Abstract: A circuit comprising a first power node for connection to a positive voltage of a DC link, a second power node for connection to a negative voltage of the DC link and a mid-point power node for connection to a mid-point voltage of the DC-link, the circuit further comprising a three-level neutral point clamped converter module and a brake resistor connection.

Abstract: A circuit comprising a first power node for connection to a positive voltage of a DC link, a second power node for connection to a negative voltage of the DC link and a mid-point power node for connection to a mid-point voltage of the DC-link, the circuit further comprising a three-level neutral point clamped converter module and a brake resistor connection.

Abstract: A circuit comprising a first power node for connection to a positive voltage of a DC link, a second power node for connection to a negative voltage of the DC link and a mid-point power node for connection to a mid-point voltage of the DC-link, the circuit further comprising a three-level neutral point clamped converter module and a brake resistor connection.

Abstract: An inverter circuit, coupled to a two-level DC voltage supply and being able to form a five-level output voltage is described, together with a method for operating the inverter circuit. The inverter circuit comprises a series connection of six unidirectional power semiconductor switches, each coupled to an antiparallel diode, between the positive and negative nodes of the supplying DC voltage. The inverter circuit further comprises a series connection of two internal capacitors between the cathodes of the first and the fifth switches of the series connection, the connection point of the capacitors being coupled to the internal node of the inverter circuit. In use, the unidirectional power semiconductor switches are controlled in order to set the voltage of the output of the inverter circuit.

Abstract: A circuit comprising a first power node for connection to a positive voltage of a DC link, a second power node for connection to a negative voltage of the DC link and a mid-point power node for connection to a mid-point voltage of the DC-link, the circuit further comprising a three-level neutral point clamped converter module and a brake resistor connection.

Abstract: An inverter circuit, coupled to a two-level DC voltage supply and being able to form a five-level output voltage is described, together with a method for operating the inverter circuit. The inverter circuit comprises a series connection of six unidirectional power semiconductor switches, each coupled to an antiparallel diode, between the positive and negative nodes of the supplying DC voltage. The inverter circuit further comprises a series connection of two internal capacitors between the cathodes of the first and the fifth switches of the series connection, the connection point of the capacitors being coupled to the internal node of the inverter circuit. In use, the unidirectional power semiconductor switches are controlled in order to set the voltage of the output of the inverter circuit.

Abstract: A piston type compressor wherein the position of the piston highest pressure point is indicated and the rotor of the motor at the optimal starting angle aligned prior to the actual compression operation by providing a pre-pulse to rotate the rotor of the motor at least one full rotation at a certain frequency, during rotation measuring the load torque by the frequency converter as well as indicating the maximum load torque point and at the end aligning the rotor of the motor at the optimal starting angle of about 180° from the maximum pressure angle, and at the beginning of the actual compression operation setting the rotor position opposite to the maximum torque angle by feeding direct current to the stator winding and starting the motor by supplying maximum motor current to the motor to give the maximum torque and acceleration.

Abstract: A piston type compressor wherein the position of the piston highest pressure point is indicated and the rotor of the motor at the optimal starting angle aligned prior to the actual compression operation by providing a pre-pulse to rotate the rotor of the motor at least one full rotation at a certain frequency, during rotation measuring the load torque by the frequency converter as well as indicating the maximum load torque point and at the end aligning the rotor of the motor at the optimal starting angle of about 180° from the maximum pressure angle, and at the beginning of the actual compression operation setting the rotor position opposite to the maximum torque angle by feeding direct current to the stator winding and starting the motor by supplying maximum motor current to the motor to give the maximum torque and acceleration.