Abstract:
The invention is designed for vehicles having two electrical power supply systems and corresponding differentiated voltage level charges and two batteries operating at a first and a second voltage level. A bidirectional voltage converter cooperates with both systems whose input and output stages are galvanically insulated and include a switch. The batteries are connected to said input and output at a first and a second voltage level so that said bidirectional converter can provide a first reduced voltage mode and a second increased voltage mode. The passive components, e.g. the magnetic components and capacitances, of said stages have been chosen to provide an identical transitional behavior in both modes when a disruption occurs in the regulating system either in the charge or the input voltage.

Description:
FIELD OF THE INVENTION 
     The present invention refers to a dual voltage electrical distribution system applicable to vehicles which possess two network sectors and charges prepared to operate at two different voltage levels, for example at 42 V and at 14 V, generated by at least two batteries, one of which is at a first voltage level of, e.g. 36 V, and another at a second lower voltage level of, e.g. 12 V, there being at least one voltage converter associated with the two said network sectors. 
     The present invention is useful in the automotive industry. 
     BACKGROUND OF THE INVENTION 
     In modern vehicles there is a tendency towards increasing electrical and electronic equipment which results in a growing consumption of electrical energy. This makes it advisable to increase the current nominal voltage of the vehicle&#39;s electrical system by up to three times, that is, from the current 14 V DC to 42 V DC. However, due to the conveniently calculated and designed current manufacturing and installation infrastructures of electrical systems which already exist in the automotive industry, a sudden transition from one voltage to another is made very difficult. 
     A solution has been proposed in order to avoid said sudden transition, which consists of implementing an electrical and electronic distribution system architecture for the vehicle using networks operating at two different voltage levels, which has been called “dual voltage system”. Thus, some components will continue to work at 14 V, as until now, so that it will not be necessary to introduce changes in their electrical control and distribution networks, while other components will come to work at 42 V, with a more appropriate output and/or optimisation of their performance. 
     Said dual voltage system may be basically achieved in two ways: either with a single 42 V battery and a unidirectional DC/DC voltage converter from 42 to 14 V; or with two 14 and 42 V batteries respectively, and a bidirectional DC/DC voltage converter from 14 to 42 V or vice versa. 
     The converter is a key piece of the new system in any of the solutions. 
     Patent WO 97/28366 is an example of the utility of having a dual voltage system in automotive vehicles, describing an ignition system for internal combustion engines which uses a dual voltage electrical supply, with a higher voltage to produce a high-intensity electric arc and a lower voltage to cause ionisation. A signal controller analyses the ionisation signal to determine a series of parameters concerning the correct operation of the ignition. 
     Patent WO 95/13470 describes another ignition system for internal combustion engines supplied by dual voltage supplied by a single supply source and subsequently dualised by a DC/DC voltage converter. 
     Patent EP-A-0892486 describes a unidirectional converter device to supply dual voltage from a single supply source. 
     The introduction of the new architecture of the dual voltage system in automotive vehicles carries with it an increase in the complexity of electrical networks. The system includes, as stated hereinbefore, one or two accumulators or batteries, a converter and one or more distribution boxes in which electronic signal and power control means are centralised, including a microprocessor and electrical protection means. The vehicle also comprises an electric generator, usually an alternator, which supplies current to the accumulator or accumulators by means of a rectifier, and which also directly supplies most of the components when the vehicle is running. 
     Increasing the voltage (Volts.) threefold (42 V) involves the reduction of current (A) for the same amount of power. Fewer amperes mean smaller cable cross-section for supplying current, with consequently less weight and lower consumption. 
     References to the subject and objects of this invention are also found in different publications, among which the following may be mentioned: J. G. Kassakian “Challenges of the new 42 V architecture and progress on its international acceptance” VDI 98 Baden-Baden; Intersociety Energy Conversion Engineering Conference (IECEC) “Multiple Voltage Electrical Power Distribution System for Automotive Applications” 31st. Washington 96; “Draft specification for 42 V battery in a 2-voltage vehicle electrical system for BMW and Daimler-Benz SICAN” 29.6.98; MIT Auto-Consortium-42V Net Research Unit #1 “DC/DC converters for Dual Voltage Electrical Systems”. 
