JPH09117066A - System interconnection power supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system interconnection power supply system in which an inverter main circuit is previously diagnosed for failures and the interconnecting operation thereof can be started after it is determined that no failure is present. SOLUTION: An inverter main circuit 2 and an AC relay 13 are connected between DC input terminal 6 and AC output terminal 7 and controlled through a main control circuit 17 and a PWM control circuit 20. A current flowing into the inverter main circuit 2 is detected by means of a DC current sensor 15. The main control circuit 17 operates the inverter main circuit 2 while opening the AC relay 13 and the inverter main circuit 2 is self-diagnosed based on the fact that a current is detected by the DC current sensor 15 or not during that interval. The AC relay 13 is closed only when no failure is present thus starting the interconnecting operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid-connected power supply system for converting a DC output obtained from a DC power supply such as a solar cell into an AC output for reverse power flow to a commercial power system.

[0002]

2. Description of the Related Art In recent years, a photovoltaic power generation device as shown in FIG. 8 has been put into practical use as a system interconnection power supply system. In the device, the DC output obtained from the solar cell (1) is converted to an AC output through the inverter main circuit (2) and then supplied to the domestic load (5), and the surplus power is commercial power. system
Reverse flow is made to (3). Here, the inverter main circuit (2)
The operation of the inverter is controlled by the inverter control circuit (4).

The inverter main circuit (2) is a solar cell
A low-frequency link type inverter main circuit that performs pulse width modulation (PWM) on the DC output of (1) by switching the system frequency (50 Hz or 60 Hz) and a high-frequency link type inverter main circuit shown in FIG. 1 are known. ing. The high frequency link type inverter main circuit is, as shown in FIG. 1, a high frequency push-pull circuit that performs pulse width modulation on the DC output of the solar cell by switching at a high frequency of 20 to 40 kHz.
High frequency transformer for insulation provided with (8)
The output pulse obtained from the secondary side of the high frequency transformer (9) with (9) installed is a sine wave of the system frequency after passing through the rectifier circuit (10), full bridge folding circuit (11) and filter circuit (12). After being converted to, it is output to the commercial power system.
Also, at the output end of the filter circuit (12), an AC relay (13) that should be turned on / off when the main inverter circuit is stopped
And the breaker (14) that should be opened when a failure occurs are connected.

When the above inverter main circuit is started,
First, after turning on the AC relay (13), a drive signal is supplied to the high frequency push-pull circuit (8) and the full-bridge folding circuit (11) to operate both circuits. by this,
The DC power from the solar cell input to the DC input terminals (6) (6) is converted into AC power and supplied to the commercial power system from the AC output terminals (7) (7).

[0005]

By the way, if the AC relay (13) is turned on in a state where an element constituting the inverter main circuit has a failure such as a short circuit, as shown in FIG. Breakers (14) and breakers installed at appropriate places upstream to the interconnection point for the commercial power system.
Overcurrent may flow to the breakers (not shown), and these breakers may trip.

For example, as shown in FIG. 3 (a), when the AC relay (13) is turned on while the diode D constituting the rectifier circuit (10) is short-circuited, the path shown in the figure is instantaneously displayed. Then, the current I flows from the commercial power system side into the filter circuit (12) and the full-bridge loopback circuit (11), and the overcurrent protection function of the inverter control circuit causes the inverter main circuit to fall into a standby state. Also, as shown in FIG.
When the AC relay (13) is turned on while the switching element S1 constituting the full-bridge loopback circuit (11) is short-circuited, the filter circuit (12 ) And the full-bridge turn-back circuit (11), the current I flows, and the inverter main circuit also falls into a standby state. When the magnitude of the current I exceeds a certain level, the breaker (14) shown in FIG. 1, the breaker of the distribution board to which the inverter main circuit is connected, or the breaker installed further upstream is connected. , It will trip due to overcurrent.

Once these breakers trip,
It is troublesome because it is necessary to close it manually after restoration of the faulty part. Further, even if the breaker trip does not occur, it is dangerous to connect the main inverter circuit to the commercial power system with a failure.

