JP4365171B2 - Power converter and power conditioner using the same - Google Patents

Description

  The present invention relates to a power conversion device capable of obtaining a smooth AC output waveform by combining a plurality of inverters, and a power conditioner that links a distributed power source to a system using such a power conversion device. .

In a conventional power conditioner, for example, as shown in a solar power conditioner, the voltage is boosted using a chopper from a distributed power source that is a solar cell, and a PWM controlled inverter is inserted in the subsequent stage to generate an output AC voltage. is doing.
The basic operation of such a conventional power conditioner will be described below. The DC power output from the solar cell drives the internal control power supply of the power conditioner, and the internal circuit can operate. Using the DC / DC converter unit, the voltage of the solar cell is boosted to a voltage required to connect to the grid. The inverter unit performs PWM switching so that the output current has a phase synchronized with the system voltage. Since there is a reactor and a capacitor connected to the inverter unit, AC power is output to the system (see, for example, Non-Patent Document 1).

In addition, the conventional power conditioner uses a PWM-controlled inverter. Conventionally, there is a power conversion device in which output terminals of a plurality of single-phase output inverters are connected in series to reduce harmonics, which will be described below. To do. N single-phase output inverter bridges capable of three-level output each having an isolated input, and by connecting the output terminals of each single-phase output inverter bridge in series, an n-stage single-phase output power converter Constitute. Further, the amplitude ratio of the amplitudes V1 to Vn of the output voltages of the n single-phase output inverter bridges is set to V1: V2: ..: Vn = 1: 2: ..: 2 ^n-1 (for example, patents) Reference 1).

JP 11-89242 A "Development of solar power conditioner type KP40F" OMRON TECHNICS Vol.42 No.2 (Vol.142) 2002,

  In a conventional power conditioner, a filter for smoothing a switching waveform chopped by PWM control of an inverter unit is installed on the output side. Also, an EMI removal filter is provided so that harmonic noise due to switching does not flow into the system. As described above, since the sine wave current and voltage are generated at the output by using the switching operation of the inverter unit, the switching frequency has to be increased to reduce the size of the smoothing filter. For this reason, there has been a problem that the harmonic current due to switching increases and the size of the EMI removal filter that suppresses the system noise inflow of harmonic noise increases. Further, when the switching frequency is increased, there is a problem that the loss of the switching elements constituting the inverter unit increases.

  Further, in the conventional power conversion device as described above, many inverter circuits are required to reduce harmonics, and each inverter requires an insulated DC power source. It has been difficult to obtain such a plurality of DC power sources from a distributed power source such as a solar cell with a stable voltage because the apparatus becomes very complicated.

The present invention has been made to solve the above-described problems, and is a power conversion device in which a plurality of AC sides of a single-phase inverter are connected in series and multiplexed, and the device structure is complicated. Therefore, it is an object to stably obtain the voltages of a plurality of DC power sources even when the status of the distributed power source changes.
In addition, by using such a power conversion device, it is possible to reduce the smoothing filter capacity of the output, reduce the harmonics, and obtain a power conditioner that can supply a stable output even when the status of the distributed power supply changes. Objective.

A power converter according to the present invention comprises a single-phase multiple converter in which a plurality of AC sides of a single-phase inverter that converts DC power of a DC power source into AC power are connected in series, and is selected from the plurality of single-phase inverters. The output voltage is gradation controlled by the total sum of the generated voltages by the predetermined combination, and power is supplied to the load . A plurality of the DC power source comprising an upper SL input of each single-phase inverter via a DC / DC converter having a voltage control means for controlling the voltage of each of the DC power source is generated from the distributed power supply, the plurality of DC power supply Vm, V2,..., Vm in order from the smallest DC voltage
V2 is twice or three times V1 Vn (n = 3 to m) is an integer multiple of V1, Vn ≦ V1 + 2 · ΣVk (k = 1 to n−1)
Satisfied . The DC / DC converter is provided corresponding to each of the DC power supplies to be voltage controlled, and the voltage control means includes a reactor having a winding ratio substantially proportional to a voltage ratio of the DC power supplies. Arranged in each DC / DC converter, the plurality of reactors have their magnetic fluxes linked to each other.
In the power converter according to the present invention, for a predetermined DC power source among the plurality of DC power sources, a combination of the discharge in the gradation control and the charging by the charge of another DC power source flows out from the predetermined DC power source. Control is performed so that the average value of the current becomes substantially zero, and the voltage of the other DC power source is controlled by the DC / DC converter.

