Motor drive architecture for variable frequency alternating current loads

A motor control system with a three-phase active front-end drive including short circuit protection, comprising:

• a multi-level converter having a converter neutral common point configured to transfer power from a three-phase alternating current (AC) power source to a first direct current (DC) bus, the first direct current bus having a positive terminal, a negative terminal, and neutral common point;
• a second DC bus having a positive terminal and a negative terminal, the second DC bus operably connected to the first DC bus, with the positive terminal of the second DC bus operably connected to the positive terminal of the first DC bus, and the negative terminal of the second DC bus operably connected to the negative terminal of the first DC bus;
• an inverter operably connected to a second DC bus;
• the inverter configured to draw power from the positive terminal of the second DC bus and negative terminal of the second DC bus to provide a plurality of motor excitation signals, the inverter having an inverter neutral common point;
• a neutral point selection device operably connected to the first DC bus neutral common point of the first DC bus and selectively connectable to at least one of the converter neutral common point and the inverter neutral common point, the bus selection device configured to disconnect the at least one of the converter neutral common point and the inverter neutral common point from the first DC bus neutral common point under selected conditions;
• a motor operably connected to the inverter, the motor configured to receive the plurality of motor excitation signals;
• and
• an inrush current limiter, wherein the multilevel converter includes the inrush current limiter, the inrush current limiter comprises a bypass diode and a series positive temperature coefficient thermistor selectively shunted by an active switching device.

A method of controlling a three-phase active front- end drive configured for connection to a three phase alternating current power source;

• the method comprising:
• operably connecting a multi-level converter having a converter neutral common point to transfer power from the three phase alternating current (AC) power source to a first direct current (DC) bus, the first DC bus having a positive terminal, a negative terminal, and a neutral common point;
• operably connecting a second DC bus to the first DC bus, the second DC bus with a positive terminal of the second DC bus operably connected to the positive terminal of the first DC bus , and a negative terminal of the second DC bus operably connected to the negative terminal of the first DC bus;
• configuring an inverter operably connected to the second DC bus to draw power from the positive terminal of the second DC bus and negative terminal of the second DC bus to provide a plurality of motor excitation signals, the inverter having an inverter neutral common point;
• and
• operably connecting a neutral point selection device to the first DC bus neutral common point of the first DC bus and selectively connecting to at least one of the converter neutral common point and the inverter neutral common point, the bus selection device configured to disconnect the at least one of the converter neutral common point and the inverter neutral common point from the first DC bus neutral common point under selected conditions,
• wherein the multilevel converter comprises an inrush current limiter, the inrush current limiter comprises a bypass diode and a series positive temperature coefficient thermistor selectively shunted by an active switching device.