System and method for coupling to variable dc bus voltage of an inverter

Abstract

A voltage command estimator is configured to estimate a minimum required variable DC bus voltage based on a first direct-axis current / voltage command, a first quadrature-axis current / voltage command, a second direct-axis current / voltage command, and a second quadrature-axis current / voltage command within a corresponding time interval. The voltage command estimator is configured to provide the estimated minimum required variable DC bus voltage to a voltage regulator to adjust the observed voltage level of the variable DC bus to the estimated minimum required variable DC bus voltage, thereby maintaining the operation of the first motor under the first variable load and the second motor under the second variable load at the time interval, as commanded by the voltage / current command.

Description

Technical Field

[0001] This disclosure relates to a system and method for connecting a variable DC bus voltage to an inverter.

[0002] Related applications

[0003] This application claims the filing date and priority of U.S. Provisional Application No. 62 / 861,792, filed on June 14, 2019, which is incorporated herein by reference in its entirety. Background Technology

[0004] In some existing vehicle systems, the DC bus voltage is fixed at a level that determines the available AC output of the inverter to power an electric motor or other load. If the DC bus voltage level is designed to be higher than the required level, the capacitors connected to the DC bus and the inverter switches may experience increased thermal stress; thus, their lifespan is reduced. Therefore, there is a need for a system and method for a variable DC bus voltage connected to an inverter, wherein the system and method are well-suited to reducing the thermal stress on the DC bus capacitors or the switches within one or more inverters. Summary of the Invention

[0005] According to one embodiment, a method and system are configured to control a first inverter and a second inverter coupled to a variable DC voltage bus. The inverter inputs of the first and second inverters are coupled to the variable DC voltage bus, and the inverter outputs are connected to a first variable load and a second variable load. A sensor (e.g., a voltage sensor) measures the observed voltage level of the variable DC voltage bus at time intervals. In the first inverter, a first electronic data processor is configured to determine a first torque command and / or a first speed command, including a first direct-axis current / voltage command and a first quadrature-axis current / voltage command, based on the first variable load of the first motor machine. In the second inverter, a second electronic data processor is configured to determine a second torque command and / or a second speed command, including a second direct-axis current / voltage command and a second quadrature-axis current / voltage command, based on the second variable load of the second motor machine.

[0006] A voltage command estimator is configured to estimate a minimum required (e.g., target) variable DC bus voltage based on a first direct-axis current / voltage command, a first quadrature-axis current / voltage command, a second direct-axis current / voltage command, and a second quadrature-axis current / voltage command within a corresponding time interval. The voltage command estimator is configured to provide the estimated minimum required variable DC bus voltage (e.g., the command estimator determines the larger of the variable DC bus voltage required for a first variable load on the first machine or a second variable load on the second machine) to a voltage regulator to adjust the observed voltage level of the variable DC bus to the estimated minimum required (e.g., target) variable DC bus voltage to maintain the operation of the first motor under the first variable load and the second motor under the second variable load at the time interval, as commanded by the voltage / current command. Attached Figure Description

[0007] Figure 1 It is a block diagram of an embodiment of a first electric motor connected to a first inverter powered by a variable DC bus, a second electric motor connected to a second inverter powered by a variable DC bus, and a voltage regulator for adjusting the voltage level of the variable DC bus based on command data from a command estimator.

[0008] Figure 2 It is a graph illustrating a schematic example of the required DC bus voltage versus time under assumed transient loads for a first variable load and a second variable load (minimum estimated target or).

[0009] Figure 3 This is a schematic diagram illustrating the switches of a first inverter and a second inverter, which are fed by a variable DC bus with capacitors to reduce ripple current on the variable DC bus.

[0010] Figure 4 It is a graph illustrating the reduction in the root mean square (RMS) current of the DC bus through a capacitor, which filters out some unwanted ripple current or AC signal components on the variable DC bus compared to a comparable fixed DC bus.

[0011] Figure 5 It is a graph showing the switching energy versus time for an inverter switch for a fixed DC bus to a variable DC bus, the variable DC bus satisfying the minimum estimated target DC voltage level required by the variable DC bus based on load conditions (e.g., transient load conditions on an inverter-driven motor machine).

[0012] Figure 6It is a block diagram of another embodiment of a first motor connected to a first inverter powered by a variable DC bus, a second motor connected to a second inverter powered by a variable DC bus, and a voltage regulator for adjusting the voltage level of the variable DC bus based on command data from a command estimator having configurable filtering, slew-rate, and margin.

[0013] Figure 7 This is a flowchart of one embodiment of a method for providing a regulator with an estimated minimum required (e.g., target) variable DC bus voltage.

[0014] Figure 8 This is a flowchart of another embodiment of a method for providing a regulator with an estimated minimum required (e.g., target) variable DC bus voltage. Detailed Implementation

[0015] Figure 1 This is a block diagram of one embodiment of a system 11 for connecting to a variable DC bus voltage of an inverter. Figure 1 In this configuration, a first electric machine 12 is connected to a first inverter 14 powered by a variable DC bus (e.g., observable at DC bus terminal 30). A second electric machine 112 is connected to a second inverter 114 powered by a variable DC bus. In one embodiment, a voltage regulator 34 is connected to DC bus terminal 30. The voltage regulator 34 is configured to operate based on a command estimator 36 (e.g., V...). DC (Voltage command estimator) to adjust the voltage level of the variable DC bus.

