METHOD FOR RECONFIGURING AN ELECTRIC MACHINE

Abstract

Method for reconfiguring an electric machine including a rotor arranged to rotate with an angular speed (), the electric machine being arranged to pass from a first configuration (config.sub.1) to a second configuration (config.sub.2), the method comprising the steps of: a) determining in real-time a real speed threshold (.sub.real_th) depending on the current operating condition of the electric machine; b) checking if the angular speed () of the rotor is greater than said real speed threshold (.sub.real_th); c) in positive case, no reconfiguration is performed from the first configuration (config.sub.1); d) in negative case: d.1) determining the current configuration of the electric machine; d.2) selecting a reconfiguring decision method; d.3) deciding whether to reconfigure the electric machine or not and, in positive case, reconfiguring the electric machine.

Claims

1. Method for reconfiguring an electric machine including a rotor arranged to rotate with an angular speed (), the electric machine being arranged to pass from a first configuration (config.sub.1) to a second configuration (config.sub.2), the method comprising the steps of: a) determining in real-time a real speed threshold (.sub.real_th) depending on the current operating condition of the electric machine; b) checking if the angular speed () of the rotor is greater than said real speed threshold (.sub.real_th); c) in positive case, no reconfiguration is performed from the first configuration (config.sub.1); d) in negative case: d.1) determining the current configuration of the electric machine; d.2) selecting a reconfiguring decision method; d.3) deciding whether to reconfigure the electric machine or not and, in positive case, reconfiguring the electric machine.

2. Method according to claim 1, wherein the step of determining the real speed threshold (.sub.real_th) comprises performing an estimation of the temperature of magnets of the rotor.

3. Method according to claims 1, wherein the steps are repeated sequentially, when multiple reconfigurations of the electric machine are considered in series, or wherein the steps a)-d) are executed in parallel, when multiple reconfigurations of the electric machine are considered in parallel.

4. Method according to claim 3, comprising the steps of: determining a first, second, . . . , n.sup.th real speed threshold (.sub.real_th1, .sub.real_th2, . . . , .sub.real_thn); checking if the angular speed () of the rotor is greater than the real speed thresholds (.sub.real_th1, .sub.real_th2, . . . , .sub.real_thn), respectively, in positive case, no reconfiguration from or to the first configuration (config.sub.1), the second configuration (config.sub.2), . . . , an n+1.sup.th configuration (config.sub.nth), respectively, is performed; in negative case: determining the current configuration of the electric machine; selecting a reconfiguring decision method; deciding whether to reconfigure the electric machine or not and, in positive case, reconfiguring the electric machine.

5. Method according to claim 1, wherein the value of the real speed threshold (.sub.real_th) is determined in the following interval: $0.92\frac{V_{\mathrm{dc}}}{\sqrt{3}\left[\left[{}_{\mathrm{mo}}+\left(T-T_0\right)\right]+N_{\mathrm{rot}}{N}_{\mathrm{stat}}{I}_{\mathrm{rot}}\right]}{}_{{\mathrm{real}}_{\mathrm{th}}}1.8\frac{V_{\mathrm{dc}}}{\sqrt{3}\left[\left[{}_{\mathrm{mo}}+\left(T-T_0\right)\right]+N_{\mathrm{rot}}{N}_{\mathrm{stat}}{I}_{\mathrm{rot}}\right]}$ wherein: .sub.mo and T.sub.0 are respectively a reference magnetic flux and a respective reference temperature of the electric machine; is the thermal coefficient of a permanent magnet material of magnets of the rotor; T is the magnet temperature; N.sub.rot and N.sub.stat are respectively the number of turns of windings on the rotor and the number of turns of windings on a stator of the electric machine; I.sub.rot is the current flowing in the rotor windings; V.sub.dc is a supply voltage of the electric machine.

Description

[0039] Further characteristic and advantages of the present invention will become apparent from the following description, provided merely by way of non-limiting example, with reference to the attached drawings, in which:

[0040] FIG. 1 is a block diagram of the step of a reconfiguration method of the prior art;

[0041] FIG. 2 shows a circuit of an electric axle wherein an UGO phenomenon can happen;

[0042] FIG. 3a shows a graph of the rotor speed vs. the shaft torque of an electric machine during UGO phenomenon;

[0043] FIG. 3b shows a graph of the rotor speed vs. the power regenerated to the power supply during UGO phenomenon;

[0044] FIG. 3c shows a graph of the rotor speed vs. the current flowing in the electric machine during UGO phenomenon;

[0045] FIG. 4 shows a first graph of a fixed threshold .sub.fixed_th applied to an electric machine;

[0046] FIG. 5 shows a second graph of the fixed threshold .sub.fixed_th applied to an electric machine;

[0047] FIG. 6 shows a third graph of a fixed threshold .sub.fixed_th applied to an electric machine;

[0048] FIG. 7 is a block diagram of the steps of a reconfiguration method according to the present invention;

[0049] FIG. 8 shows a block diagram of the steps of the reconfiguration method executed in parallel,

[0050] FIG. 9 shows a graph of variable thresholds .sub.real_th applied to an electric machine with three possible configurations;

[0051] FIG. 10 shows a graph with a first line representing the voltage supply of an electric machine intersecting a second line representing the induced voltage produced by the electric machine.

[0052] With reference to the drawings, FIG. 7 is a block diagram of the steps of a reconfiguring method according to the present invention.

[0053] The method according to the present invention is applied to an electric machine including a rotor, arranged to rotate at a certain angular speed , said rotor including a magnet.

