JP2012039813A - System interconnection inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: two wires were penetrated into a current detector (ACCT) as means for detecting an inverter output current including a high frequency component required to control a system interconnection inverter device, so workability during manufacturing was poor and a large ACCT capacity was necessary.SOLUTION: A filter output current is detected by a shunt resistor 9 and a capacitor current of a filter circuit 6 is detected by a small-capacity ACCT13. The inverter output current including the high frequency component is obtained by calculating the detected currents.

Description

  The present invention relates to a grid-connected inverter device for converting DC power from a DC power source such as a solar battery into AC power and connecting it to an AC power system.

  As a conventional grid-connected inverter device, a single-phase inverter circuit using a switching element having a full bridge configuration that switches DC power to AC by switching DC power, as shown in JP-A-9-308263, and a high-frequency component It is known to have a reactor and a filter circuit composed of a capacitor that removes. In such a grid-connected inverter device, in order to obtain an output that matches the target, the inverter output current (Iio) is detected, and the single-phase inverter circuit is PWM-driven by feedback control. Further, in order to prevent a direct current component from flowing into the alternating current output, detection and suppression control of the direct current component is performed.

Japanese Laid-Open Patent Publication No. 9-308263 (page 6-8, Fig. 1-2)

In the conventional grid-connected inverter device, in order to detect the inverter output current (Iio) described above, the current flowing from the high voltage side switching element and the low voltage side switching element of one arm of the full bridge to the reactor, The current flowing through the capacitor of the filter circuit connected to the other arm is detected using a single current detector (ACCT). Therefore, this ACCT has to pass two wires as shown in FIG. 12, and there is a problem that workability at the time of manufacture is poor. In addition, this ACCT must have a capacity suitable for measuring the inverter output current. For example, in the case of a photovoltaic power generation system with AC 230 V and 6 kW output, the inverter output current becomes a large current of about 26 A at the maximum, so the ACCT capable of measuring it is large in size and expensive.
As for the detection of the direct current component, since the direct current component cannot be detected by the ACCT, it is necessary to use a separate DCCT (direct current detector) or a shunt resistor. DCCT is expensive, and when a shunt resistor is used, an insulation amplifier and an insulation power supply circuit for supplying power to the insulation amplifier are necessary. Therefore, the DCCT is also expensive, and the cost of the grid-connected inverter device increases. there were.

  The present invention has been made to solve the above-described problems of the grid-connected inverter device, and obtains a grid-connected inverter device that can detect the inverter output current with good workability at the time of manufacture and at low cost. Is.

A grid-connected inverter device according to the present invention includes an inverter circuit including a switching element having a full bridge configuration that converts DC power into AC power, a reactor that is connected to each phase arm output of the inverter circuit, and removes high-frequency components. A filter circuit comprising a capacitor, a control means for PWM driving the inverter circuit, a first current detector for detecting an output current of the filter circuit, and a second current detector for detecting a capacitor current of the filter circuit And an arithmetic means for calculating an inverter output current including a high frequency component from the output current of the filter circuit and the capacitor current of the filter circuit.

In the present invention, the inverter output current is calculated from the output current of the filter circuit detected by the first current detector and the capacitor current of the filter circuit detected by the second current detector. The work of passing the two wires is eliminated, and the workability during manufacturing is improved. Further, since the capacitor current of the filter circuit has a smaller value than the inverter output current, the capacity of the second current detector can be reduced, so that the second current detector can be miniaturized.

