ELECTRIC DRIVE SYSTEM

Abstract

Electric drive system (15), comprising: a voltage bus with a positive bus rail (19+) and a negative bus rail (19-) and a DC bus voltage across the bus rails (19+, 19-); a battery pack (20) that is connected between the positive bus rail (19+) and the negative bus rail (19-) of the voltage bus and provides a battery voltage (V bat + , V bat - ) delivers; a DC / DC converter (30) comprising a set of semiconductor switches (34) connected between the positive bus rail (19+) and the negative bus rail (19-) and having a bypass switch (S0, 32) connected to the positive bus rail (19+), wherein the DC / DC converter (30) is configured as a buck / boost converter; a traction power inverter module (40), TPIM (40), with a DC side connected to the DC-DC converter (30) at an inverter bus voltage (31+, 31-) and with an AC side, AC, wherein the TPIM (40) is configured to direct the inverter bus voltage (31+, 31-) and thereby generate an AC bus voltage at phase lines (48); a rotating electric machine (16) connected to the AC side of the TPIM (40) and powered via the AC bus voltage; and a controller (50) configured to provide a required output power of the DC-DC converter (30) based on a requested operating mode, a target speed (N) 16 ) and a target torque (T 16 ) of the electrical machine (16) calculated to compare the required output power with a calibrated power threshold, and: if the required output power exceeds the calibrated power threshold, close the bypass switch (S0, 32) and thereby bypass the DC-DC converter (30); and If the required output power is less than the calibrated power threshold, a minimum loss voltage (V) MIN-L ) from a loss card (52) and then the minimum loss voltage (V MIN-L ) to use as a target control voltage of the DC-DC converter (30) in order to optimize the efficiency of the electric drive system (15) with the bypass switch (S0, 32) open; where the bypass switch (S0, 32) is a mechanical relay or bidirectional semiconductor switch.

Description

[0001] Electric drive systems rely on torque generated by one or more rotating electric machines and transmitted to a coupled load. Electric machines are often configured as multiphase alternating current (AC) devices powered by a DC bus and a battery pack. A power converter module is therefore used as part of the electric drive system to either invert or rectify an input voltage, with the operation performed by the power converter module depending on the specific operating mode.

[0002] During regenerative operation, for example, the control of the ON / OFF states of individual inverter switches located within the inverter module is used to rectify an AC input voltage from the electric machine when operating as a generator, with the inverter module producing a DC output voltage. This DC output voltage is then used to recharge the individual battery cells of the aforementioned battery pack. The control of the same inverter switches during drive / motor operation is used to invert an input DC voltage from the DC bus / battery pack, thereby providing an AC output voltage suitable for powering the electric machine.

[0003] Additionally, the voltage level on the DC bus can be regulated with a DC-DC converter. Such a device contains another group of semiconductor switches whose ON / OFF line states are controlled in response to a DC input voltage to achieve a required DC output voltage. Electric drive systems can operate at relatively low torque / power levels for a significant portion of a drive cycle, for example, in electric vehicle applications. A miniaturized DC / DC converter is therefore a viable hardware option for such applications, with such an approach being used, for example, in United States Patent No. US 10,110,103 B1 by Hao et al., which is hereby incorporated by reference in its entirety.

[0004] While the torque characteristics in the upper speed range are sacrificed to some extent as a result of using such a miniaturized converter, the reduced torque characteristics have the associated advantage of improving the overall efficiency of the electric drive system.

[0005] DE 11 2009 000 549 T5 describes an electric motor control device. The electric motor control device comprises a power conversion device for generating an alternating voltage via a switching actuator of a power semiconductor device, an electric motor with a coil winding to which the alternating voltage from the power conversion device is applied, and a control device for controlling the switching actuator of the power conversion device. The control device controls the switching actuator of the power conversion device such that the voltage change rate during the reversal of the polarity of the alternating voltage is relatively low when the alternating voltage exceeds a predetermined value.

[0006] DE 10 2015 102 410 A1 describes a traction battery module for supplying energy to a traction inverter for an electric drive motor of a vehicle, comprising at least one battery module and a battery module inverter connected to the battery module to provide a supply voltage for the traction inverter. Furthermore, an electric powertrain for a vehicle and a method for supplying energy to a traction inverter for an electric drive motor of a vehicle by means of a traction battery module comprising at least one battery module are disclosed, wherein a battery module inverter is connected to the battery module to provide a supply voltage for the traction inverter.