  Moreover, the power conditioner by this invention outputs a predetermined alternating voltage and alternating current using the said power converter device, is connected to a system | strain in parallel, and connects the said distributed power supply to this system | strain.

In such a power converter, a smooth output voltage waveform can be obtained with high accuracy by combining the voltages of the single-phase inverters. For this reason, the output smoothing filter capacity is greatly reduced. In addition, since the number of times of switching can be reduced, harmonic EMI can also be reduced. Furthermore, since the voltage of the DC power supply can be controlled by the voltage control means, it is possible to stably obtain the voltages of a plurality of DC power supplies without complicating the device structure even when the status of the distributed power supply changes.
Further, in a power conditioner using such a power converter, the output smoothing filter capacity can be reduced, and the EMI removal filter that suppresses the inflow of harmonic noise into the system can be downsized or omitted. Stable output can be supplied even if the value changes.

Embodiment 1 FIG.
Hereinafter, a power conditioner according to Embodiment 1 of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating a power conditioner according to Embodiment 1 of the present invention.
As shown to Fig.1 (a), the alternating current side of several single phase inverter 1a, 1b, 1c is connected in series, and a single phase multiple converter is comprised. As shown in FIG. 1B, each single-phase inverter 1a to 1c is composed of a plurality of self-extinguishing semiconductor switching elements such as IGBTs having diodes connected in antiparallel, and a smoothing capacitor C1 as a DC power source. The DC power from ~ C3 is converted into AC power and output, and the load 3 is supplied with power.

Further, as shown in the figure, a chopper circuit including a reactor L3 and a switching element S1 is installed in the subsequent stage of the distributed power source 2 such as sunlight or a fuel cell. The chopper circuit boosts the DC voltage obtained by the distributed power supply 2 to a predetermined value (note that it may be stepped down or stepped up / down). The boosted voltage is DC smoothed by a DC / DC converter circuit composed of a diode D3 and a smoothing capacitor C3, and a voltage Vc charged to the smoothing capacitor C3 is obtained.
Further, since the reactor L2 and the reactor L1 are coupled to the reactor L3 and the magnetic flux, when the voltage is generated in the reactor L3, the voltage is also generated in the reactors L2 and L1, and similarly, the diode L2 and the smoothing capacitor C2 are configured. DC / DC converter circuit, and a DC / DC converter circuit composed of a diode D1 and a smoothing capacitor C1, and DC smoothed to obtain voltages Vb and Va charged in the smoothing capacitors C2 and C1. When the number of turns is set so that the counter electromotive force generated in the reactors L3, L2, and L1 has a predetermined relationship, the direct current voltage obtained by each DC / DC converter circuit (hereinafter simply referred to as a converter) is also converted into the turn ratio. The relationship is proportional to
In FIG. 1, the chopper circuit including the reactor L3 and the switching element S1 (hereinafter simply referred to as the switch S1) has a non-insulated configuration, but a flyback configuration using a transformer or a forward type Any configuration is acceptable.

Each of the single-phase inverters 1a to 1c described above is connected to the subsequent stage of the smoothing capacitors C1 to C3, and these single-phase inverters 1a to 1c can generate positive and negative voltages and zero voltages as outputs. By combining the generated voltages of the three single-phase inverters 1a to 1c, a predetermined voltage is generated by gradation control as the sum.
The relationship between the DC voltages Va, Vb, and Vc of each bit (hereinafter referred to as a reactor and a capacitor, and a group of inverters) is a different value (Va <Vb <Vc), 1: 2: 3, 1: 2 : 4, 1: 2: 5, 1: 2: 6, 1: 2: 7, 1: 3: 4, 1: 3: 5, 1: 3: 6, 1: 3: 7, 1: 3: 8 , 1: 3: 9. In each case, the relationship between the output logic (combination pattern) of the single-phase inverters 1a to 1c of each bit and the output gradation (voltage level) of the single-phase multiple converter in which they are connected in series is shown in FIG. Is shown in the logical table. In the case of 1: 2: 3 with the smallest number of output gradations, the illustration is omitted for convenience.

