KR20210108894A - Power converter for controlling power flow of hydrogen generating system based on renewable energy - Google Patents

Abstract

In accordance with the present invention, provided is a power conversion device of a hydrogen conversion system of renewable energy including: a water electrolyzing unit positioned at the midpoint between a renewable energy source and a system connected to each other through a transmission line, and receiving renewable energy power through the transmission line to produce hydrogen and oxygen; a fuel cell for producing power from the hydrogen produced by the water electrolyzing device to transmit the same to the system; and a power conversion device installed between the water electrolyzing device, the fuel cell, and the power transmission line. The power conversion device of the present invention comprises: a power conversion unit for connecting a system during power reception of a water electrolyzing device and power generation of a fuel cell; and a controller for controlling the water electrolyzing device, the fuel cell and the power conversion unit on the basis of a renewable energy generation output power (P(t)) and a system voltage (Vg(t)). The power conversion unit includes: an AC conversion unit for converting AC power of the system into DC power; a DC conversion unit for adjusting voltage of the DC power; a current control unit for controlling a current flow during power reception of the water electrolyzing device and power generation of the fuel cell to prevent generated power of the fuel cell from being input into the water electrolyzing device; and a power buffer for preventing sudden fluctuation in voltage and current that may occur due to operations of the AC conversion unit, the DC conversion unit and the current control device. Therefore, overvoltage and low voltage of a connected system are solved.

Description

Power converter for controlling power flow of hydrogen generating system based on renewable energy

The present invention relates to a power conversion device for controlling the power flow of a renewable energy hydrogen conversion system.

Renewable energy, especially solar and wind power, can theoretically be used anywhere by generating electricity, and since it is based on the radiant heat of the sun, it does not use a separate fuel after installation, so it has been attracting attention as an energy source that does not generate greenhouse gases. It has secured practicality and economic feasibility comparable to traditional energy generation through technological development and market development in various fields. However, there is a large variation in efficiency depending on the installation location, and it has output variability in units of seconds and 1 year as long as it is impossible to control, so it is called Variable Renewable Energy (VRE).

In addition to resolving the variability, as the installed capacity of the VRE increases, a supply-demand imbalance problem with the power required for the load occurs due to the change in the generation output of the VRE. A storage system is required.

1 is a conceptual diagram of Power to Gas and its utilization.

In this situation, as shown in FIG. 1, water is electrolyzed to obtain hydrogen, and synthetic fuel is produced based on hydrogen, and a hydrogen-based renewable energy storage system and power gasification (Power) that produce electric power through a fuel cell in such an energy storage body. to Gas) concept emerged. Compared with the electrochemical energy storage method currently widely used, it is shown in FIG. 2 and Table 1 below.

Figure 2 (A) is a battery-based renewable energy storage system, Figure 2 (B) is a view showing a hydrogen-based renewable energy storage system.

Renewable energy storage method battery energy storage hydrogen energy storage Appropriate storage capacity Several kWh to several tens of MWh Hundreds of MWh to several TWh storage duration A few minutes to 1 day 1 hour to several months Power to Power Efficiency 80-95% 20~40% (P2G 50~75%) Utilization outside of power lowness height capacity expansion cost directly proportional to capacity Decrease according to capacity

Comparison of main characteristics of renewable energy storage methods

3 is a comparison table comparing the characteristics of each type (electrolyte) of a water electrolyzer and a fuel cell.

A water electrolyzer and a fuel cell have a stack in which electrochemical cells are stacked as a major component in common. Theoretically, one stack can perform both water electrolysis and fuel cell power generation, but it is known that it can be applied to high-temperature fuel cells with the same catalyst and low activation resistance of the anode and cathode, and the operating temperature is room temperature. It is technically very difficult to simultaneously and stably apply and operate two types of catalysts on a pair of cell electrodes for use in a low-temperature environment around 200°C. 3 is a table showing a comparison according to the operating principle (electrolyte) of water electrolysis and a fuel cell.

In addition, the water electrolyzer and the fuel cell operate as a DC power load and power source, respectively. In order to maintain the efficiency and lifespan of a stack or cell, fluctuations (ripple) of voltage and current must be small. However, in a widely used commercial AC system, voltage and frequency may vary due to power supply and demand and transmission loss due to the distance from the power plant. An isolating transformer must be included inside to suppress the variability from the system.

4 is a structural connection diagram of a power feeding device of a water electrolyzer, showing the configuration of non-insulated and insulated DC/AC inverters.

FIG. 4A is a diagram showing a simple rectification method, and FIG. 4B is a diagram illustrating a PWM converting method. Before the water electrolyzer was used as a power storage means, it was okay to use a diode-based rectification method, but the efficiency can be improved by applying an AC/DC converter based on a pulse width modulation (PWM) method.

5 is an exemplary circuit diagram of a DC/AC inverter that can be used in a water electrolytic converter. Fig. 5(A) shows a non-insulating type, and Fig. 5(B) shows an insulating type.

4 (B) and 5 (B) have high similarity in configuration only with opposite directions, and are similar to the basic configuration of a charging/discharging power converter used in a battery-type energy storage method. Inefficiency may occur that a plurality of power converters must be included to control the input/output of one system.

The method of converting and storing VRE into hydrogen through a water electrolyzer and generating electric power through fuel cell power generation has advantages in secondary usability such as large-capacity long-term storage and synthesis gas production. From the point of view of the whole system, the efficiency is low compared to the storage method through the battery.

Registration No. 10-1816839, Announced on January 9, 2018, Composite power circuit and control method for new and renewable energy direct link type hydrogen generator

The present invention provides a power conversion device for controlling the operation so that the water electrolysis device does not reuse the output of the fuel cell in a renewable energy hydrogen conversion system combining a water electrolysis device and a fuel cell.

In addition, the present invention provides a technology for configuring a power conversion device so that the power conversion device for power reception and the power conversion device for power generation can be integrated and operated in a renewable energy hydrogen conversion system, and according to the system situation and need, power reception and A power conversion device for controlling power generation is provided.