     Kazimierczuk M K et al. “Topologies of Bidirectional PWM DC—DC power converters” PROCEEDINGS OF THE NATIONAL AEROSPACE AND ELECTRONICS CONFERENCE. (NAECON 1993), US, NEW YORK, IEEE, VOL 1, pages 435441, describes a power system of an aircraft for normal and emergency operation (see FIG. 1) as well as several block diagrams and topologies of bidirectional converters, in particular FIG. 3 equivalent to the topology of FIG. 3 of the drawings of this invention, which are detailed in the preamble of claim  1  of the invention. 
     BRIEF EXPLANATION OF THE INVENTION 
     In accordance with the invention, the dual voltage electrical distribution system will to be implemented using a bi-directional voltage converter, with its input and output stages galvanically insulated, and including in each of said stages a switching device, whose bi-directional converter has said batteries at a first voltage level and at a second voltage level connected to said inputs and outputs, so that said bi-directional converter circuit provides two energy transfer modes which constitute a first mode of voltage reduction and a second mode of voltage raising, having chosen the passive components, that is the magnetic components and capacitances of said stages to provide an identical transitory behaviour in both modes when either a disturbance in the charge or in the input voltage enters into the regulation system. 
     More specifically, the proposed bi-directional converter is a galvanically insulated DC version of a converter circuit with the Cuk topology, symmetrical with respect to the area of insulation, in which said batteries are connected to its input and output at a first voltage level and at a second voltage level respectively, with a capacitance in parallel with each of said voltage sources, in addition to the storage capacitance typical of the topology, in series with the inductances of the input and output circuit, said switching device being arranged in the input and output stages of the converter, on each side of said galvanic insulation. 
     The main differences between the basic unidirectional converter circuit and the proposed converter are: 
     a) bi-directional power flow; 
     b) no change in output voltage polarity; 
     c) simplification of the converter control design. 
     The invention will be better understood from the following description given in connection with the attached drawings. 
     Until now, the converter has been situated in some part of the electrical networks separated from the distribution box or boxes. However, this arrangement has several drawbacks, such as: an increase in the connection cabling which, on the one hand, involves a greater voltage drop and, on the other, affects the manufacturing cost, the vehicle&#39;s weight and, consequently, fuel consumption; also, a greater occupation of the volume inside the already scarce space of the engine compartment; an increase in the fixing points of components to the vehicle with greater complexity of assembly; an increase in the number of electrical components subjected to vibration, which reduces the system&#39;s reliability; a redundancy of systems, for example, a microprocessor for the converter and a microprocessor for the distribution box; greater difficulty for thermal dissipation of components arranged in separate boxes; greater difficulty in achieving electromagnetic compatibility due to the incorporation of cables which produce high frequency emissions which cause interference in the components of the distribution box. 
     The invention also proposes to incorporate said bi-directional voltage converter in an electrical distribution box of the vehicle, together with centralised electronic signal and power control means, including a microprocessor and electrical protection means. 
     The invention will be better understood from the following description of embodiments, with reference to illustrative drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In said drawings: 
     FIG. 1 is a schematic drawing of a unidirectional voltage converter according to the state of the art, specifically corresponding to the example of embodiment of FIG. 10 of said patent U.S. Pat. No. 4,184,197; 
     FIG. 2 shows the principle of the dual voltage electrical distribution system in accordance with this invention; 
     FIG. 3 shows an example of a possible embodiment of a bi-directional converter circuit in accordance with this invention, with a schematic indication of the voltage switching source. 
     FIG. 4 corresponds to a diagram of the double loop control used to manage the bi-directional converter circuit according to FIG. 3; 
