JP6631311B2 - Power generation system - Google Patents

Description

  The present invention relates to a variable-speed power generation system, and more particularly to a PLL control method when switching from an independent operation to an interconnected operation without an instantaneous interruption.

  FIG. 1 shows a single connection diagram of a hydraulic variable speed power generation system using a permanent magnet synchronous generator.

  When the AC system 19 is normal, the converter device 6 performs MPPT control (maximum output follow-up control) on the power generation device 1 and operates in an interconnected operation with the AC system 19.

  When a system abnormality occurs in the AC system 19 during the interconnection operation, the bus-side switch 20 is opened, the operation of the interconnection interconnection control inverter 8 is stopped, and the water turbine 2 is instructed by the control unit 18 having received the failure information. To stop. The power generation energy until the turbine 2 stops is consumed by the braking resistor 10b by the operation of the switching device 10a of the braking unit 9.

  The control unit 18 outputs an operation mode switching command to the power generation device 1 and the converter device 6 so that the power generation device 1 and the converter device 6 shift from the interconnection operation to the independent operation. In response to the operation mode switching command, the generator control inverter 7 changes from the generator speed constant control or the torque constant control to the DC voltage constant control, and the grid interconnection control inverter 8 switches from the DC voltage constant control to the AC voltage constant control. Switches.

  As a result, a desired AC voltage is supplied to the specific load 16, and independent operation can be realized. At this time, the relationship between the load conditions of the power generation device 1 and the specific load 16 is such that power generation of the power generation device 1 ≥ power consumption of the specific load 16.

JP 2014-27762 A JP 2010-226871 A JP 2005-20870 A JP 2000-184602 A

  When the AC system 19 returns to the normal state during the self-sustaining operation, it is necessary to perform the interconnected operation synchronized with the AC system 19 without an instantaneous interruption in order to secure and improve the reliability of the power supply to the specific load 16.

  As described above, it is an issue in the power generation system to quickly shift from the independent operation to the interconnection operation.

  The present invention has been made in view of the above-mentioned conventional problems, and one aspect thereof is a generator connected to an energy source and a generator control inverter connected between the generator and an AC system. And a converter unit having a grid-connected inverter, and a control unit that outputs a command to the generator control inverter and the grid-connected inverter. When the transition from the independent operation to the interconnection operation is performed, it is determined whether the independent phase is delayed or advanced with respect to the system phase.If the independent phase is a phase delayed from the system phase, the reference phase is set for each sampling cycle. A value obtained by adding the correction amount to the lead angle is added to the autonomous phase. If the autonomous phase is a phase advanced from the system phase, a value obtained by subtracting the correction amount from the reference phase advance angle for each sampling cycle is used in advance. It was added to the self phase, characterized by adding the reference phase advance angle for each sampling period from the time when the phase difference is equal to or less than the threshold value of the self phase with the line phase to the self phase.

  In one embodiment, the correction amount is 3 ° to 10 °.

  Further, as one aspect, an interconnection transformer connected to the converter device, a bus switch connected between the interconnection transformer and the AC system, the interconnection transformer and the bus switching A specific load connected between the AC power supply and the power supply, and having an independent operation function of supplying power to the specific load when the AC system is abnormal.

  Further, as one aspect, when the AC system is restored, the generator control inverter switches from the DC voltage constant control in the independent operation mode to the speed constant control or the torque constant control in the interconnection operation mode. I do.

  In one embodiment, the energy source is a water wheel.

  Advantageous Effects of Invention According to the present invention, in a power generation system, it is possible to quickly shift from an independent operation to an interconnected operation.

FIG. 1 is a single connection diagram illustrating a power generation system according to a first embodiment. 6 is a timing chart showing a switching operation between an interconnection operation and an independent operation. 9 is a timing chart showing a phase calculation process of the independent phase PLL control process. 9 is a flowchart of an independent phase. 9 is a flowchart of a self-sustaining phase PLL control process. FIG. 5 is an enlarged view of FIG. 4 in the case of a lag phase. FIG. 5 is an enlarged view of FIG. 4 in the case of a leading phase.

  Hereinafter, Embodiments 1 and 2 of the power generation system according to the present invention will be described in detail with reference to FIGS.

[Embodiment 1]
First, a power generation system according to the first embodiment will be described with reference to FIG. In the first embodiment, a description will be given of a hydraulic power generation system. FIG. 1 shows a single connection diagram of a hydraulic variable speed power generation system using a permanent magnet synchronous generator. This hydraulic power generation system is interconnected to an AC system 19 via an interconnection transformer 17, a specific load 16, and a bus-side switch 20.

