JPH0398420A - Arm short-circuit detector for power converter - Google Patents

Abstract

PURPOSE:To prevent breaking, burning, etc., by outputting a detecting signal only in the case of an arm short circuit and turning the switching element of power conversion OFF when voltage on the DC power supply side suddenly drops. CONSTITUTION:DC supply voltage VD is applied at a point A through a parallel circuit 13, and the potential of a detecting output e1 is elevated to the positive side at all times by the fluctuation of VD and the effect of a differential capacitor 11. The detecting output e1 is clamped within the range of the voltage of a power supply 17 for detection by the effects of clamping diodes 14a, 14b. When DC supply voltage VD suddenly drops by an arm short circuit, the detecting output e1 also drops instantaneously. When the value of the detecting output e1 is made lower than a comparison level e2, a comparator 15 is operated, a detecting signal e3 rises, and the arm short circuit is detected. The detection of the arm short circuit is stored in a flip-flop circuit 18, and transmitted over a control circuit 26 as the OFF command e4 of transistors, and the OFF command is transmitted over all transistors Q1-Q4 of an inverter 21.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to an arm short circuit detection circuit for a power converter. (Prior Art) In power conversion systems, various protection measures are employed to protect switching elements and power converters themselves from overcurrents and the like. Conventionally, in many cases, power converters such as inverters are protected from overcurrent by turning off switching elements such as transistors when the load current exceeds a predetermined value. However, there are many cases where arm short circuits are not protected because they are problems inside the power converter, and when protecting against arm short circuits, a current detection current transformer (CT) is installed in the pull absorbing capacitor circuit or transistor circuit.
), and arm shortness was detected when the current value detected by this CT exceeded a predetermined value. Figure 8 shows a voltage source inverter system equipped with a conventional arm short circuit detection circuit. In the figure, the voltage of a three-phase AC power source 2l is rectified by a rectifier 22, and is connected to its output side or applied to an inverter 24 via a pull absorption capacitor 23. The inverter 24, each arm of which is composed of transistors Q1 to Q4, performs a reverse conversion operation in response to an on/off command from the control circuit 26, and the load 25 is supplied with alternating current power.

In such an inverter system, for example, Q. ，
Q. If both are turned on at the same time and an arm short circuit occurs, the transistor will be destroyed.

In order to prevent this inconvenience, conventionally, as shown in FIG. 8, a current detection CT28 is provided in the circuit of the ripple absorbing capacitor z3 or the circuit constituting the transistors Q1 to Q4, and the current value detected by this CT2g is set to a predetermined value. The arm short-circuit detection circuit 29 detects that the value exceeds the value of the transistors Q1-Q. was turned off.

(Problem to be solved by the invention) However, in reality, the arm short circuit detection method described above has the following problems and tends not to be used much. 1) CT2g is made up of an iron core and windings, so it is heavy and expensive. 2) Inserting the CT28 requires several tens of extra wires on the inverter side, which increases the inductance of the wires and adversely affects the switching operation of the inverter. 3) Recently, in order to minimize the inductance of this wiring, laminate bar wiring, which is a layered layer of copper strips and insulating films, has been used, so there is no room for inserting CT2g. In this way, in the past, CT was used to detect arm short circuits, which caused various problems as described above. The present invention has been proposed in order to solve the above problems, and when an arm short circuit occurs, it can be reliably detected without using CT to prevent destruction or burnout of switching elements and power converters. An object of the present invention is to provide an arm short circuit detection circuit for a power converter that prevents arm short circuits.

(Means for solving the problem) As a result of repeated consideration of the above problems, the inventors have
We focused on the fact that the terminal voltage of the ripple absorption capacitor includes a large pull voltage even in normal conditions, but when the arm is short-circuited, a large short-circuit current suddenly flows, resulting in a large and sudden drop in the capacitor voltage. We have also found that by paying attention to the terminal voltage of this ripple absorbing capacitor, it is possible to detect an arm short circuit without using a conventional CT.

That is, the first invention provides an arm short-circuit detection circuit for use in a power converter that has a ripple absorbing capacitor on the DC power source side and is provided with at least two upper and lower arms of semiconductor switching elements, in which the terminal of the ripple absorbing capacitor is a voltage sudden drop detection means for detecting a sudden drop in the voltage between the voltage and outputting a signal corresponding to the voltage; and outputting a comparison result between the output signal of the voltage sudden drop detection means and a signal corresponding to a predetermined comparison level as a detection signal. and comparing means, and detects a sudden drop in the voltage between the terminals of the ripple absorbing capacitor based on the detection signal, thereby detecting the occurrence of an arm short circuit.

