Ripple-reduced converter for hybrid drive systems

Abstract

The present disclosure relates to a ripple-reduced converter for a hybrid drive system. A powertrain system for a vehicle includes a DC / DC converter and a controller. The DC / DC converter includes an inductor and an output capacitor and is connected between a traction battery and an electric drive unit. The controller may be configured to, in response to an electrical connection between the vehicle and an AC power grid, connect the output capacitor and the inductor in series between terminals of the traction battery to absorb reactive power from the AC power grid.

Description

Technical Field

[0001] The present application generally relates to electric machines and DC / DC converter systems configured to reduce current ripple during charging of electric vehicles via an AC grid. Background Art

[0002] Electrified vehicles, including hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs), rely on traction batteries to power the traction motors used for propulsion, and rely on power inverters between the traction battery and the traction motors to convert direct current (DC) power to alternating current (AC) power. Typical AC traction motors are three-phase motors that can be powered by three sinusoidal signals, each driven 120 degrees apart in phase. Traction batteries are configured to operate within a specific voltage range and provide maximum current. Alternatively, traction batteries are referred to as high-voltage batteries. However, improved performance of the motors can be achieved by operating them at a different voltage range, typically a voltage higher than the traction battery terminal voltage. Similarly, the current demand used to drive the onboard motors 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 includes a DC / DC converter and a controller. The DC / DC converter includes an inductor and an output capacitor and is connected between a traction battery and an electric drive unit. The controller may be configured to, in response to an electrical connection between the vehicle and an AC power grid, connect the output capacitor and the inductor in series between terminals of the traction battery to absorb reactive power from the AC power grid.

[0005] According to one embodiment of the present invention, the DC / DC converter is a bidirectional DC / DC converter.

[0006] According to one embodiment of the present invention, the DC / DC converter is a buck-boost DC / DC converter.

[0007] A method of controlling a powertrain includes, in response to an electrical connection between an AC grid and an electric vehicle including the powertrain, modulating, by a controller, a high-side switch of a DC / DC converter according to reactive power from the AC grid to transfer power through an inductor of the DC / DC converter, thereby absorbing a portion of the reactive power in an output capacitor of the DC / DC converter.

[0008] A powertrain system for a vehicle includes a controller configurable to connect an output capacitor and an inductor of a DC / DC converter in series between terminals of a traction battery to absorb reactive power from the AC grid in response to an electrical connection between the vehicle and the AC grid.

[0009] According to an embodiment of the present invention, the powertrain system further comprises an integrated charger configured to form an electrical connection between the AC grid and the DC / DC converter via neutral terminals of both the first and second electric machines.

[0010] According to one embodiment of the present invention, the DC / DC converter is a bidirectional DC / DC converter.

[0011] According to one embodiment of the present invention, the DC / DC converter is a buck-boost DC / DC converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a diagram of an electrified vehicle having an electric machine and a DC / DC converter configured to reduce current ripple during charging of the electric vehicle via an AC grid.

[0013] Figure 2 is a diagram illustrating a typical powertrain system and energy storage component of a hybrid vehicle including an AC grid charging component.

[0014] Figure 3 This is a schematic diagram of an on-board DC / DC converter.

[0015] Figure 4 is a schematic diagram of a hybrid vehicle powertrain including an AC grid charger, a traction battery, and a converter configured to direct reactive power to a DC bus capacitor.

[0016] Figure 5 is a schematic diagram of a power-split hybrid vehicle powertrain including an integrated AC grid charger, a traction battery, and a converter configured to direct reactive power to a DC bus capacitor.

[0017] Figure 6is a graphical illustration of AC characteristics of a charging assembly and a variable voltage converter assembly during AC charging of a hybrid vehicle.

[0018] Figure 7 is a diagram of a control system for a hybrid vehicle converter.

[0019] Figure 8 is a flow chart of a control system for a converter directing reactive power to a DC bus capacitor.

[0020] Figure 9 is a diagram of a hybrid vehicle powertrain including an AC grid charger, a DC / DC converter, a traction battery, and an inverter / motor with balancing capacitors.

[0021] Figure 10 is a diagram of a hybrid vehicle powertrain including an AC grid charger, a DC / DC converter, a traction battery, and an inverter / motor configured to balance power during charging. DETAILED DESCRIPTION

[0022] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and other embodiments may take various 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.

[0023] Single-phase alternating current (AC) chargers for electric vehicles typically deliver AC ripple at various frequencies. Typically, the most significant frequency component is twice the grid frequency or line frequency, and the grid input power has a pulse shape with a DC offset (Pin_dc), a large AC component (twice the line frequency), and a peak-to-peak value of 2 (Pin_dc). This power ripple causes a current ripple at twice the grid frequency on the battery side, requiring additional circuitry to protect the battery. In addition, there are current ripples at other frequencies, such as harmonics of different orders due to grid distortion and the switching frequency of the charger's semiconductor switches. In order to filter out these ripples, the charger requires a large DC link capacitor. Such a large-capacity capacitor increases the cost, size, and weight of the charger.

[0024] Since electric vehicles are not moving during AC grid charging, their electric drive systems (e.g., powertrain or electric drive systems), which include the traction drive inverter and motor, are typically disconnected from the battery. Here, the DC / DC converter is operated to absorb reactive power in the inductor and output capacitor.

[0025] A device and method are presented that utilize an electric drive system and operate the electric drive system as a low-frequency current compensator during charging. A powertrain system is disclosed that includes a capacitor selectively connected between a neutral terminal of a Y-wound electric motor and a negative terminal of a motor inverter. In another embodiment, a controller for the powertrain system is configured to modulate the inverter's switches at a frequency higher than the line frequency during AC grid charging to cause current to flow through one phase winding of the electric motor and return current through a different phase winding of the electric motor.

