Electrical power converter

A method of converting a three phase AC input into a DC output, the method comprising:

• rectifying the three phase AC input to obtain a rectified intermediate voltage across an upper intermediate node, a lower intermediate node and a middle intermediate node, wherein a phase input of the three phase AC input having a highest voltage is applied to the upper intermediate node, a phase input of the three phase AC input having a lowest voltage is applied to the lower intermediate node, and a phase input of the three phase AC input having an intermediate voltage between the highest voltage and the lowest voltage is applied to the middle intermediate node, and
• boosting the rectified intermediate voltage to obtain the DC output,
• wherein boosting the rectified intermediate voltage comprises connecting the middle intermediate node to a buck-boost circuit, and connecting a boost circuit across the upper and lower intermediate node, wherein outputs of the boost circuit and the buck-boost circuit are connected in parallel, wherein the boost circuit comprises an upper boost circuit connected between a common node and the upper intermediate node and a lower boost circuit connected between the lower intermediate node and the common node, wherein boosting the rectified intermediate voltage comprises operably connecting an input filter comprising inductors and star-interconnected capacitors to the upper intermediate node, the lower intermediate node and the middle intermediate node, and connecting a star point of the capacitors to the common node,
• connecting an output filter comprising a series of at least two filter capacitors across two output terminals, and connecting the common node to a midpoint of the output filter
• individually controlling pulse width modulated control signals fed to semiconductor switches of the upper boost circuit, the lower boost circuit and the buck-boost circuit,
• measuring a voltage at the common node and determining an offset value representative of a difference between the measured voltage of the common node and a setpoint voltage of the common node, and using the offset value to adapt the pulse width modulated control signals.

An electrical converter for converting a three-phase AC input into a DC output, the electrical converter comprising:

• three phase input terminals and two output terminals,
• a phase selector for connecting the three-phase AC input provided at the three phase input terminals to an upper intermediate node, a lower intermediate node and a middle intermediate node of the electrical converter, the phase selector comprising three rectifier bridge legs connected to the upper intermediate node and the lower intermediate node and first semiconductor switches that are actively switchable for selectively connecting the middle intermediate node to the three phase input terminals,
• a controller configured to control switching of the first semiconductor switches according to a switching pattern in which the phase input terminal having an intermediate voltage between the highest voltage and the lowest voltage is connected to the middle intermediate node,
• a boost circuit for converting a voltage at the upper intermediate node and the lower intermediate node to an output voltage at the two output terminals,
• a buck-boost circuit having an output connected to the two output terminals in parallel with an output of the boost circuit, the buck-boost circuit comprising at least two second semiconductor switches that are actively switchable, wherein the at least two second semiconductor switches are connected in series across the output terminals, wherein the middle intermediate node is connected to a first common node of the at least two second semiconductor switches, and
• an output filter comprising a series of at least two filter capacitors connected across the output terminals;
• wherein the boost circuit comprises a second common node, an upper boost circuit comprising a third actively switchable semiconductor switch connected across the upper intermediate node and the second common node, and a lower boost circuit comprising a fourth semiconductor switch connected across the second common node and the lower intermediate node,
• wherein the second common node is connected to a midpoint of the output filter,
• wherein the electrical converter comprises an input filter, the input filter comprising inductors operably connected to each one of the upper boost circuit, the lower boost circuit and the buck-boost circuit,
• wherein the input filter comprises capacitors operably connected to the inductors, wherein the capacitors are interconnected in a star connection and wherein the second common node is connected to a star point of the star connection,
• wherein the controller comprises a first current controller configured to generate a first pulse width modulated control signal for the at least two second semiconductor switches, a second current controller configured to generate a second pulse width modulated control signal for the third semiconductor switch, and a third current controller configured to generate a third pulse width modulated control signal for the fourth semiconductor switch, and
• wherein the controller is configured to determine an offset value representative of a difference between a measured voltage of the second common node and a setpoint voltage of the second common node and to adapt the first, second and third pulse width modulated control signals on the basis of the offset value.