Patent Publication Number: US-2018033224-A1

Title: Alternating current (ac) load pre-charge protection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 62/369,645 filed on Aug. 1, 2016, the disclosure of which is hereby incorporated in its entirety by reference herein. 
    
    
     TECHNICAL FIELD 
     Aspects disclosed herein generally relate to an AC load pre-charge protection circuit and method. These aspects and others will be discussed in more detail herein. 
     BACKGROUND 
     U.S. Publication No. 2016/0152156 to Pritelli et al. discloses an electronic device for controlling the electric charge of a load electrically supplied by a battery pack. The electronic device includes: a support; a control module integrated in the support; an electric pre-charging circuit of the load controlled by the control module; and an electric active discharge circuit of the load controlled by the control module. The electric pre-charging circuit comprises at least one first solid-state switch and is integrated on the support. The electric active discharge circuit includes at least one second solid-state switch and is integrated on the support. The first solid-state switch and the second solid-state switch can be configured to work either as a switch or as a variable resistor. 
     SUMMARY 
     In at least one embodiment, a vehicle apparatus including a power conversion device is provided. The power conversion device is further configured to receive a direct current (DC) output voltage and invert the DC output voltage into an alternating current (AC) based signal to drive one or more AC loads in a vehicle. The power conversion device is further configured to measure the DC output voltage during a pre-charge operation and to provide a diagnostic threshold during the pre-charge operation based on the measured DC output voltage. The power conversion device is further configured to determine a plurality of accumulated values during the pre-charge operation, each accumulated value is indicative of a measured current across a resistive element. The power conversion device is further configured to compare the plurality of accumulated values to the diagnostic threshold during the pre-charge operation. 
     In at least another embodiment, a vehicle apparatus including a power conversion device is provided. The power conversion device is configured to invert a direct current (DC) output voltage into an alternating current (AC) based signal to drive one or more AC loads in a vehicle and to measure the DC output voltage during a pre-charge operation. The power conversion device is further configured to provide a diagnostic threshold during the pre-charge operation based on the measured DC output voltage and to measure a current across a resistive element. The power conversion device is further configured to determine a plurality of accumulated values during the pre-charge operation and each accumulated value is indicative of a measured current across the resistive element. The power conversion device is further configured to compare the plurality of accumulated values to the diagnostic threshold during the pre-charge operation. 
     In at least another embodiment, a method for pre-charge protection is provided. The method includes receiving a direct current (DC) output voltage at a power conversion device and inverting the DC output voltage at the power conversion device into an alternating current (AC) based signal to drive one or more AC loads in a vehicle. The method further includes measuring the DC output voltage during a pre-charge operation and providing a diagnostic threshold during the pre-charge operation based on the measured DC output voltage. The method further includes determining a plurality of accumulated values during the pre-charge operation, each accumulated value being indicative of a measured current across a resistive element and comparing the plurality of accumulated values to the diagnostic threshold during the pre-charge operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the present disclosure are pointed out with particularity in the appended claims. However, other features of the various embodiments will become more apparent and will be best understood by referring to the following detailed description in conjunction with the accompany drawings in which: 
         FIG. 1  depicts a system that provides AC load pre-charge protection in accordance to one embodiment; 
         FIG. 2  depicts various waveforms for current, voltage, a diagnostic threshold, and a plurality of accumulated values in accordance to one embodiment; 
         FIG. 3  depicts a method for monitoring current (or power) based on a measured bulk voltage that is provided to the system in accordance to one embodiment; 
         FIG. 4  depicts a waveform for a measured current and a measured bulk voltage (or measured voltage of the capacitance load) of the inverter in accordance to one embodiment; and 
         FIG. 5  depicts various pulse impulse power characteristics for various resistors. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     The embodiments of the present disclosure generally provide for a plurality of circuits or other electrical devices. All references to the circuits and other electrical devices and the functionality provided by each are not intended to be limited to encompassing only what is illustrated and described herein. While particular labels may be assigned to the various circuits or other electrical devices disclosed, such labels are not intended to limit the scope of operation for the circuits and the other electrical devices. Such circuits and other electrical devices may be combined with each other and/or separated in any manner based on the particular type of electrical implementation that is desired. It is recognized that any circuit or other electrical device disclosed herein may include any number of microcontrollers, graphics processor unit (GPU), integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or other suitable variants thereof) and software which co-act with one another to perform operation(s) disclosed herein. In addition, any one or more of the electrical devices may be configured to execute a computer-program that is embodied in a non-transitory computer readable medium that is programmed to perform any number of the functions as disclosed. 
