JP2016059132A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly efficient power conversion device with high output density.SOLUTION: There is provided a power conversion device including an inverter unit, a filter unit, an initial stage charge unit, a switchover unit and a control circuit. The inverter unit includes a plurality of legs having a plurality of switching elements and a flying capacitor by which DC power supplied from a DC power supply is converted into AC power. The filter unit suppresses a harmonic component. The initial stage charge unit makes a current flow in a predetermined period after initiating the DC power supply. The switchover unit, after a lapse of the predetermined period, changes in a manner that a current which flows through the initial stage charge unit flows through a load. The control circuit determines a start and a lapse of the predetermined period, to switch between a current path which flows through the initial stage charge unit and a current path which flows through the load.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a power conversion apparatus.

  There is a multi-level power converter that suppresses harmonic components of the output voltage by changing the output voltage in multiple stages. In a multi-level power conversion device, a filter for approximating the output waveform to a sine wave can be reduced in size, and a switching element having a low withstand voltage can be used, so that high output density can be realized as a whole device. be able to. In such a power conversion device, higher efficiency is desired.

JP 2008-92651 A

  Embodiments of the present invention provide a power converter with high power density and high efficiency.

  According to the embodiment of the present invention, a power conversion device including an inverter unit, a filter unit, an initial charging unit, a switching unit, and a control circuit is provided. The inverter unit converts DC power supplied from the DC power source into AC power. The inverter unit includes: a first input terminal connected to an output terminal on the high potential side of the DC power supply; a second input terminal connected to an output on the low potential side of the DC power supply; the first input terminal; A plurality of legs connected to the second input terminal. Each of the plurality of legs is connected between a first upper switching element connected between the first input terminal and the second input terminal, and between the first upper switching element and the first input terminal. A second upper switching element, a first lower switching element connected between the first upper switching element and the second input terminal, the first lower switching element and the second input terminal, A second lower switching element connected between, one end connected between the first upper switching element and the second upper switching element, the first lower switching element and the second lower side A charge storage device having a second end connected between the switching device and an output terminal connected between the first upper switching device and the first lower switching device. No. The filter unit is connected between the output terminal and the load, and outputs AC power in which harmonic components of the AC power are suppressed. The initial charging unit is connected in parallel with the load, and charges the charge storage element for a predetermined period after the DC power supply is activated. The switching unit is connected in series with the filter unit between the output and the load, cuts off a path of a current flowing through the initial charging unit after the lapse of the predetermined period, and supplies a current to the load. Shed. The control circuit determines the start or elapse of the predetermined period, switches between a current path flowing through the initial charging unit and a current path flowing through the load, and a plurality of sets set for each of the plurality of legs. Based on the modulated wave and a plurality of carrier signals set in each of the first upper switching element and the second switching element of the wind number leg, the first upper switching element and the second upper switching element ON / OFF of the element, the first lower switching element, and the second lower switching element is controlled.

It is a block diagram showing typically the example of composition of the power converter concerning a 1st embodiment. FIG. 2A is a block diagram schematically illustrating a specific example of the configuration of the switching unit and the initial charging unit of the power conversion device according to the first embodiment. FIG. 2B is a block diagram schematically illustrating a configuration of a modification of the power conversion device according to the first embodiment. FIG. 3A to FIG. 3D are timing diagrams of operation waveform examples schematically showing the operation of the control circuit in the steady operation state of the power conversion device according to the first embodiment. FIG. 4A to FIG. 4C are timing diagrams of operation waveform examples schematically representing an operation when the power conversion device according to the first embodiment transitions from a startup state to a steady state. It is a block diagram showing typically the example of composition of the power converter concerning a 2nd embodiment. It is a block diagram showing typically the example of composition of the power converter concerning a 3rd embodiment.

Each embodiment will be described below with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings. Further, in the present specification and each drawing, the same reference numerals are given to the same elements as those described above with reference to the previous drawings, and detailed description thereof will be omitted as appropriate.

  In the present specification, the state where the power conversion device is in a steady operation or in a steady operation means a state in which the input voltage Vin applied between the inverter input terminals is a specified input voltage. The specified input voltage is an input voltage that guarantees the performance of the power converter, and is a rated input voltage Vin (max) that can supply a rated load current to the load. In the steady operation state, the voltage applied to the charge storage elements constituting the inverter unit is in a substantially constant state, that is, a steady state. In addition, the time when the power converter is in the starting state or when starting is the period from when the DC-DC converter is started, the inverter unit is operated, and the power converter starts operating to the transition to the steady operation state. It shall be said. In the initial stage of the start-up state, the charge storage elements constituting the inverter unit are in the initial state, that is, the applied voltage is 0V or almost 0V.

(First embodiment)
FIG. 1 is a block diagram schematically illustrating a configuration example of the power conversion device according to the first embodiment.
As shown in FIG. 1, the power converter 10 has an input connected to the output of a DC-DC converter 2 that is a DC power supply device. The power conversion device 10 has a load 4 connected to the output. The DC-DC converter 2 has an input connected to the power generator 1. The power conversion device 10 is detachably connected to the DC-DC converter 2 and the load 4 via, for example, a connector. In the specification of the present application, “connection” includes not only the case of being connected in direct contact but also the case of being electrically connected via another conductive member or the like. In addition, the case of magnetic coupling through a transformer or the like is also included in “connection”.

  The power generator 1 is a solar cell panel, for example. The power generation device 1 may be a device that generates DC power, such as a fuel cell, in addition to a solar cell panel. Moreover, the electric power generating apparatus 1 may rectify | convert the generated alternating current power and converted into direct current power like a gas turbine engine. The power generation apparatus 1 may be any power source capable of supplying DC power, and the DC-DC converter 2 may be selected in a circuit system so as to match the output of the power generation apparatus 1.

  The DC-DC converter 2 supplies direct-current power to the power conversion device 10. The DC-DC converter 2 receives the supply of non-stable DC power from the power generation device 1 such as a solar battery panel, and outputs stabilized DC power. The DC-DC converter 2 may be a step-up circuit that converts a low voltage into a high voltage, or may be a step-down circuit that converts a high voltage into a low voltage. Further, it may be a step-up / down circuit that generates a stabilized DC voltage regardless of the level of the voltage generated by the power generation device 1.

  The DC-DC converter 2 has output terminals 2 a and 2 b for connecting to the input terminal of the power conversion device 10. The DC-DC converter 2 has a control signal input terminal 2c for starting an operation for generating or outputting an output voltage by an external signal, or for controlling the stop of the operation. For example, a voltage corresponding to a two-level logic value is input to the control signal input terminal 2c. When the control signal input terminal 2c receives an input signal having a voltage of “1” level, that is, a high level, the DC-DC converter 2 performs an operation of generating or outputting an output voltage. When a voltage of “0” level, that is, a low level is input to the control signal input terminal 2c, the DC-DC converter 2 stops the operation of generating or outputting the output voltage. The correspondence between the logical value level of the control signal input terminal 2c and the operation state of the DC-DC converter 2 is not limited to the above case. That is, when the control signal input terminal 2c is at a low level, an operation for generating the output voltage of the DC-DC converter 2 is performed. When the control signal input terminal 2c is at a high level, the operation of the DC-DC converter 2 is performed. May be stopped. In addition, the input level of the control signal input terminal 2c is set to a plurality of levels, and the output voltage level of the DC-DC converter 2 is set for each level, or the DC− The output voltage of the DC converter 2 may be made to correspond continuously.

  The load 4 is an AC load. The load 4 is, for example, an electronic device that operates by supplying AC power. The load 4 may be, for example, a power system such as a power transmission line that supplies power to a power receiving facility of a consumer.

  The power conversion device 10 converts the DC power supplied from the DC-DC converter 2 into AC power corresponding to the load 4, and outputs the converted AC power to the load 4. The power conversion device 10 outputs active power to the load 4. The power converter 10 is a so-called power conditioner. The voltage of the AC power output from the power conversion device 10 is, for example, 100 V (effective value) or 200 V (effective value). The frequency of the AC power output from the power converter 10 is, for example, 50 Hz or 60 Hz.

  The power conversion device 10 includes a main circuit 12 and a control circuit 14. Main circuit 12 includes an inverter unit 21, a filter unit 23, a switching unit 24, and an initial charging unit 25.

