Patent Publication Number: US-11021069-B1

Title: Multisource magnetic integration using a current source fed transformer structure with decoupled secondary windings

Description:
TECHNICAL FIELD 
     This disclosure relates to automotive power electronics components. 
     BACKGROUND 
     An electric or hybrid vehicle may contain one or more motors for propulsion. The vehicle may also contain a traction battery to provide energy for the motor and an auxiliary battery to support low voltage loads. As the motor, traction battery, and auxiliary battery may require different electrical parameters, electrical communication between them may require modification of the power provided or consumed. 
     SUMMARY 
     An automotive power system includes a traction battery, an auxiliary battery, and a matrix transformer with two separate cores, a primary winding wound around each of the cores, a first secondary winding wound around one of the cores, and a second secondary winding galvanically isolated from the first secondary winding and wound around the other of the cores. The system also includes circuitry that transfers power from an AC source to the primary winding, to transfer power from the first secondary winding to the traction battery, and to transfer power from the second secondary winding to the auxiliary battery. The circuitry includes a first active bridge having a switching frequency range, and a pair of series connected capacitors and an inductor center tapping the capacitors to form a capacitor-inductor-capacitor resonant network electrically connected between the first active bridge and primary winding and tuned to have a resonant frequency defined by the switching frequency range. The system further includes a controller that operates the first active bridge to maintain a magnitude of current through the primary winding constant independent of load variation at the first and second secondary windings. 
     An automotive power system includes a traction battery, an auxiliary battery, and a matrix transformer with two separate cores, a primary winding wound around each of the cores, a first secondary winding wound around one of the cores, and a second secondary winding galvanically isolated from the first secondary winding and wound around the other of the cores. The system also includes primary circuitry that transfers power from an AC source to the primary winding, first secondary circuitry that transfers power from the first secondary winding to the traction battery, and second secondary circuitry that transfers power from the second secondary winding to the auxiliary battery. The second secondary circuitry includes a center tapped active bridge, a resonant capacitor, and an inductor-capacitor low pass filter that matches an output impedance of the center tapped active bridge to an input impedance of the inductor-capacitor low pass filter. The resonant capacitor is electrically connected in parallel with the inductor-capacitor low pass filter at a center tap of the center tapped active bridge such that under zero load conditions at the second secondary winding, current through the second secondary winding and the center tapped active bridge is greater than zero. 
     An automotive power system has a traction battery, an auxiliary battery, and a matrix transformer with two separate cores, a primary winding wound around each of the cores, a first secondary winding wound around one of the cores, and a second secondary winding galvanically isolated from the first secondary winding and wound around the other of the cores. The system also has circuitry, that transfers power from an AC source to the primary winding, including a bidirectional inverter, a first active bridge having a switching frequency range, a DC link capacitor between the bidirectional inverter and first active bridge, and a pair of series connected capacitors and an inductor center tapping the capacitors to form a capacitor-inductor-capacitor resonant network electrically connected between the first active bridge and primary winding and tuned to have a resonant frequency defined by the switching frequency range. The system also has a controller that operates the first active bridge to maintain a magnitude of current through the primary winding constant independent of load variation at the first and second secondary windings, and circuitry, that transfers power from the first secondary winding to the traction battery, including a second active bridge, a DC output filter capacitor, and matching network circuitry configured to match an output impedance of the matrix transformer to an input impedance of the second active bridge. The system further has circuitry, that transfers power from the second secondary winding to the auxiliary battery, including a third active bridge, a resonant capacitor, and an inductor-capacitor low pass filter configured to match an output impedance of the third active bridge to an input impedance of the inductor-capacitor low pass filter. The third active bridge is a center tapped active bridge. The resonant capacitor is electrically connected in parallel with the inductor-capacitor low pass filter at a center tap of the center tapped active bridge such that under zero load conditions at the second secondary winding, current through the second secondary winding and the center tapped active bridge is greater than zero to permit the controller to maintain the magnitude of current through the primary winding constant independent of load variation at the first and second secondary windings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified circuit model. 
