Active power buffer circuits and power converters

Abstract

This improves the efficiency of adjusting pulsating power using an active power buffer circuit connected in series with a DC power supply and a single-phase inverter. [Solution] The active power buffer circuit is connected in series between a DC power supply and the DC side of a single-phase inverter, and comprises: a first converter having a first inductor and configured to adjust the first DC voltage at the first end in one direction; a second converter having a second inductor and configured to adjust the second DC voltage at the second end in one direction; and a controller for controlling the first converter and the second converter, wherein the first end and the second end are connected in series such that the directions of the first DC voltage and the second DC voltage are opposite to each other, and the series-connected first end and second end connect the DC power supply and the DC side of the single-phase inverter, and the first inductor and the second inductor are coupled inductors.

Description

[Technical Field]

[0001] This disclosure relates to an active power buffer circuit and a power conversion device. [Background technology]

[0002] Non-patent document 1 discloses a configuration (series compensation method) in which the pulsation of DC power that occurs when DC power from a DC power source is converted to AC power by a single-phase inverter is adjusted by a converter connected in series with the DC power source and the single-phase inverter. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] D. Neumayr, GC Knabben, E. Varescon, D. Bortis, and JW Kolar, “Comparative evaluation of a full- and partial-power processing active power buffer for ultracompact single-phase dc / ac converter systems”, IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 9, no. 2, pp. 1994-2013, 2021. DOI: 10.1109 / JESTPE.2020.2987937. [Overview of the project] [Problems that the invention aims to solve]

[0004] In a configuration where DC power from a DC power supply is converted into AC power by a single-phase inverter, the DC power converted by the single-phase inverter pulsates at a frequency twice the power supply frequency on the AC side. As a method for regulating the pulsation of DC power, for example, a series compensation method (Non-Patent Document 1) that performs regulation by a converter connected in series with a single-phase inverter is known, but there is room for efficiency improvement in the implementation example described in Non-Patent Document 1. The present disclosure aims to improve the efficiency of pulsating power regulation by an active power buffer circuit connected in series between a DC power supply and a single-phase inverter. [Means for Solving the Problems]

[0005] An active power buffer circuit according to a first aspect is an active power buffer circuit connected in series between a DC power supply and the DC side of a single-phase inverter, comprising: a first converter having a first inductor and configured to be capable of unidirectionally regulating a first DC voltage at a first end; a second converter having a second inductor and configured to be capable of unidirectionally regulating a second DC voltage at a second end; and a controller that controls the first converter and the second converter, wherein the first end and the second end are connected in series such that the directions of the first DC voltage and the second DC voltage are opposite to each other, the series-connected first end and second end connect between the DC power supply and the DC side of the single-phase inverter, and the first inductor and the second inductor are coupled inductors. In this case, it is possible to improve the efficiency of pulsating power regulation by the converter connected in series between the DC power supply and the single-phase inverter. An active power buffer circuit according to a second aspect is the active power buffer circuit according to the first aspect, wherein the first converter is a first reversible chopper circuit, and the second converter is a second reversible chopper circuit. In this case, positive and negative bidirectional voltages can be regulated. The active power buffer circuit according to the third aspect is the active power buffer circuit according to the first aspect or the second aspect, wherein the first converter includes a first capacitor at the first end, and is the first reversible chopper circuit in which a series connection of a first switching element and a buffer capacitor, and a second switching element are connected in parallel to the series connection of the first capacitor and the first inductor, and the second converter includes a second capacitor at the second end, and is the second reversible chopper circuit in which a series connection of a third switching element and the buffer capacitor, and a fourth switching element are connected in parallel to the series connection of the second capacitor and the second inductor. The active power buffer circuit according to the fourth aspect is the active power buffer circuit according to any one of the first to third aspects, wherein the controller controls the first converter and the second converter such that a first magnetic field generated by a first current flowing through the first inductor and a second magnetic field generated by a second current flowing through the second inductor approach the same magnitude in the same direction. In this case, the coupled inductor can be reduced in size. The active power buffer circuit according to the fifth aspect is the active power buffer circuit according to any one of the first to fourth aspects, wherein the controller controls the first converter such that a first AC component, which is a component having a frequency twice the fundamental frequency of the AC voltage on the AC side of the single-phase inverter, is included in the first DC voltage, and controls the second converter such that a second AC component, which is a component having a frequency twice the fundamental frequency, is included in the second DC voltage. In this case, fluctuations in the voltage of the DC power supply can be suppressed. The active power buffer circuit according to the sixth aspect is the active power buffer circuit according to any one of the first to fifth aspects, wherein the controller controls the phase difference between the first AC component and the second AC component. In this case, adjustment of power pulsation becomes easy. The power conversion device according to the seventh aspect includes the active power buffer circuit according to any one of the first to sixth aspects, and a single-phase inverter that converts DC power from a DC power supply into AC power for an AC power supply. [Brief explanation of the drawing]

