Method to operate a bidirectional two-stacked phase shifted DC-to-DC converter in pre-charge mode

Abstract

A method of operating a bidirectional DC-to-DC converter is presented. The method includes pre-charging two high voltage capacitors so that a voltage across each of the high voltage capacitors is balanced. Each high voltage capacitor is coupled to an input of one of the two stacked phase shift full bridge converters of the DC-to-DC converter. The pre-charging is performed by closing, by a controller coupled to the DC- to-DC converter, a first bypass static switch, and a second bypass static switch, and operating, by the controller, the full bridge converters at the same time by performing a switching sequence. The bidirectional DC-to-DC converter includes a primary and secondary side connected by at least one transformer. The DC-to-DC converter includes two stack phase shift full bridge converters on the primary side, each one connected to a respective transformer each of which connects to, on the secondary side, a full bridge converter.

Description

METHOD TO OPERATE A BIDIRECTIONAL TWO-STACKED PHASE SHIFTEDDC-TO-DC CONVERTER IN PRE-CHARGE MODECROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of Indian Provisional Application No. 202311063191 filed September 20, 2023.BACKGROUND

[0001] DC-to-DC converters are used in automotive applications to supply systems of different voltage levels throughout a vehicle. A common automotive application is to enable DC power from a high voltage battery to be used to supply lower DC voltages that power components such as headlights, interior lights, motorized windows, etc.

[0002] For example, a DC-to-DC converter is used in electric or hybrid vehicles, where a high voltage (HV) network having capacitors and a battery of several hundred volts (e.g., 400V or 800V) is used to provide energy to the electric motor, and a low voltage (LV) network having a battery (e.g., 14 V or 28 V) is used to supply the control and comfort equipment of the vehicle. Such a DC-to-DC converter is typically inserted between the two HV and LV batteries with galvanic isolation for safety reasons and is used to transform and transfer the energy from the HV battery to the LV battery when the vehicle is running.

[0003] Bidirectional circuit systems enable a bidirectional current flow between an input and output of the circuit system so that energy can be pulled back into the HV battery. A bidirectional DC-to-DC converter can operate in two modes: a buck, or forward, mode, and a boost, or reverse, mode. In buck mode, the energy is transferred from the high voltage side, e.g., high voltage battery, to the low voltage side, e.g., the low voltage battery. In boost mode, the low voltage battery becomes a source to precharge a high voltage capacitor. Thus, boost mode can also be referred to as a pre-charge mode.

[0004] The phase shifted full bridge converter can be used in a DC-to-DC converter to convert a high voltage to an intermediate distribution voltage. However, phase shift full bridge converters are not a popular choice for bidirectional operation because they are not symmetrical on the primary and secondary sides causing voltage overshoot across the primary side transformer which may damage the magnetic devices of the circuitry.BRIEF SUMMARY

[0005] A bidirectional DC-to-DC converter and a method to operate the bidirectional DC-to-DC converter in a pre-charge mode are presented. Through certain implementations of the described circuitry and methods, the bidirectional DC-to-DC converter can operate with a high voltage input of up to 1000V DC. In the pre-charge mode, the bidirectional DC-to-DC converter can fully charge a DC high voltage capacitor at the input of the bidirectional DC-to-DC converter from a 14 V DC or a 28 V DC low voltage battery.

[0006] A bidirectional DC-to-DC converter includes a primary side, the primary side including two stacked phase shift full bridge converters, a first phase shift full bridge converter and a second phase shift full bridge converter. The first phase shift full bridge converter and the second phase shift full bridge converter are connected in series. The first phase shift full bridge converter is coupled to a first transformer and the second phase shift full bridge converter is coupled to a second transformer. The bidirectional DC-to-DC converter further includes a secondary side including two connected full bridge converters, a first full bridge converter and a second full bridge converter. The first full bridge converter is coupled at its input to the first transformer and includes a first inductor and the second full bridge converter is coupled at its input to the second transformer and includes a second inductor. The bidirectional DC-to-DC converter further includes a first bypass static switch positioned in parallel to the first inductor and a second bypass static switch positioned in parallel to the second inductor.