In a second aspect of the invention, the arm short-circuit detection circuit includes an upper arm short-circuit detection circuit and a lower arm short-circuit detection circuit, respectively, corresponding to an upper arm section and a lower arm section each including at least two or more upper and lower arms semiconductor switching elements. In addition, the power supply circuit of each of these detection circuits is constituted by one system of positive and negative power supplies whose reference potential is the potential at the connection point of the upper arm part and the lower arm part. .

(Function) In the first invention, the voltage on the DC power supply side is taken into the voltage sudden drop detection means as the voltage of the pull absorbing capacitor, converted into a detection signal corresponding to the voltage, and outputted to the comparison means. The comparison means compares the detection signal with a predetermined comparison level determined by the level setter and outputs the comparison result. Now, when the voltage on the DC power supply side suddenly drops, the voltage sudden drop detection means and comparison means determine whether the sudden voltage drop is due to an arm short circuit or some other cause, and output a detection signal only if the arm short circuit is the cause. However, this detection signal ultimately acts to turn off the switching element of the power converter.

Further, in the second invention, the upper arm short-circuit detection circuit and the lower arm short-circuit detection circuit provided corresponding to the upper arm section and the lower arm section of the power converter are connected to a single system having a common reference potential. Since it operates with positive and negative power supplies, even if the arm section of the power converter is multi-staged, the structure of the power supply circuit will not become complicated.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the configuration of a typical inverter system to which an embodiment of the invention No. 2 is applied. The AC power from the AC power supply 2l is rectified by the rectifier 22, and the rectifier 22
Each arm supplies DC power to an inverter 24 composed of transistors Q1 to Q4. The transistors Q1 to Q4 are operated by on/off signals from the control circuit 26, and the inverter 24 supplies high frequency current to the load 25. Further, a ripple absorbing capacitor 23 is provided close to the input side of the inverter 24 in order to absorb high frequency ripple current entering the inverter 24. Then, the terminal voltage of this capacitor 23 is led to an arm short circuit detection circuit 27, and a command is sent from this arm short circuit detection circuit 27 to a control circuit 26.

FIG. 2 shows this arm short circuit detection circuit 27 in a block diagram. In the figure, the input voltage Vo of the inverter 24 (the voltage between the terminals of the capacitor 23, ie, the DC power supply voltage) is input to the voltage sudden drop detection means l. The voltage sudden drop detection means (2) detects a change in Vo and outputs its detection output e1 to the comparison means 2. The comparison means 2 compares the detection output e0 with a comparison level e2 determined by a predetermined level setter 3, and outputs the comparison result to the detection signal output/holding means 4 as a detection signal e3. Here, e
When 1 becomes smaller than 02, the comparison means 2 outputs a detection signal e3 to the detection signal output/holding means 4, and the detection signal output/holding means 4 outputs an off command e4 for all transistors.

FIG. 3 is a circuit diagram showing a specific example of this arm short circuit detection circuit 27 in detail.

In the same figure, a differential capacitor 11 and a lifting resistor l2
A parallel circuit 13 with 13 and a series circuit 14 of clamp diodes 14a and 14b connected with the same polarity constitute the voltage sudden drop detection means 1 in FIG.

One terminal of the parallel circuit l3 is connected to the 10 terminal of the DC power supply of the inverter 24, and the other terminal is connected to the clamp diode l4a, 1.
It is connected to one point A between 4b. Further, the anode side of the clamp diode 14b is connected to one terminal side of the DC power supply.

Further, the comparator 15 corresponds to the comparing means 2 in FIG. 2, and the point A is connected to the inverting input terminal of this comparator 15, and its non-inverting input terminal is connected to the level setting device 3 in FIG. It is connected to the variable resistor 16. Furthermore, the output terminal of the comparator 15 is connected to a flip-flop circuit l8 as the detection signal output/holding means 4 shown in FIG.
Its output terminal is connected to the control circuit 26 of FIG.

Note that a detection voltage 117 (voltage AS) is connected between both ends of the series circuit 14 and the variable resistor 16, and between each power supply terminal of the comparator 15 and the flip-flop circuit l8, and serves as a DC power supply in FIG. The negative polarity side terminals of the rectifier 22 and the detection power supply 17 are connected to each other.

FIG. 4 is a time chart showing an example of the operation of the arm short-circuit detection circuit 27 shown in FIG. In the figure, In is the current flowing into the inverter 24, and during period I, a normal current is repeatedly generated at a cycle of several μs, and during period ■, a large abnormal current occurs due to an arm short circuit. In addition, the DC power supply voltage Vo (voltage of the ripple absorption capacitor 23) has a normal pull voltage Vr due to the normal load current in the period ■, and in the period ■? This shows how Vo suddenly fell due to a short arm. Furthermore, 81. e3 and e4 correspond to exHe3 and e4 in FIG. The DC power supply voltage Vo is usually a high voltage of several tens to hundreds of square meters, and the voltage es of the detection power supply 17 is IO
It has a low constant voltage around V.

