JP2017028982A - Power conversion device and control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device capable of reducing the difference between an instruction value and actual output power when small power is instructed, and a control method for the same.SOLUTION: A controller 12 of a power conversion device 1 having an AC/DC converter 11 and a DC/DC converter 10 compares the absolute value of an AC voltage target value based on an AC voltage with a DC voltage target value based on a DC power supply voltage. On the basis of its magnitude relationship, a control system is executed in which a period of executing a voltage step-up operation based on a switching operation in which one of the AC/DC converter 11 and the DC/DC converter 10 serves as a subject, and a period of executing a voltage step-down operation based on the switching operation in which the other serves as a subject appear alternately. In addition, when a period during which current becomes discontinuous under the state that an electrical conduction passage is secured in only one direction of a DC reactor 16 within the DC/DC converter 10 appears, at least the period secures an electrical conduction passage in both the directions of the DC reactor 16 within the DC/DC converter 10.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power conversion device and a control method thereof.

The power conversion device for providing the power generated by the photovoltaic power generation panel or the power stored in the storage battery to the load connected to the power system is the output voltage of the photovoltaic power generation panel or the terminal voltage of the storage battery. And a DC / DC converter for boosting the voltage and an inverter for converting direct current into alternating current.
In this case, the DC / DC converter boosts the voltage input from the photovoltaic power generation panel or the storage battery to a constant voltage equal to or higher than the required AC peak value by high-frequency switching and outputs the boosted voltage to the DC bus. The inverter converts this constant voltage into an AC waveform by high-frequency switching and outputs it.

  Here, in the above power conversion device, the DC / DC conversion unit and the inverter always perform high-frequency switching. High frequency switching causes a corresponding switching loss, which causes the conversion efficiency to deteriorate. In order to reduce the switching loss and increase the conversion efficiency, for example, it is possible to apply a control method in which the DC / DC conversion unit and the inverter are alternately switched within one AC cycle (for example, Patent Documents). 1). In this case, the switching frequency as the whole power converter is reduced.

JP 2014-241714 A

  However, it has been found that there is a case where the output as instructed cannot be obtained in the power conversion device adopting the above control method. In particular, when a small output power is instructed within the range of possible output power, there is a tendency that a difference appears between the command value and the actual output power. Therefore, when controlling the power of the storage battery so that the reverse power is not supplied to the system side beyond the power receiving point, it is complicated to suppress the output of the storage battery in consideration of the difference between the command value and the actual output value. Must operate. This is not particularly a problem, but there is room for improvement in order to obtain a higher quality power converter.

  In view of this problem, an object of the present invention is to provide a power conversion device and a control method thereof that can reduce the difference between a command value and actual output power when a small power is instructed.

  According to one expression as an object, the present invention is a power conversion device provided between a load connected to an AC circuit and a DC power source, the voltage sensor detecting the AC voltage of the AC circuit, An AC / DC converter provided between a load and a DC bus; a capacitor connected to the DC bus; a DC reactor provided between the DC bus and the DC power supply; and the DC reactor A high-side switch having a parallel diode provided between the DC reactor and the high potential side circuit of the DC bus, and a parallel diode provided between the DC reactor and the low potential side circuit of the DC bus. A DC / DC converter including a low-side switch, a current sensor that detects a current flowing through the DC reactor, and a voltage across the DC power supply as a DC power supply voltage. The absolute value of the AC voltage target value based on the AC voltage and the DC voltage target value based on the DC power supply voltage are compared with each other, and based on the magnitude relationship, the AC / DC converter and the DC A control method in which a period in which boosting is performed by a switching operation mainly using one of the DC / DC converters and a period in which voltage lowering is performed by a switching operation mainly using the other is executed, and When a period in which current is discontinuous occurs in a state in which a current-carrying path is ensured only in one direction of the DC reactor in the DC / DC conversion unit, at least the period includes both of the DC reactors in the DC / DC conversion unit. And a control unit that secures an energization path in the direction.

  Moreover, according to one expression as the method, the present invention is provided between a load connected to an AC circuit and a DC power supply, and an AC / DC conversion unit provided between the load and a DC bus; A high-side switch having a parallel diode, provided between the DC bus and the DC power supply, provided between the DC reactor, and the DC reactor and the high potential side electric circuit of the DC bus; A method for controlling a power converter comprising: a DC / DC conversion unit including a low-side switch having a parallel diode provided between the DC reactor and a low-potential side circuit of the DC bus, the AC voltage The absolute value of the AC voltage target value based on DC and the DC voltage target value based on the DC power supply voltage are compared with each other, and based on the magnitude relationship, the AC / DC converter and the DC / D Performing a control in which a period in which boosting is performed by a switching operation mainly using one of the converters and a period in which a voltage lowering is performed by a switching operation mainly using the other are performed, and the DC / DC When a period in which current is discontinuous occurs in a state where an energization path is ensured only in one direction of the DC reactor in the conversion unit, at least the period is energized in both directions of the DC reactor in the DC / DC conversion unit. This is a method for controlling a power conversion device that secures a route.

  In addition, about the said power converter device and its control method, if a power system (commercial power system) is connected to an alternating current circuit, and direct-current power supply is a storage battery, it can also respectively express as follows.

  That is, according to another expression as an object, the present invention is a power conversion device provided between a power system and a load connected to the power system and a storage battery, and detects an AC voltage of the power system. A voltage sensor; an AC / DC converter provided between the load and the DC bus; a capacitor connected to the DC bus; a DC reactor provided between the DC bus and the storage battery; and A high side switch having a parallel diode provided between the DC reactor and the high potential side circuit of the DC bus, and provided between the DC reactor and the low potential side circuit of the DC bus. A DC / DC converter including a low-side switch having a parallel diode, a current sensor for detecting a current flowing through the DC reactor, and a voltage across the storage battery A voltage sensor to detect as a voltage, an absolute value of an AC voltage target value based on the AC voltage and a DC voltage target value based on the storage battery voltage are compared with each other, and based on the magnitude relationship, the AC / DC converter and Executing a control method in which a period in which boosting is performed by a switching operation mainly using any one of the DC / DC converters and a period in which voltage reduction is performed by a switching operation mainly using the other appear alternately; and When a current larger than a predetermined value flows through the DC reactor, an energization path is secured in one direction of the DC reactor in the DC / DC converter, and when a current smaller than the predetermined value flows through the DC reactor, the DC reactor A DC / DC converter, and a controller that secures a current-carrying path in both directions of the DC reactor.

  Further, according to another expression of the present invention, the AC / DC provided between the power system and the load connected to the power system and the storage battery, and provided between the load and the DC bus, A high-side switch having a parallel diode provided between the converter and the DC bus and the storage battery, and provided between the DC reactor and the DC reactor and the high potential side electric circuit of the DC bus; And a DC / DC conversion unit including a low-side switch having a parallel diode provided between the DC reactor and a low-potential side electric circuit of the DC bus, The absolute value of the AC voltage target value based on the AC voltage and the DC voltage target value based on the storage battery voltage are compared with each other, and based on the magnitude relationship, the AC / DC converter and the Executing a control in which a period in which boosting is performed by a switching operation mainly using any one of the C / DC conversion units and a period in which a voltage lowering is performed by a switching operation mainly by the other appear alternately; and When a current larger than a predetermined value flows through the DC reactor, an energization path is secured in one direction of the DC reactor within the DC / DC converter, and when a current smaller than the predetermined value flows through the DC reactor, the DC / DC It is the control method of a power converter device which ensures an energization path in both directions of the direct-current reactor in a conversion part.

  According to the present invention, the difference between the command value and the actual output power can be reduced.

