2-6 1000 Series / Guide to Installation, Troubleshooting, and Maintenance
2.3.2 Drive Architecture
The general function of the drive is to convert a fixed voltage and frequency from an
electrical power source into a variable voltage and frequency for controlling an AC
motor. The basic architecture of the 1100, 1105, and 1110 drives is shown in Figure 2-2,
that of the 1120 drive in Figure 2-3, that of the 1130 and 1230 drives in Figure 2-4, and
that of the 1200 in Figure 2-5.
A rectifier section is used on the 1100, 1105, 1110, and 1200 drives to convert the fixed
AC line voltage into a DC bus voltage. The 1120 is a modular design intended for
operating a number of units from a common DC bus. Low-power drives use a diode
rectifier and resistors to charge the bus capacitors, which is then bypassed by a contact
once the bus is up to full voltage. Medium- and high-power drives use silicon-controlled
rectifiers (SCRs) to control the charging of the bus capacitors. High-power drives provide
for optional twelve-pulse (six-phase) connection of the input to reduce harmonic currents.
The 1110 drive is designed for single-phase operation using two, rather than three, AC
line voltage terminals. A rectifier control coordinates the charging of the bus.
A link choke and bus capacitors in the 1100, 1105, and 1110 drives form a filter that
smoothes the output of the rectifier section into a steady DC voltage. An optional
dynamic brake device on these units allows regenerative energy from the load to be
dissipated in an external resistor when the drive is braking. The link choke and dynamic
brake device are normally part of the converter supplying the DC bus to 1120 units.
A converter section is used on the 1130 and 1230 drives to regulate power flow between
the AC line and DC bus. The converter uses an insulated gate bipolar transistor (IGBT)
bridge to rectify the AC line voltage into a DC bus voltage. This section also regenerates
energy from the DC bus to the AC line when the drive is braking.
An inverter section consisting of six insulated gate bipolar transistors (IGBTs) is used to
power an AC motor. This section can produce sine-wave motor voltages and currents of
any desired amplitude by rapidly switching the IGBTs using a technique called pulse-
width modulation (PWM). A gate driver is used to pass switching signals from the drive
controller to the IGBTs.
Overall operation of the unit is regulated by a drive control that incorporates a digital
signal processor (DSP) and a digital current regulator (DCR) or digital space vector
(DSV) control. This high-speed digital control uses both voltage and current feedback to
regulate the output to the motor. Optional encoder and resolver interfaces are available to
provide closed-loop control of motor velocity and/or position. A dual encoder option is
available to slave the motor to other sections of a machine or to reduce machine
resonance using dual transducer control. Variable-frequency drive (VFD) operation is an
option for controlling AC motors in simple applications.
A keypad and display on the control module provide access to operating and setup
parameters. The control module also provides analog and digital inputs that can be used
as input to and output from the drive. Serial communication channels are also available
for connecting drives to process controllers, communication networks, programmable
controllers, or personal computers.
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