Abstract: A voltage saturation prevention algorithm used as at least part of a method of controlling an electric vehicle, wherein the electric vehicle comprises an electric motor, a controller, and an inverter. The controller receives a control signal with an instruction to operate the electric motor, then sends a switching signal corresponding to the control signal to the inverter, wherein the inverter provides a plurality of output signals for operation of the electric motor. The method includes determining the expected amplitude of the plurality of output signals based on the instruction to operate the electric motor, calculating the amount of modification of the plurality of output signals required to prevent the expected amplitude from reaching a saturation value, and modifying, based on the calculation, the instruction to operate the electric motor to prevent the expected amplitude from reaching the saturation value. The method is implemented in software, without any additional hardware.

Abstract: A circuit portion comprising a clock domain is disclosed. A first clock is arranged to clock components in the clock domain. An analogue to digital converter is clocked by a second clock with a duty cycle. The second clock is derived from the first clock. The analogue to digital converter is arranged to output a feedback signal upon finishing a conversion of a sample, and the feedback signal is arranged to control the duty cycle.

Abstract: Capacitor balancing of a dual three-level (3L) T-type converter based on silicon carbide (SiC) discrete semiconductors was performed with the converter feeding an open-ends induction motor (OEIM). A model predictive control (MPC) using a two step cost function calculation was developed to balance the DC link capacitors and control the machine torque simultaneously. The number of redundant switching states used was reduced without affecting the operating voltage vectors, which substantially reduced the computational time. A simulation and experimental results are in good agreement.

Abstract: There is described a method of controlling an inverter supplying power to a permanent magnet AC, PMAC, motor having a plurality of phase windings, The method comprises: selecting a first phase winding of the PMAC motor; electrically connecting the first phase winding to a first DC terminal of a DC link circuit at a first time, and maintaining the connection between the first phase winding and the first DC terminal: determining a flux difference between the first phase winding and a second phase winding of the PMAC motor; selecting a second time to electrically connect the second phase winding to the first DC terminal; electrically connecting the second phase winding to the first DC terminal at the second time; and maintaining the connection between the second phase winding and the first DC terminal. The second time is selected based on the determined flux difference.

Abstract: Disclosed is an AC motor drive (600) for a three phase, 400 Hz., AC induction motor. The application is a constant speed, constant load application. An AC power source with a wide variation in voltage and frequency is rectified to establish a DC bus. A three phase full wave bridge inverter operates on this source. A cascaded sinusoidal reference signal generator (225) generates three sinusoidal voltages 120° phase shifted from one another. These pure sinusoidal reference help reduce harmonic currents. A high PWM frequency is used to operate the power switches of the bridge to reduce current harmonics. The speed regulator (220) generates an error voltage between a speed command voltage and a feedback of DC voltage that is equivalent to the RMS value of the terminal voltage of the motor for speed regulation. The harmonic content of the DC bus current is extracted to provide short circuit protection.

Abstract: An escalator monitoring system includes a data collection device disposed near parts of an escalator that need to be monitored for collecting data of the parts; a data transmittal device used to transmit data relevant to safe operation of the escalator; a local data processing device or cloud processors used to receive the data relevant to the safe operation of the escalator, to compare it against a threshold value stored therein and derived from the parts in normal operating conditions, and to respond to comparison result.

Abstract: A motorized shade comprising a motor adapted to lower or raise a shade material for selectively covering an architectural opening based on a position of the sun. The motorized shade comprises a controller adapted to drive the motor phase according to a startup sequence by ramping up amplitude form an initial amplitude to a startup amplitude and ramping up frequency from an initial frequency to a drive frequency, drive the motor phase according to a full drive sequence to move the shade material by driving the motor phase according to a sinusoidal waveform at a set maximum amplitude and at a drive frequency, and drive the motor phase according to a wind down sequence by reducing frequency from the drive frequency to an end frequency and reducing the amplitude from the maximum amplitude to an end amplitude.

