Abstract: A circuit for use in a switched mode power supply comprising includes an integrated circuit, a transformer, a capacitor, a low voltage circuit and a current limiting resistor. The IC jitters the switching frequency of the switch based on a bias voltage of the integrated circuit. The IC also includes a current source configured to supply current for operation of the switching regulator when insufficient current is available from the bias input pin. The transformer includes primary, secondary and auxiliary windings. The primary winding receives a rectified line voltage and is coupled to the switch. The capacitor is coupled between the bias input pin and ground. The low voltage circuit is coupled to the auxiliary winding, and provides current to the bias input pin. The current limiting resistor limits current produced by the low voltage circuit to less than that required for operation of the IC.

Abstract: A power converter for powering a gradient coil (22) of a magnetic resonance examination system, comprising: a plurality of essentially identical switching cells (14, 16, 18), each switching cell (14, 16, 18) having a plurality of switching members (52) that are provided to switch between a conducting state configuration and an essentially non-conducting state configuration, and the switching cells (14, 16, 18) being provided to switch at at least a fundamental switching frequency fSW and in a pre-determined temporal relationship to each other, a pulse control unit (20) provided to control the pre-determined temporal relationship of switching of the switching cells (14, 16, 18) by providing switching pulses to the switching members (52) of the switching cells (14, 16, 18), wherein the pulse control unit (20) is provided to determine a correction for the pre-determined temporal relationship of the switching of the switching cells (14, 16, 18) from at least one electrical quantity each of each one of the plurali

Abstract: A power converter includes a first arm configured by connecting a diode to a switching element, a second arm configured by connecting a diode to another switching element, a third arm formed of a first bidirectional switch configured by connecting switch elements, and a fourth arm formed of a second bidirectional switch configured by connecting other switch elements. An inverter circuit is configured by connecting the first and second arms in series between terminals of a direct current power source circuit, by connecting the third arm between a terminal of an alternating current power source and an output terminal, and by connecting the fourth arm between the output terminal and another output terminal. The control mode of the inverter circuit is switched between control modes at a timing at which at least one common arm continues a conductible condition.

Abstract: The invention relates to an electric motor having a stator and a rotor. The electric motor also comprises a controller, wherein the controller is connected to the stator and/or rotor, and is designed for applying current to the stator and/or rotor for rotating the rotor. According to the invention, the controller comprises a pulse width modulator designed for controlling a power output of the electric motor, in order to generate a predetermined number of different current application patterns. The current application patterns each represent a power output of the electric motor, and preferably comprise a time sequence of current pulses, each having a current pulse duration.

Abstract: A carrier generating unit applies a carrier that monotonically decreases to a switching control unit during either one of a first period that is a period immediately following a period in which a voltage command value is a value not more than a minimum value of the carrier, the voltage command value taking a first predetermined value larger than the minimum value of the carrier in the first period, and a second period that is a period immediately preceding a period in which the voltage command value is not less than a maximum value of the carrier, the voltage command value taking a second predetermined value smaller than the maximum value in the second period.

Abstract: There is provided a power controller including a drive circuit connected to a DC power supply to apply a first voltage to the drive circuit and configured to supply power to an external load, a current detection circuit configured to detect a current flowing in the drive circuit by converting the current into a second voltage corresponding to the current, and a current-voltage control unit configured to generate a reference voltage corresponding to a limit value of the current flowing in the drive circuit when the first voltage is applied to the drive circuit, and configured to control the drive circuit to operate in a desired current according to the first voltage, based on a comparison result of the reference voltage and the second voltage.

Abstract: A ripple compensation apparatus comprises a ripple detection unit to detect a ripple on a dual DC bus, a waveform generation unit to generate a modulated waveform based on a base waveform and the detected ripple, and a multi-phase control signal generation unit to receive the modulated waveform and to generate at least one pulse width modulated control signal based on the modulated waveform.

Abstract: A system includes power electronics inverters connected in a network. The power electronics inverters can utilize measurements at local terminals, without a need to exchange information between other power electronics inverters.

