JP2005264850A - Cogeneration device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cogeneration device having highly efficient operation in all operation regions. <P>SOLUTION: The cogeneration device comprises an engine 2, a generator 3 to be driven by the engine 2, an inverter 5 for inverting the AC output of the generator 3 into AC power of predetermined voltage and frequency, an exhaust heat recovery device 6 for recovering the exhaust heat of the engine, and an operation control device 12 using a first control mode for controlling the speed of the engine 2 corresponding to output power when the output power output from the inverter 5 to the outside is a first preset threshold value or higher and using a second control mode for controlling the output of the inverter to be variable while fixing the speed of the engine to a fixed value when the output power is lower than the first threshold value. When the output power is lower than the first threshold value, a purpose function which shows the performance of the cogeneration device for a predetermined purpose as compared with the case of using a commercial power source and an auxiliary heat source for a power load and a heat load is the maximum with the speed of the engine 2 being the fixed value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention includes a generator unit that generates first power using fuel supplied from the outside, an inverter that converts the first power into second AC power having a predetermined voltage and frequency, and a generator The present invention relates to a cogeneration apparatus including an exhaust heat recovery apparatus that recovers exhaust heat discharged from a unit, and more particularly, to an operation control technique capable of improving energy efficiency of the cogeneration apparatus.

In recent years, the development of distributed energy systems aimed at reducing CO ₂ emissions and saving energy has been actively developed and put into practical use. The use of the power generation system is expected to progress rapidly in the future. In particular, a gas engine cogeneration apparatus that can supply both heat and electric power is attracting attention because of its high overall energy efficiency because it can effectively use not only electric power but also thermal energy generated by the gas engine at the same time.

By the way, as operation control of the cogeneration apparatus, there are control for causing the gas engine to perform rated operation at a preset rotation speed, and control for performing load follow-up operation by increasing / decreasing the rotation speed of the gas engine following the fluctuation of the power load. As an example of the former, each control method is disclosed, for example, in Patent Document 1 below, and as an example of the latter, for example, Patent Document 2 below.
JP 2000-87801 A Japanese Patent Laid-Open No. 10-280971

  However, as the operation control of the cogeneration apparatus, both the first control for fixing the engine speed and the second control for making the engine speed variable are both in a specific operation region, that is, a constant value of the cogeneration apparatus. In the output range, high-efficiency operation is possible and energy-saving performance as a cogeneration device is demonstrated. However, high-efficiency operation is not maximized in the entire operation region.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a cogeneration apparatus capable of high-efficiency operation over the entire operation region.

  In order to achieve this object, a first characteristic configuration of a cogeneration apparatus according to the present invention includes an engine that generates rotational energy using fuel supplied from the outside, and a first alternating current from the rotational energy of the engine. A generator that generates electric power; an inverter that converts the first AC power into second AC power having a predetermined voltage and frequency; and an exhaust heat recovery device that recovers exhaust heat exhausted from the engine. A first control mode for controlling the engine speed in accordance with the output power when the output power output from the inverter to the outside is equal to or greater than a preset first threshold power If the output power is less than the first threshold power, the engine speed is fixed to a constant value and the output of the inverter is variable. A cogeneration apparatus comprising an operation control apparatus that performs control in the second control mode, and compared with a case where a commercial power source and an auxiliary heat source are used for the same power load and heat load when the output power is less than the first threshold power The objective function representing the performance for a predetermined purpose is that the engine speed increases at a constant value compared to a case where the engine speed is variably controlled according to the output power.

  According to the first characteristic configuration of the cogeneration device, the output power output from the cogeneration device to the outside (the net output power obtained by subtracting the power consumed in the cogeneration device from the output power of the inverter) is the first. Below 1 threshold power, by fixing the engine speed to a constant value, the objective function of the cogeneration system increases compared to the case where the speed is variably controlled according to the output power. The objective function can be improved. Furthermore, if the constant value is appropriately selected, it is possible to perform control to fix the objective function at a constant value that maximizes or substantially maximizes the objective function, and the objective function can be further improved.

  The inventor of the present application has found that an output power range in which the objective function is maximized when the engine speed is fixed to the constant value is present in a low output region of the output power. It has been found that the engine speed at which the objective function is maximized increases as the output power increases in the region where the upper limit value of is exceeded. As a result, when the upper limit value of the output power range is set to the first threshold power and the output power is less than the first threshold power, the output power is equal to or higher than the first threshold power in the second control mode in which the engine speed is fixed. Then, by controlling the operation in the first control mode in which the engine speed is variable, it is possible to control the engine speed that optimizes a predetermined objective function in the entire output power range (operation region).

  Therefore, in the cogeneration apparatus of this characteristic configuration, when the control value of the output power is determined separately according to the power load or the power load and the grid connection state at the time of grid connection, the determined output power In contrast, it is possible to operate at an engine speed that optimizes the objective function.

  In addition to the first characteristic configuration, the second characteristic configuration is preset according to the output power when the operation control device controls the engine speed in the first control mode. The number of rotations is controlled, and the preset number of rotations is determined by selecting the number of rotations that maximizes the objective function from among a plurality of rotation number candidates that can output the output power.

  According to the second characteristic configuration of the cogeneration apparatus, when the output power changes at or above the first threshold power, the engine operation control is performed at a preset rotational speed corresponding to the output power. The engine speed can be controlled to optimize the function. Further, it is not necessary to perform control while calculating the objective function each time the output power changes, and the control is simplified.

