Patent ID: 12224692

It should be noted that the Figures are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these Figures have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar feature in modified and different embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG.1, reproduced from EP16190311A1 referred to above, is a schematic block diagram of an electric motor system100, which uses a sensorless locked rotor detector120. The electric motor system100includes a motor control circuit101, motor102, and power source119. The motor control circuit101includes a processor103, driver circuit105, and measurement circuits106. Processor103includes a sensorless locked rotor detector120, which may be implemented in hardware or in software by accessing or including memory to store the sensorless locked rotor detector120. In whatever form implemented, the sensorless locked rotor detector120may include first, second and third calculation modules121,122,123for calculating first and second BEMF values, a filtered BEMF value and a BEMF error threshold value based on outputs from the measurement circuits106. The first calculation module121computes the second estimated BEMF voltage value êqas the q coordinate component of an estimated BEMF value. The second calculation module122computes the filtered BEMF difference value as the filtered difference between the first estimated BEMF voltage value êδand the second estimated BEMF voltage value êq. The third calculation module123computes the BEMF error threshold value as a function of the estimated rotor angular speed value {circumflex over (ω)}, subject to a minimum or baseline threshold BEMF value.

Measurement circuits106include a current measurement circuit107and a DC bus voltage measurement circuit108. The motor102includes a rotor109, stator110and shaft111, the shaft111being mechanically coupled to the rotor109. Windings are disposed in the motor102, which are connected to the motor control circuit101by conductors112,113,114. The conductors112,113,114are connected to outputs of the driver circuit105and to inputs of the measurement circuits106. The measurement circuits106are connected to the processor103by one or more connection lines116. The processor103is connected to the driver circuit105by one or more connection lines115to allow the processor103to control the driver circuit105. The power source119is connected to the driver circuit105via live (L) and neutral (N) conductors117,118to provide power for the driver circuit105. The power source119may be provided with more than two outputs, for example in a three phase system.

The current measurement circuit107obtains one or more current measurements ia, ib, icof the motor102windings. The DC bus voltage measurement circuit108obtains corresponding voltage measurements of the motor102windings. Such measurements can be complex measurements, including a direct (d) component and a quadrature (q) component.

FIG.2illustrates an electric motor system200based on the electric motor system100described above in relation toFIG.1but with the motor102comprising a rotor speed sensor201. A rotor speed signal from the rotor speed sensor201is transmitted to the detector220. The detector220may be configured to perform the same operations as the sensorless locked rotor detector together with a further function to detect a fault in the current measurement circuit107based on the above mentioned BEMF values together with a demanded rotor speed and a measured rotor speed.

FIG.3illustrates a more detailed schematic diagram of the electric motor system200ofFIG.2, indicating in more detail the components of the motor control circuit101, including the detector280, motor drive circuit105and measurement circuits106. The motor drive circuit105and measurement circuits106are distributed among the components shown inFIG.3, with the measurement circuits comprising the Clarke transformation block241, Park transformation block242, and BEMF observer271. Operation of the system200is similar to that disclosed in EP16190311A1 with the addition of a required or demanded speed input ωreqand a measured rotor speed input ωmeasinput to the detector280together with the outputs of estimated voltage value êδand estimated speed value {circumflex over (ω)} from the BEMF observer271.

The electric motor system200comprises control system elements101for providing fault detection based on BEMF observation with rotor speed estimation together with measured and requested speed values. The motor control circuit101includes ramp block231, speed control block232, quadrature-current (Q-current) control torque block233, field control block234, direct-current (D-current) control flux block235, inverse Park transformation block236, direct-current (DC) bus ripple elimination block237, space vector modulation block238, alternating-current-to-direct-current (AC-to-DC) power conversion block239, inverter block240, Clarke transformation block241, Park transformation block242, and BEMF tracking observer block271for estimating position and speed.

In operation, the ramp block231receives a requested angular velocity signal ωreqat input247and provides an output248to adjustment block270. Adjustment block270receives an estimated angular velocity signal {circumflex over (ω)} at output249of BEMF observer block271. Adjustment block270subtracts {circumflex over (ω)} from ωreqto provide an angular velocity control signal to speed control block232at output250. Speed control block232may be implemented, for example, using a proportional integral (PI) controller. Speed control block232provides an output signal to adjustment block245at output251. Adjustment block245receives a signal from Park transformation block242at output252. Adjustment block245subtracts the signal at output252from the signal at output251to provide a signal at output253to Q-current control torque block233. Q-current control torque block233may be implemented, for example, using a PI controller. Q-current control torque block233provides a signal Uq at output254to inverse Park transformation block236. In this case, the signal Uq represents the q coordinate component for the rotor related orthogonal coordinate reference frame system (d,q).