Therefore, an object of the present invention is to diagnose the presence or absence of a failure in the inverter main circuit in advance when connecting the inverter main circuit to the commercial power system, and confirm that there is no failure, and then commercial power. It is to provide a grid-connected power supply system that can be connected to a grid.

[0009]

A system interconnection power supply system according to the present invention includes an inverter main circuit for converting DC power obtained from a DC power supply into AC power, and a power line between the inverter main circuit and a commercial power system. An intervening switching mechanism, a control circuit for controlling the operation of the inverter main circuit and the switching mechanism,
It is composed of a current sensor that detects a direct current flowing into the inverter main circuit. Here, the control circuit operates the inverter main circuit for a certain period of time with the switching mechanism opened, and determines whether the inverter main circuit has a failure or not depending on whether the current sensor detects a current of a certain level or more during this period. And a protection means for connecting the inverter main circuit to the commercial power system by closing the switching mechanism only when no failure is found by the failure self-diagnosis means.

In the above grid-connected power supply system, when no failure occurs in the inverter main circuit, even if the inverter main circuit is operated with the switching mechanism open, the output end of the inverter main circuit is Since it is open, no current loop is formed in the main circuit and therefore no output from the current sensor. As a result, the failure self-diagnosis means determines that there is no failure, and accordingly, the protection means closes the opening / closing mechanism and connects the inverter main circuit to the commercial power system.

On the other hand, when a failure such as a short circuit occurs in any element of the inverter main circuit, if the inverter main circuit is operated with the opening / closing mechanism open, the Since a closed loop is formed by the element in which a failure has occurred, a current exceeding a certain level flows in the closed loop due to the supply of electric power from the DC power supply. This current is detected by the current sensor. As a result, the failure self-diagnosis means determines that there is a failure, and in response to this, the protection means maintains the open / close mechanism in an open state and blocks interconnection of the inverter main circuit. Therefore, overcurrent does not flow from the commercial power system side into the inverter main circuit.

In a specific configuration, the inverter main circuit includes a primary side inverter circuit that performs pulse width modulation on the output of the DC power supply by switching at a frequency higher than the system frequency, and an output pulse of the primary side inverter circuit to the system frequency. It is equipped with a secondary side inverter circuit for converting to a sine wave and outputting it to the commercial power system, and an insulating transformer interposed between the primary side inverter circuit and the secondary side inverter circuit. The circuit is constructed.

In another specific configuration, the inverter main circuit subjects the output of the DC power supply to pulse width modulation by switching the system frequency, and converts the output pulse obtained by this into a sine wave for commercial power. An inverter circuit for outputting to the system and an insulating transformer connected to the output end of the inverter circuit are provided, and by this, an inverter main circuit of a low frequency link system is configured.

More specifically, the inverter main circuit is composed of a plurality of switching elements, and the failure self-diagnosis means has a current loop that bypasses the failure point by turning on at least one of these switching elements. The inverter main circuit is operated by turning on / off the plurality of switching elements in a sequence that is not formed. According to the specific configuration, in the failure diagnosis, when the plurality of switching elements forming the inverter main circuit are turned on / off, the current loop is prevented from being formed even though the inverter main circuit has no failure. Therefore, the correct diagnosis result is always obtained.

[0015]

According to the system interconnection power supply system of the present invention, when the inverter main circuit is connected to the commercial power system, it is diagnosed in advance whether or not the inverter main circuit has a failure, and it is confirmed that there is no failure. Then, the interconnection operation is started. Therefore, even when a failure occurs, breaker trip as in the past does not occur, and it is possible to always connect to the system in a safe state.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment in which the present invention is applied to the solar power generation device of FIG. 1 will be specifically described with reference to the drawings. The inverter device installed in the solar power generator is
As shown in Fig. 1, DC power from a solar cell (for example, DC
A pair of DC input terminals (6) for inputting 200V)
(6) and AC power to be supplied to the commercial power system (for example, A
A pair of AC output terminals (7) for taking out C200V)
High frequency push-pull circuit (8), high frequency transformer (9), rectifier circuit (10), full bridge folding circuit between (7)
(11), the filter circuit (12), the AC relay (13) and the breaker (14) are connected in series to form a high frequency link type inverter main circuit.