According to an aspect of the present invention, a water electrolyzer for producing hydrogen and oxygen by receiving renewable energy power through a transmission line and receiving renewable energy power through a transmission line, located at a midpoint between a renewable energy source and a system connected to each other by a transmission line, and the water electrolyzer produced by the A power conversion device for a renewable energy hydrogen conversion system including a fuel cell that generates electric power from hydrogen and transmits it to a system, and a power conversion device installed between a water electrolyzer and a fuel cell and a power transmission line. Based on the power conversion unit and the renewable energy generation output power (P(t)) and the grid voltage (Vg(t)) for performing grid connection during battery power generation, a controller for controlling the water electrolyzer, the fuel cell and the power conversion unit Including, the power conversion unit, the AC conversion unit for converting the AC power of the system into the DC power, the DC conversion unit for adjusting the voltage of the DC power, and by controlling the current flow during power reception and fuel cell power generation of the water electrolysis device, It includes a current control unit for preventing the fuel cell power generation from being input to the water electrolyzer, and a power buffer for preventing sudden changes in voltage and current that may occur due to the operation of the AC conversion unit, the DC conversion unit, and the current control unit.

The AC conversion unit can adjust the amount of power received and generated power through pulse width modulation (PWM) by a switching element under the control of the controller and reduces the ripple, and the DC conversion unit includes an insulation transformer and the current ripple of the received power and generated power can be minimized.

The current control unit includes an input/output control unit for controlling the entire system input/output according to the first control signal (S ₁ ) of the controller, and an electrolysis input control unit for controlling whether the water electrolysis device is receiving power according to _{the second control signal (S 2 ) of the controller;} , it may include a fuel cell output control unit for controlling whether the fuel cell is generated according to the third control signal (S _{3 ) of the controller.}

The current control unit may further include a power buffer charging/discharging control unit for controlling whether the power buffer is charged/discharged according to the fourth control signal S _{4 of the controller.}

The DC converter includes a water electrolytic converter that boosts or steps down the DC voltage displayed as the output of the AC converter to the operating voltage of the electrolyzer, and a fuel cell converter that boosts or steps down the operating voltage of the fuel cell to the DC voltage of the AC converter. , even if the DC voltage of the AC converter is different from the operating voltage of the electrolyzer, power can be received from the AC converter to the electrolyzer, and even if the DC voltage of the AC converter and the operating voltage of the fuel cell are different, power is transmitted from the fuel cell to the AC converter This may be possible.

The DC converter further includes a power buffer charging/discharging converter that converts the operating voltage of the power buffer into the DC voltage of the AC converter, so that even if the DC voltage of the AC converter and the operating voltage of the power buffer are different, power reception and transmission may be possible.

The water electrolytic converter consists of two or more water electrolytic converter unit modules connected in parallel based on the capacity of the water electrolyzer, and the fuel cell converter includes two or more fuel cell converter unit modules in parallel based on the number or capacity of fuel cells. The power buffer charging/discharging converter may be configured by connecting two or more power buffer charging/discharging converter modules in parallel based on the number or capacity of the power buffers.

When the first current command value (I* _{1 (t)) that commands the first current measurement value (I 1} (t)) flowing into the current control unit through the AC conversion unit is greater than 0 (I ₁ (t) > 0), The controller transmits a closing signal (S ₂ =1) to the electrolysis input control unit, an open signal (S ₃ = 0) to the fuel cell output control unit, and conversely, the first current command value ( When I* ₁ (t)) is less than 0 (I* ₁ (t) < 0), the controller transmits an open signal (S ₂ =0) to the electrolytic input control unit, and a closing signal (S 2 =0) to the fuel cell output control unit S ₃ =1) can be transmitted.

When the renewable energy generation output (P(t)) is greater than or equal to a predetermined value (Pg), or when the grid voltage (Vg(t)) _{rises above a predetermined high voltage value (V H} ) and continues for more than a predetermined time, the controller The input/output control unit, the electrolysis input control unit, the power buffer charging/discharging control unit are driven, and the fuel cell output control unit is controlled to terminate the operation, and the power received by the AC conversion unit is the amount of power required for voltage stabilization and the regeneration that the electrolysis device can receive Renewable energy by following the larger value among the energy generation amount, the operation power of the electrolytic receiving device follows the receiving power of the AC converting unit, and the difference between the receiving power of the AC converting unit and the operating power of the receiving electrolytic device as the charging/discharging power of the power buffer It is possible to prevent an increase in the system voltage Vg(t) due to an increase in the output P(t), and to stably convert renewable energy generation power into hydrogen.

When the associated system voltage (Vg(t)) _{drops below a predetermined low voltage value (V L} ) and continues for a predetermined time or longer, the controller drives the input/output control unit, the fuel cell output control unit, and the power buffer charge/discharge control unit, The input control unit is controlled to terminate driving, and the transmission power of the AC conversion unit follows the amount of power required for stabilization of the grid voltage (Vg(t)), and the power generated by the fuel cell follows the transmission power of the AC conversion unit. By using the difference between the power transmitted by the converter and the power generated by the fuel cell as the charging/discharging power of the power buffer, a drop in the grid voltage (Vg(t)) due to the imbalance between the renewable energy and the load is prevented.

When the renewable energy generation output (P(t)) is greater than or equal to a predetermined value (Pg) or the grid voltage (Vg(t)) associated with the renewable energy hydrogen conversion system rises above a _{predetermined high voltage value (V H ),} When the fuel cell is generating power, the controller controls the power generation amount of the fuel cell to be 0, and after the power generation amount of the fuel cell becomes 0, the fuel cell output controller controls the driving end state.

When the water electrolyzer is operating in a state where the associated grid voltage (Vg(t)) is _{lowered to a predetermined low voltage value (V L} ) or less, the controller receives and electrolyzes the operating power of the water electrolyzer until it becomes zero. It is lowered at a predetermined rate defined as a predetermined multiple of the device's own capacity, and after the operation power of the water electrolyzer becomes 0, the water electrolysis input control unit can be controlled so that the driving end state is reached.

According to the present invention, it is possible to provide a power conversion device for controlling the power flow of the renewable energy hydrogen conversion system that absorbs variations in the renewable energy output power and solves the overvoltage and low voltage of the linked system.

