Abstract: An uninterrupted power supply (UPS) device with uninterrupted neutral from input to output utilizes the same converter for converting rectified AC power and battery power to positive and negative high voltage (HV) rails. A simple circuit is utilized for connecting the battery to the conversion components of the PFC circuit without adverse affect on the performance of the PFC circuit, and while holding the battery substantially connected to neutral. In a first embodiment, the circuit comprises a simple combination of four diodes and a pair of high pass capacitors arranged so that in both power line and battery supply modes the battery is balanced around neutral. In a second, preferred embodiment, one terminal of the battery is connected directly to neutral.

Abstract: When a PWM signal generating unit (10) sets a duty D of a PWM signal based on command signals (10c), the PWM signal generating unit (10) sets a phase difference ? between each of the PWM signals based on a relation formula of ? (degree)=360 (degree)×D (%)/100 (%), and generates and outputs first PWM signals (10a) and second PWM signals (10b) in which the duty is D (%) and the phase difference is ? (degree). The first PWM signals (10a) and the second PWM signals (10b) are respectively supplied to a first load driving circuit (21) and a second load driving circuit (22) to operate a first motor fan (3) and a second motor fan (4) by a PWM control, respectively.

Abstract: With self oscillating pulse width modulators, using a hysteretic comparator to change the output duty cycle according to the input signal, as often used for example for Class-D amplifiers or switching regulators, the frequency varies with output power and supply voltage. The disclosed invention presents a method to drastically reduce the frequency variation by introducing the combination of an analog and a digital feedback loop to shift the hysteretic threshold, ideally by providing a single absolute value, which is proportional to the pulse frequency and by alternating the polarity of shifting the hysteretic threshold, based on the actual output pulse phase.

Abstract: In a fly-back DC voltage conversion circuit, a transformer accumulates energy during the on-state of a switching element, and the accumulated energy is outputted from a secondary winding during the off-state of the switching element. The switching element is placed in the on-state when the accumulated energy is completely outputted from the secondary winding. A voltage applied to the switching element is differentiated by a capacitor to detect a discharge termination point at which the current of the transformer becomes zero to change a switching frequency of the switching element. The DC voltage conversion circuit can attain control in a current boundary state without significantly increasing cost.

Abstract: A control circuit is described in which a single input terminal receives digital control signals and analog control signals. In accordance with the principles of the invention, the control circuit includes an automatic power down circuit to place the control circuit into a low power draw or “sleep” mode whenever predetermined conditions are present. The automatic power down circuit monitors the single input terminal and when no demand for motor operation occurs for a predetermined period of time, the automatic power down circuit operates to place the control circuit into the low power draw mode.

Abstract: The present invention includes a method for thermal management in a voltage source inverter. The method includes sensing a low output frequency condition, determining a zero vector modulation responsive to the sensed low output frequency condition, and applying the determined zero vector modulation to reduce thermal stress in the voltage source inverter. The step of determining the zero vector modulation responsive to the sensed low output frequency condition includes mapping an output voltage requirement to a space vector structure and determining state switching space vectors based on the mapped output voltage requirement.

Abstract: The invention relates to a system for controlling the speed of a motor (1) of an electric fan unit comprising a field-effect transistor (3) that controls the motor (1) using pulse-width modulation, the field-effect transistor (3) being connected to a circuit (5) comprising a voltage source (7) and a resistive element (9) in series, the circuit (5) is connected between the gate (G) of the field-effect transistor (3) and a second source (S2) that is connected to a first source (S1) of the field-effect transistor (3), via an inductor (11) in order to allow a reduction in the slope of the current as the field-effect transistor (3) switches.

Abstract: A switching system, preferably for use in the power supply of motor vehicles, and having one chargeable energy memory of a specific voltage level and consumers situated in the circuit of the energy memory is further developed so that a significant power load is thoroughly prevented even in the case of a high momentary power requirement of the electric consumers. The energy memory is designed for this purpose as power-limiting primary memory (1) to ensure the operation of a first group of consumers (2). The switching system further has a secondary energy memory (4) chargeable proceeding from the primary energy memory (1) which makes energy available to a second group of consumers (5) so that during energy delivery from the secondary energy memory (4) to the consumers (5) of the second group a feedback to the primary energy memory (1) is thoroughly prevented even during loading of the same by consumers (2) of the first group.