     FIG. 5 is a schematic drawing showing the current flows in a dual voltage electrical system of a vehicle which incorporates an electrical distribution box with a bi-directional converter in accordance with the invention, in combination with a second electrical distribution box which includes a unidirectional converter, corresponding to a de-centralised distribution, that is, with a voltage conversion distributed in several areas of the vehicle; 
     FIG. 6 is equivalent to the foregoing but shows a centralised assembly, in which only one electrical distribution box includes said bi-directional converter; 
     FIG. 7 shows an example of a possible organisation in a vehicle of the proposed system, de-centralised, with several electrical distribution boxes, including converters in at least two of them, one of said converters being bi-directional; and 
     FIGS. 8,  9  and  10  are graphs of examples of simulations in averaged current control mode of the bi-directional converter according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a converter circuit galvanically insulated by the transformer  8  which corresponds to the Example of FIG. 10 of U.S. Pat. No. 4,184,197, that is, with an inductance  2  in series with the input voltage source and another inductance  5  in series with the charge  11 . In that converter the transformer  8  with the transformation ratio N is disconnected from the direct voltage by means of the condensers  3 ,  4 . The input source is indicated by the number and the voltage switching source by the reference  6 . Other components are the transistor  7  associated with the switching device  6  and the diode  10  and condenser  9  in the output sector of the converter, in accordance with said well-known topology in the state of the art. 
     In the diagram of FIG. 2, which illustrates the principle of the electrical distribution system according to the invention, an alternator A is represented and also at least one first battery B 36  or 36 V DC accumulator which, in combination, constitute a power generator unit for a vehicle. The joint action of the alternator A and said first battery B 36  provides the 42 V of the first network R 42 . 
     The system provides for the use of a second battery B 12  or 12 V DC accumulator, constituting a second power generator suitable for supplying a second network R 14 , jointly with the alternator A, at 14 V. As an interface between both networks a bi-directional voltage conversion block  20  is provided. Each network supplies its own charges which are indicated here by the numerical references  21  and  22 , which will be connected by appropriate means, represented in diagrammatic form here by corresponding switches  23 ,  24 . The diagram of said FIG. 2 also includes a starter motor SM, controlled by means of a corresponding connection switch  25 . 
     With reference to FIG. 3, the converter with a Cuk topology with galvanic insulation has a transformer with a ratio of            N   pF       N   aF       =       N   aB       N   pB                              
     two switches  33  and  34 , both controlled by a signal switching source  51  (see also FIG.  4 ), which will apply the current functions U(t) and U(t) with work cycles D and  1 -D respectively, and two diodes  35  and  36 . In this converter, the transformer  8  with a transformation ratio N is disconnected from the direct current by means of the condensers Ca and Cb. If the same voltage polarity is desired at the input and the output, the winding of the primary must be the reverse of the secondary. The ratio N will be designed in such a way that, Vi being the input voltage and Vo the output voltage of the converter            N   pF       N   aF       =       N   aB       N   pB                              
     is complied, where D′= 1 -D. The minimum values of the inductors Lef and Leb and of the condensers Ca and Cb will be chosen according to the maximum current and voltage ripple respectively needed. 
     OPERATING MODES 
     Voltage reduction mode: Vi→charges  38  (connection through the switch  32 ). 
     In this operating mode the switch  33  (which can be implemented by a MOS FET transistor, for example) will switch with a work cycle D and the interrupter  34  will be permanently open. 
     During the interval D′×Ts, when the switch  33  is open, the current to the input Iia charges the inductor Lef and the condenser Ca, and the reflected current of the secondary NsF of the transformer  8  charges the condenser Cb. The inductance Leb of the output discharges to the charge  38  and the diode  36  conducts the sum of the current of the secondary and that of the output. 
     During the interval D′×Ts, when the switch  33  is closed, the input current Iia charges Lef. the reflected current in the secondary of the discharge of Ca discharges Cb and charges Leb, supplied by the high-capacity condenser Cof of the output. In this case, the switch  33  conducts the sum of the input current Iia and that of the primary NpF of the transformer  8 , the diode  36  remaining in open circuit. 
     Voltage raising mode: Vo→charges  37  (connected by the switch  31 ). 
