Frequency converter for different mains voltages
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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.
86 Citations
58 Claims
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1-29. -29. (Canceled)
- 30. A method for speed controlling an electric motor by means of a frequency converter, the frequency converter comprising a rectifier, an inverter and a control device, said frequency converter being connectable to one of several mains voltages and the control device limiting the maximum electrical output power of the frequency converter when the actual mains voltage is lower than the maximum nominal mains voltage for which the frequency converter is designed, wherein a DC/DC converter between rectifier and inverter is regulated to output a DC voltage (Udc) that is kept constant during operation at each one of the several mains voltages, that a limit value signal (Ilim, Plim) is compared with one ore more measured (Urec, Irec, Udc, Idc, T) or calculated (Pinv) parameters, that the control device limits the maximum output power by reducing the motor frequency generated by the inverter, and that during said limitation the frequency converter controls the speed of the electric motor within a power range up to the limited maximum output power.
- 41. A frequency converter for speed controlling an electric motor, the frequency converter comprising a rectifier, an inverter and a control device, said frequency converter being connectable to one of several mains voltages and the control device limiting the maximum electrical output power of the frequency converter when the actual mains voltage is lower than the maximum nominal mains voltage for which the frequency converter is designed, wherein a boost converter between rectifier and inverter regulates the intermediary voltage (Udc) to a value that is kept constant during operation at each one of the several mains voltages, that a first limit value signal (Ilim, Plim) is compared with one ore more measured (Urec, Irec, Udc, Idc, T) or calculated (Pinv) parameters, that the control device limits the maximum output power by reducing the motor frequency generated by the inverter if the measured value is greater than the first limit value, and that a second limit value (Ioc) representing the hardware current limit of the inverter is adjustable during operation of the frequency converter, and that an over current signal (OC) is given if a current measuring signal exceeds the second limit value.
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54. A method for generating an over current signal (OC) in a frequency converter which speed controls an electric motor, the over current signal being generated when the value of a measured current exceeds the value of a current reference signal (IOC) which is variable during the operating period of the frequency converter, wherein the characteristic of the current reference signal in a memory element of the frequency converter is replaceable and can be made dependent on different variables such as motor frequency and/or inverter temperature and/or the expected load torque.
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55. A frequency converter comprising an electronic circuit for detecting over current, the circuit consisting of a comparator, which compares a current measuring signal with a current reference signal which is generated by a reference generator, the comparator sending an over current signal, when the current measuring signal is larger than the current reference signal, the current reference signal being variable during the operating period of the frequency converter, wherein a current reference characteristic is stored in a programmable memory element, that the characteristic is dependent on at least one first variable (A1, A2, An, S1, S2, Sn) and replaceable by a second characteristic, which is dependent on at least one second variable (A1, A2, An, S1, S2, Sn), and that the reference generator loads the current reference characteristic from the memory element and generates a pulse-width modulated current reference signal.
- 56. A frequency converter for speed 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 (Ioc,Iref) which is reference for a current control loop, and that an analog measurement value is feedback value for said current control loop.
Specification