1 is a conceptual diagram of Power to Gas and its utilization.
Figure 2 (A) is a battery-based renewable energy storage system, Figure 2 (B) is a view showing a hydrogen-based renewable energy storage system.
3 is a comparison table comparing the characteristics of each type (electrolyte) of a water electrolyzer and a fuel cell.
4 is a diagram showing a structure connection diagram of a power feeding device of a water electrolyzer, (A) a simple rectifying method, and (B) a PWM converting method.
5 is an example of a circuit diagram of a DC/AC inverter, showing (A) non-isolated type and (B) isolated type.
6 is a view showing a renewable energy hydrogen conversion system including a power conversion device according to an embodiment of the present invention.
7 is a view showing an electrode reaction equation and electrode reaction voltage of water electrolysis according to the pH of water.
FIG. 8 is a diagram of a power converter showing detailed configurations of a DC converter and a current controller of FIG. 6 .
9 is a view showing the configuration of a power conversion device in the case where the electrolytic converter and the fuel cell converter are each configured with a plurality of converter modules according to an embodiment of the present invention.
10 is a view showing the control connection of the controller inside the renewable energy hydrogen conversion system of FIG.
11 and 12 are flowcharts illustrating a control method of the power conversion device of the renewable energy hydrogen conversion system of FIG. 6 .

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to intentions or customs of users and operators. Therefore, the definition should be made based on the content throughout this specification.

6 is a view showing a renewable energy hydrogen conversion system including a power conversion device according to an embodiment of the present invention.

The renewable energy hydrogen conversion system 1000 is associated with the renewable energy source 10 and the system 20 . The renewable energy hydrogen conversion system 1000 includes a power conversion device 100, a water electrolysis device 200, a hydrogen storage device 300, a fuel cell 400, and an auxiliary device (not shown) supporting the above devices. include

The power conversion device 100 is in charge of receiving power from the water electrolyzer 200 and connecting the grid 20 when the fuel cell 400 is generated. The power conversion device 100 converts the AC power of the grid 20 into DC power and supplies it to the water electrolyzer 200 , converts the DC power generation output of the fuel cell 400 into AC power, and sends it to the grid 20 . transmit

The water electrolyzer 200 is located at a midpoint between the renewable energy power generation source 10 and the system 20 that are connected to each other through a power transmission line, and receives renewable energy power through the transmission line to produce hydrogen and oxygen.

The fuel cell 400 generates electric power from the hydrogen produced by the water electrolyzer 200 and transmits the electric power to the system 20 .

The operating voltage is determined according to the number of cells stacked on the water electrolyzer 200 and the water electrolysis stack (not shown), and the fuel cell 400 depends on the number of cells stacked on the fuel cell stack (not shown). The operating voltage is determined accordingly.

The power converter 100 includes a power converter 110 and a controller 120 .

The power conversion unit 110 absorbs the output fluctuation of the renewable energy power generation source 10 according to the control of the controller 120 and solves the overvoltage and low voltage of the associated system 20 of the renewable energy hydrogen conversion system 1000 of control the power flow.

The controller 120 communicates with the power conversion device 100 , the water electrolysis device 200 , the hydrogen storage device 300 , and the fuel cell 400 and controls the energy flow. The controller 120 controls the water electrolysis device 200, the fuel cell 400 and the power conversion unit 100 based on the renewable energy generation output (P(t)) and the system voltage (Vg(t)). can

The power conversion unit 110 may include an AC conversion unit 112 , a current control unit 114 , a DC conversion unit 116 , and a power buffer 118 .

The AC converter 112 connects the inside of the system 1000 that is an AC environment with the system 20 that is an AC environment. The AC converter 112 converts AC power of the system 20 into DC power. The AC converter 112 may adjust the amount of power received and the amount of power generated through pulse width modulation (PWM) by a switching element, and may reduce ripple.

The current control unit 114 is located near the DC conversion unit 116 and adjusts the power flow inside the system 1000 according to the charging/discharging situation. The current control unit 114 controls the current flow during the power reception of the water electrolysis device 200 and the power generation of the fuel cell 400 so that the generated power of the fuel cell 400 is not input to the water electrolysis device 200 .

The current control unit 114 checks the abnormalities of the relays that can connect or block the circuit as needed therein, the capacitors for suppressing the abnormal high voltage/low voltage caused by the on/off of the relay, and the circuit. It may include a combination of protection components such as a fuse that blocks.

The DC converter 116 adjusts the voltage between the water electrolysis device 200 and the fuel cell 400 in the system 1000 , and the power converter 100 . The DC converter 116 boosts the voltage of the DC power. The DC converter 116 may include an insulation transformer (not shown) to minimize the current ripple of the received power and the generated power. In addition, the DC converter 116 may adjust the voltage of the power buffer 118 and the voltage of the power converter 110 .

The power buffer 118 buffers the shock at the time of charging/discharging conversion to prevent sudden fluctuations in voltage and current that may be caused by the operation of the AC conversion unit 112 , the DC conversion unit 116 , and the current control unit 120 . .

7 is a view showing an electrode reaction equation and electrode reaction voltage of water electrolysis according to the pH of water.

The electrochemical reaction formula and the anode reaction potential of water are V ₀ =1.229V as shown in FIG. 7, but the actual cell voltage of water electrolysis is an overvoltage due to the resistive component as shown in Equation 1 (a), and the fuel cell 400 ) is expressed as a voltage drop due to the internal resistance as shown in Equation (1) (b). Therefore, a difference occurs between _{the operating voltage V Electolyzer} of the stack of the water electrolyzer 200 _{and the operating voltage V FuelCell} of the stack of the fuel cell 400 even though they have the same number of stacks. The power buffer 118 may also have a difference in operating voltage from the water electrolyzer 200 and the fuel cell 400 depending on specifications.

[Equation 1]

In order to correct this, the DC converter 116 may include three types of converters as shown in FIG. 8 .

FIG. 8 is a view showing the power conversion device 100 showing details of the current control unit 114 and the DC conversion unit 116 of FIG. 6 .

The current control unit 114 may include an input/output control unit 810 , an electrolysis input control unit 820 , a power buffer charging/discharging control unit 830 , and a fuel cell output control unit 840 .

