JP2000236623A - Overvoltage-detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain with a simple constitution an overvoltage-detecting device which can detect the instantaneous overvoltage of a system power source. SOLUTION: An overvoltage detecting device 60 drops the system voltage of a system power source 52 by means of a potential transformer 62. Consequently, a voltage that can be dropped by means of an A/D converter 76 and changes according to the voltage waveform of the system voltage is inputted to the converter 76. The converter 76 outputs the voltage after A/D conversion with a prescribed sampling timing. Therefore, the instantaneous value of the system voltage at every sampling time is inputted to an arithmetic section 78. the arithmetic section 78 detects the occurrence of an overvoltage which is higher than an effective value by computing the effective value, along with the detection of the instantaneous overvoltage of the system voltage form the voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overvoltage detecting device for detecting an overvoltage of an AC power supply.

[0002]

2. Description of the Related Art In recent years, a system interconnection system for connecting (interconnecting) a photovoltaic power generator to a commercial power system has become widespread. In such a system interconnection system, DC power generated by a solar cell is converted into AC power by an inverter device and regenerated to system power.

In such a system interconnection system, an overvoltage of a system voltage is detected for protection of a load connected to a system power supply and protection of the system interconnection system itself, and the inverter device is stopped or the inverter device is stopped. And system power supply.

Incidentally, a voltage detection circuit 150 shown in FIG. 5 is generally used for detecting the voltage of such a system power supply. In the voltage detection circuit 150, after the voltage of the system power supply 52 is reduced by the PT 152, full-wave rectification is performed by the rectification circuit 154 using a plurality of comparators. Then, the input value of the input port 1 of the microcomputer 158 is smoothed by using an execution value conversion IC
Enter 60. In the microcomputer 158, the input DC voltage is A / D converted by the A / D converter 162, and the voltage is read.

The microcomputer 158 detects from this voltage whether or not an overvoltage has occurred in the system power supply 52.

In recent years, it has been desired to protect not only the overvoltage of the effective value of the AC power supply but also the instantaneous overvoltage to more reliably protect the inverter device.

However, in the above-described voltage detection circuit, a CR circuit is connected to an IC for converting an effective value.
The time required for detection is 10 due to the time constant of this CR circuit.
It has exceeded 0 msec. The system power supply has a frequency of 5
0Hz-60Hz, 1 cycle period is 16.6msec
２０20 msec.

[0008] In order to detect the effective value of the system voltage, a detection time of 100 msec is sufficient, but it is difficult to detect an instantaneous overvoltage in this time.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has an overvoltage detecting apparatus capable of shortening a detection time with a simple circuit configuration and reliably detecting an instantaneous overvoltage. The purpose is to propose.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a transformer for lowering the voltage of a system power supply and outputting a voltage that changes in accordance with the voltage waveform of the system power supply. A / D conversion means for A / D converting the transformed voltage at a predetermined sampling time;
Determining means for determining whether or not the voltage of the AC power supply exceeds a predetermined value based on the output of the converting means.

According to the present invention, the voltage of the system power supply is transformed by the transformer into a voltage range that can be processed by the A / D converter, and the voltage is converted to the A / D at a predetermined sampling time.
Convert.

In general, the sampling cycle of the A / D converter can be made extremely shorter than the cycle of the power supply of the system power supply, so that the A / D converter can read the instantaneous value of the system voltage for each sampling time. .

Thus, not only the effective value of the system power supply but also the instantaneous value can be detected, and not only the effective value but also the instantaneous value overvoltage can be detected.

According to a second aspect of the present invention, the determination means determines that an overvoltage has occurred in the AC power supply when the output of the A / D conversion means exceeds a predetermined voltage continuously for a predetermined number of times. It is characterized by doing.

According to the present invention, an overvoltage is detected from the sampling period and the number of times. Thereby, erroneous determination due to harmonics or the like can be prevented, and instantaneous overvoltage of the system power supply can be accurately detected.

Further, the invention according to claim 3 is characterized in that the A / D
A calculating means for calculating an effective value of the AC power supply from an output of the converting means, wherein the determining means determines that an overvoltage has occurred in the AC power supply based on a calculation result of the calculating means. .