  The inverter unit 21 is connected in series to the output of the DC-DC converter 2. The filter unit 23 is connected in series between the inverter unit 21 and the load. The switching unit 24 is connected in series between the inverter unit 21 and the filter unit 23. The initial charging unit 25 is connected to the switching unit 24 and connected in parallel with the load 4.

  The inverter unit 21 converts the DC power generated by the power generation device 1 into DC power having a stabilized DC voltage supplied via the DC-DC converter 2, for example, having a carrier frequency of several kHz to several tens kHz. The equivalent carrier frequency is converted into a high-frequency AC power having a frequency of several tens to several hundreds of kHz.

  The filter unit 23 suppresses harmonic components of the AC power output from the inverter unit 21. The filter unit 23 is, for example, a so-called sine wave filter that approximates AC power output from the inverter to a sine wave. The filter unit 23 may include, for example, not only a sine wave filter but also a noise filter (EMI filter) for removing noise.

  The switching unit 24 is connected in series between the outputs 21 U and 21 V of the inverter unit 21 and the filter unit 23. Switching unit 24 includes a path for connecting load 4 and initial charging unit 25 in parallel.

  The switching unit 24 supplies the output of the inverter unit 21 to the load 4 via the filter unit 23 when the power conversion device 10 is in a steady operation state. When the power conversion device 10 is in the activated state, the switching unit 24 disconnects the outputs 21U and 21V of the inverter unit 21 from the path of the current flowing through the load 4 and connects the path including the initial charging unit 25. After the power conversion device 10 transitions from the startup state to the steady operation state, the switching unit 24 cuts off the path of the current flowing from the inverter unit 21 to the initial charging unit 25 and causes the current to flow from the inverter unit 21 to the load 4.

FIG. 2A is a block diagram schematically illustrating a specific example of the configuration of the switching unit and the initial charging unit of the power conversion device according to the first embodiment.
As shown in FIG. 2A, the switching unit 24 includes switches 31a and 31b and switches 32a and 32b. The switches 31 a and 31 b are connected in series between a node 36 to which the initial charging unit 25 and the load 4 are connected in parallel and the load 4. The switches 31a and 31b are, for example, MOSFETs. Since an alternating current flows through the path to which the switches 31a and 31b are connected, the switches 31a and 31b need to be turned on / off with respect to the current flowing in both directions. Since a diode is formed parasitically between the drain and source of the MOSFET, the switches 31a and 31b are connected to each other so that no current flows through these diodes. The switches 31a and 31b may have their drains connected to each other. The switches 32 a and 32 b are connected in series between the node 37 where the initial charging unit and the load 4 are connected in parallel and the initial charging unit 25. Since the alternating current flows through the path to which the switches 32a and 32b are connected, the switches 32a and 32b need to be turned on / off with respect to the current flowing in both directions. Similarly to the switches 31a and 31b, the switches 32a and 32b are connected to each other between sources or drains. When a mechanical switch such as an electromagnetic relay or a bidirectional switch such as a triac is used instead of the switches 31a and 31b and the switches 32a and 32b, a single switch may be connected.

  The switching unit 24 is connected between the outputs 21U and 21V of the inverter unit 21 and the filter unit 23 as shown in FIG.

FIG. 2B is a block diagram schematically illustrating a configuration of a modified example of the power conversion device according to the first embodiment.
As shown in FIG. 2 (b), the switching unit 24 may be connected between the filter unit 23 connected to the outputs 21 U and 21 V of the inverter unit 21 and the load 4. By connecting the switching unit 24 between the filter unit 23 and the load 4, the voltage / current to be handled is not included in the voltage / current to be handled compared to the case where the switching unit 24 is placed in front of the filter unit 23. There are advantages such as easy circuit layout.

  The configurations of the switches 31a and 31b and the switches 32a and 32b are not limited to the above. The switching unit 24 connects the load 4 and the initial charging unit 25 in parallel, and determines whether the path includes the load 4 or the path including the initial charging unit 25 according to the command of the control circuit 14. Select exclusively. All of the circuit configurations for the current flow path are included in this embodiment. For example, the switches 31a and 31b may be connected in series between the node 37 and the load 4 (or the filter unit). The switches 32 a and 32 b may be connected in series between the node 36 and the initial charging unit 25.

  2A and 2B, the output of the inverter unit corresponds to two single-phase inverters. However, in the case of a three-phase output inverter, a load is provided for each phase. The switch on the side and the switch on the pseudo load side may be connected.

  In the case where the power conversion device 10 is a power conditioner with a 5 kW output, for example, a current flowing through the load is a current of 25 A (effective value) at 200 V (effective value). Therefore, it is desirable that the switches 31a and 31b on the load 4 side have a low on-resistance. The on resistance of the switches 31a and 31b is preferably as small as possible. A plurality of MOSFETs or the like may be connected in parallel in order to lower the on-resistance of a so-called bidirectional switch having a common MOSFET source.

  The current flowing through the switches 32 a and 32 b on the pseudo load 34 side is as small as about 1/10 to 1/100 of the current flowing through the load 4. Here, the load 4 is a rated load, and the flowing current is the maximum value and the rated load current. Further, the current flowing through the switches 32a and 32b is within a limited period (generally within several hundred ms to several s) when the power conversion apparatus 10 is activated. From this, it is possible to use switches 32a and 32b having larger on-resistance than the switches 31a and 31b. For example, the on-resistance of the switches 32a and 32b can be set to 10 mΩ to 100 mΩ. Switch elements such as MOSFETs smaller than the load-side switches 31a and 31b can be used.

  The initial charging unit 25 bypasses the current flowing from the inverter unit 21 to the load 4 when the power conversion device 10 is in the activated state. The initial charging unit 25 includes another current path for charging the charge storage element that forms the inverter unit 21. The initial charging unit 25 is, for example, a pseudo load 34 including a resistance element, as shown in FIGS. 2 (a) and 2 (b). For the pseudo load 34, for example, a resistance value is set such that a current of 1/10 to 1/100 can flow with respect to the maximum value (rated load) of the current flowing through the load 4.

  In this way, the main circuit 12 converts the DC power supplied from the power generator 1 through the DC-DC converter 2 into AC power corresponding to the load 4 when the power converter 10 is in a steady operation state. Convert. Further, when the power conversion device 10 is in the activated state, the main circuit 12 does not supply the direct current power supplied from the power generation device 1 via the DC-DC converter 2 to the load 4, and supplies it to the initial charging unit 25. Supply.

  The main circuit 12 may further include, for example, a noise cut filter or a transformer. The noise cut filter is provided, for example, between the DC-DC converter 2 and the inverter unit 21 and suppresses noise included in DC power supplied from the DC-DC converter 2. For example, the transformer is provided between the filter unit 23 and the load 4, and transforms AC power output from the filter unit 23.

  The control circuit 14 is, for example, a processor such as a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). For example, the control circuit 14 reads out a predetermined program from the memory 16 and sequentially processes the program, thereby comprehensively controlling each unit of the power conversion apparatus 10. Specifically, the control circuit 14 controls conversion from DC power to AC power by the inverter unit 21. The control circuit 14 controls the switching unit 24 according to the state of steady operation or the startup state of the power conversion device 10. As shown in FIG. 1, the memory 16 storing the program is provided separately from the control circuit 14 and may be connected to the control circuit 14 via the bus 18 or may be provided in the control circuit 14. The memory 16 may be a storage device using a semiconductor element such as a ROM (Read Only Memory) or a RAM (Random Access Memory), a magnetic storage medium such as a hard disk device or an optical disk device, a magneto-optical storage medium, or an optical storage medium. Or a plurality of these may be connected to the bus 18 and used.

A detailed configuration of the inverter unit 21 will be described.
The inverter unit 21 includes a high potential side input terminal 20a, a low potential side input terminal 20b, and a plurality of legs LG1 and LG2. The high potential side input terminal 20 a is connected to the high potential side output terminal 2 a of the DC-DC converter 2. The low potential side input terminal 20 b is connected to the low potential side output terminal 2 b of the DC-DC converter 2. Thus, the inverter unit 21 is connected to the DC-DC converter 2 via the input terminals 20a and 20b. The DC power supplied from the DC-DC converter 2 is input between the input terminals 20a and 20b.

  Hereinafter, in this specification, the DC-DC converter 2 is connected to the power conversion device 10, and the input voltage Vin between the input terminals 20 a and 20 b of the power conversion device 10 is the output terminal 2 a of the DC-DC converter 2. It is assumed that it is equal to the output voltage between 2b. The output voltage of the DC-DC converter 2 may be expressed as the input voltage Vin of the power conversion device 10.

