Electric vehicle ground fault monitoring system

Abstract

The present disclosure provides an "Electrified Vehicle Ground Fault Monitoring System". An electrified vehicle charger includes a diode bridge, a contactor, and a controller. The diode bridge may be configured to rectify an alternating current (AC) source. The contactor may couple the AC source to a traction battery. The controller may be configured to open the contactor in response to a magnitude of a potential across a diode of the bridge exceeding a threshold, the magnitude corresponding to a neutral point crossing of the potential of the AC source.

Description

Technical Field

[0001] The present application generally relates to a monitoring system for an electrified vehicle powertrain having an isolated high voltage system configured to detect a ground fault. Background Art

[0002] Electrified vehicles (EVs), including hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs), rely on traction batteries to provide power to traction motors for propulsion and power inverters in between to convert direct current (DC) power to alternating current (AC) power. A typical AC traction motor is a three-phase motor that can be powered by 3 sinusoidal signals, each driven at 120 degrees phase separation. The traction battery is configured to operate and provide current within a specific voltage range. However, by operating within a different voltage range, typically at a voltage greater than the traction battery terminal voltage, improved motor performance can be achieved. Similarly, the current demand to drive the vehicle motor is often referred to as high current. The traction battery may alternatively be referred to as a high voltage battery and the components of the electric drive (e.g., traction motor, inverter, converter, battery, converter, etc.) are referred to as high voltage electrical systems or components in a high voltage powertrain. Along with this high voltage electrical system is a low voltage electrical system that typically operates at a nominal voltage of 12V. The low voltage electrical system provides power for many onboard systems such as radio / navigation systems / vehicle controllers. Low voltage power systems typically use conductors for the positive low voltage and the vehicle chassis to carry the negative low voltage, while high voltage power systems have dedicated conductors for carrying positive and negative high voltages. Summary of the invention

[0003] An electrified vehicle charger includes a diode bridge, a contactor, and a controller. The diode bridge may be configured to rectify an alternating current (AC) source. The contactor may couple the AC source to a traction battery. The controller may be configured to open the contactor in response to a magnitude of a potential across a diode of the bridge exceeding a threshold, the magnitude corresponding to a neutral point crossing of the potential of the AC source.

[0004] A method of operating a vehicle charger includes measuring, by a controller and in response to a potential of an alternating current (AC) source transitioning between positive and negative voltages, a voltage across a rectifier diode of the AC source, and disabling the charger in response to the measurement exceeding a threshold.

[0005] An electrified vehicle charger includes a diode bridge and a controller. The diode bridge may be configured to rectify an alternating current (AC) source and include a first diode having an anode coupled to a phase terminal of the AC source and a second diode having a cathode coupled to a neutral point terminal of the AC source. The controller may be configured to disable the charger in response to the first diode conducting and the second diode not conducting at a zero crossing of the AC source. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is an illustration of an electrified vehicle configured with an integrated charger.

[0007] Figure 2 is a diagram of a hybrid vehicle showing a typical powertrain and energy storage component including a variable voltage and frequency converter.

[0008] Figure 3 is a schematic diagram of an electrified powertrain configured with an integrated charger.

[0009] Figure 4 is a schematic diagram of an electrified powertrain system configured as an integrated charger coupled to a TT grounding system, illustrating a ground fault.

[0010] Figure 5 is a schematic diagram of an electrified powertrain system configured as an integrated charger coupled to a TN ground system, showing a ground fault.

[0011] Figure 6 is a graphical illustration of the electrical characteristics of the battery positive terminal and chassis faults in the TT system versus time.

[0012] Figure 7 is a graphical illustration of the electrical characteristics of the battery positive terminal and chassis faults in the TT system versus time.

[0013] Figure 8 is a graphical illustration of the electrical characteristics of the battery negative terminal and chassis faults in the TT system versus time.

[0014] Fig. 9 is a schematic diagram of an electrified powertrain system configured as an integrated charger coupled to a split-phase TN ground system, showing a ground fault.

[0015] Fig.10 is a graphical illustration of the electrical characteristics of a battery positive terminal and chassis fault versus time in a split-phase TN system. DETAILED DESCRIPTION

[0016] 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 forms and alternative forms. The drawings are not necessarily drawn to scale; some features may be enlarged or minimized to show the details of specific components. Therefore, the specific structural details 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 adopt the present invention in different ways. As will be understood by those of ordinary skill in the art, the various features illustrated and described with reference to any one of the accompanying drawings may be combined with the features shown in one or more other drawings to produce embodiments that are not explicitly illustrated or described. The combination of features shown provides representative embodiments for typical applications. However, for specific applications or embodiments, various combinations and modified forms of features consistent with the teachings of the present disclosure may be expected.

[0017] Electrified vehicles typically have high-voltage subsystems and low-voltage systems. The high-voltage subsystem may include a traction battery, a DC-DC converter, a DC-AC inverter, and a motor. The low-voltage system may include a low voltage (accessory battery or 12-volt battery), an engine starter, vehicle accessories such as power seats, power windows, power doors, power locks, and window defrosters, and a vehicle control module, as well as subsystems including anti-lock brakes, airbags, safety systems, adaptive steering, adaptive cruise control, radiator fans, distributors, in-vehicle entertainment, telecommunications units, instrument clusters, vehicle displays, and other low-voltage components. In most vehicle embodiments, the low-voltage system is not isolated from the chassis because the chassis acts as a return path for the current. This is achieved by isolating the positive voltage using insulators such as insulated wires and cables while shorting the negative terminal of the battery with the vehicle chassis. This uses the chassis as a return path, thereby reducing the need for insulated wires and cables for all negative voltages. However, in most hybrid or electric vehicle embodiments, the high-voltage system is electrically isolated because neither the negative voltage nor the positive voltage is short-circuited with the chassis. The high voltage system is configured so that both the negative and positive terminals are isolated, which typically uses an insulated negative cable and an insulated positive cable. In this way, the high voltage subsystem is said to be at high impedance or ungrounded (floating) relative to the chassis (or ground). In this way, the potential of the negative or positive wire or cable can be substantially greater or less than the vehicle chassis or ground. To avoid accidental discharge, electric / hybrid drive vehicles use an insulation monitoring system or ground fault detection system to check and monitor the integrity of the high voltage (HV) system (including the insulation of wires, cables and components).

