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Sie befinden sich hier: Wiki der Fakultät Elektro- und Informationstechnik » Professoren Webseiten » Heinz Rebholz » Course A Power Electronics
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professoren_webseiten:rebholz:course_a_power_electronics [2025/02/06 14:50] – [Measurement, Simulations and Calculations] hrebholzprofessoren_webseiten:rebholz:course_a_power_electronics [2025/03/06 20:59] (aktuell) – [Simulink] hrebholz
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 It is just as important as the simulation itself to check whether the results are plausible. If, for example, currents > 100A or voltages in the MV range occur in the simulation, you should not trust the result under any circumstances.  It is just as important as the simulation itself to check whether the results are plausible. If, for example, currents > 100A or voltages in the MV range occur in the simulation, you should not trust the result under any circumstances. 
  
-<WRAP center round todo 60%>+<WRAP center round todo 80%>
 **Task 1a)** **Task 1a)**
 Create the circuit diagram of a buck converter consisting of a switching element, diode, coil, capacitor and load. Determine the load resistance so that the required power is set at the output. Create the circuit diagram of a buck converter consisting of a switching element, diode, coil, capacitor and load. Determine the load resistance so that the required power is set at the output.
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 Diodes always incur power loss, primarily caused by the voltage drop across the device. Thus, the freewheeling diode is often replaced by a second power switch, leading to the commonly used half-bridge topology. This is a clever solution, especially when using MOSFETs as switches. MOSFETs always come with an intrinsic diode, known as the body diode. Therefore, even if the MOSFET is not activated, the body diode can serve as the freewheeling diode. The body diode, of course, exhibits the same poor power loss characteristics as the previously used diode. Therefore, we activate the MOSFET to allow the current to flow through the MOSFET instead of the diode.The rule to avoid short circuits is as follows: whenever the high-side MOSFET is turned off, the low-side MOSFET is turned on. However, this introduces another problem. Since the switching speed of the devices is not infinite, a certain amount of delay is required before turning on the low-side MOSFET after the high-side MOSFET is turned off, and vice versa. This delay is referred to as dead time. With ideal switches, we do not need any deadtime. However, you can equip the PWM generator with a deadtime function, as we will need it later Diodes always incur power loss, primarily caused by the voltage drop across the device. Thus, the freewheeling diode is often replaced by a second power switch, leading to the commonly used half-bridge topology. This is a clever solution, especially when using MOSFETs as switches. MOSFETs always come with an intrinsic diode, known as the body diode. Therefore, even if the MOSFET is not activated, the body diode can serve as the freewheeling diode. The body diode, of course, exhibits the same poor power loss characteristics as the previously used diode. Therefore, we activate the MOSFET to allow the current to flow through the MOSFET instead of the diode.The rule to avoid short circuits is as follows: whenever the high-side MOSFET is turned off, the low-side MOSFET is turned on. However, this introduces another problem. Since the switching speed of the devices is not infinite, a certain amount of delay is required before turning on the low-side MOSFET after the high-side MOSFET is turned off, and vice versa. This delay is referred to as dead time. With ideal switches, we do not need any deadtime. However, you can equip the PWM generator with a deadtime function, as we will need it later
  
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 **Task 2a)** **Task 2a)**
 Replace the diode in your simulation with an additional ideal switch and run the simulation again. Now, the calculated current values should match the simulated ones pretty well.\\ Replace the diode in your simulation with an additional ideal switch and run the simulation again. Now, the calculated current values should match the simulated ones pretty well.\\
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 Datasheet: {{ :professoren_webseiten:rebholz:irf320.pdf |}} Datasheet: {{ :professoren_webseiten:rebholz:irf320.pdf |}}
  
-<WRAP center round todo 60%>+<WRAP center round todo 80%>
 **Task 3a)** **Task 3a)**
 Replace the ideal switches with the MOSFET model. Be sure to set the correct gate-source voltages.\\ Replace the ideal switches with the MOSFET model. Be sure to set the correct gate-source voltages.\\
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 Datasheet: {{ :professoren_webseiten:rebholz:infineon-irs2890ds-ds-v01_00-en.pdf |}} Datasheet: {{ :professoren_webseiten:rebholz:infineon-irs2890ds-ds-v01_00-en.pdf |}}
  
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 **Task 4a)** **Task 4a)**
 Add the driver circuit to your simulation and check the functionality. The general behavior should be the same as before! The simulation time now might significantly increases depending on how fast your computer is. Use the datasheed to complete the circuit.\\ Add the driver circuit to your simulation and check the functionality. The general behavior should be the same as before! The simulation time now might significantly increases depending on how fast your computer is. Use the datasheed to complete the circuit.\\
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   * All PCB traces that carry a high current must be included in the overall consideration. The following values can be assumed as a rule of thumb. Inductance 1µH/m for supply lines or 10nH/cm for conductor tracks.The resistance can be estimated as 0,5mOhm/cm for a 35µm track with 1cm width.   * All PCB traces that carry a high current must be included in the overall consideration. The following values can be assumed as a rule of thumb. Inductance 1µH/m for supply lines or 10nH/cm for conductor tracks.The resistance can be estimated as 0,5mOhm/cm for a 35µm track with 1cm width.
  
