9.2.1 Frequency Inverter Application

Isolated ΔΣ modulators are being widely used in frequency inverter designs because of their high ac and dc performance. Frequency inverters are critical parts of industrial motor drives, photovoltaic inverters (string and central inverters), uninterruptible power supplies (UPS), electrical and hybrid electrical vehicles, and other industrial applications.

Figure 56 shows a simplified schematics of the AMC1306Mx in a typical frequency inverter application as used in industrial motor drives with shunt resistors (R_SHUNT) used for current sensing. Depending on the system design, either all three or only two motor phase currents are sensed.
The Manchester coded bitstream output of the AMC1306Ex minimizes the wiring efforts of the connection between the power board and the control board; see Figure 57. This bitstream output also allows the clock to be generated locally on the power board without the having to adjust the propagation delay time of each DOUT connection to fulfill the setup and hold time requirements of the microcontroller.

In both examples, an additional fourth AMC1306 is used to support isolated voltage sensing of the dc link. This high voltage is reduced using a high-impedance resistive divider and is sensed by the device across a smaller resistor. The value of this resistor can degrade the performance of the measurement, as described in the Isolated Voltage Sensingsection.

Figure 56. The AMC1306Mx in a Frequency Inverter Application

Figure 57. The AMC1306Ex in a Frequency Inverter Application