JPH07107751A - Inverter circuit - Google Patents

Abstract

PURPOSE:To cut off switching elements, which keep ON in a reflux mode, within a controllable current value even if an arm short-circuit occurs during the reflux mode operation by detecting the currents flowing through the first- fourth switching elements with three current transformers. CONSTITUTION:When an arm short-circuit occurs during a reflux mode operation at this time, a current (i) in the reflux mode operation also flows through switching elements (SE) Sw1 and SW3 or SEs SW2 and SW4 in addition to a short-circuit current i0. Currents I1 and I3 or I2 and I4 (the total value of the short-circuit current i0 and the current (i) in the reflux mode) flowing through the SEs SW1 and SW3 or the SEs SW2 and SW4 are detected with current transformers CTa-CTc. Therefore, even if the arm short-circuit occurs during the reflux mode operation, the cut-off currents of the SEs SW1-SW4 can be set at the maximum values with in the controllable current values. Furthermore, the SEs SW1-SW4, which keep ON during the reflux mode operation, can be cut off within the controllable current value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an inverter circuit,
Specifically, the present invention relates to a single-phase or multi-phase voltage-type inverter circuit in which power semiconductor switches such as GTO, IGBT, and transistor are bridge-configured.

[0002]

2. Description of the Related Art Generally, an inverter circuit is for converting a DC voltage into an AC voltage by turning ON / OFF a switching element, and its concrete circuit configuration is shown in FIG.

As shown in the figure, a direct current power source 1 is connected to a first to a fourth switching elements SW _{1 to} SW ₄ and free wheeling diodes D _{1 to} D ₄ in a bridge configuration, and the _first and _fourth switching elements SW _{1 to} SW ₄ are connected in series. An intermediate connection point a between the second switching elements SW ₁ and SW ₂ and the third and fourth switching elements SW ₃ and
The load 2 is connected between the intermediate connection point b of SW ₄ . With this circuit configuration, the first and fourth switching elements SW
₁ , SW _4, and third and second switching elements SW
The DC voltage from the DC power supply 1 is converted into an AC voltage by alternating ON and OFF of ₃ and SW ₂ .

In such an inverter circuit, for some reason, the first and second switching elements SW ₁ , S
W ₂ , or third and fourth switching elements SW ₃ , SW
A short circuit (arm short circuit) condition in which ₄ turns on at the same time may occur. In order to prevent the destruction of the circuit element due to the occurrence of the arm short circuit, a current transformer CT is usually provided on the direct current side of the inverter circuit, and the current transformer CT further reduces the short circuit current within the controllable current value. as it can be detected, connecting the current limiting reactor 3 and a reflux diode 4 limits the current flowing into the switching element SW ₁ to SW _4. In the figure, 5 is a fuse.

Accordingly, in this inverter circuit, when the arm short circuit occurs, it detects the short-circuit current by the current transformer CT, so as to shut off the switching element SW ₁ to SW ₄ in that controllable current value, the circuit Inverter protection is performed by preventing damage to the elements.

[0006]

When the load 2 of the inverter circuit described above is a load such as a reactor or a capacitor that generates reactive power, the output voltage Vout and the output current Iout of the inverter circuit are as shown in FIG. Shows the waveform characteristics. In this waveform characteristic, for example, when the output voltage Vout is positive and the output current Iout is negative,
As shown in (a), the first and fourth switching elements SW
_{When 1} and SW ₄ are turned on and the free wheeling diodes D ₁ and D ₄ are energized to enter the regenerative mode in which the currents shown by the arrows in the figure flow, and the output voltage Vout and the output current Iout are both positive, As shown, the first and fourth switching elements S
When W ₁ and SW ₄ are turned on to enter the powering mode in which the current shown by the arrow in the figure flows and the output voltage Vout is 0 and the output current Iout is positive, the second and fourth switching operations are performed as shown in FIG. The elements SW ₂ and SW ₄ are turned on, the freewheeling diode D ₂ is energized, and the freewheeling mode is reached in which the current shown by the arrow in the drawing flows.

