JPH10304572A - Solar light power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a backward current by applying a PLL control system as a means for controlling the phase synchronization of a power source voltage in a solar light power generation system, monitoring always the phase error component of a distribution system voltage and an inverter output voltage, highly precisely detecting the error component, independently of the condition of a load connected with the linkage point of the inverter when the distribution system is interrupted, and surely analyzing the distribution system. SOLUTION: A phase-detecting means 101 receives a voltage feedback signal from a PT 56 connected with a linkage point, and controls a voltage (v) of distribution system 58 and an output voltage (v') of the inverter 52 in such a manner that the voltages have the same phase. The error of the phasedetecting means 101 causes a phase difference between the voltage (v) of the distribution system 58 and the output voltage (Δω) of the inverter 52. In order to correct the phase difference, a correction value Aco is increased or decreased, and phase synchronization of both of the voltages and an inverter output current (i) is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photovoltaic power generation system.

[0002]

2. Description of the Related Art FIGS. 5 and 6 show an example of a photovoltaic power generation system proposed in the Transactions of the Institute of Electrical Engineers of Japan, B.114, No. 4, 1994. FIG. FIG. 6 and FIG. 6 are characteristic diagrams showing frequency versus gain characteristics and frequency versus phase characteristics of two bandpass filters (hereinafter referred to as BPFs) 541 and 542. 5 is a solar cell, 52 is an inverter, 53 is an isolation transformer, 54 is two analog bandpass filters, 55 is a control unit of the inverter, and 56 is a measuring transformer for monitoring the AC voltage at the interconnection point [ Reference numeral 57 denotes a load device connected to the interconnection point, and 58 denotes a distribution system serving as a commercial power supply. The system switch 59 is a reverse power flow prevention switch for preventing a current from flowing from the inverter 52 to the power distribution system 58 when the power distribution system 58 fails.

[0003] The solar power generation system operates as follows. The DC power generated by the solar cell 51 is converted into AC power by the inverter 52 and is connected to the power distribution system 58 via the insulating transformer 53 and the system switch 59. Meanwhile, BPF5
As shown in FIG. 6, the center frequencies of 41 and 542 are set at, for example, two points each of 48 Hz and 52 Hz, and the differential value of the frequency versus the gain becomes 50 at 50 Hz therebetween.
The design is made so that the magnitude of frequency versus phase is zero. Here, the voltage of the distribution system (for example, frequency 50 Hz)
v joins the BPF 54 via the PT 56,
As for the output signal i * of 54, the control system is stabilized at 50 Hz, which is the frequency point where the phase characteristic is zero from the characteristic of FIG. i *
Is a command value input to the control unit 55,
Performs pulse width modulation control (hereinafter referred to as PWM control) based on the command of i *, and makes the output i of the inverter 52 in phase with i *. At this time, since v and i * have the same phase, i is also v
In phase with respect to. Therefore, during normal operation, the output voltage v 'of the inverter has the same frequency, phase and voltage as the distribution system v, and the output current i of the inverter is controlled so that the power factor becomes 1 with respect to the distribution system voltage v. .

When the power distribution system 58 is out of service due to construction or accident, the output voltage v 'of the inverter 52 is directly applied to the load device 57, and the inverter output current i is connected to the interconnection point. It is controlled based on the voltage determined by the load. At this time, if the load device 5
If 7 is an inductive load such as a motor, the output voltage v 'of the inverter has a leading phase with respect to the current i. For this reason, the output current i * of the BPF has a leading phase with respect to the output current i of the inverter, so that i * controls i in the direction of increasing the frequency according to the frequency versus phase characteristic of FIG. As the frequency command value of i * increases, the gain of the control system becomes large, and i and i * become in phase. Load device 5
If 7 is capacitive, the control unit 55 controls to decrease the frequency of i and moves to around 48 Hz. Therefore,
The control unit 55 can detect a power failure of the power distribution system 58 by monitoring the output frequency of the inverter, thereby turning off the system switch 59 and disconnecting the inverter 52 and the power distribution system 58.

