Stacked voltage converter for an electrified vehicle

Abstract

The present disclosure relates to a stacked voltage converter for an electrified vehicle. A power conversion system includes a power converter having an output terminal electrically isolated from an input terminal. The power conversion system also includes circuitry configured to connect a voltage input from a power source to the input terminal and to provide an output voltage to a load, the output voltage being a series combination of a voltage between the voltage input and the output terminal.

Description

TECHNICAL FIELD

[0001] The present application relates to a power converter for electrified vehicle applications. BACKGROUND

[0002] Electrified vehicles include hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs). Electrified vehicles include traction batteries that store energy for propulsion and other purposes. Traction batteries are configured to operate within a particular voltage range. However, improved performance of electric machines can be achieved by operating at different voltage ranges, which are typically higher than the voltage of the traction battery. Many electrified vehicles include a variable voltage converter for converting the voltage of the traction battery to the voltage level required by the electric machine. SUMMARY

[0003] A vehicle includes an isolated power converter having input terminals connected to a power source and a load connected across a series combination of an output of the isolated power converter and the power source. The vehicle also includes a controller configured to operate the isolated power converter such that a ratio of power delivered to the input terminals of the isolated power converter to a total power delivered to the load is less than a predetermined ratio.

[0004] The predetermined ratio can be selected based on an efficiency of the isolated power converter. The controller can also be configured to increase the predetermined ratio in response to an increase in the efficiency of the isolated power converter. The vehicle can also include a switching element configured to selectively short the output terminals of the isolated power converter. The controller can also be configured to operate the switching element to connect the load across the power source. The vehicle can also include a capacitor connected across the series combination. The power source can be a traction battery. The isolated power converter can be configured for bidirectional operation.

[0005] A power conversion system includes a power converter having an output terminal electrically isolated from an input terminal. The power conversion system also includes circuitry configured to connect a voltage input from a power source to the input terminal and to provide an output voltage to a load, the output voltage being a series combination of the voltage input and a voltage between the output terminal.

[0006] The output voltage can be higher than the voltage input. The power conversion system can also include a controller configured to operate the power converter such that a ratio of power delivered to the input terminals of the power converter to total power delivered to the load is less than a predetermined ratio. The predetermined ratio can be selected based on an efficiency of the power converter. The predetermined ratio can increase as the efficiency of the power converter increases. The circuit can also include a switching element disposed between the output terminals, the switching element configured to selectively short the output terminals. The power conversion system can also include a capacitor connected across the series combination. The power converter can be configured for bidirectional operation.

[0007] A method includes connecting a power source to an input of an isolated power converter. The method also includes connecting an output of the isolated power converter in series with the power source to provide power to an electrical load. The method also includes operating the isolated power converter at a power level such that a ratio of power provided to the isolated power converter to total power delivered to the electrical load is less than a predetermined ratio.

[0008] The predetermined ratio can be based on an efficiency of the isolated power converter. The predetermined ratio can increase as the efficiency increases. The predetermined ratio can be selected such that power losses associated with providing power to the electrical load are less than conversion power losses associated with using an output of a non-isolated power converter across the electrical load. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a diagram of a hybrid vehicle showing a typical powertrain and energy storage assembly.

[0010] Figure 2 is a diagram of a viable variable voltage converter configuration.

[0011] Figure 3 is a block diagram of a power conversion system utilizing a non-isolated power converter.

[0012] Figure 4 is a first viable configuration diagram of an isolated power converter.

[0013] Figure 5 is a second viable configuration diagram of an isolated power converter.

[0014] Figure 6 is a diagram depicting a circuit of a power conversion system utilizing an isolated power converter.

[0015] Figure 7are graphs depicting power loss in a range of efficiencies and power ratios for non-isolated power conversion systems and power conversion systems utilizing isolated power converters. DETAILED DESCRIPTION

[0016] Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various alternative forms. The drawings are not necessarily to scale; some features can be exaggerated or minimized for purposes of illustration. Specific structural and functional details disclosed herein are not to be interpreted as limiting but are merely representative bases for teaching one skilled in the art to employ the present application with regard to other situations. As those skilled in the art will readily appreciate, various features that are, or have become, established common within the art are not specifically mentioned or illustrated in order to avoid obscuring the novelty of the present application. The various features illustrated and described herein are not meant to be exhaustive or limiting, the particular embodiments chosen for purposes of illustration will not limit the scope of the application but rather the scope of the application is to be afforded the full breadth that such embodiments and their equivalents warrant.

[0017] Figure 1 An electrified vehicle 112, which can be referred to as a plug-in hybrid electric vehicle (PHEV), is depicted. The plug-in hybrid electric vehicle 112 can include one or more electric machines 114 mechanically connected to a hybrid drive 116. The electric machine 114 is capable of operating as a motor or generator. Further, the hybrid drive 116 is mechanically connected to an engine 118. The hybrid drive 116 is also mechanically connected to a drive shaft 120, which is mechanically connected to a wheel 122. The electric machine 114 can provide propulsion and regenerative capability when the engine 118 is on or off. The electric machine 114 can also function as a generator and can provide fuel economy benefits by recovering energy that is typically lost as heat in a friction braking system. The electric machine 114 can also reduce vehicle emissions by allowing the engine 118 to operate at more efficient speeds and allowing the hybrid electric vehicle 112 to operate in an electric-only mode with the engine 118 off under certain conditions. The electrified vehicle 112 can also be a battery electric vehicle (BEV). In a BEV configuration, the engine 118 can be absent. In other configurations, the electrified vehicle 112 can be a full hybrid electric vehicle (FHEV) without plug-in capability.