The input/output control unit 810 controls the entire input/output of the renewable energy hydrogen conversion system 1000 according to _{the first control signal S 1 of the controller 120 .}

The electrolysis input control unit 820 may control whether the electrolysis device 200 receives power according to _{the second control signal S 2 of the controller 120 .}

The fuel cell output control unit 840 may control whether the fuel cell is generated according to _{the third control signal S 3 of the controller 120 .}

The power buffer charging/discharging control unit 830 may control whether to charge/discharge the power buffer 140 according to _{the fourth control signal S 4 of the controller 120 .}

The DC converter 116 may include an electrolytic converter 850 , a power buffer charging/discharging converter 860 , and a fuel cell converter 870 . When the DC side voltage of the AC conversion unit 112 and the operating voltage of the water electrolysis device 200 or the fuel cell 400 and the power buffer 118 are different, the DC converter 116 is configured to operate the devices 110, 200, 400) may be configured to enable power reception and transmission of the power conversion device 100 even if the DC voltages between them are different.

The input voltage of the water electrolytic converter 850 is maintained to be the same as the DC side voltage (hereinafter, DC voltage) shown as the output of the AC conversion unit 112 , and the output voltage of the water electrolytic converter 850 is that of the water electrolysis device 200 . is the driving voltage. The water electrolytic converter 850 may step-up or step-down the DC voltage displayed as the output of the AC conversion unit 112 to the operating voltage of the water electrolysis device 200 .

The input voltage of the fuel cell converter 870 is the same as the operating voltage of the fuel cell 400 (ie, the output voltage of the fuel cell 400 ), and the operating voltage of the fuel cell 400 is the operating voltage of the AC converter 112 . becomes the input voltage. To this end, the fuel cell converter 870 may step-up or step-down the operating voltage of the fuel cell 400 to the DC voltage of the AC converter 112 . Therefore, even if the DC voltage of the AC converter 112 and the operating voltage of the electrolyzer 200 are different, it is possible to receive power from the AC converter 112 to the electrolyzer 200, and Even if the DC voltage and the operating voltage of the fuel cell 400 are different, power may be transmitted from the fuel cell 400 to the AC converter 112 .

The input voltage of the power buffer charging/discharging converter 860 is the same as the operating voltage of the power buffer 118 , and the output voltage of the power buffer 118 is a voltage that is input to the AC converter 112 from the operating voltage. To this end, the power buffer charging/discharging converter 860 may _{convert the voltage V B} of the power buffer 118 into a DC voltage of the AC converter 112 . Therefore, even if the DC voltage of the AC converter 112 and the operating voltage of the power buffer 118 are different, power reception and transmission are possible.

The size of the power buffer 118 should be large enough to cope with the above factors in order to prepare for the case where the output variability of the renewable energy source 10 is large or the linkage system 20 is unstable. In this case, the internal DC voltage of the power conversion device 100 _{can be synchronized with the voltage V B} of the power buffer 118, and according to an embodiment, the power buffer charging/discharging converter 860 and the power buffer charging/discharging control unit ( 830) can be excluded.

Renewable energy generation output (P(t)) is greater than or equal to a predetermined value (Pg), or the grid voltage (Vg(t)) of the grid 20 linked to the renewable energy hydrogen conversion system 1000 is a predetermined high voltage value ( When _{it rises above V H} and lasts longer than a predetermined time (τ), the current control unit 120 drives the input/output control unit 810, the electrolysis input control unit 820, the power buffer charging/discharging control unit 830, and the fuel The driving of the battery output control unit 840 is terminated. To this end, the controller 120 generates a first control signal (S ₁ ) as a closing signal (S ₁ =1), transmits it to the input/output control unit 810, and transmits the second control signal (S ₂ ) as a closing signal (S). ₂ = 1) is generated and transmitted to the electrolytic input control unit 820, and the fourth control signal (S ₄ ) is generated as a closing signal (S ₄ = 1) and transmitted to the power buffer charging/discharging control unit 830, The third control signal S ₃ may be generated as an open signal S ₃ =0 and transmitted to the fuel cell output control unit 840 .

The power received by the AC converter 112 follows the larger value of the amount of power required for voltage stabilization and the amount of renewable energy that the electrolysis device 200 can receive, and the operating power of the electrolysis device 200 is converted to AC. It tracks the received power of the unit 112 . The system voltage ( It is possible to prevent the rise of Vg(t)) and convert renewable energy generation power into hydrogen stably.

When the grid voltage (Vg(t)) associated with the renewable energy hydrogen conversion system 1000 _{drops below a predetermined low voltage value (V L} ) and lasts more than a predetermined time (τ), the current control unit 120 is an input/output control unit 810 , the fuel cell output control unit 840 , and the power buffer charging/discharging control unit 830 are driven, and the driving of the electrolysis input control unit 820 is terminated. To this end, the controller 120 generates a first control signal (S ₁ ) as a closing signal (S ₁ =1) and transmits it to the input/output control unit 810, and transmits the third control signal (S ₃ ) as a closing signal (S). ₃ = 1) is generated and transmitted to the fuel cell output control unit 830, and a fourth control signal (S ₄ ) is generated as a closing signal (S ₄ = 1) and transmitted to the power buffer charging/discharging control unit 830, The second control signal S ₂ may be generated as an open signal (S ₂ =0) and transmitted to the electrolytic input control unit 810 .

The transmission power of the AC conversion unit 112 tracks the amount of power required for stabilization of the system voltage Vg(t), and the generated power of the fuel cell 400 tracks the transmission power of the AC conversion unit 112, The difference between the power transmitted by the AC converter 112 and the power generated by the fuel cell 400 is the charging/discharging power of the power buffer 118, and the system voltage (Vg(t)) drops due to the imbalance between the renewable energy and the load. to prevent

Renewable energy generation output (P(t)) is greater than or equal to a predetermined value (Pg) or the grid voltage (Vg(t)) associated with the renewable energy hydrogen conversion system 1000 rises above a _{predetermined high voltage value (V H )} When the fuel cell 400 is generating power, the controller 120 controls the power generation amount of the fuel cell 400 to be 0, and after the power generation amount of the fuel cell 400 becomes 0, the fuel cell output control unit ( 840) is controlled to be in the driving end state.

