JP6715685B2 - Power conversion device and power conversion method - Google Patents

Description

The present invention relates to a power conversion device and a power conversion method, and more particularly to a power conversion device and a power conversion method suitable for protecting a main circuit configuration and a main circuit.

Power converters using semiconductor switching elements are widely used in fields such as industry, home appliances, transportation, automobiles, and power/social infrastructure systems. Industrial power converters of several hundred kW or more are often composed of an assembly including a plurality of semiconductor switching elements. In such a power converter, even if an accident occurs such that the semiconductor switching element is short-circuited, the protective means in the power converter can quickly separate the accident phase and suppress the effect on the sound phase. It is desired to reduce downtime before restoration. In response to this demand, a protection method is often used in which a fuse is inserted at a place where the DC circuit section inside the power converter is connected.

In this way, a fuse is inserted in the DC circuit to protect the power converter, and a circuit in which a diode and a capacitor are connected in series is added so that the fuse can be blown quickly in the event of a short circuit in the semiconductor switching element. Are described in, for example, Japanese Patent Laid-Open No. 2014-96892.

JP 2014-96892 JP

The above-mentioned conventional technology is a protection circuit for a configuration in which a smoothing capacitor is held together in three phases. On the other hand, power converters for industrial and power/social infrastructure systems are becoming higher in voltage for the purpose of reducing loss. In such high-voltage power converters, parts such as semiconductor switching devices have high breakdown voltage/ A high current type is used. When a circuit is configured with three phases at once, the distance between the smoothing capacitor and the semiconductor switching element is increased to secure insulation distance and creepage distance. As the distance increases, the parasitic inductance of the main circuit increases. When the parasitic inductance becomes large, the semiconductor switching element may be damaged by the jump voltage generated between the terminals of the semiconductor switching element when switching the semiconductor switching element. Therefore, an additional circuit that suppresses the jump voltage such as a snubber circuit is required. It becomes necessary and leads to an increase in size of the power converter.

As described above, power converters, particularly high-voltage power converters, have problems in that it is difficult to achieve both miniaturization and suppression of the effect of the accident phase on the healthy phase during a short-circuit accident.

An object of the present invention is to provide a power conversion device and a power conversion method that can reduce the size of the power conversion device and can easily restore the power conversion device when an accident occurs.

To achieve the above object, in the present invention, a plurality of phase circuits forming a phase are provided, the plurality of phase circuits partially include a common DC voltage section, and each of the plurality of phase circuits comprises: A switching circuit configured of a semiconductor switching element for performing power conversion operation, an AC terminal connected to the switching circuit, a plurality of capacitors connected in parallel between the switching circuit and the DC voltage unit, and The fuse is connected between the switching circuit and the DC voltage section.

Alternatively, for each phase, a semiconductor switching element, an assembly including a first capacitor, a second capacitor, and wiring, and a common DC circuit to which the DC circuit of the assembly is connected in parallel, The first capacitor and the second capacitor are connected in parallel to the DC circuit of the assembly, the first capacitor terminal is connected to the assembly DC circuit in the vicinity of the semiconductor switching element, and the second capacitor terminal is the first capacitor. In comparison with the above, the configuration is such that a fuse is inserted in a part of the wiring that is connected to the common DC circuit side of the assembly DC circuit and that connects the first capacitor terminal connection point and the second capacitor terminal connection point.

According to the present invention, it is possible to reduce the inductance of the DC circuit that is expected from the semiconductor switching element, and as a result, it is possible to downsize the device. In addition, since the fuse can be blown by the discharge current of the capacitor in the assembly, it is possible to suppress the effect of the accident phase on the sound phase in the event of a short-circuit accident, and it is possible to perform simple restoration by replacing parts only in the accident phase.

1 is a configuration of a power converter according to a first embodiment of the present invention. FIG. 3 is a diagram illustrating a current flow in the first embodiment of the present invention. It is a figure explaining a circuit structure and a current course in the case of a reference example. It is a figure explaining the circuit structure and current path of a reference example. 6 is a configuration of a power converter according to a third embodiment of the present invention. 6 is a configuration of a power converter according to a fourth embodiment of the present invention. It is a figure explaining the circuit using the semiconductor switching element in this invention. It is a figure explaining the circuit using the semiconductor switching element in this invention. It is explanatory drawing of the electric current which flows from the capacitor in this invention.

Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings.

Example 1 will be described. Figure 1 shows the circuit configuration of the power converter. In this embodiment, a three-phase two-level converter will be described as an example. The main circuit of this power converter is composed of circuits 102a, 102b, and 102c that construct one phase, and the DC terminals of 102a, 102b, and 102c are common DC circuit 100a (also referred to as DC voltage unit (positive electrode)), 100b (also referred to as DC voltage unit (negative electrode)) are connected in parallel. 102a, 102b, 102c are provided with a disconnecting structure (not shown) between them and a common DC circuit, and can be removed or replaced for each phase.

The circuits (102a, 102b, 102c) for constructing one phase form, for example, U phase, V phase, W phase, and each terminal (104a), terminal (of the circuit (102a, 102b, 102c) for constructing one phase (terminal 104b) and terminal (104c) are connected to the U-phase, V-phase, and W-phase terminals of the three-phase AC power generator. As a result, an AC motor (not shown) is driven, or regenerative power is converted into DC.

For example, taking the circuit (102a) for constructing one phase as an example, the circuit (102a) for constructing one phase has a switching element (401) on the positive side as a circuit (101) as shown in FIG. A pair of the positive side reverse diode (402), a pair of the negative side switching element (401) and the negative side reverse diode (402) are connected in series. Via the wiring (positive electrode) (108a) connected to the circuit composed of semiconductor switching elements to the DC circuit (100a), through the wiring (negative electrode) (109a) connected to the circuit composed of semiconductor switching elements Connected to the DC circuit (100b). The connection point between the positive side switching element (401) and the positive side reverse diode (402) and the negative side switching element (401) and the negative side reverse diode (402) pair is the input/output. It becomes the terminal (104a).

The switching element (401) converts the DC power between the DC circuit (100a) and the DC circuit (100b) into AC power by switching such as PWM and outputs it from the terminal (104a) or the terminal (104a). It converts the AC power from DC into DC and outputs it to DC circuit (100a) and DC circuit (100b).

The switching element (401) performs power conversion by alternately switching up and down by a gate drive circuit and a gate control circuit (not shown). The switching element (401) is controlled by the PWM modulation method by comparing the modulated wave with the carrier wave by a PWM control circuit (not shown).

The circuits (102b) and (102c) for constructing the other one phase have the same configuration as the circuit (102a) for constructing the one phase.

In the circuit (102a) forming one phase, the first capacitor (100a) and the DC circuit (100b) are placed in parallel so as to be in close proximity to the circuit (101a) composed of semiconductor switching elements. Install 103a). The circuit has the configuration shown in FIG. Although the IGBT (401) is used as the semiconductor switching element in FIG. 7, it may be replaced with another semiconductor switching element (transistor, GTO, thyristor, etc.). In this way, the current path (C100) from the capacitor (103a) to the circuit (101a) composed of semiconductor switching elements becomes small, so that the parasitic inductance of the current path can be made small. Here, since the jump voltage applied between the terminals when the IGBT (401) is switched is determined by the parasitic inductance and the current change (di/dt), the jump voltage can be suppressed by the configuration. Therefore, the snubber circuit for protecting the semiconductor switching element from the jump voltage is not required, and the power converter can be downsized.

The configuration and the mechanism thereof, which is a feature of the present invention and which realizes the suppression of the accident ripple to the healthy phase by utilizing the second capacitor, will be described below.

The power converter shown in this embodiment is provided in an assembly provided for each phase, a first capacitor (103a) provided in the immediate vicinity of the semiconductor switching element (101a), and a wiring connected to the terminals of the capacitor (103a). Separately from the fuses (105a and 106a) and the first capacitor (103a), on the common DC circuit (100a and 100b) side, between the DC circuit (100a) and DC circuit (100b). It is characterized in that a second capacitor (107a) is provided.

With this configuration, when a short circuit accident occurs in the semiconductor switching element, it is possible to blow the fuse only in the fault phase, and it is possible to reduce the effect on the healthy phase assembly (102b, 102c). ..

The current flow when the fuse is blown will be described with reference to FIG.

