Abstract: A method for starting an electric motor, the motor having a main machine, exciter, and permanent magnet generator (PMG), each having a stator and a rotor, with each rotor mounted to a common shaft, the method comprising starting the main machine in an asynchronous mode by applying a starting current to the stator of the main machine to induce a damper current in a damper winding of the main rotor to generate a starting torque that initiates the rotation of the common shaft, and then running the main machine in synchronous mode by supplying running current from the exciter rotor to the main machine rotor.

Abstract: A sensorless driving method for a single phase alternating current permanent magnet motor is described. The method comprises a starting drive mode and a stable drive mode.

Abstract: The brushless motor driver includes a sample and hold circuit which samples and holds a first value of the first comparison signal in a first case in which a current is forced to flow from a first phase coil of the three-phase brushless motor to a second phase coil and no current is forced to flow to a third phase coil in a first period having a preset setting time and a second value of the first comparison signal in a second case in which a current is forced to flow from the second phase coil to the first phase coil and no current is forced to flow to the third phase coil in a second period having the preset setting time subsequent to the first period. The brushless motor driver includes an addition circuit which adds up the first value and the second value sampled and held by the sample and hold circuit and outputs an addition signal depending upon a result of the addition.

Abstract: An observer (404), operating during a time when open loop control (402) is being used to drive a synchronous motor (401), the output of the observer (404) being a signal, E_I_angle, related to the angle between a rotational EMF vector and the current excitation vector, the observer (404) determining the angle by an iterative calculation incorporating a summation term, the summation term summing the variation of the quadrature component of a rotational EMF vector relative to an estimated EMF position vector, and using the angle output of the observer to update the estimate of the rotational EMF position vector. In a further aspect of the invention the observer output signal, E_I_angle, can be used to determine the transition to closed loop control (405), when the observer output signal reaches a value indicating conditions close to pull out conditions.

Abstract: A motor controller is configured to perform positioning of a rotor of a brushless motor immediately when power supply is turned on, and not after actually receiving a target value related to control for the brushless motor from a main ECU, which determines the target value. The motor controller finishes or is performing the rotor positioning, when the target value is received from the main ECU. For this reason, the motor controller can start rotation control for the brushless motor in accordance with the received target value in a short period of time.

Abstract: A method and device for controlling the starting time of a vehicle mounted thermal engine coupled mechanically to a polyphase rotary electrical machine with an inductor. The electrical machine includes phase windings and sensors for the position of a rotor, and is connected to an on-board electrical network. The method uses pre-fluxing by establishing an excitation current in the inductor for a predetermined pre-fluxing time, before establishment of phase currents. These phase currents are controlled by signals phase-shifted by an angle which varies according to a speed of rotation of the electrical machine, relative to synchronization signals produced by the sensors. During the starting time, the angle of phase-shifting is additionally dependent on a voltage of the on-board electrical network, in a range contained between a first and second voltages, with the second voltage being higher than the first. In the method, the starting time is independent from the voltage of the on-board electrical network.

Abstract: A motor control device includes an inverter circuit including a plurality of switching elements connected into a three-phase bridge configuration and converting a direct current into a three-phase alternate current, a current detecting element connected to a direct current side of the inverter circuit, thereby generating a signal corresponding to a current value, a PWM signal generating unit which determines a rotor position based on phase currents of the motor and generates a three-phase PWM signal pattern so that the signal pattern follows the rotor position, and a current detecting unit detecting phase currents based on the signal generated by the current detecting element and the PWM signal pattern. The PWM signal generating unit generates the three-phase PWM signal pattern so that the current detecting unit is capable of detecting two phase currents in synchronization with advent of two fixed time-points within a carrier period of the PWM signal respectively.

Abstract: Provided are a device and method of stopping an induction motor. The includes: a frequency commanding unit for generating an operating frequency corresponding to a rotational speed command of the induction motor; a q-axis and d-axis V/F converter for outputting a first q-axis voltage (Vq1) proportional to the generated operating frequency and a first d-axis voltage (Vd1) proportional to a 0 frequency; a q-axis PI current controller for outputting a second q-axis voltage (Vq2) for stopping the induction motor when the operating frequency reaches a stopping frequency; a d-axis PI current controller for outputting a second d-axis voltage (Vd2) for stopping the induction motor when the operating frequency reaches the stopping frequency; and a selection unit for selecting and outputting the first q-axis and d-axis voltages (Vq1 and Vd1) or the second q-axis and d-axis voltages (Vq2 and Vd2) according to the operating frequency generated by the frequency commanding unit.

