Abstract: This invention relates to a T-type three-level inverter circuit. The circuit includes an absorption unit.

Abstract: An AC photovoltaic module includes a DC photovoltaic module for converting solar energy to DC electrical power, and an inverter for converting DC electrical power to AC electrical power, the inverter being adapted for connection to a frame portion of the module and being sized and configured, and provided with arrangements of electrical components thereof, to dispense heat from the inverter, whereby to prolong operational life and reliability of the inverter.

Abstract: A circuit for providing damping in an electromagnetic interference (EMI) filter with an inductor-capacitor (LC) circuit, includes at least one capacitor connected to receive a common-mode current from the LC circuit; a current sensor that senses the common-mode current; a linear amplifier that amplifies the sensed common-mode current; and a power amplifier that receives the amplified sensed common-mode current and outputs a voltage which creates a damping impedance for frequencies of the common-mode current less than a threshold frequency and absorbs the common-mode current for frequencies greater than the threshold frequency.

Abstract: First windings of a first common mode transformer and second windings of a second common mode transformer are connected in series via connection lines. The windings are connected to an AC power supply via connection lines. The first windings are connected to a three-phase motor via connection lines, a converter, and an inverter. High-frequency leakage currents flowing in the connection lines are detected as a common mode voltage by a winding for common mode voltage detection. An output voltage is inputted via a filter to a voltage amplifier unit that amplifies the output voltage, and the amplified voltage is applied to a winding via a capacitor in substantially a same direction as a direction of the common mode voltage. As a result, leakage currents are reduced by induced voltages on the windings.

Abstract: A switching power supply has a function of improving a power factor, and outputs insulated DC. The switching power supply performs two kinds of controls for switching devices exclusive to each other: controlling of a switching device provided in a direction in which the discharging of a primary-side smoothing capacitor is prohibited at the time of suspension of commercially available AC power and near the zero cross of an input voltage; and causing a switching device provided between the output side of a third winding and the primary-side smoothing capacitor to control a charging current, thereby charging a capacitor in a boosted manner.

Abstract: A feedback control circuit for a power converter and a power converter system, includes a sampling network, configured to sample an input or output of the power converter, and output a first sampled signal; a filtering network, configured to receive the first sampled signal and output a second sampled signal, the filtering network filtering a ripple signal at a preset frequency out from the first sampled signal, so as to remain signals therein outside the preset frequency, while maintaining a phase delay between the second sampled signal and the first sampled signal within a preset range; a control and drive circuit, configured to receive the second sampled signal, and regulate in accordance with the second sampled signal a control signal outputted from the control and drive circuit to the power converter.

Abstract: A neutral point clamped three-phase three-level inverter is connected to a first DC power supply and single-phase inverters are connected in series with AC output lines of individual phases of the three-phase three-level inverter such that sums of output voltages of the three-phase three-level inverter and output voltages of the respective single-phase inverters are output to a load through a smoothing filter. An output control unit controls the three-phase three-level inverter so that the individual phases of the three-phase three-level inverter output primary voltage pulses at a rate of one pulse per half cycle and controls the individual single-phase inverters by PWM, so that output voltages to the individual phases of the load form sine waves of which phases are offset by 2?/3 from one phase to another, the sine waves having the same peak value.

Abstract: A motor driving apparatus is provided that performs AC/DC conversion by suppressing harmonics of the input at the time of normal operation, while on the other hand, allowing system operation to continue in the event of an overload by avoiding system stoppage.

Abstract: The present invention relates to valve current control method based on modular multi-level converter, this method includes the control of the low frequency oscillations of the current and that of double frequency harmonic component; For said low frequency oscillations of the current, the control method includes some steps as below: first, calculate the half of the sum of the upper arm current and the lower arm current, it is the valve DC current component, said DC current component is arm circulating current; Secondly, comparing the actual value of the arm circulating current to setting value of that, the error is obtained, after some signal processing, additional output set voltage is obtained.

Abstract: In order to reduce the average power of the ringing noise, the present invention provides a power converter comprising: an arm circuit including a high-voltage side switching device to which a first diode is connected in parallel and a low-voltage side switching device to which a second diode is connected in parallel; and a main power supply connected to a series circuit of the high-voltage side switching device and the low-voltage side switching device, wherein a connecting point between the high-voltage side switching device and the low-voltage side switching device is connected to a load, and a resonant frequency calculated from inductances of wirings of a closed circuit including the first diode, the second diode, and the main power supply and a capacitance across the first diode is different form that calculated from the inductances of the wirings and a capacitance across the second diode.