It is a block diagram of the grid connection inverter apparatus which shows Embodiment 1 of this invention. It is a block diagram of the calculating means of the grid connection inverter apparatus which shows Embodiment 1 of this invention. It is an operation | movement figure of the full bridge inverter circuit of the grid connection inverter apparatus which shows Embodiment 1 of this invention. It is an inverter output current detection characteristic figure of the grid connection inverter apparatus which shows Embodiment 1 of this invention. It is another block diagram (partial drawing) of the grid connection inverter apparatus which shows Embodiment 1 of this invention. It is a block diagram of the grid connection inverter apparatus which shows Embodiment 2 of this invention. It is another block diagram (partial drawing) of the grid connection inverter apparatus which shows Embodiment 2 of this invention. It is a block diagram of the calculating means of the grid connection inverter apparatus which shows Embodiment 3 of this invention. It is a block diagram of the grid connection inverter apparatus which shows Embodiment 4 of this invention. It is a block diagram of the calculating means of the grid connection inverter apparatus which shows Embodiment 4 of this invention. It is a block diagram of the calculating means of the grid connection inverter apparatus which shows Embodiment 5 of this invention. It is an external view of the ACCT part of the conventional grid connection inverter apparatus.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a system interconnection inverter device according to Embodiment 1 for carrying out the present invention. First, the outline will be described. The output of DC power generated by the solar cell 1 is connected to the input of the grid interconnection inverter device 2, converted into AC power by the grid interconnection inverter device 2, and output. This AC output is consumed by a load (not shown) such as an electric device in the house, and is connected (connected) to the AC power system 3, and if there is surplus power, it is caused to flow backward.
Next, the structure in the grid connection inverter apparatus 2 is demonstrated in detail. The output of the solar cell 1 is connected to the input of the grid interconnection inverter device 2, that is, the input of the DC-DC converter 4, and the output of the DC-DC converter 4 is connected to the full bridge inverter circuit 5. The full-bridge inverter circuit 5 includes two arms corresponding to the U phase and the W phase, and each arm has a high voltage side switching element A, a low voltage side switching element B, a high voltage side switching element C, and a low voltage side switching element, respectively. D. The connection between the high voltage side switching element and the low voltage side switching element of each phase arm is the output of each phase arm, and the input of the filter circuit 6 is connected to the output of each phase arm. The filter circuit 6 includes a reactor 7a and a reactor 7b, a capacitor 8a and a capacitor 8b, and an interphase capacitor 8c. One end of the reactor 7a (7b) is connected to each phase arm output, and the reactor 7a (7b) The other end of the capacitor 8a (8b) is connected to the other end, and the other end of the capacitor 8a (8b) is connected to the low voltage side of the full bridge inverter circuit 5. A connection point between the other end of the reactor 7a (7b) and one end of the capacitor 8a (8b) is an output of each phase of the filter circuit 6. An interphase capacitor 8c is connected between the other end of the reactor 7a and the other end of the reactor 7b. The U-phase side output of the filter circuit 6 is connected to the U-phase of the AC power system 3 via the first current detector. In the first embodiment, a shunt resistor 9 is used as the first current detector. The W-phase side output of the filter circuit 6 is connected to the W-phase of the AC power system 3. The signal obtained by the shunt resistor 9 is input to the insulation amplifier circuit 10, and the output of the insulation amplifier circuit 10 is input to the arithmetic means. In the first embodiment, a computing unit 11 composed of DSP and DSP software is used as computing means. The computing unit 11 may be constituted by a microcomputer or a logic circuit. Note that the power source for driving the insulation amplifier circuit 10 is provided by the insulation power source circuit 12. The current path (capacitor lead wire) flowing through the interphase capacitor 8c is disposed so as to penetrate the second current detector. In the first embodiment, the ACCT 13 is used as the second current detector. The signal output of the ACCT 13 is input to the amplifier circuit 14, and the output of the amplifier circuit 14 is input to the arithmetic unit 11. The output of the calculator 11 is input to the control means. In the first embodiment, an inverter control circuit 16 constituted by DSP and DSP software is used as the control means. The inverter control circuit 16 may be configured by a microcomputer or a logic circuit. The output of the inverter control circuit 16 is connected to the full bridge inverter circuit 5 through a gate drive circuit (not shown).

