Power transmission unit, method of controlling current, fuel cell system and medium

Abstract

The embodiment of the invention relates to a power transmission unit and a method for controlling current flowing through the power transmission unit. The power transmission unit includes a first switch turned on and off at a first duty cycle; a second switch turned on and off at a second duty cycle less than the first duty cycle; the inductance element is connected between the first switch and the second switch, and the current of the inductance element is associated with a first duty ratio and a second duty ratio; and a controller configured to determine a total duty ratio that is a sum of the first and second duty ratios based on an actual phase current and a desired phase current of the inductive element, and adjust the first and second duty ratios based on the determined total duty ratio. According to the embodiment of the invention, the first duty ratio and the second duty ratio are adjusted through the total duty ratio, and the first duty ratio and the second duty ratio can change along with the change of the total duty ratio, so that the first duty ratio and the second duty ratio can be adjusted to proper values, and the current flowing through the inductance element reaches a proper value. Therefore, low-current control can be realized.

Description

Technical Field

[0001] Embodiments of the present disclosure generally relate to the field of power transmission, and in particular to a power transmission unit, a method of controlling current of the power transmission unit, a fuel cell system, and a machine-readable storage medium. Background Art

[0002] For a fuel cell power system, a power transmission unit (PTU) is used to transfer electrical energy from a fuel cell power system (e.g., a fuel cell stack) to a power battery (e.g., a high voltage battery (HVbattery)). If a fuel cell engine is used in a hybrid vehicle, the number of batteries is usually more than 400, and the output voltage of the fuel cell and the voltage of the high voltage battery overlap. Therefore, the PTU usually supports a buck-boost mode, a boost mode, and a buck mode to achieve stable current control.

[0003] If the PTU operates in the boost-buck mode, the non-complementary boost-buck control method is used to reduce the phase current ripple of the PTU and reduce the phase inductance value. Therefore, it is necessary to further enhance or improve the non-complementary boost-buck control method. Summary of the invention

[0004] Embodiments of the present disclosure provide a power transmission unit, a method of controlling current of the power transmission unit, a fuel cell system, and a machine-readable storage medium.

[0005] According to a first aspect of the present disclosure, there is provided a power transmission unit for transmitting electric power of a fuel cell stack to a power battery, the power transmission unit comprising: a first switch configured to be turned on and off at a first duty cycle; a second switch configured to be turned on and off at a second duty cycle that is smaller than the first duty cycle; an inductor element connected between the first switch and the second switch and through which currents are associated with the first duty cycle and the second duty cycle; and a controller configured to determine a total duty cycle as a sum of the first duty cycle and the second duty cycle based on an actual phase current and a desired phase current of the inductor element, and to adjust the first duty cycle and the second duty cycle based on the determined total duty cycle.

[0006] According to a second aspect of the present disclosure, a method for controlling the current of a power transmission unit is provided, wherein the power transmission unit is used to transmit the electric power of a fuel cell stack to a power battery, and the power transmission unit includes: a first switch configured to be turned on and off at a first duty cycle; a second switch configured to be turned on and off at a second duty cycle; and an inductor connected between the first switch and the second switch and the current flowing therethrough is associated with the first duty cycle and the second duty cycle. The method includes: obtaining a desired phase current for the inductor; obtaining an actual phase current flowing through the inductor; determining a total duty cycle as the sum of a first duty cycle and a second duty cycle based on the desired phase current and the actual phase current; adjusting the first duty cycle and the second duty cycle based on the total duty cycle; and controlling the turning on and off of the first switch based on the adjusted first duty cycle and the turning on and off of the second switch based on the adjusted second duty cycle to control the current flowing through the inductor.

[0007] According to a third aspect of the present disclosure, a fuel cell system is provided, comprising: a fuel cell stack; a power battery; and a power transmission unit according to the first aspect of the present disclosure, configured to transmit electric power of the fuel cell stack to the power battery.

[0008] According to a fourth aspect of the present disclosure, a machine-readable storage medium is provided, wherein machine-executable instructions are stored on the machine-readable storage medium, wherein the machine-executable instructions are executed by a processor to implement the steps of the method according to the second aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present disclosure.

[0010] Figure 1A A schematic diagram illustrating a connection relationship between a power transmission unit, a fuel cell stack, and a power battery according to an embodiment of the present disclosure is illustrated;

[0011] Figure 1B A schematic diagram of current flow and a current curve diagram when a power transmission unit according to an embodiment of the present disclosure operates in a boost-buck mode are illustrated;

[0012] Figure 2 FIG. 1 illustrates a variation trend diagram of the instantaneous current of an inductor in a continuous current mode (CCM) (solid line) and a discontinuous current mode (DCM) (dashed line) according to an embodiment of the present disclosure;

[0013] Figure 3FIG. 1 illustrates a schematic structural diagram of a controller of a power transmission unit according to an embodiment of the present disclosure;

[0014] Figure 4 FIG. 1 illustrates a variation trend diagram of the instantaneous current on the inductor in a boost-buck mode and when Vin is greater than Vout according to an embodiment of the present disclosure;

[0015] Figure 5 FIG. 1 illustrates a variation trend diagram of the instantaneous current on the inductor in a boost-buck mode and when Vin is less than Vout according to an embodiment of the present disclosure;

[0016] Figure 6 A flow chart illustrating a method of controlling current of a power transmission unit according to an embodiment of the present disclosure; and

[0017] Figure 7 A schematic block diagram of an example device implementing an embodiment of the present disclosure is illustrated.

