JPH0225033B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an operation control method for a variable speed pumping system that can be operated at any rotation speed using an induction machine with secondary excitation, and in particular to a governor-free operation in pumping. The present invention relates to an operation control method suitable for.

[Background of the invention]

Conventional pumped storage power generation systems using synchronous machines are not able to adjust the load during pumping, and due to changes in the power required by the grid and changes in the head during pumping during power generation and pumping operations, the system The disadvantage was that the efficiency of the process varied.

For this reason, research is underway to operate the above system at maximum efficiency, regardless of power generation or lift. In order to achieve the above objectives, as known in Paper No. 553 of the 1981 National Conference of the Institute of Electrical Engineers of Japan, "Variable Speed Operating Characteristics of Large-Capacity Synchronous Motors," a pumped storage generator, which is a conventional synchronous machine, was replaced with an induction generator with secondary excitation. By using a so-called variable speed system that is operated by a machine,
Research is underway to achieve this, with the aim of making it possible to operate the system at its highest rate, regardless of power generation or head. However, although there are the above-mentioned papers regarding such a system, there is no mention of a specific control method.

[Purpose of the invention]

The object of the present invention is to compensate for the above-mentioned drawbacks and provide an operation control system that stably controls the system during governor-free operation in a variable speed pumping system that operates with high efficiency under various operating conditions during pumping.

[Summary of the invention]

In a variable speed pumping system, the operating conditions for achieving a desired pump output are determined by the relationship between the pump head, rotation speed, and the opening degree of the guide vane of the pump. Of these, the efficiency of variable speed pumping systems is determined by the rotation speed and guide vane opening. Therefore, when the lift height and rotational speed are fixed, the guide vane opening degree is controlled to achieve the highest efficiency. On the other hand, the above rotation speed is determined by the difference between the pump output and the electric motor input. Therefore, it is necessary to control the phase angle of the secondary excitation voltage so that the motor input matches the command value. In a variable speed pumping system using an induction machine with secondary excitation, the phase angle of the secondary excitation voltage is controlled in this way, and the opening degree of the guide vane is also controlled.

From the above, in the present invention, specifically, during governor free operation, values obtained by converting the difference between the command value and the actual value of power and the difference between the target value and the actual value of frequency into power are used. In addition to controlling the phase angle, the opening degree of the guide vane is also controlled.

[Embodiments of the invention]

FIG. 1 shows an outline of a variable speed electric motor M, and both the primary and secondary sides of the electric motor are composed of three-phase windings.

In the figure, 1 indicates a stator and 2 indicates a rotor. 5
a to 5c are the stator a, b, and c phase windings; 6a to 5c are the stator a, b, and c phase windings;
6c shows the a, b, and c phase windings of the rotor. Furthermore,
When the rated frequency and slip are S, the speed of the rotor is (1-S), and by exciting the excitation winding of the rotor at the frequency of slip S, the rotating magnetic field of the rotor is reduced to zero slip (synchronous speed ), which is the same as the speed of the rotating magnetic field of the stator. Here, by detecting the slip frequency using the rotation speed of the rotor and exciting the secondary windings 5a to 5c with a voltage according to the slip frequency, even if the operation is performed at an arbitrary rotation speed, the A voltage at the system frequency can be generated in the armature winding. That is, in the example shown in FIG. 1, the rotating magnetic field of the rotor is as follows: ・(1−S)+・S= (1), and an output at the rated frequency can be obtained regardless of slippage. In this system, the gist of the present invention is to devise a system that can stably control the pumping water to a target value at any rotation speed during governor-free operation.

FIG. 2 shows a specific example of the conventional system, and shows a case where the variable speed electric motor M is connected to the grid 10 and is operating. 10 is the power system,
1 and 2 indicate the same stator and rotor as in FIG. Given the head H and output command P ₀ ,
The output command P ₀ is given to the phase angle calculation section 16 via the delay circuit 15 .

