Patent ID: 12237802

DESCRIPTION OF EMBODIMENTS

With reference to the drawings, an embodiment of the present disclosure will be described in detail below. In the drawings, the same or corresponding part is denoted by the same reference numeral, and the description thereof will not be repeated.

EMBODIMENT

FIG.1is a schematic diagram illustrating a configuration of a wind power generation system100according to an embodiment. Wind power generation system100is an example of a horizontal axis type (propeller type) wind power generation system. As illustrated inFIG.1, wind power generation system100includes a wind turbine1, a generator3, and a control device5. When the power generation system of the embodiment is a hydraulic power generation system, a water turbine is provided instead of wind turbine1.

Wind turbine1includes a main shaft2. Generator3includes a three-phase synchronous generator in which a permanent magnet is used. Generator3is fastened to main shaft2by a coupling or the like. As required, a speed-increasing gear may be provided between main shaft2and generator3. Wind turbine1is rotated by kinetic energy of wind, and main shaft2rotates generator3. In wind power generation system100, control device5is connected to generator3through a brake circuit4. Generator3sends generated power to control device5through brake circuit4. The generated power is converted into DC power or AC power having a different frequency by control device5and then supplied to a supply target6. For example, supply target6is a battery or a system power supply.

FIG.2is a view illustrating a brake operation by brake circuit4. Generator3outputs the generated power generated by a rotating operation to each of a power line Pu, a power line Pv, and a power line Pw as three-phase (U-phase, V-phase, and W-phase) generated power. Control device5includes a power conversion unit51. A rectifier circuit51R included in power conversion unit51receives the three-phase generated power from each of power line Pu, power line Pv, and power line Pw. Rectifier circuit51R is an alternate current (AC)/direct current (DC) converter. Rectifier circuit51R converts the three-phase generated power into DC power. Voltage sensor VS detects the generated voltage of generator3.

Brake circuit4includes a switch Sw1, a switch Sw2, a switch Sw3, a resistor R1, a resistor R2, and a resistor R3. Switch Sw1and resistor R1are connected in series between power line Pu and power line Pv. Switch Sw2and resistor R2are connected in series between power line Pv and power line Pw. Switch Sw3and resistor R3are connected in series between power line Pw and power line Pu.

Control device5electrically generates braking force by closing switches Sw1to Sw3of brake circuit4to decelerate rotation speed of wind turbine1. By short-circuiting the phases of generator3by brake circuit4, current due to an electromotive voltage generated by power generation flows through an armature of generator3. Electromagnetic induction generated by the current generates the braking force acting in a direction opposite to a direction in which the armature rotates by the wind. Hereinafter, brake in which phases are short-circuited by brake circuit4to apply the braking force to wind turbine1is referred to as “electric brake”. In addition, short-circuiting between the phases by brake circuit4is referred to as “operating the electric brake”. Furthermore, releasing switches Sw1to Sw3of brake circuit4is referred to as “stopping the electric brake” and “releasing the brake”.

Although the configuration in which the phases of power line Pu, power line Pv, and power line Pw are short-circuited in order to operate the electric brake has been described inFIG.2, the electric brake may be operated by short-circuiting power lines Pu to Pw and the ground as illustrated inFIG.3.

FIG.3is a view illustrating a configuration of a modification of the brake circuit. In brake circuit4ofFIG.3, the configuration of brake circuit4in which switches Sw1to Sw3are provided between power lines Pu, Pw, Pv and the ground is illustrated. Also in the configuration ofFIG.3, switches Sw1to Sw3are closed by a control signal from control device5, whereby the phases of generator3are short-circuited through the ground and the current flows through the armature. Therefore, the braking force can be generated with respect to wind turbine1. Brake circuit4includes a current sensor IS2that measures the current value.

FIG.4is a block diagram illustrating a function of wind power generation system100. Control device5includes power conversion unit51and a control unit52. Power conversion unit51converts the generated power received from power lines Pu, Pv, Pw inFIG.2into a format supplying the generated power to supply target6.