[0018] In the various drawings, the same or corresponding reference numerals represent the same or corresponding parts. DETAILED DESCRIPTION

[0019] Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein, but rather these embodiments are provided for a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are only for exemplary purposes and are not intended to limit the scope of protection of the present disclosure. The embodiments of the present disclosure described below with reference to the accompanying drawings are only for exemplary purposes.

[0020] As described above, the PTU is connected between the fuel cell stack and the power battery to transfer electrical energy from the fuel cell power system to the power battery. The control unit of the fuel cell stack often indicates a small current control, such as a battery control of less than 20A. The small current control instruction requires that the current (for example, the average current within a cycle) of the components (for example, on the inductor) contained in the PTU also reaches a smaller current value. However, due to the influence of the duty cycle of each switch (for example, MOS tube, NMOS or PMOS) contained in the PTU, the current on the inductor is often large, resulting in an average current within a cycle that is much larger than the small current indicated by the control unit of the fuel cell stack, especially when the PTU operates in boost-buck mode, so the small current indicated by the control unit cannot be achieved.

[0021] At least to solve the above and other potential problems, an embodiment of the present disclosure provides a power transmission unit capable of realizing small current control. The power transmission unit includes a first switch configured to be turned on and off at a first duty cycle; a second switch configured to be turned on and off at a second duty cycle that is less than the first duty cycle; an inductor connected between the first switch and the second switch and the current flowing therethrough is associated with the first duty cycle and the second duty cycle; a controller configured to determine a total duty cycle as the sum of the first duty cycle and the second duty cycle based on the actual phase current and the expected phase current of the inductor, and to adjust the first duty cycle and the second duty cycle based on the determined total duty cycle. By adjusting both the first and second duty cycles based on the total duty cycle, the first and second duty cycles will change with the change of the total duty cycle, so that both the first and second duty cycles can be adjusted to appropriate values, so that the current flowing through the inductor reaches an appropriate value. Therefore, when the stack control unit gives a small current control instruction, stable small current control can be realized by continuously adjusting the first and second duty cycles based on the determined total duty cycle.

[0022] The following will refer to Figure 1A and Figure 1B The step-up and step-down working modes of PTU are introduced. Figure 1A A schematic diagram showing the connection relationship between a power transmission unit, a fuel cell stack and a power battery according to an embodiment of the present disclosure is shown.

[0023] like Figure 1A As shown, the PTU 100 can be connected between the fuel cell stack 200 and the high voltage battery 300 to transmit the power of the fuel cell stack 200 to the high voltage battery 300. If the PTU 100 operates in the boost-buck mode, the non-complementary boost-buck control method is used to reduce the phase current ripple of the PTU and reduce the phase inductance value. The output voltage of the fuel cell stack 200 can be input to the PTU 100 as the input voltage Vin, and the output voltage Vout of the PTU 100 can be input to the high voltage battery 300.

[0024] In some embodiments, the working mode of the PTU 100 may depend on the size of Vin and Vout, by sampling the input voltage Vin and obtaining the voltage Vout of the high-voltage battery (for example, the control unit of the high-voltage battery may output the voltage Vout once every 1 millisecond), thereby using the ratio of Vout / Vin to determine the working mode of the PTU 100. If Vout / Vin is less than 1, the buck mode is used; if Vout / Vin is greater than 1, the boost mode is used; and if Vout / Vin is close to 1, the boost-buck mode is used, and the boost-buck mode is used to connect the buck mode and the boost mode.

[0025] like Figure 1A As shown, the PTU 100 may include four MOS transistors M1 to M4, and each MOS transistor may be, for example, an NMOS transistor, wherein the MOS transistor M1 may also be referred to as a first switch, which is turned on and off at a first duty cycle D1; and the MOS transistor M3 may also be referred to as a second switch, which is turned on and off at a second duty cycle D3. The PTU 100 may also include diodes T1 to T4 connected between the source and the drain of each MOS transistor. The MOS transistors M1 and M2 are connected in series, and the MOS transistors M3 and M4 are connected in series. The PTU 100 also includes an inductor element L, one end of which is connected between the MOS transistors M1 and M2, for example, between the source of the MOS transistor M1 and the drain of the MOS transistor M2, and the other end of the inductor element L is connected between the MOS transistors M3 and M4, for example, between the source of the MOS transistor M4 and the drain of the MOS transistor M3. As shown in FIG. Figure 1A As shown, the drain of MOS tube M1 and the source of MOS tube M2 can be connected to the fuel cell stack 200, so that the output voltage of the fuel cell stack 200 is input to the PTU 100 as the input voltage Vin. In addition, the drain of MOS tube M4 and the source of MOS tube M3 can be connected to the high-voltage battery 300, so that the output voltage Vout of the PTU 100 is input to the high-voltage battery 300.

[0026] like Figure 1A As shown, the fuel cell stack 200 includes a fuel cell control unit (FCCU) 201, which can be used to control the current of the battery stack 200 so that its current is stable at a certain current value. Generally, the current of the battery stack 200 is slightly smaller than the current of the inductor element L in a stable state. For example, if the fuel cell control unit 201 indicates that the stable current of the battery stack 200 is 20A, then the phase current of the inductor element L in a stable state (i.e., the average current in one cycle) is about 25A.