  For example, in the case of Table J, Va, Vb, and Vc have a relationship of 1: 3: 9, and an output voltage of 14 gradations of 0 to 13 is obtained as a sum of these generated voltages. Thereby, an extremely smooth output voltage waveform close to a sine wave can be obtained. Note that the output voltage waveform can be made smoother by increasing the number of bits.

Here, a condition for obtaining a smooth output voltage is that there is no voltage jump in each output gradation level, and the voltage difference between each output gradation level needs to take a constant value. In order to satisfy this condition, it is desirable to satisfy the following relationship.
Vc and Vb should be approximately an integral multiple of Va.
Vb should be 2 or 3 times Va.
Vc should be (Va + Vb) · 2 + Va or less.
The same applies to the case where there are four or more bits, and it is desirable to satisfy the following relationship.
In order from the smallest DC voltage, V1, V2,.
V2 must be twice or three times V1.
Vn (n = 3 to m) is an integral multiple of V1, and Vn ≦ V1 + 2 · ΣVk (k = 1 to n−1).

  In order to obtain the relationship between the DC voltages Va, Vb, and Vc as shown in FIG. 2, it is necessary to set the DC voltages Va, Vb, and Vc of each bit to predetermined values in advance. For example, in the case of the configuration shown in FIG. 1, the turns ratio of the reactors L1 to L3 may be set so as to have a relationship of Va to Vc in each table of FIG.

In this embodiment, an extremely smooth output voltage waveform close to a sine wave can be obtained by gradation control based on a combination of the voltages of each bit, so that the smoothing output filter can be omitted or the capacity can be reduced. Cost reduction, size reduction, and simplification of the power converter can be realized. In addition, the number of times of switching is remarkably reduced as compared with the conventional PWM control, and thereby harmonics are drastically reduced. As a result, the EMI removal filter that suppresses the inflow of harmonic noise into the system can be omitted, or the capacity can be significantly reduced.
Further, a converter having reactors L1 to L3 is provided for each bit, the magnetic fluxes of these reactors L1 to L3 are linked to each other, and the magnitude of the back electromotive force generated by each reactor L1 to L3 is as follows. It is made proportional to the magnitude of the DC voltage of the bit. Thereby, even if there is only one switch S1 constituting the chopper circuit, a different DC voltage can be easily generated for each bit from the distributed power source 2 by the chopper circuit at a time, and the device configuration can be simplified.

Embodiment 2. FIG.
In this embodiment, a case will be described in which power is supplied to a commercial line (system) by the power conditioner shown in the first embodiment.
FIG. 3 is a configuration diagram in the case where power is supplied to the system by the power conditioner shown in FIG. As shown in the figure, a power conditioner is connected in parallel to the system, and a reactor Lf is inserted in series with the power conditioner on the power conditioner side of this connection point. Reference numeral 5 denotes a system power supply.
Since the power system has already established the voltage, it is necessary to operate the system so that the inverter current flows. By inserting the reactor Lf in series with the power conditioner, an excessive current due to a potential difference between the power conditioner and the system is prevented from flowing.

FIG. 4 is a configuration diagram to which a control function of the power conditioner is added, in which 6 is a bit pattern forming circuit and 7 is a current control circuit.
As shown in the figure, the current flowing out of the power conditioner is detected by the current sensor 9, and the current control circuit 7 switches the chopper circuit comprising the reactor L3 and the switch S1 so that the current becomes a predetermined current target value. By controlling S1, the output voltage from the chopper circuit is controlled. As described above, the chopper circuit boosts the DC voltage obtained by the distributed power supply 2 to a predetermined value, and the boosted voltage is DC smoothed by the converters (D3, C3) to obtain the voltage Vc. Further, since the reactor L2 and the reactor L1 are linked with the magnetic flux of the reactor L3, when a voltage is generated in the reactor L3, a voltage is also generated in the reactors L2 and L1. Thus, the DC voltage of each bit is generated from the distributed power supply 2 by controlling the switch S1 of the chopper circuit.