In addition, power conversion unit51includes an internal sensor unit InS and rectifier circuit51R. Internal sensor unit InS includes voltage sensor VS and a current sensor IS. Voltage sensor VS detects the generated voltage of generator3after rectification. Current sensor IS detects the current flowing through the circuit in power conversion unit51. Rectifier circuit51R converts the three-phase generated power received by control device5into DC power.

Control unit52includes an electric brake control unit EB and an arithmetic unit53. Arithmetic unit53includes a central processing unit (CPU) and a memory (both not illustrated). As described with reference toFIG.1, in wind power generation system100, the phases are short-circuited by brake circuit4to generate the braking force with respect to the rotation of wind turbine1. That is, when switches Sw1to Sw3of brake circuit4are closed by the control signal from electric brake control unit EB, the braking force against the rotation of wind turbine1is generated.

Arithmetic unit53receives detection signals from an external sensor unit ExS and a temperature sensor41. External sensor unit ExS includes a tachometer11and a torque meter12. Tachometer11measures the rotation speed of wind turbine1. Torque meter12detects torque generated in wind turbine1by wind. Temperature sensor41detects the temperature of brake circuit4including resistors R1to R3. External sensor unit ExS may be configured to be able to detect a charge amount of supply target6when supply target6is a battery.

FIG.5is a view illustrating map control. A horizontal axis inFIG.5represents the rotation speed of wind turbine1, and a vertical axis inFIG.5represents an output value (generated power) of generator3. In the map control, the output value of generator3is controlled by adjusting a duty ratio in performing switching control to a predetermined duty ratio according to the rotation speed. Thus, control device5can uniquely determine the output value of generator3for a certain rotation speed. For example, when wind turbine1is rotating at rotation speed a, generator3outputs an output value b.

Rotation speed L inFIG.5is a rotation speed at which cutout is executed. The cutout is a mechanical and electrical protection function of preventing excessive rotation of wind turbine1. When wind turbine1rotates at speed higher than specific speed from a mechanical and electrical viewpoint of wind turbine1, mechanical and electrical reliability of wind turbine1decreases. Hereinafter, a state in which wind turbine1is rotating at the rotation speed at which the mechanical and electrical reliability are lowered may be referred to as “overrotation”. In wind power generation system100, in order to prevent the overrotation of wind turbine1, the braking force is generated on wind turbine1to decelerate wind turbine1. Rotation speed L is previously determined based on an allowable rotation speed determined from a mechanical and electrical specification of wind turbine1. Rotation speed L may be set to a rotation speed slower than the allowable rotation speed instead of the allowable rotation speed itself. Rotation speed L is desirably set as speed at which the electric brake can be operated continuously to sufficiently decelerate. For example, it is also conceivable that the mechanical strength of wind turbine1is high and rotation speed L can be set to a high speed. However, when rotation speed L is too fast when the cutout is executed, the torque applied by the wind exceeds the braking force of the electric brake, and there is a possibility that the rotation speed of wind turbine1cannot be sufficiently decelerated. For this reason, rotation speed L is set as speed at which at least the rotation speed of wind turbine1can be decelerated when the electric brake is operated.

Furthermore, timing at which the cutout is executed may be determined based on an electrically allowable range (a rated voltage, a rated current, and the like) determined in power conversion unit51. This is because when the voltage exceeding the allowable range is applied to power conversion unit51, a failure of power conversion unit51may be generated. In this case, the timing of executing the cutout is determined according to whether the value of an output value M is within the allowable range of power conversion unit51.

As described above, in wind power generation system100, when strong wind is generated, the rotation speed of wind turbine1is decelerated based on the rotation speed of wind turbine1or the generated power of generator3from the viewpoint of mechanical and electrical protection. That is, when wind turbine1rotates at rotation speed L, control device5short-circuits the phases of generator3by brake circuit4to start the operation of the electric brake. Control device5of wind power generation system100of the embodiment continuously operates the electric brake until the release condition is satisfied after the operation of the electric brake is started.