[0005]

The conventional photovoltaic power generation system is configured as described above.
It is possible to detect a power failure with an accuracy of. Preventing reverse power flow in the event of a system failure in a photovoltaic power generation system is an important function for ensuring the safety of the power system and preventing electric shock for workers performing maintenance and restoration work. Detection is required. In order to perform detection by frequency shift with high accuracy in the configuration of FIG. 5, it is required to increase the Q (filter sharpness) of the BPF. For this purpose, use a precision-grade element with little variation in the constants of the element itself, such as reactance, capacitor, and resistance, or use an element with excellent temperature characteristics to make the center frequency of the filter as close as possible to the design value. Measures are needed. There is a concern that the use of such an element will increase the cost. Also, in the mounting design, it is necessary to increase the noise resistance by performing high-density mounting in order to reduce the influence of the stray capacitance and the reactance of the wiring, and the cost of the shielding material and noise suppression components for that purpose cannot be ignored. In addition, when there is a light load and no load, or when a large number of capacitive loads or inductive loads are connected to the same wiring system, the phase shift of the output current of the inverter becomes small, and a frequency shift may not occur. .

SUMMARY OF THE INVENTION An object of the present invention is to eliminate a frequency detection error due to the influence of hardware such as variation of elements in a frequency shift method which is one of power failure detection, and to ensure a high accuracy without depending on a load condition. The purpose of the present invention is to prevent a reverse power flow by detecting a power outage and quickly disconnecting from the power distribution system.

[0007]

SUMMARY OF THE INVENTION The above-mentioned object is achieved by the well-known P
This can be achieved by using some signals of the LL (Phase Locked Loop) control system. Although the PLL control can be realized by control processing of an analog circuit or a microcomputer, the description will be made based on the control block diagrams of the microcomputer of FIGS. 7A and 7B. FIG. 7A shows an example in which the power distribution system is a three-phase alternating current. The α-β conversion unit 71 converts the U-phase and W-phase phase voltages into two-axis orthogonal coordinates, and the α-β converted orthogonal coordinates. To a stationary coordinate, a d-q converter 72, a PI compensation system 73 for proportional / integral (hereinafter referred to as PI) control, and a sin for generating a sin wave and a cos wave by the phase command θd * '.
/ Cos generating section 74. ω0 * is data to be added each time. For example, the inverter is operated at an output frequency of 50 Hz, and the number of additions in one cycle is 10
When it is set to 0 times, ω0 * becomes 3.6 °. Δω is a correction value for the error of the reactive voltage component Vd, and creates a phase command value θd * that changes from 0 ° to 360 ° based on the integrated value 75 of the sum with ω0 *. In addition, since the effective component and the invalid component are out of phase by 90 °, in order to calculate the invalid voltage component,
from the 76 phase command value θd * 'delayed by 90 ° from θd *
n / cos generating section 74 generates sinθ and cosθ, and α
The values of the α-axis and the β-axis after the −β conversion 71 and the above-mentioned sin θ and cos θ
Perform the dq conversion 72 to calculate the invalid voltage component Vd.

The control is performed so that Vd becomes zero. During normal operation, the phase voltages of the U-phase and the W-phase have a phase difference of 240 ° and the voltage is constant and stable. Correction value Δω of PI compensation system 73
Is calculated from the error of Vd subjected to the dq conversion 72. Due to this Δω, the phase command value θd * 'slightly increases or decreases,
sin θ and cos θ for performing the dq conversion 72 are adjusted, and the error of Vd is corrected to zero. Accordingly, the deviation of Δω also changes near zero.

