Abstract: A cascaded power electronic transformer and a method for controlling the same are provided. The method includes: calculating electrical angles ?i1 and ?kps of an sth transformer and a compensation electrical angle ?j of a jth transformer; adding the compensation electrical angle ?j to the electrical angle ?kps of the jth transformer, to obtain a compensated electrical angle ?kps of the jth transformer; and calculating a square wave of a bridge arm voltage of each of the m primary converters and the r secondary converters of the sth transformer based on the electrical angle ?i1 and the electrical angle ?kps of the sth transformer after compensation.

Abstract: A matchless plasma source is described. The matchless plasma source includes a controller that is coupled to a direct current (DC) voltage source of an agile DC rail to control a shape of an amplified square waveform that is generated at an output of a half-bridge transistor circuit. The matchless plasma source further includes the half-bridge transistor circuit used to generate the amplified square waveform to power an electrode, such as an antenna, of a plasma chamber. The matchless plasma source also includes a reactive circuit between the half-bridge transistor circuit and the electrode. The reactive circuit has a high-quality factor to negate a reactance of the electrode. There is no radio frequency (RF) match and an RF cable that couples the matchless plasma source to the electrode.

Abstract: The present application provides a power supply apparatus, a three-phase power supply system and a control method, including N modules, where N is a positive integer greater than or equal to 2, and each module includes: a transformer, including a primary winding and a first secondary winding; and a first switch unit connected to the first secondary winding of the transformer, where primary windings of transformers of the N modules are connected in series, the first switch unit operates in one of a bypass mode, an open-circuit mode and a modulation mode, an output of each module is controlled by the first switch unit, so as to make the power supply apparatus provide voltages of different amplitudes according to power demand, and transformers with large volume and heavy weight, such as a centralized line frequency transformer or a multiple-winding transformer, are no longer required.

Abstract: A cascaded power electronic transformer and a method for controlling the same are provided. The method includes: calculating electrical angles ?i1 and ?kps of an sth transformer and a compensation electrical angle ?j of a jth transformer; adding the compensation electrical angle ?j to the electrical angle ?kps of the jth transformer, to obtain a compensated electrical angle ?kps of the jth transformer; and calculating a square wave of a bridge arm voltage of each of the m primary converters and the r secondary converters of the sth transformer based on the electrical angle ?i1 and the electrical angle ?kps of the sth transformer after compensation.

Abstract: A method for controlling an inverter-based resource having a power converter connected to an electrical grid includes receiving, via a regulator of a controller of the inverter-based resource, a plurality of power signals. The method also includes determining, via the regulator, a power error signal as a function of the plurality of power signals. Further, the method includes receiving, via the regulator, a dynamic multiplier factor from a supervisory controller. Moreover, the method includes applying, via the regulator, the dynamic multiplier factor to one or more gains of the regulator to determine one or more modified gains. In addition, the method includes applying the one or more modified gains to the power error signal to obtain an intermediate power signal. Thus, the method includes generating, via the regulator, one or more control commands for the power converter as a function of the intermediate power signal.

Abstract: A vector control method and system of a permanent magnet motor (PMM) comprising a step of counting parameters of components of a power cable line (channel) (PCL), between the PMM and a regulated voltage source (RVS), wherein counting at least parameters of an inductance, a resistance and a capacitance of elements of the PCL. Providing voltage sag compensation mode by controlling the RVS DC-link voltage parameter using a voltage sag control unit, and controlling the PMM frequency parameter by changing current and/or voltage PMM parameters counting changes in the RVS DC-link voltage parameter and a nominal power parameter of the PMM.

Abstract: The present specification relates to a wireless power receiving device, receiving method, and receiving system, the device comprising individual rectifiers for each receiving coil, wherein the individual rectifiers comprise isolators for isolating a receiving coil for PC0 from a receiving coil for PC1.

Abstract: A method for controlling a power converter, which in particular has partial power converters connected in parallel, is provided. The method includes determining a nominal voltage for the power converter; and dividing an output voltage for the power converter into a number of, in particular equal, voltage ranges. The voltage ranges are limited by a discrete upper voltage limit and a discrete lower voltage limit and the voltage ranges can be adjusted by switching the power converter, in particular the partial power converters. The method includes allocating the nominal voltage a voltage range with a discrete upper and lower voltage limits; allocating a first switch setting to the lower voltage limit; allocating a second switch setting to the upper voltage limit; and switching between the first switch setting and the second switch setting so that the power converter generates an actual voltage corresponding to the nominal voltage.

