JP6242128B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter that can be connected to a power system, and more particularly, to a power converter that supports a plurality of DC power inputs.

  In some photovoltaic power generation systems, as shown in FIG. 3, a solar cell string 2 composed of a plurality of solar modules 21 is connected to a power conversion device 101 (for example, Patent Document 1). In this power conversion device 101, DC voltages from a plurality of solar cell strings 2 are respectively input to a plurality of voltage adjustment circuits 111 in the power conversion device 101, and boosted to a predetermined DC voltage in these voltage adjustment circuits 111. Is done.

  These voltage adjustment circuits 111 are connected in parallel to the inverter circuit 112, and the DC voltage boosted by each voltage adjustment circuit 111 is converted into an AC voltage by the inverter circuit 112 and the filter circuit 113 and output to the commercial power system 3 or the like. The

  The control unit 114 of the voltage adjustment circuit 111 includes an MPPT control unit and a drive signal generation unit, each of which is composed of a separate microcomputer, and is provided for each voltage adjustment circuit 111.

  By the way, in the power generation system linked to the electric power system, at the time of a sag (instantaneous voltage drop), the output power before the occurrence of the sag is quickly restored, that is, provided with an FRT (continuous operation at the time of sag). Has been requested. For this reason, the power conversion device 101 has been required to have a fast response processing capability.

JP 2009-151832 A

However, when the plurality of control units 114 are separately provided in the plurality of voltage adjustment circuits 111 of the power conversion device 101, it is difficult to realize high-speed response processing capability. Specifically, (in the illustrated example, the first to third input current Iin ₁ ~Iin ₃₎ input current Iin to the voltage regulating circuit 111 is inputted from the solar cell string 2 detected by the input current detecting means 117 Then, the control unit 114 corresponding to the voltage adjustment circuit 111 monitors, and when the input current Iin decreases, it is determined that a voltage decrease has occurred in the power system 3. However, even if the voltage of the power system 3 decreases, not all the control units 114 can detect this. Moreover, not all the control parts 114 can detect the voltage drop of the electric power grid | system 3 simultaneously. This is because the amount of power generation differs for each solar cell string 2 and it is difficult to detect a decrease in the current Iin from the solar cell string 2 with a small amount of power generation.

  On the other hand, if the control units 114 of the plurality of voltage adjustment circuits 111 are connected by communication, it is possible to notify all the control units 114 of the occurrence of a voltage drop in the power system 3 or the elimination of the voltage drop. However, because there is a communication delay, if the control unit 114 of the voltage adjustment circuit 111 has dealt with after the occurrence of the voltage drop of the power system 3 or the cancellation of the voltage drop is notified, a high-speed response cannot be performed.

  Accordingly, an object of the present invention is to provide a power conversion device having a high-speed response processing capability while including a plurality of voltage adjustment circuits.

  In order to achieve the above object, a power conversion device according to one configuration of the present invention is a power conversion device that is connected to a plurality of DC power supplies and outputs AC power that can be linked to a power system. A plurality of voltage adjustment circuits for boosting a DC voltage supplied from a DC power source to the same predetermined voltage setting value, and an inverter circuit connected in parallel to the plurality of voltage adjustment circuits, the plurality of voltage adjustments An inverter circuit for converting a DC voltage boosted by the circuit into an AC voltage; and the plurality of voltage adjustment circuits based on each DC current and each DC voltage respectively input from the plurality of DC power supplies to the plurality of voltage adjustment circuits. Voltage adjusting circuit control means for controlling the voltage adjusting circuit, and the voltage adjusting circuit control means is configured as a single microcomputer.

  According to this configuration, since the voltage adjustment circuit control means for controlling the plurality of voltage adjustment circuits is configured in a single microcomputer, the processing executed when the state change such as the occurrence of an abnormality occurs The voltage adjusting circuit control means executes it without delay and with certainty. Therefore, a high-speed response processing capability can be realized for the control of the voltage adjustment circuit.

  In a preferred embodiment, the voltage adjustment circuit control means detects a change in state in the electric power system, and when the change is detected, each DC current input to the plurality of voltage adjustment circuits from the plurality of DC power sources, respectively. And a power system state change processing unit for storing at least one of the DC voltages.

