cycle varying between 20% to 80%.

Time

0s 0.05s 0.10s 0.15s 0.20s 0.25s 0.30s 0.35s 0.40s 0.45s 0.50s 0.55s 0.60s 0.65s 0.70s 0.75s 0.80s 0.85s 0.90s 0.95s 1.00sV(Z2:C) V(R3:2) V(L1:1,R2:2) V(Z2:C,D3:2)

0V

0.5V

1.0V

1.5V

2.0V

2.5V

3.0V

(0.000,2.3725)

(0.000,56.939m)

(0.000,570.613m)

(0.000,2.9431)


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Figure 11 - Dynamic (AC) Test of the Boost Switched Power Supply with 1N4001 diode

Figure 12 - Dynamic (AC) Test of the Boost Switched Power Supply with MR852 diode

The goal was providing 5V output to a load of 1kOhm from a 3V. As in the to next plot the duty cycle to get the desired output was 60% duty cycle as shown in both figures 9 and 10, with 1N4001 and MR582 diodes:

Figure 13 - Desired 5V output using the standard diode 1N4001

Time

0s 10ms 20ms 30ms 40ms 50ms 60ms 70ms 80ms 90ms 100ms 110ms 120ms 130ms 140ms 150ms 160msV(R2:2)

2.0V

3.0V

4.0V

5.0V

SEL>>

I(L2)-40mA

0A

40mA

80mA


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Figure 14 - Desired 5V output using the standard diode MR582

The follow equations are used to get the desired output voltage with the components of circuit that are available in lab:

!"#$!"#

= !!!!

Equation (2) For Vout = 5 V For Vin = 3V

So, from equation 2, D = 0.4 or 40% !

!= !

!!!

D=0.4

In equation 3, with the highest inductor found in lab 1mH, the frequency is 10Khz according to the follow equation:

𝑉𝑜𝑢𝑡 = 𝑉𝑖𝑛1+ 1+ 2𝐷

!𝑅𝑇𝐿

2 (3)

5 = 3 ∗1+ 1+ 2 ∗ 0.4

! ∗ 1000 ∗ 𝑇1𝑚𝐻

2 (3) Solving for T, T=100uS Which is a frequency of 10Khz. The same used in our circuit in lab Also the smallest inductance value that would guarantee CCM is calculated as shown in Equation 4:

Time

0s 10ms 20ms 30ms 40ms 50ms 60ms 70ms 80ms 90ms 100ms 110ms 120ms 130ms 140ms 150ms 160msV(R2:2)

2.0V

3.0V

4.0V

5.0V

6.0V

SEL>>

I(L2)-40mA

0A

40mA

80mA


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𝐿 𝑐𝑟𝑖𝑡 = 𝐷(1− 𝐷)!𝑅2𝑓 (4)

With equation 4, for Lcrit:

𝐿 𝑐𝑟𝑖𝑡 = 0.4(1− 0.4)!1000

2 1100𝑥10!!

𝑳 𝒄𝒓𝒊𝒕 = 7.2mH adding 25% for security margin it becomes 9mH. Close to the 1mH that has been used in the lab. *****According to the next equation 2, to get the 5V output voltage the duty cycle should be around 40%, but as the inductor and diode are not ideal, there is a drop of voltage on them, which makes the output smaller than it should be, the desired 5V. To compensate this drop of voltage on the diode and inductor was necessary to increase the duty cycle to 60%. Then, as is shown in figure 13 and 14 the 5V output voltage was obtained****** The operation with the two different diodes is shown in the next table:

Table 2 - Efficiency of the circuit with the fast recovery (MR852) and standard diode (1N4001)

10KHz

MR852

Duty Cycle Pin(mW) Pout(mW) Efficiency

Pin Efficiency 20% 36.00 12.00 33.33333333 7.11 79.18424754 30% 57.00 16.00 28.07017544 Pout

40% 75.00 20.00 26.66666667

5.63

50% 93.00 24.00 25.80645161

60% 108.00 26.00 24.07407407

70% 126.00 29.00 23.01587302

80% 144.00 30.00 20.83333333

1N4001

Duty Cycle pin(mW) pout(mW) Efficiency

Pin Efficiency 20% 39.00 11.00 28.20512821 7.11 77.6371308 30% 57.00 15.00 26.31578947 Pout

40% 78.00 18.00 23.07692308

5.52

50% 96.00 22.00 22.91666667

60% 114.00 23.00 20.1754386

70% 129.00 25.00 19.37984496

80% 141.00 25.00 17.73049645

The power efficiency is calculated using the follow equation:


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𝜂 = !"#$!"#

. 100 𝜂 = Efficiency 𝑃𝑜𝑢𝑡 = Output Power 𝑃𝑖𝑛 = Input Power Comparing the two diodes, the fast recovery time MR582 presents a better efficiency to the standard diode. The reason for this, is because the A silicon diode has a typical voltage drop of 0.6 to 0.7 volts, while a MR582 diode has a voltage drop of 0.45 volts. This lower voltage drop can be used to give higher switching speeds and better system efficiency. Lab Assignment Part1) The equipment used to this lab: IRG4BC10U-ND IGBT 1N4001 standard power diode MR852RL Fast Recovery Power diode 1mH Inductor 1000 Ohm Resistor 1uF Capacitor Standard EE laboratory Bench equipment For part 1 the I-V characteristics of IGBT were plotted:

Figure 15 - Plot of characteristics of IGBT IxV

To plot the image on figure 11 the collected data are shown in table 3.