[0016] According to one embodiment, the method and system 11 are configured to control a first inverter 14 and a second inverter 114 connected to a variable DC voltage bus or DC bus terminal 30. The inverter inputs of the first inverter 14 and the second inverter 114 are connected to a variable DC voltage bus at DC bus terminal 30, and the inverter outputs are connected to a first variable load (e.g., a first electric machine 12) and a second variable load (e.g., a second electric machine 112). A sensor 32 (e.g., a voltage sensor) measures the observed voltage level of the variable DC voltage bus at DC bus terminal 30 at time intervals. In the first inverter 14, a first electronic data processor 24 is configured to determine a first torque command and / or a first speed command, including a first direct-axis current / voltage command and a first quadrature-axis current / voltage command, based on the first variable load of the first electric machine 12. In the second inverter 114, the first electronic data processor 124 is configured to determine a second torque command and / or a second speed command, including a second direct-axis current / voltage command and a second quadrature-axis current / voltage command, based on the second variable load of the second electric machine 112.

[0017] In one configuration, the first inverter 14 operates to control the first electric machine 12 in one or more of the following modes: voltage control mode, torque control mode, sensorless position mode, phase shift control mode, triangular waveform control mode, trapezoidal waveform control mode, or space vector pulse width modulation control mode. For example, in an illustrated configuration, the first inverter 14 operates or controls the first electric machine 12 in voltage control mode, while the second inverter 114 operates or controls the second electric machine 112 in torque control mode.

[0018] Sensorless position mode means that the electric motor is not associated with an encoder, resolver, or magnetic field sensor, or with a magnet embedded in the rotor shaft of the electric motor to estimate the rotor position, rotor speed, or torque. Instead, the machine state estimator and control modules (16, 116) detect or estimate (e.g., based on signal feedback from the phase output) the rotor position, rotor speed, and / or torque of the electric machine or electric motor (12, 112).

[0019] However, in alternative embodiments, the electric motor or electric machine may be associated with an encoder, a resolver, a magnetic field sensor and a magnet embedded in the rotor shaft of the electric motor or another machine sensor for detecting or estimating the rotor position, rotor speed or torque of the electric machine, wherein the output of the machine sensor is connected to a corresponding inverter or machine state estimator and control module (16, 116).

[0020] The voltage command estimator 36 is configured to estimate a minimum required variable DC bus voltage based on a first direct-axis current / voltage command, a first quadrature-axis current / voltage command, a second direct-axis current / voltage command, and a second quadrature-axis current / voltage command within a corresponding time interval. The voltage command estimator 36 is configured to provide the estimated minimum required variable DC bus voltage (e.g., the command estimator determines the larger of the variable DC bus voltage required for a first variable load on the first machine or a second variable load on the second machine) to the voltage regulator 34 to adjust the observed voltage level of the variable DC bus to the estimated minimum required variable DC bus voltage to maintain the operation of the first motor 12 under the first variable load and the second motor 112 under the second variable load at the time interval, as commanded by the voltage / current command.

[0021] In one embodiment, the first module 10 includes a first inverter 14 coupled to the first electric machine 12. The first inverter 14 can be controlled to operate in a primary control mode (e.g., voltage control mode) and a generation mode of the first electric machine 12. The second module 110 includes a second inverter 114 coupled to the second electric machine 112. The second inverter 114 can be controlled to operate in a secondary control mode (e.g., torque control mode) and a monitoring mode of the second electric machine 112. The primary control mode may be the same as or different from the secondary control mode. In one embodiment, the first inverter 14 and the second inverter 114 may (e.g., optionally) operate by means of an offset phase of the AC output signal to provide interleaving that reduces ripple current and / or ripple voltage of the variable DC bus. The first inverter 14 and the second inverter 114 have their DC inputs coupled to DC bus terminals 30. Capacitors 28, or DC link capacitors 28, are connected across or in parallel with respect to the terminals of the DC bus.

[0022] Sensor 32 (e.g., a voltage sensor) is connected to DC bus terminal 30. Additionally, voltage regulator 34 is connected to DC bus terminal 30 and may be connected in parallel with or wired to sensor 32. First module 10, first inverter 14, or first electronic data processor 24 provides one or more data messages to voltage command estimator 36; second module 110, second inverter 114, or second electronic data processor 124 provides one or more data messages to voltage command estimator 36. The data messages may include any one of the following: (1) a first torque command and / or a first speed command based on a first variable load of the first electric machine 12, including a first direct-axis current / voltage command and a first quadrature-axis current / voltage command; and (2) a second torque command and / or a second speed command based on a second variable load of the second electric machine 112, including a second direct-axis current / voltage command and a second quadrature-axis current / voltage command. Furthermore, voltage command estimator 36 may estimate the commanded estimated variable DC bus voltage based on the data messages received from first module 10, second module 110, or both.