  The third characteristic configuration includes a generator unit that generates first power using fuel supplied from the outside, and converts the first power into second AC power having a predetermined voltage and frequency. A cogeneration apparatus comprising an inverter and an exhaust heat recovery device that recovers exhaust heat exhausted by the generator unit, wherein the output power output to the outside from the inverter is preset second threshold power In the above case, the control is performed in the third control mode in which the output of the inverter is made variable and controlled according to the output power. When the output power is less than the second threshold power, the output of the inverter is constant. An operation control device that performs control in a fourth control mode that controls the difference between the output power and the second threshold power to be consumed by a built-in electric heater, the output power being the second power When the power is smaller than the value power, the control in the fourth control mode is more preferable than the third control mode in comparison with the case where a commercial power source and an auxiliary heat source are used for the same power load and heat load. The objective function representing the performance for the purpose of the system is increased.

  According to the third characteristic configuration of the cogeneration apparatus, the output power output from the cogeneration apparatus to the outside (the net output power obtained by subtracting the power consumed in the cogeneration apparatus from the output power of the inverter) is the first. Below 2 threshold powers, the objective function of the cogeneration apparatus can be improved by controlling in the fourth control mode in which the inverter output is fixed and the difference between the output power and the second threshold power is consumed by the built-in electric heater.

  The inventor of the present application controls the output of the inverter by following the decrease in the output power when the constant power output from the generator unit is output as output power by controlling the inverter. It has been found that the objective function can be increased by fixing the output of the inverter to a constant value in the output region and consuming the difference between the output power and the second threshold power with the built-in electric heater. As a result, the upper limit value of the low output region of the output power is set to the second threshold power, and when the output power is less than the second threshold power, the output power is the second threshold power in the fourth control mode with the inverter output fixed. In the above, inverter control that optimizes a predetermined objective function in the entire output power range (operation region) is possible by controlling the operation in the third control mode in which the inverter output is made variable following the output power. It becomes.

  Therefore, in the cogeneration apparatus of this characteristic configuration, when the control value of the output power is determined separately according to the power load or the power load and the grid connection state at the time of grid connection, the determined output power In contrast, an inverter output that optimizes the objective function can be operated.

  In the fourth feature configuration, in addition to the first feature configuration or the second feature configuration, the operation control device is configured such that the output power is equal to or higher than a predetermined second threshold power that is smaller than the first threshold power. When the power is less than electric power, the engine speed is fixed to a constant value, and control is performed in a fifth control mode in which the output of the inverter is varied and controlled according to the output power. When the power is less than the threshold power, the engine speed is fixed to a constant value, the output of the inverter is fixed to a constant value, and the difference between the output power and the second threshold power is consumed by a built-in electric heater. When the control is performed in the sixth control mode that controls the output power and the output power is smaller than the second threshold power, the objective function increases when the control is performed in the sixth control mode rather than the fifth control mode. There is in point to do.

  According to the fourth characteristic configuration of the cogeneration apparatus, the objective function is further optimized by performing the control in the second control mode, and the control in the sixth control mode when the output power is equal to or lower than the second threshold power. Is made. Therefore, in addition to the operational effect of the first or second characteristic configuration, the operational effect of the third characteristic configuration is added, and the engine speed that optimizes a predetermined objective function in the entire output power range (operating region) The number and inverter output can be controlled.

  In the fifth feature configuration, in addition to the first, second, or fourth feature configuration, the setting of the first threshold power is a use mode and a time zone of exhaust heat recovered by the exhaust heat recovery device. It can be changed in accordance with at least one of the above.

  In the sixth feature configuration, in addition to the third or fourth feature configuration, the setting of the second threshold power is at least one of a use form and a time zone of exhaust heat recovered by the exhaust heat recovery device. It is in the point which can be changed according to either.

The objective function of the cogeneration apparatus is an index representing the performance for a predetermined purpose of the cogeneration apparatus compared to the case where the commercial power supply and the auxiliary heat source are used for the same power load and heat load. In the case of energy saving, the purpose is to comprehensively compare the efficiency of power generation / transmission facilities using commercial power sources and the efficiency of auxiliary heat sources (for example, gas boilers) with the power generation efficiency and exhaust heat recovery efficiency of cogeneration equipment It becomes a function. However, if the power generation equipment used by the commercial power source varies depending on the time zone, the power generation efficiency changes, and the load of the auxiliary heat source varies depending on the use form of the exhaust heat, thereby changing the efficiency. The above purpose is the same for CO ₂ emission reduction. Therefore, according to the fifth or sixth characteristic configuration of the cogeneration apparatus, even if the definition of the objective function differs depending on the time zone or the use form of the exhaust heat, the optimization of the objective function corresponding to the change of the objective function is possible. I can plan.

  The seventh feature configuration is that, in addition to any one of the feature configurations described above, the objective function is expressed as a linear sum of power generation efficiency and exhaust heat recovery efficiency of the cogeneration apparatus. Here, the linear sum is obtained by multiplying the power generation efficiency by a predetermined coefficient, multiplying the exhaust heat recovery efficiency by a predetermined coefficient, and adding the two together.

  According to the seventh characteristic configuration of the cogeneration apparatus, by appropriately selecting a predetermined coefficient that multiplies the power generation efficiency and a predetermined coefficient that multiplies the exhaust heat recovery efficiency, various objective functions can be obtained. Even when the definition of the objective function varies depending on the time zone or the utilization form of exhaust heat, it can be handled by changing the coefficient.

In the eighth feature configuration, in addition to any of the feature configurations described above, the objective of the objective function is one of energy consumption reduction, CO ₂ emission reduction, and energy cost reduction by the cogeneration device. There is a point.

