JP2991580B2 - System connection operation method and system connection operation device of induction generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system interconnection operation system of an induction generator which is effective for a cogeneration system (cogeneration system), and to a system interconnection operation device.

[0002]

2. Description of the Related Art At present, conservation and development of resources are extremely important issues, but effective utilization of existing energy is also important. In such a trend, a cogeneration system that can simultaneously extract two types of energy, electrical energy and thermal energy, from one fuel source is extremely effective for effective use of existing energy and conservation of resources. In other words, it is an energy management technology that is evaluated as creating a new energy source and that definitely contributes to society.

[0003] cogeneration system itself is not new, its effectiveness is recognized extend the problem of environmental pollution typified by enhancement and NO _X and SO _X in recent energy saving is posed, resurfaced I've been.

[0004] Focusing on electric energy in a cogeneration system, if a rotating system such as a gas turbine, a gas engine, or a diesel engine is employed as a prime mover, a synchronous generator or an induction generator is used to convert shaft power of the prime mover into electric energy. It is well known that machines are used. It is also well known that the interconnection of the cogeneration system and the commercial power supply is indispensable for the effective use of energy. This interconnection operation at least stabilizes the voltage and frequency; The following advantages can be obtained: simplification of power purchase; reduction of power purchase contract; improvement of generator load factor; power supply without interruption;

[0005] On the other hand, it is also a fact that in the grid-connected operation, various technical and legal restrictions occur. The biggest limitation is the prevention of islanding of the cogeneration system. This is because when the commercial power supply stops, the generated power of the cogeneration system that is connected to the commercial power supply flows out to the commercial power supply side, adversely affecting other consumers connected to the same distribution line, or This is because it will hinder the company from turning on the power again and maintaining the distribution lines. In order to prevent this, the "protection relay method" is defined in the "Technical Guidelines for Interconnection of Grid". Until now, even if surplus power is generated in the cogeneration system, the system interconnection system does not allow the surplus power to flow into the system, that is, does not recognize reverse power flow. As long as the protection relay method specified in the above guidelines is followed, the power receiving circuit breaker is tripped at the same time as the loss of the commercial power supply, and when the power is transmitted backward, it is confirmed that the distribution line has no voltage and the power company cuts off. The vessel had been turned on. Therefore, even if the generator used in the cogeneration system has a slight difference in the type and number of relays used, the synchronous generator and the induction generator were treated almost the same.

However, in recent years, from the viewpoint of effective utilization of energy, there has been a tendency that surplus electric power generated by cogeneration is actively reverse-flowed to distribution lines of electric power companies.
Power companies have also begun to purchase surplus power. Even in the case of reverse power flow, prevention of islanding operation of cogeneration is one of the biggest issues. Therefore, when employing a synchronous generator as the islanding detection system in the reverse power flow system, many systems such as a reactive power detection system, a power factor detection system, an active power detection system, and a system impedance detection system have been studied. In addition, the protection relay method is complicated and expensive, and there is a problem in whether or not detection is performed reliably.At least at present, reverse power flow in synchronous generators has not been solved technically. Instead, it is limited to cogeneration in which a DC output is converted into AC power by an inverter, such as a fuel cell or solar power generation.

[0007]

When an induction generator is used as a generator in a cogeneration system, parallel operation with another power supply system is indispensable as is well known, and this is a drawback of the induction generator. This is an advantage in reverse power flow operation from the opposite viewpoint. That is, in the case of reverse power flow operation, if the commercial power supply is lost, the power generation operation of the induction generator is lost unless the synchronous power generator is operated in parallel with another synchronous power generator in the premises. In other words, the greatest advantage of an induction generator is that it never goes into islanding. Therefore, in the case where the cogeneration system uses reverse power flow, there is no other alternative than the induction generator at present, and the electric power company also recognizes the reverse power flow operation method only for the induction generator in the rotary cogeneration system.

[0008] However, almost all generators currently used in cogeneration systems are synchronous generators, and there are very few examples of using induction generators. The induction generator does not require an exciter, so its structure and equipment are simple and easy to maintain.

[0009] It is sturdy to use a cage type rotor,
Higher rotation speeds can be used compared to salient-pole synchronous machines, and the size can be reduced.

[0010] In the case of a short-circuit accident, continuous current does not flow because the short-circuit current attenuates quickly.

No synchronization is required.

[0012] Even in the case of parallel operation, no governor is required. Although there are many advantages such as this, excessive current flows during parallel operation, and in the case of a large-capacity machine, there is a disadvantage that the system voltage is adversely affected. Therefore, when an induction generator is used, a reactor must be installed to prevent this excessive current, but this is disadvantageous in terms of cost and space.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is possible to suppress an excessive current without using a reactor, and to connect a power grid of an induction generator that enables a reverse power flow type grid connection operation. It is to provide a method and a device.

