This is a Non-Provisional Patent Application, filed under the Paris Convention, claims the benefit of European Patent (EP) Application Number 14305591.1 filed on 22 Apr. 2014 (22 Apr. 2014), which is incorporated herein by reference in its entirety.
The present invention relates to magnetic bearings and more particularly to the compensation of reactive power in a magnetic bearings inductive position sensor.
Magnetic bearings are used in different rotating machines such as electric motors, compressor, turbines or the like in order to maintain the axial or/and radial positions of a rotating shaft by means of magnetic fields acting on a rotor of the machine.
The bearing force is built using a pair of electromagnets connected to switching amplifiers (classically one switching amplifier per electromagnet) for which the control voltage is adapted by a controller via a correction network. The position of the rotor assembly is detected by position sensors. However, as these sensors are inductive and the inductance value is relative to the rotating machine size, it is necessary to compensate the exact reactive current by means of capacitors to minimize to oscillators losses and dimensions.
In this prior art configuration, capacitors 16, 18 are adjusted to minimize the reactive currents I1 and I2 in the primary windings 22A and the secondary windings 22B of the HF transformer respectively. Due to the number of parameters for each sensor (the sensor inductance value, the capacitance value of the cable, the global inductance value) and the uncertainties on the relaying cable length (the rotating machine 10 can be far (hundreds of meters) from the electronic magnetic bearing controller 14), the capacitor tuning is made at the machine locating by re-worked soldering on the printed circuit board of the electronic magnetic bearing controller.
The present invention aims to eliminate the above disadvantages by a more convenient and flexible tuning with an automatic compensation procedure in lieu of a final tuning of the position sensors on the machine location or at OEM location as currently.
For this, it is proposed an electronic magnetic bearing controller for controlling the position of a rotor of an electrical machine supported by an active magnetic bearing the position of which being measured by at least one inductive position sensor having an inductive coil, the controller comprising an automatic reactive power compensation device for automatically compensating the reactive power consumed by the at least one inductive position sensor.
Preferably, the automatic reactive power compensation device receives a reactive current I1, I2 proportional to the current in the inductive coil and delivers a compensation current Icomp across windings of a HF transformer the secondary windings of which being connected to the inductive coil through a relaying cable.
According to different variants, the windings can be primary windings of the HF transformer and the reactive current is a current I1 across the primary windings or the windings can be secondary windings of the HF transformer and the reactive current is a current I2 across the secondary windings or the windings can be auxiliary windings of the HF transformer and the reactive current is a current I1 across primary windings of the HF transformer or a current I2 across secondary windings of the HF transformer.
According to a first embodiment of the invention, the automatic reactive power compensation device comprises a static compensation of reactive current formed by a parallel bank of capacitors each connected in series with an electronic switch controlled by a control circuit receiving the reactive current and delivering open or close control signals for the n electronic switches.
Preferably, that the electronic switches are thyristors or triacs.
According to a second embodiment of the invention, the automatic reactive power compensation device comprises a dynamic compensation of reactive current formed by a half-bridge of two electronic devices each connected in series with a capacitor and controlled by a control circuit receiving the reactive current and delivering a Pulse-width modulation (PWM) control signal for the two electronic devices.
Preferably, that the electronic devices are MOSFET or Silicon Carbide (SiC) MOSFET.
Advantageously, the control circuit comprises a PWM inverter logic operating at a switching frequency between 200 kHz and 1 MHz and receiving a reference voltage from a Proportional-Integral controller (PI controller) which receives an error signal generated by the difference between the reactive current and a reference current. And the reference current is provided by a multiplier receiving on the one hand a set voltage from a PI controller which receives an error signal generated by the difference between a voltage Vdc applied to the two electronic devices and a reference voltage VdcRef and on the other hand a measured voltage Vcomp.
Preferably, the electronic magnetic bearing controller of the invention further comprises a high frequency oscillator generator delivering an output voltage V1 at a high frequency (comprised between 10 and 40 kHz, typically about 20 kHz) for the primary windings to that it is connected.
