Power Management of Permanent Magnet Synchronous Motor Drives Using Machine Current Limitation

Abstract

Various technical schemes for controlling the operation of an electric machine, such as a permanent magnet synchronous motor (PMSM) drive, or a motor control system to prevent excessive machine current or voltage in a PMSM drive are described. The systems and methods employ a torque control algorithm for a PMSM that uses constraints on both machine current and voltage capabilities in the PMSM drive, and online torque command modification based on a maximum allowable torque under these machine current and voltage constraints.

Description

Technical Field

[0001] The present application generally relates to methods and systems for controlling the operation of an electric machine, such as a permanent magnet synchronous motor (PMSM) drive or a motor control system. More specifically, the present application relates to methods and systems for limiting machine current and voltage in a PMSM drive to prevent excessive machine current or voltage in the PMSM drive. An exemplary embodiment is provided in an electric power steering (EPS) system. Background Art

[0002] Permanent magnet synchronous motor (PMSM) is gaining more and more attention in electric drive applications due to its properties such as high power density, easy controllability and improved reliability. The most widely adopted control technique for PMSM is vector control, in which all alternating current (AC) signals are converted into direct current (DC) signals through a reference frame transformation. Subsequently, the control system is implemented in a synchronous rotating or d / q reference frame using current regulators. Summary of the invention

[0003] According to one or more embodiments, a system and method are provided that are configured to determine a torque command that is limited to within a maximum torque of a PMSM for a specified maximum DC link voltage and does not exceed a specified maximum PMSM current limit; and to perform a maximum torque to current ratio (MTPA) calculation using the torque command to determine a current command for PMSM control.

[0004] According to one aspect of one or more exemplary embodiments, the system and method are further configured to determine whether the PMSM voltage exceeds a specified maximum DC link voltage of the system; and when the PMSM voltage does not exceed the specified maximum DC link voltage, use the current command from the MTPA calculation for PMSM control.

[0005] According to an aspect of one or more exemplary embodiments, when the MTPV calculation determines that the PMSM voltage exceeds a specified maximum DC link voltage, the system and method are further configured to perform an MTPV calculation to determine: a current command for PMSM control that achieves the maximum torque of the PMSM for a specified maximum DC link voltage when the maximum torque of the PMSM is determined to be less than or equal to a given torque command; and a current command for PMSM control that achieves the given torque command when the maximum torque of the PMSM is determined to be greater than the given torque command.

[0006] According to one aspect of one or more exemplary embodiments, when it is determined during the MTPV calculation that the maximum torque of the PMSM is greater than the given torque command, the system and method are further configured to reduce the PMSM voltage until the maximum torque of the PMSM is substantially equal to the given torque command for a specified motor speed, and then determine a current command for PMSM control.

[0007] According to one or more embodiments, a system and method are provided, which are configured to determine a torque command limited to a maximum torque of a motor; perform a maximum torque to current ratio (MTPA) calculation using the torque command to determine a current command for motor control; perform a maximum torque to voltage ratio (MTPV) calculation that modifies the current command as needed to meet system voltage constraints; calculate a motor current value; use the current command from a torque control module for motor control when the calculated motor current value does not exceed a specified maximum motor phase current limit; and determine an updated current command for motor control based on a selected current angle when the calculated motor current value exceeds the specified maximum motor phase current limit. The selected current angle is determined using a search operation for the motor current angle, so that: if the calculated motor current exceeds the specified maximum motor phase current limit, the magnitude of the calculated motor current is fixed at the specified maximum motor phase limit, and the motor current is updated from The selected current angle is swept toward 0 until the modified torque increases and becomes equal to the torque commanded by the torque control module and the voltage is less than or equal to the specified maximum DC link voltage of the motor.

[0008] According to one aspect of one or more exemplary embodiments, the system and method are further configured to perform a search operation on the selected current angle by scanning the current angle α to obtain V dq and T e , where I is determined using the following equation dq :

[0009] I d =I m，max cosα, and

[0010] I q =I m,max sinα,

[0011] Among them I m,max is to specify the maximum motor phase current limit, and use I dq Determine V in the following equation dq and T e :

[0012] V d =RI d +ωe L q I q ,

[0013] V q =RI q +K e ω m -ω e L d I d ,

[0014]

[0015] Where R is the motor circuit resistance (ohms), L d is the d-axis inductance (henry), L q is the q-axis inductance (henry), K e is the motor voltage constant (volts / radian / second), ω m is the mechanical motor speed (r / s), ω e is the electric motor speed (radians per second), N p is the number of motor poles.

[0016] These and other advantages and features will become more apparent from the following description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the present disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0018] Figure 1 A block diagram depicting an exemplary embodiment of an EPS system according to aspects of the present disclosure;

[0019] Figure 2 depicts a block diagram of an exemplary torque control algorithm for a PMSM according to aspects of the present disclosure;

[0020] Figure 3 Depicts the operating region in a PMSM drive; and

[0021] Figure 4 The current command trajectory of the PMSM drive under MTPA operation is depicted.

[0022] Figure 5 The voltage trajectory under MTPA operation of the PMSM drive is depicted.

