Rockwell Automation SA500 AC Power Modules - Manual (Page 11)

Introduction 1-3
1.2 SA500 Drive Overview
An SA500 drive consists of a DC Bus Supply and a Power Module which supplies
three-phase AC power to an induction motor or a permanent magnet brushless motor.
The SA500 DC Bus Supply rectifies three-phase 230 VAC power to provide a constant
DC voltage for the Power Module. A three-phase bridge consisting of three SCRs and
three diodes controls the currents during charging of the DC bus capacitor. During
charging, the phase angle of the SCR firing is shifted as a function of time to control
the charging current.
The DC Bus Supply includes a braking circuit, consisting of a bi-polar transistor switch
and a resistor. A DC-to-DC converter within the Power Module senses the DC bus
voltage and switches the braking resistor across the DC bus if a preset threshold is
exceeded. If the capacity of the internal braking resistor is exceeded, the drive’s ability
to dissipate energy may be increased by using an external braking resistor. See
instruction manual S-3017 for more information.
Depending upon the power drawn by the individual Power Modules, the DC Bus
Supply can support up to six Power Modules, each powering one motor. If more than
six Power Modules need to be supplied by a common DC bus, if the capacity of the
DC bus is exceeded, or if the capacity of the braking circuit is exceeded, a
custom-designed DC bus supply may be used with the SA500 Power Modules. The
custom DC bus may be regenerative or non-regenerative. Energy storage capacitors
must be provided with the custom DC bus (or separately). See Appendix C for more
information.
The SA500 Power Module consists of the PMI Regulator (commonly referred to as the
PMI) and power circuitry to invert the DC bus voltage to three-phase 230 VAC for the
motor. The power bridge consists of six bipolar transistors (three dual-transistor
modules).
The PMI receives its operating system, all configuration data, and all commands
including the torque reference from a UDC module in the AutoMax rack via fiber-optic
cables. The PMI executes the torque control algorithm that controls the motor. The
control type is determined by the operating system contained in the PMI. There are
four types of control available: 1) vector, 2) brushless, 3) vector - speed loop
enhanced, and 4) brushless - speed loop enhanced. The operating system is selected
during UDC module configuration.
The UDC module executes the outer (major) control loops. The UDC task (task A or
task B, depending upon the fiber-optic port to which the Power Module is connected)
controls drive sequencing and the alignment of the resolver in brushless applications.
The UDC task provides the torque reference to the PMI and communicates with other
upper-level control tasks in the AutoMax rack.
The UDC module and the PMI are tightly synchronized through the fiber-optic link.
The PMI sends all feedback signals, including warning and fault information, speed
feedback, rail data, and gain data, to the UDC before each UDC task scan. Speed
feedback sampling in the Power Module is synchronized to within 1 µsec of the UDC
scan. The operating system in the PMI continuously performs diagnostic checks and
displays the results on the Power Module faceplate LEDs.
The PMI also provides connections to digital and analog rails, as well as digital drive
I/O. The PMI scans the rail and drive I/O while the regulation algorithm is running. This
permits the I/O data to be integrated into the control algorithm as required.