Variable voltage converter based on flying capacitor

Abstract

The present invention relates to a variable voltage converter based on a flying capacitor. A powertrain system for a vehicle may include a variable voltage converter (VVC) and a controller. The variable voltage converter may include an inductor, a bus capacitor, and a flying capacitor. The controller may be configured to: in response to a power demand signal exceeding a threshold, modulate a switch of the variable voltage converter so that an inductor current generated by a collapsing field of the inductor is directed into the flying capacitor or the bus capacitor, so that the bus capacitor voltage exceeds the flying capacitor voltage; and in response to the power demand falling below the threshold, modulate the switch so that the flying capacitor is connected in parallel with the bus capacitor.

Description

Technical Field

[0001] The present application generally relates to a DC / DC converter with a flying capacitor configured to provide a boosted voltage to an electric machine during a propulsion mode of an electric vehicle. Background Art

[0002] Electrified vehicles (EVs), including hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs), rely on a traction battery to power the traction motor used for propulsion, and on a power inverter between the traction battery and the traction motor to convert direct current (DC) to alternating current (AC). A typical AC traction motor is a three-phase motor that can be powered by three sinusoidal signals, each driven with 120 degrees of phase separation. The traction battery is configured to operate within a specific voltage range and provide maximum current. The traction battery is alternatively referred to as a high-voltage battery. However, improved performance of the motor can be achieved by operating it within a different voltage range, which is generally higher than the terminal voltage of the traction battery. Similarly, the current demand used to drive the vehicle's motor is often referred to as high current.

[0003] Furthermore, many electrified vehicles include a DC-DC converter (also known as a variable voltage converter (VVC)) to convert the voltage of the traction battery to the operating voltage level of the electric machines. The electric machines, which may include traction motors and generators, can require high voltages and currents. Due to these voltage and current requirements, the battery module and the power electronics module are often in constant communication. Summary of the Invention

[0004] A powertrain system for a vehicle may include a variable voltage converter (VVC) and a controller. The VVC may include an inductor, a bus capacitor, and a flying capacitor. The controller may be configured to: in response to a power demand signal exceeding a threshold, modulate a switch of the VVC such that an inductor current generated by a collapsing field of the inductor is directed into the flying capacitor or the bus capacitor, causing a bus capacitor voltage to exceed the flying capacitor voltage; and in response to the power demand signal falling below the threshold, modulate the switch such that the flying capacitor is connected in parallel with the bus capacitor.

[0005] According to one embodiment of the present invention, the flying capacitor is connected between the upper connection point between the first switch and the second switch and the other connection point between the third switch and the fourth switch, and the inductor is connected between the positive input terminal and the midpoint between the second switch and the third switch.

[0006] According to one embodiment of the present invention, the controller is further configured to alternately allow the inductor current to flow into the flying capacitor and the bus capacitor connected in series through the switch, or to allow the inductor current to flow into the bus capacitor when the flying capacitor is connected in series with the bus capacitor through the switch and is bypassed by a diode.

[0007] According to one embodiment of the present invention, the controller is further configured to: in response to the power demand signal transitioning to a negative direction, connect the flying capacitor in parallel with the bus capacitor, and operate the switch in a pass mode in a steady state to allow charge to flow, wherein the first switch, the second switch, and the fourth switch are turned on, and the third switch is turned off.

[0008] A method of controlling a converter of a powertrain system includes directing current into an inductor of the converter to generate a field; and then, in response to a power demand signal exceeding a threshold, causing the field to collapse to allow charge to flow to a flying capacitor to increase a voltage of a bus capacitor such that the voltage of the bus capacitor exceeds the voltage of the flying capacitor.

[0009] A vehicle includes an electric motor, a variable voltage converter (VVC), and a controller. The electric motor may be configured to propel the vehicle. The VVC may include an inductor, a bus capacitor, and a flying capacitor. The controller may be configured to modulate switches of the VVC so that an inductor current generated by a collapsing field of the inductor at a drive voltage of the electric motor is boosted through the flying capacitor and directed into the bus capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a diagram of an electrified vehicle having an electric machine, an inverter, and a variable voltage converter configured to reduce current ripple during charging of the electric vehicle from an AC grid.

[0011] Figure 2 is a diagram of a hybrid vehicle showing a typical powertrain and energy storage components including a variable voltage converter.

[0012] Figure 3 is a schematic diagram of a power inverter of a power electronics module.

[0013] Figure 4 is a diagram of a hybrid vehicle powertrain including a traction battery, an inverter, and a variable voltage converter with a flying capacitor.

[0014] Figure 5 is a graphical representation of control signals for switches of a variable voltage converter and load current versus time.

[0015] Figure 6 is a graphical representation of the variable voltage converter step-up ratio versus duty cycle.

[0016] Figure 7 is a flow chart of a control system for a variable voltage converter that directs reactive power to a balancing capacitor.

[0017] Figure 8 is a graphical representation of control signals for switches of a variable voltage converter and system electrical characteristics versus time. DETAILED DESCRIPTION

[0018] Embodiments of the present disclosure are described herein. However, it will be understood that the disclosed embodiments are merely examples, and that other embodiments may take various forms and alternative forms. The figures are not necessarily drawn to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to utilize the invention in various forms. As will be understood by those of ordinary skill in the art, the various features shown and described with reference to any one of the figures may be combined with features shown in one or more other figures to produce embodiments that are not explicitly shown or described. The combinations of features shown provide representative embodiments for typical applications. However, various combinations and variations of features consistent with the teachings of the present disclosure may be desired for specific applications or implementations.

[0019] A typical drive system for an EV / HEV may include a direct current (DC) power source (i.e., a high-voltage battery), a variable voltage converter (VVC), an inverter, and a motor. The VVC may be a bidirectional boost converter configured to boost the battery voltage to the operating voltage of the motor / generator and inverter. Practical aspects of a typical drive system include: as power demand increases, multiple power devices connected in parallel may be required to output higher current / higher power to meet the demand. The parallel connection of multiple power devices can lead to current sharing issues between the parallel-connected power devices. As a result, system efficiency may be affected. Furthermore, in a typical drive system, the output voltage range of the boost converter may be limited as efficiency decreases based on the step-up ratio, which is the ratio of the high-voltage DC voltage (Vdc) to the battery input (Vb) (e.g., Vdc / Vb>2). To improve the performance of electric powertrains (e-drives), a VVC with a wide output voltage range is required.