[0023] The first inverter 14 includes a first inverter 14 switch that outputs AC to the first electric machine 12 according to one or more phases of the AC output. For example... Figure 1 As illustrated, a three-phase connection exists between the first inverter 14 and the first electric motor 12. A first data processor 24 controls the switching state of the first inverter 14 switches via control signals according to a control mode or modulation scheme. These control signals are provided to the control terminals (e.g., gate terminals or base terminals) of each switch via one or more data ports 18. The first inverter switch 26 is in... Figure 3The diagram shows an insulated gate bipolar junction transistor (including S1 to S12).

[0024] The first inverter 14 includes a first electronic data processor 24, a data storage device 22, and one or more data ports 18 that can communicate with each other via a data bus 20. Furthermore, the data ports 18 are coupled to a first machine state estimator and control module 16 and a first inverter switch 26. The first machine state estimator and control module 16 is arranged to receive electrical signals from the AC output phase of the inverter switch 26, which the first electronic data processor 24 can use to estimate rotor position, rotor speed, rotor torque, and other possibilities. Transmission lines or conductors connecting the first machine state estimator and control module 16 and the phase output terminals of the first inverter switch 26 are illustrated as dashed lines to indicate that the conductors are optional. Therefore, in an alternative embodiment, the first machine state estimator and control module 16 may obtain sensor data from machine sensors (not shown) associated with the rotor of the first electric machine 12.

[0025] The second inverter 114 includes a second inverter switch 126 that outputs AC power to the second electric machine 112 according to one or more phases. For example... Figure 1 As illustrated, a three-phase connection exists between the second inverter 114 and the second electric motor 112. The second data processor 124 controls the switching state of the second inverter switch 126 via control signals according to a control mode or modulation scheme. These control signals are provided via one or more data ports 118 to the control terminals (e.g., gate terminals or base terminals) of each switch. Figure 3 The diagram shows an insulated gate bipolar junction transistor (including S1 to S12).

[0026] The second inverter 114 includes a second data processor 124, a data storage device 122, and one or more data ports 118 that can communicate with each other via a data bus 120. Furthermore, the data ports 118 are coupled to a second machine state estimator and control module 116 and a second inverter switch 126. The second machine state estimator and control module 116 is arranged to receive electrical signals from the AC output phase of the inverter switch 126, which the second electronic data processor 124 can use to estimate rotor position, rotor speed, rotor torque, and other possibilities. Transmission lines or conductors connecting the second machine state estimator and control module 116 and the phase output terminals of the second inverter 114 switch are illustrated as dashed lines to indicate that the conductors are optional. Therefore, in an alternative embodiment, the second machine state estimator and control module 116 can obtain sensor data from machine sensors (not shown) associated with the rotor of the second electric machine 112.

[0027] Figure 2 This is a graph illustrating a schematic example of the variable DC bus voltage 201 versus time 202 required (e.g., the target minimum estimate) under assumed transient load conditions. Figure 2 As illustrated, the vertical axis represents the required DC bus voltage 201 (e.g., in volts), while the horizontal axis represents the time 202 (e.g., in seconds) in response to hypothetical or modeled load changes or arbitrary transient load conditions for a work vehicle, which includes a system 11 associated with the work vehicle (e.g., an off-road work vehicle) for propelling the vehicle or driving the equipment via an electric motor or actuator.

[0028] exist Figure 2 In the diagram, the first minimum estimated variable DC bus voltage is indicated by a dashed line, while the second minimum estimated variable DC bus voltage is indicated by a solid line. According to one embodiment, for each time interval, the voltage command estimator 36 determines the larger or maximum of the first minimum estimated variable DC bus voltage and the second minimum estimated variable DC bus voltage to adjust the final target variable DC bus voltage at the DC bus terminal 30.

[0029] like Figure 2 As illustrated, the first minimum estimated variable DC bus voltage is associated with the first electric machine 12 operating in power generation mode or another operating mode; the second minimum estimated variable DC bus voltage is associated with the second electric machine 112 operating in monitoring mode or another operating mode.

[0030] The first voltage deviation 207 of the first minimum estimated variable DC bus voltage is less than the second voltage deviation 209 of the second minimum estimated variable DC bus voltage. Furthermore, the first required voltage change or first slew rate per unit time of the first minimum estimated variable DC bus voltage is less than the second voltage change or second slew rate per unit time of the second minimum estimated variable DC bus voltage. Therefore, by minimizing the required voltage change or required slew rate per unit time of the estimated variable DC bus voltage at DC bus terminal 30, the life of the electric motor is potentially increased by reducing machine winding insulation stress (e.g., thermal stress that can be transmitted to machine bearings and / or electric motor stress).