The bit pattern forming circuit 6 detects the voltage of the system by the voltage detection means 8 and forms in advance an output gradation voltage level and an output bit pattern (combination pattern) from which a system voltage instantaneous value can be obtained.
A current flows through the reactor Lf due to the difference between the instantaneous voltage of the system and the voltage of the power conditioner. The high-frequency difference voltage is smoothed by the reactor Lf. Subtle control of the current is controlled by the chopper switch S1 by the current control circuit 7. Specifically, the duty of the switch S1 is changed. As a result, the DC voltage of each bit changes, and the output voltage waveform 10 is adjusted as shown in FIG. 5A to determine the current supplied to the system.
As shown in FIGS. 5B and 5C, when the current supplied to the system is to be increased, the voltage level of the output voltage waveform is slightly increased, and when the current is to be decreased, the output voltage waveform is increased. The voltage level is slightly reduced. 10a is an output voltage waveform when the voltage level is reduced, 10b is an output voltage waveform when the voltage level is increased, and 11 is a reference waveform for representing a difference between the output voltage waveforms 10a and 10b.

What is necessary is just to set so that the electric current target value of the electric current supplied to a system | strain may be decided with the electric power generation amount of the distributed power supply 2. FIG. For simplicity, the current amount is set to be higher if the voltage of the distributed power source 2 is higher. Since the distributed power source 2 generally has a characteristic that the voltage decreases when a large amount of current is output, the power can be efficiently extracted by performing such control.
By controlling the current supplied to the system as described above, the distributed power source 2 can be connected to the system with high reliability.

In addition, the control accuracy of the voltage difference between the instantaneous voltage of the system and the voltage of the power conditioner can be improved by applying PWM control in advance to the voltage output method of the single-phase inverter of a predetermined bit.
As described above, the current flows through the reactor Lf due to the difference between the instantaneous voltage of the system and the voltage of the power conditioner. As shown in FIG. 6, the output voltage waveform is changed by applying PWM control to the voltage output method. It is possible to approach a smoother target value. For example, as shown in the voltage relationship of Va: Vb: Vc of 1: 3: 9, even if the 14 gradation voltages from 0 to 13 can be output, only the gradation control without adding the PWM control can reduce the reactor Lf. If the capacity is small, the high-frequency current that flows due to the voltage difference may increase.
By applying simple PWM control to the predetermined single-phase inverter output selected by the output bit pattern at each output gradation level, and smoothing the high-frequency waveform with the reactor Lf, a smoother output voltage waveform is obtained. It is done. As a result, the smoothing output filter can be reduced in capacity, and the control accuracy of the differential voltage between the instantaneous voltage of the system and the voltage of the power conditioner can be improved, and the current flowing through the system can be controlled with higher accuracy. For this reason, an excessive current does not flow between the power conditioner and the system. At this time, in order to apply PWM control to the voltage output method at each output gradation level, depending on the voltage relationship of Va: Vb: Vc, it is necessary to apply PWM control to the outputs of a plurality of single-phase inverters.

Embodiment 3 FIG.
Next, adjustment of the average current flowing in the smoothing capacitors C1 to C3 of each bit in the power conditioner shown in the second embodiment will be described below.
FIG. 7 shows that output gradation levels of 1 to 7 can be output when the DC voltage relationship of each bit is 1: 2: 4 (here, the voltage corresponding to one gradation is expressed as 10). The output bit pattern is shown.
As shown in FIG. 7A, it can be seen that a plurality of output bit patterns exist for the same output gradation voltage. When the bit output is -1, the single-phase inverter operates to charge the smoothing capacitor of the bit, and when the bit output is 1, the single-phase inverter operates to discharge the smoothing capacitor. By properly using the charging and discharging, it is possible to adjust the average current flowing in the smoothing capacitor.

  In FIG. 7B, the output bit pattern is selected so that the average current flowing through the smoothing capacitors C1 and C2 of the DC voltages Va and Vb is reduced. For example, the smoothing capacitor C2 is only charged when the output voltage level is 20 or less, and when the output voltage level is 50 or more, only the discharge pattern can be selected. By selecting the output bit pattern in this way, the average current flowing through the smoothing capacitors C1 and C2 of the DC voltages Va and Vb is reduced, and the reactors L1 and L2 of the bits and the capacity of the converter can be greatly reduced. Thereby, cost reduction can be achieved.