Next, the operation of the grid-connected inverter device in the first embodiment will be described with reference to FIGS. The full bridge inverter circuit 5 operates as follows based on a command from the inverter control circuit 16. First, in the half cycle (section E in FIG. 3) when the phase on the high voltage side in the AC power system 3 is the U phase, the high voltage side switching element A of the arm connected to the U phase is shown in FIG. The switching operation by PWM drive as shown in c) is performed. Further, the low voltage side switching element B of the same arm is driven to be inverted with respect to the high voltage side switching element A (FIG. 3D). During this time, the high-voltage side switching element C of the arm connected to the W phase is turned off (FIG. 3E), and the low-voltage side switching element D is turned on (FIG. 3F). In the next half cycle (section F in FIG. 3), that is, in the case where the phase on the high voltage side in the AC power system 3 is the W phase, the switching element C performs a switching operation by PWM driving, and the switching element D is the switching element C. In contrast, inversion driving is performed. Then, the switching element A is turned off and the switching element B is turned on. This operation is repeated thereafter. By these operations, the full-bridge inverter circuit 5 outputs an inverter output current (Iio) including a high frequency component as shown in FIG. The output of the full bridge inverter circuit 5 is removed from the high frequency component by the filter circuit 6 and is output from the filter circuit 6 as a smooth sine wave filter output current (Ifo) as shown in FIG. The And if the load in a house is driven or surplus electric power generate | occur | produces, it can reversely flow into the alternating current power grid 3. FIG.
In the PWM control as described above, the switching element of the phase arm on the low voltage side in the AC power system 3 is fixed on or off for a half cycle, so that no switching loss occurs. Therefore, such PWM control has a feature that conversion from DC power to AC power can be realized with high efficiency.
The filter circuit 6 may be constituted by the reactors 7a and 7b, capacitors 8a and 8b and the interphase capacitor 8c shown in FIG. 1, or may be constituted only by the reactors 7a and 7b and the capacitors 8a and 8b. . In the configuration in which the interphase capacitor 8c is added, the effect of increasing the capacitor capacity in order to increase the filter capability is great, and there is an advantage that the space can be saved as a whole.

  In order to convert the DC power generated by the solar cell 1 into AC power by the full bridge inverter circuit 5 and to link it to the AC power system 3, the inverter control circuit 16 targets the current value and phase of the inverter output current. It is necessary to instantaneously control the feedback so that Therefore, it is necessary to always detect the inverter output current output from the full bridge inverter circuit 5. A method for detecting the inverter output current will be described below. The U-phase filter output current (Ifou) is detected by the shunt resistor 9. Since this is the current after passing through the filter circuit 6, the high-frequency component is removed to form a smooth sine wave. Since the reference potential of the power system circuit connected to the shunt resistor 9 is different from the reference potential of the control system circuit such as the arithmetic unit 11 or the inverter control circuit 16, the output signal of the shunt resistor 9 is not insulated. Cannot be connected to the arithmetic unit 11 or the like. Therefore, the output signal of the shunt resistor 9 is input to the insulation amplifier circuit 10 to be amplified, and the output is sent to the arithmetic unit 11. The power supply to the insulation amplifier circuit 10 is supplied by the insulation power supply circuit 12. Further, the current (Iuw) flowing through the interphase capacitor 8 c in the filter circuit 6 is detected by the ACCT 13. Here, a high frequency component of the current output from the full bridge inverter circuit 5 flows. The computing unit 11 calculates an inverter output current (Iio) including a high frequency component as shown in FIG. 3B by using these Ifou and Iuw. That is, as shown in FIG. 2, Iio is obtained by calculation using the input Ifou and Iuw. The calculation method will be described below.

