JPH1084634A - Reverse power flow prevention device in cogeneration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smoothly maintain a generated voltage similar to that of a power system, by providing a non-contact switch element for instantaneously connecting a power absorber to the output ends of a main generator when a reverse power flow is detected by reverse power flow detection means. SOLUTION: A power absorber 18 is equipped with a non-contact switch element 22 and a capacitor 23. By doing this, if there is a fluctuation in a load 13, a load to the main generator 8 is suddenly decreased and a reverse power flow phenomenon appears. This is detected by a reversed power flow detector 16 and a controller 25 immediately stops the operation of an inverter 15. And if the non-contact type switch element 22 is instantly turned on and a load 13 is connected to the DC side of an inverter 15, power generated at the main generator 8 is rectified by the inverter 15 through a transformer 14 and flows to a power absorber 18. As a result, stable operation can be realized without generating a reverse power flow in response to a sudden fluctuation in load.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverse power flow prevention device in a cogeneration system (hereinafter abbreviated as CGS).

[0002]

2. Description of the Related Art Conventionally, power consumed by customers has been purchased from a power company. Recently, however, consumers have their own distributed power supply systems, which are power generation facilities that generate power using a prime mover such as a diesel engine. While operating it to cover its own power consumption, consumers purchase electricity from the power company's power system to cover the shortfall from this system, and also reduce the exhaust energy generated by the prime mover of the distributed power system. So-called CGS for reuse has come to be used.

[0003] In this CGS, a system for supplying power from a power company and a power system of its own power generation equipment are synchronously coupled, and both powers of a distributed power supply system are continuously used without power interruption. Grid connection becomes possible.

[0004]

In this way, no reverse power flow, in which power flows back to the power company's power system when the system is linked, is not recognized. Therefore, the power is distributed from the distributed power system to the power company's system. When the occurrence of reverse power flow is detected,
By operating a circuit breaker, the distributed power supply system is to be disconnected from the power system of the power company. With a distributed power supply that uses an engine or the like as the power source of the generator, the control to reduce the supply power due to the inertia of the engine when the electrical load suddenly drops cannot catch up, and the generated voltage becomes the system voltage before the circuit breaker operates. Higher, causing a reverse flow. As a countermeasure, the amount of power expected to fluctuate is used from the power grid to prevent reverse power flow even if a load fluctuates.As a result, a certain amount of power from the high-cost power grid is purchased. Will enter.

In order to eliminate such inconvenience, as shown in FIG. 4, when a reverse flow of the system is detected by the current sensor 101 or the like, the control device 102 issues an instruction to the generator 103 to lower the generated power. On the other hand, the connection of the standby load 104 is turned on, and the power load is increased to prevent reverse power flow. In this method, since the power circuit is turned on and off by a switch having a contact mechanism, a time delay occurs in turning on and off the power circuit, and the constant load of the preliminary load 104 causes a constant load fluctuation. There is a problem that can only deal with.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to overcoming the above-mentioned problems of the prior art, and has an object to consume electric power generated by a generator connected to a prime mover and to provide a power company. In a distributed power supply system connected to the power system in synchronization with the power supply of the power system,
When the voltage of the distributed power supply is going to rise due to load fluctuation,
It is an object of the present invention to provide a reverse power flow prevention device for a cogeneration system that can maintain a generated voltage smoothly at the same level as the power system without disconnecting from the power system.

In order to achieve the above object of the present invention, the present invention consumes power generated by a main generator connected to an engine and synchronizes the power with a power supply of a power system of a power company. In a distributed power supply system connected to a power system, a main generator connected to a power system to supply power to an own load, and energy recovery means for recovering exhaust energy discharged by the engine and superimposing the exhaust energy on an output of the main generator. ,
A reverse power flow detecting means for detecting reverse power flow, which is located between a power absorber for instantaneously absorbing power, and a connection point between the main generator and a power supply of a power system, and the reverse power flow detecting means detecting reverse power flow; And a non-contact type switching element that instantaneously connects the power absorber to the output terminal of the main generator, thereby providing a reverse power flow prevention device in a cogeneration system. The power absorber includes a capacitor or a heating resistor, and the capacitor or the heating resistor instantaneously absorbs power. The power absorber provided with a capacitor is provided with regenerative means for regenerating the stored power to the output side of the main generator. The heating resistor is a heater for heating water in the water heater.

[0008]

Next, an embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, reference numeral 1 denotes a diesel engine as a prime mover. The diesel engine 1 uses a high-efficiency diesel engine in which a combustion chamber, a piston head, and an exhaust system are made of a high heat-resistant ceramic such as a nitride, and does not require a cooling device. For details of this engine, see, for example,
It is described in Japanese Patent Application Laid-Open No. 314916 and has a well-known configuration, and thus a detailed description thereof is omitted. At the tip of an exhaust pipe 2 of the diesel engine 1, a turbine 3 in which blades, turbine scrolls, and the like are made of ceramics having high heat resistance is connected. The rotating shaft 4 of the turbine 3 is directly connected to the rotating shaft of a turbine generator 5 having a continuous rating of 200,000 rotations. A rectifier 6 is connected to an output end of the turbine generator 5.