Abstract: A multilevel stage of a bidirectional AC power converter, comprising: a set of switches in series, a set of capacitors in series, the set of capacitors being in parallel with the set of switches; a number of sets of diodes in series; a center tap along the set of switches in series; and a pair of taps, respectively after the first and before the last switch of the set of switches in series; wherein each node between respective capacitors is connected to a node between respective diodes. A converter first stage for a 3-level converter has 6 switches, two capacitors, and two diodes, with the junction between diodes connected to the junction between capacitors, and the diode legs between switches 2-3 and 4-5. The center tap is between switches 3-4, and the pair of taps between switches 1-2 and 5-6.

Abstract: Example implementations relate to a power control system for controlling transmission of power from one or more power supply devices to one or more loads of a modular server enclosure. The power control system includes an electronic fuse and a threshold control unit. The electronic fuse is connected between one or more loads and the one or more power supply devices of the modular server enclosure. The threshold control unit is connected to the electronic fuse and to the one or more power supply devices. The threshold control circuit dynamically adjusts a threshold current for the electronic fuse based on a power supply capacity of the one or more power supply devices. The electronic fuse controls the transmission of the power from the one or more power supply devices to the one or more loads based on threshold current and a load current drawn by the one or more loads.

Abstract: The present disclosure relates to a method for controlling a converter, in particular power converter of a wind power installation. The converter has a plurality of, preferably parallel, converter modules. The method includes the following steps: driving a first converter module, such that the converter module generates a first electrical AC current in a first switch position, driving a second converter module, such that the converter module generates a second electrical AC current in a second switch position, superposing the first electrical AC current and the second electrical AC current to form a total current, detecting the total current of the converter, determining a virtual current depending on the first and second switch positions, and changing the first switch position of the first converter module and/or the second switch position of the second converter module depending on the total current and the virtual current.

Abstract: Two inverters provided at respective both ends of open-end windings are appropriately controlled. A rotating electrical machine control device (1) that can control a first inverter (11) and a second inverter (12) by a plurality of control schemes, respectively, the control schemes differing from each other in at least one of a switching pattern and a switching frequency and being independent of each other, has a control mode in which the first inverter (11) and the second inverter (12) are controlled by the same control scheme in a first speed region (VR1) in which the rotational speed of a rotating electrical machine (80), and the first inverter (11) and the second inverter (12) are controlled by different control schemes in a second speed region (VR2) in which the rotational speed of the rotating electrical machine (80) is higher than in the first speed region (VR1).

Abstract: A gate driver circuit comprises an auxiliary winding, a voltage summer, an auxiliary voltage bus, a gate driver integrated circuit (IC), and a controller. The auxiliary winding is positioned adjacently to the inductor and configured to inductively couple with the inductor. The voltage summer comprises a pair of diodes coupled to the auxiliary winding and a pair of capacitors coupled to the pair of diodes. The auxiliary voltage bus is configured to receive a summed voltage from the voltage summer based on a sum of voltages stored in the pair of capacitors. The gate driver IC is configured to receive a voltage from a positive rail of the auxiliary voltage bus and to output a gate control signal to control a switching device based on the received voltage and based on a pulse signal generated by the controller.

Abstract: A turboelectric generator system includes a gas turbine engine which includes, in fluid flow series, a gas-generator compressor, a combustor, a gas-generator turbine, and a variable-speed free power turbine. The system further comprises a variable-frequency electric machine rotatably connected with the free power turbine and a power converter configured to convert a variable frequency electrical output from the electric machine to a fixed frequency output.

Abstract: In one embodiment, an apparatus comprises a coil structure comprising a first coil and a second coil, each of the first coil and the second coil having a first side portion, a center portion, and a second side portion, wherein the first side portion forms a first angle with the center portion and the second side portion forms a second angle with the center portion, and a layer of magnetic material adjacent to the center portion of the first coil and the center portion of the second coil, the first coil and the second coil being configured such that when a current flows in a first spatial direction in the first coil a current flows in a second spatial direction different from the first spatial direction in the second coil. In one embodiment, the apparatus further comprises a power circuit configured to provide a time-varying current to the coil structure and a battery configured to provide a direct current to the power circuit.

