Interleaved DC-DC Converter for Electrified Vehicles

Abstract

The present disclosure provides "an interleaved DC-DC converter for an electrified vehicle". A DC-DC voltage converter for an electric vehicle is connected between a battery pack and a DC link having an upper link capacitor and a lower link capacitor. When a target voltage on the link is less than twice the battery voltage, the capacitors are charged in series from two interleaved switch legs of the converter simultaneously for a portion of time and are charged in series from only one of the switch legs for a portion of time. When the target voltage is between 2 times and 4 times the battery voltage, the upper capacitor is charged separately from the two legs for a portion of time, is charged separately from only one of the legs for a portion of time, the lower capacitor is charged separately from the two legs for a portion of time, and is charged separately from only one of the legs for a portion of time.

Description

Technical Field

[0001] The present invention generally relates to a direct current to direct current (DC-DC) converter in an electric drive system for an electrified vehicle, and more particularly to a interleaved converter for providing reduced current ripple and increased current capability within an increased voltage gain range. Background Art

[0002] Electric vehicles, such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs), use inverter-driven motors to provide traction torque. A typical electric drive system may include a direct current (DC) power source (such as a battery pack or a fuel cell) coupled to a DC-DC converter (also referred to as a variable voltage converter or VVC) through a contactor switch to regulate the main bus voltage across a main DC link capacitor. A three-phase motor inverter is connected between the main bus and the traction motor to convert the DC bus power into an alternating current (AC) voltage, which is coupled to the windings of the motor to propel the vehicle. During vehicle deceleration, the motor can be driven by the vehicle wheels and used to deliver electrical power to charge the battery during regenerative braking of the vehicle, where the DC-DC converter operates in the opposite direction to convert the generated power into a voltage suitable for charging the battery pack. In some vehicles, there may also be another three-phase inverter to connect the DC bus to a generator, which is driven by an internal combustion engine to charge the battery.

[0003] Using appropriate power switch modulation, the VVC can operate in a boost mode (converting to a higher voltage), a buck mode (converting to a lower voltage), or a through mode (no change in voltage). For use in a hybrid electric vehicle drive system, the VVC is also configured to selectively provide bidirectional power flow.

[0004] A typical VVC includes at least one phase bridge having an upper transistor switching device and a lower transistor switching device (e.g., insulated gate bipolar transistor, IGBT) connected in series across the DC link capacitor. The intermediate junction between the switching devices is connected to the source battery via an inductor. An electronic controller provides switching signals (i.e., gate signals) to turn on and off the switching devices according to a modulation scheme that provides the desired VVC mode. Pulse width modulation is typically used to control the stepwise increase in voltage of the VVC, where the duty cycle of the switching signal can be changed to regulate the VVC voltage to a desired amplitude.

[0005] High-power / high-current DC-DC converters typically employ interleaved multiphase inputs (i.e., two or more parallel phase bridges) in the converter to obtain a rated current higher than the current capacity of only one phase bridge. Additionally, interleaved DC-DC converters greatly reduce battery current ripple. The inductors connecting each phase bridge of the interleaved DC-DC converter to the battery pack can be independent inductors, or they can be inductively coupled.

[0006] Even with a multiphase architecture, there are still voltage gain limitations. The gain is determined by the duty cycle D defined as T 接通 / T s where T 接通 is the conduction duration of the lower switching device and T s is the switching period. Based on the duty cycle, the voltage gain G is determined by the formula . When the voltage gain G is greater than two, the converter efficiency drops sharply as the duty cycle D increases. Thus, the voltage gain of conventional DC-DC converters is typically limited to less than three. In wide speed range operation, a higher voltage gain is desired to reduce motor inverter losses. Additionally, operating the DC-DC converter at a higher duty cycle most of the time results in higher power losses and high voltage stress within the phase bridge switching devices. Therefore, an improved DC-DC converter is needed that can provide a higher voltage gain at a reduced duty cycle.