It is a single line connection figure showing an example of a charge and discharge system provided with a power converter concerning one embodiment of the present invention. It is an example of the detailed circuit diagram of a power converter device. It is the figure of the voltage waveform which showed notionally the operation | movement in case the power converter device is charging the storage battery. It is the figure of the voltage waveform which showed notionally the operation | movement in case the power converter device is discharging the storage battery. It is a figure which shows schematic structure of the measurement system containing a power converter device. It is a graph which shows the simulation result when the command value of output electric power is 2000W and the output current target value is 10A by the switching system with one of the switches off. It is a graph which shows a simulation result when the command value of output electric power is set to 2000 W and the output current target value is 10 A in the always complementary switching method. It is a graph which shows the simulation result when the command value of output electric power is 2000 W, the output current target value is 10 A, and the “predetermined value” of the direct current of the DC reactor is 1 A in the switching method of the present embodiment. It is a graph which shows the simulation result when the command value of output electric power is set to 200W and output current target value 1A by the switching system which one side of a switch is OFF. It is a graph which shows a simulation result when the command value of output electric power is set to 200 W and the output current target value is 1 A in the always complementary switching method. It is a graph which shows the simulation result when the command value of output electric power is 200 W, the output current target value is 1 A, and the “predetermined value” of the DC reactor current is 1 A in the switching method of the present embodiment. It is the figure which expanded the scale of the electric current value of the vertical axis | shaft in FIG. It is the figure which expanded the scale of the electric current value of the vertical axis | shaft in FIG. It is the figure which expanded the scale of the electric current value of the vertical axis | shaft in FIG.

[Summary of Embodiment]
The gist of the embodiment of the present invention includes at least the following.

  (1) This is a power conversion device provided between a load connected to an AC circuit and a DC power supply, between the voltage sensor for detecting the AC voltage of the AC circuit, and the load and the DC bus. An AC / DC converter provided in the DC bus, a capacitor connected to the DC bus, a DC reactor, and a high potential of the DC reactor and the DC bus. A DC including a high-side switch having a parallel diode provided between the DC circuit and a low-side switch having a parallel diode provided between the DC reactor and the low-potential side circuit of the DC bus. A DC / DC converter, a current sensor that detects a current flowing through the DC reactor, a voltage sensor that detects a voltage across the DC power supply as a DC power supply voltage, and a control It is those with a door. The control unit compares the absolute value of the AC voltage target value based on the AC voltage with the DC voltage target value based on the DC power supply voltage, and based on the magnitude relationship, the AC / DC conversion unit and the DC / DC A control method is executed in which a period in which boosting is performed by a switching operation mainly using one of the DC converters and a period in which voltage reduction is performed by a switching operation mainly by the other appear alternately, and the DC When a current discontinuous period occurs in a state where an energization path is ensured only in one direction of the DC reactor in the DC / DC converter, at least the period is bidirectional of the DC reactor in the DC / DC converter. Secure the energization path.

  In such a power conversion device, the period in which the voltage is boosted by one of the AC / DC converter and the DC / DC converter and the period in which the voltage is decreased by the other appear alternately, Execute the “minimum switching conversion method” to reduce the number of switching. In this case, it is known that the current flowing through the DC reactor in the DC / DC conversion section becomes a pulsating flow. The pulsating flow includes high-frequency inductor ripple due to switching. When the pulsating flow including the inductor ripple approaches 0, the current value tends to enter a minus region due to the fluctuation width of the inductor ripple. However, in the state where the energization path is secured only in one direction of the DC reactor in the DC / DC converter, a period in which the current is discontinuous occurs. When the current becomes discontinuous, the original average value cannot be detected accurately. Therefore, in this power conversion device, when a period in which the current is discontinuous occurs in a state where the energization path is ensured only in one direction of the DC reactor in the DC / DC conversion unit, at least the period is in the DC / DC conversion unit. In order to secure an energization path in both directions of the DC reactor. As a result, when a current (small current) that is likely to be discontinuous in one direction flows through the DC reactor, bidirectional current flow is possible in the DC reactor. As a result, when the command value of output power is relatively small, the difference between the output power of the power converter and the command value can be reduced.

(2) Further, in the power conversion device of (1), when the DC / DC conversion unit is output from the DC power source and the DC / DC conversion unit is boosted, the control unit does not generate the discontinuous period. Hold the high side switch off to operate the low side switch, when the discontinuous period occurs, operate the high side switch and the low side switch in a complementary manner,
When the DC power supply is output from the DC power supply and the DC / DC converter is not boosted, the control unit holds both the high-side switch and the low-side switch off when the discontinuous period does not occur. When the discontinuous period occurs, the high side switch is kept on and the low side switch is kept off.
In this case, it is possible to reduce the difference between the output power of the power converter and the command value when the DC power source is discharged.

(3) Moreover, in the power converter of (1), when the DC / DC converter is stepped down and the DC power supply is charged, the control unit does not generate the discontinuous period. Hold the low side switch off to operate the high side switch, and when the discontinuous period occurs, operate the high side switch and the low side switch in a complementary manner,
When charging the DC power supply without causing the DC / DC converter to step down, the control unit keeps the high-side switch on and the low-side switch off when the discontinuous period does not occur Even when the discontinuous period occurs, the high-side switch is kept on and the low-side switch is kept off.
In this case, the difference between the input power to the power conversion device and the command value during charging of the DC power supply can be reduced.

  (4) On the other hand, from another point of view, an AC / DC converter provided between a load connected to an AC circuit and a DC power supply, and provided between the load and a DC bus, and the DC bus And the DC power supply, a DC reactor, a high-side switch having a parallel diode provided between the DC reactor and the high potential side circuit of the DC bus, and the DC reactor, And a DC / DC converter including a low-side switch having a parallel diode provided between the DC bus and a low-potential side electric circuit. In this control method, the absolute value of the AC voltage target value based on the AC voltage and the DC voltage target value based on the DC power supply voltage are compared with each other, and based on the magnitude relationship, the AC / DC converter and the DC A control is performed in which a period in which boosting is performed by a switching operation mainly using one of the DC / DC converters, and a period in which voltage reduction is performed by a switching operation mainly by the other appear alternately. When a current discontinuous period occurs in a state where an energization path is ensured only in one direction of the DC reactor in the DC / DC converter, at least the period is bidirectional of the DC reactor in the DC / DC converter. Secure the energization path.

  In such a control method for a power conversion device, a period in which boosting is performed by one of the AC / DC conversion unit and the DC / DC conversion unit and a period in which stepping down is performed by the other appear alternately. The “minimum switching conversion method” is executed to reduce the number of switching operations as a whole. In this case, it is known that the current flowing through the DC reactor in the DC / DC conversion section becomes a pulsating flow. The pulsating flow includes high-frequency inductor ripple due to switching. When the pulsating flow including the inductor ripple approaches 0, the current value tends to enter a minus region due to the fluctuation width of the inductor ripple. However, in the state where the energization path is secured only in one direction of the DC reactor in the DC / DC converter, a period in which the current is discontinuous occurs. When the current becomes discontinuous, the original average value cannot be detected accurately. Therefore, in this power conversion device, when a period in which the current is discontinuous occurs in a state where the energization path is ensured only in one direction of the DC reactor in the DC / DC conversion unit, at least the period is in the DC / DC conversion unit. In order to secure an energization path in both directions of the DC reactor. As a result, when a current (small current) that is likely to be discontinuous in one direction flows through the DC reactor, bidirectional current flow is possible in the DC reactor. As a result, when the command value of output power is relatively small, the difference between the output power of the power converter and the command value can be reduced.

  In addition, about said (1)-(4), if an electric power system (commercial power system) is connected to an alternating current circuit, and direct-current power supply is a storage battery, respectively of the following (5)-(8) It can be expressed as follows.

