WO2019083432A1

WO2019083432A1 - Power management for fuel cell assembly

Info

Publication number: WO2019083432A1
Application number: PCT/SE2018/051078
Authority: WO
Inventors: Björn WESTERHOLM
Original assignee: Myfc Ab
Priority date: 2017-10-26
Filing date: 2018-10-23
Publication date: 2019-05-02
Also published as: SE542416C2; SE1751325A1

Abstract

The invention provides a method and a system of power management suitable for use in a range extender for an electric vehicle. The range extender comprises a primary circuit with a fuel cell assembly (10) comprising a plurality of fuel cell segments (14), each segment comprising a plurality of in-plane fuel cells (12) connected in series on a support (16). A hydrogen feed means is provided comprising a valve (20) for each segment (14) for controlling flow into each segment. A secondary circuit comprising a plurality of DC-DC converters converts the voltage to a predetermined value. A power circuit comprising an inverter is arranged to receive the output from the secondary circuit and for providing a three-phase voltage. A control unit comprises circuitry configured to implement the method. The method comprises monitoring the voltage of each individual fuel cell in the assembly, and recording deviations from a set value of said voltage. If a voltage of one of said in-plane fuel cells(12) deviates from said set value by a predetermined amount, closing the valve (20) for the segment (14) in question where said cell (12) is located, thereby shutting off said segment (14) from power generation.

Description

POWER MANAGEMENT FOR FUEL CELL ASSEMBLY

The present invention relates to management of power draw from fuel cell assemblies comprising large numbers of fuel cells, in particular to range extenders comprising such fuel cell assemblies.

Background of the Invention

In fuel cell assemblies comprising large numbers of fuel cell units, e.g. for use as range extenders in electrically powered vehicles, it is essential to be able to control the power draw such that the power delivered is kept constant.

Each fuel cell can be individually monitored and if some cell or cells should become deficient it is desirable to maintain the output in a controlled manner. Summary of the Invention

The object of the invention is to provide a power management method and system that is able to handle situations where fuel cell efficiency may differ in the assembly.

A method of operating such a system is defined in claim 1.

Thus, there is provided a method of power management suitable for use in a range extender for an electric vehicle, the range extender comprising a primary circuit comprising a fuel cell assembly. The assembly comprises a plurality of fuel cell segments, each segment comprising a plurality of in-plane fuel cells connected in series on a support. The segments are arranged on a framework. There is a hydrogen feed means comprising a valve for each segment for controlling flow into each segment. A secondary circuit comprises a plurality of DC-DC converters, one for each segment for converting the voltage to a predetermined value. There is also a power circuit comprising an inverter arranged to receive the output from the secondary circuit and for providing a three-phase voltage, and a control unit comprising circuitry configured to implement the method. The method comprises monitoring the voltage of each individual fuel cell in the assembly, and recording deviations from a set value of said voltage. If a voltage of one of said in-plane fuel cells deviates from said set value by a predetermined amount, the valve for the segment in question where said cell is located is closed, thereby shutting off said segment from power generation.

A power management system is defined in claim 5.

It comprises a primary circuit comprising a fuel cell assembly, the assembly comprising a plurality of fuel cell segments, each segment comprising a plurality of in-plane fuel cells connected in series on a support. The segments are arranged on a framework. A hydrogen feed means is provided comprising a valve for each segment for controlling flow into each segment. There is a secondary circuit comprising a plurality of DC-DC converters, one for each segment for converting the voltage to a predetermined value. A power circuit is provided comprising an inverter arranged to receive the output from the secondary circuit and for providing a three-phase voltage: There is a control unit which is configured to monitor the voltage of each individual fuel cell in the assembly, and to record deviations from a set value of said voltage stored in memory. The control unit is configured to close the valve for the segment in question where the cell is located, and to shut off said segment from power generation, based on a deviation of a voltage of a cell from said set value by a predetermined amount. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus not to be considered limiting on the present invention, and wherein Fig. 1 schematically illustrates a power management system;

Fig. 2 is a detail of the connection of a fuel cell segment to a control interface;

Fig. 3 is a schematic illustration of a REX in operation;

Fig. 4 illustrates a RX in which one fuel cell segment is malfunctioning; and Figs. 5a-b illustrate monitoring and control with the system. Detailed Description of Preferred Embodiments

In Fig. 1 a fuel cell assembly 10 comprising a large number of fuel cells 12 (in the order of 200-300 cells) is shown. The assembly is built up from a plurality of segments 14, comprising a support 16 on which the fuel cells 12 are arranged electrically in series in an "in-plane" configuration, i.e. they are mounted side-by- side on the support 16.

"In-plane" means that the cells are provided on a flat support and next to each other in an elongated configuration, i.e. opposed to a "stacked" configuration, in which cells are placed on top of each other.

The fuel cells are preferably very thin air-breathing polymer electrolyte fuel cells suitably having a design as disclosed e.g. in applicants patents EP 1 810 357, EP 2 008 335 and EP 2 201 631.