  In this example, the inverter unit 21 includes two legs, a first leg LG1 and a second leg LG2. The first leg LG1 includes two arms, a first upper arm UA1 and a first lower arm LA1. The first upper arm UA1 is connected to the input terminal 20a on the high potential side. The first lower arm LA1 is connected between the first upper arm UA1 and the low potential side input terminal 20b. The second leg LG2 includes two arms, a second upper arm UA2 and a second lower arm LA2. The second upper arm UA2 is connected to the input terminal 20a on the high potential side. The second lower arm LA2 is connected between the second upper arm UA2 and the low potential side input terminal 20b.

  Thus, each leg LG1, LG2 is connected in parallel between each input terminal 20a, 20b. In each leg LG1, LG2, “upper side” and “lower side” do not mean an arrangement in the vertical direction. In each leg LG1, LG2, “upper side” means the side where the potential of the input DC voltage is higher, and “lower side” means the side where the potential of the input DC voltage is lower. In other words, the upper arms UA1 and UA2 are arms on the high potential side. In other words, the lower arms LA1 and LA2 are arms on the low potential side.

  In this example, the inverter unit 21 is a so-called single-phase inverter having two legs and four arms. The inverter unit 21 converts DC power into single-phase AC power. The inverter unit 21 may be a three-phase inverter that converts DC power into three-phase AC power. In the case of a three-phase inverter, the inverter further includes a third leg connected in parallel to the first leg LG1 and the second leg LG2.

  As described above, the output power of the power conversion device 10 may be single-phase AC power or three-phase AC power. What is necessary is just to set the output electric power of the power converter device 10 according to the load 4. FIG. When the inverter unit 21 is a three-phase inverter, a filter unit 23 is provided for each phase of the three-phase AC power. That is, when the inverter unit 21 is a three-phase inverter, three filter units 23 are provided.

  The first upper arm UA1 of the first leg LG1 includes a first upper switching element U1 connected between the input terminals 20a and 20b, and a second connected between the first upper switching element U1 and the input terminal 20a. And an upper switching element U2.

  The first lower arm LA1 of the first leg LG1 includes a first lower switching element X1 connected between the first upper switching element U1 and the low potential side input terminal 20b, and a first lower switching element X1. And a second lower switching element X2 connected between the input terminal 20b on the low potential side.

  The first leg LG1 includes a first charge storage element CU1. One end of the first charge storage element CU1 is connected between the first upper switching element U1 and the second upper switching element U2. The other end of the first charge storage element CU1 is connected between the first lower switching element X1 and the second lower switching element X2.

  Similarly to the first leg LG1, the second leg LG2 includes the first upper switching element V1, the second upper switching element V2, the first lower switching element Y1, the second lower switching element Y2, and the first leg switching element Y2. Charge storage element CV1. Since the configuration of the second leg LG2 is substantially the same as the configuration of the first leg LG1, detailed description thereof is omitted.

  For example, capacitors are used for the first charge storage elements CU1 and CV1. The first charge storage elements CU1, CV1 are called, for example, flying capacitors. That is, the inverter unit 21 is a so-called flying capacitor circuit type inverter.

  The first leg LG1 further includes a third upper switching element U3, a third lower switching element X3, and a second charge storage element CU2. The third upper switching element U3 is connected between the second upper switching element U2 and the input terminal 20a on the high potential side. The third lower switching element X3 is connected between the second lower switching element X2 and the low potential side input terminal 20b. One end of the second charge storage element CU2 is connected between the second upper switching element U2 and the third upper switching element U3. The other end of the second charge storage element CU2 is connected between the second lower switching element X2 and the third lower switching element X3.

  Similarly, the second leg LG2 further includes a third upper switching element V3, a third lower switching element Y3, and a second charge storage element CV2.

  Thus, in the inverter unit 21, three switching elements are connected in series to each of the arms UA1, UA2, LA1, and LA2. The second charge storage element CU2 generates an intermediate voltage between the DC-DC converter 2 and the first charge storage element CU1. The first charge storage element CU1 generates a voltage intermediate between the second charge storage element CU2 and the reference potential. Similarly, the second charge storage element CV2 generates a voltage intermediate between the DC-DC converter 2 and the first charge storage element CV1. The first charge storage element CV1 generates a voltage intermediate between the second charge storage element CV2 and the reference potential. For this reason, the charge storage elements CU1, CU2, CV1, and CV2 are sometimes referred to as intermediate capacitors.

  As a result, the inverter unit 21 can change the level of the output voltage to 3 levels with the upper arm, 3 levels with the lower arm, and 7 levels in total including the reference potential level. That is, the inverter unit 21 is a 7-level multi-level inverter. The number of switching elements provided in each arm UA1, UA2, LA1, LA2 may be two, or four or more. The level of the voltage output from the inverter unit 21 may be 5 levels or 9 levels or more.

  Thus, when the inverter unit 21 that changes the level of the output voltage to 7 levels is used, the volume of the filter unit 23 can be reduced by about 85% compared to the case of 2-level output. For example, when the volume of the filter unit 23 in the case of 2-level output is about 750 cc, in this example, the volume of the filter unit 23 can be about 112 cc. Therefore, the power converter 10 can be increased in output density. The “output density” is the ratio of the output power of the power converter 10 to the volume of the power converter 10.

  Further, as will be described in detail below, in the state of steady operation of the power conversion device 10, the input voltage of the inverter unit 21 is divided by the charge storage elements, so that the withstand voltage of the switching elements constituting the inverter unit 21 is reduced. Can be set. Therefore, further downsizing and higher output density can be realized for the two-level output inverter.

  The inverter unit 21 includes first upper switching elements U1 and V1, second upper switching elements U2 and V2, first lower switching elements X1 and Y1, second lower switching elements X2 and Y2, and a first charge. The storage elements CU1 and CV1 need only be included at least. When three or more switching elements are provided in each of the arms UA1, UA2, LA1, and LA2, a plurality of charge storage elements are provided in the inverter unit 21. The number of charge storage elements is a value obtained by subtracting 1 from the number of switching elements of the arms UA1, UA2, LA1, and LA2. One end of each charge storage element is connected to a connection point between two adjacent switching elements of the upper arm. The other end of each charge storage element is connected to a connection point between two adjacent switching elements of the lower arm.

  In the inverter unit 21, the connection points between the first upper arm UA1 and the first lower arm LA1 and the connection points between the second upper arm UA2 and the second lower arm LA2 are outputs 21U and 21V. In other words, the connection point between the first upper switching element U1 and the first lower switching element X1 and the connection point between the first upper switching element V1 and the first lower switching element Y1 are the outputs 21U and 21V. Become. The filter unit 23 and the initial charging unit 25 are connected in series to the outputs 21U and 21V of the inverter unit 21.

  For example, self-extinguishing elements are used for the switching elements U1 to U3, X1 to X3, V1 to V3, and Y1 to Y3. More specifically, for example, MOSFET (Metal Oxide Semiconductor Field Effect Transistor), GTO (Gate Turn-Off thyristor), IGBT (Insulated Gate Bipolar Transistor), or the like is used. In order to cope with higher frequency and higher output density, a switching element using silicon carbide (SiC) or gallium nitride (GaN) can be used.

  Each of the switching elements U1 to U3, X1 to X3, V1 to V3, and Y1 to Y3 includes a pair of main electrodes and a control electrode that controls a current flowing between the main electrodes. The control electrode is, for example, a gate electrode. Each switching element U1-U3, X1-X3, V1-V3, Y1-Y3 is connected in series in each main electrode.

  Each switching element U1-U3, X1-X3, V1-V3, Y1-Y3 changes to an ON state and an OFF state according to the voltage applied to a control electrode. Each switching element U1-U3, X1-X3, V1-V3, Y1-Y3 will be in an ON state, for example when a 1st voltage is applied to a control electrode. Each of the switching elements U1 to U3, X1 to X3, V1 to V3, Y1 to Y3 is applied when a second voltage lower than the first voltage is applied to the control electrode or when no voltage is applied to the control electrode. Turns off. The off state is a state in which substantially no current flows between the main electrodes. The off state may be, for example, a state in which a weak current in a range that does not affect the power conversion in the inverter unit 21 flows between the main electrodes. In other words, the on state is a first state in which current flows between the main electrodes. The off state is a second state in which the current flowing between the main electrodes is lower than the first state. In this example, the switching elements U1 to U3, X1 to X3, V1 to V3, and Y1 to Y3 are normally-off types. Each switching element U1-U3, X1-X3, V1-V3, Y1-Y3 may be a normally-on type.

