JPS60160376A - Filter circuit of sinusoidal wave inverter - Google Patents

Abstract

PURPOSE:To reduce the loss of an inverter main circuit for a load varying in a wide range by controlling the capacitor current of an LC filter circuit in response to the load state. CONSTITUTION:When a load 6 is heavy, a controller 57 sets switches 53, 55 to ON state, and when the load is light, it controls to OFF state. The inductance element of the filter becomes only a reactor 51 in the heavy load, and the capacitance element becomes the sum of the capacities of the capacitors 54, 56. On the contrary, the inductance element becomes series of the reactor 51, 52 in the light load, and the capacitance element becomes only the capacitor 54.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a filter circuit for a sine wave inverter.

(Prior art and problems) In general, sine wave inverters that output a sine wave output voltage, such as CVCFs (constant voltage/constant frequency AC power supplies) used in AC uninterruptible power supply systems (UPS), have harmonics in their output voltage. In order to remove waves, a filter circuit consisting of a reactor and a capacitor is installed between the inverter main circuit and the load.The capacitance of this filter circuit is designed according to the inverter capacity, so the inverter main circuit is The difference between the current flowing from the circuit into the filter capacitor and the current drawn at full load is small.Therefore, there is no difference between the loss in the inverter main circuit at no load and the loss at full load.

Regarding the loss in the inverter main circuit, since in most cases the load is constant or the operation is stopped in general usage conditions, the loss in the impark main circuit is rarely a problem. However, for loads that vary over a wide range from light loads to heavy loads, the loss in the inverter main circuit during light loads becomes a large loss in terms of power efficiency. In particular, in the case of a solar power generation system that uses solar energy, the energy source is limited, so there is no problem with reduced efficiency due to loss in the inverter main circuit, and the load is not one that has large load fluctuations such as in a general household. It becomes a big problem. In other words, in general households, the electricity used at night is at a light load, such as when only the refrigerator is operated, but during the day, heavy loads often occur, resulting in a wide range of load fluctuations, and the power supply may be interrupted even during light loads. Because this is not possible, the generated energy stored during the day is wasted due to losses in the inverter main circuit.

(Objective of the Invention) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a filter circuit that reduces loss in an inverter main circuit even when the load fluctuates over a wide range.

(Summary of the Invention) The present invention is characterized in that the capacitor current of the LC filter circuit is controlled according to the load condition.

(Example) FIG. 1 is a circuit diagram showing one embodiment of the present invention.

Power generated by the solar cell 1 is stored in a battery 2 to ensure DC power for the inverter main circuit 3.

The inverter main circuit 3 is subjected to constant voltage/leg frequency output control by an impark control circuit 4. The LC filter circuit 5 removes high decoy waves from the AC output from the inverter main circuit 3 and supplies the AC output of a sinusoidal voltage to the load 6 . The control circuit 4 obtains the output voltage and frequency of the filter circuit 5 as the detection output of the transformer 7, performs feedback control for constant voltage/leg frequency control of the main circuit 3, and further converts the load current to the current transformer 8. Provides overload protection as a detection output.

Although not shown, the control circuit 4 is connected to the impark main circuit 3.
1, such as failure of commutation? ! Provides protection against type r abnormalities.

In a sine wave inverb with a LC filter circuit that forms nine sine wave output voltages, the filter circuit 5 connects a reactor 51 and five series circuits in series between the inverter main circuit 3 and the load 6. It has a reactor5. switch 5 in parallel. and a capacitor 5 in parallel with the load 6
4, a series circuit of a switch 56 and a capacitor 56, and a switch 5. and 5. It has a filter control circuit 5□ that controls on/off depending on the load current. The control circuit 57 uses the detection output of the current transformer 8 to obtain nine control outputs according to the load current. Here, reactor 51I beam axle 51
It is assumed that the reactance of the capacitor 56 is also larger than that of the capacitor v54.

In such a filter circuit, when the load 6 is heavy, the control circuit island controls the switches 5m, 5s (for example, silisk switches) to be in the on state, and when the load is light, the control circuit island controls the off state pressure. Accordingly, under heavy loads, the inductance element of the filter circuit becomes 5. The capacitance elements are capacitors 54 and 5. is the sum of the capacitances. Conversely, under light loads, the inductance element beams axles 51 and 5. (#) in series, the only capacitance element is the capacitor 54.

Therefore, with a heavy load, a small inductance (51) is required to supply a large load current, and a large capacitance (5,) is used to obtain the LC constant necessary for harmonic rejection, and with a light load, a small load current is supplied. The current flowing through the capacitor 5 is limited by setting the inductance as large as possible (5, 5) to have the required number of LCs.This reduces the loss in the inverter main circuit 3 at light loads and improves power efficiency. can be made higher.

FIG. 2 is a main circuit diagram showing another embodiment of the present invention.

The filter circuit 9 includes a reactor 5. and 5. 5. Switch on the load side for parallel connection. , a reactor 5, and a switch 5. Connect a capacitor 5° to the connection point of switch 58
A capacitor 54 is provided in parallel with the series circuit of the capacitor 56 and the capacitor 56. Also in this embodiment, switch 5. The same effects as in the embodiment shown in FIG. 1 can be obtained by controlling ON when the load is heavy and controlling OFF when the load is light. In this embodiment, only one switch 5a is required, and the number of switches can be reduced.

In addition, in the embodiments described above, the case is shown in which the LC constant is switched from the load current, but in a case where there is a large correlation between the load and time, such as in a general household, it is preferable to switch according to the time of day (for example, nighttime and daytime). This can be realized with a simple switching means that eliminates the need for load current detection means.

Further, although the case where the number of switching stages is two is shown, power efficiency can be further improved by using three or more stages.

(Effects of the Invention) According to the present invention, the capacitor current can be controlled depending on the load condition without impairing the harmonic reduction rate, and as a result, the power loss in the inverter main circuit during light loads can be reduced. power efficiency.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the invention, and FIG. 2 is a circuit diagram showing another embodiment of the invention. DESCRIPTION OF SYMBOLS 1... Solar cell, 2... Battery, 3... Inverter main circuit, 4... Inverter control circuit, 5, 9...
・Filter circuit, 6...Load% 51 + 51...
・Reactor, 54゜56...Capacitor s5m+5
1*5M...Switch, 57...Filter control circuit. Procedural amendment (voluntary) - 1986 Patent Review No. 15408 2, Name of invention Sine wave inverter filter circuit 3, Relationship with the person making the amendment Case Applicant (610) Meidensha Co., Ltd. 4, Agent 5, Suiseikai Building, 1-29 Akashi-cho, Chuo-ku, Tokyo 104, Subject of amendment (1) Column of “Detailed Description of the Invention” in the specification (2) Description of “Detailed Description of the Invention”
"Brief explanation of the drawings" column (3) Contents of amendment to drawing 1 (1) Specification, page 7, line 14 [Switch ja J is followed by "to switch! 9" added. (2) Add r and js J following "switcher 8" on page 8, line 4 of the same book. (3) Same book, same page, lines 6 to 8: “And...
can. ” to be deleted. (4) On page 9 of the same book, line 14, “Evening 8” is followed by “,
Add "Yuukai". (6) Amend Figure 2 as shown in the attached sheet.

Claims (1)

[Claims] In an LC filter circuit that converts the output of the inverter main circuit into a sinusoidal voltage with harmonics removed and supplies power to the load, the smaller the load, the greater the inductance of the axle in series with the load and the smaller the capacitance of the capacitor in parallel with the load. A sine wave inverter filter circuit comprising: