JPS61106070A - Defect detection of circuit bridge type inverter - Google Patents

Abstract

PURPOSE:To detect a defect simply without delay by disposing two AC current transformers to detect the output differences of the both transformers. CONSTITUTION:A DC power source 1 is converted into AC through single-phase bridge inverter by thyristors 2-5 to supply it to a load 6. In this case, an AC current transformer 7 for detecting the currents of the thyristors 2, 4 and an AC current transformer 8 for detecting the output current (load current) of the inverter are provided. Thus, when a defect occurs (e.g., the thyristor 5 is fired when the thyristors 2, 3 are energized), the power source 1 is shortcircuited by the thyristors 2, 5 to flow the excess current thereto. The voltage applied to the load 6 becomes zero to attenuate the current. The both currents are detected by the transformers 7, 8 and a difference is generated between the both outputs. The occurrence of the power source shortcircuit can be known by the detection of the difference.

Description

[Detailed Description of the Invention] [Fields of Industrial Application] The present invention is applicable to all application fields of single-phase bridge inverters, and its main applications include induction heating power supplies, simple compact power supplies, and fluorescent lamp drive power supplies. There are devices, etc.

[Congo's technology and its problems]

In a bridge type inverter, for example, detecting a short circuit in the DC power supply only requires monitoring the power supply current, but this usually requires an expensive DC transformer or a shunt to isolate the voltage and connect it to the control circuit. This required an isolated amplifier, etc. Furthermore, as another method, it is known to detect a short circuit by detecting an increase in the discharge current of a smoothing capacitor disposed on the DC side.

In any case, since these methods become detectable only after the current value reaches a certain level compared to the normal current value, there is a delay in detection in principle.

In a bridge type inverter, two sets of series-connected switching elements are connected to the DC power supply, either directly or indirectly, so if the - set of switching elements fails, an overcurrent will occur due to a short circuit in the power supply. It flows to both switching elements and even destroys the healthy element. In order to avoid this, it is necessary to promptly detect a short circuit in the power supply and take rescue measures such as gate operation of the switching element or temporary interruption of the power supply to protect healthy elements. For this reason, the above-mentioned means and the protection method of arranging a quick-cutting fuse have been adopted, but both are expensive.

It could not be said to be sufficient as complete protection could not be achieved due to operation delays.

In addition, in recent years, the operating speed of various switching elements has been improved, and when applied to inverters, the operating speed of various switching elements has been improved.
It has become possible to output at 0 kilohertz, and along with this, even higher speed protection operations are required.

[Structure of the invention]

In view of the above-mentioned points, the present invention detects the output difference between the two AC current transformers by arranging two AC current transformers, thereby detecting the difference in the output of both AC current transformers. However, it also provides a simple and completely new device that can detect failures without delay. Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 shows the main part configuration of an embodiment according to the present invention, in which 1 is a DC power supply, 2, 3, 4.5 are thyristors as switching elements connecting a single-phase bridge inverter, 6 is a load, 7 and 8 are AC current transformers.

Here, some of the thyristors 2, 3, 4, and 5 require a commutation circuit for arc extinguishing, but since they are not directly related here, they will be omitted. In addition, some bridge type inverters are equipped with feedback diodes and various current limiting reactors for inductive loads, but these are provided as appropriate, and this is the simplest circuit example that does not matter for the purpose of explaining the present invention. Figure 1 shall be used.

In FIG. 1, an AC current transformer 7 is for detecting the current of the thyristor 2.4, and is provided so that the current of the thyristor 2 and the current of the thyristor 4 are passed to the primary side in opposite directions. Here, since the current waveforms of the thyristors 2.4 are the same waveforms having a phase difference of 180°, there is no need to use a DC type as described above. Further, the AC current transformer 8 detects the output current of the inverter, that is, the load current. Note that the illustration of the secondary side circuit of both the AC current transformers 7 and 8 is omitted.

Next, the operation of such a circuit will be explained with reference to FIG.

Figure 2 shows the waveforms of each part of the circuit in Figure 1, where (a) is the current of thyristor 2, (b) is the current of thyristor 4, (
C) shows the detected current of the AC current transformer 7, and 2) shows the detected current of the AC current transformer 8. Here, FIG. 2 is shown assuming that the load 6 is a pure resistance. This naturally occurs when the load is inductive or capacitive, but it does not affect the operation of the present invention as will be described later. .