Abstract: A converter arrangement converts an alternating input voltage having an input frequency into an alternating output voltage having an output frequency. The converter arrangement includes a direct converter on an input side having a plurality of input terminals and input-side converter units, transformers, the number of which matches the number of input terminals, and a direct converter on an output side having output-side converter units, and a number of output terminals, which number matches the number of input terminals. Each transformer is connected on the primary side to each input terminal via one each input-side converter unit, and is connected on the secondary side to each output terminal via one each output-side converter unit.

Abstract: Disclosed is a method for balancing at least one component of the power supplied by two inverters powered in parallel in a power grid of a railway vehicle, the method including:—a step for measuring the variation of a component of a current supplied by a first inverter, in order to obtain a measured variation; and—a step for modifying a control setpoint of the first inverter as a function of the measured variation.

Abstract: Methods and systems are provided for heating a cabin of a vehicle using an alternator of the vehicle. In one example, a method may include operating in a first operating mode to heat a cabin of a vehicle, the first operating mode including shorting an alternator output of an alternator of the vehicle to ground, and closing a coolant valve positioned between a coolant system of an engine of the vehicle and an alternator coolant circuit.

Abstract: At least one of a plurality of generators is a first generator configured such that a relationship of a generator output voltage with respect to a generator active power output from the generator to a corresponding first AC wiring portion has a predetermined first drooping characteristic. The control device is configured to generate a drive signal for a power conversion device by deciding a target value of a first control element such that a relationship of an AC wiring portion voltage with respect to a power conversion device active power output from the power conversion device to a first AC wiring portion corresponding to a first generator has a predetermined second drooping characteristic and correcting the target value of the first control element according to a DC voltage at a DC wiring portion.

Abstract: Wireless resonant inductive power receivers for achieving detuning for a resonant wireless power transfer system including cooperative power sharing is described. Cooperative power sharing allows for detuning one or more wireless received coupled to a wireless charger to alter the power received at each wireless receiver.

Abstract: A contactless card is powered by an antenna connected to the input of a rectifier. An output of the rectifier is coupled to a processing unit that consumes a first current output from the rectifier. A current regulation circuit is connected to the output of the rectifier. The current regulation circuit operates to absorb a second current from the output of the rectifier such that a sum of the first and second currents is a constant current.

Abstract: Disclosed is a wireless power receiver for receiving power wirelessly. According to an embodiment of the present disclosure, a wireless power receiver wirelessly receiving power may include a first power receiver receiving first power from a first power transmitter, a second power receiver receiving second power from a second power transmitter, and a shielder disposed between the first power receiver and the second power receiver to substantially shield influx of the first power into the second power receiver and to substantially shield influx of the second power into the first power receiver.

Abstract: An airbag apparatus inflates to be spread such that a front side and both sides of at least one occupant are surrounded. The airbag apparatus includes an airbag's bag body that has the first bag body, the second bag body, and the third bag body which are integrally formed and inflate to be spread on one side, the front side, and the other side of the occupant; and an energy absorbing portion that causes an upper portion of the first bag body and an upper portion of the third bag body to be coupled to a vehicle body, generates a load reaction force for supporting the airbag's bag body when the occupant is restrained, and allows the airbag's bag body to move.

Abstract: In one embodiment, a wireless power transfer coil structure comprises a wheel core comprising an annulus portion and at least two spoke portions arranged substantially symmetrically with respect to a geometric center of the annulus portion, the wheel core formed from a magnetic material, and a coil located on an outer surface of the annulus portion of the wheel core. In one embodiment, the wireless power transfer coil structure further comprises at least one solenoidal coil wound around the at least two spoke portions of the wheel core. In one embodiment, the at least one solenoidal coil is wound around one of the at least two spoke portions of the wheel core in a first direction and wound around another of the at least two spoke portions of the wheel core in the first direction.

Abstract: The present invention provides for a system that makes use of a system power supply enable switch controlled by a near field communications (NFC) frontend with energy harvesting. In one embodiment, RF power in the 13.56 MHz band generated by a NFC counterpart (such as a mobile phone) is detected by the energy harvesting unit being part of the battery-unpowered NFC communication device. After activation, the system can perform actions required to communicate to the presented device (i.e., the NFC counterpart). Later, the system can switch itself into the unpowered state again. In another embodiment, this feature can also be used to control an NFC protection circuitry very quickly after the NFC device is exposed to an external HF (high frequency) field.

Abstract: Systems, methods and apparatus are disclosed for wireless power transfer using multiple receive coils. In one aspect a wireless power receiver is provided that is configured to receive wireless power from a wireless power transmit coil. The wireless power receiver includes a first receive coil having a first mutual coupling with the transmit coil. The wireless power receiver further includes a second receive coil having a second mutual coupling with the transmit coil. The wireless power receiver further includes a load coupled to at least one of the first receive coil and the second receive coil for receiving the wireless power.