[0007] A method of operating the bidirectional DC-to-DC converter, as described above, in a pre-charge mode includes pre-charging two high voltage capacitors so that a voltage across each of the high voltage capacitors is balanced. Each high voltage capacitor is coupled to an input of one of the two stacked phase shift full bridge converters of the DC-to-DC converter. The pre-charging is performed by closing, by a controller coupled to the DC-to-DC converter, the first bypass static switch, closing, by the controller, the second bypass static switch, and operating, by the controller, the full bridge converters at the same time by performing a switching sequence.

[0008] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0009] FIG. 1 illustrates a schematic diagram of a first example implementation of a bidirectional DC-to-DC converter.

[0010] FIG. 2 illustrates a schematic diagram of two back-to-back switches.

[0011] FIG. 3 illustrates a schematic diagram of the bidirectional DC-to-DC converter of FIG. 1 operated by a first switching step.

[0012] FIG. 4 illustrates a schematic diagram of the bidirectional DC-to-DC converter of FIG. 1 operated by a second switching step.

[0013] FIG. 5 illustrates a schematic diagram of the bidirectional DC-to-DC converter of FIG. 1 operated by a third switching step.

[0014] FIG. 6 illustrates a schematic diagram of the bidirectional DC-to-DC converter of FIG. 1 operated by a fourth switching step.

[0015] FIG. 7 illustrates a schematic diagram of a second example implementation of a bidirectional DC-to-DC converter.DETAILED DESCRIPTION

[0016] A bidirectional DC-to-DC converter and a method to operate the bidirectional DC-to-DC converter in a pre-charge mode are presented. Through certain implementations of the described circuitry and methods, the bidirectional DC-to-DC converter can operate with a high voltage input of up to 1000V DC. In the pre-charge mode, the bidirectional DC-to-DC converter can fully charge a DC high voltage capacitor at the input of the DC-to-DC converter from a 14 V DC or a 28 V DC low voltage battery. As an example, utilizing one embodiment of the bidirectional DC-to- DC converter, a DC high voltage capacitor of 5000 pF connected at the input to the bidirectional DC-to-DC converter can be fully charged within 2-3 sec from a 28 V DC low voltage battery in a pre-charge mode.

[0017] FIG. 1 illustrates a schematic diagram of a first example implementation of a bidirectional DC-to-DC converter. The bidirectional DC-to-DC converter includes a primary side and a secondary side connected by one or more transformers. The DC-to- DC converter includes two stack phase shift full bridge converters on the primary side, each one connected to a respective transformer each of which connect to, on the secondary side, a respective full bridge converter.

[0018] Referring now to FIG. 1, on its primary side, the DC-to-DC converter 100 includes two stacked phase shift full bridge converters, a first phase shift full bridgeconverter 102 and a second phase shift full bridge converter 104, connected in series. A high voltage battery (not shown) and a DC high voltage capacitor 106 (Cl) can be connected to the input of the stacked phase shift full bridge converters.

[0019] Each of the two stacked phase shift full bridge converters, e.g., the first phase shift full bridge converter 102 and the second phase shift full bridge converter 104, is connected at its input to a corresponding capacitor, high side stack one capacitor 108 (C2) and high side stack two capacitor 110 (C3), respectively. In operation, the voltage from the high voltage battery will be divided by two such that half of the voltage will be input (e.g., a voltage across each of the high side stack one capacitor 108 and high side stack two capacitor 110) to each of the stacked phase shift full bridge converters. For example, if the high voltage battery has a voltage of 800V DC, each of the first phase shift full bridge converter 102 and the second phase shift full bridge converter 104 will have 400 V DC at its input.

[0020] A controller 112 can be integrated with the DC-to-DC converter 100 or be a separate component from the DC-to-DC converter 100. Controller 112 can be implemented using one or more processors (executing suitable software instructions), state machines, and / or logic circuits.

