JP7041582B2 - AC generator short circuit brake circuit - Google Patents

Description

The present invention relates to a short-circuit brake circuit of an alternator in a wind power generator or the like.

For example, when the rotation speed of a wind turbine becomes excessive in a wind power generator, a mechanism is known that generates a braking torque so as to reduce the rotation speed in order to protect the wind turbine and the alternator connected to the wind turbine. .. Patent Documents 1, 2 and 3 describe a so-called short-circuit brake mechanism in which an output current is increased by short-circuiting between transmission lines through which an alternator output current flows, and as a result, a braking torque is generated in the alternator. Is disclosed.

Patent Document 3 discloses a fail-safe mechanism in which a short-circuit brake circuit is activated by a latch relay so that after the relay is turned on, the relay is not opened unless a signal to turn it off is input.

Japanese Unexamined Patent Publication No. 2000-199473 Japanese Unexamined Patent Publication No. 2007-189770 Japanese Unexamined Patent Publication No. 2008-118807

Here, the short-circuit brake of the AC generator has a problem that the braking torque does not work when the generator rotates at high speed. For example, in a synchronous generator, when a short-circuit current flows when a rotor forming a field approaches a stator composed of an armature coil through which an output current flows, the rotor and the stator repel each other to generate braking torque. On the other hand, if a short-circuit current flows when the rotor moves away from the stator, the rotor and the stator also repel each other, and in this case, an acceleration torque in the direction opposite to the braking torque is generated, which hinders braking.

In view of the above problems, an object of the present invention is to provide a short-circuit brake circuit capable of effectively generating braking torque even at high speed rotation in an alternator such as a wind power generator.

In order to achieve the above object, the present invention provides the following configurations.
-The mode of the short-circuit brake circuit of the alternator according to the present invention is
A short-circuit current path that is connected between transmission lines through which the output current of an alternator flows and can be controlled to conduct or cut off.
During the period of the phase in which the output current increases, the short-circuit current path conducts with respect to the output current, and during the period of the phase in which the output current decreases, the short-circuit current path is cut off with respect to the output current. It is characterized by having a control circuit configured as described above.
In the above embodiment, the short-circuit current paths have first and second switching elements connected in series in opposite directions to each other and each having a control end.
The control circuit has a current transformer, the primary coil of the current transformer is inserted and connected in series with one of the transmission lines, and one end of the secondary coil is secondary to the control end of the first switching element. The other end of the coil is connected to the control end of the second switching element, respectively.
It is preferable that the first and second switching elements are on / off controlled by the voltage generated in the secondary coil of the current transformer by the output current.
-In the above embodiment, when the rotation speed of the alternator is less than the predetermined set value, the short-circuit brake circuit is maintained in the stopped state, and when the rotation speed of the alternator exceeds the predetermined set value. It is preferable to further have a switching circuit for switching the short-circuit brake circuit so as to be in an operating state.

The short-circuit brake circuit of the alternator of the present invention is short-circuited when the short-circuit current path between the transmission lines of the generator becomes conductive when the output current of the alternator increases and the output current of the alternator decreases. The current path is cut off. Therefore, since the short-circuit current flows only during the period in which it can act as the braking torque on the rotor of the alternator, the brake can be effectively applied.

FIG. 1 is a diagram schematically showing an example of a short-circuit brake circuit of the present invention. 2 (a) to 2 (g) schematically show an example of a voltage waveform or a current waveform in the short-circuit brake circuit of FIG. FIG. 3 is a diagram showing the operation of modes I and II of the short-circuit brake circuit of FIG. FIG. 4 is a diagram showing the operation of modes III and IV of the short-circuit brake circuit of FIG. FIG. 5 is a diagram for explaining the effect of the present invention.

Hereinafter, embodiments of the short-circuit brake circuit of the alternator according to the present invention will be described in detail with reference to the drawings. The alternator to which the present invention is applied is a synchronous generator. A permanent magnet type synchronous generator is preferable, but an electromagnet type synchronous generator may also be used.

The present invention is preferably applied to the three-phase alternating current output of a wind power generator alternator. In the case of three-phase alternating current, braking torque can be generated in the alternator to brake rotation by passing a short-circuit current between the transmission lines of two of the three phases. As a result, the brake can be applied to the rotation of the wind turbine.

