Patent Publication Number: US-2015084414-A1

Title: Isolation contactor transition polarity control

Description:
BACKGROUND 
     1. Technical Field 
     The technical field relates generally to electric and hybrid-electric motor vehicles and, more particularly, to control over state changes of high voltage isolation contactors used on such vehicles. 
     2. Description of the Technical Field 
     Hybrid electric vehicles are usually equipped with one or more high voltage direct current electrical power distribution subsystems over which power is supplied to vehicle traction motors and other high voltage loads. A representative configuration of such power subsystems might include two 350 volt direct current (DC) sub-systems and one 700 volt DC sub-system or bus. Current flow between hybrid-electric drive train motor/generator(s), or more precisely, an alternating current to direct current inverter/rectifier, and high voltage storage batteries connectable to at least one of these DC sub-systems is bi-directional. Current can change direction depending upon whether the vehicle high voltage storage batteries are receiving or supplying power to the motor/generator(s). 
     High voltage isolation contactors have been used to control the energization and de-energization of the high voltage DC power distribution sub-systems on vehicles and additionally to control the flow of power to vehicle electrical loads. It has been long recognized that the action of opening a high voltage isolation contactor in any direct current circuit can substantially reduce the service life of the contactors due to arcing. As illustrated by U.S. Pat. No. 567,137 to Hewlett, “magnetic blow-out” contactors or circuit breakers have long been in long. Blow-out magnets can urge an electrical arc formed on opening of device contacts along with the magnetic flux lines of the blow-out magnet away from the contacts thereby lengthening and disrupting the arc. 
     Operation of a high voltage blow-out type isolation contactor is contingent on the contactor being wired “correctly” with regard to polarity of the circuit, that is, the direction current flow. If the polarity of the circuit is opposite of the polarity of the high voltage isolation contactor, then as the contacts begin to open the blow-out magnet&#39;s flux lines tend to urge the arc into, instead of away from, the contact area. This reinforces a situation which the blow-out magnets were intended to prevent. High voltage isolation contactors configured with blow-out magnets are quite effective in increasing contactor life in circuits where the polarities of the high voltage circuits are consistent with the polarity of the isolation contactors. 
     Because current flow on some hybrid electric vehicle DC power buses is subject to changing direction, the polarity of the electrical potential for at least one high voltage distribution sub-system is also subject to change. During the generation mode of a hybrid electric vehicle operation—defined by the traction motor/generator(s) producing sufficient electrical potential to support both the vehicle&#39;s immediate electrical needs as well as the electrical needs of the high voltage batteries—the polarity of the high voltage distribution sub-system flows from the traction motor/generator(s) through the high voltage isolation contactors to the high voltage storage batteries and the remaining high voltage distribution sub-systems. This scenario is referred to here as “positive polarity.” Negative system polarity is defined as the flow of electrical potential out of the high voltage batteries through the high voltage isolation contactors to the traction motor/generator(s) as well as the remaining high voltage vehicle architecture. 
     High voltage power distribution sub-system polarity reversals can occur frequently under certain circumstances. One such scenario is where the traction motor/generator(s) is/are generating power but the rate of power generation is on the borderline of meeting power demands from the vehicle&#39;s various electrical loads, for example, electric accessory motors, DC-to-DC converters, truck equipment manufacturer (TEM) integrated body equipment and the like. Under these circumstances it is possible that the polarity on any of the vehicle&#39;s high voltage power distribution sub-systems can change in polarity frequently, particularly if the loads on the accessories are changing. This in turn can reduce the effectiveness of the blow-out magnets for the interruption of arcs resulting from opening of the contactors. 
