CN117318161B - Fuel cell power generation system - Google Patents
Fuel cell power generation system Download PDFInfo
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- CN117318161B CN117318161B CN202311609902.0A CN202311609902A CN117318161B CN 117318161 B CN117318161 B CN 117318161B CN 202311609902 A CN202311609902 A CN 202311609902A CN 117318161 B CN117318161 B CN 117318161B
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- 239000000446 fuel Substances 0.000 title claims abstract description 89
- 238000010248 power generation Methods 0.000 title claims abstract description 51
- 239000003990 capacitor Substances 0.000 claims abstract description 40
- 230000004044 response Effects 0.000 claims description 39
- 238000000034 method Methods 0.000 claims description 30
- 230000008859 change Effects 0.000 claims description 9
- 230000002457 bidirectional effect Effects 0.000 claims description 7
- 230000009286 beneficial effect Effects 0.000 abstract description 2
- 230000008569 process Effects 0.000 description 14
- 238000010586 diagram Methods 0.000 description 11
- 230000001276 controlling effect Effects 0.000 description 9
- 238000004146 energy storage Methods 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
- H02J1/12—Parallel operation of dc generators with converters, e.g. with mercury-arc rectifier
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
- H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/30—The power source being a fuel cell
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- Fuel Cell (AREA)
Abstract
The application discloses a fuel cell power generation system, which comprises a fuel cell FC, a DC/DC unit, a super capacitor SC and a DC/AC unit which are sequentially connected in series, wherein the output end of the DC/AC unit is connected with a power grid in a grid-connected manner; wherein the fuel cell FC is adapted to provide steady state power to the grid; the supercapacitor SC is adapted to provide abrupt dynamic power to the grid, and the voltage minimum of the supercapacitor SC is defined to be equal to or greater than the minimum bus voltage value required for grid connection. The beneficial effects of this application: compared with the parallel connection of the fuel cell FC and the super capacitor SC in the traditional fuel cell power generation system; the series structure is adopted, so that when the fuel cell FC is in a low-voltage state, the DC/DC unit close to the fuel cell FC has no requirement on boosting capacity, and the working efficiency of the system is improved. And the number of the units of the system is not increased, and the cost is not influenced.
Description
Technical Field
The application relates to the technical field of power grid power generation, in particular to a fuel cell power generation system.
Background
A schematic topology of a conventional fuel cell power generation system is shown in fig. 1. The fuel cell is connected to the bus through a DC/DC unit (direct current converter), and the energy storage element is connected to the bus through a bidirectional DC/DC unit (bidirectional direct current converter); the fuel cell and the energy storage element are connected in parallel with each other and are connected to the grid via a DC/AC unit (inverter) via a common bus. The energy storage element may be a super capacitor, or may be a battery, for example, a super capacitor.
Based on the system of fig. 1, fig. 2 is a schematic diagram of a control structure of a conventional fuel cell power generation system. Fuel cell side DC/DC unit control bus voltage v bus The bidirectional DC/DC unit controls the dynamic power output by the super capacitor. Specifically, the high-frequency current i in the DC/AC unit-side bus is sampled inv_dy And uses the high-frequency current as currentThe loop instruction controls. Therefore, the output current of the super capacitor can track the dynamic current, so that the super capacitor provides dynamic power, and the output power of the fuel cell changes slowly, thereby meeting the dynamic characteristic of the fuel cell.
Based on the above, the conventional fuel cell power generation system has the following drawbacks in use:
(1) When the voltage of the fuel cell is low, the structure of the common bus bar requires a large boosting capability of the DC/DC unit on the fuel cell side, but the overall efficiency of the system will be relatively low due to the high boosting comparison.
(2) The control process of the whole fuel cell power generation system is complex and inconvenient to implement.
Disclosure of Invention
It is one of the objects of the present application to provide a fuel cell power generation system that addresses at least one of the above-mentioned drawbacks of the related art.