Abstract: A system for a non-hybrid vehicle is provided. The system includes an electromagnetic device structured to couple to an engine and generate AC electrical power from the engine. The system also includes an AC-to-DC inverter structured to receive and change the AC electrical power to regulated DC electrical power. Additionally, the system includes an electrical path coupled to the AC-to-DC inverter and configured to provide the regulated DC electrical power directly to an electrically-powered accessory at or above 28 volts DC.

Abstract: A motor drive device includes a first drive circuit to control an energization period of a first upper arm switch and a first lower arm switch connected to one end of a coil, a second drive circuit to control an energization period of a second upper arm switch and a second lower arm switch connected to another end of the coil, a current detection circuit to detect current flowing through the coil and output a current detection signal indicating a detection result of the current, a first protection circuit to determine whether overcurrent has occurred based on the current detection signal and output a first enable signal indicating a determination result to the first drive circuit, and a second protection circuit to determine whether overcurrent has occurred based on the current detection signal and output a second enable signal indicating a determination result to the second drive circuit.

Abstract: The invention relates to a method (400) for regulating an electric machine (190), comprising at least one first filter (140) and at least one second filter (142, 144). The method has the steps of: ascertaining (410) a feedback variable (Idq); filtering (412) a specifiable GW matching variable (Idq*); ascertaining (414) the filtered feedback variable without fundamental components (IdqWo-Funda); filtering (416) the filtered feedback variable without fundamental components (IdqWo-Funda); ascertaining (418) a filtered feedback variable without harmonic components (IdqFunda); and energizing (480) at least one winding of the electric machine (190) on the basis of the filtered feedback variable without harmonic components (IdqFunda).

Abstract: An electric motor control device includes an electronic control unit configured to perform switching control of a switching element of an inverter in PWM control mode when a modulation degree is less than a first predetermined value, perform switching control of the switching element in square wave control mode when the modulation degree is greater than or equal to a second predetermined value, and perform switching control of the switching element in intermediate control mode when the modulation degree is greater than or equal to the first predetermined value and less than the second predetermined value. The intermediate control mode uses a switching pattern in which, in a pulse pattern in the square wave control mode, a slit or a short pulse having the same width as the slit is formed according to whether a pulse is present at the time when a phase current crosses zero.

Abstract: A power device with a protection circuit is provided. The power device includes a power module, a power output terminal, a converter module, a bus capacitor, and a protection circuit. The power module receives an input power. The converter module, the protection circuit, and the bus capacitor is electrically connected between the power module and the power output terminal. The protection circuit is configured for overvoltage protection when the input power being overvoltage, suppressing the surge current when booting up the power device, and regulating the voltage on the bus capacitor under overvoltage and undervoltage conditions.

Abstract: In order to improve a method for selecting a frequency converter for a refrigerant compressor unit comprising a refrigerant compressor and an electric drive motor in such a way that the frequency converter is optimised for the application in question, it is proposed that a working state suitable for the operation of the refrigerant compressor unit is selected in an application field of an application diagram of the refrigerant compressor, that an operating frequency is selected for this selected working state, and that, on the basis of drive data, a working state operating current value corresponding to the selected working state and the selected operating frequency is ascertained for the operation of the refrigerant compressor unit.

Abstract: A power conversion apparatus capable of supplying a required reactive power while dynamically changing a dead band near 0 reactive current and maintaining a balance of DC voltage is provided. The power conversion apparatus including a three-level converter, a PWM controller for the three-level converter, an input current detector of the three-level converter, a coordinate converter that converts the current into a d-axis and q-axis current feedback, the reactive power control unit that controls a reactive power and outputs an reactive current reference, a d-axis current control unit having a dead band part for setting the d-axis current reference with hysteresis characteristics in the q-axis current feedback, and outputs the d-axis voltage reference, a q-axis current control unit that outputs a q-axis voltage reference based on the q-axis current reference, an inverse coordinate converter that outputs a three-phase AC voltage command based on the d-axis and q-axis voltage reference.

