JP5469120B2 - Power generation output control system and control method for distributed power supply - Google Patents

Description

  The present invention is a technology that aims to suppress output fluctuations such as renewable energy and improve the overall power generation efficiency of the power supply system of the distributed power source by combining and controlling a gas engine and a fuel cell.

  In recent years, various distributed power sources such as photovoltaic power generation, fuel cells, and power generation gas engines have been put into practical use and introduced. Adopting such a distributed power source as an in-house power generation facility in a building can be expected to reduce greenhouse gas emissions, reduce the amount of power supplied by power companies, or in the event of an earthquake or fire There are various advantages that it is easy to ensure self-supporting stability. Therefore, it is expected that power supply systems using distributed power sources will be widely used in the future.

By the way, in the power supply system using the distributed power source, when the distributed power source and the commercial system (power company's power network) are used together (system interconnection) and the distributed power source is operated, the output of renewable energy Fluctuations can affect the power system. In particular, when solar power generation, which is expected to be introduced in large quantities in the future, will be incorporated into a power supply system using distributed power sources, the output of solar power generation will fluctuate depending on the amount of solar radiation, and the balance between power demand and supply will be disrupted. Frequency fluctuations can occur.
Since there are machines that move depending on the numerical value of this frequency, it is generally not preferable that a frequency fluctuation of ± 0.2 Hz or more occurs in a 50 Hz system. In addition, if only a power company is required to compensate for load fluctuations in a commercial system, a large burden is placed on the power company's ability to adjust for load fluctuations.
Therefore, in recent years, it has been required to operate a distributed power supply individually following its load, and in particular, when solar power generation is introduced, it is required to operate so as to suppress the output fluctuation. If it does in this way, the burden on the electric power company side of load fluctuation control concerning a commercial system can be reduced.

Also, in the power supply system using the above distributed power source, it is preferable to minimize the amount of energy consumed in power generation. Taking such energy efficiency into consideration, the distributed power source can individually follow the load. As a conventional example of a power supply system using a distributed power source to be operated, Document 1 (Japanese Patent Laid-Open No. Hei 6-150951) is cited as a power generation system using both a fuel cell and a power generation gas engine.
The technology described in Document 1 is “A combination of a fuel cell and a gas engine for power generation that efficiently absorbs load fluctuations such as a sudden load increase while efficiently generating power. A fuel cell, and a power generation gas engine and a fuel cell connected to first and second current collecting lines for extracting power from each of them, and when the power load is lower than a set value, only the fuel cell is operated. When the load exceeds the set value, the power generation gas engine is operated and the output of the fuel cell is controlled in a state where the output maintains a stable operating point, and the output of the fuel cell exceeds the rating. It is configured to control the output of the power generation gas engine. "

The power generation system of Document 1 “is intended to be able to absorb load fluctuations such as a sudden load increase satisfactorily while using a fuel cell and a gas engine for power generation in combination and efficiently generating electric power” ( [0006]) "With sufficient utilization of the high power generation efficiency of the fuel cell, it is possible to cope with a sudden increase in load during the daytime by controlling the output of the gas engine for power generation. Is possible "([0021]).
However, the document 1 is a technique for absorbing load fluctuations by combining a fuel cell (hereinafter abbreviated as “FC” where appropriate) and a power generation gas engine (hereinafter abbreviated as “GE” where appropriate), and Although it is disclosed that a gas engine for power generation responds to daily load fluctuations, it does not target output fluctuations of renewable energy. Also, it is not intended for load fluctuations in a power supply system (so-called microgrid) using a grid-connected distributed power source, and the power generation amount of the fuel cell is reduced to increase the overall power generation efficiency of the power supply system. It does not improve.