Abstract: An interrupt signal is generated at each of rising timings of PWM signals which are produced on the basis of phase-shifted triangular wave carrier signals for phases, and voltage command values for the phases. At timings of the interrupt signals, A/D conversion of motor currents of the phases detected by a shunt is started. Interrupt signals are also produced at timings of valleys of the triangular wave carrier signals. Additionally, peak interrupt signals and valley interrupt signals are respectively produced at timings of peaks and valleys of triangular wave carrier signals for phases. Based on each of the peak interrupt signals, normality/abnormality of a switching element of an upper side of the phase corresponding to the interrupt signal is checked, and, based on each of the valley interrupt signals, normality/abnormality of a switching element of a lower side of the phase corresponding to the interrupt signal is checked.

Abstract: A converter circuit with short-circuit current protection having a DC voltage circuit (1) is proposed, which DC voltage circuit (1) is formed by a DC voltage circuit subsystem (2.1), the DC voltage circuit subsystem (2.1) having a first energy store (3) and a second energy store (4), which is connected in series with the first energy store (3), and a fuse (5). Furthermore, the converter circuit has at least one pair of branches (6) provided for each phase (R, S, T) and connected in parallel with the DC voltage circuit (1), each pair of branches (6) having power semiconductor switches. In order to achieve a low-inductance converter circuit, the fuse (5) forms the connection between the first energy store (3) and the second energy store (4).

Abstract: This specification discloses a adaptive dual-slope frequency controller for adjusting power conversion of a power supply. The converter can adjust its operating frequency according to the status of a load device. A feedback voltage, representing the load status, is used to control two pairs of charging/discharging currents of a storage capacitor in the present controller, thereby controlling the period of the voltage waveform at the capacitor. This controller can especially lower the frequency of the gate pulse of power supply to improve the overall efficiency at light load and no load.

Abstract: A motor control device is provided with a neutral point shift section. The neutral point shift section shifts a neutral point (command neutral point) of phase voltage commands so that the values of the phase voltage commands after the shifting of the neutral point come within the amplitude of a triangular wave (triangular wave signal), and inputs the phase voltage commands with the neutral point having been shifted, to a control signal output section. Thus, the motor control device is enabled to heighten the output voltage without bringing about increase in manufacturing cost and substantial delay in calculation interval.

Abstract: The invention is an electrical power converter using multiple, high frequency switching elements where the individual switching elements are operated in a synchronous, time-skewed arrangement to provide optimum ripple current cancellation.

Abstract: A pulse width modulation voltage regulator comprises a pulse width modulation circuit and a control circuit. The control circuit is operable to reduce a pulse modulation frequency of the pulse width modulation circuit when a load current increases and to increase the pulse modulation frequency of the pulse width modulation circuit when the load current decreases.

Abstract: It is an object of the invention to provide a PWM inverter control method capable of causing a reduction in a noise and energy saving to be consistent with each other by the reduction in a noise and the limit of the number of switching operations.

Abstract: A linear predictive system for a DC—DC converter including a linear predictive controller, first and second adders and a multiplier. The DC—DC converter generates an output signal and includes a digital compensation block that converts a feedback error signal into a main duty cycle signal. The linear predictive controller predicts linear changes of the main duty cycle signal in response to changes of the output signal and provides a predictive duty cycle signal. The first adder subtracts the predictive duty cycle signal from the main duty cycle signal to provide a duty cycle delta. The multiplier multiplies the duty cycle delta by a gain factor to provide a duty cycle delta sample. The second adder adds the duty cycle delta sample to the first duty cycle signal to generate an adjusted duty cycle signal.

Abstract: A control circuit is described in which a single input terminal receives digital control signals and analog control signals. A circuit coupled to the single input provides a first output to indicate that a signal at said single input terminal is a digital signal and a second output indicates that a signal at said single input terminal is an analog signal.

Abstract: A method for pulse modulation control of switching regulators includes positioning a series of parallel FET-type switches (high-side switches) between the input side of an inductor and the voltage supply. A second parallel series of FET-type switches (low-side switches) are used to connect the input side of the inductor to ground. A control module enables one or more of the high-side switches at the start of each switching cycle. The enabled high side switches remain enabled until the output of the buck-type switching regulator is within regulation or a current limit through the high-side switches has been exceeded. The control module then disables all high-side switches and enables an equivalent number of low-side switches. The low-side switches remain enabled until the output has fallen below regulation or current has ceased to flow from the inductor to the load of the regulator.