[0020] Figure 1A hybrid electric vehicle is depicted showing internal electric powertrain components configured to operate a motor inverter 4 through a variable voltage converter (VVC) 6 (e.g., a DC / DC converter) and a high-voltage traction battery 14 to cause current to flow through the windings of a motor 2. The VVC includes power devices 8, a capacitor 10, and an inductor 12. The VVC can be operated in at least three propulsion modes, including a pass-through mode, a low-boost mode, and a high-boost mode.

[0021] In the first operating mode (i.e., pass-through mode), power devices 8A, 8B, and 8D are on, and power device 8C is configured to create an open circuit so that capacitors 10A and 10B are generally connected in parallel. Here, the DC bus voltage (Vdc) to inverter 4 is substantially equal to the voltage (Vb) of battery 14 and the voltage (Vf) across flying capacitor 10A (i.e., Vdc=Vf=Vb).

[0022] The second operating mode is a low-boost mode, in which power devices 8A and 8D remain on, power devices 8B and 8C are modulated (e.g., pulse-width modulated (PWM)) as conventional boost converters, and output capacitors 10A and 10B are connected in parallel. Here, the DC bus voltage (Vdc) to inverter 4 is greater than the voltage (Vb) of battery 14 based on the duty cycle. For example, Vdc may be equal to Vb / D, where D is the duty cycle of the on-time of power device 8B.

[0023] The third operating mode is a high boost mode in which all of the power devices 8A, 8B, 8C, and 8D are modulated (e.g., PWM). During operation in this mode, the DC bus voltage (Vdc) may be greater than the maximum voltage that can be generated in the second mode. For example, the DC bus voltage (Vdc) may be boosted to the quotient of twice the battery voltage (Vb) divided by the duty cycle (D) (i.e., Vdc=2Vb / D). This will produce a flying capacitor voltage (Vf) equal to the quotient of the battery voltage (Vb) divided by the duty cycle (D) (i.e., Vf=Vb / D), and therefore, Vf may be controlled to be half the DC bus voltage (Vdc). During operation in this mode, the inductor ripple frequency (f L ) can be the switching frequency (f SW ) multiples (e.g., f L =2f SW Here, the equivalent switching frequency of the inductor is doubled, so the size and cost of the inductor can be reduced. One advantage of the third mode is that it can produce an output with higher efficiency than the second mode, however, the second mode has a larger bus capacitance and therefore can have lower ripple at the output voltage.

[0024] Figure 2 An electrified vehicle 112, which may be referred to as a plug-in hybrid electric vehicle (PHEV), is depicted. The plug-in hybrid electric vehicle 112 may include one or more electric motors 114 mechanically connected to a hybrid transmission 116. The electric motors 114 can operate as either motors or generators. Furthermore, the hybrid transmission 116 is mechanically connected to an engine 118. The hybrid transmission 116 is also mechanically connected to a drive shaft 120, which is mechanically connected to wheels 122. The electric motors 114 can provide propulsion and deceleration capabilities when the engine 118 is on or off. The electric motors 114 can also function as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system. The electric motors 114 can also reduce vehicle emissions by allowing the engine 118 to operate at a more efficient speed and allowing the hybrid electric vehicle 112 to operate in an electric mode with the engine 118 off under certain conditions. The electrified vehicle 112 may also be a battery electric vehicle (BEV). In a BEV configuration, the engine 118 may not be present. In other configurations, the electrified vehicle 112 may be a full hybrid electric vehicle (FHEV) without plug-in capability.

[0025] The traction battery or battery pack 124 stores energy that can be used by the motor 114. The vehicle battery pack 124 can provide a high-voltage direct current (DC) output. The traction battery 124 can be electrically connected to one or more power electronics modules 126. One or more contactors 142 can isolate the traction battery 124 from other components when open, and can connect the traction battery 124 to other components when closed. The power electronics module 126 is also electrically connected to the motor 114 and provides the ability to transfer energy bidirectionally between the traction battery 124 and the motor 114. For example, the traction battery 124 can provide a DC voltage, while the motor 114 can operate using three-phase alternating current (AC). The power electronics module 126 can convert the DC voltage into three-phase AC current to operate the motor 114. In regenerative mode, the power electronics module 126 can convert the three-phase AC current from the motor 114, which is acting as a generator, into a DC voltage compatible with the traction battery 124.

[0026] The vehicle 112 may include a variable voltage converter (VVC) 152 electrically connected between the traction battery 124 and the power electronics module 126. The VVC 152 may be a DC / DC boost converter configured to increase or step up the voltage provided by the traction battery 124. By increasing the voltage, the current demand may be reduced, resulting in a reduction in the wiring size of the power electronics module 126 and the electric motor 114. Additionally, the electric motor 114 may operate with higher efficiency and lower losses.

[0027] In addition to providing energy for propulsion, the traction battery 124 can also provide energy for other vehicle electrical systems. The vehicle 112 may include a DC / DC converter module 128 that converts the high-voltage DC output of the traction battery 124 into a low-voltage DC power source compatible with low-voltage vehicle loads. The output of the DC / DC converter module 128 can be electrically connected to an auxiliary battery 130 (e.g., a 12V battery) for charging the auxiliary battery 130. Low-voltage systems can be electrically connected to the auxiliary battery 130. One or more electrical loads 146 can be connected to the high-voltage bus. The electrical loads 146 can have associated controllers that appropriately operate and control the electrical loads 146. Examples of electrical loads 146 may include fans, electric heating elements, and / or air conditioning compressors.

