A power conversion system including a plurality of power conversion devices connected in parallel. Each of the plurality of power conversion devices includes: a power conversion circuit configured to convert DC to AC; and an AC filter circuit connected to an output side of the power conversion circuit. The AC filter circuit is an LC low-pass filter including a first filter reactor and an AC filter capacitor connected in an L shape. The AC filter circuit further includes a second filter reactor connected in series to the AC filter capacitor, and a resistance constructing a series circuit together with the AC filter capacitor and the second filter reactor.

An inverter system, including a pre-conversion circuit, a post-conversion circuit, and a control circuit; the pre-conversion circuit is configured to convert a voltage of a power supply into a DC voltage and output the DC voltage to the post-conversion circuit; a voltage between the pre-conversion circuit and the post-conversion circuit is a DC bus voltage; the post-conversion circuit is configured to output an alternating current; the control circuit is configured to detect a DC component of an output terminal of the post-conversion circuit, calculate a difference value of a zero value and the DC component to obtain a DC component deviation value, and perform PI adjustment on the DC component deviation value to obtain a voltage compensation value; the voltage compensation value is used to adjust the DC bus voltage.

A power conversion device, including: a voltage detector that detects a common mode voltage generated upon a switching operation of a power semiconductor device; a voltage superimposer that superimposes the common mode voltage detected by the voltage detector onto an output of the power conversion device to cancel the common mode voltage having a frequency greater than or equal to a switching frequency generated upon the switching operation of the power semiconductor device; and a residual voltage detector that detects the common mode voltage of the power conversion device superimposed by the voltage superimposer. The voltage superimposer includes a feedback mechanism for adding and superimposing the common mode voltage detected by the residual voltage detector onto the output of the power conversion device. The voltage detector includes a first choke coil and a first capacitor.

A grid access current control method without current sensor applicable to a grid-connected inverter relates to a system including a main circuit of the grid-connected inverter and a control circuit of the grid-connected inverter. The control circuit of the grid-connected inverter includes a grid access current open-loop control module and a PWM generation module; the grid access current open-loop control module includes a first proportional regulator, a second proportional regulator, a delayer, and an adder; input ends of the first proportional regulator and the second proportional regulator each are led out as an input end of a grid access current reference signal; and an output end of the first proportional regulator is connected to an input end of the adder; an output end of the second proportional regulator is connected to an input end of the delayer.

Systems and methods to estimate magnetic flux in a switched mode power supply are disclosed. An example welding-type power supply includes a switched mode power supply, comprising: a transformer configured to transform an input voltage to a welding-type voltage; a capacitor in series with a primary winding of the transformer; and switches configured to control a voltage applied to a series combination of the primary winding of the transformer and the capacitor; a voltage estimator coupled to the transformer and configured to output a signal representative of an alternating-current (AC)-coupled voltage at the capacitor; and a flux accumulator to determine a net flux in the transformer based on the voltage applied to the series combination of the primary winding of the transformer and the capacitor.

An ohmic heater for heating a food product, comprising: —a rectifier (2) for rectifying the supply voltage; —an inverter (3) comprising controlled switches (30); —a pair (4) of electrodes that can be positioned in contact with the food product to be heated, said inverter (3) being operatively interposed between the rectifier (2) and the pair (4) of electrodes; —means (5) for determining an oscillating voltage (X) generated by the rectifier (2); —a system (800) for regulating the closing duration of the switches (30) of the inverter (3) at least as a function of the corresponding voltage (X) generated by the rectifier (2) and determined at a given time instant by the means (5) for determining an oscillating voltage (X).

A system and method for an interleaved inverter including a set of module circuits and an inverter controller. The module circuits include multiple switches. The inverter controller is configured to assign a first phase shift value to each of the module circuits during a normal mode of operation and assign a second phase shift value to at least one of the module circuits during a failure mode of operation. The second phase shift value is greater than the first phase shift value.

A power transmission system can include a transformer and compensator circuit(s), each coupled between a node of the transformer and a ground connection. The compensator circuit(s) can each be configured to counteract a DC signal component of an AC signal at the transformer. The compensator circuit(s) can include a converter circuit having an AC side and a DC side and configured to convert a DC voltage on the DC side to an AC signal at the AC side. The compensator circuit(s) can include a DC link coupled to the DC side of the converter circuit. The compensator circuit(s) can include a controller configured to measure a DC signal component between the load and the ground; to determine, based at least in part on the DC signal component, a compensating signal configured to counteract the DC signal component; and to inject, by the converter circuit, the compensating signal to counteract the DC signal component.

A method of removing a direct current component at an output terminal of an MMC converter according to the present invention includes a detection step of individually detecting charging voltages charged in capacitors of a plurality of sub-modules connected in series to each other in the MMC converter; outputting an average value of the individually detected charging voltages; delaying the outputted average value by a predetermined phase to output a phase-delayed average value; outputting the average value and the phase-delayed average value as a q-axis component voltage by using a predetermined dq conversion unit; calculating an error between the q-axis component voltage and a three-phase average voltage for the q-axis component voltage; and outputting, through a pre-determined first PI control unit, an offset voltage for reducing the error.

A method of an estimator of an inner control loop controlling a three-to-single-phase converter connected to an AC power grid via a transformer includes obtaining a value of a voltage reference uRef produced by the inner control loop for the converter, obtaining a value of a secondary side current produced by the converter and measured between the converter and the transformer, obtaining a value of a primary side current produced by the converter and measured between the grid and the transformer, and obtaining a value of a primary side voltage measured between the grid and the transformer. The method also includes estimating a control current iCtrl component of the primary or secondary side current iMeas which results from the voltage reference, based on the obtained values of the voltage reference, the secondary side current, the primary side current and the primary side voltage, and feeding the estimated control current iCtrl* to the inner control loop.