[0007] German patent DE 10 2018 114 740 A1 describes an electric drive system. The drive system includes bus rails carrying a voltage, an energy storage system, and an inverter. The system includes a voltage converter connected to the bus rails, comprising an inductor, semiconductor switches, a bypass switch connected to a positive rail, and a capacitor. A multiphase electric machine is electrically connected to the inverter. A controller executes a procedure in which the operation of the converter is regulated based on the power, torque, and speed values ​​of the electric machine. The converter is selectively bypassed by closing the bypass switch under predetermined high-power / high-torque conditions, adjusting the bus voltage until it equals the battery output voltage.The bypass circuit is opened and the bus voltage is then regulated to a predetermined voltage.

[0008] US 10,110,103 B1 describes an electric drive system. The drive system includes bus lines carrying a bus voltage, an energy storage system, and a power inverter. The system includes a voltage converter connected to the bus lines and featuring an inductor, semiconductor switches, a bypass switch connected to a positive bus line, and a capacitor. A multiphase electric machine is electrically connected to the power inverter. A controller performs a procedure in which the operation of the converter is regulated based on the power, torque, and speed values ​​of the electric machine. The converter is selectively bypassed by closing the bypass switch under predetermined high-power / high-torque conditions, adjusting the bus voltage until it matches the battery output voltage.The bypass switch is opened and the bus voltage is then regulated to a predetermined voltage. Description: The invention is defined by the claims

[0009] This document discloses a control method for use with an electric drive system. The electric drive system comprises a rechargeable battery pack or other energy storage system, a DC-DC converter, a bypass switch, a traction power inverter module (TPIM), a rotating electric machine, and a controller. The DC-DC converter is configured as a buck / boost converter and is therefore capable of selectively reducing and / or increasing a given DC input voltage depending on the operating mode and converter configuration. Additionally, the DC-DC converter is downsized compared to a worst-case basic sizing scenario, where the DC-DC converter is sized to meet the peak power demand of the electric machine.

[0010] The controller regulates the ongoing operation of the TPIM / electrical machine and the buck / boost converter using a loss map, e.g., a series of lookup tables programmed in the controller's memory. In this method, the DC output voltage of the DC-DC converter is regulated to a minimum loss voltage selected from the loss map. In this way, the controller is able to optimize energy efficiency and improve the overall drive performance of the electric drive system.

[0011] To ensure responsive operation of an electric machine at peak power levels, an electric drive system typically includes a DC-DC converter sized and designed to meet the peak power demand. However, sizing for peak power results in electrical losses within the DC-DC converter and its associated power electronic components. For example, size-proportional electrical losses occur within a relatively large inductor coil of the DC-DC converter. Reducing the size of the inductor coil proportionally reduces such losses. Similarly, a capacitor bank used as part of the converter hardware can be similarly reduced in size. Electrical losses also occur within the individual semiconductor switches of the DC-DC converter, albeit to a lesser extent.The present DC-DC converter is therefore smaller compared to the typical peak-power-based alternative, e.g. from about 90-100kW to about 20-30kW in an exemplary design.

[0012] During motor operation, the DC-DC converter operates in the available down-angle system under low-speed / low-torque conditions. This mode reduces the DC bus voltage level. The same DC-DC converter can operate in boost mode under high-speed / low-power conditions to increase the DC link voltage. During regeneration modes, when the battery pack is being recharged, the DC-DC converter operates in boost mode at low speed / low torque and in buck mode at high speed / low current. The specific control voltage of the DC-DC converter is determined according to the loss characteristic map as described above.

[0013] If the DC-DC converter is alternatively configured as a scaled-down buck converter, i.e., without a boost mode, the DC-DC converter can be selectively bypassed if the buck / boost converter described above would otherwise operate in boost mode. Similarly, if the DC-DC converter is a scaled-down boost converter without a buck converter, the DC-DC converter is bypassed if the buck / boost converter described above would otherwise operate in buck converter mode. In other words, a pure buck or boost converter has no buck or boost mode, and if the algorithm described here requires operation in an unavailable mode, the DC-DC converter can be bypassed to further improve efficiency.

[0014] In an exemplary embodiment of the present method, the controller determines the current operating mode (regenerating or driving), a target speed, and a target torque of the electric machine. From these input values, the controller calculates the required output power of the DC-DC converter. The controller then compares the required output power with a calibrated power threshold, e.g., 30 kW. Above the calibrated power threshold, the DC-DC converter is selectively bypassed by closing the bypass switch. Below the calibrated power threshold, the controller accesses the loss map, e.g., one or more lookup tables that list the power losses occurring at various output voltages of the DC-DC converter, and then selects the minimum loss voltage from the loss map.In other words, calibrated loss values ​​can be recorded for each of a multitude of output voltages of the buck / boost converter. The minimum loss voltage is thus a selected output voltage with the smallest calibrated loss value.

