JP7692276B2 - Power generation system control device - Google Patents

Description

This disclosure relates to a control device for a power generation system, and in particular to a control device that reduces power consumption.

JP 2018-096236 A (Patent Document 1) discloses a wind turbine control device equipped with 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 wind turbine by short-circuiting the electric circuit. In addition, the mechanical brake unit has a contact member that acts on at least one of the interlocking members that interlock with the wind turbine as the acted upon part, and performs a braking operation that generates a braking force by the frictional force between the contact member and the acted upon part.

In the wind turbine control device of Patent Document 1, when the wind speed exceeds a threshold, the electric brake unit performs a braking operation, and then, when a predetermined switching condition is met, the mechanical brake unit performs a braking operation in addition to the electric brake unit, thereby reducing the impact during braking.

JP 2018-096236 A

The strength of the braking force of an electric brake is proportional to the rotational speed of the wind turbine, so depending on the rotational speed of the wind turbine, the electric brake may not be able to generate sufficient braking force to stop the wind turbine. On the other hand, a mechanical brake can generate a braking force stronger than that generated by an electric brake, regardless of the rotational speed of the wind turbine. However, mechanical brakes generally require an external power supply to perform the braking operation. This is true not only for wind turbines, but also for hydroelectric power generation.

In the wind turbine control device of Patent Document 1, the electric brake is activated and then the mechanical brake is activated. As a result, after the wind turbine is stopped, the mechanical brake is kept activated, thereby maintaining the wind turbine in a stopped state. Due to the characteristics of the mechanical brake, even when there is no wind and the wind turbine is completely stopped, the mechanical brake consumes power to operate. In the wind turbine control device of Patent Document 1, if the operating time of the mechanical brake is long, the power consumption of the mechanical brake may increase.

This disclosure has been made to solve these problems, and its purpose is to suppress over-rotation of a rotor while suppressing power consumption in a control device for a power generation system equipped with a mechanical brake and an electric brake.

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 brake force on the rotating body by shorting the phases. The brake device generates a brake force on the rotating body by frictional force. The control device controls the brake circuit and the brake device. When the rotation speed of the rotating body exceeds a first threshold, the control device controls the brake device to start a brake operation, and when a switching condition is established based on the rotation speed of the rotating body and the torque generated in the rotating body after the rotation speed of the rotating body falls below the first threshold, the control device stops the brake operation of the brake device and executes a brake operation by the brake circuit.

The control device for the power generation system according to the present disclosure operates the mechanical brake to slow down the rotor when the rotation speed of the rotor exceeds a first threshold value, and switches from the mechanical brake to an electric brake that consumes less power when the rotor can be decelerated with the electric brake. This makes it possible to suppress over-rotation of the rotor while suppressing power consumption.

1 is a schematic diagram showing a configuration of a wind power generation system according to a first embodiment. FIG. 2 is a block diagram for explaining the function of the wind power generation system. FIG. 11 is a diagram for explaining map control. FIG. 11 is a diagram for comparing the characteristics of a mechanical brake and an electric brake of each structure. FIG. 2 is a diagram showing the torque of the wind turbine 1 generated by wind. 10 is a flowchart illustrating a process for braking the wind turbine after cutout in the first embodiment. 13 is a flowchart illustrating a process for braking the wind turbine after cutout in the second embodiment.

The following describes in detail the embodiments of the present disclosure with reference to the drawings. Note that the same or corresponding parts in the drawings are given the same reference numerals and their description will not be repeated.

[First embodiment]
Fig. 1 is a schematic diagram showing the configuration of a wind power generation system 100 in the first embodiment. 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 wind turbine 1, a generator 3, and a control device 5. When the power generation system of this embodiment is applied to hydroelectric power generation, a water turbine is provided instead of the wind turbine 1.

