JP5410551B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device that converts direct-current power into alternating-current power, for example, a power conversion device that is used in a power conditioner that links a solar power generation device to a power system.

  In the conventional power converter, the AC output terminal of the second inverter is connected in series to one of the AC output terminals of the single-phase first single-phase inverter, and the AC output terminal of the third inverter is connected in series to the other. Some are connected to obtain an AC output voltage as a sum. The first single-phase inverter is connected to a first DC source having a first DC voltage obtained by boosting the DC voltage of the solar cell with a chopper circuit, and the second inverter is converted from the first DC source by the former converter. The third inverter is connected to the third DC source having the third DC voltage converted from the first DC source by the second converter. , Each receiving power supply. Since the first single-phase inverter outputs only for a specific period, the output is a pulse waveform at the commercial frequency, and the output voltage waveform of the power converter is a sine wave AC and the first sine wave AC. The second and third inverters output the difference from the output of the single-phase inverter (see, for example, Patent Document 1).

International Publication WO2006-090674

  The conventional power converter is configured as described above, and the first single-phase inverter performs pulse output, and the power output by the first single-phase inverter during the output period becomes the output power of the power converter. If this condition is satisfied, the power balance of the second and third inverters becomes zero and the voltage is maintained. However, it is necessary to give the second and third inverters an AC output command value that can be output by the DC bus voltage, while the first single-phase inverter outputs the output by receiving the limitation. Depending on the conditions, there is a shortage in the power balance. The shortage is compensated by the second and third inverters. For this reason, in the conventional power converter, as described above, the second and third inverters are configured to receive power supply via the first and second converters connected to the first DC source. Yes. However, there is a problem that separately using a conversion device such as the former and the second converter leads to an increase in cost and loss.

  The present invention has been made to solve the above-described problems, and an object thereof is to obtain a power conversion device that is inexpensive and has low power loss.

In the power converter according to the present invention,
A power conversion device including a first inverter, a second inverter, and a control device,
The first inverter is connected between the positive and negative terminals of a DC power source, converts the power of the DC power source into AC and outputs it through an AC output line,
The second inverter has a capacitor and a single-phase inverter circuit, the DC side of the single-phase inverter circuit is connected to the capacitor, and the AC side is connected in series to the AC output line,
The control device rises when the sine wave AC output voltage command becomes larger than a predetermined value, and outputs a pulse of one pulse that falls when the sine wave AC voltage command becomes less than the predetermined value at every half cycle of the AC output voltage command. The first inverter is controlled by transmitting a main voltage pulse command so that the first output is output as the first voltage, and the first voltage based on the compensation voltage command issued based on the AC output voltage command and the output voltage of the first inverter. The output voltage of the inverter 2 is subjected to pulse width modulation control to output the sum of the output voltages of the first and second inverters as a sine wave AC voltage, and the voltage of the capacitor in response to the compensation voltage command If the first period, which is a period during which the output voltage of the second inverter is insufficient, is present before and after the period during which the main voltage pulse is to be output. During the first period, the output voltage of the first inverter is output by pulse width modulation control to compensate for the insufficient output voltage and the second period during the period in which the main voltage pulse is to be output. The power energy supplied from the first inverter in the first period is reduced by reducing the power energy output from the first inverter by performing pulse width modulation control on the output voltage of the first inverter. It was designed to offset.

In the power converter according to the present invention,
A power conversion device including a first inverter, a second inverter, and a control device,
The first inverter is connected between the positive and negative terminals of a DC power source, converts the power of the DC power source into AC and outputs it through an AC output line,
The second inverter has a capacitor and a single-phase inverter circuit, the DC side of the single-phase inverter circuit is connected to the capacitor, and the AC side is connected in series to the AC output line,
The control device rises when the sine wave AC output voltage command becomes larger than a predetermined value, and outputs a pulse of one pulse that falls when the sine wave AC voltage command becomes less than the predetermined value at every half cycle of the AC output voltage command. The first inverter is controlled by transmitting a main voltage pulse command so that the first output is output as the first voltage, and the first voltage based on the compensation voltage command issued based on the AC output voltage command and the output voltage of the first inverter. The output voltage of the inverter 2 is subjected to pulse width modulation control to output the sum of the output voltages of the first and second inverters as a sine wave AC voltage, and the voltage of the capacitor in response to the compensation voltage command If the first period, which is a period during which the output voltage of the second inverter is insufficient, is present before and after the period during which the main voltage pulse is to be output. During the first period, the output voltage of the first inverter is output by pulse width modulation control to compensate for the insufficient output voltage and the second period during the period in which the main voltage pulse is to be output. The power energy supplied from the first inverter in the first period is reduced by reducing the power energy output from the first inverter by performing pulse width modulation control on the output voltage of the first inverter. Because it was designed to offset
An inexpensive and low-power-conversion power converter can be obtained.