[0015] The controller then regulates the actual output voltage of the DC-DC converter, either in step-down or step-up mode, or bypasses the DC-DC converter if the required mode is not available for the given converter configuration. The step-down, step-up, or bypass mode is selected based on the desired operating mode of the electric drive system, i.e., motor operation or regeneration. The mode selection also depends on whether the minimum loss voltage determined from the loss map is lower than the DC link voltage. The controller then generates commands for controlling the electric machine based on the DC bus voltage and the torque and speed of the electric machine for the direct axis ("d-axis") and the quadrature axis ("q-axis").

[0016] The bypass switch can be controlled to equalize the voltage across it, i.e., the battery pack output voltage ("battery voltage") and the DC bus voltage. The bypass switch can be implemented as a mechanical relay or a bidirectional semiconductor switch to minimize component costs and internal resistance when the bypass switch is in an ON / conducting state. It is desirable for the bypass switch to close immediately once the voltage across it is equalized. However, a typical opening time for a mechanical relay is on the order of 5–10 ms. Therefore, PWM control via specially designed converter switches can be used in certain embodiments to properly equalize the voltage across the bypass switch, as described here.

[0017] The miniaturized DC-DC converter is a bidirectional converter that can use converter switches, e.g., MOSFETs in certain embodiments, with gallium nitride (“GaN”) and silicon carbide (“SiC”) being two possible materials for the converter switches. The bypass switch can be a mechanical contactor or a semiconductor switch.

[0018] A method for controlling the electric drive system involves calculating the required output power of the DC-DC converter via a controller based on a requested operating mode, a target speed, and a target torque of the electric machine. The method also includes comparing the required output power with a calibrated power threshold and controlling the DC-DC converter via the controller. If the required output power exceeds the calibrated power threshold, the DC-DC converter control includes closing the bypass switch via the controller to bypass the DC-DC converter.If the required output power is less than the calibrated power threshold, the controller determines a minimum loss voltage from a loss map and then uses the minimum loss voltage as the target control voltage of the DC-DC converter in order to optimize the efficiency of the electric drive system.

[0019] A vehicle is also disclosed, comprising one or more road wheels and the electric drive system. In this embodiment, the controller calculates a required output power of the buck / boost converter based on a requested output speed and torque of the electric machine. If the required output power is less than a calibrated power threshold, the controller determines a minimum loss voltage of the electric drive system using a loss map. The loss map contains calibrated loss values ​​for each of a variety of output voltages of the DC-DC converter. The minimum loss voltage is one of the output voltages with the lowest magnitude among the calibrated loss values. Additionally, the controller uses the minimum loss voltage as the target control voltage of the DC-DC converter, which may include operating the DC-DC converter in buck or boost mode, if available.

[0020] The above-mentioned and other features and advantages of the present disclosure will readily become apparent from the following detailed description of the preferred embodiments for carrying out the disclosure when considered in conjunction with the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES Fig. Figure 1 is a schematic representation of an electric drive system with a miniaturized DC-DC converter, which is controlled according to the method described here. Fig. 1A and Fig. Figure 1B shows schematic representations of an alternative step-down or step-up converter, which is part of the electric drive system of Fig. 1 can be used. Fig. Figure 2 is a schematic representation of an exemplary dual-loop control logic that can be used to carry out the present procedure. Fig. Figure 3 is a flowchart illustrating a method for controlling the miniaturized DC-DC converter and the rotating electrical machine. Fig. 1 describes a minimum loss voltage. DETAILED DESCRIPTION

[0021] Referring to the figures in which the same reference numerals refer to the same components in the different views, shows Fig. 1. A mobile platform 10 with a superstructure 11 and an electric drive system 15. The mobile platform 10 can optionally be configured as a motor vehicle, robot, etc., and thus, in such configurations, be equipped with road wheels 12 in rolling contact with a roadway 14. While the mobile platform 10 is one possible example of a system that benefits from the electric drive system 15, other advantageous applications for the electric drive system 15 can also be considered, including, but not limited to, stationary power plants, mobile platforms, and other types of land, air, or water vehicles.

[0022] The electric drive system 15 comprises a multi-phase electric machine (“M”). E“) 16 with a rotatable output shaft 18. When the electric machine 16 is excited by applying a multi-phase / alternating voltage (“VAC”) to the individual phase windings 48 of the electric machine 16, an output torque (arrow T) is generated. M The electrical current is generated and delivered via the output shaft 18 to a coupled load, such as the wheels 12 in the illustrated vehicle application. The electric machine 16 can optionally be configured as a three-phase / multi-phase motor or a motor / generator unit, with each of the phase windings 48 carrying a corresponding phase current.