  In this embodiment, the output bit pattern is selected so that the average current flowing through the smoothing capacitors C1 and C2 of the DC voltages Va and Vb is small. However, it is desired to control the average current flowing through the smoothing capacitors C1 and C2 to a predetermined value. Even in this case, it is effective to select an output bit pattern. Also, by controlling the output bit pattern to change at a certain time period, the average current can be easily controlled with a predetermined value.

Embodiment 4 FIG.
In the first and second embodiments, the DC voltage ratio of each bit is matched with the winding ratio of the reactors L1 to L3 of each bit, and the DC power supply of each bit is generated through the converter circuit.
In this embodiment, as shown in FIG. 8, the reactors L1 and L2 of predetermined bits and the converter are not required by the control using the current control bit pattern forming circuit 6a and the voltage control circuit 7a.

First, as a comparative example, a case where the reactors L1 to L3 of each bit and the converter cannot be omitted will be described with reference to FIG. FIG. 9 shows the output voltage waveform of the power conditioner and the amount of discharge charge flowing out from the smoothing capacitors C1 to C3 of each bit when the relationship between the DC voltages Va, Vb and Vc of each bit is 1: 3: 9. Is shown. If the discharge charge amount after a half cycle is positive, the smoothing capacitor of that bit has released energy.
In this case, it is assumed that Va = 10V, Vb = 30V, and Vc = 90V. Here, the maximum value of the AC voltage desired to be output was defined as Vacpeak, and the change in the discharge charge amount flowing out of the smoothing capacitors C1 to C3 was examined by changing the ratio of the total value of the voltages Va to Vc. As shown in FIG. 9, under the condition of Vacpeak / (Va + Vb + Vc) = 1, the discharge charge amount after a half cycle of any bit shows a positive value. That is, the smoothing capacitors C1 to C3 of each bit need to be supplemented with electric power from the outside, and the reactors L1 to L3 and the converter are required for each bit.

Next, a case where the reactor L1 and the diode D1 of the bit of the direct-current voltage Va (hereinafter referred to as Va bit) are not required will be described.
FIG. 10A shows the power condition when the relationship between the DC voltages Va, Vb and Vc of each bit is 1: 3: 9 under the condition of Vacpeak / (Va + Vb + Vc) = 0.95. The output voltage waveform of the N and the discharge charge amount (total) flowing out from the smoothing capacitors C1 to C3 of each bit are shown. As shown in the figure, it can be seen that the total amount of discharge charge flowing out of the smoothing capacitor C1 is zero. In this state, there is no Va bit power consumption and no external power supply is required. Therefore, the reactor L1 and the diode D1 shown in FIG. 1 and FIG. 3 are not required, the circuit configuration is simplified, and the cost can be reduced.
As can be seen from the output voltage waveform in this case, compared with the case shown in FIG. 9, the pulse width, that is, the output time is shortened in the portion where the output gradation level is 13 levels. As a result, the amount of discharge charge decreases at that portion, and the total amount of discharge charge flowing out of the smoothing capacitor C1 becomes zero.

  Thus, in order to make the total amount of discharge charge flowing out of the smoothing capacitor C1 zero, the average current flowing through the smoothing capacitor C1 may be controlled to be substantially zero. As described in the third embodiment, the output bit This is possible by selecting a pattern. That is, the output bit pattern is determined and gradation control is performed so that the average current flowing through the smoothing capacitor C1 becomes substantially zero, and the pulse width is adjusted.

  10 (b) and 10 (c) are comparative examples in the case shown in FIG. 10 (a). Each bit when Vacpeak / (Va + Vb + Vc) = 0.965 and 0.94 is changed. The discharge charge amount (total) flowing out from the smoothing capacitors C1 to C3 is shown. The total amount of discharge charge flowing out of the smoothing capacitor C1 is positive when Vacpeak / (Va + Vb + Vc) = 0.965 (that is, with power consumption), and negative when Vacpeak / (Va + Vb + Vc) = 0.94 (that is, with power charging) ) You can see that it is positive.

