System and method for hybrid control of pmsm drive using two current sensors

Abstract

A method for operating a motor drive to supply power to an electric motor comprises: measuring a first phase current and a second phase current in the electric motor; calculating, based on the first phase current and the second phase current, an estimated third phase current in the electric motor; determining an estimated motor current using a current observer and based on the first phase current, the second phase current, and the estimated third phase current; determining, based on the estimated motor current, a voltage command; and commanding, based on the voltage command, an inverter to supply an alternating current (AC) power to the electric motor.

Description

[0001]Attorney Docket No.18402-05183 (713226PCT) SYSTEM AND METHOD FOR HYBRID CONTROL OF PMSM DRIVE USING TWO CURRENT SENSORS CROSS-REFERENCE TO RELATED APPLICATIONS This PCT International Patent Application claims the benefit of and priority to U.S. Provisional Patent Application Serial No. 63 / 606,158 filed on December 5, 2023 and titled “System and Method for Hybrid Control of PMSM Drive Using Two Current Sensors,” the entire disclosure of which is hereby incorporated by reference. FIELD The present disclosure relates generally to a method and system for controlling a motor drive. More specifically, the method and system of the present disclosure may be used for controlling a motor drive coupled to an electric motor configured as a traction motor for propelling a motor vehicle, such as a passenger car or truck. BACKGROUND Permanent magnet synchronous machines (PMSMs) are widely employed in servo control, automotive, aerospace and wind power generation systems due to their high power density, high efficiency, and simple structure. PMSMs are usually driven by a voltage source inverter, and motor control is performed using inputs such as current, position, and / or voltage measurements. For current measurement, a three-phase PMSM drive usually uses two or three- phase current sensors. Hardware current sensors for measuring such two and three-phase currents have substantial costs. In reality, not only the cost of the sensor itself is considered, but also the cabling, the appropriate connectors and interfaces, and all associated expenses have to be considered as well. Furthermore, current measurement error and noise inevitably exist due to various factors such as device tolerance, temperature drift and aging, and electromagnetic Attorney Docket No.18402-05183 (713226PCT) interference (EMI), which worsen the PMSM control performance. Failure of current sensors is most critical to the drive system. Even if only one current sensor malfunctions, it can prevent normal operation of a motor drive. Therefore, high accuracy three-phase current reconstruction has risen manufacturers' interest as they seek to reduce costs and improve robustness for the PMSM drive system. Traditionally, PMSM control strategies rely on accurate current measurements from all three phases (A, B, and C) using three hardware current sensors. However, this approach can increase system size and cost. To overcome these limitations, the reduced current sensor control with two hardware current sensors is provided in this disclosure. Reduced current sensor control using two-phase current sensors offers several advantages. Firstly, it simplifies the hardware design by eliminating one current sensor, reducing wiring complexity and associated costs. Furthermore, it improves system reliability by reducing the number of components that could potentially fail and offers the fault-tolerant ability of the drive system. There are two conventional methods for reduced current sensor control with two hardware current sensors: Kirchhoff's equation based two current sensors control and observer based two current sensors control. In the Kirchhoff's equation based two current sensors control, the third phase current is calculated from the measured currents of the two available phase current sensors using Kirchhoff's law. This method leverages the fact that in a balanced three-phase system, the sum of currents entering a junction point is zero. By measuring the currents in two phases and applying Kirchhoff's equation, the current in the third phase can be calculated, allowing for a complete estimation of all three phase currents. However, it is noted that the calculated current with Kirchhoff's equation will contain the sum noise of the two current phase sensors. On the other hand, the observer-based two current sensors control method employs current observers to estimate Attorney Docket No.18402-05183 (713226PCT) the unmeasured phase current. The observer-based method can provide a good noise reduction capability. However, the dynamic performance under fast load change can be limited due to the parameter variations. SUMMARY The present disclosure provides a method for operating a motor drive configured to supply power to an electric motor. The method includes: measuring a first phase current and a second phase current in the electric motor; calculating, based on the first phase current and the second phase current, an estimated third phase current in the electric motor; determining an estimated motor current using a current observer