[0007] Another potential drawback of conventional interleaved converters is that when the duty cycle D is high, high current ripple in the inductors generates greater power losses. Large inductors are needed to limit the current ripple, but they are lossy, bulky, and heavy, which is undesirable for high-power HEV applications. SUMMARY OF THE INVENTION

[0008] In one aspect of the present invention, a variable voltage converter in an electric drive system includes: a parallel switch branch having a respective upper switch device and a lower switch device connected in series between a positive node and a negative node, and each having a respective intermediate junction inductively coupled to a battery by a respective inductor. An upper link capacitor and a lower link capacitor are connected in series between a positive bus and a negative bus of the drive system. A configurable coupler has: a first switch device that selectively couples the positive node to the positive bus; a second switch device that selectively couples the positive node to a capacitor junction between the link capacitors; a third switch device that selectively couples the negative node to the capacitor junction; and a fourth switch device that selectively couples the negative node to the negative bus. A controller is configured to drive the upper switch device and the lower switch device according to a PWM gate signal having a duty cycle adapted to provide a target voltage between the buses, and the controller is configured to actuate the first switch device to the fourth switch device to selectively divert current from the switch branch to charge the link capacitors in series to provide a first voltage gain, and to charge the link capacitors individually to provide a second voltage gain greater than the first voltage gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic block diagram showing a conventional interleaved DC-DC converter with independent inductors in an electric drive device of a hybrid electric vehicle.

[0010] FIG. 2 is a schematic block diagram showing a conventional interleaved DC-DC converter with coupled inductors in an electric drive device of a hybrid electric vehicle.

[0011] Figure 3 is a graph showing typical useful voltage gains using a conventional interleaved converter.

[0012] Figure 4 is a schematic block diagram showing an interleaved DC-DC converter with independent inductors according to an embodiment of the present invention.

[0013] Figure 5 is a schematic block diagram showing an interleaved DC-DC converter with coupled inductors according to an embodiment of the present invention.

[0014] Figure 6 is a graph showing voltage gains of various modulation modes implemented according to various embodiments of the present invention.

[0015] Figure 7is a signal diagram showing the phase-bridge PWM signal and the coupler steering signal for modulation mode I-A of the present invention.

[0016] Figure 8 and Figure 9 is a schematic diagram of the present invention, which shows the current flow during different parts of the switching cycle according to modulation mode I-A.

[0017] Figure 10 is a signal diagram showing the phase-bridge PWM signal and the coupler steering signal for modulation mode I-B of the present invention.

[0018] Figure 11 and Figure 12 is a schematic diagram of the present invention, which shows the current flow during different parts of the switching cycle according to modulation mode I-B.

[0019] Figure 13 is a signal diagram showing the phase-bridge PWM signal and the coupler steering signal for modulation mode II of the present invention.

[0020] Figures 14 to 17 is a schematic diagram of the present invention, which shows the current flow during different parts of the switching cycle according to modulation mode II.

[0021] Figure 18 is a signal diagram showing the phase-bridge PWM signal and the coupler steering signal for modulation mode III of the present invention.

[0022] Figure 19 and Figure 20 is a schematic diagram of the present invention, which shows the current flow during different parts of the switching cycle according to modulation mode III.

[0023] Figure 21 is a graph showing the battery current ripple during operation in mode III to obtain a high voltage gain.

[0024] Figure 22 is a graph showing Figure 21 the current ripple in the inductor consistent with the operation in.

[0025] Figure 23 is a graph showing Figure 21 the battery voltage consistent with.

[0026] Figure 24 is a graph showing Figure 21 the DC link voltage consistent with.

[0027] Figure 25 is a graph showing Figure 21 the voltage across each of the DC link capacitors consistent with. Detailed Implementation Manner

[0028] Referring to FIG. 1, a DC-DC variable voltage converter (VVC) 10 is coupled between a DC power supply 11 (such as a battery pack or a fuel cell) and a DC link capacitor 12. A positive bus 14 and a negative bus 15 couple the capacitor 12 to a motor / generator inverter system 13. The VVC 10 has interleaved phase bridges, including a first phase bridge having an upper switching device S n1 connected in series between the buses 14 and 15 with a lower switching device S p1 . A first inductor 16 couples the junction between the switching devices S p1 and S n1 to the battery 11. A second phase bridge has an upper switching device S n2 connected in series between the buses 14 and 15 with a lower switching device S p2 . A second inductor 17 couples the junction between the switching devices S p2 and S n2 to the battery 11.

[0029] The VVC 10 can operate in a boost mode or a buck mode, where power can flow in either direction. The switching devices S p1 、S n1 、S p2 and S n2 work in an interleaved manner with the inductors 16 and 17 (having inductances L1 and L2), whereby each inductor and the corresponding phase bridge support half of the battery current (in the boost mode). Compared with the phase bridge switching signals of S p2 and S n2 , the phase bridge switching signals of S p1 and S n1 (which are in antiphase with each other) have a 180° phase shift, which achieves interleaved operation to significantly reduce the battery current ripple. Therefore, the currents i L1 and i l2 flowing through the inductors 16 and 17 have the same amplitude but have a 180° phase shift.

