Patent ID: 12244250

In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not to scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Modern electric machines have relatively high energy conversion efficiencies. The energy conversion efficiency of most electric machines, however, can vary considerably based on their operational load. With many applications, a machine is required to operate under a wide variety of different operating load conditions. In addition, the torque provided by an electric machine may vary over operation requiring a variation from a first torque to a second torque. The first torque may be a first torque level and the second torque may be a second torque level.

Controllers for electric machines may use feedforward control signals and feedback control signals. Feedforward controlling signals are provided controlling signals are typically not derived from measuring an error, but instead may be provided by an external operator. A feedback control signal is typically generated by measuring an error between an actual output and a desired output.

To facilitate understanding,FIG.1is a high level flow chart that may be used in some embodiments. A feedforward vector is determined (step104). In some embodiments, a control system of an electric machine is configured to determine the feedforward vector.FIG.2is a schematic illustration of the implementation used in some embodiments. In some embodiments, the feedforward vector (VFF)204is at least one of a feedforward voltage vector, feedforward current vector, and feedforward force vector. VFF204has a magnitude and an angle.

A feedback vector is determined (step108). InFIG.2, the feedback vector (VFB)208is at least one of a feedback voltage vector, feedback current vector, and feedback force vector. VFB208has a magnitude and an angle. The magnitude of the sum of the feedforward vector and the feedback vector is determined (step112). InFIG.2, the sum of VFF204and VFB208is shown as VSUM212and is determined inFIG.2using head to tail vector addition. In this example, VSUM212has a magnitude and angle that is different from the magnitudes and angles of both VFF204and VFB208. Various known processes may be used to determine the angle and magnitude of VSUM212.

A comparison is made between the magnitude of VSUM212and a maximum bus value (Vbus) (step116). If the magnitude of VSUM212is less than or equal to the maximum bus value Vbus, then VSUM212is provided as a control vector to the electric machine (step124). In some embodiments, the maximum bus value is at least one of a maximum bus voltage value, maximum bus current value, and maximum bus force value. InFIG.2, the magnitude of Vbusforms a section of a circle216defined by a radius Vbus. In the example, shown inFIG.2, VSUM212extends past the maximum bus value section of a circle216, therefore the magnitude of VSUM212is greater than Vbus. Therefore, in some embodiments, a new control vector is calculated according to the equation Vcontrol=VFF+k(VFB), where k is a scalar value between 0 and 1, inclusive, and where Vcontrol220has a magnitude equal to Vbusand an angle different from the angle of VSUM212, as shown inFIG.2.FIG.2shows vector k(VFF)224. InFIG.2, Vcontrol220extends to point A. In these embodiments, Vcontrol220is provided as the control vector.

In the prior art, when the magnitude of VSUMis greater than Vbusa control vector of Vprior228=k(VSUM), where k is a scalar value between 0 and 1 would be used as the control vector. Vprior228would have a magnitude equal to Vbusand an angle equal to the angle of VSUM212, as shown inFIG.2. InFIG.2, Vprior228extends to point B.

It has been found that using Vcontrol220as a control vector provides improved control compared to using Vprior228as a control vector. Vcontrol220maintains the angle between VFF204and VFB208, whereas Vprior228changes the angle between VFF204and VFB208. Maintaining the angle between VFF204and VFB208allows the resulting change to be along a more predictable profile. By using Vcontrol=VFF+k(VFB), where k is a scalar value between 0 and 1, inclusive, and where Vcontrol220has a magnitude equal to Vbus, the correction provided is in the same direction as the intended correction VFB208and is as much as possible given the limitation of not exceeding Vbus. Such a correction would provide a more direct correction path. Changing angles between VFF204and VFB208introduces control errors since changing the angle causes either influence from VFF204or VFB208in a less predictable manner. Changing the angle impairs convergence, increasing the time needed for cleaning up errors introduced by going in the wrong direction. In some embodiments, the clean up for going in the wrong direction may result in a feedback loop that slowly converges to a correct solution. The slow convergence increases inefficiency.

