JP2010011702A - Power conversion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve distortion in output current which is caused by setting dead time, relating to a power conversion apparatus in which a plurality of single-phase inverters are connected in series. <P>SOLUTION: The power conversion apparatus includes a converter which generates a DC power source (first DC power source) of an inverter 6-1 which outputs a maximum voltage among single-phase inverters provided to an inverter unit 6, a DC/DC converter which generates a DC power source (second DC power source) of inverters 6-2 and 6-3 using the first DC power source, and a control circuit 8 which applies, for control, a gate pulse with the dead time setting to a switching element in the inverter unit 6. The control circuit 8 generates a dead time correction signal based on a target current value and a PWM signal for controlling the switching element in the inverter unit 6, and generates a gate pulse for controlling the inverters 6-2 and 6-3 using an additive output of the dead time correction signal and the PWM signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power converter that converts DC power into AC power and outputs the power.

  A general power conversion device according to the prior art has an inverter circuit therein, and when controlling the output of the power conversion device, each switching element included in the inverter circuit can be controlled. Done. During this control, a period called dead time is provided so that switching elements connected in series in the upper and lower pairs of the inverter circuit (switching elements of the upper and lower arms) do not turn on at the same time. That is, within this dead time period, the switching element of the upper arm and the switching element of the lower arm are not turned on at the same time, and the occurrence of a through current caused by the turning on of both switching elements is prevented. . It is also known that when the switching signal for controlling the switching elements of the upper and lower arms is provided with a dead time, the waveform of the output current includes a distortion component.

  In recent years, a power converter configured to connect a plurality of single-phase inverters that convert DC power into AC power and output the power is known (for example, Patent Document 1).

In the power converter shown in Patent Document 1, a maximum single-phase inverter (3B-INV) using a DC voltage (V _3B ) obtained by boosting a solar voltage by a boost chopper circuit as a DC power source is disposed in the center. Single-phase inverters (1B-INV, 2B-INV) with DC power supplies (V _1B , V _2B ) supplied from the maximum DC power supply (V _3B ) on both sides of the maximum single-phase inverter (3B-INV) The AC side of each single-phase inverter (1B-INV, 2B-INV, 3B-INV) is connected in series, and between the maximum DC power supply ( _V3B ) and DC power supply ( _V1B , _V2B ) A DC / DC converter is arranged and configured to obtain an output voltage by the sum of the voltages generated by the single-phase inverters (1B-INV, 2B-INV, 3B-INV). Incidentally, the DC power source (V _1B, V _2B) supply voltage due to the supply via the respective switching elements in each single-phase inverter from the maximum DC power source _{(V 3B) (1B-INV} , 2B-INV, 3B-INV) Is done.

  In addition, there is a dead time compensator in which dead time compensation in a plurality of inverters connected in parallel is completed with one dead time compensation circuit (for example, Patent Document 2).

International Publication No. 06/090675 Pamphlet JP-A-5-030751

  By the way, there are various techniques for improving the distortion of the output current caused by setting the dead time. However, these technologies are not intended for a power conversion device configured by connecting a plurality of single-phase inverters in series as disclosed in Patent Document 1. In fact, the inventors of the present application have confirmed that the distortion of the output current is not improved when the conventional dead time correction technique is applied to the power conversion device of Patent Document 1.

  The present invention has been made in view of the above, and in a power converter configured to connect a plurality of single-phase inverters in series, improves distortion of output current caused by the setting of dead time. It is an object of the present invention to provide a power conversion device that can do this.

  In order to solve the above-described problems and achieve the object, a power converter according to the present invention has a plurality of single-phase inverters that convert a DC voltage into an AC voltage and output the AC voltage, and an AC side terminal is connected in series. In addition, an inverter unit that outputs a summed voltage generated by each of the generated voltages of the plurality of single-phase inverters, and a DC voltage from an external DC power source is boosted or lowered to output the maximum voltage of the single-phase inverters that constitute the inverter unit. A converter that generates a first DC power source that operates as a DC power source for the first inverter, and a first input that uses the first DC power source as a DC input to form one or more single-phase inverters other than the first inverter. A DC / DC converter that generates a second DC power source that operates as each DC power source for the two inverters, and the inverter unit And a control circuit that controls the switching element by applying a gate pulse in which a dead time is set. The control circuit includes current information related to an output current output from the inverter unit, and switching in the inverter unit. The dead time is corrected using a dead time correction signal generated based on a PWM signal for controlling the element.

  According to the power conversion device of the present invention, the dead time correction signal generated based on the current information related to the output current output from the inverter unit and the PWM signal for controlling the switching element in the inverter unit is used. Since the dead time is corrected, there is an effect that the distortion of the output current caused by the setting of the dead time can be improved.

