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TDFS Impedance Stability of Transmission Line Fed LED Driver - Switching

Mike Donnelly
Designer19

Member for

9 years 4 months

1,345

designs

10

groups

Original member of the PartQuest Explore development team. Modeling and Applications Specialist

Description

This example demonstrates the use of the TDFS method (Time Domain Frequency Sweep) to measure impedance stability ratio. The system is a switching DC/DC step-down power converter used for LED lighting, supplied by a battery through a long power cable.The TDFS impedance stability measurement model applies a 0.2A sinusoidal stimulus current at the point where the cable connects to the converter. The voltage at that point, as well as the stimulus current splits (toward the source and the load) are measured, and the associated source and load impedances vs. frequency are computed.The ratio of the source to load impedance is the impedance stability ratio (Tm). Similar to the open-loop frequency response requirement for closed-loop stability, Tm must not have magnitude = 1.0 at phase = 180 degrees, at any frequency.For this system, with a cable length of 400 meters and 8 AWG wire, the results show that the impedance ratio magnitude (green waveform) reaches unity (0 dB) at close to 2 kHz, where the phase (light blue waveform) is approximately 165 degress. This implies a "phase margin" of only 15 degrees, For a longer cable, this margin is further reduced. As shown in the companion example, "Transmission Line Fed LED Driver - Switching", for the cable length = 800 meters the system is unstable.This instability is the result of the "source" impedance (which includes the cable) variation over frequency, interacting with the varying load impedance. Note that at low frequency, the load effectively has a negative impedance, due to the constant power nature of the DC to DC converter.

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Step-Down (Buck) DC to DC Converter - Switching

Mike Donnelly
Designer19

Mike Donnelly

Member for

9 years 4 months

1,345

designs

10

groups

Original member of the PartQuest Explore development team. Modeling and Applications Specialist

Description

This design is a detailed circuit implementation of the more abstract "state-average" buck converter model shown in the companion design example: “Step-Down (Buck) DC to DC Converter - Continuous”. This example includes the low-pass voltage sense circuit, an op-amp implementation of the difference amplifier and the lead-lag compensator, as well as PWM switching control of a power MOSFET. Simulation results for the line and load transients are very similar to the results from the continuous model.

This design uses a number of "datasheet characterized" components, including the power MOSFET (MCH6337), freewheel diode (NRVTS560EMFS) and op-amps (MC33272A), as well as the soft-saturation inductor (XAL6060-223) and capacitor (PEG127KA3110Q) of the power stage . The parameter values of these devices were entered directly from the datasheet for the corresponding part, including the "Maximum Ratings" information.

While the simulation time for this switching circuit is significantly longer than for the abstract model, more detailed information about the circuit’s signals and components is available. This includes the component stress levels, which are monitored within all the "datasheet" models.

The companion design, "TDFS Loop Stability for Step-Down (Buck) DC to DC Converter - Switching", demonstrates a method to directly assess the open-loop frequency response, and hence the stability margin, of this converter. The TDFS (Time Domain Frequency Sweep) method circumvents the need for state-average models of the switching elements.

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Step-Down (Buck) DC to DC Converter - Switching

twocircle12
Designer244003

twocircle12

Member for

7 months 3 weeks

4

designs

groups

I'm a member of the PartQuest Explore community.

Description

This design is a detailed circuit implementation of the more abstract "state-average" buck converter model shown in the companion design example: “Step-Down (Buck) DC to DC Converter - Continuous”. This example includes the low-pass voltage sense circuit, an op-amp implementation of the difference amplifier and the lead-lag compensator, as well as PWM switching control of a power MOSFET. Simulation results for the line and load transients are very similar to the results from the continuous model.

This design uses a number of "datasheet characterized" components, including the power MOSFET (MCH6337), freewheel diode (NRVTS560EMFS) and op-amps (MC33272A), as well as the soft-saturation inductor (XAL6060-223) and capacitor (PEG127KA3110Q) of the power stage . The parameter values of these devices were entered directly from the datasheet for the corresponding part, including the "Maximum Ratings" information.

While the simulation time for this switching circuit is significantly longer than for the abstract model, more detailed information about the circuit’s signals and components is available. This includes the component stress levels, which are monitored within all the "datasheet" models.

The companion design, "TDFS Loop Stability for Step-Down (Buck) DC to DC Converter - Switching", demonstrates a method to directly assess the open-loop frequency response, and hence the stability margin, of this converter. The TDFS (Time Domain Frequency Sweep) method circumvents the need for state-average models of the switching elements.

What's this?

You must be a registered user to add a comment.

Step-Down (Buck) DC to DC Converter - Switching

twocircle12
Designer244003

twocircle12

Member for

7 months 3 weeks

4

designs

groups

I'm a member of the PartQuest Explore community.

