JP7466476B2 - Power Conversion Equipment - Google Patents

Description

This application relates to a power conversion device.

The conventional power conversion device described in Patent Document 1 combines a three-phase three-level inverter that outputs three-phase voltage from a DC power source with multiple single-phase inverters connected in series to each phase to supply power to a three-phase load. The control device for this power conversion device controls the output voltage of each phase by the sum of the voltage of each phase of the three-phase three-level inverter and each generated voltage by a predetermined combination selected from the multiple single-phase inverters. Then, for the three-phase AC voltage command vector, four space voltage vectors are selected that have a three-phase voltage sum of zero in the vicinity, and the three-phase AC voltage command vector is expressed as a time average according to the distance from the four space voltage vectors, thereby outputting a voltage that makes the zero-sequence voltage zero and makes the current waveform sinusoidal.

JP 2007-37355 A

The power conversion device described in Patent Document 1 has a multi-stage configuration with multiple inverters for each phase, and outputs a voltage close to a sine wave voltage through switching operations. However, a filter circuit is required to make the output voltage a sine wave, which leads to an increase in the size of the device configuration. Furthermore, in order to miniaturize the filter circuit, it is necessary to make each phase even more multi-stage, which leads to an increase in the number of parts, making it difficult to miniaturize and simplify the device configuration.

This application discloses technology to solve the problems described above, and aims to provide a power conversion device that can reliably output a target voltage while promoting the miniaturization and simplification of the device configuration.

The power conversion device disclosed in the present application includes a switching circuit having at least one semiconductor switching element and performing power conversion between DC power and AC power by switching operation of the semiconductor switching element, and a linear circuit having at least one semiconductor element having a control electrode and connected in series to an AC power line from the switching circuit to perform a linear operation. The switching circuit is a gradation-controlled power conversion circuit that is configured by connecting in series the AC sides of a plurality of converter circuits, each having an energy storage element and at least one semiconductor switching element, and outputs a voltage based on the sum of the outputs of the converter circuits to the AC power line, and includes one main converter whose energy storage element has a maximum voltage and other sub-converters as the plurality of converter circuits, and the voltage of the energy storage element in the sub-converter is controlled to a target voltage by charging and discharging through switching operation. The semiconductor element of the linear circuit has a conductive resistance adjusted based on an input voltage or an input current to the control electrode, and the linear circuit operates as a variable resistor, and the linear circuit is configured as an anti-series circuit in which two N-type semiconductor elements are used as at least one of the semiconductor elements and the two N-type semiconductor elements are connected in series in an anti-series circuit. The linear circuit further includes a control circuit for controlling the switching circuit and the linear circuit, and the switching circuit includes a plurality of the sub-converters. The control circuit controls the main converter and the plurality of sub-converters by switching between a plurality of switching patterns, and the total output voltages of the main converter and the plurality of sub-converters become equal in a plurality of first switching patterns that are part of the plurality of switching patterns. The control circuit switches the switching pattern between the plurality of first switching patterns to control the direction of power flowing in and out of the plurality of sub-converters, and controls the voltage of the energy storage element in the plurality of sub-converters to the target voltage by adjusting the time ratio of the plurality of first switching patterns.
The power conversion device disclosed in the present application includes a switching circuit having at least one semiconductor switching element and converting power between DC power and AC power by the switching operation of the semiconductor switching element, a linear circuit having at least one semiconductor element having a control electrode and connected in series to an AC power line from the switching circuit to perform a linear operation, and a control circuit for controlling the switching circuit and the linear circuit. The switching circuit is a gradation-controlled power conversion circuit that is formed by connecting in series the AC sides of a plurality of converter circuits each having an energy storage element and at least one semiconductor switching element, and outputs a voltage based on the sum of the outputs of the converter circuits to the AC power line. The voltages of the energy storage elements in the plurality of converter circuits are different from each other, and the voltage ratios are expressed as a power of 2 or a power of 3 whose exponents increase by 1 each, and the switching circuit includes, as the plurality of converter circuits, one main converter in which the voltage of the energy storage element is maximum and a plurality of sub-converters. The control circuit controls the main converter and the plurality of sub-converters by switching between a plurality of switching patterns. In a plurality of first switching patterns that are a part of the plurality of switching patterns, the total output voltages of the main converter and the plurality of sub-converters are equal, and the control circuit switches between the plurality of first switching patterns to control the direction of power flowing in and out of the plurality of sub-converters, and adjusts the time ratio of the plurality of first switching patterns to control the voltage of the energy storage element in the plurality of sub-converters to a target voltage.

