CN111656671A

CN111656671A - Control system for controlling switched reluctance machine, device and method

Info

Publication number: CN111656671A
Application number: CN201880086856.1A
Authority: CN
Inventors: S·黑伦
Original assignee: Punch Powertrain NV
Current assignee: Punch Powertrain NV
Priority date: 2017-11-24
Filing date: 2018-06-12
Publication date: 2020-09-11
Also published as: BE1025735B1; BE1025735A1; WO2019101372A1

Abstract

This document relates to a control system for controlling a switched reluctance machine, comprising: a rotor including rotor poles; a stator comprising sets of stator poles, each set comprising stator poles comprising a phase winding. The rotor may be moved by sequentially energizing each set of stator poles. A control system is configured to control the supply of power and includes a phase current sensor for providing a phase current signal for each set of stator poles, the phase current signal indicating an amount of phase current in one of the sets of stator poles. The control system includes a processor for acquiring phase current signals upon powering the sets of stator poles or at predetermined locations of the rotor and determining a timing for controlling powering of the corresponding set of stator poles based on the acquired phase current signals.

Description

Control system for controlling switched reluctance machine, device and method

Technical Field

The invention relates to a control system for controlling a switched reluctance machine, the switched reluctance machine comprising: a rotor comprising one or more rotor poles; a stator comprising one or more sets of stator poles, each set comprising one or more stator poles including a phase winding, such that each phase winding is associated with a respective one of the sets of stator poles; wherein the rotor is movable relative to the stator by sequentially energizing sets of stator poles via energizing the phase windings; wherein the control system is configured to control the power supply to the sets of stator poles. The invention further relates to a method of controlling a switched reluctance machine as described above, the method comprising controlling the supply of power to the sets of stator poles by a controller. The invention further relates to a switched reluctance machine and to an apparatus, such as a generator or a vehicle.

Background

The disclosed invention relates to control of Switched Reluctance (SR) motors, and more particularly to control of switched reluctance motors operating in a continuous conduction mode. In switched reluctance machines, at low speeds, torque can be adjusted primarily by controlling the magnitude of the phase currents via the switching power electronics. When the switching element is switched off, the phase current quickly drops to zero. The maximum torque depends on the phase current limit. At medium speeds, the peak current can be adjusted by controlling the relative rotor position of the on-phase. Due to the increased back electromotive force (EMF), the current will decrease even if the switching element remains active. The current trajectory is smaller after switching off the phase, which may result in less torque being generated. As the speed increases, the on angle must be advanced to reach the same peak current. The current trajectory after switching off the phase also becomes larger.

In the above, the terms 'low speed' and 'medium speed' are mentioned, which of course do not identify the exact speed range in which the switched reluctance machine operates according to the above-mentioned characteristics. However, those skilled in the art will appreciate that the applicable speed range is largely dependent on the exact motor design and other parameters that vary from switched reluctance machine to switched reluctance machine. Therefore, the terms 'low speed' and 'medium speed' cannot be linked to a directly identifiable speed range. Generally, the low and medium speed ranges have at least in common that the phase current drops and becomes zero after the phase is switched off and before the next phase starts. The situation where the current always reaches zero before the next commutation is started is called 'discontinuous conduction mode'.

However, starting from a certain speed, the current trajectory will reach an angle at which the next commutation will start. This can be avoided by reducing the closing angle (dwell angle) (the angle between switching the phases on and off), but as speed increases, power decreases. Another possibility is to control the motor in a 'continuous conduction mode', also called 'continuous current mode'. In this mode, the phase current does not go to zero between commutations. This makes it more difficult to predict the phase current waveform produced by certain firing angles (firing angle) because it depends on the current at the end of the previous commutation. Various attributes, such as, but not limited to, phase resistance and power electronics voltage drop, therefore have a significant impact on the resulting phase current waveform. With a fixed ignition angle and no other control means, the current waveform at first glance appears to be stable in continuous conduction mode, but it will continuously change due to changes in environmental conditions. For example, on a test stand, it was observed that the current waveform varied continuously as the temperature of the motor coil varied, while the firing angle remained constant. Small variations in firing angle can have a large effect on the resulting waveform compared to discontinuous conduction mode. This makes it difficult to switch between discontinuous and continuous conduction modes, especially if the accuracy of the motor model is not very good or the environmental conditions are not known exactly. This leads to insufficient performance of the motor, for example, due to the generation of undesirable torque or insufficient torque.