[0030] In FIG. 1, the inductors 16 and 17 work independently without any cross-coupling. In FIG. 2, the inductive coupling coils of the transformer 18 provide inductance for each phase bridge. By feeding the inductance of the phase bridge through inductive coupling, a smaller overall size of the inductor can be obtained.

[0031] Each of the switching devices in the VVC 10 preferably includes an insulated gate bipolar transistor (IGBT). Each IGBT has a corresponding control (e.g., base) terminal coupled to a controller (not shown), and the controller controls the switches according to various operating modes of the converter. The controller may include a motor-generator control unit (MGCU), which is of a commercially available type and as described in U.S. Patent 9,106,162 issued on August 11, 2015, which is incorporated herein by reference in its entirety.

[0032] To obtain the required voltage gain from the VVC 10, the well-known pulse width modulation (PWM) method is typically used to generate the gate signals for the IGBT switching devices. The voltage gain G (e.g., from the battery voltage V b to the DC link voltage V dc ) is defined as where the duty cycle D is the percentage of the on-time of the lower switching device of the phase bridge. As Figure 3 shown, when the duty cycle increases from zero, the gain G gradually increases from 1.0. However, known converters cannot provide a significantly useful gain higher than about three.

[0033] As Figure 4 shown in the first preferred embodiment of the present invention as dc shown, the improved variable voltage DC-DC 20 converter includes interleaved phase bridges that provide current diverted to a shunt DC link capacitor by a configurable coupler 23, and the DC link capacitor has an upper capacitor 21 and a lower capacitor 22 connected in series between the buses 14 and 15. By selectively diverting the current from the phase bridges to one or the other of the capacitors 21 and 22 (i.e., charging them individually), the voltage gain obtainable by the converter 20 is doubled. Thus, the bus voltage V dc can be controlled to reach a target voltage that is twice the voltage that could otherwise be obtained. In the present invention, the coupler 23 selectively diverts the current from the switching branches to charge the link capacitors in series to provide a first voltage gain (e.g., a gain less than 2), and when the goal is to force a voltage with a second voltage gain greater than the first voltage gain, selectively diverts the current from the switching branches to charge the link capacitors individually. The capacitances C1 and C2 of the capacitors 21 and 22 are equal, and the capacitors 21 and 22 have the same rated voltage.

[0034] The controller / driver 24 provides PWM switching signals and diversion signals to the phase bridge switching devices to actuated the switching devices in the coupler 23. In the present invention, the phase bridge is coupled between the positive node 25 and the negative node 26. The configurable coupler 23 is an open array having the following: a first switching device 27 (S p4), the first switching device 27 (S p4 ) selectively couples the positive node 25 to the positive bus 14; a second switching device 28 (S p3 ), the second switching device 28 (S p3 ) selectively couples the positive node 25 to the capacitor junction between the link capacitors 21 and 22; a third switching device 29 (S n3 ), the third switching device 29 (S n3 ) selectively couples the negative node 26 to the capacitor junction; and a fourth switching device 30 (S n4 ), the fourth switching device 30 (S n4 ) selectively couples the negative node 26 to the negative bus 15. Figure 4 Shows an embodiment in which the independent inductors L1 and L2 couple the phase bridge to the battery 11, while Figure 5 shows an embodiment that uses inductive coupling between the inductors but is otherwise the same.

[0035] The layout of the coupler 23 and the capacitors 21 and 22 has the flexibility to selectively divert the current from the phase bridge to charge the capacitors either individually or together. Thus, the controller 24 can operate the converter 20 according to several different modulation modes in order to provide an extended range of available voltage gains while always achieving low power losses.

[0036] Figure 6 Shows the voltage gain versus duty cycle curves for each of the different modulation modes disclosed below. By switching between the modes at any given time according to the target (i.e., desired) voltage gain, optimized power flow and efficiency can be obtained. Thus, for voltage gains in the range of 1 to about 2, depending on which is estimated to result in less power loss, mode I-A or mode I-B (described below) can be used, depending on various factors of the particular design, such as i) the voltage stress and current levels in each switching device; ii) the switching frequency; iii) the I-V curves of the switching devices, E 接通 、E 断开 and E rr ; and iv) the characteristics of the gate driver circuit. For voltage gains in the range of about 2 to about 4, modulation mode II is used. For voltage gains greater than about 4, modulation mode III is used. The coupler 23 can also be set to a configuration that allows the use of a conventional through mode when the desired voltage gain is 1.