  Note that a gas engine is an engine that is driven by using gas as fuel. The gas appliances and equipment are often used in cogeneration systems that generate heat and electricity, and most of them are based on the same principle as gasoline engines for automobiles. The series of steps is as follows. 1. Fuel gas and air are mixed and supplied into the cylinder (combustion chamber) in advance. The air-fuel mixture is compressed by a piston and ignited by electric sparks. 3. The air-fuel mixture after combustion (= combustion gas) expands and pushes down the piston. 4). Finally, the combustion gas is discharged from the cylinder by the piston. When the piston is lowered during the third expansion step, the outside work is performed (converted into a rotational force through the crank mechanism), and the connected generator is rotated to generate power. In addition to commercial and industrial applications, it is used as a gas cogeneration system for homes that can generate electricity with city gas, make hot water using the heat generated, and heat it. In addition to this, there is a gas turbine as the power of cogeneration.

The fuel cell is a power generation device that generates power on the principle opposite to “electrolysis of water”. Water electrolysis decomposes water into hydrogen and oxygen through electricity from outside, but the fuel cell, on the contrary, produces electricity by chemically reacting hydrogen and oxygen. Unlike normal batteries, it can continue to generate electricity by continuing to supply hydrogen and oxygen.
There are four main fuel cells: 1. Phosphoric acid form (PAFC), 2. Molten carbonate form (MCFC), 3. Solid oxide form (SOFC), 4. Solid polymer form (PEFC) The electrolyte and operating temperature are different, and there is a difference in the power generation efficiency that can be expected. A phosphoric acid fuel cell having excellent partial load efficiency is more preferred.

Japanese Patent Application Laid-Open No. 2008-154334 discloses a power conditioner used for photovoltaic power generation, wind power generation, etc., which suppresses load fluctuation viewed from the system and suppresses voltage fluctuation of the system, thereby avoiding suppression of generated power. It is intended to effectively use natural energy by preventing the generation of electricity, and when the generated power of the power generation means exceeds the load power and surplus power is generated, a predetermined charging current is set as the upper limit to the power storage means In a power conditioner equipped with a charging control means for charging, an upper limit current change for controlling a predetermined charging current according to a time-series variation of the discharge depth of the storage means so that the discharge depth does not saturate to the upper limit value or the lower limit value. It is disclosed that by providing the means, it is possible to level the load as seen from the grid even if the load power and the generated power fluctuate every day.
However, the technology that suppresses the voltage fluctuation of the system by suppressing the load fluctuation from the viewpoint of the system and the power conditioner that prevents the voltage increase of the system on the customer side are disclosed, but the combination of the gas engine and the fuel cell is disclosed. Is not described, and does not control the operation of the gas engine and the fuel cell to suppress fluctuations and improve the overall power generation efficiency of the power supply system.

  Japanese Patent Application Laid-Open No. 2009-27861 discloses a distributed power supply control method for integrated control of a plurality of distributed power supplies having different tracking performances. Disclosed is a control method for a distributed power source that enables load-following operation by a control system compatible with a digital communication network by allowing only one unit to perform autonomous high-speed load-following operation. There is no disclosure or suggestion about combining a gas engine for use with a fuel cell and reducing the load on the fuel cell to improve the overall power generation efficiency of the power supply system.

  Japanese Patent Laid-Open No. 2010-110088 discloses a distributed power supply system that can realize highly accurate load following operation when performing operation control of each distributed power supply. There is no disclosure or suggestion about increasing the overall power generation efficiency of the power supply system by reducing the load on the fuel cell to avoid a decrease in the overall power generation efficiency.

Japanese Patent Laid-Open No. 6-150951 JP 2008-154334 A JP 2009-27861 A JP 2010-110088 A

  The present invention pays attention to the fact that the gas engine has poor partial load efficiency, but has excellent response, and the fuel cell has poor response, but the partial load efficiency is excellent. It is an object of the present invention to provide a power generation output control system and a control method that suppress output fluctuation of a power supply system of a distributed power source by performing integrated control of a gas engine and a fuel cell using each difference in characteristics.