Abstract: A voltage converting apparatus includes a series connection of at least four switching elements each including at least one semiconductor device of turn-off type and a free-wheeling diode connected in anti-parallel therewith. The apparatus has a device configured to measure a parameter representative of the voltage across each free-wheeling diode when turned off and an arrangement configured to control the amount of charge stored in each diode at the moment the diode is turned-off by stopping to conduct depending upon the results of the measurement carried out by the device for controlling the voltage across the diode after turn-off thereof.

Abstract: A resonance power generator is provided. The resonance power generator includes an alternating current/direct current (AC/DC) rectifier to rectify an input signal of an alternating voltage and an AC generator to generate an AC signal based on the rectified signal that is output from the AC/DC rectifier. The resonance power generator may also include, for example, a control unit to control a frequency of the AC signal, a filter unit to remove a spurious signal or a harmonic element included in the AC signal, a voltage/current amplifier to amplify the AC signal, and a source resonator to transmit a power to a target resonator.

Abstract: An exemplary method and an apparatus implementing the method for an arrangement having a three-phase, multi-level inverter, an output LCL-filter connecting the inverter to a grid, and a virtual-ground connection between the LCL-filter and the neutral point of the DC-link. The method includes determining a zero-sequence component of an LCL-filter inverter-side current, calculating a zero-sequence damping and balancing voltage term based on the LCL-filter inverter-side current zero-sequence component and voltages over the two halves of the DC-link, and adding the zero-sequence damping and voltage balancing term to the output voltage reference.

Abstract: A control section which repeats inverter control in units of an inverter control period having a predetermined length is provided. In the control section, a phase current detection period in which a phase current is detected is provided between predetermined two inverter control periods, each of switching states of switching elements of a inverter circuit is controlled so that a voltage pulse having a larger width than a width of a voltage pulse in the inverter control period is output from a shunt resistor in the phase current detection period.

Abstract: An uninterruptable power supply (UPS) designed to switch power inputs between an alternating current mode and a battery mode by adjusting the amplitude and/or frequency windows of the input voltage so that the uninterruptible power supply accepts the unstable voltage and/or frequency. This prevents the uninterruptible power supply to switch back to the battery mode during a transfer time between the battery mode and the AC mode. The uninterruptable power supply includes a control circuit. The control circuit modifies the monitored value and/or actual amplitude and/or the frequency window when unstable amplitude and/or an unstable frequency are detected at the input terminal of the input voltage.

Abstract: Disclosed is an inverter with outputs being connected through two reactors to a utility network, whilst an energy storage capacitor (C) is connected to the PV array (P) such that the C + and ? terminals are connected to two half bridges creating an H bridge so that the AC node of one half bridge is connected to the anode of a diode (D1) and the cathode of a diode (D2). An AC node of the other half bridge is connected to an anode of a diode (D3) and a cathode of a diode (D4), whilst the diodes form a diode bridge having a positive node connected to a transistor's (V5) collector and an anode of a diode (D5), the cathode of the diode (D5) being connected to C's positive terminal.

Abstract: According to one embodiment, an electronic device includes a positive electrode, a negative electrode, a first terminal, a second terminal, a first plurality of switching elements and anti-parallel diodes coupled between the positive electrode and the first terminal and the second terminal, a second plurality of switching elements and anti-parallel diodes coupled between the negative electrode and the first terminal and the second terminal and a PiN diode coupled between the positive electrode and the negative electrode with reverse polarity.

Abstract: A power converting device is disclosed that can reduce switching loss occurring in a voltage source inverter that drives an AC motor. It is possible to supply DC power to the voltage source inverter from both a voltage source rectifier, which converts AC power from an AC generator into DC power, and a battery. A first switching circuit is inserted between the voltage source rectifier and the AC generator, and the battery is connected to the output side of the voltage source rectifier. A second switching circuit is inserted between the battery and the voltage source inverter. A third switching circuit and a reactor are inserted in series between the input side of the voltage source inverter and the input side of the voltage source rectifier. At least one of an upper arm and a lower arm of the voltage source rectifier can be chopper controlled.

