A method and system for controlling the phase current distribution of a DC-DC converter with ac power injection

Abstract

A method of controlling the phase current distribution of a DC-DC converter with AC power injection, comprising: obtaining a requested value of the stack current of a fuel cell stack electrically connected to the DC-DC converter, the amplitude of the AC power to be injected into the DC-DC converter, and the current value range of the two phases of the DC-DC converter entering boundary conduction mode; allocating the requested value of the stack current is allocated to the phase with AC power injection, or evenly distributing the requested value of the stack current between the two phases, or sequentially distributed the requested value of the stack current and the AC power between the first phase and the second phase, so that when the first phase and the second phase are injected with AC power, their corresponding phase currents do not enter the current value range of boundary conduction mode. A system for controlling the phase current distribution of a DC-DC converter with AC power injection is further proposed, comprising a controller in communication with the DC-DC converter and a fuel cell stack, the controller being configured to perform the above method.

Description

[0001] Specification

[0002] A Method and System for Controlling the Phase Current Distribution of a DC-DC Converter with AC Power Injection

[0003] Technical Field

[0004] The present invention relates to phase current distribution in DC-DC converters. In particular, a method and system for controlling the phase current distribution of a DC-DC converter with AC power injection is involved.

[0005] Background

[0006] The proton exchange membrane (PEM) in a fuel cell stack is easily damaged under certain extreme humidity conditions. Thus, it is necessary to measure and monitor the humidity of the proton exchange membrane. Conventionally, the humidity of the proton exchange membrane may be directly measured by a humidity sensor. However, the introduction of humidity sensors increases the cost and structural complexity of fuel cell systems. DC-DC converters are widely used as power output modules for power conversion between fuel cell stacks and electrical devices. They have three operating modes: continuous conduction mode (CCM), discontinuous conduction mode (DCM), and boundary conduction mode (BCM). To replace the humidity sensor, electrochemical impedance spectroscopy (EIS) has been developed to measure the humidity of the proton exchange membrane.

[0007] In this method, based on the two-phase transmission of DC power in the DC-DC converter, the humidity of the proton exchange membrane is inferred from the internal impedance of the stack in the high-frequency range (HFR) by injecting an AC signal into one of the phases and analyzing the frequency domain response of the stack voltage at that time. During the performance of the EIS measurement method, when a certain amount of DC power is requested from the DC-DC converter, the DC power of one phase of the DC-DC converter is usually first increased to a certain value, and the AC power required for performing the EIS measurement method is injected into that phase. When the DC power of the first phase reaches the certain value, the DC power of the second phase is increased to a certain set value, so that the DC power is ultimately evenly distributed between the first phase and the second phase In the above method, there are some obvious drawbacks. First, for different fuel cell stacks and batteries, the BCM current range of the EIS injection phase is different, so the data needs to be recalibrated for different fuel cell stacks and batteries to adjust the value to which the DC power pull-up of the first phase in the DC-DC converter first rises. In addition, as the stack voltage changes, the BCM operating range of the phase current will also change, and there is still a risk of transitioning to BCM from DCM.

[0008] As a result, there is a need for a method and system to control the phase current distributionof a DC-DC converter with AC power injection, which should overcome the problems present in the prior art.

[0009] Summary of the Invention

[0010] To this end, the present disclosure proposes a method of controlling the phase current distribution of a DC-DC converter with AC power injection, comprising:

[0011] obtaining a requested value of the stack current of a fuel cell stack electrically connected to the DC-DC converter, the amplitude of the AC power to be injected into the DC-DC converter, and the current value range of the two phases of the DC-DC converter entering boundary conduction mode;

[0012] during the process of increasing the phase current of the phase with injected AC power from zero to the requested value of the stack current in the two phases, if the phase current of the phase with injected AC power does not enter the current value range of boundary conduction mode, then allocating the requested value of the stack current to the phase with injected AC power;

[0013] during the process of increasing the phase current of the phase with injected AC power in the two phases from zero to the requested value of the stack current, if the phase current of the phase with injected AC power into the two phases will enter the current value range of boundary conduction mode, but the phase current of the phase with injected AC power will not enter the current value range of boundary conduction mode during the process of the phase current of the phase with injected AC power increasing from zero to half of the requested value of the stack current, then evenly distributing the requested value of the stack current between the two phases;

[0014] otherwise:

[0015] increasing the phase current of the first phase of the DC-DC converter from zero to a first threshold while AC power is injected into the first phase;

