JPH0510911B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a separately excited series type DC/AC inverter, and particularly to a separately excited series type DC/AC inverter that generates an AC voltage by inputting a DC voltage. The present invention relates to a separately excited series type DC/AC inverter that improves efficiency by preventing losses due to simultaneous firing of output switching elements in a device.

<Prior Art> This type of conventional technology will be explained below with reference to the drawings. Figure 3 is a block diagram showing an overview of a conventional separately excited series type DC/AC inverter.
The figure is the time chart of Figure 3.

Below, FIGS. 3 and 4 will be explained.

1a, 1b, and 1c (hereinafter referred to as 1) are one output stage of separately excited type (details of the U phase are shown here, but the circuit configurations of the other phases are also the same, so they are omitted). 2 is an oscillation circuit. This oscillation circuit 2
outputs an inverted signal as shown in FIG. 4, for example. Its configuration consists of a comparator Q ₁ with a reference voltage connected to its inverting terminal and a comparison voltage connected to its non-inverting terminal.
It consists of, but is not limited to. 3 is a driver transistor (npn transistor Tr ₃ ) as a first drive stage switch element 31 whose base is connected to the oscillation circuit 2 via a resistor and whose emitters are both connected to a common potential, and a second drive stage switch element. The drive stage consists of a driver transistor (pnp transistor Tr ₄ ) as 32. 4 is an output transistor (composed of a pnp transistor Tr ₅ ) whose collector is connected to the base via a resistor and whose emitter is connected to the DC power supply +V _CC of the first drive stage switch element 31 of the drive stage 3, for example. This is a switching element for alternating current output (hereinafter referred to as a first switching element). 5 is an output transistor (consisting of an npn transistor Tr ₆ ) whose collector is connected to the base of the second drive stage switch element 32 of the drive stage 3 via a resistor, and whose emitter is connected to the DC power supply -V _EE . This is a second AC output switching element (hereinafter referred to as a second switching element). The collectors of the first switching element 4 and the second switching element 5 are connected to each other, and a U-phase AC voltage is output from this connection point.

In FIG. 3, when the drive stage 3 receives an inverted signal as shown in FIG. 4 from the oscillation circuit 2,
A drive output such as the following is output to the first switching element 4 and the second switching element 5. First switching element 4 and second switching element 5
are alternately turned on and off as shown in Figure 4.
It performs an OFF ignition operation and outputs an AC voltage as shown in the figure from the series-connected connection points.

By the way, the first switching element 4 and the second switching element 5 cannot turn off immediately even when the drive signal becomes 0, but remain in the OFF state until the electric charge at the junction disappears (generally referred to as Tstg and Toff). Since the current continues to flow, as shown in FIG. 4, there is a time τ during which both AC output switching elements (hereinafter referred to as switching elements) are simultaneously in the ON state. Therefore, the DC power supplies +V _CC and -V _EE are the first,
Since the two switching elements 4 and 5 are short-circuited, an extremely large current (through current) as shown in FIG. 4 flows. As a result, the first and second switching elements 4 and 5 may be destroyed or suffer a large loss. In order to prevent this, in this conventional technology, the operation diagram of the inverter when the simultaneous ON of a pair of switching elements is prevented by setting the idle period as shown in Fig. 5 (A is the operation waveform diagram of the switching elements) and the rest period δ.B is the output waveform diagram).
A pause period was set for the input of the switching elements to prevent the pair of switching elements from firing at the same time.

<Problems to be Solved by the Invention> However, this conventional separately excited series DC inverter has the following problems.

Since Tstg and Toff vary depending on temperature and load current, in order to prevent both switching elements from turning on at the same time under any operating conditions, the rest period must be sufficiently long.
On the other hand, this has the disadvantage that under normal operating conditions, the idle period becomes wider than the time width required to prevent simultaneous ON. That is, a period occurs in which both switching elements are turned off at the same time, and no load current flows during that period. This means that it is extremely inconvenient as an AC power source for driving a load such as a motor.

The present invention has been made in view of the problems of the conventional technology, and it adds an interlock function to the conventional separately excited series type DC inverter to prevent both switching elements from firing at the same time. The object of the present invention is to provide a separately excited series type DC inverter that always realizes optimal operation of both switching elements regardless of the switching elements.