According to the eighth characteristic configuration of the cogeneration apparatus, the operation of the cogeneration apparatus can be controlled by using the energy consumption reduction effect, the CO ₂ emission reduction effect, or the energy cost reduction effect as an index. As a result, it is possible to reduce energy consumption, CO ₂ emission, or energy cost in all operation regions.

  An embodiment of a cogeneration apparatus according to the present invention (hereinafter referred to as “the present invention apparatus” as appropriate) will be described with reference to the drawings.

  As shown in FIG. 1, the device 1 of the present invention includes an engine 2 such as a gas engine or a micro gas turbine that generates rotational energy by burning city gas (corresponding to fuel supplied from the outside), and rotation of the engine 2. A generator unit 4 comprising a generator 3 that generates first AC power from energy, an inverter 5 that converts the first AC power generated by the generator 3 into second AC power having a predetermined voltage and frequency, The exhaust heat recovery device 6 that recovers exhaust heat exhausted from the engine 2 and supplies thermal energy to the heat load 32, consumes a part of the electric power output from the inverter 5, and heat energy An electric heater 7 for supplying electric power, an output control means 8 for determining a control value for controlling the net output power P1 output to the outside from the inverter 5 in accordance with the interconnection state between the power load 31 and the system power source 30, and the like; Operation control means 12 comprising a first operation control unit 9 that controls the output of the inverter 5, a second operation control unit 10 that controls the rotation speed of the engine 2, and a third operation control unit 11 that controls the operation of the electric heater 7. It is prepared for. Moreover, this invention apparatus 1 becomes a structure which supplies the electric power with respect to the electric power load 31 by connecting the output of the inverter 5 with the system power supply 30 as an example.

  The inverter 3 includes an AC / DC converter that converts the first AC power generated by the generator 3 into DC power, and the DC power converted by the AC / DC converter at the same voltage and frequency as the system power supply 30. A DC / AC conversion unit that converts the AC power into two AC powers, and an interconnection relay that interconnects the second AC power converted by the DC / AC conversion unit and the AC power of the system power supply 30. The Since the inverter 3 is realized with a known circuit configuration, a detailed description thereof is omitted.

  The exhaust heat recovery device 6 is composed of a heat exchanger, a hot water tank, an auxiliary heat source device such as a gas boiler, etc. that recovers exhaust heat exhausted from the engine 2 by heat exchange by heat exchange, It is configured to be able to supply heat energy using hot water as a medium to a heat load 32 such as hot water supply to a bathtub, bathroom, kitchen, etc., and circulating hot water supply for heating each room.

  The output control means 8 determines the interconnection state between the power load 31 and the system power supply 30 based on the measured values of an ammeter and a voltmeter (not shown) installed inside and outside the inverter 5, and the determination Based on the result or based on a preset operation plan, the control value of the output power P1 output to the outside of the device 1 of the present invention is determined. For example, when following the change of the power load 31 without performing the reverse power flow to the system power supply 30, the power consumption of the power load 31 and the output power P 1 are matched until the maximum output of the device 1 of the present invention. A control value of the output power P1 is set.

  Each of the control units 9 to 11 of the operation control unit 12 performs operation control to be described later based on the control value of the output power P1 determined by the output control unit 8. Hereinafter, three embodiments of the control operations of the control units 9 to 11 of the operation control unit 12 will be described.

  The output control means 8 and the operation control means 12 are realized by executing respective processes as software, and the whole is configured by applying a stored program type computer system such as a microcomputer.

<First Embodiment>
The operation control according to the first embodiment is executed exclusively by the first operation control unit 9 and the second operation control unit 10. As shown in FIG. 2, when the output power P1 is equal to or higher than the preset first threshold power Pt1, control in the first control mode is executed, and when the output power P1 is less than the first threshold power Pt1, control in the second control mode is executed. . In the first control mode, the second operation control unit 10 corresponds to the output power P1 by using a table in which the correspondence relationship between the output power P1 and the optimum rotational speed Rx of the engine 2 is preset and tabulated or functioned. The rotational speed R of the engine 2 is controlled by the optimum rotational speed Rx. In the second control mode, the rotational speed R of the engine 2 is controlled by fixing the optimal rotational speed Rx1 when the output power P1 is the first threshold power Pt1 in the correspondence relationship between the output power P1 and the optimal rotational speed Rx. To do. In both the first control mode and the second control mode, the first operation control unit 9 controls the output of the inverter 5 such that the output power P1 matches the control value determined by the output control means 8. To do. Here, the inverter output is P2, and an internal power load P3 that is a part of the inverter output P2 and is consumed inside the device 1 of the present invention (for example, the auxiliary machine of the generator unit 4 or the above-described electric heater 7). Then, the output power P1 is given by P1 = P2-P3. Accordingly, the first operation control unit 9 measures the internal power load P3 and controls the inverter output P2 so as to be the sum of the measured value P3 and the output power P1. If the internal power load P3 is known, the known value is used.

  Next, a method for deriving a correspondence relationship between the first threshold power Pt1 and the output power P1, which are boundary values between the first control mode and the second control mode, and the optimum rotational speed Rx will be described.

