JP2013078195A - Control method for variable-speed synchronous power generator motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method capable of operation with improved efficiency by expanding a variable speed width in a low-rotating-speed area in power generating operation of a variable-speed pumped storage power generation system by a variable-speed synchronous power generator.SOLUTION: In a control method for variable-speed synchronous power generator motor that includes a variable-speed synchronous power generator motor 1 coupled to a pump turbine 2 and operated while switched between a power generating operation and a pumping operation mode, and performing control by varying an excitation current thereof so that electric power output from the variable-speed synchronous power generator motor matches an electric power command value and the rotating speed is between an upper-limit value and a lower-limit value, the lower-limit value is varied in the power generating operation mode with active power output by the variable-speed synchronous power generator motor to expand the variable-speed width so that the lower-limit value is made smaller when the active power is small than when the active power is large, and the expansion amount of the variable-speed width is adjusted corresponding to a decrease in rotating speed due to a flow rate variation under load increase control in the power generating operation mode.

Description

  The present invention relates to a control method for a variable speed synchronous generator motor that is coupled to a pump turbine and is operated by switching to a power generation operation mode or a pumping operation mode.

Conventional variable speed synchronous generator motors can generally be operated at a constant speed, that is, a variable speed width, centered on the synchronous speed.
Further, for example, as shown in Patent Document 1, a proposal has been made that the variable speed width lower limit in the power generation operation can be operated by adjusting the variable speed width expansion amount according to the amount of active power.
However, the variable speed range expansion in Patent Document 1 does not take into account the increase in flow rate in load increase control.

Japanese Patent No. 4480777

In general, it is well known that the input during the pump operation of the pump turbine remains almost unchanged even when the opening degree of the guide vane is changed, and changes in proportion to approximately 2.5 to the third power of the rotational speed.
Since the variable speed pumped storage power generation system is introduced to realize the AFC operation even during the pumping operation, the variable speed width of the variable speed synchronous generator motor applied thereto is determined from the AFC capacity during the pumping operation.
For example, if a pump input of 300 MW is required at the synchronous speed, the input is assumed to be a pump turbine that is proportional to the cube of the rotation speed, and the variable speed width is set to 10% above and below the synchronous speed, 300 MW × ( 1.1 ³ −0.9 ³ ) = 399.3 MW-218.7 MW = 180.6 MW AFC capacity can be secured.
To operate a variable speed synchronous generator motor at ± 10% of the rated speed, the variable frequency power converter applies a voltage of ± 10% of the rated frequency (called slip frequency) to the rotor winding of the variable speed synchronous generator motor. It needs to be applied to the wire. If it is a 50 Hz system, it must be possible to produce an excitation voltage with a frequency of ± 5 Hz.

From this, the required maximum output voltage of the variable frequency power converter is a voltage obtained by multiplying the exciting current necessary for the pumping operation of 399.3 MW by the impedance of the rotor winding. This is because the magnitude of the excitation current becomes maximum when the input is 399.3 MW, and the rotor impedance is almost proportional to the applied frequency, and thus becomes the maximum at +5 Hz.
Since the rotation speed during operation with the minimum pump input 218.7 MW is -5%, the excitation frequency of the rotor is also the maximum of-and the impedance of the rotor winding is the maximum, but the excitation current is small and the variable frequency power Since the output voltage of the converter is small, it does not become a factor for determining the required maximum output voltage of the exciter.

In general, the rotational speed of the variable speed synchronous generator motor is operated within the range of the variable speed range adopted to secure the required AFC capacity. That is, the variable speed range is fixed to a variable speed range that is constant up and down with respect to the synchronous speed over the entire range of the turbine output regardless of the turbine output of the pump turbine.
Therefore, it is known from the pump turbine performance characteristics that the turbine efficiency of the pump turbine is higher as the rotational speed is lower, so it is known that it is preferable to operate at a rotational speed as low as possible. In many cases, the vehicle is operated with the speed fixed at the lower limit of the variable speed range.