The power conversion device disclosed in this application can reliably output a target voltage while promoting miniaturization and simplification of the device configuration.

1 is a block diagram showing a schematic configuration of a power conversion device according to a first embodiment; 1 is a diagram illustrating an example of a circuit configuration of a power conversion device according to a first embodiment. FIG. 11 is a diagram showing another example of the switching circuit according to the first embodiment. FIG. 11 is a diagram showing another example of the switching circuit according to the first embodiment. FIG. 11 is a diagram showing another example of the switching circuit according to the first embodiment. FIG. 11 is a diagram illustrating an example of a circuit configuration of a power conversion device according to a second embodiment. 11A to 11C are waveform diagrams of various parts for explaining the operation of the power conversion device according to the second embodiment. 11 is a diagram illustrating a control operation of a power conversion device according to a second embodiment. FIG. FIG. 11 is a diagram illustrating an example of a linear circuit according to a third embodiment. FIG. 13 is a diagram showing another example of a linear circuit according to the third embodiment. FIG. 13 is a block diagram showing a schematic configuration of a power conversion device according to a fourth embodiment. FIG. 13 is a diagram illustrating an example of a circuit configuration of a power conversion device according to a fourth embodiment. FIG. 13 is a block diagram showing a schematic configuration of a power conversion device according to a fifth embodiment. FIG. 13 is a diagram illustrating an example of a circuit configuration of a power conversion device according to a fifth embodiment.

Embodiment 1.
1 is a block diagram showing a schematic configuration of a power conversion device according to embodiment 1. Here, an example of a single-phase power conversion device that converts power between DC power and AC power is shown.
As shown in the figure, the power conversion device 100 includes a main circuit 1 and a control circuit 2 that controls the main circuit 1, and is connected to a load 3. The main circuit 1 includes a switching circuit 10 and a linear circuit 20.

The switching circuit 10 has a DC terminal, and converts DC power input to the DC terminal into AC power through switching operation and outputs it. The linear circuit 20 is connected in series to the AC power line 30 from the switching circuit 10, performs linear operation, and supplies AC power to the load 3. In this case, a resistive load is used as the load 3, but an inductive load or capacitive load may also be connected. Furthermore, it may be connected to an AC power source instead of the load 3.

Figure 2 shows an example of the circuit configuration of the main circuit 1 of the power conversion device 100. The switching circuit 11 is a typical two-level converter that outputs two voltage levels, positive and negative, and includes energy storage elements, such as capacitors C1 and C2, and at least one semiconductor switching element (hereinafter simply referred to as a switching element) Q1 and Q2. In this case, the switching circuit 11 is composed of two capacitors C1 and C2 in series and two switching elements Q1 and Q2 in series.

The switching elements Q1 and Q2 are configured by self-extinguishing switching elements such as insulated gate bipolar transistors (IGBTs) with diodes connected inversely in parallel or metal-oxide-semiconductor field-effect transistors (MOSFETs).
The switching circuit 11 outputs a stepped pseudo-sine wave voltage to the AC power line 30 by switching on and off the switching elements Q1 and Q2.

The linear circuit 21 is composed of at least one semiconductor element S1, S2. Each semiconductor element S1, S2 is composed of a first transistor such as a MOSFET having a gate electrode as a control electrode, and operates in the linear region. In this case, an N-type MOSFET is used, and the linear circuit 21 is composed of two semiconductor elements S1, S2, each of which is composed of an N-type MOSFET, connected in series in the opposite directions.