Abstract: A charging apparatus includes a DC switch circuit, a wireless power unit, a capacitive power conversion unit, and a switching power conversion unit. The charging apparatus operates in at least one of the following modes: in a constant current mode, the capacitive power conversion unit converts a bus current provided by the DC switch circuit or the wireless power unit to generate a predetermined constant charging current on a charging node to charge a battery; in a constant voltage mode, the switching power conversion unit converts a bus voltage provided by the DC switch circuit or the wireless power unit to generate a predetermined charging voltage on the charging node to charge the battery; in a first power output mode, the switching power conversion unit converts the battery voltage to generate an output voltage on a transmission interface pin.

Abstract: A transmitter device in an inductive energy transfer system includes a first transmitter coil operatively connected to a first resonant circuitry. A receiver device includes a first receiver coil operatively connected to a first resonant circuitry. The first transmitter coil and the first receiver coil form a first transformer. The transmitter device, the receiver device, or both the transmitter and receiver devices can also include an auxiliary coil or inductor, which may form an auxiliary transformer. Energy can be transferred from the transmitter device to the receiver device using the first transformer or the auxiliary transformer. The transfer of energy may be adaptively adjusted based on the efficiency of the energy transfer. For example, the transfer of energy can be adjusted based on the operating conditions of the load.

Abstract: The invention is based on a charging device, in particular for a hand tool accumulator (12), with at least one inductive voltage source (14) that is provided for supplying a charging current and comprises a first AC voltage connection point (16) and at least one further AC voltage connection point (18), with an inverter (20) comprising at least one power output (22) and at least one inverter element (24) which is electrically connected to the first AC voltage connection point (16), and with a signal transfer unit (26). It is proposed that the signal transfer unit (26) is provided for short-circuiting the at least two AC voltage connection points (16, 18) to generate a signal.

Abstract: A device for supplying electrical power to an aircraft on the ground, including two electric generators driven by an auxiliary power unit. The first generator is connected by a connection/disconnection mechanism to an aircraft network and to an electric taxiing network, to supply either an AC voltage to the aircraft network when it is connected to the aircraft network, or an AC voltage or a power to the taxiing network when it is connected to the taxiing network. The second generator is connected by the connection/disconnection mechanism to the aircraft or taxiing networks to supply the AC voltage to one of those networks.

Abstract: A step-down DC converter configured to smooth ripple voltage. The step-down DC converter includes a ripple-filtering inductor, a power isolating and converting unit, a power switch, a first capacitor, a second capacitor, a first rectifying switch, a second rectifying switch, and a first inductor. The power isolating and converting unit includes a plurality of windings for separating the step-down-DC converter into an input stage and an output stage. The power switch and the first capacitor are arranged at the input stage, and the first capacitor is connected to the power switch. The second capacitor, the first rectifying switch, the rectifying switch, and the first inductor are arranged at the output stage, the second capacitor is connected to one terminal of the first inductor, and the other terminal of the first inductor is connected to the first rectifying switch and the second rectifying switch.

Abstract: A symmetric-type UPS power system based on a nine-phase phase-shifting autotransformer includes a three-phase AC power input terminal, a three-phase AC power output terminal, a nine-phase phase-shift autotransformer, a synchronized control device for controlling output of a three-phase inverter, a power-frequency isolation transformer and three circuits of output devices; wherein the three-phase AC input terminal of the nine-phase phase-shifting autotransformer is connected to the three-phase AC power input terminal, each circuit of the output devices includes a zero-sequence suppression commutating inductor, a three-phase six-pulse rectifier, a three-phase inverter and a filter inductor which are connected with each other in sequence, each circuit of the zero-sequence suppression commutating inductor is connected to the three-phase AC output terminal of the phase-shifting autotransformer, each circuit of the filter inductor is connected to the input terminal of the power-frequency isolation transformer.

Abstract: Described is a modular switch for an electrical converter. The modular switch is provided with a first series circuit including a first controllable power semiconductor component and a first diode as well as with a second series circuit including a second diode and a second controllable power semiconductor. The connecting point between the first power semiconductor component and the first diode forms a first terminal and the connecting point between the second diode and the second power semiconductor component forms a second terminal of the modular switch. Also provided is a capacitor, wherein the first series circuit and the second series circuit and the capacitor are switched parallel to each other.