[0031] For example, if the first required voltage change or first slew rate per unit time of the first minimum estimated variable DC bus voltage is less than the second voltage change or second slew rate per unit time of the second minimum estimated variable DC bus voltage, then the first minimum estimated variable DC bus voltage can be selected within a time interval in which the first minimum estimated variable DC bus voltage is the larger or maximum of the first minimum estimated variable DC bus voltage and the second minimum estimated variable DC bus voltage. Therefore, in the illustrated example above, the lifetime of capacitor 28 (e.g., DC link capacitor 28) is potentially increased because the aforementioned first required voltage change or first slew rate per unit time of the variable DC bus voltage is less than the second voltage change or second slew rate per unit time of the second minimum estimated variable DC bus voltage.

[0032] Figure 3 This is a schematic diagram illustrating the switches (26, 126) of a first inverter 14 and a second inverter 114, both fed by a variable DC bus with capacitor 28 to reduce ripple current on the variable DC bus. The first inverter 14 and the second inverter 114 are connected to DC bus terminals 30. The first inverter 14 has a first inverter switch 26, while the second inverter 114 has a second inverter switch 126. As illustrated, the first inverter switch 26 has three phases: a first phase 301, a second phase 302, and a third phase 303. Similarly, the second inverter switch 126 has a first phase 301, a second phase 302, and a third phase 303. Each of these phases has two switches, whose switching terminals are arranged in series between the variable DC bus terminals 30. Each phase has a low-side switch and a high-side switch.

[0033] The first inverter switch 26 and the second inverter switch 126 have control terminals, such as the gate or base of a switch that controls the switching terminals. Data ports (18, 118) are connected to the control terminals via one or more conductors. The first data processor 24 can control the state, relative phase, activation, and deactivation of the first switch via the control terminals of the first switch. Similarly, the second data processor 124 can control the state, relative phase, activation, and deactivation of the second switch via the control terminals of the second switch. Furthermore, the first data processor 24 and the second data processor 124 can communicate with each other (e.g., via a communication line, a wireless communication device connected to their respective data ports (18, 118), or another mechanism) to control the relative phase of the first switch 26 with respect to the second switch 126 according to an interleaving principle, thereby reducing unwanted ripple current and / or ripple voltage on the variable DC voltage bus.

[0034] Such as combination Figure 3 exist Figure 1 As illustrated, the first electric machine (309 or 12) can operate in generator mode, while the second electric machine (310 or 112) can operate in machine monitoring mode. The first inverter 14 switches to produce a DC output with a DC current component and an AC ripple component 304. Some of the AC ripple component 308 is filtered via capacitor 28. The second inverter 114 accesses the filtered DC output 306, where some of the AC ripple component has been removed, attenuated, or filtered out. The filtered DC output is used to drive the second switch 126 to provide a three-phase AC output signal to drive the second electric machine 112 in monitoring mode.

[0035] Figure 4 This is a graph showing the root mean square (RMS) current 401 of the DC bus along the vertical axis and the time along the horizontal axis. The current value of the variable DC voltage bus 407 is indicated by a solid line, while the current value of the comparable fixed DC voltage bus 405 is indicated by a dashed line. Figure 4 This is a graph illustrating an exemplary reduction in the root mean square (RMS) current of the DC bus through capacitor 28, which filters out some unwanted ripple current or AC signal components on the variable DC bus. In one embodiment, capacitor 28 across variable DC bus terminal 30 has a reduced maximum current capacity rating 401 commensurate with the reduced peak current value of the variable DC voltage bus 407, which is lower than the peak current value of the fixed constant DC bus voltage 405. Therefore, the reduced peak current 401 tends to reduce the required size of capacitor 28 or the capacitance. For example, it may be possible to reduce the capacitance required in other ways by approximately 15% to 35%. Furthermore, the reduced peak current supports a potentially improved lifetime for capacitor 28 in the system (e.g., DC link capacitor 28).

[0036] Figure 5This is a graph illustrating the switching energy 501 versus time 502 of an inverter for a fixed DC bus versus a variable DC bus, the variable DC bus satisfying a minimum estimated target DC voltage level required for the variable DC bus based on load conditions (e.g., transient load conditions on a motor driven by the inverter). The vertical axis represents the switching energy of the inverter switches (e.g., in joules), while the horizontal axis represents time (e.g., in seconds). In one configuration, a set of semiconductor switches (26, 126) in the first inverter 14 and the second inverter 114 have a reduced time-averaged operating switching loss 504, which is associated with a reduction in the operating switching loss 503 of the variable DC bus voltage from that associated with a fixed constant DC bus voltage. The operating switching loss 504 associated with the variable DC bus voltage is illustrated as a solid line, while the operating switching loss 503 associated with the fixed constant DC bus voltage is illustrated as a dashed line. Due to the reduction of the variable DC bus voltage, the reserved component of the DC bus voltage can be used to responsively and quickly meet the transient conditions of the commanded torque required by the load conditions on the first electric machine 12, the second electric machine 112, or both in real time.