(5) This is a power conversion device provided between a power system and a load connected to the power system and a storage battery, a voltage sensor for detecting an AC voltage of the power system, the load and a DC bus, An AC / DC converter provided between the DC bus, the capacitor connected to the DC bus, the DC bus and the storage battery, a direct current reactor, and a high level of the direct current reactor and the DC bus. A high-side switch having a parallel diode provided between the potential-side electric circuit and a low-side switch having a parallel diode provided between the DC reactor and the low-potential-side electric circuit of the DC bus. A DC / DC converter, a current sensor that detects a current flowing through the DC reactor, a voltage sensor that detects a voltage across the storage battery as a storage battery voltage, It is obtained by a control unit. The control unit compares the absolute value of the AC voltage target value based on the AC voltage with the DC voltage target value based on the storage battery voltage, and based on the magnitude relationship, the AC / DC conversion unit and the DC / DC A control method is executed in which a period in which boosting is performed by a switching operation mainly using one of the conversion units and a period in which voltage reduction is performed by a switching operation mainly by the other appear alternately, and the DC reactor When a current larger than a predetermined value flows through the DC / DC converter, an energization path is secured in one direction of the DC reactor in the DC / DC converter, and when a current smaller than the predetermined value flows through the DC reactor, Thus, an energization path is secured in both directions of the DC reactor.
Note that when a current larger than a predetermined value flows is an example when a period of discontinuity does not occur. When a current smaller than a predetermined value flows, the period when a period of discontinuity occurs. It is an example. That is, the predetermined value may be set at the boundary of whether or not it becomes discontinuous.

  In such a power conversion device, the period in which the voltage is boosted by one of the AC / DC converter and the DC / DC converter and the period in which the voltage is decreased by the other appear alternately, Reduce the number of switching. Moreover, in such a power converter, when a current larger than a predetermined value flows through the DC reactor, an energization path is secured in one direction of the DC reactor in the DC / DC converter, and a current smaller than the predetermined value flows through the DC reactor. In some cases, an energization path is secured in both directions of the DC reactor in the DC / DC converter. As a result, when a current smaller than a predetermined value flows through the DC reactor, bidirectional current can flow in the DC reactor. Therefore, even if the sign of the current smaller than the predetermined value changes to the reverse polarity and becomes the reverse current, the current flows to the DC reactor. As a result, when the command value of output power is small, the difference between the output power of the power converter and the command value can be reduced.

(6) In the power converter of (5), when the storage battery is discharged and the DC / DC converter is boosted, the control unit causes a current larger than the predetermined value to flow through the DC reactor. Holds the high side switch off to operate the low side switch, and when a current smaller than the predetermined value flows through the DC reactor, operates the high side switch and the low side switch in a complementary manner,
When the storage battery is discharged and the DC / DC converter is not boosted, the controller holds both the high-side switch and the low-side switch off when a current larger than the predetermined value flows through the DC reactor. When a current smaller than the predetermined value flows through the DC reactor, the high side switch is turned on and the low side switch is held off.
In this case, the difference between the output power of the power conversion device and the command value when discharging the storage battery can be reduced.

(7) Moreover, in the power converter of (5), when the DC / DC converter is stepped down to charge the storage battery, the controller is configured to cause a current larger than the predetermined value to flow through the DC reactor. Holds the low side switch off to operate the high side switch, and when a current smaller than the predetermined value flows through the DC reactor, the high side switch and the low side switch are operated in a complementary manner,
When charging the storage battery without stepping down the DC / DC converter, the controller turns on the high-side switch and turns off the low-side switch when a current larger than the predetermined value flows through the DC reactor. And when the current smaller than the predetermined value flows through the DC reactor, the high-side switch is turned on and the low-side switch is held off.
In this case, the difference between the input power to the power conversion device and the command value when charging the storage battery can be reduced.

  (8) On the other hand, from another point of view, an AC / DC conversion unit provided between the power system and a load connected to the power system and the storage battery, and provided between the load and a DC bus; A DC reactor provided between the DC bus and the storage battery; a high-side switch having a parallel diode provided between the DC reactor and the high-potential side circuit of the DC bus; and the DC reactor. And a DC / DC conversion unit including a low-side switch having a parallel diode provided between the DC bus and a low potential side electric circuit of the DC bus. In this control method, the absolute value of the AC voltage target value based on the AC voltage and the DC voltage target value based on the storage battery voltage are compared with each other, and based on the magnitude relationship, the AC / DC conversion unit and the DC / DC Performing a control in which a period in which boosting is performed by a switching operation mainly using one of the DC converters and a period in which a voltage lowering is performed by a switching operation mainly using the other are performed, and the DC reactor When a current larger than a predetermined value flows through the DC / DC converter, an energization path is secured in one direction of the DC reactor in the DC / DC converter, and when a current smaller than the predetermined value flows through the DC reactor, Thus, an energization path is secured in both directions of the DC reactor.

  In such a control method for a power conversion device, a period in which boosting is performed by one of the AC / DC conversion unit and the DC / DC conversion unit and a period in which stepping down is performed by the other appear alternately. Reduce the overall switching frequency. Further, in such a control method, when a current larger than a predetermined value flows in the DC reactor, an energization path is secured in one direction of the DC reactor in the DC / DC converter, and a current smaller than the predetermined value flows in the DC reactor. Secures an energization path in both directions of the DC reactor in the DC / DC converter. As a result, when a current smaller than a predetermined value flows through the DC reactor, bidirectional current can flow in the DC reactor. Therefore, even if the sign of the current smaller than the predetermined value changes to the reverse polarity and becomes the reverse current, the current flows to the DC reactor. As a result, when the command value of output power is small, the difference between the output power of the power converter and the command value can be reduced.

[Details of the embodiment]
<Charging / Discharging System>
FIG. 1 is a single-line connection diagram illustrating an example of a charge / discharge system including a power conversion device according to an embodiment of the present invention. In the figure, a DC power source 2 is connected to one end of the power converter 1, and an AC circuit 3 is connected to the other end. The DC power source 2 is, for example, a storage battery (hereinafter referred to as storage battery 2). This charging / discharging system converts the AC power supplied from the AC power circuit 3 into DC power by the power converter 1 and charges the storage battery 2. Conversely, the storage battery 2 can be discharged, the DC power can be converted into AC power by the power conversion device 1, and power can be supplied to the AC circuit 3.

The power conversion device 1 includes, as main components, a DC / DC conversion unit 10 provided on the storage battery 2 side, an AC / DC conversion unit 11 provided on the AC circuit 3 side, and operations of these two conversion units. And a control unit 12 for controlling.
The control unit 12 includes, for example, a computer, and realizes a necessary control function for the two conversion units (10, 11) when the computer (computer program) is executed. The software is stored in a storage device (not shown) of the control unit 12. However, it is also possible to configure the control unit 12 with a hardware-only circuit that does not include a computer.

<Power conversion device>
<Circuit configuration>
FIG. 2 is an example of a detailed circuit diagram of the power conversion device 1.
In the figure, a power conversion device 1 is provided between a storage battery 2 and an alternating current circuit 3. The AC circuit 3 includes a consumer load 3L and a power system (commercial power system) 3S connected to the load 3L. A voltage sensor 14, a current sensor 17, and a smoothing capacitor 15 are provided on the low potential side (left side in the figure) of the DC / DC converter 10. The voltage sensor 14 is connected in parallel with the storage battery 2 and detects the voltage across the storage battery 2. Information on the detected voltage is provided to the control unit 12. The current sensor 17 detects a current flowing through the DC reactor 16 of the DC / DC conversion unit 10. Information on the detected current is provided to the control unit 12.

The DC / DC conversion unit 10 includes a DC reactor 16, a switching element Q1, and a switching element Q2, and constitutes a DC chopper circuit. As each of the switching elements Q1 and Q2, for example, a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) can be used. The MOSFET switching elements Q1, Q2 have diodes (body diodes) d1, d2 in parallel, respectively. Each switching element Q1, Q2 is controlled by the control unit 12.
Hereinafter, the upper switching element Q1 in the arm in the DC / DC conversion unit 10 is referred to as a high side switch Q1, and the lower switching element Q2 in the arm is referred to as a low side switch Q2.