Abstract: A power conversion device includes a first capacitor connected in parallel to a direct-current power supply, plural power converters that drive plural synchronous machines, a second capacitor connected in parallel to a direct-current side of power converters, a switching circuit inserted between the first and second capacitors, a switch-start instruction unit that controls starting of an operation of the power converters, and a control unit that controls the power converters based on a motor velocity and a voltage of the first capacitor. The switch-start instruction unit turns off the switching circuit while the power converters stop, turns off the switching circuit until a terminal voltage of each of the synchronous machines becomes equal to a predetermined value when each of the power converters starts operating, and turns on the switching circuit when the terminal voltage of each synchronous machine becomes equal to or smaller than the predetermined value.

Abstract: A system for providing, from a direct current (DC) voltage source, an alternating current (AC) to an electrical grid outputting a grid voltage, the system including: a transformer for coupling to the DC voltage source through a first switch controlled by a first control signal, and configured to provide a converted voltage based on a DC voltage; a rectifier coupled to the transformer, and configured to generate an envelope voltage of the converted voltage; a plurality of switches coupled to the rectifier to receive the generated envelope voltage of the converted voltage, the plurality of switches being controlled by a plurality of control signals, respectively, and configured to generate the AC from the generated envelope voltage of the converted voltage; and control apparatus coupled to the first switch and the plurality of switches, and configured to provide, based on the grid voltage, the first control signal and the plurality of control signals.

Abstract: An output current distortion compensating apparatus in an inverter is disclosed, the inverter including an inverter controller generating a PWM signal for controlling a PWM voltage generator, wherein the inverter controller includes a first dead time compensation voltage generator generating a compensation voltage based on an output current polarity of each phase in the inverter, and a second dead time compensation voltage generator generating a compensation voltage based on an output current waveform of each phase in the inverter, and wherein a first dead time compensation voltage outputted from the first dead time compensation voltage generator and a second dead time compensation voltage outputted from the second dead time compensation voltage generator are added to generate a final dead time compensation voltage, thereby preventing occurrence of hunting phenomenon in which a current is greatly fluctuated.

Abstract: A voltage control rate of an inverter has a DC component and an AC component. This AC component has a frequency which is six times a fundamental frequency of an AC voltage outputted by the inverter. Even when there are not only a fifth-order harmonic component but also a seventh-order harmonic component of a load current, a ratio between the magnitude of the AC component and the DC component can be appropriately set.

Abstract: A power conversion device includes an inverter unit and a control unit. The inverter unit includes high SWs and low SWs for each phase of coils of a motor. The control unit, in a case that the on-time of the high SWs and the low SWs is shorter than a predetermined time determined based on a dead time, changes an output voltage average value such that the on-time of the high SWs or the on-time of the low SWs becomes longer than the predetermined time. The voltage use rate can be improved without disposing a special circuit, and distortion of inter-line voltages or distortion of currents can be suppressed.

Abstract: A non-isolated inverter including a DC input-side, a capacitor connected in parallel with the DC input-side, an AC output-side connected in parallel with a load, and first and second bridge-arm units is provided. The first and second bridge-arm units are connected in parallel with the capacitor. The first bridge-arm unit includes a series forward-connection of upper and lower switch-elements, where a common-node of upper and lower switch-elements and a supplying terminal of the second bridge-arm unit are respectively connected to two terminals of the AC output-side. The upper and lower switch-elements are respectively turned on in positive and negative half cycles of an output current of the non-isolated inverter, and the generation of common-mode currents in the non-isolated inverter is suppressed under a clamping action between the upper and lower switch-elements due to there are no high-frequency voltages on the parasitic-capacitors from the non-isolated inverter to the ground.

Abstract: There is provided a method and control system for reducing noise in a power converter by controlling a switching device in the power converter according to a modulation scheme. The switching device couples a direct current (DC) source to provide an alternating current (AC) output at a particular switching frequency. The method includes the step of, in each switching period, switching the switching device between active configurations providing a finite voltage at the output and inactive configurations providing a zero voltage at the output. The ratio between the total period of time in which the switching device is in an active configuration and the total period of time in which the switching device is in an inactive configuration is the same for each switching period and is determined according to the desired voltage at the AC output.