<Means for solving the problems> In order to achieve such an object, the present invention has the following features:
An oscillation circuit 2 that outputs a signal whose polarity is alternately inverted at a constant period; a first drive stage switch element 31 and a second drive stage switch element to which the output signal of this oscillation circuit is applied to the input terminal and which alternately operate on and off. 3
2. a first AC output switching element 4 controlled by the output of the first drive stage switching element 31;
and a second AC output switching element 5 controlled by the output of the second drive stage switch 32, one end of the first AC output switching element being a positive DC power source, and the second AC output switching element One end of each element is connected to a negative DC power source, the other end of the first AC output switching element and the other end of the second AC output switching element are connected, and an AC voltage is applied from these connection ends. A separately excited series type DC/AC inverter to be obtained includes: a detection circuit 61 comprising an inverting comparator having a non-inverting terminal connected to a common potential and an inverting terminal connected to the AC voltage; and an input terminal commonly connected to the detection circuit 61. first and second drive stage switch elements whose output ends are connected to the input ends of the first drive stage switch element and the second drive stage switch element, respectively, and whose operations are opposite to each other. switching elements (Tr ₁ , Tr ₂ ), and when the output of the detection circuit is positive, turning on the first switching element keeps the first alternating current output switching element in the off state. , when the output of the detection circuit is negative, the second switching element is turned on to maintain the second AC output switching element in the off state to prevent simultaneous firing. The present invention is characterized in that an interlock circuit 6 consisting of an arc prevention circuit 62 and an arc prevention circuit 62 are provided.

<Operation> The structure is characterized in that an interlock circuit is provided in front of the pair of switching elements to prevent the pair of switching elements from firing at the same time. This interlock circuit uses a detection circuit to detect that the AC voltage, which is the output from the connection point of the first switching element and the second switching element, has returned to the midpoint, and uses the detection value of this detection circuit to switch one of the switching elements. When the input of the first switching element (for example, the first switching element) switches from the ON state to the OFF state, the first switching element
The other switching element (for example, the second switching element) is held in the OFF state by a simultaneous firing prevention circuit until the switching element becomes OFF, thereby preventing the pair of switching elements from firing at the same time.

Furthermore, between the oscillation circuit and the drive stage, (a) a detection method that inputs AC voltage as feedback, detects which region this AC voltage falls into with respect to the common potential, and outputs the inverted output; circuit and (b)
A simultaneous firing device comprising a pair of switching elements disposed between a pair of first drive stage switch elements and a second drive stage switch element, the combination of which operates in opposite directions depending on the detection value from the detection circuit. An interlock circuit consisting of a prevention circuit is provided. Then, the input of either the first switching element controlled by the output of the first drive stage switch element or the second switching element controlled by the output of the second drive stage switch element changes from the ON state.
When the switching element switches to the OFF state, the other switching element is held in the OFF state until the switching element itself becomes the OFF state. This prevents the first switching element and the second switching element from firing at the same time.

<Example> Hereinafter, the present invention will be described in detail based on the drawings.
In the following drawings, parts that overlap with those in FIGS. 3 to 5 are given the same numbers, and their explanations will be omitted. FIG. 1 is a circuit diagram of a separately excited series type DC/AC inverter which is a specific embodiment of the present invention.

Reference numeral 6 denotes an interlock circuit composed of a detection circuit 61 and a simultaneous firing prevention circuit 62. The detection circuit 61 can be configured with an inverting comparator. This inverting comparator has a common potential connected to the non-inverting terminal and an AC voltage to the inverting terminal so that the input/output is inverted when the input is 0, and detects which region it is in with respect to the common potential. It detects that the AC voltage from the connection point between the first switching element 4 and the second switching element 5 (the output at this point is assumed to be the output from this point) has returned to the midpoint. The simultaneous firing prevention circuit 62 changes the input of the first switching element 4 from the ON state to the OFF state based on the detection value of the detection circuit 61 (assuming the output at this point).
When switching to the switching state, the second switching element 5 is held in the OFF state until the first switching element 4 is definitely in the OFF state, thereby preventing the first switching element 4 and the second switching element 5 from firing at the same time. For example, the base is connected to the detection circuit 61 via a resistor, and the collector is connected to the first and second drive stage switch elements 31 and 3 of the drive stage 3.
A first switching element Tr ₁ (hereinafter referred to as
It consists of an npn transistor Tr ₁ ) and a second switching element Tr ₂ (pnp transistor Tr ₂ ).

FIG. 2 shows the time chart of FIG. 1.

Now, for example, at the point in time when the output of the oscillation circuit 2 is inverted from negative to positive (see point a in FIG. 2), the second driving stage switching element 32 and the second switching element 5
becomes OFF (see Figure 2). however,
The second switching element 5 does not immediately turn off due to Tstg and Toff (hereinafter referred to as OFF time λ), and current flows through this second switching element 5 during this OFF time λ (see Figure 2). Keep flowing. Therefore, the voltage at the point continues to be negative. Therefore, the output of the detection circuit 61 continues to be positive, and the npn transistor Tr ₁ is turned on, preventing the first drive stage switch element 31 and the first switch element 4 from turning on.

