The invention relates to a method for determining an error voltage of a current converter to which a load, in particular in the form of a three-phase machine such as an asynchronous machine, is connected, is determined and if necessary compensated, wherein an output voltage on the current converter is increased stage-by-stage or step-by-step and which is measured here as a current adjusting a step response. The invention further relates to a three-phase machine, for example in the form of an asynchronous machine having power electronics comprising a current converter and in the form of a compensation device for compensating the error voltage of the current converter. The invention further relates to a method for operating and/or controlling such a three-phase machine, in which the error voltage of the current converter is determined and compensated. According to the invention, the error voltage is determined from the current measured as a step response and from a resistance of the load, wherein said resistance is determined from a target voltage jump and from a simultaneously measured actual current jump in a relatively high current range of at least 30% of at least 50% of the rated current of the end stage of the current converter.

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.

A generalized frequency conversion system for a steam turbine generator unit. The system comprises at least a variable speed steam turbine with an adjustable rotating speed, a water feeding pump, a variable frequency generator operating at a variable speed, a speed increasing gearbox with a fixed rotating speed ratio, a variable frequency bus and an auxiliary machine. With a change in load of the unit, parameters of steam entering the variable speed steam turbine and an extracted steam amount are adjusted (changed) accordingly, so that the rotating speed of the steam turbine changes accordingly. In this way, on one hand, the rotating speed of the water feeding pump is changed through the speed increasing gearbox; and on the other hand, the frequency of alternating current outputted by the variable frequency generator is changed. In the present invention, there is no need to additionally provide other types of frequency converters, and the system is simple, reliable, low in cost and high in efficiency.

A current sourced control topology is provided for an AC motor controller that eliminates many of the problems associated with prior art motor controllers that use voltage source inverter (VSI) technologies. By controlling the output of AC current sources such as synchronously controlled down converters to directly drive each motor phase, significant efficiency gains and a reduction in electromagnetic interference is achievable.

An air conditioner includes a controlled device, a frequency converter, and a controller. The controller is configured to: determine a present operating frequency of the controlled device, and a present output current and a present input power of the frequency converter; determine a present efficiency of the frequency converter according to the present operating frequency of the controlled device and the present output current of the frequency converter; and determine a present input power of the frequency converter according to the present efficiency of the frequency converter and the present output power of the frequency converter.

The systems and methods disclosed relate to arc resistant medium voltage motor control centers for bypass and synch transfer. A drive control system comprising: a variable frequency drive cabinet comprising a variable frequency drive; a power supply line; at least one motor control cabinet having a top portion and a bottom portion, wherein the at least one motor control cabinet is arc resistant, wherein the at least one motor control cabinet comprises: a medium voltage fused bypass controller in the top portion; a medium voltage non-fused transfer controller in the bottom portion; a reactor compartment, wherein the reactor compartment is arc resistant; wherein the variable frequency drive is coupled to the power supply line and the non-fused transfer controller, and the fused bypass controller is coupled to the power supply line.

A sensor is configured to sense current, of one or more output phases of an inverter, associated with back electromotive force (back EMF) of the machine. A converter or electronic data processor is adapted to convert the sensed current into current vectors associated with a stationary reference frame. An estimator or current model is configured to estimate back-EMF vectors from the converted current vectors. A vector tracking observer or the electronic data processor is adapted to mix the back-EMF vectors and applying the mixed back-EMF vectors to a preliminary inertial model. A secondary observer or the data processor is operable to apply the output of the preliminary inertial model to a secondary inertial model in the second speed range to estimate position or motion data for the rotor.

A method and system to prevent unexpected operation of a motor when the voltage level on a DC bus drops is disclosed. The voltage level on the DC bus is monitored during a run command. When a run is commanded, the processor executes a control routine to determine a desired amplitude and frequency for the output voltage required to control the motor connected to the motor drive. If the desired frequency of the output voltage exceeds a maximum frequency for the measured voltage on the DC bus, as established by parameters stored in the motor drive, the motor drive limits the output frequency to the maximum frequency for the corresponding measured voltage. The motor drive continually monitors the measured voltage present on the DC bus and further reduces the maximum output frequency allowed during the run if the present value of the measured voltage drops below a previously measured value.

Provided is a power conversion controller in which variation in reactive power among power conversion controllers can be inhibited while maintaining the running performance of vehicles. The power conversion controller includes a power factor setter that sets a power factor based on a detection value of an overhead line voltage, and a calculator that calculates a reactive current command value by multiplying an active current command value by a tangent of a power factor angle of the power factor. The power factor setter sets a reference value set in advance as the power factor if the detection value is within a reference range, sets a value smaller than the reference value as the power factor if the detection value is below the reference range, and sets a value larger than the reference value as the power factor if the detection value is beyond the reference range.

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.