Abstract: In a method and system for an improved inverter providing power to a load, the inverter receives a direct current (DC) input. A plurality of switches included in the inverter are controlled by a plurality of control signals to generate an alternating current (AC) output in response to the DC input. A zero crossing of the AC output current provided by the plurality of switches is detected, and the controlling of the plurality of switches is delayed in response to the zero crossing. The amount of delay is adjusted responsive to a change in the DC input to effectively maintain a constant switching frequency of the inverter. The delayed AC output current of the plurality of switches is filtered to provide power to the load.

Abstract: A switched mode power supply having a regulated reflected voltage. In one embodiment, a switched mode power supply includes a power supply regulator coupled between a positive input supply rail of the power supply and a primary winding of an energy transfer element. The reflected voltage across the primary winding of the transfer element is related to the output voltage across a secondary winding of the energy transfer element according to the turns ratio of the energy transfer element. The power supply regulator is coupled to regulate the reflected voltage across the primary winding, thereby regulating the output voltage across secondary winding. In one embodiment, the reflected voltage across the primary winding is sensed through a current representative of the reflected voltage received by the power supply regulator.

Abstract: A hybrid reactive power compensation device comprises a passive type reactive power compensator and an active type reactive power compensator serially connected thereto. The passive type reactive power compensator is an AC power capacitor adapted to provide the reactive power that reduces capacity of the active type reactive power compensator. The active type reactive power compensator comprises a power converter, a DC capacitor, a high-frequency ripple filter and a controller. The hybrid reactive power compensation device can supply a linearly adjustable reactive power within a predetermined range, and is adapted to supply a current with a nearly sinusoidal waveform. Therefore, it can avoid the destruction of AC power capacitor caused by the power resonance.

Abstract: A boost quantity detecting section (103) detects a boost quantity of an inductor (L11). An operational amplifier (113) of a control section (106) compares the boost quantity detected by the boost quantity detecting section (103) with a reference voltage (ES12). When a supply voltage supplied from an AC power source (100) reduces and an output voltage is unchanged, the boost quantity detected by the boost quantity detecting section (103) increases. When a signal level of a boost quantity detection signal is higher than the reference voltage (ES12), a control section (106) reduces a target level of a switching current. The target level of the switching current decreases, so that the output voltage decreases and energy loss due to boosting reduces.

Abstract: A transformer has a primary winding connected between a pair of dc input terminals via a switch, a secondary winding connected between a pair of output terminals via a first rectifying and smoothing circuit, and a tertiary winding connected to a second rectifying and smoothing circuit for feeding a switch control circuit. Included in the switch control circuit is a switch control pulse generator circuit whereby the switch is driven to provide a constant dc voltage at the output terminals. A mode selector circuit is connected to the switch control pulse generator circuit to cause the switch to be driven continuously under normal load, and at intervals under light load. The intermittent driving of the switch is suspended, and the switch driven continuously, in the event of a drop in the output voltage of the second rectifying and smoothing circuit to a predefined value during operation in light load mode.

Abstract: A control system for an electric machine having a rotor position sensor that generates a rotor position signal, a velocity module that generates an electric angular velocity value based on the rotor position signal, a random pulse width modulation module that generates a switching period and a delay for a current cycle, and a phase angle compensation module that sums a sample rate, one half of the switching period, and the delay of a previous cycle and that outputs a delay time. The phase angle compensation module further multiplies the delay time and the electric angular velocity value and generates a compensating angle.

Abstract: A non-isolated power supply device and a method for controlling the same, wherein only one DC voltage bus is adopted and the neutral lines of the input voltage and output voltage are directly connected together. During the periods that the voltage polarities of the input voltage and output voltage are not the same, the power supply device is operated in a flyback mode to avoid the generation of an abnormal current. Otherwise, during the periods that the voltage polarities of the input voltage and output voltage are the same, the power supply device is operated in a boost mode to derive a superior efficiency.

Abstract: In a duty ratio detecting apparatus, a duty ratio detecting circuit is constructed by first and second nodes, a load current supplying circuit for supplying first and second load currents to the first and second nodes, respectively, and a current switch connected to the first and second nodes. The current switch is operated in response to first and second complementary duty ratio signals. A duty ratio maintaining circuit is constructed by third and fourth nodes for receiving and maintaining voltages at the first and second nodes, respectively. A first switch is connected between the first and third nodes, and a second switch is connected between the second and fourth nodes. The load current supplying circuit is controlled by voltages at the third and fourth nodes.