[0037] Figure 6 This is a block diagram of another embodiment of a first motor 12 connected to a first inverter 14 powered by a variable DC bus at DC terminal 30, a second motor 112 connected to a second inverter 114 powered by a variable DC bus at DC terminal 30, and a voltage regulator 34 for adjusting the voltage level of the variable DC bus based on a command estimator 136 having configurable filtering, configurable conversion rate, and configurable margin (M). Figure 6 System 111 is similar to Figure 1 System 11, but Figure 6 The system further includes a low-pass filter 38, a conversion rate module 40, and a margin estimator 42. (To be combined later...) Figure 8 Describe the operation and configuration of the low-pass filter 38, the conversion rate module 40, and the margin estimator 42.

[0038] Figure 7 A flowchart of one embodiment of a method for providing the estimated minimum required variable DC bus voltage to the regulator 34. Figure 7 The method begins in step S700.

[0039] In step S700, sensor 32 (e.g., a voltage sensor) measures the observed voltage level of the variable DC voltage bus at DC bus terminal 30 within a time interval (e.g., a sampling interval). For example, sensor 32 may have high impedance so as not to interfere with or distort any voltage measurement samples acquired at continuous intervals across DC bus terminal 30.

[0040] In step S702, in the first inverter 14, the first data processor 24 determines a first torque command and / or a first speed command, including a first direct-axis current / voltage command and a first quadrature-axis current / voltage command, based on the first variable load of the first electric machine 12.

[0041] In step S704, in the second inverter 114, the second data processor 124 determines a second torque command and / or a second speed command, including a second direct-axis current / voltage command and a second quadrature-axis current / voltage command, based on the second variable load of the second electric motor 112.

[0042] In step S706, the voltage command estimator 36 estimates or is configured to estimate the minimum required variable DC bus voltage based on the first direct-axis current / voltage command, the first quadrature-axis current / voltage command, the second direct-axis current / voltage command, and the second quadrature-axis current / voltage command within the corresponding time interval.

[0043] In step S708, the voltage command estimator 36 is configured to provide the estimated minimum required variable DC bus voltage to the voltage regulator 34 to adjust the observed voltage level of the variable DC voltage bus to the estimated minimum required variable DC bus voltage to maintain the operation of the first motor 12 under the first variable load and the second motor 112 under the second variable load at the time interval, as commanded by the voltage / current command.

[0044] Step S708 can be performed according to various technologies, which can be applied individually or cumulatively.

[0045] According to the first technique for performing step S708, the voltage command estimator 36 is configured to provide the estimated minimum (e.g., target) required variable DC bus voltage, wherein the voltage command estimator 36 is configured to limit the fluctuation of the DC bus voltage to meet or exceed the required current and corresponding required voltage level of the first motor 12 under the first variable load and the second motor 112 under the second variable load, as if the variable DC bus voltage is fixed at a constant DC level higher than the estimated minimum required variable DC bus voltage.

[0046] According to the second technique, the voltage command estimator 36 is configured to estimate the required minimum (e.g., target) variable DC bus voltage by estimating the target variable DC bus voltage as proportional to the square root of the sum of the squares of the commanded direct-axis voltage and the commanded quadrature-axis voltage for each load of, for example, the first electric machine 12 and the second electric machine 112. Furthermore, consistent with the above proportionality, the target variable DC bus voltage is the larger of the target variable DC bus voltages required by the first electric machine 12 or the second electric machine.

[0047] For example, according to the second technology, the voltage command estimator 36 is configured to estimate the variable DC bus voltage by estimating the variable DC bus voltage according to the following equation for the first electric machine 12 and the second electric machine 112:

[0048] Among them, V dc_est(EM1) It is the minimum estimated variable DC bus voltage for the first electric motor (e.g., EM1), where V* d(EM1) It is the direct-axis voltage commanded by the first inverter 14, and V* q(EM1) It is the quadrature-axis voltage commanded by the first inverter 14.

[0049] Among them, V dc_est(EM2) It is the minimum estimated variable DC bus voltage for the second electric motor (e.g., EM2), where V* d(EM2) It is the commanded direct-axis voltage of the second inverter 114, and V* q(EM2) It is the quadrature-axis voltage commanded by the second inverter 114.

[0050] It is for the first electric motor (e.g., EM1). and for a second electric motor (e.g., EM2) The maximum or larger of the values. For example, and consistent with the above equation, within each inverter, the current regulator can be based on the commanded dq axis current (I*). dq ) and the observed dq-axis current (I dq The input of the current regulator is the direct-axis voltage (V*) commanded by the output. d ) and the commanded quadrature-axis voltage (V*) q ).

[0051] According to the third technique, the voltage command estimator 36 is configured to estimate the variable DC bus voltage, wherein there exists some permissible fluctuation margin or range in the variable DC bus with respect to a virtual, baseline, or nominal fixed DC bus voltage. For example, the voltage command estimator 36 is configured to estimate the variable DC bus voltage based on one or more of the following rule-based conditional equations:

[0052] (1) Medium Fruit V dc_cmd ≤V DCThresh Then V dc_cmd =Max V dc_est(EM1，EM2) +M, where V dc_cmd It is the estimated variable DC bus voltage that is commanded, V DCThresh It is a fixed DC bus voltage threshold (e.g., 700VDC), M is the margin, and It is for the first electric motor (e.g., EM1). and for a second electric motor (e.g., EM2) The maximum or larger of the margins. The determination of the margin (M) is described in more detail below.