[0026] Figure 1 A hybrid electric vehicle is depicted showing internal electric powertrain components including an electric drive unit 2 (e.g., motor and inverter), a DC / DC converter 4, a high voltage battery 6, and a battery charger 8. The battery charger 8 may be integrated into the vehicle or may be external to the vehicle along with the AC grid 10. During vehicle charging, current flows through the inductor L of the boost converter 4 and via the high-side switch to the DC bus capacitor C. dc , the high-side switch is modulated to control the flow of current. Here, the electric drive unit 2 can be configured as an open circuit. In one embodiment, a controller (e.g., a battery boost converter controller) can selectively connect the DC bus capacitor C dc is connected in series with the inductor L so that the DC bus capacitor C dc The series combination of the inductor L is connected across the terminals of the high voltage battery 6. The controller can modulate the switches of the battery boost converter at a frequency higher than the line frequency to reduce the ripple current based on the line frequency and harmonics of the line frequency. Here, the controller (e.g., the motor inverter controller) can selectively modulate the switches of the converter 4 to absorb the reactive energy from the AC grid 10. The modulation of the high side switch of the converter 4 can be completed to absorb the reactive energy of the capacitor C dc and / or the reactive energy in the inductor L.

[0027] Figure 2An 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 started or shut down. 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 shut down 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.

[0028] 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.

[0029] 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. In addition, the electric motor 114 may operate with higher efficiency and lower losses.

[0030] 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 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 in a timely manner. Examples of electrical loads 146 may include fans, electric heating elements, and / or air conditioning compressors.

[0031] 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.

[0032] 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 the 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 decelerate the vehicle. Braking system 150 may respond to driver commands and may also operate autonomously to implement functions such as stability control. The controller of braking system 150 may implement a method for applying a requested braking force when requested by another controller or sub-function.

[0033] 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. The vehicle network is not described in detail in the accompanying drawings. Figure 1 1 , but may imply that the vehicle network may connect 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.

[0034] Figure 3 A diagram of a VVC 152 configured as a boost converter is depicted. The VVC 152 may include input terminals that may be connected to terminals of a traction battery 124 via a contactor 142. The VVC 152 may include output terminals connected to terminals of a power electronics module 126. The VVC 152 may be operated such that a voltage at the output terminals is higher than a voltage at the input terminals. The vehicle 112 may include a VVC controller 200 that monitors and controls electrical parameters (e.g., voltage and current) at multiple locations within the VVC 152. In some configurations, the VVC controller 200 may be included as part of the VVC 152. The VVC controller 200 may determine an output voltage reference. The VVC controller 200 can be based on electrical parameters and voltage references A control signal sufficient to cause the 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 200 may command the VVC 152 to provide the desired output voltage using the control signal. The specific control signal used to operate the VVC 152 may be directly related to the amount of voltage boost provided by the VVC 152.

[0035] The output voltage of the VVC 152 can be controlled to achieve a desired reference voltage. In some configurations, the VVC 152 can be a boost converter. In a boost converter configuration, the VVC controller 200 controls the duty cycle, the input voltage V in and the output voltage V out The ideal relationship between and the duty cycle D can be shown using the following equation:

[0036]

[0037] The desired duty cycle D can be determined by measuring the input voltage (e.g., the traction battery voltage) and setting the output voltage to a reference voltage. VVC 152 can be a buck converter that steps down the voltage from input to output. In a buck configuration, different expressions can be derived that relate the input and output voltages to the duty cycle. In some configurations, VVC 152 can be a buck-boost converter that can increase or decrease the input voltage. The control strategy described herein is not limited to a specific variable voltage converter topology.

[0038] Reference Figure 3 The VVC 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 transferred from the traction battery 124 to the VVC 152. An input capacitor 202 can be electrically connected in parallel with 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.

[0039] An output capacitor 204 may be electrically connected between the output terminals of the VVC 152. The output capacitor 204 may stabilize the bus voltage and reduce voltage and current ripple at the output of the VVC 152.

[0040] Further references Figure 3 The VVC 152 may include a first switching device 206 and a second switching device 208 for stepping up an input voltage to provide a stepped-up output voltage. The switching devices 206 and 208 may be configured to selectively enable current to flow to an electrical load (e.g., the power electronics module 126 and the motor 114). Each of the switching devices 206 and 208 may be individually controlled by a gate drive circuit (not shown) of the VVC controller 200 and may include any type of controllable switch (e.g., an insulated gate bipolar transistor (IGBT) or a field-effect transistor (FET)). The gate drive circuit may provide an electrical signal based on a control signal (e.g., the duty cycle of a PWM control signal) to each of the switching devices 206 and 208. A diode may be connected across each of the switching devices 206 and 208. Each of the switching devices 206 and 208 may have associated switching losses. Switching losses are power losses incurred during state changes of the switching devices (e.g., on / off and off / on transitions). Switching losses can be quantified by the current flowing through switching device 206 and switching device 208 during a transition, as well as the voltage across switching device 206 and the voltage across switching device 208. Switching devices may also have associated conduction losses that occur when the devices are turned on.

[0041] The vehicle system may include sensors for measuring electrical parameters of the VVC 152. The first voltage sensor 210 may be configured to measure an input voltage (eg, the voltage of the battery 124) and provide a corresponding input signal (V bat In one or more embodiments, the first voltage sensor 210 may measure the voltage across the input capacitor 202 corresponding to the battery voltage. The second voltage sensor 212 may measure the output voltage of the VVC 152 and provide a corresponding input signal (V dc In one or more embodiments, the second voltage sensor 212 can measure the voltage across the output capacitor 204 corresponding 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.