The wind turbine 1 includes a main shaft 2. The generator 3 includes a three-phase synchronous generator that uses permanent magnets. The generator 3 in the first embodiment 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. The generator 3 may also be a coreless structure made of a non-magnetic material. The coreless structure is a structure in which one or more coils are arranged in a concentrated winding in the circumferential direction of the stator base of the generator 3.

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 wind turbine 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 power generated by the rotational operation 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, the generator 3 is connected to the control device 5 via the 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 by the control device 5 into DC power or AC power of a different frequency, and then supplied to the supply target 6. The supply target 6 is, for example, a battery or a system power source.

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.

The control device 5 shorts the switches Sw1 to Sw3 of the brake circuit 4 to generate an electrical braking force and reduce the rotational speed of the wind turbine 1. In other words, by shorting the phases of the generator 3 with the brake circuit 4, a current flows through the armature of the generator 3. The resulting electromagnetic induction generates a braking force that acts in the opposite direction to the direction in which the armature rotates.

Figure 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 format for supplying the power 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, generated power is supplied to the supply target 6 using the power received from the power lines Pu, Pv, and Pw.

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 a circuit within the power conversion unit 51. The internal sensor unit InS may detect the charge amount of the supply target 6.

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 in FIG. 1, in the wind power generation system 100, a braking force is generated against the rotation of the wind turbine 1 by shorting the brake circuit 4. That is, a braking force against the rotation of the wind turbine 1 is generated by closing the switches Sw1 to Sw3 of the brake circuit 4 by the electric brake control unit EB. Hereinafter, shorting the switches in the brake circuit by a control signal from the electric brake control unit EB is referred to as "driving the electric brake." 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.

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 disc brake, and has friction material 71 such as a brake shoe or brake pad. Frictional force is generated when the friction material 71 comes into contact with a member that is linked to the rotating wind turbine. This generates a braking force on the wind turbine 1. Hereinafter, the mechanical brake control unit MB controlling the brake device so that the member that is linked to the wind turbine 1 comes into contact with the friction material 71 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 be electromagnetic, or a fluid type that uses hydraulics or air pressure.

The status 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 related to 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.

Figure 3 is a diagram for explaining map control. The horizontal axis in Figure 3 indicates the rotation speed of the wind turbine 1, and the vertical axis in Figure 3 indicates the output value (generated power) of the generator 3. The output value of the generator 3 changes depending on 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 to a duty ratio that is predetermined depending on the rotation speed. This makes it possible to uniquely determine the output value of the generator 3 for a certain rotation speed. For example, when the rotation speed of the wind turbine 1 is rotation speed L, the output value output by the generator 3 is output value M. Here, rotation speed L is the predetermined rotation speed at which cutout is performed.

That is, when the rotation speed exceeds the rotation speed L, the control device 5 executes the cutout. The cutout is a mechanical protection function for braking the rotation of the wind turbine 1 to prevent the wind turbine 1 from breaking down due to the wind turbine 1 over-rotating and exceeding the mechanical tolerance. That is, if the wind turbine 1 rotates at a speed exceeding the rotation 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 rotation speed of the wind turbine 1 exceeds the rotation speed L, a braking force is generated on the wind turbine 1 to slow it down. That is, the rotation speed L at which the cutout is executed is the rotation speed at which the rotation speed of the wind turbine 1 becomes the allowable rotation speed determined from the mechanical specifications of the wind turbine 1. Alternatively, the rotation speed L may be a rotation speed slower than the allowable rotation speed so as to have a margin from the allowable rotation speed. In addition, 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, the power conversion unit 51 has a set allowable range of the generated voltage. If the power conversion unit 51 is subjected to a power generation voltage that exceeds the allowable range, a malfunction may occur. Therefore, the rotation speed at which cutout is performed may be determined depending on whether the value of the output value M is within the allowable range of the power conversion unit 51.

