The drive has a switching logic which includes a means for producing a correction signal in response to the switching-in of the motor. This correction signal serves to compensate for the kinetic energy of the moving parts of the drive by moving up the lower limit valve of an error signal (derived from the difference between the actual value of the adjusting element position and a fixed value) so as to permit more accurate switching-out and stopping of the motor. Other features are added to prevent overloading, premature switching-out of the motor during starting, short circuits and the like.
In a motor speed controller for controlling an AC motor to be driven at a variable speed, a signal proportional to a load torque and a signal proportional to an output torque of the AC motor are found by current detecting means for detecting the primary current of the AC motor, and integrated over the speed changing period, and the integrated values are divided by the values corresponding to the amounts of speed change during the speed changing period so that the moment of inertia can be computed. In addition, there is provided means for changing the rate of output frequency change caused by the output frequency command into a value according to the calculated moment of inertia. Moreover, there is provided a circuit for detecting a sudden change of the calculated moment of inertia, so that when a sudden change occurs, an abnormality signal is generated.
Heavily relied upon network devices require backup power systems. To efficiently allocate power, a highly programmable backup power system is desired. The present invention discloses a redundant power supply unit that provides backup power to network devices. The redundant power supply unit will supply power to the network devices in the case that their local internal power supplies fail. Furthermore, if there is a power outage from the utility company, the redundant power supply will supply power to the network devices from a internal battery pack. When the internal battery pack is engaged, the redundant power supply uses programmed control logic that controls how the power from internal battery pack will be allocated. Specifically, since the power from the batteries is limited, it can be used to power some network devices for a certain amount of time and other network devices for a longer amount of time. Furthermore, the power from the batteries can be allocated depending on the voltage level of the battery thus, when the battery voltage drops below a certain threshold the power supply may disconnect power to some units and maintain power to others.