Abstract: Electronic circuits for controlling the speed of a motor include a receiving node coupled to receive a speed command signal representative of a desired final speed of the motor. A speed control circuit applies a selected amount of power to a motor to allow a speed of the motor to approach a predetermined final speed, where the selected amount of power provided is based on the desired final speed of the motor. A signal represents the speed of the motor and a feedback circuit uses the signal to regulate the speed of the motor by phase-locking the speed of the motor to the speed command signal once the speed of the motor falls within a predetermined threshold of the final speed. Methods for controlling the speed of a motor are also disclosed.

Abstract: A method of controlling a brushless motor that includes exciting a winding of the motor for a conduction period over each electrical half-cycle of the motor. The length of the conduction period is defined by a waveform that varies periodically with time. Additionally, a control system that implements the method, and a motor system that incorporates the control system.

Abstract: An electrical machine system including a permanent magnet assembly having a magnetic field and a plurality of conductive coils, the magnet assembly and coils arranged for relative rotation between the coils and magnetic field in the manner of an electrical generator or motor, the system further comprising a current injector electrically connected to said coils and arranged selectively to supply a current signal thereto, the current signal being asynchronous with the frequency of rotation between the permanent magnet assembly and coils so as to heat and thereby demagnetise one or more magnet within said permanent magnet assembly.

Abstract: The present invention discloses a start-up circuit for a motor driving IC. The activation circuit includes a determination unit, for generating a determination result indicating an operating mode of the motor driving IC according to an external pulse width modulation signal, and an output unit, for outputting an activation signal according to the determination result and a pulse width modulation activation signal. A duty of the pulse width modulation activation signal is greater than a duty of the external pulse width modulation signal.

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 microcomputer that outputs a pulse signal controlling an ultrasonic motor includes a digital/analog, D/A, conversion set register that stores a D/A conversion set value setting an amplitude value of the pulse signal, a D/A converter that generates the amplitude value based on the D/A conversion set value, a first compare register that stores a first compare register value setting a frequency of the pulse signal, a second compare register that stores a second compare register value setting a duty ratio of the pulse signal, a counter that outputs a count value, a first comparator that compares the first compare register value with the count value to generate a first comparison result signal, and a second comparator that compares the second compare register value with the count value to generate a second comparison result signal.

Abstract: A control system controls a multiphase rotating machine by a 120° energization process and a PWM process. In the 120° energization process, respective ones of switching elements of a high side arm and switching elements of a low side arm of a power conversion circuit are turned on. In the PWM process, the switching elements of the power conversion circuit turn on/off so that two phases that are connected to the switching elements that are in the on-state are alternately rendered conductive to the high potential side input terminal and the low potential side input terminal of the power conversion circuit.

Abstract: A system and method for calibrating an interior permanent magnet (IPM) motor with an optimized maximum torque per ampere trajectory curve. The system and method use a real-time particle swarm technique that requires less known parameters than standard maximum torque per ampere trajectory techniques.

Abstract: A system and method are presented for aligning a rotor in a motor. The motor may include the rotor and a plurality of pairs of electromagnets. One or more pairs of electromagnets may be excited at a first excitation level. The one or more pairs of electromagnets may be less than all of the plurality of pairs of electromagnets. The excitation of the one or more pairs of electromagnets may be increased to a second excitation level over a first period of time. The excitation of the one or more pairs of electromagnets may be decreased to a third excitation level over a second period of time. Exciting the one or more pairs of electromagnets, increasing the excitation, and decreasing the excitation may cause the rotor to stop in a known position.

Abstract: Identification without shaft encoder of electrical equivalent circuit parameters of a three-phase asynchronous motor comprising: -standstill position search of the rotor, so that the d flux axial direction of the rotor is aligned opposite the cc axial direction of the stator; -test signal voltage supply U1d in the d flux axial direction of the motor whereby the q transverse axial direction remains without current; -measuring signal current I1d of the d flux axial direction of the motor; -identification of equivalent circuit parameters of the motor based on the test signal voltage U1d and on the measuring signal current I1d in the d flux axial direction; whereby the rotor remains torque-free. The method used to control electrical drives. An identification apparatus for a synchronous motor and a motor control device comprising the apparatus, whereby identified equivalent circuit parameters can be used to determine, optimize and monitor a motor control.