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

Line L1 shows the braking force of the mechanical brake. The braking force of the mechanical brake is not dependent on the rotational speed of the wind turbine 1, and a constant torque Tb of braking force acts on the wind turbine 1. Line L2 shows the braking force of the electric brake when the generator 3 has a core structure. Line L3 shows 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. In other words, the faster the rotational speed, the stronger the braking force of the electric brake.

When the generator 3 has a core structure, the braking force of the electric brake has a large inductor value relative to the internal resistance value, and the reactance component increases depending on the rotation speed (frequency), causing a torque saturation phenomenon, resulting in a maximum torque Ta at rotation speed A as shown in Figure 4. In other words, rotation speed A is the rotation speed at which the braking force by the brake circuit 4 is maximum. Region D1 in Figure 4 shows a region of rotation speeds faster than rotation speed A where saturation occurs. Region D2 in Figure 4 shows a region of rotation speeds slower than rotation speed A where torque saturation occurs.

As described above, when the generator 3 has a core structure, saturation occurs, whereas when it has a coreless structure, torque saturation is unlikely to occur. As for mechanical brakes and electric brakes, as described above, mechanical brakes require external power consumption, but can generate a strong braking force as shown in Figure 4. On the other hand, electric brakes do not require external power consumption, but can generate a weaker braking force than mechanical brakes, as shown in Figure 4.

Figure 5 is a diagram showing the torque of the wind turbine 1 generated by the wind. The horizontal axis in Figure 5 indicates the rotational speed of the wind turbine 1, and the vertical axis in Figure 5 indicates the torque generated in the wind turbine 1. As shown in Figure 5, a typical characteristic of a wind turbine is that the generated torque reaches a peak at a certain rotational speed. That is, as shown in Figure 5, when the rotational speed is X, maximum torque TY is generated in the wind turbine 1.

In other words, the slower the rotation speed of the wind turbine 1 is relative to rotation speed X, the less brake torque is required to brake the wind turbine 1. For example, at a rotation speed close to the wind turbine 1 being stopped, almost no brake torque is required to brake the wind turbine 1. Therefore, at a rotation speed close to the stopped state, driving a mechanical brake with a strong braking force as shown in Figure 4 will apply more brake torque than necessary, consuming more power than necessary.

Figure 6 is a flow chart for executing the braking process for the wind turbine 1 after cutout in the first embodiment. The control device 5 judges whether 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. A state in which the rotational speed of the wind turbine 1 exceeds the rotational speed L is, for example, a state in which a storm or strong wind has occurred and the wind turbine 1 may rotate excessively. If 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. In other words, the wind power generation system 100 executes normal power generation control assuming that a storm or strong wind has not occurred.

When the rotational speed of the wind turbine 1 exceeds the rotational speed L (YES in step S1), the control device 5 activates 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 generate a braking force sufficient to decelerate the rotational speed of the wind turbine 1, which rotates 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 activating the mechanical brake, the control device 5 determines whether the switching condition is met (step S3).

The switching condition is a condition for determining whether the wind turbine 1 can be sufficiently braked by the electric brake. In the first embodiment, the control device 5 determines that the switching condition is satisfied when the rotation speed of the wind turbine 1 becomes the rotation 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 rotation speed of the wind turbine 1 and the torque generated in the wind turbine 1. Since the generator 3 in the first embodiment is a generator having a core structure, the relationship between the braking force of the electric brake and the rotation speed is shown by the line L2 in FIG. 4. As shown by the line L2, the rotation speed A is the rotation speed at which the braking force is maximized when the generator 3 has a core structure. In the wind power generation system 100 in the first embodiment, the timing at which the switching condition is satisfied can be made earlier by setting the timing at which the switching from the mechanical brake to the electric brake is maximized. This makes it possible to shorten the driving time of the mechanical brake and suppress power consumption. Furthermore, in step S2, the mechanical brake is activated, so that 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.

