CN-112087155-B - System and method for variable DC bus voltage coupled to an inverter

CN112087155BCN 112087155 BCN112087155 BCN 112087155BCN-112087155-B

Abstract

The voltage command estimator is configured to estimate a minimum required variable DC bus voltage based on the first direct current/voltage command, the first quadrature current/voltage command, the second direct current/voltage command, and the second quadrature current/voltage command over respective time intervals. 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 voltage bus to the estimated minimum required variable DC bus voltage in order to maintain operation of the first electric machine under the first variable load and the second electric machine under the second variable load at the time interval as commanded by voltage/current commands.

Inventors

LI DAN
WU LONG
ZHU GUANGQI

Assignees

迪尔公司
迪尔公司

Dates

Publication Date: 20260421
Application Date: 20200615
Priority Date: 20191015

Claims (16)

1. A method for controlling a first inverter and a second inverter coupled to a variable DC voltage bus, wherein an inverter input is coupled to the variable Direct Current (DC) voltage bus and an inverter output is connected to a first variable load and a second variable load, the method comprising: Measuring an observed voltage level of the variable DC voltage bus over a time interval; Determining, in a first inverter, a first torque command and/or a first speed command comprising a first direct current/voltage command and a first quadrature current/voltage command based on the first variable load of a first electric machine, a real-time transient load condition on the first electric machine requiring the first direct current/voltage command and the first quadrature current/voltage command to maintain operation over the time interval; Determining, in a second inverter, a second torque command and/or a second speed command comprising a second direct-axis current/voltage command and a second quadrature-axis current/voltage command based on the second variable load of a second electric machine, the second direct-axis current/voltage command and the second quadrature-axis current/voltage command being required by a real-time transient load condition on the second electric machine to maintain operation over the time interval; Estimating a minimum required variable DC bus voltage based on the first direct current/voltage command, the first quadrature current/voltage command, the second direct current/voltage command, and the second quadrature current/voltage command over respective time intervals, and Providing an estimated minimum required variable DC bus voltage to a voltage regulator to adjust the observed voltage level of the variable DC voltage bus to the estimated minimum required variable DC bus voltage to maintain operation of the first electric machine under the first variable load and the second electric machine under the second variable load at the time interval, the operation commanded by the voltage/current command, Wherein the voltage regulator has a configurable slew rate and the voltage command provided to the voltage regulator includes a slew rate that meets or exceeds a minimum slew rate required for the first and second electric machines to meet the commanded current/voltage in real time over the time interval.
2. The method of claim 1, wherein providing the estimated minimum required variable DC bus voltage further comprises limiting fluctuations in variable DC bus voltage to meet or exceed a required current and a corresponding required voltage level of the first electric machine under the first variable load and the second electric machine under the second variable load such that the variable DC bus voltage is fixed at a constant DC level above the estimated minimum required variable DC bus voltage.
3. The method of claim 1, wherein estimating the variable DC bus voltage is accomplished by estimating a 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. A method according to claim 3, wherein the target variable DC bus voltage is the greater of the target variable DC bus voltages required by the first or second electric machine.
5. The method of claim 1, wherein estimating the variable DC bus voltage further comprises estimating the variable DC bus voltage according to the following equation: , wherein, Is a minimum estimated variable DC bus voltage for the first electric machine, wherein V d(EM1) is the commanded direct-axis voltage of the first inverter and V q(EM1) is the commanded quadrature-axis voltage of the first inverter; , wherein, Is a minimum estimated variable DC bus voltage for the second electric machine, wherein V d(EM2) is the commanded direct-axis voltage of the second inverter and V q(EM2) is the commanded quadrature-axis voltage of the second inverter; Is for the first electric machine And for the second electric machine Is the maximum value of (a).
6. The method of claim 1, wherein estimating the variable DC bus voltage further comprises 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 is the commanded estimated variable DC bus voltage, V DCThresh is the fixed DC bus voltage threshold, M is the margin, and Is for the first electric machine And for the second electric machine Wherein the maximum value of (c), wherein, Is a minimum estimated variable DC bus voltage for the first electric machine, Is a minimum estimated variable DC bus voltage for the second electric machine.
7. The method of claim 4, wherein estimating the variable DC bus voltage further comprises: the margin (M) is determined from one or more of (a) a deviation or standard deviation of the fixed DC bus voltage threshold, (b) a percentage of the fixed DC bus voltage threshold, (c) a fixed or constant DC voltage over a range, and (d) actual or predicted DC bus fluctuations that are dependent on load dynamics or historical data associated with a particular task or machine executing such a task and stored in a data storage device.
8. The method of claim 1, wherein estimating the variable DC bus voltage further comprises estimating the variable DC bus voltage according to the following equation: If it is > Then V dc_cmd = Otherwise, V dc_cmd = V DCThresh , wherein, Is a minimum estimated variable DC bus voltage for the first electric machine, wherein, Is a minimum estimated variable DC bus voltage for the second electric machine, wherein V dc_cmd is the commanded estimated variable DC bus voltage and V DCThresh 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 or commanded variable DC bus voltage.
10. The method of claim 6, further comprising: Applying a voltage slew rate or a maximum voltage deviation per time to the filtered minimum required variable DC bus voltage, wherein the applied voltage slew rate meets or exceeds a minimum slew rate required for the first and second electric machines to meet the commanded current/voltage in real time over the time interval.
11. The method of claim 10, further comprising sending the filtered and converted variable bus voltage to the voltage regulator of the variable DC bus voltage.
12. The method of claim 1, wherein a capacitor across the variable DC bus has a reduced maximum current capacity rating commensurate with a variable peak current value of the variable DC voltage bus that is lower than a peak current value of a fixed constant DC bus voltage.
13. The method of claim 1, wherein a set of semiconductor switches in the first inverter and the second inverter have reduced time-averaged operational switching losses associated with a reduction of the variable DC bus voltage from a fixed constant DC bus voltage commensurate with a peak voltage of the variable DC bus voltage.
14. The method of claim 3, wherein the first variable load is the first electric machine and the second variable load is the second electric machine.
15. The method of claim 10, wherein the voltage conversion rate is 5000V/s.
16. A system for controlling a first inverter and a second inverter coupled to a variable DC voltage bus, wherein an inverter input is coupled to the variable Direct Current (DC) voltage bus and an inverter output is connected to a first variable load and a second variable load, the system comprising: a sensor for measuring an observed voltage level of the variable DC voltage bus over a time interval; A first inverter configured to determine a first torque command and/or a first speed command comprising a first direct current/voltage command and a first quadrature current/voltage command based on the first variable load of a first electric machine, real-time transient load conditions on the first electric machine requiring the first direct current/voltage command and the first quadrature current/voltage command to maintain operation over the time interval; A second inverter configured to determine a second torque command and/or a second speed command comprising a second direct-axis current/voltage command and a second quadrature-axis current/voltage command based on the second variable load of a second electric machine, real-time transient load conditions on the second electric machine requiring the second direct-axis current/voltage command and the second quadrature-axis current/voltage command to maintain operation over the time interval; A voltage command estimator for estimating a minimum required variable DC bus voltage based on the first direct current/voltage command, the first quadrature current/voltage command, the second direct current/voltage command, and the second quadrature current/voltage command over respective time intervals, and The voltage command estimator is configured to provide an estimated minimum required variable DC bus voltage to a voltage regulator to adjust the observed voltage level of the variable DC voltage bus to the estimated minimum required variable DC bus voltage to maintain operation of the first electric machine under the first variable load and the second electric machine under the second variable load at the time interval, the operation commanded by the voltage/current command, Wherein the voltage regulator has a configurable slew rate and the voltage command provided to the voltage regulator includes a slew rate that meets or exceeds a minimum slew rate required for the first and second electric machines to meet the commanded current/voltage in real time over the time interval.