  Using the same device of the present invention device 1 or the same model as the present device 1, the rotational speed R of the engine 2 is changed stepwise from a low rotation to a high rotation (for example, 600 rpm to 2800 rpm), and a plurality of outputs are provided. For each electric power P1, the power generation efficiency Ye and the exhaust heat recovery efficiency Yh of the device 1 of the present invention at each rotation speed are obtained by experiments. The power generation efficiency Ye is obtained by the ratio of the output power P1 output from the inverter 5 to the primary energy (the amount of heat of city gas) input to the device 1 of the present invention and effectively used outside, as described above. The internal power load P3 is excluded. The exhaust heat recovery efficiency Yh is the recovered heat of exhaust heat exhausted from the engine 2 with respect to the primary energy (the amount of heat of city gas) input to the device 1 of the present invention. It is given by the ratio of the net heat output that can be effectively used with the heat load 32 after subtracting the amount of heat released at.

  Since the output of the engine 2 is given by the product of the rotational speed R and the torque of the engine 2, there are many combinations of the rotational speed and the torque for a certain engine output. Here, looking only at the shaft output efficiency of the engine 2, the efficiency is better when the engine 2 is operated at a low rotation and a high torque. Further, the relationship between the engine speed R and the output voltage Vg of the generator 3 is such that the output voltage Vg increases in proportion to the speed. For example, when the rotational speed R = 800 rpm and 140V, the rotational speed R = 2400 rpm and 420V. By the way, the conversion efficiency of the inverter 5 is maintained at a high efficiency of, for example, about 95% when the output voltage Vg of the generator 3 is a predetermined voltage (for example, 350 V) or higher. The conversion efficiency of the inverter 5 rapidly decreases as Vg decreases, and decreases to about 70% at 140 V (rotation speed R = 800 rpm). The shaft output of the engine 2 is high efficiency in the low rotation range, but the conversion efficiency of the inverter 5 is high efficiency in the high rotation range. Therefore, the total power generation efficiency Ye is the optimum rotation speed according to the output power P1. Will be different.

  Further, the overall efficiency (Ye + Yh) of the inventive device 1 as a cogeneration device does not change much compared to the power generation efficiency Ye with respect to the change in the engine speed R at the same output power P1. Therefore, the exhaust heat recovery efficiency Yh exhibits a characteristic opposite to the power generation efficiency Ye with respect to the engine speed R.

  Now, since the cogeneration device generates two energies of electric power and heat energy with respect to the input primary energy (the amount of heat of city gas), the purpose shown in Equation 1 as an index for evaluating the performance of the cogeneration device Using the function Ix, it is possible to compare the performance with power supply and thermal energy supply using a commercial power source and an auxiliary heat source for the same power load and heat load. Here, the commercial power source and the auxiliary heat source are alternative means when the cogeneration apparatus is not used, and are temporarily called a conventional apparatus. In the device 1 of the present invention, city gas is used as the primary energy, and a gas boiler is assumed as an auxiliary heat source device of the exhaust heat recovery device 6, so that the auxiliary heat source of the conventional device is also assumed to be a gas boiler using city gas as fuel. To do.

(Equation 1)
Ix = (Ke × Ye + Kh × Yh) × 100 (%)

In Equation 1, Ke is a coefficient for comparing and comparing the power generation efficiency of the cogeneration apparatus and the power generation efficiency of the commercial power supply, and the setting differs depending on the performance to be compared. Kh is a coefficient for comparing and comparing the exhaust heat recovery efficiency of the cogeneration apparatus and the thermal efficiency of the auxiliary heat source (gas boiler) of the conventional apparatus, and the setting differs depending on the performance to be compared. The performance to be compared is a target performance to be improved by the introduction of a cogeneration apparatus, and examples thereof include energy consumption reduction, CO ₂ emission reduction, energy cost reduction, and the like.

  For example, in the performance comparison for the purpose of reducing energy consumption, the coefficients Ke and Kh of the objective function Ix shown in Equation 1 are the reciprocal of the thermal power plant efficiency 0.4 and the thermal efficiency of a general gas boiler, respectively. It is given by the reciprocal of 0.88. Here, when the cogeneration apparatus is more energy-saving than the conventional apparatus by combining power and heat energy, the objective function Ix of Equation 1 exceeds 100 (%). Therefore, Ix> 100 is a condition for the device 1 of the present invention to have high performance for a predetermined purpose as compared with the conventional device. Furthermore, if the objective function can take the maximum value in all the operation regions, the optimum operation is performed for the predetermined purpose (for example, energy consumption reduction).

  Here, when the purpose is to reduce the amount of energy consumption, the rotational speed R of the engine 2 is changed stepwise in the manner described above, and the power generation efficiency Ye and the exhaust heat recovery efficiency obtained for each of a plurality of types of output power P1. By substituting Yh into the objective function Ix of Equation 1, it is possible to derive the characteristics of the objective function Ix with the rotation speed R as a parameter for a plurality of types of output power P1. For example, characteristics as shown in FIG. 3 can be obtained. In FIG. 3, six cases of 800, 1200, 1600, 2000, 2400, and 2800 (rpm) are shown as the rotation speed R for simplicity of explanation.

  In the present embodiment, as shown in FIG. 3, when the output power P1 is 1500 W or less, the objective function Ix increases when the rotational speed R is 1200 rpm, and when the output power P1 is 1500 W or more, the output power P1 increases. It can be seen that the optimum rotational speed Rx of the engine 2 that maximizes the objective function Ix also increases. Accordingly, since the relationship between the output power P1 and the objective function Ix having the rotation speed R as a parameter, the relationship between the output power P1 and the optimum rotation speed Rx that gives the maximum value of the objective function Ix is obtained. The number of revolutions of the engine 2 in the first control mode and the second control mode is used for control. Further, from the correspondence relationship between the output power P1 and the optimum rotation speed Rx, the output power P1 at the boundary point at which the optimum rotation speed Rx does not decrease even if the output power P1 is decreased becomes the first threshold power Pt1. In the example shown in FIG. 3, the first threshold power Pt1 is 1500 W, and the fixed rotation speed Rx1 in the second control mode is 1200 rpm.