First, consider the case where the U phase has a positive half cycle. At this time, the inverter output current (Iiou) output from the U-phase arm output of the full bridge inverter circuit 5 is divided into the current Iuw flowing through the interphase capacitor 8c, the current Iun flowing through the capacitor 8a, and the filter output current Ifou. That is,
Iiou = Iuw + Iun + Ifou
Here, the capacitances of the capacitors 8a, 8b, and 8c of the filter circuit 6 are known, and are Cun, Cwn, and Cuw, respectively. As described above, when the U phase is a positive half cycle, the switching elements A and B perform the switching operation, and the switching element D is fixed to ON. In this case, as an equivalent circuit of the capacitor unit of the filter circuit 6, Between Cu and N (N is the low voltage side of the full bridge inverter circuit 5), Cuw and Cwn are connected in series, and Cun is connected in parallel thereto. Since Iuw can be detected by the ACCT 13, if a ratio calculation is performed between Iuw and the capacitance of the capacitor in consideration of an equivalent circuit, a current (Iuw + Iun) divided from the inverter output current (Iiou) to the capacitor can be calculated. That is,
Iuw + Iun = Iuw * {1+ (Cun / Cuw) + (Cun / Cwn)}
Therefore,
Iiou = Ifou + Iuw * {1+ (Cun / Cuw) + (Cun / Cwn)}
When the U phase is a negative half cycle (that is, the W phase is a positive half cycle), the inverter output current (Iiow) output from the W phase arm output of the full bridge inverter circuit 5 flows to the interphase capacitor 8c. The current Iuw is divided into the current Iwn flowing through the capacitor 8b and the filter output current Ifow. That is,
Iiow = Iuw + Iwn + Ifow
Here, Ifow has the same value as the current (Ifou) that can be detected by the shunt resistor 9, it can be replaced with Ifou. In addition, by the capacitance ratio of capacitors and Iuw that can be detected by the ACCT 13, as described above,
Iiow = Ifou + Iuw * {1+ (Cwn / Cuw) + (Cwn / Cun)}
Thus, Ifou + Iuw * {1+ (Cun / Cuw) + (Cun / Cwn)} if the U phase is a positive half cycle, Ifou + Iuw * {1+ if the W phase is a positive half cycle By (Cwn / Cuw) + (Cwn / Cun)}, the entire period of the inverter output current Iio including high-frequency components can be obtained.
Here, especially when Cuw = Cun = Cwn,
Iiou = Ifou + 3 * Iuw
Iiow = Ifou + 3 * Iuw
When the U phase has a positive half cycle and the W phase has a positive half cycle,
Iio = Ifou + 3 * Iuw
Can be obtained.
As described above, the total current flowing through the capacitors 8a, 8b, 8c of the filter circuit 6 is calculated from the capacitance ratio of the capacitors 8a, 8b, 8c of the filter circuit 6 and the current Iuw flowing through the capacitor 8c. By calculating the sum of the output current of the circuit 6, the inverter output current can be calculated.

Next, the current capacity of the ACCT 13 will be described. Consider the capacitance Cuw of the interphase capacitor 8c as 8 μF. The voltage Vac of the AC power system 3 is 230 V, and the frequency fac is 50 Hz. At this time, the current flowing through the interphase capacitor 8c is
Iuw = (2 * π * fac) * Cuw * Vac = 0.58 [Arms]
It becomes. That is, the current capacity of the ACCT 13 in this case is sufficient if it can measure a current of about 1 [Arms].

  FIG. 4 is a diagram comparing the inverter output current detection characteristics of the conventional grid-connected inverter device and the inverter output current detection characteristics of the grid-connected inverter device in the first embodiment. In a frequency band higher than about 1 kHz, the gain characteristic variation is smaller and the phase characteristic change is smaller in the first embodiment than in the detection characteristic in the conventional apparatus. That is, it can be seen that the characteristics are more preferable in terms of control stability.

  Moreover, the value of the alternating current power or alternating current output to the alternating current electric power grid | system 3 from a grid connection inverter apparatus may be displayed on the indicator prepared separately as a power generation output by sunlight. For this purpose, a measuring instrument for detecting AC power or AC current, for example, a current detector such as ACCT, DCCT, or shunt resistor is required. However, the shunt resistor for detecting the filter output current in the present invention is shared. Can do.

As described above, in the first embodiment, the filter output current is detected by the shunt resistor 9, the current flowing through the interphase capacitor 8c is detected by the ACCT 13, and the inverter output current is obtained by calculating them. The work of passing two wires through the ACCT is eliminated, and the workability during manufacturing is improved.
Further, since the capacitor current of the filter circuit 6 is smaller than the inverter output current, the current capacity of the ACCT 13 can be reduced, and therefore the size of the ACCT can be reduced and the price can be reduced.
Further, since the current flowing in the capacitors 8a, 8b, 8c is calculated based on the capacitance ratio of the capacitors 8a, 8b, 8c and the current flowing in the interphase capacitor 8c, there is only one current detector for detecting the capacitor current. That's it.
Furthermore, the detected inverter output current characteristic is more preferable from the viewpoint of control stability because the fluctuation of the gain characteristic is small and the change of the phase characteristic is small as compared with the prior art.
Further, since the filter output current detected by the shunt resistor 9 can be used for other purposes such as output display, the system-connected inverter device can be configured at a lower cost.

