JPH0636680B2 - Variable speed generator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a variable speed power generator, and in particular, it is suitable when a pump turbine (or turbine) that is a drive machine has a so-called S-shaped characteristic in a turbine region. The present invention relates to a variable speed generator.

[Conventional technology]

The variable-speed power generator to which the present invention is applied uses a wound-rotor induction generator as a generator driven by a pump turbine or a turbine (hereinafter simply referred to as a turbine). AC excitation through. For this reason, the output frequency of the generator can be set to an arbitrary turbine speed while maintaining the system frequency, and the turbine can be operated at a speed with good turbine efficiency, or the generator is used as a motor to perform variable speed pumping operation. It is attracting attention because it sometimes has the characteristic of being able to perform AFC operation while operating as an electric motor.

By the way, the water turbine of this variable speed generator also has so-called S-shaped characteristics like the conventional fixed speed turbine, and measures to avoid this are indispensable. Japanese Patent Application Laid-Open No. 59-72998 discloses S at the stage of shifting from no load to rated load in a variable speed generator.
We propose a method to avoid entering the unstable driving area of the character characteristics. In this known example, in order to prevent the operating point of the hydraulic turbine from entering the S-shaped characteristic region, the guide blade opening control of the hydraulic turbine is prioritized over the rotational speed control by the induction generator. That is, while controlling the generator output according to the output command given to the generator, first the guide vane opening is brought to the opening corresponding to the output after the change as rapidly as possible, and the rotation speed optimization control is thereafter changed. This is to carry out the construction, and there is an effect that it is possible to prevent entering into an unstable operation region having an S-shaped characteristic when the water turbine is started.

[Problems to be solved by the invention]

However, the variable speed power generator is operated under different conditions from moment to moment, and it is fully expected that the variable speed generator will approach or enter the unstable operation region during normal operation other than startup. Is not effective as an avoidance / escape measure in this case.

In view of the above, it is an object of the present invention to provide a variable speed power generation device that can approach an unstable operation region and return to a stable operation region.

[Means for solving problems]

In the present invention, the current operating point is grasped on the turbine characteristic diagram, and the rotational speed of the turbine is forcibly reduced when approaching the unstable operating region.

As a concrete measure for reducing the rotation speed, the frequency conversion device is controlled to increase the generator output, or the guide vane opening is controlled to decrease the turbine output, thereby lowering the rotation speed.

[Action]

In the turbine characteristics, the stable operation side is a region where the rotational speed of the turbine is low, and in the variable speed power generator in which the rotational speed can be selected independently of the system frequency, it is possible to return to the stable operating side by decreasing the rotational speed.

The turbine is accelerated or decelerated due to the difference between the turbine output and the generator output. Therefore, it is effective to increase the generator output or reduce the turbine output when lowering the rotation speed.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. Among them, the embodiment of FIG. 1 is for returning to the stable operation side by increasing the output of the distribution machine, and the variable speed power generator and its control device will be described prior to the description of the contents of the invention.

In FIG. 1, reference numeral 1 denotes an induction machine, which is rotationally driven by a water turbine 2 which is directly connected to its rotor, and a secondary excitation controller 3 having a frequency converter on a secondary winding 1b of the induction machine 1. The AC exciting current adjusted to have a predetermined phase according to the rotation speed of the induction machine 1 is supplied by the induction winding 1, and the primary winding 1a of the induction machine 1 outputs the AC power having the same frequency as the AC system 4. Variable speed operation is performed. In addition, 12 is a transformer for excitation, and the variable speed power generator is configured as described above. One of the operating ends of this variable speed power generator is the secondary excitation control device 3, and the slip phase detector 7 is used for this control.
Is provided for detecting the slip phase S _P equal to the difference between the voltage phase of the AC system 4 and the secondary side rotation phase of the induction machine expressed in electrical angle. The rotor of the slip phase detector is provided with a three-phase winding connected in parallel with the primary winding 1a of the induction machine 1, and the stator side of the slip phase detector 7 has only an electrical angle of π / 2. One ball converter is provided at each different position, and a signal in which the voltage phase of the AC system 4 viewed from the secondary side of the induction machine 1 matches is detected by the hall converter and converted into the slip phase S _P.