Abstract: The invention relates to a network feed device (10) for feeding electrical energy from a DC energy source (12) into a three-phase AC supply network (32), where the DC voltage of a DC intermediate circuit (24) is converted by means of at least one inverter unit (14) into a three-phase voltage and is fed by means of a transformer device (16) comprising three network transformer windings (38) into the AC supply network (24). The invention is characterized in that a first winding terminal of the network transformer windings (38) is connected to a half-bridge (30) of a first inverter device (14a), and a second winding terminal of the network transformer windings (38) of the transformer device (16) is connected to a half-bridge of a second inverter device (14b).

Abstract: The present invention relates to a switched-mode power supply apparatus and a corresponding method. For an effective compensation of non-linearities caused by dead-time and voltage drops in the switching power amplifier of the apparatus, an apparatus is proposed comprising a switching power amplifier (14) for amplifying a signal supplied by an external signal source (11) and for supplying a load voltage and/or load current to a load (15), and a control unit (12; 12b) for controlling the switching of said switching power amplifier based on a timing setting, said control unit being adapted for simulating the behavior of the switching power amplifier by predicting the average load voltage and/or load current for at least two, in particular a plurality of, timing settings for a desired load voltage and/or load current based on state information about the present state of the switching power amplifier.

Abstract: In an inverter apparatus, an output voltage of an active filter circuit that steps up and smoothes a DC voltage is converted into an AC voltage by an inverter circuit. The active filter circuit includes a capacitor and a rectifier device connected between an input node and an output node. An inductor, one end of which is connected to the input node and the other end of which is connected the output node through the rectifier device, and a switch device connected between the other end and a low-potential-side line, and a first control circuit for the switch device are provided. The inductor stores energy while the switch device is on and releases the energy while the switch device is off. The rectifier device conducts such that the stored energy of the inductor is released.

Abstract: A reactive energy compensator that can be electrically connected to an AC electrical network, including at least one input direct voltage bus, at least one voltage inverter including switches and first and second capacitors having first and second voltages at their terminals, control means for the switches, including computation means capable of generating a target control current, means for combining the target control current and the output current from the inverter, means for transmitting a control signal capable of driving the switches, and correction means for the control signals of the switches, the correction means being capable of adding a balancing current to the target control current, the balancing current being able to correct the target control current so as to reduce the difference between the values of the first and second voltages, the target control current being increased for an even harmonic of the network frequency.

Abstract: An optimized pseudo-random period pattern can reduce audible noise in a system that includes an inverter circuit configured to provide power to an electric machine. A system can include a PWM optimization module (POM) comprising the PPP. A carrier period for a carrier signal used to provide PWM inverter drive signals can be selected in accordance with the PPP. The PPP can be expressed as an array of 200-400 elements, each element a period belonging to a finite set of 2 or more predetermined periods. A period can be selected by index from the array, and the index incremented to progress through the PPP, which can be repeated upon its completion. The PPP can be optimized to reduce audible noise while mitigating inverter losses. Modeling techniques can determine the number of array elements, the number of possible periods, and the period values that optimize the PPP.

Abstract: A power converter for effectively reducing switching noise is provided. The power converter comprises a capacitor 111; switching devices Q11a and Q11b connected to the capacitor 111 in parallel; and a controller 105 that controls each switching device individually to perform switching operations. Each of the switching devices Q11a and Q11b forms a closed circuit together with the capacitor 111. The controller 105 controls the switching devices Q11a and Q11b to perform switching operations of switching ON or OFF at different timings such that at least two closed circuits including the switching devices Q11a and Q11b mutually cancel ringing voltages occurring therein, each ringing voltage occurring due to the switching operations performed by a corresponding switching device and having a frequency defined by an inductance of a corresponding closed circuit and an output capacity of a switching device included in the corresponding closed circuit.

Abstract: An inverter device includes a voltage command value output unit that outputs a voltage command value, voltage sensors that detect output voltage from a switching circuit, a Fourier transform unit that performs frequency analysis on the output voltage detected by the respective voltage sensors, and a voltage correction value calculation unit that obtains harmonics with respect to a drive frequency of the switching circuit subjected to the frequency analysis by the Fourier transform unit and obtains a voltage correction coefficients for correcting the voltage command value so as to cancel the harmonics. The voltage correction value calculation unit calculates coefficients each for each degree of the harmonics and determines whether the coefficients converges when calculating the coefficients so as to obtain the voltage correction coefficients based on the coefficients which are determined to converge.