[0037] Figure 7 Shows mode I-A. Shows the signals for driving the phase bridge switches S p1 、S n1 、S p2 and S n2The PWM switching signals, where pulses 31 and 32 represent the lower switching devices S n1 and S n2 in their on states. Pulses 31 and 32 have an on-time D·T S , which is a part of the period time T S . Mode I-A is limited to using a duty cycle D less than about 0.5. As is known in the prior art, the widths of pulses 31 and 32 are obtained by comparing the duty cycle D with a triangular carrier signal. Shown are the gate drive signals for the coupler switches S p3 , S n3 , S p4 and S n4 , which are configured to charge capacitors 21 and 22 in series for a part of the time (e.g., during the time when both upper phase bridge switches S p1 and S p2 are on), and are configured to charge only one of capacitors 21 or 22 for a part of the time period (e.g., when the corresponding one of the lower phase bridge switches S n1 or S n2 is on). The resulting output voltage is as follows:

[0038]

[0039] The current flow according to mode I-A at time t1( Figure 7 ) is shown in Figure 8 , where the currents from both phase bridges are simultaneously applied in series across both link capacitors. At a later time t2( Figure 7 ), the current flow according to mode I-A is shown in Figure 9 , where the current from one phase bridge is diverted to charge only the upper link capacitor alone (i.e., while replenishing the inductor of the other phase bridge). Similarly, the lower link capacitor is charged separately from the opposite phase bridge later in the period.

[0040] Figure 10 Shows mode I-B, where the PWM switching signals for the phase bridge are shown. The configuration of the switching devices in coupler 23 for mode I-B mimics a conventional converter by continuously connecting both upper phase bridge switch devices S p1 and S p2 to the positive bus 14 and connecting both lower phase bridge switch devices S n1 and S n2 to the negative bus 15. Thus, at time t1, when both upper phase bridge switches S p1 and S p2 are on, both link capacitors are charged in series by both phase bridges, as shown in Figure 11As shown. At other times (such as Figure 10 t2 shown), when one of the upper phase bridge switches S p1 and S p2 is disconnected, both link capacitors are charged in series by only one phase bridge, as Figure 12 shown. The resulting output voltage is as follows:

[0041]

[0042] In mode II (i.e., when the target voltage gain is between 2·V b and 4·V b ), only the link capacitors are charged individually. Figure 13 shows the mode of actuation signals for the coupler switch devices S p3 、S n3 、S p4 and S n4 in mode II. Mode II charges the upper link capacitor individually from both phase bridges during part of the time, as Figure 16 shown. Mode II charges the upper link capacitor individually from only the second phase bridge during part of the time, as Figure 15 shown. Mode II charges the lower link capacitor individually from both phase bridges during part of the time, as Figure 14 shown. And finally, mode II charges the lower link capacitor individually from only the first phase bridge during part of the time, as Figure 17 shown. Thus, the phase bridge current is always diverted to at least one capacitor. In mode II, the duty cycle is in the range 0 ≤ D < 1. The actuation signal S p3 can be obtained by the following logical operation:

[0043]

[0044] where X is related to the carrier waveform, as Figure 13 shown.

[0045] In mode III (i.e., when the target voltage gain is greater than 4·V b ), like in mode II, only the link capacitors are charged individually. However, in mode III, sometimes the switch devices S p3 、S n3 、S p4 and S n4 are all disconnected, and no charging current is diverted to the capacitors. Additionally, mode III is preferably used only when the duty cycle D is greater than or equal to 0.5. Figure 18 shows the mode of actuation signals for the coupler switch devices S p3 、S n3 、S p4 and Sn4 The pattern of the actuation signal. Pattern III charges the upper link capacitor only from one of the switch branches alone for a part of the time and charges the lower link capacitor only from one of the switch branches alone for a part of the time.