[0021] The first phase shift full bridge converter 102 includes primary-side switches (individually labeled as QI, Q2, Q3, and Q4) controlled by controller 112. The second phase shift full bridge converter 104 includes primary-side switches (individually labeled as Q5, Q6, Q7, and Q8) controlled by controller 112. The first phase shift full bridge converter 102 is connected to the first transformer 114 at its output. The second phase shift full bridge converter 104 is connected at its output to second transformer 116. The primary-side switches (QI, Q2, Q3, Q4, Q5, Q6, Q7, and Q8) can be MOSFET devices suitable to operate at 650 V DC.

[0022] The secondary side of the DC-to-DC converter 100 is coupled via a respective transformer, first transformer 114 and second transformer 116, to the primary side. On its secondary side, the DC-to-DC converter 100 includes two full bridge converters, a first full bridge converter 118 and a second full bridge converter 120, connected to one another. In some cases, the first full bridge converter 118 can be connected to the second full bridge converter 120 in parallel (as shown in FIG. 1). With the first full bridge converter 118 and the second full bridge converter 120 connected in parallel, the low voltage battery 122 of 14 V DC can fully charge the high side stack one capacitor 108 and the high side stack two capacitor 110. In other cases, the firstfull bridge converter 118 can be connected to the second full bridge converter 120 in series (as shown in FIG. 7).

[0023] The first full bridge converter 118 is connected to the first phase shift full bridge converter 102 via first transformer 114. The second full bridge converter 120 is connected to the second phase shift full bridge converter 104 via second transformer 116. The first full bridge converter 118 includes secondary-side switches Qsl, Qs2, Qs3, and Qs4 controlled by controller 112. In addition, the first full bridge converter 118 includes a first inductor 124 (LI) connected to the secondary-side switches Qsl, Qs2, Qs3, and Qs4. The second full bridge converter 120 includes secondary-side switches Qs5, Qs6, Qs7, and Qs8 controlled by controller 112. In addition, the second full bridge converter 120 includes a second inductor 126 (L4) connected to the secondary-side switches, Qs5, Qs6, Qs7, and Qs8. The secondary-side switches are semiconductor switches that can be MOSFET devices.

[0024] The secondary side of the DC-to-DC converter 100 can be connected to a low voltage battery 122. The low voltage battery 122 can be utilized to pre-charge the high side stack one capacitor 108 (C2) and high side stack two capacitor 110 (C3) in a pre-charge, or boost, mode. The high side stack one capacitor 108 and the high side stack two capacitor 110 can be pre-charged through the operation of controller 112 which operates the primary-side switches of the first phase shift full bridge converter 102 and the second phase shift full bridge converter 104 (QI, Q2, Q3, Q4, Q5, Q6, Q7, and Q8) and the secondary-side switches of the first full bridge converter 118 and the second full bridge converter 120 (Qsl, Qs2, Qs3, Qs4, Qs5, Qs6, Qs7, and Qs8). Through operations of the controller 112, the high side stack one capacitor 108 and the high side stack two capacitor 110 can be pre-charged according to the proposed method.

[0025] Each of the first full bridge converters, e.g., first full bridge converter 118 and second full bridge converter 120, include a respective inductor, e.g., first inductor 124 (LI) and second inductor 126 (L4). However, when operating with such a high level of voltage, e.g., up to 1000V DC on the high voltage battery in pre-charge mode, the semiconductor devices, e.g., MOSFET devices, of the phase shift full bridge converters 102, 104 and the full bridge converters 118, 120 cannot withstand a high voltage overshoot caused by the inductors. Thus, bypass static switches, first bypass static switch 128 (SI) and second bypass static switch 130 (S2), are respectively positioned in parallel to each of the first inductor 124 (LI) and the second inductor 126 (L4) in order to bypass the inductors in pre-charge mode. The controller 112 controls theclosing of the bypass static switches 128, 130 (SI, S2) for the pre-charge mode and opening the bypass static switches 128, 130 (SI, S2) when transitioning back to buck mode.

