Frequency converter for different mains voltages
AssigneeDanfoss Drives A/S
InventorsKenneth Skaug, Michael Toennes, Nils-Ole Harvest, Egon Krogh, Andreas Aupke
Life of this patent
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Abstract
The invention is directed to controlling an electric motor by means of a frequency converter. The frequency converter can be connected to one of several different mains voltages. According to the present invention, the maximum output power of the frequency converter, is limited when the actual mains voltage is lower than the maximum nominal mains voltage, for which the frequency converter is designed, and during the limitation the frequency converter controls the speed of the motor within a power range up to a limited maximum output power. This gives a genuine multi-voltage unit, which can be connected to a wide range of mains voltages.
Claims25
A method for controlling an electric motor by means of a frequency converter, the method comprising the steps of:
- comparing a limit value signal with one or more measured or calculated parameters;
- and
- limiting a maximum output power when the one or more measured or calculated parameters exceeds the limit value signal by reducing a motor frequency generated by an inverter;
- wherein the frequency converter is connectable to one of several mains voltages and a control device limits the maximum electrical output power of the frequency converter when an actual mains voltage is lower than a maximum nominal mains voltage for the frequency converter, a converter between a rectifier and the inverter is regulated to output an intermediary circuit voltage that is kept constant during operation at each one of the several mains voltages, and during said limitation of the maximum output power the frequency converter controls a speed of the electric motor within a power range up to the limited maximum output power.
A frequency converter for controlling an electric motor, the frequency converter comprising:
- a rectifier for providing a rectifier output voltage;
- a converter for regulating the rectifier output voltage to produce an intermediary voltage;
- an inverter for inverting the intermediary voltage and generating a motor frequency;
- and
- a control device;
- wherein said frequency converter is connectable to one of several mains voltages, the intermediary voltage is kept constant at each one of several mains voltages and the control device limits the maximum electrical output power of the frequency converter when an actual mains voltage is lower than a maximum nominal mains voltage for the frequency converter by comparing a first limit value signal with one or more measured or calculated parameters and reducing the motor frequency generated by the inverter if the measured or calculated parameter is greater than the first limit value signal;
- and
- wherein a second limit value representing the hardware current limit of the inverter is adjustable during operation of the frequency converter, and that an over current signal is given if a current measuring signal exceeds the second limit value.
A frequency converter for controlling an electrical motor, the converter comprising electronic control circuitry wherein a digital controller generates a PWM signal which is led to an analogue lowpass filter and converted into an analogue reference value which is a reference for a current control loop, and an analog current measurement value is a feedback value for said current control loop;
- wherein the analogue reference value is led to a first input of a comparator and the analogue current measurement value is led to a second input of the comparator;
- and
- wherein the PWM signal is led into an analogue multiplier placed between the digital controller and the analogue lowpass filter, said analogue multiplier multiplying the PWM signal to a signal representing a curve profile of a mains voltage.
Dependencies are inferred from the claim text.