On the other hand, when the turbine output of the pump turbine, that is, the electrical output of the variable speed synchronous generator motor is low, the magnitude of the excitation current can be small, so there is a margin in the excitation voltage, and the excitation voltage is reduced by further reducing the rotational speed. Can be big. That is, when the output is low, the rotation speed can be further reduced.
Paying attention to this, when the output is small during power generation operation, there is an advantage that operation with higher turbine efficiency can be achieved by lowering the lower limit of the variable speed range.
Similarly, during the pumping operation, in the case of the low pumping input operation, that is, when the rotational speed is low, the lower limit of the variable speed range can be increased, so that it is possible to operate with a smaller pumping input. In other words, there is an advantage that the AFC capacity can be further increased.
Therefore, it can be said that operating at a constant variable speed range over the entire turbine output of the pump turbine misses the opportunity to improve efficiency in a region where the turbine output is low. It can be said that the opportunity to expand AFC capacity is missed.
In other words, the variable speed pumped storage power generation system using the variable speed synchronous generator motor has a problem that the power generation efficiency in the low rotation speed region and the pumped AFC capacity can be improved during the water turbine operation or the pump operation.

As a proposal for solving this problem, a proposal shown in Patent Document 1 has been made.
According to Patent Document 1, the means for controlling the rotational speed of the variable speed synchronous generator motor is configured such that the rotational speed command value can be changed in accordance with the power command value. Rather than fixing the lower limit speed of the speed change range, when the power command value is low, a lower speed command value can be output exceeding the lower limit of the variable speed range.
In general, the excitation current during power generation operation of a variable speed synchronous generator motor is considered to be roughly proportional to its output, so if the rotational speed command value is changed in proportion to the power command value, it will automatically be output over the entire output range. High efficiency operation is possible.

However, generally, the generated power of the power plant is periodically changed based on a power command value corresponding to the power demand. Therefore, when the actual power of the variable speed synchronous generator motor is controlled by the AC exciter in response to the power increase command, even if the actual power increases constantly, the flow rate accompanying the increase in the actual power of the turbine as shown in FIG. The change is not constant and changes greatly in the middle to high load range.
For this reason, in order to change the flow rate corresponding to the actual power greatly in the middle to high load region, the output of the water turbine needs to follow.
However, since the turbine is a mechanical system, the follow-up is slow and the flow rate corresponding to the actual power cannot be flowed, so the actual output is obtained by releasing the rotational energy of the variable speed synchronous generator motor until the turbine output follows. There was an event that the rotation speed decreased. As a result, there was a problem that the lower limit of the variable speed range was transiently below.

  The present invention has been made to solve the above-described problems, and can be operated with improved efficiency by expanding the variable speed range in the low rotational speed region during the power generation operation of the variable speed synchronous generator motor. It is an object of the present invention to obtain a control method that prevents deviation from the lower limit of the variable speed width due to a decrease in the rotational speed in the load region.

The present invention includes a variable speed synchronous generator motor that is coupled to a pump turbine and is operated by switching to a power generation operation mode or a pumping operation mode, and by changing the excitation current, the electric power output from the variable speed synchronous generator motor is increased. In the control method of a variable speed synchronous generator motor that controls the rotational speed so as to coincide with an electric power command value and fall between an upper limit value and a lower limit value, the lower limit value is set to the variable speed synchronization in the power generation operation mode. The variable speed is increased by changing the active power output from the generator motor so that the lower limit value is smaller than when the active power is large when the active power is small, and the flow rate in the load increase control in the power generation operation mode The expansion amount of the variable speed range is adjusted in response to a decrease in rotational speed due to fluctuations.

  According to this invention, since the command value for the rotational speed of the variable speed synchronous generator motor can be changed in accordance with the power command and the flow rate change, the command value for the rotational speed is fixed to the lower limit speed of the variable speed width. Rather, when the power command value is low, a lower speed command value can be issued beyond the lower limit of the variable speed range, and automatically without deviating from the variable speed range from the intermediate load to the entire range including the high load range. Can be operated with high efficiency.