[0009] Next, when the power distribution system loses power, the inverter automatically generates its own output voltage. Then, the inverter performs an α-β conversion 71 and a dq conversion 72 on the output voltage generated by the inverter to obtain an invalid voltage component Vd.
As described above, the PLL control adjusts the compensation value Δω of the PI compensation system 73 so that Vd becomes zero. However, Vd
Is completely reduced to a circuit [operational amplifier or A / D
Converter, etc.) and the calculation accuracy of the microcomputer are limited. Since this Vd has an error, the integral gain of the PI compensation system 73 accumulates the error and the control diverges. That is, since the inverter controls the ineffective component Vd of the output voltage generated by the inverter itself to zero, the control does not converge and diverges unless Vd is completely zero. As the control diverges, the compensation value Δω increases and decreases, causing a frequency shift. For example, if the error of Vd is positive, the frequency decreases, and if it is negative, the frequency shifts in the increasing direction.

FIG. 7 (b) shows a case where the distribution system is a three-phase AC or a single-phase AC, and the symbols of the respective parts correspond to those of FIG. 7 (a). A signal generation circuit 77 for generating a signal at a voltage point and a sample / hold circuit 78 for holding a phase command value θd * are added, and an α-β conversion unit 71, a dq conversion unit 72, and a sin / c
This is the point that the os generator 74 has been removed, and the other symbols are the same as those in FIG. When the single-phase alternating current is controlled by the PLL, a signal is generated at the zero crossing point of the power supply voltage, and the signal 77 is used to hold the phase command value θd * in the sample / hold circuit 78. The control corrects Δω so that the phase command value θd * becomes 0 ° at the zero crossing point. If a power failure occurs in the power distribution system, no signal is output from the zero-cross signal generation circuit 77, so the phase command value θd
* Is not updated by the sample / hold circuit 78, and the value held by the sample / hold circuit 78 becomes an error.
An error accumulates due to the integral gain of the PI compensation system 73 and Δω
Control increases and decreases, causing a frequency shift.
When the distribution system is a three-phase AC, the same operation can be performed by inputting the line voltage or the phase voltage to the interconnection point zero cross signal generation circuit 77 as the interconnection point AC voltage.

From the above, the power failure detection of the distribution system is performed by detecting the correction value Δω of the reactive voltage component Vd when the distribution system is a three-phase AC, and the phase of the zero-crossing voltage point when the distribution system is a three-phase AC or a single-phase AC. This is performed by constantly monitoring the correction value Δω of the command value. That is, if the correction value Δω is equal to or greater than a predetermined value, it is determined that a frequency shift has occurred, and if the inverter is stopped to be disconnected from the power distribution system, reverse power flow can be prevented. In addition, a deviation of the correction value is obtained for each sampling, and when the deviation becomes equal to or more than a predetermined value, it is determined that there is an abnormality, and reverse power flow can be prevented. further,
It is also possible to take the absolute value of the deviation of the correction amount for each sampling, determine that the value is greater than or equal to a predetermined value, and determine that an abnormality has occurred, thereby preventing reverse power flow. If the above method is performed by a microcomputer or the like, hardware becomes unnecessary, so that the frequency detection point does not shift due to the influence of the variation of the element and the temperature, and there is no signal delay due to the element, so that accurate power distribution is achieved. The power outage determination of the system becomes possible. Further, since a series of processing is performed in the microcomputer, noise resistance is improved as compared with the determination by hardware. Further, since hardware is not required, it is not necessary to use an element having high temperature characteristics and high accuracy, so that the cost is reduced. On the other hand, if a power failure occurs in the power distribution system, the error of the reactive voltage component Vd and the error of the phase command θd * at the zero-cross voltage point cannot be corrected, and the error is integrated by the integral gain of the PI compensation system 73, and the frequency shift is reduced. As a result, the power failure of the distribution system can be reliably detected without being affected by the load conditions connected to the interconnection point.

[0012]

1 and 2 show an embodiment of the present invention. FIG. 1 is a block diagram and FIG. 2 is a schematic flowchart.