Further, the output voltage Vout is negative and the output current Iou
In the regenerative and powering modes in which t is positive and the output voltage Vout and the output current Iout are both negative, the second and third switching elements SW ₂ and SW ₃ are turned on, and the output voltage V
In the return mode in which out is 0 and the output current Iout is in the negative state, the first and third switching elements SW ₁ and SW ₃ are turned on, and a current flows in the load 2 in the opposite direction to the above case. In this way, the inverter circuit repeats the regeneration mode, the power running mode, and the return mode.

In the conventional inverter circuit, the first
~ Fourth switching element SW₁ ~ SW_Four Current flowing through
Is detected by the current transformer CT provided on the DC side.
Therefore, in the case of the regeneration mode and the power running mode described above,
Is each of the first to fourth switching elements SW₁ ~ SW_Four To
There is no problem because the current flowing can be detected by the current transformer CT.
However, in the case of the reflux mode, as shown in FIG.
Sea urchin second and fourth switching element SW₂ , SW_Four 〔or
Is the first and third switching elements SW₁ , SW ₃ ] To
Since the flowing current i flows in a closed loop,
It cannot be detected by the current transformer CT.

As a result, when an arm short circuit occurs due to an accident or an erroneous pulse in the return mode, only the short-circuit current i ₀ flows through the current transformer CT, but the second and the second turned ON during the return mode. In addition to the above-mentioned short-circuit current i ₀ , the current i in the return mode flows through the four switching elements SW ₂ , SW ₄ [or the first and third switching elements SW ₁ , SW ₃ ]. Therefore, at the time of detecting the short circuit current i ₀ by current transformer CT, the switching element SW ₁ to SW ₄ which has been ON in the reflux mode is controllable current value that can block the switching elements SW ₁ to SW ₄ A current exceeding the limit of (5) flows, and the switching elements SW _{1 to} SW ₄ are destroyed by cutting off the current.

In order to prevent the switching elements SW _{1 to} SW ₄ from being destroyed, the current flowing through the switching elements SW _{1 to} SW ₄ should be taken into consideration in advance in the current transformer CT. or the short-circuit detection level kept lower by that amount, or by increasing the current limiting reactor 3, to limit the short circuit current i ₀ which flows into the switching element SW ₁ to SW ₄ by reducing the rise of the short circuit current i ₀ There was a need. However, in the former case, it becomes difficult to accurately detect the short-circuit current i _0, and it is difficult to set the cutoff currents of the switching elements SW _{1 to} SW ₄ within the limits of the controllable current value, and the switching element SW ₁
~ SW ₄ is not available at maximum capacity, and in the latter case,
The current limiting reactor 3 becomes large and its loss is large, resulting in high cost.

Therefore, the present invention has been proposed in view of the above problems, and an object thereof is to be able to accurately detect the short-circuit current even when an arm short circuit occurs in the return mode, and to provide a switching element. It is to provide an inverter circuit that can utilize the maximum power.

[0012]

As a technical means for achieving the above object, the present invention provides a bridge construction of first to fourth switching elements, and first and second serially connected first and second switching elements.
In the inverter circuit in which the load is connected between the intermediate connection point of the switching element of and the intermediate connection point of the third and fourth switching elements, one current transformer that detects the current flowing through the load is connected to the load. At the same time, two current transformers for detecting a current flowing through the switching element are connected to the first and third or second and fourth switching elements, respectively.

[0013]

In the inverter circuit according to the present invention, the first to fourth
Since the current flowing through the switching element can be accurately detected by the three current transformers, it becomes easy to set the cutoff current of the switching element to the maximum within the controllable current value, and arm short circuit occurs during the return mode. Even if occurs, the switching element that has been turned on during the return mode can be reliably cut off within the controllable current value.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an inverter circuit according to the present invention will be described with reference to FIG. The same or corresponding parts as those in FIGS. 2 to 4 are designated by the same reference numerals, and a duplicate description will be omitted.

The feature of the present invention is that the load 2 is used as shown in FIG.
One current transformer CTa that detects the current flowing through the load 2 is connected to the load 2, and two current transformers CTb and CTc that detect the current flowing through the switching elements SW _{1 to} SW ₄ are connected to the second
And the fourth switching elements SW ₂ , SW ₄ [or the first
And the third switching elements SW ₁ , SW ₃ ].