[0026] In some cases, each bypass static switch 128, 130 (SI, S2) can be configured as a power contactor. In another case, each bypass static switch 128, 130 (SI, S2) can be configured as back-to-back power switches. FIG. 2 illustrates a schematic diagram of two back-to-back power switches, first power switch 202 and second power switch 204. The diodes of each of the back-to-back power switches are positioned in opposite directions. The back-to-back power switches operate so that when each switch is OFF, the respective bypass static switch operates as an open contact and when each switch is ON the respective bypass static switch operates as closed contact.

[0027] Operating the DC-to-DC converter 100 in buck mode, the DC-to-DC converter 100 can operate to deliver 14V or 28V, across the low voltage battery 122 from an input voltage range (e.g., from the high voltage battery) of up to 1000V DC across the DC high voltage capacitor 106 (Cl). The DC-to-DC converter 100 also operates in pre-charge mode, or boost mode, the pre-charge mode describing a mode where the energy is transferred from the low voltage battery 122 to the high voltage side to fully charge DC high voltage capacitor 106 (Cl).

[0028] In pre-charge mode, it is desired to charge high voltage capacitors, high side stack one capacitor 108 (C2) and high side stack two capacitor 110 (C3), so that the voltage across each of the high voltage capacitors 108, 110 (C2, C3) is balanced between the two. Thus, the proposed method pre-charges the high side stack one capacitor 108 (C2) and the high side stack two capacitor 110 (C3) so that a voltage across each of these high voltage capacitors is balanced. In order to distribute the voltage evenly between the high side stack one capacitor 108 (C2) and the high side stack two capacitor 110 (C3), the controller 112 operates the full bridge converters, e.g., the first full bridge converter 118 and the second full bridge converter 120, at the same time by performing a switching sequence. The method can be performed to pre-charge the high voltage capacitors 108, 110 (C2, C3) within a predefined time period, for example, within 2-3 seconds.

[0029] Through the operation of the controller 112, both the high side stack one capacitor 108 (C2) and the high side stack two capacitor 110 (C3) can be charged so that the voltage across each of the first phase shift full bridge converter 102 and second phase shift full bridge converter 104 is balanced. In addition, through the operation ofthe controller 112, the DC high voltage capacitor 106 (Cl) is charged to the full input voltage. The bypass static switches 128, 130 (SI, S2) are closed prior to commencement of the pre-charge operation. Thus, in order to commence the pre-charge operation, the controller 112 closes the first bypass static switch 128 (SI) and second bypass static switch 130 (S2). Example operations of controller 112 in performing the switching sequence are shown and described with respect to FIG. 3, FIG. 4, FIG. 5, and FIG. 6.

[0030] FIG. 3 illustrates a schematic diagram of the bidirectional DC-to-DC converter of FIG. 1 operated by a first switching step. Controller 112 performs the first switching step 300 by tuming-ON primary-side switches Q2, and Q6, and tuming-ON the secondary-side switches Qsl, Qs4, Qs5, and Qs6. Referring to FIG. 3, after the controller 112 performs the first switching step 300, a current flow from the secondary side to the primary side of the DC-to-DC converter 100 is illustrated by the arrows. It can be seen that with the first bypass static switch 128 (SI) and the second bypass static switch 130 (S2) closed, the current flow bypasses the first inductor 124 (LI) and the second inductor 126 (L4). Power circulates between the MOSFET of Q2 and the diode of Q4 and between the MOSFET of Q6 and the diode of Q8 (e.g., Q2 and Q6 are tuming- ON). A third inductor 328 (LR2) of the first phase shift full bridge converter 102 and a fourth inductor 326 (LR3) of the second phase shift full bridge converter 104 store energy.