On the other hand, the optimal opening degree of the guide vane 12 is determined in block 25 according to a function given in advance from the lift height H and the rotation speed N, and this output is given to the servo system 14 to guide the guide vane with a time delay. This is the opening degree of the vane 12. Reference numeral 13 denotes a pump, whose characteristics are determined by the guide vane opening degree and rotation speed N with a delay of the servo system 14. This pump characteristic causes the rotor 2 of the variable speed machine to rotate. Reference numeral 11 indicates a speed generator, and the speed N is detected by the output of this generator. Reference numeral 19 indicates a current transformer, 20 indicates a voltage transformer, and the active power deriving section 21 connects the current transformer 19.
Based on the output of the voltage transformer 20, the active power is calculated. 16 is a phase angle calculating section of the secondary winding, and the output of the active power deriving section 21 and the delay circuit 15
The phase angle is calculated using the output command P ₀ with a time delay of . 17 is a setting section that sets the amount of excitation of the secondary circuit, and 18 is a voltage adjustment section that controls the voltage value of the amount of excitation. Reference numerals 23a, 23b, and 23c are phase shift units that shift phases in order to apply the excitation amount set by the secondary winding excitation amount setting unit 17 to the a, b, and c phases. 6a, 6b, and 6c are excitation windings that excite the a, b, and c phases with excitation amounts phase-shifted by the phase shifters 23a to 23c. In this way, control is performed by calculating the phase angle of the secondary winding based on the difference between the power control command value P ₀ and the actual output. On the other hand, the opening degree of the guide vane 12 is controlled to the optimum value based on the lift height and rotation speed.

As is clear from this figure, conventional systems do not have a so-called governor-free function that responds to fluctuations in grid frequency. As a result, the grid frequency was changing significantly due to an imbalance between the grid's power generation capacity and load. In contrast, in this system, as shown in Figure 3, the power control amount is calculated based on the difference between the target frequency value and the actual frequency, and this value is added to the power command value.
Control the grid frequency to the target value.

By doing so, the unbalanced power can be absorbed or compensated for by the variable speed machine, so it is possible to prevent the system frequency from decreasing or increasing, and it is possible to ensure a stable supply of electric power.

FIG. 3 shows an example in which the difference between the reference frequency ₀ and the actual frequency _L is detected and the power control command value P ₀ is controlled based on this value.

Block 40 shows the transfer function of the frequency detection section, and the actual frequency _L is obtained via the transfer function of block 40, and this output and the reference frequency ₀
The calculation unit 41 calculates the difference. This output is multiplied by a coefficient in the calculation section 42. The output of the calculation section 42 is added to the control command value 45 via the limiter 43 in the calculation section 44 . Arithmetic unit 4 obtained in this way
Using the output of 4 as the output command value P ₀ in Figure 2,
As is clear from FIGS. 2 and 3, the initial objective is achieved by adjusting the amount of AC excitation of the motor 2.

Incidentally, generally, a Francis pump is used as the pump 13, and in this case, the relationship between pump output and efficiency is shown as shown in FIG. In this figure, the horizontal axis represents the pump output, the vertical axis represents the efficiency, and the rotational speed is shown as a parameter. _P1 ,
P ₂ represents the pump output, η ₁ and η ₂ represent the efficiency, N ₁ and N ₂ represent the rotational speed, and Y ₁ and Y ₂ represent the guide vane opening degree.
At output P ₁ , rotation speed N ₁ and guide vane opening Y ₁
So, at output P ₂ , rotation speed N ₂ and guide vane opening Y ₂
This shows that the maximum efficiency η ₁ and η ₂ are obtained at each output. As described above, the rotational speed at which efficiency is the highest varies depending on the output, and the gist of the present invention is to operate at these points of maximum efficiency even during governor-free operation.

Figure 5 shows, as an example of how to find the guide vane opening for the highest efficiency from the rotational speed N and head H, the horizontal axis shows the rotational speed N and the vertical axis shows the point where the efficiency of the system is the highest at each operating point. The guide vane opening degree Y is plotted on the axis, and the lifting height is shown as a parameter. This figure shows the case where lift height H ₁ > lift head H ₂ . In this figure, if the rotation speed changes from N ₁ to N ₂ during operation with a lifting head of H ₁ , the guide vane opening will change from Y _{1 to N 2} .
Indicates that Y ₂ needs to be controlled.

On the other hand, when the motor rotational speed deviates from the rated value, by using the slip frequency as information on the excitation circuit, an output at the rated frequency can be obtained as described above.

Next, a specific example of secondary excitation will be explained. Second
As shown in the figure, the three-phase secondary excitation winding is expressed as follows.

That is, the phase angle Δδ of the functions for obtaining the excitation amounts of the a, b, and c phases is controlled by the command P ₀ . The a, b, and c phase voltages of the secondary excitation circuit are Va,
When Vb and Vc are given, Va=Esin (2π·s+δ ₀ +Δδ) Vb=Esin (2π·s+δ ₀ +Δδ−120°) Vc=Esin (2π·s+δ ₀ +Δδ−240°) (2). Here, E is a voltage value determined by slip and the operating state of the variable speed machine, δ ₀ is a phase angle determined by the operating state of the variable speed machine, and Δδ is a phase angle controlled by the output of the control command section.