  In FIG. 1, reference numeral 1 denotes a power generator, 6 denotes a converter, and 18 denotes a control unit.

  The power generator 1 has a water wheel 2, a flywheel 4, and a permanent magnet synchronous generator (hereinafter, referred to as a generator) 3 as energy sources, and these are connected via a bearing not shown. It should be noted that the flywheel 4 is not an essential component, but rather a system without the flywheel 4 is generally used. In addition, the power generation device 1 includes a flow rate adjusting unit (for example, a governor) 5 for adjusting the flow rate of the water turbine 2.

  The converter device 6 includes a generator control inverter 7, a system interconnection control inverter 8, a DC capacitor 13 connected to a DC link between the inverters, a braking unit 9 having a switching device 10a and a braking resistor 10b, It has.

  The converter device 6 includes an LCR filter 14 composed of a reactor L, a capacitor C, and a resistor R, a generator-side switch 11 connected to the generator 3 side, and a system side connected to the AC system 19 side. It includes a switch 12, a connection voltage detection transformer 15, and a synchronization voltage detection transformer 21.

  The control unit 18 sends and receives signals such as outputting an operation command to the converter device 6 and adjusts the flow rate of the water turbine 2 via the flow rate adjusting means 5.

  FIG. 2 shows a timing chart of the switching operation from the interconnection operation to the independent operation and from the independent operation to the interconnection operation.

  First, the switching operation from the interconnection operation to the independent operation will be described. When a power failure occurs in the AC system 19, the system interconnection control inverter 8 detects a system failure and stops the interconnection operation. The control unit 18 that has received the system failure information opens the bus-side switch 20. When the converter device 6 confirms through the control unit 18 that the busbar-side switch 20 has been opened, the generator control inverter 7 and the system interconnection control inverter 8 switch control modes to shift to independent operation. The generator control inverter 7 switches the control mode from the generator speed constant control or the torque constant control to the DC voltage constant control, and the grid interconnection control inverter 8 switches the control mode from the DC voltage constant control to the AC voltage constant control. As shown in FIG. 2, there is a time Δtoff from the power failure of the system to the start of the cushion output period. This switching is not instantaneous interruption switching.

  Next, the switching operation from the independent operation to the interconnection operation will be described. When the converter device 6 confirms the system restoration of the AC system 19, the converter device 6 starts the PLL control with the system voltage phase while continuing the independent operation.

  The first embodiment relates to a PLL control of an output voltage phase (hereinafter, referred to as an independent phase) of a system interconnection control inverter 8 and a phase of a system voltage (hereinafter, referred to as a system phase) during the self-sustaining operation. When the phase synchronization between the self-sustained phase and the system phase is completed, the generator control inverter 7 and the system interconnection control inverter 8 switch the control mode, and switch on the bus-side switch 20 according to a command from the control unit 18 to perform the interconnection operation. Move to The generator control inverter 7 switches the control mode from DC voltage constant control to generator speed constant control or torque constant control, and the grid interconnection control inverter 8 switches from AC voltage constant control to DC voltage constant control. This switching is instantaneous interruption switching.

  In FIG. 3 to FIG. 7 below, 50 Hz (period: 20 ms) is considered as a reference. The phase waveform increases linearly from 0 ° to 360 ° as shown in FIG. 3 and returns to 0 ° with 360 ° as the peak. If the sampling period Δt is 1 μs, the reference phase lead angle Δθref is 0.18 ° / μs. Although the phase is generated by integrating the reference phase lead angle Δθref, in practice, a phase waveform of 0 ° to 360 ° is generated every 20 ms by adding the reference phase lead angle Δθref every sampling period Δt.

  FIG. 4 is a flowchart showing a process for generating a self-sustaining phase. The generation process of the self-sustaining phase will be described with reference to FIG. The self-sustained phase is generated by a self-sustained oscillation self-sustained phase command value.

  S11: When it is confirmed that the AC system 19 is out of power, the self-sustaining operation is started.

  S12: The generation of the independent phase φ is started. Set φ to zero as the initial value. A predetermined value is set for the sampling period Δt, and a predetermined value is set for the reference phase lead angle Δθref.

  S13: φ = φ + Δθref is calculated for each sampling period Δt.

  S14: It is determined whether the self-sustained phase φ is 360 °. If the autonomous phase φ is not 360, the operation of S13 is performed for each sampling period Δt. That is, the reference phase lead angle Δθref is added every sampling period Δt.