[0023] Figure 6 Depicted is a block diagram of an improved exemplary torque control algorithm for a PMSM according to aspects of the present disclosure.

[0024] Figure 7 Depicted is a block diagram of another improved exemplary torque control algorithm for a PMSM according to aspects of the present disclosure.

[0025] Figure 8 Depicted is a block diagram of yet another improved exemplary torque control algorithm for a PMSM according to aspects of the present disclosure. DETAILED DESCRIPTION

[0026] Reference is now made to the accompanying drawings, wherein the present disclosure will be described with reference to specific embodiments, but is not limited to the specific embodiments, it being understood that the disclosed embodiments are merely illustrative of the present disclosure, which may be embodied in various or alternative forms. The drawings are not necessarily drawn to scale; some features may be enlarged or minimized to show details of particular components. Therefore, the specific structures or functions disclosed herein are not to be construed as limiting, but merely as a representative basis for teaching those skilled in the art to employ the present disclosure in a variety of ways.

[0027] The terms "module" and "sub-module" used herein refer to one or more processing circuits (such as application specific integrated circuits (ASICs)), electronic circuits, processors (shared, dedicated or groups) and memories for executing one or more software or firmware programs, combinational logic circuits, and / or other appropriate components that provide the functionality. It is understood that the sub-modules described below can be combined and / or further divided.

[0028] PMSM torque control is achieved through current control, which usually uses current and position measurements. Among various control strategies, field-oriented control (FOC) is the most commonly used current control technique, in which all AC signals are transformed into DC signals through a reference frame transformation. Subsequently, the control system is implemented in a synchronous rotating or d / q reference frame using the transformed current feedback.

[0029] In order to achieve the best PMSM control performance with respect to torque or efficiency, the machine current and voltage must be properly controlled. Various algorithms have been developed for PMSM control to achieve better trajectory tracking accuracy, thereby improving system performance. None of these previous algorithms is used for PMSM optimal current trajectory control; however, the algorithm proposed in this paper achieves optimal PMSM control while considering both machine and / or inverter current limits and voltage limits.

[0030] The exemplary embodiments provided herein provide an advantageous and new PMSM control scheme for optimal current trajectory control within the constraints of machine current and voltage capabilities in a PMSM drive. According to the exemplary embodiments described herein, machine current and voltage limits are converted into equivalent PMSM torque limits in a PMDM drive system and implemented by modifying the online torque command according to the maximum allowable torque under the machine current and voltage constraints. The torque control scheme of the exemplary embodiment limits the machine current and voltage respectively, while also ensuring the optimal current trajectory for maximizing the PMSM torque. Therefore, the improved torque control algorithm of the exemplary embodiment prevents potential effects caused by excessive machine current or voltage in a PMSM drive system. The improved torque control algorithm of the exemplary embodiment can be applied to all electric drive systems employing PMSM and is not limited to any specific application.

[0031] This article refers to Figure 1 and Figure 2 An example EPS system and torque control algorithm for a PMSM drive are described, followed by reference to Figure 6 , 7 8 describe exemplary embodiments of an improved torque control algorithm for a PMSM drive.

[0032] Referring now to the accompanying drawings, the technical solution will be described with reference to specific embodiments, rather than limiting thereof. Figure 1 is an exemplary embodiment of an electric power steering system (EPS) 40 suitable for implementing the disclosed embodiments.

[0033] Referring now to the accompanying drawings, the technical solution will be described with reference to specific embodiments, rather than limiting thereof. Figure 1 is an exemplary embodiment of an electric power steering system (EPS) 40 suitable for implementation of the disclosed embodiments. The steering mechanism 36 is a rack and pinion type system and includes a toothed rack (not shown) within a housing 50 and a pinion (also not shown) located below a gear housing 52. As the operator inputs, the steering wheel 26 (e.g., hand wheel, etc.), shown below, is rotated, the upper steering shaft 29 is rotated, and the lower steering shaft 51 connected to the upper steering shaft 29 by a universal joint 34 rotates the pinion. The rotation of the pinion moves the rack, which moves the tie rods 38 (only one shown), which in turn moves the steering knuckles 39 (only one shown), which rotate the steerable wheels 44 (only one shown).

[0034] The electric power steering assistance is provided by a control device generally indicated by reference numeral 24 and includes a controller 16 and an electric machine 46, which may be a permanent magnet synchronous motor (PMSM), hereinafter indicated as motor 46. The controller 16 is powered by a vehicle power supply 10 via line 12. The controller 16 receives a vehicle speed signal 14 representing the vehicle speed from a vehicle speed sensor 17. The steering angle is measured by a position sensor 32, which may be an optically encoded sensor, a variable resistor sensor, or any other suitable type of position sensor, and supplies a position signal 20 to the controller 16. The motor speed may be measured using a tachometer or any other device and transmitted to the controller 16 as a motor speed signal 21. The speed may be measured, calculated, or measured and calculated, indicated as ω m For example, the motor speed ω m can be calculated as the change in motor position θ measured by the position sensor 32 over a specified time interval. For example, it can be calculated by the equation ω m =Δθ / ΔtThe motor speed ω m is determined as the derivative of the motor position θ, where Δt is the sampling time and Δθ is the change in position during the sampling interval. Alternatively, the motor speed can be derived from the motor position as the time rate of change of position. It should be appreciated that there are many well-known methods for performing a derivative.

