TDFS

MikeVBW
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Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

TDFS Loop Stability for Buck DC to DC Converter - Switching

瀧澤登
Designer123146

瀧澤登

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7 years 7 months

365

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Description

This design demonstrates the use of the TDFS (Time Domain Frequency Sweep) simulation method, to measure the open-loop frequency response of an operating closed-loop system containing switching elements.The stability of the "Buck DC to DC Converter - Switching" design is assessed. This is a switching circuit, it does not use a state-average model for the modulator, so the standard AC Analysis method cannot be used. Rather, the frequency response is generated from time-domain simulation results. The TDFS approach can also be used for systems that contain sampling or digital control aspects.This particular example is directly comparable to the design titled "TDFS Loop Stability for Buck DC to DC Converter - State Average". In that design, both the TDFS and AC Analysis methods are used to measure the open loop transfer function of an equivalent non-switching circuit.Note that the approach used to characterize the loop stability, by injecting a small sinusoidal stimulus signal in series with the loop and then measuring the complex ratio of the ground referenced return signal to the injected signal, is described in:D. Venable, “Testing Power Sources for Stability”, Venable technical paper #1, Venable Industries

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TDFS Input Impedance of Step-Down (Buck) DC to DC Converter - Switching My

Galina
Designer21

Galina

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11 years 1 month

104

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Description

This example demonstrates the use of the TDFS method (Time Domain Frequency Sweep) to measure the input impedance of a switching DC/DC power converter. The converter circuit is identical to the design shown in the companion example: “Step-Down (Buck) DC to DC Converter - Switching”.In this example, the TDFS impedance measurement model applies a 12V DC bias to the line input, in addition to a sinusoidal stimulus with 3V peak amplitude, and a frequency range from 3 kHz to 30 kHz. The input current is measured and the impedance vs. frequency is computed. The results show that the impedance magnitude (blue waveform) is approximately 5.0 Ohms at low frequency, This is approximately the reflected value of the 1 Ohm load resistor, multiplied by the effective DC/DC conversion ratio squared: 1 Ohm * (12.0/5.0)**2 = 5.76 OhmThe phase measurement (red waveform) shows -175 degrees at low frequency, indicating that this is effectively a "negative resistance". That is, the input current decreases when the line voltage increases. This behavior can be observed directly in the time domain waveforms, where the line voltage (brown waveform) and the input current (green waveform) are almost completely out of phase at 3 kHz. This negative impedance, or constant power load characteristic, can be destabilizing in power distribution systems. This will be demonstrated in a related design, and in Part 3 of the TDFS Blog Series, coming soon!

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Laser Temperature Regulator TDFS

Mike Donnelly
Designer19

Mike Donnelly

Member for

11 years 1 month

1,706

designs

10

groups

Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

TDFS Input Impedance of Step-Down (Buck) DC to DC Converter - Switching

Mike Donnelly
Designer19

Mike Donnelly

Member for

11 years 1 month

1,706

designs

10

groups

Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

Description

This example demonstrates the use of the TDFS method (Time Domain Frequency Sweep) to measure the input impedance of a switching DC/DC power converter. The converter circuit is identical to the design shown in the companion example: “Step-Down (Buck) DC to DC Converter - Switching”.In this example, the TDFS impedance measurement model applies a 12V DC bias to the line input, in addition to a sinusoidal stimulus with 3V peak amplitude, and a frequency range from 3 kHz to 30 kHz. The input current is measured and the impedance vs. frequency is computed. The results show that the impedance magnitude (blue waveform) is approximately 5.0 Ohms at low frequency, This is approximately the reflected value of the 1 Ohm load resistor, multiplied by the effective DC/DC conversion ratio squared: 1 Ohm * (12.0/5.0)**2 = 5.76 OhmThe phase measurement (red waveform) shows -175 degrees at low frequency, indicating that this is effectively a "negative resistance". That is, the input current decreases when the line voltage increases. This behavior can be observed directly in the time domain waveforms, where the line voltage (brown waveform) and the input current (green waveform) are almost completely out of phase at 3 kHz. This negative impedance, or constant power load characteristic, can be destabilizing in power distribution systems. This will be demonstrated in a related design, and in Part 3 of the TDFS Blog Series, coming soon!

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TDFS Open-Loop Frequency Response for PMSM/SVM Motion Control System

Mike Donnelly
Designer19

Mike Donnelly

Member for

11 years 1 month

1,706

designs

10

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Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

Description

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Switched-Capacitor Filter Frequency Response using TDFS

DGB
Designer12

DGB

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11 years 1 month

116

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Description

This design shows the use of the TDFS (Time Domain Frequency Sweep) method to measure the frequency response of two low-pass filters. One is just a simple RC filter circuit with 1 kHz cut-off frequency. The other is an equivalent filter using a switched-capacitor implementation.Both small-signal AC (frequency domain) and TDFS (time-domain) analyses are run, and both give the same results for the RC filter. However, because of the switching aspect of the switched-capacitor filter, the results of the AC analysis are meaningless for that circuit. However, the TDFS approach is valid for that filter also, as well as for any other circuit or system containing switching, sampled data or digital content.For reference, note in the schematic that the R-C filter is connected to channel 1 of the TDFS instrument, and the switched capacitor filter is connected to channel 2, hence the v1 and v2 distinction in the name of the results for the magnitude (dbMag) and phase. Both are measured relative to the stimulus input vosc, the oscillator output.

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TDFS Loop Stability for Buck DC to DC Converter - State Average

DGB
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DGB

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11 years 1 month

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Description

This design uses both TDFS and standard AC Analysis methods to assess the stability of a closed-loop system. The design is the "Buck DC to DC Converter", using a state-average model for the modulator function. The use of state-average models supports AC Analysis, but TDFS (Time Domain Frequency Sweep) is also used to show the equivalency of the methods. Note that the TDFS approach can be used for systems that do not support AC Analysis, such as switching circuits or systems that contain sampling or digital control aspects. This particular example is directly comparable to the design "TDFS Loop Stability for Buck DC to DC Converter - Switching". In that design, the TDFS method is used to measure the open loop transfer function of an operational switching circuit.Note that the approach used to characterize the loop stability, by injecting a small sinusoidal stimulus signal in series with the loop and then measuring the complex ratio of the ground referenced return signal to the injected signal, is described in:D. Venable, “Testing Power Sources for Stability”, Venable technical paper #1, Venable Industries

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TDFS Loop Stability for Automotive Buck DC to DC - Continuous

Mike Donnelly
Designer19

Mike Donnelly

Member for

11 years 1 month

1,706

designs

10

groups

Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

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