Flux Estimator

Abstract

An aspect of the invention relates to a flux estimator (1) for estimating air-gap flux in a permanent magnet electric motor having a rotor and a stator, the flux estimator (1) comprising a resistance compensation stage having a first multiplying digital-to-analog converter (23) and an inductance compensation stage having a second multiplying digital-to-analog converter (25). The flux estimator (1) is configured to determine a first gain (Ku) for compensating for a stator resistance (Ra) and to determine a second gain (KLa) for compensating for a stator inductance (La). The first gain (Ku) is provided to the first multiplying digital-to-analog converter (23) of the resistance compensation stage to generate a first output signal (VIAR) providing a scaled representation of the voltage drop across the stator resistance (Ra) per phase. The second gain (KLa) is provided to the second multiplying digital-to-analog converter (25) of the inductance compensation stage to generate a second output signal (IA_LA) providing a scaled representation of the stator inductance (La) per phase. An air gap flux estimation signal (PSI_MON) is generated based on the first output (VIAR) and the second output (IA_LA). Aspects of the present invention also relate to a motor control unit (3), a control system (5), and a pump (4).

Description

[Technical field]

[0001] The present disclosure relates to a flux estimator suitable for estimating air-gap flux in an electric motor, and aspects of the present disclosure also relate to a motor control unit, a control system, and a pump. [Background technology]

[0002] It is known to estimate air-gap flux to provide accurate control of permanent magnet (PM) electric motors. The flux estimator may be implemented solely in hardware as a hardware flux estimation circuit. Typically, the hardware flux estimation circuit is specific to a particular model of electric motor. For example, the hardware flux estimation circuit may be tuned to a particular motor type (or variant) to provide optimal control performance. For multiple types (or variants) of electric motors, different drive variants may be required to tune the hardware flux estimation circuit. Different drive variants may also be required for different variants of electric motors within a particular product family. It would be advantageous to not require different drive variants to accurately estimate air-gap flux for different motor types, e.g., different variants of electric motors. This allows the same drive to be used for two or more different types or variants of electric motors.

[0003] The use of software-only solutions to estimate the air-gap flux via an observer is also known and is widely used in industry today. However, the accuracy of software-only solutions may be relatively low, especially at low speeds, since they rely on an estimated motor terminal voltage combined with measured motor current to estimate the motor Back EMF. At very low speeds, the accuracy of the estimated Back EMF signal may be very poor, since tolerances in the inverter power stack, such as switching dead time and dead time compensation, greatly affect the Back EMF signal as a percentage of the very low Back EMF signal. This drawback can be overcome by implementing open loop control algorithms or high frequency injection algorithms that sense the magnet position at rest. The use of these techniques is disadvantageous in high speed applications, such as turbomolecular pumps (TMPs).

[0004] Open loop control systems are not suitable for TMP applications, which are traditionally high inertia pump systems with little mechanical damping at high speeds. The little mechanical damping can lead to speed overshoot, especially at low speeds, if the motor is not tightly controlled by a closed loop speed and position solution. Thus, the use of open loop control algorithms can be unreliable once the TMP begins to rotate at speeds above a mechanical rotation of about 5 Hz. Although it is necessary to start rotation with an open loop algorithm, it is also essential that the TMP controller transitions to closed loop control at very low speeds to overcome the small mechanical damping of the TMP.

[0005] High frequency injection can be used to characterize the inductance of the stator (Lq and Ld) components of an electric motor. The saturation profile of the motor's inductance can be determined by injecting current at high frequency. This inductance saturation profile is characterized for the entire 360° rotation range of the electric motor. However, this technique requires large currents to observe the saturation profile, especially for non-salient permanent magnets. This large current creates design overhead for the inverter power stack and can lead to demagnetization of the permanent magnets if the current injection is too high and in the opposite direction to the magnetization of the permanent magnets. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to address one or more of the shortcomings associated with the prior art. [Means for solving the problem]

[0007] Aspects and embodiments of the present invention provide a flux estimator, a motor control unit for controlling the operation of an electric motor, and a control system as set forth in the claims.