On the other hand, a main generator 8 is connected to a rotating shaft of the diesel engine via a gear mechanism 7. The output end of the main generator 8 is connected to a power system of a power company via two circuit breakers 9 and 10. An output end 11 of the main generator is connected to a private load 13 via a transformer 12. The output terminal 11 is connected to the output terminal of the inverter 15 via the transformer 14. The input terminal of the inverter 15 is connected to the rectifier 6. 1
6 is a reverse power flow detector, and 17 is a load current detector. A power absorber 18 is connected to an output terminal of the rectifier 6.

The power absorber 18 has a series circuit of a diode 19 and a switching element 20, a non-contact type switching element 22 in which a diode 21 is connected in parallel, and a capacitor 23. Is connected to the inductor 24. This capacitor 23
It is an electric double layer capacitor and has a capacitance of several kilofarads to several tens of kilofarads. Reference numeral 25 denotes a control device, which controls synchronous parallel operation with the power system of the main generator 8 and the inverter 15, reverse power flow determination, control of the power absorber 18, and the like. Further, as shown in FIG.
6, six switching elements 15a to 15f
Are connected in parallel with diodes 15g to 15l each serving as a freewheel operation and a rectifier.

Next, the operation of the embodiment of the present invention will be described. In the steady operation state, the diesel engine 1 drives the generator 8, the control device 25 controls the main generator 8 and the engine, and performs the synchronous parallel operation control with the power system, and transfers the generated power only to the load 13. It is performing an operation such as sending. Further, the turbine 3 is driven by the exhaust gas discharged from the diesel engine 1, and the exhaust gas energy contained in the exhaust gas is recovered by the turbine generator 5 through the turbine 3, is converted to DC by the rectifier 6, After being converted into AC at 15, the AC is superimposed on the electric power supplied to the load 13 via the output terminal of the main generator 8 via the transformer 14.

For some reason, the load 13 fluctuates, the load on the main generator 8 is rapidly reduced, and a reverse power flow phenomenon appears.
When the reverse power flow detector 16 detects this, the control device 25 immediately stops the operation of the inverter 15. Freewheel diodes 15g to 15l are connected to the switching elements 15a to 15f of the inverter 15, respectively.
Since these form a three-phase bridge rectifier circuit, when the non-contact type switching element 22 is instantaneously turned on and a load is connected to the DC side of the inverter 15 in this state, the power generated by the main generator 1 becomes The free wheel diodes 15g to 15l of the inverter 15 rectify the power via the transformer 14, and when the power absorber 18 connected thereto is in a state of absorbing power, this becomes a load and power flows into it.

Since the rectifier 6 is connected to the DC side of the inverter 15, the power generated by the turbine generator 5 is rectified by the rectifier 6 into DC, and the power absorber 18 connected to the rectifier 6 rectifies the power. This is a load when power is absorbed, and power flows into this.

Next, the operation of the power absorber 18 will be described. When the reverse power flow phenomenon occurs, the power absorber 18 must absorb the surplus power, and the contactless switching element 2
When the switch 2 is turned on, the DC power instantaneously flows into the capacitor 23. At this time, the surplus power is automatically absorbed from the higher voltage of the main generator 1 or the turbine generator 5, that is, the higher surplus power. Will be.

As the reverse power flow decreases, the power generation state of the main generator 1 or the turbine generator 5 is controlled to an optimum state. Therefore, the switching element 22 shifts to a chopping operation and limits the current flowing into the capacitor 23. The amount of absorbed power is reduced, and finally, the switching element 22 is turned off to stop the absorption of power.

When the main generator 1 and the turbine generator 5 settle to the optimum voltage, the portion where the voltage of the capacitor 23 is higher than the DC voltage, that is, the portion higher than the input voltage of the power absorber 18 is connected in series to the switching element 22. Diode 21
Regenerated through When the voltage of the DC part and the voltage of the capacitor 23 become the same, the regenerative operation becomes impossible. In this state, when the next surplus power is generated, the capacitor 23 cannot absorb the surplus power. Therefore, the switching element 20 is caused to perform a chopping operation. When the switching element 20 is turned on, a current flows through the inductor 24, and the energy of the capacitor 23 is moved and stored therein. When the switching element 20 is turned off, the energy stored in the inductance 24 is released, whereby the voltage at the connection point between the switching element 20 and the inductor 24 increases. When this voltage becomes higher than the voltage on the DC side of the inverter 15, regeneration is performed to the DC section through the diode 19, and the voltage of the capacitor 23 decreases. For this reason, the charged amount of the capacitor 23 is reduced, and is prepared for the next surplus power absorption.