When the water electrolyzer 200 is operating in a state in which the grid voltage Vg(t) associated with the renewable energy hydrogen conversion system 1000 _{is lowered to a predetermined low voltage value (V L ) or less, the controller 120} decreases the operating power of the water electrolyzer 200 at a predetermined rate defined as a constant multiple of the self-capacitance of the water electrolyzer 200 until it becomes zero. The controller 120 controls the water electrolysis input control unit 820 to be in the driving end state after the operation power of the electrolysis apparatus 200 becomes 0.

9 is a diagram showing the configuration of the power conversion device 100 when the electrolytic converter 850 and the fuel cell converter 870 are each configured with a plurality of converter modules according to an embodiment of the present invention.

As shown in FIG. 9 , the electrolytic converter 850 may include a plurality of modules 850-1 to 850-m, and the fuel cell converter 870 includes a plurality of modules 870-1 to 870-m. n) can be configured.

In the DC converter 130 , the electrolytic converter 850 may be configured by connecting two or more electrolytic converter unit modules 850-1 to 850-m in parallel based on the capacity of the electrolytic device 300 . .

The fuel cell converter 870 may be configured by connecting two or more fuel cell converter unit modules 870 - 1 to 870 -n in parallel based on the number or capacity of the fuel cells 400 .

Although not shown, the power buffer charging/discharging converter 860 may also be configured by connecting two or more power buffer charging/discharging converter modules in parallel based on the number or capacity of the power buffers 118 .

As shown in FIG. 9, when the electrolytic converter 850, the fuel cell converter 870, or the power buffer charge/discharge converter 860 constitutes a converter with a plurality of modules, the controller 120 controls each converter. The operating power of the composing modules should be distributed. For example, the controller 120 may include each water electrolytic converter unit module 850 - 1 to 850 -m of the water electrolytic converter 850 or each fuel cell converter unit module 870 - 1 to 850 - m of the fuel cell converter 870 . 870-n), a distribution process of designating an output command value and transmitting it to the electrolytic converter 850 or the fuel cell converter 870 may be performed. At this time, the command value delivered to the converter can be equally distributed by dividing the current in charge of the converter by the number of modules, or the rated capacity of the modules can be sequentially distributed so that the operating module operates close to the rated operation.

FIG. 10 is a view showing the control connection of the controller 120 inside the renewable energy hydrogen conversion system 1000 of FIG. 6 .

10 shows how the controller 120 in the renewable energy hydrogen conversion system 100 communicates with the detailed elements of the power conversion device 100 from the configuration of FIG. did. Hereinafter, the control configuration and control flow of the power conversion device 100 related to the present invention during the operation of the controller 120 will be mainly described.

The controller 120 may be defined as communicating with the AC conversion unit 112 , the current control unit 114 , and the DC conversion unit 116 . In addition to the AC conversion unit 112 , the current control unit 114 and the DC conversion unit 116 , the controller 120 includes an electrolytic input control unit 820 , an electrolytic converter 850 , a fuel cell output control unit 840 , and a fuel cell. The converter 870, the AC conversion unit 112, and the input/output control unit 810 may be configured as a communication method for each input/output circuit to directly control the control unit 810.

Also, when the power buffer charging/discharging converter 860 for the power buffer 118 is essential due to the difference in voltage specifications, the controller 120 controls the power buffer charging/discharging converter 860 and the power buffer charging/discharging control unit 830. have a signal The input/output control unit 810, the electrolysis input control unit 820, the power buffer charging/discharging control unit 830, and the fuel cell output control unit 840 may define the open and closed states of the circuit as well as whether the operation is performed, respectively. If the related parameters are simplified, the controller 120 may be configured to include a switch operable through a signal.

To this end, the controller 120 may transmit an open/close signal to the input/output control unit 810 using _{the first control signal S 1} and check the state, and receive the electrolysis using _{the second control signal S 2 .} It is possible to transmit the open/close signal to the input control unit 820 and check the state, and to transmit the open/close signal to the power buffer charging/discharging control unit 830 using _{the fourth control signal (S 4 ) and check the state} In addition, an open/close signal may be transmitted to the fuel cell output control unit 840 using the third control signal S _{3 and the state may be checked.}

The controller 120 measures the value of the current flowing in the electrolytic converter 850 , the fuel cell converter 870 , and the circuit connected from the power buffer charging/discharging converter 860 to the current controller 120 when included in the configuration. can do. In addition, the controller 120 designates a second current command value (I * ₂ (t)) for the electrolytic converter 850 and a third current command value (I * ₃ (t)) for the fuel cell converter 870 . can _{The controller 120 is, if necessary, the first current command value (I * 1} (t)) of the AC conversion unit 1110 induced by the current command value and the situation of the system 20 and the power buffer charge/discharge converter 860. 4 Current command value (I* ₄ (t)) can be specified. Here, the first current command value (I * _{1 (t)) is a value for commanding the first current measurement value (I 1} (t)), which is a direct current flowing from the AC conversion unit 112 to the current control unit 114 . indicates.

Hereinafter, in response to the output power (P(t)) and the grid voltage (Vg(t)) of the renewable energy source 10 to which the controller 120 is linked, the power conversion device 100 components in the system 1000 Describes how to be controlled.

The electric power that can be transmitted from the renewable energy source 10 to the grid 20 is defined as (P(t)), which is the capacity of the grid 20 to which the renewable energy source 10 is connected, and the renewable energy generator and power transmission company. is a predetermined value defined by the contract capacity of

The reference point of the grid voltage (Vg(t)) is set to V _G , which is different depending on the time of grid connection of the system, but in this description, it is regarded as 220 [V], the domestic phase-neutral voltage standard. In addition, the power reception reference voltage (V _H ) and the power generation reference voltage (V _F ) of the renewable energy hydrogen conversion system 1000 are defined as predetermined values within the voltage standard of the AC system 20 . The reception reference voltage is higher than the reference point, and the power generation reference voltage is lower than the reference point.