[0008] According to one aspect of the invention, there is provided a flux estimator for estimating air-gap flux in a permanent magnet electric motor having a rotor and a stator, the flux estimator comprising a resistance compensation stage having a first multiplying digital-to-analog converter and an inductance compensation stage having a second multiplying digital-to-analog converter, the flux estimator comprising: determining a first gain for compensating for a stator resistance; determining a second gain for compensating for a stator inductance; providing a first gain to a first multiplying digital-to-analog converter of a resistance compensation stage to generate a first output signal providing a scaled representation of the voltage drop across the stator resistance for each phase; providing a second gain to a second multiplying digital-to-analog converter of the inductance compensation stage to generate a second output signal providing a scaled representation of the stator inductance for each phase; generating an airgap flux estimation signal based on the first output and the second output; The flux estimator may be a hardware flux estimator, for example a flux estimation circuit. The flux estimator may be an integrated type suitable for use with multiple electric motor types (or variations). In at least certain embodiments, the flux estimator may be used without requiring different circuit variations specialized for each motor type. The accuracy of the air-gap flux estimation may be improved compared to conventional flux estimators. In at least certain embodiments, the air-gap flux estimation may be improved during low and very low speed operation of the electric motor. This may improve control of the electric motor.

[0009] In at least certain embodiments, the first gain and / or the second gain can be determined based on the type (or model) of the electric motor. To enable the type determination, an identification module can be associated with the electric motor. The first gain and / or the second gain for one or more different types of electric motors can be stored, for example, in a look-up table or database. For example, the first gain and / or the second gain can be obtained from a look-up table.

[0010] The flux estimator can be configured to receive a first gain. The first gain can be received from a control unit, such as a motor control unit. The flux estimator can be configured to receive a second gain. The second gain can be received from a control unit, such as a motor control unit. The control unit can include at least one processor configured to execute motor control software. The at least one processor can be configured to output the first gain and / or the second gain.

[0011] The voltage drop across the stator resistance can be calculated as the product of the motor phase current and the stator resistance.

[0012] The flux estimator can be configured to determine a scaled integral over time of a voltage difference between the motor terminal voltage and the voltage drop across the stator resistance. An airgap flux estimation signal can be generated based on the determined scaled integral.

[0013] An airgap flux estimate signal may be calculated as the difference between the determined and scaled integral value and the second output.

[0014] The scaled representation of the stator inductance may be the scaled product of the stator inductance and the motor phase currents.

[0015] The first gain is JPEG2025511065000002.jpg11150, where VAN is the phase voltage with respect to the artificial neutral and Va is the motor terminal voltage.

[0016] The second gain is JPEG2025511065000003.jpg11150, where La is the stator inductance, Ku is the first gain, kint is the integrator gain, and Ki is the current gain.

[0017] The flux estimator may comprise a storage device. At least one data set is stored in the storage device, for example in a database. The or each data set may include a predetermined first gain and / or a predetermined second gain for the permanent magnet electric motor. The flux estimator may be configured to determine the first gain and the second gain by accessing the database.

[0018] The flux estimator can be configured to identify the electric motor. The flux estimator can identify a type or model of the electric motor. The flux estimator can be configured to select a data set corresponding to the identified electric motor to determine the first gain and / or the second gain. The flux estimator can access a storage device to read the data set associated with the identified electric motor.

[0019] The flux estimator can be configured to identify the electric motor by supplying a current to determine a saturation profile of the motor inductance. The current supplied to the permanent magnet electric motor can be a high frequency current. The flux estimator can be configured to identify the permanent magnet electric motor based on the determined saturation profile.

[0020] The flux estimator can be configured to determine the first gain based on an estimated motor terminal voltage and / or to determine the second gain based on a measured stator inductance. In at least certain embodiments, the first gain and / or the second gain can be determined based on determined parameters of the electric motor. This can facilitate determining the first gain and / or the second gain. In at least certain embodiments, the first gain and / or the second gain can be determined without requiring identification of the type or model of the electric motor.

[0021] The flux estimator may be configured to receive at least one signal indicative of an operating parameter of the electric motor. The flux estimator may be configured to dynamically modify the first gain and / or the second gain based on the or each operating parameter of the electric motor. In at least certain embodiments, the flux estimator may modify the airgap flux estimation based on the one or more operating parameters. The operating parameter may include an operating temperature of the electric motor. Alternatively or additionally, the operating parameter may include an operating speed of the electric motor.