The AC voltage output by the main circuit 1, i.e., the AC voltage Vout applied to the load 3, is detected by the voltage sensor 4 and controlled to a voltage command value that is the desired voltage, in this case a sine wave voltage. The difference between the AC voltage Vout applied to the load 3 and the output voltage of the switching circuit 11 is applied to the linear circuit 21. The linear circuit 21 is composed of semiconductor elements S1 and S2 that operate in the linear region, and operates as a variable resistor.

The control circuit 2 controls the switching of the switching elements Q1 and Q2 in the switching circuit 11. It also controls the gate voltage, which is the input voltage to the control electrodes of the semiconductor elements S1 and S2 in the linear circuit 21 (in this case, the gate electrodes), to adjust the conductive resistance of the semiconductor elements S1 and S2 and control the AC voltage Vout to be the voltage command value, i.e., a sine wave voltage. In other words, the linear circuit 21 operates as a variable resistor so that the difference between the voltage command value of the AC voltage Vout and the output voltage of the switching circuit 11 is applied.

A specific control of the linear circuit 21 will be described below.
The output voltage of the linear circuit 21 is the AC voltage Vout output by the main circuit 1. The control circuit 2 calculates the deviation between a voltage command value and the AC voltage Vout detected by the voltage sensor 4, and uses a controller to control the gate voltages of the semiconductor elements S1 and S2 in the linear circuit 21. The controller may be a proportional controller or the like.
For example, when the deviation obtained by subtracting the detected AC voltage Vout from the voltage command value is positive, that is, when it is desired to increase the output voltage (AC voltage Vout), the controller increases the gate voltage and decreases the resistance values (conduction resistances) of the semiconductor elements S1 and S2 of the linear circuit 21. As a result, the output voltage approaches the voltage command value.

As described above, in the power conversion device 100, the AC voltage Vout is controlled to a sinusoidal voltage that is a voltage command value by the linear circuit 21, so that it is possible to omit or reduce the size of additional circuits such as a filter circuit that is usually provided downstream of the main circuit 1. In addition, the linear circuit 21 does not require an energy storage element to which the main circuit voltage is applied, so that the circuit configuration and control configuration can be simplified.
Therefore, the power conversion device 100 can reliably output the target voltage while promoting miniaturization and simplification of the device configuration.

The linear circuit 21 may have an energy storage element called a linear amplifier. In this case, the voltage of the energy storage element needs to be controlled from outside the linear circuit 21, which leads to an increase in size of the linear circuit 21. However, in addition to operating as a variable resistor, it becomes possible to add and output the voltage of the energy storage element. In this application, the term "linear circuit" also refers to the linear amplifier.

In the above embodiment, the linear circuit 21 is controlled so that the output voltage (AC voltage Vout) approaches the voltage command value, but the present invention is not limited to this. When an AC power supply or the like is connected to the output terminal of the main circuit 1, and the output current is controlled to a current command value that is a desired output current, the linear circuit 21 is controlled as follows.
The control circuit 2 calculates the deviation between the current command value and the output current detected by a current sensor (not shown) or the like, and uses a controller to control the gate voltages of the semiconductor elements S1 and S2 in the linear circuit 21. The controller may be a proportional controller or the like.

For example, when the deviation obtained by subtracting the detected output current from the current command value is positive, i.e., when it is desired to increase the output current, the controller increases the gate voltage and the resistance value (conduction resistance) of the semiconductor elements S1 and S2 of the linear circuit 21 decreases. As a result, the output current approaches the current command value. In this case as well, the output voltage (AC voltage Vout) approaches the sine wave voltage, which is the target voltage.
Therefore, the power conversion device 100 can reliably output the target voltage while promoting miniaturization and simplification of the device configuration.

Furthermore, in the above embodiment, the semiconductor elements S1 and S2 in the linear circuit 21 are first transistors such as MOSFETs having a gate electrode, but a second transistor that is a bipolar transistor having a base electrode as a control electrode may be used. In this case as well, the linear circuit 21 is configured by connecting the N-type semiconductor elements S1 and S2 in series in the opposite directions to each other.
Then, the base current, which is the input current to the base electrode, is controlled to adjust the conductive resistance of the semiconductor elements S1 and S2, and the linear circuit 21 is operated as a variable resistor. This makes it possible to realize the same operation as in the case where the first transistor is used, and to obtain the same effect.