Due to the characteristic of the electric brake, when wind turbine1receives the wind while the phases are short-circuited by brake circuit4, the rotation of wind turbine1does not completely stop. Because the electric brake operation is continuously operated after the cutout is executed, the rotation speed of wind turbine1gradually decreases from rotation speed L. Thereafter, when the braking force applied by the electric brake and the torque rotating main shaft2by the wind are balanced, an equilibrium state is obtained. As described above, the electric brake generates the braking force using the electric energy acting on the armature of generator3by receiving the wind.

Even when wind turbine1is in the equilibrium state, wind turbine1continues to rotate at a relatively slow rotation speed due to the characteristic of the electric brake having internal resistance. The rotation speed of wind turbine1in the equilibrium state is affected by the wind speed. That is, when the wind speed in the equilibrium state is high, the torque rotating main shaft2increases, and wind turbine1continues to rotate while maintaining the predetermined speed even in the equilibrium state. On the other hand, when the wind speed in the equilibrium state is weak, the torque rotating main shaft2is weakened, and wind turbine1rotates at the speed close to a stopped state in the equilibrium state. As described above, the electric brake is operated based on the generation of the strong wind, and the rotation of wind turbine1can be maintained at the rotation speed lower than rotation speed L, so that wind turbine1can be mechanically and electrically protected.

Here, when the timing at which the electric brake is released is not appropriate, there is a possibility that the power generation efficiency of wind power generation system100is lowered or wind turbine1is damaged. For example, when the timing at which the electric brake is released is late, there is a case where wind turbine1cannot be rotated although the wind speed is sufficiently weakened to the extent that normal power generation control can be performed. In this case, although there is no possibility that wind turbine1rotates excessively because the wind speed is sufficiently weakened, the electric brake is continuously operated, and the normal power generation control cannot be performed. Accordingly, power generation efficiency is reduced.

When the timing at which the electric brake is released is early, the rotation of wind turbine1is started although the wind speed is not sufficiently weakened. In wind turbine1in which the braking force is no longer applied, the rotation speed is accelerated by the strong wind, and wind turbine1is overrotated, and the cutout is executed again. That is, when the timing at which the electric brake is released is too early, processing for releasing the electric brake and the cutout are frequently repeated. As a result, the start and stop of the operation of the electric brake are frequently repeated, and the acceleration and deceleration of the rotation of wind turbine1are repeated. Thus, opening and closing operations of switches Sw1to Sw3are excessively repeated, and the degradation of brake circuit4can be promoted. In addition, the degradation of wind turbine1can be promoted by excessively repeating the acceleration and deceleration of wind turbine1.

Therefore, in the wind power generation system100, it is desirable to release the operation of the electric brake at the time when the wind speed is weakened to such an extent that the wind turbine1does not overrotate. It is conceivable to use an anemometer in order to determine the wind speed, but cost can increase because the anemometer is relatively expensive. Control determining the timing at which the electric brake is released without using the anemometer in wind power generation system100of the embodiment will be described below.

FIG.6A,FIG.6BandFIG.6Care views illustrating a relationship between the wind speed and the voltage in the wind power generation.FIG.6A,FIG.6BandFIG.6Care views illustrating a relationship with the torque acting on main shaft2by the wind. The wind speed is a wind speed around wind turbine1. The torque is torque acting on main shaft2included in wind turbine1by the wind. The torque is detected by torque meter12. As illustrated inFIG.6A, in the wind power generation, the torque acting on main shaft2by the wind is generally proportional to the square of the wind speed.