[0018] Here, systems and methods are disclosed for detecting leakage current to the vehicle chassis or ground based on a fault between the positive terminal of the battery and ground via measuring the input voltage of a non-isolated charger. These methods include: making volt-second measurements at the voltage input in small time intervals during AC line zero crossings, making amplitude measurements of the charger at the voltage input during AC line zero crossings, and making harmonic content measurements at the voltage input of the non-isolated charger. The ground fault characteristics depend largely on the grounding system. The neutral state supplied by the utility company varies from country to country in different grounding systems. In addition, a country may have multiple grounding systems. Each grounding system has a unique implementation. A theoretical model describing the impact of HV ground faults on vehicles connected to TT grounding systems and TN grounding systems will be disclosed.

[0019] Figure 1 A vehicle with a high voltage system and a high voltage charger system is depicted. Here, an alternating current (AC) source 2 is rectified by a bridge rectifier 4 to convert the AC power to direct current (DC) power. The DC power then flows through the windings of the motor via the neutral point terminal of a "wye-wound" motor 6. After passing through the phase windings of the motor 6, the power passes through a DC / AC inverter 8. The power then passes through a DC / DC converter 10 (e.g., a buck / boost converter) and is then filtered via a storage capacitor 14 and stored in a battery 12. In this system, both the positive and negative terminals and the bus are isolated so that the high voltage bus floats relative to the vehicle chassis potential or ground potential. Figure 1 The integrated charger architecture provides a solution that effectively utilizes existing hardware in the vehicle. Since charging and driving operations do not occur at the same time, using the same hardware to perform both functions is an excellent solution to reduce the cost of electric vehicles. In addition, system efficiency and size can be further reduced.

[0020] Figure 2Depict an electrified vehicle 112 that may be referred to as a plug-in hybrid electric vehicle (PHEV). The plug-in hybrid electric vehicle 112 may include one or more motors 114 mechanically coupled to a hybrid transmission 116. The motor 114 may be capable of operating as a motor or a generator. In addition, the hybrid transmission 116 is mechanically coupled to an engine 118. The hybrid transmission 116 is also mechanically coupled to a drive shaft 120, which is mechanically coupled to wheels 122. The motor 114 may provide propulsion and deceleration capabilities when the engine 118 is turned on or off. The motor 114 may also act as a generator and may provide fuel economy benefits by recovering energy that is typically lost as heat in a friction brake system. The motor 114 may 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 while the engine 118 is turned off under certain conditions. The electrified vehicle 112 may also be a battery electric vehicle (BEV). In a BEV configuration, the engine 118 may not exist. In other configurations, the electrified vehicle 112 may be a full hybrid electric vehicle (FHEV) without plug-in capability.

[0021] 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 coupled 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 connect the traction battery 124 to other components when closed. The power electronics module 126 is also electrically coupled 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, and the motor 114 can operate on three-phase alternating current (AC) to function. The power electronics module 126 can convert the DC voltage into a three-phase AC current to operate the motor 114. In the regenerative mode, the power electronics module 126 can convert the three-phase AC current from the motor 114 acting as a generator into a DC voltage compatible with the traction battery 124.

[0022] The vehicle 112 may include a variable voltage converter (VVC) 152 electrically coupled 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 motor 114. Additionally, the motor 114 may operate with better efficiency and lower losses.

[0023] In addition to providing energy for propulsion, the traction battery 124 may 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 source compatible with low voltage vehicle loads. The output of the DC / DC converter module 128 may be electrically coupled to an auxiliary battery 130 (e.g., a 12V battery) for charging the auxiliary battery 130. The low voltage system may be electrically coupled to the auxiliary battery 130. One or more electrical loads 146 may be coupled to the high voltage bus. The electrical loads 146 may have associated controllers that operate and control the electrical loads 146 as appropriate. Examples of electrical loads 146 may be fans, electric heating elements, and / or air conditioning compressors.

[0024] The electrified vehicle 112 may be configured to recharge the traction battery 124 from an external power source 136. The external power source 136 may be a connection to an electrical outlet. The external power source 136 may be electrically coupled to a charger or electric vehicle supply equipment (EVSE) 138. The external power source 136 may be a distribution network or transmission grid provided by an electric company. The EVSE 138 may provide circuitry and control to regulate and manage energy transfer between the power source 136 and the vehicle 112. The external power source 136 may provide DC 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 coupled to a charger or an onboard power conversion module 132. The power conversion module 132 may regulate the power supplied from the EVSE 138 to provide the 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.

[0025] One or more wheel brakes 144 may be provided for decelerating the vehicle 112 and preventing the movement of the vehicle 112. The wheel brakes 144 may be hydraulically actuated, electrically actuated, or some combination thereof. The wheel brakes 144 may be part of a braking system 150. The braking system 150 may include other components that operate the wheel brakes 144. For simplicity, the accompanying drawings depict a single connection between the braking system 150 and one of the wheel brakes 144. Connections between the braking system 150 and other wheel brakes 144 are shown. The braking system 150 may include a controller for monitoring and coordinating the braking system 150. The braking system 150 may monitor the braking components and control the wheel brakes 144 for vehicle deceleration. The braking system 150 may respond to driver commands and may also operate autonomously to implement features such as stability control. The controller of the braking system 150 may implement a method of applying the requested braking force when requested by another controller or sub-function.

