Abstract: A motor driving apparatus includes an AC-DC conversion unit configured to rectify an AC power supplied from an external AC power source, a DC link unit configured to stabilize a voltage rectified by the AC-DC conversion unit, and a DC-AC conversion unit configured to supply the AC power to a motor using the DC voltage from the DC link unit. The DC link unit may include one pair of film capacitors configured to remove a ripple of the rectified voltage, and the DC-AC conversion unit may include a 3-level inverter receiving the DC voltage from the one pair of film capacitors to supply the AC power to the motor.

Abstract: An electrical system including a three phase AC input supply and three or more H-bridge converter cells. Each H-bridge converter cell has: an active front end rectifier for receiving the three phase AC input supply and transforming it into a DC supply, thereby providing a rectifier current ii; a capacitor suitable to receive a capacitor current iC, the capacitor smoothing the DC supply; and an inverter suitable to receive an inverter current io, wherein io=ii?iC, said inverter transforming the received inverter current io into a single phase AC supply. The system also including a control subsystem, which provides a signal to each active front end rectifier to vary its respective rectifier current ii such that the difference between the rectifier current ii, provided by the active front end rectifier, and the inverter current io, received by the inverter, is substantially zero.

Abstract: A regenerative drive device and a method for configuring the DC link of a regenerative drive device are disclosed. The multilevel regenerative drive device may include an inverter having a plurality of power components and a converter having a plurality of power components. The multilevel regenerative drive device may also include a direct current (DC) link bridging the inverter and the converter, the DC link including a capacitor, an inverter neutral point, and a converter neutral point independent of the inverter neutral point. Alternatively, the inverter neutral point and the converter neutral point may be connected.

Abstract: Systems and methods for controlling the operating speed and the torque of an electric motor using an operational model are described. An operational model for the electric motor, including a plot of engine performance parameters, is used for reference, and a most efficient output path, which may pass through an optimal operation region in the operational model, is selected. The most efficient output path may be determined, for example, according to locations of a current output state and a to-be-reached target state in the operational model, enabling the operating state of the motor to reach the target state from the current operating state. By selecting a more efficient output path, the operating efficiency of the motor may be optimized, the life of a battery improved and/or the operating mileage of the vehicle may be increased, without significantly reducing the driving experience.

Abstract: A control system for an electric motor comprises a current sensing means arranged to produce a current sensing output indicative of electric current in the motor, current control means arranged to receive the current sensing output and to output a voltage demand indicative of voltages to be applied to the motor, and current sensing correction means arranged to monitor the voltage demand to measure distortion in the current sensing output and to generate a correction signal which is arranged to correct the distortion.

Abstract: A motor driving apparatus includes a rectifying circuit to rectify an AC power supplied from an external AC power source, one pair of film capacitors to output a DC voltage and a neutral point voltage by removing a ripple of a voltage rectified by the AC-DC conversion unit, a 3-level inverter to supply a driving current to a motor using the DC voltage applied from the DC link unit, and a control module to control the 3-level inverter. The control module includes a motor speed control module to control the rotation of the motor, a DC voltage control module to stabilize the DC voltage, a neutral point voltage control module to stabilize the neutral point voltage, and a stabilizing voltage limiting module to control the DC voltage control module and the neutral point voltage control module according to an output of the motor speed control module.

Abstract: Methods, systems and computer readable storage devices for a four quadrant voltage limiter that limits a commanded phase voltage to within a volt second capability of an inverter by maintaining a rotor flux and folding back a torque under both motoring and regeneration torque commands. In one embodiment: (a) in a motoring operation, an upper limit for a q-axis voltage is enforced; and (b) in a regeneration operation a lower limit for the q-axis voltage is enforced.

Abstract: An electromechanical system includes an inverter drive, a component arranged during operation to generate a variable force having one or more periodic frequency components, and processing circuitry arranged to determine the power output of the inverter drive, measure a difference between the power output and a reference power output, and control an output frequency of the inverter drive as a function of the measured difference, so as to stabilise the power output during operation of the component. Other example electromechanical systems, inverter drives and methods are also disclosed.