  In addition, diodes are connected to the switching elements U1 to U3, X1 to X3, V1 to V3, and Y1 to Y3. Each diode is connected in parallel to each main electrode of each switching element U1-U3, X1-X3, V1-V3, Y1-Y3. The forward direction of each diode is connected in the opposite direction to the direction of current flowing between the main electrodes. That is, each diode is a so-called free-wheeling diode.

  The control circuit 14 is connected to the switching elements U1 to U3, X1 to X3, V1 to V3, and Y1 to Y3 of the inverter unit 21. Specifically, the control circuit 14 is connected to each control electrode of each switching element U1-U3, X1-X3, V1-V3, Y1-Y3. The control circuit 14 controls on / off of the switching elements U1 to U3, X1 to X3, V1 to V3, and Y1 to Y3. For example, the control circuit 14 inputs a control signal to the control electrodes of the switching elements U1 to U3, X1 to X3, V1 to V3, and Y1 to Y3, and changes the voltage of the control signal, thereby changing the switching elements U1 to U1. ON / OFF of U3, X1 to X3, V1 to V3, and Y1 to Y3 is controlled. The control signal is a so-called gate signal. Thereby, the control circuit 14 converts DC power into AC power corresponding to the load 4.

FIG. 3A to FIG. 3D are timing diagrams of exemplary operation waveforms schematically showing the operation of the control circuit in the steady operation state of the power conversion apparatus 10 according to the first embodiment.
As shown in FIGS. 3A to 3D, the control circuit 14 compares the carrier signals CS1 to CS3 with the modulated wave MW, and compares the switching elements U1 to U3, X1 to X3, and V1 to V3. , Y1 to Y3 are turned on / off to control the duty cycle.

  FIG. 3A illustrates an example of carrier signals CS1 to CS3 and a modulated wave MW used for controlling the switching elements U1 to U3 and X1 to X3 of the first leg LG1. Since the modulation wave MW is set for each leg LG1, LG2, in this example, two modulation waves MW are actually set.

  The carrier signal is set for each of the upper switching elements U1 to U3 and V1 to V3 or for each of the lower switching elements X1 to X3 and Y1 to Y3 in each leg LG1 and LG2. That is, in this example, six carrier signals are set. The carrier signal set in each switching element of the first leg LG1 can also be used in common for each switching element of the second leg LG2. Therefore, in this example, at least three types of carrier signals are prepared.

  The carrier signal CS1 is an example of a carrier signal used for controlling the first upper switching element U1. The carrier signal CS2 is an example of a carrier signal used for controlling the second upper switching element U2. The carrier signal CS3 is an example of a carrier signal used for controlling the third upper switching element U3.

  FIG. 3B is an example of a control signal for the first upper switching element U1 generated based on the modulated wave MW and the carrier signal CS1. FIG. 3C is an example of a control signal for the second upper switching element U2 generated based on the modulated wave MW and the carrier signal CS2. FIG. 3D is an example of a control signal for the third upper switching element U3 generated based on the modulated wave MW and the carrier signal CS3.

  Modulated wave MW and carrier signals CS1 to CS3 change periodically. The modulation wave MW is, for example, a sine wave. The frequency of modulated wave MW is set according to the frequency of AC power output from main circuit 12. The frequency of the modulation wave MW is, for example, 50 Hz or 60 Hz. Each carrier signal CS1-CS3 is, for example, a triangular wave. The carrier signals CS1 to CS3 may be sawtooth waves or trapezoidal waves. The frequencies of the carrier signals CS1 to CS3 are higher than the frequency of the modulated wave MW. The frequency of each of the carrier signals CS1 to CS3 is, for example, about 0.5 kHz to 25 kHz. The frequencies of the carrier signals CS1 to CS3 are substantially the same.

  The carrier signals CS1 to CS3 are set with a phase shift of 120 degrees. The phase of the carrier signal is set according to the number of carrier signals. For example, when each arm is a five-level inverter including two switching elements, two carrier signals are set, and the phase of each carrier signal is shifted by 180 degrees. For this reason, the inverter part 21 may be called a carrier phase shift signal generation system.

  The control circuit 14 compares the modulated wave MW with the carrier signals CS1 to CS3. For example, the control circuit 14 turns on the upper switching elements U1 to U3 and turns off the lower switching elements X1 to X3 when the modulated wave MW is equal to or higher than the carrier signals CS1 to CS3. In this case, the control circuit 14 turns off the upper switching elements U1 to U3 and turns on the lower switching elements X1 to X3 when the modulated wave MW is less than the carrier signals CS1 to CS3. As described above, the control circuit 14 alternately turns on and off the upper switching elements U1 to U3 and the lower switching elements X1 to X3. On the contrary, when the modulated wave MW is equal to or higher than the carrier signal CS, the upper switching elements U1 to U3 may be turned off and the lower switching elements X1 to X3 may be turned on.

  The control circuit 14 controls each of the legs LG1 and LG2 as described above. Thereby, the control circuit 14 controls on / off of each switching element U1-U3, X1-X3, V1-V3, Y1-Y3. That is, the conversion from DC power to AC power by the inverter unit 21 is controlled.

  For the control method in the steady operation state of the flying capacitor circuit type inverter unit 21, for example, “Study on capacitor selection guideline in flying capacitor multi-level converter” Vol.131, No.12 pp.1393- 1400 "is described in detail.

  In the state of steady operation of the 7-level flying capacitor type power converter 10 as in the present embodiment, the charge storage elements CU1 and CV1 are charged to a voltage of about (1/3) Vin (max). The charge storage elements CU2 and CV2 are charged to a voltage of about (2/3) Vin (max). When each switching element is off, a voltage of (1/2) (1/3) Vin (max) is applied. Therefore, the withstand voltage of the switching element of the power conversion device 10 with the input voltage Vin can be one corresponding to (1/3) Vin (max).

  On the other hand, when the DC-DC converter 2 starts operation, the input voltage Vin is not applied to the inverter input terminals 20a and 20b. Therefore, the charge storage elements CU1, CU2, CV1, and CV2 do not store charges, and the voltage across the charge storage elements CU1, CU2, CV1, and CV2 is 0V or almost 0V. Since all the switching elements are off, in such an initial state, when the specified input voltage Vin (max) is applied to the inverter input terminals 20a and 20b, the switching elements U3, X3, V3, and Y3 An excessive voltage up to (1/2) Vin (max) is applied to. Vin (max) is, for example, about 330V. In the state of steady operation, a voltage of about 110V should be applied. However, when the power converter 10 is started, an excessive voltage of about 165V is applied to the switching elements U3, X3, V3, and Y3. Therefore, in severe cases, the switching elements U3, X3, V3, and Y3 may be damaged.

  When the DC-DC converter 2 is a booster circuit, an output voltage corresponding to the input voltage of the DC-DC converter 2 is output when the DC-DC converter 2 starts to operate. The input voltage Vin of the device 10 is not 0V. In this specification, even when the DC-DC converter 2 has a value of Vin as described above, it is included in the present embodiment when the voltage level is equal to or lower than the overvoltage level of the switching element.

  In order to reduce the size of the power conversion device 10 and achieve high power density, the loss of the power conversion device 10 needs to be reduced. The loss of the power conversion device 10 is largely related to the loss when the switching element is on. The loss of the power conversion device 10 increases as the ON voltage of the switching element increases. It is known that the on-resistance when the switching element is a MOSFET increases in proportion to the square of the drain-source breakdown voltage (breakdown voltage) to the power of 2.5. When a switching element with a high breakdown voltage is used, the loss of the power conversion device 10 increases exponentially. For this reason, using a switching element having an excessive rating with a withstand voltage that is three times or more that during steady operation due to an excessive voltage at the time of start-up results in using a switching element having a larger die size, thus increasing efficiency. This is contrary to high power density.

  The power conversion device 10 of the present embodiment includes a switching unit 24 connected in series between the outputs 21U and 21V of each phase of the inverter unit 21 and the load 4. The switching unit 24 cuts off the current flowing through the load 4 when the power conversion device 10 is started up, and passes the current through the initial charging unit 25. The initial charging unit 25 includes a pseudo load 34 that can flow a current of about 1/10 to 1/100 of the rated current flowing through the load 4.