[0023] The electric drive system 15 of Fig. 1 comprises a battery pack 20 or another application-specific energy storage system. The electric drive system 15 also includes a DC / DC converter 30 and a traction power inverter module (“TPIM”) 40. As described below, the DC / DC converter 30 can be configured in various ways as a step-down / step-up converter ( Fig. 1) Down-converter ( Fig. 1A) or upconverter ( Fig. 1B) shall be carried out, wherein the disclosed method 100 can be adapted for each of the different embodiments. The battery pack 20 contains a plurality of battery cells 22, e.g., rechargeable lithium-ion battery cells, arranged in a stack, and a capacitor 24 arranged in parallel with the battery cells 22. The number and arrangement of the battery cells 22 can vary depending on the intended use, e.g., ninety-six or more such battery cells 22 are used in certain high-voltage applications. A battery voltage (V bat + , V bat - ) is connected to the positive and negative battery voltage rails 19 + and 19 - supplied, with a DC bus voltage (V dc + and V dc - ) on the inverter bus rails 31 + and 31 -downstream, i.e., on the output side of the DC-DC converter 30, is present. When the DC-DC converter 30 is active and the bypass switch S0 is open, the battery voltage (V) differs. bat + , V bat - ) from the DC bus voltage (V dc + , V dc - ) depending on the control scheme used for the DC-DC converter 30.

[0024] The TPIM 40, which is electrically connected to the phase windings 48 of the electric machine 16, contains a first plurality of semiconductor switches 44, hereinafter referred to as inverter switches 44 for clarity. The inverter switches 44 are arranged in upper and lower sets as shown, the terms “upper” and “lower” referring to the inverter switches 44 connected to the positive and negative inverter busbars 31. + or 31 -are connected. The inverter switches 44 can be designed as voltage-controlled bipolar switching devices in the form of insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), broadband gap devices, or other suitable switches with a corresponding gate terminal (G) to which a gate voltage signal (arrow GC) is applied to change the corresponding ON / OFF state of the inverter switches 44.

[0025] With reference to Fig. 1 The DC-DC converter 30 is optionally configured as a buck / boost converter with an additional set of semiconductor switches 34, hereinafter referred to as converter switches 34. As can be seen, the buck and boost modes of such a DC-DC converter 30 are voltage-reducing and voltage-boosting operating modes, respectively. Like the inverter switches 44, the converter switches 34 can also consist of high-efficiency switches such as gallium nitride (“GaN”) or silicon carbide (“SiC”) MOSFETs, IGBTs, or other suitable switching devices, arranged in upper and lower switching sets. Each of the upper converter switches 34 is connected to a corresponding one of the lower converter switches 34 via a corresponding voltage branch 37A and 37B, with an induction coil 36 extending between the voltage branches 37A and 37B.

[0026] The DC-DC converter 30 from Fig. 1 additionally contains a bypass switch 32, which for clarity is also labelled S0. The bypass switch 32 is selectively opened or closed in response to switching control signals (arrow CC) transmitted by a controller (C) 50. The bypass switch 32 can optionally be constructed from an electromechanical relay, e.g., a bidirectional mechanical GaN or SiC relay. The bypass switch 32 is connected between the positive battery voltage rail 19 + and the positive inverter bus rail 31 + arranged. The closing of the bypass switch 32 in response to the switching control signals (arrow CC) thus causes the DC-DC converter 30 to be bypassed, the specific conditions requiring the closing of the bypass switch 32 and the resulting bypassing of the DC-DC converter 30 being determined in real time by the controller 50 as below with reference to Fig. 3 will be determined.

[0027] Shortly Fig. 1A and Fig. As referred to in 1B, the DC-DC converter 30 can alternatively be used as a miniaturized step-down converter ( Fig. 1A) or miniaturized upconverter ( Fig. 1B) be set up. The embodiment of Fig. 1A operates during low-speed / low-torque driving modes to reduce the inverter bus voltage from the battery voltage level to a lower value, and in a high-speed / low-current regeneration mode to reduce the inverter bus voltage between inverter bus rails 31. + and 31 - to reduce to the level of the battery voltage, and can be selectively bypassed under other conditions. The boost converter variant of Fig. 1B can be operated under high-speed / low-power conditions during driving modes to raise the inverter bus voltage from the battery voltage level to a higher value, during regeneration modes under low-speed / low-torque conditions to raise the inverter bus voltage to a battery voltage level, and can be selectively bypassed under other conditions. As with Fig. 1 use the embodiments of Fig. 1A and Fig. 1B use switch S0 as a bypass switch to bypass the DC-DC converter 30.