The invention will be better understood and further details and advantages thereof will appear more clearly in the following description with reference to the accompanying drawings illustrating embodiments of the invention, and in which:
A first embodiment of an electronic magnetic bearing controller of the rotating machine with a reactive power compensation device of an inductive coil of at least one position sensor of a magnetic bearing of this rotating machine is illustrated in
As in the prior art, the primary windings 22A of the HF transformer 22 receives on its input terminals 28A, 28B the outputs of the high frequency oscillator generator 30 (delivering an output voltage at a high frequency comprised between 10 and 40 kHz and typically about 20 kHz) the input of which results from a comparison (by a comparator 32) of the output reference 34 and the differential output of a voltage measurement 36 across the inductance coil 12 through the sensing wire 38. Similarly, the output terminals 20A, 20B of the secondary windings 22B of the HF transformer 22 are connected to the input terminals 24A, 24B of the relaying cable 26 connecting the electronic magnetic bearing controller 14 to the rotating machine 10. The length of the relaying or transmitting cable can vary from few meters to hundreds of meters and consequently the capacitance of the cable can vary from few nano Farads to some decades of nano Farads. So, basically, the current to be compensated into the inductive coil 12 having a typical value between 250 μH and 1 mH can vary from 0.5 to 2 Amperes.
According to the invention, an automatic reactive power compensation device 40 is provided for automatically compensating the reactive power consumed by the inductive coil 12 of the position sensor. More particularly, the automatic reactive power compensation device receives a reactive current I1 proportional to the current in the inductive coil and delivers a compensation current Icomp across the primary windings 22A of a HF transformer 22 the secondary windings 22B of which being connected to the inductive coil through the relaying cable 26. As illustrated, I1 is extracted on one input terminal 28A at the primary windings 22A of the HF transformer 22.
On the contrary, in the configuration of
As another alternative, in the configuration of
With this static compensation consisting of switching a fixed number of capacitors according to the reactive current to compensate, it is possible to obtain either an over or an under compensation but not a thin adjustment of the reactive current.
More particularly, as detailed in
With this dynamic configuration consisting of generating or absorbing reactive power without requiring a bank of capacitors, it is possible to control and to compensate in real time the reactive current whatever is the reactive current to be compensated, the cable length and the number of bearing sensor coils connected to the machine. If for any reason, the machine is disconnected or the bearing sensors are partially or totally broken, the reactive current is no more compensated or partially compensated by adjusting in real time the compensating current Icomp.
The invention is particularly suitable for active magnetic bearings of important machines like chiller or turbo-expander for example as for active magnetic bearings within smaller systems like HVAC for cars or trucks.
Although preferred embodiments have been shown and described, it should be noted that any changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.
Number | Date | Country | Kind |
---|---|---|---|
14305591 | Apr 2014 | EP | regional |
Number | Name | Date | Kind |
---|---|---|---|
3936727 | Kelley, Jr. | Feb 1976 | A |
3963978 | Kelley, Jr. | Jun 1976 | A |
3992661 | Kelley, Jr. | Nov 1976 | A |
4052648 | Nola | Oct 1977 | A |
4433276 | Nola | Feb 1984 | A |
4469998 | Nola | Sep 1984 | A |
5793623 | Kawashima | Aug 1998 | A |
7642666 | Ichinose | Jan 2010 | B2 |
20050231214 | Howard | Oct 2005 | A1 |
20080106099 | Ichinose | May 2008 | A1 |
20090108833 | Ziegler | Apr 2009 | A1 |
20100102560 | Ichinose | Apr 2010 | A1 |
20110035114 | Yoneda | Feb 2011 | A1 |
20110187109 | Ichinose | Aug 2011 | A1 |
20120019188 | Fukutani et al. | Jan 2012 | A1 |
20130328317 | Himmelmann | Dec 2013 | A1 |
20140009969 | Yuzurihara | Jan 2014 | A1 |
20140021934 | Wu | Jan 2014 | A1 |
Number | Date | Country |
---|---|---|
3409448 | Sep 1984 | DE |
1422492 | May 2004 | EP |
2004097333 | Nov 2004 | WO |
2011111058 | Sep 2011 | WO |
Entry |
---|
Translation of foreign Patent document DE 3409448 A1 (Year: 1984). |
Number | Date | Country | |
---|---|---|---|
20150300407 A1 | Oct 2015 | US |