Disclosed embodiments are directed to a technique to remove DC offset from current measurement signals through shunt resistors in digital signal processing for current reconstruction when using discontinuous pulse width modulation (DPWM). Such measurements regarding current are pertinent to a feedback loop used for a system including a DC-link capacitor, inverter, and motor. A method of removing DC offset comprises: determining a three-phase output current signal of an inverter, wherein the inverter is coupled to a motor and a power supply; producing a voltage signal based on the three-phase output current signal and the resistances of one or more shunt resistors disposed in the inverter; applying an analog gain circuit to the voltage signal; processing the voltage signal with an analog-to-digital converter (ADC); applying a DC offset corrector to the voltage signal; and performing current reconstruction on the voltage signal to produce a continuous current signal.

Provided is a method for generating a multiphase electrical alternating current having a sinusoidal fundamental wave in each phase by a multiphase inverter of a wind power installation. The multiphase inverter is controlled by a tolerance band method which respectively has an upper and a lower band limit for each of the phases of the inverter. The inverter has, for each phase, an upper switch for generating a positive sine half-wave of the alternating current of the phase and a lower switch for generating a negative sine half-wave of the alternating current of the phase. The method includes generating the positive sine half-wave by the upper switch and generating the negative sine half-wave by the lower switch based on the band limits of the phase, and changing at least one of the band limits such that a signal component superimposed on the respective sinusoidal fundamental wave is reduced.

A power supply includes: a rectifier circuit which has a plurality of rectifier switching elements, and separately extracts a positive voltage and a negative voltage for every phase from a primary power source of three-phase alternating current, respectively; a smoothing circuit which has a pair of smoothing capacitors connected in series to each other to be charged by the rectifier circuit, and a plurality of smoothing inductors respectively arranged between the rectifier circuit and the smoothing capacitors; a inverter circuit which has a plurality of inverter switching elements and inverts output of the smoothing circuit into alternating current; and a control circuit which controls switching of the plurality of rectifier switching elements so that output voltage of the smoothing circuit becomes a desired voltage, and electrical current flowing to each phase of the rectifier circuit becomes a desired electrical current.

Disclosed embodiments are directed to a technique to remove DC offset from current measurement signals through shunt resistors in digital signal processing for current reconstruction when using discontinuous pulse width modulation (DPWM). Such measurements regarding current are pertinent to a feedback loop used for a system including a DC-link capacitor, inverter, and motor. A method of removing DC offset comprises: determining a three-phase output current signal of an inverter, wherein the inverter is coupled to a motor and a power supply; producing a voltage signal based on the three-phase output current signal and the resistances of one or more shunt resistors disposed in the inverter; applying an analog gain circuit to the voltage signal; processing the voltage signal with an analog-to-digital converter (ADC); applying a DC offset corrector to the voltage signal; and performing current reconstruction on the voltage signal to produce a continuous current signal.

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.

A power conversion device includes a first bridge circuit, a second bridge circuit, and an inductance element connected between a first AC terminal of the first bridge circuit and a second AC terminal of the second bridge circuit The controller calculates a passing current passing through the inductance element based on a difference between a first alternating current flowing between the first AC terminal and the inductance element and a second alternating current flowing between the second AC terminal and the inductance element, and detects a first DC component included in the passing current. The controller changes a duty in at least one of the first AC voltage and the second AC voltage to cancel the detected first DC component, the duty being a ratio of a positive potential period and a negative potential period.

An ohmic heater for heating a food product, comprising: 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 a rectifier (2) of the supply voltage and the pair (4) of electrodes; a transformer (6) located between the inverter (3) and the pair (4) of electrodes for regulating the amplitude of the voltage; means (7) for determining the continuous component of the current in a zone downstream of the inverter (3) and upstream or at the transformer (6); a system (800) for regulating the closing duration of the switches (30) of said inverter (3) that operates as a function of the means (7) for determining the continuous component by minimising/suppressing said continuous component.

Provided is a method for generating a multiphase electrical alternating current having a sinusoidal fundamental wave in each phase by a multiphase inverter of a wind power installation. The multiphase inverter is controlled by a tolerance band method which respectively has an upper and a lower band limit for each of the phases of the inverter. The inverter has, for each phase, an upper switch for generating a positive sine half-wave of the alternating current of the phase and a lower switch for generating a negative sine half-wave of the alternating current of the phase. The method includes generating the positive sine half-wave by the upper switch and generating the negative sine half-wave by the lower switch based on the band limits of the phase, and changing at least one of the band limits such that a signal component superimposed on the respective sinusoidal fundamental wave is reduced.

The presence of injected DC has harmful consequences for a power grid system. A piecewise sinusoidal ripple voltage wave at the line-frequency that rides on the main capacitor bank of the power converter is observed. This observation leads to a new DC detection elimination method. Three DC elimination methods for this ripple component are disclosed to allow dissipation of DC energy through heat and/or electromagnetic wave, or to allow transformation of this energy into usable power that is fed back into the power grid.