Therefore, by selecting or controlling the value of Vacpeak / (Va + Vb + Vc), the power consumption of the Va bit can be made zero. Accordingly, the Va voltage is automatically detected by detecting the DC voltage of the smoothing capacitor C1 of Va bit or by detecting or calculating the discharge charge amount from the smoothing capacitor C1 and changing the value of Vacpeak / (Va + Vb + Vc). Bit power consumption can be controlled to zero.
Note that changing the value of Vacpeak / (Va + Vb + Vc) is nothing but changing the voltages of Vb and Vc by the reactors L2 and L3 and the switch S1. That is, the output bit pattern is determined and gradation control is performed so that the average current flowing through the smoothing capacitor C1 becomes substantially zero, and the voltages Vb and Vc are changed by the chopper circuit.

Next, a case where the Vb-bit reactor L2 and the diode D2 are unnecessary will be described.
FIG. 11A shows the output voltage waveform of the power conditioner when the relationship between the DC voltages Va, Vb and Vc of each bit is 1: 3: 9 under the condition of Vacpeak / (Va + Vb + Vc) = 0.807. It shows the discharge charge amount (total) flowing out from the smoothing capacitors C1 to C3 of each bit. As shown in the figure, it can be seen that the total amount of discharge charge flowing out of the smoothing capacitor C2 is zero. In such a state, there is no Vb bit power consumption and no external power supply is required. Therefore, the Vb-bit reactor L2 and the diode D2 are not required.
In the case of the Vb bit, since the DC voltage Vb is higher than Va, the reactor L2 and the diode D2 are also relatively large. However, since these can be made unnecessary, the circuit configuration can be simplified and the cost can be reduced. It will be big.

11 (b) and 11 (c) are comparative examples in the case shown in FIG. 11 (a), and each bit when Vacpeak / (Va + Vb + Vc) = 0.8257, 0.804 is changed. The discharge charge amount (total) flowing out from the smoothing capacitors C1 to C3 is shown. The total amount of discharge charge flowing out of the smoothing capacitor C2 is positive when Vacpeak / (Va + Vb + Vc) = 0.8257 (that is, with power consumption), and negative when Vacpeak / (Va + Vb + Vc) = 0.804 (that is, with power charging). Therefore, the power consumption of the Vb bit can be made zero by selecting or controlling the value of Vacpeak / (Va + Vb + Vc). Therefore, by detecting the DC voltage of the smoothing capacitor C2 of Vb bit, or detecting or calculating the discharge charge amount from the smoothing capacitor C2, and automatically changing the value of Vacpeak / (Va + Vb + Vc), Vb Bit power consumption can be controlled to zero.
Note that changing the value of Vacpeak / (Va + Vb + Vc) is nothing but changing the voltages of Va and Vc by the reactors L1 and L3 and the switch S1. That is, the output bit pattern is determined and gradation control is performed so that the average current flowing through the smoothing capacitor C2 becomes substantially zero, and the voltages Va and Vc are changed by the chopper circuit.

Next, the case where the reactors L1 and L2 and the diodes D1 and D2 of the Va and Vb bits are not necessary will be described.
FIG. 12A shows the output voltage waveform of the power conditioner when the relationship between the DC voltages Va, Vb and Vc of each bit is 1: 3: 9 under the condition of Vacpeak / (Va + Vb + Vc) = 0.996. It shows the discharge charge amount (total) flowing out from the smoothing capacitors C1 to C3 of each bit. In this case, the pulse width is adjusted at portions where the output gradation level is the 10th level and the 11th level. As shown in the figure, it can be seen that the total amount of discharge charge flowing out from the smoothing capacitors C1 and C2 is zero. In such a state, there is no power consumption in both the Va bit and the Vb bit, and no external power supply is required. Accordingly, the reactors L1 and L2 for the Va and Vb bits and the diodes D1 and D2 are unnecessary, and the circuit configuration can be simplified and the cost can be further reduced.