(1) Circuit Configuration FIG. 1 is a diagram schematically showing an example of the short-circuit brake circuit of the present invention. The short-circuit brake circuit of the present invention is provided for a pair of transmission lines through which an output current from an alternator (not shown) flows. The output current of the alternator is a sine wave.

In the circuit of FIG. 1, terminals 1 and 2 are connected to the output terminal of the alternator. The terminals 3 and 4 are connected to a load that can take various forms (for example, a power supply circuit such as a switching power supply). The line between the terminals 1 and 3 is the first transmission line r, and the line between the terminals 2 and 4 is the second transmission line s.

In the case of a three-phase output AC generator composed of R phase, S phase, and T phase, the short-circuit brake circuit of FIG. 1 can be independently provided between each line. Of course, this circuit can also be applied to a single-phase output AC generator.

The short-circuit brake circuit of the present invention includes a short-circuit current path 5 connected between the transmission line r and the transmission line s, and a control circuit 6 that can be controlled so that the short-circuit current path 5 is conducted or cut off. There is.

<Short circuit current path>
The short-circuit current path 5 is composed of first and second switching elements Q1 and Q2. The first and second switching elements Q1 and Q2 are connected in series between the transmission line r and the transmission line s in opposite directions, and each has a control end.

Here, the switching elements Q1 and Q2 are n-channel MOSFETs. The drain of the switching element Q1 is connected to the first transmission line r, and the drain of the switching element Q2 is connected to the second transmission line s. The sources of the switching elements Q1 and Q2 are connected to each other, and the connection point is grounded.

As a preferred example, the external diodes D1 and D2 are connected in the same direction as the body diodes of the switching elements Q1 and Q2. The roles of the external diodes D1 and D2 are the same as those of the body diode. That is, even if the switching elements Q1 and Q2 are in the off state, current can flow as long as the direction is in the forward direction of the external diode (or body diode). The switching elements Q1 and Q2 in the present invention include a body diode or an external diode that is opposite to the direction of the main current in the on state.

<Control circuit>
The control circuit 6 has a current transformer CT. The primary coil n1 of the current transformer CT is inserted and connected in series to one of the pair of transmission lines, here, the first transmission line r. One end (here, the winding start end) of the secondary coil n2 of the current transformer CT is connected to the control end of the switching element Q1, and the other end (here, the winding end) is connected to the control end of the switching element Q2. Therefore, the switching elements Q1 and Q2 are on / off controlled by the potentials generated at one end and the other end of the secondary coil n2 of the current transformer CT by the output current.

In the current transformer CT, the ratio (current transformer ratio) of the current flowing through the primary coil n1 and the secondary coil n2 is generally set to be extremely large (for example, 400: 1, 100: 1, etc.). The current transformer ratio is also the turns ratio of the secondary coil n2 and the primary coil n1. In FIG. 1, the winding start ends of the primary coil n1 and the secondary coil n2 are indicated by black circles. In the illustrated example, the input terminal side is the winding start end, but the output terminal side may be the winding start end.

Further, the control ends of the switching elements Q1 and Q2 are connected to the cathodes of the Zener diodes Z1 and Z2, and the anodes of the Zener diodes Z1 and Z2 are grounded. The Zener diodes Z1 and Z2 are for protecting the switching elements Q1 and Q2, and define the upper limit of the voltage applied to the control end.

Further, the resistance R connected between one end and the other end of the secondary coil n2 is an element for preventing the secondary coil of the current transformer CT from being opened.

<Operation stop switching circuit>
Further, the short-circuit brake circuit has a switching circuit 7 for switching between operation and stop. The switching circuit 7 maintains the short-circuit brake circuit in a stopped state when the rotation speed of the alternator is less than a predetermined set value. The rotation speed of the alternator can be detected by any known rotation speed detecting means. The rotation speed detecting means here includes a means for determining the rotation speed by detecting the output voltage of the alternator. When the rotation speed detecting means detects that the rotation speed of the alternator exceeds a predetermined set value, the switching circuit 7 is switched so as to put the short-circuit brake circuit into an operating state.

