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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

TDFS Impedance Stability of Transmission Line Fed LED Driver - Switching

Designer19

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11 years 4 months

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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

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.

Three Phase Power System

Designer19

Member for

11 years 4 months

designs

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

Automotive Electrical Power Distribution System

Designer19

Member for

11 years 4 months

designs

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 automotive electrical power distribution system example includes multiple vehicle sub-systems and components. It supports sizing analysis for wires and fuses, under both static and transient loading conditions. This includes multi-discipline (i.e. electro-thermal-mechanical) dynamic operations such as incandescent lamp in-rush current and motor start-up conditions. The example also demonstrates the special characteristics and design considerations needed for constant power loads, such as switching converters used in LED Driver circuits.

This system also uses a special “direction sensitive” current monitor model that can help identify sneak circuits (i.e. unintended current paths), such as the one found in the “door-ajar”, ignition switch, chime and dome lamp interconnect circuit. Challenge: See if you can find it before running the simulation!

After you run the simulation, a "Component Messages" window will pop up and show several problems with the system. These include a "reverse current detected" (i.e. current flow in the opposite direction from the expected) in the wire that carries current to the dome lamp to indicate a door is ajar. Current reversals are often due to a "sneak circuit" in design, which can lead to undesired function or behavior of the system. In this case, the reverse current is showing that if the driver puts the key in the ignition and turns on the dome lamp to read a map, the warning chime will sounds even though there are no doors ajar!

The other message indicates that the fuse supplying the flasher circuit has blown, shortly after the hazard flasher is turned on. Clearly this fuse is undersized to supply all 4 flasher lamps together, but operates fine with when just 2 are operated for normal turn signaling. You can try other operational conditions for this system to test for proper fuse sizing. For example, try changing the LED constant power pulse_value to 50W instead of 20W. You can also change the fan inertia to 200u Kg*meter^2, up from 100u. To fix the problem caused by the increase motor inertia (and correspondingly longer time transitioning for stall to normal operating load current), try increasing the fan fuse I^2*T value from 5 to 36, to represent the performance of a slower-blowing fuse.