Abstract: A pulse count motor control device that connects to a central control unit through a first interface and to at least one motor through a second interface. A microprocessor integrated into the motor control device then allows it to directly monitor and drive the motor or motors in accordance with pulse count technology methods.

Abstract: The power converters employing the provided methods and controllers are proposed. The controller includes: a signal preprocessor for generating a current signal according to a sensed current of the transformer, an integrator electrically connected to the signal preprocessor for integrating the current signal and offering an integrated signal, a synthesizer electrically connected to the integrator for receiving and synthesizing the integrated signal and a slope compensation signal to generate a synthesized signal, an operational amplifier of a control loop for generating an amplified error signal, and a PWM comparator electrically connected to the operational amplifier and the synthesizer for comparing the amplified error signal and the synthesized signal and generating a PWM signal to turn on and off a switch of the transformer accordingly.

Abstract: A high bandwidth, feed-forward oscillator generates a ramp or sawtooth voltage for controlling the operation of a pulse width modulator-based, switched DC power supply circuit. The oscillator is operative to effectively immediately adjust the slope of each rising and falling portion of the ramp/sawtooth signal, as necessary, in proportion to the magnitude of the input voltage, while maintaining the frequency of the ramp waveform effectively constant. A comparator network establishes a difference between peak and valley portions of the sawtooth in accordance with input voltage. In response to a change in input voltage a control circuit modifies the value of the difference between the peak and valley portions to define a new set of respective peak and valley portions VpeakNEW and VvalleyNEW, and immediately causes the sawtooth waveform to transition to the new set of respective peak and valley portions VpeakNEW and VvalleyNEW at said prescribed frequency.

Abstract: A method with which the load current and thus the load moment of an asynchronous motor that is controlled via a phase-controlled two-phase thyristor power controller, can be easily influenced so as to allow a smooth starting operation. According to a first embodiment, the ignition point is determined in the controlled phase in order to adapt the flow angles of the subsequent current half waves. According to a second embodiment, the ignition point of the subsequent current half waves is brought forward in both controlled phases.

Abstract: Methods and apparatus are provided for controlling a stand-alone four-leg three-phase inverter. The inverter three-phase output is converted from AC domain elements to corresponding DC domain elements. The DC domain elements are processed into combined regulating and imbalance compensating signals, including over-current limiting. The compensating signals are restored to corresponding AC domain signals, and are processed into control inputs for the inverter, in order to stabilize the inverter output when connected to an unbalanced load. The inverter controller can be implemented entirely in software as a control algorithm.

Abstract: A system and method are disclosed to limit a maximum duty cycle and/or provide a volt-second clamp for a pulse-width modulated (PWM) signal. Depending on the circuit topology, this approach can limit the absolute duty cycle or operate as a volt-second clamp in which the duty cycle is limited as a function of a variable input control voltage, such as a line voltage. The duty cycle can be selectively programmed by setting one or more external reference components, such as one or more respective resistors. Additionally, through component matching, desired clamping can be achieved with a high level of accuracy.

Abstract: A generator of at least one pulse width modulated signal, including: a generator of a sawtooth signal a generator of high and low reference signals defining, based on a set-point signal, a linear range of each ramp of the sawtooth signal at least one element of comparison of the sawtooth signal with each of the reference signals and at least one element of logic combination of the comparison results, providing the pulse width modulated signal.

Abstract: A current detection method for an electric motor which detects phase currents of the electric motor driven by a power converter that provides ON/OFF control of bridge-connected switching elements, based on a pulse-width modulation excitation pattern, to convert a direct current into poly-phase alternating currents. The method includes connecting a current detecting element which produces a signal corresponding to a current value at the direct current side of the power converter and changing the pulse-width modulation excitation pattern by executing a shift of time of any of the phases of the pulse-width modulation excitation pattern so that a signal directly or indirectly corresponding to the phase currents is produced at the current detecting element. The method also includes detecting the phase currents of the electric motor based on the signal produced at the current detecting element and the excitation pattern which has been changed.