The switching circuit 7 shown in FIG. 1 is a switch S connected between both ends of the secondary coil n2 of the current transformer CT. The switch S is closed when the rotation speed of the alternator is less than a predetermined set value. When the switch S is closed, the secondary coil n2 of the current transformer CT is in a short-circuited state. In this case, since the control ends of the switching elements Q1 and Q2 of the short-circuit current path 5 have a ground potential, both the switching elements Q1 and Q2 are in a cutoff state. Further, any of the body diodes of the switching elements Q1 and Q2 and the external diodes D1 and D2 are always in the opposite direction to the output current of the alternator. Therefore, the short-circuit current does not flow in the short-circuit current path 5.

Further, when the secondary coil n2 is in the short-circuited state, the primary coil n1 is also equivalent to the short-circuited state. Therefore, when the switch S is closed, the output current of the alternator flows to the terminals 3 and 4 as a load current.

When the rotation speed of the alternator exceeds a predetermined set value, the switch S is opened. This starts the short circuit brake circuit. As long as the switch S is open, the short circuit brake circuit remains operational.

The switch S maintains a closed state (short-circuit brake circuit is stopped) by continuously supplying a control signal from the outside, and is in an open state (short-circuit brake circuit is operating) when the control signal from the outside disappears. Is preferable. This makes it possible to realize a fail-safe mechanism for the short-circuit brake circuit. However, the present invention also includes a configuration in which the switching device 7 is not fail-safe, that is, a configuration in which the switch S is maintained in an open state (a short-circuit brake circuit is in an operating state) by being supplied with a control signal from the outside. do.

The switching circuit 7 can have various configurations other than the configuration shown in FIG. 1. For example, by providing an intermediate terminal on the secondary coil n2 and continuing to apply a sufficiently large negative voltage between the intermediate terminal and the ground potential, the switching elements Q1 and Q2 are kept in an off state, and thus a short-circuit brake circuit. Can be kept in a stopped state.

(2) Circuit operation FIGS. 2 (a) to 2 (g) schematically show an example of a voltage waveform or a current waveform in the operating state of the short-circuit brake circuit of FIG. 1 (that is, the switch S is in the open state). .. The horizontal axis is time, and the vertical axis is an arbitrary unit.

FIG. 2A shows the output current Ig output from the alternator. However, the waveform of the sine wave of the output current Ig in FIG. 2A is the waveform when the short-circuit brake circuit of the present invention is not operated at this frequency. Actually, when the short-circuit brake circuit is operated and the short-circuit current flows, the waveform of the output current Ig is different from the waveform of FIG. 2A. FIG. 2A is a waveform used as a reference for the phases of current and voltage at each location in the short-circuit brake circuit.

FIG. 2B shows the voltage Vn1 (potential at the winding start end) generated in the primary coil n1 of the current transformer CT in the operating state of the short-circuit brake circuit, and FIG. 2C shows the voltage Vn2 (winding start end potential) generated in the secondary coil n2. Potential). When the voltage Vn1 whose phase is shifted by 90 ° is generated in the primary coil n1 due to the output current of the alternator, the voltage Vn2 is generated in the secondary coil n2 according to the turns ratio of the current transformer CT. The voltage Vn2 is applied to the control ends of the switching elements Q1 and Q2, respectively. As a result, as shown in FIGS. 2 (d) and 2 (e), the switching elements Q1 and Q2 contradictably repeat the on state and the off state.

FIG. 2 (f) shows the short-circuit current flowing in the short-circuit current path of the short-circuit brake circuit, and FIG. 2 (g) shows the load current flowing to the output terminal. Next, the operation of the short-circuit brake circuit will be described in detail with reference to FIGS. 3 and 4.

The operation of the short-circuit brake circuit is roughly divided into the following four modes according to the phase of the output current of the alternator.
-Mode I: Phase in which the positive output current increases-Mode II: Phase in which the positive output current decreases-Mode III: Phase in which the negative output current increases-Mode IV: Phase in which the negative output current decreases

Here, when the term "output current increases" or "output current decreases" means that the absolute value of the current increases or decreases regardless of the polarity or direction of the current. Hereinafter, the operation of the short-circuit brake circuit of FIG. 1 will be described for each mode.

