Unterschiede

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--- professoren_webseiten:rebholz:course_a_power_electronics [2025/05/05 15:54] – [Simulation] hrebholz
+++ professoren_webseiten:rebholz:course_a_power_electronics [2025/06/27 07:17] (aktuell) – [PWM-Signals] hrebholz
@@ Zeile 84: / Zeile 84: @@
 {{ :professoren_webseiten:rebholz:irs2890.png?200 |}}
 Gate drivers are often equipped with additional features. Our driver can detect overcurrents and if necessary, will turn off all MOSFETs for safety. Since overcurrents in a simulation tool will not damage your PC or notebook, you can ignore this feature in the simulation. Pull up the RFE output and connect ITRIP to ground. \\
-Datasheet: {{ :professoren_webseiten:rebholz:infineon-irs2890ds-ds-v01_00-en.pdf |}}
+Datasheet: {{ :professoren_webseiten:rebholz:infineon-irs2890ds-ds-v01_00-en.pdf |}} \\
+Download {{ :professoren_webseiten:rebholz:irs2890ds.zip |}}  the model file for LTSpice.
 <WRAP center round todo 80%>
@@ Zeile 248: / Zeile 249: @@
 <WRAP center round todo 80%>
 **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 of the µC for the high-side and low-side MOSFET. \\
 **Task 9b**
 Measure the minimum and maximum of the adjustable deadtime.\\
@@ Zeile 275: / Zeile 276: @@
 **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\\
+Attention: To measure the gate source voltage of the high-side MOSFET at differential voltage probe is needed. Do you now why? \\
 **Task 10b**
 How long does it take to bring the gate-source voltage to the desired value?\\
 **Task 10c**
-Determine the same values for turning the MOSFET off and for the low-side MOSFET.\\
+Determine the same values for turning the MOSFET off and for the low-side MOSFET. Do you also need a diffential probe? \\
 **Task 10d**
 Now set the frequency to 30 kHz. Does this make sense? What is your conclusion for the minimal duty cycle?
@@ Zeile 378: / Zeile 380: @@
 Please use the following parameters: \\
 Switching Frequency: 20kHz\\
-Inductor: 100µF \\
+Inductor: 100µH \\
 Capacitor: 4700µF \\
 Load: 25W, 5V, 5A \\
@@ Zeile 468: / Zeile 470: @@
 **Task 18b** \\
 Observe the output currents and compare the currents for the different control schemes.\\
-There are a total of three significant reasons to choose T/2 offset clocking. What are they?\\
+There are a total of three significant reasons to choose T/2 offset clocking. What are they? \\
+Write a few centences about:\\
 . Current Ripple: \\
-. Zero voltage output:
+. Zero voltage output: \\
 . Heat distribution:
@@ Zeile 478: / Zeile 481: @@
 The output voltage becomes positive for PWM duty cycles greater than 0.5, and correspondingly negative for values below 0.5. In the case of simultaneous clocking on both sides, the following can be observed: at D = 0.5, the average output voltage is 0 V. As we know, in power electronics, we are almost always concerned with average values. This means that even though the average is 0 V, the RMS value can still be greater than zero. Since we are switching at several kHz, the motor naturally cannot respond quickly enough to the rapid changes in direction. However, if we were to switch at a very low frequency, we would see the motor physically oscillate back and forth in real time. If the effective current is greater than 0 A, this means that power is being converted and continuous losses are introduced into the motor. This is, of course, not efficient and certainly not desirable.\\
-You have probably already discovered yourself that at D = 0.5, the output current becomes exactly zero, without any circulating reactive power.
+You have probably already discovered yourself that at D = 0.5, the output current becomes exactly zero, without any circulating reactive power if we use the PWMs with T/2 offset.
+==== Experiment ====
+Lets try the full bridge with our DIY board. As a first step, we will look at the signals without the motor connected. Once we are sure that everything is correctly wired, we can operate the motor.\\
+**Hardware requirements**\\
+Make sure, that the driver circuit of the second half bridge V is assembled correctly. Check the PWM signals with the oscilloscope.\\
+**Software requirements**\\
+In order for current to flow through the motor, it is essential to activate the diagonal MOSFET pairs of the full bridge simultaneously—i.e., Q1 together with Q4 or Q2 together with Q3. Control laws typically refer to the high-side switches rather than the low-side ones. To ensure that Q4 is activated in sync with Q1 (or Q3 with Q2), we can apply a simple trick: operate bridge leg V with an inverted control signal relative to bridge leg U. This avoids the need for a 180° phase-shifted triangular carrier in PWM generation. In this case, the duty cycle for leg V becomes:
+Duty_V = 1 − Duty_U
+This inversion effectively ensures complementary switching of the corresponding low-side Mosfet, simplifying the implementation of the control scheme.\\
+Within Simulink just us a simple sum block:
+{{ :professoren_webseiten:rebholz:simulink_t-2.png?direct&400 |}}
+Additionally, using the microcontroller in combination with Simulink, we have the capability to implement a phase shift between PWM signals. For our purposes, the two relevant configurations are 0° and 180° phase shift. As described earlier, the mathematical trick used to compute the duty cycle for phase V by inverting the duty of phase U automatically results in a T/2 (i.e., 180°) phase-shifted switching pattern between the two bridge legs.
+If we wish to revert this automatic phase shift, we can do so by using a slider or parameter in Simulink to apply an additional 180° phase shift, effectively canceling out the original offset and returning to in-phase (0°) operation.
+{{ :professoren_webseiten:rebholz:simulink_phase-shift.png?direct&600 |}}
+<WRAP center round todo 80%>
+**Task 19a**
+Setup Simulink for full bridge operation. Measure the PWM Signals for Q1 and Q4 and check if you can apply synchronous and phase shifted PWM signals. Please do this with no load connected and without power supply.\\
+**Task 19b**\\
+Set the duty cycle to D = 0.5. Connect the load (DC motor) and the power supply. Consider how you can verify that your full bridge is operating correctly.
+</WRAP>