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

If the switching condition is not satisfied (NO in step S3), the control device 5 repeats the process of step S3. If 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 falls below the lower limit (step S5). The lower limit is, for example, a wind speed that indicates that the environment in which the wind turbine 1 is installed is no longer in a storm or strong wind state, and is a predetermined wind speed. If the wind speed is equal to or greater than the lower limit (NO in step S5), the control device 5 repeats the process. That is, the electric brake is maintained in the driven state. If the wind speed falls below the lower limit (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.

In this way, in the wind power generation system 100 of the first embodiment, when the rotational speed of the wind turbine 1 exceeds the rotational speed L, the mechanical brake is activated. This allows the mechanical brake to generate a strong braking force, and the rotational speed of the wind turbine 1 can be decelerated to below the allowable rotational speed.

In addition, when the rotational speed of the wind turbine 1 is sufficiently decelerated and the conditions for switching to the electric brake are met, the operation of the mechanical brake can be stopped and the electric brake can be switched to. This allows the wind power generation system 100 to shorten the operating time of the mechanical brake, suppressing the power consumption for operating the mechanical brake while suppressing over-rotation of the wind turbine 1.

[Embodiment 2]
In the wind power generation system 100 of the first embodiment, the control for activating the mechanical brake at a timing when a strong braking force is required has been described. In the second embodiment, the control for early deceleration by activating the electric brake in addition to the mechanical brake in a state where a strong braking force is required will be described. Note that the description of the configuration of the wind power generation system 100 of the second embodiment that overlaps with the wind power generation system 100 of the first embodiment will not be repeated.

Figure 7 is a flowchart for executing the braking process for the wind turbine 1 after cutout in embodiment 2. In embodiment 2, the control device 5 executes steps S2a and S4a in Figure 7 instead of steps S2 and S4 in the flowchart shown in Figure 6.

When the rotation speed exceeds the rotation speed L (YES in step S1), the control device 5 activates both the mechanical brake and the electric brake (step S2a). This allows a stronger braking force to be generated compared to when only the mechanical brake is activated, and the timing at which the switching condition is met can be advanced. In other words, the operating time of the mechanical brake can be further shortened. Also, when the switching condition is met (YES in step S3), the control device 5 stops operating the mechanical brake (step S4a). This allows the wind power generation system 100 in embodiment 2 to be controlled to a state in which only the electric brake is activated after the switching condition is met.

The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. In addition, although an example of application of this control device to a wind power generation system has been shown, it can also be applied to a hydroelectric power generation system.

1 Wind turbine, 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 Status monitoring unit, 100 Wind power generation system, A, L, X Rotational speed, D1, D2 Area, EB Electric brake control unit, ExS External sensor unit, IS Current sensor, InS Internal sensor unit, L1 to L3 Lines, Pu, Pv, Pw Power lines, R1 to R3 Resistors, Sw1 to Sw3 Switches, TY, Ta, Tb Torque, VS Voltage sensor.

Claims (3)

A control device for a power generation system that supplies power to a supply target,
The power generation system includes:
A rotating body;
a generator that is rotated by the rotor and generates 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;
a control device for controlling the brake circuit and the brake device,
The control device includes:
When the rotation speed of the rotating body exceeds a first threshold value, the brake device is controlled so as to start a braking operation;
A control device that, when a switching condition determined based on the rotational speed of the rotating body and the torque generated on the rotating body is satisfied after the rotational speed of the rotating body falls below the first threshold value, stops the braking operation of the brake device and performs braking operation by the brake circuit. The rotating body is rotated by wind,
The control device according to claim 1 , wherein the switching condition further includes at least one of a condition that a reference period has elapsed after the brake device has started a braking operation, and a condition that a wind speed has decreased below a reference wind speed. The generator includes an iron core and a coil wound around the iron core,
the switching condition includes a condition that the rotation speed of the rotating body is reduced below a second threshold value that is lower than the first threshold value,
3. The control device according to claim 1, wherein the second threshold value is a rotation speed at which the braking force caused by short-circuiting the brake circuit is maximized.

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