Furthermore, there are various circuit configurations for the switching circuit 10 other than the switching circuit 11 shown in FIG. 2, and these can be similarly applied.
3A, 3B, and 3C are diagrams showing other examples of the switching circuit according to the first embodiment. These are three-level converters capable of outputting three-level voltages, positive, negative, and 0. In particular, FIG. 3A shows switching circuit 12 which is a T-type three-level converter, FIG. 3B shows switching circuit 13 which is a diode-clamped three-level converter, and FIG. 3C shows switching circuit 14 which is a flying capacitor-type three-level converter.

As shown in FIG. 3A, the switching circuit 12 includes two series-connected capacitors C1 and C2, two series-connected switching elements Q1 and Q2, and two switching elements Q3 and Q4 connected in series in the opposite directions. The switching elements Q3 and Q4 are connected between the midpoint of the two series-connected capacitors C1 and C2 and the midpoint of the two series-connected switching elements Q1 and Q2. The switching elements Q3 and Q4 are configured as self-extinguishing switching elements similar to the switching elements Q1 and Q2.

As shown in FIG. 3B, the switching circuit 13 includes two series-connected capacitors C1 and C2, four series-connected switching elements Q11, Q12, Q21, and Q22, and two series-connected diodes D1 and D2. The diodes D1 and D2 are connected between the midpoint of the switching elements Q11 and Q12 constituting the upper arm and the midpoint of the switching elements Q21 and Q22 constituting the lower arm, and the midpoint of the two series-connected diodes D1 and D2 is connected to the midpoint of the two series-connected capacitors C1 and C2.

As shown in FIG. 3C, the switching circuit 14 includes two capacitors C1 and C2 connected in series, four switching elements Q11, Q12, Q21, and Q22 connected in series, and a capacitor C3 that is an energy storage element. Capacitor C3 is connected between the midpoint of the switching elements Q11 and Q12 that constitute the upper arm and the midpoint of the switching elements Q21 and Q22 that constitute the lower arm.

As described above, the linear circuit 21 operates as a variable resistor so that the difference between the voltage command value of the AC voltage Vout applied to the load 3 and the output voltage of the switching circuit 10 is applied. By increasing the number of levels of the output voltage of the switching circuit 10, the stepped voltage that is the output voltage of the switching circuit 10 can be made to approach the voltage command value of the AC voltage Vout more closely. This allows the voltage applied to the linear circuit 21 to be reduced, thereby reducing losses.

In addition, since the linear circuit 21 behaves like a resistor, it is necessary to ensure that the voltage drop is in the same direction as the output current. In other words, when the polarity of the AC current is positive, the voltage output by the switching circuit 10 is controlled to be greater than the voltage command value, and when the polarity of the AC current is negative, the voltage output by the switching circuit 10 is controlled to be smaller than the voltage command value.

The above-mentioned T-type, diode clamp type and flying capacitor type switching circuits 10 can also be configured to output multi-level voltages with an even greater number of levels, such as five or seven levels. These are possible with known technology, so a detailed description will be omitted. By using a switching circuit 10 that outputs a large number of multi-level voltages in this way, the voltage applied to the linear circuit 21 can be further reduced, and losses can be further reduced.

Embodiment 2.
In the above-mentioned first embodiment, the switching circuit 10 in the main circuit 1 of the power conversion device 100 is configured with one converter circuit, but in this second embodiment, it is configured with a plurality of converter circuits.
FIG. 4 is a diagram illustrating an example of a circuit configuration of a power conversion device according to the second embodiment.
As shown in the figure, the main circuit 1 is configured by connecting in series a switching circuit 16 and a linear circuit 21. The switching circuit 16 is a gradation control type power conversion circuit, and is configured by connecting in series the AC sides of multiple (N) converter circuits 15 (15A, 15B2 to 15BN). The linear circuit 21 is the same circuit as in the first embodiment.