Further, an active power detector 9 is provided for controlling the secondary excitation control device 3, and the active power P is the power generation output command P ₀ ′.
It is used as a feedback signal for. The power generation output command P ₀ ′ and the slip phase signal S _P are input to the secondary excitation device 3 so that the output detection signal P of the induction machine 1 detected by the active power detector 9 becomes equal to the power generation output command P ₀ ′. In addition, the AC exciting current supplied to the secondary winding 1b of the induction machine 1 is controlled. Specifically, the control method proposed in Japanese Examined Patent Publication No. 57-60645 can be applied.

The other operation end of the variable speed power generator is the guide blade 11 of the water turbine 2.

Next, the control device for these operating ends will be described. A water wheel characteristic function generator 5 generates a proper guide blade opening degree command Ya and a proper rotation speed command Na from a power generation output command P ₀ and a water level signal H from the outside. If the water level fluctuation is small, the water level signal H can be omitted. Reference numeral 16 denotes a rotation speed control device which compares the proper rotation command Na with the rotation speed signal N detected by the rotation speed detector 6 to correct the guide blade opening correction signal ΔY.
Is output. Then, the proper guide blade opening command Ya from the water wheel characteristic function generator 5 is added to the guide blade opening correction signal ΔY by the adder 21 and input to the guide blade driving device 10 so that the opening of the guide blade 11 is added to this. Adjusted accordingly
_T is controlled.

FIG. 2 shows an embodiment of the rotation speed control device 16 among them. Reference numeral 17 denotes a comparator which outputs the rotation speed deviation ΔN. This rotation speed deviation ΔN is input to 18 comparison elements K1 and 19 integration elements (K2 / S), and their outputs are added by the adder 20.
Is added to obtain a guide blade opening correction signal ΔY.

In FIG. 1, the control device of the circuit portion except 25, 26, 30, 31 is conventionally known,
Input P ₀ and H to ensure stable operation. FIG. 3 shows how the various amounts of each part change when the power generation output command P ₀ is increased, and it can be understood that after the command P ₀ changes, the various amounts stabilize in a new operating state. . The variation of various components in the transient state will be described below with reference to FIG.

In the control device configured as described above, when the power generation output command P ₀ is increased stepwise as shown in FIG. 3A, for example, the power generation output P is increased stepwise at time t0. The power generation output P of the induction machine 1 is shown in Fig. 3 (g).
As shown in, the power generation output command P ₀ rises following the change. On the other hand, after the power generation output command P ₀ is given, the power generation output P
The response of the opening Y of the guide blade 11 is slower than the response of. Therefore, the turbine output PT becomes smaller than the power generation output P, and the rotation speed N is temporarily decelerated after the power generation output command P ₀ suddenly changes. Thereafter, at the time point t1, the power generation output P and the turbine output PT become equal and the rotation speed N Is minimal. Since the speed deviation ΔN is positive at this time point t1, the guide blade opening correction signal ΔY is positive, and the guide blade opening Y further rises above the proper guide valve opening command Ya. Therefore, the turbine output PT becomes larger than the power generation output P, and the rotation speed N begins to rise as shown in FIG. 3 (f). Then, as the rotation speed N increases, the proper rotation speed command N
The deviation from “a” becomes small, the water turbine output PT decreases as the guide blade opening correction signal ΔY decreases, and the acceleration of the rotation speed N decreases.

Using the embodiment of FIG. 1, the speed deviation Δ in the steady state
N becomes zero by the integral element 19. On the other hand, the deviation between the proper guide blade opening command Ya from the turbine characteristic function generator 5 and the guide blade opening Y corresponds to the error between the turbine characteristic stored in the turbine characteristic function generator 5 and the actual characteristic of the turbine 2. It is possible to make it almost zero by increasing the accuracy of the turbine characteristic function. Therefore, the guide vane opening deviation (Ya
It is only necessary that the integration element 19 generate only -Y).

The above will be explained again using the formula.

The secondary excitation device 3 has an integral element or the like incorporated to match P with P ₀ , and in the steady state, P = P ₀ (1) The integral element incorporated in the rotational speed control device 16 causes N = in the steady state. Na (2) Further, when the guide vane drive device 10 is in a steady state, Y = Ya + ΔY (3) Also, in a steady state, the turbine output P _T and the generator output P are the same, P = P _T = f (H, Y, N) (4) Furthermore, since the optimum guide vane opening command Ya should have been originally given so as to correspond to P ₀ under the water level H at that time and N = Na, P ₀ = f (H, Ya, Na) (5) When combined as above, Y = Ya, that is, ΔY = 0 in the steady state.
The gain K1 of the proportional element 18 having a braking effect is increased and the gain K2 of the integral element 19 is relatively decreased to increase the response speed of the guide blade opening as much as possible. On the other hand, as shown in FIGS. 3 (a) and 3 (f), the turbine output PT and the rotation speed N are settled without vibration.