A DC current sensor (1) is provided on the line from one DC input terminal (6) to the high frequency push-pull circuit (8).
5) is attached, and the AC current sensor (1) is installed in the line from the full bridge turn-back circuit (11) to the filter circuit (12).
6) is installed. A pair of DC input terminals (6) (6)
The solar cell operating voltage Vn obtained from the DC current sensor (15), the solar cell operating current In obtained from the DC current sensor (15), and the inverter output voltage S obtained from the pair of AC output terminals (7) and (7)
a and the inverter output current Sb obtained from the AC current sensor (16) are supplied to the main control circuit (17) composed of a microcomputer, whereby the current command value Io
Is created. The current command value Io is supplied to the PWM control circuit (20) composed of a digital signal processor, whereby a drive signal for the switching elements G1 and G2 forming the high frequency push-pull circuit (8),
Drive signals are generated for the switching elements S1 to S4 that form the full-bridge folding circuit (11).

FIGS. 7 (a) to 7 (e) show how signal processing is performed in the process in which the DC power from the solar cell is converted into AC power by the inverter main circuit. That is, FIG.
The direct-current power shown in (a) is subjected to PWM control with a switching frequency of 20 to 40 kHz by the high-frequency push-pull circuit (8) to create the modulated pulse shown in FIG. 7 (b). The modulated pulse is generated by the rectifier circuit (10) in FIG.
After being rectified as shown in (c), the full bridge folding circuit (1
By (1), as shown in Fig. 7 (d), the switching frequency is folded back according to the system frequency (50Hz or 60Hz), and further, through the filter circuit (12), the AC power of the system frequency shown in Fig. 7 (e). Is converted to.

The main control circuit (17) shown in FIG. 1 has a maximum power point tracking function for gradually changing the operating point of the solar cell toward the optimum operating point where the maximum power can be obtained. That is, the output voltage Sa and the output current Sb of the inverter main circuit
The output power is calculated from the output power, and the voltage command value for defining the operating voltage is increased or decreased by a very small amount to determine the increase or decrease of the output power, and the voltage command value Io is increased in the direction of increasing the output power.
Is changed to gradually bring the operating point of the solar cell closer to the optimum operating point.

Further, the main control circuit (17) includes a protection function processing section (1
8) and a failure self-diagnosis processing unit (19). The failure self-diagnosis processing unit (19) is a high frequency push-pull circuit (8) and a full-bridge folding circuit with the AC relay (13) open.
(11) is operated only for a certain period of time, and whether or not a circuit element has a failure (short circuit) is self-diagnosed depending on whether or not a current is detected by the DC current sensor (15) during this period.
The protection function processing unit (18) responds to the diagnosis result by the failure self-diagnosis processing unit (19) only when the failure does not occur.
The C relay (13) is closed to start the interconnection operation to the commercial power system.

Here, the operation principle of the failure self-diagnosis processing unit (19) will be described with reference to FIGS. As described above, the failure self-diagnosis processing unit (19) operates the high frequency push-pull circuit (8) and the full-bridge folding circuit (11) for a certain period of time with the AC relay (13) open. As shown in 4, if the full-bridge loopback circuit (11) is turned on / off in the same sequence as in the normal interconnection operation, the full-bridge loopback circuit (11) will be used even if there is no short circuit in the circuit element.
In addition, a closed loop is formed in the filter circuit (12) by bypassing the faulty part in the path shown in the figure, and the closed loop is caused by the charging current of the capacitor C constituting the filter circuit (12). A current I flows. As a result, the original failure self-diagnosis function malfunctions.

Therefore, in this embodiment, at the time of failure self-diagnosis, the full-bridge turn-back circuit (11) is turned on / off in the sequence shown in FIGS. 5 (a) and 5 (b). That is, in the first half of the self-diagnosis period (250 msec), the switching elements S1 and S3 are turned on and the switching elements S2 and S4 are turned off, and in the second half of the self-diagnosis period (250 msec), the switching elements S1 and S3 are turned off. S2 and S4 are turned on. In this case, when the switching element S1 is on, the switching element S4 is off, and when the switching element S2 is on, the switching element S3 is off, so that the current as shown in FIG. No loop is formed.

