Control device for power generation system

Abstract

To suppress the excessive rotation of a rotator while suppressing power consumption in a control device of a generation system equipped with a mechanical brake and an electric brake.SOLUTION: A generation system is equipped with a rotator, a generator, a brake circuit, a brake device, and a control device. The control device controls the brake circuit and the brake device. The control device controls the brake device to start brake action when the rotation speed of the rotator exceeds a rotation speed L. After the rotation speed of the rotator falls below a first threshold value, a switching condition determined based on the rotation speed of the rotator and torque generated on the rotator is established, the brake device is controlled to stop the brake action and short-circuit the brake circuit.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to a control device for a power generation system, and particularly to a control device for suppressing power consumption.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2018-096236 (Patent Document 1) discloses a windmill control device including an electric brake unit and a mechanical brake unit. The electric brake unit performs a braking operation (so-called short brake) that generates a force against the rotational force of the windmill by short-circuit braking to short-circuit an electric circuit. Further, the mechanical brake unit includes a contact member that acts on at least one of the interlocking members interlocked with the windmill as an acted-on part, and performs a braking operation that generates a braking force by the frictional force between the contact member and the acted-on part.

[0003] In the windmill control device of Patent Document 1, when the wind speed becomes equal to or higher than a threshold value, the electric brake unit is made to perform a braking operation, and then, in response to a predetermined switching condition being satisfied, in addition to the electric brake unit, the mechanical brake unit is made to perform a braking operation, thereby reducing the impact during braking.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the braking force of the electric brake is proportional to the rotational speed of the wind turbine, depending on the rotational speed of the wind turbine, the electric brake may not be able to generate sufficient braking force to brake the wind turbine. On the other hand, the mechanical brake can generate a braking force stronger than that generated by the electric brake without depending on the rotational speed of the wind turbine. However, generally, the mechanical brake requires an external power supply to perform the braking operation. This is not limited to wind turbines but also applies to hydropower generation.

[0006] In the wind turbine control device of Patent Document 1, after driving the electric brake, it is switched to the mechanical brake. Thereby, after stopping the wind turbine, by continuously driving the mechanical brake, the state in which the wind turbine stops is maintained. Due to the characteristics of the mechanical brake, even when the wind turbine is completely stopped in a windless state, power is consumed in the mechanical brake for driving. In the wind turbine control device of Patent Document 1, when the driving time of the mechanical brake becomes long, the power consumption of the mechanical brake can increase.

[0007] The present disclosure has been made to solve such problems, and an object thereof is to suppress over-rotation of a rotating body while suppressing power consumption in a control device of a power generation system including a mechanical brake and an electric brake.

Means for Solving the Problems

[0008] The control device according to the present disclosure is a control device for controlling a power generation system that supplies power to a supply target. The power generation system includes a rotating body, a generator, a brake circuit, a brake device, and a control device. The generator is rotated by the rotating body and generates three-phase AC power. The brake circuit is connected to the generator and generates a braking force on the rotating body by short-circuiting between phases. The brake device generates a braking force on the rotating body by frictional force. The control device controls the brake circuit and the brake device. When the rotational speed of the rotating body exceeds a first threshold value, the control device controls the brake device to start a braking operation. After the rotational speed of the rotating body falls below the first threshold value, when a switching condition determined based on the rotational speed of the rotating body and the torque generated on the rotating body is satisfied, the control device stops the braking operation of the brake device and executes the braking operation by the brake circuit.

Effect of the Invention

[0009] The control device of the power generation system according to the present disclosure operates a mechanical brake to decelerate the rotating body when the rotational speed of the rotating body becomes excessively large exceeding a first threshold value, and switches from the mechanical brake to an electric brake with low power consumption when the rotating body can be decelerated even by the electric brake. Thereby, over-rotation of the rotating body can be suppressed while suppressing power consumption.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0012] [Embodiment 1] FIG. 1 is a schematic diagram showing the configuration of a wind power generation system 100 in Embodiment 1. The wind power generation system 100 is an example of a horizontal axis type (propeller type) wind power generation system. As shown in FIG. 1, the wind power generation system 100 includes a windmill 1, a generator 3, and a control device 5. When applying the power generation system of this embodiment to hydroelectric power generation, a water turbine is provided instead of the windmill 1.