     SUMMARY 
     A method of operating an electrical power distribution system on a hybrid-electric vehicle in which the power distribution system includes at least a first dual mode electrical motor/generator, high voltage traction batteries, bi-directional direct current power transmission lines connectable between the dual mode electrical motor/generator and the high voltage fraction batteries, first and second isolation contactors including magnetic blow out and connected into the power transmission lines to exhibit opposed polarity and an electrical system controller. The method comprises, responsive to a request to deenergize the electrical power distribution system, a step for determining the polarity of current on the bi-directional direct current power transmission lines. Once the polarity has been determined the isolation contactor of corresponding polarity is selected to be opened. Either before or after the selection of a contactor, steps are taken to establish steady state operation of the bi-directional direct current power transmission lines. During steady state operation the polarity of power flow on the transmission lines is to remain unchanged. Then the selected isolation contactor is opened. The non-selected isolation contactor is opened after the selected isolation contactor is opened. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a high level block diagram of a control system for a hybrid-electric drive train for a motor vehicle. 
         FIG. 2  is a schematic of a high voltage power distribution system for the drive train of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, like reference numerals and characters may be used to designate identical, corresponding, or similar components in differing drawing figures. 
     Referring now to the figures and in particular to  FIG. 1 .  FIG. 1  is a generalized a high level schematic of a control system  22  for a hybrid-electric drive train  20  for a vehicle. Hybrid-electric drive trains have generally been of one of two types, parallel and series. In parallel hybrid-electric systems propulsion torque can be supplied to drive wheels by an electrical motor, by a fuel burning engine, or a combination of both. In series type hybrid systems drive propulsion is directly provided only by the electrical motor. Illustration of the methods of isolation contactor control disclosed here is not limited to a particular hybrid-electric system. Hybrid-electric drive train  20  is configurable for series, parallel and blended series/parallel operation and the system operates in any mode. A multiple configuration drive train such as hybrid-electric drive train  22  illustrates numerous possible scenarios by which the drive train can produce polarity reversals within a high voltage power distribution system  19 . 
     Hybrid-electric drive train  20  includes an internal combustion (IC) engine  28  and two dual mode electrical machines (motor/generators  30 ,  32 ) which can be operated either as generators or motors. Motor/generator  32  operating alone or together with motor/generator  30  can be used to provide for vehicle propulsion. Either of motor/generators  30 ,  32  can also generate electricity by regenerative braking of drive wheels  26  or by being driven by the IC  28  engine. In hybrid-electric drive train  20  the IC machine  28  can provide direct propulsion torque or can be operated in a series type hybrid-electric drive train configuration where it is limited to driving one or both of the electrical motor/generators  30 ,  32 . Hybrid-electric drive train  20  also includes a planetary gear  60  for combining power output from the IC engine  28  with power output from the two electrical motor/generators  30 ,  32 . A transmission  38  couples the planetary gear  60  with the drive wheels  26 . Power can be transmitted in either direction through transmission  38  and planetary gear  60  between the propulsion sources and drive wheels  26 . During braking planetary gear  60  can deliver torque from the drive wheels  26  to the motor/generators  30 ,  32  or, if the vehicle is equipped for engine braking, to engine  28 , distribute torque between the motor/generators  30 ,  32  and IC engine  28 . 
     A plurality of clutches  52 ,  54 ,  56  and  58  provide various options for configuring the electrical motor/generators  30 ,  32  and the engine  28  to propel the vehicle through application of torque to the drive wheels  26 , to generate electricity from electrical motor/generators  30 ,  32  from the engine, and to generate electricity from the electrical motor/generators  30 ,  32  by back driving them from the drive wheels  26 . Electrical motor/generators  30 ,  32  may be run in traction motor mode to power drive wheels  26 , or they may be back driven from drive wheels  26  to function as electrical generators, when clutches  56  and  58  are engaged. Electrical motor/generator  32  may be run in traction motor mode or generator mode while coupled to drive wheels  26  by clutch  58 , planetary gear  60  and transmission  38  while at the same time clutch  56  is disengaged allowing electrical motor/generator  30  to be back driven through clutch  54  from engine  28  to operate as a generator. Conversely clutch  56  may be disengaged and clutch  58  engaged and both motor/generators  30 ,  32  run in motor mode. In this configuration motor/generator  32  can propel the vehicle while motor/generator  32  is used to crank engine  28 . Clutch  52  may be engaged to allow the use of IC engine  28  to propel the vehicle or to allow use of a diesel engine, if equipped with a “Jake brake,” to supplement vehicle braking When clutches  52  and  54  are engaged and clutch  56  disengaged engine  28  can concurrently propel the vehicle and drive motor/generator  30  to generate electricity. Still further operational configurations are possible although not all are used. Elimination of some configurations can allow clutch  58  to be considered as “optional” and to be replaced with a permanent coupling. 