[0016] increasing the phase current of the second phase of the DC-DC converter from zero to a second threshold while maintaining the phase current of the first phase at the first threshold and continuing to inject AC power into the first phase;

[0017] stopping the injection of AC power into the first phase while maintaining the phase current of the second phase at the second threshold and injecting AC power into the second phase while increasing the phase current of the first phase from the first threshold to a third threshold;

[0018] after the phase current of the first phase reaches the third threshold, increasing the phase currents of the first and second phases simultaneously so that the requested value of the stack current is evenly distributed between the first and second phases,

[0019] wherein the third threshold is greater than the second threshold, the second threshold is greater than the first threshold, and the corresponding phase currents of the first phase and the second phase do not enter the current value range of boundary conduction mode when each of the first and second phases is injected with AC power.The present disclosure further proposes a system for controlling the phase current distribution of a DC-DC converter with AC power injection, the DC-DC converter being electrically connected to a fuel cell stack, and the system comprising a controller in communication with the DC-DC converter and the fuel cell stack and configured to:

[0020] obtain a requested value of the stack current of a fuel cell stack, the amplitude of the AC power to be injected into the DC-DC converter, and the current value range of the two phases of the DC-DC converter entering boundary conduction mode;

[0021] during the process of increasing the phase current of the phase with injected AC power from zero to the requested value of the stack current in the two phases, if it is determined that the phase current of the phase with injected AC power does not enter the current value range of boundary conduction mode, then control the DC-DC converter to allocate the requested value of the stack current to the phase with injected AC power;

[0022] during the process of increasing the phase current of the phase with injected AC power in the two phases from zero to the requested value of the stack current, if it is determined that the phase current of the phase with injected AC power into the two phases will enter the current value range of boundary conduction mode, but the phase current of the phase with injected AC power will not enter the current value range of boundary conduction mode during the process of the phase current of the phase with injected AC power increasing from zero to half of the requested value of the stack current, then control the DC-DC converter to evenly distribute the requested value of the stack current between the two phases;

[0023] otherwise:

[0024] control the DC-DC converter to increase the phase current of the first phase of the DC-DC converter from zero to a first threshold while AC power is injected into the first phase;

[0025] control the DC-DC converter to increase the phase current of the second phase of the DC-DC converter from zero to a second threshold while maintaining the phase current of the first phase at the first threshold and continuing to inject AC power into the first phase;

[0026] control the DC-DC converter to stop the injection of AC power into the first phase while maintaining the phase current of the second phase at the second threshold and injecting AC power into the second phase while increasing the phase current of the first phase from the first threshold to a third threshold;

[0027] after the phase current of the first phase reaches the third threshold, control the DC-DC converter to increase the phase currents of the first and second phases simultaneously so that the requested value of the stack current is evenly distributed between the first and second phases, wherein the third threshold is greater than the second threshold, the second threshold is greater than the first threshold, and the corresponding phase currents of the first phase and the second phase do not enter the current value range of boundary conduction mode when each of the first and second phases is injected with AC power.

[0028] The present disclosure further proposes a computer program product comprising computerinstructions that, when executed by a processor, implement the method according to the present disclosure.

[0029] Brief Description of the Drawings

[0030] FIG. 1 shows a schematic circuit diagram of a DC-DC converter;

[0031] FIG. 2 shows a flowchart of a method for controlling the phase current distribution of a DC-DC converter with AC power injection according to the present disclosure;

[0032] FIG. 3 shows a schematic diagram of the change in phase current in a DC-DC converter when the method according to the present disclosure is performed; and

[0033] FIG. 4 shows a schematic block diagram of a system for controlling the phase current distribution of a DC-DC converter with AC power injection according to the present disclosure.

[0034] Detailed Description of the Embodiments

[0035] FIG. 1 shows a schematic circuit diagram of a DC-DC converter. The method and system for controlling the phase current distribution of a DC-DC converter with AC power injection according to the present disclosure involve a DC-DC converter commonly used as a power output module in a fuel cell stack.

[0036] As shown in FIG. 1, the circuit of the DC-DC converter is a two-phase parallel circuit. The circuit primarily comprises a first-phase inductor Pha1L and a second-phase inductor Pha2L, a current sensor iphal for measuring the phase current of the first phase, a current sensor ipha2 for measuring the phase current of the second phase, and a plurality of switching transistors. Wherein, the switching transistors Q1H, Q1L, Q3H, and Q3L are the switching transistors that control the phase current of the first phase. By controlling the duty cycle of each of these switching transistors, the current flowing through the first-phase inductor Pha1L and measured by the current sensor iphal can be adjusted. The switching transistors Q2H, Q2L, Q4H, and Q4L are the switching transistors that control the phase current of the second phase. By controlling the duty cycle of each of these switching transistors, the current flowing through the second-phase inductor Pha2L and measured by the current sensor ipha2 can be adjusted. In addition, UiNin FIG.

