A computer-implemented method for controlling a ramp-up of a voltage in a DC-link, a computer-readable storage medium, a variable speed drive, and a system including a variable speed drive configured to carry out the method.

An electrical power system 100 is described. The electrical power system 100 comprises: a first electrical sub-system 101, 102, 103, 105 having a first voltage; a second electrical sub-system having a second voltage; a power converter 104, 106 connected between the first electrical sub-system and the second electrical sub-system and configured to convert between the first voltage and the second voltage; an impedance synthesizer 14 connected in an intermediate circuit that connects the power converter to the first electrical sub-system, the impedance synthesizer 14 comprising an active bridge circuit 140. The electrical power system further comprises a control system 150 configured to control a switching operation of a plurality of power semiconductor switches 141.sub.L-H, 142.sub.L-H of the active bridge circuit 140 to control an output voltage V.sub.out of the impedance synthesizer 14, whereby the impedance synthesizer 14 emulates a Differential-Mode filter or a Common-Mode filter.

An AC/DC converter including a PFC circuit. The PFC circuit includes: a reactor; a first thyristor and a second thyristor; at least one switching element; and a capacitor. When an input of an alternating-current voltage is started, with a function of the switching element being made inactive, a controller executes a soft start by adjusting a pulse width when each of the thyristors is turned ON by changing a timing when each of the thyristors is turned ON based on a phase angle.

The invention discloses systems (100) and methods (200, 300) for reducing the effect of even-order harmonics in supply voltage on the DC side components in AC-DC converters having any kind of controlled power electronic switches or their combinations. The method involves modifying the time of firing the various switches (112, 114) through a control logic arrives at through either measuring or estimating the DC bus voltage or the input AC voltage. The proposed control methods are useful in ASDs where full bridge configuration is used for AC to DC conversion. The proposed control may also be used in ASDs where a half bridge rectifier system is used. The proposed method reduces the stress on the DC bus capacitor and increases the lifetime of the capacitor. It further reduces the peak current through the device, which reduces stress on the rectifier components. It also reduces the Total Harmonic Distortion (THD.sub.i) of the line current.