Abstract: A converter comprises a first inverter for converting a first multi-phase AC voltage into a DC voltage and a second inverter for converting the DC voltage into a second multi-phase AC voltage. A method for controlling the electrical converter comprises: switching the first inverter such that a first common mode voltage is generated in the first multi-phase AC voltage; switching the second inverter such that a second common mode voltage is generated in the second multi-phase AC voltage, wherein the first common mode voltage and the second common mode voltage are synchronized such that the first common mode voltage and the second common mode voltage cancel each other at least partially.

Abstract: A negative voltage protection system includes a negative voltage comparison circuit, a signal processing circuit, a driving circuit, a driving output circuit, a power device, and a coil module. When the coil module generates a back electromotive force, the coil module outputs a negative voltage. When an intensity of the negative voltage detected by the negative voltage comparison circuit is greater than a predetermined value, the signal processing circuit generates a control signal to the driving circuit. The driving circuit controls the driving output circuit and the power device to reduce the intensity of the negative voltage according to the control signal.

Abstract: Object of the present disclosure is to improve accuracy of over-temperature protection of an electric motor. A control device controls an inverter main circuit for driving the electric motor. An electric power conversion circuit controller acquires DC voltage input to the inverter main circuit, output voltage of the inverter main circuit, motor amperage of current flowing through the electric motor, and motor frequencies indicating rotation rate of the electric motor. Based on at least one of the DC voltage, output voltage, motor amperage and motor frequencies, a motor loss estimator calculates a stator loss and rotor loss, each including fundamental and harmonic losses of the electric motor. Based on the inverter output voltage, stator loss and rotor loss, the electric power conversion circuit controller outputs an actual control value for control of the inverter main circuit.

Abstract: An electronic switch controller, an electronic switch control method, an electronic switch and an electronic device are disclosed. The processor comprises voltage-stabilized power supplies, a processor and a driving circuit; the processor is connected between the voltage-stabilized power supplies and a measurement device to receive working parameters of the power supply, a load and the electronic switch measured by the measurement device, read duty cycle parameters matching with the working parameters, calculate a new duty cycle with the duty cycle parameters and the working parameters, adjust the current control signal to a PWM signal having the new duty cycle, and send the PWM signal to the driving circuit; and the driving circuit is connected between the voltage-stabilized power supplies and the load to control the rotation speed of the motor in the load.

Abstract: Systems and methods for controlling the operating speed and the torque of an electric motor using an operational model are described. An operational model for the electric motor, including a plot of engine performance parameters, is used for reference, and a most efficient output path, which may pass through an optimal operation region in the operational model, is selected. The most efficient output path may be determined, for example, according to locations of a current output state and a to-be-reached target state in the operational model, enabling the operating state of the motor to reach the target state from the current operating state. By selecting a more efficient output path, the operating efficiency of the motor may be optimized, the life of a battery improved and/or the operating mileage of the vehicle may be increased, without significantly reducing the driving experience.

Abstract: A heat pump device includes a compressor including a compression mechanism that compresses a refrigerant and a motor that drives the compression mechanism, an inverter that applies a voltage for driving the motor, a converter that applies a voltage to the inverter, an inverter control unit that generates a driving signal for driving the inverter, and a converter control unit that generates a driving signal for driving the converter. The inverter control unit includes a heating-operation-mode control unit that controls a driving-signal generating unit such that the driving-signal generating unit outputs, as inverter driving signals, PWM signals for heating the compressor without rotationally driving the motor by feeding a high-frequency current that the motor cannot follow in a heating operation mode.

Abstract: A method for limiting the torque of a permanent magnet AC motor includes a torque limit controller. The torque limit controller at least in part bases the torque limit on a selected direct voltage limit. The selected direct voltage limit may be used in combination with other torque limit conditions to generate the torque demand for the AC motor.

Abstract: A power converter can be controlled to generate a target output power. The control process may include obtaining a target current reference for the power converter, sensing an output current of the power converter, and determining a difference between the target current reference and the sensed output current. The next switching duty cycle for the next switching period of the switching circuits in the power converter can be derived based on at least the present switching duty cycle of the present switching period, and the difference between the target current reference and the sensed output current. The switching circuits of the power converter can then be switched according to the derived next switching duty cycle in the next switching period.

Abstract: A method for operating an electrical machine, in particular for making available drive power for a drive train of a motor vehicle, the electrical machine being controlled by several phase currents, the method including sensing an electrical variable that represents the torque delivered by the electrical machine; and monitoring the torque. A degradation of the electrical machine is taken into consideration in the monitoring of the torque.