According to the present invention, the effective value of the system voltage is calculated from the voltage sampled by the A / D converter and the number of times of sampling, and it is determined from the calculated effective value whether an overvoltage has occurred.

The effective value can be easily calculated from the sampled voltage, so that the instantaneous overvoltage and the effective value overvoltage can be easily detected.

As described above, according to the present invention, the sampling time of the voltage can be extremely shortened with respect to the frequency of the system power supply which is the commercial power, so that the effective value as well as the instantaneous value of the system voltage can be detected. .

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a schematic configuration of a photovoltaic power generator 10 applied to the present embodiment. The solar power generation device 10 includes an inverter 50. The inverter 50 is provided with an inverter circuit 18 together with a microcomputer (hereinafter, referred to as the “microcomputer 14”).

The inverter circuit 18 is provided with a switching element 20 using, for example, an IGBT, and the switching element 20 is bridge-connected. The inverter circuit 18 is connected to the microcomputer 14 via the IGBT drive circuit 16, and the switching element 20 is turned on / off based on a switching signal output from the microcomputer 14.

The inverter 50 is provided with a booster circuit 24. DC power generated by the solar cell array 12 composed of a number of solar cell modules is input to the booster circuit 24 via the capacitor 22. . The booster circuit 24 boosts the input DC power to a predetermined voltage. The DC power boosted to a predetermined voltage by the booster circuit 24 is input to the inverter circuit 18 via the capacitor 26.

On the other hand, the microcomputer 14 is connected to a U-phase voltage detection circuit 30, a V-phase voltage detection circuit 32, and a zero-cross detection circuit 28. Each of the U-phase voltage detection circuit 30, the V-phase voltage detection circuit 32, and the zero-cross detection circuit 28 is connected to a system power supply 52 that is a commercial power supply.
The phase voltage detection circuit 30 is, for example, a single-phase three-wire 100/200.
The voltage between the U phase of the system power supply 52 which is V and the ground is detected, and the V phase voltage detection circuit 32 detects the voltage between the V phase and the ground. Further, the zero-crossing detection circuit 28 is configured to output a voltage between the U-phase and the V-phase of the system power supply 52 (hereinafter referred to as “system voltage”).
Is 0V, that is, the timing at which the phase of the system voltage switches.

The microcomputer 14 includes a U-phase voltage detection circuit 30,
The V-phase voltage detection circuit 32 and the zero-cross detection circuit 28 detect the voltage and phase (zero-cross point) of the system power supply 52.

The microcomputer 14 controls a switching signal for driving the switching element 20 based on the detected voltage and phase of the system power supply 52. That is, the microcomputer 14 drives the switching element 20 based on the voltage and the phase of the system power supply, thereby converting the DC power input from the booster circuit 24 into AC power according to the voltage and the phase of the system power supply 52. It has become. , The inverter circuit 18 includes the reactors 34 and 35 and the capacitor 3
6 is connected to a distribution board 42 via a filter circuit 38 constituted by the circuit board 6 and a parallel-off conductor 40, and since the distribution board 42 is connected to the system power supply 52, the inverter 50 is connected to the system power supply 52. Connected to.

The power output from the inverter circuit 18 has a sawtooth waveform, and the filter circuit 38 removes harmonic components, thereby outputting AC power whose voltage and phase match those of the system power supply 52.

The microcomputer 14 includes a generated voltage detection circuit 44
And the generated current detection circuit 46 together with the inverter circuit 18
Is connected to a current detection circuit 48 for detecting a current output from. The microcomputer 14 determines the power generated by the solar cell array 12 from the power generation voltage detected by the power generation voltage detection circuit 44 and the power generation current detected by the power generation current detection circuit 46.
By performing T control (maximum power tracking control), the power generated by the solar cell array 12 is efficiently output to the system power supply 52.

The microcomputer 14 constantly monitors whether or not the system power supply 52 has failed. When the system power supply 52 fails, the microcomputer 14 operates the parallel-off conductor 40 to open the contacts, thereby connecting the system power supply 52 and the inverter. Cut off 50,
The so-called independent operation of the inverter 50 is prevented.