[0053] (2) If V dc_est(EM1) >V dc_est(EM2) Then use V dc_cmd =V dc_est(EM1) Otherwise, V dc_cmd =V DCThresh , where V dc_est(EM1) It is the minimum estimated variable DC bus voltage for the first electric motor (e.g., EM1); where V dc_est ( EM2) It is the minimum estimated variable DC bus voltage for the second electric motor (e.g., EM2), where V dc_cmd It is the estimated variable DC bus voltage that is commanded, and V DCThresh It is a fixed DC bus voltage threshold (e.g., 700VDC).

[0054] According to the fourth technique for performing step S708, the voltage command estimator 36 is configured to estimate the target variable DC bus voltage by determining a configurable margin (M) for the minimum required DC bus voltage, wherein the margin (M) is determined based on one or more of the following: (a) a deviation or standard deviation of a fixed DC bus voltage threshold (e.g., historically observed and recorded in data storage device 22 during machine operation), (b) a percentage of a comparable fixed DC bus voltage threshold (e.g., 700VDC), (c) a fixed or constant DC voltage within a range (e.g., 10 to 25VDC) of a comparable fixed DC bus threshold (e.g., 700VDC or lower), and (d) actual or predicted DC bus fluctuations that depend on load dynamics or are associated with historical data collected and stored in data storage device 22 for a specific task or by a machine (or its apparatus, tools, and actuators) performing such a task. In one embodiment, the bandwidth of the low-pass filter is configurable, the slew rate is configurable, and the margin is load-dependent or load-based configurable, where the load may depend on the specific work task of the vehicle (e.g., a loader), such as loading a truck to a minimum height, stacking, or excavating. Therefore, the configurable margin (M) of the variable DC bus is based on actual or predicted DC bus fluctuations that depend on load dynamics.

[0055] Figure 8 This is a flowchart of another embodiment of a method for providing the estimated minimum required variable DC bus voltage to the regulator. Figure 7 The method is similar to Figure 8 The method is just Figure 8 The method further includes steps S710 and S712. Similar steps, methods, procedures, or features are indicated by similar reference numerals.

[0056] In step S700, sensor 32 (e.g., a voltage sensor) measures the observed voltage level of the variable DC voltage bus at DC bus terminal 30 within a time interval (e.g., a sampling interval). For example, sensor 32 may have high impedance so as not to interfere with or distort any voltage measurement samples acquired at continuous intervals across DC bus terminal 30.

[0057] In step S702, in the first inverter 14, the first data processor 24 determines a first torque command and / or a first speed command, including a first direct-axis current / voltage command and a first quadrature-axis current / voltage command, based on the first variable load of the first electric machine 12.

[0058] In step S704, in the second inverter 114, the second data processor 124 determines a second torque command and / or a second speed command, including a second direct-axis current / voltage command and a second quadrature-axis current / voltage command, based on the second variable load of the second electric motor 112.

[0059] In step S706, the voltage command estimator 36 estimates or is configured to estimate the minimum required variable DC bus voltage based on the first direct-axis current / voltage command, the first quadrature-axis current / voltage command, the second direct-axis current / voltage command, and the second quadrature-axis current / voltage command within the corresponding time interval.

[0060] In step S708, the voltage command estimator 36 is configured to provide the voltage regulator 34 with the estimated minimum required variable DC bus voltage to adjust the observed voltage level of the variable DC voltage bus to the estimated minimum required variable DC bus voltage to maintain the operation of the first motor 12 under the first variable load and the second motor 112 under the second variable load at the time interval, as commanded by the voltage / current command.

[0061] In step S710, the voltage command estimator 36 or the low-pass filter 38 applies a low-pass filter to remove high-frequency noise from the minimum required DC bus voltage of the variable DC bus. The voltage command estimator 36 can adjust the filter parameters based on the first variable load and the second variable load during any corresponding time interval.

[0062] Step S710 can be performed according to various procedures, which can be applied individually or cumulatively. In a first procedure, a low-pass filter 38 (e.g., a 10Hz discrete filter) is applied to the estimated minimum required variable DC bus voltage to remove high-frequency noise from the minimum required DC voltage (e.g., the commanded variable DC voltage). In a second procedure, the low-pass filter 38 has an adjustable or configurable bandwidth, attenuation, and frequency response that can be adjusted based on a first variable load, a second variable load, or both. The higher bandwidth of the low-pass filter can improve the responsiveness to command changes to alter the target minimum required DC voltage of the variable DC voltage bus, but the disadvantage is a larger high-frequency and noise content, which may affect the potential reliability and accuracy of the commanded change to the target minimum required DC voltage.