  Exemplary embodiments of a power conversion device suitable for the present invention will be described below in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

(Configuration of power converter)
FIG. 1 is a diagram illustrating a configuration of a power conversion device according to an embodiment of the present invention. More specifically, FIG. 1 illustrates a case where the power conversion device according to the embodiment is applied to a power generation system linked to a commercial system. It is a figure which shows an example.

  In FIG. 1, a solar cell module 11 that is an external DC power source is connected to an input terminal 20 that is a DC input terminal of the power converter 2, and an output terminal 22 that is an AC output terminal has a frequency of 50 Hz or 60 Hz. A commercial system (hereinafter simply referred to as “system”) 3 for supplying AC power is connected. In the power conversion device 2 configured in this way, the DC power supplied from the solar cell module 11 is converted into AC power, and surplus power is regenerated to the grid 3 side through interconnection with the grid 3, and the insufficient power is Supplied from system 3 side.

  As a configuration for realizing the functions described later including the functions described above, the power conversion device 2 according to the present embodiment includes a converter 4, an inverter unit 6, an output filter circuit 7, a control circuit 8, and a DC / DC converter 12. Etc.

  The converter 4 boosts or steps down the DC voltage from the solar cell module 11 and converts it to a predetermined DC voltage. Note that when it is assumed that the DC voltage input to the converter 4 is always smaller than the DC voltage output from the converter 4, it is sufficient to have the function of boosting only.

  The inverter unit 6 includes inverters 6-1 to 6-3 that are a plurality of single-phase inverters (three are exemplified in FIG. 1).

  At the DC side terminal of the inverter 6-1 (terminal on the converter 4 side), the bus capacitor 5-1 that functions as the first DC power source connects the output terminal of the converter 4 and the DC side terminal of the inverter 6-1. The DC power from the solar cell module 11 is smoothed and stored in the bus capacitor 5-1 via the converter 4.

  At each DC terminal of the inverters 6-2 and 6-3 (terminal on the DC / DC converter 12 side), the bus capacitors 5-2 and 5-3 functioning as the second DC power supply are connected to the DC of each single-phase inverter. DC buses connected to the side terminals are respectively connected to the bus capacitors 5-2 and 5-3 from the DC / DC converter 12 which operates using the DC power stored in the bus capacitor 5-1 as a DC input. DC power is smoothed and accumulated respectively.

  In the AC side terminal (terminal on the system 3 side) of the inverter 6-1, the inverter 6-2 is connected to one of the AC side terminals, and the inverter 6-3 is connected to the other side of the AC side terminal.

  In the AC side terminal of the inverter 6-2, the inverter 6-1 is connected to one of the AC side terminals, and one of the input side terminals of the output filter circuit 7 is connected to the other side of the AC side terminal. In the side terminal, the inverter 6-1 is connected to one of the AC side terminals, and the other of the input side terminals of the output filter circuit 7 is connected to the other of the AC side terminals.

  The control circuit 8 generates and outputs signals necessary for controlling and driving the converter 4, the inverters 6-1 to 6-3 constituting the inverter unit 6, and the DC / DC converter 12.

(Detailed configuration of power converter)
FIG. 2 is a diagram showing a more detailed configuration of the inverter unit 6 and the control circuit 8 which are the main components of the power conversion device according to the present embodiment. In the configuration shown in FIG. FIG. 5 is a diagram illustrating a circuit configuration from ˜5-3 to an output filter circuit 7 and a detailed configuration of a control circuit 8;

  In FIG. 2, inverters 6-1 to 6-3 constituting the inverter unit 6 include a plurality of self-extinguishing semiconductor switching elements, for example, IGBTs, in which diodes are connected in antiparallel.

  The inverter unit 6 includes two self-extinguishing semiconductor switching elements, for example, IGBTs, which are diodes connected in antiparallel as shorting switches for short-circuiting between the AC terminals 24a and 24b of the inverter 6-1. Are connected in series to the inverter 6-1.

  In the switch circuit 13, a terminal 30a that is one terminal of the switch circuit 13 and is connected to the AC side terminal 24a of the inverter 6-1 is connected to the AC side terminal 26b of the inverter 6-2. The terminal 30b that is the other terminal of the switch circuit 13 and is connected to the AC side terminal 24b of the inverter 6-1 is connected to the AC side terminal 28a of the inverter 6-3.

  The inverter unit 6 can output a non-zero or zero voltage as an output voltage by the action of the switch circuit 13.