In order to create a stable and predictable current waveform in the continuous conduction mode, some kind of feedback control is required. Various improvements have been proposed in the art. For example, some solutions are based on controlling the peak current to achieve control of the continuous conduction mode. However, this requires a rather complex algorithm to find the peak current during commutation.

Disclosure of Invention

It is an object of the present invention to provide a control system which allows to overcome the problems of the prior art and to enable to control a switched reluctance machine in a continuous conduction mode in an efficient and relatively straightforward manner.

To this end, a control system for controlling a switched reluctance machine is provided, the switched reluctance machine comprising: a rotor comprising one or more rotor poles; a stator comprising one or more sets of stator poles, each set comprising one or more stator poles including a phase winding, such that each phase winding is associated with a respective one of the sets of stator poles; wherein the rotor is movable relative to the stator by sequentially energizing each set of stator poles; wherein the control system is configured to control the supply of power to the sets of stator poles, the control system including or being operatively connected to a phase current sensor configured to provide phase current signals for one or more of the sets of stator poles, the phase current signals being indicative of an amount of phase current present in a corresponding one of the sets of stator poles; wherein the control system comprises a processor configured to, upon powering one or more of the sets of stator poles or at a predetermined position of the rotor relative to the stator, acquire phase current signals for the corresponding set of stator poles and determine a control signal for controlling the powering of the corresponding set of stator poles based on the acquired phase current signals.

The invention is based on the following insight: the timing of energization of the respective sets of stator poles can be easily implemented to obtain the phase current values at fixed timings or predetermined positions during each commutation. In fact, energization may be applied as a trigger to derive a phase current value from a phase current signal received from a phase current sensor. This value can then be used to control the timing of the following operations: controlling the energization of a corresponding set of stator poles. In this way, in the event that phase current accumulation is detected, the control system can control this, for example, to set the power-off timing differently. Alternatively or additionally, the controller may adjust the timing of switching the stator pole groups in different power supply modes (e.g., freewheel modes), as further explained herein below. The timing of the various power modes may thus be adjusted depending on the required correction.

Advantageously, such triggering can also be easily used to perform the reading of the phase current values, since the energization will be triggered anyway by the control system. Thus, in some embodiments, each set of stator poles of a switched reluctance machine includes one or more phase switches for enabling activation and deactivation of the set of stator poles by operation of the phase switches; wherein the processor is configured to provide a control signal to at least one phase switch of a respective one of the sets of stator poles, such as to activate the set of stator poles for enabling the sequential powering. In some of these embodiments, the control signals include an activation signal and a deactivation signal for turning on and off one or more phase switches of a respective set of stator poles, wherein the processor is configured to acquire phase current signals for the set of stator poles while providing the activation signal for turning on the phase switches, such as to power the respective set of stator poles, and to use the phase current signals to determine the timing of providing the deactivation signal to one or more of the at least one phase switches of the respective set of stator poles. The activation signal of the switch can conveniently be used to trigger the extraction of the phase current value from the phase current signal. As can be appreciated, other trigger signals may be used for this purpose as well, or alternatively a dedicated trigger may be generated. However, the use of an activation signal eliminates the need to generate a dedicated trigger, which thereby reduces the overall complexity of the system.

As an alternative to obtaining phase current signals for a respective set of stator poles upon supplying power to the set of stator poles, the phase currents may also be measured at predetermined rotor positions. The position may be, for example, a fixed position, a predetermined position for each set point, or a position of a scheduled phase switch. Various implementations are possible for determining the position of the rotor relative to the stator. For example, the controller may cooperate with the sensors to establish the angular position of the rotor or to obtain such information in a different manner.