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 **Task 5a)** **Task 5a)**
 Add parasitic elements to the inductor, capacitor and pcb traces. Estimate a trace length to connect the MOSFET leads of about 1cm.\\ Add parasitic elements to the inductor, capacitor and pcb traces. Estimate a trace length to connect the MOSFET leads of about 1cm.\\
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 When we think of reactive currents or reactive power, we usually think of AC voltage systems but not of a step-down converter. But let's imagine the following scenario: The load resistor increases, or the load is lost— for example, because you turned it off or due to a broken connection. The DC-DC converter still attempts to regulate the output voltage to 5V with a constant duty cycle. In the half-bridge configuration, the high-side MOSFET will charge the output capacitor, while the low-side MOSFET discharges the capacitor within the same cycle. This creates a circulating current between the output capacitor and the power supply. You can easily demonstrate this behavior with a simulation. However, in the lab, it might be dangerous. Why? During the discharge of the capacitor, the circuit behaves like a boost converter. If the input voltage source cannot handle negative currents, it might get damaged. In many cases, however, the reactive current generates losses, and the bulk capacitor at the input of the buck converter can absorb the reverse current. When we think of reactive currents or reactive power, we usually think of AC voltage systems but not of a step-down converter. But let's imagine the following scenario: The load resistor increases, or the load is lost— for example, because you turned it off or due to a broken connection. The DC-DC converter still attempts to regulate the output voltage to 5V with a constant duty cycle. In the half-bridge configuration, the high-side MOSFET will charge the output capacitor, while the low-side MOSFET discharges the capacitor within the same cycle. This creates a circulating current between the output capacitor and the power supply. You can easily demonstrate this behavior with a simulation. However, in the lab, it might be dangerous. Why? During the discharge of the capacitor, the circuit behaves like a boost converter. If the input voltage source cannot handle negative currents, it might get damaged. In many cases, however, the reactive current generates losses, and the bulk capacitor at the input of the buck converter can absorb the reverse current.
  
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 **Task 6a)** **Task 6a)**
 Run the simulation with verly light load respectively a very high ohmic load resistor e.g. 100kOhms. Observe the capacitor current and the current through the MOSFETs. What is bad about this mode of operation? \\ Run the simulation with verly light load respectively a very high ohmic load resistor e.g. 100kOhms. Observe the capacitor current and the current through the MOSFETs. What is bad about this mode of operation? \\
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 Download: {{ :professoren_webseiten:rebholz:schematic_diy_power_pcb.pdf |}} Download: {{ :professoren_webseiten:rebholz:schematic_diy_power_pcb.pdf |}}
  
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 **Task 7** **Task 7**
 Do you know the function of each component on the circuit board? If not, consider the function of the individual circuit parts together with the data sheet. \\ Do you know the function of each component on the circuit board? If not, consider the function of the individual circuit parts together with the data sheet. \\
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   * Capacitor: 860010581025    * Capacitor: 860010581025 
  
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 **Task 8** **Task 8**
 Complete the following tables using the data sheets. What do you notice in particular? \\ Complete the following tables using the data sheets. What do you notice in particular? \\
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 The power PCB is controlled with the help of a Simulink experiment. The microcontroller exchanges data cyclically with the PC via the serial interface.\\ The power PCB is controlled with the help of a Simulink experiment. The microcontroller exchanges data cyclically with the PC via the serial interface.\\
 +Dowload the lastes Simulink experiment to control the DIY Power PCB: {{ :professoren_webseiten:rebholz:vorlage_course_a_basis_v01_2021b.zip |Simulink Version 2021b}}
  
 +{{ :professoren_webseiten:rebholz:control_pannel_simulink.png?direct&1000 |}}
  
-- Connection, COM- Port, Start, Stop+If you can not establish a connection to the board double check the COM port settings. 
 +For safety reasons (PC protection) please always us an isolation device: [[https://wiki.ei.htwg-konstanz.de/professoren_webseiten/rebholz/diypowerpcb#isolation|Link]]
  
 ===== Before you start ===== ===== Before you start =====
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 For every electronic circuit, there are two main golden rules: For every electronic circuit, there are two main golden rules:
  
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   * Voltage sources, especially capacitors, must not be short-circuited.\\   * Voltage sources, especially capacitors, must not be short-circuited.\\
   * Current flows must not be interrupted, especially if they are routed through inductors.    * Current flows must not be interrupted, especially if they are routed through inductors. 
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 Safety warnings: Safety warnings:
  
