KR20080066575A - Electric power generating device - Google Patents

Abstract

An electric power generator is provided to allow an operational frequency setting unit to change the frequency of a field current of the power generator, so that the rotational number of a positive displacement steam expander can be adjusted. A power generator(1) is connected to a power system(2) through a transformer(3). The power generator receives a high-pressure steam having a predetermined pressure from a high-pressure steam header(4). The power generator includes a screw expander(5) and a generator(6). The screw expander is a kind of a displacement steam expander to convert an expansion force of a high-pressure steam into a rotational force. A current is input into a field winding(7). The current is supplied through the transformer of the power system. The current has a frequency changed by a field frequency converter(8).

Description

Power plant {ELECTRIC POWER GENERATING DEVICE}

The present invention relates to a power generation device.

A power generation device for driving a generator by turning a turbine with steam is widely used. Further, secondary use of low pressure steam discharged from a turbine is also described, for example, in Japanese Patent Laid-Open No. 2006-2576 and Japanese Patent Laid-Open No. 2004-100657.

In a power generation apparatus using a turbine, it is difficult to control the pressure of the low pressure steam discharged from the turbine, the stable supply of the low pressure steam is difficult, and the use of the low pressure steam is limited.

Thus, the availability of volumetric steam expanders such as screw expanders is considered. The volumetric steam expander has a flat characteristic that the torque is determined by the difference between the air supply pressure (primary side pressure) and the exhaust pressure (secondary side pressure) without depending on the rotational speed, and the steam flow rate is proportional to the rotational speed.

Even if a volumetric steam expander is used, in order to use the low pressure steam universally and efficiently, the pressure of the low pressure steam does not fluctuate even when the use amount of the low pressure steam changes, so that a buffer tank or You need to install a large header. However, since the buffer capacity cannot be increased indefinitely, there is a problem that the buffer pressure decreases when the amount of low pressure steam continues to increase, and the buffer pressure increases when the amount of low pressure steam continues to decrease.

Further, Japanese Patent Laid-Open No. 2005-176496 describes a technique for controlling the rotation speed of a turbine by setting a frequency of a generator.

In view of the above problems, it is an object of the present invention to provide a power generation device capable of keeping the pressure on the secondary side constant even when the amount of use of the low pressure steam on the secondary side changes.

In order to solve the above problems, the power generation apparatus according to the present invention, the volumetric steam expander for converting the expansion of steam into a rotational force, a generator connected to the rotary shaft of the volumetric steam expander, and setting the operating frequency of the generator A control for changing the set frequency of the generator operating frequency setting means in accordance with the deviation of the generator operating frequency setting means, the pressure detector for detecting the exhaust pressure of the volumetric steam expander, and the target value of the exhaust pressure detected by the pressure detector; By means.

According to this configuration, since the pressure on the secondary side decreases when the amount of low-pressure steam increases, the pressure drop on the secondary side is detected to increase the frequency of the generator, that is, the rotational speed of the volumetric expander, and the steam flow rate of the volumetric expander. The pressure on the secondary side can be recovered by making more than the amount of low pressure steam used. Accordingly, the control means is negative to the set frequency of the generator operating frequency setting means by a deviation from the target value of the exhaust pressure so as to change the set frequency of the generator operating frequency setting means higher when the exhaust pressure is lowered. Just give feedback.

In addition, the power generation device of the present invention preferably has a low pressure flow path having a buffer capacity in order to secondaryly use the steam exhausted by the volumetric steam expander.

Further, in the power generation apparatus of the present invention, desirable flat output characteristics are obtained if the volumetric steam expander is a screw expander.

In addition, the power generation device of the present invention can supply the generated power to a generally available power system by having a frequency converter for frequency converting the generated power of the generator into a commercial frequency.

Further, in the power generation apparatus of the present invention, the number of rotations of the volumetric steam expander can be appropriately controlled by changing the frequency of the field current of the generator in the generator operating frequency setting means.

In addition, the power generation apparatus of the present invention includes a flow rate control valve on the air supply side of the volumetric steam expander, and the control means includes the rotation speed equivalent value as the lower limit value when the rotation speed equivalent value of the generator is equal to or less than a predetermined lower limit value. You may control the setting frequency of the said generator operation frequency setting means to hold | maintain, and you may control the opening degree of the said flow regulating valve to maintain the said exhaust pressure to the said target value.