     In this operating mode the switch  34  will switch with a work cycle  1 -D and the switch  33  will be permanently open. 
     During the interval D×Ts, when the switch  34  is open, the current to the input Iib charges the inductor Leb and the condenser Cb, and the reflected current of the secondary NsB of the transformer  8  charges the condenser Ca. The inductance Lef of the output discharges to the charge  37  and the diode  35  conducts the sum of the current of the secondary and that of the output. 
     During the interval D×Ts, when the switch  34  is closed, the input current Iib charges Leb, the reflected current in the secondary of the discharge of Cb discharges Ca and charges Lef, supplied by the high-capacity condenser Cob of the output. In this case, the switch  34  conducts the sum of the input current Iib and that of the primary NpB of the transformer  8 , the diode  35  remaining in open circuit. 
     Aanlysis of the Conventer, Stationary and Dynamic Regime 
     The transfer function in stationary regime in each operating mode, that is, in voltage raising mode and in voltage reduction mode, is the following:                a)                   Reduction                 mode                   (     Vi   =       42   -&gt;   Vo     =   14       )                 V   o       V   i       =       1   N     ·     D     1   -   D                       b)                   Raising                 mode                   (     Vi   =       14   -&gt;   Vo     =   42       )                 V   o       V   i       =     N   ·       1   -   D     D                                    
     where D is the work ratio of the control signal U(t), and N is the ratio of turns of the transformer. 
     As mentioned hereinbefore, the Cuk converter is a system without non-linear minimum phase. These features make the control design difficult if what must be ensured is a good dynamic response, robustness and stability for a wide interval of operating points (many conditions of different charge and line). 
     In particular, the position of the open loop complex conjugated poles of the converter is completely dependent on the work ratio D of the control signal of the converter U(t). 
     Since the converter is bi-directional, two different converters have to be controlled with a single control panel. 
     Using the small signal model derived from the averaged space model of the state of the converter, and assuming separable dynamics, the dynamics in open loop for both modes are: 
     a) Reduction mode (Vi=42→Vo=14)          f   p1d     =       1   -   D       2      π            L   eb              C   a          C   b             N   2          C   a       +     C   b                           f   p2d     =     1     2      π            L   eb          C   of                       f   zd     =         1   -   D         2      π            L   ef              C   a          C   b             N   2          C   a       +     C   b                                        
     b) Raising mode (Vi=14→Vo=42)          f   p1u     =     D     2      π            L   eb              N   2          C   a          C   b             N   2          C   a       +     C   b                           f   p2u     =     1     2      π            L   eb          C   ob                       f   zu     =       D       2      π            L   ef              N   2          C   a          C   b             N   2          C   a       +     C   b                                        
     where fp 1  are the rapid poles and determine the energy transfer dynamics, while the poles fp 2  are slow and depend on the design conditions of the ripple of the output voltage. Finally, the fz are the zeros of the converter. 
     Design Commitments 
     The condition of separability of the poles means that the slow poles must be situated as far as possible from the rapid poles. Consequently, 
     fp 1 d=10.fp 2 d 
     fp 1 u=10.fp 2 u 
     In order to simplify the design of the control loops, the converter must have an equally dynamic behaviour in both operating modes, and as a result an operating point is obtained in which it is required that D= 1 -D. Therefore, the work ratio must be D=0.5. This work ratio is slightly different from the switching ratio used optimally, which, in the Cuk converter, reaches D=0.33 (see S. Cuk, “Switching DC to DC converter with zero input or output current ripple” in Proc. IEEE Industry Appl. Soc. Annual Meet., Toronto, Ont., Canada, 1978 pp 1131-1146. 
     When the work ratio of the nominal work point is fixed at D=0.5, the reduction and raising ratio in stationary regime depends only on the ratio of turns N of the transformer, which consequently must be N=3 to achieve the transformation  42 → 14  (and vice versa). 
     Having fixed the values of the work ratio D, the ratio of turns of the transformer N, and fixing the conditions of dynamic equality (fp 1 d=fp 1 u, fp 2 d=fp 2 u, fzd=fzu) the ratios between the different elements of energy storage will be as follows: 
     