     It is generally known to provide a pre-charge circuit in a vehicle. Generally, such circuits utilize a high surge power rated resistor to withstand the amount of power that is dissipated across the resistor during the pre-charge operation. Such a resistor generally adds cost and may affect the pre-charge time due to the power dissipation properties of the resistor. Aspects disclosed herein may eliminate the need for utilizing the high surge power rated resistor to mitigate such cost and to avoid adversely affecting the pre-charge time. 
       FIG. 1  depicts a vehicle apparatus  10  that provides AC load pre-charge protection in accordance to one embodiment. The vehicle apparatus  10  generally includes one or more batteries  12  for powering a vehicle  14 . The one or more batteries  12  is generally located in a low voltage zone  13  for powering any number of devices (not shown) within the low voltage zone that operate within the vehicle  14 . A DC/DC converter  18  is operatively coupled to the one or more batteries  12  for receiving a low voltage output therefrom. An inverter  20  (e.g., a power conversion device in a high voltage zone) is operatively coupled to the DC/DC converter  18  to receive a boosted voltage therefrom. 
     The inverter  20  generates an AC output for powering various AC loads  22  such as motors, consumer electronic devices, etc. The inverter  20  includes a pre-charge circuit  21  to limit inrush current and to thereby prevent any number of capacitors (not shown) from being damaged by the inrush current. A pre-charge operation is generally performed when initially connecting a voltage source to a load with a capacitive load. 
     The pre-charge circuit  21  generally includes a pre-charge resistor  24  (e.g., a resistive element), a switching device  26  (e.g., MOSFET), a resistor  28  (or current sensing resistor  28 ), a gain circuit  30 , and a microprocessor  32 . A pre-charge voltage (e.g., V  pre   _   charge ) is provided to the pre-charge resistor  24  and to the switching device  26  during the pre-charge operation. The current sensing resistor  28  generates current which is indicative of the current flowing through the pre-charge resistor  24  when the voltage is applied to the pre-charge resistor  24  during the pre-charge operation. The gain circuit  30  amplifies the current across the pre-charge resistor  24 . The microprocessor  32  receives the current from the gain circuit  30  to determine the current that flows across the pre-charge resistor  24 . In one example, the pre-charge resistor  24  may be  51  ohms. It is recognized that the pre-charge resistor  24  may be any other suitable value. 
     The pre-charge circuit  21  includes an input  23  for receiving a voltage indicative of a bulk voltage from the DC/DC converter  18  during the pre-charge operation. In general, the inverter  20  generates the AC output in response to the bulk voltage (or DC output voltage) from the DC/DC converter  18 . The bulk voltage range for a 120 V system may be 100 to 182 V and the bulk voltage range for a 240 V system may be 200 to 364 V. A voltage divider network  36  steps down the bulk voltage into a voltage that is suitable by the microprocessor  32  to determine (or measure) the bulk voltage output from the DC/DC converter  18 . The voltage divider network  36  scales the bulk voltage down from over 100 V into a voltage somewhere within a range of, for example, 0 to 5 volts. Once in this range, an analog to digital converter (ADC) (not shown) within the microprocessor  32  converts the analog version of the scaled down voltage to digital counts. The microprocessor  32  then executes software to obtain values corresponding to the bulk voltage. 