Abstract: Sinusoidal pulse width modulation (SPWM) control techniques, computer readable mediums, and apparatus are presented for operating a multilevel converter, in which a desired AC node voltage level is determined through comparison of a plurality of carrier signals or values to at least one reference signal or value, and a switching state is selected from a plurality of redundant switching states corresponding to the desired AC node voltage level for generating switching control signals based at least partially on a switched capacitor voltage balancing goal or other control objective.

Abstract: A rack system for a server includes a number of server units, which includes first to the third sets of server units, voltage converter, first to third power supply circuits. The voltage converter receives and converters a three-phase alternating current (AC) power signal to provide first to third single-phase power signals. The first to the third sets of power supply circuits respectively provides first to third direct current (DC) power signals according to the first to the third single-phase power signals. The first set to the third set of server units is respectively powered by first to the third DC power signals or respectively powered by first part, second part, and third part of the first to the third DC power signals.

Abstract: A power supply unit (1) that is to be connected to different types of power supply networks includes an input (2) to receive AC power from the power supply network and an output (3) for providing power to an electrical device. The electrical device may for example be a computer, a telecom infrastructure device, inductive cooking/heating systems or an on-board charger of an electrical automotive vehicle. The power supply unit (1) includes at least two converters (4) that are connected between the inputs (2) and the output (3) and it further includes a controllable switching arrangement (5). The switching arrangement (5) includes a number of controllable switches (6) to controllably connect the converters (4) in different configurations to the input (2) and therefore also controllably to different supply lines of the power supply network.

Abstract: A modular voltage source converter (100) comprises a plurality of cells conformal to a basic cell design comprising a first and a second terminal, a capacitor and at least two switches arranged in a half-bridge or full-bridge configuration. In the converter, a first group is formed by a number n of cells (101-k, k=1, n) connected serially at their terminals, and a second group is formed by an equal number n of cells (102-k, k=1, n) connected serially at their terminals. The terminals of the cells (101-k) in said first group are connected, via a resistive or inductive connection element (110-k), to the terminals of corresponding cells (102-k) in said second group.

Abstract: A power supply includes a plurality of electronic components including one or more of a rectifier and a switching transistor, an input port configured to receive electrical energy from a power source and a circuit board comprising a cavity. At least one of the rectifier and the switching transistor is embedded in the cavity. The cavity is arranged proximal to the input port such that at least a portion of thermal energy generated by one or more of the rectifier and the switching transistor is dissipated from the power supply by way of the input port.

Abstract: We describe a photovoltaic power conditioning unit comprising: both dc and ac power inputs; a dc link; at least one dc-to-dc converter coupled between dc input and dc link; and a dc-to-ac converter coupled between dc link and ac output. The dc-to-dc converter comprises: a transformer having input and output windings; an input dc-to-ac converter coupled between dc input and input winding; and an ac-to-dc converter coupled between output winding the dc link. The output winding has a winding tap between the first and second portions. The ac-to-dc converter comprises: first and second rectifiers, each connected to a respective first and second portion of the output winding, to the dc link and winding tap; and a series inductor connected to the winding tap. Rectifiers are connected to the winding tap of the output winding via the series inductor wherein the series inductor is shared between the first and second rectifiers.

Abstract: A power module, which is connected to a power source, includes a rectifying unit, a filtering unit and an inverter. The rectifying unit has three legs. The filtering unit is connected to the rectifying unit, and the inverter is connected to the filtering unit. One of the three legs has two switching elements connected in series, and another one of the three legs has two rectifying elements connected in series. In addition, a power conversion apparatus including the power module is also disclosed.

Abstract: A boosting AC-to-DC converter An AC-to-DC converter may include a main rectifier, a first auxiliary rectifier, a second auxiliary rectifiers and a transformer assembly. The transformer assembly may include a set of primary windings arranged in a first multiphase configuration and connected to the main rectifier, a first set of secondary windings arranged in a second multiphase relationship and connected to the first auxiliary rectifier and a second set of secondary windings arranged in a third multiphase configuration and connected to the second auxiliary rectifier. The second multiphase configuration of the first set of secondary windings and the third multiphase configuration of the second set of secondary windings may be in phase shifting relationships relative to the first multiphase configuration of the set of primary windings.

