Step-Down | PartQuest™ Explore

Este es un ejemplo complementario del diseño: "Estabilidad de impedancia TDFS del controlador LED alimentado por línea de transmisión - Conmutación". En esta versión, se agrega un interruptor para encender dos de los LED después de 2 ms, para inyectar una carga transitoria en el sistema. Este transitorio expondrá la gravedad de la respuesta de llamada amortiguada en la entrada del convertidor o la inestabilidad del sistema si la relación fuente / impedancia de carga es inadecuada.

La configuración inicial para este diseño utiliza una longitud de cable de 400 metros con 8 AWG = 2.1 mOhm / metro conductores y un condensador de entrada del convertidor = 22uF. Esto es consistente con el diseño complementario. Puede intentar usar un cable de mayor longitud (por ejemplo, 800 metros, 5 AWG = 1 mOhm / metro) haciendo una copia de este diseño y volviendo a ejecutar la simulación. Verá que el circuito se vuelve inestable en esa longitud más larga. También puede probar valores más grandes de capacitancia de entrada para mitigar el problema de inestabilidad.

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Buck Converter PWM Modulator Line Transient Demo

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TDFS Loop Stability for Step-Down DC to DC (Buck) Converter - Switching

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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 TDFS (Time Domain Frequency Sweep) Loop Stability Instrument Model. It is used to compute the open-loop transfer function of an operating (closed-loop) switching power converter. There is no need for state-average or continuous equivalent models for the modulator section of the design, as normally needed for frequency-domain (or "AC") analysis. Rather, the actual circuit component models can be used directly, because the open-loop transfer function is computed from time-domain simulation results.In this case, the converter is operating at 200kHz switching frequency, and is converting the 12V DC input to a regulated 5V output, while supplying a 5A current to the 1 Ohm load resistor. The TDFS measurement instrument indicates that the open-loop gain crossover frequency is at 26 kHz, and the phase margin is just under 60 degrees. This verifies that the opamp-based lead-lag compensator is providing adequate stability margin under these operating conditions.Note that the TDFS instrument model characterizes the open loop transfer function by injecting a small sinusoidal stimulus signal in series with the loop, and then measures the complex ratio of the return signal to the injected signal, is described in:D. Venable, “Testing Power Sources for Stability”, Venable technical paper #1, Venable Industries.The companion example, "Step-Down (Buck) DC to DC Converter - Switching", shows the line and load transient response of this converter design. Another companion example, "Step-Down (Buck) DC to DC Converter - Continuous", uses a state-average model of the switching (or modulator) section of the converter, so it supports traditional "AC" or frequency-domain analysis.

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