Abstract: The present application makes it possible to measure a PWM signal in a wide frequency range. A PWM signal measurement device (20) includes: a first duty cycle measurement unit (24) of a capture type configured to measure a frequency (f) and a duty cycle of a PWM signal (Sc); a voltage measurement unit (23) configured to measure a smoothed voltage (Vad) obtained by smoothing the PWM signal using a smoothing circuit (13); a second duty cycle measurement unit (25) of a smoothing type configured to measure a duty cycle of the PWM signal on the basis of a measured voltage value (Vadm) of the smoothed voltage; and a measurement-type selecting unit (26) configured to select one of the capture type or the smoothing type on the basis of a measured value of the frequency and a measured value of the smoothed voltage.

Abstract: The inverter (110) comprises input terminals (IT+, IT?), output terminals (OT), controllable switches (Q, Q?) connected to the input terminals (IT+, IT?) and to the output terminals (OT) and a control device (116) configured to control the controllable switches (Q, Q?) so as to convert a DC voltage at the input terminals (IT+, IT?) into an AC voltage at the output terminals (OT) intended to drive an asynchronous electric motor (108) to achieve a target torque (T*), selectively: in a first mode of operation in which the target torque (T*) is determined according to a torque determination method, and in response to a rotor temperature (Tr), in a second mode of operation in which losses in the rotor are decreased relative to the first mode of operation while the target torque (T*) remains determined according to the torque determination method of the first mode of operation.

Abstract: A power conversion device includes an inverter, a current detector, a frequency analysis processor, a storage, a determination unit, a reference rotational rate change unit, and a rate controller. The determination unit determines a frequency at which a signal component having a magnitude exceeding a prescribed value has been detected among frequency components of a load current, generates restriction information for excluding a reference rotational rate for a rotational rate corresponding to the detected frequency based on a determination result after the determination, and causes the storage to store the generated restriction information. The reference rotational rate change unit changes a reference rotational rate of an electric motor so that mechanical resonance of the detected frequency is avoided based on the stored restriction information. The rate controller controls a rotational rate of the inverter using the changed reference rotational rate.

Abstract: Systems and methods for position determination in an electric machine are provided. Aspects include a DC power source connected to an inverter circuit, an electric motor comprising a rotor and a stator, wherein an output of the inverter circuit is connected to a plurality phase of windings, and a controller configured to operate the electric motor and the inverter circuit, wherein the controller is further configured to determine one or more inactive phase windings from the plurality of phase windings, supply a voltage to the inactive phase windings, receive, from a current sensor connected to the electric motor, a current for each inactive phase winding of the inactive phase windings, determine an inductance for each inactive phase winding of the inactive phase winding based on the current, and determine a position of the rotor in the electric motor based on the inductance for each inactive phase winding.

Abstract: A drive device for an AC motor includes: an adaptive observation unit that adaptively estimates an angular velocity of a rotor of an AC motor; a speed control unit that determines a first torque command with which an angular velocity command matches an average value of an estimated angular velocity; a phase lead amount calculation unit that calculates, based on a disturbance frequency, a phase lead amount of a transfer function from a true angular velocity to a model deviation; a vibration suppression control unit that determines, based on a frequency of load torque pulsations, the model deviation, and the phase lead amount, a second torque command with which speed pulsations in the AC motor are suppressed; and a torque control unit that controls a torque of the AC motor based on the first torque command and the second torque command.

Abstract: In a method for monitoring the operation of an electric motor and a lifting mechanism, the motor current is acquired, and the electric motor has, for example, an electromagnetically actuable brake, e.g., a holding brake. In the method, a pre-magnetization is performed when the electric motor is switched on, the characteristic of the acquired values of the motor current is monitored for an exceeding of a permissible measure of deviation from a setpoint characteristic, and a brake of the electric motor is activated, e.g., remains applied.