and based on the first phase current, the second phase current, and the estimated third phase current; determining, based on the estimated motor current, a voltage command; and commanding, based on the voltage command, an inverter to supply an alternating current (AC) power to the electric motor. The present disclosure also provides a motor drive system. The motor drive system includes: an inverter having at least three pairs of switches operable to supply an alternating current (AC) power to an electric motor; a first current sensor configured to measure a first phase current in the electric motor; a second current sensor configured to measure a second phase current in the electric motor; and a controller. The controller is configured to: calculate, based on the first phase current and the second phase current, an estimated third phase current in the electric motor; determine an estimated motor current using a current observer and based on the first phase current, the second phase current, and the estimated third phase current; determine, based on the estimated motor current, a voltage command; and command, based on the voltage command, the inverter to supply the AC power to the electric motor. Attorney Docket No.18402-05183 (713226PCT) BRIEF DESCRIPTION OF THE DRAWINGS Further details, features and advantages of designs of the invention result from the following description of embodiment examples in reference to the associated drawings. FIG.1 shows a schematic block diagram of a system, in accordance with an aspect of the present disclosure; FIG. 2 shows a schematic block diagram of a motor drive with hybrid current observer, in accordance with an aspect of the present disclosure; FIG. 3 shows a graph illustrating speed (in rpm) and Torque (in Nm) over a common time scale for an electric motor operated by a motor drive system using various different control techniques; FIG. 4 shows a graph illustrating d-axis current and q-axis current over a common time scale for an electric motor operated by a motor drive system using various different control techniques; FIG. 5 shows a bar graph showing current and torque peak-to-peak ripple for a motor drive system operated using various different control techniques; FIGS. 6A – 6D show graphs illustrating, over a common time scale, Torque (in Nm), d-axis current, q-axis current, and errors in estimated d-axis and q-axis currents for an electric motor operated by a motor drive system using various different control techniques; and FIG. 7 shows a flow chart of steps in a method for operating a motor drive, in accordance with some embodiments of the present disclosure. DETAILED DESCRIPTION Referring to the drawings, the present invention will be described in detail in view of following embodiments. Attorney Docket No.18402-05183 (713226PCT) To overcome the technical limitations of the existing approaches, the present disclosure provides a hybrid method for two current sensor control. This hybrid method combines the strengths of both techniques – superior dynamic performance of Kirchhoff's equation-based method and noise reduction capabilities of the observer-based method. By leveraging the synergies between these two techniques, the method and system of the present disclosure may provide enhanced overall performance of two current sensor control PMSM drives. The hybrid two current sensor control method of the present disclosure can mitigate potential current overshoot that can result from observer-based methods while also reducing noise that can be introduced using Kirchhoff's equation for estimating phase currents. FIG. 1 shows a block diagram of system 10 in accordance with an aspect of the present disclosure. The system 10 is provided in a vehicle 12 having four wheels 14. The system 10 includes an inverter 20 having at least three pairs of solid-state switches 22, such as field effect transistors (FETs) configured to switch current from a DC power supply 23 and to generate an AC power upon a set of motor leads 24. The motor leads 24 transmit electrical power between the inverter 20 and an electric motor 26. The electric motor 26 may be a permanent magnet synchronous motor (PMSM). The electric motor 26 may be used as a motor, a generator, or as a motor / generator that functions as both a motor and a generator. The electric motor 26 may be coupled to one or more of the wheels 14 of the vehicle 12 for driving the vehicle 12. Alternatively, the electric motor 26 may be used for one or more ancillary functions in the vehicle 12, such as for operating an actuator, a fan, a pump, etc. In some embodiments, the system 10 of the present disclosure may have a non-vehicular application, such as for motor control in industrial or manufacturing applications. Attorney Docket No.18402-05183 (713226PCT) A first current sensor 28a is arranged to measure current in one of the motor leads 24, and a second current sensor 28b is arranged to measure current in another one of the motor leads 24. In some embodiments, and as shown on FIG.1, the current sensors 28a, 28b measure A- phase current ia, and B-phase current ibon corresponding ones of the motor leads 24. However, the system 10 may measure current on any two of the motor leads 24. The system 10 may include other sensors, such as voltage sensors