According to this configuration, in the air-cooled generator cooled by a fan provided on the rotating shaft, the rotation speed of the generator is excessively lowered, the cooling capacity is insufficient, and the problem of overheating can be prevented.

As the rotation speed equivalent value, a rotation speed detector for detecting the rotation speed of the generator may be provided, and the rotation speed detected by the rotation speed detector may be the rotation speed equivalent value. Alternatively, the set frequency may be the rotation speed equivalent value.

As described above, in the power generation apparatus of the present invention, by controlling the rotation speed of the generator in accordance with the exhaust pressure of the volumetric steam expander, the steam pressure on the secondary side can be kept constant regardless of the amount of low pressure steam used on the secondary side. .

From this, embodiment of this invention is described, referring drawings.

1 shows a power generator 1 according to the first embodiment of the present invention. The power generator 1 is connected to the electric power system 2 via a link transformer 3.

The power generator 1 is supplied with a high pressure steam at a predetermined pressure Ps (for example, 5 MPa) from the high pressure steam header 4, and is a screw which is a kind of volumetric steam expander that converts expansion of the high pressure steam into rotational force. The expander 5 and the synchronous generator 6 connected to the rotating shaft of the screw expander 5 are provided.

The field winding 7 of the generator 6 is supplied with a current supplied from the electric power system 2 via the associated transformer 3 and converted into an arbitrary frequency by the field frequency converter 8. The field frequency converter 8 includes a converter 9 for forward-converting the supplied commercial frequency current to a direct current, and an inverter 10 for switching the output of the converter 9 by a semiconductor to convert it into an alternating current of a desired frequency. Consists of

The rotor of the synchronous generator 6 rotates in synchronization with the field current applied to the field winding 7, and generates electric power having the same frequency as the field current. That is, the operating frequency of the generator 6 is set by the inverter 10.

In addition, the output of the generator 6 is converted into a commercial frequency by the output frequency converter 11, and is led to the electric power system via the link converter 3. The output frequency converter 11 also includes a converter 12 and an inverter 13 similarly to the field frequency converter 8. In the inverter 10, an output frequency is set by a program-controlled control device (control means) 14. That is, in this embodiment, the inverter 10 and the control apparatus 14 mainly play the role of a generator operating frequency setting means.

The screw expander 5 converts the expansion force of the high pressure steam into a rotational force, and exhausts the low pressure steam. The steam exhausted by the screw expander 5 is stored in the buffer tank 15, and supplied to the demand facility that uses the low pressure steam secondaryly through the low pressure steam flow passage 16. The exhaust pressure Pd of the screw expander 5 is detected by the pressure detector 17, converted into an electrical signal, and input to the control device 14.

The control apparatus 14 inputs the target pressure Pt of the exhaust pressure Pd from the console 18, and sets the inverter 10 by the deviation with respect to the target pressure Pt of the exhaust pressure Pd. It is supposed to give negative feedback about the frequency. For example, the control apparatus 14 is a value obtained by multiplying the deviation Pd-Pt with respect to the target pressure Pt of the exhaust pressure Pd by a negative constant, and the integral of the deviation Pd-Pt. PID control which adds the value which multiplied the constant of and the derivative value of the deviation Pd-Pt multiplied by the negative constant to the set frequency of the inverter 10 is performed.

Here, the target pressure Pt is set to the pressure (for example, 0.8 MPa) which is optimal for the secondary use in the low pressure steam demand facility designed in consideration of the total efficiency with the screw expander 5.

For example, when the amount of use steam in the demand equipment of low pressure steam is larger than the amount of exhaust steam Qe of the screw expander 5, the amount of steam in the buffer tank 15 decreases gradually, and the buffer tank 15 ), That is, the exhaust pressure Pd of the screw expander 5 decreases. Then, since the control apparatus 14 gives negative feedback to the set frequency of the inverter 10, the output frequency of the inverter 10 raises and the field frequency of the generator 6 raises.