Abstract: A method of operating an electric motor is disclosed. The method includes: starting the electric motor in an open loop control mode; operating an estimator that estimates operating conditions of the electric motor; and, while the electric motor is in the open loop control mode, evaluating a first parameter of the estimator. The method further includes: in response to the evaluation of the first parameter, determining whether the estimator has converged; and in response to a determination that the estimator has not converged within a predetermined period of time after starting the electric motor, signaling a first fault condition.

Abstract: A power converter can be controlled to generate a target output power based on a reactive power reference and an active power reference. The control process may include monitoring a time-varying power signal (e.g., a power grid voltage signal from a power grid), and filtering the time-varying power signal to derive a filtered sine component of the time-varying power signal and a filtered cosine component of the time-varying power signal. A sine coefficient and cosine coefficient each based on at least the reactive power reference and the active power reference can be determined, and applied to the filtered sine component and filtered cosine component of the time-varying power signal, respectively. A target current reference of the power converter can then be set to include a sum of the current reference sine component and the current reference cosine component.

Abstract: A modular converter having a plurality of converter modules for converting an input voltage into an output voltage to be supplied to a load by receiving a control input reference vector, a control input vector and a control input parameter vector; determining a control output reference vector from the control input reference vector, the control input vector and the control input parameter vector in a first control stage; and controlling the converter modules by generating switching signals based on the control output reference vector in a further control stage.

Abstract: A power supply device includes: an input determination section configured to determine which one of a commercial power supply and a power generator is an input power supply, and to generate a determination signal; a conversion section of a switching type configured to convert an input voltage into an output voltage; and a drive-signal generation section configured to be supplied with determination output from the input determination section, and to generate a switching drive signal for the conversion section, the drive-signal generation section being configured to serve as a power-factor correction control section and to generate the switching drive signal when the determination signal indicates that the commercial power supply is the input power supply, and being configured to serve as a maximum power point tracking control section and to generate the switching drive signal when the determination signal indicates that the power generator is the input power supply.

Abstract: The present application discloses an apparatus including: a motor model that reflects a characteristic of a motor and includes at least inputs pertaining to a first quantity of state and a second quantity of state and an output pertaining to a third quantity of state; a comparator that calculates a difference between the third quantity of state in an actual motor and the third quantity of state output from the motor model; and an amplifier that amplifies an output of the comparator at a predetermined gain. The first quantity of state in the actual motor is input into the motor model as the first quantity of state, and an output of the amplifier is input into the motor model as the second quantity of state. The apparatus then uses the output of the amplifier as an estimated value of the second quantity of state in the actual motor.

Abstract: A traction motor system calculates motor flux by generating a real time effective resistance of a resistance grid calculated from motor torque and measured voltage on a DC link. Calculating effective resistance avoids solely relying on DC link voltage, which can be influenced by conditions such as wheel slip and drop out of one or more resistance grids. The effective resistance calculation is based on nominal motor values using known power levels and conditions. From these nominal values and the effective resistance, various scaling factors based on actual motor power can be generated and used to adjust a nominal flux reference to more accurately reflect actual motor flux. The scaling factors include power and torque scaling factors and a resistance scaling factor that is active during conditions such as wheel slip.

Abstract: A system is provided that includes a plurality of power units each configured to supply power. Additionally, the system includes a plurality of contacts each configured to toggle an electrical connection of each of the plurality of power units as a network. Moreover, the network is configured to supply power to a load. Furthermore, the system includes a controller configured to control when each of the plurality of contacts toggle according to a power state, and the power state includes information regarding a charge of each power unit, a load demand, and a supplied power being supplied by the plurality of power units.

Abstract: A motor drive device according to one embodiment of the present invention includes a converter (2) for converting an AC voltage input from a main power supply into a DC voltage, a DC link unit (4) for rectifying the DC voltage output from the converter, an inverter (10) for converting the DC voltage rectified by the DC link unit into an AC voltage for driving a motor using a semiconductor switching element, a voltage application unit (6) that is provided independently of the main power supply to apply a voltage to the DC link unit, a voltage detector (7) for detecting a voltage of the DC link unit after application of the voltage by the voltage application unit, and an abnormality determination unit (8) for determining the presence or absence of an abnormality of the DC link unit based on the voltage detected by the voltage detector.