     The selective engagement or disengagement of clutches  52 ,  54  and  56  allows hybrid-electric drive train  20  to be configured to operate in a “parallel” mode, in a “series” mode, or in a blended “series/parallel” mode. To configure drive train  20  for series mode operation clutches  54  and  58  (if present) can be engaged and clutches  52  and  56  disengaged. Propulsion power is then provided by motor/generator  32  and motor/generator  30  operates as a generator. To implement drive train  20  for parallel mode operation at least clutches  52  and  58  are engaged. Clutch  54  is disengaged. Motor/generator  32  and IC engine  28  are available to provide direct propulsion. Motor/generator  30  may be used for propulsion. A configuration of drive train  20  providing a mixed parallel/series mode has clutches  52 ,  54  and  58  engaged and clutch  56  disengaged. Motor/generator  32  operates as a motor to provide propulsion or in a regenerative mode to supplement braking IC engine  28  operates to provide propulsion and to drive motor/generator  30  as a generator. 
     Hybrid-electric drive train  20  draws on two reserves of energy, one for the electrical motor/generators  30 ,  32  and a fuel tank  62  for the IC engine  28 . Electrical energy for the motor/generators  30 ,  32  may be stored directly in capacitors but more commonly is sourced from batteries  34 . Batteries  34  are subject to charging and discharging. The availability of power from the electrical power reserve may be measured in terms of its state of energization (SOE) or, more usually with batteries, in terms of its state of charge (SOC). 
     Traction batteries  34  may be charged from external sources or by operation of the drive train  20 . As already described, electrical motor/generators  30  and  32  may operate as generators, either together or independently, to supply energy through a hybrid inverter  36  and a high voltage bus  17  of high voltage power distribution system  19  to recharge traction batteries  34 . Hybrid inverter  36  provides voltage step down or step up and, if motor/generators  30 ,  32  are alternating current devices, current rectification and de-rectification between the three phase synchronous motor/generators and battery  34 . Fuel from the fuel tank  62  may be converted to electrical energy which is used to charge the traction batteries  34 . Traction batteries  34  may also be recharged through regenerative braking. 
     Control over drive train  20 , the hybrid inverter  36 , fraction batteries  34  and power system  19  isolation contactors  64 ,  68  (see  FIG. 2 ) is implemented by a control system  22 . Control system  22  may be implemented using controller area networks (CAN) based on a public data link  18  and a hybrid system data link  44 . Control system  22  coordinates operation of the elements of the drive train  20  and the service brakes  40  in response to operator/driver commands to move (ACC/TP) and stop (BRAKE) the vehicle received through an electronic system controller (ESC)  24 . The control system  22  selects how to respond to the operator commands including deenergization of the power distribution system  19  while protecting power distribution system  19  components from damage. 
     In addition to the data links  18 ,  44 , control system  22  includes the controllers which broadcast and receive data and instructions over the data links  18 ,  44 . Among these controllers is the ESC  24 . ESC  24  is a type of body computer and is not assigned to a particular vehicle system. ESC  24  has various supervisory roles and is connected to receive directly or indirectly various operator/driver inputs/commands including brake pedal position (BRAKE), ignition switch position (IGN) and accelerator pedal/throttle position (ACC/TP). ESC  24 , or sometime the engine controller  46 , can also be used to collect other data such as ambient air temperature (TEMP). In response to these and other signals ESC  24  generates messages/commands which may be broadcast over data link  18  or data link  44  to an anti-lock brake system (ABS) controller  50 , the gauge cluster controller  48 , the transmission controller  42 , the engine control unit (ECU)  46 , hybrid controller  48 , a pair of accessory motor controllers  12 ,  14  and through a remote power unit (RPM)  70  to control opening and closing of isolation contactors  64 ,  66  and  68  as shown in  FIG. 2 . 