[0042] An input inductor 214 (often referred to as a boost inductor) may be electrically connected in series between the traction battery 124 and the switching device 206 and the switching device 208. The input inductor 214 may switch between storing energy in the VVC 152 and releasing energy from the VVC 152, thereby providing a variable voltage and current as the output of the VVC 152 and achieving a desired voltage boost. A current sensor 216 may measure the input current through the input inductor 214 and provide a corresponding current signal (I L The input current through input inductor 214 may be a function of the voltage difference between the input voltage and the output voltage of VVC 152, the on-time of switching devices 206 and 208, and the inductance L of input inductor 214. VVC controller 200 may include circuitry for scaling, filtering, and digitizing the signal from current sensor 216.

[0043] The VVC controller 200 may be configured to control the output voltage of the VVC 152. The VVC controller 200 may receive input from the VVC 152 and other controllers via the vehicle network and may determine control signals. The VVC controller 200 may monitor the input signals To determine the control signal. For example, the VVC controller 200 may provide a control signal corresponding to the duty cycle command to the gate drive circuit. The gate drive circuit may then control each of the switching devices 206 and 208 based on the duty cycle command.

[0044] The control signals provided to VVC 152 can be configured to drive switching devices 206 and 208 at a specific switching frequency. Within each cycle of the switching frequency, switching devices 206 and 208 can be operated at a specific duty cycle. The duty cycle defines the amount of time that switching devices 206 and 208 are in the on and off states. For example, a 100% duty cycle can cause switching devices 206 and 208 to operate in a continuously on state with no interruptions. A 0% duty cycle can cause switching devices 206 and 208 to operate in a continuously off state with no interruptions. A 50% duty cycle can cause switching devices 206 and 208 to operate in the on state for half a cycle and in the off state for half a cycle. The control signals for the two switches 206 and 208 can be complementary. That is, the control signal sent to one of the switching devices (e.g., switching device 206) can be the inverse of the control signal sent to the other switching device (e.g., switching device 208). The use of complementary control of switching devices 206 and 208 is suitable for avoiding a breakdown condition if current flows directly through high-side switching device 206 and low-side switching device 208. High-side switching device 206 is also referred to as pass device 206 and low-side switching device 208 is also referred to as charge device 208.

[0045] The current controlled by switching devices 206 and 208 may include a ripple component having an amplitude that varies with the current amplitude, the duty cycle, and the switching frequency of switching devices 206 and 208. The worst-case ripple current amplitude occurs during conditions of relatively high input current relative to the input current. When the duty cycle is fixed, an increase in the inductor current causes an increase in the ripple current amplitude. The ripple current amplitude is also related to the duty cycle. The highest amplitude ripple current occurs when the duty cycle is equal to 50%. Based on these facts, it may be beneficial to implement measures to reduce the ripple current amplitude under conditions of high current and mid-range duty cycles.

[0046] When designing VVC 152, the switching frequency and the inductance value of inductor 214 can be selected to meet the maximum allowable ripple current amplitude. A ripple component can be a periodic variable present in a DC signal. A ripple component can be defined by its amplitude and frequency. A ripple component can have harmonics within the audible frequency range, which can increase the vehicle's noise signature. Furthermore, ripple components can make it difficult to accurately control devices powered by the power supply. During switching transients, switching devices 206 and 208 may disconnect at the maximum inductor current (DC current plus ripple current), which can cause large voltage spikes across switching devices 206 and 208. Due to size and cost constraints, the inductance value can be selected based on the conduction current. Typically, as current increases, the inductance decreases due to saturation.

[0047] The switching frequency can be selected to limit the magnitude of the ripple current component under worst-case scenarios (e.g., conditions of maximum input current and / or conditions with a duty cycle approaching 50%). The switching frequency of switching devices 206 and 208 can be selected to be a frequency (e.g., 10 kHz) that is higher than the switching frequency (e.g., 5 kHz) of the motor / generator inverter connected to the output of VVC 152. In some applications, the switching frequency of VVC 152 can be selected to be a predetermined fixed frequency. The predetermined fixed frequency is typically selected to meet noise and ripple current specifications. However, the selection of a predetermined fixed frequency may not provide optimal performance over the entire operating range of VVC 152. The predetermined fixed frequency may provide optimal results under a specific set of operating conditions, but may be a compromise under other operating conditions.

[0048] Increasing the switching frequency can reduce the ripple current amplitude and lower the voltage load on switching devices 206 and 208, but may result in higher switching losses. Although the switching frequency can be selected for worst-case ripple conditions, the VVC 152 may only operate under worst-case ripple conditions for a small percentage of the total operating time. This can result in unnecessarily high switching losses, which can reduce fuel economy. Furthermore, a fixed switching frequency can concentrate the noise spectrum within a very narrow range. The increased noise density within this narrow range can cause significant noise, vibration, and harshness (NVH) issues.

[0049] The VVC controller 200 can be configured to change the switching frequency of the switching devices 206 and 208 based on the duty cycle and input current. Changing the switching frequency can improve fuel economy and reduce NVH issues by reducing switching losses while maintaining a ripple current target under worst-case operating conditions.

[0050] During relatively high current conditions, switching devices 206 and 208 may experience increased voltage stress. At the maximum operating current of VVC 152, it may be desirable to select a relatively high switching frequency so that the ripple component amplitude is reduced and switching losses are at a reasonable level. The switching frequency may be selected based on the input current amplitude, such that the switching frequency increases with increasing input current amplitude. The switching frequency may be increased to a predetermined maximum switching frequency. The predetermined maximum switching frequency may be a level that provides a compromise between lower ripple component amplitude and higher switching losses. The switching frequency may be varied in discrete steps or continuously within the operating current range.