[0028] The electrified vehicle 112 may be configured to recharge the traction battery 124 via an external power source 136. The external power source 136 may be connected to an electrical outlet. The external power source 136 may be electrically connected to a charger or electric vehicle supply equipment (EVSE) 138. The external power source 136 may be the power distribution grid or the grid provided by a public utility. The EVSE 138 may provide circuitry and controls to regulate and manage energy transfer between the power source 136 and the vehicle 112. The external power source 136 may provide DC power or AC power to the EVSE 138. The EVSE 138 may have a charging connector 140 for plugging into a charging port 134 of the vehicle 112. The charging port 134 may be any type of port configured to transfer power from the EVSE 138 to the vehicle 112. The charging port 134 may be electrically connected to a charger or an onboard power conversion module 132. The power conversion module 132 may condition the power supplied from the EVSE 138 to provide appropriate voltage and current levels to the traction battery 124. The power conversion module 132 may interface with the EVSE 138 to coordinate power delivery to the vehicle 112. The EVSE connector 140 may have pins that mate with corresponding recesses of the charging port 134. Alternatively, the various components described as being electrically coupled or connected may transfer power using wireless inductive coupling.

[0029] One or more wheel brakes 144 may be provided to slow down and prevent vehicle 112 from moving. Wheel brakes 144 may be hydraulically actuated, electrically actuated, or some combination thereof. Wheel brakes 144 may be part of a braking system 150. Braking system 150 may include other components for operating wheel brakes 144. For simplicity, the figures depict a single connection between braking system 150 and one of wheel brakes 144. Connections between braking system 150 and other wheel brakes 144 are implicit. Braking system 150 may include a controller to monitor and coordinate braking system 150. Braking system 150 may monitor the brake components and control wheel brakes 144 to slow the vehicle. Braking system 150 may respond to driver commands and may also operate autonomously to implement functions such as stability control. When requested by another controller or sub-function, the controller of braking system 150 may implement a method for applying the requested braking force.

[0030] The electronic modules in the vehicle 112 may communicate via one or more vehicle networks. The vehicle network may include multiple channels for communication. One channel of the vehicle network may be a serial bus such as a controller area network (CAN). One of the channels of the vehicle network may include Ethernet as defined by the Institute of Electrical and Electronics Engineers (IEEE) 802 family of standards. Other channels of the vehicle network may include discrete connections between modules and may include power signals from the auxiliary battery 130. Different signals may be transmitted over different channels of the vehicle network. For example, a video signal may be transmitted over a high-speed channel (e.g., Ethernet) while control signals may be transmitted over CAN or discrete signals. The vehicle network may include any hardware components and software components that assist in transmitting signals and data between modules. Although the vehicle network is Figure 1 Not shown, but implied, the vehicle network may be connected to any electronic modules present in the vehicle 112. A vehicle system controller (VSC) 148 may be present to coordinate the operation of the various components.

[0031] Typically, the VVC 152 is configured as a boost converter. The VVC 152 may include input terminals that may be connected to terminals of the traction battery 124 via contactors 142. The VVC 152 may include output terminals that are connected to terminals of the power electronics module 126. The VVC 152 may be operated to cause a voltage at the output terminals to be higher than a voltage at the input terminals. The vehicle 112 may include a VVC controller that monitors and controls electrical parameters (e.g., voltage and current) at various locations in the VVC 152. In some configurations, the VVC controller may be included as part of the VVC 152. The VVC controller may determine an output voltage reference. The VVC controller can be based on electrical parameters and voltage reference A control signal sufficient to cause VVC 152 to achieve the desired output voltage is determined. In some configurations, the control signal may be implemented as a pulse width modulated (PWM) signal, wherein the duty cycle of the PWM signal varies. The control signal may operate at a predetermined switching frequency. The VVC controller may use the control signal to command VVC 152 to provide the desired output voltage. The specific control signal used to operate VVC 152 may be directly related to the amount of voltage boost provided by VVC 152.

[0032] Reference Figure 2 The VVC 152 can increase or "step up" the potential of the power provided by the traction battery 124. The traction battery 124 can provide high-voltage (HV) DC power. In some configurations, the traction battery 124 can provide a voltage between 150 volts and 400 volts. The contactor 142 can be electrically connected in series between the traction battery 124 and the VVC 152. When the contactor 142 is closed, HV DC power can be transferred from the traction battery 124 to the VVC 152. An input capacitor can be electrically connected in parallel with the traction battery 124. The input capacitor can stabilize the bus voltage and reduce any voltage and current ripple. The VVC 152 can receive the HV DC power and increase or "step up" the potential of the input voltage according to the duty cycle. Typically, an output capacitor is electrically connected between the output terminals of the VVC 152 and the input of the power electronics module 126 to stabilize the bus voltage and reduce voltage and current ripple at the output of the VVC 152.

[0033] Reference Figure 3 , a system 300 is provided for controlling a power electronics module (PEM) 126 . Figure 3 The PEM 126 is shown as including a plurality of switches 302 (e.g., IGBTs) configured to collectively operate as an inverter having a first phase leg 316, a second phase leg 318, and a third phase leg 320. Although the inverter is shown as a three-phase converter, the inverter may include additional phase legs. For example, the inverter may be a four-phase converter, a five-phase converter, a six-phase converter, etc. Furthermore, the PEM 126 may include multiple converters, each inverter in the PEM 126 including three or more phase legs. For example, the system 300 may control two or more inverters in the PEM 126. The PEM 126 may also include a DC-to-DC converter having high-power switches (e.g., IGBTs) to convert the power electronics module input voltage to the power electronics module output voltage via step-up, step-down, or a combination thereof.

[0034] like Figure 3As shown, the inverter can be a DC to AC converter. In operation, the DC to AC converter receives DC power from the DC power link 306 via the DC bus 304 and converts the DC power into AC power. The AC power is converted to AC power via the phase current i a 、i b and i c transmission to drive an AC motor, also referred to as motor 114 (such as in Figure 3 ). In this example, the DC power link 306 may include a DC battery to provide DC power to the DC bus 304. In another example, the inverter may operate as an AC-to-DC converter that converts AC power from the AC motor 114 (e.g., a generator) into DC power, where the DC bus 304 may provide DC power to the DC power link 306. In addition, the system 300 may control the PEM 126 in other power electronics topologies.