[0006] [Figure 1] This figure shows the configuration of a power system in which the series-compensated converter described in Non-Patent Document 1 is implemented. [Figure 2] This figure shows an example configuration of a power system in which the active power buffer circuit according to this embodiment is implemented. [Figure 3] This diagram shows the configuration of an active power buffer circuit. [Figure 4] This is a block diagram illustrating the control of the first and second converters by the control device. [Figure 5] This figure shows the specifications set for the simulation of the power system according to this embodiment. [Figure 6] This figure shows the waveform of the AC voltage generated on the AC side of a single-phase inverter. [Figure 7] This diagram shows the waveforms of the buffer capacitor voltage, the first DC voltage, and the second DC voltage. [Figure 8] This diagram shows the waveforms of the current flowing through the AC load, the current output by the DC power supply, and the current flowing from the DC power supply to the single-phase inverter. [Modes for carrying out the invention]

[0007] The background of the present invention will be explained with reference to the attached drawings. Figure 1 shows the configuration of a power system 100 in which the series-compensated active power buffer circuit 101 described in Non-Patent Document 1 is implemented. The power system 100 comprises an active power buffer circuit 101, a DC power supply 110, a single-phase inverter 120, and a DC link capacitor 140. The single-phase inverter 120 converts DC power from the DC power supply 110 into AC power and supplies it to the AC load 130. At this time, the DC power converted by the single-phase inverter 120 pulsates at a frequency twice the fundamental frequency of the AC load 130. In the series compensation method shown in Figure 1, the pulsation of the DC power is adjusted by the active power buffer circuit 101. The single-phase inverter 120 is denoted as DC / AC.

[0008] The active power buffer circuit 101 is connected in series with the DC power supply 110 and the single-phase inverter 120. The active power buffer circuit 101 includes a capacitor 102, an inductor 103, a switch circuit 104, and a buffer capacitor 105. The active power buffer circuit 101 adjusts the pulsation of DC power by adjusting the voltage of the capacitor 102, which is connected in series with the DC power supply 110 and the single-phase inverter 120. The voltage of the capacitor 102 is adjusted by the switch circuit 104. This disclosure provides an embodiment of a series compensation method for adjusting pulsation of DC power, which improves the efficiency of adjusting pulsating power by a converter connected in series with a DC power supply and a single-phase inverter. The embodiment will be described in detail below with reference to the attached drawings.

[0009] <Configuration of Power System 1> Figure 2 shows an example configuration of a power system 1 in which the active power buffer circuit 10 according to this embodiment is implemented. Power system 1 comprises an active power buffer circuit 10, a DC power supply 60, a single-phase inverter 70, a DC link capacitor 80, and a control device 200. Power system 1 is connected to an AC power supply 90. In Figure 2, the single-phase inverter 70 is denoted as DC / AC. In power system 1, the DC power converted by the single-phase inverter 70 pulsates at a frequency twice the fundamental frequency of the AC power supply 90, as in the case of Figure 1. In this embodiment, the pulsation of the DC power is adjusted by the active power buffer circuit 10.

[0010] The active power buffer circuit 10 is connected in series between the DC power supply 60 and the single-phase inverter 70. The active power buffer circuit 10 comprises a first converter 20 and a second converter 30.