Since the rotation speed of the screw expander 5 is proportional to the field frequency of the generator 6, when the exhaust pressure Pd decreases, the rotation speed of the screw expander 5 increases. Then, with the increase of the rotation speed of the screw expander 5, the exhaust vapor quantity Qe of the screw expander 5 increases. When the amount of exhaust steam Qe becomes larger than the amount of used steam Qu of the demanding equipment, the amount of steam in the buffer tank 15 increases, and the pressure of the buffer tank 15, that is, the exhaust pressure Pd of the screw expander 5. To increase.

When the exhaust pressure Pd is higher than the target pressure Pt, since the control device 14 feeds negative feedback to the set frequency of the inverter 10, the field frequency of the generator 6 is lowered, causing the screw expander ( The exhaust vapor amount Qe of 5) decreases.

As described above, in the power generation device 1, the control device 14 controls the field frequency of the generator 6, so that the exhaust pressure Pd of the screw expander 5 can be most efficiently used in demand equipment. Can be maintained.

2, the power generation apparatus 1 of 2nd Embodiment of this invention is shown. In this embodiment, the same code | symbol is attached | subjected to the component same as 1st Embodiment, and description is abbreviate | omitted. In this embodiment, the generator 6 employs an induction generator of the air-cooled type. In addition, the power generation device 1 of the present embodiment includes a rotation sensor 19 for detecting the rotation speed of the generator 6 and a flow rate adjustment valve for restricting the flow path of the high pressure steam on the air supply side of the screw expander 5 ( 20) is installed.

In this embodiment, the rotation speed of the generator 6 which the rotation sensor 19 detected is input into the control apparatus 14. When the rotation speed of the generator 6 becomes below a predetermined lower limit rotation speed, the control apparatus 14 controls the set frequency of the inverter 10, regardless of the exhaust pressure Pd of the screw expander 5, The rotation speed of the generator 6 is maintained above the lower limit rotation speed. In that case, the control means 14 PID-controls the opening degree of the flow regulating valve 20 so that exhaust pressure Pd may be kept at target value Pt.

The generator 6 is cooling the windings by a cooling fan provided on the rotating shaft of the rotor. However, if the rotation speed is too low, the cooling becomes insufficient and there is a risk of overheating. Therefore, by setting the lower limit rotation speed in advance in consideration of the characteristics of the cooling fan of the generator 6, the internal temperature of the generator 6, and the like, it is possible to prevent the problem caused by insufficient cooling of the generator 6. Can be.

Thus, the rotation speed of the generator 6 falls when the secondary usage amount Qu of the low pressure steam is very small, and the exhaust pressure Pd rises. Therefore, the flow rate adjusting valve 20 restricts the air supply flow path of the screw expander 5 to reduce the steam flow rate, thereby lowering the exhaust flow rate Qe and lowering the exhaust pressure. To prevent the pressure rise.

In addition, when the rotation speed of the generator 5 is equal to the lower limit rotation speed, the control for opening the flow rate adjustment valve 20 is given priority over the control for raising the set frequency of the inverter 10. That is, when the rotation speed of the generator 5 is higher than the lower limit rotation speed, the flow regulating valve 20 will always be fully open.

In this embodiment, although the rotation sensor 19 is provided and the rotation speed of the generator 6 is detected, since the rotation speed of the generator 6 is approximated to the rotation speed synchronized with the field frequency, the inverter 10 The control may be simplified by considering the set frequency as the rotation speed of the generator 6.

3 shows a power generator 1 of a third embodiment of the present invention. In this embodiment, the same code | symbol is attached | subjected to the component same as 1st Embodiment, and description is abbreviate | omitted. In the generator 21 according to the present embodiment, a motor generator capable of switching so-called retrograde driving and regenerative driving is employed. The generator 21 is preferably a permanent magnet embedded type in which a permanent magnet is embedded in the rotor and a winding is included in the stator.

The output frequency converter 22 is connected to the generator 21. This output frequency converter 22 is constituted by an inverter 23 and a converter 24. Although not shown, the inverter 23 and the converter 24 are all composed of three-phase so-called half-bridge circuits composed of diodes connected in series, and switching elements such as IGBTs connected in parallel to the half-bridge circuits.