[0018] The traction battery or battery pack 124 stores energy that can be used by the electric machine 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 electronic 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 electronic modules 126 are also electrically connected to the electric machine 114 and provide the ability to transfer energy bi-directionally between the traction battery 124 and the electric machine 114. For example, the traction battery 124 can provide a DC voltage while the electric machine 114 can operate under three-phase alternating current (AC) to function. The power electronic modules 126 can convert the DC voltage to three-phase AC current to run the electric machine 114. In a regenerative mode, the power electronic modules 126 can convert three-phase AC current from the electric machine 114 acting as a generator to a DC voltage compatible with the traction battery 124.

[0019] The vehicle 112 can include a variable voltage converter (VVC) 152 electrically connected between the traction battery 124 and the power electronic modules 126. The VVC 152 can 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 requirement can be reduced, resulting in a reduction in the size of the wiring for the power electronic modules 126 and the electric machine 114. In addition, the electric machine 114 can operate at higher efficiency and lower losses.

[0020] The traction battery 124, in addition to providing energy for propulsion, can also provide energy for other vehicle electrical systems. The vehicle 112 can include a DC / DC converter module 128 that converts the high voltage DC output of the traction battery 124 to a low voltage DC supply 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 operate and control the electrical loads 146 when appropriate. Examples of electrical loads 146 can be fans, electric heating elements, and / or air conditioning compressors.

[0021] The electrified vehicle 112 can be configured to recharge the traction battery 124 from an external power source 136. The external power source 136 can be connected to an electrical outlet. The external power source 136 can be electrically connected to a charger or electric vehicle supply equipment (EVSE) 138. The external power source 136 can be a distribution network or grid provided by a public utility. The EVSE 138 can provide circuitry and controls to regulate and manage the transfer of energy between the power source 136 and the vehicle 112. The external power source 136 can provide DC or AC power to the EVSE 138. The EVSE 138 can have a charging connector 140 for plugging into the charging port 134 of the vehicle 112. The charging port 134 can be any type of port configured to transfer power from the EVSE 138 to the vehicle 112. The charging port 134 can be electrically connected to a charger or on-board power conversion module 132. The power conversion module 132 can regulate the power supplied by the EVSE 138 to provide suitable voltage and current levels to the traction battery 124. The power conversion module 132 can interact with the EVSE 138 to coordinate the transfer of power to the vehicle 112. The EVSE connector 140 can have pins that mate with corresponding sockets of the charging port 134. Alternatively, the various components described as electrically coupled or electrically connected can use wireless inductive coupling to transfer power.

[0022] One or more wheel brakes 144 can be provided for slowing and preventing movement of the vehicle 112. The wheel brakes 144 can be hydraulically driven, electrically driven, or some combination thereof. The wheel brakes 144 can be part of a brake system 150. The brake system 150 can include other components to operate the wheel brakes 144. For simplicity, the figure depicts a single connection between the brake system 150 and one wheel brake 144. Connections between the brake system 150 and the other wheel brakes 144 are implied. The brake system 150 can include a controller for monitoring and coordinating the brake system 150. The brake system 150 can monitor brake components and control the wheel brakes 144 for vehicle deceleration. The brake system 150 can be responsive to driver commands and can also operate autonomously to implement functions such as stability control. The controller of the brake system 150 can implement methods to apply requested brake forces when requested by another controller or sub-function.

[0023] The electronic modules in the vehicle 112 can communicate via one or more vehicle networks. The vehicle networks can include multiple channels for communication. One channel of the vehicle network can be a serial bus such as a controller area network (CAN). One of the channels of the vehicle network can include an Ethernet network defined by the Institute of Electrical and Electronics Engineers (IEEE) 802 family of standards. Other channels of the vehicle network can include discrete connections between modules and can include power signals from the auxiliary battery 130. Different signals can be transmitted over different channels of the vehicle network. For example, video signals can be transmitted over a high speed channel (e.g., Ethernet) while control signals can be transmitted over a CAN or discrete signals. The vehicle network can include any hardware components and software components that facilitate the transmission of signals and data between modules. The vehicle network is not shown in Figure 1 but it is implicit that the vehicle network can be connected to any electronic module present in the vehicle 112. A vehicle system controller (VSC) 148 can be provided to coordinate the operation of the various components.

[0024] Figure 2 A schematic diagram of the VVC 152 configured as a boost converter is depicted. The VVC 152 can include input terminals that can be connected to the terminals of the traction battery 124 through the contactors 142. The VVC 152 can include output terminals that are connected to the terminals of the power electronics module 126. The VVC 152 can be operated to cause the voltage at the output terminals to be higher than the voltage at the input terminals. The vehicle 112 can include a VVC controller 200 for monitoring and controlling electrical parameters (e.g., voltage and current) at various locations within the VVC 152. In some configurations, the VVC controller 200 can be included as part of the VVC 152. The VVC controller 200 can determine an output voltage reference based on the electrical parameters and the voltage reference sufficient to cause the VVC 152 to achieve the desired output voltage. In some configurations, the control signal can be implemented as a pulse width modulation (PWM) signal, where the duty cycle of the PWM signal is varied. The control signal can operate at a predetermined switching frequency. The VVC controller 200 can utilize the control signal to command the VVC 152 to provide the desired output voltage. The control signal that operates the VVC 152 can be directly related to the amount of voltage boost provided by the VVC 152.