According to some embodiments, the processor is configured to compare the acquired phase current signal with a reference phase current value for said determination of timing. The comparison with the reference value may be implemented to detect the difference and actively control the timing of the de-energizing of the respective set of stator poles depending thereon. Various implementations of this active control are possible, depending on the control strategy to be implemented. In some embodiments, the control system is configured to obtain the reference phase current value from at least one of: memory, data repository, wireless data network, wired data network, or a dedicated network, such as a vehicle integrated data network. In general, the reference values may be acquired during initialization or testing of the switched reluctance machine and may then be stored in a look-up table for use during operation of the switched reluctance machine.

According to some embodiments, for said determination of timing, the processor is configured to adjust the timing in dependence on said comparison of the phase current signal with the reference phase current value. For example, according to a preferred embodiment, to perform the adjustment, the processor is configured for at least one of: shortening a duration in which the respective set of stator poles is energized and/or lengthening a duration in which the respective set of stator poles is not energized when the phase current signal indicates the phase current value is greater than the phase current reference value, such as by advancing a timing of turn-off of the respective set of stator poles; and extending a duration in which the respective set of stator poles is energized and/or shortening a duration in which the respective set of stator poles is not energized when the phase current signal indicates that the phase current value is less than the phase current reference value, such as by delaying a timing of a turn-off of the respective set of stator poles. By advancing the timing, the phase current present in the set of stator poles will become lower at the start of the next commutation. Also, by delaying the timing of the de-energizing, the set of stator poles will remain activated longer, thereby causing the remaining phase current to be higher at the beginning of the next commutation.

According to some embodiments, the control system further comprises or is operatively connected to a position sensor configured to provide a position signal indicative of an angular position of the rotor relative to the stator to the processor. This enables the control system to control the de-energized position, i.e., the angular position in which the corresponding set of stator poles is de-energized or off. For example, to determine the timing, the processor is configured to determine a reference angular position of the rotor based on the phase current signals, the control system being configured to de-energize the corresponding set of stator poles upon the rotor reaching the reference position.

According to a second aspect, a switched reluctance machine is provided, comprising a control system according to one or more of the preceding claims. According to yet a third aspect, there is provided an apparatus comprising the switched reluctance machine of claim 10, the apparatus being at least one of a generator, a vehicle, or a motor-driven device.

According to a fourth aspect of the invention, the invention relates to a method of controlling a switched reluctance machine comprising: a rotor comprising one or more rotor poles; a stator comprising one or more sets of stator poles, each set comprising one or more stator poles including a phase winding, such that each phase winding is associated with a respective one of the sets of stator poles; wherein the rotor is movable relative to the stator by sequentially energizing sets of stator poles; wherein the method comprises the following steps: controlling, by a controller, power to each set of stator poles; and obtaining phase current signals from the phase current sensors for one or more of the sets of stator poles, the phase current signals indicating an amount of phase current present in a corresponding one of the sets of stator poles; the method further comprises the following steps: upon powering one or more of the sets of stator poles, obtaining phase current signals for the corresponding set of stator poles; and determining a timing of de-energizing of the corresponding set of stator poles based on the acquired phase current signals.

Drawings

The invention will be further elucidated by the description of some embodiments of the invention with reference to the drawing. The detailed description provides examples of possible embodiments of the invention, but should not be construed as describing the only embodiments falling within the scope. The scope of the invention is defined by the claims, and the description is to be regarded as illustrative instead of limiting on the invention. In the drawings:

fig. 1 schematically illustrates in cross-section a rotor and a stator of a 4-phase 16/12 switched reluctance machine;

FIG. 2 shows a schematic circuit topology of a typical inverter for a four-phase switched reluctance machine;

FIG. 3A provides operating characteristics of a multi-phase switched reluctance machine at low rotor speeds;

FIG. 3B provides operating characteristics of a multi-phase switched reluctance machine at medium rotor speeds;

FIG. 3C provides operating characteristics of a multi-phase switched reluctance machine at high rotor speeds;

FIG. 4 provides typical performance characteristic torque vs. rotor speed for a conventionally controlled poly-phase switched reluctance machine when only discontinuous conduction mode is used;

FIG. 5 schematically illustrates phase current characteristics of a multi-phase switched reluctance machine operated using the control system and/or method of the present invention;

FIG. 6 provides typical performance characteristic torque vs. rotor speed for a conventionally controlled poly-phase switched reluctance machine when the continuous conduction mode is also used;

fig. 7 schematically shows a method according to an embodiment of the invention.