Abstract: Motors, such as DC motors, and methods and systems for operating a motor, are described. The motor is optionally an electronically commutated motor. The motor comprises one or more electromagnets and a controller device to control the electromagnets. The controller device is configured to calibrate the motor operation in a desired installation to determine the torque needed to achieve a desired operating speed by causing the motor to ramp up to the desired speed, measuring an electric current needed to operate the motor at the desired speed, and setting a value corresponding to a first speed tap using the measured electric current. The controller device is configured to operate the motor in a substantially constant torque mode using the set value at least after the completion of the calibration operation. The motor may be configured for use in a ventilation system, such as an HVACR system.

Abstract: Energization to armature windings of a brushless motor in a driven state is interrupted when an energization pattern of the energization shifts to a specific energization pattern determined in advance among a plurality of energization patterns to stop the brushless motor. Also, the brushless motor that has been stopped is started by energizing the armature windings of the brushless motor in the specific energization pattern.

Abstract: Simple AC circuitry driving a brush-less motor having a rotor consisting of alternate polarity permanent magnet poles, with the rotor journaled in a stator with a like number of wound poles having only two free ends for energizing. The motor is using only two AC electronic switches for starting and accelerating, and an AC switch to run the motor at synchronous speed. It has higher efficiency than previously known circuits, uses less parts and is less costly.

Abstract: Various embodiments of an electric motor and electronic control for an electric motor are disclosed. An exemplary electric motor comprises a single-phase brushless permanent magnet electric motor. In exemplary embodiments, the electronic motor control is configured to commutate an electric motor at a frequency other than line frequency, perform pulse width modulation, and drive the electric motor with a drive waveform that approximates the counter-electromotive force of the motor.

Abstract: A motor drive control device is configured to control driving of a brushless DC motor including a stator having drive coils, a rotor having plural magnetic poles, and plural position detecting units that output position detection signals representing position of the rotor with respect to the stator. The motor drive control device includes a drive voltage generating unit configured to generate and output drive voltages to the motor to drive the motor. An abnormality detecting unit can be used to detect abnormality of the position detection signals. When abnormality of at least one of the position detection signals has been detected by the abnormality detecting unit, the motor drive control device can drive the motor based on at least one of the remaining position detection signals excluding the position detection signal that has been detected as abnormal.

Abstract: A blower motor assembly having a variable speed motor that is suitable for replacing a PSC motor in a residential HVAC (heating, ventilation, and air conditioning) system. The blower motor assembly includes a variable speed motor and motor controller; a first power input for receiving a plurality of AC power signals from a control device for use in determining an operating parameter for the motor; and a second power input for receiving AC power from an AC power source for powering the motor controller even when no AC power signals are received by the first power input.

Abstract: A conventional method used for a startup mode for a brushless direct current (DC) motor employed complementary inductive rise times. Specifically, inductive rise times rise times for a driving state and its complementary state were compared to one another such that when the inductive rise times cross a switching point had been reached. This methodology, however, significantly affects the efficiency of the driving torque and power consumption. Here, however, a derivative of the inductive rise time is employed, which can determine the switching event without the need for a use of a complementary state, improving motor performance.

Abstract: A fan rotary speed controlling device includes a first signal generating circuit, a second signal generating circuit, a pulse width modulation (PWM) circuit and a switching circuit. The first signal generating circuit receives a real frequency signal and a target frequency signal, and generates a first signal according to the real frequency signal and the target frequency signal. The second signal generating circuit generates a second signal according to the first signal. The PWM circuit generates a PWM signal according to the second signal. The switching circuit is electrically connected with the PWM circuit and outputs a control signal to control the rotary speed of the motor. Hence, the fan rotary speed controlling device boosts the accuracy and the stability of the fan rotary speed.