[0035] When the steering wheel 26 is turned, the torque sensor 28 senses the torque applied to the steering wheel 26 by the vehicle operator. The torque sensor 28 may include a torsion bar (not shown) and a variable resistor type sensor (also not shown), and the torque sensor 28 outputs a variable torque signal 18 related to the amount of twist on the torsion bar to the controller 16. Although the sensor 28 is a torque sensor, any other suitable torque sensing device using known signal processing techniques will suffice. In response to various inputs, the controller sends a command 22 to the electric motor 46, which provides torque assistance to the steering system through the worm 47 and the worm gear 48, thereby providing torque assistance to the vehicle steering.

[0036] It should be noted that although the disclosed embodiments are described by reference to motor control for electric power steering applications, it should be understood that these references are illustrative only and the disclosed embodiments may be applied to any motor control application employing an electric motor, such as steering, valve control, etc. In addition, the references and descriptions herein may be applicable to many forms of parameter sensors, including but not limited to torque, position, speed, etc. It should also be noted that references herein to electric machines include but are not limited to motors, and for the sake of brevity and simplicity, reference will be made only to motors without limitation.

[0037] In the depicted control system 24, the controller 16 uses torque, position, speed, etc. to calculate a command for delivering the required output power. The controller 16 is configured to communicate with various systems and sensors of the motor control system. The controller 16 receives signals from each system sensor, quantifies the received information, and provides an output command signal in response thereto, in this example, for example, to the motor 46. The controller 16 is configured to generate a corresponding voltage from an inverter (not shown, which can be optionally incorporated into the controller 16 and referred to as the controller 16 herein) so that when the voltage is applied to the motor 46, the desired torque or position is generated. In one or more examples, the controller 24 operates in a feedback control mode (as a current regulator) to generate the command 22. Alternatively, in one or more examples, the controller 24 operates in a feedforward control mode to generate the command 22. Since these voltages are related to the position and speed of the motor 46 and the desired torque, the position and / or speed of the rotor and the torque applied by the operator are determined. The position encoder is connected to the steering shaft 51 to detect the angular position θ. The encoder can sense the rotational position based on optical detection, magnetic field changes, or other methods. Typical position sensors include potentiometers, resolvers, synchronizers, encoders, etc., and combinations comprising at least one of the foregoing. The position encoder outputs a position signal 20 indicative of the angular position of the steering shaft 51 (and thereby the angular position of the motor 46).

[0038] The desired torque may be determined by one or more torque sensors 28 transmitting a torque signal 18 indicative of the applied torque. One or more exemplary embodiments include such a torque sensor 28, and the torque signal 18 therefrom, may be responsive to a flexible torsion bar, T-bar, spring, or similar device (not shown) configured to provide a response indicative of the applied torque.

[0039] In one or more examples, the temperature sensor 23 is located at the motor 46. Preferably, the temperature sensor 23 is configured to directly measure the temperature of the sensing portion of the motor 46. The temperature sensor 23 transmits a temperature signal 25 to the controller 16 for processing and compensation as specified herein. Typical temperature sensors include thermocouples, thermistors, thermostats, etc., and combinations including at least one of the foregoing sensors, which provide a calibratable signal proportional to a specific temperature when properly placed.

[0040] Position signal 20, speed signal 21 and torque signal 18 are applied to controller 16. Controller 16 processes all input signals to generate values ​​corresponding to each signal, and obtains rotor position value, motor speed value and torque value that can be used for processing in the algorithm specified in this article. Typically, linearization, compensation and filtering are also performed on the measurement signals such as those described above as desired to enhance the characteristics or eliminate undesirable characteristics of the acquired signals. For example, the signal can be linearized to increase the processing speed, or to solve the large dynamic range of the signal. In addition, frequency-based or time-based compensation and filtering can be used to eliminate noise or avoid undesirable spectral characteristics.

[0041] In order to perform the specified functions and the desired processing and calculation thereof (e.g., identification of motor parameters, control algorithms, etc.), the controller 16 may include, but is not limited to, a processor, a computer, a digital signal processing (DSP), a memory, a storage device, a register, a timing, an interrupt, a communication interface, and an input / output signal interface, etc., and a combination including at least one of the foregoing. For example, the controller 16 may include input signal processing and filtering to achieve accurate sampling and conversion or acquisition of such signals from the communication interface. Additional features of the controller 16 and certain processing therein are discussed in detail later herein.

[0042] In one or more examples, the technical solution described herein facilitates power management of the electric drive portion (i.e., the motor control system) of the EPS system. It should be noted that although the technical solution is described herein using an embodiment of an electric power steering system, the technical solution can be applied to any other motor control system used in any other PMSM.

