JPH03173360A - Inverter circuit - Google Patents

Abstract

PURPOSE:To prevent a short-circuit accident by maintaining a switch OFF for a predetermined time when the switch is switched ON, OFF in an inverter circuit for driving an induction motor. CONSTITUTION:An inverter circuit is composed of an oscillator 1, a timer 2 and a converter 3. The oscillator 1 generates a pulse signal having 50% duty, and outputs normal and reverse outputs Q, Q of a filp-flop circuit 11 of its output unit. The timer 2 has two monostable multivibrators MA, MB, which receive the signals Q, Q, and output pulse signals (A), (B) for a predetermined time. The pulse widths of the signals (A), (B) are reduced smaller than those of the signals Q, Q. The converter 3 has switch units 31, 32, 33, 34. The units 31, 32, 33, 34 are closed while the signal A is positive. The units 32, 33 are closed during the positive period of the signal B. That is, pause time interrupts the ON of the switches.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application! [!7) The present invention mainly relates to an inverter circuit for driving an induction motor.

(Prior art) Induction TS motors (hereinafter referred to as motors) used in home appliances and other products are driven by AC electric power at a commercial frequency, and when AC power at a commercial frequency is directly applied to the motor, It is known that the rotational speed can be adjusted by connecting a variable resistor to the secondary winding of the motor and changing the secondary resistance. However, there are various drawbacks in terms of power loss due to heat generation and resistance loss of the secondary resistor, adjustment range, etc. Therefore, in recent years, means for changing the rotational speed of the motor by frequency conversion has been frequently used. This is an AC IIF with a commercial frequency of tlI, and the power is first converted to direct r/mad power, then converted again to AC power of the desired frequency, and the converted AC power of the desired frequency is supplied to the moku to generate the desired power. It obtains the power of rotational speed.

The present invention particularly relates to an inverter circuit that converts the above-mentioned direct current into alternating current power. Inverter circuits that have been widely used in the past are basically known as parallel type inverter circuits and series type inverter circuits. As shown in Figure 6 (0), a parallel inverter connects two switch sections (consisting of an iristor and a trigger circuit) and a transformer winding in a loop, and connects the transformer winding in parallel. A commutating capacitor is connected to the terminal, and a DC voltage is applied between the neutral point of the @ line and the connection point of both switch sections, and the load is connected to the secondary winding of the transformer. The direction of the magnetic field of the transformer @ cotton is switched by the alternating on-off operation, and an alternating current voltage is generated in the transformer's secondary winding.The series inverter circuit is as shown in Figure 7 (b). A switch section, a commutating reactor, and a switch section are connected in series between the DC power supply, and a commutating capacitor and a load are connected in series between the midpoint of the commutating reactor and the negative pole. The off-state operation charges and discharges the commutating capacitor and applies an alternating current voltage to the load.

(Problems to be Solved by the Invention) The conventional parallel inverter circuit and series inverter circuit described above do not directly apply DC voltage to the load, but instead apply AC voltage to the load via a transformer or a commutating capacitor. It is applied. However, by forming a circuit that alternately applies DC voltage to the load, AC power can be easily obtained.

The circuit consists of four switch sections a as illustrated in FIG.
, b.

c and d are connected in the form of a bridge circuit, and a DC power supply and a load are respectively connected between the opposing connection points, and the facing switch parts a,
When each pair of switch parts d and switch parts S and C are bare, and each pair is turned on and off alternately, a rectangular waveform alternating current voltage is applied to the load.

In the inverter circuit based on the above-mentioned switch bridge circuit, each switch section a, b, c.

Even if you try to operate d at the same time, there is a risk that there will be a slight time difference in the on-off transition operation of the switch section due to the circuit configuration of the switch section and characteristic errors of the electronic components used, so the load will not pass. There is a risk that a large current will flow and destroy the circuit.

Therefore, the present invention aims to provide a circuit which prevents the risk of circuit damage in the above-mentioned direct conversion inverter circuit.

(Means for Solving the Problems) An inverter circuit according to the present invention connects four switch sections in a bridge circuit configuration, connects one DC power source between opposing connection points, and connects one DC power source between the other opposing connection points. Connect the load, set the switch parts facing each other as one set, and turn each set alternately on and off [1
In an inverter circuit that supplies alternating current power to a load, the control section that performs on-off control of the switch section includes an oscillation section that determines the output frequency, and a switch section that controls the on-off switching of the switch section for a predetermined period of time. The device is characterized in that it includes a timer section for maintaining the off state.

(Function) When the switch parts facing each other form a set and perform on-off operations alternately with the switch parts of other sets, a rectangular alternating current voltage is applied to the load, and the voltage of each switch part is applied to the load. During on-off transition, the off state is maintained for a predetermined period of time, so even if there is a slight temporal difference in the operating characteristics of the switch section, the error will be absorbed by the off-maintenance time, so there is no short circuit? There is no risk of H flow occurring.

(Example) Next, examples of the present invention will be explained.

The inverter circuit according to the present invention includes an oscillation section 1. Timer section 2
The oscillator 1 has an oscillator 2 splitter, etc., and emits a pulse signal of an arbitrary frequency with a duty ratio of 50%, and its output section outputs a forward and reverse output. A flip-flop circuit 11 is provided as shown in FIG.