Each segment typically comprises 10-50 individual fuel cells and the assembly 10 can typically comprise 5-20 segments 14. Depending on application these numbers can vary greatly.

The segments 14 are in turn mounted on a framework 18 which preferably functions as a cooling means for the fuel cell assembly 10. Such framework structure is disclosed in applicants co-pending application SE- 1750268-3, filed on March 10, 2017.

Hydrogen is fed to the fuel cells in a series manner for each segment, illustrated by arrows H. To each segment 14 a valve 20 is associated for enabling shutting off supply of hydrogen if need arises. The valve can be provided as shown in Fig. 1, i.e. at one end of a segment 14 as a separate structure, or alternatively integrated in the support 16 on which the individual fuel cells 12 are mounted.

Reference is made to the above application SE- 1750268-3 for details regarding the design of a fuel cell assembly of this type, usable as a range extender. Each fuel cell is commonly capable of delivering a voltage of 0,6 V at 5 A, although performance of cells is a design choice to some extent. For a segment 14 containing Z fuel cells having the above indicated performance, each segment 14 would deliver 24 V and 5 A (= 120 W), and for an assembly having 20 segments the total output would thus be about 480 V at 5 A.

The power from each segment 14 is transferred via an Interface (to be described below) to a Secondary Circuit. The Secondary Circuit contains DC-DC converters for providing a suitable output voltage.

The DC-DC converters are conventional, i.e. capable of delivering a constant output voltage. The DC-DC converters in the Secondary Circuit, i.e. one for each segment 14, are coupled in parallel such that they deliver a voltage that will be the average of the voltages of each individual converter.

The output from the Secondary Circuit is fed to a Power Circuit comprising a conventional Power Inverter. The Inverter transforms the output to three-phase electric power at a voltage suitable for powering e.g. an electric motor in a vehicle, or for charging a battery of an electric vehicle. Suitable voltage could be 380 V at 48 A.

The Interface between Primary Circuit and Secondary Circuit will now be described.

Reference is made to co-pending application entitled "Dynamic electric load", application number SE- 17XXXXXX-X, filed on the same day as the present application, which describes control algorithms and electronics for managing power draw in fuel cell assemblies in general in more detail.

As mentioned above, the fuel cells 12 are coupled in series on each respective segment 14 and deliver an output voltage to the Interface via power lines 13', 13" on the support structure 16. In addition to the power lines, suitably there are signal lines 15, one for each individual cell 12 for monitoring the performance of the cells by measuring the actual output voltage of each cell. Each segment 14 is coupled to the Interface via a coupling means 26 (described in connection with Fig. 2), and the voltages of the cells 12 are fed to the Control Unit via the Interface. If the Control Unit detects an anomaly in one or more cells that affects the performance of a segment 14 it can shut off the feed valve 20 for hydrogen to this segment to abort its function in order that an imbalance be avoided in the power draw from the total assembly.

In a simpler embodiment only the voltage of an entire segment 14 is monitored, and similarly, if the voltage drops too much due to malfunction of one or more cells 12, the Control Unit will close the segment in question by stopping hydrogen feed to the segment by closing the valve 20 in question.

Now reference is made to Fig. 2. Each segment 14 of an entire fuel cell assembly and comprising the plurality of fuel cells 12 suitably comprises a support 18 which in preferred embodiments is a circuit board type structure. At the output end of a segment 14, i.e. the end coupled to the interface, the circuit board is provided with a connecting tab 22 where individual signal and power lines preferably are fanned out to contact pads 24, so as to make contact structures simpler, as shown in Fig. 2.

In Fig. 2 two power lines 13', 13", and a limited number of signal lines 15 are shown, but if the number of cells 12 is large, i.e. in the order of 30 or more, the fanning out will become more important.

The contact tab 22 having the plurality of pads 24 thereon is inserted in a mating slot 25 in a coupling means 26, schematically indicated with a broken line in Fig. 2. This coupling means 26 is in turn connected to the Control Unit, as shown in Fig. 1.

Now the function will be described with reference to Figs. 3 and 4.

Thus, normal mode of operation when the range extender has been activated, and the initial startup phase has been run through, there will be a constant flow of hydrogen gas from a hydrogen source. The individual segments 14 are coupled in parallel with respect to the hydrogen flow from the source. Possibly the valves 20 may have to be adjusted in order that the same flow rate for the hydrogen through all segments 14 is ascertained, such that each segment will deliver essentially the same power output, at least in an initial phase.

Thus, in accordance with the invention, when the assembly is up and running at the desired power draw the Control Unit continuously monitors the voltage over each segment in the entire assembly, via the above described signal lines and the interface structure.

The control unit receives input signals via a bus, indicated with a broken line arrow IP going from the interface to the Control Unit. The voltage level of the individual cells is compared to a set desired voltage stored in memory in the Control Unit. If the cell voltage drops below a set threshold value indicating the output of the entire segment will be jeopardized, i.e. will differ significantly from the desired output, the Control Unit will have to decide whether to disconnect the segment in question or not. Also, the voltage should never exceed 1,2 V. Since an anomaly could be intermittent and thus only temporarily cause a drop, there needs to be some delay before the decision to disconnect is taken.