[0043] Figure 2 1 depicts a block diagram of an example torque control algorithm 170 for a PMSM. The block diagram depicts a motor control system 100 in which for a given DC link voltage V derived from the battery 110 DC and motor (mechanical) speed ω m , calculate the maximum torque T e,max , which is then combined with the given torque command by the torque limit module 120 Comparison is made to generate a final torque command within the system capacity Will Sent to the maximum torque to current ratio (MTPA) module 130 to calculate the current command and and is sent to the maximum torque to voltage ratio (MTPV) module 140 to check the corresponding PMSM voltage v m Whether it exceeds the DC link voltage V DC The maximum feasible value constrained If the PMSM voltage vm Not exceeding v m =V m,max , the current command calculated by the MTPA module 130 is used as the final command for PMSM control and Otherwise, a different command is generated by the MTPV block 140 and to meet the PMSM voltage constraints. Thus, the motor control system 100 facilitates motor torque control and motor current control. Subsequently, the final current command is sent to the current regulator 150 of the PMSM 160. The current regulator ensures current tracking and thus torque tracking. Here, "tracking" refers to the closeness of the output current (or torque) to the desired current (or torque) requested by the current command (torque command).

[0044] According to an exemplary embodiment, an improved torque control algorithm for a PMSM drive is provided that actively performs machine current and voltage management. Figure 3 The various operating modes of the PMSM drive system depicted can facilitate the development of the algorithm. There are two main operating regions (i.e., MTPA and MTPV) in the PMSM drive system. Figure 3 The current commands in these two different regions are generated using MTPA and MTPV techniques or operations to achieve the best current command trajectory and thus achieve the best motor control. Essentially, the MTPA operation is used to determine the dq current command and Generates torque command with minimum machine current The MTPV operation determines the current command in the voltage saturation region (i.e., when the voltage command magnitude is equal to the DC link voltage) such that the current command produces a torque as close as possible to the requested torque command to ensure an optimal current trajectory. Both MTPA and MTPV techniques or operations utilize estimates of machine and inverter parameters (which involves a machine model that takes into account nonlinearities) to determine the current command online.

[0045] In addition to regions I and III, there is a transition region between them (in Figure 3 In the figure, it is represented as region II), where And v m =V m,max In this region, field weakening is performed to keep the machine voltage at V m,max while keeping the final torque command the same as the original torque command.

[0046] Machine current and voltage management are critical in PMSM drives and must be considered in the control system to ensure that the machine operates under optimal operating conditions. First, it must be ensured that the voltage of a given PMSM system is within the voltage capacity to avoid failure of the control algorithm. In addition, the machine current must be kept below a certain maximum limit. This is because the machine current affects the power loss and heat dissipation inside the machine and is directly related to the inverter design that must be able to carry the maximum machine current. If the machine current is higher than the device rated power, the inverter may fail. Therefore, the machine current must be carefully managed within the device rated current to avoid inverter failure and thus improve system reliability. In addition, well-controlled machine current can reduce the requirements for device ratings during the inverter design process, which helps in hardware circuit design with reduced cost components.

[0047] Prior art mainly considers optimal current trajectory control so that torque or efficiency can be maximized. However, prior art does not consider the maximum machine current. In order to prevent potential problems caused by high machine current, a PMSM control scheme with maximum machine current limit and optimal current trajectory control is desired to enhance system design while ensuring maximum torque or efficiency in a PMSM drive.

[0048] The PMSM control scheme described herein according to an exemplary embodiment ensures machine current and voltage limit targets, has the ability to ensure maximum torque or efficiency, is easy to implement online, and has good accuracy over the entire operating range of the machine. In order to actively limit the machine current, a PMSM operating trajectory analysis must be performed, such as Figure 3 shown.

[0049] There are two main working areas (MTPA and MTPV) in the PMSM drive system. Figure 3 In the figure, they are represented as region I and region III respectively. The current commands in these two different regions are generated using MTPA and MTPV techniques respectively to achieve the best current trajectory and thus the best motor control. Essentially, MTPA technology is used to determine the dq current command and Generates torque command with minimum machine current The MTPV technique determines the current command in the voltage saturation region (i.e., when the voltage command amplitude is equal to the DC link voltage or when the machine impedance is limited) so that the current command generates a torque as close as possible to the requested torque command. Both techniques use parameter estimation results and a machine model that takes nonlinearity into account to determine the current command online. In addition to regions I and III, there is also a transition region between them (in Figure 3 In the figure, it is represented as region II), where And v m =V m,maxIn this region, field weakening is performed to keep the machine voltage at V m,max while keeping the final torque command the same as the original torque command.

[0050] exist Figure 4 The MTPA trajectory of PMSM is shown in Fig. 2. As can be seen from the figure, for a given torque command (e.g. T e =0.2pu), there are many dq currents i that meet the torque requirements d and i q However, there is a final machine current i m The minimum point is the MTPA operation point under the torque command. Connecting all MTPA operation points under various torque commands obtains a continuous MTPA trajectory. MTPA operation is very desirable in PMSM drive systems because it tracks the torque command while maintaining the minimum machine current, minimizing machine losses. However, as the MTPA trajectory is extended, the DC link voltage V m,max The fact that the voltage capacity is determined (such as Figure 5 As shown in Figure 2), MTPA operation eventually becomes infeasible. Given a torque command or motor speed ω m An increase in will contribute to higher PMSM voltages and accelerate the approach to the voltage capability curve. After the MTPA operating region and before the MTPV operation, there may be an area where field weakening is performed and a given torque requirement can still be met. Once the PMSM enters its MTPV operating region, the torque command can no longer be tracked. Instead, the maximum possible torque T within the PMSM voltage capability can be used. e,max to ensure the best current trajectory. Figure 3 Waveforms in notable PMSM drives are given to illustrate the different operating regions.