  S15: If the autonomous phase φ is 360 °, the autonomous phase φ is set to 0 °, and the process returns to S13.

  The above is the method for generating the independent phase φ. The waveform is a waveform like the system phase φg in the lower left diagram of FIG. 3, returns to 0 ° when it reaches 360 °, and generates a repeated waveform.

  FIG. 5 is a flowchart showing the independent phase PLL control processing. The independent phase PLL control processing will be described with reference to FIG. The feature of the first embodiment is from the time the AC system 19 recovers power until the AC system 19 synchronizes with the self-sustaining phase.

  S1: The voltage of the system bus is detected by the voltage detecting transformer for synchronization 21 to determine whether or not the AC system 19 is restored. If the AC system 19 has recovered, the process proceeds to S2, and if the AC system 19 has not recovered, the process proceeds to S13 (FIG. 4). The restored system phase φg is detected by the synchronization voltage detection transformer 21.

  S2: Check the phase relationship between the system phase φg and the independent phase φ. The reference is the system phase φg.

  S3: It is determined whether or not the phase deviation between the system phase φg and the independent phase φ is within a preset threshold range. That is, it is determined whether or not the phase deviation = | independent phase φ−system phase φg | When the phase deviation is larger than the threshold, the process proceeds to S4, and when the phase deviation is equal to or smaller than the threshold, the process proceeds to S7.

  S4: The magnitude of the independent phase φ and the system phase φg are compared. If the autonomous phase φ ≦ the system phase φg, the process proceeds to S5. If the autonomous phase φ> the system phase φg, the process proceeds to S6.

  S5: If the autonomous phase φ is delayed, as shown in FIG. 6, assuming that the phase difference is Δφ, the system phase φg1 at time t0, the autonomous phase φ1, and the system phase φg1> the autonomous phase φ1. An operation for reducing the difference (operation for advancing the phase) is required.

  The difference between the system phase φg and the self-sustained phase φ is reduced by increasing the self-sustained phase lead angle Δθ2 obtained by adding the correction amount θcom to the reference phase advance angle Δθref every sampling period Δt. Since the reference phase advance angle Δθref + correction amount Δθcom = independent phase advance angle Δθ2 is added for each sampling period Δt after time t0, the inclination becomes large from time t0, and the phase difference between the system phase φg and the independent phase φ is reduced. Shrink. Synchronization is completed when the phase difference between the system phase φg and the self-sustained phase φ becomes equal to or less than a predetermined threshold at time t1.

  After the time t1, the addition of the correction amount Δθcom is stopped and only the reference phase lead angle Δθref is added, so that the autonomous phase φ has the same gradient as the system phase φg, and the system phase waveform becomes the autonomous phase waveform.

  S6: If the autonomous phase φ is advanced, as shown in FIG. 7, it is assumed that the phase difference is Δφ, and at time t0, the system phase φg1 and the autonomous phase φ1 have the system phase φg1 <the autonomous phase φ1. An operation for reducing the difference (an operation for delaying the phase) is required.

  The difference between the system phase φg and the self-sustained phase φ is reduced by adding the self-sustained phase lead angle Δθ2 obtained by subtracting the correction amount Δθcom from the reference phase advance angle Δθref at each sampling period Δt. After time t0, the reference phase advance angle Δθref−correction amount Δθcom = independent phase advance angle Δθ2 is added for each sampling period Δt, whereby the slope becomes small from time t0, and the phase difference between the system phase φg and the independent phase φ is calculated. Shrink. Synchronization is completed when the phase difference between the system phase φg and the self-sustained phase φ becomes equal to or less than a predetermined threshold at time t1.

  After the time t1, the subtraction of the correction amount Δθcom is stopped, and only the reference phase lead angle Δθref is added, so that the autonomous phase φ has the same gradient as the system phase φg, and the system phase waveform becomes the autonomous phase waveform.

  S7: If the phase deviation is equal to or smaller than the threshold, the independent phase PLL control is completed, and the synchronization is completed.

  S8: The addition or subtraction of the correction amount Δθcom is stopped, and the independent phase φ = φ + Δθref is set.

  S9: It is determined whether the self-sustained phase φ is 360 °. If the autonomous phase φ is not 360 °, the process returns to S8 for each sampling period Δt.

  S10: If the self-supporting phase φ is 360 °, the self-supporting phase φ is returned to 0, and the process proceeds to S8.