[0025] further reference to Figure 2VVC 152 can include first and second switching devices 206 and 208 for boosting the input voltage to provide an elevated output voltage. Switching devices 206 and 208 can be configured to selectively pass current to an electrical load (e.g., power electronics module 126 and motor 114). Each switching device 206, 208 can be independently controlled by a gate drive circuit (not shown) of VVC controller 200 and can include any type of controllable switch (e.g., an insulated gate bipolar transistor (IGBT) or a field effect transistor (FET)). The gate drive circuit can provide an electrical signal to each of switching devices 206 and 208 based on a control signal (e.g., a duty cycle of a PWM control signal). A diode can be connected across each of switching devices 206 and 208. Switching devices 206 and 208 can each have an associated switching loss. Switching loss is a power loss that occurs during a state change (e.g., on / off transition and off / on transition) of a switching device. Switching loss can be quantified by the current flowing through switching devices 206 and 208 and the voltage across switching devices 206 and 208 during the transition. Switching devices can also have an associated conduction loss that occurs when the device is on.

[0026] The output voltage of VVC 152 can be controlled to achieve a desired reference voltage. In some configurations, VVC 152 can be a boost converter. In a boost converter configuration, VVC controller 200 controls the duty cycle of the control signals of first and second switching devices 206 and 208, input voltage V in , output voltage V out , and duty cycle D can be shown using the following equation:

[0027]

[0028] The desired duty cycle D can be determined by measuring the input voltage (e.g., traction battery voltage) and setting the output voltage to the reference voltage. Duty cycle D can represent the duty cycle of first switching device 206. Second switching device 208 can be operated with a duty cycle that is the complement of D (e.g., 100% - D). VVC 152 can be a buck converter that decreases voltage from input to output. In a buck configuration, different expressions relating input and output voltages to duty cycle can be derived. In some configurations, VVC 152 can be a buck-boost converter that can increase or decrease the input voltage. The control strategies described herein are not limited to a particular variable voltage converter topology.

[0029] Referring to Figure 2VVC 152 can increase or "step up" the voltage 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 transmitted from the traction battery 124 to the VVC 152. The input capacitor 202 can be electrically connected in parallel to the traction battery 124. The input capacitor 202 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 voltage potential of the input voltage according to the duty cycle.

[0030] The output capacitor 204 can be electrically connected between the output terminals of the VVC 152. The output capacitor 204 can stabilize the bus voltage and reduce voltage and current ripple at the output of the VVC 152.

[0031] The vehicle system can include sensors for measuring electrical parameters of the VVC 152. The first voltage sensor 210 can be configured to measure the input voltage (e.g., the voltage of the battery 124) and provide a corresponding input signal (V bat ) to the VVC controller 200. In one or more embodiments, the first voltage sensor 210 can measure the voltage across the input capacitor 202, which corresponds to the battery voltage. The second voltage sensor 212 can measure the output voltage of the VVC 152 and provide a corresponding input signal (V dc ) to the VVC controller 200. In one or more embodiments, the second voltage sensor 212 can measure the voltage across the output capacitor 204, which corresponds to the DC bus voltage. The first voltage sensor 210 and the second voltage sensor 212 can include circuitry for scaling the voltage to a level suitable for the VVC controller 200. The VVC controller 200 can include circuitry for filtering and digitizing the signals from the first voltage sensor 210 and the second voltage sensor 212.

[0032] The input inductor 214 can be electrically connected in series between the traction battery 124 and the switching devices 206, 208. The input inductor 214 can convert between storing energy in the VVC 152 and releasing energy from the VVC 152, enabling a variable voltage and current to be provided as an output of the VVC 152, and enabling a desired voltage step-up to be achieved. The current sensor 216 can measure the input current flowing through the input inductor 214 and provide a corresponding current signal (I L). The input current flowing through the input inductor 214 can be the result of the voltage difference between the input voltage and the output voltage of the VVC 152, the on-time of the switching devices 206 and 208, and the inductance L of the input inductor 214 acting in concert. The VVC controller 200 can include circuitry for scaling, filtering, and digitizing the signal from the current sensor 216.

[0033] The VVC controller 200 can be configured to control the output voltage of the VVC 152. The VVC controller 200 can receive inputs from the VVC 152 or other controllers over a vehicle network and determine a control signal. The VVC controller 200 can monitor the input signals to determine the control signal. For example, the VVC controller 200 can provide a control signal corresponding to a duty cycle command to the gate drive circuit. The gate drive circuit can then control each switching device 206, 208 based on the duty cycle command.

[0034] The control signal of the VVC 152 can be configured to drive the switching devices 206, 208 at a predetermined switching frequency. Within each cycle of the switching frequency, the switching devices 206, 208 can be operated at a specified duty cycle. The duty cycle defines the amount of time that a selected switching device is in an on state and an off state. For example, a 100% duty cycle can cause a selected switching device to operate in a continuous on state with no off time. A 0% duty cycle can cause a selected switching device to operate in a continuous off state with no on time. A 50% duty cycle can cause a selected switching device to operate in an on state for half of the cycle and in an off state for half of the cycle. The control signals of the two switching devices 206, 208 can be complementary. That is, the control signal provided to the first switching device 206 can be the inverse of the control signal provided to the second switching device 208. For example, if the first switching device 206 is on, the second switching device 208 should be off.

[0035] Power converters can be divided into non-isolated power converters and isolated power converters. A non-isolated power converter can be a power converter in which there is an electrical path between the input and the output of the power converter. The input and the output of a non-isolated converter can share a common ground or terminal. In contrast, an isolated converter provides galvanic isolation (e.g., electrical separation) between the input and the output. In an isolated converter, there is no direct conductive path between the input and the output. An isolated converter can include a transformer between the input and the output to achieve the galvanic isolation.

