CG-1280 Rev. N 09/13 - General Dynamics SATCOM Technologies

Overview2.4.2.1 AZ and EL Drive InvertersOne of the critical advantages of the 7200 ACS over many other systems is theuse of variable frequency drive inverters to control the speed of standard threephaseinduction motors for AZ and EL antenna motion. This approach has severaldistinct advantages over the commonly used and simplistic on/off contactor controlof motor power. First, inverters allow General Dynamics to offer two-speedcontrol in a standard configuration without the problems associated with specialdual-wound motors or clumsy clutching arrangements. Secondly, the invertersoffer precision motor control by ramping motor speeds up and down in a controlledmanner rather than simply switching full motor power on and off and having tocontend with inertial coasting of the motor rotor and the related axis overshoot. Inaddition to these two distinct advantages, the inverter drives offer superior motorprotection through sophisticated electronic motor overcurrent protection. Motorcurrent is continuously monitored and compared against allowable levels fordifferent conditions. Should the actual measured current exceed the allowablelevels, the inverter trips and the drive is disabled. The inverter then has thecapability to automatically reset and continue operation, provided the currentremains within allowable limits.2.4.2.2 Polarization Motor Control (POL and 4th Axis)A three-axis system uses a single-speed AC synchronous stepping motor for feedassembly rotation (POL). In the four-axis system a pair of single-speed ACsynchronous stepping motors are used for feed assembly rotation. Both POLmotors are controlled and powered from the 7150 drive cabinet. Drive power tothe POL motor(s) is switched, according to the required direction of rotation, byrelays located on the Relay PCB. A resistance-capacitance (RC) network in thedrive cabinet provides the proper phase relationship to each motor.2.4.2.3 Drive Cabinet Control LogicMotor drive commands and interlock functions in the drive cabinet are performedwith relay logic operating at +24 VDC, which is derived from a regulated powersupply. Commands can be received from the ACU, or PMCU, for motor speed anddirection. The Drive Reset is controlled from the Relay PC board and theEmergency Stop is located on the right side of the enclosure. The drive cabinetrelay logic then commands the axis drives accordingly. Likewise, limit switchesmounted on the structure activate relays in the drive cabinet upon engagement toform axis interlocks and provide the appropriate fault reporting to the ACU.2-19