[0027] The current flowing through the inductor element L is associated with the duty cycle D1 of the MOS transistor M1 and the duty cycle D3 of the MOS transistor M3. These two duty cycles can be controlled, for example, as described below. Figure 3 The controller 1 to be described controls so that the current flowing through the inductor element L changes, that is, controls the change trend of the current of the inductor element L (that is, the phase current or the curve slope).

[0028] The following will refer to Figure 1B To describe the current flow direction and current change trend when the power transmission unit of the embodiment of the present disclosure works in the boost-buck mode. Figure 1BAs shown, the currents of the circuit diagrams shown in the upper left figure (I), the middle left figure (II) and the lower left figure (III) are respectively as follows Figure 1B The three broken lines I, II and III in each cycle of the upper right and lower right graphs are shown. Figure 1B In the upper right figure of , it shows the situation where Vin is greater than Vout; but Figure 1B The lower right figure shows the situation where Vin is less than Vout.

[0029] exist Figure 1B In the example shown, Figure 1B As shown in the upper left figure (I), in the first stage, at the beginning of the stage, both MOS transistors M1 and M3 are turned on, and at the end of the first stage, MOS transistor M3 is turned off. For example, if the duty cycle of MOS transistor M3 is 0.15, then in the first cycle, at the time corresponding to 0.15Ts, MOS transistor M3 is turned off. Therefore, in the first stage, as shown by the dotted line i1, the current flows through MOS transistor M1, inductor element L and MOS transistor M3. Figure 1B As shown in the upper right figure and the lower right figure, the current in the first stage has a rising slope of Vin / L as shown by the broken line I. Therefore, in the first stage, the current flowing through the inductor current L increases.

[0030] like Figure 1B As shown in the left middle figure (II), in the second stage, since M3 has been turned off, the circuit of the inductor element L will find another path to continue the current. In the second stage, the MOS tube M3 is turned off and the MOS tube M1 is turned on, but at the end of the second stage, the MOS tube M1 is turned off. For example, if the duty cycle of the MOS tube M1 is 0.95, then in the first cycle, at the moment corresponding to 0.95Ts, the MOS tube M1 is turned off. Therefore, in the second stage, as shown by the dotted line i2, the current flows through the MOS tube M1, the inductor element L and the diode T4 to achieve energy transfer. In the second stage, the change trend of the current of the inductor element L, that is, the slope is (Vin-Vout) / L. When Vin is greater than Vout, as shown by the broken line II in the upper right figure, the slope is positive, so the current increases; when Vin is less than Vout, as shown by the broken line II in the lower right figure, the slope is negative, so the current decreases.

[0031] like Figure 1B As shown in the lower left figure (III), in the third stage, the M1 tube is also turned off. In order to continue the current, as shown by the dotted line i3, the current of the inductor element L will flow through the diode T2, the inductor element L and the diode T4. In this third stage, Figure 1B As shown by the broken line III in the upper right figure and the lower right figure, the changing trend of the current of the inductor element L, that is, the downward slope is (-Vout) / L. Therefore, in this stage, the current flowing through the inductor current L decreases.

[0032] When the PTU works in the boost-buck mode, the duty cycles D3 of the MOS tube M1 and the MOS tube M3 are different. Usually, the duty cycle D3 of the MOS tube M3 is smaller than the duty cycle D1 of the MOS tube M1. That is, the moment when the MOS tube M3 is turned off is earlier than the moment when the MOS tube M1 is turned off. Figure 1B As shown. In some technologies, in order to simplify the duty cycle contribution calculation, the duty cycle D1 of the MOS tube M1 can be set to a constant of 0.95, and the phase current (i.e., the slope of the current curve, or the value obtained by dividing the envelope area of ​​the current curve by the cycle time) is adjusted by changing the duty cycle D3 of the MOS tube M3. When Vout / Vin approaches the switching threshold, hysteresis calibration is performed to switch between multiple modes to avoid unnecessary frequent switching.

[0033] When Vin is higher than Vout and FCCU 201 requires small current control (i.e., the indicated current of the battery stack is smaller, or the average value or phase current of the current of the inductor element L in one cycle is smaller), for example, lower than 20A, based on conventional technology, there is a risk of being unable to control the small current in the battery stack 200. Because even if the duty cycle D3 of the MOS tube M3 is close to 0, but the duty cycle D1 of the MOS tube M1 is still maintained at 0.95, then when the MOS tube M1 is turned off (i.e., corresponding to the moment of 0.95Ts), a higher current (e.g., 70A to 80A) will still be reached, resulting in the instantaneous current average value of the inductor element L in one cycle being much larger than the indicated 20A, and therefore, the small current control in the battery stack 200 cannot be achieved.

[0034] Figure 2 An exemplary variation trend diagram of the instantaneous current of the inductor element L in the continuous current mode (CCM) (solid line) and the discontinuous current mode (DCM) (dashed line) is shown.

[0035] like Figure 2As shown by the solid line in the example, when Vin is greater than Vout, when the PTU operates in the current continuous mode, in one cycle (from time 0 to time Ts), before the MOS tube M3 is turned off (turned off at the moment corresponding to the duty cycle D3), the current of the inductor L rises along the first line segment A1; before the MOS tube M1 is turned off (turned off at the moment corresponding to the duty cycle D1), the current of the inductor L rises along the first line segment A2; after the MOS tube M1 is turned off, the current of the inductor L drops along the third line segment A3, and the end current of the first cycle is higher than the start current of the first cycle. In the second cycle (i.e., from time Ts to time 2Ts), the instantaneous current on the inductor L still increases from the current at the end of the first cycle according to a curve similar to the first cycle (not shown). When the phase current (i.e., the envelope area of ​​the curve / cycle time) is close to the large current indicated by the FCCU 201, the start current and end current of the inductor L in a certain cycle will be basically the same, and stabilize at this value to achieve stable current control of the battery stack.