[0011] The first converter 20 comprises a first capacitor 21, switching elements SW1 and SW2, an inductor 40-1, and a buffer capacitor 50, and is configured to adjust the DC voltage in one direction. The second converter 30 comprises a second capacitor 31, switching elements SW3 and SW4, an inductor 40-2, and a buffer capacitor 50, and is configured to adjust the DC voltage in one direction. Inductors 40-1 and 40-2 constitute a coupled inductor 40. The buffer capacitor 50 is common to both the first converter 20 and the second converter 30. The switching elements SW1, SW2, SW3, and SW4 are, for example, MOSFETs. Adjustable in one direction means that only the positive voltage or only the negative voltage can be adjusted. Switching elements SW1, SW2, SW3, and SW4 are examples of the first switching element, second switching element, third switching element, and fourth switching element, respectively.

[0012] In the following, the voltage across buffer capacitor 50 is v b This will be written as follows. The voltages across the first capacitor 21 and the second capacitor 31 will be denoted as the first DC voltage v1 and the second DC voltage v2, respectively. The currents flowing through the coupling inductor 40 in the first converter 20 and the second converter 30 will be denoted as the first current i1 and the second current i2, respectively. The first current i1 is considered positive when it flows from the coupling inductor 40 to the first capacitor 21. The second current i2 is considered positive when it flows from the second capacitor 31 to the coupling inductor 40.

[0013] The coupled inductor 40 is constructed by winding a coil around a core. The inductors 40-1 and 40-2 that make up the coupled inductor 40 are wound in phase. Inductor 40-1, which makes up the coupled inductor 40, is an example of the first inductor in the first converter 20, and inductor 40-2, which makes up the coupled inductor 40, is an example of the second inductor in the second converter 30. A first current i1 flows through inductor 40-1, and a second current i2 flows through inductor 40-2, and these currents generate a magnetic field. Hereinafter, the magnetic field generated by the first current i1 will be referred to as the first magnetic field, and the magnetic field generated by the second current i2 will be referred to as the second magnetic field. The operation of the active power buffer circuit 10 will be described in detail later.

[0014] The DC power supply 60 outputs a DC voltage. Below, the output voltage of the DC power supply 60 is given as v s This is how it is written. Also, the current output from the DC power supply 60 is i s This is how it is written. Examples of DC power sources 60 include storage batteries, converters connected to storage batteries, converters connected to solar cells, and converters connected to generators.

[0015] The single-phase inverter 70 converts DC power from the DC power supply 60 into AC power and supplies power to the AC power supply 90. At this time, the DC power converted by the single-phase inverter 70 pulsates at a frequency twice the fundamental frequency of the AC voltage on the AC side. The single-phase inverter 70 is composed of, for example, a full-bridge circuit in which four transistors are arranged in a bridge configuration. In the following, the current flowing from the DC power supply 60 to the single-phase inverter 70 is i dn This is how it is written. The active power buffer circuit 10 and the single-phase inverter 70 can be considered as part of a power conversion device.

[0016] The DC link capacitor 80 is connected between the two DC current paths on the DC side of the single-phase inverter 70. The DC link capacitor 80 is, for example, a ceramic capacitor, a film capacitor, an electrolytic capacitor, etc. Voltage v of DC link capacitor 80 dc It pulsates at a frequency twice that of the fundamental frequency of the AC power supply on the AC side.

[0017] The control device 200 controls the first converter 20 and the second converter 30. The control device 200 controls the opening and closing of the switching elements SW1, SW2, SW3, and SW4, and adjusts the voltages of the first capacitor 21 and the second capacitor 31. The control device 200 is an example of a controller. The control mechanism of the control device 200 will be described later.

[0018] <Operation of the active power buffer circuit 10> Figure 3 shows the configuration of the active power buffer circuit 10. The active power buffer circuit 10 shown in Figure 3 is a modified version of the active power buffer circuit 10 shown in Figure 2 for illustrative purposes, and the configuration is identical. In addition to the active power buffer circuit 10, Figure 3 also shows a DC power supply 60 and a DC link capacitor 80. As shown in Figure 3, diodes D1, D2, D3, and D4, which are not shown in Figure 2, are connected in parallel with each switching element SW1, SW2, SW3, and SW4.

[0019] The first converter 20 is a first reversible chopper circuit in which a series connection of a first capacitor 21 and an inductor 40-1 is connected, and a series connection of a switching element SW1 and a buffer capacitor 50, and a switching element SW2 are connected in parallel. In the following, the part of the first converter 20 that includes the first capacitor 21 will be referred to as the first end 22, and the part that includes the buffer capacitor 50 will be referred to as the third end 23. The first converter 20 exchanges power bidirectionally between the first capacitor 21 and the buffer capacitor 50, adjusting the first DC voltage v1 at the first end 22. The power exchange between the first capacitor 21 and the buffer capacitor 50 will be described below.