The operation of each part will be explained in detail below.

The DC power supply voltage VD is applied to point A via the parallel circuit 13, and the potential of +61 is constantly pulled up to the positive side due to changes in VD and the effect of the differential capacitor 11. and. e1 further includes a clamp diode 14a. Due to the effect of l4b, the voltage is clamped within the range of the voltage e5 of the detection power source l7. Therefore, in the normal state (period I), e■ shows a waveform that sticks to the upper side of e5 due to the effect of the lifting resistor l2, and only the lower end of the Vo ripple where the DC power supply voltage VD changes sharply is transmitted. .

If Vn suddenly drops due to an arm short circuit in this condition,
eE also drops instantly, and when the value of eE falls below the comparison level e2, the comparator? 5 is activated, the detection signal e3 rises, and an arm short circuit is detected. This is stored in the flip-flop circuit 18 as e4 in the control circuit 2.
6, all transistors Q1 to Q of the inverter 24
Give an off command to 4.

By the way, when the transistor is turned off and the arm short-circuit current becomes zero, e■ increases and the detection signal e3 is no longer output. However, since there is a risk that a transistor-on command will be issued again and the transistor will be destroyed, it is important that the flip-flop circuit 18 holds the detection signal.

In the circuit shown in FIG. 3, for example, the differential capacitor 11 is approximately 100 pF, and the lifting resistor 12 is approximately 1M.
It can be constructed with minute parts of about Ω, 0.1W, so it is small and
It becomes possible to manufacture and provide a lightweight and low-cost arm short circuit detection circuit 27.

Furthermore, as shown in Figure 5, fluctuations in the DC power supply voltage Vo include not only ripples Vr due to normal inverter operation, but also slow and large fluctuations in the power supply voltage (see Figure 5(a)), ripples due to the rectifier 22 as a power supply, etc. In addition, a sudden drop due to an instantaneous power outage (see figure 1) should also be considered normal, and only a sudden drop due to an arm short circuit (see figure 3) should be detected as an abnormality. The detection level of such a delicate sudden drop in voltage can be set using the differential capacitor 11. This can be done freely by adjusting the lifting resistor l2 and the variable resistor 16, respectively.

In the above embodiment, an arm short circuit detection circuit using an analog method was explained, but the voltage sudden drop detection means 1,
A part or all of the comparison means 2, level setter 3, detection signal output/holding means 4, etc. may be constructed by digital circuits.

Next, an embodiment of the second invention will be described based on FIGS. 6 and 7.

First, according to the arm short circuit detection circuit according to the first invention, when an arm short circuit occurs, it can be detected reliably without using a CT to prevent destruction, burnout, etc. of switching elements and power converters. is now possible.

However, when the arm short circuit detection circuit described above is applied to a power converter having two upper and lower arm sections 100 and 200 as shown in FIG. It is necessary to connect the circuit 271 and the lower arm short circuit detection circuit 272 to the lower arm 200, respectively. Here, each short circuit detection circuit 27
1, 272 is substantially the same as that shown in FIG.

In this case, the reference potential for detecting an arm short circuit is the potential Ml. Since the lower arm short-circuit detection circuit 272 has a different potential M2 at one end ND of the lower arm 200, the power supply for each arm short-circuit detection circuit 271, 272 as shown in FIG.
), (C) shows two isolated power sources 171.
, 172 are required. In addition, Fig. 6 (B), (C
) at each power source 171, 172 potential (terminal) P1,
Ml, P2, and M2 are respective potentials (terminals) in each arm short-circuit detection circuit 271, 272 in the same figure (A), respectively.
It corresponds to Due to this configuration, in a power converter that has two upper and lower arm sections, the power supply circuit becomes complicated in order to detect arm short circuits, which creates new problems such as increased costs and increased device size. become.

Therefore, the second invention aims to simplify the configuration of the power supply circuit in an arm short-circuit detection circuit applied to a power converter having multiple arm sections. An embodiment of the second invention will be described below with reference to FIG.

In FIG. 7(A), the upper arm short circuit detection circuit 271
has the same configuration as in FIG. 6, and the upper arm portion l00
and the positive power supply 170A in the power supply 170 of FIG. 7 CB) based on the potential M1 of the connection point MD of the lower arm part 200
(between M1 and P1) is its power source.