[0036] like Figure 2 As shown by the dotted line in the example, when Vin is greater than Vout, when the PTU works in the discontinuous current mode, in the first cycle (from time 0 to time Ts), before the MOS tube M3 is turned off, the current of the inductor element L rises along the first line segment B1; before the MOS tube M1 is turned off, the current of the inductor element L rises along the second line segment B2; after the MOS tube M1 is turned off, the current of the inductor element L drops along the third line segment B3. However, compared with the continuous current mode, since the duty cycle of the MOS tube M3 is relatively small, the current value at the vertex of the first line segment B1 is smaller than the current value at the vertex of the first line segment A1, and the same is true for the line segment B2. In this way, before the end of the first cycle, the current on the inductor element L drops to 0 along the line segment B3. For this discontinuous current mode, the phase current on the inductor (i.e., the envelope area of ​​the curve / cycle time) is smaller than the phase current in the continuous current mode, so compared with the continuous current mode, it is possible to achieve control of a smaller current.

[0037] In the conventional technology, since the duty cycle D3 of the MOS tube M3 is greater than 0, the current flowing through the inductor L will increase dramatically during the on-time of the MOS tube M3. When Vin is greater than Vout, after the MOS tube M3 is turned off, the current increases until the moment corresponding to the duty cycle of 0.95 (i.e., the moment of 0.95Ts), and then decreases. Figure 2It can be seen that even if the current of the inductor element L changes in the current discontinuous mode, in the first cycle, the envelope of the current change curve also produces a large area. In the subsequent cycles, even if the duty cycle D3 of the MOS tube M3 becomes 0, because the duty cycle D1 of the MOS tube M1 is still fixed at 0.95, a triangular envelope will be generated, and the vertex of the envelope is located at the moment of 0.95Ts in the corresponding cycle. Even if the duty cycle D3 becomes 0, the current at the vertex (for example, 70A) is greater than or much greater than the small current indicated by the fuel cell stack control unit FCCU 201 (for example, less than 20A), so the area of ​​the generated triangular envelope divided by Ts will be much greater than the small current indicated by FCCU 201, so small current control cannot be achieved.

[0038] Therefore, in some technologies, even when DCM is used and D3 is adjusted to 0, in this period, the instantaneous current of the inductor L may reach a large value (for example, 70 A or more) that is much larger than the indicated current (for example, 20 A or less), so the average current (i.e., phase current) calculated by the envelope area is also much larger than the small current of 20 A. Therefore, in these technologies, even if the current discontinuous mode is adopted and even if D3 is adjusted to zero, small current control cannot be achieved.

[0039] To this end, the embodiments of the present disclosure propose a new way to allocate duty cycles. Figure 3 1 is a schematic diagram of the structure of the controller 1 of the power transmission unit 100 according to an embodiment of the present disclosure. The controller 1 can implement the new method of allocating duty cycles.

[0040] According to an embodiment of the present disclosure, the controller 1 can dynamically determine the total duty cycle Dtotal of the duty cycle D1 of the MOS tube M1 and the duty cycle D3 of the MOS tube M3 based on the expected phase current and the actual phase current of the inductor element L, and dynamically adjust D1 and D3 based on the determined total duty cycle Dtotal, so that D1 and D3 are dynamically reduced. Based on the reduced D1 and D3, the MOS tube M1 and the MOS tube M3 are continuously controlled so that the instantaneous current on the inductor element L is further reduced, so that the Dtotal determined by the controller 1 is also reduced, and then D1 and D3 are further reduced until D3 is reduced to zero, and D1 is also reduced to a suitable value. In some embodiments, D3 can be reduced to zero first, and then D1 can be continuously adjusted to reduce it until D1 is reduced to a suitable value.

[0041] In some embodiments, the phase current is the average current in one cycle, that is, the average current obtained by dividing the curve envelope area of ​​the instantaneous current on the inductor element L by one cycle time. In some embodiments, the time of one cycle is 32 μs, and it is unlikely to collect the instantaneous current of each μs, so the instantaneous current on the inductor element L is sampled once every 4 μs in the cycle, and then the average value of 8 sampled values ​​is taken as the measured phase current of the inductor element L.

[0042] In some embodiments, the controller 1 determines the expected phase current iphase_DC* of the inductor element L based on the expected stack current istack* and the actual stack current istack_act. The expected stack current is specified by the FCCU 201. When performing low current control, the expected stack current specified by the FCCU 201 may be, for example, less than or equal to 20A. When performing high current control, the expected stack current specified by the FCCU 201 may be, for example, greater than or equal to 200A. The actual stack current is also obtained by sampling and averaging the measured stack current.

[0043] like Figure 3 As shown, the controller 1 may include a first closed-loop circuit 10, which receives the desired stack current istack* from the FCCU 201 and the actual stack current istack_act measured from the battery stack 200, and performs proportional integration based on the two to obtain the desired phase current iphase_DC*, which may be a direct current. Figure 3 As shown, the controller 1 may further include a second closed-loop circuit 20, which receives the actual phase current iphase_act measured from the inductor element L and the desired phase current iphase_DC* output from the first closed-loop circuit 10 to calculate a total duty cycle Dtotal, wherein the actual phase current iphase_act is obtained by sampling and averaging as described above.