  Even if the output power P1 is decreased in the low output region of the output power P1, the optimum rotational speed Rx does not decrease. As described above, when the engine rotational speed R is decreased, the conversion efficiency of the inverter 5 is significantly decreased. Therefore, in the exhaust heat recovery efficiency Yh, there is a certain amount of heat released from the exhaust heat recovery device 6 regardless of the engine speed R. Therefore, if the engine speed R is decreased, the exhaust heat recovery efficiency Yh is also substantially reduced. It is thought that this is caused by a decline in the temperature.

Second Embodiment
The operation control according to the second embodiment is executed exclusively by the first operation control unit 9 and the third operation control unit 11. As shown in FIG. 4, when the output power P1 is greater than or equal to the preset second threshold power Pt2, control in the third control mode is executed, and when the output power P1 is less than the second threshold power Pt2, control in the fourth control mode is executed. . In the third control mode, the first operation control unit 9 performs control by making the output P2 of the inverter 5 variable according to the output power P1. Specifically, the first operation control unit 9 controls the inverter output P2 so that the output power P1 matches the control value determined by the output control means 8, and the relationship P1 = P2-P3 is maintained. In the fourth control mode, the first operation control unit 9 fixes the output of the inverter 5 to a constant value P2x, and the third operation control unit 11 operates the electric heater 7 to output power P1 and the second threshold value. Control is performed so as to consume the difference in power Pt2. Therefore, when the output power P1 becomes smaller than the second threshold power Pt2 in a state where the inverter output P2 is fixed to the constant value P2x, in order to maintain the relationship of P1 = P2x−P3, the internal power load P3 It is necessary to increase the power consumption by operating the electric heater 7. The increase is given by (Pt2-P1). In the present embodiment, it is assumed that the second operation control unit 10 performs control while fixing the rotational speed R of the engine 2 to a constant value.

  Next, a method for deriving the second threshold power Pt2, which is a boundary value between the third control mode and the fourth control mode, will be described.

  Using the same device of the present invention device 1 or the same model as the present device 1, a plurality of second threshold power Pt2 candidates are selected, and each second output power P1 is set to each second threshold power Pt2. The inverter 5 and the electric heater 7 are controlled in the corresponding third control mode or fourth control mode, and the power generation efficiency Ye and the exhaust heat recovery efficiency Yh of the device 1 of the present invention are obtained by experiments. The definitions of the power generation efficiency Ye and the exhaust heat recovery efficiency Yh are as described in the first embodiment, and the power generation efficiency Ye and the exhaust heat recovery efficiency Yh are measured in the same manner.

  Next, when the power generation efficiency Ye and the exhaust heat recovery efficiency Yh are obtained under the conditions of the output power P1 and the second threshold power Pt2, as in the first embodiment, by substituting into the objective function of Formula 1, a plurality of ways can be obtained. The characteristic of the objective function Ix with the second threshold power Pt2 as a parameter can be derived with respect to the output power P1. For example, characteristics as shown in FIG. 5 are obtained. In FIG. 5, three cases of 2000 W, 1000 W, and 0 W are shown as the second threshold power Pt <b> 2 for ease of explanation. In the case of Pt2 = 2000W, the output P2 of the inverter 5 is always fixed at 2000W + P3 within the range of the second threshold power Pt2 shown in FIG. 5, and the difference between the second threshold power Pt2 (= 2000W) and the output power P1 is Consumed by the heater 7 (fourth control mode). In the case of Pt2 = 1000 W, within the range of the second threshold power Pt2 shown in FIG. 5, the output power P1 is 1000 W or more and the inverter output P2 is variable to maintain the relationship of P1 = P2-P3 (third control mode ), The output power P1 is less than 1000 W, the output P2 of the inverter 5 is fixed at 1000 W + P3, and the difference between the second threshold power Pt2 (= 1000 W) and the output power P1 is consumed by the electric heater 7 (fourth control mode) . In the case of Pt2 = 0 W, the inverter output P2 is always variable to maintain the relationship P1 = P2-P3 in the range of the second threshold power Pt2 shown in FIG. 3 control mode).

  In the present embodiment, as shown in FIG. 5, when the output power P1 is less than 1000 W, when Pt2 = 1000 W (fourth control mode) and Pt2 = 0 W (third control mode) are compared, Pt2 = 1000 W is It can be seen that the objective function Ix is large. That is, when the second threshold power Pt2 is set to 1000 W, when the output power P1 is smaller than the second threshold power Pt2, the control in the fourth control mode rather than the third control mode increases the objective function Ix, The device 1 of the present invention can be operated with higher efficiency and energy saving.

  Further, as shown in FIG. 5, when the output power P1 is 1000 W or more, when comparing Pt2 = 1000 W (third control mode) and Pt2 = 0 W (third control mode), both are controlled in the third control mode. The conditions become the same and the objective function Ix matches. On the other hand, it can be seen that Pt2 = 2000 W (fourth control mode) has a smaller objective function Ix than Pt2 = 1000 W (third control mode) and Pt2 = 0 W (third control mode). Here, in the fourth control mode region, the output power P1 and the objective function Ix have linear characteristics.