Field control block234provides a field control signal to adjustment block246at output255. Adjustment block246receives a motor current vector signal id from Park transformation block242at output256, where id is the d coordinate component that is collinear to the rotor flux d coordinate. Adjustment block246subtracts the id signal at output256from the field control signal at output255and provides a signal at output257to D-current control flux block235. D-current control flux block235may be implemented, for example, using PI controller. D-current control flux block235provides a signal Ud at output258to inverse Park transformation block236. In this case, the signal Ud represents the d coordinate component for the rotor related orthogonal coordinate reference frame system (d,q).

Inverse Park transformation block236provides a signal Uα at output259to DC bus ripple elimination block237and to the BEMF observer block271, and also provides a signal Uβ at output260to DC bus ripple elimination block237and to the BEMF observer block271. In this case, the signals Uα, Uβ represent orthogonal coordinate components for the stator related orthogonal coordinate reference frame system (α, β). DC bus ripple elimination block237receives a signal Udcbus from output265of AC-to-DC power conversion block239. DC bus ripple elimination block237provides compensation for ripple on the signal Udcbus and provides signals at outputs261and262to space vector modulation block238. Space vector modulation block238provides pulse width modulation (PWM) motor drive signals PWMa,b,cto inverter block240at outputs263. A line conductor117provides a line voltage to AC-to-DC power conversion block239. A neutral conductor118provides a neutral voltage to AC-to-DC power conversion block239. AC-to-DC power conversion block239provides DC voltages to inverter block240at one or more outputs265which are filtered using DC bus capacitor264across the20outputs. Inverter block240provides motor drive signals at conductors112,113, and114to electric motor102according to PWM motor drive signals PWMa,b,c.

Conductors112,113, and114from electric motor102provide signals (e.g., ia, iband ic) to inputs of Clarke transformation block241. Clarke transformation block241provides signals iαand iβto Park transformation block242and to BEMF observer block271at outputs266and267. Park transformation block242receives sin, cos ({circumflex over (θ)})—the sine and cosine of the estimated the rotor flux angle {circumflex over (θ)} relative to stator phase—at output269from BEMF observer block271. Park transformation block242provides a d component motor current vector signal (e.g., id) at output256to adjustment block246and a q component motor current vector signal (e.g., iq) at output252to adjustment block245, where the d coordinate component of the motor current vector idis collinear to the rotor flux d coordinate, and where the q coordinate component of the motor current vector iqis orthogonal to the rotor flux d coordinate. BEMF observer block271provides estimated angular velocity signal {circumflex over (ω)} to adjustment block270and to position and speed observer block271at output249. BEMF observer block271also provides sin, cos ({circumflex over (θ)}) at output269to inverse Park transformation block236and to Park transformation block242. In addition, the BEMF observer block271provides estimated BEMF signal value êδat output272, though this value may also be used by the BEMF observer block271to generate the angle error θerror.

The motor102is provided with a position or rotation sensor201, the output from which provides a measured rotor speed signal ωmeas. The detector280also generates an estimated angular velocity signal {circumflex over (ω)} (which specifies the rotor angular speed) and one or more of the BEMF voltage values êδand êγ. Using one or more of these estimated quantities, detector280may execute one or more algorithms to derive a BEMF error threshold value (BEMFErrorThreshold) and a filtered BEMF difference value (BEMFErrorFilt) for processing with the estimated rotor angular speed value and measures rotor speed signal to detect one or more types of faults.

Further details of the operation of the BEMF observer271are described in EP16190311A1, which describes the use of the BEMF error threshold value to determine a blocked rotation fault without the use of a position or rotation sensor on the motor. In applications where these and other types of faults need to be detected in time to prevent damage occurring to the motor or driving circuit, a motor speed sensor201can be used in combination with the outputs from the BEMF observer271.