The fuse (105a) is inserted so that one of the terminals of the semiconductor switching element (101a) and the DC circuit 100a are separated by fusing. The fuse (106a) is inserted so as to disconnect the other side of the semiconductor switching element (101a) from the DC circuit (100b) by fusing.

When the semiconductor switching element is short-circuited, electric charge is first discharged from the capacitor (103a) adjacent to the circuit (101a) configured by the semiconductor switching element to the circuit (101a) configured by the semiconductor switching element (current path (200) ). Since the voltage across the terminals of the capacitor (103a) decreases due to the charge discharge, a current flows from the capacitor (107a) through the fuse (105a), the current is blown through the fuse (current path (201)), and the accident phase occurs. It is disconnected from the DC voltage section (100a, 100b). Since the capacitor (107a) is provided in the same assembly as the circuit (101a) composed of semiconductor switching elements, the parasitic inductance from the capacitor (107a) to the circuit (101a) composed of semiconductor switching elements is of a normal phase. It is smaller than the parasitic inductance from the capacitor in the assembly (102b and 102c) to the circuit (101a) configured by the semiconductor switching element in the fault phase (102a). Therefore, the current required to blow the fuse in the accident phase is supplied from the capacitor (107a). By supplying the current for blowing the fuse from the capacitor (107a), the terminal voltage of the capacitor (107a) drops, so that the current also flows from the sound phase. To reduce the effect on the sound phase, compared to the parasitic inductance from the capacitor (107a) to the circuit (101a) composed of semiconductor switching elements, the sound phase generated by the wiring (L10・L20) connecting each phase It is desirable that the parasitic inductance from the capacitor to the capacitor (107a) is sufficiently large. The resonance frequency determined by the capacitance of the capacitor (107a) and the parasitic inductance of the current path (201) is more than four times the resonance frequency determined by the parasitic inductance of the capacitor (103b) and the current path (203). Therefore, it is desirable to select the parasitic inductance of the wiring (L10) connecting each phase and the capacitance of each capacitor. This allows the fuse to be blown by the current (800) flowing from the capacitor (107a) in the fault phase until the current (801) flowing from the sound phase reaches the peak value, as shown in FIG. 9, for example. Become. This is the mechanism for reducing the effect on the sound phase when a semiconductor switching element has a short circuit fault.

As a comparative example, the flow of fuse blowing when there is no capacitor (107a) in the immediate vicinity of the fuse will be described with reference to FIG. Here, the leftmost phase (102a) is the accident phase and the other phases (102b and 102c) are the healthy phases. When a short circuit occurs in the semiconductor switching element in this configuration, electric charge is first discharged from the capacitor (103a) adjacent to the circuit (101a) configured by the semiconductor switching element (current path (200)), and then the healthy phase ( The electric charge is discharged from the capacitor (103b) of (102b/102c) (current path (202)), so that the fuse is blown, so that not only the fault phase (102a) but also the fuse of the sound phase (102b/102c) Fatigue accumulates. Therefore, when recovering from an accident, it is necessary to recover not only the accident phase but also the other phases.

Next, as a comparative example, a case where there is no capacitor (103a) arranged in the immediate vicinity of the circuit (101a) composed of semiconductor switching elements will be described with reference to FIG. In this configuration, in the event of a short circuit accident in the semiconductor switching element, the fuse is blown by discharging the electric charge from the capacitor (107a) arranged in the immediate vicinity of the fuse, so that the current from the other phase is the same as in the configuration shown in FIG. Inflow is suppressed and the fuse only in the accident phase is blown. However, since the current path (C200) from the capacitor (107a) to the circuit (101a) composed of semiconductor switching elements becomes large, the parasitic inductance of the current path becomes large. Therefore, there is a concern about the jumping voltage when switching the semiconductor switching element, a protection circuit such as a snubber circuit is required, and the power converter becomes large.

As described above, according to the present embodiment, the inductance of the DC circuit expected from the semiconductor switching element can be reduced, so that it is not necessary to add a snubber circuit, and as a result, the power converter can be downsized. In addition, since the fuse can be blown by the discharge current of the second capacitor in the assembly, it is possible to suppress the effect of the fault phase on the sound phase in the event of a short circuit fault, and it is possible to recover by replacing parts only in the fault phase.