In order to achieve at least one of the above objects, the technical scheme adopted in the application is as follows: the fuel cell power generation system comprises a fuel cell FC, a DC/DC unit, a super capacitor SC and a DC/AC unit which are sequentially connected in series, wherein the output end of the DC/AC unit is connected with a power grid in a grid-connected manner; wherein the fuel cell FC is adapted to provide steady state power to the grid; the supercapacitor SC is adapted to provide abrupt dynamic power to the grid, and the voltage minimum of the supercapacitor SC is defined to be equal to or greater than the minimum bus voltage value required for grid connection.
Preferably, the fuel cell power generation system includes two DC/DC units, DC/DC unit #1 and DC/DC unit #2, respectively; the DC/DC unit #1 is connected in series between the fuel cell FC and the super capacitor SC, and the DC/DC unit #2 is connected in series between the super capacitor SC and the DC/AC unit; at the same time, the limitation of the voltage minimum of the supercapacitor SC is released.
Preferably, the DC/DC unit #1 adopts a three-level DC/DC topology, the DC/DC unit #2 and the upper bus and the lower bus both adopt a bidirectional buck/boost circuit, and the DC/AC unit adopts a three-level NPC circuit.
Preferably, the control loop of the DC/DC unit #1 is adapted to control the voltage of the supercapacitor SC, which is controlled by the voltage of the supercapacitor SCThe voltage of the stage capacitor SC is used as feedback to obtain, after control, a switching tube S for controlling the DC/DC unit #1 1 And S is 2 Duty cycle d of (2) S1 And d S2 The method comprises the steps of carrying out a first treatment on the surface of the The control loop of the DC/DC unit #2 is suitable for controlling the upper and lower bus voltages, and the upper and lower bus voltages are used as feedback to obtain the switch tube S for controlling the DC/DC unit #2 3 To S 6 Duty cycle d of (2) 3 To d 6 The method comprises the steps of carrying out a first treatment on the surface of the The DC/AC unit adopts a traditional dq0 control loop; wherein the response bandwidth of the control loop of DC/DC unit #2 is higher than the response bandwidth of DC/DC unit # 1.
Preferably, the control loop of the DC/DC unit #1 is a sum-difference control loop, and the super capacitor SC is regarded as capacitors SC1 and SC2 connected in parallel to the bus; the specific control process is as follows:
s100: voltage v of super capacitor SC sc1 And v sc2 Respectively performing difference sum and sum to obtain voltage sum feedback v sc_sum And voltage difference feedback v sc_dif ；
S200: voltage and feedback v sc_sum And voltage and command V sc_sum * The current reference i is output through the PI controller after comparison L1 * The method comprises the steps of carrying out a first treatment on the surface of the Reference the current to i L1 * Output current i to fuel cell FC L1 The sum d of duty ratio is output through PI control after comparison sum ；
S300: feedback v of the voltage difference sc_dif And voltage difference command V sc_dif * The difference d of the duty ratio is output through the PI controller after comparison dif ；
S400: based on the sum of the duty cycles d sum And difference d of duty cycle dif Calculating to obtain a switching tube S 1 And S is 2 Duty cycle d of (2) S1 And d S2 。
Preferably, in step S200, the voltage of the supercapacitor SC and the command V sc_sum * Adapted to vary with power at a maximum value V sc_max And a minimum value V sc_min Dynamic change is carried out between the two; so that the supercapacitor SC is suitable for charging in the event of a sudden load power drop, in which case the load power risesThe supercapacitor SC is adapted to discharge at this time.