[0051] If the machine current limit I m,max is considered as a PMSM control constraint in the existing torque control algorithm 170, and the torque command must be modified accordingly. This poses a challenge because the maximum allowable torque to prevent the machine current from exceeding its limit is unknown, and it is difficult to analytically solve the maximum allowable torque to maintain the optimal current trajectory due to the complexity of MTPA and MTPV technologies. Exemplary embodiments provide a technical solution to this problem. In order to solve this problem, an improved torque control algorithm (e.g., referring to Figure 6 , 7The example algorithms 170', 170" and 180 described in and 8 implement a maximum torque search based approach that takes into account the maximum machine current, avoiding the analytical complexity of the maximum torque calculation given the machine current limit. For example, the improved torque control algorithm of the illustrative embodiment can be executed by a processing device such as controller 16.

[0052] Figure 6 1 shows a flow chart of a PMSM control scheme including an improved torque control algorithm 170' that takes into account current and voltage capabilities. The improved torque control algorithm 170' that takes into account current and voltage capabilities is implemented by modifying the current command calculation process of the existing torque control algorithm 170. Specifically, an additional constraint of the machine current limit is added to the torque search operation 120' to find the maximum torque within the system capacity, which simultaneously ensures that the machine current is within the limit I m,max The maximum torque is then sent to the MTPA operation 130 and the MTPV operation 140' to calculate the current command for optimal current trajectory tracking and

[0053] Continue to refer to Figure 6 The improved torque control algorithm 170' performs the torque limiting operation 120' to determine the torque command It is limited to the maximum DC link voltage specified for V m,max The maximum torque T of PMSM e,max within the specified PMSM current value I m,max The improved torque control algorithm 170' also uses the torque command MTPA operation (130) is performed to determine the current command for PMSM control and

[0054] To calculate T e,max The mathematical equation is as follows:

[0055] V d =RI d +ω e L q I q (1)

[0056] V q =RI q +K e ω m -ω e L d I d (2)

[0057]

[0058]

[0059]

[0060] Equation (1) and Equation (2) are the motor voltage equations. Equation (3) is the torque equation. Equation (4) is the voltage constraint. Equation (5) is the motor phase current constraint. Figure 6 The objective of the optimization implemented by the exemplary embodiment of is to maximize the torque in equation (3) while satisfying the constraints of voltage and motor current. Note that in these equations, R is the motor resistance (ohms), L is d is the d-axis inductance (henry), L q is the q-axis inductance (henry), K e is the motor voltage constant (volts / radian / second), ω m is the mechanical motor speed (radians per second), ω e is the speed of the electric motor (radians per second), N p is the number of magnetic poles of the motor 160 .

[0061] Further references Figure 6 The improved torque control algorithm 170' performs an MTPV operation (140') that determines whether the PMSM voltage exceeds a specified maximum DC link voltage of the system (block 142), and when the PMSM voltage v m does not exceed the specified maximum DC link voltage V m,max When the current command from the MTPA calculation is and For PMSM control (block 143). When the MTPV calculation 140' determines the PMSM voltage v m exceeds the specified maximum DC link voltage V m,max (block 142), the improved torque control algorithm 170' is further configured to determine the maximum torque T of the PMSM e,max Is it less than or equal to the given torque command? (Block 144). When determining the maximum torque T of the PMSM for a specified maximum DC link voltage e,max When the given torque command is less than or equal to the given torque command, the MTPV calculation 140 ′ determines a current command for PMSM control that achieves the maximum torque T of the PMSM for the specified maximum DC link voltage. e,max (Block 145). When the maximum torque T of the PMSM e,max Exceeds the given torque command When , the MTPV calculation 140 ′ determines the following current command for PMSM control: This current command achieves a given torque command (Box 148).

[0062] Figure 6 The improved torque control algorithm 170' in can achieve optimal torque control in the PMSM drive. Figure 3 Some operating points in region II of the PMSM operation (i.e. when V m,max The maximum torque is higher than that with field weakening. The non-optimal operation of the PMSM drive is due to the fact that the machine voltage is not used optimally. Therefore, optimization can be performed to achieve better machine voltage utilization, such as Figure 7 The operation of the improved torque control algorithm 170" for better voltage utilization is similar to that of Figure 6 The operations described in the improved torque control algorithm 170' are the same as those described in the improved torque control algorithm 170', except that the modified MTPV algorithm 140" determines the maximum torque T of the PMSM. e,max Exceeds the given torque command (Block 144) Another step (Block 146) is added to the operation (Block 149) performed afterwards.