Each converter circuit 15 has an energy storage element, for example, a capacitor V (V1 to VN) and at least one semiconductor switching element Q. The switching circuit 16 converts power between DC power and AC power by switching operation, and outputs a voltage based on the sum of the AC outputs of the converter circuits 15 to the AC power line 30.
The N converter circuits 15 (15A, 15B2 to 15BN) are composed of one main converter 15A that outputs two-level or three-level voltages as shown in the above embodiment 1, and (N-1) sub-converters 15B2 to 15BN that are composed of single-phase full-bridge circuits.

The switching circuit 16 is capable of outputting multiple levels of AC voltage by summing the outputs of the N converter circuits 15. Compared to the first embodiment, the number of elements or capacitors used is reduced to output multiple levels of voltage, which is suitable for miniaturizing and simplifying the device configuration.
In addition, the switching circuit 16 can easily output a multi-level output voltage, and can make the stepped voltage, which is the output voltage, closer to the voltage command value of the AC voltage Vout. This allows the voltage applied to the linear circuit 21 to be reduced, and loss to be reduced.

For convenience, the voltages of the capacitors V1 to VN of each converter circuit 15 are denoted as V1 to VN.
For example, when the capacitor voltage V1 of the main converter 15A is 1, the capacitor voltages V2 to VN of the sub-converters 15B2 to 15BN are 1/2, 1/4, 1/8, ... (1/2^N). In other words, the voltage ratio of the capacitor voltages in ascending order (VN to V1) is expressed as a power of 2 ratio with the exponent increasing by 1.
By setting in this way, the number of levels of the output voltage of the switching circuit 16 can be effectively increased, and the number of levels calculated by (2^(N+1)-1) can be output.

As another example, when the capacitor voltage V1 of the main converter 15A is 1, the capacitor voltages V2 to VN of the sub-converters 15B2 to 15BN are 1/3, 1/9, 1/27, ... (1/3^N). In other words, the voltage ratio of the capacitor voltages in ascending order (VN to V1) is expressed as a power of 3 ratio with the exponent increasing by 1.
By setting in this way, the number of levels of the output voltage of the switching circuit 16 can be effectively increased, and the number of levels calculated by (3^N) can be output.

Next, the operation of the switching circuit 16 when N=3, that is, the switching circuit 16 is composed of the main converter 15A and two sub-converters, that is, the first and second sub-converters 15B2 and 15B3, will be described as an example.
Fig. 5 is a waveform diagram of each part for explaining the operation of the power conversion device, and Fig. 6 is a diagram for explaining the control operation of the power conversion device.

FIG. 5 shows waveforms of the AC voltage Vout output from the main circuit 1 to the load 3, the output voltage VM of the main converter 15A, the output voltage VA of the first sub-converter 15B2, the output voltage VB of the second sub-converter 15B3, and the voltage across the linear circuit 21, i.e., the voltage VX applied to the linear circuit 21.
The output voltage of the switching circuit 16 is a total output voltage obtained by adding together the output voltage VM of the main converter 15A, the output voltage VA of the first sub-converter 15B2, and the output voltage VB of the second sub-converter 15B3. The difference voltage between the AC voltage Vout output to the load 3 and the output voltage of the switching circuit 16 becomes the voltage VX applied to the linear circuit 21.

As shown in FIG. 6, the voltage ratio of the capacitor voltages V1, V2, and V3 of the main converter 15A and the first and second sub-converters 15B2 and 15B3 is 4:2:1. The value of the capacitor voltage V3 of the second sub-converter 15B3 is 1 pu, and the voltage waveforms in FIG. 5 also use the same voltage units [pu]. That is, the amplitude of the output voltage VM is 4 pu, the amplitude of the output voltage VA is 2 pu, and the amplitude of the output voltage VB is 1 pu.

The three converter circuits 15A, 15B2, 15B3 each output three-level output voltages, positive, negative, and 0, and by combining these, switching operations can be performed using 27 (=3×3) types of switching patterns SwP1 to SwP27.
The output of the switching circuit 16 is the sum of these output voltages, and can be any voltage between -7 pu and +7 pu in increments of 1 pu.