  In order to achieve the above object, a distributed power generation output control system or a control method for a distributed power supply according to the present invention includes at least a combined power generation output control system for a combined power generation gas engine and a fuel cell. When the load fluctuation occurs in the power supply system of the distributed power source, the power generation amount of the power generation gas engine and the total power generation amount of the fuel cell are changed according to the change in the power receiving point power at the connection point of the commercial power system. In the power generation output control system that controls the power supplied to the load to be constant, the control reduces the output of the fuel cell so that the share of the power generation amount of the gas engine is maximized, and supplies the load to the load. A required load characteristic for maintaining the supplied power constant is realized, and fluctuations of the power supply system of the distributed power source are suppressed.

Furthermore, the power generation system of the distributed power source includes renewable energy such as solar power generation or wind power generation.
Still further, the fuel cell is controlled in a range where its own partial load efficiency is excellent.
Still further, the power generation gas engine is adapted to respond to instantaneous load fluctuations in consideration of renewable energy and the rise time constant of the fuel cell, and is controlled near the rated value with the highest power generation efficiency.

The power generation output control system and control method for a distributed power supply according to the present invention controls the power generation system so that the total power generation efficiency of the power supply system of the distributed power supply is maximized with respect to the power load at that time. And energy saving effect is optimized.
Moreover, since energy consumption is suppressed by this, the required power generation amount of the system power can be reduced by the power generation of the distributed power source, and the use of renewable energy can contribute to the energy saving of the entire system power consumption.
Moreover, since output fluctuation suppression is performed in a power supply system using a distributed power source, the burden of adjustment capability for load fluctuation on the commercial system on the power company side is reduced, and load fluctuation suppression of the power supply system is optimal. It can be realized with the total power generation efficiency.

FIG. 1 shows an overall conceptual diagram of a power generation output control system for a distributed power source according to the present invention. FIG. 2 is a diagram for explaining fluctuation suppression in the power generation output control system of the distributed power source of FIG. FIG. 3 shows a flowchart of output control of the power generation gas engine and the fuel cell when the power receiving point power (Pr) decreases. FIG. 4 shows an example of efficiency characteristics of the power generation gas engine and the fuel cell. FIG. 5 is a diagram for explaining a comparison between the case where the output of the power generation gas engine is changed with respect to the fluctuation suppression control and the fluctuation suppression control of the present invention in the power generation output control system of the distributed power source. . FIG. 6 is a diagram for explaining a comparison of the overall power generation efficiency of the entire power supply system when the output of the power generation gas engine is changed with respect to the fluctuation suppression of FIG. 5 and when the fluctuation suppression control of the present invention is performed. is there.

FIG. 1 shows an overall conceptual diagram of a power generation output control system for a distributed power source according to the present invention.
In FIG. 1, 1 is a commercial power system, and 7 is a receiving point power 7 (Pr) at a connection point between the distributed power system 15 and the commercial power system 1. A load 2 (Pl), a power generation gas engine 3 (Pge), a fuel cell 4 (Pfc), and a solar power generation 5 (Ppv) are connected to the power system 8 in the distributed power source. Data line is connected. In the present invention, the load 2 (Pl), the photovoltaic power generation 5 (Ppv), and the receiving point power 7 (Pr) are as shown in 10, 13, 14 (2), 5), 1)). 6, only the measurement is performed, and as shown in 11, 12 (3) and 4)), only the power generation gas engine 3 (Pge) and the fuel cell 4 (Pfc) are measured and fluctuation suppression control is performed.

In addition, Pr, Pl, Pge, Pfc, and Ppv in parentheses indicate respective amounts of electric power (used electric power or generated electric power), which are as follows.
Pl = Pge + Pfc + Ppv + Pr (Formula 1)
In other words,
Pr = Pl− (Pge + Pfc + Ppv) (Formula 2)
It becomes.