[0014]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a system for an induction generator, which is connected to a commercial power supply via a circuit breaker. Detecting the rate of change of the rotation speed of the induction generator in a state where the rotation speed of the induction generator is constant within a predetermined time and the rotation speed of the induction generator is within a predetermined range. Based on the rate of change of the rotational speed, a time when the rotational speed of the induction generator reaches the synchronous speed is predicted and calculated, and a predetermined time required for closing the circuit breaker earlier than a time obtained as a result of the predicted calculation. Output a closing signal of the circuit breaker.

Further, the present invention provides a rotation speed detecting means for detecting the rotation speed of the induction generator, and a change rate calculation for calculating a change rate of the rotation speed of the induction generator based on an output of the rotation speed detector means. Means for predicting and calculating a time point at which the rotational speed of the induction generator reaches a synchronous speed when the rate of change of the rotation speed of the induction generator is constant over a predetermined time and the rotation speed of the induction generator is within a predetermined range. System means of the induction generator by means of calculating means and closing command means for outputting a closing signal of the circuit breaker at a time earlier by a predetermined time required for closing the circuit breaker than a time point obtained as a result of the prediction calculation. This constitutes a system operation device.

[0016]

With the above arrangement, when the rate of change of the rotation speed of the induction generator becomes constant, it becomes possible to predict and calculate the time when the rotation speed reaches the synchronous speed. By outputting a circuit breaker closing command at a time obtained by subtracting the time required for closing the circuit breaker from the time obtained as a result of the prediction calculation, the output of the induction generator is almost reached when the synchronous speed is almost reached. Connected to the system power supply.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

In general, when an induction machine is started, an excessive rush current first flows as shown in FIG. 3, and after about 0.5 to 1 cycle, gradually decreases (starting current) to reach the rated current. How to suppress this starting current is a point in using the induction machine.

The current characteristics of the induction generator are shown in FIG. 4 when the horizontal axis represents the slip and the vertical axis represents the current value, and the slip S = 0.
That is, when the power supply is connected to the power supply at the synchronous speed, the current value theoretically becomes zero, but an inrush current flows with a slight phase shift. This inrush current disappears after 0.5 to 1 cycle, and as shown in the output characteristics of the induction generator in FIG.
When the rotation speed of the prime mover is increased to the rated rotation speed, that is, the rotation speed corresponding to the rated slip S 'of the induction generator, the generator generates a rated output and the current value becomes the rated value.

As a method of suppressing an excessive current from an inrush current to a rated current, a power supply breaker is accurately turned on at a synchronous speed.

In order to increase the impedance, a reactor is inserted only when connecting to a system power supply.

The winding impedance is increased only when connected to the system power supply. The present invention focuses on the method of (1), and performs the rotation speed control. In order to perform this control, it is necessary to suppress the absolute value of the excessive current and to shorten the duration thereof.
= 0, that is, a control for accurately detecting the synchronization speed and closing the circuit breaker at that time is required.

[0023] FIG. 6 is one of the obtained relation between the duration of the rotational speed and excessive current when connected to a commercial power source while operating the induction generator 4 pole at 50H _Z (cycle) experimentally . Synchronous speed of the four-pole machine 50H _Z in 1500rp
Since it is m, it can be seen that if the slip S = 0 is accurately detected and connected to a commercial power supply, the excessive current can be reduced and the duration thereof can be shortened.

[0024] Therefore, in the present invention, every moment changing by detecting the rotational speed of the prime mover to calculate the rate of change of the rotational speed, before only than to predict the time t ₀ when reaching the synchronous speed Delta] t (t ₀ - At the time of Δt), a closing command is given to the circuit breaker.

FIG. 1 is a system diagram of a system for operating an induction generator according to the system interconnection operation system of the present invention.

In FIG. 1, reference numeral 1 denotes a power receiving circuit breaker connected between a system (commercial) power supply and a distribution line 2, 3 denotes a load connected to the distribution line 2, and 4 denotes a motor driven by fuel gas. Is an induction generator rotated by the gas engine 4, and 6 is a system-interruption circuit breaker connected between the induction generator 5 and the distribution line 2. The rotation speed of the gas engine 4 is detected by a rotation speed detector 7, and the controller 8 includes a CPU, and based on the change in the rotation speed detected by the rotation speed detector 7, the time t at which the induction generator 5 reaches the synchronous speed. ₀ is calculated, and based on the result, a command to turn on the system interlock breaker 6 is output.

Next, with reference to FIG. 2, a description will be given of how the controller 8 in the above system controls the closing of the system-interconnection breaker 6.

