Patent Publication Number: US-2021194242-A1

Title: Hazardous voltage pre-charging and discharging system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This PCT International Patent application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 62/725,399 filed on Aug. 31, 2018, titled “High Voltage Pre-Charging And Discharging System And Method,” the entire disclosure of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to hazardous voltage direct current systems in electric vehicles. More particularly, the present disclosure relates to a unit that pre-charges the system and also discharges the voltage in the system. 
     BACKGROUND OF THE DISCLOSURE 
     Electric passenger vehicles, such as purely electric or hybrid electric vehicles are in common use in the passenger vehicle industry as well as the commercial vehicle industry (such as trucks and buses). Electric vehicles rely on hazardous voltage direct current (HVDC) in their use. Hazardous-voltage systems with a large capacitive load can be exposed to high electric current during initial turn-on. Unlike some HVDC applications, which may be turned on in rare occasions such as initial power up of utility power distribution, HVDC systems for electric vehicles require a power up frequently. In most electric vehicle systems, the HVDC system is powered up multiple times per day. 
     Thus, it is desirable to pre-charge the powerline voltages of a HVDC system during an initial power on to limit the inrush current during the power up procedure. Without pre-charging, the peak inrush current at power-up can stress the electric components of the system, thereby reducing its reliability and life-span. Pre-charging the system can increase the lifespan and reliability of the components in a high-voltage system. 
     In electric vehicles, pre-charging resistors in the system is necessary in order to avoid charging the capacitors in the system with the peak inrush current, and to avoid damaging the wiring, relays, battery, or fuses. However, electric vehicle standards also require that the HVDC circuit be free of voltage within a short time after it has been switched off. 
     Prior electric vehicle systems utilize two separate functional elements to achieve the requirements of pre-charging the system at power up and discharging the voltage in the system after shutdown. Each functional element forms one relay and one resistor. 
     In view of the foregoing, there remains a need for improvements to pre-charging and discharge units. 
     SUMMARY OF THE INVENTION 
     A circuit for pre-charging and discharging a hazardous voltage direct current system includes a pair of first electric contacts connected to a pair of second electric contacts via first and second lines; a first relay in the form of main contactors disposed on the first and second lines having an open state that breaks a connection between the first and second contacts and a closed state that makes the connection between the first and second contacts, and a partially open state that makes a connection along the first line and breaks a connection along the second line; a first bypass line extending from the first line at a point disposed between the main contactors and the second electric contacts, a second bypass line extending from the second line at a point disposed between the main contactors and the first electric contacts, and a third bypass line having a resistor and extending from the second line at a point disposed between the main contactors and the second electric contacts; a second relay having a first state that connects the first and third bypass line and a second state that connects the second and third bypass lines; wherein the system includes an initial state in which the main contactors are in the open state and the second relay is in the first state, wherein the system includes a startup state with the second relay in the second state and the main contactors are in the partially open state, wherein the system includes an operating state where the main contactors are in the closed state, and wherein the system includes a shutdown state with the main contactors in the open state and the second relay in the first state. 
     In one aspect, the main contactors are configured to make and break the connection along the first and second lines at each line independent of the other line. In another aspect, the main contactors are two separate relays. 
     In one aspect, the first electric contacts are attached to a battery. In one aspect, the second electric contacts are attached to electric vehicle components. 
     In one aspect, the resistor operates as a passive discharge unit in the initial state. 
     In one aspect, in the startup state, the circuit pre-charges components connected to the second electric contacts. In one aspect, in the operating state, the resistor is bypassed. 
     In one aspect, in the shutdown state, the resistor discharges energy present in the components connected to the second electric contacts. 
     In another aspect of the disclosure, a method for pre-charging and discharging a hazardous voltage direct current system includes providing a system in an initial state, wherein a first relay in the form of main contactors disposed on first and second lines connecting a first set of contacts and a second set of contacts are open, and wherein a second relay is in a first state connecting a first bypass line to a third bypass line having a resistor, such that the resistor is in series with the second contacts via the first and second lines; switching the second relay to a second state to connect a second bypass line to the third bypass line and making a connection on the first line between the first and second contacts and, in response thereto, pre-charging components connected to the second contacts from the first contacts via the resistor; in response to pre-charging, making a connection on the second line to connect the first contacts to the second contacts without the resistor; and opening the main contactors and switching the second relay to the first state and, in response thereto, discharging voltage from components connected to the second contacts. 
     In one aspect, the method includes charging the resistor when the second relay is in the second state and the main contactors are partially open, wherein the first contacts are connected to a battery. 
     In one aspect, the step of discharging the voltage from the components includes thermally discharging the components at the resistor. 
     In one aspect, the resistor is bypassed when the second relay is in the second state and the main contactors are closed. 
     In one aspect, the main contactors selectively makes and breaks a connection between the first contacts and the second contacts, wherein the first contacts are connected to a battery. 
