JP2842916B2 - Inverter circuit - Google Patents

Description

The present invention relates to an inverter circuit for converting DC power into AC power.

[Prior Art] FIG. 5 shows a conventional inverter circuit. The Figure 5 A smoothing capacitor 12 is connected in parallel to the DC power source 11, across the smoothing capacitor 12, an inverter 13 of the switching element Q ₁ to Q ₄ of the full bridge configuration is connected. That is, in this example, each of the switching elements Q _{1 to} Q ₄ is a bipolar transistor, and the transistor Q ₁ and the emitter are connected to the collector of the transistor Q ₂ .
Transistors Q ₁ and Q ₂ are connected in series in the forward direction, similarly, transistors Q ₃ and Q ₄ are connected in series in the forward direction, and these two series connections are connected in parallel, that is, transistors Q ₁ and Q
₃ are connected to each other, and the emitters of the transistors Q ₂ and Q ₄ are connected to each other. Switching element
The connection point between Q ₁ and Q ₃ is connected to the positive electrode side of DC power supply 11, and the connection point between switching elements Q ₂ and Q ₄ is connected to the negative electrode side of DC power supply 11. Each of the switching elements Q ₁ to Q ₄ and diode D ₁ to D ₄ in opposite polarities in parallel is connected. The connection point of the switching elements Q ₁ and Q _{2 and} the connection point of the switching elements Q ₃ and Q ₄ are respectively connected to the first and second output terminals 1 through a low-pass filter 14.
Connected to 5,16. The diodes D _{1 to} D ₄ prevent the switching elements Q _{1 to} Q _{4 from} being destroyed by the back electromotive force when the load connected between the first and second output terminals 15 and 16 has an inductance component. is there.

In this circuit, the switching elements Q ₁ , Q ₄ and Q ₂ , Q ₃ are alternately turned on to convert the DC power of the DC power supply 11 into AC power and output it to the first and second output terminals 15, 16. . In the conventional inverter circuit to obtain a predetermined wave height V _AC to the AC output, it is necessary to use a DC power source 11 of a voltage substantially equal to the peak value V _AC.

DC power supply 1 with a voltage lower than the peak value V _AC of the AC output voltage
In order to use 1, conventionally, as shown in FIG. 5B, the AC output voltage of the inverter 13 is boosted by the transformer 17 or as shown in FIG. A DC / DC converter 18 was inserted between the two to raise the DC voltage to the required voltage.

"Problems to be Solved by the Invention" In the circuit of FIG. 5A, the DC power supply 11 needs to have a voltage substantially equal to the peak value of the AC output. Will be done. In particular, when a secondary battery is used for the DC power supply 11, it is necessary to connect a large number of cells in series, which causes problems such as an increase in cost and a decrease in reliability.

Further, since the transformer 17 is used in the circuit of FIG. 5B, there is a problem that the whole device is large and overlaps.

In the circuit of FIG. 5C, the number of components of the DC / DC converter 18 and its control circuit increases, and there are problems such as a decrease in efficiency and an increase in cost.

As described above, the conventional inverter circuit has problems such as restrictions on the selection range of parts to be used, an increase in cost, an increase in space and weight, a decrease in efficiency, and the like.

According to the present invention, the reactor is connected in series between the DC smoothing capacitor and the switching element of the inverter, and the connection points between the two switching elements of the inverter and the reactor are separated. A diode is connected between them, and a connection point between the two switching elements of the inverter and the DC smoothing capacitor is disconnected to connect a diode between them.

This consists of a short-circuit the inverter one arm during the normal switching operation, by providing the function of the step-up chopper to the inverter by utilizing a reactor to obtain an AC output of higher peak value V _AC than the voltage of the DC power source.

"Embodiment" An embodiment of the present invention is shown in FIG. 1, and portions corresponding to those in FIG. 5 are denoted by the same reference numerals.

In this embodiment, one end of the reactor 21 is connected to one end (positive side) of the smoothing capacitor 12, and the other end of the reactor 21 is connected to the switching element Q ₁ of the inverter 13. Reactor 21 is inserted in series. The switching element of inverter 13
The connection sides of Q ₁ and Q _{3 with} the reactor 21 are separated from each other,
Diode D ₅ is connected between these. This example shows a case of using a transistor as a switching element Q ₁ to Q _4, therefore the anode of the diode D ₅ to the collector of the transistor Q ₁ is connected, the cathode of the diode D ₅ to the collector of the transistor Q ₃ is connected . Similarly the cathode of the diode D ₆ to the emitter of the transistor Q ₂ is connected to the anode of the diode D ₆ to the emitter of the transistor Q ₄ is connected. A second capacitor 22 is connected between the first and second output terminals 15 and 16.