[0044] In one example, if Figure 3As shown, the first closed-loop circuit 10 may include a first comparator 11 and a first proportional-integral controller (PI) 12, respectively. The first comparator 11 may receive the desired stack current istack* and the actual stack current istack_act, and the output of the first comparator 11 is input to the first proportional-integral controller 12, so that the first closed-loop circuit 10 outputs the desired phase current iphase_DC*. The second closed-loop circuit 20 may include a second comparator 21 and a second proportional-integral controller (PI) 22, respectively. The second comparator 21 receives the desired phase current iphase_DC* and the actual phase current iphase_act, and the output of the second comparator 21 is input to the second proportional-integral controller 22, so that the second closed-loop circuit 10 outputs the total duty cycle Dtotal.

[0045] like Figure 3 As shown, the current control structure of the PTU 100 includes two closed loops, the outer closed loop is the stack current closed loop, the input of which is the stack current istack* received from the FCCU 201 and the actual stack current istack_act measured from the battery stack, and the output of which is the desired phase current iphase_DC*. The inner closed loop is the inductor phase current closed loop, the input of which is the actual phase current iphase_act measured from the inductor element L and the desired phase current iphase_DC* output from the first closed loop circuit 10, and the output is Dtotal. The outer closed loop is used to eliminate the steady-state error in the stack current.

[0046] Continue to refer Figure 3 The controller 1 further includes a duty cycle adjustment circuit 30, which adjusts and distributes D1 and D3 based on the determined total duty cycle Dtotal, so that both D1 and D3 are reduced, and then the reduced D1 and D3 are used to continue to control the MOS tube M1 and the MOS tube M3, respectively, so that the current on the inductor element L related to the duty cycle D1 and D3 also changes. In some embodiments, the value of D1 can be determined based on the total duty cycle Dtotal, and then the value of D3 can be set based on the total duty cycle Dtotal and D1.

[0047] In some embodiments, when the total duty cycle Dtotal determined by the second closed-loop circuit 20 is greater than or equal to 0.95, the duty cycle adjustment circuit 30 can set D1 to 0.95 and set D3 to Dtotal minus 0.95. In the case of small current control, the current given by the FCCU 201 is less than the current current, so the expected phase current will be less than the current actual phase current, so the total duty cycle determined by the second closed-loop circuit 20 will be in a decreasing trend. The above two closed loops will continuously reduce Dtotal, and Dtotal can be reduced from an initial value greater than or equal to 0.95 (for example, about 1.1) to less than 0.95. When the Dtotal determined by the second closed-loop circuit 20 is less than 0.95, D1 can be set to the newly determined Dtotal, so that D1 is less than the fixed value set at the beginning (that is, 0.95), that is, the on time of the MOS tube M1 becomes shorter, and at this time D3 is set to 0, that is, the MOS tube M3 will be in a disconnected state.

[0048] The following will refer to Figure 4 An example variation trend diagram of the instantaneous current on the inductor L in the boost-buck mode and when Vin is greater than Vout according to an embodiment of the present disclosure is described.

[0049] refer to Figure 4 For example, after FCCU 201 gives a small current control, the inductor element L will choose to work in the discontinuous current mode instead of the continuous current mode. In the first cycle, since the determined Dtotal is still greater than 0.95, for example, 1.1, the duty cycle adjustment circuit 30 sets D1 to 0.95 and D3 to 1.1-0.95=0.15. Then in the first cycle, before 0.15Ts, the instantaneous current of the inductor element L increases at the slope of Vin / L. At 0.15Ts, D3 is turned off, and the instantaneous current of the inductor element L will flow through the diode T4 next to the MOS tube M4. Since Vin is greater than Vout, the current will increase at the slope of (Vin-Vout) / L to the moment of 0.95Ts. At 0.95Ts, D1 is turned off, the inductor L flows through diodes T2 and T4, and the instantaneous current of the inductor L drops to 0 at a slope of -Vout / L. In some embodiments, the current of the inductor L drops to 0 earlier than the end of the cycle.

[0050] like Figure 4 As shown, for the sake of explanation, it is assumed that in the second cycle, Dtotal decreases from the initial 1.1 to 1, so D1 will continue to be fixed at 0.95, and D3 will be equal to 0.05. Compared with the current curve envelope of the first cycle, the current curve envelope area of ​​the second cycle is reduced.

[0051] Since the FCCU 201 gives a small current control, Dtotal drops to 0.95 in a certain cycle after the first cycle. For ease of explanation, Figure 4 As shown, assuming that in the third cycle, Dtotal drops to 0.95, at this time Dtotal is still greater than or equal to 0.95, and the duty cycle adjustment circuit 30 still sets D1 to a fixed value of 0.95, but D3 will be equal to 0 at this time. Figure 4 As shown, in the third cycle, at the start point of the cycle, D3 is turned off, so the current starts to rise from the start point of the cycle at a slope of (Vin-Vout) / L to the moment of 0.95Ts. At the moment of 0.95Ts, D1 is turned off, and the instantaneous current of the inductor element L will drop to 0 at a slope of -Vout / L. By comparing the envelope areas of the current curves of the inductor element L in the second cycle and the third cycle, it can be seen that the envelope area of ​​the third cycle is smaller than the envelope area of ​​the second cycle, that is, the phase current of the inductor element L further decreases with the passage of time.