[0020] Switching elements SW1 and SW2 are exclusively controlled by the control device 200 (see Figure 2), so that when one is ON, the other is OFF. In addition, to suppress the formation of a short circuit caused by switching elements SW1 and SW2 being ON at the same time, a dead time is provided in which both switching elements SW1 and SW2 are OFF.

[0021] First, consider the case where switching element SW1 is ON and switching element SW2 is OFF. In this case, current flows from the buffer capacitor 50 to the first capacitor 21 via the ON switching element SW1 and the inductor 40-1 that constitutes the coupling inductor 40. Magnetic energy is stored in the inductor 40-1, and the first capacitor 21 is charged.

[0022] The switching element SW1 is turned off. At this time, current flows from the inductor 40-1, which constitutes the coupling inductor 40, to the first capacitor 21 and the diode D2. The magnetic energy of the inductor 40-1 is consumed, and the first capacitor 21 is charged. The voltage of the first capacitor 21 is adjusted by the ratio of the on and off periods of the switching element SW1. Through these operations, power is supplied from the buffer capacitor 50 to the first capacitor 21. Next, consider the case where switching element SW1 is in the off state and switching element SW2 is in the on state. In this case, current flows from the first capacitor 21 to inductor 40-1 of the coupling inductor 40, and magnetic energy is stored in inductor 40-1.

[0023] Switching element SW2 is turned off. When both switching elements SW1 and SW2 are off, current flows from the first capacitor 21 through the coupling inductor 40 and diode D1 to the buffer capacitor 50. Here, the buffer capacitor 50 is charged by the sum of the voltage across the first capacitor 21 and the energy stored in the coupling inductor 40. Through these operations, power is supplied from the first capacitor 21 to the buffer capacitor 50. In this way, the first converter 20 exchanges power between the first capacitor 21 and the buffer capacitor 50. The first converter 20 is configured to convert power bidirectionally between the first end 22 and the third end 23.

[0024] The second converter 30 is a second reversible chopper circuit in which a series connection of a switching element SW3 and a buffer capacitor 50, and a switching element SW4 are connected in parallel to a series connection of a second capacitor 31 and an inductor 40-2 that constitutes a coupled inductor 40. In the following, the part of the second converter 30 that includes the second capacitor 31 will be referred to as the second terminal 32, and the part that includes the buffer capacitor 50 will be referred to as the fourth terminal 33. The second converter 30 exchanges power bidirectionally between the second capacitor 31 and the buffer capacitor 50, adjusting the second DC voltage v2 at the second terminal 32. The second converter 30 operates in the same manner as the first converter 20. The second converter 30 is configured to convert power between the second end 32 and the fourth end 33 in both directions.

[0025] In the active power buffer circuit 10, the first converter 20 and the second converter 30 are connected in series such that the directions of the first DC voltage v1 at the first terminal 22 and the second DC voltage v2 at the second terminal 32 are opposite to each other. The first terminal and the second terminal connect the DC power supply 60 and the DC side of the single-phase inverter 70 (see Figure 2).

[0026] <Control by control device 200> The control device 200 controls the first converter 20 and the second converter 30 such that the first magnetic field and the second magnetic field generated by the first current i1 and the second current i2 approach the same direction and the same magnitude. Herein, the sum of the first current i1 and the second current i2 is defined as a common-mode current i Σ (i Σ =i1+i2), and the difference between the first current i1 and the second current i2 is defined as a differential-mode current i Δ (i Δ =i1-i2). The control device 200 controls the first converter 20 and the second converter 30 such that the common-mode current i Σ approaches zero. As a result, the first magnetic field generated by the first current i1 and the second magnetic field generated by the second current i2 strengthen each other, increasing the inductance, so that the coupled inductor 40 can be reduced in size. Furthermore, since the number of turns of the coil is reduced, conduction loss can be reduced and efficiency can be improved.