Preferably, the voltage and the command V sc_sum * Power P to grid side G Inversely proportional, and the voltage and the command V sc_sum * Power P to grid side G The slope of the relationship curve of (2) is a constant value; and then by the power P to the power grid side G And obtaining the required voltage and the command V according to the relation curve sc_sum * The method comprises the steps of carrying out a first treatment on the surface of the When the power P at the power grid side G Zero, voltage and command V sc_sum * Take the maximum value V sc_max The method comprises the steps of carrying out a first treatment on the surface of the When the power P at the power grid side G At rated power P rate At the time, voltage and command V sc_sum * Take the minimum value V sc_min 。
Preferably, the loop control procedure of the DC/DC unit #2 is as follows:
s500: voltage feedback v of upper bus dc1 With corresponding voltage command V dc1 * The current reference i is output through the PI controller after comparison L3 * ；
S600: voltage feedback v of lower bus dc2 With corresponding voltage command V dc2 * The current reference i is output through the PI controller after comparison L4 * ；
S700: reference the current to i L3 * And AND i L4 * Current feedback i with upper and lower bus bars respectively L3 And i L4 After comparison, the output of the PI controller is used for controlling the switch tube S 3 To S 6 Duty cycle d of (2) 3 To d 6 。
Preferably, the response bandwidth of the control loop of DC/DC unit #2 is at least 10 times the response bandwidth of DC/DC unit # 1.
Preferably, the response bandwidth of the control loop of DC/DC unit #1 is 1Hz and the response bandwidth of the control loop of DC/DC unit #2 is 100Hz.
Compared with the prior art, the beneficial effect of this application lies in:
compared with the parallel structure of a common bus of the traditional fuel cell power generation system; the series structure is adopted, so that when the fuel cell FC is in a low-voltage state, the DC/DC unit close to the fuel cell FC has no requirement on boosting capacity, and the working efficiency of the system is improved. And the number of the units of the system is not increased, and the cost is not influenced. Meanwhile, the serial structure of the fuel cell power generation system can simplify the loop control process, and is convenient to implement.
Drawings
Fig. 1 is a schematic diagram of a topology of a conventional fuel cell power generation system.
Fig. 2 is a schematic diagram of a control structure of the fuel cell power generation system shown in fig. 1.
Fig. 3 is a schematic view of the structure of one embodiment of the fuel cell power generation system of the present invention.
Fig. 4 is a schematic diagram of a topology structure corresponding to the fuel cell power generation system shown in fig. 3 according to the present invention.
Fig. 5 is a schematic view showing the structure of another embodiment of the fuel cell power generation system of the present invention.
Fig. 6 is a schematic diagram of a topology structure corresponding to the fuel cell power generation system shown in fig. 5 according to the present invention.
Fig. 7 is a schematic diagram of the power flow of the fuel cell power generation system of fig. 5 in steady state according to the present invention.
Fig. 8 is a schematic diagram of power flow and status of the fuel cell power generation system of fig. 5 in a dynamic state according to the present invention.
Fig. 9 is a schematic diagram of loop control of the fuel cell power generation system of fig. 5 in steady state according to the present invention.
Fig. 10 is a schematic diagram of loop control of the fuel cell power generation system of fig. 5 in accordance with the present invention.
Fig. 11 is a schematic diagram illustrating a state of dynamic management of the supercapacitor according to the present invention.
Fig. 12 is a schematic diagram of a loop structure for dynamically adjusting a voltage command of a super capacitor according to the present invention.
Detailed Description
The present application will be further described with reference to the specific embodiments, and it should be noted that, on the premise of no conflict, new embodiments may be formed by any combination of the embodiments or technical features described below.
In the description of the present application, it should be noted that, for the azimuth terms such as terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., the azimuth and positional relationships are based on the azimuth or positional relationships shown in the drawings, it is merely for convenience of describing the present application and simplifying the description, and it is not to be construed as limiting the specific protection scope of the present application that the device or element referred to must have a specific azimuth configuration and operation, as indicated or implied.
It should be noted that the terms "first," "second," and the like in the description and in the claims of the present application are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order.
The terms "comprises" and "comprising," along with any variations thereof, in the description and claims of the present application are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements that are expressly listed or inherent to such process, method, article, or apparatus.