The response of the conventional variable speed power generator has been described above. In short, according to this device, various amounts can be kept stable by controlling the turbine input and the power generation output in a balanced manner. However, in the device of the present invention in which the circuits 25, 26 and 30 are newly added, the power generation output correction signal ΔP _{1 is} output from the signal correction circuit 25.
Is extracted to increase the power generation output, while no correction is made to the guide vane opening (turbine output side). Such input / output imbalance control causes a decrease in rotation speed so that it can be easily inferred from the description of FIG. The present invention activates such unbalanced control when approaching the unstable operation region of the turbine characteristic, and the unstable operation phenomenon of the turbine will be described below.

In general, pump turbines, especially runners and other equipment of high-lift pump turbines, in order to obtain high lift during pump operation,
It is designed to exert sufficient centrifugal pump action.

However, this design adversely affects the turbine operation of the pump turbine. In particular, it is considered inevitable to accompany a characteristic called an S-shaped characteristic described later. The characteristics of the pump turbine used in this design are the number of revolutions per unit head (N ₁ ) and the flow rate per unit head (Q ₁ ) under a predetermined guide vane opening.
Where indicated by characteristic curve representing the relationship between, the characteristic curve, in the water turbine operation region, a first portion decreasing values accompaniment with Q ₁ to the increase in the value of N ₁ is decreased the value of N ₁ And a second portion in which the value of Q ₁ decreases with. For convenience of explanation, in the present specification, the second portion is referred to as S
It is called a character characteristic part. Further, the characteristic of the pump turbine in the S-shaped characteristic portion will be hereinafter referred to as the S-shaped characteristic. In hydraulic turbine operation in the S-shaped characteristic portion, the torque per unit head (T ₁ ) also decreases as the number of revolutions per unit head (N ₁ ) decreases.

Normally, the turbine operation of the pump turbine is performed in the first part. However, when the number of revolutions per unit head (N ₁ ) sharply increases due to a sudden decrease in load or the like, the water turbine may plunge into the S-shaped characteristic portion. Once the S-shaped characteristic portion is entered, it is virtually impossible to continue operating the variable speed machine.

The characteristics of the pump turbine having the S-shaped characteristic in the turbine operating region are shown in FIGS. 4A and 4B. In FIG. 4A, the characteristics of the pump turbine are shown as a relationship between the number of revolutions per unit head (N ₁ ) and the flow rate per unit head (Q ₁ ) using the guide vane opening as a parameter. on the other hand,
In FIG. 4B, the characteristics of the pump turbine are shown as the relationship between the number of revolutions per unit head (N ₁ ) and the torque per unit head (T ₁ ) with the same parameters.

In the above equation, the symbols N, Q, H and T are respectively
It shows the rotation speed, flow rate, effective head and torque of the pump turbine.

Characteristic curves 1 and 1'are obtained under a predetermined, relatively large guide vane opening. Characteristic curves 2 and 2'are obtained under a smaller guide vane opening. Characteristic curves 3 and 3'are obtained with a guide vane opening smaller than that.

In the a-d-h part of the characteristic curve 1, the value of Q ₁ is
It decreases with the decrease of N ₁ . As described above, this curved portion a-d-h is referred to as an S-shaped characteristic portion in this specification. Similarly, the curve portion b-e-i is S of the characteristic curve 2.
And the curved line portion c-f-j is the characteristic curve 3
Is an S-shaped characteristic part of. Such an S-shaped characteristic region shifts toward the higher N ₁ side as the guide vanes become larger.

As in FIG. 4A, also in FIG. 4B, the curved portions a'-d'-h ', b'-e'-i' and c'-
f'-j 'are characteristic curves 1', 2'and 3 ', respectively.
Is an S-shaped characteristic part of.

FIG. 4B is closely related to FIG. 4A. For example, the point x on the curve 3 in FIG. 4A that satisfies Q ₁ = Q _1X and N ₁ = N _1X corresponds to the point x ′ on the curve 3 ′ in FIG. 1B.
The point x ′ is a point that satisfies T ₁ = T _1X ′ and N ₁ = N _1X ′ (= N _1X ). Similarly, points a, b, and
c, d, e, f, h, i and j are points a ', b', c ', d', e ', f', h ', in FIG. 4B, respectively.
It corresponds to i'and j '.