[0036] Figure 3 An example of a power conversion system that applies a non-isolated converter 302 is depicted. For example, Figure 2The depicted VVC 152 is an example of a non-isolated converter. The non-isolated converter 302 can include other non-isolated converter configurations. The power input P b may be provided by the traction battery 124 or the high voltage bus. The power input P b may be defined as the product of the voltage across the input terminals of the non-isolated converter 302 and the current flowing into the non-isolated converter 302 from the traction battery 124 and / or the high voltage bus. That is, P b represents the power provided by the source. There can be power losses when current flows through the non-isolated converter 302. For example, resistive elements can cause power losses (e.g., I 2 R). The switching devices 206, 208 can be characterized by switching losses and conduction losses. The power output of the converter can be defined as the product of the voltage across the output terminals of the non-isolated converter 302 and the current flowing from the non-isolated converter 302 to the load. The ratio of the power output to the power input can be defined as the efficiency η of the converter. Since there are power losses, the efficiency is typically less than one. The power losses P loss may be represented as:

[0037] P loss = (1 - η) P b (2)

[0038] The power delivered to the load is equal to η P b . For the non-isolated converter 302, the power losses are based on the power input to the converter. Since all the power passes through the non-isolated converter 302, the entire input power P b is limited by the losses. It is generally desirable to minimize the power losses of a system.

[0039] Figure 6 An improved converter topology is depicted for improving power losses. Figure 6 The topology of the improved converter 600 includes an isolated converter 602 connected in series with the traction battery 124 and / or the high voltage bus. A variety of configurations can be used for the isolated converter 602. For example, Figure 4 A diagram of a first isolated converter 400, which can be referred to as a dual active bridge converter, is depicted. The isolated converter 400 can include a transformer 418 having a turn ratio of 1 : n. The transformer 418 includes a primary side winding and a secondary side winding. The value of n can be selected to achieve a predetermined voltage magnitude step-up at the secondary side winding. The first isolated converter 400 can include a first input terminal 430 and a second input terminal 432. A capacitor 422 can be connected across the input terminals 430 and 432. The first isolated converter 400 can include an inductor 420 connected in series with the primary side winding of the transformer 418.

[0040] Input terminals 430 and 432 can be connected to an input stage that includes a plurality of input stage switching devices 402, 404, 406, 408. Input stage switching devices 402, 404, 406, 408 can be solid state switching elements. For example, input stage switching devices can be N-channel metal oxide semiconductor field effect transistors (MOSFETs). Input stage switching devices can be other transistor types including insulated gate bipolar transistors (IGBTs). Input stage switching devices 402, 404, 406, 408 can include diodes across the associated devices. In some configurations (e.g., MOSFETs), the diodes can represent a body diode.

[0041] Input stage switching devices 402, 404, 406, 408 can be arranged to selectively connect input terminals 430 and 432 to a series combination of inductor 420 and a primary side winding of transformer 418. For example, switching device 402 can selectively connect first input terminal 430 to a first lead of inductor 420. Switching device 404 can selectively connect second input terminal 432 to the first lead of inductor 420. A second lead of inductor 420 can be connected to a first terminal of a primary side winding of transformer 418. Switching device 406 can selectively connect first input terminal 430 to a second terminal of the primary side winding of transformer 418. Switching device 408 can selectively connect second input terminal 432 to the second terminal of the primary side winding of transformer 418.

[0042] Input stage switching devices 402, 404, 406, 408 can be controlled by a controller (e.g., VVC controller 200). For example, controller 200 can provide gate drive signals to activate and disable input stage switching devices 402, 404, 406, 408. Input stage switching devices 402, 404, 406, 408 can be operated to enable energy transfer through transformer 418.

[0043] A secondary side winding of transformer 418 can be connected to an output stage that includes a plurality of output stage switching devices 410, 412, 414, 416. Output stage switching devices 410, 412, 414, 416 can be solid state switching elements. For example, output stage switching devices can be N-channel metal oxide semiconductor field effect transistors (MOSFETs). Output stage switching devices can be other transistor types including insulated gate bipolar transistors (IGBTs). Output stage switching devices 410, 412, 414, 416 can include diodes across the associated devices. In some configurations (e.g., MOSFETs), the diodes can represent a body diode.

[0044] The output stage switching devices 410, 412, 414, 416 can be arranged to selectively connect the secondary side winding of the transformer 418 to the first output terminal 434 and the second output terminal 436. For example, the switching device 410 can selectively connect a first terminal of the secondary side winding of the transformer 418 to the first output terminal 434. The switching device 412 can selectively connect the first terminal of the secondary side winding of the transformer 418 to the second output terminal 436. The switching device 414 can selectively connect a second terminal of the secondary side winding of the transformer 418 to the first output terminal 434. The switching device 416 can selectively connect the second terminal of the secondary side winding of the transformer 418 to the second output terminal 436. The smoothing capacitor 424 can be connected between the first output terminal 434 and the second output terminal 436 to smooth the resulting voltage output.

[0045] The controller 200 can be configured to operate the input stage to generate an alternating current (AC) signal to the primary side winding of the transformer 418. The AC signal then induces a current in the secondary side winding of the transformer 418.

[0046] The control signals sent by the controller 200 to the isolation converter 400 can be configured to drive the input stage switching devices 402, 404, 406, 408 as PWM signals at a predetermined switching frequency. Within each cycle of the switching frequency, the input stage switching devices 402, 404, 406, 408 can be operated at a specified duty cycle. The duty cycle defines the amount of time the switching devices 402, 404, 406, 408 are in the on state and the off state. For example, a 100% duty cycle can cause the input stage switching devices 402, 404, 406, 408 to operate in a continuous on state with no off time. A 0% duty cycle can cause the input stage switching devices 402, 404, 406, 408 to operate in a continuous off state with no on time. A 50% duty cycle can cause the input stage switching devices 402, 404, 406, 408 to operate in the on state for half the cycle and in the off state for half the cycle. The control signals to the input stage switching devices 402, 404, 406, 408 can be complementary. That is, the control signal sent to one of the switching devices (e.g., 402) can be the inverse of the control signal sent to the complementary switching device (e.g., 404). Such operation ensures that the output is not simultaneously connected to both input terminals 430 and 432 (e.g., prevents shorting the input terminals 430 and 432 together). In some configurations, the duty cycle can vary based on a feedback signal (e.g., a voltage or current feedback) to achieve a target voltage or current to the transformer.