  According to this, since the voltage adjustment circuit control means configured to be a single microcomputer and controls a plurality of voltage adjustment circuits has the power system state change processing unit, the detection of the state change of the power system Storage of the input current and / or input voltage to the voltage adjustment circuit at the time of detection of change can also be performed for control of all voltage adjustment circuits without delay.

  Preferably, the voltage adjustment circuit control means further includes an MPPT control unit that outputs a target value so as to execute MPPT control based on each DC current and each DC voltage input to each voltage adjustment circuit, and the MPPT A drive signal generation unit that generates a drive signal for driving the corresponding voltage adjustment circuit based on the target value output by the control unit and the predetermined voltage setting value, corresponding to the plurality of voltage adjustment circuits, respectively. Have multiple.

  According to this, the power system state change processing unit of the voltage regulation circuit control means inputs the plurality of voltage regulation circuits from the plurality of DC power sources, respectively, immediately before the time point when the state change in the power system is detected. Since at least one of each DC current value and each DC voltage value is stored, when the state in the power system is recovered, if each MPPT control is performed using these input current values or input voltage values, the state before the change is quickly obtained. You can recover to the state.

  Preferably, the DC power source is a solar cell string configured by connecting a plurality of solar modules in series.

  The power conversion device according to the present invention has a high-speed response processing capability while including a plurality of voltage adjustment circuits.

It is a schematic block diagram of the electric power generation system containing the power converter device which concerns on one Embodiment of this invention. FIG. 2 is a schematic block diagram illustrating in detail a voltage adjustment circuit control unit of the power conversion apparatus of FIG. 1. It is a schematic block diagram of the electric power generation system containing the conventional power converter device.

Hereinafter, a power converter according to a first embodiment of the present invention will be described with reference to FIG.
A power converter (power conditioner) 1 according to the present embodiment is connected to a plurality of DC power supplies 2, converts DC power output from these DC power supplies 2 into AC power, and converts the AC power into a power system 3. Linked to

  In the present embodiment, each of the DC power sources 2 includes a solar cell string configured by connecting a plurality of solar cell modules 21 in series. The number of solar cell modules 21 included in each solar cell string 2 depends on the shape and area of the place where the solar cell string 2 is installed. Therefore, some are composed of a standard number of solar cell modules 21, and others are composed of a smaller number. The number of the solar cell strings 2 is determined according to the installation mode of the photovoltaic power generation system 1 and is, for example, the number of strings of 2 to 5. Note that the DC power supply 2 may be composed of a single solar cell module 21.

  The power conversion apparatus 1 includes a plurality of voltage adjustment circuits (DC / DC converters) 11, an inverter circuit 12, a filter circuit 13, and control means 14. The voltage adjustment circuit 11 is connected to the number of one solar cell string 2, respectively. In the example shown in the figure, the number of solar cell strings 2 and voltage adjustment circuits 11 is three, but the present invention is not limited to this.

Each voltage adjustment circuit 11 boosts the input voltage Vin (first to third input voltages Vin _{1 to} Vin ₃ ), that is, the DC voltage output from the corresponding solar cell string 2 to a predetermined bus voltage set value Vset. To do. The voltage adjustment circuit 11 includes a step-up chopper circuit including a switching element (not shown) made of a reactor (not shown), IGBT, etc., a diode (not shown), and a capacitor (not shown), for example. Then, on / off of the switching element (not shown) is controlled so that the DC voltage output from the voltage adjustment circuit 11 becomes the bus voltage set value Vset. In the plurality of voltage adjustment circuits 11, the predetermined bus voltage setting value Vset is the same value.

  The inverter circuit 12 receives, in parallel, a DC bus voltage Vbus boosted from the plurality of voltage adjustment circuits 11 so as to have the predetermined bus voltage setting value Vset. The inverter circuit 12 is a three-phase inverter circuit, for example, and includes a total of six or more switching elements (not shown) made up of three pairs, and these switching elements (not shown) are controlled. . The filter circuit 13 includes a reactor (not shown) and a capacitor (not shown), and is combined with the inverter circuit 12 to output a three-phase AC voltage.