  A smoothing capacitor 19 is connected to the DC bus 18 that connects the AC / DC converter 11 and the DC / DC converter 10. The capacitor 19 has a small capacity (μF level) and exhibits a smoothing action on a voltage switched at a high frequency (for example, 20 kHz), but changes at a frequency (100 Hz or 120 Hz) about twice the commercial frequency. It does not exert a smoothing effect on voltage.

  The AC / DC converter 11 includes switching elements Q3 to Q6 that constitute a full bridge circuit. These switching elements Q3 to Q6 are, for example, MOSFETs. In the case of a MOSFET, the switching elements Q3 to Q6 have diodes (body diodes) d3 to d6, respectively. The switching elements Q3 to Q6 are controlled by the control unit 12.

  A filter circuit 21 is provided between the AC / DC converter 11 and the AC circuit 3. The filter circuit 21 includes an AC reactor 22 and a smoothing capacitor 23 provided on the AC circuit 3 side (right side in the drawing) from the AC reactor 22. The filter circuit 21 prevents passage of high-frequency noise generated in the AC / DC converter 11 so as not to leak to the AC circuit 3 side. In addition, a current sensor 24 that detects a current flowing through the AC reactor 22 is provided. Information on the current detected by the current sensor 24 is provided to the control unit 12.

  A voltage sensor 25 is provided in parallel with the capacitor 23, the load 4, and the power system 3S. On the other hand, the current sensor 26 is provided in an electric circuit connecting the load 3L and the power conversion device 1. Information on the voltage detected by the voltage sensor 25 and information on the current detected by the current sensor 26 are respectively provided to the control unit 12.

<Overview of charge / discharge operation>
The power conversion device 1 configured as described above has a bidirectional operation of an operation of charging the storage battery 2 with the power of the power system 3S and an operation of supplying power to the load 3L with the discharge power of the storage battery 2. Is possible. In both cases of charging and discharging, the AC / DC conversion unit 11 and the DC / DC conversion unit 10 perform switching operations alternately during the AC 1/2 cycle.

When charging the storage battery 2, the AC / DC converter 11 performs boosting in cooperation with the AC reactor 22, and the DC / DC converter 10 exhibits a “through” function that simply allows the voltage / current to pass therethrough. There are a state and a state where the AC / DC conversion unit 11 merely performs rectification, and the DC / DC conversion unit 10 performs a step-down operation. Note that the AC reactor 22 when the AC / DC conversion unit 11 performs boosting is a part of the AC / DC conversion unit 11.
On the other hand, when discharging the storage battery 2, the DC / DC conversion unit 10 boosts the voltage, the AC / DC conversion unit 11 performs only periodic polarity reversal, and the DC / DC conversion unit 10 is “through”. There is a state in which the AC / DC converter 11 exhibits a function and exhibits a step-down inverter function (including polarity reversal).

<Charging operation as seen from the voltage waveform diagram>
FIG. 3 is a voltage waveform diagram conceptually showing the operation of the power conversion device 1 configured as described above when, for example, the storage battery 2 is being charged.
(A) shows the absolute value (peak value about 141 V, effective value about 100 V) and DC voltage target value Vg ′ (about 48 V) of the AC voltage target value Vinv *. The AC voltage target value Vinv * is a voltage at the input end of the AC / DC converter 11 during the charging operation, which is ideally aimed at a state where the phase is delayed several degrees from this based on the AC voltage Va. It is a value that should be. If the impedance of the AC reactor 22 is ignored, Vinv * = Va. The DC voltage target value Vg ′ is a value in consideration of the voltage drop of the DC reactor 16 with respect to the storage battery voltage Vg. If the impedance of the DC reactor 16 is ignored, Vg ′ = Vg.
In addition, the voltage value said here is only an example. The control unit 12 compares these two voltages and controls the AC / DC conversion unit 11 and the DC / DC conversion unit 10 based on the comparison result.

here,
(Α) In the period from time t0 to t1, t2 to t3, t4 to t5, the absolute value of the AC voltage target value Vinv * is smaller than (or less than Vg ′) the DC voltage target value Vg ′.
(Β) Also, for example, in the period of time t1 to t2, t3 to t4, the absolute value of the AC voltage target value Vinv * is equal to or greater than the DC voltage target value Vg ′ (or larger than Vg ′).
Therefore, the conversion unit mainly performing the switching operation is changed according to the case of (α) or (β).
In the case of Vg ′ = | Vinv * |, the absolute value of the AC voltage target value Vinv * is smaller than the DC voltage target value Vg ′ since it may be included in either one of (α) and (β). The case will be described focusing on the case where the absolute value of the AC voltage target value Vinv * is larger than the DC voltage target value Vg ′.

  First, as shown in (b), in a period (t0 to t1, t2 to t3, t4 to t5) in which the absolute value of the AC voltage target value Vinv * is smaller than the DC voltage target value Vg ′, the control unit 12 The DC / DC converter 11 is switched to perform boosting in cooperation with the AC reactor 22. In addition, the switching said here means the high frequency switching of about 20 kHz, for example, and is not the low frequency switching of the grade which performs synchronous rectification (twice the commercial frequency) (the following is the same).

  On the other hand, in these periods (t0 to t1, t2 to t3, t4 to t5), the DC / DC converter 10 is in a state in which the low side switch Q2 is off and the high side switch Q1 is on, and the voltage / current is directly passed (passed). ). The vertical stripe pattern shown in (b) is actually a PWM (Pulse Width Modulation) pulse train, and the duty varies depending on the potential difference for boosting to the DC voltage target value Vg ′. As a result, the voltage appearing on the DC bus 18 has a waveform as shown in (c).

Further, in a period (t1 to t2, t3 to t4) in which the absolute value of the AC voltage target value Vinv * is greater than the DC voltage target value Vg ′, the control unit 12 stops the switching operation of the AC / DC conversion unit 11, Instead, the DC / DC converter 10 is switched to perform step-down. The AC / DC converter 11 that has stopped the switching operation is in a state of performing full-wave rectification by the diodes d1 to d4.
The vertical stripe pattern shown in (d) is actually a PWM pulse train, and the duty varies depending on the potential difference between the absolute value of the AC voltage target value Vinv * and the DC voltage target value Vg ′. As a result of the step-down, a desired DC voltage target value Vg ′ shown in (e) is obtained, whereby the storage battery 2 can be charged.

  As described above, the AC / DC conversion unit 11 and the DC / DC conversion unit 10 perform the switching operation alternately, and when one of them performs the switching operation, the other stops the switching operation. That is, the AC / DC converter 11 and the DC / DC converter 10 each have a switching operation stop period. Thus, compared with a control method in which the two conversion units always perform switching operation, this control method can significantly reduce the switching loss of the power conversion device 1 as a whole.

<Control specifications during charging>
Here, various quantities in the power conversion device 1 are defined as follows.
Ia *: target current value from the power system 3S Iin: DC current detection value of the DC / DC converter 10 (current sensor 17)
Iin *: target current value of the DC / DC converter 10 Iinv *: target AC current of the AC / DC converter 11 Ig *: target DC current of the storage battery 2 Ic: current flowing through the capacitor 19 Ica: current flowing through the capacitor 23 Current

Va: AC voltage Vg: Battery voltage Vinv *: AC voltage target value of the AC / DC converter 11 Vo *: Voltage target value on the DC bus 18 side of the DC / DC converter 10 Pin: Input power to the battery 2 P _LOSS : power loss of power converter 1 η: power conversion efficiency of power converter 1

The average value <Pin> of the input power Pin to the storage battery 2 is
<Pin> = <Iin × Vg> (1)
It is. The symbol <> represents an average value (the same applies hereinafter).
Moreover, the average value <Ia *> of the current target values from the power system 3S is
<Ia *> = <Ig * × Vg> / (η × <Va>) (2)
It is. Here, η is a constant representing the conversion efficiency of the power conversion device 1.
The current target value Ia * is
Ia * = (2 ^1/2 ) × <Ia *> × sin ωt (3)
It is.