[0031] FIG. 4 illustrates a schematic diagram of the bidirectional DC-to-DC converter of FIG. 1 operated by a second switching step. Controller 112 performs the second switching step 400 by tuming-ON the secondary-side switches Qsl and Qs6. Referring to FIG. 4, after the controller 112 performs the second switching step 400, a current flow from the secondary side of DC-to-DC converter 100 to the primary side of the DC-to-DC converter is illustrated by the arrows. The primary-side switches (QI, Q2, Q3, Q4, Q5, Q6, Q7, and Q8) are in the freewheeling state, i.e., there is no active switching for the primary-side switches and no energy is transferred from the secondary side to the primary side. It can be seen that with the first bypass static switch 128 (SI) and the second bypass static switch 130 (S2) remaining closed, the current remains in the same direction on the primary side. The third inductor's 328 (LR2) stored energy from the first switching step 300 now gets transferred to the high side stack one capacitor 108 through the diodes of QI and Q4 so that it gets charged. Likewise, the fourth inductor's 326 (LR2) stored energy from the first switching step 300 now getstransferred to the high side stack two capacitor 110 through the diodes of Q5 and Q8 so that it gets charged.

[0032] FIG. 5 illustrates a schematic diagram of the bidirectional DC-to-DC converter of FIG. 1 operated by a third switching step. Controller 112 performs the third switching step 500 by tuming-ON the primary-side switches QI, and Q5, and turning - ON the secondary-side switches Qs2, Qs3, Qs7 and Qs8. Referring to FIG. 5, after the controller 112 performs the third switching step 500, a current flow from the secondary side to the primary side of the DC-to-DC converter is illustrated by the arrows. It can be seen that with the first bypass static switch 128 (SI) and the second bypass static switch 130 (S2) remaining closed, the current flow bypasses the first inductor 124 (LI) and the second inductor 126 (L4). Power circulates between the MOSFET of QI and the diode of Q3 and between the MOSFET Q5 and the diode of Q7 (e.g., QI and Q5 are tuming-ON). The third inductor 328 (LR2) of the first phase shift full bridge converter 102 and the fourth inductor 326 (LR3) of the second phase shift full bridge converter 104 store energy.

[0033] FIG. 6 illustrates a schematic diagram of the bidirectional DC-to-DC converter of FIG. 1 operated by a fourth switching step. Controller 112 performs the fourth switching step 600 by tuming-ON the secondary-side switches Qs2 and Qs8. Referring to FIG. 6, after the controller 112 performs the fourth switching step, a current flow from the secondary side of DC-to-DC converter 100 to the primary side of the DC-to-DC converter is illustrated by the arrows. The primary-side switches (QI, Q2, Q3, Q4, Q5, Q6, Q7, and Q8) are in the freewheeling state, i.e., there is no active switching of the primary-side switches, and no energy is transferred from the secondary side to the primary side. It can be seen that with the first bypass static switch 128 (SI) and the second bypass static switch 130 (S2) remaining closed, the current remains in the same direction on the primary side. Power flows between Q3 diode, the high side stack one capacitor 108 (C2), and Q2 diode. Likewise, power flows between the Q7 diode, the high side stack two capacitor 110 (C3), and the Q6 diode.

[0034] FIG. 7 illustrates a schematic diagram of a second example implementation of a bidirectional DC-to-DC converter. As stated previously, the first full bridge converter 118 and second full bridge converter 120 can be connected in a series configuration as well as the parallel configuration shown in FIG. 1. The series configuration of the first full bridge converter 118 and the second full bridge converter 120 is illustrated in FIG. 7. With the first full bridge converter 118 and the second fullbridge converter 120 connected in series, the low voltage battery 122 of 28 V DC can fully charge the high side stack one capacitor 108 (C2) and the high side stack two capacitor 110 (C3). Having the first full bridge converter 118 and the second full bridge converter 120 able to be connected in either parallel or series allows the same circuitry to deliver two different low voltage power options, e.g., 14 V DC or 28 V DC, respectively.

[0035] Although the subject matter has been described in language specific to structural features and / or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts that would be recognized by one skilled in the art are intended to be within the scope of the claims.

Claims

CLAIMSWhat is claimed is:

1. A bidirectional DC-to-DC converter, comprising: a primary side comprising two stacked phase shift full bridge converters, a first phase shift full bridge converter and a second phase shift full bridge converter, connected in series wherein the first phase shift full bridge converter is coupled to a first transformer and the second phase shift full bridge converter is coupled to a second transformer; a secondary side comprising two connected full bridge converters, a first full bridge converter and a second full bridge converter, the first full bridge converter is coupled at its input to the first transformer and includes a first inductor and the second full bridge converter is coupled at its input to the second transformer and includes a second inductor; and a first bypass static switch positioned in parallel to the first inductor and a second bypass static switch positioned in parallel to the second inductor.