In addition, in FIG. 7(A), the lower arm short-circuit detection circuit 272' has one end of the parallel circuit 13 described in the embodiment of the first invention connected to one end ND of the lower arm 200. , the negative power supply 170B (between M1 and Nl) in the power supply 170 in FIG. 7(B), which is based on the potential M1 as well as the upper arm short circuit detection circuit 271, serves as its power supply. That is, if we focus on the power supply 170, this power supply 1
Reference numeral 70 is a single power supply system consisting of a positive power supply 170A and a negative power supply 170B based on the potential M1. As a result, the power supply circuit for the upper and lower arm short-circuit detection circuits 27l and 272 can be made by dividing one system of DC power into two parts, so that the power supply circuit can be simplified compared to the case of FIG. 6. In addition, the upper and lower arm short circuit detection circuit 2 in this embodiment
The operations of the circuits 71 and 272 are substantially the same as those of the arm short circuit detection circuit 27 in the first aspect of the invention, and in this embodiment as well, various advantages can be obtained by omitting the CT.

In each of the above embodiments, the present invention is applied to an inverter using a transistor as a switching element, but it is also applicable to an inverter using other semiconductor elements as a switching element. It goes without saying that the present invention can also be applied to power converters such as choppers and converters as long as they are provided with two or more semiconductor switching elements.

(Effects of the Invention) As described above, according to the first or second invention, it is decided to detect an arm short circuit by detecting the terminal voltage of the pull absorbing capacitor that suddenly drops when the arm short circuit occurs. There is no need to use a CT as in the case of the present invention, and as a result, it is possible to provide an arm short-circuit detection circuit that is small, lightweight, and has no wiring inductance. It also has the advantage that it can be applied to power converters that use recent laminate bar wiring and the like.

Furthermore, the setting of the detection level of the setting device or the detection level of sudden voltage drop can be done by properly setting the level setting device, voltage sudden drop detection means, etc., respectively, to make it possible to clearly distinguish between arm short circuits and other voltage drop causes such as momentary power outages. This has the effect that only arm short circuits can be detected accurately and with high precision.

In addition, according to the second invention, it is possible to simplify the structure of the power supply circuit, thereby reducing costs and downsizing the device.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram when one embodiment of the first invention is applied to an inverter system, Fig. 2 is a block diagram showing the configuration of the above embodiment, and Fig. 3 is a circuit diagram of the above embodiment configured using an analog system. Figure 4 is a waveform diagram showing the operation of each part of the circuit shown in Figure 3. Figure 5 is a reference diagram to supplement the waveform diagram shown in Figure 4. FIG. 7 is a circuit diagram illustrating an embodiment of the second invention, and FIG. 8 is a circuit diagram illustrating the prior art. 23... Ripple absorption capacitor 27... Arm short circuit detection circuit 170... Power supply 170A... Positive power supply 170B.
...Negative power supply 271...Upper arm short circuit detection circuit

Claims (2)

[Claims] (1) In an arm short-circuit detection circuit used in a power converter that has a ripple absorption capacitor on the DC power supply side and is provided with at least two upper and lower arms of semiconductor switching elements, there is a sudden drop in the voltage between the terminals of the ripple absorption capacitor. and a comparison means that outputs a comparison result between the output signal of the voltage sudden drop detection means and a signal corresponding to a predetermined comparison level as a detection signal. An arm short circuit detection circuit for a power converter, comprising: detecting the occurrence of an arm short circuit by detecting a sudden drop in the voltage between the terminals of the ripple absorbing capacitor using the detection signal. (2) An arm short-circuit detection circuit for use in a power converter having a ripple absorbing capacitor on the DC power supply side and having at least two upper and lower arms of semiconductor switching elements, wherein the voltage between the terminals of the ripple absorbing capacitor is voltage sudden drop detection means for detecting a sudden drop in voltage and outputting a signal corresponding to the voltage; and comparison means for outputting a comparison result between the output signal of the voltage sudden drop detection means and a signal corresponding to a predetermined comparison level as a detection signal. and an arm short circuit detection circuit that detects the occurrence of an arm short circuit by detecting a sudden drop in the voltage between the terminals of the ripple absorption capacitor based on the detection signal, wherein the arm short circuit detection circuit detects at least two upper and lower arms. An upper arm short-circuit detection circuit and a lower arm short-circuit detection circuit are provided corresponding to the upper arm section and the lower arm section, each of which is provided with a semiconductor switching element, and a power supply circuit for each of these detection circuits is connected to the upper arm section. An arm short-circuit detection circuit for a power converter, characterized in that it is configured with a single system of positive and negative power supplies whose reference potential is the potential at the connection point of the upper arm and the lower arm.