[0013] The windmill 1 includes a main shaft 2. The generator 3 includes a three-phase synchronous generator using permanent magnets. The generator 3 in Embodiment 1 generates electricity using a coil wound around an iron core. That is, the stator base of the generator 3 is made of a magnetic material, and the coil is wound around the magnetic material. Hereinafter, the structure in which the coil is wound around the magnetic material is referred to as a core structure. Note that the generator 3 may have a coreless structure made of a non-magnetic material. The coreless structure is a structure in which one or a plurality of coils are arranged in concentrated winding in the circumferential direction of the stator base of the generator 3.

[0014] The generator 3 is fastened to the main shaft 2 by a coupling or the like. If necessary, a speed increaser may be provided between the main shaft 2 and the generator 3. The windmill 1 is rotated by the kinetic energy of the wind, and the main shaft 2 rotates the generator 3. The generator 3 outputs the generated electric power as three-phase (U-phase, V-phase, and W-phase) power to the power lines Pu, Pv, and Pw, respectively. In the wind power generation system 100, a control device 5 is connected to the generator 3 via a brake circuit 4. The control device 5 receives three-phase power from the power lines Pu, Pv, and Pw, respectively. The control device 5 controls the received three-phase power. The three-phase power is converted into DC power or AC power with different frequencies by the control device 5 and then supplied to the supply target 6. The supply target 6 is, for example, a battery or a grid power source, etc.

[0015] The brake circuit 4 includes a switch Sw1, a switch Sw2, a switch Sw3, a resistor R1, a resistor R2, and a resistor R3. The switch Sw1 and the resistor R1 are connected in series between the power line Pu and the power line Pv. The switch Sw2 and the resistor R2 are connected in series between the power line Pv and the power line Pw. The switch Sw3 and the resistor R3 are connected in series between the power line Pw and the power line Pu.

[0016] The control device 5 generates an electrical braking force by short-circuiting the switches Sw1 to Sw3 of the brake circuit 4 to reduce the rotational speed of the windmill 1. That is, by short-circuiting the phases of the generator 3 by the brake circuit 4, a current flows through the armature of the generator 3. Due to the electromagnetic induction caused by this, a braking force acting in the direction opposite to the direction in which the armature rotates is generated.

[0017] FIG. 2 is a block diagram for explaining the functions of the wind power generation system 100. The control device 5 includes a power conversion unit 51 and a control unit 52. The power conversion unit 51 converts the power received from the power lines Pu, Pv, and Pw into a form for supplying to the supply target 6. The power conversion unit 51 includes, for example, an inverter and an AC (Alternate Current) / DC (Direct Current) converter. In the wind power generation system 100, the generated power is supplied to the supply target 6 using the power received from the power lines Pu, Pv, and Pw.

[0018] The power conversion unit 51 includes an internal sensor unit InS. The internal sensor unit InS includes a voltage sensor VS and a current sensor IS. The voltage sensor VS detects the generated voltage of the generator 3. The current sensor IS detects the current flowing through the circuit in the power conversion unit 51. The internal sensor unit InS may detect the charge amount of the supply target 6.

[0019] The control unit 52 includes a CPU (Central Processing Unit) and a memory. The control unit 52 includes an electric brake control unit EB, a mechanical brake control unit MB, and a state monitoring unit 53. As described with reference to FIG. 1, in the wind power generation system 100, by short-circuiting the brake circuit 4, a braking force is generated against the rotation of the windmill 1. That is, when the switches Sw1 to Sw3 of the brake circuit 4 are closed by the electric brake control unit EB, a braking force against the rotation of the windmill 1 is generated. Hereinafter, short-circuiting the switch in the brake circuit by the control signal from the electric brake control unit EB is referred to as "the electric brake is driven". The characteristics of the electric brake controlled by the electric brake control unit EB differ depending on whether the structure of the generator 3 is a core structure or a coreless structure, as will be described later.

[0020] The mechanical brake control unit MB controls the brake device 7 included in the wind turbine 1. The brake device 7 is, for example, a drum brake or a disk brake, and has a friction material 71 such as a brake shoe or a brake pad. When the friction material 71 comes into contact with a member interlocked with the rotating wind turbine, a frictional force is generated. Thereby, a braking force is generated on the wind turbine 1. Hereinafter, the control of the brake device by the mechanical brake control unit MB so that the member interlocked with the wind turbine 1 and the friction material 71 are in contact with each other is referred to as "the mechanical brake is driven". The mechanism by which the mechanical brake control unit MB operates the friction material 71 may employ an electromagnetic type, a fluid type using hydraulic pressure or pneumatic pressure, or the like.