     In general, the pre-charge circuit  21  is configured to store values (e.g. via memory either external or internal to the microprocessor  32 ) corresponding to the measured bulk voltage output by the DC/DC converter  18  and to store a corresponding diagnostic threshold based on measured bulk voltage. The pre-charge circuit  21  compares either the measured current across the current sensing resistor  28  to the diagnostic threshold or compares a calculated power (based on the measured current and the resistance of the current sensing resistor  28 ) to the diagnostic threshold. If the measured current exceeds or calculated power exceeds the diagnostic threshold, then the pre-charge circuit  21  may deactivate the pre-charge operation. 
     For example, the microprocessor  32  may measure a plurality of accumulated values (i.e., current or power) within a time interval (e.g., or between a first time set point T 0  and a second time set point T 1 ) and compares the latest accumulated measured value after a predetermined number of counts has been reached to the diagnostic threshold. The microprocessor  32  includes a timer (not shown) that is initiated once the pre-charge operation has started. The timer generates a reoccurring count that increases over time within the time interval. If the latest accumulated measured value has exceeded the diagnostic threshold, then the pre-charge circuit  21  may deactivate the pre-charge operation. If the latest accumulated measured value has not exceeded the diagnostic threshold, then the microprocessor  32  allows the pre-charge operation to continue. 
       FIG. 2  depicts a waveform for current, voltage, the diagnostic threshold, and accumulated values in accordance to one embodiment. Waveform  50  generally corresponds to the amount of current flowing through the pre-charge resistor  24  during the pre-charge operation. The first time set point T 0  corresponds to a start point of the pre-charge operation and the second time set point T 1  corresponds to an end-point of the pre-charge operation. The first time set point T 0 , the second time set point T 1  and corresponding time set points between the first time set point T 0  and the second time set point T 1  form a pre-charge time interval. Waveform  52  generally corresponds to the measured bulk voltage within the inverter  20 . Waveform  54  generally corresponds to a diagnostic threshold that may vary based on the bulk voltage output by the DC/DC converter  18 . A corresponding power threshold value or current threshold value is stored as the diagnostic threshold based on the measured bulk voltage. It is recognized that there can be any number of diagnostic thresholds utilized by the microprocessor  32  where each of the diagnostic thresholds correspond to a particular measured bulk voltage. 
     Waveform  56  illustrates a plurality of accumulated power measurements in which the measurements are detected to exceed the diagnostic threshold  54  before the second time set point T 0  has been reached. Waveform  58  illustrates a plurality of accumulated values (or accumulated power values) that do not exceed the diagnostic threshold  54 . As can be seen, waveform  58  crosses the diagnostic threshold  54  after the pre-charge operation has occurred. 
     The microprocessor  32  may accumulate the power (or current measurements) (or accumulated values) for each count at, for example, 133 μs or other suitable value. In this example, if after 14 samples (or other suitable time sample value), the accumulated value exceeds the diagnostic threshold (e.g., see waveform  56 ) at some time between the first time set point T 0  and the second time set point T 1  (or within the pre-charge time interval), then the microprocessor  32  terminates the pre-charge operation to preserve the overall integrity of the pre-charge resistor  24 . If on the other hand after  14  samples (or other suitable sample value), the accumulated value does not exceed the diagnostic threshold (e.g., see waveform  58 ) at some time between the first time set point T 0  and the second time set point T 1  (or within the pre-charge time interval), then the microprocessor  32  allows the pre-charge operation to continue. Thus, it can be seen that by accumulating the measurements at small sample sizes, the pre-charge circuit  21  may characterize the amount of current flowing through the pre-charge resistor  24  at a faster rate and quickly disable the pre-charge operation sooner in order to preserve the integrity of the pre-charge resistor  24 . Further, this condition negates the use of high surge power resistors that may be used as a pre-charge resistor and reduces the overall cost for the pre-charge resistor. 