[0035] Continue to refer to Figure 3 Each of the phase bridges 316, 318, and 320 in the inverter includes a power switch 302. The power switch 302 can be implemented by various types of controllable switches. In one embodiment, each power switch 302 can include a diode and a transistor (eg, an IGBT). Figure 3 The diode is marked as D a1 、D a2 、D b1 、D b2 、D c1 and D c2 ,and Figure 3 The IGBTs are marked as S a1 、S a2 、S b1 、S b2 、S c1 and S c2 . Power switch S a1 、S a2 、D a1 and D a2 It is part of the phase bridge A of the three-phase converter. Figure 3 In FIG, it is marked as the first phase bridge A 316. Similarly, the power switch S b1 、S b2 、D b1 and D b2 is part of the phase bridge B 318 of the three-phase converter, and the power switch S c1 、S c2 、D c1 and D c2It is part of the phase bridge C 320 of the three-phase converter. The inverter may include any number of power switches 302 or circuit elements depending on the specific configuration of the inverter. The diode (D xx ) and IGBT(S xx ) are connected in parallel, however, since the polarity is reversed for proper operation, this configuration is often referred to as an anti-parallel connection. The diodes in this anti-parallel configuration are also referred to as freewheeling diodes.

[0036] like Figure 3 As shown, set the current sensor CS a , CS b and CS c To sense the currents in phase bridges 316, 318 and 320 respectively. Figure 3 The current sensor CS is shown separated from the PEM 126. a , CS b and CS c However, depending on the configuration of the PEM 126, the current sensor CS a , CS b and CS c May be integrated as part of the PEM 126. Figure 3 Current sensor CS in a , CS b and CS c are mounted to phase bridges A, B and C (i.e. Figure 3 The phase bridges 316, 318 and 320 in the system are connected in series and provide feedback signals i for the system 300 respectively. as 、i bs and i cs (also Figure 3 Feedback signal i as 、i bs and i cs The current signal may be a raw current signal processed by the logic device (LD) 310, or may be embedded with data or information about the current flowing through the phase bridges 316, 318, and 320, respectively, or may be encoded with the data or information. In addition, the power switch 302 (e.g., IGBT) may include current sensing capability. The current sensing capability may include a device configured to provide a current signal indicating i as 、i bs and i cs The data / signal may indicate the direction, magnitude, or both direction and magnitude of the current flowing through phase bridges A, B, and C, respectively.

[0037] Refer again Figure 3, the system 300 includes a logic device (LD) or controller 310. The controller or LD 310 may be implemented by various types of electronic devices and / or microprocessor-based computers or controllers, or a combination thereof. To implement the method of controlling the PEM 126, the controller 310 may execute a computer program or algorithm that is embedded with or encoded with the method and stored in volatile memory 312 and / or permanent memory 312. Alternatively, the logic may be encoded into discrete logic, a microprocessor, a microcontroller, or a logic array or gate array stored on one or more integrated circuit chips. As Figure 3 As shown in the embodiment, the controller 310 receives and processes the feedback signal i as 、i bs and i cs To control the phase current i a 、i b and i c , so that the phase current i a 、i b and i c Flow through the phase bridges 316, 318, and 320 and into the corresponding windings of the motor 114 according to various current or voltage patterns. For example, the current pattern may include the phase currents i flowing into and out of the DC bus 304 or the DC bus capacitor 308. a 、i b and i c pattern. Figure 3 The DC bus capacitor 308 in FIG. 1 is shown as separate from the PEM 126 . However, the DC bus capacitor 308 may be integrated as part of the PEM 126 .

[0038] like Figure 3 As shown, a storage medium 312 such as a computer readable memory (hereinafter referred to as "memory") can store a computer program or algorithm embedded with or encoded with the method. In addition, the memory 312 can store data or information about various operating conditions or components in the PEM 126. For example, the memory 312 can store data or information about the current flowing through each phase bridge 316, 318, and 320. Figure 3 As shown, the memory 312 may be part of the controller 310. However, the memory 312 may be located in any suitable location accessible to the controller 310.

[0039] like Figure 3As shown, the controller 310 sends at least one control signal 236 to the power converter system 126. The power converter system 126 receives the control signal 236 to control the switching configuration of the inverter, thereby controlling the current flowing through each phase bridge 316, 318, and 320. The switching configuration is a set of switching states of the power switches 302 in the inverter. Generally speaking, the switching configuration of the inverter determines how the inverter converts power between the DC power link 306 and the motor 114.

[0040] To control the switching configuration of the inverter, the inverter changes the switching state of each power switch 302 in the inverter to a closed state or an open state based on the control signal 236. In the illustrated embodiment, to switch the power switches 302 to a closed state or an open state, the controller or LD 310 provides a gate voltage (Vg) to each power switch 302, thereby driving the switching state of each power switch 302. The gate voltage Vg a1 、Vg a2 、Vg b1 、Vg b2 、Vg c1 and Vg c2 (exist Figure 3 ) controls the switching state and characteristics of each power switch 302. Figure 3 302. Although shown as a voltage-driven device, the inverter can be a current-driven device or can be controlled by other strategies that switch the power switch 302 between a closed state and an open state. The controller 310 can change the gate drive of each IGBT based on the speed of the motor 114, the mirror current, or the temperature of the IGBT switch. The gate drive change can be selected based on multiple gate drive currents, in which the gate drive current change is proportional to the change in the IGBT switching speed.