Abstract: The present invention relates to an electrical device for charging accumulator means (5), said electrical device comprising: a motor (6) connected to an external mains (11); an inverter (2) connected to the phases of said motor (6); and switching means (4) integrated into the inverter (2), said switching means (4) being configured to permit said motor (6) to be supplied and to permit the accumulator means (5) to be charged by the inverter (2). According to the invention, said electrical device further includes, for each phase of said motor (6), an RLC low-pass filter (18) connected, on the one hand, to the mid-point (16) of the phase of said motor (6) and, on the other hand, to ground.

Abstract: An inverter apparatus comprising a first switch group that is connected to a DC power source and includes a first switch and a second switch connected in series; a capacitor that has one end thereof connected to a first connection point between the first switch and the second switch; a second switch group that is connected in parallel with the capacitor and includes a third switch and a fourth switch that are connected in series; a switch control section that controls an ON/OFF state of the first switch, the second switch, the third switch, and the fourth switch to convert DC voltage from the DC power source into AC voltage and output the AC voltage from a second connection point between the third switch and the fourth switch; and a smoothing circuit that is connected to the second connection point and normalizes a pulse waveform of the AC voltage.

Abstract: The invention comprises a high frequency inductor filter apparatus coupled with an inverter yielding high frequency harmonics and/or non-sixty Hertz output. For example, an inductor/converter apparatus is provided that uses a silicon carbide transistor to output power having a carrier frequency, modulated by a fundamental frequency, and a set of harmonic frequencies. A filter, comprising an inductor having a distributed gap core material and optional magnet wires, receives power output from the inverter/converter and processes the power by passing the fundamental frequency while reducing amplitude of the harmonic frequencies.

Abstract: The present invention relates to a near zero current-ripple inversion circuit including top and bottom cells, a transformer (T1) comprising primary windings (P1, P2) and a secondary winding (S1), and at least one middle cell connected in series between the top and bottom cells. The top cell comprises two capacitors (C1, C2) and a switch (Q1) each connecting to the middle cell, and an inductor (Lr1) and the primary winding (P1) connected in series between the capacitor (C1) and switch (Q1), wherein the switch (Q1) is connected to the capacitors (C1, C2) respectively. The bottom cell comprises a capacitor (C3) and a switch (Q2) each connecting to the middle cell, and an inductor (Lr2) and the primary winding (P2) connected in series between the capacitor (C3) and switch (Q2), wherein the primary winding (P2) is connected to the middle cell, and the capacitor (C3) and switch (Q2) are connected.

Abstract: The invention relates to a method for controlling a multi-phase power converter having at least two phase modules (100) comprising valve branches (T1, . . . , T6) having bipolar subsystems (10, 11) connected in series, at low output frequencies (f). According to the invention, a target value (u1 (t), . . . , u6 (t)) of a valve branch voltage overlaps a common-mode voltage (uCM(t)) such that a sum of two valve branch voltages (u1 (t), U2 (t) or U3 (t), U4 (t) or U5 (t), U6 (t)) of each phase module (100) equals an intermediate circuit voltage (Ud) of said multi-phase power converter. In this manner a known converter having a triphase power converter comprising distributed energy accumulators on the grid and load side, or merely on the load side, may be utilized as a drive converter, which may start up from the idle state.

Abstract: A pulse width modulation controller and method for output ripple reduction of a jittering frequency switching power supply detect the current of a power switch of the switching power supply to generate a current sense signal, and adjust the gain or the level of the current sense signal according to the switching frequency of the power switch to adjust the on time of the power switch, to reduce the output ripple of the switching power supply caused by the jittering frequency of the switching power supply.

Abstract: The present invention generally relates to power electronic switching circuits and in particular to inverter modules employing two or more controlled switches that can be used with reactive loads. An inverter circuit is provided which includes first and second input terminals for being connected to a DC power source; first and second output terminals for outputting an AC voltage; at least one metal oxide semiconductor field effect transistor, MOSFET, having a parasitic body diode. The inverter circuit further includes at least one disabling element for disabling said body diode. This may result in an improved efficiency of the inverter circuit in combination with a reactive power capability. Further, a semiconductor switching device is disclosed, comprising at least one metal oxide semiconductor field effect transistor, MOSFET, and at least one insulated gate bipolar transistor, IGBT, wherein said MOSFET and said IGBT are connected in parallel.