FIG.4illustrates an example of a series of measured and calculated values for a motor control system in which a fault may be determined using a measured motor speed in combination with calculated BEMF values.FIG.4illustrates motor speed, calculated BEMF voltages, motor torque and motor currents for a simulated series of operations covering a startup period401, a no-load period402, a transient loaded period403and a fault injection period404. During the startup period401, the motor speed demand signal405rises and the measured and estimated motor speeds406(which are indistinguishable inFIG.4due to overlap) rise along with the demand signal405. Along with this, the calculated BEMF values407,408,409change accordingly. A lower BEMF bound409and an upper BEMF bound408lie either side of a calculated BEMF value407during this period and during the subsequent non-load period402and load transient period403. The upper and lower bounds408,409define the BEMF error threshold and the calculated BEMF value407is the estimated BEMF signal êδ, as described in more detail in EP16190311A1. At the start of the fault injection period404, a gradual gain fault is introduced, which leads the estimated BEMF signal êδto move outside the BEMF error threshold defined by the upper and lower bounds408,409.

As in EP16190311A1, a fault may be detected if the estimated BEMF signal407lies outside the threshold region defined by upper and lower bounds408,409or if the estimated rotor angular speed value406falls below a minimum stall speed. Another type of fault may be detected if the measured rotor angular speed value406differs from the required rotor speed ωreqor estimated rotor speed {circumflex over (ω)} by no more than a predefined amount, for example within +/−5% or +/−10%. A measure of the actual rotor speed is required for determination of such faults, which may relate to faults within the motor control circuit101rather than in the motor102. Such faults may for example result from a gain or offset error in the current measurement circuit107, which may be gradual or abrupt, or from an input to the current measurement circuit107being disconnected. Such faults can be detected when the estimated BEMF signal lies outside the BEMF threshold defined by the upper and lower bounds408,409while the measured rotor speed value406is within a rotor speed error threshold. In a general aspect therefore, a fault in the motor control circuit may be detected by the detector280when the estimated BEMF signal êδlies outside of a calculated BEMF error threshold and the measured rotor angular speed is within a rotor speed error threshold.

The fault may for example be indicated, as shown inFIG.4, by the measured rotor speed406being maintained after injection of the fault (i.e. at the start of the fault injection period404) while the estimated BEMF value407falls outside the BEMF error threshold. As the estimated BEMF signal407rises above the upper BEMF bound408within around 50 ms of the fault being injected, the calculated torque411rises above the measured torque410and the measured currents413begin to rise, while the measured rotor speed406remains constant. In other examples, a fault may be indicated by the calculated torque and measured currents rising, falling or oscillating while the measured speed is maintained within the rotor speed error threshold.

An advantage of determining a fault in the motor control circuit using a combination of the estimated BEMF signal and a measured rotor speed is that the fault can be detected prior to the motor exhibiting any changes that may result from the error. Any damage that might result from the fault could therefore be prevented by detecting the fault early and, for example, disabling the motor.

FIG.5illustrates a schematic diagram of a method of detecting a fault in a PMSM control circuit during operation of the PMSM. In a first step501, the detector280receives an estimated BEMF value êδand an estimated rotor speed value {circumflex over (ω)} from the BEMF observer271, a measured rotor speed ωmeasfrom the rotor speed sensor201and a required rotor speed ωreqfrom the driving circuit105. The detector280then calculates a BEMF error threshold, BEMFErrorThresholdand a rotor speed threshold (step502), the rotor speed threshold being determined from either or both of the estimated rotor speed value {circumflex over (ω)} and the required rotor speed ωreq. The detector280then compares the estimated BEMF value êδto the BEMF error threshold value (step503) and the measured rotor speed to the rotor speed threshold. If the estimated BEMF value êδis outside the BEMF error threshold and the measured rotor speed ωmeasis within the rotor speed threshold, a fault is detected (step504). The detector280may then disable the motor and/or output a fault indication (step505).

Other fault detection processes may also operate along with the above described process, for example to monitor the measured rotor speed compared to the required motor speed to detect a locked rotor fault.

From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of memory systems, and which may be used instead of, or in addition to, features already described herein.

Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

For the sake of completeness it is also stated that the term “comprising” does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality, a single processor or other unit may fulfil the functions of several means recited in the claims and reference signs in the claims shall not be construed as limiting the scope of the claims.