[0063] In fact, the maximum torque T of the PMSM is determined in the MTPV operation 140” e,max Exceeds the given torque command (Block 144) Thereafter, the machine voltage V may be controlled by manually adding the voltage limit to the algorithm 170" (Block 146) m,max The voltage limit value may be a specified parameter value in the program code implementing the algorithm 170 ″, or may be determined empirically or iteratively. The algorithm 170 ″ reduces the PMSM voltage V m,max , until the maximum torque T of PMSM e,max Basically equal to the given torque command for a specified motor speed By reducing V according to block 146 m,max And make better use of V m,max , so that V m,max The maximum torque under field weakening is equal to The machine current can be kept to a minimum, which is advantageous in a PMSM drive as described above.

[0064] Since the machine 160 and the inverter 150 can be designed to carry the machine current under most operating conditions (i.e., all operating conditions without machine and inverter design optimization through machine current limitation), the machine current without any limitation will not cause damage to the machine 160 and the inverter 150 in the PMSM drive system most of the time except for the narrow transition region under large torque command after the MTPA region. Thus, according to another exemplary embodiment, an improved torque control algorithm 180 is provided, which adopts Figure 8 The current commands shown are modified after the command generation.

[0065] like Figure 8 As shown, the improved torque control algorithm 180 adopts the same Figure 2 The improved torque control algorithm 180 is implemented by first calculating the machine current i at the output of the existing torque control algorithm 170. m (Block 182) to implement machine current limiting. If the machine current i m No more than I m,max (Block 184), the improved torque control algorithm 180 uses the current command from the torque control algorithm 170 for motor control (Block 186). m More than I m,max (Block 184), the improved torque control algorithm 180 determines an updated current command for motor control based on the selected current angle, such as Figure 8 As shown in blocks 190, 192 and 194 in FIG. m Exceeding limit I m,max , the magnitude of the current is fixed at the limit value (block 190), and the angle α is changed from Sweep gradually toward 0 (block 192) until the modified torque increases and becomes equal to the commanded torque and the voltage is less than or equal to the maximum voltage V m,max This search is performed because if the current is limited only to the maximum limit I m,max If the angle α is unchanged, it may result in a significantly reduced modified torque even if the voltage constraint is still satisfied. (where only the d-axis current is non-zero and the q-axis current is zero (ie, the torque is zero)) changes towards zero because the maximum torque output lies at an angle between these two extremes.

[0066] The search operation for the selected current angle (block 192) includes scanning the current angle α to obtain V dq and T e , where I is determined using the following equation dq :

[0067] Id =I m，max cosα

[0068] I q =I m,max sinα

[0069] Among them I m,max is the specified maximum motor phase current limit and is calculated using the following equation using I dq Determine V dq and T e :

[0070] V d =RI d +ω e L q I q ,

[0071] V q =RI q +K e ω m -ω e L d I d ,

[0072]

[0073] Where R is the motor circuit resistance (ohms), L d is the d-axis inductance (henry), L q is the q-axis inductance (henry), K e is the motor voltage constant (volts / radian / second), ω m is the mechanical motor speed (radians per second), ω e is the electric motor speed (radians per second), N p is the number of motor poles.

[0074] In the improved torque control algorithm 180 (which provides i after the existing torque control algorithm 170 m In the limiting module 180), if the PMSM current limit is not exceeded, the original current command from the existing torque control algorithm 170 is and will be passed directly to the current regulator 150 most of the time. m Higher than I m,max In the case of a large torque command in a specific area, further calculations are performed to generate new and (e.g., blocks 190, 192, and 194) such that the PMSM current and voltage limits are not exceeded. Figure 6The illustrated technical solution 170 is the same, but can potentially save computing resources.

[0075] exist Figure 6 , 7 Each of the exemplary technical solutions given in the exemplary embodiments of 8 can give the expected results regarding the optimal current trajectory tracking considering the machine current and voltage capacity. m Higher than I m,max situation, Figure 6 , 7 The exemplary technical solutions given in the exemplary embodiments of 8 can generate new and This ensures that the PMSM current and voltage limits are not exceeded.

[0076] Machine current limiting is necessary in electric drives to help protect the motor, inverter, and other components of the electric drive system. Although existing techniques are available for motor current management, these existing techniques have disadvantages. For example, an offline calibration can be performed; however, the calibrated current limit is generally too conservative. Moreover, offline calibration must be performed for different motors, which is time consuming. In addition, due to the offline nature of these techniques, the current and torque commands are not optimal because the dynamically changing operating conditions of the PMSM 160 are not taken into account. On the other hand, while dynamic techniques that iteratively modify the motor torque command are more accurate, they are computationally complex to implement.

[0077] For many reasons, Figure 6 , 7 The exemplary embodiments of the present invention provide a technical solution for motor current management that is superior to the previous current limiting techniques. For example, the exemplary embodiments are computationally efficient solutions because the additional motor current constraints (e.g., Figure 2 The torque control algorithm 170 and Figures 3 to 5 PMSM working area or mode and trajectory analysis in ). In addition, Figures 6 to 8 Several exemplary embodiments of provide a convenient tradeoff between accuracy and complexity. Figures 6 to 8 The exemplary embodiment of the invention takes into account the dynamic changes of the operating conditions through the online limiting capability, and is able to dynamically limit the maximum motor current, applicable to all permanent magnet synchronous machines under all conditions.