The internal circuit voltage (V _{PCS ) of the power converter 100 is the same as the voltage (V B} ) of the power buffer 118 , and in the case of the configuration as shown in FIG. 7 , the internal circuit voltage (V _PCS ) of the power converter 100 is The DC voltage of the water electrolyzer 200 and the DC voltage of the fuel cell 400 may be any value within the range of both extremes.

At an arbitrary time t, the amount of current flowing into the system 1000 from the system 20 through the AC converter 112 is I ₁ (t), the amount of input current of the electrolytic converter 850 is I ₂ (t), The output current amount of the fuel cell converter 870 is defined as I ₃ (t) and the charging current amount of the power buffer 118 _{is defined as I 4} (t), and the following Equation 2 holds for the defined current amount. However, since the purpose of the system 1000 is to store renewable energy and maintain the voltage of the system 20, the fuel cell 400 and the water electrolyzer 200 do not operate simultaneously, so I ₂ (t) and I _{One of 3} (t) has a value of 0.

[Equation 2]

The current control unit 114 operates the water electrolysis device 200 to receive power from the system 20, is converted through the AC conversion unit 112, and is converted to a first current measured value I ₁ ( When the first current command value (I* ₁ (t)) for commanding t)) is greater than 0 (I* ₁ (t) > 0), the controller 120 sends a closing signal to the electrolytic input control unit 820 ( S ₂ =1) and transmits an open signal (S ₃ =0) to the fuel cell output control unit 840 .

Conversely, in order to generate power through the fuel cell 400, when the first current command value (I* ₁ (t)) is less than 0 (I* ₁ (t) < 0), the controller 120 receives the electrolysis input control unit ( An open signal (S ₂ =0) is transmitted to the _{820 , and a close signal (S 3} =1) is transmitted to the fuel cell output control unit 840 . This is expressed by the following Equation (3).

<Equation 3>

11 and 12 are flowcharts illustrating a control method of the power conversion device 100 of the renewable energy hydrogen conversion system 1000 of FIG. 6 .

The controller 120 receives the renewable energy output power (P(t)) and the system voltage (Vg(t)) value ( 1110 ).

Renewable energy output power (P(t)) is increased (P(t)>Pg) above a predetermined voltage value (Pg) (1112), or the grid voltage (Vg(t)) of the grid 20 is based on the power reception When it rises above the voltage (V _H ) (Vg(t)>V _H ) ( 1114 ), the controller 120 receives the first current command value (I ₁ *(t)) to receive the AC conversion unit 112 . Then, the controller 120 transmits the closing signal (S ₁ =1) to the input/output control unit 810 (1116).

The controller 120 _{checks whether I 3} (t) is 0, and when the third current I ₃ is 0 (1118), transmits an open signal (S ₃ =0) to the fuel cell output control unit 840, A closing signal (S ₂ =1) is transmitted to the water electrolysis input control unit 820 to prepare for the operation of the water electrolysis device 200 ( 1120 ).

[Equation 4]

At this time, when the fuel cell 400 is operating and the third current I ₃ is greater than 0 (I ₃ (t) > 0) 1118, the controller 120 controls the third current command value I* ₃ ( t)) to 0 to lower the output of the fuel cell 400 to 0 (1122), and when the actual power generation output of the fuel cell 400 becomes 0, an open signal (S) to the fuel cell output control unit 840 ₃ = 0), and a closing signal (S ₂ =1) is transmitted to the electrolysis input control unit 820 to prepare the operation of the electrolysis apparatus 200 ( 1120 ). This can be expressed by Equation 5.

[Equation 5]

Even after enough time τ to determine that the change in the renewable energy output power P(t) and the grid voltage Vg(t) is trending, the conditions such as Equations 4 and 5 may be maintained. In other words, when the grid voltage (Vg(t)) is the grid voltage (Vg(t)) is the reception reference voltage (V _H ) or more (Vg(t-τ)>V _H ) (1124), the renewable energy output power When (P(t)) is greater than or equal to the predetermined voltage value (Pg) (P(t-τ)>Pg) 1124 , the second current command value I ₂ * (t)) is added (1210).

The controller 120 calculates the first current command value (I ₁ *(t)) of the AC conversion unit 112 and the second current command value (I ₂ *(t)) of the electrolytic converter 850 to the AC conversion unit (112) and transfer to the electrolytic converter 860 (1210). AC converting unit first current command value (I ₁ * (t)) of 112 and a power reception by Equation below in the second current command value (I ₂ * (t)) is a value that varies according to the time of the converter (850) It is defined through the same or similar process as 6, and the difference between the actual current value and the command value is changed by the PWM method On/Off Duty Ratio control.

In addition, according to the first current command value (I ₁ *(t)) of the AC conversion unit 112 and the second current command value (I _{2 *(t)) of the electrolytic converter 850, the AC conversion unit 112 is} When the first measured current I ₁ (t) and the second current measured value I ₂ (t) are determined, the input current I ₄ (t) of the current buffer 140 is the current measured value I ₁ (t) )) and the current measurement value (I ₂ (t)) is determined (1210).

[Equation 6]

α, β, and γ in Equation 6 and γ are predetermined constant values, and γ has a positive value of 1 or less.

을 이용하여 제2 전류지령치(I₂*(t))를 결정하도록 제어할 수 있다(1216, 1218). When the conditions of Equations 4 and 5 are released, that is, the grid voltage (Vg(t)) of the grid 20 _{is less than or equal to the power reception reference voltage (V H} ) (Vg(t)≤V _H ) (1212) , when the renewable energy output power (P(t)) is less than or equal to a predetermined voltage value (Pg) (P(t)≤Pg) 1214 , the controller 120 sets the operating power of the water electrolyzer 200 to 0 or Equation to gradually decrease to a predetermined minimum value greater than 0

It is possible to control to determine the second current command value (I ₂ *(t)) by using (1216, 1218).

_{The reduction width} of this process may be multiplied by a predetermined constant δ with respect to the rated current value (I 2Max ) of the water electrolyzer 200 .

This can be expressed by Equation (7).

[Equation 7]

In Equation 7, δ is a predetermined constant value, and δ has a positive value of 1 or less.