Abstract: A motor control apparatus and method are provided. The motor control apparatus may include a power supply device supplying power to a motor, a power control device selectively blocking current supplied to the motor depending on whether or not the current supplied from the power supply device to the motor is greater than a reference current value, a controller that controls an intensity of the current supplied from the power supply device to the motor, and a load torque detector that detects a load torque generated by the motor as the motor rotates. The controller controls a maximum value of the current to be supplied to the motor so that the maximum value is less than the reference current value when the maximum value of the load torque detected by the load torque detector is greater than a maximum motor output due corresponding to the reference current value.

Abstract: A linear compressor which can perform the natural cooling capacity modulation, even if a capacitor connected to a motor is removed. The linear compressor includes a fixed member having a compression space therein, a movable member linearly reciprocated in the fixed member to compress a refrigerant sucked into the compression space, and one or more springs provided to elastically support the movable member in the motion direction of the movable member. The compressor also includes a motor connected to the movable member to linearly reciprocate the movable member in the axial direction, and a motor control unit performing the cooling capacity modulation by the reciprocation of the movable member according to a load, by controlling an AC voltage applied to the motor so that a stroke of the movable member can be proportional to the magnitude of the AC voltage applied to the motor.

Abstract: A control system for an electric three-phase variable speed motor includes an inverter for providing power to the motor and a control arrangement for controlling the inverter. The control arrangement includes a d and q axis currents determining module configured to repeatedly determine d and q axis currents based on detected currents of the motor. An MTPA control block repeatedly generates reference d and q axis currents based on the determined d and q axis currents and a ratio value such that the ratio of the reference d and q axis currents is equal to the ratio value, which is set to unity. A switching signal generation module repeatedly generates switching signals to control the inverter based on the reference d and q axis currents. A fine adjustment module calculates a magnitude of a current or power of the motor and determines an optimum compensation ratio value.

Abstract: A control method includes monitoring changes in torque produced by a traction motor when an excitation frequency of current supplied to the traction motor changes, determining if the torque produced by the traction motor decreases when the excitation frequency of the current supplied to the traction motor increases, and responsive to the torque produced by the traction motor decreasing when the excitation frequency increases, preventing the excitation frequency of the current supplied to the traction motor from increasing further.

Abstract: A method for controlling an electric drive, having an inverter, an electric motor and control means configured in a first operating state of the electric drive to control the electric drive to run in a constant operating point, determine and store a value of an output voltage of the inverter or a value of a flux reference of the inverter, and a value of a switching frequency of the inverter with which a determined input power of the electric drive is lowest. The controller is configured in a second operating state of the electric drive to control the electric drive to use the stored values to run in the operating point.

Abstract: A hybrid-electric vehicle and method of controlling a hybrid-vehicle is provided. The vehicle includes a traction battery, at least one electric-machine, and a controller. The controller is configured to alter a voltage between the battery and the electric-machine based on a measured voltage of the battery or the high voltage bus. In response to an indication that the measured voltage is faulty during a drive cycle, the controller instead alters the voltage between the battery and the electric machine based on a substituted battery voltage signal such that the electric-machine remains operable for the drive cycle.

Abstract: A hybrid-electric vehicle method of controlling a hybrid electric vehicle is provided. The vehicle includes a traction battery, at least two electric-machines, and a controller. The controller is configured to, in response to a faulted condition one of the electric-machines during a drive cycle, command the other of the electric-machines to function in a mode in which torque output is restricted to a threshold value that depends on a voltage of the battery to maintain vehicle propulsion during the drive cycle.

Abstract: There is provided a method for determining an abnormality during operation of a high voltage disconnect switch, the method comprising: determining a current position of an arm of the high voltage disconnect switch operatively connected to a motor, the motor being operated for driving the arm of the high voltage disconnect switch; determining a torque of the motor corresponding to the current position of the arm; comparing the torque of the motor to a torque threshold for the current position of the arm; and outputting an abnormality signal based on the comparison.