It is a block diagram which shows the structure of the power converter device which is Embodiment 1 of this invention. It is a wave form diagram which shows the output voltage of a 1st and 2nd single phase inverter. It is a wave form diagram which shows the change of the entrance / exit of the electric power energy to a 2nd single phase inverter. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is a PAD figure of the control apparatus of FIG. It is a block diagram of the power converter device which is Embodiment 2. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is a PAD figure of the control apparatus of FIG. FIG. 6 is a configuration diagram of a power conversion device according to a third embodiment. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is explanatory drawing for demonstrating operation | movement of a power converter device. It is a PAD figure of the control apparatus of FIG. It is a block diagram of the power converter device which is Embodiment 4. FIG. 20 is a PAD diagram of the control device of FIG. 19. FIG. 10 is a configuration diagram of a power conversion device according to a fifth embodiment. It is a wave form diagram for demonstrating the effect at the time of shifting the phase of the triangular wave carrier of a 1st and 2nd single phase inverter 180 degree | times. FIG. 10 is a configuration diagram of a power conversion device according to a sixth embodiment. It is a block diagram of the modification of the power converter device which is Embodiment 6. FIG. It is a block diagram of the other modification of the power converter device which is Embodiment 6. FIG.

Embodiment 1 FIG.
1 to 10 show a first embodiment for carrying out the present invention. FIG. 1 is a configuration diagram showing a configuration of a power converter, and FIG. 2 is a diagram of first and second single-phase inverters. FIG. 3 is a waveform diagram showing a change in power energy in and out of the second single-phase inverter. 4 to 9 are explanatory diagrams for explaining the operation of the power conversion device, and FIG. 10 is a PAD diagram (PROBLEM ANALYSIS DIAGRAM) of the control device of FIG.

  In FIG. 1, a first single-phase inverter 3 as a first inverter has a single-phase full bridge circuit 3b and AC output lines 3c and 3d. The full bridge circuit 3b is composed of four field effect transistors (FETs) 3a which are switching means. The second single-phase inverter 4 as the second inverter includes a single-phase full bridge circuit 4 b and a capacitor 5. The single-phase full bridge circuit 4b is composed of four field effect transistors (FETs) 4a as switching means. As the switching means, not only the FET but also a semiconductor element having a self-extinguishing capability such as an IGBT or the like can be appropriately used. The capacitor 5 functions as a DC power source on the single-phase inverter side that accumulates electric charges. A capacitor 2 is connected to a DC power source 1 such as a solar battery, and DC power is supplied to the first single-phase inverter 3. Capacitor 2 smoothes the voltage of the DC bus.

  The AC output side of the second single-phase inverter 4 is connected in series to one AC output line 3 c of the first single-phase inverter 3. The control device 10 includes a threshold voltage adjusting device 11 and a processing device 12 and controls the first single-phase inverter 3 and the second single-phase inverter 4. The threshold voltage adjusting device 11 includes a subtractor 111 and a PI control device 112. As the processing apparatus 12, a DSP (DIGITAL SIGNAL PROCESSOR), an FPGA (FIELD PROGRAMMATE GATE ARRAY), or the like is used. The power conversion device 100 is configured as described above. Then, a sine wave single-phase AC output voltage Vo is applied from the power conversion device 100 to a load 7 such as a power system through the smoothing filter 6.

  Next, the operation will be described. Under ideal conditions, the waveform of the output voltage V1 of the first single-phase inverter 3 is a pulse waveform that rises at time t1 and falls at time t2, as shown in FIG. The control device 10 transmits a pulse-like target voltage command V1REF (FIG. 2A) as a main voltage pulse command to the first inverter 3. The target voltage command V1REF has a main voltage pulse rise command S1 and a fall command S1. The rise command S1 of the main voltage pulse is the main output voltage V1 at the time point t1 when the sine wave AC output voltage command VoREF becomes equal to or higher than a first threshold voltage VTHB1 (constant or variable, which will be described later) as a predetermined value. It is transmitted so that a voltage pulse rises. The falling command S2 is transmitted so that the main voltage pulse falls at the time t2 when the AC output voltage command VoREF becomes smaller than the first threshold voltage VTH1. The first inverter 3 outputs the output voltage V1 as the main voltage pulse at a rate of one pulse with respect to the half cycle of the sinusoidal AC output voltage command VoREF in response to the target voltage command V1REF. The period from when the main voltage pulse rising command S1 is transmitted until the falling command S2 is transmitted is a period during which the main voltage pulse should be output in the present invention.

  The first threshold voltage VTHB1 can be obtained from the voltage VC1 of the capacitor 2 that is the DC power supply on the single-phase inverter side and the effective value VoRMS of the AC output voltage Vo of the power converter 100. For example, when the output power factor is 1, the power Pmain output from the first single-phase inverter 3 only needs to match the total output power Po of the power converter. Therefore, the AC voltage value at the phase θth where the following equation (1) holds is the threshold voltage VTHB1. Here, Vp is the peak voltage of the sine wave AC voltage, and Ip is the peak current of the sine wave AC current.

  The control device 10 gives an output voltage command V2REF as a compensation voltage command to the second single-phase inverter 4 so that the AC output voltage Vo of the power conversion device 100 becomes a sine wave, as shown in FIG. Output voltage V2 is output by the PWM control method. The output voltage command V2REF is a command for the voltage to be output from the second single-phase inverter 4. The output voltage command V2REF is output to the second single-phase inverter 4 so as to correct the difference based on the difference between the sinusoidal AC output voltage command VoREF and the output voltage V1 of the first single-phase inverter 3. Is done. The AC side of the second single-phase inverter 4 is connected in series to the AC output line 3 c of the first single-phase inverter 3. Therefore, the output voltage V1 of the first single-phase inverter 3 and the output voltage V2 of the second single-phase inverter 4 are added, and a sine wave AC output voltage Vo is output from the power converter 100. The output voltage command V2REF may be output based on the difference between the sinusoidal AC output voltage command VoREF and the target voltage command V1REF of the first single-phase inverter 3, and there is substantially no difference.