  The control circuit 8 includes a Td (dead time) correction value determination unit 9, a first gate pulse generation circuit 10-1, a second gate pulse generation circuit 10-2, and an addition processing unit 14. The Td correction value determination unit 9 generates a dead time correction value (dead time correction signal) based on the PWM signal and the target current value. The dead time correction value generated by the Td correction value determination unit 9 and the PWM signal are input to the addition processing unit 14. The first gate pulse generation circuit 10-1 generates and outputs a gate pulse for controlling the inverter 6-1 and the switch circuit 13 based on the PWM signal. The second gate pulse generation circuit 10-2 generates a gate pulse for controlling the inverter 6-2 and the inverter 6-3 based on the output of the addition processing unit 14, that is, the addition output of the dead time correction value and the PWM signal. Is generated and output.

  Here, the voltages of the bus capacitors 5-1 to 5-3 will be described. The voltage of the bus capacitor 5-1 that is the DC input source of the inverter 6-1 is the voltage of the bus capacitor 5-2 and 5-3 that is the DC input source of the inverters 6-2 and 6-3 that are other inverters. Usually bigger than. On the other hand, as for the voltage of the bus capacitor 5-2 and the voltage of the bus capacitor 5-3, either may be large, or both voltages may be equal. That is, assuming that the voltages (equal to the bus voltage in each inverter) of the bus capacitors 5-1 to 5-3 when the inverter unit 6 is operating are V1, V2, and V3, V1 is between these voltages. > V2 and V1> V3.

  These inverters 6-1 to 6-3 can generate positive, negative, and zero voltages as outputs, and the inverter unit 6 outputs a voltage as a sum total of these generated voltages by gradation control. To do. This output voltage is smoothed by, for example, an output filter circuit 7 that combines a reactor and a capacitor, and a desired AC voltage is supplied to the system 3. In addition, since more detailed operation | movement is disclosed appropriately by the gazette of above-mentioned patent document 1, further detailed description here is abbreviate | omitted.

(Main operation of power converter)
Next, the operation of the main part of the power conversion device according to the present embodiment will be described with reference to the drawing of FIG. Here, FIG. 3 is a waveform diagram showing a state of dead time correction of the power conversion device according to the present embodiment. The correspondence relationship between the waveforms shown in FIGS. 2A to 2J and the configuration diagram of FIG. 2 is as follows.

(A) Output voltage of inverter 6-1 (corresponding to output voltage between AC terminals 24a and 24b)
(B) Output voltage of inverters 6-2 and 6-3 (corresponding to voltages generated by inverters 6-2 and 6-3)
(C) Waveform obtained by smoothing output voltages of inverters 6-2 and 6-3 (d) Waveform obtained by adding output voltages of inverters 6-1 to 6-3 (corresponding to input waveform to output filter circuit 7)
(E) Target current value (input to Td correction value determination unit 9)
(F) Polarity of target current value (g) Polarity of output voltage of inverters 6-2 and 6-3 (h) Dead time correction value (corresponding to output of Td correction value determination unit 9)
(I) Output current after passing through the output filter circuit (corresponding to the output of the output filter circuit 7 when dead time correction is not performed)
(J) Output current after passing through the output filter circuit (corresponding to the output of the output filter circuit 7 when dead time correction is performed)

  The waveforms shown in FIGS. 3A and 3B are typical output voltage waveforms when the power converter of FIG. 2 is operated and a sine wave current is supplied to the system 3. As can be understood from the waveform shown in FIG. 3 (a), since the inverter 6-1 is subjected to low-frequency switching control, the output voltage of the inverter 6-1 is almost affected by the dead time. Absent. On the other hand, as can be understood from the waveform shown in FIG. 3B, the inverters 6-2 and 6-3 are affected by dead time because high-frequency switching control is performed. When the waveform shown in FIG. 3 (b) is expressed by a smoothed waveform, the waveform shown in FIG. 3 (c) is obtained, and FIG. 3 (d) is obtained by adding FIG. 3 (a) and FIG. 3 (b). Is a waveform input to the output filter circuit 7.

  The Td correction value determination unit 9 receives the target current value (FIG. 3 (e)) and the PWM signal used when controlling the inverters 6-2 and 6-3. The Td correction value determination unit 9 determines each polarity of the input target current value and the PWM signal (FIG. 3 (f) and FIG. 3 (g)). The polarity of the PWM signal for controlling the inverters 6-2 and 6-3 and the polarity of the output voltage of the inverters 6-2 and 6-3 are the same or equivalent. The Td correction value determination unit 9 performs a determination process related to the dead time correction value from the obtained polarity determination data.