Abstract: A driver circuit for driving an electrical load includes an input terminal pole connecting the driver circuit to an AC voltage source, an output terminal pole connecting the driver circuit to the load, a rectifier circuit connected to the input terminal pole for converting an AC voltage into a pulsating DC voltage, and a control element connected to the rectifier circuit and to the output terminal pole. The control element has a switch and a controller, the controller switching the switch on and off by means of a pulse train signal, wherein an electrical output value of the driver circuit is adjustable by switching the switch. The controller is configured to vary at least one time-based value of the pulse train signal within one period of the pulsating DC voltage such that a driver current is adjusted at the output terminal pole having a defined waveform within the period.

Abstract: Single-phase voltage operation techniques are provided for a three-phase drive system. A drive system may include a rectifier configured to couple to a three-phase AC voltage source. The rectifier may be configured to convert AC voltage from the three-phase AC voltage source to a direct current (DC) voltage. The drive system may also include a controller configured to send a plurality of switching signals to a plurality of switches in the rectifier such that the plurality of switching signals minimizes a current provided to the rectifier when only a single-phase of the three-phase AC voltage source is available.

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 power supply apparatus of a home appliance which meets standby power regulation of 0.5 watts using one SMPS. As compared with a general circuit which meets the standby power regulation using two or more SMPSs, it may be possible to curtail expenses required for addition of a separate standby only SMPS and miniaturize a PCB, resulting in a reduction in cost. Further, in a washing machine employing a motor, a circuit is provided to bypass a back EMF generated in the motor even if AC power is not supplied to the washing machine due to occurrence of a power failure or unplugging of the washing machine. Therefore, it may be possible to prevent a PCBA from being damaged due to the back EMF.

Abstract: In a system for controlling a rotary machine, a circuit outputs an AC voltage to be applied to a rotary machine. A storage stores therein measurement-error information indicative of a measurement error of the measuring unit. A torque-feedback adjuster manipulates a phase of the output voltage of the circuit based on the rotational angle of the rotary machine measured by a measuring unit and the measurement-error information to adjust a torque of the rotary machine to a request torque. The phase is obtained from information fed back from the rotary machine. An abnormality determiner determines whether there is an abnormality to disable using accurate measurement-error information. A limiter limits adjustment of the torque of the rotary machine to the request torque by the torque-feedback adjuster when it is determined that there is an abnormality to disable using accurate measurement-error information.

Abstract: A power converting apparatus includes a timing signal generator and a phase determination signal generator provided in an ON/OFF signal generating unit as well as a detected current correction unit. On the basis of timing signals ts1, . . . and phase determination signals ph1, . . . , the power converting apparatus determines detected current values and phases of the detected current values fed from a DC bus current sensor at timings set in accordance with the timing signals and corrects the detected current values idc1, . . . for the individual phases obtained at the individual timings during PWM cycles to represent values which would be obtained at reference timing t0 to thereby reduce errors caused by differences in the current detecting timings for the individual phases.

Abstract: A power regeneration device according to an aspect of embodiments includes a voltage detecting unit, a signal processing unit, a phase detecting unit, and a power conversion unit. The signal processing unit generates, by using self-oscillation when the output of an AC detection signal from the voltage detecting unit is stopped due to a power outage, an AC signal whose frequency is the same as that of and whose phase is continued to that of the AC detection signal just before the stop. The phase detecting unit detects the phase of the AC power supply on the basis of the AC signal from the signal processing unit when power is recovered from the power outage.

Abstract: A servomotor drive device has a first converter, a regenerative resistor circuit having a first switching element and a regenerative resistor, a first connection part configured to connect a second converter in parallel to the regenerative resistor circuit in an attachable and detachable manner, and a first control unit configured to control the on and off states of the first switching element. The second converter has a second switching unit and a second control unit configured to return regenerative energy to an AC power source side by bringing the second switching element into the on state when the second converter is connected to the first connection part.

Abstract: A fault tolerant electric drive system includes an alternator, a motor controller and an electric motor, wherein the alternator and motor each have a plurality of corresponding independent phase windings, the motor controller having a plurality of independent phase drives corresponding to the phase windings, and a plurality of independent electric drive phases is defined by connecting each corresponding phase winding of the alternator and motor to a corresponding phase drive of the motor controller.