[0021] The state monitoring unit 53 is connected to the external sensor unit ExS. The external sensor unit ExS includes a tachometer 11, a torque meter 12, and an anemometer 13. The tachometer 11 and the torque meter 12 detect information regarding the wind turbine 1. The tachometer 11 detects the rotational speed of the wind turbine 1. The torque meter 12 detects the torque generated in the wind turbine 1. The anemometer 13 detects the wind speed at the location where the wind turbine 1 is installed.

[0022] FIG. 3 is a diagram for explaining map control. The horizontal axis in FIG. 3 indicates the rotational speed of the wind turbine 1, and the vertical axis in FIG. 3 indicates the output value (generated power) of the generator 3. The output value of the generator 3 changes according to the magnitude of the current. In map control, the output value of the generator 3 is controlled by adjusting the duty ratio during power conversion, etc., to a duty ratio predetermined according to the rotational speed. Thereby, for a certain rotational speed, the output value of the generator 3 can be uniquely determined. For example, when the rotational speed of the wind turbine 1 is the rotational speed L, the output value output by the generator 3 is the output value M. Here, the rotational speed L is a predetermined rotational speed at which cutout is executed.

[0023] That is, when the rotational speed exceeds the rotational speed L, the control device 5 executes a cutout. Cutout is a mechanical protection function for braking the rotation of the wind turbine 1 in order to prevent the wind turbine 1 from malfunctioning due to over-rotation beyond the mechanical allowable range. That is, if the wind turbine 1 rotates at a speed exceeding the rotational speed L, the wind turbine 1 rotates excessively, and the mechanical reliability of the wind turbine 1 decreases. Therefore, in the wind power generation system 100, when the rotational speed of the wind turbine 1 exceeds the rotational speed L, a braking force is generated on the wind turbine 1 to decelerate it. That is, the rotational speed L at which the cutout is executed is the rotational speed at which the rotational speed of the wind turbine 1 becomes the allowable rotational speed determined from the mechanical specifications of the wind turbine 1. Alternatively, the rotational speed L may be a rotational speed slower than the allowable rotational speed so as to have a margin from the allowable rotational speed. Also, the timing at which the cutout is executed may be determined not only from the perspective of mechanical reliability but also from the perspective of electrical circuit protection. For example, an allowable range of the generated voltage is defined for the power conversion unit 51. If a generated voltage exceeding the allowable range is applied to the power conversion unit 51, a failure may occur. Therefore, the rotational speed at which the cutout is executed may be determined according to whether the value of the output value M is within the allowable range of the power conversion unit 51.

[0024] Figure 4 is a diagram for comparing the characteristics of the mechanical brake and the electric brake. The horizontal axis in Figure 4 indicates the rotational speed of the wind turbine 1, and the vertical axis in Figure 4 indicates the braking force generated by each brake. The magnitude of the braking force is expressed as torque.

[0025] Line L1 indicates the braking force of the mechanical brake. The braking force of the mechanical brake does not depend on the rotational speed of the wind turbine 1, and a braking force of a constant torque Tb acts on the wind turbine 1. Line L2 indicates the braking force of the electric brake when the generator 3 has a core structure. Line L3 indicates the braking force of the electric brake when the generator 3 has a coreless structure. When the generator 3 has a coreless structure, the braking force of the electric brake is proportional to the rotational speed as shown in Figure 4. That is, the higher the rotational speed, the stronger the braking force of the electric brake.

[0026] When the generator 3 has a core structure, the braking force of the electric brake has a large inductance value with respect to the internal resistance value, and the reactance component increases depending on the rotational speed (frequency), so a torque saturation phenomenon occurs. Therefore, as shown in FIG. 4, the torque Ta, which is the maximum torque, is obtained at the rotational speed A. That is, the rotational speed A is the rotational speed at which the braking force by the brake circuit 4 becomes maximum. Region D1 indicates a region of rotational speed faster than the rotational speed A at which saturation occurs in FIG. 4. Region D2 indicates a region of rotational speed slower than the rotational speed A at which torque saturation occurs in FIG. 4.

[0027] As described above, saturation occurs when the generator 3 has a core structure, and torque saturation is less likely to occur when the generator has a coreless structure. Also, regarding the mechanical brake and the electric brake, as described above, the mechanical brake requires external power consumption, but as shown in FIG. 4, it can generate a strong braking force. On the other hand, the electric brake does not require external power consumption, but as shown in FIG. 4, the braking force that can be generated is weaker compared to the mechanical brake.