Abstract: In an embodiment, a method of generating a pulse-width modulated signal from an input signal includes calculating a finite number of basis functions of a first pulse-width modulated signal based on the input signal, and forming an electronic output based on the calculated finite number of basis functions.

Abstract: A control device controls an inverter controlling an output of a motor by PWM control. The control device calculates a reference frequency based on a torque and a rotation speed of the motor, calculates a random coefficient using two data tables, and calculates, as a random frequency, a value obtained by adding, to a reference frequency, a value obtained by multiplying a prescribed width by the random coefficient. The control device calculates control limit lines based on the rotation speed of the motor, and corrects the random frequency so as to fall within a range that is higher than the control limit line and lower than the control limit line. The control device generates a carrier signal having a random frequency as a carrier frequency.

Abstract: A power factor correction apparatus is applied to an alternating-current voltage apparatus and a rear end circuit. The power factor correction apparatus includes a power factor correction unit, a control unit, and a ripple detecting unit. The power factor correction unit is electrically connected to the rear end circuit and the alternating-current voltage apparatus. The control unit is electrically connected to the power factor correction unit. The ripple detecting unit is electrically connected to the rear end circuit, the power factor correction unit, and the control unit. The control unit is informed by the ripple detecting unit to control the power factor correction unit to adjust the power factor after the ripple of the signal outputted from the power factor correction unit is detected by the ripple detecting unit.

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: A power conversion system is disclosed that provides multiphase power, including phase voltages for each phase of the multiphase power. The system comprises a plurality of inverters that generate PWM output voltages based on PWM control signals. A plurality of inductive components is configured to receive the PWM output voltages to generate the phase voltages. The PWM output voltages cause circulating current flows through the inductive components. A voltage controller is employed that is responsive to the phase voltages to generate voltage modulation signals corresponding to the phase voltages. A plurality of current sharing channels are respectively associated with each of the plurality of inductive components and are configured generate current sharing modulation signals in response to the circulating current flows. The PWM control signals are generated based on modulation signals obtained by combining the current sharing modulation signals and voltage modulation signals.

Abstract: Methods and systems for a complete vehicle ecosystem are provided. Specifically, systems that when taken alone, or together, provide an individual or group of individuals with an intuitive and comfortable vehicular environment. The present disclosure includes a system to recognize the drivers and/or passengers within the automobile. Based on the recognition, the vehicle may change a configuration of the automobile to match predetermined preferences for the driver and/or passenger.

Abstract: An inverter device includes a DC positive input line and a DC negative input line, a main bridge which includes a pair of series-connected switching elements with diodes being connected in reverse parallel with the switching elements respectively, an auxiliary bridge which includes a pair of series-connected switching elements with diodes being connected in reverse parallel with the switching elements respectively and a current-limiting reactor. A plurality of sets each one of which includes the main bridge and the auxiliary bridge is connected between the DC positive and negative input lines. Each set constitutes a phase. The current-limiting reactor is connected between a common connection point of both switching elements of the main bridge and a common connection point of both switching elements of the auxiliary bridge in each set.

Abstract: A controller for controlling a power converter is described. The controller includes an input configured to receive at least one grid feedback signal, a filter, and an output. The filter is configured to receive the at least one grid feedback signal and generate an output signal that does not deviate by more than a predefined amount from the at least one grid feedback signal. The output is configured to provide a voltage command signal to the power converter that is based at least partially on the output signal.

Abstract: Provided is a maximum power point (MPP) tracker for a PV cell inverter, and a PV cell inverter. The MPP tracker decouples output power oscillations from the input power generation and extracts maximum available power from the PV cell. The PV cell inverter uses the MPP tracker and generates a sinusoidal output current from the MPP tracker output. The sinusoidal output current may be fed to a power distribution grid. The PV cell inverter may use a pulse width modulation technique to cancel harmonics in the sinusoidal output current. The circuits use a minimum number of components and avoid use of large electrolytic capacitors.