Thus, the shutting off of a segment 14 is in preferred embodiments not carried out until after a set time delay At, within which it is ascertained that the detected deviation is not only temporary. Such delay is a matter of design in the actual application, but normally a delay ranging up to several minutes can be accepted before disconnection is initiated.

If the measured voltage decreases continuously during the time delay At to an extent which has been determined to indicate a severe malfunction, the Control Unit takes that as a cause for shutting off the segment in question by closing the associated valve. This is illustrated in Fig. 5, wherein Fig. 5a shows a temporary dip in voltage which is not taken as a malfunction, whereas Fig. 5b shows a prolonged drop which is a cause for shutting off the segment. If the Control Unit decides to disconnect a segment (14) it sends an instruction via an output bus OP to shut off the valve (20) feeding hydrogen to the segment in question to render it inoperable, indicated with a crossed-over segment in Fig. 4. It should be noted that it is not strictly necessary to monitor every single cell in the entire assembly. In fact it could be sufficient to monitor the output voltage of the individual segments, in which case control becomes somewhat inferior to the above described method, but would still be a functional set-up.

The monitoring and control would essentially be the same, and the illustration in Figs 5a and 5b would be applicable also to this embodiment.

After closing said valve 20 to shut off a segment 14, the flow through the remaining segments will increase slightly and therefore the flow from the hydrogen source may have to be reduced correspondingly, indicated with a negative AF in Fig. 4.

Thus, the consequence is that the power draw from the assembly is adjusted by adjusting the hydrogen flow through the remaining segments (14).

In cases where a malfunction as described above has been detected the segment in question would have to be exchanged which is a simple matter by virtue of the slot- type coupling means 26 in the Interface structure.

The power management system described above is particularly suitable for use in range extenders for electric vehicles.

Claims

CLAIMS:

A method of power management suitable for use in a range extender for an electric vehicle, the range extender comprising a primary circuit comprising a fuel cell assembly (10), the assembly comprising a plurality of fuel cell segments (14), each segment comprising a plurality of in-plane fuel cells (12) connected in series on a support (16), the segments (14) being arranged on a framework (18), hydrogen feed means comprising a valve (20) for each segment (14) for controlling flow into each segment, a secondary circuit comprising a plurality of DC-DC converters, one for each segment (14) for converting the voltage to a predetermined value, a power circuit comprising an inverter arranged to receive the output from the secondary circuit and for providing a three-phase voltage; and a control unit comprising circuitry configured to implement the method, the method comprising monitoring the voltage of each individual fuel cell in the assembly, and recording deviations from a set value of said voltage; and if a voltage of one of said in-plane fuel cells (12) deviates from said set value by a predetermined amount, closing the valve (20) for the segment (14) in question where said cell (12) is located, thereby shutting off said segment (14) from power generation.

The method according to claim 1 , further comprising after closing said valve (20) to shut off a segment (14), adjusting the power draw from the assembly by adjusting the hydrogen flow through the remaining segments (14).

The method according to claim 1 or 2 , wherein the shutting off of a segment (14) is not carried out until after a set time delay (At), within which it is ascertained that the detected deviation is not only temporary.

The method according to any preceding claim, wherein the time delay (At) is less than 15 seconds, preferably less than 10 seconds, most preferred between 0, 1 and 5 seconds.

5. A system (10) for the power management of a range extender for an electric vehicle, comprising a) a primary circuit comprising a fuel cell assembly (10), the assembly comprising a plurality of fuel cell segments (14), each segment comprising a plurality of in-plane fuel cells (12) connected in series on a support (16), the segments (14) being arranged on a framework (18), hydrogen feed means comprising a valve (20) for each segment (14) for controlling flow into each segment (14); b) a secondary circuit comprising a plurality of DC-DC converters, one for each segment (14) for converting the voltage to a predetermined value; c) a power circuit comprising an inverter arranged to receive the output from the secondary circuit and for providing a three-phase voltage; and d) a control unit; wherein the control unit is configured to monitor the voltage of each individual fuel cell (12) in the assembly, and to record deviations from a set value of said voltage stored in memory; and wherein the control unit is configured to close the valve (20) for the segment (14) in question where the cell (12) is located, and to shut off said segment (14) from power generation, based on a deviation of a voltage of a cell (12) from said set value by a predetermined amount. 6. The system according to claim 5, wherein each segment (14) of an entire fuel cell comprises a support (18) of a circuit board type structure.

7. The system according to claim 6, wherein at the output end of a segment (14), the circuit board is provided with a connecting tab (22) where individual signal and power lines are fanned out to contact pads (24).

8. The system according to claim 7, wherein the contact tab (22) has a plurality of pads (24) thereon insertable in a mating slot (25) in a coupling means (26). 9. A range extender for electric vehicles comprising a power management system according to claim 5.

10. An electric vehicle comprising a range extender according to claim 9.