The power converter 1 also includes input voltage detection means 16 (first to third inputs) for detecting the input voltage Vin (first to third input voltages Vin _{1 to} Vin ₃ ) to each voltage adjustment circuit 11. a voltage detecting means ₁₆ 1 to 16 _3), the input current Iin (first to third input current Iin ₁ ~Iin ₃₎ detecting each input current detecting means 17 (first to to each voltage regulator circuit 11 3 input voltage detecting means 17 _{1 to} 17 ₃ ) and a DC bus voltage detecting means 18 for detecting a DC bus voltage Vbus which is an input voltage of the inverter circuit 12.

  The control means 14 includes an inverter circuit control unit 30 and a voltage adjustment circuit control unit 40. The control means 14 is composed of one microcomputer. The inverter circuit control unit 30 receives the DC bus voltage Vbus detected by the DC bus voltage detection means 18. The inverter circuit control unit 30 generates a PWM signal based on the DC bus voltage Vbus and drives a switching element (not shown) of the inverter circuit 12.

The voltage adjustment circuit control unit 40 includes an input voltage Vin (first to third input voltages Vin _{1 to} Vin ₃ ) detected by the input voltage detection unit 16, and an input current Iin ( The first to third input currents Iin _{1 to} Iin ₃ ) and the DC bus voltage Vbus detected by the DC bus voltage detection means 18 are input.

  As illustrated in FIG. 2, the voltage adjustment circuit control unit 40 includes an MPPT control unit 41 and a plurality of drive signal generation units 42 corresponding to the voltage adjustment circuits 11.

  Each MPPT control unit 41 takes out the maximum power from the solar cell string 2 by executing MPPT control (maximum power tracking control) on the corresponding voltage adjustment circuit 11. Specifically, the target input voltage Vin_ref which is the maximum power in the input voltage Vin and the input power characteristic curve of the voltage adjustment circuit is obtained by a so-called hill climbing method. However, this characteristic curve changes according to the amount of solar radiation, etc., and the target input voltage Vin_ref which becomes the maximum power changes. Since the target input voltage Vin_ref fluctuates in this way, the MPPT control unit 41 always executes MPPT control during the operation of the voltage adjustment circuit 11.

Since the solar cell strings 2 corresponding to the respective voltage adjustment circuits 11 have different amounts of solar radiation and other conditions, the target input voltages Vin_ref required by the respective MPPT control units 41 are different from each other. Therefore, the first to third target input voltages Vin_ref _{1 to} Vin_ref ₃ are obtained, respectively. Here, the input power of each voltage adjustment circuit 11 is obtained from the input voltage Vin detected by the corresponding input voltage detection means 16 (FIG. 1) and the input current Iin detected by the input current detection means 17 (FIG. 1). Each MPPT control unit 41 receives an input voltage Vin and an input current Iin.

  Each drive signal generation unit 42 is a drive signal for driving the voltage adjustment circuit 11 based on the target input voltage Vin_ref obtained by the MPPT control unit 41 and the bus voltage set value Vset, and turns on / off a switching element (not shown). A pulse signal to be controlled is generated.

  The voltage adjustment circuit control unit 40 also includes a power system state change processing unit 43 that detects a change in state in the power system 3 (FIG. 1) and performs a predetermined process when the change is detected.

The power system state change processing unit 43, the input current detecting means 17 inputs of the first to third detected respectively by (Figure 1) current Iin ₁ ～Iin _3, and each input voltage detecting means 16 (FIG. 1 ) is first to third input voltage Vin ₁ to VIN ₃ respectively detected by the input. In the power system state change processing unit 43, for example, when any one of the first to third input currents Iin _{1 to} Iin ₃ decreases, that is, when the input current Iin becomes smaller than a predetermined value, You may determine with the voltage of the electric power grid | system 3 of FIG. 1 falling. That is, when the voltage of the power system 3 decreases, the DC bus voltage Vbus detected by the DC bus voltage detection means 18 increases, and the inverter circuit control unit 30 stops the operation of the inverter circuit 12 accordingly. The input current Iin of the adjustment circuit 11 decreases. Note that the power system state change determination unit 43 in FIG. 2 has reduced any two input currents Iin among the plurality of input currents Iin _{1 to} Iin ₃ , that is, a part of the input current Iin that is not one. In this case, it may be determined that the voltage of the power system 3 has decreased.