[0022] According to one aspect of the present invention, there is provided a flux estimator for estimating air-gap flux in a permanent magnet electric motor having a rotor and a stator, the flux estimator comprising a resistance compensation stage having a multiplying digital-to-analog converter, the flux estimator comprising: determining a gain to compensate for the stator resistance; providing this gain to a multiplying digital-to-analog converter of a resistance compensation stage to determine a scaled representation of the voltage drop across the stator resistance per phase; generating an air-gap flux estimate signal based on a scaled representation of the voltage drop across the determined per-phase stator resistance; It is structured as follows.

[0023] The air gap flux estimation signal may be determined based on the stator inductance per phase, which may be predefined or calculated, for example, by a stator inductance algorithm, or may be determined using techniques described herein.

[0024] According to one aspect of the present invention, there is provided a flux estimator for estimating air-gap flux in a permanent magnet electric motor having a rotor and a stator, the flux estimator comprising an inductance compensation stage having a multiplying digital-to-analog converter, the flux estimator comprising: determining a gain to compensate for the stator inductance; providing this gain to a multiplying digital-to-analog converter of an inductance compensation stage to determine a scaled representation of the stator inductance per phase; generating an air-gap flux estimate signal based on the scaled representation of the determined per-phase stator inductance; It is structured as follows.

[0025] The airgap flux estimation signal may be determined based on the voltage drop across the stator resistance per phase. The voltage drop across the stator resistance per phase may be predefined or calculated, for example, by a voltage drop algorithm. Alternatively, the voltage drop across the stator resistance per phase may be determined using techniques described herein.

[0026] According to a further aspect of the present invention, there is provided a motor control unit for controlling operation of an electric motor having a stator and a rotor, the motor control unit comprising at least one processor and a storage device. The at least one processor may be configured to determine a type of the electric motor. Based on the determined type of the electric motor, the at least one processor may: a first gain for compensating for a stator resistance of the electric motor; and a second gain for compensating for the stator inductance of the electric motor; At least one of the following can be determined:

[0027] The at least one processor can be configured to execute motor control software. The motor control software can be embedded in the at least one processor. In at least certain embodiments, the motor control software operates in conjunction with a flux estimator to estimate air-gap flux. The accuracy of the air-gap flux estimation can be improved as compared to conventional flux estimators. In at least certain embodiments, the air-gap flux estimation can be improved during low and very low speed operation of the electric motor. This can improve control of the electric motor.

[0028] The at least one processor may be configured to output at least one of the first gain and the second gain to a flux estimator. The flux estimator may be of a type described herein.

[0029] The at least one processor can be configured to receive one or more operating parameters of the electric motor. The at least one processor can be configured to dynamically modify at least one of the first gain and the second gain based on the one or more operating parameters of the electric motor.

[0030] The control system may include a flux estimator as described herein and a motor control unit as described herein. The motor control unit may be configured to output at least one of the first gain and the second gain to the flux estimator.

[0031] According to a further aspect of the present invention there is provided a pump comprising an electric motor and a motor control unit as herein described. The pump may for example be a turbomolecular pump.

[0032] Any control unit or controller described herein may suitably comprise a computing device having one or more electronic processors. The system may comprise a single control unit or electronic controller, or different functions of the controller may be embodied or hosted in different control units or controllers. As used herein, the term "controller" or "control unit" is understood to include both a single control unit or controller, and multiple control units or controllers acting collectively to provide any defined control function. To configure a controller or control unit, a suitable set of instructions may be provided which, when executed, causes said control unit or computing device to perform the control techniques defined herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software stored on one or more memories associated with said controller for execution on said computing device. A control unit or controller may be implemented in software executed on one or more processors. The one or more other control units or controllers may be implemented in software running on one or more processors, optionally the same processor or processors as the first controller. Other suitable configurations may also be used.

[0033] It is expressly intended that within the scope of this application, the various aspects, embodiments, examples, and alternatives, in particular individual features, described in the above paragraphs, claims and / or in the following description and drawings, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination, except where such features are incompatible. The applicant reserves the right to modify the claims of the original application or to file any new claims accordingly, including the right to amend the claims of the original application to correspond to and / or incorporate any features of any other claim not so claimed in the original application.

