JPH0731052A - Solo operation preventive unit for system interconnection inverter - Google Patents

Abstract

PURPOSE:To prevent solo operation of a system interconnection inverter at the time of balance power interruption by normally shifting the phase of output current from the inverter every predetermined time and monitoring the variation of voltage phase thereby detecting power interruption. CONSTITUTION:During normal counting operation of a timer 14, a frequency divider 12 divides the frequency of a clock 13 such that the frequency and phase of output current from a power converter 2 match those of the system through a phase locked loop 16 and a phase variation detector 15 is masked during that interval. When the timer 14 counts up every 2 sec, for example, the frequency division ratio of the frequency divider 12 varies and the phase of output current from the power converter 2 is shifted while at the same time the phase variation detector 15 is unmasked. This constitution prevents the solo operation positively with no erroneous function at the time of balance power interruption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid-connected inverter that converts power generated by a solar cell or the like into alternating current, and supplies the load to the commercial power system by connecting it to a load. The present invention relates to an isolated operation prevention device for a grid-connected inverter that prevents the occurrence.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration example of a conventional system interconnection inverter. In FIG. 3, 1 is a solar cell, 2 is a power converter, 3 is a voltage relay, 4 is a frequency relay, and 5 is a switch. , 6 is a commercial power system, and 7 is a load. Usually, the DC power generated by the solar cell 1 is converted into AC by the power converter 2, and is connected to the commercial power system 6 and supplied to the load 7. Since the AC output of the power converter 2 is connected to a commercial power system having an extremely low impedance, a current control method is generally adopted and the power converter 2 operates as a so-called current source. That is, the generated power of the solar cell 1 is converted into AC power by directly controlling the amplitude of the alternating current of the power conversion device 2 according to the generated power of the solar cell 1.

The alternating current output from the power converter 2 is
A high power factor with a small reactive component is desired, and is usually controlled so as to output a sine wave current that matches the voltage phase of the commercial power system 6.

By the way, maintenance in the commercial power system 6
When performing a work power outage for inspection, etc., it is necessary to open the switches above the power outage segment to make the power outage segment non-voltage,
If a grid-connected inverter as shown in Fig. 3 is installed in the power outage section, stop the power converter 2 at the same time as the power outage,
It is necessary to open the switch 5 and disconnect the grid interconnection inverter from the commercial power grid. In the unlikely event that the power converter 2 does not stop and the switch 5 does not open, a voltage is applied to the power failure section by the grid interconnection inverter, resulting in a very dangerous state.

Now, in order to detect a power failure in the commercial power system and disconnect the grid-connected inverter, generally, the voltage and frequency of the commercial power system 6 (hereinafter referred to as system voltage and system frequency) are determined by the voltage relay 3 and the frequency relay 4. You just need to monitor the For example, set the voltage relay 3 to the nominal value of the system voltage ±
If 10% and the frequency relay are set to the nominal value of the system frequency ± 1%, the system voltage or the system frequency deviates from this range due to the power failure, and the power failure can be detected.

However, although it is extremely rare, the output power of the power converter 2 and the load 7 at the time of a power failure of the commercial power system 6.
If the power consumption of is balanced between active and reactive components, the output of the grid-connected inverter, which should have been out of power, will hardly change in voltage and frequency, and will charge the load 7 for a long time. Therefore, so-called isolated operation occurs. In this case, the output voltage of the power converter 2 hardly changes when the active component is balanced at the time of power failure, and the output frequency hardly changes when the reactive component is balanced. Therefore, if both are balanced, it is not possible to detect a power failure with either the voltage relay 3 or the frequency relay 4.

Even in the past, in order to solve this,
A method of monitoring the harmonic voltage included in the system voltage (Japanese Patent Publication No. 63-50941) and a method of monitoring the periodic fluctuations of the system frequency (Japanese Patent Laid-Open No. 3-242979) have been devised. If it is made good, there is an unavoidable problem that a malfunction always occurs.

An object of the present invention is to solve the above-mentioned problems, to reliably detect a power failure in a commercial power system to disconnect a grid-connected inverter, and to perform an independent operation in which almost no malfunction always occurs. To provide a protection device.

[0009]

In order to achieve the above object, according to the present invention, a phase shift means for shifting an output current phase of a grid interconnection inverter every predetermined time, and a phase shift means for synchronizing with the timing of the phase shift are provided. A means for monitoring the voltage phase change of the commercial power system is provided, and when the voltage phase change exceeds a predetermined level, the grid interconnection inverter is disconnected from the commercial power system.