configured to measure voltages upon or between the motor leads 24. If voltage sensors are available, they can be used as inputs for the provided approach. The system 10 of FIG. 1 also includes an electronic control unit (ECU) 30 in communication with the current sensor 28 to measure the currents in the motor leads 24. The ECU 30 may also be in functional communication with the inverter 20 to control operation of the inverter 20 and / or to monitor parameters measured by sensors associated with the inverter 20. The ECU 30 includes a processor 32 coupled to a storage memory 34. The storage memory 34 stores instructions, such as program code for execution by the processor 32, in an instruction storage 36. The storage memory 34 also includes data storage 38 for holding data to be used by the processor 32. The data storage 38 may record, for example, values of the parameters measured by the current sensor 28 and / or the outcome of functions calculated by the processor 32. A speed / position sensor 42 may measure a rotational position θ of the electric motor 26 that corresponds to an electrical rotational position θe. Alternatively or additionally, the speed / position sensor 42 may measure a rotational speed ω of the electric motor 26 that corresponds to an electrical rotational speed ωeof the electric motor 26. In some embodiments, the speed / position sensor 42 may include an encoder or a resolver connected to a shaft 40 of the electric motor 26. The speed / position sensor 42 may communicate the rotational position θ and / or the rotational speed ω of the electric motor 26 to the ECU 30. Attorney Docket No.18402-05183 (713226PCT) The machine equations for a PMSM in the rotating direct-quadrature (dq) reference frame considering system uncertainties and unknown external disturbance can be represented as shown in equations (1) and (2): ^^^^ ^^ ൌ ^^ ^^ ௗௗ ^ ௗ ^ ^^ௗ^^^െ ^^^^^^^^^ ^ ^^ௗ^ ^ ^1^ 2^ where ud,and uqrepresent d-axis and q-axis voltages, respectively; idand iqrepresent d-axis and q- axis currents, respectively; Ld and Lq represent d-axis and q-axis inductances, respectively; ψf is permanent magnet flux linkage; Rsis the winding resistance; ωeis the electrical rotational speed; fd, and fqrepresent system uncertainties and unknown external disturbance in the d-axis and q- axis, respectively; ∆^^^,∆^^^,∆^^ௗand ^^^^^are parameter variation terms between real motor parameter and corresponding nominal parameters. Edand Eqrepresent d-axis and q-axis unknown external disturbance terms, respectively. Assuming resistance variation, inductance variation, permanent magnetic flux linkage variation and external disturbance variation are small and can be ignored, the dynamic equation of an interior PMSM (IPMSM) in the dq-axis can be represented as equation (3): ^^^^ௗ^^ௗ^^ ^^^^^^^^ ì^^^ ^ ^^ௗ^ Attorney Docket No.18402-05183 (713226PCT) The PMSM state space model developed is given as shown in equation (4): ^^^^ ^ ^^^^ൌ ^^^^ ^ ^^^^^4^ ^^ ൌ ^^^^where A, B, and C are each respectively defined as: ^^ ^^ െ^1 1 é^^^ െ 0 ù é 0ù ê ^^ௗ^^^ௗ^^ௗú ê ^^ௗú ^^ ൌê ^^ ^^ 1ú ê 1ú ê െௗ^^ െ^ ,^^ ൌ0 , ^^^^^0 െú ê ú ê^ ^^^^ú ê ^^^ú ê0 0 0 0ú ê0 0ú ë0 0 0 0 ûë0 0 û^^ ൌ ^1 0 0 00 1 0 0^, and where ^^ ൌ ^^^ௗ ^^^ ^^ௗ ^^^^் is the state vector,^^ ൌ ^^^ௗ ^^^^ െ ^^^^^^^^் is the input vector, and ^^ ൌ ^^^ௗ ^^^^் is the output vector.The observer structure can be written as equation (5): ^^^^^ ^ ^^^^ൌ ^^^^^ ^ ^^^^ ^ ^^^^^ െ ^^^^^5^ ^^^ ൌ ^^^^^ ^^ ൌ ^^^ ^ ்where ^^ଶ^^ଷ^^ସ^^ ^^ ^^ ^^൨ is the observer gain matrix and the superscript T represents the ହ^ ^ ଼transpose of the matrix; k1, k2,…, k8are observer gain coefficients. The symbol “^” represents the estimated value. In the Luenberger observer, the system dynamic performance is determined by eigenvalues of (A-KC). െ^^ ் ^ െ^^ ^^ 2^^^^ ௗ^^^^ ^ଶ The coordinate transformations in FIG.2 are defined as shown in equations (7) and (8): Attorney Docket No.18402-05183 (713226PCT) 2^^ 2^^ 2^^^^^^^ ^^^^ ^^^^^^^ ^^^ െ^3^ ^^^^^^^ ^^^ ^^ 3 ^^7^where ^^^is the A schematic block diagram of a motor drive 100 in accordance with an aspect of the present disclosure is shown in FIG. 2. The motor drive 100 includes a controller 102 that is configured to implement several computational functions. The controller 102 may include the ECU 30 and may implement the associated functions in hardware, software, or in a combination of hardware and software. The controller 102 includes a speed / torque controller 104 configured to generate a current command ^^∗^^, ^^∗^^. The speed / torque controller 104 may use a control loop, such as a proportional-integral (PI) loop or a proportional-integral-derivative (PID) loop to generate the current command ^^∗^^, ^^∗^^. The speed / torque controller 104 may be configured as a speed controller to cause the electric motor 26 to rotate at the electrical rotational speed ωein accordance with a speed command ^^∗^^. Alternatively, or additionally, the speed / torque controller 104 may be configured as a torque controller to cause the electric motor 26 to produce an output torque in accordance with a torque command ^^^∗^. The controller 102 also includes a current regulator 106 configured to generate a voltage command ud, uqbased on the current command ^^∗^^, ^^∗^^and based on an estimated current ଙ̂^^, ଙ̂^^. The