[0027] The control device 200 controls the first converter 20 such that a first AC component, which is a frequency twice the fundamental frequency of the AC voltage on the AC side of the single-phase inverter 70, is included in the first DC voltage v1. The control device 200 also controls the second converter 30 such that a second AC component, which is a frequency twice the fundamental frequency of the AC voltage on the AC side of the single-phase inverter 70, is included in the second DC voltage v2. Then, the pulsating component included in the voltage v of the DC link capacitor 80 dc is compensated by the first DC voltage v1 and the second DC voltage v2, thereby suppressing power pulsation in the DC power supply 60.

[0028] The control device 200 controls the amplitude difference and phase difference between the first AC component included in the first DC voltage v1 and the second AC component included in the second DC voltage v2. The control device 200 performs control such that the DC component of the first DC voltage matches the DC component of the second DC voltage. Then, the control device 200 performs control such that the amplitude of the first AC component matches the amplitude of the second AC component.

[0029] Figure 4 is a block diagram illustrating the control of the first converter 20 and the second converter 30 by the control device 200. The control device 200 includes a moving average filter (MA) 201 and a buffer voltage controller (PI b )202, moving average filter (MA)203, and DC voltage controller (PI) dc )204 and current controller (PI Σ )205 and current controller (PI Δ It comprises a 206 and a duty cycle controller 207.

[0030] The moving average filter (MA) 201 uses the voltage v across buffer capacitor 50. b The detected value is obtained, and the voltage v b The average value is output. The period of the moving average filter (MA) 201 is set to, for example, a period with a frequency twice that of the fundamental frequency of the AC voltage on the AC side of the single-phase inverter 70. Buffer voltage controller (PI) b )202 is the voltage v across buffer capacitor 50 b The average value is the target value v * b Adjust to that.

[0031] The moving average filter (MA) 203 uses the voltage v of the DC link capacitor 80. dc The detected value is obtained, and the voltage v dc The average value is output. The period of the moving average filter (MA) 203 is set to, for example, a period with a frequency twice that of the fundamental frequency of the AC voltage on the AC side of the single-phase inverter 70. DC voltage controller (PI) dc )204 is the voltage v of the DC link capacitor 80 dc The average value is the target value v * dc (buffer voltage controller (PI) b Adjust to the control amount of 202.

[0032] Current controller (PI) Σ )205 is the common mode current i Σ The first converter 20 and the second converter 30 are controlled so that the value approaches 0. Current controller (PI) Δ )206 is the differential mode current i Δ The target value (DC voltage controller (PI) dc Controls the amount of manipulation.

[0033] The duty cycle controller 207 outputs the duty cycles d1 and d2 of the switching element SW1 of the first converter 20 and the switching element SW3 of the second converter 30. The duty cycle controller 207 is a current controller (PI Σ )205, current controller (PI Δ Convert the voltage-dimension value output from 206 into a duty cycle.

[0034] Figure 5 shows the specifications set for the simulation of the power system 1 according to this embodiment. Figure 5 shows each parameter, its corresponding sign, and its value. m The magnetization inductance of the coupled inductor 40 is k c The coefficients are shown. Below, the simulation results for power system 1 with the specifications shown in Figure 5 are presented.

[0035] Figure 6 shows the waveform of the AC voltage generated on the AC side of the single-phase inverter 70. The vertical axis represents voltage (V), and the horizontal axis represents time (ms). As shown in Figure 2, the voltage v is applied to the AC side of the single-phase inverter 70. p and voltage v n Determine the voltage v p and voltage v n This refers to the voltage of the AC power supply 90V. g Between, v g =v p -v n The following relationship holds. Figure 6 shows the voltage v across the DC link capacitor 80. dc And, voltage v p And voltage v n The waveform is shown as shown in Figure 6, voltage v dc By pulsating it at twice the fundamental frequency of the AC side, an AC voltage with a frequency of 50 Hz can be obtained.