2. The bidirectional DC-to-DC converter of claim 1, further comprising a controller that operates primary-side switches of the two stacked phase shift full bridge converters and secondary-side switches of the two connected full bridge converters according to a switching sequence in a pre-charge mode.

3. The bidirectional DC-to-DC converter of claim 1, wherein each of the first bypass static switch and the second bypass static switch comprise two back-to-back power switches.

4. The bidirectional DC-to-DC converter of claim 1, wherein each of the first bypass static switch and the second bypass static switch comprise a power contactor.

5. The bidirectional DC-to-DC converter of claim 2, wherein the two stacked phase shift full bridge converters include the primary-side switches QI, Q2, Q3, Q4, Q5, Q6, Q7, and Q8.

6. The bidirectional DC-to-DC converter of claim 5, wherein the primary-side switches are MOSFET devices.

7. The bidirectional DC-to-DC converter of claim 2, wherein the two connected full bridge converters include secondary-side switches Qsl, Qs2, Qs3, Qs4, Qs5, Qs6, Qs7, and Qs8.

8. The bidirectional DC-to-DC converter of claim 1, wherein the first full bridge converter and the second full bridge converter are connected in parallel and coupled to a low voltage battery to deliver 14 V DC in a pre-charge mode.

9. The bidirectional DC-to-DC converter of claim 1, wherein the first full bridge converter and the second full bridge converter are connected in series and coupled to a low voltage battery to deliver 28 V DC in a pre-charge mode.

10. A method of operating the bidirectional DC-to-DC converter of claim 1 in a pre-charge mode, the method comprising: pre-charging two high voltage capacitors so that a voltage across each of the two high voltage capacitors is balanced, wherein each high voltage capacitor is coupled to an input of one of the two stacked phase shift full bridge converters of the DC-to-DC converter, the pre-charging performed by: closing, by a controller coupled to the bidirectional DC-to-DC converter, the first bypass static switch; closing, by the controller, the second bypass static switch; and operating, by the controller, the two connected full bridge converters at a same time by performing a switching sequence.

11. The method of claim 10, wherein the first phase shift full bridge converter includes primary-side switches QI, Q2, Q3, and Q4, wherein the second phase shift full bridge converter includes primary-side switches Q5, Q6, Q7, and Q8, wherein the first full bridge converter includes secondary-side switches Qsl, Qs2, Qs3, and Qs4, and wherein the second full bridge converter includes secondary-side switches Qs5, Qs6, Qs7, and Qs8.

12. The method of claim 11, wherein performing the switching sequence comprises performing first switching step, performing a second switching step, performing a third switching step, and a performing a fourth switching step.

13. The method of claim 12, wherein performing the first switching step comprises: tuming-ON the primary-side switches Q2 and Q6; and tuming-ON the secondary-side switches Qsl, Qs4, Qs5 and Qs6.

14. The method of claim 12, wherein performing the second switching step comprises: tuming-ON the secondary-side switches Qsl and Qs6.

15. The method of claim 12, wherein performing the third switching step comprises: tuming-ON the primary-side switches QI and Q5 on the primary side; and tuming-ON the secondary-side switches Qs3, Qs2, Qs7, and Qs8 on the secondary side.

16. The method of claim 12, wherein performing the fourth switching step comprises: tuming-ON the secondary-side switches Qs2 and Qs8.

17. The method of claim 10, wherein the method is performed within a predefined period of time.

18. The method of claim 17, wherein the predefined period of time is 2-3 sec.

19. The method of claim 10, wherein each of the first bypass static switch and the second bypass static switch comprise two back-to-back power switches.

20. The method of claim 10, wherein each of the first bypass static switch and the second bypass static switch comprise a power contactor.

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