[0063] In step S712, the voltage command estimator 36 or the slew rate module 40 applies the voltage slew rate per time or the maximum voltage deviation to the filtered minimum required DC voltage, wherein the applied voltage slew rate meets or exceeds the minimum slew rate required for the first electric machine 12 and the second electric machine 112 to meet the commanded current / voltage in real time within the time interval. The minimum slew rate is determined by the load for a particular machine and the working task borne by the machine, its appliances, its actuators, and its tools that causes the load, wherein the load requires a certain change in voltage per unit time to be met by the first electric machine 12 and the second electric machine 112.

[0064] Step S712 can be performed using various techniques, which can be applied individually or cumulatively. Under a first technique, the conversion rate module 40 configures or adjusts the conversion rate and the margin associated with the minimum required DC voltage based on or based on a first variable load, a second variable load, or both, wherein the aforementioned variable load may depend on the specific work task of the vehicle (e.g., a loader), such as loading a truck to a minimum height, stacking, or excavating. Under a second technique, the conversion rate module 40 applies a voltage conversion rate (e.g., 2.5V / 500 microseconds or 5000V / s) or the maximum voltage deviation per time to the filtered minimum required DC voltage, wherein the applied voltage conversion rate meets or exceeds the minimum conversion rate required for the first electric machine 12 and the second electric machine 112 to meet the commanded current / voltage in real time within the time interval. Under a third technique, the conversion rate module 40 sends the filtered, converted variable bus voltage to the voltage regulator 34 of the variable DC bus voltage.

[0065] although Figure 1 and Figure 6 The illustration depicts a system and method applied to a configuration with two machines connected to a variable DC voltage bus; however, the concepts set forth above in this disclosure can be extended to multiple machines connected to a variable DC voltage bus. For example, a multi-machine configuration requires that the corresponding minimum required DC bus voltage for each inverter can be guaranteed in a timely manner (e.g., by time intervals or consecutive time intervals), for example, in a four-inverter configuration where four inverters are connected in parallel to the DC bus terminals.

[0066] Although this disclosure has been illustrated and described in detail in the accompanying drawings and the foregoing description, such illustrations and descriptions should be considered exemplary rather than limiting in nature. It should be understood that illustrative embodiments have been shown and described, and protection is intended for all changes and modifications falling within the spirit of this disclosure. It will be noted that alternative embodiments of this disclosure may not include all the features described, but will still benefit from at least some of the advantages of such features. Those skilled in the art can readily devise their own embodiments that incorporate one or more of the features of this disclosure and fall within the spirit and scope of the invention as defined by the appended claims.

Claims

1. A method for controlling a first inverter and a second inverter connected to a variable DC voltage bus, wherein, The inverter input is connected to a variable DC voltage bus, and the inverter output is connected to a first variable load and a second variable load, the method comprising: Measure the observed voltage level of the variable DC voltage bus within the time interval; In the first inverter, a first torque command and / or a first speed command, including a first direct-axis current / voltage command and a first quadrature-axis current / voltage command, are determined based on the first variable load of the first electric machine, where the real-time transient load conditions on the first electric machine require the first direct-axis current / voltage command and the first quadrature-axis current / voltage command to maintain operation within the time interval; In the second inverter, a second torque command and / or a second speed command, including a second direct-axis current / voltage command and a second quadrature-axis current / voltage command, are determined based on the second variable load of the second electric machine. The real-time transient load conditions on the second electric machine require the second direct-axis current / voltage command and the second quadrature-axis current / voltage command to maintain operation within the time interval. The minimum required variable DC bus voltage is estimated based on the first direct-axis current / voltage command, the first quadrature-axis current / voltage command, the second direct-axis current / voltage command, and the second quadrature-axis current / voltage command within the corresponding time interval; and The estimated minimum required variable DC bus voltage is provided to the voltage regulator to adjust the observed voltage level of the variable DC bus to the estimated minimum required variable DC bus voltage, so as to maintain the operation of the first motor under the first variable load and the second motor under the second variable load at the time interval, the operation being commanded by the voltage / current command. The voltage regulator has a configurable switching rate, and the voltage command provided to the voltage regulator includes a switching rate that satisfies or exceeds the minimum switching rate required for the first motor and the second motor to meet the commanded current / voltage in real time within the time interval.

2. The method according to claim 1, wherein, Providing the estimated minimum required variable DC bus voltage further includes: limiting the fluctuation of the variable DC bus voltage to meet or exceed the required current and corresponding required voltage levels of the first motor under the first variable load and the second motor under the second variable load, such that the variable DC bus voltage is fixed at a constant DC level higher than the estimated minimum required variable DC bus voltage.

3. The method according to claim 1, wherein, The variable DC bus voltage is estimated by making the target variable DC bus voltage proportional to the square root of the sum of the squares of the commanded direct-axis voltage and the commanded quadrature-axis voltage for each load.

4. The method according to claim 3, wherein, The target variable DC bus voltage is the larger of the target variable DC bus voltage required by the first electric machine or the second electric machine.