[0028] FIG. 5 is a diagram showing the torque of the windmill 1 generated by the wind. The horizontal axis in FIG. 5 indicates the rotational speed of the windmill 1, and the vertical axis in FIG. 5 indicates the torque generated in the windmill 1. As shown in FIG. 5, as a characteristic of a general windmill, the generated torque reaches a peak at a predetermined rotational speed. That is, as shown in FIG. 5, the maximum torque TY is generated in the windmill 1 when the rotational speed is X.

[0029] That is, the slower the rotational speed of the windmill 1 is than the rotational speed X, the smaller the braking torque required to brake the windmill 1 becomes. For example, at a rotational speed close to the stop state of the windmill 1, almost no braking torque is required to brake the windmill 1. Therefore, driving a mechanical brake with a strong braking force as shown in FIG. 4 at a rotational speed close to the stop state will apply a braking torque more than necessary and consume more power than necessary.

[0030] FIG. 6 is a flowchart for executing the braking process of the wind turbine 1 after cutout in Embodiment 1. The control device 5 determines whether or not the rotational speed of the wind turbine 1 exceeds a predetermined rotational speed L (step S1). The rotational speed L is the rotational speed at which cutout is executed. The state where the rotational speed of the wind turbine 1 exceeds the rotational speed L is, for example, a state where a storm or strong wind occurs and the wind turbine 1 can rotate excessively. When the rotational speed of the wind turbine 1 is less than the rotational speed L (NO in step S1), the control device 5 repeats the process of step S1. That is, assuming that no storm or strong wind occurs, the wind power generation system 100 executes normal power generation control.

[0031] When the rotational speed of the wind turbine 1 exceeds the rotational speed L (YES in step S1), the control device 5 drives the mechanical brake (step S2). That is, the control device 5 controls the brake device 7 to start the braking operation. The brake device 7 is configured to be able to generate a braking force sufficient to decelerate the rotational speed of the wind turbine 1 rotating at the rotational speed L. As a result, the rotational speed of the wind turbine 1 becomes at least slower than the rotational speed L. After driving the mechanical brake, the control device 5 determines whether or not the switching condition is satisfied (step S3).

[0032] The switching condition is a condition for determining whether the wind turbine 1 can be sufficiently braked by the electric brake. In Embodiment 1, the control device 5 determines that the switching condition is satisfied when the rotational speed of the wind turbine 1 reaches the rotational speed A shown in FIG. 4 and the torque detected by the torque meter 12 is equal to or less than a predetermined reference torque. That is, the switching condition is determined based on the rotational speed of the wind turbine 1 and the torque generated in the wind turbine 1. Since the generator 3 in Embodiment 1 is a generator having a core structure, the relationship between the braking force of the electric brake and the rotational speed is shown by line L2 in FIG. 4. As shown by line L2, the rotational speed A is the rotational speed at which the braking force is maximized when the generator 3 has a core structure. In the wind power generation system 100 in Embodiment 1, by setting the timing for switching from the mechanical brake to the electric brake to the timing at which the braking force of the electric brake is maximized, the timing at which the switching condition is satisfied can be advanced. Thereby, the driving time of the mechanical brake can be shortened, and power consumption can be suppressed. Further, in step S2, since the mechanical brake is driven, the control device 5 can reduce the rotational speed of the wind turbine 1 from the rotational speed L at which the mechanical reliability of the wind turbine 1 or the reliability of the power conversion unit 51 may decrease.

[0033] Further, the switching condition may be determined based on conditions other than the rotational speed of the wind turbine 1 and the torque generated in the wind turbine 1. For example, the switching condition includes at least one of the conditions that a reference period has elapsed since the driving of the mechanical brake was started, the wind speed detected by the anemometer 13 has dropped below the reference wind speed, the current flowing through the armature coil of the generator 3 has dropped below the reference current, and the generated voltage has dropped below the reference voltage. The reference torque, the reference period, the reference wind speed, the reference current, and the reference voltage can be appropriately determined by actual machine experiments or simulations. The switching condition may be determined based only on the rotational speed without using torque. When torque is not used, the switching condition may be, for example, that the rotation of the wind turbine 1 has completely stopped.

[0034] When the switching condition is not satisfied (NO in step S3), the control device 5 repeats the process of step S3. When the switching condition is satisfied (YES in step S3), the control device 5 stops driving the mechanical brake and drives the electric brake (step S4). After driving the electric brake, the control device 5 determines whether the wind speed measured by the anemometer 13 is lower than the lower limit value (step S5). The lower limit value is, for example, the wind speed indicating that the environment where the wind turbine 1 is installed is no longer in a storm or strong wind state, and is a predetermined wind speed. When the wind speed is equal to or higher than the lower limit value (NO in step S5), the control device 5 repeats the process. That is, the state in which the electric brake is driven is maintained. When the wind speed is lower than the lower limit value (YES in step S5), the control device 5 stops driving the electric brake (step S6) and ends the process. That is, the wind power generation system 100 resumes normal power generation control and supplies power to the supply target 6.