[0028] The controller 50 communicates with the electric machine 16 via a Controller Area Network (“CAN”) bus or another communication bus and can be configured as a standalone device or as a distributed control unit. Although in Fig. With reference to paragraph 1, the connectivity of the controller 50 to the electrical drive system 15 may include transmission conductors and / or wireless control links or paths suitable for transmitting and receiving the control signals (arrow CC). The controller 50 may include a processor (P) and a sensible, non-temporary memory (M), including read-only memory in the form of optical, magnetic, or flash memory. The controller 50 also includes a sufficient amount of random-access memory and electrically erasable, programmable read-only memory, as well as a high-speed clock, analog-to-digital and digital-to-analog circuitry, input / output circuitry and devices, and suitable signal conditioning and buffering circuitry.Computer-readable instructions are recorded in a memory (M) embodying a procedure 100, wherein the execution of this logic by the processor (P) causes the controller 50 to control the flow of electrical power within the electrical drive system 15.

[0029] In the present method 100, the controller 50 is programmed to receive a commanded motor torque requested by the operator or generated autonomously (arrow T). 16 ). Such a value can be provided by a motor control processor (not shown) of the electric machine 16, e.g. using a lookup table defined by the power and the target speed (arrow N). 16 ) of the electric machine 16 is indicated or referenced. The controller 50 uses the target torque (arrow T). 16 ) of the motor and the target speed (arrow N) 16) of the motor, in order to determine precisely when the bypass switch 32 is to be opened or closed according to the procedure 100. This is done as described below on the basis of a minimum loss voltage taken from a loss map 52 stored in the memory (M) or otherwise accessible to the controller 50.

[0030] Fig. Figure 2 shows, as an example, the two-circuit control logic 50L for the implementation of the present procedure 100 via the controller 50. Fig. 1 when determining one of two different operating modes of the electric drive system 15, i.e., driving and regenerating. To illustrate consistency, the control for a buck-boost version of the DC-DC converter 30 is described, with modifications for the alternative buck and boost versions of the respective Fig. 1A and Fig. 1B is possible.

[0031] In motor operation, i.e., when the electric machine 16 is excited in its capacity as an electric traction motor under operating conditions with low speed / low torque, the controller 50 operates the DC-DC converter 30 in push-pull mode. This control process regulates the intermediate circuit voltage between the converter busbars 31. + and 31 - from Fig. 1 effectively reduced. Under high-speed / low-power operating conditions, the controller 50 operates the DC-DC converter 30 in boost mode to increase the intermediate circuit voltage. In regenerative operation, the controller 50 operates the DC-DC converter 30 in boost mode at low speeds / low torque and in buck mode at high speeds / low power.

[0032] The 50L control logic enables efficiency optimization of the 15 electric drive system. Fig. 1 based on the ordered torque (arrow T) 16) and the rotational speed (arrow N) 16 ) as well as the aforementioned loss map 52. For each combination of input speed and torque setpoint, the controller 50 evaluates the magnitudes of various predetermined power losses recorded in the loss map 52 for a range of different output voltages of the DC-DC converter 30, e.g., 100–500 V. The minimum value in the loss map 52 has a corresponding voltage, referred to here as the “minimum loss voltage.” The controller 50 uses this value as the target / control voltage for the DC-DC converter 30 and also adjusts the d-axis and q-axis commands to the electric machine 16 as needed, based on speed, torque, and minimum loss voltage.

[0033] In the exemplary embodiment of the control logic 50L, an electronic control module (“ECM”) 150, i.e., a logic and hardware component of the controller 50, receives from Fig. 1, which is used to control the operation of the in Fig. The target torque (arrow T) is used in the DC-DC converter 30 shown on the far right. 16 ), the target speed (arrow N 16 ) and the current battery voltage (V bat ) and then compares the received values ​​with the lookup tables (“LUT”) that represent the loss map 52. These values ​​can be calibrated in the case of loss map 52 or measured, calculated, or otherwise determined in real time for the target torque, target speed, and battery voltage. The minimum loss voltage (“V”) mentioned above MIN-L “) is used, as mentioned above, as the control voltage for the DC-DC converter 30.

[0034] The loss card 52 outputs the minimum loss voltage and, based on the torque and speed, the current operating mode ("OM"), i.e., the aforementioned motor or regeneration mode. The ECM 150 can receive the minimum loss voltage and the current operating mode as input signals. Downstream of the ECM 150, separate control loops L1 and L2, respectively, control the operation of the DC-DC converter 30 and the TPIM 40 in response to the output signals of the ECM 150.