Abstract: A voltage adjusting circuit includes an inducing circuit configured to induce a voltage from electromagnetic waves, a first rectifying circuit configured to rectify an output signal of the inducing circuit, a second rectifying circuit configured to rectify the output signal of the inducing circuit, a first regulator configured to regulate an output signal of the first rectifying circuit, and a second regulator configured to regulate an output signal of the second rectifying circuit.

Abstract: Provided is a resonance power receiver, including a first resonator, a second resonator to receive a resonance power and a phase shifter to shift the phase of the signal received via the second resonator such that the signal received via the first resonator and the signal received via the second resonator are in phase.

Abstract: An exemplary embodiment of the present disclosure illustrates a rectifying module, which is operable for rectifying an alternating current (AC) signal into a direct current (DC) signal. The rectifying module includes a transmission line, at least one rectifying unit, and at least one pattern. The transmission line is configured for receiving and transmitting the alternating current signal. The rectifying unit is arranged neighboring to the transmission line for operatively coupling with the transmission line to receive a part of the alternating current signal and rectifies the alternating current signal into the DC signal. The pattern is configured to be a hollow grounding structure and the pattern is disposed under the dual-line coupling areas of the rectifying unit neighboring to the transmission line.

Abstract: There is disclosed an apparatus and method to reduce total harmonic distortion input into a 24-pulse autotransformer system and the autotransformer system itself. The 24-pulse autotransformer system is configured to receive an input of a first voltage and produce an output voltage of a second voltage. The system includes a pair of autotransformers coupled to an AC power source. One winding of each phase of the first autotransformer has a turn ratio to effect a decrease in the voltage across said winding over a symmetric voltage value and a second winding of each phase of the first autotransformer has a turn ratio to effect a decrease in the voltage across said winding over a symmetric voltage value, thereby reducing total harmonic distortion (THD) in the input current to the system without a zero sequence blocking transformer.

Abstract: Provided is a method for detecting a PoE (power over Ethernet) device comprising applying a positive polarity of a first current source to one of a first and second data pairs of an Ethernet connection to a powered device (PD) and a negative polarity of the first current source to the other of the first and second data pairs, applying a positive polarity of a second current source to a first spare pair of the Ethernet connection and a negative polarity of the first current source to a second spare pair of the Ethernet connection, simultaneously measuring a first voltage across the first current source and a second voltage across the second current source, discontinuing application of the first current source and measuring a third voltage across the second current source, and determining a configuration of the PD using the measured first, second and third voltages.

Abstract: An energy recovery system is provided that can be used in place of a resistive termination. The energy recovery system can simulate the behavior and performance of a resistive termination, while recovering at least some of the energy that would otherwise have been dissipated within the termination. In one embodiment, the energy recovery system includes a rectification system having a plurality of tuned rectifier circuits and an RF input network to provide input power distribution to the plurality of tuned rectifier circuits and input impedance shaping to shape the collective input impedance of the plurality of tuned rectifier circuits as seen at the RF input port of the RF input network.

Abstract: A resistance compression network uses transmission line sections having asymmetric lengths to compress the resistance range of multiple loads. In some embodiments, the characteristic impedance of the transmission line sections is related to the geometric mean of the load resistance range. The resistance compression network may be used within, for example, an energy recovery system or in any other application where a reduction in the resistance range of multiple loads is desired.

Abstract: An induction heating device includes the following elements: a resonance circuit; a power factor improvement circuit for boosting rectified output, supplying the output to an inverter, and improving the power factor of a commercial alternating current; and a load material detector for detecting the material of the load. The inverter includes switching elements forming a full-bridge circuit. The drive frequency of the switching elements is switched between a frequency substantially equal to a resonance frequency of the resonance circuit and a frequency substantially 1/n time (n being an integer equal to or larger than two) thereof, according to a detection result of the load material.

Abstract: A method is described for controlling a plurality of parallel-connected power converters 20a, 20b, each of which operates in accordance with a pulse width modulation (PWM) strategy defined by an independent voltage carrier signal and an independently controllable modulating sinusoidal voltage signal which are used to generate a PWM command signal for each PWM strategy. The voltage carrier signals of the PWM strategies have the same switching period and desynchronisation of the PWM command signals causes an unwanted circulating current to flow between the power converters 20a, 20b. The method thus comprises providing the independently controllable modulating sinusoidal voltage signal of the PWM strategy of at least one of the plurality of power converters 20a, 20b with a dc voltage offset to modify the PWM command signal of the at least one power converter and thereby increase the synchronisation of the PWM command signals so that the magnitude of any unwanted circulating current is reduced.