[0037] 1 represents the input voltage of the DC-DC converter, while II out represents the output voltage of the DC-DC converter.

[0038] The DC-DC converter circuit in FIG. 1 may form a boost circuit or a buck-boost circuit by controlling the connection and disconnection of different switching transistors.

[0039] When a certain output power is requested from the fuel cell stack, the current distribution between the two phases of the DC-DC converter can be controlled by controlling the duty cycle of each of the switching transistors. When performing the EIS measurement method to measure the humidity of the proton exchange membrane in a fuel cell stack, the injection of AC power into the DC-DC converter may also be achieved by controlling the duty cycle of each switching transistor.FIG. 2 shows a flowchart of a method for controlling the phase current distribution of a DODO converter with AC power injection according to the present disclosure. The method primarily comprises the following steps:

[0040] S101 : Obtain a requested value of the stack current of a fuel cell stack electrically connected to the DC-DC converter, the amplitude of the AC power to be injected into the DC-DC converter, and the current value range of the two phases of the DC-DC converter entering boundary conduction mode (BCM);

[0041] S201: During the process of increasing the phase current of the phase with injected AC power from zero to the requested value of the stack current in the two phases of the DC-DC converter, if the phase current of the phase with injected AC power does not enter the current value range of boundary conduction mode, then allocate the requested value of the stack current to the phase with injected AC power;

[0042] S301: during the process of increasing the phase current of the phase with injected AC power in the two phases of the DC-DC converter from zero to the requested value of the stack current, if the phase current of the phase with injected AC power into the two phases will enter the current value range of boundary conduction mode, but the phase current of the phase with injected AC power will not enter the current value range of boundary conduction mode during the process of the phase current of the phase with injected AC power increasing from zero to half of the requested value of the stack current, then evenly distribute the requested value of the stack current between the two phases of the DC-DC converter;

[0043] if the judgment results in steps S201 and S301 are both negative, then the following steps are performed:

[0044] S401 : Increase the phase current of the first phase of the DC-DC converter from zero to a first threshold while the AC power is injected into the first phase;

[0045] S501: Increase the phase current of the second phase of the DC-DC converter from zero to a second threshold while maintaining the phase current of the first phase at the first threshold and continuing to inject the AC power into the first phase;

[0046] S601: Stop the injection of the AC power into the first phase while maintaining the phase current of the second phase at the second threshold and injecting the AC power into the second phase while increasing the phase current of the first phase from the first threshold to a third threshold;

[0047] S701: After the phase current of the first phase reaches the third threshold, increase the phase currents of the first and second phases simultaneously so that the requested value of the stack current is evenly distributed between the first and second phases.

[0048] Wherein, the third threshold is greater than the second threshold, the second threshold is greater than the first threshold, and the corresponding phase currents of the first phase and the second phase do not enter the current value range of boundary conduction mode when each of the first and second phases is injected with AC power.Wherein, the first threshold, the second threshold, and the third threshold can be determined based on the input voltage and output voltage Uout of the DC-DC converter, the switching period and duty cycle of the switching transistors contained in the DC-DC converter, and the amplitude of the AC power.

[0049] Overall, the purpose of the above method is to prevent the phases injected with AC power in the DC-DC converter from entering BCM. Because AC power has peaks and troughs, if the phase to which AC power is injected is in BCM, the phase may switch back and forth between CCM and DCM within one injection cycle of AC power (e.g., within one sine cycle), making it impossible to control the current of the phase superimposed with AC power using a single set of control logic.

[0050] Compared to the phase current distribution methods in DC-DC converters when performing EIS measurements in the prior art, the method according to the present disclosure ensures that neither phase of the DC-DC converter enters BCM and eliminates the need for calibration of a stationary fuel cell stack. Therefore, the versatility of the method is significantly improved while reducing its complexity.

[0051] The steps of the method according to the present disclosure will be described in detail below. In step S101, the requested value of the stack current electrically connected to the DC-DC converter is first obtained. The requested value of the stack current is the current value of the DC power to be distributed between the two phases of the DC-DC converter. The amplitude of the AC power to be injected into the DC-DC converted is then obtained, which is the amplitude of the AC power to be injected into the DC-DC converter when performing electrochemical impedance spectroscopy (EIS) to measure the humidity of the proton exchange membrane of the fuel cell stack.

