Patent Application
20220302864
The present disclosure relates to a switched reluctance machine, and to a method of controlling a circuit of a motor phase of a switched reluctance motor.
Switched reluctance motors are often used as prime movers in electric drive systems because they are inexpensive to use and robust in operation. An inverter topology with asymmetrical half bridges is usually used, which is connected to the phases of the motor without a star point.
The classic inverter topology for three-phase switched reluctance motors consists of six power switches. It is composed of three independent asymmetrical H-bridges. The upper power switch of each H-bridge in conjunction with the lower diode provides the regulation of the current in the connected winding strand. The lower power switch in conjunction with the upper diode enables rapid decommutation against the full DC supply voltage during the transition from one motor strand to another.
When designing switched reluctance machines, a compromise must be made between high torque in the lower speed range and maximum speed. However, it is desirable to provide both a wide speed band and a high starting torque.
From the disclosure document DE 43 30 386 A1, a switched reluctance motor is known which has a tap located in the middle of the phase winding, which is connected on the one hand to a first pole via a freewheeling half-switch and on the other hand to the other pole of the DC voltage source via an additional switching transistor. When a predetermined torque is reached, half the number of pole windings is disconnected by the switch so that a higher torque can be achieved.
Example embodiments of the present disclosure provide switched reluctance machines that each provide a wide speed band and high starting torque in a simple manner.
A switched reluctance machine according to an example embodiment of the present disclosure includes a ferromagnetic rotor, a stator with stator poles each including a winding with at least one winding strand. At least two winding strands of a stator pole or at least two winding strands arranged on diametrically opposed stator poles are associated with a motor phase, the at least two winding strands being between a first supply line connected to a DC voltage source and a second supply line connected to a ground connection, and each winding strand being assigned an upper electronic switch (high-side) and a lower electronic switch (low-side) each including a freewheeling diode arranged in parallel. The switched reluctance machine further includes a controller to control the electronic switches of the circuits as a function of the position of the rotor, the at least two winding strands of a motor phase being connected together in a common circuit via a cross branch in such a way that the at least two winding strands of a motor phase are switchable between a parallel connection and series connection by the control of the electronic switches.
The two winding strands of a motor phase are connected asymmetrically therein.
The fact that the winding strands can be operated both in parallel connection and in series connection only by switching the electronic switches enables the motor to provide a wide speed range as well as a high starting torque. The number of windings can be varied by a factor of two for the same number of windings per winding strand. However, it may also be provided that the number of windings per winding strand is different.
Preferably, the controller includes a microprocessor or an FPGA, which causes a switchover from series connection to parallel connection after the reluctance motor reaches a predetermined speed. At high rotational speeds, the winding strands are thus preferably operated in parallel connection. It is also conceivable to make the switching dependent on the torque of the reluctance motor or on a predefined speed gradient.
It is advantageous if two winding strands of a motor phase define a winding strand pair, with one of the winding strands of a winding pair being in an asymmetrical half bridge including the two electronic switches and the two freewheeling diodes and the second winding strand being in a symmetrical half bridge as used in rotating field machines. In other words, parallel to the asymmetrical half-bridge, a third, upper electronic switch and a fourth, lower electronic switch are in series between the two supply lines. A freewheeling diode is associated with the third and fourth electronic switches, and the third and fourth electronic switches are connected to the freewheeling diodes via a center tap respectively between the electronic switches and the freewheeling diodes. Two nodes defined thereby are in turn connected to a third node between the lower electronic switch of the first winding strand and the first winding strand via the cross branch, with the second winding strand being in the cross branch. By controlling the electronic switches, it is possible to switch between parallel and series connection of the winding strands. Due to the described connection of the two winding strands, no additional electronic components are necessary. The circuit can be scaled as required. With two winding strands per phase, only four electronic switches are provided in total, two per winding strand. The number of electronic switches increases to n+x with n>=x>=2 for n winding strands per phase.
In general, the electronic switches can be, for example, MOSFET switches or bipolar transistors, especially IGBT switches.
Furthermore, a drive system according to an example embodiment of the present disclosure including a switched reluctance motor described above is provided. The drive system is preferably an electric drive system in an electrically powered vehicle.
In addition, a method of controlling a circuit of a motor phase of a switched reluctance motor according to an example embodiment of the present disclosure includes a switched reluctance motor with a ferromagnetic rotor, a stator, and a controller. The stator includes stator poles, the stator poles each including a winding with at least one winding strand, at least two winding strands of a stator pole or at least two winding strands on diametrically opposed stator poles being assigned to a motor phase, the at least two winding strands being between a first supply line connected to a DC voltage source and a second supply line connected to an earth connection, and each winding strand being assigned an upper electronic switch (high-side) and a lower electronic switch (low-side) each having a freewheeling diode arranged in parallel. The controller controls the electronic switches of the circuits as a function of the position of the rotor, the at least two winding strands of a motor phase being connected together in a common circuit via a cross branch.
