Power converter

Abstract

The bidirectional AC / DC converter (201) performs power conversion between the AC system (102) and the DC bus 205 to control the AC system voltage (Vac) according to the AC system voltage command value in order to manage the voltage quality of the AC system (102). The first bidirectional DC / DC converter (202) performs power conversion between the DC system (103) and the DC bus (205) to control the DC system voltage (Vdc) according to the DC system voltage command value in order to manage the voltage quality of the DC system (103). The second bidirectional DC / DC converter (203) performs power conversion between the DC bus (205) and the power storage device (206) to control the DC bus voltage (Vdcbus) according to the DC bus voltage command value.

Description

[[Technical Field]]

[0001] The present disclosure relates to a power conversion device. [[Background Art]]

[0002] From the perspective of promoting decarbonization, the introduction of distributed power sources such as photovoltaic power generation and storage batteries into power systems has been increasing. These distributed power sources generally output DC (Direct Current) voltage, while existing commercial grids and distribution grids are constructed based on the power supply system using AC (Alternating Current) voltage (AC power distribution). Therefore, when connecting a distributed power source to a commercial grid or a distribution grid, the connection is generally made via a power conversion device including a DC / AC converter.

[0003] Furthermore, since the DC voltage directly output by a distributed power source fluctuates greatly, in a configuration in which the distributed power source is directly connected to a DC / AC converter, the DC voltage output by the distributed power source may be insufficient relative to the magnitude of the AC voltage, which may force the operation of the DC / AC conversion circuit to be stopped.

[0004] For this reason, a configuration has been proposed in which a DC / DC converter and a DC bus are separately arranged between a distributed power source and an AC / DC converter, and the voltage of the DC bus is controlled within an appropriate range by the DC / DC converter.

[0005] For example, Japanese Patent No. 7424195 (Patent Document 1) describes a configuration in which a distributed power source such as photovoltaic power generation and a storage battery is connected to a power system via a DC / DC conversion circuit, a DC bus, and an AC / DC conversion circuit. Furthermore, Patent Document 1 also describes a configuration in which a new DC / AC conversion circuit is connected to the DC bus to connect with the AC output of another distributed power supply facility, and a configuration in which the DC bus is connected to the DC bus of another distributed power source. [[Prior Art Documents]] [[Patent Documents]]

[0006] [Patent Document 1] Patent No. 7424195 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] While configurations connecting distributed power sources to AC systems, such as those described in Patent Document 1, are widely used, the concept of DC power distribution is being newly proposed as the proportion of distributed power sources increases. DC power distribution changes the distribution system itself to a DC voltage-based supply method, allowing each distributed power source to be connected to the distribution system only through a DC / DC conversion circuit, without the need for DC / AC conversion. This reduces the number of power conversion stages, thereby improving power conversion efficiency.

[0008] However, replacing the numerous power distribution facilities already built on AC power distribution with facilities suitable for DC power distribution is a matter of considerable effort and time, and is therefore a concern as it will not be easily realized. For this reason, an AC / DC hybrid power distribution system has been proposed, which involves creating areas within the existing AC power distribution system that will partially utilize DC power distribution.

[0009] On the other hand, in such AC / DC hybrid power distribution systems, it is necessary to maintain and manage the voltage at an appropriate quality in both the AC power distribution domain (hereinafter referred to as the AC system) and the DC power distribution domain (hereinafter referred to as the DC system).

[0010] This disclosure was made to solve these problems, and the purpose of this disclosure is to provide a power converter for AC-DC hybrid power distribution that can perform power conversion between AC and DC systems while also being able to manage the voltage quality of both AC and DC systems. [Means for solving the problem]

[0011] According to certain aspects of this disclosure, a power converter is provided. The power converter is connected between a three-phase or single-phase AC system requiring voltage quality control and a DC system requiring voltage quality control. The power converter comprises a bidirectional AC / DC converter, a first bidirectional DC / DC converter, a second bidirectional DC / DC converter, and a control device for controlling the bidirectional AC / DC converter, the first bidirectional DC / DC converter, and the second bidirectional DC / DC converter. The bidirectional AC / DC converter performs power conversion between the AC system and the DC bus. The first bidirectional DC / DC converter performs power conversion between the DC system and the DC bus. The second bidirectional DC / DC converter performs power conversion between a power storage device and the DC bus. The control device is configured to perform a first control that controls power conversion by a bidirectional AC / DC converter to control the voltage of the AC system according to an AC system voltage command value in order to manage the voltage quality of the AC system; a second control that controls power conversion by a first bidirectional DC / DC converter to control the voltage of the DC system according to a DC system voltage command value in order to manage the voltage quality of the DC system; and a third control that controls power conversion by a second bidirectional DC / DC converter to control the voltage of the DC bus according to a DC bus voltage command value. [Effects of the Invention]

[0012] According to this disclosure, a bidirectional AC / DC converter that generates AC system voltage as a voltage source, and a first bidirectional DC / DC converter that generates DC system voltage as a voltage source, perform power conversion between a DC bus whose voltage is controlled by the second bidirectional DC / DC converter and the AC system and the DC system, respectively. This configuration makes it possible to manage the voltage quality of both the AC system and the DC system while performing power conversion between the AC system and the DC system. [Brief explanation of the drawing]