The curve nr is an unloaded flow rate curve. The intersections α, β, γ of the curves 1, 2, 3 and the curve nr are the curves 1 ′,
It corresponds to the intersection points α ′, β ′, γ ′ between 2 ′, 3 ′ and the straight line T ₁ = 0.

Next, it will be explained that the embodiment of FIG. 1 can prevent entry into the unstable operation region. Incidentally, in the circuit of FIG. 1, 30, 31, 25 and 26 are parts added by the present invention. When the power generation output command P ₀ is decreased at time 0 in FIG. 5 showing the state quantities of the respective parts in FIG. 1, the optimum guide valve opening command Ya and the optimum rotation speed command Na are also decreased, and as a result, the guide valve opening Y, turbine output P _T , and power generation output P also decrease. However, since the decreasing speed of the power generation output P is faster than that of the turbine output, the acceleration force acts and the rotation speed excessively increases. By the way, the operating point in the state before time 0 is at point K in FIG. 4A on characteristic 1 which is determined by the guide valve opening Y and the rotation speed N, and after the power generation output is reduced, the new guide valve opening L point is set. However, the change in the guide valve opening is relatively slow, and the operating point follows the characteristic 1 due to the increase in the number of revolutions.
Approach r. Time t _{0 in} FIG. 5 indicates the time when the speed reaches the speed on the characteristic nr.

Reference numeral 30 in FIG. 1 denotes a speed correction unit, which divides the actual rotation speed N by the square root of the effective free fall He to obtain the rotation speed N ₁ per unit free fall. This N ₁ corresponds to the horizontal axis of FIG. 4A. On the other hand, the reference speed derivation unit 31 determines the reference speed N _1P, which is the limit, from the input Y, because the limit number of revolutions at which the operation shifts to unstable operation differs depending on the guide valve opening Y. In addition, an output that makes the power generation amount correction signal ΔP ₁ variable according to the opening degree Y is given. The signal correction circuit 25 has N ₁ > N _1P and outputs a correction signal ΔP ₁ according to the guide valve opening Y at that time.
Although ΔP ₁ is output at time t ₀ in FIG. 5, the command influenced by ΔP ₁ is only P ₀ ′ and increases, but the guide valve opening command Ya and the rotation speed command Na are constant. . As a result, the power generation output P increases according to P ₀ ′, but the guide valve opening Y determined by Ya and the turbine output P _T do not change. However, in the example of the figure, it is shown that the number is being reduced to the point corresponding to the change at time 0. Therefore, the turbine output P _T and the power generation output P become P> P _T , and the deceleration force acts on the turbine to rapidly reduce the rotational speed N. Since N ₁ <N _1P due to the decrease in N, and the signal correction circuit 25 returns to ΔP ₁ = 0,
Eventually, the apparatus shown in FIG. 1 becomes stable at each amount commensurate with the output after the decrease at time 0. The operating point after stabilization is point K in FIG. 4A.

FIG. 6 shows another embodiment of the present invention, in which the output of the signal correction circuit 25 is not applied to the power generation output command P ₀ , but to the optimum rotation speed command Na, and Na ′ = Na
Finally, the guide valve opening Y is controlled by -ΔNa. In this case, the correction signal is not ΔP ₁ corresponding to the power generation output, but ΔNa corresponding to the rotation speed. However, since the method of obtaining this is the same as that of the embodiment of FIG. 1, its description is omitted here. In FIG. 7, the power generation output command P ₀ decreases at time 0, and as a result, the turbine rotation speed N increases, and at time t ₀ , the signal correction circuit 25 in FIG. 6 detects N ₁ > N _1P and corrects the correction signal ΔN.
The waveform of each part when a is output is shown. In this figure, the operation up to the time point t ₀ is the same as in FIG.
The operation after ₀ will be described.

First, the correction signal ΔNa acts to decrease the optimum rotation speed command Na, and the corrected command Na ′ rapidly decreases after the time point t ₀ . Further, since the final guide valve opening command Ya ′ is obtained by adding the optimum guide valve opening command Ya and the corrected opening command ΔY obtained according to the corrected speed command Na ′ by the adder 21, Ya ′ also rapidly narrows the guide valve opening Y due to the decrease in Na ′. As a result, the turbine output P _T decreases rapidly. On the other hand, looking at the power generation output command P ₀ side, the correction signal ΔNa for avoiding entry into the unstable region does not act on P ₀ at all, so the command P ₀ and the actual power generation output P are constant. Is.