[0026] 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 channel of the vehicle network may include Ethernet as defined by the Institute of Electrical and Electronics Engineers (IEEE) 802 series of standards. Additional 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 via different channels of the vehicle network. For example, a video signal may be transmitted via a high-speed channel (e.g., Ethernet) while control signals may be transmitted via CAN or discrete signals. The vehicle network may include any hardware and software components that facilitate the transmission of signals and data between modules. The vehicle network is not described in detail in the accompanying drawings. Figure 2 1, but may imply that the vehicle network may be connected to any electronic modules present in the vehicle 112. A vehicle system controller (VSC) 148 may be present to coordinate the operation of the various components.

[0027] Typically, the VVC 152 is configured as a boost converter. The VVC 152 may include an input terminal that may be coupled to a terminal of the traction battery 124 via a contactor 142. The VVC 152 may include an output terminal coupled to a terminal of the power electronics module 126. The VVC 152 may be operated so that a voltage at the output terminal is greater than a voltage at the input terminal. The vehicle 112 may include a VVC controller that monitors and controls electrical parameters (e.g., voltage and current) at various locations within the VVC 152. In some configurations, the VVC controller may be included as part of the VVC 152. The VVC controller may determine a reference output voltage The VVC controller can be based on electrical parameters and reference voltage To determine a control signal sufficient to cause the VVC 152 to reach the desired output voltage. In some configurations, the control signal may be implemented as a pulse width modulation (PWM) signal, where the duty cycle of the PWM signal is varied. The control signal may operate at a predetermined switching frequency. The VVC controller may use the control signal to command the VVC 152 to provide the desired output voltage. The specific control signal that operates the VVC 152 may be directly related to the amount of boost provided by the VVC 152.

[0028] refer to Figure 2 , the VVC 152 can increase or "boost" 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 coupled in series between the traction battery 124 and the VVC 152. When the contactor 142 is closed, the HVDC power can be transferred from the traction battery 124 to the VVC 152. The input capacitor can be electrically coupled to the traction battery 124 in parallel. The input capacitor can reduce any voltage and current ripple. The VVC 152 can receive the HV DC power and increase or "boost" the voltage potential of the input voltage according to the duty cycle. Typically, the output capacitor is electrically coupled between the output terminal of the VVC 152 and the input of the power electronics module 126 to stabilize the bus voltage and reduce the voltage and current ripple at the output of the VVC 152.

[0029] Figure 3 is a schematic diagram of an electrified powertrain 300 with an integrated charger. An alternating current (AC) source 302 is rectified by a bridge rectifier 304 to convert the AC power into rectified (AC) power. The rectified AC power then flows through the windings of a "Y-wound" motor 306 via the neutral point terminal of the motor. A three-phase interleaved power factor correction (PFC) converter is created using the stator windings and inverter switches of the machine. The windings of the motor 306 act as coupling inductors, and the inverter switches are controlled to adjust the gate current to achieve unity power factor on the input AC side. The direct current (DC) link capacitor between the inverter 308 and the DC-DC converter acts as an energy storage capacitor for supplying power to the battery during the zero crossing of the input ac voltage. Afterwards, the power passes through a DC / DC converter 310 (e.g., a buck / boost converter), and then is filtered via a storage capacitor 314 and stored in a battery 312. In this system, neither the positive and negative terminals nor the bus are isolated, so that the high voltage bus has a conductive path to the phase and neutral point connections of the AC grid.

[0030] Ground faults caused by insulation loss between energized conductors and the vehicle chassis are a concern for people who use the vehicles. Plug-in electric vehicles (PEVs) are designed to operate worldwide. Regulations for grounding systems vary greatly from country to country. It is critical that vehicles are designed to operate reliably and safely in environments with different grounding systems. The International Electrotechnical Commission (IEC) covers a wide range of technologies, including electrical installations of buildings, as published in IEC 60364. The IEC 60364 standard defines the installation and implementation of three grounding systems: TT, TN, and IT. The present disclosure provides solutions for reducing the effects of ground faults as they relate to vehicle implementations.

[0031] The connection to the facility grid is primarily used to power the connected loads. In the case of an electric vehicle, the facility AC source 302 is connected to the power processing conversion system 300 to charge the battery 312. Although the battery 312 is a load in this context, it can also be a source of energy when charging when a ground fault condition is encountered.

[0032] Single-phase voltage is supplied at different voltage levels and is achieved by various means. The utility grid provides power in the form of single phase by providing two wires that carry the alternating current to the consumer load. Despite the differences in the grounding system, single phase is provided by two means called single-phase power and dual / split-phase power. The difference between these two methods lies in the type of connection to the distribution transformer. In the case of a single-phase system, one of the two power lines is used to supply the load with a single-phase line, while the other wire is connected to the neutral point. In the case of dual / split-phase power, both power lines supplied by the facility are phase lines, and the neutral line is not used to carry the load current. Single-phase systems are generally used due to their flexibility. It allows low-power loads to be supplied by a single-phase power system, while high-power loads are supplied by dual / split-phase power systems. In the United States, 120 volts provided by a single-phase power system are used to power low-power loads such as TVs, lights, refrigerators, etc. High power loads such as water heaters, AC compressors, etc. are powered by 240 volt power circuits supplied by dual / split phase electricity; dual / split phase is formed by taking two 120V phases shifted 180 degrees from each other and providing 240V to the consumer.

[0033] Regarding loads, plug-in electric vehicles (PEVs) are new products on the market and can be easily integrated into existing AC utility grids. Original vehicle manufacturers (OEMs) design their vehicles to operate at universal input AC voltages. In order to utilize existing low-voltage public distribution systems, vehicles should be able to charge in both single-phase and dual / split-phase configurations. The J1772 standard includes recommended practices for AC Level 1 and AC Level 2 charging levels as well as conductive charging couplers and electrical interfaces. J1772 and other similar standards treat AC input voltage levels and their connection to the vehicle as a voltage source. However, they take neither the type of grid nor its coupling configuration with the substation transformer into account.