Abstract: An electric motor system is described. The electric motor system includes a drive circuit configured to supply variable frequency current and a contactor configured to supply line frequency current, wherein the drive circuit includes a three-phase inverter and an H-bridge including two phases of the inverter. The electric motor system also includes an electric motor and a controller. The controller is configured to control the inverter to supply variable frequency current to the electric motor over a first duration and determine to control the drive circuit to transition from supplying variable frequency current to supplying line frequency current. The controller is also configured to determine a polarity of a sensed alternating current (AC) voltage, disable at least two switches of the H-bridge, and control the contactor to close, thereby preventing the contactor and the inverter from energizing the electric motor at the same time once the contactor is closed.

Abstract: A method for determining the angle of the rotor of an electric motor includes receiving a first rotor position signal from a rotor position sensor by using a control unit, the first rotor position signal including a plurality of orders; determining the angular velocity of the electric motor at least by way of the first rotor position signal by using an angular velocity module of the control unit; determining a first base signal by way of the determined angular velocity and the first rotor position signal by using a first filter module of the control unit; and determining the angle of the rotor at least by way of the determined first base signal by using an angle module of the control unit.

Abstract: Systems, apparatuses, and methods for efficient operation of a switch arrangement are described. Selectively operating one of a plurality of parallel-connected switches at different times along a period of a periodic waveform may allow for improved efficiency, uniform loss-spreading, and enhanced thermal design of an electronic circuit including use of power switches.

Abstract: A method for operating a system having at least two mechanically coupled asynchronous motors, a computer program implementing the method and a system operating in accordance with the method are disclosed. One asynchronous motor is selected as master, with the other asynchronous motor(s) selected as slave(s). An effective (master) flux angle is measured in the motor selected as master and used as a basis for a setpoint value for controlling the flux angle of every other motor (slave) in the system. The flux angle of every slave motor is adjusted to the setpoint value as part of the control operation.

Abstract: A power tool has a functional component, a motor, a power supply module, a controller and a drive circuit including a first drive terminal and a second drive terminal respectively electrically connected to a first power terminal and a second power terminal of the power supply module, multiple high-side switches wherein high-side terminals of the high-side switches are respectively electrically connected to the first drive terminal, and multiple low-side switches wherein low-side terminals of the low-side switches are respectively electrically connected to the second drive terminal. The controller is configured to output a first control signal to one high-side switch to place it in an on or off state and output a second control signal to one low-side switch to place it in the other state. The low-side terminal of one high-side switch is connected to the high-side terminal of one low-side switch.

Abstract: Methods and systems are provided for managing environmental conditions and energy usage associated with a site. One exemplary method of regulating an environment condition at a site involves a server receiving environmental measurement data from a monitoring system at the site via a network, determining an action for an electrical appliance at the site based at least in part on the environmental measurement data and one or more monitoring rules associated with the site, and providing an indication of the action to an actuator for the electrical appliance.

Abstract: A method for determining a motor angle, may include deriving a sensor weight and a sensorless weight via a cross product of an actual current vector and a model-based sensored current vector and a cross product of the actual current vector and a model-based sensorless current vector; and determining a final motor angle by applying the sensor weight and the sensorless weight to each of a sensored angle and a sensorless angle.

Abstract: This power conversion device comprises: a power converter including a switching element; and a control unit which controls the power converter. The control unit calculates a torque electric current detection value and an excitation electric current detection value from an electric current flowing to an external device, and when an absolute value of the torque electric current detection value is greater than or equal to the excitation electric current detection value, performs control such that the excitation electric current detection value follows the torque electric current detection value.

Abstract: A motor-driving control system includes an actuator configured to generate rotational force by driving received current, a current provider configured to provide current to the actuator while repeatedly turning on and off the current at a preset period and duty, and a controller configured to estimate a rotation position or a rotation speed of the actuator in a section in which the current of the current provider is turned on or off and to control the current provider to follow a speed command based on the estimated rotation position or rotation speed.