FIG. 6A shows a failure self-diagnosis operation when the diode D constituting the rectifier circuit (10) is short-circuited due to a failure. In the secondary winding of the high frequency transformer (9) and the rectifier circuit (10), a closed loop is formed in the illustrated route,
By operating the high frequency push-pull circuit (8) in this state, current flows through the primary winding of the high frequency transformer (9),
A current I will be induced in the closed loop on the secondary side.
As a result, the DC current sensor 15 detects an instantaneous overcurrent exceeding a certain level.

Further, FIG. 6B shows a failure self-diagnosis operation when the switching element S2 constituting the full bridge folding circuit (11) is short-circuited due to a failure. A closed loop is formed in the secondary winding of the high frequency transformer (9), the rectifier circuit (10) and the full bridge folding circuit (11) in the illustrated route, and the high frequency push-pull circuit (8) operates in this state. A current flows through the primary winding of the high frequency transformer (9), and a current I is induced in the closed loop on the secondary side. As a result, the DC current sensor 15 detects an instantaneous overcurrent exceeding a certain level.

Therefore, the failure self-diagnosis processing section (19) of the main control circuit (17) shown in FIG. 1 judges that a failure has occurred based on the current detection signal In from the DC current sensor (15), and protects it. A signal to that effect is supplied to the processing unit (18). In response to this, the protection function processing unit (18) maintains the AC relay (13) in an open state and outputs the drive signal to be supplied to the high frequency push-pull circuit (8) and the full bridge folding circuit (11). Apply gate block. As a result, the high frequency push-pull circuit (8) and the full bridge folding circuit (11) are stopped.

FIG. 2 specifically shows the operations of the failure self-diagnosis processing section (19) and the protection function processing section (18) of the main control circuit (17). First, in step S1, the AC relay is turned off, and the switching elements G1 and G2 of the high-frequency push-pull circuit and the switching elements S1 to S4 of the full-bridge folding circuit are gate-blocked to set the standby state. To do.

Next, in step S2, it is determined whether or not all the operating conditions for the inverter main circuit are satisfied. If YES, the process proceeds to step S3 to switch the switching elements G1 and G2 of the high frequency push-pull circuit. The gate block is released and the operation of the high frequency push-pull circuit is started. Then, in step S4, the switching elements S1 and S3 of the full-bridge loopback circuit are turned on, the switching elements S2 and S4 are turned off, and the timer is reset to zero.

Thereafter, in step S5, it is determined whether or not a DC instantaneous overcurrent is detected. If YES, it is determined that an element short circuit is found, and the process returns to step S1.
If NO, the timer is 250 msec in step S6.
If NO, step S if NO
The current detection of 5 is repeated. If YES, step S7
And the switching elements S2 and S4 of the full-bridge folding circuit are turned on, and the switching elements S1 and S4 are turned on.
Turn off 3 and reset the timer to 0.

Then, in step S8, it is determined whether or not a DC instantaneous overcurrent is detected. If YES, it is determined that an element short circuit has been detected, and the process returns to step S1.
If NO, the timer is 250 msec in step S9.
If NO, step S if NO
The current detection of 8 is repeated. If YES, step S1
Move to 0.

The failure self-diagnosis of the present invention is performed by the above procedure, and if there is a failure, the standby state of step S1 is maintained. If there is no failure, the process proceeds to normal inverter startup processing.

That is, in step S10, the switching elements G1 and G2 of the high frequency push-pull circuit and the switching elements S1 to S4 of the full-bridge folding circuit are gate-blocked, and then in step S11, the AC relay is applied. To turn on. Next, in step S12, the presence / absence of an AC instantaneous overcurrent is detected based on the current detection signal from the AC current sensor (16), and the presence / absence of an element short circuit is thereby determined. When a short circuit of the element is found, the standby state of step S1 is set. When the short circuit of the element is not found, the process proceeds to step S13,
Switching elements G1 and G of the high frequency push-pull circuit
2 and the gate blocks for the switching elements S1 to S4 of the full-bridge folding circuit are released, and the operations of the high-frequency push-pull circuit and the full-bridge folding circuit are started.