[0041] Also like Figure 3As shown, each of the phase bridges 316, 318 and 320 includes two switches 302. However, only one switch in each of the phase bridges 316, 318 and 320 can be in a closed state without short-circuiting the DC power link 306. Therefore, in each phase bridge, the switching state of the lower switch is generally opposite to the switching state of the corresponding upper switch. The upper switches are generally referred to as high-side switches (i.e., 302A, 302B, 302C) and the lower switches are generally referred to as low-side switches (i.e., 302D, 302E, 302F). Therefore, the high state of the phase bridge refers to the upper switch in the phase bridge being in a closed state and the lower switch being in an open state. Similarly, the low state of the phase bridge refers to the upper switch of the phase bridge being in an open state and the lower switch being in a closed state. As a result, the IGBTs with current mirroring capability can be all IGBTs, a subset of IGBTs (e.g., S a1 、S b1 、S c1 ) or a single IGBT.

[0042] exist Figure 3 During the active state of the three-phase converter example shown in FIG, two situations may occur: (1) two phase bridges are in a high state while the third phase bridge is in a low state, or (2) one phase bridge is in a high state while the other two phase bridges are in a low state. Thus, one phase bridge in the three-phase converter (which can be defined as the "reference" phase for a given active state of the inverter) is in a state opposite to the states of the other two phase bridges (or "non-reference" phases) having the same state. Thus, the non-reference phases are either both in a high state or both in a low state during the active state of the inverter.

[0043] Solid-state devices (SSDs), such as insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), or bipolar junction transistors (BJTs), are widely used in various vehicle applications and industrial applications, such as electric motor drives, power inverters, DC-DC converters, and power modules. The operation of IGBTs and MOSFETs is voltage-controlled, where the operation is based on the voltage applied to the gate of the IGBT or MOSFET, while the operation of BJTs is current-controlled, where the operation is based on the current applied to the base of the BJT. Here, the use of SSDs or high-power relays can be used to control, change, or regulate the current between the vehicle's battery and the motor.

[0044] Figure 4is a diagram of a hybrid vehicle powertrain 400 including an electric machine 402, an inverter (e.g., a DC / AC converter) 404, a variable voltage converter (VVC) 406, and a battery 414. The VVC includes four power devices (408A, 408B, 408C, and 408D), a flying capacitor (C f )410A, DC bus capacitor (C dc ) 410B and a boost inductor 412. The VVC 406 can operate in at least three modes, including a pass mode, a low boost mode, and a high boost mode.

[0045] In the first operating mode (i.e., pass mode), power devices 408A, 408B, and 408D are on, and power device 408C is configured to create an open circuit so that capacitors 410A and 410B are generally connected in parallel. Here, the DC bus voltage (Vdc) to inverter 404 is substantially at the voltage (Vb) of battery 414 and the voltage (Vf) across flying capacitor 410A (i.e., Vdc=Vf=Vb).

[0046] The second operating mode is a low-boost mode, in which power devices 408A and 408D remain on, power devices 408B and 408C are modulated by a controller (e.g., pulse width modulation (PWM)) in a manner similar to that of a conventional boost converter, and output capacitors 410A and 410B are connected in parallel. Here, the DC bus voltage (Vdc) to inverter 404 is greater than the voltage (Vb) of battery 414 based on the duty cycle. For example, Vdc may be equal to Vb / D, where D is the duty cycle of the on-time of power device 408B.

[0047] The third operating mode is a high-boost mode, in which power devices 408A, 408B, 408C, and 408D are all modulated (e.g., PWM). Modulation can use complementary signals for the high-side matching driver and the low-side matching driver, for example, the matching high-side driver and low-side driver are S1 408A and S4 408D and S2 408B and S3 408C. In this example, the control signals for S1 408A and S4 408D can be switched in opposite directions at substantially the same time, while the control signals for S2 408B and S3 408C can be switched in opposite directions at substantially the same time (at a different time than the switching time of S1 408A and S4 408D). In addition, the control signals may include an offset or delay so that a DC path to ground is not formed by turning on both the high-side switch and the low-side switch at the same time. In addition, since the on-time and off-time may require more or less time, some control signals may include further delays.

[0048] In this high boost operating mode, the DC bus voltage (Vdc) can be greater than the maximum voltage that can be generated in the second mode (e.g., the maximum boost voltage of a conventional boost converter). For example, the DC bus voltage (Vdc) can be boosted to the quotient of twice the battery voltage (Vb) divided by the duty cycle (D) (i.e., Vdc=2Vb / D). This will produce a flying capacitor voltage (Vf) equal to the quotient of the battery voltage (Vb) divided by the duty cycle (D) (i.e., Vf=Vb / D), and therefore, Vf can be controlled to be half the DC bus voltage (Vdc). During operation in this mode, the inductor ripple frequency (f L ) can be the switching frequency (f SW ) multiples (e.g., f L =2f SW Here, the equivalent switching frequency of the inductor is doubled, so the size and cost of the inductor can be reduced. One advantage of the third mode is that it can produce an output with higher efficiency than the second mode, however, the second mode has a larger bus capacitance and therefore can have lower ripple at the output voltage.

[0049] The VVC 406 has a multi-level topology configuration. Therefore, the VVC 406 has the advantage of being able to achieve the same high DC bus voltage (Vdc) as a conventional boost converter while using power devices with lower voltage ratings. This is because the power devices are connected in series, so the breakdown voltage is distributed across all four power devices. Therefore, IGBTs or even power MOSFETs with lower voltage ratings can be used for the switches / power devices, providing cost, performance, and efficiency improvements.

[0050] Additionally, the VVC 406 has three different operating modes (i.e., pass-through mode, low-boost mode, and high-boost mode, each with a different boost ratio (Vdc / Vb)). This provides more freedom when configuring the system to improve system efficiency optimization, especially for systems that may require a high boost ratio.

[0051] Furthermore, the ripple frequency of the inductor 412 is generally twice the switching frequency. In other words, the equivalent switching frequency of the inductor is doubled, thereby further reducing the size and cost of the inductor.

[0052] Furthermore, although the proposed VVC 406 has four power devices 408A to 408D compared to two power devices in a conventional boost converter, the four power devices 408A to 408D of the VVC 406 allow for fault-tolerant operation. For example, if S1 408A or S4 408D fails (e.g., is short-circuited), the VVC 406 can still operate in pass-through mode or low-boost mode, making it possible to boost the battery voltage to a high-voltage DC bus voltage.