Abstract: A method for starting a multiphase, sensorless commutated, brushless electric motor. The method has three operating phases. A start-up phase in which the motor is operated from a standstill with specified commutation times. An acceleration phase in which the motor is accelerated up to a nominal speed, wherein the commutation times are determined on the basis of the zero crossings of the BEMF voltage of the non-energized stator phase windings. And a stationary operating phase in which the nominal speed is kept constant. The transition from the start-up phase into the acceleration phase takes place when, during the start-up phase, a predetermined number of successive zero crossings of the BEMF voltage in the expected order in the expected motor phases have been identified. The transition from the acceleration phase into the stationary phase takes place once the nominal speed has been reached.

Abstract: A mechanism for a motor controller for engaging a spinning motor is provided. A power section is configured to provide power to the motor. A control is configured to control the power section. The control is configured to search for a motor frequency of the motor by applying a small excitation voltage to the motor, and the excitation voltage is initially applied at a voltage frequency which is a maximum frequency. The control is configured to track the motor frequency until the motor frequency is below an equivalent speed command and engage the motor by applying a higher voltage to the motor.

Abstract: A drive apparatus includes a magnet rotor having a plurality of magnetic poles that are magnetized, a stator having a magnetic pole portion that opposes each pole of the magnet rotor, a coil configured to excite the magnetic pole portion, a position detector configured to detect a position of the magnet rotor, a first driver configured to switch an electrification state of the coil in accordance with a preset time interval, a second driver configured to switch an electrification state of the coil in accordance with an output of the position detector, and a controller configured to select the first driver when the output of the position detector is less than a first threshold, and to select the second driver when the output of the position detector is equal to or larger than the first threshold.

Abstract: A motor control unit determines whether a rotor of an electric motor is in rotation or not after the motor control unit is started up but before an initial operation, based on an encoder count value after the start-up of the motor control unit. When the electric motor is stopped, the initial operation is carried out so as to learn a correction value of phase difference between the encoder count value and an actual current-supply phase. When the electric motor is still rotated due to its inertia, a motor-stop control is carried out before the initial operation in order to completely stop the rotation of the rotor. In the motor-stop control, electric power is supplied to windings of two phases at the same time.

Abstract: In a synchronous machine starting device, a timing detection unit outputs a first position signal indicating a timing at which a value of an armature voltage passes a prescribed reference level. A feedback operation unit calculates an error of an estimated phase based on the estimated phase, an estimated rotational speed of a rotor, an armature voltage, and an armature current, updates the estimated phase and the estimated rotational speed based on the calculated phase error, and outputs a second position signal indicating the updated estimated phase. A frequency detection unit detects a current rotational speed of the rotor based on the first position signal, as an initial value of the estimated rotational speed. A selector circuit selects the first position signal and the second position signal in this order, and outputs a selected position signal to the power conversion control unit.

Abstract: The invention relates to an electrical drive having a motor with a rotor and a stationary stator, which has a coil arrangement, and having a motor controller for controlling the motor, with the motor controller being configured to pass current through the coil arrangement in order to produce an excitation field, with the coil arrangement having a plurality of coil winding sections, and with each coil winding section having a plurality of coil sections, wherein the polarity of at least one coil section of the plurality of coil sections of each coil winding section can be selectively reversed with respect to the other coil sections of the coil winding section. The drive is particularly suitable for use for an electrical tool.

Abstract: A self-adapting soft-starter device includes an electric current limiter limiting electric current supplied to the motor to a preset maximum current limit, a ramp-up time determiner determining the actual ramp-up time of the electric motor, a storing device storing a preset minimum ramp-up time, a comparator comparing the determined actual ramp-up time with the preset reference ramp-up time, a replacing device replacing the preset maximum current limit with an auto-adapted current limit based upon the outcome of the comparison between the determined actual ramp-up time and the preset reference ramp-up time. The soft-starter automatically optimizes the maximum current limit driven by the motor to match its load requirements which is useful to cater for load variations with time during the lifetime of the product in the application by avoiding the need for human intervention to change the soft-starter settings. Wear and tear is also reduced, extending motor lifetime.

Abstract: A method for determining a direction of rotation for an electronically commutated motor (ECM) is described. The motor is configured to rotate a blower and the method comprises rotating the blower using the ECM and determining if the resulting blower rotation is indicative of the desired direction of rotation for the blower.