[0034] In the vehicle, the modules enclosing the energized parts of the voltage class B circuits are housed in conductive housings. It is through international standards and good judgment that these housings are conductively connected to the vehicle chassis. ISO 6469 Part 3 requires that the resistance between two exposed conductive parts of a voltage class B circuit that may be touched by a person is less than 0.1Ω. Therefore, during the fault condition, protection against exposure to significantly different potentials is always maintained by equipotential bonding, resulting in a potential equalization system. In addition, the conductors forming the potential equalization should be able to withstand the maximum current in the case of a single fault.

[0035] To quantify the impact of a ground fault, an analysis can be performed using a model of an ideal non-isolated charger. The charger model represents operation at unity input power factor. This model applies the assumption that the charger remains stable under fault conditions (e.g., the charger ideally performs power conversion between the terminals to which it is connected). A generalized model is created with two dependent current sources. The input current source simulates the ac input current of the charger when operating at unity power factor. The output current source simulates the output current of the charger when charging the battery at a defined open circuit voltage.

[0036] Figure 4 is a schematic diagram of an electrified powertrain 400 having an integrated charger coupled to a TT grounding system, showing a ground fault. An alternating current (AC) source 402 is rectified by a bridge rectifier 404 to convert the AC power to direct current (DC) power. The bridge rectifier 404 has four diodes D1, D2, D3 and D4. The DC current then passes through a generalized non-isolated charger 406 having an input element 406A and an output element 406B. Here, element 406 represents the windings of the motor 306, inverter 308 and DC / DC converter 310. The output element 406B is coupled to a battery model 408. Shown in this schematic 400 is a positive bus fault resistance (R 故障+ )410 and the negative bus fault resistance (R 故障- )412. The vehicle chassis has a chassis grounding resistance (RG )414 and neutral point grounding resistance (R N )416.

[0037] Figure 4 The model shown does not take into account losses in the charger. Therefore, it is assumed that the output power from element 406B is equal to the input power of element 406A averaged over one AC line cycle. The simulated resistance across element 406A is the input AC resistance seen by the AC grid, which can be represented by equation (1).

[0038]

[0039] Based on the assumption that the charger operates at a unity input power factor, the input current of the charger can be expressed by equation (2).

[0040]

[0041] And the charger output current from element 406B is the DC current delivered to the load (battery 408) and can be expressed by equation (3).

[0042]

[0043] A generalized model for a non-isolated charger can be created by yoke element 406A and element 406B. A first order battery model 408 is created by a voltage source representing the open circuit voltage of the battery for a particular charger state operation. In addition, the internal resistance of the battery is represented by R 电池 This is a series resistor in the battery current path. The voltage across element 406B is the voltage developed at the slave current source due to the current flowing to the battery. 电池 The voltage generated on the battery directly corresponds to the amount of power delivered to the battery. Figure 4 A non-isolated charger is shown connected to an AC grid 402 via a full-bridge diode rectifier 404 , with the output of the non-isolated charger connected to a battery 408 .

[0044] The voltage (i.e., Vac) at the AC source 402 terminals, called "phase" and "neutral", is the facility AC voltage. This voltage is assumed to be sinusoidal. It is also assumed in this model that the input current is sensed by measuring the current flowing through the terminals, called "phase". The charger is controlled so that the input current is in phase with the input voltage controlled by the modulated charger switch. The nature (characteristics and waveform) of the ground fault current depends on the control strategy and sensor placement. In one embodiment, a voltage sensor is placed at the output of the full-bridge rectifier and is used to measure the differential voltage of the rectifier output voltage. In another embodiment, a voltage sensor is placed at the input of the charger and is used to measure the AC source voltage. In addition to using a voltage sensor to measure voltage, the concept can also use a current sensor to measure current. Detection of faults can be achieved via current or voltage. For example, in one embodiment, a current sensor is placed at the input of the full-bridge rectifier. If the current sensor is placed at the node connecting diodes D1 and D2, a fault between the positive bus terminal and ground can be detected using the proposed method. Similarly, if a current sensor is placed between the nodes connecting diodes D3 and D4, a fault between the negative bus terminal and ground can be detected. In addition, the controller of the power factor converter can be designed to control the sensed phase current to follow a sinusoidal reference voltage whose magnitude is adjusted according to the AC voltage source magnitude and the simulated resistance Re. And, the reference current can be controlled to be in phase with the measured AC source voltage.

[0045] To illustrate the assumption, the well-known power factor correction (PFC) boost rectifier circuit 404 is considered as an example. The output of the boost rectifier 404 is connected to a large energy storage capacitor. This energy storage capacitor balances the power difference between the charger input port and the output port. This allows the charger to output constant power when its input is AC. Since this capacitor does not consume any real power, the average input AC power is equal to the output power during steady-state operation. Therefore, the input port and output port of the charger can be decoupled because the input port is mainly controlled to regulate the input current to be in phase with the input voltage, and its amplitude depends on the resistor Re determined by the root mean square AC input voltage and the output power given in equation (1).

[0046] The choice of grounding system has a significant impact on the safety and electromagnetic compatibility of the power supply source. The magnitude and flow of fault current in the system are unique to the type of grounding system. Current through the ground does not occur under all fault conditions. A fault that excites an exposed conductive part creates a potential difference between this exposed conductive part and the ground, causing a potential shock hazard in the event of touching this exposed conductive part. According to the IEC 60364 standard, circuits connected to the facility grid require protective equipotential bonding and automatic disconnection in the event of a fault. Each circuit should have a protective conductor. The connection method of this protective conductor is different in each grounding system. In this section, a detailed model of each grounding system should illustrate the connection of the protective conductor associated with the vehicle. In addition, the quantification of the ground fault current in each grounding system is provided.

[0047] Figure 4 Figure 1 shows the TT grounding system, which is usually used when the electrical installation cannot provide a safe and reliable grounding device for its users. Countries that use the TT system may include Algeria, the United Arab Emirates, Belgium, Denmark, Egypt, France, Greece, Italy, Japan, Kenya, Luxembourg, Morocco, Tunisia, Spain, Portugal and Turkey. In the TT system, the power supply system is connected to the ground through a resistor R N The pole of 416 is firmly grounded. The neutral line is used to provide power to single-phase loads. The consumer ground is independent of the facility grounding system and is connected to the ground electrode and resistor R G 414 Making a local connection.