Detailed Description

Fig. 1 schematically shows a multi-phase switched reluctance machine (SRM or SR machine), in particular a multi-phase switched reluctance machine motor 1. The electrical machine 1 comprises a stator 2, the stator 2 comprising a plurality of coils 6 and stator poles 7. In fig. 1, the electric machine 1 and the coils 6 of the stator 2 are schematically shown in cross-section around a core 8. Thus, in fig. 1, the windings of each coil 6 are visible on both sides of the core 8. The stator poles 7 form the core 8 of the coil 6.

The electrical machine 1 further comprises a rotor 3, the rotor 3 comprising a plurality of counter poles 10 for interacting with the stator poles 7. The rotor 3 can be fixed relative to the shaft 4, for exampleThe sub 2 rotates. The coils 6 of the stator 2 are associated with the phase stages 12, 13, 14 and 15 of the electrical machine 1 such that each coil 6 of the plurality of coils of the stator 2 is associated with a respective one of the phase stages 12-15. In the figure, the phase steps 12-15 are also indicated by phase step numbers

(phase step 12) of the phase sequence,

(phase step 13) of the phase-change,

(phase step 14) and

(phase order 15).

In FIG. 1, the phase steps

(12) Is supplied with power and the counter pole 10 and phase stage of the rotor 3

(12) And (6) aligning. By following a phase step

(13) Supplied with power, the rotor 3 will rotate clockwise to bring the counter-pole 10 and the phase step

And (6) aligning. Alternatively, by being phase steps

(13) Supplied with power, the rotor 3 will rotate anticlockwise to bring the counter-pole 10 and the phase step

And (6) aligning. Thus, the rotor 3 may depend on the phase order

And

(12-15) to rotate in either direction.

The motor shown in fig. 1 is a 4-phase 16/12 switched reluctance motor consisting of 4 switchable phase stages, where each phase stage comprises 4

stator poles

7 and 12 rotor poles distributed across a full turn. The application of the calibration method of the present invention is not limited to this type of motor, but may be applied to other types of switched reluctance motors, such as 2-phase 4/2, 4-phase 8/6, 3-phase 6/4, 3-phase 12/8, 5-phase 10/8, 6-phase 12/10, 7-phase 14/12, 8-phase 16/14, or any other configuration. Furthermore, even though many of the embodiments described herein explain the present invention as applied to a radial flux electric machine, the teachings of the present invention are not so limited and are equally applicable to an axial flux electric machine. Fig. 2 shows the most common topology of an inverter 18 for controlling an SR machine. Although the associated number of switching stages for a phase may be different, the inverters for SR machines having different numbers of phases may be similar. In fig. 2, a switching stage of phase a of the SR machine has been generally labeled I. Each phase has two switching elements and four diodes, two of which are clamped at-U when the phase is de-energized_DCThe voltage level. This has been illustrated for phase a, with element 24 schematically showing the coils of the stator poles of phase a. The semiconductor-type switching elements 22 and 23 enable switching of the phase, such as to energize and de-energize the coil 24 and to switch the phase into a freewheeling (freewheeling) state, as explained below. Clamping diodes 27 and 28 enable the coil to be clamped at-U when phase a is de-energized_DCThe voltage level.

In the circuit shown in fig. 2, when both the switching elements 22 and 23 are closed, the phase voltage is + U_DC. Phase a is energized ('ON') and the conduction path is from switching element 22 to switching element 23 via coil (or coils) 24. When only one switching element (which may be switching element 22 or switching element 23) is closed, the phase voltage approaches 0V. The phase is 'freewheeling' ('FW') and current is allowed to flow freely through the phase (freewheeling). When both of the switching elements 22 and 23 are turned onThe applied phase voltage is-U_DC(if any current flows through this phase). The phase is powering down ('OFF'). The conduction path is from diode 27 through coil (or coils) 24 to diode 28.