[0053] Figure 5 is used for variable voltage converters (VVC) (e.g. Figure 4 4. FIG. 5 shows a graphical diagram 500 of a control signal 502 (e.g., VVC in FIG. 4) and an inductor current 504 (e.g., the current flowing into inductor 412) versus time 506. The control signal 502 includes a first signal (S1) 502A having a first curve 508A (e.g., the control signal for switch 408A), a second signal (S2) 502B having a second curve 508B (e.g., the control signal for switch 408B), a third signal (S3) 502C having a third curve 508C (e.g., the control signal for switch 408C), and a fourth signal (S4) 502D having a fourth curve 508D (e.g., the control signal for switch 408D). The inductor current 504 (e.g., the current flowing into inductor 412) is shown versus time 506 as a current curve 510. At a first time 512, the switches (e.g., 408B and 408C) for the flying capacitor (e.g., 410A) are complementary switched, such that the high-side switch S2 (e.g., 408B) is turned off and the low-side switch S3 (e.g., 408C) is turned on, while the other high-side switch (e.g., 408A) is turned off (e.g., open) and the low-side switch (e.g., 408D) is turned on (e.g., closed or shorted). Thus, current flows from the battery (e.g., battery 414) and flows through the inductor (e.g., 412), thereby inducing a field in the inductor.

[0054] The inductor current 510 increases until a second time 514 at which the outer switches (e.g., 408A and 408D) for the flying capacitor (e.g., 410A) complementarily switch so that the high-side switch S1 (e.g., 408A) is on and the low-side switch S4 (e.g., 408D) is off, while the other high-side switch (e.g., 408B) is off (e.g., open) and the other low-side switch (e.g., 408C) is on (e.g., closed or shorted). This causes the field of the inductor (e.g., 412) to collapse, and thus causes current to flow from the battery to the inductor, then to the flying capacitor (e.g., 410A), onto the high-voltage DC bus, and then back to the battery.

[0055] At a third time 516, the outer switches (e.g., 408A and 408D) for the flying capacitor (e.g., 410A) are complementary switched, so that the high-side switch S1 (e.g., 408A) is turned off and the low-side switch S4 (e.g., 408D) is turned on, while the inner high-side switch (e.g., 408B) is turned off (e.g., open circuit) and the inner low-side switch (e.g., 408C) is turned on (e.g., closed or short circuited). Therefore, current flows from the battery (e.g., battery 414) and flows through the inductor (e.g., 412), thereby inducing a field in the inductor.

[0056] Again, the inductor current 510 increases until a fourth time 518, at which the inner switches (e.g., 408B and 408C) for the flying capacitor (e.g., 410A) complementarily switch, causing the high-side switch S2 (e.g., 408B) to turn on and the low-side switch S3 (e.g., 408C) to turn off, while the other high-side switch (e.g., 408A) turns off (e.g., open) and the other low-side switch (e.g., 408D) turns on (e.g., closed or shorted). This causes the field of the inductor (e.g., 412) to collapse, and thus causes current to flow from the battery (e.g., 414) to the inductor (e.g., 412), then to the flying capacitor (e.g., 410A) and back to the battery (e.g., 414).

[0057] This is a complete cycle because the control signal at time 512 is equal to the signal at time 520. Here, one cycle is from the first time point 512 to the second time point 520. Average characteristics are determined for one cycle, for example, the average inductor current 504 is measured for one cycle, and the average flying capacitor voltage and the average bus capacitor voltage are measured for one cycle (e.g., time 512 to time 520). Figure 5 is a graphical representation of a dynamic system that changes over time (as shown by a changing control signal that results in a changing inductor current). In contrast to dynamic operation, a steady-state operating mode is one during which the control signal does not change. For example, Figure 5 One cycle of the high boost mode of operation is shown, in which the switches are modulated to boost the output voltage. When the VVC transitions to pass mode, switches S1 (408A), S2 (408B), and S4 (408D) are turned on while switch S3 (408C) is turned off, and all switches remain in these conductive states, which can be referred to as a steady-state mode of operation during pass mode.

[0058] Figure 66 is a graphical diagram 600 of a variable voltage converter's boost ratio 602 versus duty cycle 604. In this diagram, the VVC boost ratio (Vdc / Vb) is shown during three different operating modes of a VVC (e.g., VVC 406). This demonstrates that there is more freedom in selecting an operating mode for system efficiency optimization. A first curve 608 illustrates the unity-gain pass mode. The low-boost mode, illustrated by the second curve 610, illustrates an operating principle similar to that of a conventional boost converter. Here, because the converter efficiency decreases dramatically as the boost ratio increases with decreasing duty cycle, or because the equivalent series resistance (ESR) of the inductor increases, outputting the desired voltage at too high a boost ratio (e.g., >5) is unfeasible. However, in the high-boost mode, illustrated by the third curve 612, the boost ratio 602 is doubled at the same duty cycle compared to the low-boost mode curve 610. Consequently, the output voltage can be raised to a higher level.

[0059] Figure 7 FIGURE 7 is a flow chart of a control system 700 for a variable voltage converter that directs reactive power to a balancing capacitor. Here, a conventional boost converter control block 704 generates a reference signal D0 that includes the duty cycle of a PWM signal. The reference signal is combined with a signal from a floating capacitor offset 702. The floating capacitor offset 702 first converts the floating capacitor voltage (V f ) and the floating capacitor reference voltage (V f * ) is compared to the floating capacitor reference voltage (V f * ) is then regulated by the regulator 710. The regulated output is limited by the limiter 712, and the output is combined with the reference signal D0. The combination of the limiter output and the reference signal D0 is performed twice. First, the limiter output is added to the reference signal D0 to generate a gating signal for the outer flying capacitor switches (e.g., S1 and S4). The gating signal is modulated according to a first carrier to generate an S1 / S4 gating signal. Then, the limiter output is subtracted from the reference signal D0 to generate a second gating signal for the inner flying capacitor switches (e.g., S2 and S3). The gating signal is modulated according to a second carrier to generate an S2 / S3 gating signal. The first carrier signal and the second carrier signal can be the same carrier, or can be associated or related based on a delay. The control algorithm for the VVC in high boost mode has been verified by simulation, in which both the high voltage DC bus voltage Vdc and the floating capacitor voltage Vf are controlled.