[0036] Figure 7 shows the voltage v across buffer capacitor 50. b This figure shows the waveforms of the first DC voltage v1 and the second DC voltage v2. The vertical axis represents voltage (V), and the horizontal axis represents time (ms). The first converter 20 is a reversible chopper, and the voltage v b The voltage is converted between and the first DC voltage v1. Also, the second converter 30 is a reversible chopper, and the voltage v b The voltage is converted between the first and second DC voltage v2. Therefore, the voltage v b The first DC voltage v1 and the second DC voltage v2 are set to values ​​greater than the first DC voltage v1 and the second DC voltage v2. The first DC voltage v1 and the second DC voltage v2 are the voltages of the DC link capacitor 80 v dc It compensates for the pulsating component contained in the DC power supply 60 and the voltage v s To suppress power pulsation in the voltage. Therefore, the first DC voltage v1 and the second DC voltage v2 are voltage v dc The control device 200 controls the phase difference to compensate for the pulsating components contained in the signal.

[0037] Figure 8 shows the current i flowing through the AC power supply 90. g , the current i output by the DC power supply 60 s And the current i flowing from the DC link capacitor 80 to the single-phase inverter 70 dn This diagram shows the waveform. The vertical axis represents current (A), and the horizontal axis represents time (ms). Current i flows from the DC link capacitor 80 to the single-phase inverter 70. dn It pulsates at 100 Hz, which is twice the fundamental frequency, and shows a peak-to-peak pulsation of 18.4 A. Meanwhile, the current i output by the DC power supply 60 s The current is maintained at 9.2A in DC. The pulsation of the AC voltage on the AC side, which occurs during power conversion by the single-phase inverter 70 and is twice the fundamental frequency of the AC voltage, is suppressed from affecting the DC power supply 60.

[0038] In the power system 100 shown in Figure 1, a 33 μH inductor is required to achieve the same level of current pulsation suppression effect as in the power system 1 described above. In contrast, in power system 1, the total inductance of the coupled inductor 40 is 15.8 μH. By using the coupled inductor 40, the active power buffer circuit 10 can be miniaturized. Furthermore, the conduction loss in this embodiment is calculated to be 1.05W at full load. Using the switching loss at 9.2A and the average operating voltage of 70V, the expected switching loss for each half-bridge (SW1~SW4) of the active power buffer circuit 10 is 0.6W. Considering that the capacitor loss is 1.6W, the efficiency at full load is calculated to exceed 99.8%.

[0039] The above embodiment is merely an example and is not limited thereto. For example, in the example shown in Figure 3, the active power buffer circuit 10 is connected in series with the DC power supply 60 and the negative side of the single-phase inverter 70, but it may also be connected in series with the positive side. Furthermore, although reversible chopper circuits are shown as the first converter 20 and the second converter 30, the circuit is not limited to these, and any circuit capable of converting power in both directions and equipped with a coupling inductor is acceptable. Furthermore, while the example in Figure 3 shows a MOSFET as the switching element, it is not limited to this. For example, bipolar transistors, JFETs, IGBTs, etc., may also be used. Also, the diodes D1, D2, D3, and D4 shown in Figure 3 may be, for example, diodes connected in parallel with the switching element, or they may be the body diodes of the MOSFET.