By setting the magnitude of Vcontrolto be equal to Vbus, k may be determined by solving a quadratic equation. In some embodiments, VFF204=(a,b) and VFB208=(c,d) and Vbus=R, so that
k=[−(ac+bd)+√{square root over (2abcd−a2d2−b2c2+(c2+d2)R2])}/(c2+d2)

Various embodiments may be used in various electric machines. To facilitate understanding,FIG.3is a block diagram of an electric machine system300that may be used in some embodiments. The electric machine system300comprises a polyphase electric machine304, a power inverter308, a power source312, and an inverter controller316. In the specification and claims, the polyphase electric machine304may be a polyphase motor or a polyphase generator. Therefore, in the specification and claims, the power inverter308is a power converter for either a polyphase motor or a polyphase generator. Such a power inverter308may also be called a power rectifier. In some embodiments, the power source312is a DC power source. One or more feedback signals are provided from the polyphase electric machine304to the inverter controller316. In some embodiments, the inverter controller comprises a limiter controller320.

In some embodiments, the inverter controller316may be located within the power inverter308. In some embodiments, the inverter controller316may be outside of or separate from the power inverter308. In some embodiments, part of the inverter controller316may be within the power inverter308and part of the inverter controller316may be outside of or separate from the power inverter308. In some embodiments, the inverter controller316provides switching signals to the power inverter308. In some embodiments, the limiter controller320may be located within the inverter controller316. In some embodiments, the limiter controller320may be outside of or separate from the inverter controller316. In some embodiments, part of the limiter controller320may be within the inverter controller316and part of the limiter controller320may be outside of or separate from the inverter controller316. In some embodiments, the limiter controller320provides Vcontrol220to the inverter controller316. The limiter controller320described herein may be implemented in a wide variety of different manners including using software or firmware executed on a processing unit such as a microprocessor, using programmable logic, using application specific integrated circuits (ASICs), using discrete logic, etc., and/or using any combination of the foregoing.

In some embodiments, where the polyphase electric machine304is operated as a 3 phase motor, the power inverter308is responsible for generating three-phase AC power from the DC power supply312to drive the polyphase electric machine304. The three-phase input power, denoted as phase A42a, phase B42b, and phase C42c, is applied to the windings of the stator of the polyphase electric machine304for generating a rotating magnetic field. The lines depicting the various phases,42a,42b, and42care depicted with arrows on both ends indicating that current can flow both from the power inverter308to the polyphase electric machine304when the machine is used as a three-phase motor and that current can flow from the polyphase electric machine304to the power inverter308when the polyphase electric machine304is used as a generator. When the polyphase electric machine304is operating as a generator, the power inverter308operates as a power rectifier, and the AC power coming from the polyphase electric machine304is converted to DC power being stored in the DC power supply312.

FIG.4illustrates conventional sinusoidal three-phase current42a,42b, and42cdelivered to/produced by the polyphase electric machine304during excitation used in some embodiments. Phase B, denoted by curve42b, lags phase A, denoted by42a, by 120 degrees. Phase C, denoted by curve42c, lags phase B by 120 degrees. The three-phased current42a,42b, and42cis continuous (not pulsed) and has a designated amplitude of approximately 20 amps. It should be appreciated that 20 amps are only a representative current amplitude, and the current amplitude may have any value. In an example, a first phase current42amay provide phase A42a, the second phase current42bmay provide phase B42b, and the third phase current42cmay provide phase C42c. In some embodiments, a three-phase voltage may be provided instead of a three-phase current.

Some embodiments may use an abc frame of reference.FIG.5illustrates a three-phase power representation in an abc frame of reference that may be used in some embodiments.FIG.5shows axis a, axis b, and axis c that are 120° apart. In some embodiments, the current or voltage shown by curve42ais shown along axis a, the current or voltage shown by curve42bis shown along axis b, and the current or voltage shown by curve42cis shown along axis c. For example, at T1shown inFIG.4, curve42ais at a positive maximum and curves42band42care at equal negative values. Therefore, curve42aprovides current or voltage vector Va504, curve42bprovides current or voltage vector Vb508, and curve42cprovides current or voltage vector Vc512. The sum of Va+Vb+Vc=VTot516. In the example shown inFIG.4, the magnitude of VTot516will be constant a will rotate in a counter-clockwise direction around the origin. In some embodiments, VTot516is designated as a space vector. V-rot516.