[0035] With regard to the control loop L1, which is used for the DC-DC converter 30, the ECM 150 outputs a control voltage signal CC. 30 to the DC-DC converter 30, which specifies the minimum loss voltage according to the loss map 52. For example, the control voltage signal CC can be 30be a proportional voltage signal that controls a specific output voltage of the DC-DC converter 30, where the output voltage is equal to the minimum voltage drop. The DC link voltage via the inverter DC link rails 31 + and 31 - It is thus set to the minimum loss voltage.

[0036] Still in relation to Fig. 2. Control loop L2 regulates the operation of the TPIM 40, which is connected to the DC-DC converter 30 such that the regulation of the output voltage of the DC-DC converter 30 affects the input voltage of the TPIM 40 and vice versa. The TPIM 40 is connected to the phase lines 48 of the electric machine 16. As part of control loop L2, the ECM 150 issues a q-axis command. iq* on a first node N1 and a d-axis command id* to a second node N1, based on the minimum loss voltage. As used in technical language, the term "d-axis current control" refers to a flux-generating current control acting on the direct axis of a rotating dq reference frame, while the q-axis current control (quadrature axis) is the torque-generating current of the electric machine 16. The first node N1 also receives the magnitude of the q-axis current as a feedback term (i q ) from an axis transformation block 66, subtracts this q-axis term from the q-axis command iq* and passes the difference to a proportional integral (“PI”) logic block 60q. Similarly, the second node N2 receives a d-axis current as a feedback term (i d ) from axis conversion block 66, subtracts the d-axis feedback term (i d ) from the d-axis command id* and transfers the difference to a PI logic block 60d.

[0037] Within the PI logic blocks 60q and 60d, the controller 50 applies a q-axis voltage (d q ) and a d-axis stress (d d ) from, where the q-axis stress (d q ) and the d-axis stress (d d ) represent a required adjustment to the current voltage commands to the TPIM 40. The magnitude of such voltage settings can be limited via a voltage limiting block (“LIM”) 62, e.g., using a bandpass filter, and fed into an axis transformation block 64. Within the transformation block 64, the controller 50 transforms the rotating d q-Reference frame into a fixed reference frame, i.e., the reference frame αβ. As can be estimated, the particular choice of transformation used for implementation in the control logic 50L depends on the choice of current controller used to implement loop L2, where the control within frame αβ is typical for the control of multiphase electrical machines.

[0038] The voltage outputs of block 64 are therefore the transformed voltages d ∝ and d β which are then fed as control voltages into a modulation block 65, where block 65 is a pulse width modulation controller (“PWM”) in the non-limiting configuration shown. In response to the control voltages d ∝ and d β The modulation block 65 outputs several gate voltage signals to the gate terminals (G) of the individual inverter switches 44 (see Fig. 1) In an exemplary three-phase embodiment of the electrical machine 16, for example, there would be six such gate signals, as the number “6” in Fig. 2 is displayed. The excited TPIM 40 then supplies current to the electric machine 16. The phase voltages are measured / calculated and entered into the phase transformation block 66, together with a current rotational position (θ). r ) of rotor 18, which is controlled by a position sensor S p is measured. The phase transformation block 66 then generates the currents i q and i d the q-axis and d-axis as feedback terms, which in turn, as mentioned above, are fed into nodes N1 and N2.

[0039] With reference to Fig. 3. Procedure 100 begins according to an exemplary embodiment with block B102. The controller 50 receives the target speed (arrow N). 16 ) and the target torque (arrow T) 16 ) of the electric machine 16, as in Fig. Figure 2 illustrates this, which may include the processing of pedal travel or other control inputs from a human operator or an autonomous controller. The controller 50 calculates the required input power (“CALC P”) to the electric machine 16 using the target speed and torque before proceeding to block B104.

[0040] In block B104, controller 50 compares the required input power with a calibrated power threshold (“P < CAL?”). The calibrated power threshold might be, for example, 30-40 kW in an application where the peak power demand can reach 90-100 kW, i.e., 30-40 percent of the peak power. If the required input power exceeds the power threshold, the process 100 switches to block B106, or alternatively to block B110.

[0041] Block B106 includes the determination, via controller 50, of whether the DC-DC converter 30 must be bypassed in the current operating mode ("OM = DC-DC?"). Block B106 may include checking the state of switch S0, for example, using a control signal sent to switch S0 and / or processing status bits of switch S0 via controller 50. Procedure 100 proceeds to block B108 if the DC-DC converter 30 is to be bypassed according to such criteria. Otherwise, procedure 100 proceeds directly to block B128.