Figure 2 shows how to select the capacitance of the capacitor (107a) placed in the immediate vicinity of the fuse. In the second embodiment, which is a modification of the first embodiment (similarly to other embodiments), only different parts will be described. Therefore, the parts whose description is omitted are the same as those in the first embodiment. When the semiconductor switching element (402) inside the circuit (101a) composed of the semiconductor switching element has a short circuit fault, the fuse (105a) is blown by the discharge current of the capacitor (107a) as shown in the first embodiment. It The fuse is blown by the discharge current Is(A) flowing to blow the fuse and the Joule integral value Is ² t(A ² s) determined by the discharge time ts(s).

Here, the resistance of the current path (201) at the time of short circuit accident is Rs (Ω), the voltage before discharge of the capacitor (107a) is V0 (V), the voltage after discharge is V1 (V), and the capacitor (107a) Let Cf(F) be the capacitance of, and the time t(s) required to discharge the capacitor voltage from V0(V) to V1(V) can be calculated by Eq. (1). That is, the time to blow the fuse in the case of a short circuit failure is determined by the characteristics of the fuse (Joule integral value Is ² t(A ² s)), the resistance in the case of a short circuit failure, and the capacitance of the fuse (107a) for blowing the fuse. Therefore, the capacitance of the fuse blowing capacitor (107a) is selected according to the time when the fuse is to be blown when the semiconductor switching element (402) has a short circuit failure. The selected component is adopted.

t(s)=-Cf×Rs×ln(V0/V1) …Equation (1)

Figure 5 shows an example of a 3-phase 3-level converter. In addition to the DC circuit (300a) (also referred to as the DC voltage unit (positive electrode)) and the DC circuit (300b) (also referred to as the DC voltage unit (negative electrode)), the DC circuit (300c) (also referred to as the DC voltage unit (common)) Composed. A capacitor (308a) is provided between the DC circuit (300a) and the DC circuit (300c), and a capacitor (308b) is provided between the DC circuit (300c) and the DC circuit (300b).

Of the wiring (positive) (309) connected to the circuit composed of semiconductor switching elements of the circuit (301) that constitutes one phase and the wiring (common) (311) connected to the circuit composed of semiconductor switching elements A capacitor (303a) is provided between them, and a capacitor (303b) is provided between the wiring (311) and a wiring (negative electrode) (310) connected to a circuit composed of semiconductor switching elements.

The fuse (305a) is connected between the wiring (309) and the DC circuit (300a) of the circuit (301) forming one phase, and the fuse (307a) is connected between the wiring (311) and the DC circuit (300c). The fuse (306a) is provided between the circuit 310 and the DC circuit (300b), and the circuit (301) that constructs one phase is switched between the wiring (309) and the wiring (310) as shown in FIG. Four pairs of the element (401) and the reverse diode (402) are connected in series, and the connection point of the pair of two upper switching elements (401) and the reverse diode (402) and two lower switching elements (401 ) And the connection point of the pair of reverse diodes (402) are connected by two diodes (501) connected in series. One of the circuits formed by connecting four pairs of the switching element (401) and the reverse diode (402) in series is connected to the DC circuit (300a) via the wiring (309), and the other is connected to the DC circuit via the wiring (310). Connected to the circuit (300b). The connection point of the two diodes (501) is connected to the DC circuit (300c) via the wiring (311). The connection point of the pair of two upper switching elements (401) and reverse diode (402) and the connection point of the pair of two lower switching elements (401) and reverse diode (402) are input/output terminals (304). Becomes The circuits that make up the other phase are similarly configured.

The circuit (301) shown in FIG. 8 functions at so-called three levels by PWM modulation, and outputs positive output, zero output, and negative output to the input/output terminal 304, or converts the AC power of the input/output terminal 304 to DC. Convert power to.

Similar to the first embodiment, the circuit is configured in the order of the capacitor (308a/308b), the fuse (305a/306a/307a), the capacitor (303a/303b), and the semiconductor switching element (301). The effects and operations of this configuration are similar to those of the first embodiment.