[0034] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings. [Brief description of the drawings]

[0035] [Figure 1] 1 shows a schematic diagram of a motor control unit and flux estimator for controlling operation of an electric motor according to an embodiment of the present invention; [Diagram 2] 2 shows a schematic diagram of the motor control unit shown in FIG. 1. [Diagram 3] 2 shows a schematic diagram of the flux estimator shown in FIG. 1. [Figure 4] FIG. 4 shows a block diagram illustrating a terminal voltage estimator of the flux estimator shown in FIG. 3. [Figure 5A] FIG. 4 shows a block diagram illustrating a stator resistance gain block of the flux estimator shown in FIG. 3. [Figure 5B] FIG. 4 shows a block diagram illustrating a stator resistance gain block of the flux estimator shown in FIG. 3. [Figure 6A] FIG. 4 shows a block diagram illustrating the stator resistance compensation and integral gain block of the flux estimator shown in FIG. 3. [Figure 6B] FIG. 4 shows a block diagram illustrating the stator resistance compensation and integral gain block of the flux estimator shown in FIG. 3. [Figure 7A]4 shows a block diagram illustrating the stator inductance compensation and integral gain block of the flux estimator shown in FIG. 3. [Figure 7B] 4 shows a block diagram illustrating the stator inductance compensation and integral gain block of the flux estimator shown in FIG. 3. [Figure 8] 4 shows a block diagram illustrating a flux estimation gain block of the flux estimator shown in FIG. 3. [Figure 9] FIG. 4 shows a circuit diagram of a first circuit that operates as a terminal voltage estimator for the flux estimator shown in FIG. 3. [Figure 10] FIG. 13 shows a circuit diagram of a second circuit that acts as a motor stator resistance gain block for the flux estimator. [Figure 11] 13 shows a circuit diagram of a third circuit that operates to determine resistance compensation for the flux estimator. [Figure 12] FIG. 13 shows a circuit diagram of a fourth circuit that operates as an integration stage of the flux estimator. [Figure 13] 13 shows a circuit diagram of a fifth circuit operative to determine the motor stator inductance gain of the flux estimator 1. [Figure 14] 13 shows a circuit diagram of a sixth circuit operative to estimate air-gap flux of an electric motor; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] A flux estimator 1 for estimating air-gap flux of an electric motor 2 according to an embodiment of the present invention will now be described with reference to the accompanying drawings. The flux estimator 1 is implemented in hardware and, at least in certain embodiments, may provide improved accuracy at low operating speeds. Furthermore, the flux estimator 1 may be used with different types or models of electric motors 2. A motor controller 3 is provided for controlling the electric motor 2. The flux estimator 1 outputs an estimated air-gap flux to the motor controller 3. The flux estimator 1 and the motor controller 3 collectively form a control system 5 for controlling operation of the electric motor 2.

[0037] The electric motor 2 in this embodiment is a drive motor for a turbomolecular pump, generally designated by reference numeral 4. The turbomolecular pump operates to pump process gas in an industrial process. It will be appreciated that the flux estimator 1 can be used to estimate the air-gap flux of an electric motor 2 used in other applications. The electric motor 2 is a permanent magnet (PM) electric motor. The electric motor 2 is supplied with a three-phase alternating current. As shown diagrammatically in Figure 1, the electric motor 2 comprises a rotor 6 and a stator 7.

[0038] 3 shows a schematic diagram of a motor control unit 3. The motor control unit 3 comprises one or more electronic processors 8 and a system memory 9. A set of computational instructions is stored in the system memory 9. When executed by the one or more electronic processors 8, the instructions cause the one or more electronic processors 8 to perform the method(s) described herein. The estimated air-gap flux is output to an embedded motor control software executed by the one or more electronic processors provided in the motor control unit 3. In a variant, the flux estimator 1 can be integrated in the motor control unit 3.

[0039] The motor control unit 3 is suitable for use with a number of different types of electric motors 2. The different motor types may have different operating characteristics that require different control strategies. Exemplarily, the air-gap flux may vary depending on the type of electric motor 2. The flux estimator 1 is configured to dynamically estimate the air-gap flux depending on the determined electric motor type. The motor control unit 3 is configured to identify the electric motor 2 as one of a number of motor types. The motor types are predefined in this embodiment. The motor types may correspond, for example, to a number of different electric motors of a product configuration. The motor types have different (electrical) operating parameters, which may, for example, be predefined according to experimental data. As described herein, the motor control unit 3 is configured to compensate for the different operating parameters of each of the number of motor types.