[0060] In short, Figure 7A control method for a VVC in high-boost mode is shown. There are essentially two control objectives in this high-voltage mode. The first is to control the output fault voltage Vdc to follow a reference voltage based on the needs of the motor / generator inverter. The second is to control the floating capacitor voltage Vf to be roughly half of Vdc. In addition, the two PWM carriers (carrier 1 and carrier 2) can be in phase or out of phase. And the conventional control for boost control can be any existing control method that can adjust the output voltage of the boost converter (including single voltage closed-loop control, voltage and current dual-loop control, analog or digital control methods).

[0061] Figure 8 is a graphical diagram 800 of control signals 802 for switches of a variable voltage converter and system electrical characteristics ( 804 , 806 , 808 , and 810 ) versus time 812 . Figure 8 FIG4 shows a simulation waveform of a VVC (eg, 406) operating in a high step-up ratio mode. In this simulation, the reference voltage V f * The reference voltage of the high voltage DC bus voltage Vdc is 600 V. The inductor current 804 has the same Figure 5 8. Curve 816 has a sawtooth pattern similar to curve 510. DC bus voltage 806 has curve 818 with ripple at the switching frequency, flying capacitor voltage 808 has curve 820 also with ripple at the switching frequency, and battery voltage 810 has curve 822 that is substantially constant based on the capacitance of the flying capacitor and the DC bus capacitor.

[0062] The control signal 802 includes a first signal (S1) 802A having a first curve 814A (e.g., a control signal for switch 408A), a second signal (S2) 802B having a second curve 814B (e.g., a control signal for switch 408B), a third signal (S3) 802C having a third curve 814C (e.g., a control signal for switch 408C), and a fourth signal (S4) 802D having a fourth curve 814D (e.g., a control signal for switch 408D). The inductor current 804 (e.g., the current flowing to the inductor 412) is shown as a current curve 816 with respect to time 812. Figure 5 The switching waveform is similar to Figure 8In the embodiment of the present invention, at a first time, the switches (e.g., 408B and 408C) for the flying capacitor (e.g., 410A) are complementary switched, so that the high-side switch S2 (e.g., 408B) is turned off and the low-side switch S3 (e.g., 408C) is turned on, while the other high-side switch (e.g., 408A) is turned off (e.g., open circuit) and the low-side switch (e.g., 408D) is turned on (e.g., closed or short circuit). As a result, current flows from the battery (e.g., battery 414) and flows through the inductor (e.g., 412), thereby inducing a field in the inductor. Thereafter, the field collapses to increase the voltage so that when the field collapses, the voltage is applied to one of the capacitors (e.g., first to the flying capacitor and then to the DC bus capacitor).

[0063] Reference Figure 5 and Figure 8 , determine the average system characteristics for one period (e.g., time 512 to time 520). For example, the average value of the flying capacitor voltage 808 and the average value of the bus capacitor voltage 806 are measured for one period (e.g., time 512 to time 520). Figure 8 As shown, in high boost mode, when the flying capacitor is used to boost the voltage applied to the bus capacitor, the average bus capacitor voltage 806 is higher than the average flying capacitor voltage 808, and the average flying capacitor voltage 808 is higher than the average battery voltage 810. In normal boost mode, the flying capacitor is connected in parallel with the bus capacitor, the average bus capacitor voltage 806 is substantially equal to the average flying capacitor voltage 808, and both the average bus capacitor voltage 806 and the average flying capacitor voltage 808 are higher than the average battery voltage 810. Finally, in pass-through mode, the average bus capacitor voltage 806 is substantially equal to the average flying capacitor voltage 808, and the average flying capacitor voltage 808 is substantially equal to the average battery voltage 810. In this steady-state pass-through mode, power can be transferred from the battery to the motor or from the motor to the battery.

[0064] The control logic or functions performed by the controller may be represented by a flowchart or similar diagram in one or more of the accompanying figures. These figures provide representative control strategies and / or logic that can be implemented using one or more processing strategies (such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc.). Therefore, the various steps or functions shown may be performed in the order shown, in parallel, or omitted in some cases. Although not always explicitly shown, those skilled in the art will recognize that one or more of the steps or functions shown may be repeated depending on the specific processing strategy used. Similarly, the order of processing is not necessarily required to achieve the functions and advantages described herein, but is provided for ease of illustration and description. The control logic may be implemented primarily in the form of software executed by a microprocessor-based vehicle, engine, and / or powertrain controller (such as a controller). Of course, the control logic may be implemented in the form of software, hardware, or a combination of software and hardware in one or more controllers, depending on the specific application. When implemented in software, the control logic may be provided in one or more computer-readable storage devices or media that have stored data representing code or instructions executed by a computer to control the vehicle or its subsystems. The computer-readable storage device or medium may include one or more of a number of known physical devices that utilize electronic, magnetic, and / or optical storage to store executable instructions and associated calibration information, operating variables, and the like.

[0065] The processes, methods or algorithms disclosed herein may be transmitted to a processing device, a controller or a computer, or implemented by the processing device, a controller or a computer, wherein the processing device, the controller or the computer may include any existing programmable electronic control unit or a dedicated electronic control unit. Similarly, the processes, methods or algorithms may be stored in a variety of forms as data and instructions that can be executed by a controller or a computer, wherein the various forms include, but are not limited to, information permanently stored in a non-writable storage medium (such as a read-only memory (ROM) device) and information variably stored in a writable storage medium (such as a floppy disk, a magnetic tape, a compact disk (CD), a random access memory (RAM) device, and other magnetic and optical media). The processes, methods or algorithms may also be implemented in a software executable object. Alternatively, the processes, methods or algorithms may be implemented in whole or in part using appropriate hardware components (such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a state machine, a controller or other hardware components or devices) or a combination of hardware components, software components and firmware components.