[0047] The controller 200 can be configured to operate the output stage to generate a direct current (DC) signal for a connected electrical load. The output stage can function as a rectifier (e.g., via a body diode) to convert the AC signal into a DC signal at the output terminals. The controller can operate the output stage switching devices 410, 412, 414, and 416 to achieve rectification. The isolation converter 400 can be bidirectional, allowing power to be transmitted in the opposite direction. That is, power from the output stage can be transferred back to the input stage. For example, during regenerative braking, the inverter can return power from the electric motor to the traction battery via the isolation converter 400. The controller 200 can provide control signals to operate the output stage switching devices 410, 412, 414, and 416 to transfer power back to the input stage. Note that in bidirectional operation, the roles of the input and output stages described above can be reversed. That is, the output stage can be operated to generate an AC signal, and the input stage can be operated to rectify the AC signal into a DC signal at the input terminals 430 and 432.

[0048] In another example, Figure 5 A schematic diagram of a second isolated converter 500, which may be referred to as a series resonant converter, is depicted. The isolated converter 500 may include a transformer 518 having a turns ratio of 1:n. The transformer 518 includes a primary winding and a secondary winding. The value of n may be selected to achieve a predetermined voltage amplitude increase at the secondary winding. The second isolated converter 500 may include a first input terminal 530 and a second input terminal 532. A capacitor 522 may be connected across the input terminals 530 and 532. The second isolated converter 500 may include an inductor 520 and a second capacitor 526 connected in series with the input side of the transformer 518. In some configurations, the inductor 520 may be integrated into the transformer 518.

[0049] Input terminals 530 and 532 may be connected to an input stage that includes a plurality of input stage switching devices 502, 504, 506, 508. The input stage switching devices 502, 504, 506, 508 may be solid-state switching elements. For example, the input stage switching devices may be N-channel metal oxide semiconductor field effect transistors (MOSFETs). The input stage switching devices may be other transistor types including insulated gate bipolar transistors (IGBTs). The input stage switching devices 502, 504, 506, 508 may include diodes connected across the associated devices. In some configurations (e.g., MOSFETs), the diodes may represent intrinsic body diodes.

[0050] The input stage switching devices 502, 504, 506, 508 can be arranged to selectively connect the input terminals 530 and 532 to a series combination of the inductor 520, the second capacitor 526, and the primary side winding of the transformer 518. For example, the switching device 502 can selectively connect the first input terminal 530 to a first lead of the second capacitor 526. The switching device 504 can selectively connect the second input terminal 532 to the first lead of the second capacitor 526. A second lead of the second capacitor 526 can be connected to a first lead of the inductor 520. A second lead of the inductor 520 can be connected to a first terminal of the primary side winding of the transformer 518. The switching device 506 can selectively connect the first input terminal 530 to a second terminal of the primary side winding of the transformer 518. The switching device 508 can selectively connect the second input terminal 532 to the second terminal of the primary side winding of the transformer 518.

[0051] The input stage switching devices 502, 504, 506, 508 can be controlled by a controller (e.g., the VVC controller 200). For example, the controller 200 can provide gate drive signals to activate and disable the input stage switching devices 502, 504, 506, 508. The input stage switching devices 502, 504, 506, 508 can be operated to enable energy transfer through the transformer 518.

[0052] The secondary side winding of the transformer 518 can be connected to an output stage including a plurality of output stage switching devices 510, 512, 514, 516. The output stage switching devices 510, 512, 514, 516 can be solid state switching elements. For example, the output stage switching devices can be N-channel metal-oxide-semiconductor field-effect transistors (MOSFETs). The output stage switching devices can be other transistor types including insulated-gate bipolar transistors (IGBTs). The output stage switching devices 510, 512, 514, 516 can include a diode across the associated device. In some configurations (e.g., MOSFETs), the diode can represent a body diode.

[0053] The output stage switching devices 510, 512, 514, 516 can be arranged to selectively connect the secondary side winding of the transformer 518 to the first output terminal 534 and the second output terminal 536. For example, the switching device 510 can selectively connect a first terminal of the secondary side winding of the transformer 518 to the first output terminal 534. The switching device 512 can selectively connect the first terminal of the secondary side winding of the transformer 518 to the second output terminal 536. The switching device 514 can selectively connect a second terminal of the secondary side winding of the transformer 518 to the first output terminal 534. The switching device 516 can selectively connect the second terminal of the secondary side winding of the transformer 518 to the second output terminal 536. The smoothing capacitor 524 can be connected between the first output terminal 534 and the second output terminal 536 to smooth the generated voltage output.

[0054] The controller 200 can be configured to operate the input stage to generate an alternating current (AC) signal to the primary side winding of the transformer 518. The AC signal then induces a current in the secondary side winding of the transformer 518.