         FIG. 2  is a circuit schematic for a proposed integrated charger/generator. 
         FIG. 3  is a schematic diagram of switch gate pulse timing. 
         FIG. 4  is a schematic diagram of a controller implementation. 
         FIGS. 5A and 5B  are plots of dual active bridge voltage and current versus time. In  FIG. 5A , power to the high voltage battery is 10 kW and power to the low voltage battery is 2 kW. In  FIG. 5B , power to the high voltage battery is 10 kW and power to the low voltage battery is 0 kW. 
         FIG. 6A  shows connection of a resonant capacitor at the input of an output low pass filter. 
         FIG. 6B  shows a plot of network input impedance magnitude versus frequency. 
         FIGS. 7A and 7B  are coil current, resonant capacitor voltage, and output current plots for low voltage circuitry. In  FIG. 7A , power to the high voltage battery is 10 kW and power to the low voltage battery is 1 kW. In  FIG. 7B , power to the high voltage battery is 10 kW and power to the low voltage battery is 0 kW. 
         FIGS. 8A and 8B  are gate command, voltage, and current plots for metal-oxide semiconductor field-effect transistors of an active bridge of the low voltage circuitry of  FIGS. 7A and 7B . In  FIG. 8A , power to the high voltage battery is 10 kW and power to the low voltage battery is 1 kW. In  FIG. 8B , power to the high voltage battery is 10 kW and power to the low voltage battery is 0 kW. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present disclosure are described herein. However, the disclosed embodiments are merely exemplary and other embodiments may take various and alternative forms that are not explicitly illustrated or described. 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 of ordinary skill in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desired for particular applications or implementations. 
     Introduction 
     New circuit topologies and transformer structures are proposed herein to serve the purpose of regulating power flow among three power sources: an AC source, a high voltage (HV) battery, and a low voltage (LV) battery. Efficient magnetic coupling among these sources is achieved by a current source fed transformer structure with decoupled secondary windings. This circuit enables grid-to-vehicle (G2V) and vehicle-to-grid (V2G) bidirectional power transfer operations while charging the LV (auxiliary) battery. Additionally, in the case when the AC grid is absent, this circuit can be used as an onboard generator for supplying power to AC loads connected to the vehicle. Changing between these modes does not require relays or switching devices to reconfigure the circuit. 
     To illustrate the issue, a simplified equivalent circuit model  10  is created, as shown in  FIG. 1 . A current source  12  models the circuit driving a primary winding  14 , and equivalent impedances model the circuits loading the secondary windings  16 ,  18 . From this circuit, the power delivered to the winding  16 , P 2 , and the winding  18 , P 3 , is expressed by eq. 1 and eq. 2, respectively. 
                     P   2     =             X   12     ⁢     I   1     ⁢     I   2       2     ⁢     cos   ⁡     (       θ   1     -     θ   2     -     π   2       )         +           X   23     ⁢     I   2     ⁢     I   3       2     ⁢     cos   ⁡     (       θ   3     -     θ   2     -     π   2       )                   (   1   )                 P   3     =             X   13     ⁢     I   1     ⁢     I   3       2     ⁢     cos   ⁡     (       θ   1     -     θ   3     -     π   2       )         +           X   23     ⁢     I   2     ⁢     I   3       2     ⁢     cos   ⁡     (       θ   2     -     θ   3     -     π   2       )                   (   2   )               
Where X 11  is the self-reactance of the primary winding  14 , X 22  and X 33  are the self-reactances of the secondary windings  16 ,  18  respectively, R 2  and R 3  are the real components of the equivalent impedances loading the secondary windings  16 ,  18  respectively, X 2  and X 3  are the imaginary components of the equivalent impedances loading the secondary windings  16 ,  18  respectively, X 12 , X 13 , and X 23  are the mutual reactances between the primary and secondary windings  14 ,  16 , the primary and secondary windings  14 ,  18 , and the secondary windings  16 ,  18  respectively, and θ 1 , θ 2 , and θ 3  are the phases of the currents I 1 , I 2 , and I 3  respectively. Thus, power delivered to the winding  16  is dependent on the magnitude and phase of current through the winding  18 . Load variation in the winding  18  will impact the power delivered to the winding  16 . Similarly, load variation in the winding  16  will impact the power delivered to the winding  18 . Due to such inherent coupling between all the windings  14 ,  16 ,  18 , independent power regulation at each of the secondary windings  16 ,  18  is challenging.
 