FIG.6Bis a view illustrating a relationship between the current and the torque. The current inFIG.6Bis current generated by generator3. As illustrated inFIG.6B, in the wind power generation, the torque acting on main shaft2by the wind is generally proportional to the current flowing through generator3. When the resistance value is constant, the current is proportional to the voltage. Consequently, considering the relationship between the detection value of voltage sensor VS and the wind speed based on the relationships inFIGS.6A and6B, the relationship in which the voltage is proportional to the square of the wind speed can be derived as illustrated inFIG.6C. Accordingly, using the relationship between the voltage and the wind speed inFIG.6C, the wind speed can be uniquely estimated from the detection value of voltage sensor VS. As described above, due to the characteristic of the electric brake, when the electric brake is continuously operated after the brake operation is executed by the cutout and when the strong wind is generated, the rotation of wind turbine1is not completely stopped and continues to rotate at the relatively slow speed. Accordingly, even when the electric brake is held, the relationship between the voltage and the wind speed inFIG.6Cis established.

Reference wind speed inFIG.6Cmeans a wind speed at which wind turbine1does not accelerate to rotation speed L even when the electric brake is released in the equilibrium state after the brake operation is executed by the cutout. That is, control device5can determine that the normal power generation control can be performed without frequently repeating the start and stop of the operation of the electric brake even when the electric brake is released when the rotation speed of wind turbine1becomes the reference speed. The reference wind speed is appropriately determined by an actual machine experiment or simulation. As illustrated inFIG.6C, the detection value of voltage sensor VS is a voltage value Vth at the reference wind speed. Therefore, the release condition that is the condition releasing the electric brake is a condition that the detection value of voltage sensor VS is lower than voltage value Vth.

In wind power generation system100of the embodiment, whether the wind speed is lower than the reference wind speed is determined from the detection value of voltage sensor VS using the relationship between the detection value of voltage sensor VS and the wind speed inFIG.6Cwithout using the anemometer. Thus, in wind power generation system100, the electric brake operated due to the generation of the strong wind can be released at the appropriate timing. When the electric brake is released if the wind speed is greater than or equal to the reference wind speed, the operation the start and stop of the electric brake is frequently repeated to promote the degradation of wind turbine1.

In addition, when the operation of the electric brake is not released even though the wind speed is lower than the reference wind speed, the normal power generation control cannot be performed, and the power generation efficiency decreases. In wind power generation system100, the decrease in the power generation efficiency can also be prevented by releasing the brake at the timing when the wind speed falls below the reference wind speed. Because voltage sensor VS used for the power conversion is used without providing the anemometer, wind power generation system100that performs the brake control can be implemented while suppressing an increase in cost.

Furthermore, because the number of turns of the coil of generator3is constant, the rotation speed of the rotor of generator3is proportional to the induced electromotive force. That is, control device5can derive the wind speed based on the rotation speed measured by tachometer11without using voltage sensor VS. For example, as illustrated inFIG.6C, control device5can determine that the detection value of voltage sensor VS is voltage value Vth when the rotation speed reaches rotation speed Rth. Wind power generation system100can determine whether the wind speed is the reference wind speed using rotation speed Rth.

FIG.7is a flowchart illustrating an example in which the electric brake is released using voltage sensor VS after the start of the brake operation by the cutout. Control device5determines whether the rotation speed of wind turbine1exceeds predetermined rotation speed L (step S11). When the rotation speed of wind turbine1is less than or equal to rotation speed L (NO in step S11), control device5repeats the processing of step S11. That is, wind power generation system100performs the normal power generation control assuming that no strong wind is not generated.

When the rotation speed of wind turbine1exceeds rotation speed L (YES in step S11), control device5starts the operation of the electric brake (step S12). That is, control device5controls electric brake control unit EB to close switches Sw1to Sw3of the brake circuit. The electric brake is configured to generate the braking force sufficient to decelerate the rotation speed of wind turbine1rotating at rotation speed L. Thus, the rotation speed of wind turbine1becomes the speed lower than rotation speed L.

In control device5, in the state where the electric brake is continuously operated after step S12, as described above, the braking force and the torque applied by the wind are in the equilibrium state, and wind turbine1rotates at the relatively slow speed. Control device5determines whether the release condition is satisfied based on the detection value or the rotation speed of voltage sensor VS in the equilibrium state (step S13).