     In another aspect of the disclosure, a system for pre-charging and discharging a hazardous voltage direct current system is provided comprising: a pair of first electric contacts connected to a pair of second electric contacts via an electric circuit, the first contacts configured for attachment to a battery and the second contacts configured for attachment to further components; a first relay in the form of main contactors disposed on the circuit; a second relay disposed on the circuit; a single resistor disposed on the circuit; wherein the system has a pre-charging state in which the first and second relays connect the single resistor between the first and second electrical contacts to pre-charge the further components; wherein the system has a discharge state in which the first and second relays connect the single resistor with the second electrical contacts to discharge the further components; wherein the system is configured to perform both a pre-charge and discharge with no additional resistors other than the single resistor and no additional relays other than the first and second relays. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a schematic circuit diagram illustrating a circuit for a pre-charging and voltage discharge unit, illustrating an initial state of the circuit; 
         FIG. 2  is a schematic circuit diagram illustrating a startup state of the circuit in which the resistor is charged by a battery; 
         FIG. 3  is a schematic circuit diagram illustrating an operating state in which the resistor is bypassed; 
         FIG. 4  is a schematic circuit diagram illustrating a shutdown state in which voltage is discharged into the resistor; and 
         FIG. 5  is a partial view of the circuit including additional resistors disposed on the circuit. 
     
    
    
     DESCRIPTION OF THE ENABLING EMBODIMENT 
     Referring to  FIG. 1 , a system  10  for managing the voltage in an electric vehicle is provided. The electric vehicle includes a hazardous-voltage direct current (HVDC) system, where peak inrush current occurs in the HV circuit at power up, and high voltages are present in the HV circuit after switching off. The system includes a circuit  12  that is configured to both pre-charge the system  10  at power up and to discharge the hazardous voltage in the system  10  after switching off. 
     As is typical in electric vehicles, the system  10  includes a battery  13 , the poles of which are connected to one end of the circuit  12  at KL 1 , which may also be referred to as first contacts. The system further includes further components connected to the opposite end of the circuit  12  at KL 2 , which may also be referred to as second contacts. The further components may include components of the electric vehicle including hazardous voltage components such as the electric motor, an inverter, DC/DC charger, and the like. 
     The circuit  12  includes main contactors (designated as RY 1 ) that, when closed, transfers current from the battery  13  at KL 1  to the further components at KL 2 .  FIG. 1  illustrates an initial, inactive state, where the main contactors are open, such that current will not flow from the battery  13  at KL 1  to the remainder of the system. RY 1  may be implemented as two separate relays, or the second pole may have a separate smaller bridging relay, which could be integrated into RY 2 . The circuit  12  further includes a first line  14  shown at the bottom of the circuit diagram and extending from KL 1  to KL 2 . The first line  14  includes a switch  14   a  coupled to the main contactors RY 1 , which is open in the initial state. The circuit also includes a second line  16  that extends from KL 1  to KL 2 , similar to the first line  14 . The second line  16  includes a switch  16   a  coupled to the main contactors RY 1 , which is open in the initial state. The main contactors RY 1  controls the switches  14   a  and  16   a  to be either open or closed. When both switches  14   a  and  16   a  are closed, battery  13  will power components connected to KL 2 . In a pre-charge state,  14   a  is closed, and  16   a  is open, which may be referred to as a partially open state of the main contactors RY 1 . 
     As shown throughout the figures, the main contactors are shown schematically as a single unit connected to each of the first and second lines  14 ,  16  to make and break the connection of the first and second lines  14 ,  16 . However, the main contactors may be configured to independently make and break the connection at each of the lines  14 ,  16 , and may be in the form of two separate contactors or relays for independent control of making and breaking the connection. For instance, in  FIG. 2 , the connection of the first line  14  is made, while the connection of the second line  16  is broken. For the purposes of this disclosure, the main contactors RY 1  may also be referred to as a main relay or a first relay. 
     The circuit  12  further includes a set of bypass lines that can be connected or disconnected from the flow of current depending on the state of the circuit  12 . A first bypass line  18  extends from the first line  14  toward a second relay RY 2 . A second bypass line  20  extends from the second line  16  toward the second relay RY 2 . A third bypass line  22  extends from the second relay RY 2  to the second line  16 . 
     The second relay RY 2  operates as a switch to make or break the connection between the third bypass line  22  and one of the first bypass line  18  or the second bypass line  20 . Thus, the second relay RY 2  controls which pair of bypass lines are connected. In one state of the second relay RY 2 , shown in  FIG. 2 , the second bypass line  20  and the third bypass line  22  are connected via the second relay RY 2  and the first bypass line  18  is disconnected at the second relay RY 2 , thereby creating a flow path parallel to the second line  16  and separating the first line  14  and the second line  16  from each other. The main contactors RY 1  are disposed between the respective line contacts of the second line  16  with the second and third bypass lines  20  and  22 . 