Abstract: A resolver signal processing device includes an output signal state detection unit and a disconnection detection unit. The output signal state detection unit calculates a sum of squares of a signal with a first phase and a signal with a second phase which are output signals of a two-phase output type resolver based on the output signals. The disconnection identification unit outputs information representing a disconnection state of any of a first signal system which supplies an excitation signal of the resolver and a second signal system of the output signals based on a size of a variation range in which the sum of squares periodically changes.

Abstract: A steering drive system for a steering system of a transportation vehicle having a first control unit for actuating a first winding circuit of a steering drive motor with a test circuit to make available a defined changing test signal and a second control unit for actuating a second winding circuit of the steering drive motor, wherein a test signal reception circuit of the second control unit receives the test signal, and wherein the second control unit actuates the steering drive motor based on the presence or absence of the test signal.

Abstract: The present disclosure provides an inverter control device for estimating the magnetic flux of a rotor, and calculating and compensating for a slip frequency on the basis of a torque current and a magnetic flux current, to control the speed of an electric motor. To this end, the present invention may comprise: a command voltage generation unit for outputting a three-phase PWM voltage with respect to a command frequency to an inverter on the basis of voltage/frequency operation; and a slip frequency determination unit for determining a slip frequency on the basis of the phase current and phase voltage of an electric motor driven by the inverter.

Abstract: A system (110) and method of controlling a three-phase active harmonic filter (160) with a three-phase converter having inputs for connection to a three-phase AC source (112), the three-phase converter having three phase legs, each phase leg of the three phase legs of the three-phase converter includes a first switching device operably connected to a first power supply rail and a second switching device operably connected to a second supply rail, the three-phase converter operably connected to a controller. The controller is configured to determine an operating characteristic of the AHF and operable to control the first and second switching devices of each phase leg of the three phase legs with a first PWM strategy, compare the operational characteristic of the AHF to a selected threshold, and employ a second PWM strategy if the operational characteristic exceeds a selected threshold.

Abstract: An actuator includes an inverter, a stator, a movable part, a controller, an injector, a current detector, and an estimator. The inverter is driven by a power generated by the axial force of an engine, etc. The stator includes an armature coil driven by the inverter. The movable part applies a driving force to at least one of a rudder surface of a tailplane of the airplane, etc. The controller controls the inverter in accordance with a signal from a maneuvering system. The injector injects a high-frequency signal into the coil. The current detector detects a coil current. The estimator estimates a position of the movable part.

Abstract: Control logic for a power sharing system on a hybrid propulsion aircraft, utilizing parallel multiple control loops outputting difference commands which provide bumpless transfer between control loops without integrator wind up or reset logic, allowing for efficient load distribution between electric generators and batteries powering electric motors.

Abstract: An ECU includes plural sensor units and plural control units. The sensor units include magnetic field detection elements for detecting a rotation of a motor, and output mechanical angles related to the rotation angle in one rotation and count values related to the number of rotations of the motor, respectively. One rotation of the motor is divided into indefinite regions, in which detection deviation of the count values may occur, and definite regions, in which no detection deviation occurs. The definite region of the count value is set to deviate from the definite region of the other count value. Absolute angle calculation units calculate the absolute angles using the count values of the definite regions.

Abstract: A method for controlling marine vessel speed includes determining a setpoint vessel speed, which is constant while the system is operating in a cruise control mode. The method includes using vessel speed feedback control to adjust operational characteristics of the engine so as to achieve the setpoint vessel speed. The method also includes determining a measured vessel speed and filtering the measured vessel speed. In response to determining that the measured vessel speed is within a given range of the constant setpoint vessel speed, the method includes transitioning to the cruise control mode and comparing the filtered measured vessel speed to the constant setpoint vessel speed for purposes of the feedback control.