Two winding strands of a motor phase define a winding strand pair, with one of the winding strands of a winding pair being in an asymmetrical half bridge including the two electronic switches and the two freewheeling diodes, and a second winding strand being in a symmetrical half bridge. In parallel with the asymmetrical half-bridge, a third and a fourth electronic switch are in series between the supply lines, and a freewheeling diode is associated with the third and fourth electronic switch. The third and fourth electronic switches are connected to the freewheeling diodes via a center tap in each case between the electronic switches and the freewheeling diodes. Two nodes defined thereby are in turn connected to a third node between the lower electronic switch of the first winding strand and the first winding strand via the cross branch, the second winding strand being arranged in the cross branch.
The method includes, optionally, operating the circuit in series connection by turning on an upper electronic switch of the first winding strand and a lower, fourth electronic switch and turning off the other two electronic switches and allowing current to flow through the upper electronic switch into the first winding strand and then through the cross branch and the second winding strand and the fourth electronic switch so that the winding current of both winding strands connected in series increases, or operating the circuit in parallel connection, by turning on the two upper electronic switches and the lower electronic switch associated with the first winding strand, and turning off the lower, fourth electronic switch so that current flows in parallel through the two upper electronic switches, the two winding strands, and then through the lower electronic switch of the first winding strand.
The number of windings can thus be varied by switching the electronic switches of the H-bridges on and off. The number of turns per winding can be the same or different, depending on the application. If the windings are connected in series, a higher induced flux and thus a higher torque is made possible. With a parallel connection, on the other hand, the inductance is reduced and thus also the induced reverse voltage.
Preferably, the controller includes a microprocessor or an FPGA, which causes a switchover from series connection to parallel connection after the reluctance motor reaches a predetermined speed. At high speeds, the winding strands are thus preferably operated in parallel connection. It is also conceivable to make the switching dependent on the torque of the reluctance motor or on a predefined speed gradient.
The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings.
Example embodiments of the disclosure are explained in more detail below with reference to the drawings. Identical or functionally identical components are provided with the same reference signs across the figures.
The diode D5 allows switching between series and parallel connection of the winding strands L1,L2 by the electronic switches Q1,Q2,Q3,Q4.
This asymmetrical connection of the two winding strands L1,L2 allows switching between series connection and parallel connection of the winding strands L1,L2 by the electronic switches Q1,Q2,Q3,Q4.
The winding of a phase of the machine has two or more winding strands arranged symmetrically around the circumference of the stator and wound on protruding poles. The at least two winding strands that make up a phase winding are interconnected as previously described, so that they can be connected in series or in parallel.
The number of windings of the winding strands can be different. In the context of the disclosure, the winding strands may also be pole winding pairs, in which case the winding strands have an equal number of windings. In this case, the stator pole winding pairs of each pair of opposite stator poles are connected together.
In general, the electronic switches can be, for example, MOSFET switches or bipolar transistors, especially IGBT switches.
Switching from series connection to parallel connection is preferred taking place when a nominal speed is exceeded, but this can also be made dependent on the speed gradient or the load. If the winding strands are connected in series, a higher induced flux and thus a higher torque is made possible. With a parallel connection, on the other hand, the inductance is reduced and thus also the induced counter voltage.
In application areas where a wide speed range and a high starting torque are required, such as in a vehicle drive, in particular motor vehicle drive, the ratio of speed range, starting torque and machine volume can be improved. Furthermore, this also increases efficiency in the lower speed range, which accounts for a double-digit share in motor vehicle driving cycles.
For high power applications where the electrical switches are doubled to provide the required power, the electrical switches can be used to implement the previously described interconnection of the winding strands without additional switches.
The symmetrical connection is particularly suitable for systems with high safety requirements, as it offers a high level of redundancy. In the event of failure of one winding strand, the remaining strand can be operated, enabling emergency operation with half the phase power. The asymmetrical connection, on the other hand, is characterized by higher efficiency and low costs, since the additional diode can be dispensed with.
While example embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 122 461.6 | Aug 2019 | DE | national |
This is a U.S. national stage of PCT Application No. PCT/EP2020/073454, filed on Aug. 21, 2020, with priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) being claimed from German Application No. 10 2019 122 461.6, filed Aug. 21, 2019, the entire disclosures of which are hereby incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/073454 | 8/21/2020 | WO |