[0046] At time t1 ( Figure 18 ), the current flow according to Pattern III is shown in Figure 19 , where the current from the first phase bridge S p1 is applied only across the upper link capacitor alone. At a later time t2 (when no phase bridge outputs any current), the switching devices S p3 , S n3 , S p4 and S n4 are all turned off, and no charging current is supplied to the capacitor. At a later time t3 ( Figure 18 ), the current flow according to Pattern III is shown in Figure 20 , where the current from the second phase bridge S p2 is applied only across the lower link capacitor alone. As in Pattern II, the resulting output voltage is as follows:

[0047]

[0048] The simulation results for Pattern III are shown in Figures 21 to 25 based on such an embodiment: where L1 = L2 = 100 μH; C1 = C2 = 800 μF; V b = 200 V; and the DC bus voltage is boosted to 1000 V (i.e., the voltage gain is 5 and the duty cycle is 0.6). The average value of the battery current ( Figure 21 ) is 998 A, and the peak-to-peak ripple is 40 A, even though each inductor current ripple is 120 A peak-to-peak ( Figure 22 ). Therefore, compared with the inductor current ripple, there is a sharp reduction in the battery current ripple in the converter of the present invention. Each phase bridge and its inductor carry only an average current of 499 A, which is half of the battery current. The overall DC bus voltage of 1000 V is stable ( Figure 24 ), and a good balance is maintained between the two capacitors ( Figure 25 ), with each capacitor maintaining 500 V. Therefore, even if the inductor remains small, the battery current ripple is very low. The smaller the inductor size, the less inductor loss, the smaller the package size, and the lower the cost.

[0049] Although the DC-DC converter described above has two phase bridges, the present invention is not limited thereto. The present invention can be easily extended to converters with three or more interleaved phase bridges, which will result in even higher currents, lower ripples, and higher voltage gains.

[0050] According to the present invention, a variable voltage converter in an electric drive system includes: a parallel switch branch having a respective upper switch device and a respective lower switch device connected in series between a positive node and a negative node, and each having a respective intermediate junction inductively coupled to a battery by a respective inductor; an upper link capacitor and a lower link capacitor connected in series between a positive bus and a negative bus of the drive system; a configurable coupler having: a first switch device that selectively couples the positive node to the positive bus; a second switch device that selectively couples the positive node to a capacitor junction between the link capacitors; a third switch device that selectively couples the negative node to the capacitor junction; and a fourth switch device that selectively couples the negative node to the negative bus; and a controller configured to drive the upper switch device and the lower switch device according to a PWM gate signal having a duty cycle adapted to provide a target voltage between the buses, and the controller is configured to actuate the first switch device to the fourth switch device to selectively divert current from the switch branch to charge the link capacitors in series to provide a first voltage gain, and to charge the link capacitors individually to provide a second voltage gain greater than the first voltage gain.

[0051] According to one embodiment, the battery supplies a battery voltage V b , and wherein the controller actuates the configurable coupler according to a plurality of modes, the plurality of modes including: a first mode used when the target voltage is less than 2·V b , wherein the first mode charges the two link capacitors in series from both switch branches for a part of the time, and wherein the first mode charges the two link capacitors in series from only one of the switch branches for a part of the time; and a second mode used when the target voltage is between 2·V b and 4·V b , wherein the second mode charges the upper link capacitor individually from both switch branches for a part of the time, wherein the second mode charges the upper link capacitor individually from only one of the switch branches for a part of the time, wherein the second mode charges the lower link capacitor individually from both switch branches for a part of the time, and wherein the second mode charges the lower link capacitor individually from only one of the switch branches for a part of the time.

[0052] According to one embodiment, the first mode limits the duty cycle to less than about 0.5, wherein the first mode charges the upper link capacitor solely from one of the switch legs during part of the time, and wherein the first mode charges the lower link capacitor solely from the other of the switch legs during part of the time.

[0053] According to one embodiment, the second mode does not include charging the two link capacitors in series.

[0054] According to one embodiment, the multiple modes further include: a third mode used when the target voltage is greater than 4·V b wherein the third mode charges the upper link capacitor solely from one of the switch legs during part of the time, and wherein the third mode charges the lower link capacitor solely from one of the switch legs during part of the time.

[0055] According to one embodiment, the multiple modes further include: a direct - through mode used when the target voltage is not greater than V b wherein the duty cycle of the direct - through mode is set to zero, and wherein the first switch device and the fourth switch device are actuated, and the second switch device and the third switch device are not actuated.

[0056] According to one embodiment, the corresponding inductors are inductively coupled.

[0057] According to one embodiment, the switch devices include insulated - gate bipolar transistors.