The operating characteristics of the SR machine are shown in figures 3A to 3C for low, medium and high rotor speeds. Considering fig. 3A for low rotor speeds, curve 29 shows phase current i, which depends on the angular position of the rotor for one phase step of the SR machine. The torque T generated is shown as curve 35, while curve 36 shows the flux linkage ψ. In flux linkage versus phase current diagram 37, surface 40 spanned by curve 38 indicates the amount of work transferred by a single commutation of that phase order. Similarly, fig. 3B and 3C illustrate these characteristics for medium and high rotor speeds. In fig. 3B, for a medium rotor speed, curve 53 shows phase current i, which depends on the angular position of the rotor for the respective phase step. The torque T generated is shown as curve 55, while curve 56 shows the flux linkage ψ. In flux linkage versus phase current diagram 57, surface 58 spanned by curve 59 indicates the amount of work transferred by a single commutation of that phase order. In fig. 3C, for high rotor speeds, curve 63 shows phase current i, which depends on the angular position of the rotor for the respective phase step. The torque T generated is shown as curve 65, while curve 66 shows the flux linkage ψ. In flux linkage versus phase current diagram 67, surface 68 spanned by curve 69 indicates the amount of work transferred by a single commutation of that phase order.

Referring to fig. 3A, at low speed of rotor 3, torque T35 may be primarily adjusted by controlling the magnitude of phase current I29 via switching power electronics. The phase step, in which the phase current I29 is then accumulated rapidly, is supplied at the switch-on angle 30. When switching elements 22 and 23 are switched off at angular position 31, phase current i drops rapidly to zero. The maximum torque generated during commutation depends on the phase current limit.

Referring to fig. 3B, at medium speed, the peak current 53 can be adjusted by controlling the relative rotor position 51 that turns on the phase. Due to the increase in back electromotive force (back EMF), the current 53 will decrease even if the switching element remains active before turning off the corner 52. The current trajectory is smaller after the phase is switched off at 52, which may result in a smaller torque T being generated, as can be seen at 55. As the speed increases, the on angle 51 must be advanced (shifted to the left in the figure) to reach the same peak current 53. The current trajectory after switching off the phase at 52 also becomes larger (its end point moves further to the right in the curve 53).

At a certain speed, the current trajectory will reach an angle at which the next commutation will start. This is where the high rotor speed region begins, which can be seen in fig. 3C. Reducing the closing angle (the angle between phase on and off between positions 61 and 62) may avoid this, but also reduces power and reduces work W with increasing speed. The situation where the current always reaches zero before the next commutation is started is called 'discontinuous conduction mode'. In the high speed region, the motor 1 can be controlled in a 'continuous conduction mode', also referred to as 'continuous current mode'.

In this continuous conduction mode, phase current 63 does not go to zero between commutations. This makes it more difficult to predict the phase current waveforms produced by certain firing angles 61 and 62, since it depends on the current i at the end of the previous commutation. Thus, properties such as phase resistance, power electronics voltage drop, etc., have a significant impact on the resulting phase current waveform. With fixed ignition angles 61 and 62 and no other control means, the current waveform at first glance appears to be stable in continuous conduction mode, but it will continuously change due to changes in environmental conditions. For example, on a test stand, it was observed that the current waveform varied continuously as the motor coil temperature varied, while the firing angles 61 and 62 remained unchanged. Small variations in firing angle can have a large effect on the resulting waveform compared to discontinuous conduction mode. This makes it difficult to switch between discontinuous and continuous conduction modes, especially if the accuracy of the motor model is not very good or the environmental conditions are not known exactly.

The performance characteristics of a conventionally controlled SR machine are illustrated in fig. 4 with a torque versus speed diagram. At low speeds, the amount of torque T delivered is determined by the current limit through the coil and is therefore a constant value (region 70). At medium speed, the amount of torque will decrease as the rotor speed increases. TheThe reduction will be proportional to 1/ω as shown in region 71. At high rotor speeds, in region 72, decreasing the closing angle to control phase current in the phase step results in a decrease in torque T, which is related to 1/ω²And (4) in proportion.