[0051] The VVC controller 200 can be configured to reduce the switching frequency in response to the current input being lower than a predetermined maximum current. The predetermined maximum current can be the maximum operating current of the VVC 152. The change in switching frequency can be based on the amplitude of the current input to the switching device 206 and the switching device 208. When the current is greater than the predetermined maximum current, the switching frequency can be set to a predetermined maximum switching frequency. As the current decreases, the amplitude of the ripple component decreases. By operating at a lower switching frequency when the current decreases, switching losses are reduced. The switching frequency can be varied based on the power input to the switching device. Since the input power is a function of the input current and the battery voltage, the input power and the input current can be used in a similar manner.

[0052] Because ripple current is also affected by the duty cycle, the switching frequency can vary based on the duty cycle. The duty cycle can be determined based on the ratio between the input voltage and the output voltage. Similarly, the switching frequency can also vary based on the ratio between the input voltage and the output voltage. When the duty cycle approaches 50%, the predicted ripple current amplitude is maximum, and the switching frequency can be set to a predetermined maximum frequency. The predetermined maximum frequency can be the maximum switching frequency value selected to minimize the ripple current amplitude. The switching frequency can vary in discrete steps or continuously within the duty cycle range.

[0053] The VVC controller 200 may be configured to reduce the switching frequency from a predetermined maximum frequency in response to the magnitude of the difference between the duty cycle and the duty cycle value at which the predicted ripple component amplitude is maximum (e.g., 50%). When the magnitude of the difference is less than a threshold, the switching frequency may be set to the predetermined frequency. As the magnitude of the difference decreases, the switching frequency may be increased toward the predetermined maximum frequency to reduce the ripple component amplitude. When the magnitude of the difference is less than a threshold, the switching frequency may be set to the predetermined maximum frequency.

[0054] The switching frequency may be limited between a predetermined maximum frequency and a predetermined minimum frequency. The predetermined minimum frequency may be a frequency level greater than a predetermined switching frequency of the power electronics module 126 connected to the output of the variable voltage converter 152. The switching frequency may also be based on parasitic inductance associated with the gate of the IGBT.

[0055] Figure 4 Schematic diagram 300 of a hybrid vehicle powertrain system including an AC grid 310, a battery charger 308, a traction battery 306, a DC / DC converter 304, and an electric drive unit 302. Electric drive unit 302 includes an electric motor and an inverter for driving the electric motor. During propulsion, DC / DC converter 304 is configured to boost the battery voltage to an operating voltage across a DC bus capacitor 312, and during charging, DC / DC converter 304 is configured to direct reactive power to DC bus capacitor 312. Typically, a battery boost converter is used to boost a lower battery voltage to a higher DC bus voltage, enabling easier electric motor control and greater efficiency in many hybrid electric vehicles (HEVs) and some battery electric vehicles. This figure is a diagram of a standalone single-phase charger, which can be a Level 1 AC single-phase charger, a Level 2 AC single-phase charger, or a Level 3 AC single-phase charger. Here, the battery boost converter 304 (also referred to as a DC / DC converter or variable voltage converter (VVC)) includes a high-side switch 314, a low-side switch 316, an inductor 318, and a DC bus or output capacitor 320. The high-side and low-side switches (314 and 316) are typically solid-state devices (SSDs), such as insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), or bipolar junction transistors (BJTs), which are widely used in various automotive 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.

[0056] Here, an SSD or high-power relay can be used to control, change, or modulate the current between the vehicle's battery and the motor / electric drive unit 302. However, when charging, the switches (314 and 316) can be modulated to reduce power ripple. The ripple reduction method uses the semiconductor switches (314 and 316) of the battery boost converter 304 to direct reactive ripple power to the DC link capacitor 320 in the battery boost converter 304. Frequencies other than the grid frequency are generally considered, for example, the ripple at a frequency twice the grid frequency can be selected because this frequency component is generally the most severe ripple component (for example, when the input voltage and input current have a unity power factor, which is the case for most commercial chargers). However, because the electric drive system is not running during charging and the ripple is transferred to the battery side by the charger, this method and structure can be used for non-unity power factor situations and can be used for other frequency components by adjusting the inductor value, capacitor value, modulation duty cycle, and modulation frequency.

[0057] Figure 5 This diagram shows a power-split hybrid vehicle powertrain system that includes an AC grid charger, a traction battery, and a converter configured to direct reactive power to a DC bus capacitor. This system is an integrated charger for electric vehicles that utilizes the onboard electric drive system to perform battery charging functions. In this topology, the electric motor and generator windings function as inductors, and the respective inverters of the electric motor and generator are commanded to perform power factor correction (PFC) functions.

[0058] exist Figure 5In FIG, hybrid vehicle powertrain 400 includes an electric drive unit 402, which can be configured to provide torque to drive the vehicle's wheels or generate current by harnessing the rotational force of the wheels. Within electric drive unit 402, an electric motor 424 is connected to a motor inverter 422 that converts AC current into direct current (DC). In this example, electric drive unit 402 also includes a generator 428 connected to a generator inverter 426. During vehicle operation, a high-voltage traction battery 406, which may have a parallel-connected smoothing capacitor 412, is used to provide propulsion to rotate the electric motor and to store energy captured by the electric motor from the rotational energy of the wheels. When the vehicle is not in motion, it may be desirable to increase the state of charge (SOC) of battery 406 by connecting it to an AC grid 410 via a battery charger, which in this example is electric drive unit 402. One effect of using AC grid 410 is that harmonics of the grid frequency can generate voltage spikes that are propagated to the battery and components of powertrain 400. Here, the DC / DC boost converter or battery boost converter 404 includes an inductor 408, a high-side switch 414, a low-side switch 416, and a capacitor 420. When charging, the electric drive unit 402 can connect the neutral terminals of the motor 424 and the generator 428 to the AC grid 410 and modulate the switches of the motor inverter 422 and the generator inverter 426 to transfer reactive power through the inductive windings of the motors 424 / 428. This allows the current flowing through the windings of the motors 424 / 428 to flow to the battery boost converter 404, so that when the capacitor 420 and the inductor 408 are connected via the switch 414, the current is absorbed by the capacitor 420 and the inductor 408. The current is controlled via the pull-up switch (e.g., 414) and the pull-down switch (e.g., 416).