Abstract: A controller of a power converter including an inverter that includes plural semiconductor switching elements. The controller suppresses an error between a voltage command and an inverter output voltage and responds to a voltage command at a high speed. The controller includes a voltage command generator that generates a voltage command signal and a switching pattern calculator that calculates and outputs, based on the voltage command signal, a switching pattern of a synchronous PWM system in which an average value of an inverter output voltage matches the voltage command signal.

Abstract: A distributed power supply system in which no simultaneous disconnection from the system occurs when a system voltage momentarily drops is provided. It includes an inverter circuit that converts a direct current power generated by a direct current power supply and that supplies the alternating current power to an alternating current power supply power system, and an inverter control circuit for carrying out PWM control of the inverter circuit, wherein the inverter control circuit includes a three-phase voltage command signal generation unit, that is configured of a three-phase fundamental wave signal generation unit that generates three-phase fundamental wave signals from two phase components of voltage detected by a voltage detector, and a third harmonic signal generation unit that adds together third harmonic components of respective phases, having a predetermined amplitude, generated based on the three-phase fundamental wave signals.

Abstract: A power converter is provided. The power converter includes a converter leg including switches for converting power. The power converter also includes a controller for switching the switches using a pulse width modulation technique. The power converter further includes an interface inductor coupled to the converter leg for avoiding a reverse recovery of current in the switches during operation.

Abstract: A polarity switching circuit includes: a first current-limiting resistor and a second current-limiting resistor connected to a DC high voltage; a first transistor switch, a second transistor switch, a fourth transistor switch, and a fifth transistor switch respectively controlled by a first PWM signal and a second PWM signal; a third transistor and a sixth transistor switch whose control terminals are respectively connected to the first transistor switch and the fourth transistor switch; a first filter connected to the second transistor switch and the third transistor switch and a contact of a piezoelectric actuator; and a second filter connected to the fifth transistor switch and the sixth transistor switch and another contact of the piezoelectric actuator. When the first and the second PWM signal are switching between a high level and a low level, output AC voltages with smoothed AC waveforms are supplied to the contacts of the piezoelectric actuator.

Abstract: The multifunctional power converter apparatus and method includes an input power stage configured to receive a DC input voltage from a DC power source and convert the DC input voltage to an AC or DC output voltage. At least one electrical power conversion electronic circuit is connected to an output of the input power stage, a DC output circuit; an AC output circuit; and a controller configured to control the input power stage, the DC output circuit and the AC output circuit. The controller is configured to automatically control the power converter output voltage based on a preselected user input.

Abstract: A controller for a load drive system which can reduce a ripple current which flows in a smoothing capacitor even when an inverter is PWM controlled with a two-phase modulation includes a converter for changing an output voltage of a DC power supply, an inverter for transforming a DC voltage outputted from the converter into a three-phase AC voltage to be applied onto a load and a smoothing capacitor provided in parallel between the converter and the inverter includes an inverter controller for PWM controlling the inverter with a two-phase modulation and a converter controller for PWM controlling the converter.

Abstract: A high power control system includes: a single energy source; an energy source management unit configured to manage the energy source; a controller configured to output a PWM control signal under control of the energy source management unit; a plurality of inverters configured to convert a direct current into an alternating current under control of the PWM control signal of the controller; a plurality of filters coupled to output terminals of the inverters; and a plurality of switches configured to regulate connections between the filters and a load under control of a regulation control signal of the controller.

Abstract: The noise generated from a power converter is suppressed by increasing the noise frequency to a level not lower than the maximum frequency of the human audible range. To obtain the frequency of an output current harmonic component as a noise source which has exceeded the maximum frequency of the human audible range, it is adequate to determine that the frequency of a driving carrier wave for the individual converter cells in the power converter, in which the phases of the carrier wave for the converter cells are mutually shifted by a given value between the converter cells, meets the following equation.