The power system state change processing unit 43 also periodically receives the input first to third input currents Iin _{1 to} Iin ₃ and the input first to third input voltages Vin _{1 to} Vin _3. Record. When determining the voltage drop occurs, the respective input of the immediately preceding current Iin ₁ ~Iin _3, and each input voltage Vin ₁ to VIN _3, respectively, the recovery time of the control current value Iin_str and recovery time control voltage value Vin_str (No. 1 to the third recovery control current values Iin_str _{1 to} Iin_str ₃ and the recovery control voltage values Vin_str _{1 to} Vin_str ₃ ). Since the storage unit 44 stores the recovery control current values Iin_str _{1 to} Iin_str ₃ and the recovery control voltage values Vin_str _{1 to} Vin_str ₃ as described above, when the voltage drop of the power system 3 (FIG. 1) is resolved. Inputs these to each MPPT control, and the MPPT control is resumed. Therefore, it is possible to quickly reach the target input voltage Vin_ref that becomes the maximum power P.

  Here, conditions such as the amount of solar radiation of the solar cell string 2 (FIG. 2) rarely change significantly during a short moment of short time such as within 1 second, so the input voltage Vin of the voltage adjustment circuit It is very likely that the input power characteristic curve hardly changes. Therefore, the recovery-time control current value Iin_str and the recovery-time control voltage value Vin_str immediately before the detection of the voltage drop of the system power 3 stored in the storage unit 44 of FIG. 2 are input to the MPPT control unit 41 immediately before the detection. Very likely close to Thereby, all the MPPT control parts 41 can track rapidly the target input voltage Vin_ref used as the maximum electric power.

Returning to FIG. 1, the voltage adjustment circuit control unit 40 also includes a first through third input voltage Vin ₁ to VIN ₃ respectively detected by the input voltage detecting means 16, respectively, by the input current detecting means 17 Based on the detected first to third input currents Iin _{1 to} Iin ₃ and the DC bus voltage Vbus detected by the DC bus voltage detection means 18, various state changes and Abnormality can be judged. In particular, since the voltage adjustment circuit control unit 40 can grasp all the detected values and all the changes thereof, it is possible to reliably determine a state change or an abnormality by comparing these values with each other.

The voltage adjustment circuit control unit 40 also calculates the total power generation amount of the solar cell string 2 from the _first to _third input voltages Vin _{1 to} Vin ₃ and the first to third input currents Iin _{1 to} Iin ₃ ( Vin ₁ × Iin ₁ + Vin ₂ × Iin ₂ + Vin ₃ × Iin ₃ ) may be calculated. Thereby, the electric power generation amount of the solar cell string 2 can be monitored.

Next, an exemplary operation of the power conversion device according to the present embodiment will be described.
Assume that the voltage of the power system 3 in FIG. 1 decreases during normal operation. As a result, the DC bus voltage Vbus increases. Therefore, when the DC bus voltage Vbus exceeds a predetermined upper limit value, a determination unit (not shown) of the inverter circuit control unit 30 determines a decrease in the voltage of the power system 3. Then, the operation of the inverter circuit 12 is stopped. When the operation of the inverter circuit 12 is stopped, the input voltage Vin of each voltage adjustment circuit 11 becomes an open voltage. For this reason, the input current Iin of the voltage adjustment circuit 11 decreases.

When any one of the first to third input currents Iin _{1 to} Iin ₃ becomes smaller than a predetermined value, the power system state change processing unit 43 in FIG. It is determined that the reduction has occurred, and the MPPT control of the MPPT control unit 41 is stopped so that the drive signal generation unit 42 stops the drive signal generation. Next, the power system state change processing unit 43 converts each input current Iin and each input voltage Vin immediately before detecting a voltage drop in the power system into a recovery control current value Iin_str (first to third recovery times). Control current values Iin_str _{1 to} Iin_str ₃ ) and recovery control voltage values Vin_str (first to third Vin_str _{1 to} Vin_str ₃ ) are stored in the storage unit 44.