Now, in FIG. 2, at time Tl, thyristor 2,
3 conducts and supplies current to the load 6t in the direction shown.

At this time, the thyristors 4 and 5 are turned off and their currents are zero. Here, each AC current transformer 7.8 is connected to a thyristor 2.8. The current in the load 6 is detected and the output shown in FIG.

Assuming that thyristors 2 and 3 are turned off and thyristor 4.5 is made conductive at time T2, Fig. 2 (a),
As shown in (b), the current in the thyristor 2 becomes zero, current flows in the thyristor 4, and a current in the opposite direction is supplied to the load 6. Then, the primary side currents of AC current transformers 7 and 8 are also reversed, so that outputs in opposite directions are produced.

It is assumed that the thyristors 2 and 3 are energized again at time T3, and these operations are repeated thereafter under normal conditions.

In such an operation, the current values applied to the AC current transformers 7.8 are equal and therefore produce equal outputs. Next, regarding the case where a failure occurs, thyristor 2.
It is assumed that the thyristor 5 is ignited due to some kind of erroneous operation or failure at the time T6 when the thyristor 3 is energized.

Then, the DC power supply 1 is short-circuited by the thyristor 2.5, and an excessive current limited by the circuit impedance flows through the thyristor 2.5. Therefore, the AC current transformer 7 detects the excessive current and produces an output proportional to this.

On the other hand, as the thyristor 3.5 becomes conductive to the load 6, the applied voltage becomes almost zero, the current also attenuates, and the output of the AC current transformer 8 also becomes zero.

In this way, the AC current transformers, which were equal under normal conditions, 7.8
Due to the occurrence of a short circuit in the power supply, one of the outputs increases and the other becomes zero. Note that in the case of an inductive load, etc., the load current does not immediately become zero at time T6, but decreases at a rate determined by the time constant of the load, but in any case, the output of the AC current transformer 7 increases. There is no change in the fact that the output of the AC current transformer 8 decreases, and therefore, the occurrence of a power supply short circuit can be detected by the difference between the outputs of both AC current transformers.

From this, the outputs of both AC current transformers as described above are compared by a control circuit (not shown), and if the absolute value of the output of AC current transformer 7 exceeds that of AC current transformer 8, for example, a failure occurs. It is clear that the failure can be detected by considering it as an occurrence.

The reason why the absolute value is taken is that each AC current transformer has positive and negative polarity outputs, and as a result, the polarities of the two sets of AC current transformer outputs do not necessarily have to match.
For example, even if the polarity in FIG. 2(a) is reversed, the operation will not be affected. Furthermore, this fault detection method uses a method of specifically detecting ζζ regardless of the current value itself, which was caused by the conventional detection current exceeding a certain limit value.

〔Effect of the invention〕

According to the present invention, since the occurrence of a power supply short circuit can be detected without delay in operation by simply installing an AC current transformer, healthy elements of the inverter circuit can be easily protected in the event of a failure.
Furthermore, it is possible to eliminate the need to reduce the utilization rate of the switching element due to a delay in failure detection, and to provide a useful device that can fully utilize the element's ability.

[Brief explanation of drawings]

FIGS. 1 and 2 are circuit diagrams showing the configuration of main parts of an embodiment according to the present invention, and diagrams showing waveforms of each part thereof. l...DC power supply, 2, 3, 4.5...
Thyristor, 6...Load, 7.8...
AC current transformer, T1. T2゜T3. T...at the moment.

Claims (1)

[Claims] In a bridge type inverter comprising four sets of switching elements connected in a bridge shape, the currents of two sets of switching elements connected to the same polarity side of a DC power supply among the four sets of switching elements are directed in opposite directions. A first AC current transformer that causes the primary side to be energized and a second AC current transformer that causes the inverter output current to be energized to the primary side are provided, and the instantaneous value of the first AC current transformer output is 2. A failure detection circuit for a bridge type inverter, characterized in that it detects that the instantaneous value of the output of the AC current transformer exceeds the absolute value.