On the other hand, the alternating current target value Iinv * for the AC / DC converter 11 takes into account the capacitance Ca of the capacitor 23.
Iinv * = Ia * −s CaVa (4)
It is. Here, “s” is a Laplace operator (the same applies hereinafter).

Further, the AC voltage target value Vinv * is set such that the impedance of the AC reactor 22 is Za.
Vinv * = Va−Za Iinv * (5)
It is.

Also, the input voltage target value Vo * to the DC / DC converter 10 is
Vo * = Max (absolute value of Vg + Z Iin, Vinv *) (6)
It can be. “Max” represents the larger one in (). Z is the impedance of the DC reactor 16. Here, (Vg + Z Iin) is the aforementioned DC voltage target value Vg ′.

Also, the DC / DC converter current target value Iin * is
Iin * =
{(Iinv * × Vinv *) − (s C Vo *) × Vo *} /
(Vg + ZIin) (7)
It is.

In addition, when the electrostatic capacity C and the power loss P _{LOSS of} the capacitor 19 are sufficiently smaller than (Iinv * × Vinv *), the following formula (8) is established. Iin * obtained by this equation (8) can be used as Iin included in the right side of equations (6) and (7).
Iin * = (Iinv * × Vinv *) / Vg (8)

  As described above, when the control unit 12 outputs the voltage of the portion where the absolute value of the AC voltage target value Vinv * to the AC / DC conversion unit 11 is higher than the DC voltage target value (Vg + Z Iin). When the DC / DC converter 10 is operated and the voltage of the portion where the absolute value of the AC voltage target value Vinv * to the AC / DC converter 11 is lower than the DC voltage target value (Vg + Z Iin) is output. Is controlled so as to operate the AC / DC converter 11. Thus, the switching loss of the AC / DC conversion unit 11 and the DC / DC conversion unit 10 can be reduced, and DC power can be output with higher efficiency.

  Furthermore, since both the DC / DC conversion unit 10 and the AC / DC conversion unit 11 operate based on the target value set by the control unit 12, even if the operation is performed so that the high-frequency switching periods of both circuits are switched alternately. Further, it is possible to suppress the occurrence of phase shift or distortion in the alternating current input to the AC / DC converter 11.

<Discharge operation as seen in voltage waveform diagram>
FIG. 4 is a voltage waveform diagram conceptually showing the operation when the power conversion device 1 is discharging the storage battery 2.
(A) shows the absolute value (peak value about 141 V, effective value about 100 V) and DC voltage target value Vg ′ (about 48 V) of the AC voltage target value Vinv *. The AC voltage target value Vinv * is a voltage at the output terminal of the AC / DC conversion unit 11 during the discharge operation, which is ideally aimed at a state where the phase is advanced several degrees more than the AC voltage Va. It is a value that should be. If the impedance of the AC reactor 22 is ignored, Vinv * = Va. The DC voltage target value Vg ′ is a value in consideration of the voltage drop of the DC reactor 16 with respect to the storage battery voltage Vg. If the impedance of the DC reactor 16 is ignored, Vg ′ = Vg.
In addition, the voltage value said here is only an example. The control unit 12 compares these two voltages and controls the AC / DC conversion unit 11 and the DC / DC conversion unit 10 based on the comparison result.

  First, in a period (t1 to t2, t3 to t4) in which the absolute value of the AC voltage target value Vinv * is greater than the DC voltage target value Vg ′, the control unit 12 switches the DC / DC conversion unit 10 to increase the voltage. This is performed ((b) of FIG. 4). As a result, the voltage shown in (c) appears on the DC bus 18.

On the other hand, in a period (t0 to t1, t2 to t3, t4 to t5) in which the absolute value of the AC voltage target value Vinv * is smaller than the DC voltage target value Vg ′, the control unit 12 uses the AC / DC conversion unit 11 as an inverter. The switching operation is performed and the voltage is lowered ((d) in FIG. 4). Separately from this switching operation, the AC / DC converter 11 inverts the polarity of energization for each cycle of a frequency (for example, 100 Hz) corresponding to twice the frequency of the power system 3S. This switching operation is extremely slow compared to, for example, a 20 kHz switching operation. On the other hand, while the AC / DC converter 11 is performing the switching operation (t0 to t1, t2 to t3, t4 to t5), in the DC / DC converter 10, both the high side switch Q1 and the low side switch Q2 are off. In this state, the voltage / current is directly passed (passed) through the diode d1.
As a result, the desired AC waveform shown in (e) is obtained.

<Control specifications during discharge>
Here, as in the case of charging, various quantities in the power conversion device 1 are defined as follows.
Ia *: target current value to AC circuit 3 Iin: DC current detection value of DC / DC converter 10 (current sensor 17)
Iin *: target current value of the DC / DC converter 10 Iinv *: target AC current of the AC / DC converter 11 Ig *: target DC current of the storage battery 2 Ic: current flowing through the capacitor 19 Ica: current flowing through the capacitor 23 Current

Va: AC voltage Vg: Battery voltage Vinv *: AC voltage target value of the AC / DC converter 11 Vo *: Voltage target value on the DC bus 18 side of the DC / DC converter 10 Pin: Output power from the battery 2 ( Reverse input power)
P _LOSS : Power loss of power converter 1 η: Power conversion efficiency of power converter 1

The average value <Pin> of the output power Pin from the storage battery 2 is
<Pin> = <Iin × Vg> (1 ′)
Moreover, the average value <Ia *> of the current target value to the AC circuit 3 is
<Ia *> = <Ig * × Vg> / (η × <Va>) (2 ′)
It is. Here, η is a constant representing the conversion efficiency of the power conversion device 1.
The current target value Ia * is
Ia * = (2 ^1/2 ) × <Ia *> × sin ωt (3 ′)
It is.

On the other hand, the alternating current target value Iinv * for the AC / DC converter 11 takes into account the capacitance Ca of the capacitor 23.
Iinv * = Ia * + s CaVa (4 ′)
It is.

Further, the AC voltage target value Vinv * is set such that the impedance of the AC reactor 22 is Za.
Vinv * = Va + Za Iinv * (5 ′)
It is.

Also, the input voltage target value Vo * to the DC / DC converter 10 is
Vo * = Max (Vg−Z Iin, absolute value of Vinv *) (6 ′)
It can be. “Max” represents the larger one in (). Z is the impedance of the DC reactor 16. Here, (Vg−Z Iin) is the DC voltage target value Vg ′.

Also, the DC / DC converter current target value Iin * is
Iin * =
{(Iinv * × Vinv *) + (s C Vo *) × Vo *} /
(Vg-ZIin) (7 ')
It is.

In addition, when the electrostatic capacity C and the power loss P _{LOSS of} the capacitor 19 are sufficiently smaller than (Iinv * × Vinv *), the following formula (8 ′) is established. Iin * obtained by this equation (8 ′) can be used as Iin included in the right side of equations (6 ′) and (7 ′).
Iin * = (Iinv * × Vinv *) / Vg (8 ′)

  As described above, when the control unit 12 outputs a voltage at a portion where the absolute value of the AC voltage target value Vinv * of the AC / DC conversion unit 11 is higher than the DC voltage target value (Vg−Z Iin). Operates the DC / DC converter 10 and outputs a voltage in a portion where the absolute value of the AC voltage target value Vinv * of the AC / DC converter 11 is lower than the DC voltage (Vg−Z Iin). Is controlled so as to operate the AC / DC converter 11. Thus, the switching loss of the AC / DC conversion unit 11 and the DC / DC conversion unit 10 can be reduced, and DC power can be output with higher efficiency.