  The second single-phase inverter 4 is different from a general PWM inverter that has only positive power. For example, when the power factor of the AC output is 1, as shown in FIG. 3, the output power P1 of the second single-phase inverter 4 has a positive polarity and a negative polarity. When the polarity is positive, the capacitor 5 of the second single-phase inverter 4 is discharged and electric energy is released. When it is negative, power energy is supplied and charged. If the output period of the first single-phase inverter 3 is controlled so that these positive and negative power energies are the same, it is necessary to prepare a separate power source such as a conventional converter for the second single-phase inverter 4. There will be no. In other words, if the balance of the power energy of the second single-phase inverter 4 is controlled to be zero, there is no need to separately prepare a power source like the conventional converter for the second single-phase inverter 4. Become.

  By the way, in practice, the electrical characteristics of the direct-current power source 1 such as a solar cell as an input and the electrical characteristics of the load 7 typified by the power system as an output are not always the same, and the threshold voltage VTHB1 also changes depending on the conditions. For example, as shown in FIG. 4A, consider an operation at a time t1 when the AC voltage is positive and the rising point of the main voltage pulse output of the first single-phase inverter 3 is reached. The time point t1 is a time point at which the rising command S1 of the main voltage pulse of the target voltage command V1REF should be transmitted to the first single-phase inverter 3, and is also a time point at which the main voltage pulse should rise. The output voltage command V2REF of the second single-phase inverter 4 is higher than the voltage VC2 between the terminals of the capacitor 5, and a period Ta during which the second single-phase inverter 4 cannot output may occur before time t1. . In this case, since the output voltage command V2REF is higher than the voltage VC2 between the terminals of the capacitor 5 in the period Ta, the second single-phase inverter 4 is short of the output voltage of the second single-phase inverter 4. Cannot output. Therefore, the control device 10 performs control so that the first single-phase inverter 3 partially performs high-frequency switching operation by PWM control as shown in FIG. Compensates for output voltage. The first single-phase inverter 3 compensates for the output voltage that is insufficient in the period Ta, so that the power conversion apparatus 100 outputs the sine wave-shaped AC output voltage Vo. The period Ta is a first period in which the voltage of the capacitor 5 is insufficient with respect to the compensation voltage command V2REF in the present invention and the output voltage V2 of the second inverter 4 is insufficient. The period Ta is also an output impossible period in which the output voltage of the second single-phase inverter 4 is insufficient.

  However, in this case, the first single-phase inverter 3 outputs power energy in the period Ta in which the normal output is not performed. For this reason, the output becomes excessive, and the capacitor 5 of the second single-phase inverter 4 is charged excessively. Therefore, as shown in FIG. 6A, the first single-phase inverter 3 performs high-frequency switching control by PWM control during the period Tb (details will be described later) to reduce the output, It adjusts so that the electric power energy which a 1st single phase inverter outputs becomes the output electric power required for a power converter device, and prevents excessive output. The period Tb is the second period of the present invention. The period Tb is a period after the time point t1, is a period during which the first inverter 3 was supposed to output the main voltage pulse, and is also a power adjustment PWM period for decreasing the output. Note that the start point of the period Tb is a time point t1 (see FIG. 5A) when the AC output voltage command VoREF for the first single-phase inverter 3 becomes larger than the first threshold voltage VTHB1. This time is also the end point of the period Ta.

  The period Tb is set as follows. Due to the switching operation of the first single-phase inverter 3 in the period Ta (see FIG. 5A), the power energy output from the first single-phase inverter 3 becomes excessive, and the voltage VC2 of the capacitor 5 becomes the predetermined capacitor voltage. When the target voltage VC2REF is exceeded, a second threshold voltage VTHB2 that is higher than the reference first threshold voltage VTHB1 by a control amount β as a predetermined control amount is obtained. A method for obtaining the control amount β (see FIG. 6A) will be described later. When the AC output voltage command VoREF becomes larger than the second threshold voltage VTHB2, the first single-phase inverter 3 starts outputting the main voltage pulse as usual. This time is the end point of the period Tb. Note that this period Tb is originally an initial part of the rise of the main voltage pulse, and PWM control is performed in this initial part.

  In the period Tb, a difference Dp (a negative value) between the power energy (power amount) when the first single-phase inverter 3 is switched by PWM control in the period Tb and the power energy when the first single-phase inverter 3 is not switched is a negative value in the period Ta. The process ends when the power energy Pg supplied from the first single-phase inverter 3 becomes the same. That is, the process ends when the power energy difference Dp and the power energy Pg are offset. In this embodiment, as shown in the waveform of the output voltage V2 in FIG. 6A, the operation of the second single-phase inverter 4 is stopped during the period Ta and the period Tb, and the supply of voltage is not performed. not going. If the voltage VC2 of the capacitor 5 of the second single-phase inverter 4 has dropped below the target voltage VC2REF for some reason, such as load fluctuation, the threshold voltage is set to the first threshold voltage VTHB1 regardless of the above. And the capacitor 5 of the second single-phase inverter 4 may be charged.