FIG. 6 shows another embodiment of the 3-phase 2-level converter. Similar to the first embodiment, the first capacitor (103a) is installed close to the circuit (101a) composed of the semiconductor switching element, and the circuit (101a) composed of the semiconductor switching element and the first capacitor ( The circuit composed of 103a) is made into one circuit group (700), and the circuit group is connected in parallel to the fuses (105a and 106a). In this embodiment, two parallel circuit configurations are shown, but the number of parallel circuits may be different. The same applies to the configuration shown in the third embodiment.

100a/300a... DC voltage part (positive electrode), 100b/300b... DC voltage part (negative electrode), 101/101a/101b/301... Circuit composed of semiconductor switching elements, 104a/104b/304... terminal (AC output terminal) ), 105a, 106a, 105b, 106b, 305a, 306a, 307a... Fuses, 102a, 102b, 102c, 302a, 302b, 302c... Phase-constituting circuits, 103a, 103b, 107a, 303a, 303b, 308a, 308b... Capacitor, 108/309... Wiring connected to a circuit composed of semiconductor switching elements (positive electrode), 109/310... Wiring connected to a circuit composed of semiconductor switching elements (negative electrode), 200/201/202/ 203... Current path, 300c... DC voltage section (common), 311... Wiring connected to circuit composed of semiconductor switching element (common), 401... IGBT, 402... Diode, 700... Composed of semiconductor switching element Circuit group consisting of circuits and capacitors, 800/801... Current for blowing fuses, C100/C200... Current path, L10/L20... Wiring for connecting between phases

Claims (7)

A plurality of phase circuits forming a phase are included, and the plurality of phase circuits partially include a common DC voltage unit, and each of the plurality of phase circuits is configured by a semiconductor switching element to perform a power conversion operation. Switching circuit, an AC terminal connected to the switching circuit, a plurality of capacitors connected in parallel between the switching circuit and the DC voltage unit, and connected between the switching circuit and the DC voltage unit Has a fuse that is
The plurality of capacitors connected in parallel is composed of a first capacitor connected in proximity to the switching circuit and a second capacitor connected in parallel with the first capacitor, and the first capacitor The power conversion device, wherein the fuse is inserted in a wire connecting the second capacitor, and the second capacitor has a capacitance necessary for melting the fuse in a desired time. The power conversion device according to claim 1, wherein a parasitic inductance of a wiring connecting the capacitor in each phase circuit and a semiconductor switching element of the phase is smaller than a parasitic inductance of a wiring connecting each phase. The resonance frequency determined by the inductance between the circuit formed by the second capacitor and the semiconductor switching element in an arbitrary phase and the capacitance of the second capacitor in the arbitrary phase according to claim 1, A power conversion device having a resonance frequency determined by the inductance between the first capacitors in a phase different from the phase and the capacitance of the first capacitor in the different phase, which is four times or more. The assembly according to any one of claims 1 to 3, wherein one phase is composed of the plurality of semiconductor switching elements, the capacitor, the wiring, and the fuse, and is configured as one assembly. The power conversion device is characterized in that it can be removed together. 2. The power conversion device according to claim 1, wherein the capacitance of the fuse blowing capacitor is selected according to the fuse blowing time when the semiconductor switching element has a short circuit failure. 2. The DC voltage section according to claim 1, wherein the DC voltage section is a positive DC voltage section, a negative DC voltage section, and a common DC voltage section, and a capacitor is arranged between the DC voltage section and the common DC voltage section. Capacitor is arranged between the voltage unit and the negative DC voltage unit, and a fuse is arranged corresponding to each of the positive DC voltage unit, the negative DC voltage unit and the common DC voltage unit. Converter. A method of controlling a power conversion device, comprising: a plurality of phase circuits forming a phase, wherein the plurality of phase circuits partially include a common DC voltage part, wherein each of the plurality of phase circuits is a semiconductor switching device. Power conversion is performed by switching operation of the element, and the jumping voltage of the semiconductor switching element is absorbed by a plurality of capacitors connected in parallel between the switching circuit that performs the switching operation and the DC voltage unit, and the plurality of capacitors connected in parallel are absorbed. The capacitor is composed of a first capacitor connected in close proximity to the switching circuit and a second capacitor connected in parallel with the first capacitor, and connects the first capacitor and the second capacitor. fuses are inserted into the wiring, power conversion method for breaking operation by the fuse during an accident.

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