[0054] In a first step 100, the real speed threshold .sub.real_th is evaluated (or determined) in real-time manner as detailed here below, then, in step 102, it is checked if a current angular speed is greater than the real speed threshold .sub.real_th.

[0055] In positive case, in step 104 there is no reconfiguration.

[0056] In negative case, in step 106, the current configuration of the electric machine is determined in a manner per s known, then, in step 108, a reconfiguring decision method per s known is selected. After that, in step 110, it is decided whether to reconfigure the electric machine or not (according to predetermined selection strategies based on a control logic of the electric machine) and, in positive case, in step 112, the reconfiguration of the electric machine is performed.

[0057] The determination in real-time manner of the real speed threshold .sub.real_th of step 100 is done by performing a temperature estimation of the magnet of the rotor and then applying deterministic equations to such temperature estimation, by performing a predictive logic process or by applying an analytical model of the full electric machine, in manners per se known.

[0058] In particular, the real speed threshold .sub.real_th is function not only of the temperature of the magnet but also of the supply voltage and, if present, of the current in the rotor. The supply voltage and the current in the rotor can be measured using respective sensors.

[0059] In a more specific way, the real speed threshold .sub.real_th can be evaluated with the following relationship:

[00003]$\left[\left[{}_{\mathrm{mo}}+\left(T-T_0\right)\right]+N_{\mathrm{rot}}{N}_{\mathrm{stat}}{I}_{\mathrm{rot}}\right]{}_{{\mathrm{real}}_{\mathrm{th}}}=\frac{V_{\mathrm{dc}}}{\sqrt{3}}+2V_{\mathrm{diode}}+V_{\mathrm{stat}}$ [0060] where: [0061] .sub.mo and T.sub.0 are respectively a predetermined reference magnetic flux and a respective reference temperature, evaluated by test or simulation; [0062] is the thermal coefficient of the permanent magnet material, and it is given by its producer through datasheet or evaluated with test; [0063] T is the magnet temperature which varies during electric machine operation, and it is estimated or measured with sensors; [0064] N.sub.rot and N.sub.stat are respectively the number of turns of the windings on the rotor, if present, and the number of turns of the windings on the stator, predetermined during a design phase; [0065] I.sub.rot is the current flowing in the rotor windings, if present, measured with sensors; [0066] V.sub.dc is the voltage of the supply, which varies during electric machine operation and is measured with sensor; [0067] V.sub.diode is the voltage drop across a recirculation diode; [0068] V.sub.stat is the voltage drop across the stator windings of the electrical machine.

[0069] In order to take in consideration non-linearities caused by magnetic saturation, leakage fluxes and edge effects of temperature-magnetic flux relationship, moreover, to neglect the voltage drops across diodes and electrical machine windings, an interval for the real speed threshold .sub.real.sub.th can be considered:

[00004]$0.92\frac{V_{\mathrm{dc}}}{\sqrt{3}\left[\left[{}_{\mathrm{mo}}+\left(T-T_0\right)\right]+N_{\mathrm{rot}}{N}_{\mathrm{stat}}{I}_{\mathrm{rot}}\right]}{}_{{\mathrm{real}}_{\mathrm{th}}}1.8\frac{V_{\mathrm{dc}}}{\sqrt{3}\left[\left[{}_{\mathrm{mo}}+\left(T-T_0\right)\right]+N_{\mathrm{rot}}{N}_{\mathrm{stat}}{I}_{\mathrm{rot}}\right]}$

[0070] The interval limits are obtained by considering the UGO effects shown in FIGS. 3a-3c. As can be seen in those figures, if by any means the real speed threshold .sub.real.sub.th computed is far distant from the real value the UGO effects increase rapidly with dangerous consequences. Therefore, in order to allow a margin of error in the real speed threshold .sub.real.sub.th computation due to non-linearities but at the same time guarantee the system safety, a predetermined error, advantageously an 8% error, is accepted, as this tolerance allows the UGO effects to be less than 5% of the maximum one possible.

[0071] The steps of FIG. 7 can be repeated sequentially, when multiple reconfigurations of the electric machine are considered in series, or in parallel, when multiple reconfigurations of the electric machine are considered in parallel.

[0072] FIG. 8 shows a block diagram of the steps of the reconfiguration method of the present invention when executed in parallel.

[0073] In a first step 200 a first, second, . . . , n.sup.th real speed threshold .sub.real_th1, .sub.real_th2, . . . , .sub.real_thn are evaluated (or determined) in real-time manner as here above detailed, then, in step 202, it is checked if a current angular speed is greater than the real speed thresholds .sub.real_th1, .sub.real_th2, . . . , .sub.real_thn, respectively.

[0074] In positive case, in step 204 no reconfiguration is performed, and the method can start again at step 200. In negative case, in step 206, the current configuration of the electric machine is determined in manner per se known and finally, in step 208, a reconfiguration decision method per s known is selected.

[0075] After that, in step 210, it is decided whether to reconfigure the electric machine or not and, in positive case, in step 212, the reconfiguring of the electric machine is performed.

[0076] The method can then be repeated in recursive manner.

[0077] FIG. 9 shows a graph of two variable thresholds .sub.real_th1 and .sub.real_th2 applied to an electric machine to pass from a first configuration config.sub.1, to a second configuration config.sub.2 and to a third configuration config.sub.3. In a first alert area 300 there is no reconfiguration to or from the first configuration config.sub.1 and the second configuration config.sub.2, while in a second alert area 302 there is no reconfiguration to or from the first configuration config.sub.1.

[0078] Clearly, the principle of the invention remaining the same, the embodiments and the details of production can be varied considerably from what has been described and illustrated purely by way of non-limiting example, without departing from the scope of protection of the present as defined in the attached claims.