Here, when the second current measurement value I ₂ becomes 0, it is defined that the water electrolysis device 200 is terminated. When the second current measurement value (I ₂ ) becomes 0 ( 1218 ) and the operation of the water electrolysis device 200 is terminated, the controller 120 sends an open signal (S ₂ =0) to the water electrolysis input control unit 820 . In addition, the operation of the input/output control unit 820 is stopped by electrolysis, and an open signal (S ₁ =0) is added to the input/output control unit 810 to stop the operation of the input/output control unit 810 ( 1220 ).

Referring back to FIG. 11 , according to an embodiment of the present invention, the grid voltage Vg(t) is lower than a _{certain voltage value V L due to a change in the renewable energy output power P(t), a sudden load surge, etc.} , the system voltage Vg(t) is restored through fuel cell operation (1150). To this end, the controller 120 adds a closing signal (S ₁ =1) to the input/output control unit 810, and in this case, the first current command value I* ₁ (t) is less than 0 (1152).

When the second current measurement value I2 is 0 and thus the electrolysis apparatus 200 is not in operation ( 1154 ), the controller 120 transmits an open signal (S ₂ =0) to the electrolysis input control unit 820 . and transmits a closing signal (S ₃ =1) to the fuel cell output control unit 840 ( 1156 ).

When the trend in which the system voltage (Vg(t)) _{decreases below a certain voltage value (V L} ) continues even after a predetermined time (Vg(t-τ) < V _L ) ( 1160 ), the fuel cell 400 operates The energy stored in the power buffer 118 is temporarily used until a possible state, but the voltage measurement value of the power buffer 118 at this time, which is the time when a situation occurs in the memory (not shown) in the controller 120, is used as the power buffer. It can be stored as the reference voltage (Vs) (V _S =V _B (t)) (1230). This procedure can be expressed by Equation (8).

[Equation 8]

That is, if the grid voltage (Vg(t)) is _{smaller than the reference low voltage (V L} ) and this state is maintained even after a certain period of time has elapsed (Vg(t-τ)<V _L ), the The first current command value (I* ₁ (t)) is a predetermined value obtained by multiplying the value obtained by subtracting _{the reference point (V G} ) of the grid voltage from the second current measurement value (I ₂ (t)) and the grid voltage (Vg(t)) multiplied by β is adjusted to the smaller of the value of and 0.

When the water electrolysis device 200 is in operation (1154), the controller 120 causes the second current command value (I * ₂ (t)) for the water electrolysis converter 850 to be gradually decreased to decrease the water electrolysis device 200 ) is controlled to gradually decrease ( 1158 ), and as shown in FIG. 12 , after completing the operation of the water electrolyzer 200 , the above procedure is performed ( 1230 ).

In a state where the water electrolysis device 200 is not in operation (I ₂ (t) = 0) (1154), the controller 120 adds an open signal (S ₂ =0) to the water electrolysis input control unit 820, _{A closing signal (S 3} =1) is added to the fuel cell output control unit 840 ( 1156 ).

[Equation 9]

After that, when the system voltage Vg(t) is restored within a predetermined range (Vg(t)>V _L ) 1232 , a portion of the power generation output of the fuel cell 400 is excluded for use in charging the power buffer 118 . The remainder is transmitted to the grid 20 (1234, 1236).

When the voltage (V _B (t)) of the power buffer 118 reaches the reference voltage (Vs) of the power buffer 118 ( 1234 ), the controller 120 determines that the renewable energy hydrogen conversion system 100 is system stabilization. It is determined that the purpose has been accomplished and the fuel cell 400 is controlled not to generate any more output. In detail, the AC conversion unit 112 transmits the entire output of the fuel cell 400 to the system 20, but gradually decreases the power generation output P(t) to 0 (1238, 1240). In this process, the decrease in the output of the fuel cell 400 may _{be determined by multiplying the rated output current I 3Max} of the fuel cell 400 by a predetermined constant δ. This process is represented by Equations (10) and (11).

When this process is finished, the controller 120 adds an open signal (S ₁ =0) to the input/output control unit 810 to stop the operation, and applies an open signal (S ₃ =0) to the fuel cell output control unit 840 to Stop the operation (1242).

[Equation 10]

[Equation 11]

The control method expressed by the equations from Equation 2 to Equation 11 can be variously modified as an example of a method of absorbing the renewable energy output power (t)) fluctuations and solving the overvoltage and the undervoltage of the linked system 20 . .

An aspect of the present invention may be implemented as computer-readable codes on a computer-readable recording medium. Codes and code segments implementing the above program can be easily inferred by a computer programmer in the art. The computer-readable recording medium includes all types of recording devices in which data readable by a computer system is stored. Examples of the computer-readable recording medium include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical disk, and the like. In addition, the computer-readable recording medium may be distributed in network-connected computer systems, and may be stored and executed as computer-readable codes in a distributed manner.

The above description is only one embodiment of the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to implement it in a modified form without departing from the essential characteristics of the present invention. Accordingly, the scope of the present invention should not be limited to the above-described embodiments, but should be construed to include various embodiments within the scope equivalent to the content described in the claims.

100: power conversion device 110: power conversion unit
120: controller 112: AC conversion unit
114: current control unit 116: DC conversion unit
118: power buffer 200; water electrolyzer
300: hydrogen storage device 400: fuel cell
810: input/output control unit 820: electrolysis input control unit
830: power buffer charge/discharge control unit 840: fuel cell output control unit
850: water electrolytic converter 860: power buffer charging and discharging converter
870: fuel cell converter

Claims (12)