Next, the current of the second switching element 5 is turned OFF.
It disappears after the time λ has elapsed, and returns to the midpoint (see point b in FIG. 2), and the output of the detection circuit 61 is inverted (see FIG. 2). Therefore, the npn transistor Tr ₁ is turned off and the output of the oscillation circuit 2 is turned on, so the first drive stage switch element 31 and the first switch element 4 are turned on (see FIG. 2), and the voltage at the point quickly becomes positive.

A similar operation is performed when the output of the oscillation circuit 2 is reversed from positive to negative (these points are taken as points c and d, and the OFF time is expressed as μ).

Note that the first and second drive stage switching elements 31 and 32 controlling the first and second switching elements 4 and 5
When the switching element turns OFF, a reverse bias input is applied, as expressed as the rest period ρ and ξ. is effective for stabilizing operation). The pause periods ρ and ξ are automatically created by detecting the ON state of the switching element.

By repeating the above operations, it is possible to obtain an ideal AC waveform which solves the drawbacks of the conventional technology as shown in FIG.

In FIG. 1, the switching elements and drive switching elements are not limited to those described here, and can be constructed using, for example, FETs or the like. Further, the names such as the first and second switching elements are given for convenience, and are not intended to be rigid. In short, the AC output is detected and fed back, and when one switching element input switches from the ON state to the OFF state according to this feedback value, the other switching element input is switched from the ON state to the OFF state according to the feedback value. It is sufficient if the switching element has a function of keeping the switching element in an OFF state.

<Effects of the Invention> As described above in detail with reference to the embodiments, in a separately excited series DC/AC inverter configured by a pair of switching elements,
When the input of one switching element is switched from ON to OFF by feeding back the AC output to the front stage of the pair of switching elements, the other switching element will not turn ON until this switching element is definitely turned OFF. The present invention is equipped with an interlock circuit that enables highly efficient DC/AC conversion without being affected by variations or fluctuations in the OFF time of switching elements, and has a configuration that prevents losses due to simultaneous firing of a pair of switching elements. A separately excited series DC/AC inverter can be realized. Furthermore, even if the output terminal is accidentally brought into contact with +V _CC or -V _EE , the circuit can be configured to automatically stop operation, so high reliability can be achieved (for example, when the first switching element 4 is ON
It can be seen that if the output is brought into contact with +V _CC at the time of , +V _CC and -V _EE will not be short-circuited by the second switching element 5. Also, if the output is brought into contact with +V _CC while the second switching element 5 is ON, Tr ₂ is turned ON, so the second switching element 5 is immediately turned OFF and protected). There is an effect.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a separately excited series DC/AC inverter which is a specific embodiment of the present invention, Fig. 2 is a time chart of Fig. 1, and Fig. 3 is a conventional separately excited series DC inverter. FIG. 4 is a block diagram showing an outline of an AC inverter, FIG. 4 is a time chart of FIG. 3, and FIG. 5 is an operation diagram of the inverter when a pair of switching elements is prevented from being turned on simultaneously by setting a pause period. 2... Oscillation circuit, 3... Drive stage, 6... Interlock circuit, 61... Detection circuit, 62... Simultaneous firing prevention circuit.

Claims (1)

[Scope of Claims] 1. An oscillation circuit 2 that outputs a signal whose poles are alternately inverted at a constant cycle, and a first drive stage switch element 31 to which the output signal of this oscillation circuit is applied to the input terminal and alternately operates on and off. and a second drive stage switch element 32, a first AC output switching element 4 controlled by the output of the first drive stage switch element 31, and a second drive stage switch element 4 controlled by the output of the second drive stage switch 32. It consists of a switching element 5 for AC output, one end of the first switching element for AC output is connected to a positive DC power supply, one end of the second switching element for AC output is connected to a negative DC power supply, and the first switching element for AC output is connected to a negative DC power supply. In a separately excited series type DC-AC inverter in which the other end of the AC output switching element and the other end of the second AC output switching element are connected and AC voltage is obtained from this connection end, a common potential is applied to the non-inverting terminal. a detection circuit 61 consisting of an inverting comparator to which the AC voltage is connected and whose inverting terminal is connected to the alternating current voltage, and whose input terminals are commonly connected and connected to the output terminal of the detection circuit, and the output terminals are respectively connected to the first drive The detection circuit comprises first and second switching elements (Tr ₁ , Tr ₂ ) connected to the input terminals of the stage switch element and the second drive stage switch element, and whose operations are inverse to each other. When the output of the detection circuit is positive, the first switching element is turned on to maintain the first AC output switching element in the off state, and when the output of the detection circuit is negative, the second switching element is turned on. and a simultaneous firing prevention circuit 62 which holds the second AC output switching element in an OFF state to prevent simultaneous firing by turning on the switching element. Characteristic separately excited series type DC/AC inverter.