[0010]

According to the islanding prevention device of the present invention configured as described above, the output current phase of the grid-connected inverter is constantly shifted every predetermined time. Since it is extremely low, shifting the output current phase of the grid interconnection inverter does not affect the phase of the grid voltage at all. However, when a power failure occurs, the voltage impedance changes according to the shift of the current phase due to the impedance of the load. Therefore, if this is monitored, the occurrence of the power failure can be reliably detected.

Further, since the voltage phase change is monitored in synchronization with the phase shift timing and is masked during the other periods, it is almost impossible to detect the voltage phase change due to other causes and cause a malfunction. Absent. Furthermore, if a power failure is detected only when this voltage phase change is detected a plurality of times in succession, it is possible to virtually eliminate the occurrence of malfunction.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing one embodiment of the present invention, and FIG. 2 is a diagram showing its operation, which will be described below with reference to the drawings. Figure 1
In the power converter 2, 11 is a sine wave generator, 12 is a frequency divider, 13 is a clock, 14 is a timer, 15 is a phase change detector, and 16 is a PLL (phase locked loop). Is.

At all times, while the timer 14 is counting, the frequency divider 12 divides the frequency of the clock 13 by the PLL 16 so that the frequency and phase of the output current of the power converter 2 match the system frequency. The phase change detector 15 is masked so as not to operate. Timer 14 is about 2
When counting up every second, the frequency division ratio of the frequency divider 12 changes, the output current phase of the power converter shifts, and at the same time, the mask of the phase change detector 15 is released and detection becomes possible.

For example, the frequency division ratio of the frequency divider 12 is always 10
If the frequency division ratio is set to 9 for one cycle in accordance with the count-up of the timer 14 and the zero cross of the system voltage, the maximum value of the phase shift is about 36 degrees (60 Hz).
Time). However, when the commercial power system 6 is normal,
As mentioned above, its impedance is extremely low,
Figure 2. The change in the output current phase of the power converter 2 does not affect the system voltage phase at all as shown in b (T2 = T1),
As a result, the phase change detector 15 does not detect.

However, if a power failure occurs and a balance state occurs, the change in the output current phase of the power converter 2 will be as shown in FIG. As shown in c, the load 7 appears as it is as the output voltage phase change, and the phase change detector 15 can detect this. In this case, the phase change value Δφ is obtained by 2π (T1−T2) / T1, and the detection threshold value may be set to about 10 degrees.

When the load 7 is a transformer, a rotating machine, or the like, a large inrush current flows when these are turned on, and a phase change exceeding 10 degrees may occur in the system voltage even under normal conditions. However, the detectable period of the phase change detector 15 is as shown in FIG. As shown in d, it is only about 1 to 2 cycles after the timer 14 counts up, and considering that the count-up is every 2 seconds, it is extremely unlikely that these input timings and detection timings coincide with each other, resulting in malfunction. It is thought that there is almost no occurrence. Also,
If the phase change detector 15 detects the power failure only when the phase change detector 15 detects the phase change twice or more continuously every two seconds, the malfunction can be virtually eliminated at the expense of some delay in the detection of the power failure. it can.

[0017]

As described above, according to the present invention, the output current phase of the continuous system interconnection inverter is shifted at every predetermined time, and the power failure is detected by monitoring the voltage phase change caused by the power failure. Therefore, there is an effect that it is possible to reliably prevent the islanding operation that occurs at the time of the balance power failure without malfunction.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the device of the present invention.

FIG. 2 is a diagram showing the operation of the device of the present invention.

FIG. 3 is a diagram showing a configuration example of a conventional general grid interconnection inverter.

[Explanation of symbols]

 1 solar cell 2 power converter 3 voltage relay 4 frequency relay 5 switch 6 commercial power system 7 load 11 sine wave generator 12 frequency divider 13 clock 14 timer 15 phase change detector 16 PLL (phase locked loop)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H02M 7/48 M 9181-5H

Claims (1)

[Claims] 1. In a grid-connected inverter that uses a battery generated power as a DC power supply and supplies power to a load by linking with a commercial power grid, the output current phase of the grid-connected inverter is shifted every predetermined time. Phase shift means, means for monitoring the voltage phase change of the commercial power system in synchronization with the phase shift timing of the phase shift means, and when the voltage phase change exceeds a predetermined level once or a plurality of times. An isolated operation preventing apparatus for a grid-connected inverter, comprising: a switch that cuts off the grid connection with the commercial power system.