     Accessory motor controllers  12 ,  14  control high voltage accessory motors  13 ,  15  in response to directions from other CAN nodes, primarily ESC  24 . High voltage accessory motors  13 ,  15  are direct current motors employed to support the operation of components such as an air conditioning compressor (not shown), a battery cooling loop pump (not shown) or a power steering pump (not shown). On many hybrid-electric vehicles there is no reasonable option of powering such components directly from the internal combustion engine due to the engine&#39;s sporadic availability and the motors  12 ,  14  driving the accessory components are parasitic loads on a motor/generator  30 ,  32  when operating in generator mode or on the traction battery  34 . The loads produced by these applications can be highly variable, for example, under conditions where a vehicle  102  is caught in slow moving traffic greater demands may be made on power steering. Under conditions of high heat and humidity greater demands are likely to be placed on air conditioning and for battery cooling and thus the motors which drive the compressor pumps used with these systems tend to appear as larger loads the power distribution system  19 . Power draw by accessory systems can be reported to ESC  24  over CAN hybrid data link  44 . 
     Operator demand for power on drive train  20  power is a function of accelerator/throttle position (ACC/TP). ACC/TP is an input to the ESC  24  which passes the signal to the hybrid supervisory control module  48 . Where engine  28  is supplying power both for propulsion and for charging of the traction batteries  34  an allocation of the available power from engine  28  is made by the hybrid supervisory control module  48 . 
     Referring now to  FIG. 2 , control over the energization state or, put more particularly, de-energization of portions of the high voltage electrical power distribution system  19  through operation of isolation contactors  64  and  68  is discussed. High voltage electrical power distribution system  19  includes three sub-systems  17 ,  74 ,  76 . The power distribution sub-systems  17 ,  74 ,  76  are formed from several electrical conductors. A near ground conductor  27  is connected to a grounded terminal of high voltage fraction battery  34 A through isolation contactor  64  to one terminal of inverter  36 . The positive (normally the ungrounded terminal) of traction battery  34 A is connected by a high voltage conductor  29  to the negative terminal of traction battery  34 B. The positive terminal of traction battery  34 B is connected through a resistor pre-charge circuit  63  to isolation contactor  68  and from there to the remaining terminal of inverter  36  by a high voltage conductor  27 . Electrical current transmission over the conductors  25 ,  27 ,  29  is direct current, but bi-directional. The direction of flow depends upon whether current is being sourced by traction battery packs  34 A,  34 B or flowing into the traction battery packs. 
     Sub-system  17  carries a DC potential of 700 volts between near ground conductor  25  and high voltage conductor  27  when the sub-system is energized. Sub-system  74  supports a potential of 350 volts between high voltage (350 volt) conductor  29  and the near ground conductor  25 . Sub-system  76  supports a potential of 350 volts between the high voltage (350 volt) conductor 29 and the high voltage (700 volt) conductor  27 . 
     High voltage power distribution system  19  may be de-energized by opening either of isolation contactors  64 ,  68 . Isolation contactor  64 ,  68  are of a fixed polarity design. They are equipped with magnetic blow-outs for suppression of arcing during opening of the contactors. First isolation contactor  64  is physically in a series relationship with the near ground conductor  25  between battery pack  34 A and inverter  36 . Second isolation contactor  68  is in a series relationship within conductor  27  with the positive terminal of traction battery  34 B and inverter  36 . The high voltage isolation contactors  64 ,  68  are oriented in an opposing/reversed polarity relationship (one with regards to the other) within the circuit. 
     When batteries  34 A,  34 B are discharging power flow is into inverter  36 . When batteries  34 A,  34 B are being charged power flow is out of inverter  36 . Reversal of the direction of current flow through the isolation contactors  64 ,  68  can depend changes in whether inverter  36  is drawing or sourcing power. If hybrid inverter  36  is drawing power then batteries  34 A and  34 B are sourcing power. It is possible that batteries  34 A,  34 B and hybrid inverter  36  will concurrently source power, particularly during periods of mild regenerative braking and heavy loads. It is during such periods that the possibility of frequent reversal of current flow can arise. 