1 shows the case where the other ends of the capacitors 8a and 8b of the filter circuit 6 are connected to the low voltage side of the full bridge inverter circuit 5. However, as shown in FIG. Even if the other end of the capacitors 8a and 8b is connected to the high voltage side of the full-bridge inverter circuit 5, the same effect can be obtained because the inverter output current can be calculated in the same manner by changing to the operation corresponding to the configuration. be able to.

Embodiment 2. FIG.
FIG. 6 is a configuration diagram of a grid-connected inverter device in the second embodiment for carrying out the present invention. In the second embodiment, the interphase capacitor 8c used in the first embodiment is omitted. The other ends of the capacitors 8 a and 8 b of the filter circuit 6 are connected to each other, and further connected to the low voltage side of the full bridge inverter circuit 5. The current path between the point where the other ends of the capacitors 8 a and 8 b are connected to the low voltage side of the full bridge inverter circuit 5 is configured to penetrate the ACCT 13.

In the second embodiment, the inverter output current Iio is obtained by calculating the filter output current Ifou and the currents Iun and Iwn flowing through the capacitors 8a and 8b. Next, the calculation method will be described. First, consider the case where the U phase has a positive half cycle. At this time, the inverter output current (Iiou) output from the U-phase arm output of the full bridge inverter circuit 5 is divided into the current Iun flowing through the capacitor 8a and the filter output current Ifou. That is,
Iiou = Iun + Ifou
Similarly, when the U phase has a negative half cycle (ie, the W phase has a positive half cycle)
Iiow = Iwn + Ifow
Note that Ifow has the same value as the current (Ifou) that can be detected by the shunt resistor 9, it can be replaced with Ifou.
Iiow = Iwn + Ifou
Here, in the PWM control of the full-bridge inverter circuit 5, as described above, in the half cycle in which the U phase is positive, the high voltage side switching element C of the W phase arm is turned off and the low voltage side switching element D is turned on. Since it is fixed, no high-frequency current flows through the capacitor 8b. Similarly, in the half cycle in which the U phase is negative, the high voltage side switching element A of the U phase arm is fixed off and the low voltage side switching element B is fixed on, so that no high frequency current flows through the capacitor 8a. Therefore, high frequency components cannot be detected over the entire period only by monitoring the current of one of the capacitors 8a and 8b. In the second embodiment, since the currents of both the capacitors 8a and 8b are monitored by the ACCT 13, high frequency components can be detected over the entire period.
Thus, an inverter output current (Iio) including a high frequency component is obtained by Iun + Ifou when the U phase is a positive half cycle and by Iwn + Ifou when the W phase is a positive half cycle.

As described above, in the second embodiment, the filter output current is detected by the shunt resistor 9, the other ends of the capacitors 8a and 8b of the filter circuit 6 are connected by the ACCT 13, and the low voltage of the full bridge inverter circuit 5 Since the inverter output current is obtained by detecting the current flowing in the current path between the two sides and calculating them, there is no need to pass the two wires through the ACCT as in the first embodiment. Workability at the time is improved.
Further, since the current flowing through the capacitors 8a and 8b of the filter circuit 6 is smaller than the inverter output current, the current capacity of the ACCT 13 can be reduced, and therefore the size of the ACCT can be reduced and the price can be reduced. can do.
Moreover, since it comprised so that the current of the current path | route between the point where the other end of capacitor | condenser 8a, 8b was connected and the low voltage side of the full bridge inverter circuit 5 was detected, the electric current detection which detects a capacitor | condenser current Only one vessel is required.

FIG. 6 shows the case where the other ends of the capacitors 8a and 8b of the filter circuit 6 are connected to the low voltage side of the full bridge inverter circuit 5. However, as shown in FIG. Even if the other end of the capacitors 8a and 8b is connected to the high voltage side of the full bridge inverter circuit 5, the same effect can be obtained.