As described above, the generator 21 is a motor generator that can switch between the reverse operation and the regenerative operation. The inverter 23 and the converter 24 connected to the generator 21 have a function as an inverse conversion circuit (narrow inverter) for generating AC power from DC power, and a forward conversion circuit for generating DC power from AC power ( Function as a narrow converter) can be switched. In other words, when the generator 21 is driven in reverse (operated as a motor), the inverter 23 functions as an inverse conversion circuit (narrow inverter) that generates AC power from DC, and at the same time, the converter 24 Can serve as a forward conversion circuit (narrow converter) for generating direct current power from alternating current power. Then, when the generator 21 is regeneratively operated (operated as a generator), the inverter 23 and the converter 24 reverse each other's functions.

Since the generator 21 is of a permanent magnet embedded type, the magnet torque based on the suction and repulsion of the pole of the rotating magnetic field and the magnetic pole of the permanent magnet of the rotor, and the suction of the pole of the rotating magnetic field and the pole of the rotor of the rotating magnetic field are used. Generates a reluctance torque based on This magnet torque and reluctance torque, and thus the total generated torque, are changed by the so-called current phase angle (current phase angle becomes positive maximum torque in the range of 0 ° to 45 °, and in the range of 135 ° to 180 ° Minus maximum torque). The power generation device 1 of the present embodiment is configured to control the total generated torque of the generator 21, and furthermore, to control the rotation speed of the generator 21 by appropriately adjusting its current phase angle. have. Specifically, the power generator 1 of the present embodiment transmits a pulse width modulated gate signal from the control device 14 to the switching element of the inverter 23 described above to perform appropriate switching, thereby generating a generator ( It is comprised so that control of the total generation torque of 21, and also control of the rotation speed of the generator 21 is possible. That is, in this embodiment, the inverter 23 and the control apparatus 14 mainly play the role of a generator operating frequency setting means.

In addition, this invention is not limited to embodiment mentioned above. For example, a matrix converter may be employed in place of the output frequency converter 22 in the power generator 1 of the third embodiment of the present invention. Compared with adopting a converter and an inverter for converting from AC to DC, and from DC to AC again, the use of a matrix converter for converting from AC to direct AC has advantages in terms of small size, light weight, and high efficiency.

1 is a schematic diagram showing a configuration of a power generator according to a first embodiment of the present invention.

Fig. 2 is a schematic diagram showing the configuration of a power generation device of a second embodiment of the present invention.

3 is a schematic diagram showing a configuration of a power generator according to a third embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

1: power generation device

2: power system

3: linkage transformer

4: high pressure steam header

5: screw inflator

6: generator

7: field winding

8: field frequency converter

9, 12: Converter

10, 13: Inverter

14: control device

17: pressure detector

Claims (9)

A volumetric steam expander that converts expansion of steam into rotational force, A generator connected to the rotary shaft of the volumetric steam expander, Generator operating frequency setting means for setting an operating frequency of the generator; A pressure detector for detecting the exhaust pressure of the volumetric steam expander; And a control means for changing the set frequency of the generator operating frequency setting means in accordance with the deviation from the target value of the exhaust pressure detected by the pressure detector. The power generation apparatus according to claim 1, wherein the control means performs negative feedback with respect to a set frequency of the generator operation frequency setting means by a deviation from a target value of the exhaust pressure. The power generation apparatus according to claim 1, wherein a low pressure flow path having a buffer capacity is provided in a flow path of steam exhausted by the volumetric steam expander. The apparatus of claim 1, wherein the volumetric steam expander is a screw expander. The power generation apparatus according to claim 1, further comprising a frequency converter for frequency converting the generated power of the generator into a commercial frequency. The generator according to claim 1, wherein the generator operating frequency setting means sets the operating frequency of the generator by changing the frequency of the field current of the generator. The flow rate control valve is provided on the air supply side of the volumetric steam expander, and the control means is adapted to maintain the rotational speed equivalent value at the lower limit when the rotational speed equivalent value of the generator is equal to or less than a predetermined lower limit value. A power generation apparatus for controlling the set frequency of the generator operating frequency setting means and for controlling the opening degree of the flow regulating valve to maintain the exhaust pressure at the target value. 8. The power generation apparatus according to claim 7, further comprising a rotation speed detector for detecting the rotation speed of the generator, wherein the rotation speed detected by the rotation speed detector is the rotation speed equivalent value. The power generation apparatus according to claim 7, wherein the set frequency is the rotational speed equivalent value.

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