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   * The components and the load resistor can reach temperatures > 100°C, posing a risk of burns.   * The components and the load resistor can reach temperatures > 100°C, posing a risk of burns.
   * If the polarity of the electrolytic capacitors is incorrect, they can explode or outgas. If you are not sure, please ask!   * If the polarity of the electrolytic capacitors is incorrect, they can explode or outgas. If you are not sure, please ask!
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 <wrap hi>**Therefore follow the procedure for each test setup:**</wrap> <wrap hi>**Therefore follow the procedure for each test setup:**</wrap>
  
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   * The power supply has to be  switched off each time a change is made in the setup and during probe connections.   * The power supply has to be  switched off each time a change is made in the setup and during probe connections.
   * Before you start a measurement, consider the points to be measured in the schematic. Use a printed copy of the schematic!\\   * Before you start a measurement, consider the points to be measured in the schematic. Use a printed copy of the schematic!\\
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 The most important task of the microcontroller is to generate the PWM signals. Thus, we first start and check the signals. The most important task of the microcontroller is to generate the PWM signals. Thus, we first start and check the signals.
  
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 **Task 9a** **Task 9a**
 Use two oscilloscope probes to visualize the output signals for the high-side and low-side MOSFET. \\ Use two oscilloscope probes to visualize the output signals for the high-side and low-side MOSFET. \\
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-<WRAP center round todo 60%>+<WRAP center round todo 80%>
 **Task 10a** **Task 10a**
 Measure how long it takes for the driver to start doing anything when it receives a high signal and turns on the high-side MOSFET\\ Measure how long it takes for the driver to start doing anything when it receives a high signal and turns on the high-side MOSFET\\
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 Duty: Ramp up to 50% \\ Duty: Ramp up to 50% \\
  
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 **Task 11a** **Task 11a**
 Connect the load resistor to the PCB so that the half-bridge U is loaded. Measure the output current using a current clamp. Does the measured current waveform match your expectations? \\ Connect the load resistor to the PCB so that the half-bridge U is loaded. Measure the output current using a current clamp. Does the measured current waveform match your expectations? \\
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 Duty: Ramp up to 50% \\ Duty: Ramp up to 50% \\
  
-<WRAP center round todo 60%>+<WRAP center round todo 80%>
 **Task 12** **Task 12**
 Set the starting conditions and observe the inductor current. Set the starting conditions and observe the inductor current.
Zeile 328: Zeile 331:
  
  
-<WRAP center round todo 60%>+<WRAP center round todo 80%>
 **Task 13a** **Task 13a**
 To get rid of the noise increase the frequency to 20kHz and observe the current again. \\ To get rid of the noise increase the frequency to 20kHz and observe the current again. \\
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 === Continuous / Discontinuous and Critical Current Mode === === Continuous / Discontinuous and Critical Current Mode ===
  
-1. Reduce the load current until critical current Mode +The transition from the point at which current flows back out of the capacitor occurs from the so-called critical current mode. Here, the lower reversal point of the current is set on the zero line. If the load becomes even smaller, the current in the capacitor becomes negative and flows back to the source as reactive current.
-2. Reduce until discontinuous current mode and observe the output voltage+
  
 +<WRAP center round todo 80%>
 +**Task 16a**
 +alculate the critical load resistance at which critical conduction mode (CRM) occurs.\\
 +**Task 16b**
 +Increase the load resistance until you can measure the CRM state. Check what happens if you increase the resistance further.
 +</WRAP>
  
 +Reactive currents are not always bad. They can be used to eliminate the reverse recovery of the body diode. If we exactly meet the CRM mode, there is even no switching loss because we turn on the low-side MOSFET at zero current. If it is possible to generate a small amount of negative current, we even have no switching losses at the high-side MOSFET, as it operates in zero-voltage switching. This type of power electronic circuit is called a resonant converter, and it is now commonly used in many applications. The theory behind resonant switching converters is part of the Master's course Power Electronic Systems." \\
 +
 +The reduction of the reverse recovery effect can be seen by measuring the current through the MOSFETs with a Rogowski coil. If you don't have one, it is also possible to look at the drain-source voltage of the low-side MOSFET. \\
 +
 +{{ :professoren_webseiten:rebholz:reverse_recovery1.png?direct&600 |}}
 +
 +
 +<WRAP center round todo 80%>
 +**Task 17a**
 +Consider and discuss with your neighbor why in this state the high side mosfet can be switched on at a voltage of less than 1V. This state is then referred to as ZVS zero voltage switching. \\
 +</WRAP>
  
 +<color #ffc90e>**Congratulations. Now you are ready and prepared for the exam!**</color>
  
  
professoren_webseiten/rebholz/course_a_power_electronics.1738853425.txt.gz · Zuletzt geändert: 2025/02/06 14:50 von hrebholz
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