6, there may be a plurality of switching patterns SwP for one total output voltage. For example, to output a voltage of +1 pu, one of the switching patterns SwP9, SwP12, and SwP13 is used.
Focusing on the first sub-converter 15B2, a negative voltage of -2 pu is output in switching pattern SwP9, whereas a positive voltage of +2 pu is output in switching pattern SwP12. In other words, if the current flows in the same direction, the direction of power flowing in and out of the first sub-converter 15B2 can be controlled by switching the switching pattern SwP. In other words, the capacitor voltage V2 in the first sub-converter 15B2 can be controlled by switching the switching pattern SwP.

The capacitor voltage V3 in the second sub-converter 15B3 can be controlled in a similar manner. That is, by adjusting the time ratio of the switching pattern SwP, the capacitor voltages V2, V3 in the first and second sub-converters 15B2, 15B3 are controlled to target voltages by charging and discharging through switching operations.
This improves the reliability of the output control of the switching circuit 16, and also makes it possible to prevent failures of the switching element Q and the capacitor V due to overvoltage.
Furthermore, in the first and second sub-converters 15B2, 15B3, the capacitor voltages V2, V3 are controlled by charging and discharging through the switching operation during the output operation of the switching circuit 16, so that no external power supply is required and the circuit configuration can be simplified.

Embodiment 3.
In the above-mentioned first embodiment, the linear circuit 20 is constituted by the linear circuit 21 formed by connecting the N-type semiconductor elements S1 and S2 in series in the opposite directions, but in this embodiment, another circuit configuration is shown.
7A and 7B are diagrams illustrating an example of a linear circuit according to the third embodiment.

The linear circuit 22 shown in Fig. 7A is composed of a parallel circuit of an N-type semiconductor element S3 and a P-type semiconductor element S4. The N-type semiconductor element S3 and the P-type semiconductor element S4 are bipolar transistors having a base electrode as a control electrode. The base current, which is an input current to the base electrode, is controlled to adjust the conductive resistance of the semiconductor elements S3 and S4, and the linear circuit 22 operates as a variable resistor.
Since a parallel circuit of the N-type semiconductor element S3 and the P-type semiconductor element S4 is used, a control signal can be shared between the N-type semiconductor element S3 and the P-type semiconductor element S4, and the control circuit 2 can be simplified.

The linear circuit 23 shown in FIG. 7B uses an N-type semiconductor element S5 and a P-type semiconductor element S6, which are MOSFETs having a gate voltage as a control electrode. It is configured as a parallel circuit in which a first series circuit of the N-type semiconductor element S5 and a diode D3 is connected in parallel with a second series circuit of the P-type semiconductor element S6 and a diode D4. The gate voltage, which is the input voltage to the gate electrode, is controlled to adjust the conductive resistance of the semiconductor elements S5 and S6, and the linear circuit 23 operates as a variable resistor.

In this case as well, the control signal can be shared between the N-type semiconductor element S3 and the P-type semiconductor element S4, and the control circuit 2 can be simplified.
In addition, since the N-type semiconductor element S5 and the P-type semiconductor element S6 are made of MOSFETs, they have internal parasitic diodes and cannot block reverse current, but the reverse current is prevented by connecting diodes D3 and D4 in series, respectively, allowing the linear circuit 23 to operate linearly with high reliability.

In this third embodiment, the linear circuits 22 and 23 operate in the same manner as in the first embodiment, and the power conversion device 100 can reliably output the target voltage while promoting miniaturization and simplification of the device configuration, as in the first embodiment.

Embodiment 4.
In the above-mentioned first and second embodiments, a single-phase power conversion device 100 with a neutral point or a ground point as a reference has been shown, but in the fourth embodiment, a single-phase power conversion device 100 with a line-to-line reference will be shown.
FIG. 8 is a block diagram showing a schematic configuration of a power conversion device according to the fourth embodiment.
The power conversion device 100 includes a main circuit 1A and a control circuit 2 that controls the main circuit 1A, and is connected to a load 3A. For convenience, the control circuit 2 is not shown in the figure.

As shown in the figure, the main circuit 1A includes a switching circuit 10A and two linear circuits 20A. The switching circuit 10A has a DC terminal, and converts DC power input to the DC terminal into AC power through switching operation and outputs it. Two AC power lines 30A are drawn from the switching circuit 10A, and each AC power line 30A is connected to a load 3A via a linear circuit 20A connected in series with the switching circuit 10A.