  As described above, when the power conversion device 10 is started, the charge storage elements CU1, CU2, CV1, and CV2 are excessively caused by flowing a current smaller than the current that flows to the load 4 to the initial charging unit 25 including the pseudo load 34. It will not be charged.

  All the switches 31 a, 31 b, 32 a, and 32 b of the switching unit 24 are controlled to be turned on / off by the control circuit 14. Specifically, in a steady operation state in which the charge storage elements CU1, CU2, CV1, and CV2 are charged with a specified voltage Vin (max), the switches 31a and 31b are turned on at the load 4 side, and the pseudo load 34 side is turned on. The switches 32a and 32b are turned off. When the power generation device 1 starts power generation (for example, sunlight hits the solar cell panel and starts power generation), the DC-DC converter 2 is activated using the control signal input terminal 2c, and the input voltage Vin is applied to the power conversion device 10. Is applied and the power conversion device 10 is activated, the switches 31a and 31b are turned off and the switches 32a and 32b are turned on.

  The control circuit 14 includes a control unit 41, a changeover switch drive unit 42, a frequency determination unit 43, a carrier generation unit 44, a modulated wave generation unit 45, and a comparison unit 46.

  The control unit 41 exchanges data via the memory 16 and the bus 18. The control unit 41 sequentially executes the program steps stored in the memory 16. The control unit 41 controls the changeover switch drive unit 42, controls the frequency determination unit 43, or controls the modulated wave generation unit 45 according to the program steps read from the memory 16.

  The changeover switch drive unit 42 is connected to the switches 31 a, 31 b, 32 a, and 32 b of the changeover unit 24 according to a command from the control unit 41 and controls on / off of these.

  The frequency determination unit 43 determines the frequency of each of the carrier signals CS <b> 1 to CS <b> 3 (hereinafter referred to as a carrier frequency) according to a command from the control unit 41 and inputs the determined frequency value to the carrier generation unit 44. For example, the frequency determination unit 43 sets the carrier frequency according to a setting value input from a host controller (not shown).

  The maximum value of the carrier frequency is, for example, about 33 kHz in consideration of loss during switching of the switching element. As described above, since the power conversion device 10 operates by shifting the phases of the six carrier frequencies, the maximum value of the substantial carrier frequency (equivalent carrier frequency fcar) of the power conversion device 10 is, for example, 6 times 33 kHz. Of about 200 kHz. On the other hand, considering the size of the filter and the like, the minimum value of the equivalent carrier frequency fcar is, for example, about 6 kHz. That is, the minimum value of the carrier frequency is about 1 kHz, for example.

  The carrier generation unit 44 generates carrier signals CS <b> 1 to CS <b> 3 for each phase of the frequency determined by the frequency determination unit 43. The output of each phase of the carrier generation unit 44 is connected to the comparison unit 46. The carrier generation unit 44 inputs the generated carrier signals CS1 to CS3 of each phase to the comparison unit 46.

  In the modulated wave generation unit 45, for example, a sine wave as a reference is set as a power command value in accordance with a command from the control unit 41. The output of the modulated wave generation unit 45 is input to the comparison unit. The signal waveform generated by the modulation wave generation unit 45, that is, the modulation wave MW, can be a sine wave having an amplitude, frequency, and phase set in accordance with a command from the control unit 41. In the present specification, the ratio between the amplitude of the modulation wave MW and the amplitude of the carrier signal generated by the carrier generation unit 44 is referred to as a modulation rate Rm. When the amplitude of the modulated wave MW is equal to the amplitude of the carrier signals CS1 to CS3, the modulation rate Rm = 1 (100%), and when the amplitude of the modulated wave MW is 0, the modulation rate Rm = 0 (0%) And The modulation factor Rm can be set to a specific value (for example, “1”) according to a command from the control unit 41, and can be changed stepwise or continuously. The modulated wave generation unit 45 is connected to the comparison unit 46 and inputs the generated modulated waves MW to the comparison unit 46.

  The power command value is input to the power conversion apparatus 10 from, for example, a host controller that controls the power system. Each power command value may be generated in the power converter 10. For example, when the DC-DC converter 2 is a solar cell panel, the power at the optimum operating point obtained from the output voltage and output current of the solar cell panel may be used as the power command value.

  As described with reference to FIGS. 3A to 3D, the comparison unit 46 compares the input modulated waves MW with the carrier signals CS1 to CS3. Thereby, the comparison part 46 produces | generates the control signal of each switching element U1-U3, X1-X3, V1-V3, Y1-Y3 from each modulation wave MW and each carrier signal CS1-CS3. The control circuit 14 inputs each control signal generated by the comparison unit 46 to the control electrode of each switching element U1 to U3, X1 to X3, V1 to V3, Y1 to Y3, and each switching element U1 to U3, X1 to X1. Control on / off of X3, V1 to V3, and Y1 to Y3.

FIG. 4A to FIG. 4C are timing diagrams schematically showing examples of operation waveforms when the power conversion device 10 according to the first embodiment transitions from a startup state to a steady operation state. is there.
FIG. 4A is a diagram illustrating a change with time of the modulation rate Rm.
FIG. 4B is a diagram illustrating a time change of the output voltage of the DC-DC converter 2, that is, the input voltage Vin of the power converter 10.
FIG. 4C is a diagram illustrating temporal changes in the on / off states of the switches 31 a and 31 b and the switches 32 a and 32 b of the switching unit 24.

  In the startup state of the power conversion device 10, the waveform of the output voltage of the DC-DC converter 2 input to the power conversion device 10, that is, the input voltage waveform 61 of the power conversion device rises in a finite time. The rise time ts of the output voltage of the DC-DC converter 2 is determined by the power of the load connected to the output of the DC-DC converter 2, for example. When a constant load is connected to the output of the DC-DC converter 2, the output of the DC-DC converter 2 rises with a substantially constant rise time ts.

  When the input voltage Vin of the power conversion device 10 is lower than the specified input voltage Vin (max), it is applied across the charge storage elements CU1, CU2, CV1, CV2 constituting the inverter unit 21. The voltage also becomes a low voltage value according to Vin.

  In the power conversion device 10 of the present embodiment, a period in which Vin is low within the rise time ts of the output voltage of the DC-DC converter 2 is used. By charging the charge storage elements CU1, CU2, CV1, and CV2 in the inverter unit 21 during the rise time ts, the voltage across the charge storage elements CU1, CU2, CV1, and CV2 becomes the rated input voltage Vin (max). It is possible to prevent the voltage across the maximum voltage at.

  The power conversion device 10 is activated at time t0. The power conversion device 10 is activated by, for example, increasing the input voltage Vin of the power conversion device 10 by inputting a control signal to the control signal input terminal 2c of the DC-DC converter 2. At time t0, the control circuit 14 sets the modulation rate Rm of the power converter 10 to 1 (modulation rate setting waveform 63).

  Note that the manner in which the output voltage of the DC-DC converter 2 increases may vary depending on the circuit system of the DC-DC converter 2. In the case of a step-down circuit or a step-up / step-down circuit, the waveform 61 of the output voltage of the DC-DC converter 2 rises from almost 0 V as shown by the solid line in FIG. On the other hand, the waveform 62 of the output voltage in the case of the booster circuit may rise from a voltage in the vicinity of the input voltage V + of the DC-DC converter 2 instead of 0 V, as indicated by a one-dot chain line in FIG. Therefore, it is necessary to determine the timing control when starting up the power converter 10 in consideration of the circuit system of the DC-DC converter 2.

  At time t0, as shown in the load side switch state waveform 65 in FIG. 4C, the control circuit 14 sets the switches 31a and 31b of the switching unit 24 to OFF. Therefore, no current flows through the load 4. Further, as shown in the pseudo load side switch state waveform 64 in FIG. 4C, the switches 32a and 32b are turned on by the control circuit 14 so that a current flows through the pseudo load 34 of the initial charging unit 25. Set to

  In the period from time t0 to t1, the output voltage of the DC-DC converter 2 is stabilized at a specified output voltage (= rated input voltage Vin (max)). Therefore, the activation time ts of the power conversion apparatus 10 is “t1”. The rated input voltage is, for example, 330V.