  If an intermediate value of 1000 W to 2000 W is selected as a candidate for the second threshold power Pt2, the control is performed in the third control mode when the output power P1 is equal to or greater than the intermediate value, and in the fourth control mode when the output power P1 is less than the intermediate value. However, the gradient of the characteristic is intermediate between Pt2 = 2000 W and Pt2 = 1000 W, and the objective function Ix is not necessarily the maximum in the entire region where the output power P1 is less than the intermediate value. That is, there is a region where the objective function Ix is smaller than Pt2 = 0 W (third control mode). Furthermore, when an intermediate value of 0 W to 1000 W is selected as a candidate for the second threshold power Pt2, there is clearly a second threshold power Pt2 with a larger objective function Ix in a region where the output power P1 is less than 1000 W. Accordingly, in the present embodiment, as shown in FIG. 5, the second threshold power Pt2 is set to 1000 W, the output power P1 is 1000 W or more and control in the third control mode, and the output power P1 is less than 1000 W and the fourth control is performed. When the control in each mode is executed, an operation capable of optimizing the objective function Ix in the entire region of the output power P1 becomes possible.

  In summary, the second threshold power Pt2 is set by selecting a plurality of second threshold power Pt2 candidates and performing a third control corresponding to each second threshold power Pt2 for each of the plurality of output powers P1. The inverter 5 and the electric heater 7 are controlled in the mode or the fourth control mode, and the power generation efficiency Ye and the exhaust heat recovery efficiency Yh of the device 1 of the present invention are obtained by experiments. Then, by substituting the power generation efficiency Ye and the exhaust heat recovery efficiency Yh into Equation 1, the objective function Ix is obtained, and the characteristic of the objective function Ix using the second threshold power Pt2 as a parameter for a plurality of types of output power P1 is derived. . Then, from the obtained characteristic of the objective function Ix, when the output power P1 is smaller than the second threshold power Pt2, the second threshold value at which the objective function Ix increases when the control is performed in the fourth control mode rather than the third control mode. The maximum value of the power Pt2 is extracted.

  In the low output region of the output power P1, the power generation efficiency Ye is extremely reduced. However, when the control is switched from the third control mode to the fourth control mode when the output of the generator 3 is constant, the output of the inverter 5 increases. As a result, the output load of the generator 3 increases and the exhaust heat recovery efficiency Yh due to the exhaust heat recovery of the engine 2 decreases, but the exhaust heat recovery efficiency Yh due to the heating of the electric heater 7 increases above that, The objective function Ix increases. Therefore, in the low output region of the output power P1, the output of the inverter 5 is fixed to a constant value P2x, the electric heater 7 is operated, and control is performed so as to consume the difference between the output power P1 and the second threshold power Pt2. Thus, the objective function Ix is improved.

<Third Embodiment>
The operation control according to the third embodiment is executed by the first operation control unit 9, the second operation control unit 10, and the third operation control unit 11. As shown in FIG. 6, when the output power P1 is equal to or higher than the first threshold power Pt1 set in advance, the control in the first control mode is less than the second threshold power Pt2 set lower than the first threshold power Pt1. When the control in the fifth control mode is less than the second threshold power Pt2, the control in the sixth control mode is executed. In the first control mode, the second operation control unit 10 corresponds to the output power P1 by using a table in which the correspondence relationship between the output power P1 and the optimum rotational speed Rx of the engine 2 is preset and tabulated or functioned. The rotational speed R of the engine 2 is controlled by the optimum rotational speed Rx. In the fifth and sixth control modes, the second operation control unit 10 fixes the optimal rotational speed Rx1 when the output power P1 is the first threshold power Pt1 in the correspondence relationship between the output power P1 and the optimal rotational speed Rx. The rotational speed R of the engine 2 is controlled. In the first and fifth control modes, the first operation control unit 9 controls the inverter output P2 so as to coincide with the control value determined by the output control means 8 and to maintain the relationship of P1 = P2-P3. In the sixth control mode, the first operation control unit 9 fixes the output of the inverter 5 to a constant value P2x, and the third operation control unit 11 operates the electric heater 7 to output power P1 and the second threshold power Pt2. Control to consume the difference. Therefore, when the output power P1 becomes smaller than the second threshold power Pt2 in a state where the inverter output P2 is fixed to the constant value P2x, in order to maintain the relationship of P1 = P2x−P3, the internal power load P3 It is necessary to increase the power consumption by operating the electric heater 7. The increase is given by (Pt2-P1).

  In the third embodiment, the second control mode in the first embodiment is divided into the third control mode and the fourth control mode in the second embodiment, and is set as the fifth control mode and the sixth control mode, respectively. Therefore, the control in the fifth control mode executes the control in the second and third control modes at the same time, and the control in the sixth control mode executes the control in the second and fourth control modes at the same time. Become. Therefore, in this embodiment, the features of the first embodiment and the second embodiment are combined, and the objective function Ix can be further optimized in the entire region of the output power P1.

  The first threshold power Pt1 that is the boundary value between the first control mode and the fifth control mode, the second threshold power Pt2 that is the boundary value between the fifth control mode and the sixth control mode, and the output power P1 and the optimum rotational speed Rx The method of deriving the correspondence relationship is the same as that described in the first embodiment and the second embodiment, respectively, and redundant description is omitted.

  Hereinafter, another embodiment will be described.