Some embodiments may use an αβ frame of reference.FIG.6illustrates a three-phase power representation in an αβ frame of reference that may be used in some embodiments. The a-axis, b-axis, and c-axis that are 120° apart as shown inFIG.5are replaced by two orthogonal axes called axis α and axis β, as shown. Instead, of describing current or voltage vector Va504, current or voltage vector Vb508, and current or voltage vector Vc512using three axes, the same vectors may be described using two coordinates of the two orthogonal axes, axis α and axis β. In addition, VTot516can be described using two coordinates. In the example shown inFIG.4at time T1, the magnitude of VTot516will be constant and will rotate in a counter-clockwise direction around the origin. Coordinates in the abc frame of reference may be transformed to or from coordinates of the αβ frame of reference using the direct Clarke Transformation or the Inverse Clarke transformation.

Some embodiments may use the dq frame of reference. In the dq frame of reference, there are two orthogonal axes, which are the direct (d) axis and the quadrature (q) axis. The αβ frame of reference is a static or stationary frame of reference that coincides with a static or stationary stator. The dq frame of reference is a rotating frame of reference that rotates with the rotor. A Park Transformation may be used to transform coordinates from the αβ frame of reference to the dq frame of reference. In the example shown inFIG.4at time T1, current or voltage vector Vdalong the rotating d axis and current or voltage vector Vqalong the rotating orthogonal q axis are constant. Vd+Vq=VTot, which would also be constant and stationary in the rotating dq frame of reference but would be rotating when transformed into a stationary frame of reference.

FIG.7illustrates a three-phase power representation in a dq frame of reference with a d axis and an orthogonal q axis. At some times VTot704is a constant vector since the dq frame of reference rotates with the rotor. In some embodiments, VTot704is the same as VFF204, shown inFIG.2. VTot704is used to maintain the equilibrium (or current state) of the electric machine in order to provide a constant output, such as constant torque. In order to change the torque output of the electric machine, the current or voltage provided to the electric machine must be changed. In some embodiments, the change in the current or voltage in order to change the force provided by the electric machine to a target force is represented by VFB708, which may be the same as VFB208, shown inFIG.2. In some embodiments, VFB208is proportional to a desired current derivative vector term dIdq/dt. In some embodiments, VSUM712is defined as being equal to VTot704+VFB708. If the magnitude of VSUM712is greater than the amount of power that can be handled by the electric machine Vbus, then, for the reasons explained above, some embodiments provide a power vector Vcontrol720defined by the equation, Vcontrol=VTot+k(VFB), where k is a value between 0 and 1, inclusive, and where Vcontrol720has a magnitude equal to Vbus. Vcontrol720provides Vd, which is the d component of Vcontrol720, and Vq, which is the q component of Vcontrol720.

In some embodiments, the electric machine system300, shown inFIG.3, may have an improved efficiency by being a pulsed electric machine system. Examples of such pulsed torque electric machines are described in U.S. Pat. No. 10,742,155 filed on Mar. 14, 2019, U.S. patent application Ser. No. 16/353,159 filed on Mar. 14, 2019, and U.S. Provisional Patent Application Nos. 62/644,912, filed on Mar. 19, 2018; 62/658,739, filed on Apr. 17, 2018; and 62/810,861 filed on Feb. 26, 2019. Each of the foregoing applications or patents is incorporated herein by reference for all purposes in their entirety. In such applications, the torque level transitions occur very frequently (potentially many times a second) and efficient transition control enables even higher efficiency operation. In addition, in some embodiments of pulsed electric machine systems where efficiency is most important, fast transitions are more important than a smooth transition.