Abstract: Cross-channel interference can be a problem in multi-channel switched power systems. A multi-channel switched power converter is provided a reference count generator that generates a reference count signal that is commonly distributed to multiple, pulse width modulating (PWM) channels of the converter. The common reference count signal counts through a sequence of successive timing values. Events in each channel are scheduled relative to the common reference count. Examples of such events include the amplification or de-application of a driving voltage pulse to an inductive means of the channel and the taking of voltage and current measurement samples. Cross channel interference is avoided or minimized by scheduling or re-scheduling events in each active channel so that they do not occur simultaneously in potentially-interfering channels, for example the taking of a current measurement sample in one channel and the turning on of an inductance-driving voltage pulse is a second channel.

Abstract: An inverter control apparatus and method of a three-phase motor includes disposing three maximum phase voltage vectors each having an equivalent angle interval corresponding to maximum values of each phase voltage; setting maximum phase voltage vector regions by predetermined angles with respect to each of the maximum phase voltage vectors; setting minimum phase voltage vectors corresponding to the maximum phase voltage vectors in between the maximum phase voltage vector regions; obtaining a desirable voltage by turning on a first switch and turning off a second switch, both connected to the phase terminal of a corresponding maximum phase voltage in each maximum phase voltage vector region; and changing a duty ratio of control signals with respect to other two switches corresponding to the other two phase voltages.

Abstract: A power converter includes a first sampling device 5 which samples a first command current value for a power conversion device 2 during a second cycle and produces a second command current value; a second sampling device 6 which samples a first detected current value pertaining to a load 3 and produces a second detected current value; a command voltage value calculator 9 for calculating a command voltage value from the second command current value and the second detected current value; a comparator 11 for comparing the second command voltage value with a triangular wave carrier signal, to thereby produce a first pulse width modulation (PWM) signal; and a multi-pulse prevention device 12.

Abstract: A method and an apparatus for compensating reactive power and/or harmonic currents in an alternating-current network by means of a frequency converter (1) feeding an alternating-current load (3), which frequency converter has a mains bridge (10) and at least one load bridge (11), said bridges being provided with controllable semiconductor switches. In the method, the reactive power and/or harmonic currents in the alternating-current network are measured, the load of the mains bridge of the frequency converter is measured, and the reactive power and/or harmonic currents in the alternating-current network are compensated by means of the frequency converter when the mains bridge is running at less than full capacity or has no load.

Abstract: A power distribution system includes an ac power source; a power bus connected to the ac power source; a capacitor bank shunt-connected to the power bus; and an active filter shunt-connected to the power bus. The active filter includes current sensors, an inverter and an inverter control. Each current sensor senses current flowing through a corresponding capacitor of the capacitor bank. The inverter control, in response to the current sensors, controls the inverter to inject harmonic currents into the power bus.

Abstract: A switched mode power supply having a regulated reflected voltage. In one embodiment, a switched mode power supply includes a power supply regulator coupled between a positive input supply rail of the power supply and a primary winding of an energy transfer element. The reflected voltage across the primary winding of the transfer element is related to the output voltage across a secondary winding of the energy transfer element according to the turns ratio of the energy transfer element. The power supply regulator is coupled to regulate the reflected voltage across the primary winding, thereby regulating the output voltage across secondary winding. In one embodiment, the reflected voltage across the primary winding is sensed through a current representative of the reflected voltage received by the power supply regulator.

Abstract: A hybrid reactive power compensation device comprises a passive type reactive power compensator and an active type reactive power compensator serially connected thereto. The passive type reactive power compensator is an AC power capacitor adapted to provide the reactive power that reduces capacity of the active type reactive power compensator. The active type reactive power compensator is consisted of a power converter, a DC capacitor, a high-frequency ripple filter and a controller. The hybrid reactive power compensation device can supply a linearly adjustable reactive power within a predetermined range, and is adapted to provide with a serial-connected virtual harmonic damping. Therefore, it can avoid the destruction of AC power capacitor caused by the power resonance.

Abstract: An inverter circuit of an induction heating rice cooker which controls a switching frequency of an inverter in a variable manner according to a variation in an input voltage and drives the inverter at the controlled switching frequency. The inverter circuit comprises a power supply circuit for rectifying and filtering a commercial alternating current (AC) voltage to supply the input voltage to the induction heating rice cooker. The inverter performs a switching operation based on the input voltage from the power supply circuit to heat the rice cooker. The inverter circuit further comprises an inverter driving circuit for outputting a drive pulse to control the switching frequency of the inverter in the variable manner according to the input voltage from the power supply circuit and drive the inverter at the controlled switching frequency.