  Furthermore, since both the DC / DC conversion unit 10 and the AC / DC conversion unit 11 operate based on the target value set by the control unit 12, even if the operation is performed so that the high-frequency switching periods of both circuits are switched alternately. Further, it is possible to suppress the occurrence of a phase shift or distortion in the alternating current output from the AC / DC converter 11.

<Control features>
The above control (charging / discharging) does not always cause the DC / DC conversion unit 10 and the AC / DC conversion unit 11 to perform a switching operation, but reduces the switching as a whole by alternately creating a pause time. Conversion method ". In such a power conversion device 1, a period in which boosting is performed by one of the AC / DC conversion unit 11 and the DC / DC conversion unit 10 and a period in which stepping down is performed by the other appear alternately. Reduce the overall switching frequency. Thereby, the switching loss as the power converter device 1 can be reduced, and the efficiency of power conversion can be improved.

In addition, when the control by the above minimum switching conversion systems is performed, it turns out that the electric current which flows into the DC reactor 16 when discharging the storage battery 2, for example, becomes a pulsating flow. The pulsation cycle of this pulsating flow is ½ of the cycle of the power system 3S. That is, the current flowing through the DC reactor 16 is a pulsating flow, and becomes zero every cycle. The timing at which the pulsating flow flowing through the DC reactor 16 becomes 0 is the same timing as the zero crossing of the AC current. In addition, when charging the storage battery 2, it turns out that the electric current which flows into the direct current reactor 16 becomes a pulsating flow similarly.
Hereinafter, the control of the DC / DC conversion unit 10 in consideration of the pulsating flow will be specifically described.

<< Additional control of DC / DC converter >>
Next, additional control for the DC / DC converter 10 will be described.
As a switching method of the DC / DC conversion unit 10, there are generally the following methods. The following methods (i) and (ii) are reference examples and are not embodiments.

(I) Switching method in which one is off During the boost operation, the high-side switch Q1 is held off, and the low-side switch Q2 is repeatedly turned on and off by PWM control.
During the step-down operation, the low-side switch Q2 is held off, and the high-side switch Q1 is repeatedly turned on / off by PWM control.

(Ii) Always complementary switching system In both step-up operation and step-down operation, the two switches Q1 and Q2 are repeatedly turned on and off by PWM control. When the high-side switch Q1 is on, the low-side switch Q2 is off and the high-side switch Q1 is off In this case, a complementary operation is always performed in which the low side switch Q2 is turned on.

In the present embodiment, switching is performed to switch (i) and (ii) above according to conditions. This is hereinafter referred to as a switching method.
Specifically, under the control of the control unit 12, when a current larger than a predetermined value flows through the DC reactor 16, an energization path is secured in one direction of the DC reactor 16 in the DC / DC conversion unit 10. On the other hand, when a current smaller than a predetermined value flows through the DC reactor 16, an energization path is secured in both directions of the DC reactor 16 in the DC / DC converter 10. The high-side switch Q1, its parallel diode d1, and the low-side switch Q2 are involved in the energization path. Note that when a current larger than a predetermined value flows is an example when a period in which the current flowing through the DC reactor 16 is discontinuous does not occur. When a current smaller than a predetermined value flows, it is discontinuous. It is an example when a period occurs. That is, the predetermined value may be set at the boundary of whether or not it becomes discontinuous.

  For example, when the storage battery 2 is discharged, the above-mentioned one direction is the direction of the current flowing through the DC reactor 16 in FIG. 2 in the right direction. When a current smaller than a predetermined value flows through the DC reactor 16, the current may have a reverse polarity (reverse current). However, by securing a current-carrying path in both directions of the DC reactor 16, a reverse current can also flow. . Thus, the knowledge that the difference between the command value (Vinv * × Iinv *) of the output power and the actual output power can be reduced by not blocking the reverse current is obtained.

  If the said knowledge is demonstrated in detail, the electric current which flows into the DC reactor 16 will be a pulsating flow, and will be 0 for every period. The timing at which the pulsating flow flowing through the DC reactor 16 becomes 0 is the same timing as the zero cross of the AC voltage / AC current. In the minimum switching conversion method, the AC / DC conversion unit 11 performs high-frequency switching in the vicinity of the zero cross and its front and back. However, depending on the voltage on the DC power supply side, the DC / DC converter 10 also performs a switching operation with a phase in the vicinity of the zero cross.

  The pulsating flow that flows through the DC reactor 16 includes high-frequency inductor ripple due to switching. When the pulsating flow including the inductor ripple approaches 0, the current value tends to enter a minus region due to the fluctuation width of the inductor ripple. However, in that case, in a state where the energization path is ensured only in one direction of the DC reactor 16 in the DC / DC conversion unit 10, a period in which the current becomes discontinuous occurs. When the current becomes discontinuous, the original average value cannot be detected accurately. Therefore, in the power conversion device 1, when a period in which the current is discontinuous occurs in the state where the energization path is ensured only in one direction of the DC reactor 16 in the DC / DC conversion unit 10, at least the period is DC. An energization path is ensured in both directions of the DC reactor 16 in the DC converter 10. Thus, when a current (small current) that is likely to be discontinuous in one direction flows through the DC reactor 16, bidirectional current flow is possible in the DC reactor 16. As a result, it is considered that the difference between the output power of the power converter and the command value can be reduced when the output power command value is relatively small.

  For example, when the current flowing through the DC reactor 16 is large (for example, 10 A), the amplitude of the pulsating current is large, and the high-frequency inductor ripple is swung in a sufficiently high current range from the 0 level, so that the current swings in the reverse polarity. There is no significant influence on the detected current value even if it is slightly reversed. Therefore, the current sensor 17 can detect the current with high accuracy. As a result, it is considered that the control accuracy is improved.

  On the other hand, when the current flowing through the DC reactor 16 is small (for example, 1 A), the amplitude of the pulsating current is small and the high-frequency inductor ripple swings near 0 level. . In that case, if the current that tries to swing in the reverse polarity is interrupted as in (i) above, the current sensor 17 cannot detect the original current when it tries to swing in the reverse polarity, resulting in an inconvenience. A continuous waveform is sampled and detected. For this reason, the detected value lacks accuracy.

In order to ensure energization in the reverse direction, it is conceivable to always turn on the switching element Q1 in a complementary manner. In that case, however, the advantage of the minimum switching conversion scheme that attempts to reduce the switching loss is reduced.
Thus, it has been concluded that a switching method in which complementary switching is performed only when necessary.

Specifically, the control unit 12 in the case of discharging the storage battery 2 and boosting the DC / DC conversion unit 10 holds the high-side switch Q1 off when a current larger than a predetermined value flows through the DC reactor 16. The low side switch Q2 is operated, and when a current smaller than a predetermined value flows through the DC reactor 16, the high side switch Q1 and the low side switch Q2 are operated complementarily.
Further, when the storage battery 2 is discharged and the DC / DC converter 10 is not boosted, the controller 12 turns off both the high-side switch Q1 and the low-side switch Q2 when a current larger than a predetermined value flows through the DC reactor 16. When a current smaller than a predetermined value flows through the DC reactor 16, the high side switch Q1 is kept on and the low side switch Q2 is kept off.
In this case, the difference between the output power of the power converter 1 and the command value when the storage battery is discharged can be reduced.