In this inverter circuit, the current transformer CTa
Depending on CTc, the first to fourth switching elements SW ₁ to
It is possible to accurately detect the current flowing through SW ₄ . That, i _a as shown the direction and value of the current flowing through each current transformer CTa ~CTc, i _b, When i _c, the current I ₁ ~I ₄ flowing through the switching elements SW ₁ to SW ₄ following Like

The first current of the switching element _{SW 1 I 1 = i a +} i b second current switching element SW ₂ I ₂ = i _b third switching element SW ₃ of the current I ₃ = i _c -i _a Current I _{4 of} the fourth switching element SW ₄ = i _c Thus, the second and fourth switching elements SW ₂ , SW
Regarding the currents I ₂ and I ₄ flowing through ₄ , the current transformer CTb,
It can be detected directly by CTc,
Current I ₁ flowing through the switching elements SW ₁ and SW ₃ of
For I ₃ , the current i flowing through the current transformers CTa to CTc
_{It is} obtained by arithmetic processing based on _{a to ic} , and finally,
The current I ₁ ~I ₄ flowing through the first to fourth switching elements SW ₁ to SW ₄ can be detected accurately by the current transformer CTa ~CTc.

Here, when an arm short circuit occurs in the return mode, the first and third switching elements SW ₁ , S
W ₃ or second and fourth switching elements SW ₂ , SW
_In addition to the short-circuit current i ₀ , the current i in the reflux mode also flows through the current path 4, but the currents CTa to CTc cause
And the third switching element SW _1, SW ₃ and the second and fourth switching elements SW _2, the current I ₁ flowing through the SW _4, I ₃ or I _2, I ₄ [short circuit current i ₀ and the current in the reflux mode Therefore, even if an arm short circuit occurs in the return mode, the breaking current of the _first to fourth switching elements SW _{1 to} SW ₄ is the maximum within the controllable current value. The switching elements SW _{1 to} SW ₄ that have been turned on during the return mode can be reliably cut off within the controllable current value.

In the above embodiment, the case where the current transformers CTb and CTc are connected to the second and fourth switching elements SW ₂ and SW ₄ has been described, but the present invention is not limited to this. The first and third switching elements SW ₁ ,
Current transformers CTb and CTc may be connected to SW ₃ . In that case, the current I _2, I ₄ flowing in the second and fourth switching elements SW _2, SW ₄ is obtained by arithmetic processing based on the current i _a through i _c flowing to the current transformer CTa ~CTc.

[0020]

According to the present invention, the current flowing through each switching element can be accurately detected regardless of whether the inverter circuit is in the regeneration mode, the power running mode, or the freewheeling mode. Even if occurs, the switching element can be reliably cut off within the controllable current value, and the reliability of circuit protection is significantly improved.

Further, since the switching element can be cut off at the maximum within the controllable current value, the switching element can be used with the maximum capacity, and the current limiting reactor for limiting the current flowing into the switching element can be made small, resulting in loss. Can be reduced, the size can be reduced, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an inverter circuit according to the present invention.

FIG. 2 is a circuit diagram showing a conventional inverter circuit.

FIG. 3 is a waveform diagram showing a relationship between output voltage and output current in the inverter circuit.

FIG. 4 is a partial circuit diagram showing an operating state of an inverter circuit, in which (a) shows a regenerative mode, (b) shows a power running mode, and (c) shows a return mode.

[Explanation of symbols]

SW ₁ to SW ₄ first to fourth switching elements CT _a to CT _c current transformer a, b intermediate connection points 2 load

Claims (1)

[Claims] 1. A first-fourth switching element is configured in a bridge structure, and an intermediate connection point between first and second switching elements connected in series and an intermediate connection point between third and fourth switching elements. In the inverter circuit in which the load is connected between the two, one current transformer that detects the current flowing through the load is connected to the load, and two current transformers that detect the current flowing through the switching element are provided as the first and third or An inverter circuit characterized by being connected to each of the second and fourth switching elements.