Timer section 2 consists of two monostable multi-by-break M, M
The Q output of the flip-flop circuit 11 is received by M people, the Q output is received by MB, and pulse signals A and B are issued for a predetermined time to indicate that the outputs should be received. Moreover, the output times of the pulse signals A and B are set to have a cycle shorter than the cycle of the Q output (Q output) of the flip-flop circuit 11. Specifically, as shown in Fig. 4, if the output frequency of the oscillator 1 is 501 (□), the output period of the output pulse signals Q and Q of the oscillator 1 is 10 m5, so the multi-pie break MA , MU output cycle is 7m
s. The switching unit 3 has four switch units 31
．． 32, 33, and 34, each switch section 31.32
．． 33 and 34 are the switch parts 31 and 33, respectively, from the positive electrode side.
are connected in series, the switch sections 32 and 34 are also connected in series, and the series switch sections are connected in parallel to form a bridge circuit as a whole, and a load is connected between switch section connection points a and β. The specific structure of the switch section 31.32.33.34 is as shown in FIGS. 2 and 3, and includes switching transistors T1 to T4 that perform switching between the positive electrode or the negative electrode and the connection points of α and β, and It consists of photo parts H, ~H4 which performs on/off control of the switching transistors T, ~T4, and photo parts H, -1 (4 is a light emitting diode that is energized and emits light by the respective outputs of the multivibrators M ~ MB, and a light emitting diode). The light-emitting diodes of the phototransistors H and -Ha are connected to the output of the multivib daughter MA, and the on-off operation is controlled by the phototransistor, which turns the front three switching transistors T1 to T4 into an ON state when turned on. The light emitting diodes of the other H2+H3 sections are connected to the output of the multivibrator MB.

Next, the operation of the above embodiment will be explained below.

A signal of a predetermined frequency with a duty ratio of 50% is outputted from the oscillation section 1 as forward/reverse signals Q, Q, and inputted to each multi-by-break M and MB of the timer section 2.

That is, the Q output is input to M people, and the Q output is input to MB.

When each of the multivibrators M and MB receives the input, it emits pulse signals A and B for a predetermined period of time, for example, 7 ms (assuming the output of the oscillator is 50H2).

While these pulse signals A and B are being emitted, each light emitting diode is energized and emits light, turning on the transistor H1-1, and accordingly, the switching transistors T1 to T1 are turned on.
This turns on T4. Therefore, the Q of oscillator 1
When the output rises to high output (Q output is naturally low output) What about multivibrator M? ms, and during this output period, the switch section 31 and the switch section 34 are each in a conductive state, and a current flows from the 0 point to the β point in the load. Next, when the Q output rises to the high output, the switch section 32 and the switch section 33 become conductive in the same way, and the current flows from the β point to the 0 point. lE will flow, and AC power with an output frequency corresponding to the frequency of the oscillation unit 1 will be supplied to the load.

Further, a time period of 3IIS is provided between when the pair of switch sections 31 and 34 shifts from the on state to the off state and until the switch sections 32 and 33 shift to the on state. By providing this interlock time t, instantaneous short circuit due to conduction of each switch part can be reliably prevented.
It was F.

It should be noted that the present invention is not limited to the above embodiments, and the specific configurations of the oscillation section 1, timer section 2, and switch sections 31 to 34 may include any circuit element as long as it exhibits a predetermined effect. The circuit configuration used is also good.

(Effects of the Invention) As described above, the present invention connects the switch portions in a circuit-shaped manner, and connects a DC power source and a load between the opposing connection points, respectively.
In an inverter circuit that supplies power to a load by alternating on-off operations with other pairs of switch units facing each other, one pair of switch units switches on and off before the other switches to the on state. An interlock time is provided at the time of on-off switching to ensure that the pair is turned off, thereby preventing short-circuit accidents due to characteristic errors in circuit components, etc.

[Brief explanation of the drawing]

Figure 1 is a simple block diagram of the circuit of the present invention, Figure 2 is a detailed diagram of the same part, Figure 3 is a circuit diagram of the switching section, Figure 4 is a waveform diagram of each output signal, Figure 5 is a basic circuit diagram, Figure 6 shows a conventional inverter circuit (0 is a parallel inverter circuit, (
) is a series inverter circuit. 1 is the oscillation section 11, the flip-flop circuit 2 is the timer section M^, and the monostable multi-pie break 3 is the switching sections 31, 32, 33. 34 is the sui nochi part T
, ~T4 is the switching I/lasigister H, ~H4
Photo section Fig. 3 Fig. 4 Fig. 1 Fig. 2

Claims (1)

[Claims] (1) Connect the four switch sections in a bridge circuit, connect a DC power source between opposing connection points, connect a load between the other opposing connection points, and set the facing switch sections as one set,
In an inverter circuit that alternately performs on-off control for each set and supplies AC power to a load, an oscillation unit that determines an output frequency is provided in a control unit that performs on-off control of the switch unit;
An inverter circuit comprising a timer section for maintaining the switch section in an off state for a predetermined period of time when switching the switch section on and off.