After the operation of the gas engine 4 is started, the controller 8 takes in the output from the rotation detector 7 so that the rotation speed N of the gas engine 4 becomes equal to the specified rotation speed N ₀ (for example, 4
After confirming that the rotation speed is not less than 50 rpm (F-1) and that no failure has occurred (F-2), the change rate dv / dt of the rotation speed is calculated (F-3). In the case of a failure, the supply of the fuel gas is stopped depending on the degree of the failure, and the gas engine 4 is stopped (F-4).

Here, it is determined whether or not the rate of change dv / dt of the rotational speed calculated in step (F-3) is positive and a constant state has continued for a predetermined time (F-5). As when continuing is ready to predict the time t ₀ speed to reach the synchronous speed N _S it means that has increased at a constant rate of induction generator 5, the next number for the prediction computation The slip S is calculated according to 1 and it is determined whether or not its absolute value is within a preset slip value _Sa (for example, 3%) (F-6).

[0030]

## EQU1 ## Slip S = (N_S−N) / N_S  The calculated slip S is equal to the set value S_aWhen you are within
Is the time t at which the prediction operation was performed as shown in FIG.₀Breaker from
Reduce the time required for charging Δt (for example, 100 msec)
Calculated time t₁To output the closing command of the system-interconnection circuit breaker 6
(F-7). As a result of the determination in step (F-6),
S is the set value S_aIf the fuel gas is not
The gas engine 4 is adjusted by adjusting the governor (not shown) for adjustment.
(F-8) to increase or decrease the rotation speed of the induction generator 5.
Wait until the speed approaches the synchronization speed. Throw in the system-integrated breaker 6
When an ON command is issued, a timer built in the controller 8 is activated.
(F-9) to measure the time Δt required for input (F-9
-10). After the measurement of Δt, the system-integrated circuit breaker 6 is turned on.
(F-11), the output of the induction generator 5 is the distribution line 2 or even
Connected to grid power. Inrush current and initial
The dynamic current is kept small.

In the above embodiment, the rotation speed of the gas engine as the prime mover is detected to detect the rate of change of the rotation speed of the induction generator. However, the rotation speed of the induction generator may be directly detected. It is.

[0032]

As described above, according to the present invention, the rate of change of the rotational speed of the induction generator is calculated, the time at which the induction generator reaches the synchronous speed is calculated while observing this change rate, and the cutoff is performed. In consideration of the time required to turn on the circuit breaker, etc., the breaker was turned on in advance and the induction generator was connected to the system power supply.Therefore, when connecting the induction generator to the system power supply without using a reactor, excessive The current can be suppressed, and the time required for connection can be reduced. As a result, the reverse power flow system interconnection operation becomes possible, the cost for installing the reactor can be reduced, and the space for installing the reactor is not required. The present invention is preferably applied to a cogeneration system, but is also effective when applied to general induction power generation equipment.

[Brief description of the drawings]

FIG. 1 is a system diagram of a system for operating an induction generator and connecting to a system power supply according to a system interconnection operation system of the present invention.

FIG. 2 is a flowchart illustrating a closing control of a system-interruption circuit breaker according to the present invention.

FIG. 3 shows a change in a current flowing through the generator when the induction generator is connected to a system power supply.

FIG. 4 shows the relationship between the slip of the induction generator and the current.

FIG. 5 shows the relationship between the rotation speed and the output of the induction generator.

FIG. 6 shows the relationship between the rotation speed of the induction generator and the duration of the excessive current.

FIG. 7 shows a change in the rotation speed of the induction generator and a point in time when the circuit breaker is turned on.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power receiving circuit breaker 2 Distribution line 3 Load 4 Gas engine 5 Induction generator 6 System breaker 7 Revolution detector 8 Controller

Claims (2)

(57) [Claims] In a system interconnection operation method of an induction generator that is connected to a commercial power supply via a circuit breaker, a change rate of a rotation speed of the induction generator is detected with the circuit breaker released. When the change rate of the detected rotation speed is constant over a predetermined time and the rotation speed of the induction generator is within a predetermined range, the rotation speed of the induction generator is synchronized based on the change rate of the rotation speed. Predicting a time point when the vehicle reaches the speed, and outputting a closing signal of the circuit breaker at a time point earlier by a predetermined time required for closing the circuit breaker than a time point obtained as a result of the prediction calculation. Grid-connected operation of the generator. 2. A system connection operation device for an induction generator, which is connected to a commercial power supply via a circuit breaker, wherein the rotation speed detection means detects the rotation speed of the induction generator, and the rotation speed detector means. A change rate calculating means for calculating a change rate of the rotation speed of the induction generator based on the output of the induction generator; and a change rate of the rotation speed of the induction generator being constant over a predetermined time, and Prediction calculation means for predicting the time when the rotational speed reaches the synchronous speed when the rotation speed is within the range; and at a time earlier by a predetermined time required for closing the circuit breaker than a time obtained as a result of the prediction calculation. And a closing command means for outputting a closing signal of the circuit breaker.