Each linear circuit 20A is connected in series to each AC power line 30A extending from the switching circuit 10A to perform a linear operation and supply AC power to the load 3A. A line voltage is applied to the load 3A.
In this case, a resistive load is used as the load 3A, but an inductive load or a capacitive load may be connected. Furthermore, instead of the load 3A, an AC power source may be connected.

9 shows an example of the circuit configuration of the main circuit 1 A. The linear circuit 21 shown in the above-mentioned first embodiment is used for each linear circuit 20 A.
The switching circuit 10A is a line-to-line type modification of the switching circuit 16 using the gradation control type power converter shown in Fig. 4 of the second embodiment. For each of the two AC power lines 30A, N converter circuits are provided, namely, one main converter 15AA and (N-1) sub-converters 15B2 to 15BN. In this case, the main converter 15AA is configured as one circuit common to the two AC power lines 30A, and the (N-1) sub-converters 15B2 to 15BN are connected in series to each of the two AC terminals.

In this embodiment 4, as in the above embodiment 1, the target voltage can be reliably output while promoting miniaturization and simplification of the device configuration, and since the AC voltage to the load 3A is generated by the line voltage, a large voltage can be output.

Embodiment 5.
In each of the above embodiments, a single-phase power conversion device 100 is shown, but in the fifth embodiment, a three-phase power conversion device 100 is shown.
FIG. 10 is a block diagram showing a schematic configuration of a power conversion device according to the fifth embodiment.
The power conversion device 100 includes a main circuit 1B and a control circuit 2 that controls the main circuit 1B, and is connected to a three-phase load 3B. For convenience, the control circuit 2 is not shown in the figure.

As shown in the figure, the main circuit 1B includes a switching circuit 10B and three linear circuits 20B. The switching circuit 10B has an internal DC terminal, and converts the DC power input to the DC terminal into three-phase AC power by switching operation and outputs it. The AC power lines 30B of each phase of the switching circuit 10B are connected to the load 3B via the linear circuits 20B connected in series to each of them.

Each linear circuit 20B is connected in series to each AC power line 30B extending from the switching circuit 10B to perform a linear operation and supply AC power to the load 3B. A three-phase AC voltage is applied to the load 3B.
In this case, a resistive load is used as the load 3B, but an inductive load or a capacitive load may be connected. Furthermore, an AC power source may be connected instead of the load 3B.

11 shows an example of the circuit configuration of the main circuit 1A. The linear circuit 21 shown in the first embodiment is used for each linear circuit 20B.
The switching circuit 10B is obtained by transforming the switching circuit 16 using the gradation control type power converter shown in FIG. 4 of the second embodiment into a three-phase configuration. For each phase of the AC power line 30B, N converter circuits are provided, namely, one main converter 15AB and (N-1) sub-converters 15B2 to 15BN. In this case, the main converter 15AB is configured as one circuit common to the three phases, and the (N-1) sub-converters 15B2 to 15BN are connected in series to each of the three AC terminals.

In this fifth embodiment, as in the first embodiment, the target voltage can be reliably output while promoting miniaturization and simplification of the device configuration. Furthermore, since the power conversion device 100 outputs three-phase AC power, it can handle larger power than in the case of a single phase. It can also be connected to a three-phase power system.

Although the present application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.
Therefore, countless modifications not illustrated are conceivable within the scope of the technology disclosed in the present application, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment.

10, 10A, 10B, 11 to 14, 16 Switching circuit,
15 Converter circuit, 15A, 15AA, 15AB Main converter,
15B2 to 15BN: sub-converters; 20, 20A, 20B, 21 to 23: linear circuits;
30, 30A, 30B AC power line, 100 Power conversion device, D3, D4 Diode,
Q, Q1 to Q4, Q11, Q12, Q21, Q22 switching elements,
S1 to S6 are semiconductor elements, C1, C2, and V1 to VN are capacitors.