[0058] According to the present invention, a method of controlling a variable - voltage converter coupled between a battery and a DC link, wherein an upper link capacitor and a lower link capacitor are connected in series across the DC link, the method comprising the steps of: determining a target voltage to be output by the converter; when the target voltage across the DC link is less than twice the battery voltage, charging the capacitors in a first mode, wherein during part of the time the two link capacitors are charged in series from both switch legs simultaneously, and wherein during part of the time the two link capacitors are charged in series from only one of the switch legs; and when the target voltage is between 2 times and 4 times the battery voltage, charging the capacitors in a second mode, wherein during part of the time the upper link capacitor is charged separately from both switch legs, wherein during part of the time the upper link capacitor is charged separately from only one of the switch legs, wherein during part of the time the lower link capacitor is charged separately from both switch legs, and wherein during part of the time the lower link capacitor is charged separately from only one of the switch legs.

[0059] According to one embodiment, the second mode does not include charging two link capacitors in series.

[0060] According to one embodiment, the first mode limits the duty cycle to less than about 0.5, and the first mode further includes: charging the upper link capacitor only from one of the switching branches alone during a part of the time, and charging the lower link capacitor only from the other of the switching branches alone during a part of the time.

[0061] According to the present invention, when the target voltage is greater than four times the battery voltage, the capacitor is charged in a third mode, where the upper link capacitor is charged only from one of the switching branches alone during a part of the time, and where the lower link capacitor is charged only from one of the switching branches alone during a part of the time.

[0062] According to the present invention, when the target voltage is not greater than the battery voltage, the capacitor is charged in a direct-through mode, where the duty cycle is set to zero, and where the two link capacitors are charged in series simultaneously only.

[0063] According to the present invention, an electrified vehicle voltage converter includes: two interleaved phase bridges coupled to a battery; an upper link capacitor and a lower link capacitor connected in series; and a coupler device that selectively redirects current from a switching branch to charge the link capacitors in series during a part of the time and charge the link capacitors alone during a part of the time according to a required voltage gain between the battery voltage and the voltage across the link capacitors.

[0064] According to one embodiment, the coupler redirects the charging current according to multiple modes, the multiple modes including: a first mode used when the target voltage across the link capacitors is less than 2·V b where V b is the battery voltage, where the first mode charges the two link capacitors in series from both phase bridges during a part of the time, and where the first mode charges the two link capacitors in series from only one of the phase bridges during a part of the time; and a second mode used when the target voltage is between 2·V b and 4·V b where the second mode charges the upper link capacitor alone from both phase bridges during a part of the time, where the second mode charges the upper link capacitor alone from only one of the phase bridges during a part of the time, where the second mode charges the lower link capacitor alone from both phase bridges during a part of the time, and where the second mode charges the lower link capacitor alone from only one of the phase bridges during a part of the time.

[0065] According to one embodiment, the first mode limits the duty cycle for controlling the phase bridge to less than about 0.5, wherein the first mode charges the upper link capacitor solely from one of the phase bridges during a portion of the time, and wherein the first mode charges the lower link capacitor solely from the other of the phase bridges during a portion of the time.

[0066] According to one embodiment, a further feature of the present invention is a third mode used when the target voltage is greater than 4·V b wherein the third mode charges the upper link capacitor solely from one of the phase bridges during a portion of the time, and wherein the third mode charges the lower link capacitor solely from one of the phase bridges during a portion of the time.

[0067] According to one embodiment, a further feature of the present invention is a direct-through mode used when the target voltage is not greater than V b wherein the duty cycle for controlling the phase bridge in the direct-through mode is set to zero, and wherein the two link capacitors are charged solely in series simultaneously.

Claims

1. A variable voltage converter in an electric drive system, comprising: A parallel switch branch having a respective upper switch device and a respective lower switch device connected in series between a positive node and a negative node, and each having a respective intermediate junction inductively coupled to a battery by a respective inductor; An upper link capacitor and a lower link capacitor, the upper link capacitor and the lower link capacitor being connected in series between a positive bus and a negative bus of the electric drive system; A configurable coupler having: a first switch device that selectively couples the positive node to the positive bus; A second switch device that selectively couples the positive node to a capacitor junction between the upper link capacitor and the lower link capacitor; A third switch device that selectively couples the negative node to the capacitor junction; And a fourth switch device that selectively couples the negative node to the negative bus; And A controller configured to drive the upper switch device and the lower switch device according to a PWM gate signal having a duty cycle adapted to provide a target voltage between the positive bus and the negative bus, and the controller is configured to actuate the first switch device to the fourth switch device to selectively divert current from the switch branch to charge the upper link capacitor and the lower link capacitor in series to provide a first voltage gain, and to charge the upper link capacitor and the lower link capacitor separately to provide a second voltage gain greater than the first voltage gain.