Abstract: A controller (130) for compensating reactive power and selected current load harmonics in an unbalanced multi-phase power distribution system. Control current is injected from a multi-phase voltage source inverter (118) into the multi-phase power distribution system as a function of the voltage and current provided by the source inverter 118. The injected current is operative to balance the load seen by the power distribution system including non-linear/distorted and unbalanced loads in each phase. The controller includes an inner loop control processor (216), an outer loop control processor, and an adaptation processor. The adaptation processor (238) is operative to estimate a selected set of predetermined harmonic components in the periodic disturbance which is a function of the unknown system parameters, the source current, the source voltage, and their time derivatives in stationary coordinates.

Abstract: A resonant converter includes an inverter for generating an AC voltage which is fed to a resonant arrangement with a capacitor and a transformer. The circuit provides two types of secondary units, each having a secondary winding of the transformer and at least one rectifier element. Secondary units of the first and second type are then distinguished by opposite orientation. At least two output voltages are delivered on the output, a first output voltage of which being supplied as a direct output of a first-type secondary unit and a second output voltage as a “stack output” of a first-type secondary unit and a second-type secondary unit. The two output voltages can be regulated separately and independently of each other with a regulating device by suitably choosing frequency and duty cycle of a pulse width modulated voltage generated by the inverter driven by the regulating device.

Abstract: Control is carried out in such a manner that a transformer 10 constituting a DC voltage converting circuit 15 stores energy while a switching element 11 provided on the primary side of the transformer 10 is set in an ON state, and the transformer 10 outputs the energy while the switching element 11 is set in an OFF state, and furthermore, the switching element 11 is turned ON when the energy is completely output from a secondary winding 10s. For this purpose, a duration from a time that a secondary current I2 of the transformer 10 reaches zero to a time that a primary current Ip of the transformer 10 is started to flow is detected, and a switching frequency is changed by control means 16 in order to shorten the duration.

Abstract: A tapped delay line generates a fractional clock pulse signal for controlling a PWM pulse generator, such as used in a DC-DC converter. Operational parameters of the tapped delay are adjusted to maintain a desired fractional precision of the duty-cycle of the PWM clock pulse signal. In a first, phase locked loop (PLL) based embodiment, the tapped delay line-based digital PWM pulse generator includes a compensating phase locked-loop formed around an auxiliary tapped delay line that implements the voltage controlled oscillator of the PLL. In a second embodiment, the PWM pulse generator is configured as an ‘open-loop’ tapped delay line phase detector architecture, which avoids having to correlate parameters of the PLL delay line with those of the PWM delay line.

Abstract: A feed forward pulse width modulator compares a ramp signal with a control voltage to control respective states of a pulse width modulation signal. A respective cycle of the ramp signal is generated by charging a capacitor with a charging current that is proportional to input voltage until the voltage across the capacitor reaches a peak threshold that is also proportional to the input voltage. The capacitor is thereupon discharged with a discharging current proportional to the input voltage until the voltage across the capacitor reaches a (non-zero) valley threshold.

Abstract: An inverter control unit having a bridge circuit provided with controllable semiconductor switches in upper and lower circuit arms, which bridge circuit converts a direct voltage to be fed to the inverter into an alternating voltage of variable frequency and amplitude, said control unit controlling the semiconductor switches by pulse-width modulation (PWM) to generate an inverter output voltage, and said control unit comprising a first control section (21) at ground potential and a second control section (22) at the potential of the semiconductor switches, galvanically isolated channels being provided between said sections for serial transmission of control data from the first control section to the second control section and of feedback data from the second control section to the first control section.

Abstract: It is an object of the invention to provide an inverter apparatus capable of instantaneously limiting a current to prevent the breakdown of a device and operating an electric motor efficiently and stably.

Abstract: On the basis of: a first calculated value ic which is a product of a calculated value of a time of three-phase output voltages in a state where a positive bus, a negative bus, and a neutral line are connected respectively to three-phase phase output terminals, and a predicted neutral current value in the state; and second and third calculated values icx and icy which are products of a calculated value of a time of the three-phase output voltages that can take state 1 where two of the three-phase phase output terminals are connected to the positive bus or the neutral line, and a remaining one terminal is connected to the neutral line or the negative bus, and state 2 opposite to the state, and predicted neutral current values in states 1 and 2, a time ratio of state 1 and 2 during a PWM period is determined so as to make a current flowing through the neutral line close to zero, or a potential of the neutral line of the three-phase output voltages close to a voltage which is exactly the middle between voltages o