[0042] In block B108, in response to the finding in block B104 that the electric machine 16 is operating above the aforementioned calibrated power threshold, the controller 50 closes the bypass switch 32 of Fig. 1 (“S0 = 1”) to bypass the DC-DC converter 30, and then continues with block B128.

[0043] Block B110 is analogous to block B106 and includes the determination, via controller 50, of whether the DC-DC converter 30 must be active in the current operating mode ("OM = DC-DC?"). Procedure 100 continues with block B112 if the DC-DC converter 30 is not active, and alternatively with block B114 if the DC-DC converter 30 is active.

[0044] Block B112 includes opening bypass switch 32 of Fig. 1, before continuing with block B114.

[0045] In block B114, the losses of the electric drive system 10 are taken from Fig. 1 based on the loss card 52 from Fig. 2 determined. As mentioned above, the controller 50 reads the values ​​stored in the loss card 52 at various possible control voltages of the converter 30 under the same torque and speed conditions and selects the minimum loss voltage ("V"). MIN-LThe loss map 52 can be based on losses in the electric drive system 15 itself, or on the input power of the TPIM 40 or the output power of the battery pack 20 in various embodiments. The method 100 then proceeds to block B116. In block B116, the controller 50 determines whether the current operating mode is a motor operating mode (“OM = MTR?”). The method 100 continues to block B118 if the current operating mode is a motor operating mode, and to block B119 if the current operating mode is not a motor operating mode.

[0046] In block B118, the controller 50 compares the minimum loss voltage (V). MIN-L ) from block B114 with the current converter bus voltage, which is displayed as V in block B118 INV is displayed to determine which value is larger, i.e., "V MIN-L < V INV? Procedure 100 continues with block B120 if the minimum loss voltage exceeds the current converter bus voltage, and alternatively with block B122 if the converter bus voltage exceeds the minimum loss voltage.

[0047] In block B119, the minimum loss voltage (V) MIN-L ) of block B114 compared with the battery voltage to determine which value is greater, i.e., “V MIN-L < VBAT? Procedure 100 continues with block B124 if the battery voltage exceeds the minimum loss voltage, and alternatively with block B126 if the minimum loss voltage exceeds the battery voltage.

[0048] Block B120 encompasses the operation of the DC-DC converter 30 in boost mode if the DC-DC converter 30 is a boost or buck-boost type while the electric drive system is in motor operation. In such a mode, the DC-DC converter 30 increases the inverter bus voltage to the minimum loss voltage and then proceeds to block B128. If the DC-DC converter 30 is a buck converter, block B120 includes the bypass of the DC-DC converter 30 via switch S0. Fig. 1A.

[0049] Block B122 encompasses the operation of the DC-DC converter 30 in buck / boost mode while the electric drive system is in motor operation, and when the DC-DC converter 30 is a buck / boost or boost converter. In such a mode, the DC-DC converter 30 reduces the inverter bus voltage from its current level to the minimum loss voltage of block B114 and then proceeds to block B128. If the DC-DC converter 30 is a boost converter, block B122 includes bypassing the converter 30 via switch S0. Fig. 1A.

[0050] In block B124, the controller 50 operates the DC-DC converter 30 in boost mode, again when the DC-DC converter 30 is of the buck-boost type ( Fig. 1) or Boost ( Fig. 1B), and while the electric drive system is in a regenerative mode. In such a mode, the DC-DC converter 30 boosts the bus voltage to the battery voltage to charge the battery and then proceeds to block B128. If the DC-DC converter 30 is a buck converter, block B124 includes bypassing the DC-DC converter 30 via the bypass switch S0, 32 of Fig. 1A.

[0051] In block B126, the controller 50 operates the DC-DC converter 30 in step-down mode while the electric drive system is in regeneration mode, provided that the DC-DC converter 30 is configured as a step-down / step-up controller ( Fig. 1) or as a step-down regulator ( Fig. 1A) is set up. The DC-DC converter 30 reduces the bus voltage to the battery voltage before further blocking B128. Block B126 includes the bypass of converter 30 via the bypass switch S0, 32 if the DC-DC converter 30 is a boost converter, e.g., as in Fig. 1B is shown.

[0052] Block B128 includes the generation of the current commands for the d-axis and q-axis, i.e., id* and iq* based on the bus voltage and the target torque and the target speed of the electric machine 16.