Abstract: According to one embodiment, a system includes modules to detect a node voltage and an output current of a converter, a detector to obtain an effective power value, a system condition detector to detect a power supply condition in the electric system or the operating conditions of devices included in the electric system and then output a first signal, a setting unit to switch a set value to a preset first or second value and then output the set value, a unit to calculate an angular frequency of an output voltage of the converter on the basis of an output of the detector, the value, and an output of the system condition detector, and a unit to calculate a target value of the converter.

Abstract: To make it possible to avoid an unstable state with a simple configuration even one of the phases of the motor fails. A motor drive system in accordance with the present invention includes a motor to which a plurality of phase coils of five phases or more are connected in a star connection, an inverter connected to one end of each of the phase coils, the inverter being configured to convert a DC power into an AC power and supply the AC power to each phase of the motor, a power relay disposed at another end of each of the phase coils, the power relay being configured so as to be able to cut off a supply power to at least one phase coil among the plurality of phase coils of the motor by using a plurality of contact points interposed between the star-connected coils, and a control unit that generates a control signal for the inverter and thereby controls driving of the motor.

Abstract: A method is provided for determining a control scheme for a voltage source converter (VSC) with a topology of three bridge legs between each of three phases of a grid and a neutral point. The method includes: analyzing the waveform of the grid and/or a load voltage and determining an allowed period for no-swilching of the corresponding bridge leg; operating the VSC with different clamping carrier modulator frequencies, and then analyzing the balance in the operating junction temperatures and/or power losses across the active switches and also analyzing the total losses of the VSC; comparing the balance and the total losses of different clamping carrier modulator frequencies and selecting the clamping carrier modulator frequency; operating the VSC with the selected clamping carrier modulator frequency, and optimizing the balance in the operating junction temperatures and/or power losses across the active switches and the total losses of the VSC.

Abstract: A three-phase power converter includes a converter configured to convert a three phase AC power input to a DC power output, the DC power output being provided to high and low sides of a DC bus, and an inverter coupled to the DC bus and configured to convert the DC power to a three phase AC output. The inverter comprises three legs and each leg comprises a pair of solid state switches and a respective output therebetween. The power converter further includes a common mode voltage control filter comprising three filter inputs and two filter outputs, each filter input coupled to an output of a respective leg of the inverter and each filter output coupled to a respective side of the DC bus.

Abstract: A device for converting a DC voltage into an AC voltage includes a passive electronic filter having a first and second energy storage element, a third energy storage element placed between the first and second energy storage elements, a fourth energy storage element connected between a junction of the first energy storage element and the third energy storage element and an AC terminal and a fifth energy storage element connected between a junction of the second energy storage element and the third energy storage element and the AC terminal. The energy storage elements are of two different types, capacitive and inductive, with values selected to provide reduction of frequency components at two times the fundamental frequency of the AC voltage and at three times the fundamental frequency of the AC voltage.

Abstract: A device for converting a DC voltage into an AC voltage and vice versa comprises at least one phase leg with a first voltage source and a first inductor connected in series between a first DC terminal and a first AC terminal and with a second inductor and a second voltage source connected in series between the first AC terminal and a second DC terminal, where each of the voltage sources comprises at least a first and a second submodule in series-connection, each submodule comprising at least one power electronic switch connected in parallel with at least one capacitor. In the device, a passive electronic filter is arranged between the first and the second inductor as well as the first AC terminal for reducing harmonics in a circulating current.

Abstract: A method of controlling the grid-side current of a single-phase grid-connected converter having an LCL filter connected between the output of the converter and the grid includes measuring a grid voltage and at least one signal in a group of signals consisting of a grid-side current, a converter-side current and a capacitor voltage, estimating the fundamental component of the grid voltage, forming a grid-side current reference, a converter-side current reference and a capacitor voltage reference for the grid-side current of the LCL filter, forming estimates for the non-measured signals in the group of signals, forming a grid-side current difference term, a converter-side current difference term and a capacitor voltage difference term, and controlling the output voltage of the converter based on the grid voltage, a formed injection term and a formed estimate of the harmonic distortion term to produce a grid side current corresponding to the current reference.