[0035] As described above, in the wind power generation system 100 according to the first embodiment, when the rotational speed of the wind turbine 1 exceeds the rotational speed L, the mechanical brake is driven. Thereby, a strong braking force can be generated by the mechanical brake, and the rotational speed of the wind turbine 1 can be decelerated to be equal to or lower than the allowable rotational speed.

[0036] Further, when the rotational speed of the wind turbine 1 is sufficiently decelerated and the switching condition to the electric brake is satisfied, the driving of the mechanical brake can be stopped and switched to the electric brake. Thereby, in the wind power generation system 100, the driving time of the mechanical brake can be shortened, and while suppressing the power consumption for driving the mechanical brake, the over-rotation of the wind turbine 1 can be suppressed.

[0037] [Second Embodiment] In the wind power generation system 100 according to Embodiment 1, the control for driving the mechanical brake at the timing when a strong braking force is required was described. In Embodiment 2, the control for driving the electric brake in addition to the mechanical brake to perform early deceleration in a state where a strong braking force is required will be described. Note that in the wind power generation system 100 according to Embodiment 2, the description of the configuration overlapping with the wind power generation system 100 according to Embodiment 1 will not be repeated.

[0038] FIG. 7 is a flowchart for executing the braking process of the windmill 1 after cutout in Embodiment 2. In Embodiment 2, the control device 5 executes steps S2a and S4a in FIG. 7 instead of steps S2 and S4 in the flowchart shown in FIG. 6, respectively.

[0039] When the rotational speed exceeds the rotational speed L (YES in step S1), the control device 5 drives both the mechanical brake and the electric brake (step S2a). Thereby, a stronger braking force can be generated as compared with the case where only the mechanical brake is driven, and the timing at which the switching condition is satisfied can be advanced. That is, the driving time of the mechanical brake can be further shortened. Further, when the switching condition is satisfied (YES in step S3), the control device 5 stops driving the mechanical brake (step S4a). Thereby, in the wind power generation system 100 according to Embodiment 2, after the switching condition is satisfied, it is possible to control to a state where only the electric brake is driven.

[0040] It should be considered that all the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the scope of claims, and it is intended that all modifications within the meaning and scope equivalent to the scope of claims are included. Further, although this control device has shown an application example to a wind power generation system, it can also be applied to a hydraulic power generation system.

Explanation of Reference Numerals

[0041] 1 Windmill, 2 Main shaft, 3 Generator, 4 Brake circuit, 5 Control device, 6 Supply target, 11 Tachometer, 12 Torque meter, 13 Anemometer, 51 Power conversion unit, 52 Control unit, 53 Condition monitoring unit, 100 Wind power generation system, A, L, X Rotational speed, D1, D2 Region, EB Electric brake control unit, ExS External sensor unit, IS Current sensor, InS Internal sensor unit, L1~L3 Lines, Pu, Pv, Pw Power lines, R1~R3 Resistors, Sw1~Sw3 Switches, TY, Ta, Tb Torque, VS Voltage sensor.

Claims

1. A control device for a power generation system that supplies power to a supply target, wherein the power generation system includes: a rotating body; a generator rotated by the rotating body to generate three-phase AC power; a brake circuit connected to the generator and configured to generate a braking force on the rotating body by short-circuiting between phases; a brake device that generates a braking force on the rotating body by frictional force; and a control device that controls the brake circuit and the brake device, wherein the control device: controls the brake device so that the brake device starts a braking operation when the rotational speed of the rotating body exceeds a first threshold; after the rotational speed of the rotating body falls below the first threshold, when a switching condition determined based on the rotational speed of the rotating body and the torque generated in the rotating body is satisfied, stops the braking operation of the brake device and executes a braking operation by the brake circuit.

2. The rotating body is rotated by wind, and the switching condition further includes at least one of the conditions that a reference period has elapsed after the brake device starts a braking operation and that the wind speed has dropped below a reference wind speed. The control device according to claim 1.

3. The generator includes an iron core and a coil wound around the iron core, the switching condition includes the condition that the rotational speed of the rotating body has dropped below a second threshold that is lower than the first threshold, and the second threshold is the rotational speed at which the braking force by short-circuiting the brake circuit is maximized. The control device according to claim 1 or claim 2.

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