In some embodiments, the fast pulsing provides higher efficiency. In some embodiments in order to provide fast pulsing, a large VFBis used causing the magnitude of VSUM712to be greater than Vbus. In such instances, Vcontrol=VTot+k(VFB), where 0≤k<1 and where Vcontrol720has a magnitude equal to Vbusis used. Since the use of Vcontrol720improves control when compared to the prior art, the use of Vcontrol720in a pulsed situation improves control for pulsed electric machines.

In some embodiments, VFF204is pre-limited by the limiter controller320to be no greater than Vbus. Such a prelimit ensures a real solution for k. In other embodiments, VFF204is pre-limited to be no greater than F*Vbus, where F is in the range of 0.5 to 0.99. In some embodiments, F is in the range of 0.8 to 0.99. In some embodiments, F is in the range of 0.8 and 0.9. By limiting VFF204to be less than Vbus, k is greater than 0, allowing for some influence by VFB208.

Some embodiments are used in electric machine systems that use a pulsed operation to improve efficiency. An example of an electrical machine that uses a pulsed operation is described in U.S. Pat. No. 10,742,155, issued Aug. 11, 2020, to Adya S. Tripathi, which is incorporated by reference for all purposes. Pulsed electric machine control is described in U.S. Pat. No. 10,944,352; U.S. Pat. No. 11,077,759; U.S. Pat. No. 11,088,644; U.S. Pat. No. 11,133,767; U.S. Pat. No. 11,167,648; and U.S. patent application Ser. No. 16/912,313 filed Jun. 25, 2020, which are incorporated by reference for all purposes. In some embodiments, such pulsed operation continuously changes electric machine operation and requires a high rate of change. As a result, in some embodiments, the pulsed operation has a large VFB. So, in some embodiments of a pulsed operation electric machine uses a large VFB. Therefore, some embodiments provide improved pulsed operation.

In some electric machines, overmodulation may be used to increase the output voltage supplied to the motor. Overmodulation is a method of increasing the output voltage that can be supplied to a multiphase motor by allowing distortion of the output voltages.FIG.8is a schematic illustration of an embodiment with overmodulation. A circle840with a radius of Vbusshows the maximum bus value that can be provided by the electric machine controller without overmodulation. A hexagon844shows overmodulation values that are provided, where the overmodulation values are the distance from the origin to the hexagon844so that the overmodulation defines the hexagon844. The hexagon844shows that the overmodulation values vary over time. The hexagon844is a first convex boundary centered at the origin with a minimum distance from the origin of the maximum bus value Vbus. The circle840is a second convex boundary centered at the origin that is entirely on or within the second convex boundary.

At some times, the feedforward vector VFF804is a constant vector since the dq frame of reference rotates with the rotor. The feedforward vector VFF804is used to maintain the equilibrium (or current state) of the electric machine in order to provide a constant output, such as constant torque. In order to change the torque output of the electric machine, the current or voltage provided to the electric machine must be changed. In some embodiments, the change in the current or voltage in order to change the force provided by the electric machine to a target force is represented by the feedback vector VFB808. In some embodiments, VFB808is proportional to a desired current derivative vector term dIdq/dt. In some embodiments, VSUM812is defined as being equal to VFF804+VFB808. If VSUM812lies outside of the first convex boundary defined by hexagon844, some embodiments provide a power vector Vcontrol820defined by the equation, Vcontrol=VFF+k(VFB), where k is a value between 0 and 1, inclusive, and where Vcontrol820lies on the first convex boundary. Vcontrol820provides Vd, which is the d component of Vcontrol820, and Vq, which is the q component of Vcontrol820.

FIG.9is a schematic illustration of the embodiment with overmodulation where VFF904lies outside of the second convex boundary defined by the circle840and where VSUM912is defined as being equal to VFF904+VFB908lies outside of the first convex boundary defined by the hexagon844. In such a case, VFF904is scaled back by multiplying VFF904by a constant k1between 0 and 1 so that k1VFF916lies on the second convex boundary defined by the circle840. If the new sum of (k1VFF916+VFB908)924lies outside the of the first convex boundary defined the hexagon844, VFB908is scaled back by multiplying VFB908by a constant k2between 0 and 1 so that (k1VTot916+k2VFB910)928lies on the second convex boundary defined by the hexagon844.