In the CGS as described above, the main generator 1
In some cases, a water-cooled engine is used as the engine 1 that drives the chiller, and cooling water is used as hot water for a water heater in the system. FIG. 3 is a circuit diagram showing an embodiment of the present invention in such a case. 1 and 2 are denoted by the same reference numerals, description thereof will be omitted, and only new parts will be described. In FIG. 3, a heat exchanger 26 is provided in a cooling water circulation system 1 'of the engine 1, and a CGS hot water circulation system is connected to an output side thereof. In the hot water circulation system, in addition to the auxiliary heater 27 and the hot water storage tank 28, a heat recovery heater 29 that is a heating resistor that absorbs electric power instantaneously is provided. This heat recovery heater 29 is connected to the DC side of the inverter via a switching element 30. In this embodiment, the heat recovery heater 29 plays a role of the power absorber 18, and when the occurrence of the reverse power flow phenomenon is detected, the non-contact type switching element 30 is turned on and the DC power is instantaneously supplied to the heat recovery heater 29. At this time, the surplus power is automatically absorbed from the higher voltage of the main generator 1 or the turbine generator 5, that is, the surplus power is larger.

As the reverse power flow decreases, the power generation state of the main generator 1 or the turbine generator 5 is controlled to an optimum state. Therefore, the switching element 30 shifts to the chopping operation and limits the current flowing into the heat recovery heater 29. Then, the amount of absorbed power is reduced, and finally, the switching element 30 is turned off to turn off the absorption of power. In this embodiment, the recovered energy cannot be regenerated by electric power as in the above-described embodiment, but the exhaust energy can be recovered as heat for heating hot water.

Although the present invention has been described with reference to the above embodiments, various modifications and applications are possible within the scope of the present invention, and these modifications and applications are not excluded from the scope of the present invention. Absent.

[0020]

As described in detail above, the present invention provides
In a grid-linked distributed power supply system, stable operation can be realized without generating reverse power flow in response to sudden changes in load. Can be reduced, and the power can be shifted to a low-cost distributed power supply. In addition, the present invention can recover the energy absorbed to prevent reverse power flow as electric power or heat,
Therefore, it is possible to provide a system linkage distributed power supply system having good profitability.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a reverse power flow prevention device of a cogeneration system according to the present invention.

FIG. 2 is a circuit block diagram showing a main part of the reverse power flow prevention device of the cogeneration system according to the present invention in detail.

FIG. 3 is a circuit block diagram showing another embodiment of the present invention.

FIG. 4 is a circuit block diagram of a conventional reverse flow prevention device.

[Explanation of symbols]

 1 ... Diesel engine 2 ... Exhaust pipe 3 ... Turbine 4 ... Rotary shaft 5 ... Turbine generator 6 ... Rectifier 7 ... ... Gear mechanism 8 ... Main generator 9 ... Circuit breaker 10 ... Circuit breaker 11 ... Output terminal 12 ... Transformer 13 ... -Load 14-Transformer 15-Inverter 16-Reverse flow detector 17-Load current detector 18-Power absorber 19- -Diode 20-Switching element 21-Diode 22-Switching element 23-Capacitor 24-Inductor 25-Control device 26- ... Heat exchanger 27 ... Auxiliary heater 28 ... Hot water storage tank 29 ... · Heat recovery heater 101 · · · · Current sensor 102 · · · · Control device 103 · · · Generator 104 · · · · Preload

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location H02P 9/00 H02P 9/04 P 9/04 H01G 9/00 301Z

Claims (5)

[Claims] 1. A distributed power supply system for consuming power generated by a main generator connected to an engine and connecting the power system in synchronization with a power supply of a power system of a power company. A main generator for supplying power to the load, an energy recovery unit for recovering exhaust energy discharged by the engine and superimposing the exhaust energy on an output of the main generator, a power absorber for instantaneously absorbing power, and the main generator Reverse power flow detecting means for detecting reverse power flow, which is located between the power supply system and a connection point of the power system, and when the reverse power flow detecting means detects reverse power flow, the power absorber is instantaneously connected to the output terminal of the main generator. And a non-contact type switching element connected to the power generation device. 2. The apparatus for preventing reverse power flow in a cogeneration system according to claim 1, wherein the power absorber includes a capacitor, and the capacitor absorbs power instantaneously. 3. The cogeneration system according to claim 2, wherein said power absorber having said capacitor is provided with regenerative means for regenerating the stored electric power to the output side of said main generator. Reverse power flow prevention device. 4. The reverse power flow prevention device in a cogeneration system according to claim 1, wherein the power absorber includes a heating resistor, and the heating resistor absorbs power instantaneously. 5. The reverse power flow prevention device in a cogeneration system according to claim 4, wherein said heating resistor is a heater for heating water of a water heater.