Further, when the DC / DC conversion unit 10 is stepped down to charge the storage battery 2, the control unit 12 holds the low side switch Q <b> 2 off when a current larger than a predetermined value flows through the DC reactor 16, and the high side switch When Q1 is operated and a current smaller than a predetermined value flows through the DC reactor 16, the high side switch Q1 and the low side switch Q2 are operated complementarily.
In addition, when charging the storage battery 2 without causing the DC / DC conversion unit 10 to step down, the control unit 12 turns on the high side switch Q1 and turns on the low side switch Q2 when a current larger than a predetermined value flows through the DC reactor 16. The high-side switch Q1 is turned on and the low-side switch Q2 is kept off even when a current smaller than a predetermined value flows through the DC reactor 16 while being kept off.
In this case, the difference between the input power to the power conversion device 1 and the command value when charging the storage battery can be reduced.

<Verification>
FIG. 5 is a diagram illustrating a schematic configuration of a measurement system including the power conversion device 1. With this measurement system, for example, the relationship between the command value and the output power when the storage battery 2 is discharged can be examined. In the figure, the power conversion device 1 is controlled so that all of its output power (for example, 1 kW) is consumed by a load 3L (1 kW) and does not flow backward to the power system 3S. The measurement unit 6 monitors the reverse power flow based on the current detection by the current sensor 5. The measurement unit 6 can communicate with the power conversion device 1 via a communication line, acquire measurement data, and command output power. An operation command to the measurement unit 6 can be given from the personal computer 7 by short-range wireless communication or the like. When the storage battery 2 is charged, the current is reversed, and charging is performed from the power system 3 </ b> S via the power conversion device 1.

  The command value of the output power for the power converter 1 is linearly changed from minus (charge) to plus (discharge), and the measured value of the actual output power is examined. However, in the case of low power, there was a tendency for the difference between the command value and the measured value to increase.

FIG. 6 is a graph showing a simulation result when the above-mentioned (i), that is, one of the switching methods is OFF, the output power command value is 2000 W, and the output current target value is 10 A. (A) is an output current (50 Hz, period 0.02 seconds), (b) is a current flowing through the DC reactor 16, (c) is a gate signal of the low-side switch Q2, and (d) is a gate signal of the high-side switch Q1. Respectively. Since one of the switching systems is off, the high-side switch Q1 is kept off as shown in (d).
The output power (average) in this case was 2008W.

FIG. 7 is a graph showing a simulation result when the above-mentioned (ii), that is, the always complementary switching method, the output power command value is 2000 W, and the output current target value is 10 A. (A) is an output current (50 Hz, period 0.02 seconds), (b) is a current flowing through the DC reactor 16, (c) is a gate signal of the low-side switch Q2, and (d) is a gate signal of the high-side switch Q1. Respectively. Since they are always complementary switching systems, (c) and (d) are inverted 1/0.
The output power (average) in this case was 2009W.

FIG. 8 is a graph showing a simulation result when the command value of the output power is 2000 W, the output current target value is 10 A, and the “predetermined value” of the current of the DC reactor 16 is 1 A in the switching method of this embodiment. It is. (A) is an output current (50 Hz, period 0.02 seconds), (b) is a current flowing through the DC reactor 16, (c) is a gate signal of the low-side switch Q2, and (d) is a gate signal of the high-side switch Q1. Respectively. During the period in which the low-side switch Q2 is performing the switching operation, the current in the DC reactor 16 is greater than 1A, so the high-side switch Q1 is kept off. When the current flowing through the DC reactor 16 becomes smaller than 1A during the period when the DC / DC conversion unit 10 stops the switching operation, the high side switch Q1 is turned on.
The output power (average) in this case was 2009W.

FIG. 9 and FIG. 12 are graphs showing the simulation results when the above-mentioned (i), that is, one of the switching methods is OFF, the output power command value is 200 W, and the output current target value is 1A. FIG. 12 is an enlarged view of the current value scale on the vertical axis in FIG. In FIG. 9 (or FIG. 12), (a) is the output current (50 Hz, period 0.02 seconds), (b) is the current flowing through the DC reactor 16, (c) is the gate signal of the low-side switch Q2, (d ) Indicates the gate signal of the high-side switch Q1. Since one of the switching systems is off, the high-side switch Q1 is kept off as shown in (d). Here, it should be noted that there is a portion where the current shown in (b) is stuck to 0 (it is 0 because it cannot be negative) during the switching operation. That is, the current waveform is discontinuous.
The output power (average) in this case was 392W.

FIG. 10 and FIG. 13 are graphs showing the simulation results when the above-mentioned (ii), that is, the always complementary switching method, the output power command value is 200 W, and the output current target value is 1A. FIG. 13 is an enlarged view of the current value scale on the vertical axis in FIG. In FIG. 10 (or FIG. 13), (a) is the output current (50 Hz, period 0.02 seconds), (b) is the current flowing through the DC reactor 16, (c) is the gate signal of the low-side switch Q2, (d ) Indicates the gate signal of the high-side switch Q1. Since they are always complementary switching systems, (c) and (d) are inverted 1/0. As shown in (b), the current enters the negative region. That is, it does not stick to 0 as shown in FIG. 9 (the waveform is continuous).
The output power (average) in this case was 361W.

FIG. 11 and FIG. 14 show the simulation results when the command value of the output power is 200 W, the output current target value 1A, and the “predetermined value” of the current of the DC reactor 16 is 1A in the switching method of this embodiment. It is a graph which shows. FIG. 14 is an enlarged view of the current value scale on the vertical axis in FIG. In FIG. 11 (or FIG. 14), (a) is the output current (50 Hz, period 0.02 seconds), (b) is the current flowing through the DC reactor 16, (c) is the gate signal of the low-side switch Q2, (d ) Indicates the gate signal of the high-side switch Q1. During the switching operation of the low side switch Q2, when the current of the DC reactor 16 is larger than 1A, the high side switch Q1 is kept off, but when the current is smaller than 1A, the high side switch Q1 Performs a complementary switching operation to the low-side switch Q2. Further, when the current flowing through the DC reactor 16 is smaller than 1 A during the period in which the DC / DC conversion unit 10 stops the switching operation, the high-side switch Q1 is kept on. That is, also here, the high side switch Q1 operates complementarily to the low side switch Q2. As shown in (b), the current enters the negative region. That is, it does not stick to 0 as shown in FIG. 9 (the waveform is continuous).
The output power (average) in this case was 361W.

<Summary of verification>
When the command value of power is 2000 W, the command value of 2000 W is close to the command value of 2008 W or 2009 W for all three methods. On the other hand, when the power command value is a low power command value of 200 W, there is an error in all three methods. However, compared with the method (i), the always complementary switching method and the switching method of this embodiment are different in error. Is getting smaller and approaching the command value. There is no difference in numerical values between the constant complementary switching method and the switching method of this embodiment, but as is apparent from a comparison between FIG. 10 (d) and FIG. 11 (d), the switching of this embodiment is performed. The method has few switching times. Accordingly, the switching loss is reduced and the driving power is reduced as compared with the always complementary switching method.

  As described above, according to the power conversion device 1 and the control method thereof according to the present embodiment, the power can be brought close to the command value while realizing high efficiency by the minimum switching conversion method. In addition, the switching loss for bringing the electric power close to the command value is less than that of the always complementary switching method. However, if high efficiency is not given the highest priority, it is not excluded to always perform the complementary switching method.

<Others>
In the above embodiment, the DC power supply 2 is described as a storage battery, but the DC power supply 2 may be other than the storage battery. For example, the DC power source may be a solar power generation panel. In this case, the power conversion device 1 cannot perform the conversion operation in the charging direction, but converts the output of the photovoltaic power generation panel into an alternating current and supplies it to the load 3L, and even if supplied to the load 3L The surplus power can be sold by being connected to the power system 3. In this case as well, the control accuracy of power conversion can be increased by the switching method described above. Note that when bidirectional energization of the DC reactor 16 is ensured, no current flows into the photovoltaic power generation panel itself, but the current in this case can flow through the capacitor 15.