Description

This design is a detailed circuit implementation of the more abstract "state-average" buck converter model shown in the companion design example: “Step-Down (Buck) DC to DC Converter - Continuous”. This example includes the low-pass voltage sense circuit, an op-amp implementation of the difference amplifier and the lead-lag compensator, as well as PWM switching control of a power MOSFET. Simulation results for the line and load transients are very similar to the results from the continuous model.

This design uses a number of "datasheet characterized" components, including the power MOSFET (MCH6337), freewheel diode (NRVTS560EMFS) and op-amps (MC33272A), as well as the soft-saturation inductor (XAL6060-223) and capacitor (PEG127KA3110Q) of the power stage . The parameter values of these devices were entered directly from the datasheet for the corresponding part, including the "Maximum Ratings" information.

While the simulation time for this switching circuit is significantly longer than for the abstract model, more detailed information about the circuit’s signals and components is available. This includes the component stress levels, which are monitored within all the "datasheet" models.

The companion design, "TDFS Loop Stability for Step-Down (Buck) DC to DC Converter - Switching", demonstrates a method to directly assess the open-loop frequency response, and hence the stability margin, of this converter. The TDFS (Time Domain Frequency Sweep) method circumvents the need for state-average models of the switching elements.

What's this?

You must be a registered user to add a comment.

Step-Down (Buck) DC to DC Converter - Switching

twocircle12
Designer244003

twocircle12

Member for

7 months 3 weeks

4

designs

groups

I'm a member of the PartQuest Explore community.

Description

This design is a detailed circuit implementation of the more abstract "state-average" buck converter model shown in the companion design example: “Step-Down (Buck) DC to DC Converter - Continuous”. This example includes the low-pass voltage sense circuit, an op-amp implementation of the difference amplifier and the lead-lag compensator, as well as PWM switching control of a power MOSFET. Simulation results for the line and load transients are very similar to the results from the continuous model.

This design uses a number of "datasheet characterized" components, including the power MOSFET (MCH6337), freewheel diode (NRVTS560EMFS) and op-amps (MC33272A), as well as the soft-saturation inductor (XAL6060-223) and capacitor (PEG127KA3110Q) of the power stage . The parameter values of these devices were entered directly from the datasheet for the corresponding part, including the "Maximum Ratings" information.

While the simulation time for this switching circuit is significantly longer than for the abstract model, more detailed information about the circuit’s signals and components is available. This includes the component stress levels, which are monitored within all the "datasheet" models.

The companion design, "TDFS Loop Stability for Step-Down (Buck) DC to DC Converter - Switching", demonstrates a method to directly assess the open-loop frequency response, and hence the stability margin, of this converter. The TDFS (Time Domain Frequency Sweep) method circumvents the need for state-average models of the switching elements.

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C-007_DCDC_BCK_2PH_DI_10kW

bernardjames.tan
Designer236690

bernardjames.tan

Member for

2 years 4 months

386

designs

groups

Hi, good day! I hope you're having a great day!

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C-006_DCDC_BCK_DI_5kW

bernardjames.tan
Designer236690

bernardjames.tan

Member for

2 years 4 months

386

designs

groups

Hi, good day! I hope you're having a great day!

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Copy of TDFS Impedance Stability of Transmission Line Fed LED Driver - Switching - on Sun, 03/21/2021 - 11:01

077zz
Designer238846

077zz

Member for

2 years

designs

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Add a bio to your profile to share information about yourself with other SystemVision users.

Description

This example demonstrates the use of the TDFS method (Time Domain Frequency Sweep) to measure impedance stability ratio. The system is a switching DC/DC step-down power converter used for LED lighting, supplied by a battery through a long power cable.

The TDFS impedance stability measurement model applies a 0.2A sinusoidal stimulus current at the point where the cable connects to the converter. The voltage at that point, as well as the stimulus current splits (toward the source and the load) are measured, and the associated source and load impedances vs. frequency are computed.

The ratio of the source to load impedance is the impedance stability ratio (Tm). Similar to the open-loop frequency response requirement for closed-loop stability, Tm must not have magnitude = 1.0 at phase = 180 degrees, at any frequency.

For this system, with a cable length of 400 meters and 8 AWG wire, the results show that the impedance ratio magnitude (green waveform) reaches unity (0 dB) at close to 2 kHz, where the phase (light blue waveform) is approximately 165 degress. This implies a "phase margin" of only 15 degrees, For a longer cable, this margin is further reduced. As shown in the companion example, "Transmission Line Fed LED Driver - Switching", for the cable length = 800 meters the system is unstable.

This instability is the result of the "source" impedance (which includes the cable) variation over frequency, interacting with the varying load impedance. Note that at low frequency, the load effectively has a negative impedance, due to the constant power nature of the DC to DC converter.

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Copy of C-6. Buck Converter Vo=250V Io=20A

Shin_1
Designer224531

Shin_1

Member for

3 years 5 months

107

designs