[0048] According to the SAE J1772 standard, the vehicle chassis is directly connected to earth. In a TT grounding system, there is no protective conductor connecting the vehicle chassis directly to the facility neutral. Therefore, the magnitude of the fault current may be affected by the soil, the rod (R) connecting the vehicle chassis to earth, and the ground. G )414. Connect the supply neutral point to the grounded pole (R N )416 impedance limit. Soil impedance and rod resistance R N and R G Lumped.

[0049] A resistor R is connected between the positive battery terminal (BT+) and the vehicle chassis. 故障 +410 causes a fault, the resistance R between BT+ and the vehicle chassis 故障+ 410 is reduced. It is assumed that before the fault occurs, the non-isolated charger is connected to the electrical utility via a full-bridge rectifier. In addition, the non-isolated charger charges the vehicle battery pack at a constant current. The output voltage of the charger is maintained by the output voltage of the battery pack. Due to the low resistance between BT+ and the vehicle chassis, the fault current should flow through the ground. Figure 4 It is also shown that the resistor R 故障-412 A fault is induced between the negative battery terminal (BT-) and the vehicle chassis. Returning to the positive fault current, Figure 6 The flow with respect to time is shown between the positive battery terminal (BT+) and the vehicle chassis through the resistor R 故障+ 410 fault current.

[0050] Figure 5 500 is a schematic diagram of an electrified powertrain system 500 having an integrated charger coupled to a TN ground system, showing a ground fault. An alternating current (AC) source 502 is rectified by a bridge rectifier 504 to convert the AC power to direct current (DC) power. The bridge rectifier 504 has four diodes D1, D2, D3, and D4. The DC current then passes through a generalized non-isolated charger 506 having an input element 506A and an output element 506B. The output element 506B is coupled to a battery model 508. Shown in this schematic 500 is a positive bus fault resistance (R 故障+ )510 and the negative bus fault resistance (R 故障- ) 512. Since this is a TN grounding system, the vehicle chassis is directly coupled to the neutral line of the AC source 502. The vehicle chassis has a chassis grounding resistance (R G )514 and neutral point grounding resistance (R N )516.

[0051] Industrial facilities operating front-end substations may also adopt TN grounding systems, even if the external grounding system is TT. In this example, the local facility provides medium to high voltage to the facility. The substation may have a transformer to step down the supplied voltage to a low voltage level suitable for consumers. Typically, the primary side is wound in delta and the secondary side is wound in a wye shape. The neutral point of the secondary side (wye-connected winding) is firmly grounded. All exposed conductive parts are connected to this neutral point via a protective conductor. The protective conductor is designed to withstand fault currents. In addition, the neutral point connection is used to supply power to single-phase loads.

[0052] There are various methods for implementing a TN grounding system, such as TN-S, where the neutral point is used to supply current to a single-phase load, TN-C, where the neutral and protective conductors are combined in a single cable, and TN-CS, where the neutral and protective conductors are combined in a single cable only in parts of the system but are separated in different parts. In addition, a separate protective conductor is used to handle fault currents. Unlike a TT system, the fault current flows through the protective conductor and does not flow through the ground.

[0053] Protection multi-system (e.g. TN-CS) is a grounding system used to describe ground faults in vehicles connected to any type of TN network (e.g. TN-C, TN-S, TN-CS). The contact point between the vehicle and the supply system is through the electric vehicle supply equipment (EVSE) defined in SAEJ1772.

[0054] Countries that use the TN-CS system include the United States, Australia, the United Kingdom, Canada, China, Germany, South Africa, Sweden and Switzerland. Single-phase voltage is supplied at different voltage levels (120V / 240V) and is achieved through various means: single-phase electricity and two-phase / split-phase electricity. The neutral line of the power supply system is connected through a resistor R N The neutral wire is used to supply power to single-phase loads. The consumer ground is independent of the facility grounding system and is connected to the ground electrode and resistor R G Make a local connection.

[0055] For single-phase electrical implementations, the TN system has similar performance to the TT network, except that the fault current is higher, so this application will focus on the TT system, but the disclosed concepts are applicable to both TT and TN systems. Since the fault current in the TN system is no longer limited by the earth's soil resistance, the same operating conditions of BT+ to chassis and BT- to chassis faults applied in the TT grounding system are applicable to the TN system. Then, by replacing R N and R G With θ set to zero, the analytical equations derived previously for the TT network are equivalent to those for the TN network. Since the PE conductor has a high conductivity relative to the earth soil, it is expected that most of the ground fault current will not flow through the ground.

[0056] Figure 6 FIG. 6 is a graphical illustration of the electrical characteristics 600 of the battery positive terminal and chassis fault in a TT system versus time 610. The electrical utility supply voltage (Vac) 602, the input voltage (Vin) 604 of the non-isolated charger, and the current flowing through R G The current (I G )606 and the vehicle chassis voltage (V 底盘 ) 608 is shown relative to time 610. It can be appreciated that the fault current in a positive ac line cycle is different than the fault current in a negative ac line cycle.

[0057] In order to gain a deeper understanding of the characteristics of the fault current, Figure 6 The waveform shown is divided into six intervals. For positive ac line cycles and negative ac line cycles, each inverter can be based on Figure 4 The equivalent circuit is described.

[0058] The time of the first interval (state 1) is greater than or equal to (t0) 612 and less than (t1) 614. The ground fault current is equal to the input current of the charger because D1 of the rectifier 404 is the only diode that is conducting and the charger actively controls its current to simulate the resistor Re. Here, R e is the simulated resistance of the converter input stage and is used to compensate for phase shift to maintain unity power factor correction. The ground current can be obtained from Figure 6 (a) is derived and given by Eq. 4.