       
         
           L 
           cf 
           =N 
           2 
           ·L 
           eb 
         
       
     
     
       
         
           C 
           of 
           =N 
           2 
           ·C 
           ob 
         
       
     
     
       
         
           C 
           b 
           =N 
           2 
           ·C 
           a 
         
       
     
     FIG. 4 represents a possible control of the bi-directional converter by means of a double loop, of the type known as “Control in Averaged Current Mode”, consisting of an inner loop of current and an outer loop of voltage which ensure the regulation of line and charge with their own protection of the switching transitions. Thus, said control system of the bi-directional converter  50 , comprises a block  51  which controls the input current by modulating the width of PWM impulses, with a power point  52  from said inlet, which block  51  applies the functions of switching to the first and second stages of the bi-directional converter circuit  50 , illustrated in FIG. 3 and a control block  53  of outlet voltage, to which a reference voltage  56  is applied and with a voltage power point  55  from said outlet, which second block  53  provides the first one  51  with a reference current through said inner loop  54 . In this case, the charge on which the converter  37  and  38  operates is indicated by  57  in FIG.  3 . 
     With reference now to the diagram in FIG. 5, this shows only some of the current flows between the component blocks diagrammatically linked in power, a network R 42  maybe observed which operates at 42 V DC and a network  14  which operates at 14 V DC. In said FIG. 5, a first example of the electrical distribution system according to the invention is shown, organised in a de-centralised form, that is, with the voltage conversion distributed in several parts of the vehicle. In said drawing, an electrical distribution box  61  incorporates a bidirectional converter  62  schematised by means of two converter blocks  62   a ,  62   b , to generate a dual voltage and the system includes, in combination, a second distribution box  63  including another unidirectional converter  64 . In this example, the alternator A, together with the first 36 V DC battery B 36 , supply current at 42 V to the box  61  through a power switch  65 . The numeric references  67  and  68  indicate units which include centralised electronic signal and power control means, including a microprocessor and electrical protection means. Reference number  66  indicates an ignition relay, which only provides a supply to said converters  62 ,  64  or control units  67 ,  68 , in the event that the ignition switch of the automobile is closed.  69   a  and  69   c  indicate the different charges which can be connected to one or another box  61 ,  63 , which in the case of  69   a  and  69   c  are also controlled by said ignition relay  66 . 
     FIG. 6 shows a variant of the electrical distribution system in accordance with a centralised organisation, which differs from the example illustrated in FIG. 5 only in the fact that the second distribution box  63  does not include a converter, so that its management and control unit  68  is supplied from the first unit  67  with two different voltages through the networks R 42  and R 14 . The same references are used in said second Figure as in the previous Figure. 
     FIG. 7 schematically illustrates a vehicle in which a dual voltage distribution system has been implemented in accordance with what is described, in which three centralised electrical distribution boxes  61 ,  63 ,  71 , have been provided in the engine compartment, passenger compartment and boot, respectively. The first box  61  includes a power management and control unit  67  and a bidirectional converter  67 , associated with a battery B 36 . The box  36  is connected by cabling or a bus R 42  (high voltage level) and by a second bus R 14  (low voltage level) to the first box  61 . The third box  71  is connected in general to the first one  61 , as to the second  63 , and also has associated a second battery B 12 . The network  72  connects the boxes  61  and  71 . 
     FIGS. 8 to  10  show a simulation of the “Control in Averaged Current Mode” strategy. FIG. 8 is a transitory charge simulation for the voltage reduction mode. FIG. 9 is a transitory simulation for the voltage raising mode and finally FIG. 10 shows a line transitory in voltage reduction mode. 
     It is evident that other simulations for alternative simulation strategies would be possible, for example the “Control in Hysteresis Current Mode”.