Why ideal constant power loads are not the worst case condition from a control standpoint

This paper investigates the influence of control bandwidth on the stability of loads, which are interfaced through power electronic converters and are fed from a dc power source. When tightly regulated, these loads exhibit a constant power load (CPL) behavior. It is shown here that the ideal CPL assumption, prevalent in literature, may not represent the worst case in real-life applications. If the control bandwidth of the load is sufficiently high, the load behaves like a CPL, and the system stability margin decreases with the increase in output power. However, in a practical range, with a lower control bandwidth, the system stability margin is influenced critically by the converter's characteristic impedance, as well as its output power. Under these conditions, the minimum stability margin may occur at a low-power range.