[0059] The battery charger may be a Level 1 AC charger, a Level 2 AC charger, or a Level 3 AC charger as defined by the Society of Automotive Engineers (SAE), such as those described in the SAE J1772 specification and other SAE specifications. Here, the high-side switch 414 (which may be a relay, IGBT, MOSFET, or other solid-state switch) selectively connects the capacitor C between the battery terminals. dc 420 is connected in series with the inductor L408 of the battery boost converter 404. When the vehicle is connected to the AC grid and not moving, the stator windings of the motors 424 / 428 can be used to deliver current to the boost converter 404 via the inverters 422 / 426. The inverters 422 / 426 can modulate the switches or can statically engage the switches to direct the current, while the switches 414 / 416 of the converter 404 can be operated at a frequency f that is greater than the line frequency of the AC grid 410. SW Modulation is performed. The frequency f SWThe frequency (e.g., 1 KHz, 1.2 KHz, 2 KHz, 2.4 KHz, 5 KHz, or 6 KHz) may be greater than 20 times the line frequency (e.g., 50 Hz or 60 Hz).

[0060] Smoothing capacitor C dc 420 is used as an energy storage device to absorb ripple power. Inductor L408 is used to transfer reactive power to capacitor 420 and is not usually used as an energy storage device. According to the inductance value, switching frequency and low-frequency ripple amplitude of inductor 408, inductor 408 can operate in discontinuous mode or continuous mode. It should be noted that the operation of the switches of inverter 422 / 426 is such that no steady-state rotating torque is applied to the motor, because any transient torque generated by the induced field will usually be oppositely equal or balanced so that the rotating torque is substantially zero. For example, making the same (balanced) current flow through all phases of the motor will produce a balanced uniform field in the motor, thereby producing minimum rotating torque or no rotating torque. In addition, the switches of inverter 422 / 426 can be modulated to compensate for the rotor position and the characteristic differences of the electrical components of the inverter (e.g., switches, diodes and connections) and the phases of the motor.

[0061] Figure 6 FIG6 is a graphical representation 600 of AC characteristics of charging components and powertrain components versus time 602 during AC charging of a hybrid vehicle. Input power 604, inductor current 606, and bulk DC capacitor voltage 608 are graphically shown versus time 602. At time 610, when the input DC power equals the grid power, the current is zero, and at time 612 and at ½ the grid frequency (f grid ), when the current is at its minimum, the input power is zero. In these waveforms of input power, inductor current, and capacitor voltage, only the DC component and the twice grid frequency component are shown. During this measurement, the battery charger was operated so that the input voltage and input current of the battery charger achieved unity power factor, but in most cases, typical commercial chargers cannot achieve unity power factor. However, these control methods and circuits can be applied to non-unity power factor situations and systems with other frequency components.

[0062] For calculation purposes, it is assumed that all low-frequency ripple on the AC side is transferred to the battery side through the charger. The input power can then be based on:

[0063] P in =P in_dc ×(1+cos(2f grid ×2πt)) (2)

[0064] By the output capacitor C battThe absorbed reactive energy can be calculated based on the following equation:

[0065]

[0066] The voltage swing of a capacitor can be calculated based on the following equation:

[0067]

[0068]

[0069] Equation (5) provides a guideline for capacitor selection. For example, considering a 3.3kW charger with a 60Hz grid frequency, a 400V capacitor DC voltage, and a 50V capacitor voltage ripple (3300 / (4*π*60*50*400)), a 200uF capacitor can be used to meet the requirements of Equation (5).

[0070] Figure 7 FIG5 is a block diagram 500 of a control system converter signal flow of a hybrid vehicle during AC charging. The converter is controlled to direct reactive power from the AC grid charging operation to the DC bus capacitor or output capacitor. Here, the grid-side sensing items may include voltage / current (e.g., I ac and V ac ), the voltage / current may be calculated by a first control block 502 (e.g., an AC charger controller) to generate phase information and input power data. The phase information and input power data may be transmitted to a second control block 504, which may be located within the vehicle, and may be combined with the inductor Lm current (I Lm ) and capacitor voltage (V C1 ) is used together with sensed information from the motor. The output of this control flow is a converter gate signal, which is used to connect capacitor C1 (e.g., output capacitor 420) between the neutral terminal of the motor and the negative terminal of the inverter. In addition, this converter gate signal can also be used to control switches in the inverter (e.g., switches in motor inverter 422 and switches in generator inverter 426) and switches in the converter (e.g., battery boost converter 404).

[0071] Figure 8 Flowchart 700 is a control system for a DC / DC converter for directing reactive power to an output capacitor or a DC bus capacitor. At operation 702, the controller branches based on the operating mode of the hybrid vehicle. If the vehicle is not in charging mode, the controller branches back to operation 702. If the operating mode is charging mode, the controller branches to operation 704.