FIG. 5 illustrates the behavior of SR machine control in accordance with the principles of the present invention. In fig. 5, phase current versus time is shown. When a phase step is switched on at t-0 at reference numeral 73 in the figure, the phase current quickly accumulates in the stator poles of that phase step, as shown by curve 75. While the phase step is turned on 73, the phase current in that phase step is compared to the reference phase current 78. Based ON the difference 74 between the actual phase current at switch-ON and the reference phase current 78, the processor of the control system determines how to adjust the ON state of a phase step (i.e., the set of stator poles associated with that phase step), such as to approach the reference phase current level 78 upon the next commutation start (i.e., switch-ON angular position). The ON state is adjusted by adjusting one or more of the OFF angle and/or FW angle. Here, the OFF angle is an angular position at which the phase step is switched to the OFF state; referring to fig. 2, this is a state in which both the switching elements 22 and 23 are turned off. Further, the FW angle is an angular position at which the phase step is switched to the freewheel state; referring to fig. 2, this is a state in which one of the switching elements 22 or 23 is turned off and the other is turned on.

As will be appreciated, the processor has a certain budget only in terms of angular position (and hence time within commutation) to extend the length of the ON state of the phase step. This is because sub-optimal performance due to e.g. the generation of counter-torque interfering with the operation of the next phase order is prevented. However, within this budget, the processor calculates the ON state adjustment Δ needed to bridge the gap between the phase current at turn-ON and the reference level 78 at the start of the next commutation₁(reference numeral 76).

During the first commutation 75, the maximum extension of the ON state Δ₁To this first commutation. According to the invention, this adjustment of the ON state can be achieved by delaying the turn-OFF moment of the phase step switch-OFF, in other words by shifting the angular position (OFF angle) of the phase step switch-OFF. This will extend the freewheel state by Δ₁. Alternatively or additionally, according to the inventionIn the illustrated embodiment, adjusting the phase current at the turn-on of the next commutation can also be accomplished by adjusting the FW angle. This will affect the phase current level during the ON state and thus also the remaining phase current after switching off.

During the first commutation, the maximum adjustment is achieved by the processor and although the difference 80 between the phase current at the on-time 79 and the reference level 78 is small at the start of the second commutation, there is still a relatively large difference. At 79, upon switching on the phase step during the second commutation, the processor again acquires the actual phase current from the phase current sensor in the switched reluctance machine and compares it to the reference phase current 78. The adjustment of the ON state is calculated by the processor and the ON state is adjusted by switching off at a later angular position to postpone the moment of switching off. This again adjusts the ON state of the phase step by an amount Δ during the freewheel state₂(reference numeral 82). Like a₁，Δ₂Similar to the maximum adjustment during this commutation. Adjusting delta if the rotor speed has not changed between the first and second commutation ₂82 is substantially equal to the adjustment delta ₁76. After 83 is turned off, the phase current drops and upon 88 being turned on, a measure of the actual phase current is obtained by the processor to calculate a difference 89 from the reference phase current 78. During the third commutation only a short extension of the ON state is required, resulting in an adjustment Δ as shown in fig. 5₃。

The reference phase current level at the on-time 78 is set such that at a given rotor speed and under given operating conditions (temperature, required torque, etc.), the maximum amount of torque is produced by obtaining a peak phase current 91 that approaches a safe level 90 under the given conditions. Both the reference phase current 78 and the safety level 90 may be determined during a test run or simulation of the switched reluctance machine, such as during a factory test. These values may be stored, for example, in a look-up table, which may be obtained from a memory in the control system. Optionally, this look-up table may also store a desired adjustment or Δ of the ON state, which depends ON the phase current difference measured during the ON phase step. These adjustments may be stored as individual adjustments to one or more of the OFF or FW angles, or absolute or relative OFF and/or FW angles. As can be appreciated, obtaining these values from the look-up table during operation may provide more flexible control possibilities.

The performance boost obtained using the control method of the present invention is shown in fig. 6. In fig. 6, a deliverable torque depending on the rotor speed is shown for controlling a switched reluctance machine using the control system or the control method according to the present invention. Curves 70 ', 71 ', 72 ' show the torque in the low, medium and high rotor speed ranges. These curve portions 70 ', 71 ', 72 ' correspond to the corresponding portions (70, 71 and 72) of the curve in fig. 4. The advantages of the control system and control method of the present invention are obtained in a high speed zone, continuous conduction mode. This is illustrated by the region 92 between the curve 72' of the high rotor speed region and the corresponding curve 72 obtained using conventional control methods. It is apparent that the amount of torque that can be transferred in the high speed range 72' is greater than that of conventional control methods. In fact, the decrease in torque T proportional to 1/ω in the mid-speed range 72 'continues at the rate 1/ω in the high-speed region 72'. Thus, the amount of torque added is considerably large compared to conventional control methods.