  <1> In the first or third embodiment, the first threshold power Pt1 used by the operation control unit 12 for determining the operation control mode is a single value set based on the objective function Ix shown in Equation 1. Explained when to use. However, the coefficients Ke and Kh of the objective function Ix are respectively the reciprocal of the thermal power plant efficiency of 0.4 and the thermal efficiency of a general gas boiler of 0.88 in the performance comparison for the purpose of reducing energy consumption. It is given as an inverse number. Therefore, when the power generation facility of the commercial power source changes depending on the time of day, for example, since the old thermal power plant is also in operation during the daytime peak hours of summer, the efficiency is about 0.4 to 0.35 Therefore, the coefficient Ke increases and the calculation result of the objective function Ix changes. As a result, it is also preferable that the first threshold power Pt1 suitable for the time zone is derived in advance, and the operation control means 12 identifies the time zone and selects and uses the appropriate first threshold power Pt1. It is a form. Further, as for the correspondence relationship between the output power P1 and the optimum rotational speed Rx, a correspondence relationship suitable for the time zone is derived in advance, and the operation control means 12 identifies the time zone, and the appropriate first threshold power Pt1. Select the correspondence and use.

  In addition, the thermal efficiency of the gas boiler differs between hot water supply demand and heating demand. That is, in the hot water supply demand, for example, the heating temperature range is around 42 ° C. from the water temperature, and in the heating demand, for example, the heating temperature range is 60 ° C. to 80 ° C. Since the efficiency with respect to the demand is reduced to 0.8, the coefficient Kh changes depending on the use form (the ratio of hot water supply and heating) of the exhaust heat recovered by the exhaust heat recovery device 6, and the calculation result of the objective function Ix changes. Moreover, the efficiency with respect to a heating demand may change the heating efficiency of the apparatus to be used with heating heat load amount. For example, in the rated operation (output 5 kW), the efficiency is 0.8. In the partial load operation (output 2 kW), when the efficiency drops to 0.75, the coefficient Kh changes and the objective function Ix is calculated. The result changes. As a result, a plurality of first threshold electric powers Pt1 suitable for various utilization forms of exhaust heat recovered by the exhaust heat recovery device 6 (ratio of hot water supply / heating, heating load state) are derived in advance, and operation control is performed. In the preferred embodiment, the means 12 identifies the usage pattern and selects and uses the appropriate first threshold power Pt1. Further, with respect to the correspondence relationship between the output power P1 and the optimum rotational speed Rx, a correspondence relationship suitable for the usage mode is derived in advance, and the operation control means 12 identifies the usage mode and sets an appropriate first threshold value. The correspondence relationship with the power Pt1 is selected and used.

  <2> In the second or third embodiment, the second threshold power Pt2 used by the operation control unit 12 for determining the operation control mode is a single value set based on the objective function Ix shown in Equation 1. Explained when to use. Also in this case, similarly to the above-described another embodiment <1>, the second threshold power Pt2 adapted to the time zone is derived in advance, and the operation control means 12 identifies the time zone, and the appropriate second threshold power It is also a preferred embodiment to select and use Pt2.

  Further, a plurality of second threshold powers Pt2 suitable for various utilization forms of the exhaust heat recovered by the exhaust heat recovery device 6 (ratio of hot water supply / heating, heating load state) are derived in advance, and the operation control means It is also a preferred embodiment that 12 identifies the usage pattern and selects and uses the appropriate second threshold power Pt2.

<3> In the first embodiment, the case where the objective function Ix for the purpose of reducing the energy consumption is used has been described. However, the purpose of the objective function Ix, that is, the performance comparison target is the energy consumption reduction. In addition to (energy saving), CO ₂ emission reduction and energy cost reduction may be used. In this case, the coefficients Ke and Kh of the objective function Ix change according to the purpose.

For example, when the purpose is to reduce CO ₂ emissions, the efficiency is different between the cogeneration system and the commercial power supply for the same output power, and furthermore, the CO ₂ emissions for the unit primary energy amount are different. The objective function Ix for the purpose of reducing CO ₂ emissions can be obtained by correcting the coefficient Ke given by the reciprocal of the efficiency 0.4 at the ratio of the CO ₂ emissions between the cogeneration system and the commercial power source. . In addition, when the auxiliary heat source of the conventional apparatus is a gas boiler, since the primary energy is the same city gas, it is not necessary to correct the coefficient Kh.

  In the case where the purpose is to reduce the energy cost, for the same output power, there is a difference between the power unit price and the gas price of the city gas used to generate the output power. Instead of the reciprocal of the efficiency of the thermal power plant, the unit price of the output power per unit kWh divided by the unit price of city gas per unit kWh is used. When the auxiliary heat source of the conventional apparatus is a gas boiler, since the primary energy is the same city gas, the coefficient Kh is not changed and the reciprocal of the thermal efficiency of the gas boiler is used.

Here, also in the case where CO ₂ emission reduction and energy cost reduction are intended, the coefficient Ke varies depending on the time zone, and the coefficient Kh is various utilization forms of the exhaust heat recovered by the exhaust heat recovery device 6 (hot water supply, heating) The ratio of the first threshold power Pt1, the second threshold power Pt2, the output power P1 and the optimum rotational speed suitable for the time zone or the usage pattern is the same as in the other embodiments <1> and <2>. The correspondence relationship with Rx is derived in advance, and the operation control means 12 identifies the time zone, and the correspondence relationship between the appropriate first threshold power Pt1, second threshold power Pt2, output power P1, and optimum rotational speed Rx. It is preferable to select and use.

  <4> In the above embodiment, the device 1 of the present invention is an operation control capable of optimizing the objective function Ix, taking as an example a gas engine type cogeneration apparatus including the generator unit 4 including the engine 2 and the generator 3. Although the method has been described, the control described in the second embodiment can be applied to, for example, a fuel cell type cogeneration apparatus in addition to the gas engine type cogeneration apparatus.