  12 (b) and 12 (c) are comparative examples in the case shown in FIG. 12 (a), and each bit when Vacpeak / (Va + Vb + Vc) = 0.818, 0.78 is changed. The discharge charge amount (total) flowing out from the smoothing capacitors C1 to C3 is shown. It can be seen that the polarity of the discharge charge amount is reversed in both the smoothing capacitors C1 and C2 when the value of Vacpeak / (Va + Vb + Vc) is 0.818 and 0.78. Therefore, by selecting or controlling the value of Vacpeak / (Va + Vb + Vc) between 0.818 and 0.78, the power consumption of the Va bit and Vb bit can be made zero. By adding the adjustment of the pulse width in gradation control to this, the power consumption of the Va bit and Vb bit can be made zero at the same time.

Accordingly, the DC voltage of the smoothing capacitors C1 and C2 of Va and Vb bits is detected, or the discharge charge amount from the smoothing capacitors C1 and C2 is detected or calculated, and the value of Vacpeak / (Va + Vb + Vc) is changed. By adjusting the pulse width, the power consumption of the Va and Vb bits can be controlled to zero simultaneously.
Note that changing the value of Vacpeak / (Va + Vb + Vc) is nothing but changing the voltage of Vc by the reactor L3 and the switch S1. That is, the output bit pattern is determined and gradation control is performed so that the average current flowing through the smoothing capacitor C2 becomes substantially zero, the pulse width is adjusted, and the voltage of Vc is changed by the chopper circuit.

The configuration shown in FIG. 8 corresponds to the case where the reactors L1 and L2 and the diodes D1 and D2 of the Va and Vb bits shown in FIG. 12 are not necessary, and the control operation will be described below.
The current control bit pattern forming circuit 6a determines the bit pattern of each output gradation and its pulse width so as to obtain the target sine wave current effective value (current target value), and changes the effective value of the output voltage. As a result, phenomena such as output voltage hunting are eliminated and stability is increased. FIG. 13 shows the state of the target current and the output voltage at that time. As shown in FIG. 13 (a), in the state where the target current is high, the effective value of the output voltage is changed by assuming that the entire current target value (sine wave) is high, and as shown in FIG. 13 (b). In a state where the current is low, the effective value of the output voltage is changed by setting the entire current target value (sine wave) as low. Thereby, it is possible to stabilize the output voltage waveform while maintaining the sine wave.

  Then, the DC voltages Va and Vb of the smoothing capacitors C1 and C2 are measured, and the voltage Vc charged in the smoothing capacitor C3 is controlled by controlling the switch S1 of the chopper circuit so that each voltage becomes a constant value. For example, if Va increases and Vb decreases, control is performed so that the voltage of Vc is increased by the chopper circuit. Conversely, if Vb increases and Va decreases, control is performed so that the voltage of Vc is decreased by the chopper circuit.

  In the fourth embodiment as well, the control accuracy of the differential voltage between the instantaneous voltage of the system and the voltage of the power conditioner can be improved by applying PWM control in advance to the voltage output method of the single-phase inverter of a predetermined bit. . By applying simple PWM control to the predetermined single-phase inverter output selected by the output bit pattern at each output gradation level, and smoothing the high-frequency waveform with the reactor Lf, a smoother output voltage waveform is obtained. It is done. As a result, the smoothing output filter can be reduced in capacity, and the control accuracy of the differential voltage between the instantaneous voltage of the system and the voltage of the power conditioner can be improved, and the current flowing through the system can be controlled with higher accuracy. For this reason, an excessive current does not flow between the power conditioner and the system.

It is a schematic block diagram which shows the power conditioner by Embodiment 1 of this invention. It is a figure which shows the relationship between the output logic and output gradation of each single phase inverter by Embodiment 1 of this invention. It is a block diagram in the case of supplying electric power to a system | strain by the power conditioner by Embodiment 2 of this invention. It is the block diagram which added the control function of the power conditioner by Embodiment 2 of this invention. It is a wave form diagram explaining the control operation of the power conditioner by Embodiment 2 of this invention. It is a wave form diagram explaining the control operation of the power conditioner by another example of Embodiment 2 of this invention. It is a figure explaining control of the power conditioner by Embodiment 3 of this invention. It is a schematic block diagram which shows the power conditioner by Embodiment 4 of this invention. It is a figure which shows the comparative example for demonstrating control of the power conditioner by Embodiment 4 of this invention. It is a figure explaining control of the power conditioner by Embodiment 4 of this invention. It is a figure explaining control of the power conditioner by Embodiment 4 of this invention. It is a figure explaining control of the power conditioner by Embodiment 4 of this invention. It is a figure explaining control of the power conditioner by Embodiment 4 of this invention.