  The operation at time t2 when the main voltage pulse falls is the same. That is, as shown in FIG. 4B, after the time point t2, when the period Ta1 in which the output voltage command V2REF of the second single-phase inverter 4 is higher than the voltage VC2 of the capacitor 5 occurs, the period Ta1 In FIG. 5, the control device 10 performs control for partially performing high-frequency switching by PWM control on the first single-phase inverter 3 as shown in FIG. The control device 10 causes the first single-phase inverter 3 to partially perform a high-frequency switching operation by PWM control to compensate for an output voltage that is insufficient in the period Ta1, and the power conversion device 100 has a sinusoidal AC output. The voltage Vo is output. In this case, since the first single-phase inverter 3 outputs power energy in the period Ta1 during which normal output is not performed, the output is excessive, and the capacitor 5 of the second single-phase inverter 4 is charged excessively. Therefore, as shown in FIG. 6B, the control device 10 PWM-controls the output voltage of the first inverter only during a period Tb1 (details will be described later) as a second period before the time t2. Reduce the output power energy.

  The control device 10 cancels the amount of power energy supplied from the first inverter 3 in the period Ta1 by reducing the power energy output by PWM control of the output voltage of the first inverter. Note that the time point t2 is a time point at which a falling command of the main voltage pulse of the target voltage command V1REF should be transmitted to the first single-phase inverter 3, and also a time point at which the main voltage pulse should fall (FIG. 2 ( a)). The period Ta1 is a period during which the second single-phase inverter 4 cannot output because the output voltage command V2REF is higher than the voltage VC2 between the terminals of the capacitor 5 and the output voltage of the second single-phase inverter 4 is insufficient. . The period Ta1 is a first period in which the voltage of the capacitor 5 is insufficient with respect to the compensation voltage command V2REF in the present invention and the output voltage V2 of the second inverter 4 is insufficient. The period Tb is also a period during which the first single-phase inverter 3 should have continued to output the main voltage pulse.

  The setting of the period Tb1 that is the power adjustment PWM period is performed in the same manner as the setting of the period Tb in FIG. In the period Tb1, a difference Dp2 (a negative value) between the power energy when the first single-phase inverter 3 is switched by PWM control in the period Tb1 and the power energy when the first single-phase inverter 3 is not switched is a first single value in the period Ta1. The power energy Pg2 supplied from the phase inverter 3 is set to be the same. That is, the difference Dp2 and the power energy Pg2 are set so as to cancel each other. In this embodiment, as shown in the waveform of the output voltage V2 in FIG. 6B, in the period Ta1 and the period Tb1, the operation of the second single-phase inverter 4 is stopped, and the voltage supply is performed. Not. If the DC voltage VC2 of the second single-phase inverter 4 is lower than the target voltage VC2REF for some reason, such as a load change, the threshold voltage is set higher than the first threshold voltage VTHB1 regardless of the above. And the capacitor 5 of the second single-phase inverter 4 may be charged.

  Further, as shown in FIG. 7A, there may occur a period Tc in which the voltage VC2 of the capacitor 5 is insufficient with respect to the compensation voltage command V2REF after the first single-phase inverter 3 after the time point t1. The period Tc is a first period in which the voltage of the capacitor 5 is insufficient with respect to the compensation voltage command V2REF in the present invention and the output voltage V2 of the second inverter 4 is insufficient. In this case, as shown in FIG. 8A, the control device 10 needs to perform PWM control on the output voltage of the first single-phase inverter 3 to compensate (supply) the voltage. However, since the first single-phase inverter 3 performs a switching operation by PWM control in the period Tc, the power energy output by the first single-phase inverter 3 is reduced. When the power energy output from the first single-phase inverter 3 decreases, the voltage VC2 of the capacitor 5 of the second single-phase inverter 4 decreases. Therefore, when the voltage VC2 of the capacitor 5 of the second single-phase inverter 4 is lower than the target voltage VC2REF, the control device 10 displays the output AC voltage command value VoREF (the output voltage V2 of the second single-phase inverter 4) as a graph. The first single-phase inverter 3 starts PWM control when it becomes higher than a third threshold voltage VTHB3 (described later) as in 9 (a). This point is the start point of the PWM control period Td (FIG. 9A) for power adjustment as the third period. Note that the third threshold voltage VTHB3 is a value lower than the first threshold voltage VTHB1 by the control amount β (described above).

  In the period Td, the power energy supplied by the switching of the first single-phase inverter 3 in the period Td cancels the power energy that has become insufficient due to the switching of the first single-phase inverter 3 in the period Tc. Set the time to be a value. If the DC voltage VC2 of the second single-phase inverter 4 has become higher than the target voltage VC2REF for some reason such as load fluctuation, the threshold voltage is increased regardless of the above, and the second single-phase inverter 4 The capacitor 5 of the phase inverter 4 may be discharged.