[0040] In this embodiment, the electric motor 2 comprises an identification module 10 that allows for the identification of the electric motor type. The identification module 10 provides an identifier that is unique for each type of electric motor 2. The identification module 10 in this embodiment comprises a resistor network with at least one resistor. The resistance value of the at least one resistor is unique for each type of electric motor 2. By determining the resistance value of the identification module 10, the motor control unit 3 can identify the type of the electric motor 2 from a predefined set. The motor control unit 3 is configured to inject a current into the identification module 10. The motor control unit 3 measures the voltage across the identification module 10 and determines the resistance value of one or more resistors based on the supplied current. The motor control unit 3 accesses a look-up table and determines the type of the electric motor 2 with reference to the determined resistance value. The look-up table in this embodiment is stored in a system memory 9. The identification module 10 is mounted on the electric motor 2, for example integrated in an on-board power supply unit. The motor control unit 3 can be located remotely from the electric motor 2, for example connected by one or more electric wires. This configuration may be used to protect the motor control unit 3, for example, if the electric motor 2 is used in a harsh environment. It is understood that other techniques may be used to identify the type of electric motor 2.

[0041] As described herein, the flux estimator 1 is configured to estimate the air-gap flux based on a first gain for compensating the stator resistance Ra and a second gain for compensating the stator inductance La. Herein, the first gain is referred to as a resistive gain Ku and the second gain is referred to as an inductive gain KLa. Typically, the resistive gain Ku and the inductive gain KLa are specific to a particular motor type. The motor control unit 3 is configured to determine the resistive gain Ku and the inductive gain KLa based on the determined motor type. The resistive gain Ku and the inductive gain KLa specific to the determined motor type are output to the flux estimator 1. The flux estimator 1 is configured to estimate the air-gap flux based on the resistive gain Ku and the inductive gain KLa. The estimated air-gap flux is output from the flux estimator 1 to the electric motor control unit 3 to enable control of the electric motor 2.

[0042] Figure 3 shows a schematic diagram of the flux estimator 1. The flux estimator 1 comprises a motor voltage terminal estimation stage 11 (shown in Figure 4), a motor stator resistance gain stage 13 (shown in Figures 5A and 5B), a motor stator resistance compensation and integration stage 15 (shown in Figures 6A and 6B), a motor stator inductance gain stage 17 (shown in Figures 7A and 7B), and a stator inductance compensation and flux estimation stage 19 (shown in Figure 8). The motor stator resistance gain stage 13 comprises a first multiplying digital-to-analog converter (MDAC) 23 for applying a resistance gain Ku to compensate the stator resistance Ra. The stator inductance compensation stage 19 comprises a second multiplying digital-to-analog converter (MDAC) 25 for applying an inductance gain KLa to compensate the stator inductance La.

[0043] Figure 3 shows a schematic diagram of the motor voltage terminal estimator stage 11. The estimator stage 11 operates to generate a first signal VAN representing a scaled version of the motor terminal voltage Va. In a balanced three-phase system, the motor terminal voltage Va is defined as the motor terminal voltage with respect to an artificial neutral. The first signal VAN is defined as VAN = Ku x Va. JPEG2025511065000004.jpg78150 where Va is the motor terminal voltage, VAN is the scaled motor terminal voltage, Vpk is the peak voltage, and Ku is the resistor gain.

[0044] 5A and 5B show schematic diagrams of the motor stator resistance gain stage 13. A stator resistance Ra for the stator 7 of the electric motor 2 is determined. The motor stator resistance gain stage 13 applies a resistance gain Ku to a first multiplying digital-to-analog converter 23 to compensate for the stator resistance Ra. The motor stator resistance gain stage 13 generates a second signal VIAR representing the motor phase currents ia and a scaled version of the per-phase stator resistance Ra. The application of the motor stator resistance gain stage to determine the scaled motor phase currents VIAR is shown in FIG. 5B. VIAR = Ku x ia x Ra = Kr x Ki x ia JPEG2025511065000005.jpg67150 where VIAR is the scaled motor phase current, Ia is the motor phase current, Ra is the stator resistance (per phase), Ku is the resistance gain, Kr is the stator resistance compensation gain, and Ki is the current gain.