One of the preferred embodiments of the present application, as shown in fig. 3 and 4, is a fuel cell power generation system including a fuel cell FC, a DC/DC unit, a supercapacitor SC, and a DC/AC unit connected in series in this order; the output end of the DC/AC unit is connected with the power grid in a grid-connected mode. When the system is in steady state, the power P on the grid side G Will come entirely from the fuel cell FC and the supercapacitor SC will not need to take on steady-state power. When the system is in dynamic state, if the power P at the power grid side G Abrupt change occurs, the super capacitor SC will bear dynamic power, while the fuel cell FC can change slowlyThus, the defect of slow dynamic response of the fuel cell FC can be effectively overcome. That is, when the fuel cell power generation system is in operation, the fuel cell FC is used to provide steady state power to the power grid and the supercapacitor SC is used to provide abrupt dynamic power to the power grid.
It can be understood that the fuel cell power generation system adopts a serial structure, the fuel cell FC is firstly boosted to the voltage of the super capacitor SC through the DC/DC unit, and then the super capacitor SC is connected with the grid through the DC/AC unit; the super capacitor SC is equivalent to a system bus. In order to ensure smooth progress of the grid connection process, the voltage of the supercapacitor SC must meet the grid connection requirement, so the minimum voltage value of the supercapacitor SC is defined to be equal to or greater than the minimum bus voltage value required for grid connection. The number of inverters is reduced compared with the conventional fuel cell power generation system, so that the cost can be effectively reduced.
It should be noted that, as can be seen from the above description, in order to meet the grid connection requirement, the minimum voltage value of the supercapacitor SC is defined, so that the voltage variation range of the supercapacitor SC is relatively small, which limits the utilization rate of the supercapacitor SC to some extent. Based on this, the foregoing scheme can be improved as follows.
In the present embodiment, as shown in fig. 5 and 6, the fuel cell power generation system includes two DC/DC units, DC/DC unit #1 and DC/DC unit #2, respectively. Wherein, DC/DC unit #1 is connected in series between fuel cell FC and supercapacitor SC, and DC/DC unit #2 is connected in series between supercapacitor SC and DC/AC unit. By setting the two DC/DC units, the limitation of the minimum voltage value of the supercapacitor SC can be released.
It can be understood that, when the fuel cell power generation system of the present embodiment is operated, the fuel cell FC is first boosted to the voltage of the supercapacitor SC by the DC/DC unit #1, and the voltage of the supercapacitor SC may be lower than the bus voltage at this time; then, the voltage is secondarily boosted to the bus voltage through the DC/DC unit #2. Thus, the boosting of the two-stage DC/DC unit for the fuel cell FC can avoid the use of a high boosting ratio for the DC/DC unit (DC/DC unit # 1) on the fuel cell FC side, and thus can effectively improve the system efficiency. In addition, compared with the conventional fuel cell power generation system of the common bus structure, the present embodiment also uses only three converters; i.e. from a cost point of view, the present embodiment does not increase the cost of the system. Therefore, in the following description, the present application will describe a fuel cell power generation system in a series structure formed of two stages of DC/DC units.
In this embodiment, the operation principles of the DC/DC unit #1, the DC/DC unit #2, and the DC/AC unit are well known to those skilled in the art. The specific structures of the DC/DC unit #1, the DC/DC unit #2, and the DC/AC unit are various; for example, as shown in fig. 6, the DC/DC unit #1 preferably adopts a three-level DC/DC topology, the DC/DC unit #2 and the upper and lower buses preferably adopt bidirectional buck/boost circuits, and the DC/AC unit preferably adopts a three-level NPC circuit.
In this embodiment, in order to facilitate description of the control process of the fuel cell power generation system of the serial structure of the present application, the operation process of the fuel cell power generation system may be first analyzed. The fuel cell power generation system comprises a steady state working state and a dynamic working state, so that the fuel cell power generation system needs to meet steady state control and dynamic compensation when grid connection is carried out.
