1-8
1.2 Control System
This section gives you a general overview of inverter control systems and features specific to the
FRENIC-Mini series of inverters.
As shown in Figure 1.8, single- or three-phase commercial power is converted to DC power in the
converter section, which is then used to charge the capacitor on the DC link bus. According to control
commands or signals generated in the control logic, the inverter modulates the electricity charged in the
capacitor to PWM (Pulse Width Modulation) format and feeds the output to the motor. The modulation
frequency is called "carrier frequency." As shown in Figure 1.7, the voltage waveform of the modulated
power source produces pulse train with positive and negative polarity synchronized with the inverter's
output command frequency. The inverter feeds the produced output as drive power with sinusoidal current
waveform like that of ordinary commercial power lines.
PWM voltage waveform Current waveform
Figure 1.7 Output Voltage and Current Waveform of the Inverter
For the set frequency given in the control logic, the accelerator/decelerator processor calculates the
acceleration/deceleration rate required by run/stop control of the motor and transfers the calculated results
to the 3-phase voltage command processor directly or via the V/f pattern generator.
Refer to Chapter 4, Section 4.7 "Drive Command Controller" for details.
The FRENIC-Mini series features a simplified magnetic flux estimator which is added in the V/f pattern
processing section. This feature automatically controls the voltage level applied to the motor according to
the motor load so as to make the motor generate more stable and higher torque even during low speed
operation. This "Simplified Torque-Vector Control" is unique to Fuji inverters.
The control logic section, which is the very brain of the inverter, allows you to customize the inverter's
driving patterns using the function code settings.
Refer to Chapter 4 "BLOCK DIAGRAMS FOR CONTROL LOGIC" for details.
Figure 1.8 Simplified Control System Diagram of FRENIC-Mini
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