voltage command ud, uqincludes d-axis and q-axis voltage values, respectively, representing a voltage to be applied by the inverter 20 to the electric motor 26. The current Attorney Docket No.18402-05183 (713226PCT) regulator 106 may use a control loop, such as a proportional-integral (PI) loop or a proportional- integral-derivative (PID) loop to generate the voltage command ud, uq. The controller 102 also includes a dq-abc transformer 108 configured to compute phase voltages ua, ub, ucbased on the voltage command ud, uqin the dq reference frame and based on the electrical rotational position θeof the electric motor 26. The dq-abc transformer 108 may implement an inverse direct-quadrature-zero transformation such as the transformation described in equation (8). The controller 102 also includes a pulse-width modulator (PWM) 110 configured to generate a plurality of gate driver signals 112 for controlling switching devices of the inverter 20 to cause the inverter 20 to generate AC power on the motor leads 24 corresponding to the phase voltages ua, ub, uc. The controller 102 also includes a Kirchhoff current estimator 120 configured to calculate an estimated C-phase current ଙ̂^^based on the A-phase current ^^^^and the B-phase current ^^^^, as measured by the first current sensor 28a, and the second current sensor 28b, respectively. This is an example configuration, and it should be appreciated that the Kirchhoff current estimator 120 configured to compute an estimate of any one phase current using known or measured values of two other phase currents in a three-phase machine. The Kirchhoff current estimator 120 may add the A-phase current ^^^^and the B-phase current ^^^^, then calculate the estimated C-phase current ଙ̂^^as an inverse of the sum of the A-phase current ^^^^and the B-phase current ^^^^. The controller 102 also includes an abc-dq transformer 122 configured to compute a preliminary estimated motor current id_kir, iq_kirthat includes a preliminary estimated d-axis current id_kirand a preliminary current iq_kirbased on the A-phase current ^^^^, the B-phase current ^^^^, and the estimated C-phase current ଙ̂^^. The abc-dq transformer 122 may Attorney Docket No.18402-05183 (713226PCT) implement a direct-quadrature-zero transformation such as the transformation described in equation (7). The controller 102 also includes a current observer 124 configured to calculate an estimated motor current ଙ̂^^, ଙ̂^^based on the preliminary estimated motor current id_kir, iq_kir, the voltage command ud, uq, and the electrical rotational speed ωeof the electric motor 26. The current observer 124 may include a Luenberger Current Observer (LCO) structure, described above, and as represented by equation (5). The estimated motor current ଙ̂^^, ଙ̂^^is supplied by the current observer 124 to the current regulator 106, which uses the estimated motor current ଙ̂^^, ଙ̂^^to generate the voltage command ud, uq. Additionally, or alternatively, the current observer 124 may use a different type of current state observer. FIG. 3 shows a graph illustrating speed (in rpm) and Torque (in Nm) over a common time scale for an electric motor operated by a motor drive system using various different control techniques. FIG. 4 shows a graph illustrating d-axis current and q-axis current over a common time scale for an electric motor operated by a motor drive system using various different control techniques. FIG. 5 shows a bar graph showing current and torque peak-to-peak ripple for a motor drive system operated using various different control techniques. Table 1, below, lists peak-to-peak values of ripple for d-axis current (Id), q-axis current (Iq), and torque for an electric motor operated by a motor drive system using various different control techniques and to produce torque varying over a range of 0 to 40 Nm. Table 1 IdRipple (A) IqRipple (A) Torque Ripple (Nm) Attorney Docket No.18402-05183 (713226PCT) FIGS. 6A – 6D show graphs illustrating, over a common time scale, Torque (in Nm), d-axis current, q-axis current, and errors in estimated d-axis and q-axis currents for an electric motor operated by a motor drive system using various different control techniques. The control techniques represented in FIGS. 3-5 and 6A – 6D include: mode 1: Healthy control with three current sensors; mode 2: Kirchhoff equation-based control with two current sensors; mode 3: Observer-based control with two current sensors; and mode 4: hybrid control with two current sensors with both Kirchhoff equation-based phase current estimation and with Observer-based control using two measured phase currents and a third estimated phase current as determined using the Kirchhoff equation and based on the two measured phase currents. A method 200 for operating a motor drive configured to supply power to an electric motor 26 is shown in the flow chart of FIG. 7. In some embodiments, the electric motor 26 is a PMSM. The method 200 can be performed by the ECU 30, in accordance with some embodiments of the present disclosure. As can be appreciated in light of the disclosure, the order of operation within the method is not limited to the sequential execution as illustrated in FIG. 7, but may be performed in one or more varying orders as applicable and in accordance with the present disclosure. The