As shown in fig. 7, when the fuel cell power generation system is in the steady-state grid connection, the grid-side power PG is entirely derived from the power P of the fuel cell FC FC The supercapacitor SC need not provide steady-state power; namely P G =P FC ，P SC =0, where P SC Representing the power of the supercapacitor SC.
As shown in fig. 8, when the fuel cell power generation system is in dynamic grid connection, the power P on the grid side is G The super capacitor SC can rapidly pass through the power P of the super capacitor SC due to the rapid response speed SC To take over the dynamic power generated by the abrupt change. The fuel cell FC can be changed slowly at this time without worrying about the influence caused by the abrupt change in power.
In this embodiment, based on the above-described operation of the fuel cell power generation system at the time of grid connection, a specific control process will be described below. As shown in fig. 9 and 10, the control loop of the DC/DC unit #1 is used to control the supercapacitor SCIs a voltage of (2); the control loop takes the voltage of the super capacitor SC as feedback, and then the control loop can obtain the switching tube S for controlling the DC/DC unit #1 1 And S is 2 Duty cycle d of (2) S1 And d S2 . The control loop of the DC/DC unit #2 is used for controlling the voltages of the upper bus and the lower bus; the control loop takes the upper bus voltage and the lower bus voltage as feedback, and then the control loop can obtain the switching tube S for controlling the DC/DC unit #2 3 To S 6 Duty cycle d of (2) 3 To d 6 . The DC/AC unit employs a conventional dq0 control loop, and the specific control process is consistent with conventional methods and is not described in detail herein. Wherein the response bandwidth of the control loop of DC/DC unit #2 is much higher than the response bandwidth of DC/DC unit # 1.
It can be understood that in this embodiment, the sampling signals, i.e. the input parameters, of the control loop are all directly acquired from the circuit topology, which is much simpler than the conventional method for controlling the bidirectional DC/DC output current by sampling the dynamic high-frequency component, and no special processing is required for the input parameters in the dynamic situation, so that the method has the advantages of simple control and easy implementation.
Specifically, as shown in fig. 9, the control loop of the DC/DC unit #1 is a sum and difference control loop. The supercapacitor SC can be seen as capacitors SC1 and SC2 connected in parallel to the bus. When the fuel cell power generation system is operating in a steady state, the specific control procedure of the control loop of the DC/DC unit #1 is as follows:
s100: voltage v of capacitors SC1 and SC2 corresponding to super capacitor SC sc1 And v sc2 Respectively performing difference sum and sum to obtain voltage sum feedback v sc_sum And voltage difference feedback v sc_dif 。
S200: voltage and feedback v sc_sum And voltage and command V sc_sum * The current reference i is output through the PI controller after comparison by the comparator L1 * . Then the current is referenced i L1 * Output current i to fuel cell FC L1 The sum d of duty ratio is output through PI control after comparison by a comparator sum 。
S300: will beVoltage difference feedback v sc_dif And voltage difference command V sc_dif * The difference d of the duty ratio is output through the PI controller after the comparison by the comparator dif 。
S400: based on the sum of the duty cycles d sum And difference d of duty cycle dif The switching tube S can be obtained through calculation 1 And S is 2 Duty cycle d of (2) S1 And d S2 。
Meanwhile, the loop control procedure of the DC/DC unit #2 is as follows:
s500: voltage feedback v of upper bus dc1 With corresponding voltage command V dc1 * The current reference i is output through the PI controller after comparison by the comparator L3 * 。
S600: voltage feedback v of lower bus dc2 With corresponding voltage command V dc2 * The current reference i is output through the PI controller after comparison by the comparator L4 * 。
S700: reference the current to i L3 * And AND i L4 * Current feedback i with upper and lower bus bars respectively L3 And i L4 After comparison, the output of the PI controller is used for controlling the switch tube S 3 To S 6 Duty cycle d of (2) 3 To d 6 。
It should be noted that the DC/DC unit #1 is based on the three-level DC/DC topology described above; as shown in fig. 6, the DC/DC unit #1 includes a switching tube S connected in parallel to upper and lower buses 1 And S is 2 . At the same time, sum of duty cycle d sum The difference d between the control loop and the duty cycle of (2) dif Is different in control loop structure. I.e. in step S200, for the sum d of the duty cycles sum Comprises a voltage and loop and a current loop; and for a difference d of duty cycle dif Comprises only a voltage difference loop. In step S400, for a duty cycle d S1 And d S2 May be the sum d of duty cycles sum Difference from duty cycle d dif The results of the comparison by the comparator are each halved.