The microcomputer 14 has an EE (not shown).
A memory such as a PROM is provided, and various set values for system interconnection protection are stored in the memory, and the microcomputer 14 performs system interconnection protection for the inverter 50 based on the set values. .

The inverter 50 by the microcomputer 14
For the operation control of, a conventionally known configuration can be used, and a detailed description is omitted in the present embodiment.

Incidentally, an overvoltage detecting device 60 is formed in the inverter 50. When the microcomputer 14 detects an overvoltage of the system voltage by the overvoltage detecting device 60,
The system interconnection protection such as the operation stop of the inverter 50 and the opening operation of the parallel-off conductor 40 is performed.

The overvoltage detection device 60 includes two instrument transformers (hereinafter referred to as “P”) each connected to the system power supply 52.
T62 ”), and as shown in FIG. 1, each of the PTs 62 is connected to an input port 66 of the microcomputer 14 via a voltage dividing circuit 64 or the like.

As shown in FIG. 2, the primary side of the PT 62 is connected to the U-phase and the ground phase (neutral point) or the V-phase and the ground phase of the system power supply 52. An AC voltage (100 V system voltage) is applied. PT6
2 steps down the 100 V system voltage to a predetermined voltage. It should be noted that the U-phase or V
The phase system voltage detection has the same configuration, and FIG. 1 shows only one of them. Hereinafter, only one of them will be described, and the other description will be omitted.

As shown in FIG. 1, the voltage dividing resistors 68A and 68B are connected to the secondary side of the PT 62, and the resistors 70A and 70B are connected to the secondary side ends.
A constant voltage (for example, 5 V) is applied between the resistors 70A and 70B.
Thus, a voltage v corresponding to the system voltage of the system power supply 52 is obtained.

That is, as shown in FIG.
Voltage division ratio and voltage division resistance 68A, 68B by 0A, 70B
The system power supply 5
Thus, a voltage v that changes according to the voltage waveform 2 is obtained.

This voltage v is supplied to an input port 66 of the microcomputer 14 via a capacitor 72 for removing noise and a diode 74 for protecting the microcomputer 14.

On the other hand, the microcomputer 14 has an A / D converter 7
6, a voltage v corresponding to the system voltage is input to the A / D converter 76. The A / D converter 76 reads the voltage v input at a predetermined sampling time and outputs the voltage v to an arithmetic unit 78 formed by a CPU or the like. That is, the voltage v which is an instantaneous value for each sampling time is input to the arithmetic unit 78.

The sampling time t of the A / D converter 76 is, for example, 70 μsec to 140 μsec (in terms of frequency,
The sampling time of an A / D converter provided in a general microcomputer (about 14 kHz to about 7 kHz) is used.

Thus, for example, by setting the frequency of the AC power supply 52 to 60 Hz and the sampling time t to 70 μsec, approximately 240
Each time, the voltage v is output to the calculation unit 78.

The arithmetic unit 78 determines whether the voltage v input via the A / D converter 76 exceeds a predetermined voltage. That is, from the voltage v input through the A / D converter 76, it is determined whether or not the instantaneous value of the system voltage at each sampling time exceeds a predetermined voltage. Is determined to exceed the predetermined voltage, it is determined that an overvoltage has occurred in the system power supply 52.

On the other hand, in the arithmetic section 78, the A / D converter 76
The effective value V of the system voltage is calculated from the output of the above, and it is determined whether or not the effective value V of the system voltage has exceeded a predetermined voltage from the calculation result, and it is determined that the effective value V of the system voltage has exceeded the predetermined voltage. Then, it is determined that an overvoltage has occurred in the system power supply 52.

When the microcomputer 14 of the inverter 50 detects the overvoltage of the system voltage in this way, it stops the inverter circuit 18 or operates the parallel-off conductor 40 to protect the inverter 50 from the overvoltage of the system power supply 52. It has become.

The operation of this embodiment will be described below.

The photovoltaic power generation device 10 includes the solar cell array 1
When the solar cell in the solar cell module forming the second receives solar light, it generates DC power according to the amount of received light. This DC power is output from solar cell array 12 to inverter 50.

In the inverter 50, the solar cell array 12
When the DC power supplied from the power supply reaches a predetermined voltage or a predetermined power, the boosting circuit 24 controlled by the microcomputer 14 boosts the power and supplies the boosted power to the inverter circuit 18.