  The operation at the time point t2 when the main voltage pulse falls is the same as shown in FIG. 7B. That is, as shown in FIG. 7B, before the time point t2, when the period Tc1 in which the output voltage command V2REF of the second single-phase inverter 4 is higher than the voltage VC2 of the capacitor 5 occurs, In this period Tc1, the control device 10 performs control for causing the first single-phase inverter 3 to partially perform a high-frequency switching operation by PWM control as shown in FIG. 8B, and outputs that are insufficient in the period Tc1. Compensate for voltage. The control device 10 compensates for the insufficient output voltage so that the power conversion device 100 outputs the AC output voltage Vo having a sine wave shape. In this case, the output energy is reduced because the first single-phase inverter 3 performs a high-frequency switching operation by PWM control in the period Tc1 for normal output. When the output energy decreases, the output becomes insufficient, and the voltage of the capacitor 5 of the second single-phase inverter 4 decreases. Therefore, in the control device 10, as shown in FIG. 9B, the first single-phase inverter 3 performs PWM control on the output voltage of the first inverter only for the period Td1 as the fifth period after the time point t2. Thus, the decrease in the power energy supplied from the first inverter 3 in the period Tc1 is offset by increasing the output power energy. The period Tc1 is a first period in which the voltage of the capacitor 5 is insufficient with respect to the compensation voltage command V2REF in the present invention and the absolute value of the output voltage V2 of the second inverter 4 is insufficient.

  Note that the setting of the period Td1 is performed in the same manner as the setting of the period Td in FIG. In the period Td1, the difference between the power energy when the first single-phase inverter 3 is switched by PWM control in the period Tc1 and the power energy when the first single-phase inverter 3 is not switched is supplied from the first single-phase inverter 3 in the period Td1. Set to be the same as the power energy. In this embodiment, as shown in the waveform of the output voltage V2 in FIG. 9B, the operation of the second single-phase inverter 4 is stopped during the period Tc1 and the period Td1, and the voltage supply is performed. Not. If the voltage VC2 of the capacitor 5 of the second single-phase inverter 4 has dropped below the target voltage VC2REF for some reason, such as load fluctuation, the threshold voltage is set to the first threshold voltage VTHB1 regardless of the above. And the capacitor 5 of the second single-phase inverter 4 may be charged.

  In the first embodiment, the second single-phase inverter 4 is stopped while the first single-phase inverter 3 is performing high-frequency switching by PWM control. For this reason, the output voltage V1 of the first single-phase inverter 3 becomes the AC output voltage Vo of the power conversion device 100 as it is, and instead of the second single-phase inverter 4, the first single-phase inverter 3 to the power conversion device 100 A voltage is output. Control such as P control and PI control may be used to determine the control amount β of the threshold voltage VTHB1. In this embodiment, PI control is performed using the threshold voltage adjustment device 11 shown in FIG. In FIG. 1, the voltage VC2 of the capacitor 5 of the second single-phase inverter 4 and the target voltage VC2REF of the capacitor 5 are input to the subtractor 111, and the deviation δ is input to the PI controller 112. The PI control device 112 determines the control amount β of the threshold voltage based on the deviation δ, and calculates the second threshold voltage VTHB2 and the third threshold voltage VTHB3 by adjusting β from the first threshold voltage VTHB1.

  And the control apparatus 10 performs the control demonstrated above, The PAD figure of the said control is shown in FIG. For example, “PWM1 ON” in FIG. 10 indicates that the first single-phase inverter 3 operates by PWM control, and “PWM1 OFF” indicates that PWM control operation is not performed.

  As described above, according to this embodiment, it is not necessary to separately provide a converter and supply the DC voltage required for the capacitor 5, so that the converter can be omitted, and an inexpensive power converter with low power loss can be provided. Can be obtained. Further, the first single-phase inverter 3 is partially operated by PWM control, so that the shortage of voltage during the period Ta during which the second single-phase inverter 4 cannot output can be compensated, and thereby the second single-phase inverter 3 Since the operation is performed even when the voltage of the capacitor 5 of the inverter 4 is set to be low, switching means such as a low breakdown voltage semiconductor element can be used for the second single-phase inverter 4 and the cost is reduced.

Embodiment 2. FIG.
11 to 14 show the second embodiment, FIG. 11 is a configuration diagram of the power conversion device, FIGS. 12 and 13 are waveform diagrams for explaining the operation, and FIG. 14 is a PAD diagram of the control device. It is. In FIG. 11, the power conversion device 200 includes a control device 20. The control device 20 has a processing device 22. Since other configurations are the same as those of the first embodiment shown in FIG. 1, the same reference numerals are given to the corresponding components and the description thereof is omitted. In this embodiment, the processing device 22 does not operate only the first single-phase inverter 3 in the period Ta, but, as shown in FIG. 12, the first single-phase inverter 3 and the second single-phase inverter 3 in the period Ta. Control is performed so that the single-phase inverter 4 outputs power energy (voltage). The second single-phase inverter 4 can output a voltage up to the DC bus voltage of the second single-phase inverter 4, that is, the voltage VC <b> 2 of the capacitor 5.