It should also be appreciated that DC/DC unit #2 is based on the aforementioned dualTo buck/boost circuit architecture; as shown in fig. 6, the DC/DC unit #2 includes a switching tube S connected in parallel to upper and lower buses 3 And S is 5 And a switching tube S connected in series with the upper and lower buses 4 And S is 6 . In practice, the DC/DC unit #2 is independent of each other and identical in structure for the control loops of the upper and lower buses. The control loop of the DC/DC unit #2 for the upper bus and the lower bus comprises a voltage loop and a current loop; voltage v of bus above control loop of upper bus dc1 For input, the switch tube S close to the upper bus can be output and controlled 3 And S is 4 Duty cycle d of (2) 3 And d 4 . Similarly, the voltage v of the lower bus of the control loop of the lower bus dc2 For input, the switch tube S close to the lower bus can be output and controlled 5 And S is 6 Duty cycle d of (2) 5 And d 6 。
It is to be understood that the control process described above is a control process in which the fuel cell power generation system is in a steady state. When the fuel cell power generation system is in the grid-connected dynamic operation, as shown in fig. 10, the specific control process is basically the same as the control process in the steady state; only the response bandwidth of the control loop of the DC/DC unit #1 is set lower than the response bandwidth of the control loop of the DC/DC unit #2. Such that the power P on the grid side G When abrupt change occurs, the supercapacitor SC can respond rapidly through the control loop of the DC/DC unit #2 to realize the power P G Dynamic compensation of (a); while the fuel cell FC responds slower through the control loop of the DC/DC unit #1, waiting for the grid-side power P G The response is slowly started after the dynamic compensation is completed. By the design, the fuel cell FC only needs to provide slow power, and the output power of the fuel cell FC can be ensured to change slowly, so that the problem of slow dynamic response of the fuel cell FC is solved.
In this embodiment, when the dynamic operation of the grid-connected fuel cell power generation system is performed, in order to ensure that the supercapacitor SC has a sufficiently fast response speed, the response bandwidth of the control loop of the DC/DC unit #2 may be set to be 10 times higher than the response bandwidth of the DC/DC unit # 1; i.e. the ratio of the response bandwidth of the control loop of DC/DC unit #2 to the response bandwidth of DC/DC unit #1 is at least 10.
It should be noted that there are mainly three cases of setting the response bandwidth of the control loop for the DC/DC unit #2 and the response bandwidth of the DC/DC unit # 1. First kind: the response bandwidth of the control loop of the DC/DC unit #2 is a normal value, and the response bandwidth of the control loop of the DC/DC unit #1 is set to be relatively low. Second kind: the response bandwidth of the control loop of the DC/DC unit #2 is set to be relatively high, and the response bandwidth of the control loop of the DC/DC unit #1 is a normal value. Third kind: the response bandwidth of the control loop of DC/DC unit #2 is set relatively high, while the response bandwidth of the control loop of DC/DC unit #1 is set relatively low. All three cases can meet the requirements of the present embodiment, and for ease of understanding, the description will be given by way of a third case and based on specific parameters. For example, as shown in fig. 10, the response bandwidth of the control loop of the DC/DC unit #1 is set to 1Hz, and the response bandwidth of the control loop of the DC/DC unit #2 is set to 100Hz; the conventional value of the response bandwidth is typically 50Hz.