At the same time, the microcomputer 14
The switching signal is controlled to the IGBT drive circuit 16 based on the voltage and the phase of the power supply 2, the power generated by the solar cell array 12, and the like. The switching element 20 of the inverter circuit 18 is turned on / off by the IGBT drive circuit 16 based on the switching signal.

The power output from the inverter circuit 18 by the on / off driving of the switching element 20 is:
By passing through the filter circuit, AC power whose voltage and phase match that of the system power supply 52 becomes AC power.
Is output to the line.

On the other hand, when the voltage of the system power supply 52 decreases due to a power failure or the like, the microcomputer 14 stops the inverter 50 or performs an opening operation of the parallel-off conductor 40 to disconnect the inverter 50 from the system power supply 52 and To prevent the islanding operation.

By the way, the inverter 50 is provided with an overvoltage detecting device 60 for detecting an overvoltage of the system power supply 52. When the system voltage of the system power supply 52 becomes abnormally high due to the overvoltage detecting device 60, In order to protect the system interconnection, the inverter 50 is stopped or the parallel-off conductor 40 is opened.

The overvoltage protection device 60 outputs a voltage v corresponding to the system voltage stepped down by the PT 62. This voltage v is a voltage that changes in accordance with the voltage waveform of the system voltage, and this voltage v is input to an A / D converter 76 provided in the microcomputer 14.

The A / D converter 76 A / D converts this voltage v at a predetermined sampling time t, and
Output to As a result, the instantaneous value of the voltage v corresponding to the system voltage at each sampling time t is input to the arithmetic unit 78.

In the arithmetic unit 78, the A / D converted voltage v
It is determined whether or not an overvoltage has occurred in the system power supply 52 based on.

The flowchart of FIG. 4 shows an example of the overvoltage detection executed by the arithmetic section 78. This flowchart is executed by, for example, starting the power generation by the solar cell array 12 and starting the operation of the microcomputer 14 and starting the A / D conversion by the A / D converter 76. When the operation of the A / D converter 76 is stopped, the operation ends.

This flowchart shows the operation of the A / D converter 76.
In the first step 100, the voltage v output from the A / D converter 76 is read. In the next step 102, it is determined whether or not the voltage v exceeds a predetermined value vs. The predetermined value vs is, for example, a voltage of 180 V or more when converted to 100 V, and is not normally generated, but is generated for a predetermined time or more even momentarily, and is thus connected to the system power supply 52. Inverter circuit 1
8 can be set to a voltage that may cause damage to the switching element 20 and the like.

When the system voltage is in the normal voltage range, since the voltage v does not exceed the predetermined value vs, a negative determination is made in step 102 and the process proceeds to step 104. In step 104, the count value C of the number of times that the voltage v continuously exceeds the predetermined value is reset (C = 0). The count value C is reset when the microcomputer 14 starts operating.

In the next step 106, the effective value V of the system voltage is calculated from the voltage v. That is, the voltage v is an instantaneous value corresponding to the system voltage for each sampling type t,
The effective value of the system voltage can be obtained by sequentially integrating the voltage v in accordance with, for example, the number of times of sampling. The calculation of the effective value can use a conventionally known method, and a detailed description thereof will be omitted in the present embodiment.

In the next step 108, it is confirmed whether or not the calculated effective value V exceeds a predetermined value Vs.

On the other hand, as shown by the two-dot chain line in FIG.
If the voltage v input from the A / D converter 76 exceeds the predetermined value vs (v ≧ vs), an affirmative determination is made in step 102 and the process proceeds to step 110.

In step 110, the count value C is counted up (C = C + 1). In step 112, it is determined whether or not the count value C has reached a predetermined number of times Cs (for example, Cs = 10) (C ≧ Cs). Confirm.

Here, when the count value C reaches the predetermined number Cs, an overvoltage of the system power supply 16 in which the instantaneous value of the system voltage rises occurs, and it is determined that the instantaneous value has become a high voltage for a predetermined time or more (step 112). Step 1)
Move to 14. In this step 114, the operation of the inverter 50 (the switching element 2 of the inverter circuit 18)
0 is stopped, the parallel-off conductor 40 is opened, and a process for an overvoltage that disconnects the inverter 50 and the system power supply 52 is performed.