In this configuration, the switching elements Q _1, Q ₄ and Q _2, Q3 and is alternately turned on in the conventional manner for example commercial frequency, is turned off, while further the switching element Q ₁ in the present invention, Q ₄ is turned on, the switching turned on and off by the element Q ₂ is for example 20 kHz, also the switching element Q _2, Q ₃ is between oN, the switching element Q ₁ is turned on and off at 20 kHz. The operation in this case will be described with reference to FIG. 2 and FIG.

The switching element Q _1, Q ₂ as shown in the section t ₁ in Figure 2,
When Q ₄ is turned on, the switching element as shown in Fig. 3A
Q _1, Q ₂ smoothing capacitor from the switching element Q ₂ through 1
Current i flowing toward 2 increases, and energy is stored in reactor 21. Since the switching element Q ₂ is ON, as shown by the dotted line from the second capacitor 22, since also prevented by the diode D ₆ trying current to flow through the switching element Q _2, the voltage of the second capacitor 22 Will be retained. Then the switching device as shown in section t ₂
When Q ₂ is turned off, the energy stored in the reactor 21 passes through the switching elements Q ₁ , Q ₄ and the diode D ₆ ,
Since the current i is supplied to the capacitor 22 (load), the current i decreases.

The second capacitor of the energy stored in this reactor 21
The peak value V _AC output voltage by the release action of the 22 can be made higher than the DC voltage V _DC. After repeating this operation for a half cycle of the inverter operation, in the next half cycle, the switching elements Q ₂ and Q ₃ are turned on, and the same operation as described above is performed by repeating the switching element Q ₁ being turned on and off. . The current flow i interval t ₃ when the switching element Q ₁ is turned ON in this case shown in FIG. 3 C, the switching element Q ₁ is OF
The flow of current i F the interval t ₄ shown in FIG. 3 D.

Detecting the current i by the current detector, a current i in the conduction period of the switching element Q ₁ and Q ₂ in each cycle,
By feedback control of the length of the conduction period using the peak value V _AC output voltage, it is possible to maintain the peak value V _AC output voltage at a constant value.

In addition, by increasing the switching frequency of the switching elements Q ₁ and Q ₂ , the size of the reactor 21 can be reduced, and the weight, space, and cost can be minimized. Moreover, the responsiveness can be improved.

As shown in FIG. 4, a diode D ₅ between the switching element Q _1, a diode D _1, a diode D ₆ may be inserted respectively between the switching element Q ₂ and the diode D6. The switching element Q ₁ to Q ₄ may be used FET.

According to the present invention as mentioned "effect of invention" above, the conventional circuit shown in FIG. 5 A, adding small, low cost of the reactor 21 and two diodes D _5, D ₆ DC power supply 1
AC output of any peak value (maximum about twice) higher than the voltage of 1 can be obtained, and the switching elements Q ₁ , Q ₂
Since the control circuit for turning ON and OFF at a high frequency is simple, the following effects can be obtained.

a. The equipment can be downsized.

b. Since the DC voltage _VDC may be low, a low-cost DC power supply can be used.

c. The main circuit configuration is simple.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a time chart showing a waveform example of each part at the time of operation, FIG. 3 is a diagram showing a current flow in each operation state of FIG. 4th
FIG. 5 is a connection diagram showing another embodiment of the present invention, and FIG. 5 is a connection diagram showing various examples of a conventional inverter circuit.

Claims (1)

(57) [Claims] 1. A DC power supply, a smoothing capacitor connected in parallel to the DC power supply, a reactor having one end connected to one end of the smoothing capacitor, a second end of the reactor, and a second end of the smoothing capacitor. an inverter composed of switching elements Q ₁ to Q ₄ of Furuburitchi configuration connected in parallel between, and an anode connected to a connection point between the reactor of the switching element Q _1, the cathode and the reactor of the switching element Q ₃ a diode D ₅ connected to a connection point of a cathode connected to a connection point between the capacitor of the switching element Q _2, the anode switching element Q ₄
Diode D connected to the connection point of the capacitor
_6, the switching element Q ₁ to Q-connected diodes D ₁ to D ₄ in parallel to each of the _four, a first output terminal derived from the connection point of the switching elements Q ₁ and Q _2, the switching inverter circuit having a second output terminal derived from the connection point of the elements Q ₃ and Q _4, these first and a second capacitor connected between the second output terminal.