Abstract: An arrangement transmits power between a DC power line and an AC power line carrying a voltage having a number of phases. The arrangement includes a number of transformers, one for each phase and a number of power transfer modules, one for each phase, connected in series between the DC power line and ground, where each module includes a first branch including series connected converter cells and a second branch including series connected switching elements. The primary winding of a transformer is connected to a corresponding AC phase conductor of the AC power line and the secondary winding is connected between a midpoint of the first branch and a midpoint of the second branch of a corresponding power transfer module.

Abstract: An alternating current chopper circuit with low noise is disclosed. The circuit includes a switching circuit, a first freewheel circuit, and a second freewheel circuit. The switching circuit has a control switching unit, which turns on and or off accordingly to a control signal. The first freewheel circuit and the second freewheel circuit are for providing a current-conducting path to the motor, when the control switching unit is turned off.

Abstract: When applying a high frequency voltage which alternates on positive and negative sides to a permanent magnet synchronous motor, a driving system of synchronous motor switches the applied voltage phase by 120 degrees successively and applies resultant voltages to three phases. A pulsating current generated by applying a high frequency voltage is detected at timing of elapse of a predetermined time ?t since an output voltage of at least one phase has changed from a state in which all output voltages of the three phases of a power converter are positive or negative. Current detection is conducted by using a DC resistor or a phase current sensor provided on a DC bus. A magnetic pole estimation unit calculates the rotor magnetic pole position of the permanent magnet synchronous motor on the basis of differences between positive side and negative side change quantities in three-phase currents obtained from detected current values.

Abstract: A voltage source converter station including a multilevel voltage source converter, for conversion of electrical power between AC and DC, and a control system. The voltage source converter includes a plurality of switching cells including switchable semiconductors, and the control system includes at least one main control unit for providing a voltage reference signal and a plurality of cell control units. Each cell control unit uses carrier based pulse width modulation for controlling the switching of a respective cell, where the main control unit is communicatively connected to the cell control units and provides the reference voltage signal to each cell control unit and each cell control unit creates a switching signal to each respective switching cell using the reference voltage signal and a carrier signal to effectuate the conversion.

Abstract: A power conditioner of a photovoltaic system is configured operate at higher accuracy. A chopper circuit, a capacitor connected in parallel to the chopper circuit, and a control circuit that controls an ON/OFF status of switch elements in the chopper circuit to control charging and discharging of the capacitor are provided. The control circuit includes a measurement control section that measures an inter-end voltage of the capacitor and a control circuit section that performs a predetermined control operation from a measurement output of the measurement circuit section. The measurement circuit section includes a differential amplifier circuit that differentially amplifies the inter-end voltage of the capacitor. The circuit control section calibrates an in-phase component in the output of the differential amplifier circuit as an in-phase error and performs the control from the calibrated output from the differential amplifier circuit.

Abstract: A power converter system includes a converter configured to be coupled to a power generation unit for receiving power from the power generation unit, and a bus coupled to the converter, wherein a voltage is generated across the bus when electricity is conducted through the power converter system. The power converter system also includes an inverter coupled to the bus and configured to supply power to an electrical distribution network, and a control system coupled to the converter and to the inverter. The control system is configured to gradually adjust the voltage across the bus during at least one of a shutdown sequence and a startup sequence of the power converter system.

Abstract: A capacitor circuit includes a first capacitor line including a film capacitor and a second capacitor line including a ceramic capacitor that are connected in parallel with each other. The second capacitor line includes an inductance element that is connected in series with the ceramic capacitor. The inductance element is set to a value such that a series resonant frequency of the first capacitor line and a series resonant frequency of the second capacitor line are matched.

Abstract: A method and an apparatus for controlling a grid-connected converter which includes a boost converter, a buck converter, and a current source inverter having an output CL filter. An input of the buck converter input is connected to an output of the boost converter, and an input of the current source inverter is connected to an output of the buck converter. The method includes controlling a boost converter input voltage, controlling a boost converter output voltage through control of a buck converter output voltage, and controlling the current source inverter to produce an AC current from the buck converter output voltage. The apparatus implements the method.

Abstract: A multiple inverter and an active power filter system are disclosed in the invention, said multiple inverter can decrease the volume and harmonics, increase the efficiency and decrease the cost, and can be applied to various occasions. The technical scheme is: the filter assembly in the multiple inverter is installed at the output inductor of the multiple inverter for filtering the harmonics.