The portion 102 in FIG. 1 corresponds to the reference numeral in FIG. 5, and a detailed description of functions and operations will be omitted. The control unit 55 is included in the phase control unit 101,
Since the power failure detection of the power distribution system 58 is performed by the signal of the phase control means 101, the BPF 54 becomes unnecessary. The insulating transformer 53 has been omitted because it is not particularly important for explanation. FIG.
The phase detection means 101 uses PLL control, and the control block diagram of FIG. 7A is inserted when the distribution system is three-phase AC, and the control block diagram of b is inserted when the distribution system is three-phase or single-phase AC. 1 in FIG. 1 is a part of the present invention. 10
Numeral 16 denotes a part for calculating the difference Δω ′ by taking a difference between data one sample before and current sampling data, and 11 to 14 denote comparators. Since Δω is signed data, it is necessary to monitor the upper and lower levels of Δω and Δω ', respectively. So, ref
1 is the upper limiter of the deviation Δω ', ref2 is the lower limiter of the deviation Δω', ref3 is the upper limiter of the deviation Δω, ref4
Is a lower limiter of the deviation Δω.

When a power failure occurs in the power distribution system, a frequency shift occurs due to the divergence of the PLL control system 101 described in the section of the means for solving the problem. At this time, the value of Δω shifts to the plus or minus side, and the comparator 1
1 and 13, Δω and Δω 'are reference voltages [ref1 and ref
3], the comparator 12
And 14 indicate that Δω and Δω 'are reference voltages [ref2 and ref4]
When the signal becomes smaller than the above, the signal is output, and the signal is transmitted to the 15 OR gates. When a signal enters one of the four inputs, the OR gate 15 outputs a trip signal 17 to notify an undescribed microcomputer of an abnormality. The microcomputer stops the inverter by the trip signal 17 and disconnects the power distribution system. At this time, .DELTA..omega. Is provided for detecting a frequency change with a slow change, and .DELTA..omega. 'Is provided for detecting a steep frequency change, and secures protection by taking two OR conditions of .DELTA..omega. And .DELTA..omega.'. . Such a function can be operated by a digital circuit. A digital circuit has higher noise resistance and a higher signal transmission speed than an analog circuit, and thus can perform a protection operation at a very high speed. FIG. 2 is a flowchart showing the operation of FIG. First, monitor Δω 21 to 21
23, and then monitor .DELTA..omega..omega. '. In any case, when any of the limiter value determination conditions 22 to 25 is met, the inverter is stopped 28. Otherwise, the data of the current sampling Δω is held 27 and the operation returns to the normal operation 2
9. For example, if the quality of the voltage waveform of the distribution system is poor, the variation width of Δω becomes large, and an over / under frequency trip is likely to occur. In such a case, if the software shown in Fig. 2 is used, the values of the upper and lower limiters can be easily changed. By performing the protection operation in (1), the circuit becomes unnecessary, and the size can be reduced.

In FIG. 3, since Δω is signed data,
FIG. 4 is a block diagram in which Δω and Δω ′ are converted into absolute values for monitoring, and a portion 100 in FIG. 1 is taken out and changed to the second embodiment. The function newly added to the circuit of FIG. 1 is an absolute value converter of 33 and 34, and the judgment condition only needs to monitor the upper limiter on the plus side. Accordingly, two comparators 31 and 32 can obtain a function equivalent to that of FIG. FIG. 4 is a flowchart of the operation of FIG. The processing of the flowchart in FIG.
4 is basically the same as the processing of the flowchart of FIG.
The functions added to the flowchart of FIG. 5 are the parts 42 and 46 for converting Δω and Δω ′ into absolute values, and the parts 43 and 44 for the limiter determination conditions. In addition, since Δω [n] is converted 42 to an absolute value, Δω [n] needs to be stored in order to calculate 26 in the latter half of the processing, so that Δω [n] is temporarily saved in a register. And return 45. The limiter judgment condition is 43 on the plus side.
And 44 may be determined. As described above, even if Δω and Δω ′ are converted into absolute values and monitored, power failure detection due to frequency shift can be performed. Further, since it is only necessary to monitor the determination condition on the plus side only, the processing is simplified.