     In another state of the second relay RY 2 , the first bypass line  18  is connected to the third bypass line  22  via the second relay RY 2 , thereby creating a flow path between the first line  14  and the second line  16 . The contact between the first bypass line  18  and the first line  14  is disposed between the main contactors RY 1  and KL 2 . The contact between the third bypass line  22  and the second line  16  is also disposed between the main contactors RY 1  and KL 2 . Thus, when the second relay RY 2  connects the first bypass line  18  to the third bypass line  22 , the first line  14  and the second line  16  are connected in the circuit, regardless of the state of the main contactors RY 1 . 
       FIG. 1  illustrates first and third bypass lines  18 ,  22  connected, but with the connection along lines  14  and  16  broken between KL 1  and KL 2 . 
     The third bypass line  22 , which as described above will connect the second line  16  to either the first line  14  or another contact point on the second line  16  depending on the state of the second relay RY 2 , includes a resistor R 1 . Thus, the second relay RY 2  will control how the resistor R 1  operates with the rest of the circuit  12 . In one state of the relay RY 1 , as shown in  FIG. 2 , the resistor R 1  is part of a flow path parallel to the second line  16  and disconnected from the first line  14 . In another state, the resistor R 1  is part of a flow path between the first line  14  and the second line  16 , as shown in  FIG. 1 . 
       FIG. 1  illustrates the system  10  in its initial and inactive state. The main contactors RY 1  are open, breaking the connection between KL 1  and KL 2  along lines  14 ,  16 . In the initial state, RY 2  is switched such that the first bypass line  18  and the third bypass line  22  are connected, and the second bypass line  20  is disconnected. Resistor R 1  is therefore part of a flow path between the first line  14  and the second line  16 , which are each connected to KL 2 . In this initial state, the resistor R 1  functions as a passive discharge circuit with KL 2  via relay RY 2 . 
     With reference to  FIG. 2 , in response to starting up the system  10 , the second relay RY 2  is switched, breaking the connection between the first bypass line  18  and the third bypass line  22 , and making the connection between the second bypass line  20  and the third bypass line  22 . In response to switching the second relay R 2 , the components connected to KL 2  are pre-charged with resistor R 1  as part of the flow path. Additionally, switch  14   a  is closed by main contactors RY 1 , while switch  16   a  remains open, such that connection is made along line  14  to complete the circuit between KL 1  and KL 2  and closing the loop for pre-charging. The circuit between KL 1  and KL 2  therefore includes the resistor R 1 . The main contactors RY 1  may be considered to be in a partially open state in this state, with the connection along line  14  being made and the connection along line  16  being broken. However, it will be appreciated that with two separate relays or contactors controlling the making and breaking of these connections, reference to being partially open may be interpreted as one connection being made and another being broken. 
     The pre-charging process is monitored and, after a pre-determined pre-charge threshold is reached, the pre-charging is complete. In response to completing the pre-charge, the main contactors RY 1  are switched to a “closed” state, as shown in  FIG. 3 . In the closed state of the main contactors RY 1 , the first line  14  and the second line  16  each connect KL 1  to KL 2 , and the system  10  is activated in its full operating mode. The second relay RY 2  remains in its state connecting the second bypass line  20  and third bypass line  22 , where the resistor R 1  is connected in parallel to the second line  16 . This parallel connection allows current to flow through the second line  16 , bypassing the resistor R 1 . 
     With reference to  FIG. 4 , upon switching off the system, the main contactors RY 1  are opened, breaking the connection along lines  14  and  16  between KL 1  and KL 2 . Thus, the components connected to KL 2  are no longer fully powered by KL 1 . The second relay RY 2  is also switched at this point, making a connection between the first bypass line  18  and the third bypass line  22 , thereby putting resistor R 1  into a path between the first line  14  and the second line  16 . The second bypass line  20  and KL 1  are disconnected and in the same state as the initial state. 
     In this shutdown state, the energy present in the components connected to KL 2  is discharged by resistor R 1  thermally. A subsequent power up of the system  10  may occur later according to the process described above. In the event of a subsequent power up occurring shortly after shutdown, the pre-charging process may be completed more quickly due to the residual energy present in KL 2 . 
     Accordingly, the system  10  described above, having the two relays RY 1  and RY 2  and the single resistor R 1  as a single functional unit disposed between KL 1  and KL 2  provides both pre-charging and discharging, without the need for a separate pre-charging unit and a separate discharge unit. 
     The resistor R 1  has been described as a single resistor. However, in some cases, the pre-charge and discharge specifications for the resistor may be different. Thus, in another approach, an additional resistor R 2  may be included on one or both of the first bypass line  18  and the second bypass line  20 , thereby changing the total serial or parallel resistance depending on the switched state of the second relay RY 2 .  FIG. 5  illustrates an example of additional resistors R 2  on both lines  18  and  20 . It will be appreciated that only one additional resistor R 2  may be included, on either line  18  or  20 . It will also be appreciated that reference to a resistor may also refer to a group of resistors disposed on a portion of a line to produce a desired resistance. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the appended claims. These antecedent recitations should be interpreted to cover any combination in which the inventive novelty exercises its utility.