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.