The release condition in the embodiment is a condition that the detection value of voltage sensor VS is lower than voltage value Vth. The release condition may be a condition that the value of the rotation speed is lower than rotation speed Rth. In addition, the release condition may be a condition that both the condition that the detection value of voltage sensor VS is lower than voltage value Vth and the condition that the value of the rotation speed is lower than rotation speed ThR are satisfied.

Control device5determines whether the detection value of voltage sensor VS detected by voltage sensor VS is lower than voltage value Vth. When the detected value of voltage sensor VS is greater than or equal to voltage value Vth (NO in step S13), control device5repeats the processing of step S13. When the detection value of voltage sensor VS is lower than voltage value Vth (YES in step S13), control device5determines that the release condition is satisfied to release the electric brake (step S14). That is, wind power generation system100resumes the normal power generation control to supply the power to supply target6.

When the release condition is a condition that the value of the rotation speed is lower than rotation speed Rth, control device5determines that the release condition is satisfied in the case where the rotation speed measured by tachometer11is less than or equal to rotation speed Rth in the equilibrium state in which the electric brake is operating. Alternatively, control device5determines that the release condition is satisfied when both the condition that the detection value of voltage sensor VS is less than or equal to voltage value Vth and the condition that the detection value of voltage sensor VS is less than or equal to rotation speed Rth are satisfied.

As described above, in wind power generation system100of the embodiment, when the release condition determined based on at least one of the detection value of voltage sensor VS and the rotation speed of wind turbine1is satisfied during the execution of the brake operation by the cutout, the brake operation by brake circuit4is released. Thus, the electric brake at the appropriate timing can be released while preventing the increase in the cost without using the anemometer, so that the decrease in the power generation efficiency can be prevented.

First Modification

As described above, the configuration, in which the wind speed is estimated based on the detection value of voltage sensor VS in the equilibrium state and the brake is released based on whether the estimated wind speed is lower than the reference wind speed, has been described in the embodiment. In a first modification, a configuration in which the wind speed from the detection value of voltage sensor VS focusing on the resistance of brake circuit4is more accurately estimated will be described.

FIG.8AandFIG.8Bare views illustrating that the relationship between the voltage and the wind speed changes due to the change in the resistance value. As described above, wind power generation system100estimates the reference wind speed based on the detection value of voltage sensor VS. As described inFIG.6C, the detection value of voltage sensor VS is proportional to the square of the wind speed. However, a shape of a curve indicating the relationship between the detection value of voltage sensor VS and the wind speed as illustrated inFIG.6Cchanges under an influence of various external factors. For example, when a combined resistance value of resistors R1to R3included in brake circuit4varies, the line indicating the relationship between the detection value of voltage sensor VS and the wind speed changes to a line L1, a line L2, or the like as illustrated inFIG.8A.

The resistance value of each of resistors R1to R3may vary depending on the temperature around brake circuit4. Therefore, the combined resistance value of resistors R1to R3also changes depending on the temperature around brake circuit4. In general, the resistance value of the resistance increases as the temperature increases, and decreases as the temperature decreases. As illustrated inFIG.8A, line L1is a curve indicating the relationship between the detection value of voltage sensor VS and the wind speed when the temperature around brake circuit4is a temperature T1. At temperature T1, the combined resistance value of resistors R1to R3is X. Line L2is a curve indicating the relationship between the detection value of voltage sensor VS and the wind speed when the temperature around brake circuit4is a temperature T2lower than temperature T1. At temperature T2, the combined resistance value of resistors R1to R3becomes Y smaller than X.