  In the period from time t0 to t1, the input voltage Vin of the power converter 10 gradually increases. Therefore, the charge storage elements CU1, CU2, CV1, and CV2 in the inverter unit 21 are charged with a voltage lower than the rated input voltage Vin (max). In the period from time t0 to time t1, the power conversion device 10 passes a current to the pseudo load 34 that consumes lower power than the load 4 that flows the rated load current. Therefore, since the current for charging the charge storage elements CU1, CU2, CV1, and CV2 is reduced, the voltage generated by the charge current to the charge storage elements can be made lower than when the current is passed through the load 4. When the charge storage element is charged, the voltage across the charge storage element does not exceed 110V for CU1 and CV1, and does not exceed 220V for CU2 and CV2, for example (when Vin (max) = 330V) ).

  During the period from time t1 to time t2, as indicated by the modulation factor setting waveform 63 in FIG. 4A, the modulation factor Rm is gradually reduced by the control circuit 14, and the output current of the power conversion device 10 is 0 A or approximately Reduced to 0A. During this period, the output of the DC-DC converter 2 is a specified output voltage value, that is, Vin (max). During this period, the control circuit 14 turns off the switches 31a and 31b on the load 4 side of the switching unit 24 and turns on the switches 32a and 32b on the pseudo load 34 side. The charging currents of the charge storage elements CU1, CU2, CV1, and CV2 flow through the pseudo load 34.

  In the period from time t0 to t2, the switching unit 24 supplies current to the pseudo load 34 of the initial charging unit 25 and charges the charge storage element in the inverter unit 21, and therefore is referred to as an initial charging phase T1.

  After the output current of the power conversion device 10 becomes approximately 0 A and the initial charging phase T1 is completed, the switch of the switching unit 24 is switched. The switches 32a and 32b are turned off by the control circuit 14, and the current path from the power conversion device 10 to the pseudo load 34 of the initial charging unit 25 is opened. The switches 31 a and 31 b are turned on by the control circuit 14 and cause a current to flow through the load 4.

  At time t3 after time t2, the switches 32a and 32b on the pseudo load 34 side are turned off so that the switches 31a and 31b and the switches 32a and 32b are not turned on at the same time, and the time t3 ′ (t3 later than the time t3). <T3 ′), the switches 31a and 31b on the load 4 side are turned on. As described above, when MOSFETs are used as the switches 31a, 31b, 32a, and 32b, the number of MOSFETs connected in parallel increases, and the parasitic input capacitance increases. Therefore, the switches 31a, 31b, 32a, and 32b are driven. It is necessary to switch at a timing that fully considers the switching delay.

  After time t3, t3 ′, at time t4, the power conversion device 10 gradually increases the modulation rate Rm from 0 toward 1 and starts supplying AC power to the load 4.

  At time t4, the input voltage Vin of the power conversion device 10 is the rated input voltage Vin (max). Further, the switches 31a and 31b on the load 4 side of the switching unit 24 are turned on, and the switches 32a and 32b on the pseudo load 34 side are in an off state.

  In the period from time t2 to time t4, the switching unit 24 performs the switching operation of the load 4 and the pseudo load 34 by the control circuit 14 and is therefore referred to as a switching phase T2.

  After the switching phase T2 is completed, the power conversion device 10 transitions to a steady operation through the adjustment stage of the modulation factor Rm. The modulation factor Rm is set to 1 by the control circuit 14.

  In the period after t4, the power conversion apparatus 10 performs the control operation according to the load 4 with the switching unit 24, the filter unit 23, and the load 4 connected to the output by the control circuit 14, and therefore the output control phase T3. I will call it.

  In the initial charging phase T1 and the output control phase T3, the current supplied to the pseudo load 34 and the load 4 is gradually changed so as not to cause a sudden load fluctuation. In the above description, the load current is changed by adjusting the modulation factor Rm and controlling the duty of the switching element. However, other methods may be used. For example, a level signal that limits the duty of the switching element in preference to the modulation wave MW may be input to the comparison unit 46. By using other similar methods, a circuit for adjusting the output power of the power converter 10 can be configured.

  Since the DC-DC converter 2 starts up with respect to a load that consumes substantially constant power by the inverter unit 21 and the pseudo load 34, the rise time ts (= t1) of the output voltage of the DC-DC converter 2 is substantially constant. It becomes. Therefore, for example, by acquiring, setting, and programming the times t1, t2, t3, and t4 in advance by measurement or the like, the above-described operations are sequentially executed as a sequence.

  In the case of the switching phase T2, the power conversion device 10 gradually decreases the output current of the power conversion device 10, and then switches to steady operation and increases the output current in the output control phase T3. Therefore, the power conversion device 10 can start smoothly and transition to steady operation without requiring a great deal of time to generate an abnormal voltage at the time of load switching or to set a transient response state.

  Development of a power conditioner system (PCS) is being promoted in anticipation of the introduction of photovoltaic power generation and storage batteries into the power system. For example, development of a PCS having a small to medium capacity of about 5 to 25 kW is underway. In PCS, high-efficiency power conversion is required.

  For example, a small-capacity PCS for home use requires not only high efficiency but also high output density. Therefore, it is necessary to design a power converter that reduces the volume while maintaining high efficiency. By using a multi-level power converter, the output waveform approaches a sine wave, so that the volume of the filter can be reduced.

  In a power conversion device that generates an intermediate voltage by a flying capacitor circuit method, generally, the voltage ripple of the charge storage element that maintains the intermediate voltage can be reduced by increasing the carrier frequency. As a result, the capacity of the charge storage element can be reduced and the volume of the charge storage element can be reduced, leading to higher output density. Moreover, since it is a multilevel power converter, it is possible to use a switching element having a small element withstand voltage. Since the conduction resistance of the switching element is approximately proportional to the square of the breakdown voltage to the 2.5th power, a low-loss power conversion device can be realized by using a low breakdown voltage element. Recently, in addition to Si, power devices using GaN or SiC have been remarkably developed and can be applied to these switching elements. For this reason, research and development of multilevel power converters using a flying capacitor circuit system are being conducted.

  From such a background, in the PCS by the multilevel power conversion device using the flying capacitor circuit method, high output density is achieved by increasing the carrier frequency and reducing the capacitor capacity. However, considering that an excessive voltage is applied to a switching element such as a flying capacitor (charge storage element) or MOSFET at the time of starting the PCS, a switching element having an excessive voltage rating must be used, Loss during operation increases. Therefore, as described above, the power conversion device according to the present embodiment can use charge storage elements and switching elements having lower withstand voltages, so that high-efficiency conversion can be realized while maintaining high output density. it can.

(Second Embodiment)
FIG. 5 is a block diagram schematically showing the power conversion device according to the second embodiment.
As shown in FIG. 5, in the main circuit 12a of the power conversion device 10a, the first leg LG1 further includes a first voltage detection unit 51U and a second voltage detection unit 52U. The first voltage detector 51U detects the voltage Vcu1 of the first charge storage element CU1. The second voltage detector 52U detects the voltage Vcu2 of the second charge storage element CU2.

  Similarly, the second leg LG2 further includes a first voltage detection unit 51V and a second voltage detection unit 52V. The first voltage detector 51V detects the voltage Vcv1 of the first charge storage element CV1. The second voltage detector 52V detects the voltage Vcv2 of the second charge storage element CV2.

  The first voltage detection unit 51U is, for example, a resistance element connected in parallel to the first charge storage element CU1. The first voltage detector 51U is not limited to this, and may have any configuration that can detect the voltage of the first charge storage element CU1. Since each voltage detection part 51V, 52U, 52V is substantially the same as the 1st voltage detection part 51U, description is abbreviate | omitted.

  In the power conversion device 10a, the control circuit 14a further includes a voltage control unit 47. The voltage control unit 47 is connected to each of the voltage detection units 51U, 51V, 52U, and 52V. The voltage control unit 47 acquires the voltages Vcu1, Vcu2, Vcv1, and Vcv2 of the charge storage elements CU1, CU2, CV1, and CV2 from the voltage detection units 51U, 51V, 52U, and 52V. The voltage controller 47 is connected to the modulated wave generator 45. The voltage control unit 47 inputs the acquired voltages Vcu1, Vcu2, Vcv1, and Vcv2 to the modulated wave generation unit 45.