It is a control block diagram which shows Embodiment 1 of this invention. It is explanatory drawing which shows the operation example of Embodiment 1 of this invention. It is explanatory drawing which shows the relationship between the turbine output and flow volume in Embodiment 2 of this invention. It is explanatory drawing which shows the operation example of Embodiment 2 of this invention. It is explanatory drawing of the operation example of Embodiment 3 of this invention. It is a control block diagram which shows Embodiment 4 of this invention. It is explanatory drawing which shows the operation example of Embodiment 4 of this invention. It is explanatory drawing which shows the example of a change of the turbine flow rate when increasing the electric power command value with respect to a variable speed synchronous generator motor.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below.
FIG. 1 is a control block diagram showing Embodiment 1 of the present invention. In FIG. 1, a variable speed synchronous generator motor 1 has its rotor driven by a pump turbine 2, and its stator winding is a generator bus 3. And connected to the power system 5 through the main transformer 4.
The AC exciter 6 is fed from the generator bus 3 via the excitation transformer 7, and AC excitation current having a frequency corresponding to the difference between the system frequency and the rotational speed is supplied to the rotor winding of the variable speed synchronous generator motor 1. To supply.
The power converter 8 detects the output of the variable speed synchronous generator motor 1 from the secondary side signal of the instrument transformer 9 connected to the generator bus 3.
The power control circuit 10 generates a control signal such that the output detected by the power converter 8 matches the signal of the power command value setter 11 and supplies the control signal to the AC exciter 6 to synchronize with the variable speed. The output of the generator motor 1 is adjusted.
The output of the variable speed synchronous generator motor 1 can be adjusted instantaneously by lowering its rotational speed to release energy, or increasing its rotational speed to absorb energy from the system. This is the greatest feature of the variable speed synchronous generator motor.

If the pump turbine 2 adjusts the output corresponding to the electric power adjusted by the variable speed synchronous generator motor 1, the rotational speed is restored to the value before the electric power adjustment.
Generally, the output control of the pump turbine is delayed from the output control of the variable speed synchronous generator motor 1 because there is a delay in the water channel system and the mechanical system.
The rotation speed setting device 12 sets a rotation speed that provides the highest efficiency for each output in the power generation operation as the optimal rotation speed, and sets an optimal rotation speed command value according to the value of the power command value setting device 11. And outputs a deviation signal from the actual rotational speed from the actual rotational speed detector 20 to the speed control circuit 13. The rotational speed control circuit 13 adjusts the guide vane opening degree of the pump turbine 2 by the servo motor 14 and the guide vane detector 15 and controls the rotational speed to be the optimum rotational speed.
Since the optimum rotational speed slightly changes in accordance with the head in a region where the output is large, a head signal is supplied from the head detector 16 to the speed setting device 12, and the optimum speed is corrected by the head.
The turbine efficiency of the pump turbine 1 depends not only on the rotational speed but also on the guide vane opening and the head.
The guide vane opening setting unit 17 increases the guide vane opening as the electric power command value is larger, and the guide vane opening is smaller as the head signal from the head detector 16 is higher.
The servo motor 14 is controlled so that the guide vane opening of the pump turbine 2 is adjusted so that the guide vane opening signal detected by the guide vane opening detector 15 matches the guide vane opening signal from the guide vane opening setting device 17. Control to the optimum value.
The power control circuit 10 takes in the system frequency detected by the system frequency detector 18 and the reference frequency from the reference frequency setter 19 and AC-excites a control signal in which a speed droop rate characteristic is added to the deviation between the power command value and the actual power. The variable speed synchronous generator motor 1 is provided to the device 6 so that the output suitable for the state of the power system 5 can be automatically output.

Next, the operation will be described.
The turbine efficiency of the pump turbine 2 for variable speed pumped storage power generation is better as the rotational speed is lower. Accordingly, the optimum rotational speed is conventionally set to the lower limit of the variable speed width of the variable speed synchronous generator motor 1 as shown in the rotational speed setting device 12 of FIG.
As a specific example, the rotation speed setting device 12 will be described in detail with reference to FIG. 4 by expanding the optimum rotation speed of the variable speed synchronous generator motor 1 having a synchronous speed of 600 r / min, a variable speed width of ± 4%, and an output of 300 MW.
Conventionally, as shown in FIG. 2A, the optimum rotational speed has been set constant at 576 r / min, which is the lower limit of the variable speed width, regardless of the power command value.
On the other hand, one of the performances of the AC exciter 6 in FIG. 1 is an allowable maximum output voltage, and it can be said that the variable speed width of the variable speed synchronous generator motor 1 is determined by this voltage.