[0059]

[0060] State 1 ends when D4 turns on. The voltage on D4 can be expressed by Equation 5

[0061]

[0062] The time of the second interval (state 2) is greater than or equal to (t1) 614 and less than (t2) 616. Diode D4 of rectifier 404 begins to conduct at time t1 614. The input voltage of the charger is determined by the supplied electrical utility voltage. The current flowing through D1 of rectifier 404 is sinusoidal and controlled by the charger so that a unity input power factor is maintained. Therefore, the ground fault current can be expressed by Equation 6.

[0063]

[0064] It can be seen that during this second interval, the ground fault current does not depend on the supplied ac voltage, but only on the battery voltage and the fault impedance. The current flowing through the phase line returns to the supply source via two paths: the soil and the neutral line of the supply. Therefore, the current flowing through D1 of the rectifier 404 is expected to be higher than the current flowing through D4 of the rectifier 404. The current flowing through D4 is negatively biased by the ground current and can be expressed by Equation 7.

[0065] I D4 =I 相 -I G (7)

[0066] The time of the third interval (state 3) is greater than or equal to (t2) 616 and less than (t3) 618. When the current flowing through D4 of the rectifier 404 is negatively biased by the ground current, D4 is reverse biased before D1 of the rectifier 404. This causes the circuit to become similar to state 1 until the electrical utility voltage turns negative. The input voltage of the non-isolated charger can be represented by equation 8.

[0067]

[0068] The time of the fourth interval (state 4) is greater than or equal to (t3) 618 and less than (t4) 620. State 4 begins once the utility voltage becomes negative. First, D3 of rectifier 404 is turned on shortly thereafter, and at time t4 620, D2 of rectifier 404 is turned on. The current flowing through D3 is equal to the ground fault current, which is also the input current of the charger. The ground fault current and the input voltage can be represented by equations 9 and 10, respectively. State 4 ends once D2 of rectifier 404 begins to conduct at time t4 620. The voltage on D2 can be represented by equation 11, and time t4 602 can be determined by equation 12.

[0069]

[0070] I G =I 输入 (t) (10)

[0071]

[0072]

[0073] The point in time when the AC source crosses zero (e.g., the point at which the potential of the AC source changes from positive to negative) is time (t3) 618. Here, it is desirable to measure a characteristic such as Vin 604 of the rectifier or the diode voltage at this point in time (t3) 618. However, the measurement may be made during a time window around the zero crossing (t3) 618, for example, the measurement may be started at a time greater than (t2) 616 and less than (t4) 620. Another aspect is the magnitude of the measurement, such as Figure 6 At time (t3) 618, Vin 604 peak value is greater than V represented by Equation 5. D4 628, but less than Vbattery 630. In one embodiment, the lower voltage threshold is V D4 628. In another embodiment, the lower threshold of the voltage magnitude may be V 电池 630% of, for example, V 电池 1 / 2, 1%, 2%, 3% or 5% of 630.

[0074] The fifth interval (state 5) is greater than or equal to (t4) 620 and less than (t5) 622. Once the voltage across D2 of rectifier 404 becomes zero, it begins to conduct. The input voltage of the charger is then determined by the utility grid voltage. The battery voltage reduces the ground current, and the ground fault current in this interval can be expressed by Equation 13.

[0075]

[0076] The sixth interval (state 6) is greater than or equal to (t5) 622 and less than (t6) 624. When the current flowing through D2 of rectifier 404 is negatively biased by the ground current, D2 will be reverse biased before D3. The reverse bias causes the circuit to operate similar to state 4 until the utility voltage becomes positive.

[0077] Figure 7 FIG. 7 is a graphical illustration of the electrical characteristics 700 of the battery positive terminal and chassis fault in a TT system versus time 710. The electrical utility supply voltage (Vac) 702, the input voltage (Vin) 704 of the non-isolated charger, and the current flowing through R G The current (I G )706 and the vehicle chassis voltage (V 底盘 ) 708 is shown relative to time 710. It can be appreciated that the fault current in the positive ac line cycle is different from the fault current in the negative ac line cycle. Here, the peaks are shown to be at least at 4.1 seconds and 4.125 seconds.

[0078] Consider the case where a 240V supply AC voltage is provided, where the output power is 3.3kW, and the battery voltage is 300V, where R N and R G Approximately 10Ω and 50Ω respectively. A fault between BT+ and the vehicle chassis is formed by introducing a 50Ω resistor between them. Figure 7 A waveform depicting the results is shown. Note that during the zero crossing of the AC line voltage, the input voltage of the charger increases to approximately equal the battery voltage. This is because, during this point in time, only one diode is conducting. It is concluded that this fault condition can cause the vehicle chassis voltage to reach a high potential, where measurements at this point can indicate a ground fault.

[0079] Figure 8 804, the input voltage (Vin) of the non-isolated charger, and the electrical characteristics of the negative terminal of the battery and the chassis fault in the TT system relative to time. G The current (I G )806 and the vehicle chassis voltage (V 底盘 )808 is shown relative to time 810.

[0080] Figure 8 Shows a fault between the negative battery terminal (BT-) and the vehicle chassis. The resistance between BT- and the vehicle chassis is R 故障- Before the fault occurred, the non-isolated charger had been coupled to the electrical utility via a full-bridge rectifier supplying a pure sinusoidal AC voltage. The non-isolated charger was charging the vehicle battery pack at a constant current. The output voltage of the charger was maintained by the output voltage of the battery pack. Figure 8Shown is the ground fault current due to the low resistance between BT- and the vehicle chassis.