[0052] The current range for the two phases of the DC-DC converter to enter boundary conduction mode can be calculated based on the input voltage Ujnand the output volume Uout of the DC-DC converter as shown in FIG. 1, the inductance values of inductors Pha1L and Pha2L in the DC-DC converter, the switching cycles and duty cycles of the various switching transistors Q1H, Q1L, Q3H, Q3L, Q2H, Q2L, Q4H, and Q4L in the DC-DC converter, and the amplitude of the AC power to be injected into the DC-DC converter.

[0053] For a DC-DC converter without AC power injection, the current value corresponding to the two phases entering BCM is a fixed value. However, for a DC-DC converter with AC power injection, the current value corresponding to the two phases entering BCM is a range of the fixed DC value plus the amplitude of the injected AC power. Fora DC-DC converter without AC power injection, the calculation process of the current value IBCM corresponding to the two phases entering BCM is described below.

[0054] For a boost circuit, the calculation formula of IBCM is as follows:

[0055] -BCM ~ ipeak / ( 1-1 )The ipeak m the above formula (1-1) is the peak current across inductors Pha1L and Pha2L in the circuit, and its calculation formula is as follows:

[0056]

[0057] Where Uout is the output voltage of the DC-DC converter shown in FIG. 1 , Um is the input voltage of the DC-DC converter shown in FIG. 1, T is the switching period of the various switching transistors in the DC-DC converter shown in FIG. 1 , and L is the inductance value of the inductor Pha1 L or Pha2L in the DC-DC converter.

[0058] The derivation of the above formula (1-2) is as follows:

[0059] <

[0060] > >

[0061]

[0062] Where d is the total duty cycle of each switching transistor shown in FIG. 1 , tonis the total charging time of inductor Pha1L or Pha2L shown in FIG. 1, the value of which is equal to the total duty cycle of each switching transistor multiplied by the switching period, and toff is the total discharging time of inductor Pha1L or Pha2L.

[0063] The above formula (1-2) is obtained by eliminating parameter d from formulas (1-3) and (1-4).

[0064] For a buck-boost circuit, the calculation formula of IBCM is as follows:

[0065]

[0066] The formula for calculating ipeak in the above formula (1-5) is as follows:

[0067]

[0068] < >

[0069] The derivation of the above formula (1-6) is as follows:

[0070]

[0071] The parameters that appear in formulas (1-5) to (1-8) are the same as the corresponding parameters that appear in formulas (1-1) to (1-4) above.

[0072] The above formula (1-6) is obtained by eliminating parameter d from formulas (1-7) and (1-8).

[0073] It should be noted that the current value IBCM that appears in each of the formulas above isthe boundary value for the two phases to enter BCM in the DC-DC converter; that is, whether the two phases have entered BCM can be determined by comparing the current values measured at current sensors iphal and ipha2 with this current value IBCM.

[0074] Based on the above formulas, the current values corresponding to the two phases of the DC-DC converter entering BCM without AC power injection can be calculated according to the input voltage UiNand output voltage Uout of the DC-DC converter, the inductance values of inductors Pha1L and Pha2L in the DC-DC converter, and the switching cycles and duty cycles of the various switching transistors contained in the DC-DC converter. When AC power is injected, the current range for the two phases to enter boundary conduction mode can be obtained based on the amplitude of the injected AC power.

[0075] It can be seen from the above formulas that the corresponding IBCM can be calculated for both a boost circuit and a buck-boost circuit. Thus, the method according to the present disclosure is applicable to both boost circuits and buck-boost circuits, which increases the versatility of the method according to the present disclosure.

[0076] Step S201 is performed next: During the process of increasing the phase current of the phase with injected AC power from zero to the requested value of the stack current in the two phases of the DC-DC converter,

[0077] if the phase current of the phase does not enter the current value range of boundary conduction mode, then allocate the requested value of the stack current entirely to the phase with injected AC power. That is, if the requested value of the stack current is low enough that even if the requested value of the stack current and the AC power injected by performing the EIS measurement method are both allocated to only one of the two phases of the DC-DC converter and the other phase is not allocated any current, the phase current of the phase to which the current is allocated will not enter the current value range of boundary conduction mode as described above, then the requested value of the stack current can be allocated to the phase with injected AC power. As such, only one phase of the two phases of the DC-DC converter is used to conduct current, which may reduce the switching losses of the switching transistors in the DC-DC converter compared to the current being distributed between the two phases.