2. The converter according to claim 1, wherein the battery supplies a battery voltage V b , and wherein the controller actuates the configurable coupler according to a plurality of modes, the plurality of modes including: When the target voltage is less than 2∙V b A first mode used when, in which the first mode charges the upper link capacitor and the lower link capacitor in series from two switching branches simultaneously for a part of time, and in which the first mode charges the upper link capacitor and the lower link capacitor in series from only one of the switching branches for a part of time; And A second mode used when the target voltage is between 2∙V b and 4∙V b in which the second mode charges the upper link capacitor separately from two switching branches during part of the time, in which the second mode charges the upper link capacitor separately from only one of the switching branches during part of the time, in which the second mode charges the lower link capacitor separately from two switching branches during part of the time, and in which the second mode charges the lower link capacitor separately from only one of the switching branches during part of the time.

3. The converter according to claim 2, wherein the first mode limits the duty cycle to less than 0.5, wherein the first mode charges only the upper link capacitor from only one of the switch branches for a portion of the time, and wherein the first mode charges only the lower link capacitor from only the other of the switch branches for a portion of the time.

4. The converter according to claim 2, wherein the second mode does not include charging the upper link capacitor and the lower link capacitor in series.

5. The converter according to claim 2, wherein the multiple modes further include: When the target voltage is greater than 4∙V b A third mode used when, in which the third mode charges the upper link capacitor only from one of the switching branches alone during a part of the time, and in which the third mode charges the lower link capacitor only from one of the switching branches alone during a part of the time.

6. The converter according to claim 2, wherein the multiple modes further include: When the target voltage is not greater than V b a direct conduction mode used, wherein the duty ratio of the direct conduction mode is set to zero, and wherein the first switching device and the fourth switching device are actuated, and the second switching device and the third switching device are not actuated.

7. The converter according to claim 1, wherein the respective inductors are inductively coupled.

8. The converter according to claim 1, wherein the upper switch device, the lower switch device, the first switch device, the second switch device, the third switch device, and the fourth switch device include insulated gate bipolar transistors.

9. A method of controlling a variable voltage converter coupled between a battery and a DC link, wherein an upper link capacitor and a lower link capacitor are connected in series across the DC link, the method comprising the steps of: Determining a target voltage to be output by the converter; When the target voltage on the DC link is less than twice the battery voltage, the upper link capacitor and the lower link capacitor are charged in a first mode, wherein during a part of the time, the upper link capacitor and the lower link capacitor are charged in series from two switch branches simultaneously, and wherein during a part of the time, the upper link capacitor and the lower link capacitor are charged in series from only one of the switch branches; And When the target voltage is between 2 times and 4 times the battery voltage, the upper link capacitor and the lower link capacitor are charged in a second mode, wherein during a part of the time, the upper link capacitor is charged separately from two switch branches, wherein during a part of the time, the upper link capacitor is charged separately from only one of the switch branches, wherein during a part of the time, the lower link capacitor is charged separately from two switch branches, and wherein during a part of the time, the lower link capacitor is charged separately from only one of the switch branches.

10. The method according to claim 9, wherein the second mode does not include charging the upper link capacitor and the lower link capacitor in series.

11. The method according to claim 9, wherein the first mode limits the duty cycle of the target voltage to less than 0.5, and wherein the first mode further includes: During a part of the time, the upper link capacitor is charged separately from only one of the switch branches, and during a part of the time, the lower link capacitor is charged separately from only the other one of the switch branches.

12. The method according to claim 9, further comprising the steps of: When the target voltage is greater than 4 times the battery voltage, the upper link capacitor and the lower link capacitor are charged in a third mode, wherein during a part of the time, the upper link capacitor is charged separately from only one of the switch branches, and wherein during a part of the time, the lower link capacitor is charged separately from only one of the switch branches.

13. The method according to claim 9, further comprising the steps of: When the target voltage is not greater than the battery voltage, the upper link capacitor and the lower link capacitor are charged in a through mode, wherein the duty ratio of the target voltage is set to zero, and wherein only the upper link capacitor and the lower link capacitor are charged in series simultaneously.

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