       FIG. 3  generally depicts an example method  60  that may be performed by the microprocessor  32  (or other suitable variant) for determining whether the measured current or calculated power measurement exceeds the diagnostic threshold. 
     In operation  62 , the microprocessor  32  determines the bulk voltage output by the DC/DC converter  18  during the pre-charge operation and selects the corresponding diagnostic threshold from a plurality of diagnostic thresholds based on the diagnostic threshold. The microprocessor  32  is configured to store any number of diagnostic thresholds for the measured current or power based on the bulk voltage at the inverter  20 . The microprocessor  32  initiates and controls the pre-charge operation. For example, the microprocessor  32  controls the initiation and termination of the pre-charge operation. 
     In operation  64 , the microprocessor  32  initiates the timer at the start of the pre-charge operation to generate a count and increase the count within the pre-charge time interval. 
     In operation  66 , the microprocessor  32  measures the current or determines the power across the pre-charge resistor  24  at the pre-charge time interval at a predetermined sampling rate. The microprocessor  32  is configured to measure a plurality of accumulated measurement values (i.e., current or power) across the pre-charge resistor  24 . For example, the microprocessor  32  measures the accumulated measurement values across the current sensing resistor  28  which provide a representation of the current or power at the pre-charge resistor  24 . 
     In operation  68 , the microprocessor  32  determines whether the number of counts exceed a predetermined number of counts. If the microprocessor  32  determines that the number of counts has exceed the predetermined number of counts, the method  60  proceeds to operation  70 . If not, then the method  60  proceeds back to operation  66 . 
     In operation  70 , the microprocessor  32  compares the latest accumulated measured value against the diagnostic threshold. If the microprocessor  32  determines that the latest accumulated measured value has not exceeded the diagnostic threshold, then the method  60  proceeds to operation  72 . If the microprocessor  32  determines that the latest accumulated measured value has exceed the diagnostic threshold, then the method  60  proceeds to operation  74 . 
     In operation  72 , the microprocessor  32  allows the pre-charge operation to continue. 
     In operation  74 , the microprocessor  32  disables the pre-charge operation. 
     It is recognized that the embodiments disclosed herein may (i) be implemented in, for example, a 400 W inverter, (ii) account for a capacitive load experience with an exponential delay in charge current after the switching device is turned on, (iii) provide current that is sensed through a current sense circuit or amplifier circuit, (iv) provide sampling at 133 μs or other suitable value and at an initial current maximum of 170/510 Ohm resistor that yields 3.13 A (for example) and that the current should decay to less than 2.5 A (for example) in 2 ms; (iv) provide measurements that are accumulated as power V.bulk*I; (v) terminate the pre-charge operation and enable an inverter bridge once accumulated power (or current) exceeds predetermined thresholds, and (vi) provide similar maximum power diagnostics that can be used for normal bridge operation for a quick acting shut down. 
       FIG. 4  depicts a waveform for the measured current and the measured bulk voltage (or measured voltage of the capacitance load) of the inverter  20  in accordance to one embodiment.  FIG. 5  depicts various pulse impulse power characteristics for various resistors. In general, during a soft start operation with a capacitive load, the pre-charge resistor  24  may dissipate a peak of 554 W with a total pulse power of 104 W over an 8 ms period. The time can be extended for larger capacitive loads to allow for greater load flexibility. The pre-charge operation can be extended for larger capacitive loads to allow for greater load flexibility. The pre-charge operation may be terminated based on output energy consumption rather than fixed by time. During shorted output conditions, the same resistor would dissipate 558 W during the same period. A lower cost pre-charge resistor 24 (e.g., MOS3) is rated for approximately 250 W for 8 ms. If the pulse is terminated at 2 ms, the MOS3 pre-charge resistor  24  may take 560 W (see  FIG. 5 ). An output of the inverter bridge may continue with operation, since no exponential decay could also be a result of high current load. Use of the MOS3 pre-charge resistor  24  may provide a cost savings over other higher rated resistors. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.