[0078] Step S301 is performed next: During the process of increasing the phase current of the phase with injected AC power in the two phases of the DC-DC converter from zero to the requested value of the stack current, if the phase current of the phase with injected AC power into the two phases will enter the current value range of boundary conduction mode, but the phase current of the phase with injected AC power will never enter the current value range of boundary conduction mode during the process of the phase current of the phase with injected AC power increasing from zero to half of the requested value of the stack current, then evenly distribute the requested value of the stack current between the two phases of the DC-DC converter. That is, a double judgment is performed in this step: First, the situation where the requested value of the stack current and the AC power corresponding to step S201 are both allocated to only one of thetwo phases of the DC-DC converter is ruled out. Second, if it is determined that during the process of the phase current of the phase with injected AC power increasing from zero to half of the requested value of the stack current, the phase current of the phase with injected AC power will not enter the current value range of boundary conduction mode, then this indicates that neither the phase current of the phase with injected AC power nor the phase current of the phase without injected AC power will enter the current value range of boundary conduction mode during the process of increasing from zero to half of the requested value of the stack current. Therefore, the requested value of the stack current can be evenly distributed between the two phases of the DC-DC converter so that neither phase enters boundary conduction mode.

[0079] The subsequent steps S401 to S701 will be described in conjunction with FIGS. 2 and 3. FIG. 3 shows a schematic diagram of the change in phase current in a DC-DC converter when the method according to the present disclosure is performed. FIG. 3 corresponds to the case where the judgment results of steps S201 and S301 are both negative; that is, the phase current of the phase with injected AC power in the two phases of the DC-DC converter increases from zero to half of the requested value of the stack current. Thus, in order to avoid entering boundary conduction mode, the requested value of the stack current cannot be directly distributed evenly between the two phases.

[0080] In FIG. 3, the horizontal axis iphal represents the phase current of the first phase in the DC-DC converter and the vertical axis ipha2

[0081] represents the phase current of the second phase. Point io on the horizontal axis corresponds to the lower requested value of the stack current mentioned in the judgment process of step S201. That is, if the requested value of the stack current is less than or equal to io , the requested value of the stack current and the AC power can be allocated to one of the two phases (the first phase in FIG. 3, but not limited thereto).

[0082] In FIG. 3, the region Z1, represented by the dashed line parallel to the vertical axis, corresponds to the current value range of boundary conduction mode of the first phase, which may also be called the forbidden zone for the first phase. The region Z2, represented by the dashed line parallel to the horizontal axis, corresponds to the current value range of boundary conduction mode of the second phase, which may also be called the forbidden zone for the second phase. If the phase current of the first phase enters the current value range of its boundary conduction mode, then the first phase will enter boundary conduction mode. If the phase current of the second phase enters the current value range of its boundary conduction mode, then the second phase will enter boundary conduction mode. Typically, the current value ranges of boundary conduction modes for the first and second phases are the same, but they may also be different. For example, if the switching cycles of the two corresponding switching transistors are different, the current value ranges for boundary conduction mode calculated by the aforementioned method may differ.

[0083] Step S401 is performed next: Increase the phase current of the first phase of the DC-DCconverter from zero to a first threshold while the AC power is injected into the first phase. Point ii shown in FIG. 3 is the first threshold mentioned above. The first threshold ii is set such that during the period when the phase current of the first phase increases from zero to the first threshold ii while AC power is injected into the first phase, the first phase will not enter boundary conduction mode; that is, it will not enter region Z1.

[0084] Specifically, the first threshold ii may be calculated by the following formula:

[0085]

[0086] Where IBCMI is the boundary current value for the first phase to enter boundary conduction mode without AC power injection, which can be calculated according to the calculation method of IBCM described in formulas (1-1) to (1-8), iEis is the amplitude of the AC power injected when the EIS method is performed, and iBUffen is an adjustable first buffer value set for the first phase; that is, iBufferi can be adjusted according to actual needs, such as for different fuel cell stacks.

[0087] When AC power is injected, if the phase current of the first phase is greater than or equal to IBCMI, this indicates that the first phase will enter boundary conduction mode. When AC power is injected, in order to avoid the first phase entering boundary conduction mode, ii is set to iBCM minus the amplitude of the injected AC power iEis and further minus the first buffer value i Buffer, thereby ensuring that the first phase will not enter boundary conduction mode during the entire process of the phase current of the first phase increasing from zero to i1. It is clear from FIG. 3 that the first phase does not enter region Zi when the phase current of the first phase reaches the first threshold .