  Therefore, if the second single-phase inverter 4 continues to output the voltage VC2 of the capacitor 5 of the second single-phase inverter 4 corresponding to the output voltage command V2REF even during the period Ta, for example, as shown in FIG. Compared with that shown in FIG. 6A, the PWM control period Tb of the first single-phase inverter 3 can be shortened. Similarly, when the first single-phase inverter 3 needs to perform PWM control during the period Tc to be normally output as the main voltage pulse, the second single-phase inverter 3 also corresponds to the output voltage command V2REF in the period Tc. If the voltage VC2 of the capacitor 5 of the single-phase inverter 4 is continuously output, the PWM control period for adjusting the electric power of the first single-phase inverter 3 as shown in FIG. Td can be shortened.

  When the period Tb or the period Td is shortened, the number of times of switching of the first single-phase inverter 3 is reduced, so that the switching loss generated in the first single-phase inverter 3 can be reduced. Further, when the period Tb or the period Td is large, the change width of the threshold voltage VTHB1 or the like is limited from the absolute value 0V to the maximum value of the AC output voltage Vo. The power conversion apparatus may not operate because the power balance cannot be secured. However, in the present embodiment, since the period Tb and the period Td can be shortened by outputting power also from the second single-phase inverter 4, the width of the input / output voltage in which the power converter can operate is widened. can do. The control device 20 performs the control described above. FIG. 14 shows a PAD diagram of the control.

Embodiment 3 FIG.
15 to 18 show the third embodiment, FIG. 15 is a configuration diagram of the power conversion device, FIGS. 16 and 17 are waveform diagrams for explaining the operation, and FIG. 18 is a PAD diagram of the control device. It is. In FIG. 15, the power conversion device 300 includes a control device 30. The control device 30 includes a PWM output amount adjustment device 31 and a processing device 32. The PWM output amount adjustment device 31 includes a subtractor 311 and a PI control device 312. Since other configurations are the same as those of the first embodiment shown in FIG. 1, the same reference numerals are given to the corresponding components and the description thereof is omitted. In this embodiment, the control device 30 operates as follows, and FIG. 18 shows a PAD diagram.

  The control device 30 gives the output voltage command V2REF of the second single-phase inverter 4 during the partial PWM control period as a variable instead of being fixed, and controls the voltage VC2 of the capacitor 5 of the second single-phase inverter 4. For example, when the voltage VC2 of the capacitor 5 is lower than the target voltage VC2REF, as shown in FIG. 16, the control amount α (FIG. 16 (b) shown in FIG. 16B is used as the output voltage command V2REF of the second single-phase inverter 4 as a predetermined control amount. )) Decrease and increase the target output command V1REF of the first single-phase inverter 3 by the control amount α. Then, the output power of the first single-phase inverter 3 becomes larger than the power to be output by the power converter, and the surplus power is charged in the capacitor 5 of the second single-phase inverter 4. VC2 rises. Note that the target output command V1REF in FIG. 16 indicates a command waveform in the partial PWM control period.

  Similarly, when the voltage VC2 of the capacitor 5 is higher than the target voltage VC2REF as shown in FIG. 17A, the output voltage command V2REF of the second single-phase inverter 4 is increased by the control amount α (FIG. 17B). The increased amount is compensated by lowering the target output command V1REF of the first single-phase inverter 3. Then, the output power of the first single-phase inverter 3 becomes smaller than the power to be output by the power converter, and the insufficient power is supplied from the capacitor 5 of the second single-phase inverter 4. VC2 decreases. Note that the target output command V1REF in FIG. 17 indicates a command waveform in the partial PWM control period.

A threshold control device such as P control or PI control may be used to determine the control amount α. In this embodiment, the PWM output amount adjusting device 31 performs PI control.
Note that the absolute value of the output voltage command V2REF of the second single-phase inverter 4 varies from 0 to the voltage VC2 of the capacitor 5 of the second single-phase inverter 4.

  As described above, according to this embodiment, the voltage of the capacitor 5 of the second single-phase inverter 4 can be controlled and an overvoltage can be prevented, so that a capacitor having an appropriate voltage can be used. Further, overvoltage can be prevented even if the voltage of the DC power supply 1 changes suddenly due to disturbance such as power flow.

Embodiment 4 FIG.
19 and 20 show the fourth embodiment. FIG. 19 is a configuration diagram of the power conversion device, and FIG. 20 is a PAD diagram of the control device. In FIG. 19, the power conversion device 400 includes a control device 40. The control device 40 includes a PWM output amount adjustment device 41 and a processing device 42. The PWM output amount adjustment device 41 includes a subtracter 411 and a PI control device 412. Since other configurations are the same as those of the first embodiment shown in FIG. 1, the same reference numerals are given to the corresponding components and the description thereof is omitted. The control device 40 operates as described below, and FIG. 20 shows a PAD diagram.

  In the present embodiment, the case where the power factor is not 1 and the phases of the output voltage and the output current are shifted can be dealt with. When the output current phase shifts, the power conversion device 400 generates a period in which the polarity of the output power energy is negative. In the above period, adding and subtracting the control amount has an adverse effect, so the control amount needs to be reversed. In the present embodiment, the correction direction of the control amount is determined by the power energy polarity PREF of the power converter. When the voltage is positive, the power energy polarity PREF is positive if the output current is positive, and the power energy polarity PREF is negative if the output current is negative. Similarly, when the voltage is negative, the power energy polarity PREF is negative if the output current is positive, and the power energy polarity PREF is positive if the output current is negative.