  The modulated wave generating unit 45 is based on the detected value of the output power, the power command value, and the voltages Vcu1, Vcu2, Vcv1, and Vcv2 acquired by the control unit 41 via the bus 18, and outputs the leg LG1 and LG2. A modulated wave MW is generated. For example, the modulation wave generator 45 generates the modulation waves MW of the legs LG1 and LG2 so that the voltages Vcu1, Vcu2, Vcv1, and Vcv2 of the charge storage elements CU1, CU2, CV1, and CV2 are substantially constant. Generate.

  The voltages Vcu1, Vcu2, Vcv1, and Vcv2 of the charge storage elements CU1, CU2, CV1, and CV2 vary depending on the conditions of the load 4 and the states of the switching elements U1 to U3, X1 to X3, V1 to V3, and Y1 to Y3. There is a case.

  In this example, the control circuit 14a controls the voltages Vcu1, Vcu2, Vcv1, and Vcv2 based on the detection results of the voltage detectors 51U, 51V, 52U, and 52V. Therefore, the voltage across the charge storage elements CU1, CU2, CV1, and CV2 is detected by directly measuring. For example, when each of the voltages Vcu1, Vcu2, Vcv1, and Vcv2 approaches a specified voltage value, the voltage control unit 47 reduces the modulation rate Rm to substantially reduce the charging current of the charge storage element. In addition, the switching elements U1 to U3, X1 to X3, V1 to V3, and Y1 to Y3 are controlled to be turned on / off.

  For example, “IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL.59, NO. .2, FEBRUARY 2012 Active Capacitor Voltage Balancing in Single-Phase Flying-Capacitor Multilevel Power Converters ”.

  Without controlling the voltages Vcu1, Vcu2, Vcv1, and Vcv2 of the charge storage elements CU1, CU2, CV1, and CV2, for example, the charge storage elements CU1 as in the voltage detection units 51U, 51V, 52U, and 52V , CU2, CV1, and CV2 may be connected in parallel with resistive elements. Thereby, for example, fluctuations in the voltages Vcu1, Vcu2, Vcv1, and Vcv2 of the charge storage elements CU1, CU2, CV1, and CV2 can be suppressed as compared with the case where no resistance element is provided. Since each voltage Vcu1, Vcu2, Vcv1, and Vcv2 can be stabilized, the power conversion device 10b can be safely operated even in the activated state. The resistance element may be connected in series to each of the charge storage elements CU1, CU2, CV1, CV2, and the like, for example.

  In the second embodiment, the voltage across the charge storage elements CU1, CU2, CV1, and CV2 can be directly detected, and the inverter unit 21a can be controlled based on the detected result. When the voltage across the charge storage elements CU1, CU2, CV1, and CV2 is detected and the voltage value is high, it is possible to prevent the charge storage element from being overcharged by reducing the drive duty of the switching element. it can. Therefore, the power converter device 10 can be started more safely.

(Third embodiment)
FIG. 6 is a block diagram schematically illustrating a power conversion apparatus according to the third embodiment.
As shown in FIG. 6, in the main circuit 12b of the power conversion device 10b, the first leg LG1 includes a first voltage detection unit 51U and a second voltage detection unit 52U, as in the second embodiment, The two legs include a first voltage detector 51V and a second voltage detector 52V. The first voltage detector 51U and the second voltage detector 52U of the first leg LG1 detect the voltage Vcu1 of the first charge accumulation unit CU1 and the voltage Vcu2 of the second charge accumulation unit CU2, respectively. The first voltage detector 51V and the second voltage detector 52V of the second leg LG2 detect the voltage Vcv1 of the first charge storage unit CV1 and the voltage Vcv2 of the second charge storage unit CV2, respectively. The first voltage detectors 51U and 51V and the second voltage detectors 52U and 52V are, for example, resistance elements. The main circuit 12b of the power conversion device 10b includes a first current detection unit 53U and a second current detection unit 53V that detect output currents Iu and Iv of the U-phase output 21U and the V-phase output 21V, respectively. The first current detector 53U and the second current detector 53V are, for example, Hall elements.

  The control circuit 14 b includes a voltage monitoring unit 48 and a current monitoring unit 49. The voltage monitoring unit 48 receives detection voltages from the first voltage detection units 51U and 51V and the second voltage detection units 52U and 52V, and determines whether or not the voltages Vcu1, Vcu2, Vcv1, and Vcv2 are within a predetermined range. Monitor. More specifically, the voltage monitoring unit 48 has an overvoltage threshold Vt (OV) for detecting the overvoltage level and a low voltage threshold Vt (LV) for detecting the low voltage level. . For example, when the input voltage is in the range of Vt (LV) to Vt (OV), the voltage monitoring unit 48 outputs “H” (high level). The voltage monitoring unit 48 outputs “L” (low level) when the input voltage falls below Vt (LV) or exceeds Vt (OV).

  The current monitoring unit 49 receives the current values Iu and Iv detected by the first current detection unit 53U and the second current detection unit 53V. The current monitoring unit 49 monitors whether or not the detected U-phase and V-phase current values Iu and Iv are each equal to or less than a predetermined value. More specifically, the current monitoring unit 49 has an overcurrent threshold It (OC) for detecting an overcurrent. For example, the current monitoring unit 49 outputs “H” (high level) when the detected current is equal to or less than It (OC), and outputs “L” (low level) when it exceeds It (OC). Output.

  The control circuit 14b includes an AND circuit 50. The AND circuit 50 receives the output of the voltage monitoring unit 48 and the output of the current monitoring unit 49, and outputs a logical product of these outputs. That is, when both the output of the voltage monitoring unit 48 and the output of the current monitoring unit 49 are “H”, “H” is output, and at least one of the output of the voltage monitoring unit 48 and the output of the current monitoring unit 49 is When it becomes “L”, “L” is output. The output of the AND circuit 50 may include a latch circuit, and the output may be latched in that state when the output is in the “L” state so that the “L” state can be maintained. The output of the AND circuit 50 is connected to the enable input of the comparison unit 46. The enable input of the comparison unit 46 generates a signal for PWM control according to the input from the carrier generation unit 44 and the modulation wave generation unit 45 when “H” is input. When “L” is input to the enable input of the comparison unit 46, the PWM control is stopped regardless of the inputs from the carrier generation unit 44 and the modulation wave generation unit 45, and all the switching elements of the inverter unit 21b are turned on. Turn off. The configuration of the above-described logic gate is not limited to this, and can be arbitrarily set. For example, when an overvoltage or overcurrent is detected, the voltage monitoring unit 48 and the current monitoring unit 49 output an “H” level signal, invert these signals and invert them, and enable the control unit 46 to enable input and control signals. You may make it input into the input terminal 2c.

  About 3rd Embodiment, operation | movement of the power converter device 10b is demonstrated. In the power conversion device 10b according to the third embodiment, the operation of the power conversion device 10b is safely stopped when a failure such as breakage of a switching element or a charge storage element occurs.

  First, consider a case where the switching element of the inverter unit 21b is damaged. When the switching element is damaged and enters the open mode, the voltage decreases or increases at least one of the voltages detected by the first voltage detection units 51U and 51V and the second voltage detection units 52U and 52V. . The voltage monitoring unit 48 detects these abnormal voltages depending on whether the overvoltage threshold Vt (OV) is exceeded or below the low voltage threshold Vt (LV), and outputs “L”. Since “L” is input to the enable input of the comparison unit 46, the comparison unit 46 turns off each switching element regardless of the inputs from the carrier generation unit 44 and the modulated wave generation unit 45. Since the output of the AND circuit 50 is also connected to the control signal input terminal 2c of the DC-DC converter 2, the operation of the DC-DC converter 2 is stopped by the input of the “L” signal.

  Even when the switching element is broken in the short mode, the voltage is decreased or increased by at least one of the voltages detected by the first voltage detection units 51U and 51V and the second voltage detection units 52U and 52V. Therefore, the voltage monitoring unit 48 outputs “L”. Alternatively, the first current detection unit 53U and the second current detection unit 53V can detect a current exceeding the threshold value, and the current monitoring unit 49 outputs “L”. When at least one of the voltage monitoring unit 48 and the current monitoring unit 49 outputs “L”, all the switching elements are turned off via the enable input of the comparison unit 46. The DC-DC converter 2 also stops operating because the control signal input terminal 2c becomes “L”.