It should also be appreciated that for a particular setting of the response bandwidth, it may be to set the bandwidth of one or more of the components of the control loop. For ease of understanding, the bandwidth setting of one component of the control loop is illustrated as an example. As shown in fig. 10, the DC/DC unit #1 sets the response bandwidth of the PI controller corresponding to the voltage and loop in the control loop to 1Hz; the DC/DC unit #2 sets the response bandwidth of PI control corresponding to the voltage loop in the control loop corresponding to the upper and lower buses to 100Hz.
In the present embodiment, in order to make the supercapacitor SC have enough energy for the power P on the grid side G When abrupt change occurs, dynamic compensation is carried out, and dynamic management is required to be carried out on the voltage of the supercapacitor SC; namely, under different power classes, the voltage corresponding to the super capacitor SC and the command V sc_sum * Dynamic changes are required. As shown in fig. 11, in step S200, the voltage of the supercapacitor SC and the command V sc_sum * Can be changed with power at the maximum value V sc_max And a minimum value V sc_min And dynamically changes. When the load power suddenly drops, the voltage corresponding to the super capacitor SC and the command V sc_sum * Can be toward the maximum value V sc_max The super capacitor SC can be charged to absorb the excessive energy in the fuel cell power generation system, and when the load power suddenly rises, the voltage corresponding to the super capacitor SC and the command V sc_sum * Can be toward the minimum value V sc_min In turn, the supercapacitor SC may discharge to compensate for the increased power demand of the load.
In this embodiment, for the voltage and command V corresponding to the supercapacitor SC sc_sum * There are various ways of dynamic adjustment, and for ease of understanding, one of them will be described below. As shown in fig. 12, the power P on the grid side is first calculated G Then power P G Sending the voltage to an adjusting module to finally generate voltage and command V corresponding to the super capacitor SC sc_sum * . The regulating module is internally provided with voltage and command V sc_sum * Power P to grid side G Is a relationship of (2); from the relationship, the voltage and the command V sc_sum * Power P to grid side G Is inversely proportional, and the slope of the relation curve is a constant value. Further, the calculated power P on the grid side is input to the regulation module G In this case, the regulating module can output the required voltage and the command V through the relation curve sc_sum * . And, on the grid side, the power P G Zero, voltage and command V sc_sum * Take the maximum value V sc_max The method comprises the steps of carrying out a first treatment on the surface of the Power P on the grid side G At rated power P rate At the time, voltage and command V sc_sum * Take the minimum value V sc_min 。
The foregoing has outlined the basic principles, main features and advantages of the present application. It will be appreciated by persons skilled in the art that the present application is not limited to the embodiments described above, and that the embodiments and descriptions described herein are merely illustrative of the principles of the present application, and that various changes and modifications may be made therein without departing from the spirit and scope of the application, which is defined by the appended claims. The scope of protection of the present application is defined by the appended claims and equivalents thereof.