  For example, in a period in which the first single-phase inverter 3 is partially PWM-controlled, the power energy polarity PREF is positive and the voltage VC2 of the capacitor 5 of the second single-phase inverter 4 is lower than the target voltage VC2REF. In this case, the output voltage command V2REF of the second single-phase inverter 4 is changed so as to decrease by a control amount γ (described later in detail) as a predetermined control amount. When the power energy polarity PREF is positive and the voltage VC2 of the capacitor 5 is higher than the target voltage VC2REF, the output voltage command V2REF of the second single-phase inverter 4 is changed to increase by γ. When the power energy polarity PREF is negative and the voltage VC2 of the capacitor 5 of the second single-phase inverter 4 is lower than the target voltage VC2REF, the output voltage command V2REF of the second single-phase inverter 4 is increased by γ To change. When the power energy polarity PREF is negative and the voltage VC2 of the capacitor 5 is higher than the target voltage VC2REF, the output voltage command V2REF of the second single-phase inverter 4 is changed in the direction of decreasing by γ.

  Note that a control device such as P control or PI control may be used to determine the control amount γ for raising or lowering the output voltage command V2REF. In this embodiment, the PWM output amount adjusting device 41 performs PI control. The controllable range of the absolute value of the output voltage command V2REF is from 0 to the voltage VC2 of the capacitor 5 of the second single-phase inverter 4.

  As described above, according to this embodiment, the present invention can be applied even when the power factor of the load is not 1.

Embodiment 5 FIG.
FIGS. 21 and 22 show the fifth embodiment, FIG. 21 is a configuration diagram of the power converter, and FIG. 22 is a case where the phases of the triangular wave carriers of the first and second single-phase inverters are shifted by 180 degrees. It is a wave form diagram for demonstrating the effect of this. In FIG. 21, the power conversion device 500 includes a control device 50. The control device 50 includes a processing device 52. Since other configurations are the same as those of the third embodiment shown in FIG. 15, the corresponding components are denoted by the same reference numerals and description thereof is omitted. The control device 50 operates as described below. The present embodiment is based on the third embodiment or the fourth embodiment.

  In the present power conversion device 500, the first single-phase inverter 3 is partially PWM-controlled in the same manner as those shown in the third and fourth embodiments. Similarly, during the PWM control period, the second single-phase inverter 4 is also PWM controlled. When the triangular wave comparison method is used for the PWM control, when the phases of the triangular wave carriers in the first single-phase inverter 3 and the second single-phase inverter 4 are the same, the first single-phase inverter 3 and the second single-phase inverter 3 The center of each pulse of the single-phase inverter 4 coincides. For this reason, when the second single-phase inverter 4 outputs positive, the voltage output at the time of one switching increases and the current ripple increases. However, when the phases of the two triangular wave carriers are shifted by 180 degrees, the centers of the pulses are shifted, so that the output voltages do not overlap or the overlapping period is shortened. Accordingly, since the voltage change width can be reduced or the period of the change width can be shortened, the current ripple can be suppressed.

  When the output of the second single-phase inverter 4 is negative, if the phase of the triangular wave carrier is shifted by 180 degrees, the change width of the voltage increases, so the phase of the triangular wave carrier is synchronized. An example of the effect of the phase shift is shown in FIG. FIG. 22 shows that the voltage ratio of the voltage VC1 of the capacitor 2 of the first single-phase inverter 3 and the voltage VC2 of the capacitor 5 of the second single-phase inverter 4 is 2 to 1, and the output of the second single-phase inverter 4 is It is positive and shows a comparison of ripple currents when the phases of two triangular wave carriers (waveform c1 and waveform c2) in the first single-phase inverter 3 and the second single-phase inverter 4 are shifted by 180 degrees. is there. FIG. 22A shows a ripple current waveform W1 when the phases of two triangular wave carriers (waveform c1 and waveform c2) are the same. FIG. 22B shows a ripple current waveform W2 when the phases of two triangular wave carriers (waveform c1 and waveform c2) are shifted by 180 degrees. 22A and 22B, the waveform a1 is the PWM output of the first single-phase inverter 3, and the waveform a2 is the PWM output of the second single-phase inverter 4. Thus, since the phases of both triangular wave carriers (waveforms c1 and c2) are not matched, ripple current can be suppressed. Therefore, it is possible to reduce a loss caused by a high frequency current in a reactor (not shown) of the filter 6.

Embodiment 6 FIG.
23 to 25 show the sixth embodiment, FIG. 23 is a configuration diagram of a power conversion device, FIG. 24 is a configuration diagram of another power conversion device which is a modification, and FIG. 25 is another modification. It is a block diagram of the other power converter device which is. In FIG. 23, the power conversion device 600 includes capacitors 2 a and 2 b connected in series, a first single-phase inverter 603 as a first inverter of three levels, and a control device 60. The first single-phase inverter 603 has AC output lines 603c and 603d. The AC output side of the second single-phase inverter 4 is connected in series to one AC output line 603 c of the first single-phase inverter 603. The control device 60 operates in the same manner as the control device 10 in the first embodiment. The operation of the power conversion device 600 differs only in the configuration of the first single-phase inverter, and the power shown in FIG. This is the same as the conversion device 100.