<Mode I>
FIG. 3A shows the circuit operation in mode I. Mode I corresponds to a period in which the phase of the output current Ig of the alternator is 0 ° to 90 ° (see FIG. 2A). The current flowing through the circuit is shown by a solid line with an arrow (the same applies to the figure below). The output current in the mode I flows in the direction of inflow from the terminal 1 and increases (see FIG. 2A). When the increasing output current flows through the primary coil n1 of the current transformer CT, a voltage at which the winding start end becomes a positive potential is induced (see FIG. 2B), and the winding start end is also positive in the secondary coil n2 by mutual induction. It produces a potential voltage (see FIG. 2 (c)).

In such a potential state of the secondary coil n2, the switching element Q1 is in the on state and the switching element Q2 is in the off state. Ignoring the gate voltage, the positive gate voltage is regarded as the on state, and the negative gate voltage is regarded as the off state. The same applies hereinafter). The switching element Q2 is in the off state, but the external diode D2 (or body diode) is in the forward direction with respect to the output current. In this case, the short-circuit current path becomes conductive. Therefore, in the mode I, the output current flows through the short-circuit current path of the terminal 1 → the switching element Q1 → the external diode D2 (or the body diode) → the terminal 2 as the short-circuit current Is1. When the short-circuit current Is1 flows, braking torque is applied to the alternator.

<Mode II>
FIG. 3B shows the circuit operation in Mode II. Mode II corresponds to a period in which the phase of the output current Ig of the alternator is 90 ° to 180 ° (see FIG. 2A). The output current of the alternator in mode II flows in the direction of flowing in from terminal 1 following mode I, but its magnitude decreases (see FIG. 2A). When the decreasing output current flows through the primary coil n1 of the current transformer CT, a voltage at which the winding end becomes a positive potential is induced (see FIG. 2B), and the winding end also has a positive potential at the secondary coil n2 due to mutual induction. (See FIG. 2 (c)).

In such a potential state of the secondary coil n2, the switching element Q1 is in the off state and the switching element Q2 is in the on state. The switching element Q2 is in the ON state, but the switching element Q1 is in the OFF state and the external diode D1 (and the body diode) thereof is in the opposite direction to the output current, so that the output current flows in the short-circuit current path. I can't. In this case, the short circuit current path is cut off. As a result, the output current flows to the terminal 3 as the load current Io1. Since the load current Io1 flows through the load connected to the subsequent stage, its magnitude is smaller than that of the short-circuit current Is1.

<Mode III>
FIG. 4A shows the circuit operation in mode III. Mode III corresponds to a period in which the phase of the output current Ig of the alternator is 180 ° to 270 ° (see FIG. 2A). The output current in mode III flows in the direction of inflow from the terminal 2 and increases (see FIG. 2A). When the increasing output current flows through the primary coil n1 of the current transformer CT, a voltage at which the winding end becomes a positive potential is induced (see FIG. 2B), and the winding ending is also positive in the secondary coil n2 by mutual induction. It produces a potential voltage (see FIG. 2 (c)).

In such a potential state of the secondary coil n2, the switching element Q1 is in the off state and the switching element Q2 is in the on state (see FIGS. 2 (d) and 2 (e)). The switching element Q1 is in the off state, but the external diode D1 (or body diode) is in the forward direction with respect to the output current. In this case, the short-circuit current path becomes conductive. Therefore, in the mode III, the output current flows through the short-circuit current path of the terminal 2 → the switching element Q2 → the external diode D1 (or the body diode) → the terminal 1 as the short-circuit current Is2 (see FIG. 2 (f)). Braking torque is applied to the alternator due to the short-circuit current Is2 flowing.

FIG. 4B shows the circuit operation in Mode IV. Mode IV corresponds to a period in which the phase of the output current of the alternator is 270 ° to 360 ° (see FIG. 2A). The output current of the alternator in mode IV flows in the direction of flowing in from terminal 2 following mode III, but its magnitude decreases (see FIG. 2A). When the decreasing output current flows through the primary coil n1 of the current transformer CT, a voltage at which the winding start end becomes a positive potential is induced (see FIG. 2B), and the winding start end is also positive in the secondary coil n2 by mutual induction. It produces a potential voltage (see FIG. 2 (c)).