[0081] Fig. 9 is a schematic diagram of an electrified powertrain 900 having an integrated charger coupled to a split-phase TN ground system, showing a ground fault. An alternating current (AC) source 902 including a first AC source 902A and a second AC source 902B coupled in series and having a center neutral point tap is rectified by a bridge rectifier 904 to convert the AC power into direct current (DC) power. The bridge rectifier 904 has four diodes D1, D2, D3 and D4. The DC current then passes through a generalized non-isolated charger 906 having an input element 906A and an output element 906B. The output element 906B is coupled to a battery model 908. Shown in this schematic 900 is a positive bus fault resistance (R 故障+ )910 and the negative bus fault resistance (R 故障 -) 912. Since this is a TN grounding system, the vehicle chassis is directly coupled to the neutral line of the AC source 902. The vehicle chassis has a chassis grounding resistance (R G )914 and neutral point grounding resistance (R N )916. The ground fault current in the two-phase / split-phase implementation is different from that in the single-phase implementation. However, both can be decomposed into six states to illustrate Fig.10 The operation shown.

[0082] Fig.10 1000 is a graphical illustration of the electrical characteristics of a battery positive terminal and chassis fault in a split-phase TN system 1000 versus time 1010. The electrical utility supply voltage (Vac) 1002, the input voltage (Vin) 1004 of the non-isolated charger, and the current flowing through R G The current (I G )1006 and the vehicle chassis voltage (V 底盘 ) 1008 is shown relative to time 1010. Using Figure 6 The timing is used as a reference.

[0083] The time of the first interval (state 1) is greater than or equal to (t0) and less than (t1). In a positive AC line cycle, the fault current causes D1 and D4 to not conduct at the same time. Once the grid voltage becomes positive, D1 is turned on first. Soon after D4 turns on, its voltage drops to zero. State 1 ends when D4 turns on. The ground fault current is equal to the input current of the charger because D1 is the only diode that is turned on and the charger actively controls its current to simulate the resistor Re.

[0084] The time of the second interval (state 2) is greater than or equal to (t1) and less than (t2). D4 starts to conduct at t1. The input voltage of the charger is determined by the supplied electrical utility voltage. The current flowing through D1 is sinusoidal and controlled by the charger so that a unity input power factor is achieved. Due to the conduction of D4, the ground current is clamped at a constant value. The magnitude of the ground current depends on the battery voltage and the fault loop impedance. The current flowing through the phase line returns to the supply source via two paths: i) the protective conductor; and ii) the supplied phase line. Therefore, the current flowing through D1 is higher than the current flowing through D4. The current flowing through D4 is negatively biased by the ground current.

[0085] The third interval (state 3) is greater than or equal to (t2) and less than (t3). When the current through D4 is negatively biased by the ground current, D4 will be reverse biased before D1, causing the circuit to become the same as state 1 until the electrical utility voltage becomes negative.

[0086] In States 4 through 6, unlike single-phase electrical implementations, States 4 through 6 occurring during a negative line cycle are the same as States 1 through 3 occurring during a positive line cycle.

[0087] In the industry, galvanic isolation is not mandatory. For isolated and non-isolated chargers, if the on-board voltage level B circuit is conductively connected to the grid, the vehicle chassis must be connected to the grid ground. Suppression of CM noise is critical for non-isolated chargers; the standards for designing control pilot circuits and maximum Y-cap values ​​are challenging for non-isolated chargers. The isolation monitoring circuits for non-isolated chargers must be compatible with various existing EVSE isolation monitoring technologies. According to ISO6469.3, fault protection for non-isolated chargers is achieved by potential equalization. Therefore, the development of new ground fault detection systems is necessary for non-isolated chargers.

[0088] In a TT grounding system, there is a clear difference in the ground fault current waveform between the fault occurring at the HV positive terminal to chassis and the HV negative terminal to chassis. The ground current in the case of a HV positive terminal to chassis fault depends on the input supply voltage, the fault loop impedance, the power delivered to the load, and the battery voltage. The ground current in the case of a HV negative terminal to chassis fault depends only on the input supply voltage and the fault loop impedance.

[0089] In TN networks, the prospective earth fault current is greater than that in TT networks. During HV faults, TN networks provide better protection against indirect contact than TT networks. Although the implementation of substation and house grounding affects the vehicle chassis voltage during an HV earth fault in TT networks, they have no effect on the chassis voltage in TN networks. Since the protective conductor has a relatively high conductivity and is connected in parallel with the earth resistance, the prospective vehicle chassis voltage never reaches dangerous voltage levels in TN networks.

[0090] 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 drawings. These drawings provide representative control strategies and / or logic that can be implemented using one or more processing strategies such as event-driven strategies, interrupt-driven strategies, multi-tasking strategies, multi-threading strategies, etc. In this way, the various steps or functions shown may be performed in the order shown, in parallel, or omitted in some cases. Although not always explicitly stated, it should be recognized by those of ordinary skill in the art that one or more of the steps or functions shown may be repeatedly performed according to the specific processing strategy used. Similarly, the processing sequence is not necessarily required to achieve the features and advantages described herein, but is provided for ease of illustration and description. The control logic may be implemented primarily in software executed by a microprocessor-based vehicle, engine and / or powertrain controller (such as a controller). Of course, depending on the specific application, the control logic may be implemented in software, hardware, or a combination of software and hardware in one or more controllers. When implemented in software, the control logic may be provided in one or more computer-readable storage devices or media, which store data representing codes or instructions executed by a computer to control a 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 electrical, magnetic, and / or optical storage devices to retain executable instructions and associated calibration information, operating variables, and the like.

[0091] The processes, methods or algorithms disclosed herein may be delivered to / implemented by a processing device, a controller or a computer, which may include any existing programmable electronic control unit or a dedicated electronic control unit. Similarly, the processes, methods or algorithms may be stored as data and instructions that can be executed by a controller or a computer in many forms, including but not limited to information permanently stored on non-writable storage media such as read-only memory (ROM) devices and information stored in a rewritable manner on writable storage media, such as floppy disks, tapes, compact disks (CDs), random access memory (RAM) devices, and other magnetic and optical media. The processes, methods or algorithms may also be implemented as software executable objects. Alternatively, the processes, methods or algorithms may be embodied in whole or in part using suitable hardware components, such as application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), state machines, controllers or other hardware components or devices, or combinations of hardware components, software components and firmware components.