Thereafter, in step S14, while monitoring the items for which the inverter main circuit should wait, for example, whether or not an AC instantaneous overcurrent has occurred, normal interconnection operation is continued, and in this process, some waiting items When occurs, the standby state of step S1 is set.

According to the fault self-diagnosis process and the protection function process described above, at the time of starting the interconnection operation, it is possible to diagnose whether or not there is a short circuit due to a failure of an element constituting the inverter main circuit while the AC relay (13) is kept off. After confirming that there is no failure, the AC relay (13) is turned on and normal interconnection operation starts, so even if there is an element short circuit,
The breaker (14) shown in FIG. 1 and the breaker (not shown) installed on the upstream side do not trip.

The description of the above embodiments is for the purpose of describing the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope thereof.
In addition, the configuration of each part of the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

For example, although the above-described embodiment is intended for the high frequency link type inverter main circuit, the same processing is performed in the system interconnection power system including the low frequency link type inverter main circuit by the same process. It is possible to diagnose failures and prevent breaker trips at the start of interconnection operation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit configuration of an inverter device according to the present invention.

FIG. 2 is a flowchart showing a failure self-diagnosis process and a protection function process by a main control circuit.

FIG. 3 is a circuit diagram showing a current loop formed by a circuit element failure of a conventional device.

FIG. 4 is a circuit diagram illustrating a problem when a full-bridge folding circuit is turned on / off in a normal sequence.

FIG. 5 is a circuit diagram showing an on / off sequence when diagnosing a failure of a full-bridge folding circuit.

FIG. 6 is a circuit diagram showing a current loop formed at the time of failure diagnosis of the present invention.

FIG. 7 is a waveform diagram showing a process of signal conversion in a high frequency link type inverter main circuit.

FIG. 8 is a block diagram showing a configuration of a solar power generation device.

[Explanation of symbols]

 (6) DC input terminal (7) AC output terminal (15) DC current sensor (8) High frequency push-pull circuit (9) High frequency transformer (10) Rectifier circuit (11) Full bridge folding circuit (12) Filter circuit (13) AC relay (14) Breaker (17) Main control circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H02M 7/538 9181-5H H02M 7/538 (72) Inventor Masahiro Maekawa Keihanhondori, Moriguchi City, Osaka Prefecture 2-5-5 Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. An inverter main circuit for converting DC power obtained from the DC power supply into AC power in a system interconnection power supply system in which a DC power supply is connected to a commercial power system via an inverter device, and an inverter main circuit. And a commercial power grid, a switching mechanism interposed between the power lines, a control circuit that controls the operation of the inverter main circuit and the switching mechanism, and a current sensor that detects a direct current flowing into the inverter main circuit. Is a means to self-diagnose whether there is a failure in the inverter main circuit by operating the inverter main circuit for a certain period of time with the switching mechanism open, and whether or not the current is detected by the current sensor during this period. Only when the failure is not found by the diagnostic means, close the opening / closing mechanism and connect the inverter main circuit to the commercial power system. A system interconnection power supply system characterized by having 2. An inverter main circuit, wherein a primary side inverter circuit that performs pulse width modulation on the output of a DC power supply by switching at a frequency higher than the system frequency, and an output pulse of the primary side inverter circuit is converted into a sine wave of the system frequency. The grid-connected power supply system according to claim 1, comprising a secondary-side inverter circuit that outputs the power to a commercial power system and an insulating transformer that is interposed between the primary-side inverter circuit and the secondary-side inverter circuit. 3. An inverter main circuit, which applies pulse width modulation to the output of a DC power supply by switching the system frequency, converts the output pulse obtained by this into a sine wave and outputs it to a commercial power system, and an inverter. The grid-connected power supply system according to claim 1, comprising an isolation transformer connected to an output end of the circuit. 4. The main inverter circuit is composed of a plurality of switching elements, and the failure self-diagnosis means forms a current loop that bypasses the failure point by turning on at least one of the switching elements. The grid-connected power supply system according to claim 1, wherein the main switching circuit is operated by turning on / off the plurality of switching elements in a sequence that does not exist.