Abstract: A system and method are presented for aligning a rotor in a motor. The motor may include the rotor and a plurality of pairs of electromagnets. One or more pairs of electromagnets may be excited at a first excitation level. The one or more pairs of electromagnets may be less than all of the plurality of pairs of electromagnets. The excitation of the one or more pairs of electromagnets may be increased to a second excitation level over a first period of time. The excitation of the one or more pairs of electromagnets may be decreased to a third excitation level over a second period of time. Exciting the one or more pairs of electromagnets, increasing the excitation, and decreasing the excitation may cause the rotor to stop in a known position.

Abstract: A method of controlling a motor is provided. The method may monitor a plurality of operational characteristics of the motor, determine an optimum transition speed of the motor based on the operational characteristics, and engage a transition of the motor between a current regulation mode of operation and a single pulse mode of operation at the optimum transition speed.

Abstract: Methods and systems for operating an inverter having a plurality of high switches and a plurality of low switches coupled to an electric motor are provided. An event indicative of deceleration of the electric motor is detected. The inverter is alternated between a first mode of operation and a second mode of operation during the deceleration of the electric motor. In the first mode of operation, each of the plurality of high switches is activated and each of the plurality of low switches is deactivated or each of the plurality of low switches is activated and each of the plurality of high switches is deactivated. In the second mode of operation, each of the plurality of high switches is deactivated and each of the plurality of low switches is deactivated.

Abstract: If magnitude relations between the output terminal voltage based on a DC negative terminal of the inverter and a threshold voltage that is a fixed value are compared, polarity thereof is changed at a predetermined rotor phase. The magnitude relation, for example, is detected by an inexpensive and simple apparatus such as a level shift circuit and a NOT circuit. The rotor phase of the permanent magnet synchronous motor is inferred on the basis of changes in the magnitude relation and if it is differentiated, a rotation speed is inferred. If the inferred values of the rotor phase and rotation speed are fed back to synchronous operation or vector control, the free-running permanent magnet synchronous motor is restarted.

Abstract: A control apparatus for an AC rotating machine that can reliably and stably start up an AC rotating machine, particularly a synchronous motor using a permanent magnet, in position-sensorless vector control thereof, includes: a steady speed calculator that calculates, during steady state control of the AC rotating machine, a rotation angular frequency of the AC rotating machine based on an AC current and voltage commands; and a start-up speed calculator that calculates, during start-up control within a predetermined period after the AC rotating machine has been started up, the rotation angular frequency of the AC rotating machine based on the AC current and the voltage commands. The control apparatus corrects during the start-up control current commands so that the AC voltage amplitude of the voltage commands will be a constant value not more than the maximum output voltage of a power converter.

Abstract: Integrated AC regenerative motor drives and operating methods are presented in which a precharging circuit is provided with an IGBT, a diode and a parallel current limiting component in an intermediate DC circuit between a switching rectifier and an output inverter, and the drive is operated in one of three modes for motoring, regenerating and precharging.

Abstract: Embodiments of the present invention provide a device and method for generating initial operating points for controlling an interior permanent magnet (IPM) machine. The method includes loading an inductance lookup table, first calculating a maximum torque per Ampere (MTPA) trajectory for a first threshold speed based on machine parameters of the IPM machine, second calculating a truncated voltage limit ellipse with monotonically increasing torque for a first speed based on the machine parameters, if the first speed is higher than the first threshold speed, determining an operating trajectory at the first speed based on at least one of the calculated MTPA trajectory and the calculated truncated voltage limit ellipse, and generating an Id,Iq map that maps an Id value and an Iq value to each torque command of a plurality of torque commands for the first speed based on the determined operating trajectory.

Abstract: A control system includes a position control module, a power control module, and a diagnostic module. The position control module applies a driving current for positioning a rotor of a motor at one of first and second positions. The power control module applies a first voltage to one of first and second phases of the motor to generate a first current after the position control module applies the driving current to position the rotor at the first position. The power control module applies a second voltage to one of the first and second phases to generate a second current after the position control module applies the driving current to position the rotor at the second position. The diagnostic module determines when the rotor is restricted from rotating based on the first and second currents.

Abstract: A brushless motor drive device switches energization modes for supplying power to two phases of a three-phase brushless motor, based on an induced voltage induced in a non-energized phase. In a case in which a target duty ratio Dt, which is a duty ratio of a PWM signal according to a manipulated variable of the brushless motor becomes less than a detection limit value Dlim, which is the lower limit of a duty ratio capable of detecting an induced voltage, there is set a detection timing (1/N) for detecting an induced voltage according to the cycle of a PWM signal, and a detection time duty ratio D1, which is a duty ratio of the PWM signal at the detection timing, is restricted to Dlim.