[0066] Although exemplary embodiments have been described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are descriptive rather than restrictive, and it should be understood that various changes may be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of the various embodiments may be combined to form further embodiments of the present invention that may not be explicitly described or shown. Although each embodiment may have been described as providing advantages or being superior to other embodiments or prior art embodiments for one or more desired characteristics, it will be appreciated by those skilled in the art that, depending on the specific application and embodiment, one or more features or characteristics may be compromised to achieve the desired overall system properties. These properties may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, maintainability, weight, manufacturability, ease of assembly, etc. Therefore, embodiments described as being inferior to other embodiments or prior art embodiments in one or more characteristics are not outside the scope of the present disclosure and may be expected to be used for specific applications.

Claims

1. A power transmission system for a vehicle, comprising: a variable voltage converter including an inductor, a bus capacitor, and a flying capacitor; The controller is configured as: in response to a power demand signal exceeding a threshold, modulating a switch of the variable voltage converter such that an inductor current generated by a collapsing field of the inductor is directed into the flying capacitor or the bus capacitor such that a voltage across the bus capacitor exceeds a voltage across the flying capacitor; In response to a power demand signal transitioning to a negative direction, operating the switch in a pass mode in a steady state to connect the flying capacitor in parallel with the bus capacitor and enable charge to flow, wherein in the pass mode, an input voltage of the variable voltage converter is equal to a voltage across the flying capacitor and a voltage across the bus capacitor.

2. The power transmission system according to claim 1, wherein: The variable voltage converter is connected between the traction battery and the electric drive unit.

3. The power transmission system according to claim 1, wherein: The switches of the variable voltage converter include four switches connected in series between a negative output terminal and a positive output terminal of the variable voltage converter.

4. The power transmission system according to claim 3, wherein: The switches of the variable voltage converter include a first switch, a second switch, a third switch, and a fourth switch. The first switch is connected between the second switch and a positive output terminal, the second switch is connected between the first switch and the third switch, the third switch is connected between the second switch and the fourth switch, and the fourth switch is connected between the third switch and a negative output terminal.

5. The power transmission system according to claim 1, wherein: The switch is an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor.

6. The power transmission system according to claim 1, wherein: The controller is further configured to, in response to the power demand signal falling below the threshold, modulate the switch such that the flying capacitor is connected in parallel with the bus capacitor.

7. The power transmission system according to claim 4, wherein: The controller is further configured to operate the switches in a steady state such that the first switch, the second switch, and the fourth switch are turned on and the third switch is turned off, so as to implement the pass mode.

8. A vehicle comprising: a motor configured to propel the vehicle; a variable voltage converter including an inductor, a bus capacitor, and a flying capacitor; a controller configured to: in a boost mode, modulate switches of the variable voltage converter so that, at a drive voltage of the motor, an inductor current generated by a collapsing field of the inductor is boosted through the flying capacitor and directed into the bus capacitor; In response to a power demand signal transitioning to a negative direction, operating the switch in a pass mode in a steady state to connect the flying capacitor in parallel with the bus capacitor and enable charge to flow, wherein in the pass mode, an input voltage of the variable voltage converter is equal to a voltage across the flying capacitor and a voltage across the bus capacitor.

9. The vehicle according to claim 8, wherein: The switch is an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor.

10. The vehicle of claim 8, wherein: The switches of the variable voltage converter include a first switch, a second switch, a third switch, and a fourth switch. The first switch is connected between the second switch and a positive output terminal, the second switch is connected between the first switch and the third switch, the third switch is connected between the second switch and the fourth switch, and the fourth switch is connected between the third switch and a negative output terminal.

11. The vehicle according to claim 10, wherein: The flying capacitor is connected between an upper connection point between the first switch and the second switch and another connection point between the third switch and the fourth switch, and the inductor is connected between a positive input terminal and a midpoint between the second switch and the third switch.

12. The vehicle of claim 11, wherein: The controller is further configured to alternately cause the inductor current to flow into the flying capacitor and a bus capacitor connected in series through the switch, or to cause the inductor current to flow into the bus capacitor when the flying capacitor is connected in series with the bus capacitor through the switch and is bypassed by a diode.

13. The vehicle of claim 11, wherein: The controller is further configured to operate the switches in a steady state such that the first switch, the second switch, and the fourth switch are turned on and the third switch is turned off, so as to implement the pass mode.

14. The vehicle of claim 8, wherein: The variable voltage converter is connected between the traction battery and the electric drive unit.

15. A method of controlling a converter of a power transmission system, comprising: directing a current into an inductor of the converter to generate a field; In response to a power demand signal exceeding a threshold, collapsing the field to allow charge to flow to a flying capacitor to increase the voltage of the bus capacitor such that the voltage across the bus capacitor exceeds the voltage across the flying capacitor; In response to a power demand signal transitioning to a negative direction, the flying capacitor and the bus capacitor are connected in parallel, and switches of the converter are operated in a pass mode in a steady state to allow charge to flow, wherein in the pass mode, an input voltage of the converter is equal to a voltage across the flying capacitor and a voltage across the bus capacitor.

16. The method of claim 15, further comprising: The switch is modulated by a controller to direct the current into the inductor and collapse the field.

17. The method of claim 16, wherein: The field collapses to allow charge to flow to the bus capacitor and the flying capacitor.

18. The method of claim 16, further comprising: In response to a power demand signal falling below the threshold, the flying capacitor and the bus capacitor are connected in parallel, and charge is directed into both the flying capacitor and the bus capacitor when the field collapses.

19. The method of claim 15, wherein: The switches include a first switch, a second switch, a third switch, and a fourth switch, wherein the first switch is connected between the second switch and the positive output terminal, the second switch is connected between the first switch and the third switch, the third switch is connected between the second switch and the fourth switch, and the fourth switch is connected between the third switch and the negative output terminal. The method further includes operating the switches in a steady state such that the first switch, the second switch, and the fourth switch are turned on and the third switch is turned off, so as to implement the pass mode.

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