The control method according to the invention is schematically shown in fig. 7. In a first step 100 in the method of fig. 7, the processor retrieves control parameters from a look-up table stored in the memory. These control parameters are based on, for example, the amount of torque requested and rotor speed, as indicated above. For example, the reference phase current level and the safety level may be obtained from a look-up table. As can be appreciated, the retrieval of the safety level from the look-up table is not necessary, but merely optional. Those skilled in the art will appreciate that the resulting adjustment of the reference phase current value and the on-time provided from the look-up table will result in the system operating within this safe level. Thus, obtaining a safe level of the current phase (reference numeral 90 in fig. 5) may be purely advantageous for monitoring purposes, e.g. for detecting whether a switched reluctance machine is malfunctioning.

In step 102, upon commutation commencement, the switching elements of a phase stage are turned ON, such as to supply power to the phase stage at an ON angle. Meanwhile, phase currents are measured by phase current sensors and actual phase current values are obtained by a processor. Next, in step 104, the acquired phase current value is compared with the reference phase current value acquired from the memory in step 100. From a look-up table or from a different algorithm or data obtained from a network or other data repository, the processor determines the required adjustment of the ON state to approach the reference phase current value at the start of the next commutation.

In step 106, the processor may shift the freewheel angle and the OFF angle to extend or shorten the duration of the power-on state of the phase step. The effect of this operation is shown, for example, in fig. 5 as discussed above. In step 108, the actual switch to freewheel state and off state during commutation will be performed by the processor at the adjusted angle.

The present invention has been described in terms of certain specific embodiments thereof. It will be appreciated that the embodiments shown in the drawings and described herein are intended for illustrative purposes only and are in no way intended to be limiting of the invention. It is believed that the operation and construction of the present invention will be apparent from the foregoing description and the accompanying drawings. It will be apparent to those skilled in the art that the present invention is not limited to any of the embodiments described herein, and that modifications are possible, as such are considered to be within the scope of the appended claims. Also, kinematic inversion is considered inherently disclosed and within the scope of the present invention. Moreover, any of the components and elements of the disclosed embodiments can be combined or incorporated into other embodiments as deemed necessary, desirable or preferred without departing from the scope of the invention as defined in the claims.

In the claims, any reference signs shall not be construed as limiting the claim. The terms 'comprising' and 'including' when used in this specification or the appended claims should not be construed in an exclusive or exhaustive sense, but rather in an inclusive sense. Thus, the use of the expression 'comprising' herein does not exclude the presence of other elements or steps than those listed in any claim. Furthermore, the words 'a' and 'an' should not be construed as limited to 'only one', but are used to mean 'at least one', and do not exclude a plurality. Features not specifically or explicitly described or claimed may additionally be included within the structure of the invention within its scope. Expressions such as "device for … …" should be read as "an assembly configured for … …" or "a member configured for … …," and should be interpreted to include equivalents of the disclosed structure. The use of expressions such as "critical", "preferred", "particularly preferred", etc. is not intended to limit the invention. Additions, deletions, and modifications within the purview of one of ordinary skill in the art may be made without departing from the spirit and scope of the invention as defined by the claims. The present invention may be practiced otherwise than as specifically described herein and limited only by the claims that follow.

Claims

1. A control system for controlling a switched reluctance machine, the switched reluctance machine comprising:

a rotor comprising one or more rotor poles;

a stator comprising one or more sets of stator poles, each set of stator poles comprising one or more stator poles comprising a phase winding such that each phase winding is associated with a respective one of the sets of stator poles;

wherein the rotor is movable relative to the stator by sequentially energizing sets of stator poles;

wherein the control system is configured to control the supply of power to the sets of stator poles, the control system comprising or being operatively connected to a phase current sensor configured to provide phase current signals in respect of one or more of the sets of stator poles, the phase current signals being indicative of an amount of phase current present in a respective one of the sets of stator poles;

wherein the control system comprises a processor configured to, upon powering one or more of the sets of stator poles or at a predetermined position of the rotor relative to the stator, acquire phase current signals for the respective set of stator poles, and determine a timing of controlling the powering of the respective set of stator poles based on the acquired phase current signals.