[0055] The control signals sent by the controller 200 to the isolated converter 500 can be configured to drive the input stage switching devices 502, 504, 506, 508 with PWM signals at a switching frequency. Within each cycle of the switching frequency, the input stage switching devices 502, 504, 506, 508 can be operated with a specified duty cycle. The duty cycle defines the amount of time the switching devices 502, 504, 506, 508 are in the on state and the off state. The control signals for the input stage switching devices 502, 504, 506, 508 can be complementary. That is, the control signal sent to one of the switching devices (e.g., 502) can be the inverse of the control signal sent to the complementary switching device (e.g., 504). Such operation ensures that the output is not simultaneously connected to both input terminals 530 and 532 (e.g., prevents shorting the input terminals 530 and 532 together). In some configurations, the duty cycle can vary based on a feedback signal (e.g., a voltage or current feedback) to achieve a target voltage or current to the transformer. The switching frequency can be selected in relation to a resonant frequency, which can be defined by the second capacitor 526, the inductor 520, and the primary side winding of the transformer 518.

[0056] The controller 200 can be configured to operate the output stage to produce a direct current (DC) signal to a connected electrical load. The output stage can operate as a rectifier (e.g., through body diodes) to convert the AC signal to a DC signal at the output terminals. The controller can operate the output stage switching devices 510, 512, 514, 516 to implement the rectification. The isolated converter 500 can be bidirectional such that power can be transmitted in the opposite direction. That is, power from the output stage can be transmitted back to the input stage. For example, during regenerative braking, the inverter can return power from the motor to the traction battery through the isolated converter 500. The controller 200 can provide control signals to operate the output stage switching devices 510, 512, 514, 516 to transmit power back to the input stage. Note that in the bidirectional mode of operation, the roles of the input stage and output stage described above can be interchanged. That is, the output stage can be operated to produce an AC signal, and the input stage can be operated to rectify the AC signal to a DC signal at the input terminals 530, 532.

[0057] Figure 6 A viable power conversion system for power distribution in an electrified vehicle is depicted. The output stage of the power supply and the isolated converter 602 are connected in series to provide a voltage for an electrical load 650. The power supply can include a traction battery 124 and a high voltage bus. The power conversion system can include circuitry configured to connect a voltage input from the power supply to the input terminals 630, 632 of the isolated power converter 602 and provide an output voltage to the load 650 that is a series combination of the voltage input and the voltage between the output terminals 634 and 636 of the isolated power converter 602. The voltage output of the series configuration is the sum of the power supply voltage and the output voltage of the isolated converter 602. For example, the isolated converter 602 can be configured as Figure 4 or Figure 5 The input terminals 630, 632 of the isolated converter 602 can be electrically connected to the terminals of the traction battery 124 such that the input voltage across the input terminals is equal to the traction battery voltage.

[0058] The resulting power conversion system can provide an elevated voltage to the electrical load 650. The power flow from the power supply to the electrical load 650 can have two paths. The first path is from the traction battery 124 and / or the high voltage bus to the electrical load 650. The first path can be referred to as the direct path. The second path is from the traction battery 124 and / or the high voltage bus to the electrical load 650 through the isolated converter 602. The second path can be referred to as the indirect path. The indirect path provides voltage elevation through the isolated converter 602.

[0059] The power conversion system can include a controller 600 configured to monitor and control operation of the isolated power converter 602. The controller 600 can include a processor for executing programs and a memory for storing programs and data. The memory can include volatile memory and non-volatile memory. The controller 600 can include interface circuitry to interface with one or more voltage and current sensors. The controller 600 can include interface circuitry to control a plurality of gate terminals of a plurality of solid state switching devices. The controller 600 can include timers and counters that can be used to coordinate timing of various input and output operations. The controller 600 can include a communication interface to communicate with other electronic modules within the vehicle.

[0060] The power converter system can include a voltage sensor configured to measure a voltage between outputs of the isolated power converter 602 (e.g., V2 612). The power converter system can include a voltage sensor configured to measure a voltage across the power source (e.g., VI 610). The power converter system can include a voltage sensor configured to measure a voltage across a series combination of the power source and an output of the isolated power converter 602 (i.e., configured to measure a voltage across the electrical load 650). The voltage sensor can interface with the controller 600 to provide voltage information used to control the isolated power converter 602. The power converter system can also include a voltage sensor configured to measure a voltage between input terminals (630, 632) of the isolated power converter 602.

[0061] The power converter system can include a current sensor configured to measure a current flowing into the input terminal 630 of the isolated power converter 602. The power conversion system can include a current sensor configured to measure a current flowing to the electrical load 650. The current sensor can interface with the controller 600 to provide current information used to control the isolated power converter 602.

[0062] The direct path results in lower power loss since the power does not pass through the conversion stage. The power loss attributable to the indirect path can be calculated as follows:

[0063] P loss = (1 - η iso ) P b1 (3)

[0064] where η iso is the efficiency associated with the isolated converter 602 and P b1 is the amount of power input to the isolated power converter 602. The power input to the isolated power converter 602 can be determined based on the voltage between the input terminals (630, 632) and the current flowing into the input terminal (e.g., 630). The efficiency of the isolated converter can be lower than a non-isolated converter (e.g., a buck converter). Figure 2the efficiency of the non-isolated power converter in the system. That is, η iso may be lower than η of the aforementioned non-isolated converter. However, if only a portion of the power flows through the isolated power converter 602, the overall losses can be reduced. The power loss can be reduced by adjusting the amount of power that flows through the isolated converter 602 (e.g., the amount defined by the power ratio). That is, P b1 may be controlled to a value that is less than P b . For example, the ratio of P b1 to P b may be controlled to a value of 10%. The total output power delivered to the load 650 is the sum of the power delivered through the direct path and the power delivered through the isolated power converter 602.