     As mentioned above, the proposed circuit topology and transformer structure are designed to regulate power flow among three sources: AC source/load, HV battery, and LV battery. The main power transformer is constructed by using two separate cores. Thus, the magnetic flux generated in the first core is decoupled/galvanically isolated from the flux generated in the second core. The transformer primary winding is wound around both cores and connected to a capacitor-inductor-capacitor (CLC) network. A secondary coil is wound around one of the cores and connected to a zero voltage switching (ZVS) resonant buck converter via their center tap point to realize bidirectional power flow from the LV battery. Another secondary winding is wound around the other of the cores and connected to a series inductor-capacitor (LC) network. By using two H-bridge inverters—one at the grid DC bus side and the other at the HV battery side—bidirectional power flow between the AC grid and HV traction battery is realized. 
     Specific Example 
     With reference to  FIG. 2 , an example power system  20  for a vehicle  22  includes a traction battery  24 , an auxiliary battery  26 , and a matrix transformer  28 . The matrix transformer  28  includes two separate cores  30 ,  32 , a primary winding  34  wound around each of the cores  30 ,  32 , a first secondary winding  36  wound around the core  30 , and a second secondary winding  38  (including portions A and B) galvanically isolated from the first secondary winding  36  and wound around the core  32 . The power system  20  also includes circuitry  40  that transfers power from an AC source  41  to the primary winding  34 , circuitry  42  that transfers power from the first secondary winding  36  to the traction battery  24 , and circuitry  43  that transfers power from the second secondary winding  38  to the auxiliary battery  26 . 
     The circuitry  40  includes a bidirectional inverter  44 , a first active bridge  45  having a switching frequency range (e.g., 200 to 400 kHz) and a plurality of switches Q G1 , Q G2 , Q G3 , Q G4 , a DC link capacitor  46  (C ES ) between the bidirectional inverter  44  and first active bridge  45 , and a pair of series connected capacitors  48  (C G1 ),  50  (C G2 ) and an inductor  52  (L G ) center tapping the capacitors  48 ,  50  to form a capacitor-inductor-capacitor (CLC) resonant network  54  electrically connected between the first active bridge  45  and primary winding  34  and tuned to have a resonant frequency defined by the switching frequency range. For example, the CLC resonant frequency could be between 190 and 410 kHz assuming the switching frequency range of the first active bridge  45  is 200 to 400 kHz. The CLC resonant frequency could also be 0.5 to 1.5 times the nominal switching frequency range of the first active bridge  45 , etc. 
     The power system  20  also includes a controller  56  that operates the first active bridge  45  to maintain a magnitude of current through the primary winding  34  constant independent of load variation at the first and second secondary windings  36 ,  38  as discussed more below. The controller further operates the second and third active bridges  60 ,  64  such that a delay time between pulse width modulated gate signals of the second active bridge  60  and pulse width modulated gate signals of the first active bridge  45  is independent of a delay time between pulse width modulated gate signals of the third active bridge  64  and the pulse width modulated gate signals of the first active bridge  45 . 
     The circuitry  42  includes a second active bridge  60  having a plurality of switches Q H1 , Q H2 , Q H3 , Q H4 , a DC output filter capacitor  62  (C F1 ), and matching network circuitry  64  (L H , C H ) that matches an output impedance of the matrix transformer  28  to an input impedance of the second active bridge  60 . 
     The circuitry  43  includes a third active bridge  64  having a plurality of switches Q L1 , Q L2 , a resonant capacitor  66  (C L ), and an inductor-capacitor low pass filter  68  (L F , C F2 ) that matches an output impedance of the third active bridge  64  to an input impedance of the inductor-capacitor low pass filter  68 . The third active bridge  64  in this example is a center tapped active bridge (the center tap is between portions A and B). The resonant capacitor  66  is electrically connected in parallel with the inductor-capacitor low pass filter  68  at a center tap of the center tapped active bridge  64  such that under zero load conditions at the second secondary winding  38 , current through the second secondary winding  38  and the center tapped active bridge  64  is greater than zero to permit the controller  56  to maintain the magnitude of current through the primary winding  34  constant independent of load variation at the first and second secondary windings  36 ,  38 . 
     As discussed more below, the resonant capacitor  62  is tuned to resonate with the inductor-capacitor low pass filter  68  such that a load impedance of the third active bridge  64  is capacitive during operation of the third active bridge  64  within the switching frequency range. 
     General Discussion 
     To decouple the interaction between the secondary coils  36 ,  38  (i.e., coil  2  and coil  3  respectively) of proposed designs, the core is designed such that the mutual reactance between the secondary coils  36 ,  38 , X 23 , is zero. This is achieved by winding coil  2  and coil  3  in the separate cores  30 ,  32  as in the example of  FIG. 2 . Hence, eq. 1 and eq. 2 can be expressed as in eq. 3 and eq. 4. Since the CLC resonant tank  54  maintains a relatively constant current circulation in the primary winding  34 , the current through the primary winding  34 , I 1 , in eq. 3 and eq. 4 is constant. Hence, the power delivered to each of the secondary coils  36 ,  38 , P 2 , P 3  respectively, depends only on the magnitude and phase of the current circulating in them. 
     