Abstract: A multiple inverter with neutral line inductor and an active power filter system are disclosed. In the disclosure, the multiple inverter comprises at least two inverter units connected in parallel, the midpoint of the direct current bus in each inverter unit is connected to the neutral line N through the respective neutral line inductor. The multiple inverter can suppress the ripple produced by the neutral line current without increasing the direct current bus capacitor.

Abstract: An inverter and an active power filter system have been disclosed in the invention, so that the application range of the inverter under the occasions of different capacitor requirement can be widened, the cost can be decreased, and the efficiency can be improved. The technical scheme is: an auxiliary capacitor module can be added on the traditional inverter structure and connected in parallel selectively with the capacitor in the inverter. In a system without connecting an external auxiliary capacitor module, the value of capacitance can be designed to be smaller to satisfy the application under normal occasions. If the device operates under the occasions having large harmonic current or having large neutral line current, the ripple current on the capacitor will be larger so that large capacitance will be required to satisfy the life requirement, therefore, the problem can be solved by a method of installing an auxiliary capacitor module.

Abstract: The present invention includes: an inverter 1 configured to perform pulse wide modulation on an output from a DC power source 5; a first capacitor pair 41 provided at an input side of the inverter and including two capacitors serially connected to form a neutral point; a second capacitor pair 42 provided at an output side of the inverter and including two capacitors serially connected to form a neutral point; a bypass path g for a leakage current formed by connecting the neutral point of the first capacitor pair and the neutral point of the second capacitor pair to each other; at least one common mode choke coil 3 provided between the first capacitor pair and the second capacitor pair and configured to suppress a common mode current generated in the inverter; and an output filter 2 configured to convert a voltage, which is outputted from the inverter and subjected to the pulse wide modulation, into a voltage in a sine wave form.

Abstract: An electric power converter includes a DC stabilization circuit (2) configured to stabilize a DC voltage from DC power supply (1), and an inverter (3) configured to convert the DC voltage stabilized by the DC stabilization circuit (2) to an AC voltage. The DC stabilization circuit (2) includes an aluminum electrolytic capacitor (4) configured to smooth the DC voltage, a saturable reactor (5) configured to prevent the DC stabilization circuit (2) from oscillating, and a film capacitor (6) configured to supply a ripple current to the inverter (3).

Abstract: A method of damping harmonic output of an inverter is provided. The method may receive output phase signals from sensors disposed at an output of the inverter and on an associated electrical grid, filter the output phase signals using a low pass filter configured to extract a fundamental component from the output phase signals, isolate harmonics from the output phase signals based on the extracted fundamental component, and subtract the harmonics from the output phase signals.

Abstract: A power conversion apparatus includes two power conversion circuits, two direct-current inductors, and a pulse-width-modulation control circuit. One of the two power conversion circuits is connected in parallel to a direct-current load or a single-phase alternating-current load, and the other of the two power conversion circuits is connected in parallel to a three-phase alternating-current load. The two power conversion circuits are connected in reverse polarity to each other via the two direct-current inductors. The pulse-width-modulation control circuit pulse-width-modulates the two power conversion circuits, allows switching between the two power conversion circuits, and realizes a bidirectional step-up/down operation between the direct-current load or single-phase alternating-current load and the three-phase alternating-current load.

Abstract: Disclosed is a system and a method for controlling torque of induction motor in electric vehicle. The system and method for controlling torque of induction motor in electric vehicle according to the present disclosure has an advantageous effect in that torque control problems caused by saturation of magnetic flux, parameters of induction motor and changes in battery voltages during control of torque in the induction motor can be solved using a look-up table (a type of data table), thereby enhancing accuracy in torque control and improving travel performance and fuel efficiency of the electric vehicle.

Abstract: The present invention is a single-phase voltage source DC-AC power converter and a three-phase voltage source DC-AC power converter.

Abstract: A power converting apparatus and a photovoltaic module are discussed. The power converting apparatus includes a converter including a tapped inductor and a first switch, the converter converting a level of an input direct current (DC) voltage and outputting the level-converted DC voltage, and an inverter including a plurality of switches, the inverter converting the level-converted DC voltage into an alternating current (AC) voltage. The inverter operates separately in a first switching mode where the inverter performs a switching operation at a first frequency for a first period of the converted AC voltage and a second switching mode where the inverter performs a switching operation at a second frequency for a second period of the converted AC voltage, the second frequency being lower than the first frequency.