[0045] The scaled motor terminal voltage VAN and the scaled motor phase current VIAR are output to a resistive compensation and integration stage 15. As shown in Figures 6A and 6B, the resistive compensation and integration stage 15 generates a third signal VINT representing a scaled integral of the motor terminal voltage Va minus the voltage drop across the motor stator resistance VIAR. The determination of the voltage difference and the application of the integrator gain Kint to determine a scaled integral value VINT of the motor terminal voltage is shown in Figure 6B. The signal is scaled (by the integrator gain Kint). JPEG2025511065000006.jpg23150 where VINT is the scaled integral of the motor terminal voltage, Ia is the motor phase current, Ra is the stator resistance (per phase), Ku is the resistor gain, and Kin is the integrator gain.

[0046] The motor stator inductance gain stage 17 generates a fourth signal IA_LA. As shown in Figures 7A and 7B, the fourth signal IA_LA represents a scaled version of the product of the motor phase currents ia and the stator inductance per phase La, where IA_LA = Ku x ia x La x Kin. The inductance gain KLa is applied to the second MDAC 25 to scale the product of the motor phase currents ia and the stator inductance La. Figure 7B shows the stage for determining the scaled product IA_LA. JPEG2025511065000007.jpg37150where IA_LA is the scaled product of the motor phase current and stator inductance, Ia is the motor phase current, La is the stator inductance (per phase), Ku is the resistor gain, Kint is the integrator gain, Ki is the current gain, and KLA is the inductance gain.

[0047] The flux estimation stage 19 generates a fifth signal PSI_MON corresponding to the airgap flux estimation signal PSI_MON. Figure 8 illustrates the determination of the airgap flux estimation signal PSI_MON. The airgap flux estimation signal PSI_MON represents a scaled estimate of the airgap flux of the motor. The airgap flux estimate is determined It is calculated as the difference between the scaled integral value VINT and the fourth signal IA_LA. JPEG2025511065000008.jpg6150 where PSI_MON is the air-gap flux estimate signal, VINT is the scaled integral of the motor terminal voltage, and IA_LA is the scaled product of the motor phase current and stator inductance.

[0048] A first circuit 100 provides the motor terminal voltage estimator stage 11 of the flux estimator 1. Figure 9 shows the first circuit 100. The estimator stage 11 receives voltage signals VAR, VBR, VCR corresponding to the respective phase voltages supplied to the electric motor 2. The estimator stage 11 outputs a first signal VAN representative of a scaled motor terminal voltage Va. The first signal VAN is output to a resistive compensation and integration stage 15.

[0049] The second circuit 200 provides the motor stator resistance gain stage 13 of the flux estimator 1. FIG. 10 shows the second circuit 200. The motor stator resistance gain stage 13 subtracts a reference offset OFFSET_REF from the motor phase currents ia to determine a stator current feedback signal IA_FBK. This signal is filtered and output to a first multiplying digital-to-analog converter 23. The product of the motor phase currents ia and the stator resistance Ra is calculated to determine a voltage drop across the motor stator resistance. A resistance gain Ku is provided to the first multiplying digital-to-analog converter 23 to compensate for the stator resistance Ra. The first multiplying digital-to-analog converter 23 scales the product of the motor phase currents ia and the stator resistance Ra by applying the resistance gain Ku to generate a second signal VIAR per phase. The motor stator resistance gain stage 13 outputs the scaled second signal VIAR.

[0050] The third circuit 300 and the fourth circuit 400 provide the resistance compensation and integration stage 15 of the flux estimator 1. Figures 11 and 12 show the third and fourth circuits 300, 400, respectively. The third circuit 300 is a summing stage that operates to subtract a first signal VAN (received from the estimator stage 11) from a second signal VIAR (received from the motor stator resistance gain stage 13). A first gain Ku is applied in the calculation to generate an output signal VAN_VIAR. The output signal VAN_VIAR from the third circuit 300 is provided as an input to the fourth circuit 400. The fourth circuit 400 comprises a flux integrator stage 410 that integrates the signal VAN_VIAR with respect to time. The signal is scaled by an integral gain Kint. The scaled integrated signal VINT is output from the fourth circuit 400. The fourth circuit 400 of this embodiment also comprises an offset error integrator stage 420.

[0051] The fifth circuit 500 provides the motor stator inductance gain stage 17 of the flux estimator 1. Figure 13 shows the fifth circuit 500. The fifth circuit 500 comprises a second MDAC 25. The motor phase currents i a and the stator inductances La per phase are multiplied and the results are scaled by an inductance gain KLa provided to the second MDAC 25. The fifth circuit 500 outputs a fourth signal IA_LA representing the scaled products of the motor phase currents i a and the stator inductances La per phase.