[0052] Since the FCCU 201 gives a small current control, Dtotal drops below 0.95 in a proper cycle. For ease of explanation, Figure 4 As shown, assume that in the fourth cycle Dtotal drops below 0.95, for example, 0.85. Since the determined Dtotal drops below 0.95, the duty cycle adjustment circuit 30 sets D1 to Dtotal, that is, 0.85 and sets D3 to 0. Figure 4 As shown, in the fourth cycle, at the starting point of the cycle, D3 is turned off, so the current starts to rise from the starting point of the cycle at a slope of (Vin-Vout) / L to the moment of 0.85Ts. At the moment of 0.85Ts, D1 is turned off, and the instantaneous current of the inductor element L will drop to 0 at a slope of -Vout / L. By comparing the envelope areas of the current curves of the inductor element L in the third cycle and the fourth cycle, it can be seen that the envelope area of ​​the fourth cycle is smaller than the envelope area of ​​the third cycle, that is, the phase current of the inductor element L further decreases with the passage of time.

[0053] Since the FCCU 201 gives a small current control, Dtotal drops to a suitable value in a suitable cycle, so that the envelope area of ​​the current in the cycle is small and the calculated phase current is close to the indicated small current (e.g., 20A or even smaller such as 5A). For ease of explanation, as Figure 4As shown, assuming that Dtotal drops to 0.74 in the fifth cycle, D1 is set to Dtotal, i.e., 0.74, and D3 is set to 0. By comparing the areas of the current curve envelopes of the inductor element L in the fifth cycle and the fourth cycle, it can be seen that the envelope area of ​​the fifth cycle is smaller than the envelope area of ​​the fourth cycle, that is, the phase current of the inductor element L further decreases with the passage of time, so that the calculated phase current can be close to the indicated small current (e.g., 20A or even smaller, such as 5A).

[0054] Therefore, in the case where Vin is greater than Vout, in the boost-buck mode, the small current control indicated by the FCCU 201 can be achieved through the new method of allocating the duty ratios D1 and D3 according to the present disclosure.

[0055] The following will refer to Figure 5 An example variation trend diagram of the instantaneous current on the inductor L in the boost-buck mode and when Vin is less than Vout according to an embodiment of the present disclosure is described.

[0056] refer to Figure 5 In the example, after the FCCU 201 gives a low current control, the inductor element L will choose to work in the current discontinuous mode. In the first cycle, since the determined Dtotal is still greater than 0.95, for example, 1.1, the duty cycle adjustment circuit 30 sets D1 to 0.95 and D3 to 1.1-0.95=0.15. Figure 5 As shown, in the first cycle, before 0.15Ts, the instantaneous current of the inductor L increases at a slope of Vin / L. At 0.15Ts, D3 is turned off, and the instantaneous current of the inductor L will flow through the diode T4 next to the MOS tube M4. Since Vin is less than Vout, the current will decrease to 0.95Ts at a slope of (Vin-Vout) / L. At 0.95Ts, D1 is turned off, and the inductor L will flow through the diodes T2 and T4, and the instantaneous current of the inductor L will decrease to 0 at a slope of -Vout / L. In some embodiments, the moment when the current of the inductor L decreases to 0 will be earlier than the end of the cycle.

[0057] like Figure 5 As shown, for the sake of explanation, it is assumed that in the second cycle, Dtotal decreases from the initial 1.1 to 1, so D1 will continue to be fixed at 0.95, and D3 will be equal to 0.05. Compared with the current curve envelope of the first cycle, the current curve envelope area of ​​the second cycle is reduced.

[0058] Since the FCCU 201 gives a small current control, Dtotal drops to a value slightly larger than 0.95, such as 0.97, in a certain cycle after the first cycle. For ease of explanation, Figure 5 As shown, assuming that in the third cycle, Dtotal drops to 0.97, at which time Dtotal is greater than or equal to 0.95, the duty cycle adjustment circuit 30 still sets D1 to a fixed value of 0.95, and then D3 is set to 0.02. Figure 5 As shown, in the third cycle, the current starts to rise from the starting point of the cycle at a slope of Vin / L to the moment of 0.02Ts. At the moment of 0.02Ts, D3 is turned off, and the instantaneous current of the inductor element L drops to 0 at a slope of (Vin-Vout) / L. Before reaching the moment of 0.95Ts, the current of the inductor element L has dropped to 0. By comparing the envelope areas of the current curves of the inductor element L in the second cycle and the third cycle, it can be seen that the envelope area of ​​the third cycle is much smaller than the envelope area of ​​the second cycle, that is, the phase current of the inductor element L further decreases with the passage of time.

[0059] Since the FCCU 201 gives a small current control, Dtotal drops to 0.95 in a proper cycle. For ease of explanation, Figure 5 As shown in Figure 2, assume that Dtotal drops to 0.95 in the fourth cycle. Then D3 will be set to 0. Figure 5 As shown, in the fourth cycle, at the starting point of the cycle, D3 is turned off, so the current is 0 from the beginning of the cycle, thereby achieving zero current control.

[0060] Therefore, compared with the case where Vin is greater than Vout, when Vin is less than Vout, small current control can be achieved more quickly, and even zero current control can be achieved. When Dtotal drops to close to 0.95, zero current control can be achieved without further decreasing Dtotal, for example, it is not necessary to decrease Dtotal to, for example, 0.74 as in the case where Vin is greater than Vout, but only D1 needs to be decreased to close to 0.95 and D3 needs to be decreased to close to 0.