In some embodiments, when there is no overmodulation, the first convex boundary and the second convex boundary are the same. So, the second convex boundary is determined by overmodulation by providing no overmodulation. In some embodiments, the second convex boundary is equal to the first convex boundary scaled according to a factor F, where F is in a range between 0.8 and 1 inclusive. In some embodiments, the first convex boundary and the second convex boundary are regular polygons or circles. In some embodiments, the first convex boundary is a regular polygon and the second convex boundary is a circle. In some embodiments, both the first convex boundary and the second convex boundary are regular polygons.

A general process that incorporates the above embodiments would determine a feedforward vector (VFF) and would determine a feedback vector (VFB). The feedforward vector (VFF) is the same as VTotThe feedforward vector (VFF) and the feedback vector (VFB) may be defined in a αβ frame of reference or a dq frame of reference, where the intersections of the axes define an origin. Although the electric machine has a maximum bus value (Vbus), when overmodulation is provided, a limiting modulated value (V mod) is determined by the amount of overmodulation provided, which is indicated by the modulation indice. The overmodulation defines a first convex boundary that is centered at the origin, where a distance from the origin to the first convex boundary is the limiting modulated value (V mod). The minimum distance from the origin to the first convex boundary is the maximum bus value (Vbus). The maximum bus value (Vbus) is used to define a second convex boundary that is centered at the origin. The second convex boundary is within or on the first convex boundary. In some embodiments, the second convex boundary is circumscribed by the first convex boundary. In some embodiments, where there is no overmodulation, the second convex boundary is the same as the first convex boundary. In some embodiments, the second convex boundary has a distance from the origin that is less than the maximum bus value (Vbus) where the second convex boundary lies entirely on or within the first convex boundary. In some embodiments, the distance from the origin to the second convex boundary is equal to F times the first convex boundary, where F is in a range between 0.8 and 1.

If the vector sum (VFF+VFB) lies on or inside the first convex boundary then a control vector of VFF+VFBis provided to the electric machine. If the vector sum (VFF+VFB) lies outside the first convex boundary then a scaled VFFof k1VFFis provided where k 1=1 if the vector VFFlies on or inside the second convex boundary and where 0<k1<1 if VFFlies outside the second convex boundary, where k1VFFlies on the second convex boundary. If the vector sum (k1VFF+VFB) lies outside the first convex boundary, then a scaled VFBof k2VFBis provided where k1VFF+k2VFBlies on the first convex boundary and 0≤k2≤1. The vector sum k1VFF+VFBis provided to the electric machine when the vector sum k1VFF+VFBlies inside the first convex boundary. The vector sum k1VFF+k2VFBis provided to the electric machine when the vector sum k1VFF+VFBlies outside the first convex boundary.

In various embodiments, polyphase machines may include but are not limited to brushless DC (BLDC) machines, permanent magnet synchronous machines (PMSM), interior permanent magnet (IPM) machines, wound rotor synchronous machines, induction machines, and synchronous reluctance machines. In some embodiments, the polyphase machine may have two or more phases. As mentioned above, polyphase machines may be polyphase motors or polyphase generators, or polyphase machines that operate both as motors and generators.

While this disclosure has been described in terms of several preferred embodiments, there are alterations, modifications, permutations, and various substitute equivalents, which fall within the scope of this disclosure. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present disclosure. It is therefore intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and various substitute equivalents as fall within the true spirit and scope of the present disclosure. As used herein, the phrase “A, B, or C” should be construed to mean a logical (“A OR B OR C”), using a non-exclusive logical “OR,” and should not be construed to mean ‘only one of A or B or C. Each step within a process may be an optional step and is not required. Different embodiments may have one or more steps removed or may provide steps in a different order. In addition, various embodiments may provide different steps simultaneously instead of sequentially. In addition, elements that are shown and described separately may also be combined in a single device or single step. For example, steps that are described sequentially may be simultaneous. In addition, steps described sequentially in one order may be performed in another order.