2. The control system of claim 1, wherein each set of stator poles of the switched reluctance machine includes one or more phase switches for enabling activation and deactivation of the set of stator poles by operation of the phase switches; wherein the processor is configured to provide control signals to at least one phase switch of a respective one of the sets of stator poles to control phase currents fed to the set of stator poles for enabling the sequential powering.

3. The control system of claim 2, wherein the control signals include activation and deactivation signals for turning on and off one or more phase switches of the respective set of stator poles, wherein the processor is configured to obtain a phase current signal for the set of stator poles while providing the activation signal for turning on a phase switch to power the respective set of stator poles, and to use the phase current signal to determine the timing of providing the deactivation signal to one or more of the at least one phase switches of the respective set of stator poles.

4. The control system of any one or more of the preceding claims, wherein said processor is configured to compare the acquired phase current signal to a reference phase current value for said determination of said timing.

5. The control system of claim 4, wherein the control system is configured to obtain the reference phase current value from at least one of: memory, data repository, wireless data network, wired data network, or a dedicated network, such as a vehicle integrated data network.

6. The control system of claim 4 or 5, wherein, for the determination of the timing, the processor is configured to adjust the timing in dependence on the comparison of the phase current signal to the reference phase current value.

7. The control system of claim 6, wherein to perform the adjustment, the processor is configured to perform at least one of:

shorten a duration in which the respective set of stator poles is energized and/or lengthen a duration in which the respective set of stator poles is not energized when the phase current signal indicates a phase current value greater than the phase current reference value, such as by advancing a timing of an off of the respective set of stator poles; and

lengthening a duration in which the respective set of stator poles is energized and/or shortening a duration in which the respective set of stator poles is not energized when the phase current signal indicates a phase current value less than the phase current reference value, such as by delaying a timing of an off of the respective set of stator poles.

8. The control system of any one or more of the preceding claims, further comprising or operatively connected to a position sensor configured to provide a position signal to the processor indicative of an angular position of the rotor relative to the stator; or

Wherein the control system is configured to determine an angular position of the rotor relative to the stator.

9. The control system of claim 8, wherein to determine the timing, the processor is configured to determine a reference angular position of the rotor based on the phase current signals, the control system configured to de-energize the respective set of stator poles upon the rotor reaching the reference position.

10. A switched reluctance machine comprising a control system as claimed in one or more of the preceding claims.

11. An apparatus comprising the switched reluctance machine of claim 10, the apparatus being at least one of a generator, a vehicle, or a motor-driven device.

12. A method of controlling a switched reluctance machine, the switched reluctance machine comprising:

a rotor comprising one or more rotor poles;

wherein the method comprises:

controlling, by a controller, power to each set of stator poles; and

obtaining phase current signals from a phase current sensor for one or more of the sets of stator poles, the phase current signals indicating an amount of phase current present in a corresponding one of the sets of stator poles;

the method further comprises:

obtaining phase current signals for one or more of the sets of stator poles upon powering the corresponding set of stator poles; and

determining a timing of de-energizing of the respective set of stator poles based on the acquired phase current signals.

13. The method of claim 12, further comprising comparing, by the controller, the acquired phase current signal to a reference phase current value for the determination of the timing.

14. The method of claim 13, wherein determining the timing comprises adjusting the timing in dependence upon the comparison of the phase current signal to the reference phase current value.

15. The method of claim 14, wherein the adjusting step is performed by at least one of:

shorten a duration in which the respective set of stator poles is energized and/or lengthen a duration in which the respective set of stator poles is not energized when the phase current signal indicates a phase current value greater than the phase current reference value, such as by advancing a timing of a turn-off of the phase; and

lengthening a duration in which the respective set of stator poles is energized and/or shortening a duration in which the respective set of stator poles is not energized when the phase current signal indicates a phase current value less than the phase current reference value, such as by delaying a timing of a turn off of the phase.