[0065] The controller 600 can be configured to control the amount of power that flows through the isolated power converter 602. To improve overall performance, the power that flows through the isolated power converter 602 can be a small fraction of the power provided to the load 650 or the power input to the power conversion system. That is, P b1 may be selected to be less than the input power P b of the non-isolated power converter. P b1 may also be selected to be less than the power delivered to the load 650. In light load conditions, the high circulating current in the isolated power converter can result in a reduction in the overall system efficiency. To improve the overall efficiency of the power conversion system, the power that flows through the isolated power converter 602 can be controlled to a predetermined power level. The power ratio can be defined as the ratio of the power delivered at the input of the isolated power converter 602 to the total power delivered to the electrical load 650. The power ratio can also be defined as the ratio of the power delivered at the input of the isolated power converter 602 to the total power provided by the power source.

[0066] The controller 600 can receive or define a voltage reference. The reference voltage can be a nominal voltage required by the electrical load 650. The reference voltage can be higher than the voltage of the traction battery 124. The controller 600 can output a control signal to the isolated power converter 602 to output a voltage (e.g., V2) from the isolated power converter such that the voltage across the electrical load 650 meets the reference voltage. The reference voltage can affect the selected power ratio. For example, as the reference voltage increases, the power ratio can increase to meet the selected reference voltage. In addition, the controller 600 can measure the current flowing to the electrical load 650, such that the power delivered to the electrical load 650 can be calculated. The controller 600 can measure the voltage between the input terminals (630, 632) of the isolated power converter 602 and the current flowing into the input terminal 630 to determine the power input to the isolated power converter 602. The controller 600 can calculate the ratio of the power input to the isolated power converter 602 to the power delivered to the electrical load 650. The controller 600 can compare the power ratio to a predetermined power ratio range that can represent a desired power ratio range. The controller 600 can receive or determine a reference power ratio. The reference power ratio can be a power ratio that results in a predetermined power conversion system efficiency. For example, the selected power ratio can reduce power losses when compared to using a non-isolated power converter (e.g., a non-isolated power converter in Figure 2 The reference power ratio can represent a maximum power ratio for achieving improved efficiency.

[0067] The controller 600 can operate the isolated power converter 602 to achieve the reference power ratio. For example, the controller 600 can output a gate drive signal to the input stage switching devices of the isolated power converter 602 to vary the frequency and / or amplitude of the current through the primary side winding of the transformer to achieve the reference power ratio. The controller 600 can be configured to adjust the power ratio at specified time intervals (e.g., a sampling rate). As the power demand of the electrical load 650 increases, the controller 600 can adjust the power ratio to maintain the reference power ratio and achieve the reference voltage. By controlling the power ratio to the reference power ratio, the overall efficiency of the power conversion system can be improved.

[0068] The power conversion system may also include a switching element 638 configured to selectively connect the output terminals of the isolation converter 602. The switching element 638 may be a relay or a solid-state switching device (e.g., a MOSFET, an IGBT). The controller 600 may include an interface for control signals for the switching element 638. The switching element 638 allows the isolation converter 602 to be removed from the power path. When the switching element 638 is closed, the traction battery 124 is directly connected to the load. When the switching element 638 is closed, the controller 200 may command the switching device of the isolation converter 602 to be disabled. In the closed state, since the traction battery 124 or the high-voltage bus is directly connected to the load 650, there may be no power conversion losses. When a higher voltage is beneficial, the switching element 638 may be opened, and some power may be directed through the isolation converter 602.

[0069] Controller 600 can be configured to operate switching element 638 to open or close based on operating conditions. When operating conditions result in a desired traction battery voltage, controller 600 can close switching element 638. Before closing switching element 638, controller 600 can ensure that there is no power flow through isolated power converter 602. When operating conditions result in a desired boosted voltage, controller 600 can open switching element 638. Controller 600 can operate isolated power converter 602 to boost the voltage to the desired voltage.

[0070] Figure 7 A graph 700 showing the percentage of losses using the disclosed power conversion system is shown. The x-axis 704 represents the efficiency of the isolated converter 602. The y-axis 706 represents the power ratio, which is the percentage of the total power flowing through the indirect path. The z-axis 708 represents the percentage of power loss in the converter system. A surface 702 is plotted that represents the performance of the converter topology for a range of efficiencies and power ratios. Non-isolated power converters (e.g., Figure 2 The performance of the non-isolated power converter in FIG. 7 is represented by plane 710 having an efficiency of 95%.

[0071] As shown in graph 700, plane 702 includes a performance improvement range 712 in which, for a range of efficiency and power ratios, the percentage of loss is lower than the percentage of loss defined by plane 710. Performance improvement range 712 represents the combination of efficiency and power ratios at which the power conversion system is less lossy than a conventional non-isolated converter. Graph 702 depicts the improvement in overall power conversion system efficiency that can be obtained by transmitting a portion of the power using isolated power converter 602. For example, operating a converter topology using isolated power converter 602 at a power ratio of 0.1 and an efficiency of 0.8 results in a system with reduced loss compared to a conventional single path converter with an efficiency of 95%. By controlling the power ratio within a predetermined range (e.g., the range defined by 712), the overall efficiency can be improved when compared to a system with a non-isolated power converter (e.g., a non-isolated power converter in Figure 2

[0072] Knowing the efficiency of isolated power converter 602 enables the identification of the maximum power ratio for which efficiency improvement is achieved. For example, at a fixed efficiency value, there is a range of power ratios that fall within performance improvement range 712. The maximum desired power ratio can be defined as the power ratio associated with the efficiency value of isolated power converter 602 that intersects with plane 710. Controller 600 can be configured to achieve the voltage reference with the minimum possible power ratio. Controller 600 can be configured to operate isolated power converter 602 at a power ratio lower than the maximum desired power ratio. The characteristic (e.g., the characteristic defined by 712) can be stored by controller 600 and retrieved to determine the maximum power ratio. Controller 600 can be configured to achieve the voltage reference with the minimum possible power ratio that is less than the maximum desired power ratio. By minimizing the power flow through isolated power converter 602, the overall system efficiency can be improved. That is, the conversion power loss can be reduced. Figure 7

[0073] A power conversion system can improve the overall efficiency of power conversion. The power conversion system provides a boosted voltage to an electrical load, which can reduce the current demand of the wiring and load. In addition, the power conversion system is bidirectional and can enable energy return to the power source by operating the isolated power converter in reverse.