[0078] This article describes various aspects of the technical solution with reference to the flowcharts and / or block diagrams of the methods, devices (systems) and computer program products according to the embodiments of the technical solution. It should be understood that each frame of the flowchart and / or block diagram and the combination of frames in the flowchart and / or block diagram can be implemented by computer-readable program instructions.

[0079] The flowcharts and block diagrams in the accompanying drawings illustrate the possible implementation architecture, functions and operations of the system, method and computer program product according to various embodiments of the present technical solution. In this regard, each frame in the flowchart or block diagram may represent a part of a module, segment or instruction, which includes one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions recorded in the frame may not occur in the order shown in the figure. For example, in fact, the two frames shown in succession can be executed substantially simultaneously, or sometimes these frames can be executed in reverse order, depending on the functions involved. It will also be noted that each frame of the block diagram and / or flowchart and the combination of frames in the block diagram and / or flowchart can be implemented by a dedicated hardware-based system that performs a specified function or action, or implements a combination of dedicated hardware and computer instructions.

[0080] It will also be understood that any module, unit, component, server, computer, terminal or device of the present example of execution instruction may include or otherwise access computer readable media, such as storage media, computer storage media or (removable and / or non-removable) data storage devices, such as disks, optical disks or tapes. Computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information such as computer readable instructions, data structures, program modules or other data. Such computer storage media may be part of the device or accessible or connectable thereto. Any application or module described herein may be implemented using computer readable / executable instructions that may be stored or otherwise maintained by such computer readable media.

[0081] Although the present disclosure has been described in detail in conjunction with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to these disclosed embodiments. On the contrary, the present disclosure may be modified to include any number of changes, alterations, substitutions, or equivalent arrangements that have not been described so far but are commensurate with the scope of the present disclosure. In addition, although various embodiments of the present disclosure have been described, it should be understood that aspects of the present disclosure may include only some of the described embodiments. Therefore, the present disclosure is not considered to be limited by the foregoing description.

Claims

1. A motor system, comprising: Permanent magnet synchronous motor PMSM; as well as A motor control system configured to limit machine current, the motor control system configured to: determining a torque command that is limited to a maximum torque of the PMSM for a specified maximum DC link voltage and does not exceed a specified maximum PMSM current limit; performing a maximum torque to current ratio MTPA calculation using the torque command to determine a current command for PMSM control; Calculate the motor current value; using the current command when the calculated motor current value does not exceed a specified maximum motor phase current limit; as well as determining an updated current command for motor control based on the selected current angle when the calculated motor current value exceeds the specified maximum motor phase current limit; wherein the selected current angle is determined using a motor current angle search operation such that: if the calculated motor current exceeds the specified maximum motor phase current limit, the magnitude of the calculated motor current is fixed at the specified maximum motor phase current limit, and The selected current angle is swept toward zero until the modified torque increases and becomes equal to the torque commanded by the motor control system and the voltage is less than or equal to the specified maximum DC link voltage of the motor.

2. The motor system according to claim 1, wherein: The motor control system is further configured to: determining whether the PMSM voltage exceeds a specified maximum DC link voltage of the system; and When the PMSM voltage does not exceed the specified maximum DC link voltage, the current command from the MTPA calculation is used for PMSM control.

3. The motor system according to claim 2, wherein: When the motor control system determines that the PMSM voltage exceeds the specified maximum DC link voltage, the motor control system is further configured to perform a maximum torque to voltage ratio MTPV calculation to determine a current command for PMSM control as follows: When the maximum torque of the PMSM is determined to be less than or equal to a given torque command, determining a current command for PMSM control that achieves the maximum torque of the PMSM for a specified maximum DC link voltage; and When the maximum torque of the PMSM is determined to be greater than a given torque command, a current command for PMSM control is determined as follows: the current command achieves the given torque command.

4. The motor system according to claim 3, wherein: When it is determined during the MTPV calculation that the maximum torque of the PMSM is greater than the given torque command, the motor control system is further configured to reduce the PMSM voltage until the maximum torque of the PMSM is substantially equal to the given torque command for a specified motor speed, and then determine a current command for PMSM control.

5. A motor control system configured to limit supply current and regeneration current, the motor control system comprising: The torque control module is configured as follows: determining a torque command limited to a maximum torque of the motor; performing a maximum torque to current ratio MTPA calculation using the torque command to determine a current command for motor control; as well as performing a maximum torque to voltage (MTPV) calculation that modifies the current command as needed to meet system voltage constraints; and The motor current limit module is configured as: Calculate the motor current value; using a current command from the torque control module for motor control when the calculated motor current value does not exceed a specified maximum motor phase current limit; as well as determining an updated current command for motor control based on the selected current angle when the calculated motor current value exceeds a specified maximum motor phase current limit; wherein the selected current angle is determined using a motor current angle search operation such that: if the calculated motor current exceeds a specified maximum motor phase current limit, the magnitude of the calculated motor current is fixed at the specified maximum motor phase current limit, and The selected current angle is swept toward zero until the modified torque increases and becomes equal to the torque commanded by the torque control module and the voltage is less than or equal to a specified maximum DC link voltage of the motor.