[0072] At operation 704, the controller calculates the input power ripple (e.g., Figure 6 P shown in ) and inverter operating losses, and proceeds to operation 706. At operation 706, the controller branches operations based on whether the input power ripple exceeds a threshold. The threshold may be based on a predetermined value, such as a maximum allowable ripple value for the battery, or determined by charging efficiency requirements and converter circuit losses. If the input power ripple is less than the threshold, the controller exits. If the input power ripple is greater than the threshold, the controller branches to operation 708.

[0073] At operation 708 , the controller connects the output capacitor between the terminals of the battery to “balance” the reactive power. After the balancing capacitor is connected, the controller proceeds to operation 710 .

[0074] At operation 710, the controller operates the converter to direct reactive power from the charging operation to the output capacitor via the converter's switches. In embodiments without an output capacitor, the controller operates the converter to direct reactive power through the converter's inductor. The controller then proceeds to operation 712. At operation 712, the controller branches operations in response to the charging status. If charging is not complete, the controller branches to operation 710 and continues operating the inverter. If charging is complete, the controller exits at operation 714.

[0075] Figure 9is a diagram of a hybrid vehicle powertrain 900 including an electric motor 902 configured to provide torque to drive the vehicle's wheels or to generate current by rotating the motor 902 using the rotational force of the wheels. The motor is connected to a motor inverter 904 that converts AC current to direct current (DC). During vehicle operation, a high-voltage traction battery 906 is used to provide propulsion to rotate the motor and to store energy captured by the motor from the rotational energy of the wheels. When the vehicle is not in motion, it may be desirable to increase the state of charge (SOC) of the battery 906 by connecting the battery 906 to the AC grid 910 via a battery charger 908. One effect of using the AC grid is that harmonics of the grid frequency can generate voltage spikes that are propagated to the battery and components of the powertrain. Because the required operating voltage of the inverter 904 and the electric motor 902 may differ from the voltage of the battery 906, a DC / DC converter 912 may be used to increase / decrease or step up / down the battery voltage to the required operating voltage. The DC / DC converter 912 (also referred to as a variable voltage converter (VVC)) may include a high-side switch 914, a low-side switch 916, an inductor 918, and an output capacitor 920. The high-side and low-side switches (914 and 916) are typically solid-state devices (SSDs), such as insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), or bipolar junction transistors (BJTs), which are widely used in a variety of automotive 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.

[0076] During propulsion, the DC / DC converter 912 is configured to boost the battery voltage to an operating voltage across the DC bus capacitor 920, and during charging, the DC / DC converter 912 is configured to direct reactive power to the DC bus capacitor 920. Typically, a battery boost converter is used to boost a lower battery voltage to a higher DC bus voltage to enable easier electric motor control and higher efficiency in many hybrid electric vehicles (HEVs) and some battery electric vehicles. This figure is a diagram of a stand-alone single-phase charger, which can be a Level 1 AC single-phase charger, a Level 2 AC single-phase charger, or a Level 3 AC single-phase charger as defined by the Society of Automotive Engineers (SAE), such as the single-phase chargers described in the SAE J1772 specification and other SAE specifications.

[0077] Here, capacitor 922 is selectively connected to the neutral terminal of motor 902 via switch 924, and the switches (928A, 928B, 928C, 930A, 930B, and 930C) of inverter 904 are modulated to transfer reactive power through inductive windings 926A, 926B, and 926C of motor 902. This allows current flowing through motor windings 926A, 926B, and 926C to flow to be absorbed by capacitor 920 when capacitor 920 is engaged via switch 924. Current is controlled via pull-up switches 928A, 928B, and 928C and pull-down switches 930A, 930B, and 930C, which are also referred to as high-side switches 928A, 928B, and 928C and low-side switches 930A, 930B, and 930C. Here, switch R1 924 (which can be a relay, IGBT, MOSFET, or other solid-state switch) selectively connects capacitor C1 922 between the neutral terminal of motor 902 and the negative bus of inverter 904. When the vehicle is connected to the AC grid and not moving, the stator windings of the motor (i.e., inductors L1, L2, and L3) can be used to deliver current to the battery boost converter 912 via inverter 904. The inverter operates at a frequency f that is greater than the line frequency of the AC grid 910. SW Modulation switches (928 and 930). The frequency f SW The frequency (e.g., 1 KHz, 1.2 KHz, 2 KHz, 2.4 KHz, 5 KHz, or 6 KHz) may be greater than 20 times the line frequency (e.g., 50 Hz or 60 Hz).

[0078] Smoothing capacitor C1 922 is used as an energy storage device to absorb ripple power. Inductor Lm represents the winding inductance of motor 902. Inductor Lm is used to transfer reactive energy to capacitor 922 and is not generally used as an energy storage device. Depending on the inductance of the windings (926A, 926B, and 926C), the switching frequency, and the low-frequency ripple amplitude, the inductor can operate in discontinuous mode or continuous mode.

[0079] The switches in the three-phase bridge are divided into two groups: three upper switches (928A, 928B, and 928C) and three lower switches (930A, 930B, and 930C). The switches in each group can operate in different modes. For example, in a first "parallel" mode, the three switches (e.g., upper switches or lower switches) operate simultaneously, so that all upper switches are activated equally and all lower switches are activated equally. Another mode is an "interleaved" mode, in which the three switches (e.g., upper switches or lower switches) are operated one-third of a switching cycle apart. A third "selective" mode allows only one or two switches to operate at a given time. Although the present invention has been described using a three-phase motor, the present invention is not limited to three-phase motors, as the present invention can also be implemented in six-phase motors, nine-phase motors, or other multi-phase motors, where a balancing capacitor is connected between the neutral terminal of the multi-phase motor and the negative terminal of the inverter for the motor. The operation of the switches is such that no steady-state rotational torque is applied to the motor because, in some embodiments, any transient torque generated by the induced field will generally be oppositely equal or balanced, such that the rotational torque is substantially zero. For example, flowing the same (balanced) current through all phases of the motor will produce a balanced, uniform field in the motor, resulting in minimal or no rotational torque. In addition, the switches can be modulated to compensate for differences in rotor position and the characteristics of the inverter's electrical components (e.g., switches, diodes, and connections) and the motor's phases (e.g., 926A, 926B, and 926C).