  Moreover, in the said embodiment, although the power converter device 1 connected to the alternating current circuit 3 containing the electric power grid | system 3S was shown, it is not restricted to this, The electric power conversion used for the stand-alone power supply system not connected with the electric power grid | system 3S The device 1 may be used.

《Supplementary Note》
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Power converter device 2 DC power supply (for example, storage battery)
DESCRIPTION OF SYMBOLS 3 AC circuit 3L Load 3S Power system 5 Current sensor 6 Measurement unit 7 Personal computer 10 DC / DC conversion part 11 AC / DC conversion part 12 Control part 14 Voltage sensor 15 Capacitor 16 DC reactor 17 Current sensor 18 DC bus 21 Filter circuit 22 AC Reactor 23 Capacitor 24 Current sensor 25 Voltage sensor 26 Current sensor d1-d6 Diode Q1 Switching element / High-side switch Q2 Switching element / Low-side switch Q3-Q6 Switching element

Claims (8)

A power converter provided between a load connected to an AC circuit and a DC power source,
A voltage sensor for detecting an AC voltage of the AC circuit;
An AC / DC converter provided between the load and a DC bus;
A capacitor connected to the DC bus;
A high-side switch having a parallel diode provided between the DC bus and the DC power source, provided between the DC reactor, and the DC reactor and the high potential side electric circuit of the DC bus; and A DC / DC converter including a low-side switch having a parallel diode provided between a DC reactor and a low potential side circuit of the DC bus;
A current sensor for detecting a current flowing through the DC reactor;
A voltage sensor for detecting a voltage across the DC power supply as a DC power supply voltage;
The absolute value of the AC voltage target value based on the AC voltage and the DC voltage target value based on the DC power supply voltage are compared with each other, and based on the magnitude relationship, the AC / DC conversion unit and the DC / DC conversion unit A control method is executed in which a period in which boosting is performed by a switching operation mainly using one of them and a period in which voltage reduction is performed by a switching operation mainly by the other appear alternately, and within the DC / DC converter In the state where the energization path is secured only in one direction of the DC reactor, when a period in which the current becomes discontinuous occurs, the energization path is provided in both directions of the DC reactor in the DC / DC converter at least during the period. A control unit to secure,
A power conversion device comprising: When the DC power supply is output from the DC power source and the DC / DC converter is boosted, the control unit operates the low side switch while keeping the high side switch off when the discontinuous period does not occur. When the discontinuous period occurs, the high side switch and the low side switch are operated in a complementary manner,
When the DC power supply is output from the DC power supply and the DC / DC converter is not boosted, the control unit holds both the high-side switch and the low-side switch off when the discontinuous period does not occur. The power conversion device according to claim 1, wherein when the discontinuous period occurs, the high-side switch is kept on and the low-side switch is kept off. When the DC / DC converter is stepped down and the DC power supply is charged, the controller operates the high side switch while keeping the low side switch off when the discontinuous period does not occur. When the discontinuous period occurs, the high side switch and the low side switch are operated in a complementary manner,
When charging the DC power supply without causing the DC / DC converter to step down, the control unit keeps the high-side switch on and the low-side switch off when the discontinuous period does not occur The power conversion device according to claim 1, wherein the high-side switch is kept on and the low-side switch is kept off even when the discontinuous period occurs. An AC / DC converter provided between a load connected to an AC circuit and a DC power supply, an AC / DC converter provided between the load and a DC bus, and provided between the DC bus and the DC power supply; A DC reactor, a high-side switch having a parallel diode provided between the DC reactor and the high potential side circuit of the DC bus, and between the DC reactor and the low potential side circuit of the DC bus A DC / DC converter including a low-side switch having a parallel diode, and a method for controlling a power converter,
The absolute value of the AC voltage target value based on the AC voltage and the DC voltage target value based on the DC power supply voltage are compared with each other, and based on the magnitude relationship, the AC / DC conversion unit and the DC / DC conversion unit Executing a control in which a period in which boosting is performed by a switching operation mainly using one of them and a period in which voltage reduction is performed by a switching operation mainly by the other appear alternately; and
When a period in which the current is discontinuous occurs in a state where the energization path is ensured only in one direction of the DC reactor in the DC / DC converter, at least the period of the DC reactor is in the DC / DC converter. A method for controlling a power conversion device that secures a current-carrying path in both directions. A power conversion device provided between a power system and a load connected to the power system and a storage battery,
A voltage sensor for detecting an AC voltage of the power system;
An AC / DC converter provided between the load and a DC bus;
A capacitor connected to the DC bus;
A DC reactor provided between the DC bus and the storage battery; a high-side switch having a parallel diode provided between the DC reactor and the high-potential side circuit of the DC bus; and the DC A DC / DC converter including a low-side switch having a parallel diode provided between a reactor and a low potential side circuit of the DC bus;
A current sensor for detecting a current flowing through the DC reactor;
A voltage sensor for detecting a voltage across the storage battery as a storage battery voltage;
The absolute value of the AC voltage target value based on the AC voltage and the DC voltage target value based on the storage battery voltage are compared with each other, and based on the magnitude relationship, any of the AC / DC converter and the DC / DC converter A control method in which a period in which the voltage is boosted by the switching operation mainly in one and a period in which the voltage is lowered by the switching operation mainly in the other is executed, and the DC reactor has a predetermined value When a large current flows, an energization path is ensured in one direction of the DC reactor in the DC / DC converter, and when a current smaller than the predetermined value flows in the DC reactor, the DC reactor in the DC / DC converter. A control unit that secures an energization path in both directions,
A power conversion device comprising: When discharging the storage battery and boosting the DC / DC conversion unit, the control unit holds the high-side switch off when a current larger than the predetermined value flows through the DC reactor, and the low-side switch When a current smaller than the predetermined value flows through the DC reactor, the high side switch and the low side switch are operated in a complementary manner,
When the storage battery is discharged and the DC / DC converter is not boosted, the controller holds both the high-side switch and the low-side switch off when a current larger than the predetermined value flows through the DC reactor. The power converter according to claim 5, wherein when the current smaller than the predetermined value flows through the DC reactor, the high-side switch is kept on and the low-side switch is kept off. When the DC / DC converter is operated in a step-down manner and the storage battery is charged, the controller holds the low-side switch off when a current larger than the predetermined value flows through the DC reactor. When a current smaller than the predetermined value flows through the DC reactor, the high side switch and the low side switch are operated in a complementary manner,
When charging the storage battery without stepping down the DC / DC converter, the controller turns on the high-side switch and turns off the low-side switch when a current larger than the predetermined value flows through the DC reactor. The power conversion device according to claim 5, wherein the high-side switch is kept on and the low-side switch is kept off even when a current smaller than the predetermined value flows through the DC reactor. Provided between an electric power system and a load connected to the electric power system and a storage battery, and provided between an AC / DC conversion unit provided between the load and the DC bus, and between the DC bus and the storage battery. A high-side switch having a parallel diode provided between the DC reactor, the DC reactor and the high potential side circuit of the DC bus, and the DC reactor and the low potential side circuit of the DC bus. A control method for a power conversion device including a DC / DC conversion unit including a low-side switch having a parallel diode provided therebetween,
The absolute value of the AC voltage target value based on the AC voltage and the DC voltage target value based on the storage battery voltage are compared with each other, and based on the magnitude relationship, any of the AC / DC converter and the DC / DC converter Performing a control in which a period in which the voltage is boosted by the switching operation mainly using one of them and a period in which the voltage is lowered by the switching operation mainly by the other, and
When a current larger than a predetermined value flows through the DC reactor, an energization path is secured in one direction of the DC reactor in the DC / DC converter, and when a current smaller than the predetermined value flows through the DC reactor, the DC / DC A method for controlling a power converter, wherein a current path is secured in both directions of the DC reactor in a DC converter.