     Battery management systems (BMS)  35 A,  35 B monitor the electrical potential flowing into and out of the high voltage battery packs  34 A,  34 B. This data is reported by the BMS  35 A,  35 B over the controller area network (CAN) data link  44 . High voltage accessory loads connected to power sub-systems  74 ,  76  include controllers and these can report load status and power draw over data link  44 . Among these systems are motor controller  12 A for a high voltage battery chiller motor  13 A, DC-to-DC converters  80 A,  80 B for a low voltage power distribution system  83  and low voltage batteries  82 A,  82 B, motor controller  12 B for power steering pump motor  13 B, a motor controller  14 A for a pneumatic compressor motor  15 A and motor controller  14 B for an HVAC (heating, ventilation and air conditioning) compressor motor  15 B. ESC  24  monitors the BMS  35 A,  35 B and load status data on the data link  44 . 
     The direction of current flow is determined by ESC  24  depending upon reports generated by battery management systems (BMS)  35 A,  35 B for the traction battery packs  34 A,  34 B. In order to deenergize the high voltage power distribution system  19  one of isolation contactors  64 ,  68  to be opened first depending upon the direction of flow of current. For a power down operation the data is used by ESC  24  to select the correct one of isolation contactors  64  or  68  to open taking into account the present polarity of the direct current flowing within the circuit. 
     Once the polarity of current flow on the conductors  25 ,  29  has been identified and the appropriate one of isolation contactors  64 ,  68  has been selected, ESC  24  commands all high voltage devices associated with the targeted circuit to assume a “steady state” condition in order to maintain the correct energy polarity relationship within the circuit and the selected isolation contactor until the selected isolation contactor can be opened. Typically a steady state period occurs with accessory loads already minimized, although this is not always the case. The duration of the steady state period is usually quite brief, on the order of a few microseconds and thus adverse consequences stemming from steady state operation should be minimized. During a steady state period the polarity of the current flow in conductors  25 ,  27 ,  29  is maintained. This may require load management to adjust to changes in the amount of power sourced from hybrid inverter  36  and/or changes in the amount of power generated by motor/generators  30 ,  32 . In addition, it is possible that traction battery packs  34 A,  34 B may be undergoing charging at near the maximum state of charge when a steady state is locked. The degree to which traction battery  34 A,  34 B can be overcharged during the short duration steady state will be minimal. The remaining, non-selected isolation contactor  64  or  68  is opened a short period after the selected isolation contactor has opened. 
     Establishing a steady state condition prevents a change of polarity in the conductors  25 ,  27  prior to opening the selected one of the isolation contactors  64 ,  68 . A polarity change occurring during the transitioning of the selected isolation contactor can result in failure to suppress an arc developed within the high voltage isolation contactor. Repeated occurrences of arcing, particularly sustained arcing, contribute to damage to the high voltage isolation contactors  64 ,  68 . Once the first isolation contactor has been transitioned open the second isolation contactor (opposing polarity) will subsequently be transitioned open. As a result, the second isolation contactor will not be subject to damage due to the absence of energy flow within the circuit despite the fact that magnetic blowout was positioned in reverse polarity at the point in time when the ESC  24  commanded the first contactor to transition to its open state. Accessory isolation contactors  43 A,  43 B used to connect accessory controllers and motors to power distribution sub-systems  74 ,  76 , respectively, are held in the current state during the steady state period. During the steady state period the various accessories can be operated in a fashion so as to exhibit a constant load. For example, the pneumatic compressor motor  15 A is operating when the steady state period begins it will continue to operate as long as the steady state period remains in effect. This can possibly result in a slight over pressurization of compressed air storage tanks on a vehicle. 
     Consideration is given the high voltage battery  34 A,  34 B SOC “dynamic margin” needed to maintain a steady power state condition in anticipation of selecting the correctly polarized isolation contactor for the current polarity of the conductors  25 ,  27 . For example: the normal upper and lower state of charge (SOC) values for the beginning and ending of a high voltage battery recharge/regeneration cycle may be normally in the 85%-25% SOC area. However, during the ESC  24  selection process the SOC range may be increased to 87%-23% SOC to allow for the additional energy inflows or outflows which may be incurred during the steady state interval.