[0052] The sixth circuit 600 provides the flux estimation stage 19 of the flux estimator 1. The sixth circuit 600 receives the scaled integral value VINT from the resistance compensation and integration stage 15 and the second output IA_LA from the motor stator inductance gain stage 17. The sixth circuit 600 subtracts the second output IA_LA from the scaled integral VINT and outputs a signal PSI_MON representing the airgap flux estimate. A positive (+ve) PSI signal voltage represents a negative (-ve) airgap flux and a negative (-ve) PSI signal voltage represents a positive (+ve) airgap flux.

[0053] A signal PSI_MON representative of the airgap flux estimate is output from the flux estimator 1 to a motor control unit 3. The motor control unit 3 is configured to control operation of the electric motor 2 depending on the estimated airgap flux. The motor control unit 3 may, for example, output a control signal CS1 (shown diagrammatically in Figure 1) to control operation of the electric motor 2.

[0054] The flux estimator 1 provides a hybrid system that utilizes a combination of hardware and software to estimate the air gap flux, and provides particular advantages in connection with the operation of pumps, such as the turbomolecular pump 3 described herein. In at least certain embodiments, the flux estimator 1 comprises: Transition from open to closed loop control at very low speeds of about 5Hz, which corresponds to a speed of about 1% Hardware measurement of motor terminal voltage Flexible / tunable gain blocks that allow dynamic software tuning of resistance and inductance compensation stages within the flux estimator topology · Compatibility with multiple motor variants without the need for multiple drive hardware variants One or more of the following may be provided:

[0055] In the above embodiment, the resistance gain Ku and / or the inductance gain KLa are selected based on the determined type of the electric motor 2. The resistance gain Ku and / or the inductance gain KLa can be optionally changed based on one or more operating parameters of the electric motor 2. The flux estimator 1 or the motor control unit 3 can modify the resistance gain Ku and / or the inductance gain KLa based on one or more operating parameters. The resistance gain Ku and / or the inductance gain KLa can be modified to compensate for one or more changing operating parameters of the electric motor 2. The resistance gain Ku and / or the inductance gain KLa can be changed, for example, based on the temperature of the electric motor 2. The temperature of the electric motor 2 can be modeled or measured by another temperature sensor 27, which is shown diagrammatically in FIG. 1. The flux estimator 1 can enable dynamic estimation of the air-gap flux, which changes based on one or more operating parameters of the electric motor 2. The temperature signal ST1 can be output to the motor control unit 3. The motor control unit 3 may modify the resistive gain Ku and / or the inductive gain KLa based on the determined temperature of the electric motor 2 .

[0056] It should be understood that various changes and modifications can be made to the present invention without departing from the scope of the application. [Explanation of symbols]

[0057] 1. Flux estimator 2 Electric motor 3 Motor Control Unit 4. Pump 5. Control System 8. Electronic Processor 9. System Memory 10 Identification Module 11 Motor voltage terminal estimation stage 13 Motor Stator Resistance Gain Stage 15 Stator resistance compensation and integration stage 17 Motor Stator Inductance Gain Stage 19 Stator inductance compensation and flux estimation stage 23 First Multiplying Digital-to-Analog Converter (MDAC) 25 Second Multiplying Digital-to-Analog Converter (MDAC) 27 Temperature Sensor

Claims

1. A flux estimator (1) for estimating an air-gap flux of a permanent magnet electric motor having a rotor and a stator, the flux estimator (1) comprising a resistance compensation stage having a first multiplying digital-to-analog converter (23) and an inductance compensation stage having a second multiplying digital-to-analog converter (25), the flux estimator (1) comprising: determining a first gain (Ku) for compensating for a stator resistance (Ra); determining a second gain (KLa) for compensating for the stator inductance (La); providing the first gain (Ku) to the first multiplying digital-to-analog converter (23) of the resistance compensation stage to generate a first output signal (VIAR) providing a scaled representation of the voltage drop across the stator resistance (Ra) per phase; providing a second gain (KLa) to the second multiplying digital-to-analog converter (25) of the inductance compensation stage to generate a second output signal (IA_LA) providing a scaled representation of the stator inductance per phase (La); generating an air-gap flux estimation signal (PSI_MON) based on the first output (VIAR) and the second output (IA_LA); The magnetic flux estimator (1) is configured as follows.