  In FIG. 24, the power conversion device 700 includes a three-phase inverter 703 as a first inverter, a second single-phase inverter 704 as a second inverter, and a control device 70. The AC output side of the second single-phase inverter 704 is connected in series to the three AC output lines 703c, 703d, and 703e of the three-phase inverter 703, respectively. The control device 70 operates in the same manner as the control device 10 in the first embodiment, and the operation of the power conversion device 700 is the same as that of the power conversion device 100 shown in FIG. 1 except for the configuration of the inverter. It is.

Moreover, as shown in FIG. 25, the power converter device 800 can also be comprised. In FIG. 25, the second single-phase inverter as the second inverter may be divided into two second single-phase inverters 804, and a control device 80 for controlling them may be provided. Control device 80 operates in the same manner as control device 10 in the first embodiment, and operation of power conversion device 800 is the same as that of power conversion device 100 shown in FIG. 1 except for the configuration of the inverter. It is. Note that the first inverter may be a single-phase inverter or a three-phase inverter. In addition, the second single-phase inverter can be configured as three or more single-phase inverters 804.
In addition, instead of the control devices 60, 70, 80 in this embodiment, a control device that operates in the same manner as the control devices 20, 30, 40, 50 shown in the second to fifth embodiments can be used. It goes without saying that power converters having various characteristics can be configured by appropriately combining the individual configurations shown in the above embodiments.

Claims (12)

A power conversion device including a first inverter, a second inverter, and a control device,
The first inverter is connected between the positive and negative terminals of a DC power source, converts the power of the DC power source into AC and outputs it through an AC output line,
The second inverter has a capacitor and a single-phase inverter circuit, the DC side of the single-phase inverter circuit is connected to the capacitor, and the AC side is connected in series to the AC output line,
The control device rises when the sine wave AC output voltage command becomes larger than a predetermined value, and outputs a pulse of one pulse that falls when the sine wave AC voltage command becomes less than the predetermined value at every half cycle of the AC output voltage command. The first inverter is controlled by transmitting a main voltage pulse command so that the first output is output as the first voltage, and the first voltage based on the compensation voltage command issued based on the AC output voltage command and the output voltage of the first inverter. The output voltage of the inverter 2 is subjected to pulse width modulation control to output the sum of the output voltages of the first and second inverters as a sine wave AC voltage, and the voltage of the capacitor in response to the compensation voltage command If the first period, which is a period during which the output voltage of the second inverter is insufficient, is present before and after the period during which the main voltage pulse is to be output. During the first period, the output voltage of the first inverter is output by pulse width modulation control to compensate for the insufficient output voltage and the second period during the period in which the main voltage pulse is to be output. The power energy supplied from the first inverter in the first period is reduced by reducing the power energy output from the first inverter by performing pulse width modulation control on the output voltage of the first inverter. A power conversion device that is designed to cancel. When the first period exists in a period during which the main voltage pulse is to be output, the control device outputs the output voltage of the first inverter by performing pulse width modulation control during the first period. Then, the output voltage of the first inverter is subjected to pulse width modulation control only for a third period before and after the period in which the main voltage pulse is to be output, while compensating for the insufficient output voltage, and from the first inverter. 2. The power conversion apparatus according to claim 1, wherein the power energy is output, and the output energy that decreases by pulse width modulation control of the first inverter in the first period is offset. The power conversion device according to claim 1, wherein the control device stops the operation of the second inverter in the first period. The power converter according to claim 1, wherein the control device operates the first inverter and the second inverter in the first period. The control device lowers the compensation voltage command when the voltage of the capacitor is lower than a predetermined capacitor voltage, and increases the compensation voltage command when the voltage of the capacitor is equal to or higher than the predetermined capacitor voltage. Item 4. The power conversion device according to Item 1. When the polarity of the output power of the power converter is positive and the voltage of the capacitor is lower than a predetermined capacitor voltage, the control device lowers the compensation voltage command and makes the voltage of the capacitor lower than the predetermined capacitor voltage. When the output voltage is high, the compensation voltage command is increased. When the polarity of the output power is negative and the voltage of the capacitor is lower than the predetermined capacitor voltage, the compensation voltage command is increased and the voltage of the capacitor is increased to the predetermined voltage. The power converter according to claim 1, wherein the compensation voltage command is lowered when the voltage is higher than a capacitor voltage. 3. The first and second inverters according to claim 1, wherein the first and second inverters use triangular wave carriers for pulse width modulation control, and are configured so that the phases of both triangular wave carriers do not coincide with each other. The power converter of any one of 4-6. The power converter according to any one of claims 1 to 6, wherein the first and second inverters are single-phase full-bridge inverters. The power converter according to claim 1, wherein the first inverter is a multilevel single-phase inverter. The first inverter is a three-phase inverter, and the AC side of the second inverter is connected in series to each phase AC output line of the first inverter. The power conversion device according to item 1. The second inverter is composed of one or a plurality of single-phase inverters, and the AC side of the single-phase inverter alone or connected in series is the AC side of the second inverter. The power conversion device according to any one of 1 to 6. The said DC power supply is a solar cell, The power converter device of any one of Claims 1-6.

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