The relationship between quantities is as follows:
Vex ≦ Vr ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Equation 1
However,
Vr: Rated output voltage of AC excitation device 6
Vex: Excitation voltage
Vex = If ・ (Rf + j ・ 2 ・ π ・ fex ・ Lf) ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Equation 2
However,
If: Excitation current = Output current of AC excitation device 6 (A)
Rf: resistance of rotor winding of variable speed synchronous generator motor 1 (Ω)
Lf: Inductance of rotor winding of variable speed synchronous generator motor 1 (H)
fex: Frequency of excitation current If (also called slip frequency) (Hz)
fex = fs-f ₀・ N / Ns ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 3
However,
fs: System frequency (Hz)
fo: System reference frequency (50 Hz or 60 Hz)
Ns: Synchronous speed of variable speed synchronous generator motor 1 (r / min)
N: Rotational speed of variable speed synchronous generator motor 1 (r / min)

Even if the output voltage of the AC excitation device 6 is fixed to a constant value, if the output of the variable speed synchronous generator motor 1 is small, the excitation current can be reduced, and it can be seen from Equation 2 that the slip frequency fex can be increased. .
For example, assuming that the variable speed width lower limit 4% can be expanded to 6.5% when the output of the variable speed synchronous generator motor 1 is 0, the new optimum rotation as shown in FIG. A number curve can be obtained.
B: N1 = 15 x Pref (pu) + 561 (rpm)

Next, let us consider a decrease in the rotational speed corresponding to an increase in the flow rate from the intermediate load to the high load region.
In this case, if the decrease in the rotational speed deviating from the variable speed range is, for example, αr / min, the new optimal rotational speed obtained from the output of the variable speed synchronous generator motor 1 as the optimal rotational speed in the high load region from the intermediate load. Control is performed so that the engine can be operated as a new optimum rotational speed C obtained by adding αr / min as shown in FIG.
By controlling in this way, the rotational speed command value is not fixed to the lower limit speed of the variable speed range, but when the power command value is low, a lower rotational speed command value is issued beyond the lower limit of the variable speed range. It is possible to improve the power generation efficiency at partial load.
In general, the excitation current during power generation operation of a variable speed synchronous generator motor is considered to be roughly proportional to its output.Therefore, the rotational speed command value is changed in proportion to the power command value, and the flow rate change in the intermediate load to high load range. If this is taken into consideration, high-efficiency operation can be performed automatically without departing from the variable speed range over the entire output range.

  As described above, according to the first embodiment of the present invention, the variable speed synchronous generator motor 1 that is coupled to the pump turbine 2 and is operated by switching to the power generation operation mode or the pumping operation mode is included, and the excitation current is changed. In the control method of the variable speed synchronous generator motor, the power generation operation is controlled so that the electric power output from the variable speed synchronous generator motor matches the power command value and the rotation speed is between the upper limit value and the lower limit value. In the mode, the lower limit value is changed by the active power output by the variable speed synchronous generator motor, and when the active power is small, the variable speed range is expanded so that the lower limit value is smaller than when the active power is large, and power generation operation is performed. In this mode, the amount of expansion of the variable speed range is adjusted in response to a decrease in rotational speed due to flow rate fluctuations in load increase control in the mode. Expanding the variable speed width in the low speed range during operation can be operated with improved efficiency, it is possible to prevent the deviation from the variable speed width lower limit due to the decrease in rotational speed in the high load region from an intermediate load.

Embodiment 2. FIG.
In the first embodiment, the case where the optimum rotational speed is set in consideration of the power command value and the flow rate change has been described. However, the flow rate change is premised on the case where the effective head is the lowest, that is, the flow rate change is the maximum. As shown in FIG. 3, if the effective head is increased, the flow rate change is reduced, and accordingly, the variable speed width is corrected so as to be further increased to improve the power generation efficiency at the partial load.
FIG. 4 shows a specific example as the second embodiment.
When the effective head is the lowest effective head, it is not different from the new optimum speed C in the first embodiment, but when the effective head is higher than the minimum head, the new optimum speed C is set in proportion to the difference. The new optimum rotational speed D corrected downward is used.
That is, in the second embodiment, the variable speed width expansion amount is adjusted in response to the flow rate fluctuation of the variable speed synchronous generator motor 1 changing according to the effective head, and the partial load The power generation efficiency at the time can be further improved.