  Next, consider the case where the charge storage element is damaged. When the charge storage element is destroyed in the open mode or the short mode, the voltage monitoring is performed when a voltage / current exceeding the threshold value of the voltage monitoring unit 48 and / or the current monitoring unit 49 is detected as described above. Since at least one of the unit 48 and the current monitoring unit 49 outputs “L”, the AND circuit 50 outputs “L”. Therefore, all the switching elements are turned off, and the DC-DC converter 2 stops operating.

  As described above, the power conversion device 10b includes the voltage monitoring unit 48 and the current monitoring unit 49 having a predetermined threshold value in the event of a malfunction such as damage to an internal element, thereby setting the threshold value. When it exceeds or falls below, the switching element can be turned off to protect the power converter 10b. In this case, since the operation of the DC-DC converter 2 connected to the input of the power converter 10b is stopped, the current flowing through the switching element damaged in the short mode can be cut off, and the power converter can be more safely performed. 10b can be protected. The use of a small-sized ceramic capacitor as the charge storage element enables high-density mounting and contributes to a higher output density. However, in the power conversion device 10b of this embodiment, even when the ceramic capacitor is damaged in the short mode. , Can be safe protection.

  When an abnormality occurs in the load 4 instead of the power conversion device 10b itself, for example, when the connection line between the power conversion device 10b and the load 4 is opened, short-circuited, or due to a malfunction of the load 4, Even when the load end of the converter 10b is opened or short-circuited, the power converter 10b can be safely protected as described above.

  In the above description, the control circuit 14b has the voltage monitoring unit 48 and the current monitoring unit 49 separately. For example, the voltage control unit 47 is provided with the threshold value of the voltage monitoring unit 48, and the voltage control unit 47 47 may be used also as the function of the voltage monitoring unit 48. In addition, it is only necessary that the operation of the switching element can be stopped in the overvoltage state or the overcurrent state detected by the voltage monitoring unit 48 or the current monitoring unit 49, and the carrier generation is not limited to the case where the operation of the comparison unit 46 is stopped. The output of the unit 44 may be stopped. Further, the output logic values of the voltage monitoring unit 48 and the current monitoring unit 49 are not limited to those described above, and may be opposite logic values or may be realized by other logic circuit configurations.

  According to the embodiment, a high-power density and high-efficiency power conversion device is provided.

The embodiments of the present invention have been described above with reference to specific examples. However, embodiments of the present invention are not limited to these specific examples. For example, an inverter unit, a filter unit, a main circuit, a high potential side input terminal, a low potential side input terminal, a leg, a first upper switching element, a second upper switching element, and a first lower side included in the power conversion device Regarding the specific configuration of each element such as the switching element, the second lower switching element, the charge storage element, the switching unit, the initial charging unit, the control circuit, the control unit, the changeover switch driving unit, the frequency determining unit, and the voltage detecting unit As long as a person skilled in the art can carry out the present invention by appropriately selecting from the well-known ranges and obtain the same effect, it is included in the scope of the present invention.
Moreover, what combined any two or more elements of each specific example in the technically possible range is also included in the scope of the present invention as long as the gist of the present invention is included.

  In addition, all power conversion devices that can be implemented by a person skilled in the art based on the above-described power conversion device as an embodiment of the present invention are included in the scope of the present invention as long as they include the gist of the present invention. Belonging to.

  In addition, in the category of the idea of the present invention, those skilled in the art can conceive of various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the present invention. .

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1 power generator, 2 DC-DC converter, 2a, 2b output terminal, 2c control signal input terminal, 4 load, 10, 10a, 10b power converter, 12, 12a, 12b main circuit, 14, 14a, 14b control circuit, 16 memory, 18 bus, 20a, 20b inverter input terminal, 21, 21a, 21b inverter unit, 21U, 21V output, 23 filter unit, 24 switching unit, 25 initial charging unit, 36, 37 node, 41 control unit, 42 switching Switch drive unit, 43 Frequency determination unit, 44 Carrier generation unit, 45 Modulated wave generation unit, 46 Comparison unit, 47 Voltage control unit, 48 Voltage monitoring unit, 49 Current monitoring unit, 51U, 51V, 52U, 52V Voltage detection unit ( Resistance element), 53U, 53V current detector, 61, 62 input voltage waveform, 63 modulation factor setting waveform, 64 pseudo load side switch H state waveform, 65 load side switch state waveform, CS1 to CS3 carrier signal, CU1, CU2, CV1, CV2 charge storage element, LG1, LG2 leg, LA1, LA2, UA1, UA2 arm, MW modulation wave, t0 to t4 time , Ts start-up time, T1 initial charge phase, T2 switching phase, T3 output control phase, U1-U3, V1-V3, X1-X3, Y1-Y3 switching element, V + DC-DC converter input voltage

Claims (8)

An inverter unit that converts DC power supplied from a DC power source into AC power,
A first input terminal connected to the high potential output of the DC power supply;
A second input terminal connected to the low potential output of the DC power supply;
A plurality of legs connected between the first input terminal and the second input terminal;
Including
Each of the plurality of legs is
A first upper switching element connected between the first input terminal and the second input terminal;
A second upper switching element connected between the first upper switching element and the first input terminal;
A first lower switching element connected between the first upper switching element and the second input terminal;
A second lower switching element connected between the first lower switching element and the second input terminal;
One end connected between the first upper switching element and the second upper switching element and the other end connected between the first lower switching element and the second lower switching element. A charge storage device having
An output terminal connected between the first upper switching element and the first lower switching element;
Including an inverter unit,
A filter unit connected between the output terminal and a load, and suppressing a harmonic component of the AC power and outputting the load to the load;
An initial charging unit that is connected in parallel with the load and charges the charge storage element in a predetermined period after the DC power supply is activated,
A switching unit that is connected in series with the filter unit between the output terminal and the load, cuts off a path of a current flowing through the initial charging unit after the predetermined period, and flows a current through the load When,
Judging the start and progress of the predetermined period, switching the current path flowing through the initial charging unit and the current path flowing through the load, and a plurality of modulation waves set for each of the plurality of legs, Based on the plurality of carrier signals set in each of the first upper switching element and the second switching element of the plurality of legs, the first upper switching element, the second upper switching element, the first A control circuit for controlling on / off of the lower switching element and the second lower switching element;
The power converter provided with.   2. The power converter according to claim 1, wherein the predetermined period includes a period until an input voltage between the first input terminal and the second input terminal reaches a rated input voltage after the DC power supply is activated. . The initial charging unit includes a pseudo load having a resistance element that consumes lower power than the load;
The switching unit includes a node connected in parallel to the load and the pseudo load, a first switch connected between the load, a first switch connected between the node and the pseudo load. 2 switches, and
In the predetermined period, the control circuit opens the first switch so as not to supply power to the load, closes the second switch, supplies power to the pseudo load, and passes the predetermined period. The power converter according to claim 1 or 2, wherein the second switch is opened later and the first switch is closed.   The control circuit restricts the switching operation of all the switching elements after the predetermined time, opens the second switch, closes the first switch, and restricts the switching operation of all the switching elements. The power conversion device according to claim 3, wherein the power conversion device is released and power supply to the load is started.   The power conversion device according to claim 3 or 4, wherein the first switch and the second switch include MOSFETs, and a plurality of the MOSFETs are connected in parallel. Each of the plurality of legs further includes a voltage detection unit that detects a voltage of the charge storage element,
6. The control unit according to claim 1, wherein the control unit controls a voltage of the charge storage element of each of the plurality of legs based on a detection result of the voltage detection unit of each of the plurality of legs. The power converter described.   6. The power conversion device according to claim 1, wherein each of the plurality of legs further includes a resistance element connected to the charge storage element. Further comprising the DC power supply,
The DC power source includes a control signal input terminal for inputting a signal for performing an operation of generating an output voltage or stopping an operation of generating an output voltage,
The inverter unit includes a current detection unit that is connected between the output terminal and the load and detects a current flowing through the output terminal;
The control circuit has a preset first threshold value, compares the first threshold value with a detection voltage of the voltage detection unit, and the detection voltage is larger than the first threshold value. A voltage monitoring unit that outputs a first stop signal for stopping the DC power supply, a second threshold value set in advance, and detected by the second threshold value and the current detection unit A current monitoring unit that compares a detected current and outputs a second stop signal that stops the DC power supply when the detected current is larger than the second threshold value;
The power converter according to claim 6 or 7, wherein at least one of the first stop signal and the second stop signal is input to the control signal input terminal.

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