[0080] Figure 101000 is a diagram of a hybrid vehicle powertrain 1000 including an electric motor 1002. Electric motor 1002 can be configured to provide torque to drive the vehicle's wheels or generate current by rotating electric motor 1002 using the rotational force of the wheels. The electric motor is connected to an electric motor inverter 1004, which converts AC current to direct current (DC). During vehicle operation, a high-voltage traction battery 1006 is used to provide propulsion to rotate the electric motor and to store energy captured by the electric motor from the rotational energy of the wheels. When the vehicle is not in motion, it may be desirable to increase the state of charge (SOC) of battery 1006 by connecting it to an AC grid 1010 via a battery charger 1008. One effect of using the AC grid is that harmonics of the grid frequency can generate voltage spikes that are propagated to the battery and components of the powertrain. Because the required operating voltage for inverter 1004 and electric motor 1002 may differ from the voltage of battery 1006, a DC / DC converter 1012 may be used to increase / decrease or step up / down the battery voltage to the required operating voltage. The DC / DC converter 1012 (also referred to as a variable voltage converter (VVC)) may include a high-side switch 1014, a low-side switch 1016, an inductor 1018, and an output capacitor 1020. The high-side and low-side switches (1014 and 1016) are typically solid-state devices (SSDs), such as insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), or bipolar junction transistors (BJTs), which are widely used in various automotive 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.

[0081] During propulsion, the DC / DC converter 1012 is configured to boost the battery voltage to an operating voltage across the DC bus capacitor 1020, and during charging, the DC / DC converter 1012 is configured to direct reactive power to the DC bus capacitor 1020. Typically, a battery boost converter is used to boost a lower battery voltage to a higher DC bus voltage to enable easier electric motor control and higher efficiency in many hybrid electric vehicles (HEVs) and some battery electric vehicles. This figure is a diagram of a standalone single-phase charger, which can be a Level 1 AC single-phase charger, a Level 2 AC single-phase charger, or a Level 3 AC single-phase charger as defined by the Society of Automotive Engineers (SAE), such as the single-phase chargers described in the SAE J1772 specification and other SAE specifications.

[0082] One effect of using an AC grid is that harmonics of the grid frequency can generate peak voltages that are propagated to the powertrain. Here, current can be directed through at least one phase of motor 1002 via inverter 1004. Current can be directed through at least one winding of the motor (e.g., 1026A, 1026B, and 1026C) and then returned through a different winding of the motor. Current is controlled via pull-up switches 1028A, 1028B, and 1028C and pull-down switches 1030A, 1030B, and 1030C. For example, current can be directed through first phase 1026A by turning on first switch 1028A, and then returned through second phase 1026B by turning on second switch 1030B. In an alternative embodiment, current can be returned through second and third phases 1026B, 1026C, by turning on second and third switches 1030B and 1030C.

[0083] Figure 10 The equivalent circuit of is essentially an H-bridge with an inductor connected across the bridge. Depending on the switch configuration, inductor Lm represents the equivalent winding inductance of the phase in series or parallel, which can have different values ​​depending on the circuit configuration. Pull-up switches 1028A, 1028B, and 1028C and pull-down switches 1030A, 1030B, and 1030C form a full-bridge inverter and are controlled to generate an inductor current I Lm The pull-up switches 1028A, 1028B, and 1028C and the pull-down switches 1030A, 1030B, and 1030C may be operated at a frequency f that is much higher (>20 times) than the line frequency of the AC grid. SW Furthermore, the pull-up switches 1028A, 1028B, and 1028C and the pull-down switches 1030A, 1030B, and 1030C can be controlled so that the inductor current I LmTrack the input power to compensate for the reactive power component of the input power. Although a three-phase motor has been used to illustrate this embodiment, the embodiment is not limited to three-phase motors because the embodiment can also be implemented in six-phase motors, nine-phase motors, or other multi-phase motors, wherein current flows out of at least one phase and returns via at least one different phase. The operation of the switch is such that no steady-state rotational torque is applied to the motor because the transient torque generated by the induced field will typically be oppositely equal or balanced in some embodiments so that the rotational torque is substantially zero. For example, the same (balanced) current is caused to flow through one phase of the motor and the current is returned via a separate different phase to produce a balanced uniform field in the motor, thereby producing minimal rotational torque or no rotational torque. Another example is: current is caused to flow through one phase of the motor and the current is returned via the remaining two phases to produce a balanced uniform field in the motor, thereby producing minimal rotational torque or no rotational torque. Additionally, the switches may be modulated to compensate for differences in rotor position and characteristics of the inverter's electrical components (eg, switches, diodes, and connections) and the motor's phases (eg, 1026A, 1026B, and 1026C).

[0084] In the following analysis, it is also assumed that the input voltage and input current have unity power factor, which is the case for most commercial chargers. However, for non-unity power factor cases and for other frequency components, the analysis will be similar. Here, two cases are studied. The first case is I Lm With a large DC value plus AC ripple, the second case is I Lm There is no DC value plus AC ripple or a small DC value plus AC ripple.