Abstract: The present invention relates to a circuit for switching an AC voltage. It contains an input terminal able to be connected to an AC voltage source, an output terminal able to be connected to a load impedance, and a first series circuit. This series circuit comprises a diode and a circuit for storing electrical charges. The series circuit has a first end connection that is connected to the input terminal and a second end connection that is connected to the output terminal. The circuit for switching an AC voltage furthermore contains a DC voltage source, which is connected to an electrical connection between the diode and the input terminal or to an electrical connection between the diode and the output terminal and is designed to impress a DC current in the diode. The circuit for switching an AC voltage finally contains a first switch that is connected to an electrical connection between the diode and the circuit for storing electrical charges at one terminal.

Abstract: An induction motor controller is provided. The induction motor controller includes a first module that derives a commanded stator voltage vector, in a rotor flux reference frame, via a rotor flux regulator loop and a torque regulator loop, which process at least partially in the rotor flux reference frame. The induction motor controller includes a second module that processes the commanded stator voltage vector to produce AC (alternating current) power for an induction motor.

Abstract: A control method of inverter for driving motor including a magnet, comprises detecting a rotation state of the motor by a rotation sensor, detecting current of the motor by a current sensor, calculating, based on a torque command value, a detection value of the rotation state detected by the rotation sensor, and detection current detected by the current sensor, a voltage command value for controlling a voltage of the motor by a controller for controlling the inverter, specifying a value of at least one of a local maximum value, a local minimum value, and an average value of the torque voltage command value included in the voltage command value as a torque determination target command value by the controller, comparing a demagnetizing determination threshold value with the torque determination target command value by the controller, and determining whether or not demagnetization of the magnet occurs in accordance with the compared result.

Abstract: Described is a method that includes receiving a reference signal including an adjustable-amplitude sine wave. The method also includes receiving a voltage feedback signal from a voltage control loop. The voltage feedback signal is a point-of-regulation sine wave, and the voltage control loop includes a first response time. The method also includes comparing the reference signal to the voltage feedback signal to generate an error value. Further, the point-of-regulation sine wave is controlled in the method based on a proportional-integral-derivative input and a current feedback signal. The proportional-integral-derivative input is based on the error value. Additionally, the method includes adjusting the reference signal based on an output of an amplitude control loop. The amplitude control loop includes a second response time that is at least one order of magnitude slower than the first response time of the voltage control loop.

Abstract: An electric motor system is described. The electric motor system includes a drive circuit configured to supply variable frequency current and a contactor configured to supply line frequency current, wherein the drive circuit includes a three-phase inverter and an H-bridge including two phases of the inverter. The electric motor system also includes an electric motor and a controller. The controller is configured to control the inverter to supply variable frequency current to the electric motor over a first duration and determine to control the drive circuit to transition from supplying variable frequency current to supplying line frequency current. The controller is also configured to determine a polarity of a sensed alternating current (AC) voltage, disable at least two switches of the H-bridge, and control the contactor to close, thereby preventing the contactor and the inverter from energizing the electric motor at the same time once the contactor is closed.

Abstract: A rotation angle estimation unit calculates a rotation angle of a rotor from a d-axis current and a q-axis current that flow into a motor of an onboard fluid machine and from a d-axis voltage command value and a q-axis voltage command value. A correction unit of an inverter device applies a pulse voltage to the motor when the motor is in a stopped state. Further, the correction unit corrects a parameter for control of the motor in accordance with a comparison result of the d-axis current and the q-axis current, which flow into the motor when the pulse voltage is applied.

Abstract: Provided is a method of controlling a multi-channel multi-phase electrical machine including a plurality of channels each with a set of phase windings connected to a converter, which method includes the steps of operating the converters to electrically phase-shift the channels; computing harmonic injection currents for a dominant harmonic on the basis of electrical quantities in a rotating reference frame; determining harmonic voltage references for the dominant harmonic on the basis of the harmonic injection currents; and regulating the AC output voltages of the channels according to the fundamental voltage references and the harmonic voltage references. Also provided is a control arrangement of a multi-channel multi-phase electrical machine; a wind turbine; and a computer program product.