This prevents the switching element 20 and the like constituting the inverter 50 from being damaged by the instantaneous overvoltage of the system power supply 52.

On the other hand, as shown by a dashed line in FIG.
Although the instantaneous voltage of the system power supply 52 is not abnormally high, when the system voltage increases as a whole, the effective value V also increases. As a result, the effective value V becomes a predetermined value Vs (for example, 140
If v) is exceeded, an affirmative determination is made in step 108 and the routine proceeds to step 114. The predetermined value Vs for the effective value V may be set based on the set value.

Thus, the inverter 50 and the system power supply 5
2 and the inverter 50 is connected to the system power supply 52
Overvoltage protection.

As described above, the overvoltage detection device 60 provided in the inverter 50 inputs the voltage v corresponding to the system voltage to the A / D converter 76 of the microcomputer 14 and
With a simple configuration in which sampling is performed by the D converter 76, not only an overvoltage of the effective value V of the system voltage but also an instantaneous overvoltage can be detected, and the inverter 50 can be reliably protected from the overvoltage of the system power supply 52.

In the present embodiment, the overvoltage detection device 60 has been described as being used as the inverter 50 of the photovoltaic power generation device 10 which is a system interconnection power generation device. The present invention is not limited to the ten inverters 50, and can be applied to a system interconnection power generation device of any configuration that matches generated power to a system power supply 52 that is a commercial power supply and outputs the power.

[0067]

As described above, according to the present invention, it is possible to detect the instantaneous value of the system voltage as well as the effective value of the system voltage with a simple configuration for stepping down the system voltage and performing A / D conversion. This provides an excellent effect that the inverter can be reliably protected not only from an overvoltage of the effective value of the system voltage but also from an overvoltage of the instantaneous value.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an overvoltage detection device to which the present invention has been applied.

FIG. 2 is a block diagram showing a schematic configuration of a photovoltaic power generator applied to the present embodiment as a grid-connected power generator.

FIG. 3 is a diagram schematically showing a change in a voltage input to an A / D converter provided in the microcomputer.

FIG. 4 is a flowchart illustrating an example of overvoltage detection.

FIG. 5 is a schematic block diagram illustrating an example of a conventional overvoltage detection circuit.

[Description of Signs] 10 Photovoltaic power generator 14 Microcomputer (A / D conversion means, calculation means, control means) 18 Inverter circuit 20 Switching element 40 Off-conductor 50 Inverter 52 System power supply 60 Overvoltage detection device 62 PT (Transformation means) 64 voltage dividing circuit (transformation means) 76 A / D converter (A / D conversion means) 78 calculation unit (calculation means, control means)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaki Banri 2-5-2-5, Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Isao Morita 2-chome Keihanhondori, Moriguchi-shi, Osaka No. 5-5 Sanyo Electric Co., Ltd. (72) Inventor Toshio Ueda 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 2G035 AA13 AA16 AB08 AC01 AC03 AC15 AD06 AD11 AD14 AD19 AD28 AD65 5G004 AA01 AB02 BA08 DC01 DC14 5G066 HA13 HB06

Claims (3)

[Claims] 1. A voltage converting means for lowering a voltage of a system power supply to output a voltage that changes in accordance with a voltage waveform of the system power supply, and A / D converting the voltage transformed by the voltage converting means at a predetermined sampling time. An overvoltage detection device comprising: A / D conversion means; and determination means for determining whether or not the voltage of the AC power supply exceeds a predetermined value based on an output of the A / D conversion means. 2. The method according to claim 1, wherein said determining means determines that an overvoltage has occurred in said AC power supply when an output of said A / D converting means exceeds a predetermined voltage continuously for a predetermined number of times. The overvoltage detection device according to claim 1. 3. An arithmetic unit for calculating an effective value of the AC power supply from an output of the A / D conversion unit, wherein the determining unit generates an overvoltage in the AC power supply based on a calculation result of the arithmetic unit. The overvoltage detection device according to claim 1, wherein the overvoltage detection device determines that the overvoltage is present.