As a result, the turbine output P _T and the power generation output P after time t ₀ become P> P _T , the deceleration force acts on the turbine, and the rotation speed decreases, and as described in FIG. Escape to. If N ₁ <N _1P due to the decrease in speed, the correction signal ΔNa disappears, and the various components of the circuit shown in FIG. 6 stabilize at values corresponding to the power generation output command P ₀ .

As described above in detail, in the variable speed power generator of the present invention, it is possible to avoid the stable operation region by reducing the rotational speed of the water turbine, and in this case, the frequency of the grid 4 should be kept constant. You can In other words, the system frequency is 2
It is a sum of the frequency _W which is determined corresponding to the frequency ₂ and water wheel rotational speed of the next winding, _W is increased or decreased to vary minute
_This is because the secondary excitation control device operates so as to keep the system frequency constant by decreasing or increasing 2.

Next, a description will be given of applicable modifications of the present invention. In the above description, the case where an induction generator is used as a variable generator has been described. However, the present invention provides a frequency converter on the primary side of the generator without changing the gist of the present invention. It can also be applied to other types of variable speed generators.

Further, as the control device, it is also possible to apply a device in which the secondary excitation control device is driven by the signal of the sum of the power generation amount command and the rotation speed command so that the guide valve opening degree is set to the optimum (in terms of efficiency) opening degree.

〔The invention's effect〕

As is apparent from the above, the effect of the present invention is that in the normal variable speed power generation mode in which the generator is inserted in the power system in parallel, the possibility of the pump turbine (or turbine) entering the S-shaped characteristic is completely eliminated, and it is stable. The point is that reliable operation can be guaranteed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of a rotation speed control device forming a part of FIG. 1, and FIGS. 3 (a) to (g) are FIG. FIG. 4A is an explanatory view showing signals of respective parts of the control device of FIG. 2, FIG. 4A is a graph of flow rate characteristics (N ₁ -Q ₁ ) of a pump turbine having an S-shaped characteristic, and FIG. 4B is similarly torque (N ₁ -T ₁ ). ₁ ) A diagram showing a graph, FIG. 5 is a diagram showing various amounts of each part of the apparatus when approaching an unstable operating region in the apparatus of FIG. 1, and FIGS. 6 and 7 are other embodiments of the present invention. FIG.

Claims (2)

[Claims] 1. An electric power is supplied to a power system by controlling an opening of a guide valve of a water turbine directly connected to the generator and an excitation control device of the generator from an actual rotation speed of the generator, a power generation output command and a water level signal. And a reference speed derivation unit that outputs a limit reference speed of the generator that shifts to an S-shaped characteristic region and a power generation amount correction signal of the generator corresponding to the opening of the guide valve. , The number of revolutions of the generator per unit head is obtained from the effective head and the actual rotation speed, and when the number of revolutions of the generator per unit head is larger than the limit reference speed, the power generation amount correction signal is And a signal correction circuit for reducing the rotation speed of the generator by adding it to a power generation output command. 2. The electric power is supplied to the power system by controlling the opening of the guide valve of the water turbine directly connected to the generator and the excitation control device of the generator from the actual rotation speed of the generator, the power generation output command and the water level signal. In a variable speed power generator for supplying a turbine generator function function generator that outputs an optimum rotation speed command and an optimum guide valve opening command of the generator from the power generation output command and the water level signal, and shifts to an S-shaped characteristic region A reference speed derivation unit that outputs a limit reference speed of the generator and a rotation speed correction signal that decreases the optimum rotation speed command in correspondence with the opening of the guide valve, and a unit from the effective head and the actual rotation speed. A signal correction circuit for determining the rotation speed of the generator per head, and outputting the rotation speed correction signal when the rotation speed of the generator per unit head is larger than the limit reference speed; Rotation speed Degree control signal is subtracted from the optimum guide valve opening command and the actual rotation speed to obtain a guide valve correction signal, and the guide valve correction signal is added to the optimum guide valve opening command to control the guide valve. A variable speed power generator, characterized in that the rotation speed of the generator is reduced.