       
         
           
             
               
                 
                   
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                     2 
                   
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     Where X 12  and X 13  are the mutual reactances between the primary and secondary windings  34 ,  36  and the primary and secondary windings  34 ,  38  respectively, I 2  and I 3  are the currents through the secondary windings  34 ,  36  respectively, and θ 1 , θ 2 , and θ 3  are the phases of the currents I 1 , I 2 , and I 3  respectively. 
     Power delivered to the secondary coils  36 ,  38  is regulated by controlling the reactance mismatch between the secondary winding self-reactance and its load reactance. The phase difference between the primary coil current and coil  2  and coil  3  currents is described by eq. 5 and eq. 6. By controlling ΔX_ 2  and ΔX_ 3 , the current in coil  2  and coil  3  is altered and effectively the power delivered to them is controlled. 
     
       
         
           
             
               
                 
                   
                     
                       
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     A relatively constant current source drives the transformer primary winding  34 . The CLC network  54  creates a resonant tank where the current magnitude in the primary winding is less sensitive to the variation in power delivered/received to either the HV battery  24  or LV battery  26 . Additionally, the series LC network  64  is used to match the reactance of the secondary winding  36  connected to the HV battery  24 . Furthermore, the reactance of the winding  38  connected to the LV battery  26  is matched by the parallel resonant capacitor  66  connected between the LV switches  64  and output low pass filter  68 . 
     Power regulation is realized by controlling the voltage phase angle between the inverter output voltages and each of the active rectifiers input voltages.  FIG. 3  shows the pulse width modulated (PWM) gate signal provided to all switches. The grid-side H-bridge  45  is driven with a fixed frequency pulses such that its output voltage is a square wave. Pulses provided to the battery side H-bridge  60  is delayed from the grid-side H-bridge pulses by a time T d1 . This time is controlled to regulate the power delivered to the HV battery  24 . Similarly, pulses provided to the resonant buck converter  64  are delayed form the grid-side H-bridge pulse by a time T d2 . This time is controlled to regulate the power delivered to the LV battery  26 . The circuit is designed such that the HV battery  24  is independently controlled by T d1  and the LV battery  26  is independently controlled by T d2 . Thus, T d1  and T d2  are independent of each other. 
     Power delivered to the batteries  24 ,  26  is regulated by either controlling the charger current magnitude or battery voltage.  FIG. 4  shows the block diagram for one possible controller implementation. Compensation networks  72 ,  74 ,  76 ,  78  are used to minimize the error between the reference and the measured feedback signals. Switches  80   82  are used to switch between current control mode and voltage control mode. PWM modulators  84 ,  86  receive output from the switches  80 ,  82  respectively. And the PWM modulators  84 ,  86  provide PWM commands to integrated on board charger/generator  88  accordingly. In the case of HV battery control, the compensation networks  72 ,  74  and switch  80  output reference singles to set the required delay time T d1 . Similar controller architecture is realized for the LV battery controller, in which case the compensation networks  76 ,  78  and switch  82  set the delay time T d2 . In the case when power is reversed and the HV battery  24  is the source, current and voltage of the DC-link bus are controlled with a controller architecture similar to what is shown in  FIG. 4 . 
     Salient waveforms are provided. Bidirectional power flow between the AC grid  41  and HV battery  24  is realized by controlling the time delay T d , between the PWM signals provided to the dual active bridges (DABs)  45 ,  60 .  FIG. 5  shows the AC port characteristics of the DABs  45 ,  60  for the case when power delivered to the LV battery  26  is 2 kW and OW. This time delay is unaffected by the power delivered to the LV battery  26 . The CLC resonant network  54  and flux path decoupling approach are effective in decoupling the load dynamics between the HV battery  24  and LV battery  26  when the AC grid  41  is the source. Hence, independent control of the power delivered to both of the batteries  24 ,  26  is achieved. 
     The LV resonant buck converter  64  is designed to realize bidirectional power flow between the AC source  41 , or the HV battery  24  and LV battery  26 . In order to reduce the reactive power circulation in the LV coil  38 , the resonant capacitor  66  is added to match the LV coil reactance to the output filter reactance.  FIGS. 6A and 6B  show the input impedance of the output filter  68 . By adding the resonant capacitor  66 , the impedance loading the LV coil  38  appears to be capacitive at the switching frequency. The resonant capacitor  38  is optimized to minimize reactive power circulation in the LV coil  38 , thus improving the efficiency of the integrated charger. 
     In order to illustrate the operation of the resonant buck converter  64 ,  FIGS. 7A and 7B  are provided to show the current in the LV coil  38 , and the voltage across the resonant capacitor  66  for the case when power delivered to the LV battery  26  is 1 kW and 0 kW. Controlling the delay time between the PWM signal provided to the LV switches  64  and grid switches  45 , the LV battery power is controlled independently from the HV battery  24 . The resonant capacitor voltage is allowed to resonant with the LV coil current. Thus, its voltage contains a large AC component.  FIGS. 8A and 8B  are provided to show that by adding the resonant capacitor  66 , the switch current is maintained low. When no power is delivered to the LV battery  26 , the LV switches  64  conduct forward current to increase the reactance mismatch between the LV coil  38  and its load reactance. 
     The processes, methods, or algorithms disclosed herein may be deliverable to or implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms may be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The processes, methods, or algorithms may also be implemented in a software executable object. 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 a combination of hardware, software and firmware components. 
     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 disclosure and claims. As previously described, the features of various embodiments may be combined to form further embodiments that may not be explicitly described or illustrated. While various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.