[0053] Using procedure 100 and control logic 50L from Fig.2. The size of the DC-DC converter 30 can be effectively reduced, e.g., to 20-30 kW or less for a peak power requirement of 90-100 kW. As can be estimated, some designs of electric vehicles require a peak power of approximately 200 kW. However, such vehicles may only require 30 kW of power for the vast majority of daily driving cycles. Using a 20-30 kW version of the DC-DC converter 30 in push-pull operation in such a design can enable a 15 percent reduction in losses.

Claims

[1] Electric drive system (15), comprising: a voltage bus with a positive bus rail (19+) and a negative bus rail (19-) and a DC bus voltage across the bus rails (19+, 19-); a battery pack (20) that is connected between the positive bus rail (19+) and the negative bus rail (19-) of the voltage bus and provides a battery voltage (V bat + , V bat - ) delivers; a DC / DC converter (30) comprising a set of semiconductor switches (34) connected between the positive bus rail (19+) and the negative bus rail (19-) and having a bypass switch (S0, 32) connected to the positive bus rail (19+), wherein the DC / DC converter (30) is configured as a buck / boost converter; a traction power inverter module (40), TPIM (40), with a DC side connected to the DC-DC converter (30) at an inverter bus voltage (31+, 31-) and with an AC side, AC, wherein the TPIM (40) is configured to direct the inverter bus voltage (31+, 31-) and thereby generate an AC bus voltage at phase lines (48); a rotating electric machine (16) connected to the AC side of the TPIM (40) and powered via the AC bus voltage; and a controller (50) configured to provide a required output power of the DC-DC converter (30) based on a requested operating mode, a target speed (N) 16 ) and a target torque (T 16 ) of the electrical machine (16) calculated to compare the required output power with a calibrated power threshold, and: if the required output power exceeds the calibrated power threshold, close the bypass switch (S0, 32) and thereby bypass the DC-DC converter (30); and If the required output power is less than the calibrated power threshold, a minimum loss voltage (V) MIN-L ) from a loss card (52) and then the minimum loss voltage (V MIN-L ) to use as a target control voltage of the DC-DC converter (30) in order to optimize the efficiency of the electric drive system (15) with the bypass switch (S0, 32) open; where the bypass switch (S0, 32) is a mechanical relay or bidirectional semiconductor switch. [2] Electric drive system (15) according to claim 1, wherein the controller (50) is configured to receive d-axis and q-axis commands (id*,iq*) for controlling the TPIM (40) and the electric machine (16) on the basis of the target torque, target speed and minimum loss voltage (V) MIN-L to generate. [3] Electric drive system (15) according to claim 1, wherein the controller (50) is configured to transmit pulse width modulation control signals, PWM control signals, to the pair of semiconductor switches (34) of the DC-DC converter (30) in order to thereby convert the DC bus voltage to the battery voltage (V bat +, V bat - ) to compensate before opening or closing the bypass switch (S0, 32). [4] Electric drive system (15) according to claim 1, wherein the semiconductor switches (34) in the DC-DC converter (30) are bidirectional gallium nitride or silicon carbide switches. [5] Electric drive system (15) according to claim 1, wherein the loss card (52) contains a lookup table filled with calibrated loss values ​​for each of a plurality of output voltages of the DC-DC converter (30), and wherein the minimum loss voltage (V MIN-L ) is a selected output voltage that has the smallest magnitude among the calibrated loss values. [6] Electric drive system (15) according to claim 1, wherein the controller (50) includes a control logic with a first control loop (L1) in which the controller (50) controls the operation of the DC-DC converter (30) via the minimum loss voltage (V MIN-L ) regulates, and a second control loop (L2) in which the controller (50) regulates the operation of the TPIM (40) via a proportional-integral current controller. [7] Electric drive system (15) according to claim 1, wherein the DC-DC converter (30) is configured as a buck / boost converter or as a boost converter and the controller (50) is configured to reduce the inverter bus voltage (31+, 31-) to the minimum loss voltage (V MIN-L ) to increase if the operating mode is motor mode, the target speed is above a speed threshold, and the required output power is less than the calibrated power threshold. [8] Electric drive system (15) according to claim 7, wherein in a regeneration mode the controller (50) is configured to reduce the inverter bus voltage (31+, 31-) to the battery voltage (V bat + , V bat - ) to increase if the target speed is below a speed threshold and the required output power is less than a calibrated power threshold. [9] Electric drive system (15) according to claim 1, wherein the DC-DC converter (30) is configured as a buck / boost converter or as a buck converter and, in driving mode, the controller (50) is configured to reduce the inverter bus voltage (31+, 31-) to the minimum loss voltage (V MIN-L ) to lower the speed if the target speed is below a speed threshold and the required output torque is less than a torque threshold.

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