Claims (5)
1. A fuel cell power generation system characterized in that: the system comprises a fuel cell FC, a DC/DC unit, a super capacitor SC and a DC/AC unit which are sequentially connected in series, wherein the output end of the DC/AC unit is connected with a power grid in a grid-connected manner; wherein the fuel cell FC is adapted to provide steady state power to the grid; the super capacitor SC is suitable for providing abrupt dynamic power to the power grid, and the minimum voltage value of the super capacitor SC is limited to be more than or equal to the minimum bus voltage value required by grid connection;
the fuel cell power generation system includes two DC/DC units, namely a DC/DC unit #1 and a DC/DC unit #2;
the DC/DC unit #1 is connected in series between the fuel cell FC and the super capacitor SC, and the DC/DC unit #2 is connected in series between the super capacitor SC and the DC/AC unit; meanwhile, the limitation of the minimum voltage value of the supercapacitor SC is released;
the DC/DC unit #1 adopts a three-level DC/DC topology, the DC/DC unit #2 and the upper bus and the lower bus both adopt a bidirectional buck/boost circuit, and the DC/AC unit adopts a three-level NPC circuit;
the control loop of the DC/DC unit #1 is suitable for controlling the voltage of the super capacitor SC, and the control loop takes the voltage of the super capacitor SC as feedback to obtain the switch tube S for controlling the DC/DC unit #1 1 And S is 2 Duty cycle d of (2) S1 And d S2 ；
The control loop of the DC/DC unit #2 is suitable for controlling the upper and lower bus voltages, and the upper and lower bus voltages are used as feedback to obtain the switch tube S for controlling the DC/DC unit #2 3 、S 4 、S 5 And S is 6 Duty cycle d of (2) 3 To d 6 ；
The DC/AC unit adopts a traditional dq0 control loop;
wherein the response bandwidth of the control loop of the DC/DC unit #2 is higher than the response bandwidth of the DC/DC unit # 1;
super capacitor SC is regarded as capacitors SC1 and SC2 connected in parallel with the bus; the specific control procedure of the control loop of the DC/DC unit #1 is as follows:
s100: super capacitor SVoltage v of C sc1 And v sc2 Respectively performing difference sum and sum to obtain voltage sum feedback v sc_sum And voltage difference feedback v sc_dif ；
S200: voltage and feedback v sc_sum And voltage and command V sc_sum * The current reference i is output through the PI controller after comparison L1 * The method comprises the steps of carrying out a first treatment on the surface of the Reference the current to i L1 * Output current i to fuel cell FC L1 The sum d of duty ratio is output through PI control after comparison sum ；
S300: feedback v of the voltage difference sc_dif And voltage difference command V sc_dif * The difference d of the duty ratio is output through the PI controller after comparison dif ；
S400: based on the sum of the duty cycles d sum And difference d of duty cycle dif Calculating to obtain a switching tube S 1 And S is 2 Duty cycle d of (2) S1 And d S2 ；
The loop control procedure of the DC/DC unit #2 is as follows:
s500: voltage feedback v of upper bus dc1 With corresponding voltage command V dc1 * The current reference i is output through the PI controller after comparison L3 * ；
S600: voltage feedback v of lower bus dc2 With corresponding voltage command V dc2 * The current reference i is output through the PI controller after comparison L4 * ；
S700: reference the current to i L3 * And AND i L4 * Current feedback i with upper and lower bus bars respectively L3 And i L4 After comparison, the output of the PI controller is used for controlling the switch tube S 3 、S 4 、S 5 And S is 6 Duty cycle d of (2) 3 To d 6 。
2. The fuel cell power generation system according to claim 1, wherein: in step S200, the voltage of the supercapacitor SC and the command V sc_sum * Adapted to vary with power at a maximum value V sc_max And minimum valueV sc_min Dynamic change is carried out between the two; so that the supercapacitor SC is adapted to charge when the load power drops suddenly; the supercapacitor SC is adapted to discharge in case of sudden load power rises.
3. The fuel cell power generation system according to claim 2, wherein: voltage and command V sc_sum * Power P to grid side G Inversely proportional, and the voltage and the command V sc_sum * Power P to grid side G The slope of the relationship curve of (2) is a constant value; and then by the power P to the power grid side G And obtaining the required voltage and the command V according to the relation curve sc_sum * ；
When the power P at the power grid side G Zero, voltage and command V sc_sum * Take the maximum value V sc_max The method comprises the steps of carrying out a first treatment on the surface of the When the power P at the power grid side G At rated power P rate At the time, voltage and command V sc_sum * Take the minimum value V sc_min 。
4. A fuel cell power generation system according to any one of claims 1 to 3, wherein: the response bandwidth of the control loop of DC/DC unit #2 is at least 10 times the response bandwidth of the control loop of DC/DC unit # 1.
5. The fuel cell power generation system according to claim 4, wherein: the response bandwidth of the control loop of DC/DC unit #1 is 1Hz, and the response bandwidth of the control loop of DC/DC unit #2 is 100Hz.
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