0

1

2

3

4

5

0 2 4 6 8 10 12 14 16

V GE [V]

Collector Current [mA]

IRG4BC10U Curve Trace


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Table 3 – Voltage applied to get threshold of IBJT

VApply(V) VGE(V) IC(mA) 1 1 0 2 1.99 0 3 2.99 0 4 3.99 0.059

4.2 4.177 0.217 4.4 4.33 0.638 4.6 4.45 1.41 4.8 4.54 2.49

5 4.61 3.77 5.2 4.66 5.21 5.4 4.68 6.95 5.6 4.66 9.05 5.8 4.63 11.29

6 4.6 13.66 7 4.45 24.7 8 4.67 32.46 9 4.94 39.5

10 5.22 46.71 11 5.46 53.99 12 5.7 61.01 15 6.25 86 20 6.96 133.2 25 7.13 186

The threshold in the device used in this experiment was VGS = 3.99V at 59uA. The datasheet of device says that VGS should be in between 3 – 6 Volts. The experiment in this lab agrees with that. Part 2) Static (DC) test of the Boost Converter (Hardware test) In this part, the same circuit as in pre lab was built to compare the results, as shown in table 4:

Table 4 - Voltage measurement of the circuit components

PreLab Lab

1N4001 MR852 1N4001 MR852

Load 2.32V 2.37V 2.38V 2.5V Inductor 55.86mV 56.93mV 4.4mV 4.6mV

Transistor 2.94V 2.9V 2.9V 2.9V Diode 616.545m 570.6mV 610mV 485mV


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As expected the results in the lab match with the ones in PreLab. The voltage across the inductor is about 10mV of difference because the values of resistance are not the same for the physical and simulated parts. Part 3) Dynamic test of converter In this part, the same steps from part 3 prelab were done: Vin= 3V Vout= 5V R=1000 Ohm The duty cycle varying from 20% to 80%:

D1N4001 (10KHz) MR582(10KHz) Duty Cycle Pin(mW) Pout(mW) Efficiency Pin(mW) Pout(mW) Efficiency

20% 24.00 16.00 66.66666667 24.00 19.00 79.16666667 30% 42.00 27.50 65.47619048 42.00 31.00 73.80952381 40% 63.00 40.00 63.49206349 66.00 46.00 69.6969697 50% 90.00 53.00 58.88888889 100.00 63.00 63 60% 130.00 72.00 55.38461538 132.00 83.00 62.87878788 70% 150.00 83.00 55.33333333 174.00 100.00 57.47126437 80% 186.00 94.00 50.53763441 220.00 124.00 56.36363636

To calculate the Pin (Input Power), the input current was multiplied by the input voltage: Pin = V . I Pin: Power V= Voltage I= Current To get the Pout (Output Power), the follow equation was used: Pout = I2 . R As expected the values simulated in PreLab agree with the Lab. Another important fact observed between the PreLab and Lab, was the efficiency, which is better or larger in Lab


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comparing to the PreLab. The reason for this is because the drop of voltage in the transistor is lower in the physical device compared to the simulated one. Therefore, more voltage goes to the output, increasing the efficiency. Conclusion

In this lab, basically the operation of a boost converter was analyzed. A boost converter stands for increasing the input voltage. In other words the boost converter has the output larger than its input in value. For that, the frequency and the inductor value have to be taken into account to get the desired output voltage. The first task in this prelab and lab was checking the threshold (VGS) of the converter, to see if they agree with the information from the datasheet. As expected the voltage was around 5V for lab and pre lab, which is in between 3 – 6 V. It is a good outcome in the part 1 of the experiment. For part 2, the static (DC) test was done and both results as shown in table 4 are close as expected. For part 3, the dynamic (DC) was analyzed and then, the efficiency outcomes in the lab were better than prelab, it happened because the drop of voltage in the transistor was smaller in lab, therefore the output voltage was larger. Also, the goal was make 5V output with an input voltage of 3V, this was possible after setting the duty cycle in 60%. The Fast Recover excels a better job to a standard diode because when there is a switching frequency applied to the transistor the fast recovery time makes it absorbing less voltage, and then more voltage goes to the output. So, the circuit is more efficient. On the other hand, if there is no switching frequency both diodes (1N4001 and MR582) operate basically in the same characteristics as shown in table 1. This is an important learning because make us able to know the limitations of the device.

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