[0061] The following will refer to Figure 6 The method 600 for controlling the current of a power transmission unit according to an embodiment of the present disclosure is described. The power transmission unit may be the power transmission unit 100 shown in FIG. 1 , and the power transmission unit 100 may include the following: Figure 3Controller 1 shown. The method for controlling the current of the power transmission unit is executed by the controller 1. The power transmission unit 100 may include a MOS tube M1 (also referred to as a first switch, which is turned on and off at a first duty cycle) and a MOS tube M3 (also referred to as a second switch, which is turned on and off at a second duty cycle). In addition, the power transmission unit 100 may also include an inductor element L, which is connected between the first switch and the second switch and the current flowing through the inductor element L is associated with the first duty cycle and the second duty cycle, that is, different setting values ​​of the first duty cycle and the second duty cycle will affect the current of the inductor element L, as described above with reference to Figure 4 and Figure 5 As described. Figure 6 As shown, in block 610, the desired phase current for the inductor element L is obtained. In some embodiments, the first closed-loop circuit 10 (ie, outer loop) of the controller 1 receives the desired stack current and the measured stack current and outputs the desired phase current based thereon.

[0062] In block 620, the actual phase current flowing through the inductor element L is obtained. In some embodiments, the actual phase current flowing through the inductor element L can be obtained by sampling the instantaneous current flowing through the inductor element L multiple times in one cycle and averaging the sampled currents.

[0063] In block 630, a total duty cycle Dtotal is determined as the sum of the duty cycle D1 of the MOS transistor M1 and the duty cycle D2 of the MOS transistor M2 based on the desired phase current and the actual phase current. In some embodiments, the second closed-loop circuit 20 of the controller 1 receives the desired phase current and the actual phase current of the inductor element L and determines the total duty cycle Dtotal based on the two.

[0064] In block 640, the duty cycle D1 of the MOS tube M1 and the duty cycle D2 of the MOS tube M2 are adjusted based on the total duty cycle. In some embodiments, in response to the determined total duty cycle being greater than or equal to 0.95, the duty cycle adjustment circuit 30 of the controller 1 sets the duty cycle D1 of the MOS tube M1 to 0.95, and sets the duty cycle D3 of the MOS tube M3 to the total duty cycle minus 0.95; and in response to the determined total duty cycle being less than 0.95, the duty cycle adjustment circuit 30 sets the duty cycle D1 of the MOS tube M1 to the total duty cycle, and sets the duty cycle D3 of the MOS tube M3 to zero.

[0065] In box 650, the MOS tube M1 controlled based on the adjusted duty cycle D1 is turned on and off, and the MOS tube M3 is turned on and off based on the adjusted duty cycle D3 to control the current flowing through the inductor element L. In the case where the FCCU 201 of the fuel cell stack gives a small current control, the total duty cycle will show a trend of gradually decreasing. In the case where the total duty cycle is greater than or equal to 0.95, the duty cycle D1 is set to 0.95, and the duty cycle D3 is equal to the total duty cycle minus 0.95, so it decreases with the decrease of the total duty cycle to 0. In the case where the duty cycle is reduced to less than 0.95, D1 is set to the total duty cycle, so D1 will also decrease with the decrease of the total duty cycle at this time to decrease to an appropriate value, so that the actually measured expected current of the inductor element L is close to the small current specified by the FCCU 201 (that is, the expected stack current).

[0066] Therefore, the method 600 for controlling the current of the power transmission unit according to the present disclosure can achieve the smaller desired stack current specified by the FCCU 201, and can even achieve a current requirement of less than 5A, so there is no blind spot for current control. The power transmission unit 100 and the method 600 for controlling the current of the power transmission unit can be simply implemented in the original software, without negative current on the stack side, and remain compatible with the previous control strategy in the high current area.

[0067] Figure 7 A schematic block diagram of an example device 700 that can be used to implement an embodiment of the present disclosure is shown. As shown, the device 700 includes a computing unit 701, which can perform various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) 702 or loaded from a storage unit 708 into a random access memory (RAM) 703. In the RAM 703, various programs and data required for the operation of the device 700 can also be stored. The computing unit 701, the ROM 702, and the RAM 703 are connected to each other via a bus 704. An input / output (I / O) interface 705 is also connected to the bus 704.

[0068] A number of components in the device 700 are connected to the I / O interface 705, which may include, for example: an input unit 706, such as a keyboard, a mouse, etc.; an output unit 707, such as various types of displays, speakers, etc.; a storage unit 708, such as a disk, an optical disk, etc.; and a communication unit 707, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 707 allows the device 700 to exchange information / data with other devices through a computer network such as the Internet and / or various telecommunication networks.

[0069] The computing unit 701 may be a variety of general and / or special processing components with processing and computing capabilities. Some examples of the computing unit 701 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various dedicated artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, digital signal processors (DSPs), and any appropriate processors, controllers, microcontrollers, etc. The computing unit 701 performs the various methods and processes described above, such as method 600. For example, in some embodiments, the method 600 may be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit 708. In some embodiments, part or all of the computer program may be loaded and / or installed on the device 700 via the ROM 702 and / or the communication unit 707. When the computer program is loaded into the RAM 703 and executed by the computing unit 701, one or more steps of the method 600 described above may be performed. Alternatively, in other embodiments, the computing unit 701 may be configured to perform the method 600 in any other appropriate manner (e.g., by means of firmware).