FIG. 2 is a diagram for explaining fluctuation suppression in the power generation output control system of the distributed power source of FIG.
As described above, in a power supply system using a distributed power supply, the power system may be affected by fluctuations in the output of renewable energy. In particular, when solar power generation, which is expected to be introduced in large quantities in the future, will be incorporated into distributed power sources, the output of solar power generation will fluctuate depending on the amount of solar radiation, and the balance between power demand and supply may be disrupted, which may cause frequency fluctuations. There is. An example of this output fluctuation is shown at 18 in FIG. Similarly, although not shown in FIG. 1, when wind power generation is incorporated into the power supply system, the amount of power generation varies depending on the wind power at that time, so the situation is the same as in the case of solar power generation. is there.
As described above, in FIG. 2, the output of the solar power generation 5 varies greatly due to the influence of the weather. In the future, if photovoltaic power generation is introduced into the power system in large quantities, there is a possibility that the balance between power supply and demand will be disrupted due to significant output fluctuations due to the weather. In addition, since the power consumption of the load changes every moment, there is a possibility that frequency fluctuations occur when the balance between the power supply and demand is lost.

Since there are machines that move depending on the numerical value of this frequency, it is not preferable that a frequency fluctuation of ± 0.2 Hz or more generally occurs in a 50 Hz system. In addition, if only a power company is required to compensate for load fluctuations in a commercial system, a large burden is placed on the power company's ability to adjust for load fluctuations. Therefore, in recent years, it has been required to operate a distributed power source by following individual loads.
In the system of the present invention, output fluctuation is suppressed using a power generation gas engine, and contribution to the commercial power system is made.

In the power generation output control shown in FIG. 1, first, fluctuation of the power reception point power (Pr) is suppressed by a power generation gas engine. This is because the control reaction speed (rise characteristic) of the power generation gas engine is good, so that it can follow the instantaneous load fluctuation well.
Next, the fuel cell power generation power (Pfc) is lowered according to the average power generation value (Pgea) of the power generation gas engine to improve the average output of the power generation power engine (Pge).
The reason for this is as follows.

FIG. 4 shows the efficiency characteristics of the power generation gas engine and the fuel cell. FIG. 4A shows that the power generation efficiency of the power generation gas engine (hereinafter simply referred to as a gas engine) increases as the output approaches 100%.
This is because the specifications of the gas engine are rated (100% operation) and the most efficient design, and the power consumption of the auxiliary equipment is constant regardless of the output. This is because the power consumption of the auxiliary equipment increases.
On the other hand, as shown in FIG. 4B, the fuel cell has almost no output dependency and the power generation efficiency is almost constant.
This is because, as in the case of a gas engine, the power consumption of the auxiliary equipment increases as the output decreases, but the fuel cell becomes more efficient as the current density decreases, so the power consumption of the auxiliary equipment and the efficiency due to the current density As shown in FIG. 4B, the efficiency of the increase is substantially constant regardless of the output.

A flowchart of the control operation is shown in FIG.
FIG. 3 shows a flowchart of the output allocation control of the gas engine and the fuel cell when the receiving point power (Pr) decreases.
・ When control is started (S21),
First, the output of the gas engine decreases in response to the decrease in receiving point power (Pr) (S22). This is because the response speed of the gas engine is fast and it can respond immediately to load fluctuations.
Next, an average output (Pgea) of the gas engine (for example, an average value of about several minutes) is calculated (S23). This is because the control fluctuates and the control system lacks stability, and the output control is matched to the response of the fuel cell.
A comparison is made as to whether the average output (Pgea) of the obtained gas engine is greater than a predetermined value K (S24).
Note that K is determined from the range of fluctuation suppression of the gas engine and the allowable reduction in efficiency.
When Pgea> K, the power generation state is continued as it is and the process is terminated (S25).
On the other hand, when Pgea ≦ K, the power generation output control of the present invention is performed, the fuel cell reduces the output (S26), and the receiving point power (Pr) increases (S27), so the gas engine increases the output. (S28). This increase in gas engine output improves the power generation efficiency of the gas engine.
As a result, the output of the distributed power source at the power receiving point is controlled to be constant, but the overall power generation efficiency of the power supply system is improved by relatively increasing the power generation efficiency of the gas engine.