method 200 includes measuring a first phase current and a second phase current in the electric motor at step 202. Step 202 may be performed by the current sensors 28a, 28b. The method 200 also includes measuring a rotational speed of the electric motor at step 204. Step 204 may be performed by a speed sensor or a position sensor operably coupled to the electric motor, such as the position sensor 42. In some embodiments, the rotational speed of the electric motor may be communicated to the ECU 30 from an external source, such as a controller associated with another system in the vehicle 12. Attorney Docket No.18402-05183 (713226PCT) The method 200 also includes calculating, based on the first phase current and the second phase current, an estimated third phase current in the electric motor at step 206. Step 206 may be performed, for example, by the processor 32 executing program instructions for implementing the Kirchhoff current estimator 120. The method 200 also includes determining, at step 208, an estimated motor current of the electric motor using a current observer and based on the first phase current, the second phase current, and the estimated third phase current. Step 208 may be performed, for example, by the processor 32 executing program instructions to implement the current observer 124. In some embodiments, the current observer 124 may include a Luenberger Current Observer (LCO). However, the current observer 124 may use a different type of current state observer. In some embodiments, step 208 includes determining a preliminary estimated motor current based on the first phase current, the second phase current, and the estimated third phase current. In some embodiments, step 208 also includes refining, by the current observer, the preliminary estimated motor current to determine the estimated motor current of the electric motor. Step 208 may include using one or more techniques for determining the estimated motor current, such as one or more calculations and / or using one or more lookup tables. The method 200 also includes determining a voltage command based on the estimated motor current of the electric motor at step 210. Step 210 may be performed, for example, by the processor 32 executing program instructions to implement the current regulator 106. Step 210 may include determining a difference between the requested motor current and the estimated motor current. In some embodiments, step 210 may include determining the voltage command based on the difference between a requested motor current and the estimated motor current. Attorney Docket No.18402-05183 (713226PCT) The method 200 also includes commanding, based on the voltage command, an inverter to supply an alternating current (AC) power to the electric motor at step 212. Step 212 may be performed, for example, by the processor 32 executing program instructions to implement the dq-abc transformer 108 and the pulse-width modulator 110 to generate the gate driver signals 112 for controlling switching devices of the inverter 20. The system and method of the present disclosure may incorporate a combination of the following features: Two Hardware Current Sensors: The method starts with two hardware current sensors that are placed to measure two-phase currents of a PMSM. Kirchhoff's Equation: One part of the hybrid method employs Kirchhoff's law to calculate the current in the third phase based on the measurements from two hardware current sensors. By mathematically inferring the third phase current using the Kirchhoff's equation, the dedicated third hardware current sensor may not be required. However, the calculated phase current in this step will contain a sum of noise from the two hardware current sensors. Current Observer: The other component of the hybrid method involves an observer-based filtering approach. This technique utilizes mathematical models and algorithms to reconstruct dq-axis current based on the measurements obtained from two hardware current sensors and calculated phase current from Kirchhoff’s equation. This current observer functions to filter out noise in current signals. The present disclosure provides a method for operating a motor drive to supply power to an electric motor. The method includes: measuring a first phase current and a second phase current in the electric motor; calculating, based on the first phase current and the second phase current, an estimated third phase current in the electric motor; determining an estimated motor current using a current observer and based on the first phase current, the second phase current, and the estimated third phase current; determining, based on the estimated motor current, Attorney Docket No.18402-05183 (713226PCT) a voltage command; and commanding, based on the voltage command, an inverter to supply an alternating current (AC) power to the electric motor. In some embodiments, the electric motor is a permanent magnet synchronous machine (PMSM). In some embodiments, calculating the estimated third phase current in the electric motor includes using Kirchoff’s law. In some embodiments, the current observer includes a Luenberger Current Observer (LCO). In some embodiments, determining the estimated motor current of the electric motor includes: computing an initial d-axis current estimate and