When performing control using the above equation, control may be performed using voltage E for a reactive power control command, and control using a phase angle Δδ for an active power control command.

An object of the present invention is to stably control pumped water during governor-free operation in the above system. Therefore, in the above configuration, it is necessary to control the phase angle (Δδ) of the excitation circuit to adjust the rotation speed and power to the target values, and to control the guide vane opening degree so as to achieve optimum efficiency. For this purpose, active power is used as information for controlling the phase angle. That is, the phase angle Δδ is set as follows: Δδ==K ₁ (P−P ₀ )dt+K _1P (P−P ₀ ) (3). Here, P ₀ is a target value of active power considering the deviation of the system frequency from the reference frequency, P is an actual value of active power, and K ₁ and K _1P are constants.

On the other hand, pump input is controlled by adjusting the guide vane opening. That is, as shown in FIG. 2, the guide vane opening degree is controlled so that it becomes the optimum guide vane opening degree given in advance based on the actual values of the lift height and the rotational speed.

Figures 6 to 8 _are diagrams for explaining _the effects _of the present invention _. T _r4 indicates the transformer, l ₁ and l ₂ indicate the power transmitter, and L ₁ and L ₂ indicate the load. In this figure, the results when the load is increased by closing the circuit breaker SW are shown in FIGS. 7 and 8. In these figures, the horizontal axis is time, the vertical axis is a curve, a is the slip frequency of the variable speed machine, and curve b is the deviation from the reference frequency of the synchronous machine other than the variable speed machine.

Figure 7 shows the results when a variable speed machine that performs pumping operation is not provided with a governor free function. Curve a showing the slip frequency of the variable speed machine has a constant value, whereas The frequency deviation from the reference value continues to decrease due to the increase in load.

FIG. 8 shows the results when the method of the present invention is adopted. Since the increase in load is compensated for by the variable speed machine, the slip frequency curve of the variable speed machine decreases. Due to this effect, the frequency of the synchronous machines other than the variable speed machine slightly decreases but remains at a constant value, which clearly shows the effect of the present invention.

〔Effect of the invention〕

According to the present invention, by providing a governor-free function that calculates a frequency deviation based on the grid frequency and a target frequency, converts this value into a power control amount, and controls the power control amount according to the frequency deviation. In governor-free operation during pumping, the system frequency can be maintained constant even when the load increases or decreases, so the effect on stability is extremely large.

Furthermore, in a pumped storage power generation system that operates as power generation during the day and as pumped storage at night to cover the fluctuating load of the grid, it can operate efficiently with respect to the electricity determined by the grid during pumped storage operation, so the economic effect is extremely large.

[Brief explanation of drawings]

Figure 1 is a diagram showing an overview of the variable speed electric system, Figure 2 is a control outline diagram of the variable speed pumping system, Figure 3 is a diagram showing an embodiment of the present invention, and Figure 4 is the output of the variable speed machine. Figure 5 is a diagram showing an example of the relationship between and efficiency, Figure 5 is a diagram showing an example of determining the optimum guide vane opening, Figure 6 is a model system for determining the effects of the present invention, and Figure 7 is a diagram in which the present invention is not adopted. As a result, FIG. 8 is a diagram showing the effect of the present invention. 1... Stator, 2... Rotor, 5a to 5c...
Stator a, b, c phase windings, 6a to 6b... rotor a, b, c phase windings, 10... system, 11...
Speed generator, 12...Guide vane, 13...Pump characteristic section, 14...Servo system, 15...Delay circuit, 16...Secondary winding phase angle calculation section, 17...2
Next winding excitation amount setting section, 18... Voltage adjustment section, 19
... Current transformer, 20 ... Voltage transformer, 21 ...
Active power derivation unit, 22a, 22b, 22c...2
Exciter a, b, c phase windings, P ₀ ...output command value,
N...Speed, 23a, 23b, 23c...Phase shift section, 25...Optimum guide vane opening calculation section, 40
...Frequency detection unit transfer function, 41, 42, 44...
...Arithmetic unit, 43...Limiter, 45...Control command value.

Claims (1)

[Claims] 1. In a variable speed pumping system consisting of an electric motor whose primary winding is connected to the power system and whose secondary winding is excited by AC, a pump coupled to the motor shaft, and a guide vane at the outlet of the pump, An operation control method for a variable speed pumping system, characterized in that a power control command value is set according to the fluctuation, and AC excitation of the motor secondary winding or the opening degree of the guide vane at the pump outlet is controlled accordingly. .