[0074] ​​The processes, methods, or algorithms disclosed herein can be embodied in hardware, software, firmware, or any combination thereof. Such processes, methods, or algorithms can be implemented in any of a variety of ways. For example, they can be implemented in software, which includes but is not limited to firmware, resident software, microcode, and / or hardware implementation. Any features described as modules, units or components can be implemented together in an integrated manner, or separately as discrete but interoperable parts. Any features described as circuits can be implemented in hardware or software, or any combination thereof. Any features described as being stored in a computer-readable storage medium (such as a ROM, RAM, or the like) can be stored on any type of computer-readable storage medium or device, including but not limited to semiconductor-based memory devices, optical storage devices, machine- readable storage devices, magnetic tape, floppy diskettes, and the like. The processes, methods, or algorithms can be implemented in any of a variety of ways. For example, they can be implemented in software, which includes but is not limited to firmware, resident software, microcode, and / or hardware implementation. Any features described as modules, units or components can be implemented together in an integrated manner, or separately as discrete but interoperable parts. Any features described as circuits can be implemented in hardware or software, or any combination thereof. Any features described as being stored in a computer-readable storage medium (such as a ROM, RAM, or the like) can be stored on any type of computer-readable storage medium or device, including but not limited to semiconductor-based memory devices, optical storage devices, machine- readable storage devices, magnetic tape, floppy diskettes, and the like.

[0075] While the foregoing describes exemplary embodiments, these embodiments are not intended to describe all possible forms of the disclosure. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, features of various embodiments can be combined to form further embodiments of the present disclosure that are not expressly described or illustrated. While one or more embodiments can have been described with regard to one or more desired characteristics, it should be understood that various changes and modifications can be made to the embodiments described and that such changes and modifications are contemplated. It is therefore intended that the appended claims cover all such changes and modifications that fall within the scope of the disclosure. Accordingly, no limitation is implied by the description set forth in the specification, which includes all valid equivalents. No single feature, process or material described herein should be considered critical or essential to the working of the application unless the context clearly indicates otherwise.

Claims

1. A vehicle comprising: an isolated power converter having input terminals connected to a power source; a load connected across a series combination of an output of the isolated power converter and the power supply; a controller configured to operate the isolated power converter such that a ratio of power delivered to an input terminal of the isolated power converter to a total power delivered to the load is less than a predetermined ratio, wherein the predetermined ratio is selected such that power losses associated with providing power to the load are less than conversion power losses associated with using an output of a non-isolated power converter across the load. 2 . The vehicle of claim 1 , further comprising a switching element configured to selectively short between output terminals of the isolated power converter.

3. The vehicle according to claim 2, wherein: The controller is further configured to operate the switching element to connect the load across the power supply.

4. The vehicle according to claim 1, wherein: The power source is a traction battery.

5. The vehicle of claim 1 further comprising a capacitor connected across the series combination.

6. The vehicle according to claim 1, wherein: The isolated power converter is configured for bidirectional operation.

7. The vehicle of claim 1, wherein: The predetermined ratio is also based on an efficiency of the isolated power converter.

8. The vehicle of claim 1, wherein: The predetermined ratio increases as the efficiency of the isolated power converter increases.

9. A power conversion system comprising: an isolated power converter having output terminals electrically isolated from input terminals; a circuit configured to: connect a voltage input from a power supply to the input terminal and provide an output voltage to a load, the output voltage being a series combination of the voltage between the voltage input and the output terminal; a controller configured to operate the isolated power converter such that a ratio of power delivered to an input terminal of the isolated power converter to a total power delivered to the load is less than a predetermined ratio, wherein the predetermined ratio is selected such that power losses associated with providing power to the load are less than conversion power losses associated with using an output of a non-isolated power converter across the load.

10. The power conversion system according to claim 9, wherein: The predetermined ratio is also selected based on an efficiency of the isolated power converter.

11. The power conversion system according to claim 9, wherein: The predetermined ratio increases as the efficiency of the isolated power converter increases.

12. The power conversion system according to claim 9, wherein: The circuit further includes a switching element disposed between the output terminals, the switching element being configured to selectively short-circuit the output terminals.

13. The power conversion system of claim 9, further comprising a capacitor connected across the series combination.

14. The power conversion system according to claim 9, wherein: The isolated power converter is configured for bidirectional operation.

15. A method for power conversion, comprising: Connect the power supply to the input of the isolated power converter; connecting an output of the isolated power converter in series with the power supply to provide power to an electrical load; The isolated power converter is operated at a power level such that a ratio of power provided to the isolated power converter to a total power delivered to the electrical load is less than a predetermined ratio, wherein the predetermined ratio is selected such that power losses associated with providing power to the electrical load are less than conversion power losses associated with an output of a non-isolated power converter used across the electrical load.

16. The method of claim 15, wherein: The predetermined ratio is also based on an efficiency of the isolated power converter.

17. The method of claim 15, wherein: The predetermined ratio increases as the efficiency of the isolated power converter increases.

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