Explanation of symbols

1a to 1c single phase inverter, 2 distributed power supply, 3 load, 5 system power supply,
C1-C3 smoothing capacitor, D1-D3 diode, L1-L3 reactor,
S1 switch.

Claims (7)

A single-phase multiple converter is configured by connecting a plurality of AC sides of a single-phase inverter that converts DC power of a DC power source into AC power in series, and each generation by a predetermined combination selected from the plurality of single-phase inverters In a power converter for supplying output to a load by controlling gradation of the output voltage based on the sum of voltages,
The plurality of DC power sources that are input to the single-phase inverters are generated from a distributed power source via a DC / DC converter having a voltage control unit that controls the voltage of each DC power source. In order from the smallest DC voltage, V1, V2,.
V2 is twice or three times V1
Vn (n = 3 to m) is an integral multiple of V1, and Vn ≦ V1 + 2 · ΣVk (k = 1 to n−1).
Satisfied,
The DC / DC converter is provided corresponding to each of the DC power supplies to be voltage controlled, and the voltage control means supplies a reactor having a turn ratio substantially proportional to the voltage ratio of the DC power supplies to each of the DC power supplies. / placed DC converters respectively within said plurality of reactors, the magnetic flux from each other you wherein the interlinked power converter. A single-phase multiple converter is configured by connecting a plurality of AC sides of a single-phase inverter that converts DC power of a DC power source into AC power in series, and each generation by a predetermined combination selected from the plurality of single-phase inverters In a power converter for supplying output to a load by controlling gradation of the output voltage based on the sum of voltages,
The plurality of DC power sources that are input to the single-phase inverters are generated from a distributed power source via a DC / DC converter having a voltage control unit that controls the voltage of each DC power source. In order from the smallest DC voltage, V1, V2,.
V2 is twice or three times V1
Vn (n = 3 to m) is an integral multiple of V1, and Vn ≦ V1 + 2 · ΣVk (k = 1 to n−1).
Satisfied,
Among the plurality of DC power supplies, for a predetermined DC power supply, the average value of the current flowing out from the predetermined DC power supply becomes substantially zero by combining the discharge in the gradation control and the charging by the charge of the other DC power supply. controlled to, said other voltage of the DC power supply, power conversion apparatus you and controls by the DC / DC converter. A single-phase multiple converter is configured by connecting a plurality of AC sides of a single-phase inverter that converts DC power of a DC power source into AC power in series, and each generation by a predetermined combination selected from the plurality of single-phase inverters In a power converter for supplying output to a load by controlling gradation of the output voltage based on the sum of voltages,
A plurality of the DC power sources serving as inputs of the single-phase inverters are generated from a distributed power source via a DC / DC converter having a voltage control means for controlling the voltage of each DC power source, and at least two or more Have different DC voltage,
Among the plurality of DC power supplies, for a predetermined DC power supply, the average value of the current flowing out from the predetermined DC power supply becomes substantially zero by combining the discharge in the gradation control and the charging by the charge of the other DC power supply. And controlling the voltage of the other DC power source with the DC / DC converter. 4. The power conversion apparatus according to claim 2 , wherein control is performed by changing a voltage level of the other DC power supply so that an average value of a current flowing from the predetermined DC power supply becomes substantially zero. 4. The power converter according to claim 2, wherein a pulse width of each output voltage level in the gradation control is controlled so that an average value of a current flowing from the predetermined DC power supply becomes substantially zero. 2. The output voltage of a predetermined single-phase inverter among the plurality of single-phase inverters is subjected to PWM control, and the output voltage by the PWM control is combined with each output voltage level in the gradation control. The power converter device in any one of -5. A power conditioner that outputs a predetermined AC voltage and AC current using the power conversion device according to any one of claims 1 to 6 and is connected to the system in parallel, and connects the distributed power source to the system.

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