[0092] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms covered by the claims. The words used in the specification are descriptive rather than limiting, and it should be understood that various changes can be made without departing from the spirit and scope of the present disclosure. As mentioned above, the features of various embodiments can be combined to form other embodiments of the present invention that may not be explicitly described or illustrated. Although various embodiments may have been described as providing advantages or being superior to other embodiments or prior art implementations relative to one or more desired characteristics, it should be recognized by those of ordinary skill in the art that one or more features or characteristics can be compromised to achieve the desired overall system properties, depending on the specific application and implementation. 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. Thus, embodiments described as being inferior to other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the present disclosure, but may be desirable for specific applications.

[0093] According to the present invention, an electrified vehicle charger is provided having: a diode bridge configured to rectify an alternating current (AC) source; a contactor coupling the AC source to a traction battery; and a controller configured to open the contactor in response to a magnitude of a potential at an output of the diode bridge exceeding a threshold, the magnitude corresponding to a zero crossing of the potential of the AC source.

[0094] According to one embodiment, the invention also features a voltage sensor coupled to the output of the diode bridge and configured to output the magnitude.

[0095] According to one embodiment, the zero crossing includes a time window before and after a time point at which the potential of the AC source transitions between positive and negative.

[0096] According to one embodiment, the time window is a percentage of a line cycle of the AC source.

[0097] According to one embodiment, the percentage of the line cycle is determined based on the minimum AC voltage source magnitude, the minimum simulated resistance, and the threshold fault resistance.

[0098] According to one embodiment, the invention also features a current sensor coupled between the AC source and the diode bridge and configured to output a signal indicative of the magnitude.

[0099] According to one embodiment, the threshold value is greater than a defined set point determined by a minimum allowed impedance between the positive high voltage DC bus and ground.

[0100] According to one embodiment, the threshold is greater than zero and less than the instantaneous high voltage DC bus differential voltage.

[0101] According to one embodiment, the AC source is a single-phase AC source or a split-phase AC source configured as a TT-grounded network.

[0102] According to the present invention, a method of operating a vehicle charger includes disabling, by a controller, the charger in response to a voltage across a diode of a rectifier for an alternating current (AC) source exceeding a threshold when a potential of the AC source changes sign.

[0103] According to one embodiment, disabling the charger comprises opening a contactor between a traction battery and the AC source.

[0104] According to one embodiment, the threshold value is greater than a defined set point determined by a minimum allowed impedance between the positive high voltage DC bus and ground.

[0105] According to one embodiment, the anode of the diode is coupled to a phase terminal of the AC source or to a neutral point terminal of the AC source.

[0106] According to one embodiment, the AC source is a single-phase AC source or a split-phase AC source of a TT network.

[0107] According to the present invention, an electrified vehicle charger is provided, having: a diode bridge configured to rectify an alternating current (AC) source and including a first diode having an anode coupled to a phase terminal of the AC source and a second diode having a cathode coupled to a neutral point terminal of the AC source; and a controller configured to disable the charger in response to the first diode conducting and the second diode not conducting at a zero crossing of the AC source.

[0108] According to one embodiment, the conduction of the first diode is defined by a current greater than a threshold value flowing through the first diode, and the non-conduction of the second diode is defined by a current less than a threshold value flowing through the second diode.

[0109] According to one embodiment, a forward voltage applied to the first diode indicates that the first diode is conducting, and a reverse voltage applied to the second diode indicates that the second diode is not conducting.

[0110] According to one embodiment, the AC source is a single-phase AC source or a split-phase AC source.

[0111] According to one embodiment, the AC source is configured as a TT grounded network.

[0112] According to one embodiment, disabling the charger comprises opening a contactor between a traction battery and the AC source.

Claims

1. An electric vehicle charger, comprising: a diode bridge configured to rectify an AC power source; a contactor coupling the AC power source to a traction battery; as well as a controller configured to open the contactor in response to a magnitude of the potential at the output of the diode bridge exceeding a threshold value, the magnitude corresponding to a zero crossing of the potential of the AC power source, the threshold value being greater than a defined set point determined by a minimum allowable impedance between a positive high voltage DC bus and ground. 2 . The electric vehicle charger of claim 1 , further comprising a voltage sensor coupled to the output terminal of the diode bridge and configured to output the magnitude. 3 . The electrified vehicle charger of claim 1 , wherein the zero-crossing point includes time windows before and after a time point at which the potential of the AC power source transitions between positive and negative.

4. The electrified vehicle charger of claim 3, wherein the time window is a percentage of a line cycle of the AC power source.

5. The electrified vehicle charger of claim 4, said percentage of line cycles being determined based on a minimum AC voltage source magnitude, a minimum simulated resistance, and a threshold fault resistance. 6 . The electrified vehicle charger of claim 1 , further comprising a current sensor coupled between the AC power source and the diode bridge and configured to output a signal indicative of the magnitude.

7. The electrified vehicle charger of claim 1, wherein the threshold is greater than zero and less than an instantaneous high voltage DC bus differential voltage. 8 . The electric vehicle charger of claim 1 , wherein the AC power source is a single-phase AC power source or a split-phase AC power source configured as a TT grounding network.

9. A method of operating a vehicle charger, comprising: The charger is disabled by a controller in response to a voltage across a diode of a rectifier for an AC power source exceeding a threshold when a potential of the AC power source changes sign, wherein the threshold is greater than a defined set point determined by a minimum allowable impedance between a positive high voltage DC bus and ground.

10. The method of claim 9, wherein disabling the charger comprises opening a contactor between a traction battery and the AC power source. 11 . The method of claim 9 , wherein an anode of the diode is coupled to a phase terminal of the AC power source or a neutral point terminal of the AC power source.

12. The method of claim 9, wherein the AC power source is a single-phase AC power source or a split-phase AC power source of a TT network.

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