[0070] The functions described above herein may be performed at least in part by one or more hardware logic components. For example, without limitation, exemplary types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chip systems (SOCs), load programmable logic devices (CPLDs), and the like.

[0071] The program code for implementing the method of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code may be executed entirely on the machine, partially on the machine, partially on the machine and partially on a remote machine as a stand-alone software package, or entirely on a remote machine or server.

[0072] In the context of the present disclosure, a machine-readable medium may be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, device, or equipment. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In addition, although each operation is depicted in a specific order, this should be understood as requiring such operations to be performed in the specific order shown or in a sequential order, or requiring that all illustrated operations should be performed to obtain the desired result. In certain environments, multitasking and parallel processing may be advantageous. Similarly, although several specific implementation details are included in the above discussion, these should not be interpreted as limiting the scope of the present disclosure. Certain features described in the context of separate embodiments can also be implemented in a single implementation in combination. On the contrary, the various features described in the context of a single implementation can also be implemented in multiple implementations individually or in any suitable sub-combination.

[0073] Although the subject matter has been described in language specific to structural features and / or methodological logical actions, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. On the contrary, the specific features and actions described above are merely example forms of implementing the claims.

Claims

1. A power transmission unit for transmitting electric power of a fuel cell stack to a power battery, the power transmission unit comprising: a first switch configured to be turned on and off at a first duty cycle; a second switch configured to be turned on and off at a second duty cycle that is smaller than the first duty cycle; an inductor connected between the first switch and the second switch and having a current flowing therethrough associated with the first duty cycle and the second duty cycle; as well as A controller is configured to determine a total duty cycle as a sum of the first duty cycle and the second duty cycle based on an actual phase current and a desired phase current of the inductor element, and to adjust the first duty cycle and the second duty cycle based on the determined total duty cycle. 2 . The power transfer unit of claim 1 , wherein the controller is further configured to determine the desired phase current based on a desired stack current and an actual stack current. 3 . The power transmission unit according to claim 2 , wherein the stack further comprises a stack control unit configured to provide the desired stack current.

4. The power transfer unit of claim 1 , wherein adjusting the first duty cycle and the second duty cycle based on the determined total duty cycle comprises: In response to the total duty cycle being determined to be greater than or equal to 0.95, setting the first duty cycle to 0.95 and setting the second duty cycle to the total duty cycle minus 0.95; as well as In response to determining that the total duty cycle is less than 0.95, the first duty cycle is set to the total duty cycle, and the second duty cycle is set to zero.

5. The power transfer unit of claim 1, wherein the controller comprises: a first closed-loop circuit, wherein the desired stack current and the actual stack current are input into the first closed-loop circuit to determine the desired phase current; as well as A second closed-loop circuit, the actual phase current and the desired phase current are input into the second closed-loop circuit to determine the total duty cycle. 6 . The power transmission unit according to claim 1 , wherein an input voltage of the power transmission unit from the fuel cell stack is greater than an output voltage output to the power battery.

7. The power transfer unit according to claim 3, wherein the power transfer unit operates in a non-complementary boost-decompression mode, and the stack control unit is configured to provide the desired stack current of less than or equal to 20 amperes. 8 . The power transmission unit according to claim 1 , wherein the controller is further configured to: sample the current flowing through the inductor element multiple times within one cycle, and calculate an average value of the sampled currents as the actual phase current.

9. A method for controlling the current of a power transmission unit, the power transmission unit being used to transmit the electric power of a fuel cell stack to a power battery, the power transmission unit comprising: a first switch configured to be turned on and off at a first duty cycle; a second switch configured to be turned on and off at a second duty cycle; and an inductor element connected between the first switch and the second switch and having a current flowing therethrough associated with the first duty cycle and the second duty cycle, the method comprising: obtaining a desired phase current for the inductive element; Acquiring an actual phase current flowing through the inductor element; determining a total duty cycle as a sum of the first duty cycle and the second duty cycle based on the desired phase current and the actual phase current; adjusting the first duty cycle and the second duty cycle based on the total duty cycle; and The first switch is controlled to be turned on and off based on the adjusted first duty ratio, and the second switch is controlled to be turned on and off based on the adjusted second duty ratio, so as to control the current flowing through the inductor element.

10. The method of claim 9, wherein obtaining a desired phase current for the inductive element comprises: The desired phase current for the inductive element is determined based on the desired stack current and the actual stack current.

11. The method of claim 9, wherein measuring the actual phase current flowing through the inductive element comprises: The current flowing through the inductor element is sampled multiple times in one cycle, and an average value of the sampled currents is calculated as the actual phase current.

12. The method of claim 9, wherein adjusting the first duty cycle and the second duty cycle based on the total duty cycle comprises: In response to the total duty cycle being determined to be greater than or equal to 0.95, setting the first duty cycle to 0.95 and setting the second duty cycle to the total duty cycle minus 0.95; as well as In response to determining that the total duty cycle is less than 0.95, the first duty cycle is set to the total duty cycle, and the second duty cycle is set to zero.

13. A fuel cell system comprising: Fuel cell stack; Power battery; as well as The power transmission unit according to any one of claims 1 to 8 is configured to transmit the electric power of the fuel cell stack to the power battery.

14. A machine-readable storage medium having machine-executable instructions stored thereon, wherein the machine-executable instructions are executed by a processor to implement the method according to any one of claims 9 to 12.

Images