  Here, when the polarity of the target current value and the polarity of the PWM signal are the same, a positive dead time correction value is output. When the polarity of the target current value and the polarity of the PWM signal are different, a negative dead time correction value is output. Is output (FIG. 3 (h)).

  The dead time correction value is input to the addition processing unit 14, added to the PWM signal, and input to the second gate pulse generation circuit 10-2. The dead time correction value is input only to the second gate pulse generation circuit 10-2 and is not input to the second gate pulse generation circuit 10-1. This is because the output voltage of the inverter 6-1 is hardly affected by the dead time because low-frequency switching control is performed on the inverter 6-1.

  The inverter 6-1 is controlled by the gate pulse from the first gate pulse generating circuit 10-1, the inverters 6-2 and 6-3 are controlled by the gate pulse from the second gate pulse generating circuit 10-2, The inverter unit 6 generates an alternating voltage. The output of the inverter unit 6 passes through the output filter circuit 7 and is smoothed, and power is supplied to the system 3.

  When the Td correction value determination unit 9 is not provided, that is, when dead time correction is not performed, the output current waveform after passing through the output filter circuit 7 is distorted as shown in FIG. On the other hand, when dead time correction is performed, the distortion of the output current waveform after passing through the output filter circuit 7 is eliminated or reduced, as shown in FIG. An output current waveform (sine wave) that is eliminated or reduced is obtained.

  In the control circuit 8 according to the present embodiment, the configuration in which the target current value and the PWM signal are input to the Td correction value determination unit 9 is illustrated, but the configuration is not limited to this configuration. For example, instead of the target current value, it is also possible to use information relating to the output current to the system 3 (the output current of the output filter circuit 7). In this case, information on the current value of the output current may be used, or phase information on the output current may be used. In consideration of smoothing the current output from the inverter unit 6 by a filter circuit different from the output filter circuit 7, the information input to the Td correction value determination unit 9 is output from the inverter unit 6. Any information may be used as long as the information is related to the current.

  In the control circuit 8 of the present embodiment, the dead time correction value generated by the Td correction value determination unit 9 is only used as a correction signal for correcting the gate pulse for controlling the inverter 6-2 and the inverter 6-3. Although used, it is of course possible to use it as a correction signal for correcting the gate pulse for controlling the inverter 6-1.

  As described above, according to the power conversion device according to the present embodiment, based on the current information related to the output current output from the inverter unit 6 and the PWM signal that controls the switching elements in the inverter unit 6. Since the dead time is corrected using the generated dead time correction signal, it is possible to improve distortion of the output current caused by the setting of the dead time.

  As described above, the power conversion device according to the present invention is useful as an invention that can improve the distortion of the output current caused by the setting of the dead time.

It is a figure which shows the structure of the power converter device concerning embodiment of this invention. It is a figure which shows a more detailed structure than the inverter unit and control circuit which are the main components of the power converter device concerning this Embodiment. It is a wave form diagram which shows the mode of the dead time correction | amendment of the power converter device concerning this Embodiment.

Explanation of symbols

2 Power Converter 3 System 4 Converter 5 Bus Capacitor 6 Inverter Units 6-1 to 6-3 Inverter 7 Output Filter Circuit 8 Control Circuit 9 Td Correction Value Determination Unit 10-1 First Gate Pulse Generation Circuit 10-2 Second Gate pulse generation circuit 11 Solar cell module 12 DC / DC converter 13 Switch circuit 14 Addition processing unit 20 Input end 22 Output end 24a, 24b, 26a, 26b, 28a, 28b AC side terminal 30a, 30b terminal

Claims (3)

An inverter unit that has a plurality of single-phase inverters that convert a DC voltage into an AC voltage and outputs the same, and that outputs a summed voltage generated by each of the plurality of single-phase inverters connected in series with each other;
A converter that generates a first DC power source that operates as a DC power source for a first inverter that boosts or lowers a DC voltage generated by an external DC power source and outputs a maximum voltage among the single-phase inverters constituting the inverter unit;
DC / DC for generating a second DC power source that operates as each DC power source for a second inverter that constitutes one or more single-phase inverters other than the first inverter, with the first DC power source as a DC input A converter,
A control circuit for applying and controlling a gate pulse in which a dead time is set to the switching element in the inverter unit;
With
The control circuit calculates the dead time using a dead time correction signal generated based on current information related to an output current output from the inverter unit and a PWM signal for controlling a switching element in the inverter unit. The power converter characterized by correcting.   The power conversion apparatus according to claim 1, wherein the dead time correction signal is output as a correction signal for a dead time set in a gate pulse for controlling the second inverter.   The power conversion apparatus according to claim 1 or 2, wherein the information on the output current output by the inverter unit is a target current value given by the control circuit.

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