[0016]

According to the present invention, the well-known PLL control is used as a means for controlling the phase synchronization of the power supply voltage, and when the power distribution system is a three-phase alternating current in particular, the correction value of the invalid voltage error component is corrected. In the case of phase alternating current or single phase alternating current, a power outage detection of the power distribution system can be performed by constantly monitoring the correction value of the error component of the phase command value at the zero-cross voltage point. For this reason, hardware is not required, cost is reduced, and noise resistance is improved as compared with a detection method using hardware. Further, since a signal delay and a shift of a detection point in hardware are eliminated, accurate power failure detection can be performed. Further, when the phase synchronization control with the power supply voltage is not normally performed, the frequency shift occurs due to the integration of the error, so that the power failure can be detected without depending on the load condition connected to the interconnection point.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a flowchart of FIG.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a flowchart of FIG. 2;

FIG. 5 is a block diagram of a conventional example of a frequency shift method.

FIG. 6 is a characteristic diagram of the frequency shift detection filter of FIG. 5;

FIG. 7 is a block diagram of a PLL control system known in power supply voltage phase synchronization control.

[Explanation of symbols]

11 to 14: comparator, 15: OR gate section, 16
... Deviation calculator, 17 trip signal, 31, 32 comparator, 33, 34 absolute value converter, 51 solar cell, 52 inverter, 53 insulating transformer, 54 bandpass filter, 55 controller 56 ... Measurement voltage detector, 57 ... Load device, 58 ... Distribution system, 59 ... System switch, 71 ... α-β converter, 72 ... dq converter, 73 ...
Proportional / integral compensation system, 74 ... sin / cos generator, 75 ... integrator.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Shoji Yaginuma 7-1-1 Higashi Narashino, Narashino City, Chiba Prefecture Inside Hitachi Keiyo Engineering Co., Ltd.

Claims (5)

[Claims] 1. A solar power generation system comprising: a solar cell; and a power converter for converting DC power generated by the solar cell into a predetermined AC power, wherein the power converter is connected to a commercial power supply to transfer power. In the system, the voltage v 'at the interconnection point is used as a feedback signal, the voltage v of the distribution system and the output voltage v' of the inverter are synchronized, and the phase difference between the two is used as an error, and a correction value Δω for correcting the error is calculated. A photovoltaic power generation system comprising: a phase control unit that performs the control, recognizes that a commercial power supply is abnormal when the correction value Δω exceeds a certain range, and cuts off connection to the commercial power supply. 2. A phase for converting any two-phase voltage of a three-phase commercial power supply into two-axis orthogonal stationary coordinates to calculate an invalid component, and using the invalid component as an error to correct the invalid component. A photovoltaic power generation system that has control means, recognizes that the commercial power supply is abnormal when the correction value exceeds a certain range, and cuts off the connection to the commercial power supply. 3. A phase control means according to claim 1, wherein a signal is generated at a zero crossing point from a voltage at an interconnection point, a phase command value is held by the signal, and a phase difference is corrected from the held phase command value. A photovoltaic power generation system that recognizes that a commercial power supply is abnormal when the correction value exceeds a certain range, and shuts off the connection to the commercial power supply. 4. The method according to claim 1, wherein the correction value of the phase control means is taken in at a certain sampling period, a deviation for each sampling is calculated, and when the deviation exceeds a certain range, it is recognized as a commercial power supply abnormality, A photovoltaic power generation system that cuts off the connection to commercial power. 5. The system according to claim 1, wherein a deviation of the correction value of the phase control means for each sampling is converted into an absolute value, and when the value exceeds a certain range, it is recognized as a commercial power supply abnormality,
A photovoltaic power generation system that cuts off the connection to commercial power.