Abstract: In a power conversion device that includes a PWM converting means for generating a PWM pulse by comparing three-phase voltage commands with a triangular wave carrier signal, a power converter for converting between a DC voltage and a three-phase AC voltage by driving a switching element according to the PWM pulse, a current detecting means for detecting a pulsed current flowing through a DC bus conductor of a main circuit, and a voltage command correcting means for correcting three-phase voltage commands, which corrects the three-phase voltage commands so that a line voltage value between the maximum phase and an intermediate phase and a line voltage value between the intermediate phase and the minimum phase are each equal to or larger than a predetermined value, the maximum phase, intermediate phase, and minimum phase being determined in correspondence to momentary values of the three-phase voltage commands arranged in descending order, if the voltage command is outside an allowable upper limit or lower limi

Abstract: An electric power converter apparatus includes an inverter circuit having a plurality of upper arm elements and a plurality of lower arm elements, a feedback controlling module calculating a voltage command value in order to control an output from the inverter circuit in a feedback control manner and a compensating module compensating the voltage command value with a compensation amount and outputting a compensated voltage command value. Each of the plurality of upper arm elements and the plurality of lower arm elements is operated to switch over based on a control signal that is set according to the compensated voltage command value and a dead time. The compensation amount is set by the compensating module in order to compensate a fluctuation in the output current due to the dead time.

Abstract: In an embodiment of a converter, a first oscillator provides switching signals for switching between charging and discharging of a capacitor, and a second oscillator is configured to add an offset voltage or a feedback-current-dependent voltage to a sawtooth waveform generated by the second oscillator switched in synchronism with the first oscillator.

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: There is disclosed a power supply stage, comprising: generating means for generating a power supply voltage from a high efficiency variable voltage supply in dependence on a reference signal; adjusting means for receiving the generated power supply voltage, and adapted to provide an adjusted selected power supply voltage tracking the reference signal in dependence thereon.

Abstract: A power supply circuit for an electric motor, the circuit comprising a plurality of inverter bridge arms, each having means for connection to a respective winding of the motor, each inverter bridge arm comprising in series a first insulated gate bipolar transistor and a junction field effect transistor that are connected to a controller, the circuit including a second insulated gate bipolar transistor connected in series with each field effect transistor and connected to the controller, and a damping resistor connected in parallel with the second bipolar transistor. An aircraft flight control member including a movable airfoil associated with at least one drive motor connected to such a power supply circuit.

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 dead-time generating circuit includes a constant current circuit; a current generating circuit generating a capacitor-charge current; and a control circuit receiving a dead time control signal and a comparator signal. The control circuit generates a dead time generating signal based on the dead time control signal and the comparator signal, and a charge/discharge signal based on the dead time generating signal. Charging or discharging of a capacitor is controlled by the capacitor-charge current in accordance with the charge/discharge signal. A voltage of the capacitor is compared with a threshold voltage in order to generate a comparator signal when the voltage of the capacitor exceeds the threshold voltage. The control circuit generates the charge/discharge signal for a duration starting from a time when the delay time has elapsed from the rise or fall timing of the dead time control signal until the control circuit receives the comparator signal.

Abstract: A correction-term adder 1 compares a maximum value max(V*) with an absolute value of a minimum value min(V*). The correction-term adder 1 selects a signal 1?max(V*) when the maximum value max(V*) is larger than the absolute value of the minimum value min(V*), on the other hand, selects a signal ?1?min(V*) when the absolute value of the minimum value min(V*) is larger than the maximum value max(V*). Thereby, a signal of correction amount ? is calculated. Moreover, the correction-term adder 1 produces a triangular-wave-shaped signal k(max(V*)+min(V*)) by multiplying a gain k by an addition signal max(V*)+min(V*) of the maximum value max(V*) and the minimum value min(V*). This triangular-wave-shaped signal k(max(V*)+min(V*)) is synchronized with the correction amount ?.

Abstract: Provided is a variable frequency drive and a rotation speed searching apparatus for an induction motor incorporated therein. The rotation speed searching apparatus is featured by scanning the rotor frequency of the induction motor and determining either the error between a detected DC-bus voltage and a set DC-bus voltage or the error between a detected output current and a set output current, so that the rotation speed of the induction motor can be searched out.

Abstract: A circuit switching element is provided that switches a step-up/step-down bidirectional chopper circuit, arranged between a DC bus and a power storage element, to a first chopper circuit or to a second chopper circuit, whose step-up and step-down characteristics are in a complementary relation. The first and second chopper circuits are used together at a time of charge and discharge. Accordingly, an AC motor drive device having mounted therein a power storage system is obtained, in which the power storage system can perform charge and discharge to and from the power storage element, regardless of a bus voltage and can increase energy use efficiency.