[0088] Step S501 is performed next: Increase the phase current of the second phase of the DC-DC converter from zero to a second threshold while maintaining the phase current of the first phase at the first threshold ii and continuing to inject the AC power into the first phase. Point i2 shown in FIG. 3 is the second threshold mentioned above. This step corresponds to the process from point ii to point i2 in FIG. 3, where the sine curve between point ii and point i2 represents the AC power injected into the first phase. The second threshold i2 is set such that during the period when the phase current of the second phase increases from zero to the second threshold i2 while AC power is injected into the first phase, the first phase will not enter boundary conduction mode; that is, it will not enter region Z1. Furthermore, when AC power is injected into the second phase in subsequent steps, the second phase will not enter boundary conduction mode; that is, it will not enter region Z2.

[0089] Specifically, the second threshold i2 may be calculated by the following formula:

[0090]

[0091] Where iBCM2 is the boundary current value for the second phase to enter boundary conduction mode without AC power injection, which can be calculated according to the calculation method of IBCM described in formulas (1-1) to (1-8), / ssis the amplitude of the AC power injected when the EIS method is performed, and i Buffed is an adjustable second buffer value set for thesecond phase; that is, iBuffer2 can be adjusted according to actual needs, such as for different fuel cell stacks. iBUffen and iBuffer2 may be the same or different.

[0092] It is clear from FIG. 3 that in step S501, when the phase current of the second phase increases from zero to the second threshold i2, the first phase with injected AC power will not enter boundary conduction mode; that is, it will not enter region Z1.

[0093] Step S601 is performed next: Stop the injection of the AC power into the first phase while maintaining the phase current of the second phase at the second threshold i2 and injecting the AC power into the second phase while increasing the phase current of the first phase from the first threshold i1 to a third threshold. Point i3 shown in FIG. 3 is the third threshold mentioned above. This step corresponds to the process from point i2 to point is in FIG. 3, where the sine curve between point i2 and point is represents the AC power injected into the second phase. The third threshold i3 is set such that during the period when the phase current of the first phase increases from the first threshold ii to the third threshold i3 while AC power is injected into the second phase, the second phase will notenter boundary conduction mode; that is, it will not enter region Z2, and the first phase and the second phase will not enter boundary conduction mode in subsequent steps. The third threshold is may, for example, be set twice as large as IBCMI and iBCM2, but is not limited thereto, as long as it is set to a value that prevents both the first phase and the second phase from entering boundary conduction mode.

[0094] Finally, step S701 is performed: After the phase current of the first phase reaches the third threshold is, increase the phase currents of the first and second phases simultaneously so that the requested value of the stack current is evenly distributed between the first and second phases. This step corresponds to the process after point is in FIG. 3. It can be seen that the respective phase currents of the first phase and the second phase have both moved away from the current value ranges Z1 and Z2 of their respective boundary conduction modes, thereby increasing the phase currents of the first phase and the second phase simultaneously so that the requested value of the stack current is evenly distributed between the first phase and the second phase, which will not cause the first phase or the second phase to enter boundary conduction mode.

[0095] It should be noted that FIG. 3 shows that when the requested value of the stack current is evenly distributed between the first phase and the second phase, the AC power is maintained and injected into the second phase. However, this disclosure is not limited thereto. The AC power may also be injected into the first phase instead, and the phase will not enter boundary conduction mode regardless of which phase has AC power injection.

[0096] Through the phase current distribution method of the first phase and the second phase of the DC-DC converter and the method of injecting AC power described in the above steps, and particularly by means of the selection of the first threshold , the second threshold i2, and the third threshold is, it is ensured that the first phase and the second phase of the DC-DC converter will never enter boundary conduction mode when the EIS method is performed, thereby improving the stability of the system. Moreover, there is no need to calibrate for different fuel cell stacks,making the implementation of the EIS method simpler and more universal.

[0097] The present disclosure further proposes a system of controlling the phase current distribution of a DC-DC converter with AC power injection. As shown in FIG. 4, a DC-DC converter 200 is electrically connected to a fuel cell stack 300. The system 10 comprises a controller 100, the controller 100 being in communication with the DC-DC converter 200 and the fuel cell stack 300 and configured to:

[0098] obtain a requested value of the stack current of the fuel cell stack, the amplitude of the AC power to be injected into the DC-DC converter 200 and the current value range of the two phases of the DC-DC converter 200 entering boundary conduction mode;

[0099] during the process of increasing the phase current of the phase with injected AC power from zero to the requested value of the stack current in the two phases, if it is determined that the phase current of the phase with injected AC power does not enter the current value range of boundary conduction mode, then control the DC-DC converter 200 to allocate the requested value of the stack current to the phase with injected AC power;