  As described above, according to the power generation system of the first embodiment, by confirming the power recovery of the AC system 19 during the self-sustained operation, the self-sustained operation can be instantaneously interrupted without the need for manual operation. , It is possible to provide a self-sustained phase PLL control system that switches to.

  In the first embodiment, since the period and the phase of the independent phase are made to coincide with the system phase at the same time, the synchronization can be performed in a single time as compared with the case where the frequency correction and the phase correction are separately performed.

  Furthermore, since the correction amount Δθcom is added for each sampling period Δt, it is possible to suppress the fluctuation at the time of interconnection.

[Embodiment 2]
FIG. 3 shows a phase calculation process of the independent phase PLL control process in the second embodiment. The system phase φg is generated by integrating the reference phase lead angle Δθref for each sampling period Δt. The reference phase lead angle Δθref is calculated from the detection value of the synchronization voltage detection transformer 21. The independent phase φ is generated by integrating the independent phase lead angle Δθ2 for each sampling cycle.

  During autonomous operation, the autonomous phase advance angle Δθ2 is the reference phase advance angle Δθref of the output frequency (50/60 Hz), and outputs a desired frequency by the autonomous phase φ integrated for each sampling period Δt.

  When the AC system 19 is restored and the self-sustained phase PLL control is started, the self-sustained phase lead angle θ2 is corrected by adding or subtracting the correction amount Δθcom to or from the reference phase lead angle Δθref, thereby correcting the integrated value for each sampling period Δt. Then, the autonomous phase φ and the system phase φg are synchronized. Whether to add or subtract the correction amount Δθcom is determined by S4 in FIG. 5 in the first embodiment (that is, the magnitude of the system phase φg and the autonomous phase φ).

  When the independent phase PLL control is performed, the specific load 16 is supplied with a desired voltage and frequency from the converter device 6, and a sudden phase jump may adversely affect the specific load 16.

  Therefore, the correction amount Δθcom is limited to 3 ° to 10 ° which is a set value range of the voltage phase jump detection method of passive islanding detection. As a result, it is possible to stably supply power to the specific load 16 even during the independent phase PLL control.

  For example, when the system phase φg and the self-sustained phase φ are shifted by 30 °, synchronization is performed at a sampling period of 30 ÷ 3-10 = 10-3.

  As described above, in the present invention, only the described specific examples have been described in detail, but it is apparent to those skilled in the art that various modifications and variations are possible within the technical idea of the present invention. It is obvious that such changes and modifications belong to the scope of the claims.

2. Energy source (water turbine)
3. Generator (permanent magnet synchronous generator)
6 ... Converter device 7 ... Generator control inverter 8 ... System interconnection control inverter 13 ... DC capacitor 18 ... Control unit 19 ... AC system φ ... Independent phase φg ... System phase Δθref… Reference phase advance angle Δθcom… Correction amount Δt… Sampling period

Claims (5)

A generator connected to the energy source;
A converter device having a generator control inverter and a system interconnection inverter connected between the generator and the AC system,
A control unit that outputs a command to the generator control inverter and the grid interconnection inverter,
A power generation system comprising:
The control unit is configured such that when the AC system recovers power and shifts from independent operation to interconnected operation,
Judge whether the autonomous phase is delayed or advanced with respect to the system phase.
When the self-sustaining phase is a phase lagging behind the system phase, a value obtained by adding a correction amount to a reference phase advance angle for each sampling cycle is added to the self-sustaining phase,
If the autonomous phase is a phase advanced from the system phase, a value obtained by subtracting a correction amount from a reference phase advance angle for each sampling cycle is added to the autonomous phase,
A power generation system, wherein a reference phase advance angle is added to the self-sustained phase every sampling period from the time when a phase difference between the self-sustained phase and the system phase becomes equal to or smaller than a threshold.   The power generation system according to claim 1, wherein the correction amount is 3 ° to 10 °. An interconnection transformer connected to the converter device,
A busbar switch connected between the interconnection transformer and the AC system;
A specific load connected between the interconnection transformer and the busbar switch,
3. The power generation system according to claim 1, further comprising an independent operation function of supplying power to the specific load when the AC system is abnormal. When the AC system is restored,
The power generator according to any one of claims 1 to 3, wherein the generator control inverter switches from the DC voltage constant control in the independent operation mode to the speed constant control or the torque constant control in the interconnection operation mode. system.   The power generation system according to any one of claims 1 to 4, wherein the energy source is a water wheel.

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