an initial q-axis current estimate; and determining the estimated motor current using the current observer and based on the initial d- axis current estimate and the initial q-axis current estimate. In some embodiments, the estimated motor current includes an estimated d-axis current and an estimated q-axis current. In some embodiments, determining the estimated motor current includes determining the estimated motor current further based on the voltage command. In some embodiments, determining the estimated motor current includes determining the estimated motor current further based on a speed of the electric motor. The present disclosure also provides a motor drive system. The motor drive system includes: an inverter having at least three pairs of switches operable to supply an alternating current (AC) power to an electric motor; a first current sensor configured to measure a first phase current in the electric motor; a second current sensor configured to measure a second phase current in the electric motor; and a controller. The controller is configured to calculate, based on the first phase current and the second phase current, an estimated third phase current in the electric motor; Attorney Docket No.18402-05183 (713226PCT) determine an estimated motor current using a current observer and based on the first phase current, the second phase current, and the estimated third phase current; determine, based on the estimated motor current, a voltage command; and command, based on the voltage command, the inverter to supply the AC power to the electric motor. In some embodiments, the electric motor is a permanent magnet synchronous machine (PMSM). In some embodiments, calculating the estimated third phase current in the electric motor includes using Kirchoff’s law. In some embodiments, the current observer includes a Luenberger Current Observer (LCO). In some embodiments, determining the estimated motor current of the electric motor includes the controller being further configured to: compute an initial d-axis current estimate and an initial q-axis current estimate; and determine the estimated motor current using the current observer and based on the initial d-axis current estimate and the initial q-axis current estimate. In some embodiments, the estimated motor current includes an estimated d-axis current and an estimated q-axis current. In some embodiments, determining the estimated motor current includes determining the estimated motor current further based on the voltage command. In some embodiments, the motor drive system further includes a sensor configured to measure a rotational speed of the electric motor, and determining the estimated motor current includes determining the estimated motor current further based on the rotational speed of the electric motor. Attorney Docket No.18402-05183 (713226PCT) The system, methods and / or processes described above, and steps thereof, may be realized in hardware, software or any combination of hardware and software suitable for a particular application. The hardware may include a general purpose computer and / or dedicated computing device or specific computing device or particular aspect or component of a specific computing device. The processes may be realized in one or more microprocessors, microcontrollers, embedded microcontrollers, programmable digital signal processors or other programmable device, along with internal and / or external memory. The processes may also, or alternatively, be embodied in an application specific integrated circuit, a programmable gate array, programmable array logic, or any other device or combination of devices that may be configured to process electronic signals. It will further be appreciated that one or more of the processes may be realized as a computer executable code capable of being executed on a machine readable medium. The computer executable code may be created using a structured programming language such as C, an object oriented programming language such as C++, or any other high- level or low-level programming language (including assembly languages, hardware description languages, and database programming languages and technologies) that may be stored, compiled or interpreted to run on one of the above devices as well as heterogeneous combinations of processors processor architectures, or combinations of different hardware and software, or any other machine capable of executing program instructions. Thus, in one aspect, each method described above and combinations thereof may be embodied in computer executable code that, when executing on one or more computing devices performs the steps thereof. In another aspect, the methods may be embodied in systems that perform the steps thereof, and may be distributed across devices in a number of ways, or all of the Attorney Docket No.18402-05183 (713226PCT) functionality may be integrated into a dedicated, standalone device or other hardware. In another aspect, the means for performing the steps associated with the processes described above may include any of the hardware and / or software described above. All such permutations and combinations are intended to fall within the scope of the present disclosure. The foregoing description is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