Embodiment 3 FIG.
FIG. 8 is a block diagram of computing means of the grid interconnection inverter device in the third embodiment for carrying out the present invention. In the third embodiment, a computing unit 17 is used as the computing means, and the configuration other than the computing unit 17 is the same as that shown in FIG. In the third embodiment, as the computing unit 17, a computing unit constituted by DSP and DSP software is used. The computing unit 17 may be constituted by a microcomputer or a logic circuit.
The ACCT can detect only the AC component of the current, whereas the shunt resistor can detect both the AC component and the DC component of the current. Ifou current data captured by a shunt resistor may be processed into an AC component-only current that does not include a DC component by averaging or the like before the calculation of Iio. For example, in the case where the filter output current Ifou output to the AC power system 3 is displayed on a separate display, it is necessary to display only the AC component value from which the DC component has been removed by calculation. Then, using the Ifou only for the AC component from which the DC component is removed by the calculation has no problem in the calculation of Iio.
Here, in the third embodiment, the filter output current Ifou that is input to the calculator 17 and is used for the calculation of Iio is the one from which the DC component is not removed. The inverter output current Iio calculated by the Ifou including the DC component and the current Iuw flowing through the interphase capacitor 8c also includes the DC component.
By the way, since it is not desirable that the DC component is superimposed on the AC power system, an upper limit value is defined for the DC component included in the current output from the grid-connected inverter device to the AC power system. Therefore, the grid-connected inverter device needs to suppress the direct current component included in the filter output current to be equal to or less than the prescribed upper limit value. By performing PWM control of the full bridge inverter circuit 5 using Iio including the DC component obtained as described above, the DC component itself can be removed from the filter output current Ifo. That is, if a DC component is superimposed in the positive direction, the full bridge inverter circuit 5 is PWM controlled so that the DC component is biased in the negative direction so as to cancel out the DC component. As a result, a filter output current from which a DC component is removed or suppressed can be output to the AC power system 3.
In the conventional configuration, since the inverter output current is detected by the ACCT, it is necessary to add a DCCT or a shunt resistor separately to detect the DC component. In addition, since the potential of the detection unit and the calculation unit is different from each other, the shunt resistor needs to be further accompanied by an insulation amplifier and an insulation power source, and is expensive in both cases. In the third embodiment, since the direct current component can be detected with substantially the same configuration as that for detecting the inverter output current Iio, the apparatus can be realized at low cost.

As described above, in the third embodiment, the filter output current is detected by the shunt resistor 9, the current flowing through the interphase capacitor 8c is detected by the ACCT 13, and the inverter output current is obtained by calculating them. Only one wire is required to pass through the cable, improving workability during manufacturing.
Further, since the current flowing through the interphase capacitor 8c is smaller than the inverter output current, the current capacity of the ACCT 13 can be reduced, and therefore the size and the price of the ACCT can be reduced.
Further, by detecting the filter output current including the DC component by the shunt resistor 9 and using it for the calculation, the DC component included in the inverter output current can be detected at low cost.

Although the third embodiment has the configuration shown in FIG. 1 and the arithmetic unit thereof is shown in FIG. 8, the arithmetic unit is not limited to the configuration shown in FIG. 5, FIG. 6, or FIG. As shown in FIG. 8, similar effects can be obtained.

Embodiment 4 FIG.
FIG. 9 is a configuration diagram of a grid interconnection inverter device according to the fourth embodiment for carrying out the present invention. The input of the filter circuit 6 is connected via a shunt resistor 18a, 18b to the connection portion of the high voltage side switching element and the low voltage side switching element of each phase arm of the full bridge inverter circuit 5, that is, the output of each phase arm. Yes. Signals obtained by the shunt resistors 18a and 18b are input to the insulation amplifier circuits 19a and 19b, and outputs of the insulation amplifier circuits 19a and 19b are input to the arithmetic means. In the fourth embodiment, a computing unit 21 composed of DSP and DSP software is used as computing means. The computing unit 21 may be constituted by a microcomputer or a logic circuit. Note that the power for driving the insulation amplifier circuits 19a and 19b is supplied by the insulation power supply circuits 20a and 20b. As the insulated power supply circuits 20a and 20b, a gate power supply for driving the switching elements of the full bridge inverter circuit 5 can be shared. A block diagram of the computing unit 21 is shown in FIG. The calculator 21 calculates the inverter output current Iio based on the inverter output current Iiou detected by the shunt resistor 18a and the inverter output current Iiow detected by the shunt resistor 18b. The calculation method will be described below.