A water electrolyzer that produces hydrogen and oxygen by receiving renewable energy power through a power line, which is located at the midpoint between the renewable energy source and the grid, which are connected to each other through a power line, and a water electrolyzer that produces power from the hydrogen produced by the power line A power conversion device for a renewable energy hydrogen conversion system, comprising: a fuel cell for transmitting power to
a power conversion unit for performing grid connection between power reception of the water electrolyzer and fuel cell power generation; and
Based on the renewable energy generation output power (P(t)) and the system voltage (Vg(t)), a controller for controlling the water electrolyzer, the fuel cell and the power conversion unit; including,
power converter,
AC conversion unit for converting AC power of the system into DC power;
DC converter for adjusting the voltage of DC power;
a current control unit that controls the current flow during power reception of the water electrolyzer and power generation of the fuel cell so that power generated by the fuel cell is not input to the water electrolyzer; and
a power buffer for preventing sudden fluctuations in voltage and current that may be caused by the operation of the AC conversion unit, the DC conversion unit and the current control unit; Power conversion device of the renewable energy hydrogen conversion system, characterized in that it comprises a. According to claim 1,
The AC conversion unit can adjust the amount of power received and generated power through pulse width modulation (PWM) by a switching element under the control of the controller, and reduces ripple,
The DC converter includes an insulation transformer, and a power converter of a renewable energy hydrogen conversion system to minimize the current ripple of received power and generated power. According to claim 1,
current control unit
an input/output controller for controlling the entire system input/output according to the first control signal (S _{1 ) of the controller;}
an electrolysis input control unit for controlling whether the electrolysis device receives power according to the second control signal (S _{2 ) of the controller;} and
a fuel cell output control unit for controlling whether the fuel cell generates power according to a third control signal (S _{3 ) of the controller;} Power conversion device of the renewable energy hydrogen conversion system, characterized in that it comprises a. 4. The method of claim 3,
The current control unit includes: a power buffer charging/discharging control unit for controlling whether the power buffer is charged/discharged according to _{the fourth control signal (S 4 ) of the controller;} Power conversion device of the renewable energy hydrogen conversion system, characterized in that it further comprises. According to claim 1,
DC converter
a water electrolytic converter that boosts or steps down the DC voltage displayed as the output of the AC conversion unit to the operating voltage of the water electrolyzer; and
a fuel cell converter that boosts or steps down the operating voltage of the fuel cell to the DC voltage of the AC converter; including,
Even if the DC voltage of the AC converter and the operating voltage of the electrolyzer are different, power can be received from the AC converter to the electrolyzer, and even if the DC voltage of the AC converter and the operating voltage of the fuel cell are different, power transmission from the fuel cell to AC converter Power conversion device of the renewable energy hydrogen conversion system, characterized in that possible. 6. The method of claim 5,
The DC converter includes: a power buffer charging/discharging converter that converts the operating voltage of the power buffer into a DC voltage of the AC converter; further including,
Power conversion device of a renewable energy hydrogen conversion system, characterized in that it is possible to receive and transmit power even if the DC voltage of the AC conversion unit and the operating voltage of the power buffer are different. 7. The method of claim 6,
The water electrolytic converter consists of two or more water electrolytic converter unit modules connected in parallel based on the capacity of the water electrolyzer,
The fuel cell converter is configured by connecting two or more fuel cell converter unit modules in parallel based on the number or capacity of fuel cells,
The power buffer charging/discharging converter is a power conversion device of a renewable energy hydrogen conversion system, characterized in that two or more power buffer charging/discharging converter modules are connected in parallel based on the number or capacity of the power buffers. 4. The method of claim 3,
When the first current command value (I* ₁ (t)) that commands the first current measurement value (I ₁ (t)) flowing in through the AC converter is greater than 0 (I* ₁ (t) > 0), the controller A closing signal (S ₂ =1) is transmitted to the electrolysis input control unit, and an open signal (S ₃ =0) is transmitted to the fuel cell output control unit,
Conversely, when the first current command value (I* ₁ (t)) is less than 0 (I* ₁ (t) < 0) in order to generate electricity through the fuel cell, the controller receives an open signal (S ₂ = 0) and transmits a closing signal (S ₃ =1) to the fuel cell output control unit. 5. The method of claim 4,
When the renewable energy generation output (P(t)) is above a predetermined value (Pg), or when the grid voltage (Vg(t)) _{rises above a predetermined high voltage value (V H} ) and continues for more than a predetermined time,
The controller drives the input/output control unit, the electrolysis input control unit, the power buffer charging/discharging control unit, and controls the fuel cell output control unit to terminate the driving,
The power received by the AC converter follows the larger of the amount of power required for voltage stabilization and the amount of renewable energy that the electrolyzer can receive, and the operating power of the electrolyzer follows the power received by the AC converter,
The difference between the receiving power of the AC converter and the operating power of the electrolyzer is used as the charging/discharging power of the power buffer to prevent the increase of the grid voltage (Vg(t)) due to the increase in the renewable energy output (P(t)), A power conversion device for a renewable energy hydrogen conversion system, characterized in that it converts renewable energy generation power into hydrogen stably. 5. The method of claim 4,
When the associated grid voltage (Vg(t)) _{drops below a predetermined low voltage value (V L} ) and continues for more than a predetermined time,
The controller drives the input/output control unit, the fuel cell output control unit, and the power buffer charging/discharging control unit, and controls the electrolysis input control unit to terminate the driving,
The power transmitted by the AC converter follows the amount of power required for stabilization of the grid voltage (Vg(t)), the power generated by the fuel cell follows the power transmitted by the AC conversion section, and the power transmitted by the AC converter and the power generated by the fuel cell A power conversion device for a renewable energy hydrogen conversion system, characterized in that by using the difference as the charging/discharging power of the power buffer, the drop of the system voltage (Vg(t)) due to the imbalance between the renewable energy and the load is prevented. 5. The method of claim 4,
When the renewable energy generation output (P(t)) is greater than or equal to a predetermined value (Pg) or the grid voltage (Vg(t)) associated with the renewable energy hydrogen conversion system rises above a _{predetermined high voltage value (V H ),} If the fuel cell is generating power,
The controller controls the power generation amount of the fuel cell to be 0, and after the power generation amount of the fuel cell becomes 0, the fuel cell output control unit controls the driving end state. 5. The method of claim 4,
When the water electrolyzer is operating in a state where the associated grid voltage (Vg(t)) is _{lowered to a predetermined low voltage value (V L ) or less,}
The controller lowers the operating power of the water electrolyzer at a predetermined rate defined as a constant multiple of the capacity of the water electrolyzer until it becomes zero,
Power conversion device of a renewable energy hydrogen conversion system, characterized in that after the operation power of the water electrolysis device becomes 0, the water electrolysis input control unit controls the driving end state.

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