This is shown schematically in FIG.
In FIG. 6, FIG. 6 (a) shows a state before control, and FIG. 6 (b) does not perform the fluctuation suppression control of the present invention, and controls the output of the gas engine when load fluctuation occurs (in this case) , Decreased). FIG. 6C shows the output state when the variation control control of the present invention is performed.
FIG. 5 is a diagram for explaining a comparison between the fluctuation suppression control operation in the case of changing the output of the gas engine with respect to the fluctuation suppression control and the case of the present invention in the power generation output control system of the distributed power source.
FIG. 5 (a) shows a control of the gas engine. When the load fluctuation (necessary power) fluctuates as shown in FIG. 31, the necessary electric power is within the power generation range (32) of the fuel cell. For example, if the fuel cell generates all power (35 locations) and the required power exceeds the rated upper limit (34) that can be generated by the fuel cell, the insufficient power controls the output (33) of the gas engine. And make up.

On the other hand, in the case of the present invention, when the load fluctuation (necessary power) fluctuates as shown in 41 as in FIG. 5 (a), even if the necessary power is within the power generation range of the fuel cell, The necessary power is first set to the lowest level (46) at which the power generation efficiency of the fuel cell does not decrease, and the insufficient power is compensated by controlling the output (45) of the gas engine.
If the required power increases, first, if the required power is within a range that can be generated by the output of the gas engine, all the power is supplemented by the output of the gas engine (47 locations), and the required power can be generated by the output of the gas engine. When the rated upper limit (44) is exceeded, the output of the fuel cell is compensated for the insufficient power (48 locations).
That is, in FIG. 5B, the gas engine output (44) is controlled to operate at as high an output as possible. By doing in this way, the efficiency of the gas engine shown to Fig.4 (a) is raised, and the electric power generation total efficiency of this whole electric power supply system becomes the maximum. It should be noted that the same movement occurs for fluctuations in the output of renewable energy.

  However, in actuality, if the fuel cell is immediately controlled in response to instantaneous load fluctuations, the control fluctuates. Therefore, the fuel cell is controlled by the average output of the gas engine (for example, about several minutes), and instantaneous load fluctuations are In order to absorb within the engine's rating, the gas engine is operated at an output near the rating.

FIG. 6C is a diagram in which the power generation output control of the present invention is performed. The output of the fuel cell is set to an output that does not cause a decrease in the power generation efficiency of the fuel cell, and the output of the gas engine is increased correspondingly. A large load power is supplied. The state transition in FIG. 6C is indicated by arrows in FIGS. 4A and 4B. 4, 21 and 24 are the operating points of FIG. 6B, and 22 and 23 are the operating points of FIG. 6C. Note that the efficiency of the fuel cell is extremely lowered when the output is below a certain output (in this case, 50%), and therefore the minimum output is determined within a range in which the efficiency does not decrease.
As shown in FIG. 6C, since the power generation efficiency of the gas engine is maximized when the power distribution generated by the gas engine and the fuel cell is determined, the power supply system takes into account that the efficiency of the fuel cell is substantially constant. The overall power generation efficiency becomes the maximum operating point.