  When the U phase is a positive half cycle, the inverter output current (Iiou) output from the U phase arm output of the full bridge inverter circuit 5 can be directly detected by the shunt resistor 18a. However, when the U phase has a negative half cycle, the current that can be detected by the shunt resistor 18a is obtained by removing the high frequency component from the inverter output current (Iiow) output from the W phase arm output by the filter circuit 6. Current returned to the U-phase arm. Therefore, the inverter output current that can be detected by the shunt resistor 18a includes a high frequency component when the U phase is a positive half cycle, but does not include a high frequency component when the U phase is a negative half cycle. Conversely, the inverter output current that can be detected by the shunt resistor 18b does not include a high frequency component when the U phase is a positive half cycle, and includes a high frequency component when the U phase is a negative half cycle. Since the PWM control of the full-bridge inverter circuit 5 requires an inverter output current including a high frequency component, the computing unit 21 includes Iiou, Iiow that include a high frequency component for each half cycle obtained by the shunt resistors 18a, 18b. To obtain Iio that includes high-frequency components in the entire period. The output of the computing unit 21 may be a value obtained by summing Iiou and Iiow as it is (2 * Iio), or may be a value (Iio) obtained by dividing the sum by two. The difference may be dealt with when the inverter control circuit 16 controls the inverter circuit 5.

  Further, the detection characteristic of the inverter output current of the grid interconnection inverter device in the fourth embodiment is equivalent to the detection characteristic of the inverter output current of the grid interconnection inverter device in the first embodiment shown in FIG. In a frequency band higher than around 1 kHz, the fluctuation of the gain characteristic is small and the change of the phase characteristic is small compared to the detection characteristic in the conventional apparatus. That is, it is a more preferable characteristic from the viewpoint of control stability.

As described above, in the fourth embodiment, the inverter output current is detected for each phase by the shunt resistors 18a and 18b, and the inverter output current Iio is obtained by the calculation. Therefore, the ACCT need not be used. became. Therefore, the work of passing the wiring through the ACCT becomes unnecessary, and the workability during the manufacturing can be further improved.
In addition, the detected inverter output current characteristic is more preferable from the viewpoint of control stability because the gain characteristic variation is smaller and the phase characteristic change is smaller than in the prior art.
Furthermore, it is possible to share the insulated power supply circuits 20a and 20b for supplying the gate power for driving the switching elements of the full bridge inverter circuit 5 as the power supply for the insulated amplifier circuits 19a and 19b for amplifying the shunt resistors 18a and 18b. Therefore, it is not necessary to add a separate device, and the device can be reduced in size and price.

Embodiment 5 FIG.
FIG. 11 is a block diagram of computing means of the grid-connected inverter device in the fifth embodiment for carrying out the present invention. In the fifth embodiment, a computing unit 22 is used as a computing means, and the configuration other than the computing unit 22 is the same as that of the grid-connected inverter device in the fourth embodiment shown in FIG. In the fifth embodiment, as the computing unit 22, a computing unit constituted by a DSP and DSP software is used. The computing unit 22 may be constituted by a microcomputer or a logic circuit.
In the fifth embodiment, input Iiou and Iiow are values including a DC component. Iio including the DC component is obtained by calculation using Iiou and Iiow including the DC component.
By performing PWM control of the full bridge inverter circuit 5 with the Iio including the DC component, the DC component included in the filter output current Ifo can be removed. That is, if a DC component is superimposed in the positive direction, the full bridge inverter circuit 5 is PWM controlled so that the DC component is biased in the negative direction so as to cancel out the DC component. As a result, a filter output current in which the DC component is suppressed can be output to the AC power system 3.
In the conventional configuration, since the inverter output current is detected by the ACCT, it is necessary to add a DCCT or a shunt resistor separately to detect the DC component. In addition, since the potential of the detection unit and the calculation unit is different from each other, the shunt resistor needs to be further accompanied by an insulation amplifier and an insulation power source, and is expensive in both cases. In the fifth embodiment, since the direct current component can be detected with almost the same configuration as that for detecting Iio, the apparatus can be realized at low cost.