[0085] in I Lm With a large DC value plus AC ripple, the inductor current is always positive, and the inductor current I Lm The AC component of the inductor tracks the input reactive power to compensate for the grid-side ripple. Here, the current ripple on the inductor can be calculated based on the following equation:

[0086]

[0087] The required inductance of the motor stator winding can be based on:

[0088]

[0089] Equation (7) provides a guideline for the recommended inductance. For example, for a 3.3kW charger with a 60Hz grid frequency, a current ripple of 50A, and an inductor DC current of 400A, a stator winding equivalent inductance of 200uH can be used to meet the requirements.

[0090] The inverter is controlled to direct the low-frequency reactive power to the inductor. The grid-side sensing items may include voltage / current (e.g., I ac and V ac ), the voltage / current can be used to generate phase information and input power data. Phase information and input power data can be used together with vehicle sensing information, which may include the current (I Lm ).

[0091] In the second case (I Lm With no DC value plus AC ripple or a small DC value plus AC ripple, the inductor current can become negative. Furthermore, the AC component of the inductor current tracks the input reactive power to compensate for grid-side ripple. Input power with unity power factor can be calculated based on the following equation:

[0092] P in_ac =P in_dc cos(2f grid ×2πt)) (8)

[0093]

[0094]

[0095] Equation (10) provides the inductor current value for compensating for twice the grid frequency ripple power at unity power factor. The polarity of the inductor current can be selected as desired to minimize the conduction losses of the circuit (e.g., conduction losses through the switches and components of the powertrain). Figure 6 Waveforms associated with characteristics of a circuit including an inductor current are shown, which is illustrative of one embodiment in which the polarity of the inductor current changes each time the inductor current becomes zero.

[0096] 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.

[0097] The processes, methods or algorithms disclosed herein may be transmitted to or implemented by a 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 or instructions that can be executed by a controller or a computer, wherein the various forms include, but are not limited to, information being permanently stored in a non-writable storage medium (such as a read-only memory (ROM) device) and information being 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 suitable 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.

[0098] 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 DC / DC converter including an inductor and an output capacitor, said DC / DC converter being connected between the traction battery and the electric drive unit; A controller is configured to, in response to an electrical connection between the vehicle and an AC grid, modulate switches of the DC / DC converter to connect the output capacitor and the inductor in series between terminals of a traction battery so that reactive power from the AC grid is directed to the output capacitor, thereby absorbing reactive power from the AC grid.

2. The power transmission system according to claim 1, wherein: The controller is further configured to vary a switching frequency of the switch based on the duty cycle and the input current to balance reactive power through an inductor and an output capacitor of the DC / DC converter. 3 . The powertrain system of claim 1 , further comprising a single-phase charger configured to form an electrical connection between the AC grid and the DC / DC converter. 4 . The powertrain system of claim 1 , further comprising an integrated charger configured to form an electrical connection between the AC grid and the DC / DC converter via neutral terminals of both the first and second electric machines.

5. The power transmission system according to claim 1, wherein: The electric drive unit includes an electric inverter and an electric motor.

6. The power transmission system according to claim 5, wherein: The controller is further configured to modulate switches of the power inverter to absorb reactive power from the AC grid in at least one phase of the electric machine.

7. The power transmission system according to claim 5, wherein: The controller is further configured to modulate switches of the power inverter so that reactive power from the AC grid is transferred through the windings of the motor to absorb reactive power from the AC grid in at least one phase of the motor and in a balancing capacitor connected between a neutral terminal of the motor and a negative terminal of the power inverter.

8. A method of controlling a power transmission system, comprising: In response to an electrical connection between an AC grid and an electric vehicle including the powertrain, a high-side switch of a DC / DC converter is modulated by a controller according to reactive power from the AC grid to transfer the reactive power through an inductor of the DC / DC converter, thereby absorbing a portion of the reactive power in an output capacitor of the DC / DC converter.

9. The method of claim 8, further comprising: In response to the electrical connection, an output capacitor of a DC / DC converter is connected between terminals of a traction battery of the powertrain.

10. The method of claim 9, further comprising: In response to the electrical connection, switches of the inverter are modulated according to reactive power from the AC grid so that the reactive power is transferred through the windings of the motor to induce a field in the Y-wound motor of the powertrain, thereby absorbing a portion of the reactive power.

11. A power transmission system for a vehicle, comprising: A controller is configured to, in response to an electrical connection between the vehicle and an AC grid, modulate switches of the DC / DC converter to connect an output capacitor and an inductor of the DC / DC converter in series between terminals of a traction battery, such that reactive power from the AC grid is directed to the output capacitor, thereby absorbing reactive power from the AC grid.

12. The power transmission system according to claim 11, wherein: The output capacitor and the inductor of the DC / DC converter are connected via switches of the DC / DC converter, which are modulated at a frequency higher than the line frequency of the AC grid.

13. The power transmission system of claim 11, further comprising a Y-shaped winding motor connected to the inverter, wherein: The controller is further configured to modulate switches of the inverter to cause current to flow in the electric machine to absorb reactive power from the AC grid in at least one winding of the electric machine in response to an electrical connection between the vehicle and the AC grid.

14. The power transmission system of claim 13, wherein: The controller is further configured to modulate switches of the inverter so that reactive power from the AC grid is transferred through the windings of the motor to balance the reactive power through the inductor and output capacitor of the DC / DC converter.

15. The power transmission system of claim 13, wherein: The controller is further configured to modulate switches of the inverter so that reactive power from the AC grid is transferred through the windings of the motor to absorb reactive power from the AC grid in at least one phase of the motor and in a balancing capacitor connected between a neutral terminal of the motor and a negative terminal of the inverter.

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