SE1751325A1

SE1751325A1 - Power management for fuel cell assembly

Info

Publication number: SE1751325A1
Application number: SE1751325A
Authority: SE
Inventors: Björn Westerholm
Original assignee: Myfc Ab
Priority date: 2017-10-26
Filing date: 2017-10-26
Publication date: 2019-04-27
Also published as: SE542416C2; WO2019083432A1

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 threephase 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 assembliescomprising large numbers of fuel cells, in particular to range extenders comprising such fuel cell assemblies.

Background of the InventionIn fuel cell assemblies comprising large numbers of fuel cell units, e.g. for use asrange 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 def1cient it is desirable to maintain the output in a controlled manner.

Summary of the InventionThe 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 rangeextender for an electric vehicle, the range extender comprising a primary circuitcomprising a fuel cell assembly. The assembly comprises a plurality of fuel cellsegments, each segment comprising a plurality of in-plane fuel cells connected inseries on a support. The segments are arranged on a framework. There is ahydrogen feed means comprising a valve for each segment for controlling flow intoeach segment. A secondary circuit comprises a plurality of DC-DC converters, onefor each segment for converting the voltage to a predetermined value. There is alsoa power circuit comprising an inverter arranged to receive the output from thesecondary circuit and for providing a three-phase voltage, and a control unitcomprising circuitry configured to implement the method. The method comprisesmonitoring the voltage of each individual fuel cell in the assembly, and recordingdeviations 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 assemblycomprising a plurality of fuel cell segments, each segment comprising a plurality ofin-plane fuel cells connected in series on a support. The segments are arranged ona framework. A hydrogen feed means is provided comprising a valve for eachsegment for controlling flow into each segment. There is a secondary circuitcomprising a plurality of DC-DC converters, one for each segment for convertingthe voltage to a predetermined value. A power circuit is provided comprising aninverter arranged to receive the output from the secondary circuit and for providinga three-phase voltage: There is a control unit which is configured to monitor thevoltage of each individual fuel cell in the assembly, and to record deviations from aset value of said voltage stored in memory. The control unit is configured to closethe valve for the segment in question where the cell is located, and to shut off saidsegment 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 thedetailed description given hereinafter and the accompanying dravvings which are givenby way of illustration only, and thus not to be considered limiting on the presentinvention, 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 theorder of 200-300 cells) is shown. The assembly is built up from a plurality ofsegments 14, comprising a support 16 on which the fuel cells 12 are arrangedelectrically 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 eachother 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 cellssuitably having a design as disclosed e.g. in applicants patents EP 1 810 357, EP2 008 335 and EP 2 201631.

Each segment typically comprises 10-50 individual fuel cells and the assembly 10can 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 preferablyfunctions as a cooling means for the fuel cell assembly 10. Such frameworkstructure is disclosed in applicants co-pending application SE-1750268-3, filed onMarch 10, 2017.

Hydrogen is fed to the fuel cells in a series manner for each segment, illustrated byarrows H. To each segment 14 a valve 20 is associated for enabling shutting offsupply 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, althoughperformance of cells is a design choice to some extent. For a segment 14 containingZ fuel cells having the above indicated performance, each segment 14 would deliver24 V and 5 A (= 120 W), and for an assembly having 20 segments the total outputwould thus be about 480 V at 5 A.

The power from each segment 14 is transferred via an Interface (to be describedbelow) 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 outputvoltage. The DC-DC converters in the Secondary Circuit, i.e. one for each segment14, 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 aconventional Power Inverter. The Inverter transforms the output to three-phaseelectric 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 presentapplication, 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 respectivesegment 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 aresignal 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 inconnection with Fig. 2), and the voltages of the cells 12 are fed to the Control Unitvia the Interface. If the Control Unit detects an anomaly in one or more cells thataffects the performance of a segment 14 it can shut off the feed valve 20 forhydrogen 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 cells12, 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 fuelcells 12 suitably comprises a support 18 which in preferred embodiments is acircuit board type structure. At the output end of a segment 14, i.e. the endcoupled to the interface, the circuit board is provided with a connecting tab 22where 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 areshown, 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 matingslot 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 20may have to be adjusted in order that the same ﬂow rate for the hydrogen throughall 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 atthe desired power draw the Control Unit continuously monitors the voltage overeach 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 arrowIP going from the interface to the Control Unit. The voltage level of the individualcells is compared to a set desired voltage stored in memory in the Control Unit. Ifthe cell voltage drops below a set threshold value indicating the output of the entiresegment will be jeopardized, i.e. will differ significantly from the desired output, theControl Unit will have to decide whether to disconnect the segment in question ornot. Also, the voltage should never exceed 1,2 V. Since an anomaly could beintermittent 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 outuntil 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 anextent which has been determined to indicate a severe malfunction, the ControlUnit takes that as a cause for shutting off the segment in question by closing theassociated valve. This is illustrated in Fig. 5, wherein Fig. 5a shows a temporarydip 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 viaan output bus OP to shut off the valve (20) feeding hydrogen to the segment inquestion 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 theentire assembly. In fact it could be sufficient to monitor the output voltage of theindividual 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 remainingsegments 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 inquestion 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

:

1. A method of power management suitable for use in a range extender for anelectric vehicle, the range extender comprising a primary circuit comprising afuel cell assembly (10), the assembly comprising a plurality of fuel cellsegments (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 aframework (18), hydrogen feed means comprising a valve (20) for each segment(14) for controlling ﬂow into each segment, a secondary circuit comprising aplurality of DC-DC converters, one for each segment (14) for converting thevoltage to a predetermined value, a power circuit comprising an inverterarranged to receive the output from the secondary circuit and for providing athree-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 setvalue by a predetermined amount, closing the valve (20) for the segment (14) inquestion where said cell (12) is located, thereby shutting off said segment (14) from power generation.

2. 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 byadjusting the hydrogen ﬂow through the remaining segments (14).

3. 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.

4. The method according to any preceding claim, wherein the time delay (At) isless 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 assemblycomprising a plurality of fuel cell segments (14), each segment comprising aplurality of in-plane fuel cells (12) connected in series on a support (16), thesegments (14) being arranged on a framework (18), hydrogen feed meanscomprising 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 fuelcell (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) inquestion where the cell (12) is located, and to shut off said segment (14) frompower 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.