As described above, in the fifth embodiment, since the inverter output current is detected for each phase by the shunt resistors 18a and 18b and the inverter output current Iio is obtained by the calculation, the ACCT need not be used. became. Therefore, the work of passing the wiring through the ACCT becomes unnecessary, and the workability during the manufacturing can be further improved.
Further, since the inverter output current of each phase including the DC component is detected by the shunt resistors 18a and 18b, and the inverter output current over the entire period including the DC component is obtained by calculating them, the inverter output current is obtained. The DC component included in the output current can be detected at a low cost.

  In addition, although Embodiment 1-5 demonstrated the case where a grid connection inverter apparatus operate | moves linked to an AC power system, this invention does not link a grid connection inverter apparatus to an AC power system. Even when it operates (for example, in the case of self-sustained operation), it can be used as a method for calculating the inverter output current.

2 System interconnection inverter device 5 Full bridge inverter circuit 6 Filter circuit 7 Reactor 8 Capacitor 9 Shunt resistance 11 Arithmetic unit 13 ACCT
16 Inverter control circuit 17 Calculator 18 Shunt resistor 21 Calculator 22 Calculator

Claims (8)

An inverter circuit composed of switching elements of a full bridge configuration that converts DC power to AC power;
A filter circuit comprising a reactor and a capacitor connected to each phase arm output of the inverter circuit to remove high-frequency components;
Control means for PWM driving the inverter circuit;
A first current detector for detecting an output current of the filter circuit;
A second current detector for detecting a capacitor current of the filter circuit;
An arithmetic means for calculating an inverter output current including a high frequency component by an output current of the filter circuit and a capacitor current of the filter circuit;
A grid-connected inverter device comprising: The computing means computes an inverter output current superimposed with a direct current component;
The grid interconnection inverter apparatus according to claim 1. The first current detector is a shunt resistor;
The second current detector is an ACCT;
The grid-connected inverter device according to claim 1 or 2, characterized by the above-mentioned. The control means PWM-drives one switching element of one arm of the inverter circuit, inverts and drives the other switching element to the one switching element, and turns off one switching element of the other arm, Repeating the cycle of turning on the other switching element;
The grid interconnection inverter device according to any one of claims 1 to 3. The filter circuit has an interphase capacitor connected between at least the phase outputs of the reactor,
The second current detector is an ACCT for detecting a current of the interphase capacitor;
The grid interconnection inverter apparatus according to any one of claims 1 to 4, wherein The filter circuit has a capacitor connected at least one end to each phase output end of the reactor, and connected at the other end to one of the high voltage side or the low voltage side of the input of the inverter circuit,
The second current detector is an ACCT that detects both currents of the capacitors;
The grid interconnection inverter apparatus according to any one of claims 1 to 4, wherein An inverter circuit composed of switching elements of a full bridge configuration that converts DC power to AC power;
A filter circuit comprising a reactor and a capacitor connected to each phase arm output of the inverter circuit to remove high-frequency components;
One switching element of one arm of the inverter circuit is PWM-driven, and the other switching element is inverted and driven with respect to the one switching element, and one switching element of the other arm is turned off and the other switching element is turned off. Control means for PWM driving the inverter circuit by repeating the turn-on cycle;
A shunt resistor that is inserted between each phase arm output of the inverter circuit and one end of the reactor of the filter circuit, and detects each phase arm output current individually;
Arithmetic means for calculating an inverter output current including a high frequency component by the sum of the respective phase arm output currents;
A grid-connected inverter device comprising: The computing means computes an inverter output current superimposed with a direct current component;
The grid interconnection inverter apparatus according to claim 7.

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