In such a potential state of the secondary coil n2, the switching element Q1 is in the on state and the switching element Q2 is in the off state (see FIGS. 2 (d) and 2 (e)). The switching element Q1 is in the ON state, but the switching element Q2 is in the OFF state and the external diode D2 (and the body diode) thereof is in the opposite direction to the output current, so that the output current flows in the short-circuit current path. I can't. In this case, the short circuit current path is cut off. As a result, the output current flows to the terminal 4 as the load current Io2 (see FIG. 2 (g)). Since the load current Io2 flows through an appropriate load connected to the subsequent stage, its magnitude is smaller than that of the short-circuit current Is2.

FIG. 5 is a diagram for explaining the effect of the present invention. FIG. 5 (a) is the same diagram as in FIG. 2 (a), and shows the correspondence between the phase of the output current Ig of the alternator and the modes I to IV.

In FIG. 5B, the rotation state of the rotor of the synchronous generator is schematically shown on the upper side, and the current flowing between the transmission lines in modes I to IV corresponding to the rotation state is shown on the lower side. Here, it is assumed that the rotor is a permanent magnet or a field coil and the stator is an armature coil. The output current is output from the armature coil.

Here, for the sake of simplicity, it is assumed that the stator is provided only at one position facing the north and south poles of the rotor at phases of 90 ° and 270 °. First, the north pole of the rotor approaches the stator in mode I and separates from the stator in mode II, then the S pole of the rotor approaches the stator in mode III and separates from the stator in mode IV.

The direction of the rotational torque of the rotor generated by an external force (for example, wind power) is indicated by the white arrow Tr. The short-circuit current Is1 flowing in the mode I causes a braking torque Tbr for the rotor, and as a result, reduces the rotational torque Tr. The load current Io1 flowing in the mode II causes an acceleration torque Tac for the rotor, but since the load current Io1 is smaller than the short-circuit current Is1, the contribution to the increase in the rotational torque Tr is small. The same applies to modes III and IV. Overall, the short-circuit currents Is1 and Is2 flow in the short-circuit brake circuit of the present invention, thereby reducing the rotational torque Tr of the rotor.

On the other hand, FIG. 5 (c) is the same as FIG. 5 (b), but shows a case where the short-circuit current Is continuously flows. For example, the short-circuit current flowing in the short-circuit brake circuit of Patent Documents 1 to 3 corresponds to this. In this case, since the short-circuit current also flows in the modes II and IV, the braking torque Tbr obtained by the short-circuit currents of the modes I and III and the acceleration torque Tac generated by the short-circuit currents of the modes II and IV are about the same. Therefore, the rotational torque Tr cannot be reduced because they cancel each other out comprehensively. This phenomenon is a problem that occurs especially in high-speed rotation. According to the present invention, this phenomenon can be improved.

The present invention is not limited to the configuration examples illustrated and described, and various modified forms are possible according to the principle of the present invention, and these are also included in the scope of the present invention.

1, 2, 3, 4 terminals 5 Short-circuit current path 6 Control circuit 7 Switching circuit Q1, Q2 Switching element r, s Transmission line D1, D2 External diode Z1, Z2 Zener diode Is1, Is2 Short-circuit current Io1, Io2 Load current

Claims (3)

A short-circuit current path that is connected between transmission lines through which the output current of an alternator flows and can be controlled to conduct or cut off.
During the period of the phase in which the output current increases, the short-circuit current path conducts with respect to the output current, and during the period of the phase in which the output current decreases, the short-circuit current path is cut off with respect to the output current. A short-circuit brake circuit for an alternator, characterized in that it is equipped with a control circuit configured as such. The short-circuit current paths are connected in series in opposite directions to each other and have first and second switching elements each having a control end.
The control circuit has a current transformer, the primary coil of the current transformer is inserted and connected in series with one of the transmission lines, and one end of the secondary coil is secondary to the control end of the first switching element. The other end of the coil is connected to the control end of the second switching element, respectively.
The short-circuit brake circuit of an alternator according to claim 1, wherein the first and second switching elements are on / off controlled by a voltage generated in a secondary coil of the current transformer by the output current. When the rotation speed of the alternator is less than the predetermined set value, the short-circuit brake circuit is maintained in a stopped state, and when the rotation speed of the alternator exceeds the predetermined set value, the short-circuit brake circuit is operated. The short-circuit brake circuit for an alternator according to claim 1 or 2, further comprising a switching circuit for switching to an operating state.

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