Description

System and method for variable DC bus voltage coupled to an inverter Technical Field The present disclosure relates to a system and method for a variable Direct Current (DC) bus voltage coupled to an inverter. RELATED APPLICATIONS The present application claims the benefit of the date and priority of the U.S. provisional application serial No. 62/861,792 filed on day 6/14 of 2019, which is incorporated herein by reference in its entirety. Background In some prior art vehicle systems, the DC bus voltage is fixed at a voltage level that can determine the available Alternating Current (AC) output of the inverter to provide an electric motor or other load. If the DC bus voltage level is designed to be higher than desired, the capacitors and switches of the inverter coupled to the DC bus may experience increased thermal stress and, therefore, reduced lifetime. Accordingly, there is a need for a system and method for variable DC bus voltage coupled to an inverter, wherein the system and method are well suited for reducing thermal stress of a DC bus capacitor or switches within one or more inverters. Disclosure of Invention 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 a variable Direct Current (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 an observed voltage level of the variable DC voltage bus over a time interval. In the first inverter, the first electronic data processor is configured to determine a first torque command and/or a first speed command comprising a first direct current/voltage command and a first quadrature current/voltage command based on the first variable load of the first electric machine. In the second inverter, the second electronic data processor is configured to determine a second torque command and/or a second speed command comprising 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. The voltage command estimator is configured to estimate a minimum required (e.g., target) variable DC bus voltage based on the first direct current/voltage command, the first quadrature current/voltage command, the second direct current/voltage command, and the second quadrature current/voltage command over respective time intervals. The voltage command estimator is configured to provide the estimated minimum required variable DC bus voltage to a voltage regulator (e.g., command estimator determines a greater of the variable DC bus voltages required by a first variable load of the first machine or the second variable load of a second machine) to adjust the observed voltage level of the variable DC voltage bus to the estimated minimum required (e.g., target) variable DC bus voltage to maintain operation of the first electric machine under the first variable load and the second electric machine under the second variable load at the time interval as commanded by a voltage/current command. Drawings FIG. 1 is a block diagram of one embodiment of a first electric machine coupled to a first inverter powered by a variable DC bus, a second electric machine coupled to a second inverter powered by the variable DC bus, and a voltage regulator for regulating a voltage level of the variable DC bus based on command data from a command estimator. Fig. 2 is a graph showing an illustrative example of the required DC bus voltage versus time under an assumed transient load (minimum estimation objective or) for a first variable load and a second variable load. Fig. 3 is a schematic diagram showing a schematic diagram of a switch of a first inverter and a second inverter fed by a variable DC bus having a capacitor to reduce ripple current on the variable DC bus. Fig. 4 is a graph showing a graphical reduction in Root Mean Square (RMS) current of a DC bus through a capacitor that filters out some unwanted ripple current or alternating signal components on the variable DC bus for a comparable fixed DC bus. Fig. 5 is a graph showing switching energy versus time for an inverter switch of a fixed DC bus versus a variable DC bus that meets a minimum estimated target required DC voltage level for the variable DC bus based on a load condition (e.g., a transient load condition on an inverter-driven electric machine). Fig. 6 is a block diagram of another embodiment of a first electric machine coupled to a first inverter powered by a variable DC bus, a second electric machine coupled to a second inverter powered by the variable DC bus, and a voltage regulator for regulating a voltage level of the variable DC bus based on command data from a command estimator having configurable filtering, slew rate, and margin. FIG. 7 is a flow chart of one embodiment o