6. The motor control system according to claim 5, wherein: The selected current angle search operation includes scanning the current angle α to obtain V d 、V q and T e ,in Use the following equation to determine I d and I q : I d =I m，max cos α, sum I q =I m,max sinα, Among them I m,max is the specified maximum motor phase current limit, and Use I d and I q Determine V in the following equation d 、V q and T e : V d =RI d +ω e L q I q , V q =RI q +K e ω m -ω e L d I d , Where R is the motor circuit resistance in ohms; L d is the d-axis inductance in Henry; L q is the q-axis inductance in Henry; K e is the motor voltage constant in volts / radian / second; ω m is the mechanical motor speed in radians per second; ω e is the electric motor speed in radians per second; N p is the number of motor poles; V d is the d-axis voltage; V q is the q-axis voltage; I d is the d-axis current; I q is the q-axis current; T e is the torque.

7. A method for limiting machine current and voltage in a motor control system, comprising: determining a torque command that is limited to a maximum torque of the permanent magnet synchronous motor (PMSM) for a specified maximum DC link voltage and does not exceed a specified maximum PMSM current limit; performing a maximum torque to current ratio MTPA calculation using the torque command to determine a current command for PMSM control; Calculate the motor current value; using the current command when the calculated motor current value does not exceed a specified maximum motor phase current limit; as well as determining an updated current command for motor control based on the selected current angle when the calculated motor current value exceeds the specified maximum motor phase current limit; wherein the selected current angle is determined using a motor current angle search operation such that: if the calculated motor current exceeds the specified maximum motor phase current limit, the magnitude of the calculated motor current is fixed at the specified maximum motor phase current limit, and The selected current angle is swept toward zero until the modified torque increases and becomes equal to the torque commanded in the torque command and the voltage is less than or equal to the specified maximum DC link voltage of the motor.

8. The method according to claim 7, wherein: The motor control system is further configured to: determining whether the PMSM voltage exceeds a specified maximum DC link voltage of the system; and When the PMSM voltage does not exceed the specified maximum DC link voltage, the current command from the MTPA calculation is used for PMSM control.

9. The method according to claim 7, wherein: When the motor control system determines that the PMSM voltage exceeds the specified maximum DC link voltage, the motor control system is further configured to perform a maximum torque to voltage ratio MTPV calculation to determine a current command for PMSM control as follows: When the maximum torque of the PMSM is determined to be less than or equal to a given torque command, determining a current command for PMSM control that achieves the maximum torque of the PMSM for a specified maximum DC link voltage; and When the maximum torque of the PMSM is determined to be greater than a given torque command, a current command for PMSM control is determined as follows: the current command achieves the given torque command.

10. The method according to claim 9, wherein: When it is determined during the MTPV calculation that the maximum torque of the PMSM is greater than the given torque command, the motor control system is further configured to reduce the PMSM voltage until the maximum torque of the PMSM is substantially equal to the given torque command for a specified motor speed, and then determine a current command for PMSM control.

11. A method for limiting supply current and regeneration current, comprising: determining a torque command limited to a maximum torque of the motor; performing a maximum torque to current ratio MTPA calculation using the torque command to determine a current command for motor control; as well as performing a maximum torque to voltage ratio MTPV calculation, the MTPV calculation modifying the current command as needed to meet system voltage constraints; Calculate the motor current value; using the current command for motor control when the calculated motor current value does not exceed a specified maximum motor phase current limit; as well as determining an updated current command for motor control based on the selected current angle when the calculated motor current value exceeds a specified maximum motor phase current limit; wherein the selected current angle is determined using a motor current angle search operation such that: if the calculated motor current exceeds a specified maximum motor phase current limit, the magnitude of the calculated motor current is fixed at the specified maximum motor phase limit, and The selected current angle is swept toward zero until the modified torque increases and becomes equal to the torque command and the voltage is less than or equal to a specified maximum DC link voltage of the motor.

12. The method according to claim 11, wherein: The search operation for the selected current angle includes scanning the current angle α to obtain V d 、V q and T e ,in Use the following equation to determine I d and I q : I d =I m，max cos α, sum I q =I m,max sinα, Among them I m,max is the specified maximum motor phase current limit, and Use I in the following equation d and I q Determine V d 、V q and T e : V d =RI d +ω e L q I q , V q =RI q +K e ω m -ω e L d I d , Where R is the motor circuit resistance in ohms; L d is the d-axis inductance in Henry; L q is the q-axis inductance in Henry; K e is the motor voltage constant in volts / radian / second; ω m is the mechanical motor speed in radians per second; ω e is the electric motor speed in radians per second; N p is the number of motor poles; V d is the d-axis voltage; V q is the q-axis voltage; I d is the d-axis current; I q is the q-axis current; T e is the torque.

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