Abstract: A method of controlling a motor, for example of an electric power steering system, includes receiving a motor torque demand signal indicative of a torque required from the motor. A current demand signal indicative of the currents to be applied to each phase to meet the torque demand is generated from the motor torque demand signal. One or more operational values from the motor are determined. The current demand signal is set as a function of one or more parameters of the motor obtained by fitting a flux linkage model to the measured operational values. A motor circuit having the permanent magnet electric motor includes a control stage arranged to generate the current demand signal in response to a torque demanded of the motor. A modifying means modifies the magnitude and/or the phase of the current demanded for each phase of the motor by the controller.

Abstract: A technique for reducing an operation noise even when a high-pass filter is used for controlling a motor is provided. A controller is used in a motor control system for driving a motor by using a drive circuit and an inverter. The controller includes a current control block. The controller performs feedforward control by using a current value, compensates for a term of a self-inductance of the motor included in a current control block by an inverse model, compensates for a phase characteristic of a transfer function of the inverse model by an advance component, and corrects a gain characteristic of the transfer function of the inverse model by a function of a physical quantity obtained based on an angular velocity of the motor, thereby compensating for a phase delay and a gain reduction of a torque output generated by the self-inductance.

Abstract: A drive apparatus for a motor having a stator and a rotor, the drive apparatus including a current detection unit configured to detect, when the motor is rotating, each of multi-phase currents flowing through coils of the stator, and a control unit for controlling the motor by sensor-less control configured to convert the detected multi-phase currents into a d-axis current Id and a q-axis current Iq in a d-q coordinate system, calculate a phase error between an actual rotational position of the rotor and an imaginary rotational position thereof by comparing the d-axis current Id with a d-axis current command value Idref and comparing the q-axis current Iq with the d-axis current command value Idref, perform control so that the phase error gets closer to zero, and output voltage command values to a motor drive circuit.

Abstract: A virtual voltage injection-based speed sensor-less driving control method for an induction motor is provided. First, a virtual voltage signal is injected into a motor flux linkage and rotating speed observer so that there is a difference between an input of the motor flux linkage and rotating speed observer and a command input of the motor. Then, based on any type of the motor flux linkage and rotating speed observer, a motor flux linkage rotation angle and a motor rotor speed are estimated, and the induction motor is driven to run normally with a certain control strategy (such as vector control).

Abstract: A compressor unit (2) for use in a refrigeration circuit, comprises at least two compressors (8, 10); and a common variable frequency drive (6), configured to be connected to a three phase grid voltage supply (4); each compressor (8, 10) having an inlet port (12) configured to be in refrigerant communication, via a suction line, with an outlet of an evaporator; an outlet port (14) configured to be in refrigerant communication, via a pressure line, to an inlet of a condenser; a compressor motor (18), particularly an alternating current induction motor, with a three phase supply line (32-1, 32-2); a power modulation means (24) for controlling the power of the compressor (8, 10) according to its load needs; wherein each compressor (8, 10) is switchable, independently from the respective other compressor(s) (8, 10), to be connected, during start-up and acceleration of the respective compressor (8, 10), to the common variable frequency drive (6), and to be connected, during rated-speed operation of the respective

Abstract: An electrical converter with at least two output phases includes a rectifier and a thyristor-based inverter interconnected by a DC link with an inductor, wherein the thyristor-based inverter includes a half-bridge with at least two half-bridge arms for each output phase of the electrical converter and each arm being provided by a thyristor. A method for switching the electrical converter includes: cyclically switching the thyristors of the inverter, such that at least one time instant, two thyristors of different half-bridge arms are switched on simultaneously, such that a pulse number, which determines at how many time instants thyristors of the inverter are switched during one stator voltage period, is lower than the number of half-bridge arms of the inverter.