[0100] during the process of increasing the phase current of the phase with injected AC power in the two phases from zero to the requested value of the stack current, if it is determined that the phase current of the phase with injected AC power into the two phases will enter the current value range of boundary conduction mode, but the phase current of the phase with injected AC power will not enter the current value range of boundary conduction mode during the process of the phase current of the phase with injected AC power increasing from zero to half of the requested value of the stack current, then control the DC-DC converter 200 to evenly distribute the requested value of the stack current between the two phases;

[0101] otherwise:

[0102] control the DC-DC converter 200 to increase the phase current of the first phase of the DC-DC converter from zero to a first threshold while AC power is injected into the first phase;

[0103] control the DC-DC converter 200 to increase the phase current of the second phase of the DC-DC converter 200 from zero to a second threshold while maintaining the phase current of the first phase at the first threshold and continuing to inject AC power into the first phase;

[0104] control the DC-DC converter 200 to stop the injection of AC power into the first phase while maintaining the phase current of the second phase at the second threshold and injecting AC power into the second phase while increasing the phase current of the first phase from the first threshold to a third threshold;

[0105] after the phase current of the first phase reaches the third threshold, control the DC-DC converter 200 to increase the phase currents of the first and second phases simultaneously so that the requested value of the stack current is evenly distributed between the first and second phases,

[0106] wherein the third threshold is greater than the second threshold, the second threshold is greater than the first threshold, and the corresponding phase currents of the first phase and thesecond phase do not enter the current value range of boundary conduction mode when each of the first and second phases is injected with AC power.

[0107] That is, the controller 300 is configured to perform the various steps of method according to the present disclosure. Since the various steps of the method have been described in detail above, they will not be repeated here.

[0108] In the system 10 of the present disclosure, the DC-DC converter 200 may be a DC-DC converter known in the art; that is, without any hardware modifications, the first phase and the second phase of the DC-DC converter can be kept from ever entering boundary conduction mode throughout the entire process of the EIS measurement method by simply controlling the stack current requested by the controller 300 and distributing the injected AC power in the two phases of the DC-DC converter, thereby improving the stability of the system. Moreover, there is no need to calibrate for different fuel cell stacks, making the implementation of the EIS method simpler and more universal.

[0109] The present disclosure further proposes a computer program product comprising computer instructions that, when executed by a processor, implement the method according to the present invention.

[0110] The present disclosure further proposes a machine-readable storage medium, which may be the aforementioned memory, which stores computer instructions that, when executed by a processor, implement the method according to the present disclosure.

[0111] The above description, with reference to the accompanying drawings, details a feasible, but not limiting, implementation of a method and system for controlling the phase current distribution of a DC-DC converter with controlled AC power injection according to the present disclosure. For those of ordinary skill in the art, without deviating from the scope and substance of the present disclosure as set forth in the claims below, modifications and additions to techniques and structures and recombinations of features in various examples shall be deemed to be included within the scope of the present disclosure. As a result, these modifications and supplements that may be conceived under the guidance of the present disclosure shall be considered as a part of the present disclosure. The scope of the present invention is defined

[0112] by the appended Claims below and comprises equivalent technologies known at the time of filing of the present disclosure, as well as unforeseen equivalent technologies.

Claims

Claims1. A method of controlling the phase current distribution of a DC-DC converter with AC power injection, comprising:obtaining a requested value of the stack current of a fuel cell stack electrically connected to the DC-DC converter, the amplitude of the AC power to be injected into the DC-DC converter, and the current value range of the two phases of the DC-DC converter entering boundary conduction mode;during the process of increasing the phase current of the phase with injected AC power from zero to the requested value of the stack current in the two phases, if the phase current of the phase with injected AC power does not enter the current value range of boundary conduction mode, then allocating the requested value of the stack current to the phase with injected AC power;during the process of increasing the phase current of the phase with injected AC power in the two phases from zero to the requested value of the stack current, if the phase current of the phase with injected AC power into the two phases will enter the current value range of boundary conduction mode, but the phase current of the phase with injected AC power will not enter the current value range of boundary conduction mode during the process of the phase current of the phase with injected AC power increasing from zero to half of the requested value of the stack current, then evenly distributing the requested value of the stack current between the two phases;otherwise:increasing the phase current of the first phase of the DC-DC converter from zero to a first threshold while the AC power is injected into the first phase;increasing the phase current of the second phase of the DC-DC converter from zero to a second threshold while maintaining the phase current of the first phase at the first threshold and continuing to inject the AC power into the first phase;stopping the injection of the AC power into the first phase while maintaining the phase current of the second phase at the second threshold and injecting the AC power into the second phase while increasing the phase current of the first phase from the first threshold to a third threshold;after the phase current of the first phase reaches the third threshold, increasing the phase currents of the first and second phases simultaneously so that the requested value of the stack current is evenly distributed between the first and second phases,wherein the third threshold is greater than the second threshold, the second threshold is greater than the first threshold, and the corresponding phase currents of the first phase and the second phase do not enter the current value range of boundary conduction mode when each of the first and second phases is injected with the AC power.