Abstract: A method for operating a polyphase machine having a pulse-width-modulated inverter includes: determining a setpoint current value respectively for a current in the longitudinal direction and/or the transverse direction based on a specified torque, ascertaining a setpoint voltage value respectively for a voltage in the longitudinal direction and/or the transverse direction with the aid of the setpoint current value and/or of an actual current value determined at the pulse-width-modulated inverter, controlling and/or regulating the polyphase machine corresponding to the ascertained setpoint voltage value. In this context it is provided that, in addition, using a model, a model value is determined respectively for the voltage in the longitudinal direction and/or the transverse direction, the difference between the setpoint voltage value and the model value is ascertained, and in response to the exceeding of a specifiable maximum difference, an error signal is triggered.

Abstract: An electric motor comprising a stator having two coil sets arranged to produce a magnetic field of the motor, each coil set comprising a plurality of coil sub-sets; and two control devices, wherein the first control device is coupled to the plurality of coil sub-sets for the first coil set and the second control device is coupled to the plurality of coil sub-sets for the second coil set and each control device is arranged to control current in the respective plurality of coil sub-sets to generate a magnetic field in each coil sub-set to have a substantially different magnetic phase to the other one or more coil sub-sets in the respective coil set; and wherein the first control device and the second control device are mounted adjacent to the stator.

Abstract: It is presented a control device for driving an electric motor, wherein a drive control signal for the electric motor is arranged to be determined using a calculated rotor flux. A direct quadrature, dq, coordinate system relating to a rotor of the electric motor is used. The control device comprises a flux estimator arranged to determine the calculated rotor flux using a quadrature axis voltage, a measured direct axis current, a measured quadrature axis current, an angular velocity, stator resistance and a direct axis inductance and an actual torque calculator arranged to obtain an actual torque estimation using the calculated rotor flux, the measured direct axis current and the measured quadrature axis current. A corresponding method is also presented.

Abstract: During motor acceleration control period that starts at time T1, if power supply output or supply current exceeds a predetermined level at time T2, PWM control in a PWM converter is turned off until a deceleration control period of T3 to T4 ends. As a result, DC link voltage (voltage of a power storage device) at the start of the deceleration control at time T3 drops to provide space for storing regenerative power; since the PWM control in the PWM converter is off during the deceleration control period, the regenerative power can be stored into the power storage device and reused in the next control cycle.

Abstract: A method is disclosed for estimating a rotation speed of an electric motor supplied by an inverter, by determining a time derivative of a stator current vector of the electric motor during a zero vector state of the inverter; and determining an estimate of the rotation speed of the electric motor on the basis of the determined time derivative of the stator current vector.

Abstract: An electric power converter includes a DC to DC converter section adjusting DC power of a battery with at least two units in series, a DC circuit having at least two DC link capacitors in series between a positive and a negative line from the DC to DC converter section, an electric power converter section connected to the DC circuit to convert DC electric power to AC electric power for a motor, a bilateral switching circuit connecting an intermediate potential point between the capacitors and an AC output point in the electric power converter section, and a short-circuit between the intermediate potential point of the DC circuit and an intermediate potential point between the battery units. Normal operation of a load is ensured even when the battery, the capacitor in the DC circuit or the switching device in the electric power converter section becomes abnormal, while achieving high efficiency.

Abstract: A method for shutting down an electric machine having a pulse-controlled inverter in the event of a malfunction. Undesirable side effects during shut-down of the electric machine may be minimized and the regular machine operation may be maximized when the electric machine is first switched to a disconnect mode in which all switches of the pulse-controlled inverter are open and subsequently is switched to a short-circuit mode in which the switches connected to the high potential are open and the switches connected to the low potential are closed.

Abstract: A control apparatus for a series-connected multi-level matrix converter includes each voltage commanding device provided for each of single-phase matrix converters to generate a voltage reference to each of the single-phase matrix converters. The series-connected multi-level matrix converter includes the single-phase matrix converters. Each of the single-phase matrix converters includes a snubber circuit and a DC voltage detecting section configured to detect a DC voltage of the snubber circuit to output a DC voltage detection value. ADC over-voltage detector is configured to output a DC over-voltage signal when the DC voltage detection value exceeds a set voltage value. A voltage modifying device is, when the DC over-voltage signal is outputted, configured to decrease the voltage reference to a corresponding single-phase matrix converter among the single-phase matrix converters based on a deviation between the DC voltage detection value and the set voltage value.