Embodiment 3 FIG.
In the first embodiment, the case where the optimum rotational speed is set in consideration of the electric power command value and the flow rate change has been described. However, when it is transiently affected by the flow rate change, the output is only increasing and the variable speed is changed. When the synchronous generator motor 1 is operating at a constant output, it is not always necessary to set the optimum rotational speed in consideration of the influence of the flow rate change.
For this reason, as shown in FIG. 5, the optimum rotational speed E considering the flow rate change only while the output is increasing is set. Is corrected to increase the variable speed range.
That is, in the third embodiment, in response to the flow rate increase control in which the power command value is fluctuating, the rotation speed target value is increased only while the output is increasing, and is restored after the power command value becomes constant. Thus, the power generation efficiency at the time of partial load can be further improved.

Embodiment 4 FIG.
In the first embodiment, the case where the optimum rotational speed is set in consideration of the electric power command value and the flow rate change has been described. As shown in FIG. 6, a switching circuit 21 is provided for controlling the rotational speed by the AC exciter 6 while the power command is increasing from an intermediate load to a high load region where a decrease in the rotational speed due to a flow rate change is a problem.
By this switching circuit 21, the section F in which a decrease in rotational speed is a problem can be returned to the circuit that performs power control by the AC exciter 6 as shown in FIG. 7 so that the rotational speed can follow the optimum rotational speed. .
As a result, while the power command is increasing from the intermediate load to the high load region, although there is a demerit that the responsiveness of the active power is reduced, the optimum rotational speed can be set to improve the power generation efficiency at the partial load.
That is, in the fourth embodiment, the rotational speed is controlled by the excitation system while the power command value varies, and the active power is controlled by the excitation system while the power command value is constant. Yes, the power generation efficiency during partial load can be further improved.
It should be noted that within the scope of the present invention, the embodiments can be freely combined, or the embodiments can be appropriately modified or omitted.

1: Variable speed synchronous generator motor 2: Pump turbine 3: Generator bus 4: Main transformer 5: Power system 6: AC excitation device 7: Excitation transformer 8: Power converter 9: Instrument transformer 10: Power control Circuit 11: Electric power command value setting device 12: Speed setting device 13: Speed control circuit 14: Servo motor 15: Guide vane opening detector 16: Head detector 17: Guide vane opening setting device 18: System frequency detector 19: Reference frequency setting device 20: Actual rotational speed detector 21: Switching circuit

Claims (4)

A variable speed synchronous generator motor coupled to a pump turbine and operated by switching to a power generation operation mode or a pumping operation mode is included, and by changing the excitation current, the power output from the variable speed synchronous generator motor is a power command value. In the control method of the variable speed synchronous generator motor that controls so that the rotational speed falls between the upper limit value and the lower limit value,
In the power generation operation mode, the lower limit value is changed by the active power output by the variable speed synchronous generator motor, and the variable speed width is set to be smaller when the active power is small than when the active power is large. As it expands,
A method for controlling a variable speed synchronous generator motor, wherein the amount of expansion of the variable speed width is adjusted in response to a decrease in rotational speed due to flow rate fluctuations in load increase control in the power generation operation mode.   2. The variable speed synchronous power generation according to claim 1, wherein an amount of expansion of the variable speed width is adjusted in response to a change in flow rate of the variable speed synchronous generator motor according to an effective head. Electric motor control method.   Corresponding to the flow rate increase control when the power command value is fluctuating, the rotational speed target value is increased only while the output is increasing, and is returned to the original value after the power command value becomes constant. The method for controlling a variable speed synchronous generator motor according to claim 1.   2. The rotation speed is controlled by an excitation system while the power command value fluctuates, and the active power is controlled by the excitation system while the power command value is constant. The control method of the variable speed synchronous generator motor as described in any one of 3.

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