2. The method according to Claim 1, wherein the magnitude of the AC power is the amplitude of the AC power to be injected into the DC-DC converter when performing electrochemical impedance spectroscopy to measure the humidity of the proton exchange membrane of the fuel cell stack.

3. The method according to Claim 1, wherein the first threshold, the second threshold, and the third threshold are determined based on the input voltage and output voltage of the DC-DC converter, the switching period and duty cycle of the switching transistors contained in the DC-DC converter, and the amplitude of the AC power.

4. The method according to Claim 1, wherein the current value range of boundary conduction mode is determined based on the input voltage and output voltage of the DC-DC converter, the inductance values of the inductor sin the DC-DC converter, the switching period and duty cycle of the switching transistors contained in the DC-DC converter, and the amplitude of the AC power.

5. The method according to any one of Claims 1-4, wherein the first threshold is the current value obtained by subtracting the amplitude of the injected AC power and a set first buffer value from the boundary current value at which the first phase enters boundary conduction mode without AC power injection.

6. The method according to Claim 5, wherein the second threshold is the current value obtained by adding the amplitude of the injected AC power and a set second buffer value to the boundary current value at which the second phase enters boundary conduction mode without AC power injection.

7. The method according to Claim 6, wherein the first buffer value and the second buffer value are adjustable values.

8. The method according to any one of Claims 1-4, wherein the third threshold is twice the larger of the boundary current value of the first phase entering boundary conduction mode without AC power injection and the boundary current value of the second phase entering boundary conduction mode without AC power injection.

9. A system (10) for controlling the phase current distribution of a DC-DC converter (200) with AC power injection, the DC-DC converter (200) being electrically connected to a fuel cell stack (300), and the system (10) comprising a controller (100), the controller (100) being incommunication with the DC-DC converter (200) and the fuel cell stack (300) and configured to:obtain a requested value of the stack current of the fuel cell stack (300), the amplitude of the AC power to be injected into the DC-DC converter (200), and the current value range of the two phases of the DC-DC converter (200) entering boundary conduction mode;during the process of increasing the phase current of the phase with injected AC power from zero to the requested value of the stack current in the two phases, if it is determined that the phase current of the phase with injected AC power does not enter the current value range of boundary conduction mode, then control the DC-DC converter (200) to allocate the requested value of the stack current to the phase with injected AC power;during the process of increasing the phase current of the phase with injected AC power in the two phases from zero to the requested value of the stack current, if it is determined that the phase current of the phase with injected AC power into the two phases will enter the current value range of boundary conduction mode, but the phase current of the phase with injected AC power will not enter the current value range of boundary conduction mode during the process of the phase current of the phase with injected AC power increasing from zero to half of the requested value of the stack current, then control the DC-DC converter (200) to evenly distribute the requested value of the stack current between the two phases;otherwise:control the DC-DC converter (200) to increase the phase current of the first phase of the DC-DC converter (200) from zero to a first threshold while AC power is injected into the first phase;control the DC-DC converter (200) to increase the phase current of the second phase of the DC-DC converter (200) from zero to a second threshold while maintaining the phase current of the first phase at the first threshold and continuing to inject AC power into the first phase;control the DC-DC converter (200) to stop the injection of AC power into the first phase while maintaining the phase current of the second phase at the second threshold and injecting AC power into the second phase while increasing the phase current of the first phase from the first threshold to a third threshold;after the phase current of the first phase reaches the third threshold, control the DC-DC converter (200) to increase the phase currents of the first and second phases simultaneously so that the requested value of the stack current is evenly distributed between the first and second phases,wherein the third threshold is greater than the second threshold, the second threshold is greater than the first threshold, and the corresponding phase currents of the first phase and the second phase do not enter the current value range of boundary conduction mode when each of the first and second phases is injected with the AC power.

10. A computer program product comprising computer instructions, wherein the computerinstructions, when executed by a processor, implement the method according to any one ofClaims 1-8.

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