Thereafter, it is assumed that the voltage drop of the power system 3 in FIG. 1 is resolved within a predetermined time (for example, within 1 second) from this voltage drop time point. Accordingly, a determination unit (not shown) of the inverter circuit control unit 30 determines that the voltage drop of the power system 3 has been resolved when the increased DC bus voltage Vbus falls below a predetermined lower limit value. Release the operation stop. When the operation stop of the inverter circuit 12 is released, the input current Iin of the voltage adjustment circuit 11 increases. The power system state change determination unit 43 determines that the voltage drop has been eliminated in the power system 3 when all the input currents Iin of the _first to third input currents Iin _{1 to} Iin ₃ are larger than a predetermined value. .

And each MPPT control part 41 of FIG. 2 restarts MPPT control. Here, when the MPPT control is restarted, the recovery-time control current value Iin_str (first to third recovery-time control current values Iin_str _{1 to} Iin_str ₃ ) and the recovery-time control voltage value Vin_str (first) stored in the storage unit 44. 1 to 3 Vin_str _{1 to} Vin_str ₃ ) are used. As described above, when the MPPT control is resumed, the recovery control current value Iin_str (first to third recovery control current values Iin_str _{1 to} Iin_str ₃ ) and the recovery control voltage value Vin_str (first to _third ) immediately before the voltage drop is detected. Since the third Vin_str _{1 to} Vin_str ₃ ) are used, the target input voltage Vin_ref at which the maximum power Pin_max is reached can be quickly reached.

  In the above embodiment, when it is determined that the voltage drop has occurred, the input current Iin and the input voltage Vin immediately before that are stored in the storage unit 44, but only one of them may be stored.

  In the above-described embodiment, the MPPT control unit 41 and the drive signal generation unit 42 necessary for driving each voltage adjustment circuit 11 are configured in a single microcomputer. Therefore, a microcomputer is provided for each voltage adjustment circuit 11. If not, all the voltage adjustment circuits 11 can operate. However, each voltage adjustment circuit 11 may be provided with a microcomputer. For example, these microcomputers may perform temperature compensation of the corresponding voltage adjustment circuit 11.

  The power converter according to the above embodiment is not limited to a solar power generation system, but can be applied to any renewable energy power generation system including a wind power generation system, a fuel cell system, a power storage system, and the like.

  As mentioned above, according to the power converter device concerning the present invention, it has a high-speed response processing capability, although it is provided with a plurality of voltage regulation circuits.

DESCRIPTION OF SYMBOLS 1 Power converter 2 DC power supply 3 Electric power system 11 Voltage adjustment circuit 12 Inverter circuit 40 Voltage adjustment circuit control means

Claims (4)

A power converter that is connected to a plurality of DC power supplies and outputs AC power that can be linked to a power system,
A plurality of voltage adjusting circuits for boosting a DC voltage supplied from each of the plurality of DC power sources to the same predetermined voltage setting value;
An inverter circuit connected in parallel to the plurality of voltage regulation circuits, wherein the inverter circuit converts the DC voltage boosted by the plurality of voltage regulation circuits into an AC voltage;
Voltage adjusting circuit control means for controlling the plurality of voltage adjusting circuits based on each DC current and each DC voltage respectively input from the plurality of DC power sources to the plurality of voltage adjusting circuits ;
A voltage adjustment circuit control unit having a power system state change processing unit that determines that the voltage of the power system has dropped when any one or a part of the plurality of DC currents is lowered ;
The voltage adjustment circuit control means is a power conversion device configured as a single microcomputer. The power conversion device according to claim 1,
The power system state change processing unit is
Detecting a change of state in the electric power system, when detecting a change, you store at least one of the DC current and the DC voltage are input from the plurality of direct current power to the plurality of voltage regulating circuits, power conversion apparatus. The power conversion device according to claim 2,
The voltage adjustment circuit control means further includes:
An MPPT control unit that outputs a target value so as to perform MPPT control based on each DC current and each DC voltage input to each voltage adjustment circuit;
A drive signal generation unit that generates a drive signal for driving a corresponding voltage adjustment circuit based on the target value output by the MPPT control unit and the predetermined voltage setting value corresponds to the plurality of voltage adjustment circuits. A plurality of power converters. In the power converter according to any one of claims 1 to 3,
The DC power supply is a power conversion device including a solar cell string configured by connecting a plurality of solar modules in series.

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