2. 2. The magnetic flux estimator (1) of claim 1, wherein determining the first gain (Ku) comprises receiving the first gain (Ku) from a control unit (3) and / or determining the second gain (KLa) comprises receiving the second gain (KLa) from a control unit (3).

3. The flux estimator (1) according to claim 1 or 2, wherein the voltage drop across the stator resistance (Ra) is the product of the motor phase current (ia) and the stator resistance (Ra).

4. The magnetic flux estimator (1) determining a scaled integral (VINT) with respect to time of the voltage difference between the motor terminal voltage (VAN) and the voltage drop across the stator resistance (VIAR); A flux estimator (1) according to claim 3, configured as follows:

5. The flux estimator (1) according to claim 4, wherein said airgap flux estimation signal (PSI_MON) is generated based on said determined and scaled integral value (VINT).

6. 6. The flux estimator (1) according to claim 5, wherein the airgap flux estimation signal (PSI_MON) is calculated as the difference between the determined scaled integral value (VINT) and the second output (IA_LA).

7. A flux estimator (1) according to any of the preceding claims, wherein the scaled representation of the stator inductance (La) is a scaled product of the stator inductance (La) and the motor phase current (Ia).

8. The first gain (Ku) is 8. The flux estimator (1) according to any of the preceding claims, wherein VAN is the phase voltage with respect to an artificial neutral and Va is the motor terminal voltage.

9. The second gain (KLa) is 9. The flux estimator (1) according to claim 1, wherein La is the stator inductance, Ku is the first gain, k int is the integrator gain and Ki is the current gain.

10. 10. A flux estimator (1) according to any of the preceding claims, comprising a storage device, wherein a database comprising at least one data set is stored in the storage device, the or each data set comprising predetermined first and second gains for the electric motor, and the flux estimator (1) is configured to determine the first and second gains by accessing the database.

11. 11. The flux estimator of claim 10, wherein the flux estimator is configured to identify the electric motor and to select the data set corresponding to the identified electric motor to determine the first gain and the second gain.

12. 12. The magnetic flux estimator (1) of claim 11, wherein the magnetic flux estimator (1) is configured to identify the electric motor by supplying a current to determine a saturation profile of the motor inductance, and the magnetic flux estimator (1) is configured to identify the electric motor based on the determined saturation profile.

13. 13. The flux estimator (1) according to any one of claims 1 to 12, wherein the flux estimator (1) is configured to determine the first gain (Ku) based on an estimated motor terminal voltage (Va) and / or to determine the second gain (KLa) based on a measured stator inductance (La).

14. 14. The flux estimator (1) according to any one of claims 1 to 13, wherein the flux estimator (1) is configured to receive at least one signal indicative of an operating parameter of the electric motor, and wherein the flux estimator (1) is configured to dynamically modify the first gain (Ku) and / or the second gain (KLa) based on the or each operating parameter of the electric motor.

15. The flux estimator (1) of claim 14, wherein the one or more operating parameters comprise an operating temperature of the electric motor.

16. A motor control unit (3) for controlling operation of an electric motor (4) having a stator (7) and a rotor (6), the motor control unit (3) comprising at least one processor (8) and a storage device (9), the at least one processor determining a type of the electric motor and, based on the determined type of the electric motor: a first gain (Ku) for compensating for a stator resistance (Ra) of the electric motor; and a second gain (KLa) for compensating for a stator inductance (La) of the electric motor; The motor control unit is configured to determine at least one of:

17. 17. The motor control unit of claim 16, wherein the at least one processor (8) is configured to output at least one of the first gain (Ku) and the second gain (KLa) to a flux estimator (1) according to any one of claims 1 to 15.

18. 18. The motor control unit (3) of claim 16 or 17, wherein the at least one processor (8) is configured to receive one or more operating parameters of the electric motor (4), and the at least one processor (8) is configured to dynamically modify at least one of the first gain (Ku) and the second gain (KLa) based on the one or more operating parameters of the electric motor (4).

19. 19. A control system (5) for controlling an electric motor (4), the control system (5) comprising a flux estimator (1) according to any one of claims 1 to 15 and a motor control unit (3) according to any one of claims 16, 17 or 18, the motor control unit (3) being configured to output at least one of the first gain (Ku) and the second gain (KLa) to the flux estimator (1).

20. A pump (4) comprising an electric motor (4) and a motor control unit (3) according to any one of claims 16 to 19.

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