Claims (7)

a switching circuit having at least one semiconductor switching element and converting power between DC power and AC power by a switching operation of the semiconductor switching element;
a linear circuit having at least one semiconductor element having a control electrode, the linear circuit being connected in series with an AC power line extending from the switching circuit to perform a linear operation;
the switching circuit is a gradation-controlled power conversion circuit that is configured by connecting in series the AC sides of a plurality of converter circuits, each having an energy storage element and at least one semiconductor switching element, and outputs a voltage corresponding to the sum of the outputs of the converter circuits to the AC power line, the plurality of converter circuits include one main converter in which the voltage of the energy storage element is maximum, and other sub-converters, the sub-converters control the voltage of the energy storage element in the sub-converter to a target voltage by charging and discharging through switching operations,
a conductive resistance of the semiconductor element of the linear circuit is adjusted based on an input voltage or an input current to the control electrode, and the linear circuit operates as a variable resistor;
The linear circuit is configured as an anti-series circuit in which two N-type semiconductor elements are used as the at least one semiconductor element and the two N-type semiconductor elements are connected in series in an anti-series manner ;
a control circuit for controlling the switching circuit and the linear circuit;
The switching circuit includes a plurality of the sub-converters.
the control circuit switches between a plurality of switching patterns to control the main converter and the plurality of sub-converters;
In a plurality of first switching patterns which are a part of the plurality of switching patterns, the total output voltages of the main converter and the plurality of sub-converters are equal to each other,
the control circuit switches between the plurality of first switching patterns to control a direction of power flowing into and out of the plurality of sub-converters, and adjusts a time ratio of the plurality of first switching patterns to control a voltage of the energy storage element in the plurality of sub-converters to the target voltage.
Power conversion equipment. The switching circuit is capable of outputting a multilevel voltage to the AC power line.
The power conversion device according to claim 1 . The voltages of the energy storage elements in the plurality of converter circuits are different from each other, and each voltage ratio is expressed as a power of 2 or a power of 3 with the exponent increasing by 1.
The power conversion device according to claim 1 or 2 . The semiconductor element of the linear circuit is a first transistor having a gate electrode as the control electrode and controlled by a gate voltage as the input voltage, or a second transistor having a base electrode as the control electrode and controlled by a base current as the input current.
The power conversion device according to any one of claims 1 to 3 . The linear circuit operates as the variable resistor so that a difference between an AC voltage command value for the power conversion device including the switching circuit and the linear circuit and a voltage output by the switching circuit to the AC power line is applied.
The power conversion device according to any one of claims 1 to 4 . When the polarity of the AC current flowing from the switching circuit to the AC power line is positive, the voltage output by the switching circuit is greater than the AC voltage command value, and when the polarity of the AC current is negative, the voltage output by the switching circuit is smaller than the AC voltage command value.
The power conversion device according to claim 5 . a switching circuit having at least one semiconductor switching element and converting power between DC power and AC power by a switching operation of the semiconductor switching element;
a linear circuit having at least one semiconductor element having a control electrode, the linear circuit being connected in series with an AC power line extending from the switching circuit to perform a linear operation;
a control circuit for controlling the switching circuit and the linear circuit;
the switching circuit is a gradation-controlled power conversion circuit that is configured by connecting in series AC sides of a plurality of converter circuits, each of which has an energy storage element and at least one semiconductor switching element, and outputs a voltage corresponding to the sum of the outputs of the converter circuits to the AC power line;
The voltages of the energy storage elements in the plurality of converter circuits are different from each other, and each voltage ratio is expressed as a power of 2 or a power of 3 with the exponent increasing by 1;
The switching circuit includes, as the plurality of converter circuits, one main converter in which a voltage of the energy storage element is maximum, and a plurality of sub-converters;
the control circuit switches between a plurality of switching patterns to control the main converter and the plurality of sub-converters;
In a plurality of first switching patterns which are a part of the plurality of switching patterns, the total output voltages of the main converter and the plurality of sub-converters are equal to each other,
the control circuit switches between the plurality of first switching patterns to control the direction of power flowing into and out of the plurality of sub-converters, and adjusts a time ratio of the plurality of first switching patterns to control a voltage of the energy storage element in the plurality of sub-converters to a target voltage.
Power conversion equipment.