[0040] <Effects> The active power buffer circuit 10 in the first aspect is an active power buffer circuit 10 connected in series between a DC power supply 60 and the DC side of a single-phase inverter 70, and comprises a first converter 20 having a first inductor and configured to adjust the first DC voltage at a first end 22 in one direction, a second converter 30 having a second inductor and configured to adjust the second DC voltage at a second end 32 in one direction, and a control device 200 that controls the first converter 20 and the second converter 30, wherein the first end 22 and the second end 32 are connected in series such that the directions of the first DC voltage and the second DC voltage are opposite to each other, the first end 22 and the second end 32 connected in series connect the DC power supply 60 and the DC side of the single-phase inverter 70, and the first inductor and the second inductor are a coupled inductor 40. In this case, the efficiency of adjusting pulsating power by the converter connected in series between the DC power supply 60 and the single-phase inverter 70 can be improved. The active power buffer circuit 10 in the second aspect is the active power buffer circuit 10 in the first aspect, where the first converter 20 is a first reversible chopper circuit and the second converter 30 is a second reversible chopper circuit. In this case, the positive and negative voltages can be adjusted in both directions. The active power buffer circuit 10 in the third aspect is the active power buffer circuit 10 in the first or second aspect, wherein the first converter 20 is a first reversible chopper circuit in which a first capacitor 21 is provided at the first end, and a first switching element SW1 and a buffer capacitor 50 are connected in series with respect to the series connection of the first capacitor 21 and the first inductor, and a second switching element SW2 is connected in parallel, and the second converter 30 is a second reversible chopper circuit in which a second capacitor 31 is provided at the second end 32, and a third switching element SW3 and a buffer capacitor 50 are connected in series with respect to the series connection of the second capacitor 31 and the second inductor, and a fourth switching element SW4 is connected in parallel. The active power buffer circuit 10 in the fourth aspect is an active power buffer circuit 10 in any one of the first to third aspects, wherein the control device 200 controls the first converter 20 and the second converter 30 so that the first magnetic field generated by the first current flowing through the first inductor and the second magnetic field generated by the second current flowing through the second inductor approach the same direction and strength. In this case, the coupled inductor 40 can be miniaturized. The active power buffer circuit 10 in the fifth aspect is an active power buffer circuit 10 in any one of the first to fourth aspects, wherein the control device 200 controls the first converter 20 so that a first AC component having a frequency twice the fundamental frequency of the AC voltage on the AC side of the single-phase inverter 70 is included in the first DC voltage, and controls the second converter 30 so that a second AC component having a frequency twice the fundamental frequency is included in the second DC voltage. In this case, fluctuations in the voltage of the DC power supply 60 can be suppressed. The active power buffer circuit 10 in the sixth aspect is an active power buffer circuit 10 in any one of the first to fifth aspects, and the control device 200 controls the phase difference between the first AC component and the second AC component. In this case, power pulsation can be easily adjusted. The power conversion device according to the seventh aspect comprises an active power buffer circuit 10 according to any one of the first to sixth aspects, and a single-phase inverter 70 that converts DC power from a DC power supply 60 into AC power from an AC power supply.

[0041] Although embodiments have been described above, the technical scope of this disclosure is not limited to the embodiments described above. It is clear from the claims that combinations of two or more of the above embodiments, as well as various modifications or improvements to the above embodiments, are also included in the technical scope of this disclosure. [Explanation of Symbols]

[0042] 1…Power system, 10…Active power buffer circuit, 20…First converter, 21…First capacitor, 30…Second converter, 31…Second capacitor, 40…Coupling inductor, 50…Buffer capacitor, 60…DC power supply, 70…Single-phase inverter, 80…DC link capacitor, 200…Control device

Claims

1. An active power buffer circuit connected in series between a DC power supply and the DC side of a single-phase inverter, A first converter having a first inductor and configured to allow adjustment of the first DC voltage at the first end in one direction, A second converter having a second inductor and configured to allow the second DC voltage at the second end to be adjusted in one direction, The system includes a controller that controls the first converter and the second converter, The first end and the second end are connected in series such that the directions of the first DC voltage and the second DC voltage are opposite to each other. The first and second ends connected in series connect the DC power supply and the DC side of the single-phase inverter. The first inductor and the second inductor are coupled inductors. Active power buffer circuit.

2. The first converter is a first reversible chopper circuit, The second converter is a second reversible chopper circuit. The active power buffer circuit according to claim 1.

3. The first converter is a first reversible chopper circuit comprising a first capacitor at the first end, a first switching element and a buffer capacitor connected in series, and a second switching element connected in parallel to the series connection of the first capacitor and the first inductor. The second converter is a second reversible chopper circuit comprising a second capacitor at the second end, and a third switching element and the buffer capacitor connected in series, and a fourth switching element connected in parallel to the series connection of the second capacitor and the second inductor. The active power buffer circuit according to claim 2.

4. The active power buffer circuit according to claim 1, wherein the controller controls the first converter and the second converter so that the first magnetic field generated by the first current flowing through the first inductor and the second magnetic field generated by the second current flowing through the second inductor approach the same direction and strength.

5. The controller controls the first converter such that a first AC component, which has a frequency twice that of the fundamental frequency of the AC voltage on the AC side of the single-phase inverter, is included in the first DC voltage. The active power buffer circuit according to claim 1, wherein the second converter is controlled such that a second AC component having a frequency twice that of the fundamental frequency is included in the second DC voltage.

6. The controller controls the phase difference between the first AC component and the second AC component, as described in claim 5.

7. An active power buffer circuit according to any one of claims 1 to 6, A single-phase inverter that converts DC power from a DC power source to AC power from an AC power source, A power conversion device equipped with the following features.

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