The total power generation efficiency of the entire power supply system is shown in FIGS.
In FIG. 6A, when the load is sufficient (for example, when solar power generation is 0 at night), the load is sufficiently present, and the gas engine (GE) and the fuel cell (FC) are at the maximum output. It is driven. In the case of FIG. 6A (GE: 160 kW, FC: 100 kW), the total power generation efficiency is 39.6% ((160 + 100) / ((160/40) + (100/39))). In the figure, the numerical value (...%) indicates the output (%).
Here, when the required load is reduced (for example, when solar power generation contributes in the daytime and the load itself is constant), in the method of changing the output of the gas engine with respect to the fluctuation, FIG. ), The output of the gas engine (GE) is lowered to correspond to the electric power (in this case, 180 kW) corresponding to the necessary load. The total power generation efficiency of the entire power supply system at this time is 34.4% ((80 + 100) / ((80/30) + (100/39))).
On the other hand, when the power generation output control system according to the present invention is used, a gas engine with a fast initial response speed reacts, but the output of the fuel cell is gradually lowered, and as shown in FIG. The output corresponding to the required load (in this case, 180 kW) is the same as described above, and the shortage is covered by the increase in the output of the gas engine (total 130 kW). In this case, the total power generation efficiency of the entire power supply system is 38.2% ((130 + 50) / ((130 / 37.5) + (50/40))).
Thus, in the case of this example, compared with the method of changing the output of the gas engine with respect to the fluctuation, the total power generation efficiency of the entire power supply system using the distributed power source is improved by about 4%.

  As described above, the power generation output control system for the distributed power supply according to the present invention receives power at the connection point of the commercial power system when output fluctuation or load fluctuation of renewable energy occurs in the power supply system using the distributed power supply. In the power generation output control system that performs integrated control so that the power generation amount of the gas engine and the total power generation amount of the fuel cell maintain the power supplied to the load constant according to the change of the point power, the power generation amount share ratio of the gas engine is By reducing the output of the fuel cell to achieve the required load and suppressing fluctuations, the efficiency of the gas engine is improved, and fluctuation generation control is performed while the fluctuation suppression control is performed. Since the overall efficiency can be maximized, industrial utility is high for energy saving and cost reduction.

DESCRIPTION OF SYMBOLS 1 Commercial power system 2 Load 3 Gas engine 4 Fuel cell 5 Solar power generation 6 Central controller 7 Power receiving point power

Claims (8)

At least a power generation output control system of a distributed power source that performs integrated control by combining a gas engine and a fuel cell, and when a load fluctuation occurs in the power supply system of the distributed power source, In the power generation output control system for controlling the power generation amount of the gas engine and the total power generation amount of the fuel cell so as to keep the power supplied to the load constant according to the change of the power receiving point,
The above control keeps the power supplied to the load constant by lowering the output of the fuel cell so that the gas engine suppresses fluctuations in the power at the receiving point and maximizes the share of power generated by the gas engine. A distributed power generation output control system that realizes required load characteristics and suppresses fluctuations in the distributed power generation system.   The power generation output control system for a distributed power source according to claim 1, wherein renewable power such as solar power generation or wind power generation is included in the power supply system of the distributed power source.   The power generation output control system for a distributed power source according to claim 1, wherein the fuel cell is controlled within a range in which its partial load efficiency is excellent.   2. The power generation output of the distributed power source according to claim 1, wherein the gas engine responds to an instantaneous load change in consideration of renewable energy and a rise time constant of the fuel cell, and is controlled near a rating. Control system. At least a power generation output control method of a distributed power source that performs integrated control by combining a gas engine and a fuel cell, and when a load fluctuation occurs in the power generation supply system of the distributed power source, In the power generation output control method for controlling the power generation amount of the gas engine and the total power generation amount of the fuel cell so as to keep the power supplied to the load constant according to the change in the power receiving point,
The above control keeps the power supplied to the load constant by lowering the output of the fuel cell so that the gas engine suppresses fluctuations in the power at the receiving point and maximizes the share of power generated by the gas engine. A power generation output control method for a distributed power source, characterized in that a required load characteristic is realized and fluctuations of the power generation and supply system of the distributed power source are suppressed.   6. The distributed power generation output control method according to claim 5, wherein the distributed power supply system includes renewable energy such as solar power generation and wind power generation.   6. The power generation output control method for a distributed power source according to claim 5, wherein the fuel cell is controlled within a range in which its partial load efficiency is excellent.   6. The power generation output of a distributed power source according to claim 5, wherein the gas engine is adapted to respond to instantaneous load fluctuations in consideration of renewable energy and a rise time constant of the fuel cell, and is controlled near a rating. Control method.