Abstract: Provided is a regenerative switched reluctance motor driving system which allows a motor to have a reduced size and weight and an increased efficiency as well as improved energy recovery efficiency at the time of regenerative braking without using a neodymium magnet. Based on an angular position of a rotor in the motor, a constant current flip-flop circuit 2 renders two current paths alternately conductive so as to allow a rectangular-wave current having a width of an electrical angle of 180° to alternately flow in two coils in the motor 3, and shifts the timing of rendering the two current paths alternately conductive, between when driving and when braking the motor 3, by a time during which the rotor is rotated by an angle corresponding to an electrical angle of 180°.

Abstract: A control system controls a multiphase rotating machine by a 120° energization process and a PWM process. In the 120° energization process, respective ones of switching elements of a high side arm and switching elements of a low side arm of a power conversion circuit are turned on. In the PWM process, the switching elements of the power conversion circuit turn on/off so that two phases that are connected to the switching elements that are in the on-state are alternately rendered conductive to the high potential side input terminal and the low potential side input terminal of the power conversion circuit.

Abstract: In a method for starting a synchronous machine, a default torque is predefined, and a rotational speed of the synchronous machine is adjusted after starting. A torque which is higher than the default torque is predefined, and the higher torque is reduced in the subsequent second step to a positive value which is less than the default torque, and is increased to the default torque in a third step.

Abstract: A method for automated startup and/or for automated operation of controllers of an electrical drive system with vibrational mechanics with the following steps: (a) determining a preliminary value of at least one parameter; (b) determining a model of the electrical drive system by determination of initially a non-parameterized model through the recording of frequency data during operation of the drive system subject to the utilization of the preliminary value of at least one parameter and the subsequent determination of parameters of the electrical drive system based on the frequency data and subject to optimization of at least one preliminary value of at least one parameter by a numerical optimization method on the basis of the Levenberg-Marquardt algorithm and (c) parameterizing at least one controller of the electrical drive system by at least one of the determined parameters.

Abstract: A method for driving a brushless direct current (DC) motor is provided. The brushless DC motor has a first phase that is coupled between a first terminal and a common node, a second phase that is coupled between a second terminal and the common node, and a third phase that is coupled between a third terminal and the common node. The first and second phases are coupled to a first supply rail and a second supply rail, respectively, such that the brushless DC motor is in a first commutation state. The first phase is then decoupled from the first supply rail so as to allow first terminal to float during a window period. A first voltage difference between the first terminal and the second terminal is compared to a second voltage difference between the third terminal and the second terminal during the window period, and the brushless DC motor is commuted to a second commutation state if the first voltage difference is approximately equal to the second voltage difference.

Abstract: An anti-noise method for the Direct Current Brushless motor System, which includes a startup circuit, phase detective circuit, motor phase commutation circuit, driving circuit, BEMF detective circuit, and frequency detector, utilizes the BEMF detective circuit to detect the BEMF induced from the coils of the outer motor, and utilizes the sampled voltage phase to determine rotation speed and phase of the external motor by the phase detection circuit and frequency detector. Further, the sampling voltage of the BEMF detection circuit is feedback controlled by the frequency detector, utilized to keep good BEMF to noise ratio, and avoids the BEMF sampling error from the system.

Abstract: Method and apparatus to start a frequency converter equipped with a direct current intermediate circuit, particularly when a permanent magnet motor whose rotor is rotating at the start-up time is connected to it, wherein the frequency converter has a network bridge (10) and load bridge (11), and the load bridge has controllable power semiconductor switches of the upper and lower branch (V1-V6) and parallel connected zero diodes (D1-D6), and a direct current intermediate circuit between them, and the said frequency converter uses a current transducer placed in the direct current intermediate circuit, and the analogue current signal composed by it features samples of the measured output currents, and the diverter switches of the frequency converter's upper branch are controlled using the bootstrap method, wherein start-up is initiated by controlling the controllable power semiconductor switch of the lower branch of at least one output phase to a conductive state for one or several periods of time, preferably of