5. The method according to claim 1, wherein, The estimation of the variable DC bus voltage further includes estimating the variable DC bus voltage according to the following equation: ,in, It is the minimum estimated variable DC bus voltage used for the first electric motor, where V* d(EM1) It is the commanded direct-axis voltage of the first inverter, and V* q(EM1) It is the quadrature-axis voltage commanded by the first inverter; ,in, It is the minimum estimated variable DC bus voltage used for the second motor machine, where V* d(EM2) It is the commanded direct-axis voltage of the second inverter, and V* q(EM2) It is the quadrature-axis voltage commanded by the second inverter; It is used for the first electric motor. and for the second electric motor The maximum value in.

6. The method according to claim 1, wherein, The estimation of the variable DC bus voltage further includes estimating the variable DC bus voltage according to the following equation: If V dc_cmd ≤ V DCThresh Then V dc_cmd = + M, where V dc_cmd It is the estimated variable DC bus voltage that is commanded, V DCThresh It is a fixed DC bus voltage threshold, M is the margin, and It is used for the first electric motor. and for the second electric motor The maximum value in, where, It is the minimum estimated variable DC bus voltage used for the first electric motor. It is the minimum estimated variable DC bus voltage used for the second electric motor.

7. The method according to claim 4, wherein, The estimation of the variable DC bus voltage further includes: The margin (M) is determined based on one or more of the following: (a) the deviation or standard deviation of the fixed DC bus voltage threshold, (b) the percentage of the fixed DC bus voltage threshold, (c) a fixed or constant DC voltage within a range, and (d) actual or predicted DC bus fluctuations that depend on load dynamics or are associated with historical data collected by a specific task or by a machine performing such a task and stored in a data storage device.

8. The method according to claim 1, wherein, The estimation of the variable DC bus voltage further includes estimating the variable DC bus voltage according to the following equation: if > Then use V dc_cmd = Otherwise, V dc_cmd = V DCThresh ,in, It is the minimum estimated variable DC bus voltage used for the first electric motor; wherein, It is the minimum estimated variable DC bus voltage used for the second electric machine, where V dc_cmd It is the estimated variable DC bus voltage that is commanded, and V DCThresh It is a fixed DC bus voltage threshold.

9. The method of claim 5, further comprising: A low-pass filter is applied to remove high-frequency noise from the minimum required variable DC bus voltage or the commanded variable DC bus voltage.

10. The method of claim 6, further comprising: The voltage slew rate or the maximum voltage deviation per time is applied to the minimum required variable DC bus voltage after filtering, wherein the applied voltage slew rate meets or exceeds the minimum slew rate required for the first motor and the second motor to meet the commanded current / voltage in real time within the time interval.

11. The method of claim 10, further comprising: The filtered and converted variable bus voltage is sent to the voltage regulator of the variable DC bus voltage.

12. The method according to claim 1, wherein, The capacitors spanning the variable DC bus have a reduced maximum current capacity rating commensurate with the variable peak current value of the variable DC voltage bus, which is lower than the peak current value of the fixed constant DC bus voltage.

13. The method according to claim 1, wherein, A set of semiconductor switches in the first inverter and the second inverter have reduced time-averaged operating switching losses, which are associated with a reduction in the variable DC bus voltage from a fixed constant DC bus voltage that is commensurate with the peak voltage of the variable DC bus voltage.

14. The method according to claim 3, wherein, The first variable load is the first electric motor and the second variable load is the second electric motor.

15. The method of claim 10, wherein the voltage conversion rate is 5000 V / s.

16. A system for controlling a first inverter and a second inverter connected to a variable DC voltage bus, wherein, The inverter input is connected to a variable DC voltage bus, and the inverter output is connected to a first variable load and a second variable load. The system includes: A sensor for measuring the observed voltage level of the variable DC voltage bus within a time interval; A first inverter is configured to determine a first torque command and / or a first speed command based on the first variable load of a first electric machine, including a first direct-axis current / voltage command and a first quadrature-axis current / voltage command, wherein real-time transient load conditions on the first electric machine require the first direct-axis current / voltage command and the first quadrature-axis current / voltage command to maintain operation within the time interval; The second inverter is configured to determine a second torque command and / or a second speed command, including a second direct-axis current / voltage command and a second quadrature-axis current / voltage command, based on the second variable load of the second electric machine, wherein the real-time transient load conditions on the second electric machine require the second direct-axis current / voltage command and the second quadrature-axis current / voltage command to maintain operation within the time interval; A voltage command estimator is configured to estimate the minimum required variable DC bus voltage based on a first direct-axis current / voltage command, a first quadrature-axis current / voltage command, a second direct-axis current / voltage command, and a second quadrature-axis current / voltage command within corresponding time intervals; and The voltage command estimator is configured to provide the voltage regulator with an estimated minimum required variable DC bus voltage to adjust the observed voltage level of the variable DC bus to the estimated minimum required variable DC bus voltage, thereby maintaining the operation of the first motor under the first variable load and the second motor under the second variable load at the time interval, the operation being commanded by the voltage / current command. The voltage regulator has a configurable switching rate, and the voltage command provided to the voltage regulator includes a switching rate that satisfies or exceeds the minimum switching rate required for the first motor and the second motor to meet the commanded current / voltage in real time within the time interval.

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