Attorney Docket No.18402-05183 (713226PCT) CLAIMS What is claimed is:

1. A method for operating a motor drive to supply power to an electric motor, comprising: measuring a first phase current and a second phase current in the electric motor; calculating, based on the first phase current and the second phase current, an estimated third phase current in the electric motor; determining an estimated motor current using a current observer and based on the first phase current, the second phase current, and the estimated third phase current; determining, based on the estimated motor current, a voltage command; and commanding, based on the voltage command, an inverter to supply an alternating current (AC) power to the electric motor.

2. The method of Claim 1, wherein the electric motor is a permanent magnet synchronous machine (PMSM).

3. The method of Claim 1, wherein calculating the estimated third phase current in the electric motor includes using Kirchoff’s law.

4. The method of Claim 1, wherein the current observer includes a Luenberger Current Observer (LCO).Attorney Docket No.18402-05183 (713226PCT) 5. The method of Claim 1, wherein determining the estimated motor current of the electric motor includes: computing an initial d-axis current estimate and an initial q-axis current estimate; and determining the estimated motor current using the current observer and based on the initial d-axis current estimate and the initial q-axis current estimate, wherein the estimated motor current includes an estimated d-axis current and an estimated q-axis current.

6. The method of Claim 1, wherein determining the estimated motor current includes determining the estimated motor current further based on the voltage command.

7. The method of Claim 1, wherein determining the estimated motor current includes determining the estimated motor current further based on a speed of the electric motor.

8. A motor drive system comprising: an inverter having at least three pairs of switches operable to supply an alternating current (AC) power to an electric motor; a first current sensor configured to measure a first phase current in the electric motor; a second current sensor configured to measure a second phase current in the electric motor; and a controller configured to: calculate, based on the first phase current and the second phase current, an estimated third phase current in the electric motor;Attorney Docket No.18402-05183 (713226PCT) determine an estimated motor current using a current observer and based on the first phase current, the second phase current, and the estimated third phase current; determine, based on the estimated motor current, a voltage command; and command, based on the voltage command, the inverter to supply the AC power to the electric motor.

9. The motor drive system of Claim 8, wherein the electric motor is a permanent magnet synchronous machine (PMSM).

10. The motor drive system of Claim 8, wherein calculating the estimated third phase current in the electric motor includes using Kirchoff’s law.

11. The motor drive system of Claim 8, wherein the current observer includes a Luenberger Current Observer (LCO).

12. The motor drive system of Claim 8, wherein determining the estimated motor current of the electric motor includes the controller being further configured to: compute an initial d-axis current estimate and an initial q-axis current estimate; and determine the estimated motor current using the current observer and based on the initial d-axis current estimate and the initial q-axis current estimate, wherein the estimated motor current includes an estimated d-axis current and an estimated q-axis current.Attorney Docket No.18402-05183 (713226PCT) 13. The motor drive system of Claim 8, wherein determining the estimated motor current includes determining the estimated motor current further based on the voltage command.

14. The motor drive system of Claim 8, further comprising a sensor configured to measure a rotational speed of the electric motor, and wherein determining the estimated motor current includes determining the estimated motor current further based on the rotational speed of the electric motor.

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