  <5> In the above embodiment, the case where the electric heater 7 is supplied with power by the AC output P2 of the inverter 5 has been described, but the electric heater 7 is converted by the internal power of the inverter 5, for example, by an AC / DC converter. The power may be supplied using a part of the direct current power.

  <6> In the above embodiment, the values of the output power P1, the engine speed R, the optimum speed Rx, the first threshold power Pt1, the second threshold power Pt2, the objective function Ix, the coefficients Ke, Kh, etc. are examples. It is shown for reference and is not limited to the values in the above embodiment.

  Moreover, although the case where the objective function Ix is expressed by a linear sum of the power generation efficiency Ye and the exhaust heat recovery efficiency Yh of the cogeneration apparatus expressed by Equation 1, the reciprocal of Ix expressed by Equation 1 is used as the objective function. It doesn't matter. In this case, optimization for a predetermined objective is performed by minimizing the objective function.

The block block diagram which shows one Embodiment of the cogeneration apparatus which concerns on this invention The figure which shows typically the operation control which concerns on 1st Embodiment of the cogeneration apparatus which concerns on this invention. Characteristic diagram showing the relationship between the output power P1 with the rotation speed R as a parameter and the objective function Ix The figure which shows typically the operation control which concerns on 2nd Embodiment of the cogeneration apparatus which concerns on this invention. A characteristic diagram showing the relationship between the output power P1 and the objective function Ix using the second threshold power Pt2 as a parameter The figure which shows typically the operation control which concerns on 3rd Embodiment of the cogeneration apparatus which concerns on this invention.

Explanation of symbols

1: Cogeneration device according to the present invention 2: Engine 3: Generator 4: Generator unit 5: Inverter 6: Waste heat recovery device 7: Electric heater 8: Output control means 9: First operation control unit 10: Second Operation control unit 11: Third operation control unit 12: Operation control means 30: System power supply 31: Power load 32: Thermal load Ix: Objective function P1: Output power P2: Inverter output P3: Internal power load Pt1: First threshold power Pt2: Second threshold power R: Engine speed Rx: Optimal speed

Claims (8)

An engine that generates rotational energy using fuel supplied from the outside, a generator that generates first alternating current power from the rotational energy of the engine, and a first voltage having a predetermined voltage and frequency. A cogeneration apparatus comprising: an inverter that converts the AC power into 2; and an exhaust heat recovery device that recovers exhaust heat exhausted by the engine,
When the output power output from the inverter to the outside is greater than or equal to a preset first threshold power, control is performed in a first control mode that controls the engine speed according to the output power, and the output power Is less than the first threshold power, an operation control device that performs control in a second control mode in which the engine speed is fixed to a constant value and the output of the inverter is variable and controlled,
If the output power is less than the first threshold power, an objective function representing the performance for a predetermined purpose of the cogeneration apparatus compared to a case where a commercial power source and an auxiliary heat source are used for the same power load and heat load is the engine. The cogeneration apparatus is characterized in that the number of rotations increases at a constant value as compared with a case where it is variably controlled according to the output power. The operation control device, when controlling the engine speed in the first control mode, controls the engine speed to be set in advance according to the output power,
2. The rotation speed set in advance is determined by selecting a rotation speed at which the objective function is maximized from a plurality of rotation speed candidates capable of outputting the output power. Cogeneration equipment. A generator unit that generates first electric power using fuel supplied from the outside, an inverter that converts the first electric power into second AC electric power having a predetermined voltage and frequency, and A cogeneration apparatus comprising an exhaust heat recovery device that recovers exhaust heat exhausted,
When the output power output from the inverter to the outside is greater than or equal to a preset second threshold power, the control is performed in a third control mode in which the output of the inverter is variably controlled according to the output power. When the output power is less than the second threshold power, a fourth control is performed such that the output of the inverter is fixed to a constant value and the difference between the output power and the second threshold power is consumed by a built-in electric heater. It has an operation control device that performs control in mode,
When the output power is smaller than the second threshold power, control in the fourth control mode rather than the third control mode uses a commercial power source and an auxiliary heat source for the same power load and heat load. A cogeneration apparatus characterized in that an objective function representing the performance of a compared cogeneration apparatus for a predetermined purpose increases. When the operation control device has the output power equal to or higher than a predetermined second threshold power smaller than the first threshold power and lower than the first threshold power, the engine speed is fixed to a constant value, and the inverter Control is performed in a fifth control mode in which the output is varied and controlled according to the output power. When the output is less than the second threshold power, the engine speed is fixed at a constant value, and the output of the inverter is constant. The value is fixed, and control is performed in a sixth control mode in which the difference between the output power and the second threshold power is controlled to be consumed by a built-in electric heater,
3. The objective function according to claim 1, wherein when the output power is smaller than the second threshold power, the objective function increases when the control is performed in the sixth control mode rather than the fifth control mode. Cogeneration equipment.   5. The setting of the first threshold power can be changed according to at least one of a usage form and a time zone of exhaust heat recovered by the exhaust heat recovery device. The cogeneration device described in 1.   5. The setting of the second threshold power can be changed according to at least one of a use form and a time zone of exhaust heat recovered by the exhaust heat recovery apparatus. Cogeneration equipment.   The cogeneration apparatus according to any one of claims 1 to 6, wherein the objective function is represented by a linear sum of power generation efficiency and exhaust heat recovery efficiency of the cogeneration apparatus. The objective of the objective function is one of energy consumption reduction, CO ₂ emission reduction, and energy cost reduction by the cogeneration device, according to any one of claims 1 to 7. Cogeneration equipment.

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