As described above, because the combined resistance value of resistors R1to R3of brake circuit4changes depending on the temperature, an error may be generated when the wind speed is estimated only from the detection value of voltage sensor VS. Accordingly, control device5of the first modification estimates the wind speed in consideration of the temperature.FIG.9AandFIG.9Bare views illustrating an example in which the detection value of voltage sensor VS is corrected based on the temperature.FIG.9Ais a flowchart correcting the detection value of voltage sensor VS. Control device5executes the flowchart inFIG.9Ain step S13ofFIG.7. Control device5acquires the temperature detected by temperature sensor41(step S20). After acquiring the temperature, control device5acquires a resistance temperature coefficient corresponding to the acquired temperature (step S21). The resistance temperature coefficient is a coefficient indicating a rate of change in the resistance value of resistors R1to R3due to the temperature change.

Control device5corrects the combined resistance value based on the resistance temperature coefficient (step S22). After correcting the combined resistance value, control device5corrects the detection value of voltage sensor VS using a calculation formula inFIG.9B.

Thus, in wind power generation system100, the wind speed can be estimated more accurately. That is, control device5can estimate the wind speed more accurately from the detection value of voltage sensor VS in consideration of the change in the resistance value due to the temperature change, so that the electric brake can be released at the appropriate timing.

Second Modification

As described above, the configuration in which wind power generation system100estimates the wind speed based on the relationship between the parameters such as the voltage, the torque, the current, the rotation speed, the resistance value, and the temperature without using the anemometer has been described. However, in an actual environment, the relationship between the above-described parameters is affected by various external factors other than the above-described parameters. It is difficult to consider all kinds of these external factors in a wide range. Accordingly, in a second modification, an example in which more accurate estimation is performed using artificial intelligence that finds a feature of the relationship with each parameter using teacher data will be described.

FIG.10is a view illustrating a configuration of a wind power generation system101acquiring a learning model. In the configuration of wind power generation system101inFIG.10, the same configuration as that of wind power generation system100will not be described again. External sensor unit ExS of wind power generation system101includes an anemometer13.

Wind power generation system101generates learning data. That is, arithmetic unit53of wind power generation system101accumulates the wind speed actually measured by anemometer13in a database200. Arithmetic unit53of wind power generation system101further acquires the detection value of voltage sensor VS at the same time as the time when the wind speed is measured, the temperature detected by temperature sensor41, the rotation speed measured by tachometer11, and the torque detected by torque meter12, and accumulates them in database200as the learning data. Database200is stored in a server or the like separate from wind power generation system101.

Database200stores the actual wind speed, the detection value of voltage sensor VS at the same time, and the like. That is, in database200, the detection value of voltage sensor VS is associated with the wind speed. Similarly, in database200, the rotation speed is associated with the wind speed. Wind power generation system100of the embodiment generates the learning model using the artificial intelligence from the learning data generated by wind power generation system101. With the generated learning model, the wind speed can be estimated with higher accuracy using the parameter such as the detection value of voltage sensor VS as an input value. Thus, when the feature can be further found from the relationship between the parameters using the artificial intelligence, in wind power generation system100, the accuracy of the estimated wind power value can be improved using the learning model.

It should be considered that the disclosed embodiment is an example in all respects and not restrictive. The scope of the present invention is defined by not the description above, but the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included in the present invention. In addition, the control device of the present invention can be applied not only to the wind power generation system but also to the hydraulic power generation system and the like.

REFERENCE SIGNS LIST

1: wind turbine,2: main shaft,3: generator,4: brake circuit,5: control device,6: supply target,11: tachometer,12: torque meter,13: anemometer,41: temperature sensor,51: power conversion unit,51R: rectifier circuit,52: control unit,53: arithmetic unit,100,100A,101: wind power generation system,200: database, EB: electric brake control unit, ExS: external sensor unit, IS, IS2: current sensor, InS: internal sensor unit, L, Rth, a: rotation speed, L1, L2: line, M, b: output value, Pu, Pv, Pw: power line, R1to R3: resistor, Sw1to Sw3: switch, T1to T3: temperature, Vth: voltage value, VS: voltage sensor, X, Y, Z: combined resistance value, c1to c3: coil, r1to r3: internal resistance