[0013] [Figure 1] This is a block diagram illustrating an example of the configuration of a power distribution system to which the power conversion device according to this embodiment is applied. [Figure 2]It is a block diagram illustrating an example of the internal configuration of the power conversion apparatus according to Embodiment 1. [Figure 3] It is a block diagram illustrating an example of the hardware configuration of the control apparatus shown in FIG. 2. [Figure 4] It is a block diagram illustrating the control function of the bidirectional AC / DC converter by the control apparatus shown in FIG. 2. [Figure 5] It is a block diagram illustrating the control function of the first bidirectional DC / DC converter by the control apparatus shown in FIG. 2. [Figure 6] It is a block diagram illustrating the control function of the second bidirectional DC / DC converter by the control apparatus shown in FIG. 2. [Figure 7] It is a block diagram for explaining the rotational coordinate conversion applicable to FIG. 4. [Figure 8] It is a block diagram illustrating an example of the internal configuration of the power conversion apparatus according to Embodiment 2. [Figure 9] It is a block diagram illustrating a control function added to the power conversion apparatus according to Embodiment 2. [Figure 10] It is a flowchart illustrating the processing of SOC management control according to Embodiment 2. [Figure 11] It is a block diagram illustrating an example of the internal configuration of the power conversion apparatus according to Embodiment 3. [Figure 12] It is a block diagram illustrating a control function added to the power conversion apparatus according to Embodiment 3. [Figure 13] It is a flowchart illustrating the processing of SOC management control according to Embodiment 3. [Figure 14] It is a block diagram illustrating an example of the internal configuration of the power conversion apparatus according to Embodiment 4. [Figure 15] It is a conceptual diagram illustrating a modified example of calculation of DC bus voltage deviation in the control function of the second bidirectional DC / DC converter. MODE FOR CARRYING OUT THE INVENTION

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated in principle.

[0015] Embodiment 1. FIG. 1 is a block diagram illustrating a configuration example of a power distribution system 10 to which the power conversion device according to the present embodiment is applied.

[0016] As shown in FIG. 1, the power distribution system 10 includes an AC (Alternative Current) system 102, a DC (Direct Current) system 103, and a power conversion device 100 connected between the AC system 102 and the DC system 103.

[0017] The power distribution system 10 is an AC-DC hybrid power distribution system including both the AC system 102 and the DC system 103. The power distribution system 10 may be a power distribution system on the premises of a specific consumer such as a factory or an office building, may be a regional power distribution system connected to a distribution substation and constructed in a certain range of area, or may be an independent power distribution system in transportation equipment such as a ship, an automobile, or an aircraft. In the present disclosure, an area including both the AC system 102 and the DC system 103 is referred to as an AC-DC hybrid power distribution system.

[0018] The power conversion device 100 performs bidirectional power conversion (AC / DC) between the AC system 102 and the DC system 103. The internal configuration and operation of the power conversion device 100 will be described in detail later.

[0019] AC system 102 is a power system that uses three-phase or single-phase AC voltage. AC system 102 may be an isolated system, disconnected from the external AC system 104. Alternatively, AC system 102 may be configured to be connectable to the external AC system 104 via relay 111, as illustrated in Figure 1. The external AC system 104 could be a commercial system for a customer's on-premises distribution system, a higher-voltage system for a regional distribution system, or a charging station for a distribution system within a transportation device. For example, when relay 111 is ON, the power from AC system 104 charges the power storage device (described later) in the AC / DC power converter 100. Then, when relay 111 is OFF, the power from the power storage device is used by the AC / DC power converter 100 to operate AC system 102 and DC system 103 independently.

[0020] AC system 102 is connected to AC distributed power supplies 105a, 105b, and AC loads 106a to 106c, etc. Each of the AC distributed power supplies 105a and 105b includes a power supply that can be connected to the AC system via an AC output terminal, such as a combination of a DC power source like solar power generation or a storage battery and an AC / DC converter (power conditioner). Note that the number of AC distributed power supplies connected to AC system 102 is not limited to the example in Figure 1 (2 units) and is arbitrary.

[0021] Each of the AC loads 106a to 106c includes equipment that operates on AC voltage, such as general household appliances. Alternatively, multiple devices used by a single customer may be considered as a single unit and counted as an AC load. Furthermore, the number of AC loads connected to the AC system 102 is not limited to the example in Figure 1 (3 units) and is arbitrary.

[0022] The AC system voltage Vac of AC system 102 fluctuates in frequency and amplitude depending on the supply and demand balance of the load and power source, or the power flow conditions. However, in order for the AC load to operate normally, it must always be maintained within certain quality standards. These quality standards are generally defined in the management regulations set by the general transmission and distribution company or in the internal wiring regulations within the customer's premises. In other words, the frequency and amplitude of the AC system voltage Vac must be controlled within the management range predetermined in accordance with the quality standards. Note that if AC system 102 is three-phase AC, the AC system voltage Vac comprehensively represents the AC voltages Vacu, Vacp, and Vauw of the three phases (U, V, W phases).

[0023] DC system 103 is a power system that uses DC voltage. DC distributed power supplies 107a and 107b and DC loads 108a to 108c are connected to DC system 103.

[0024] Each of the DC distributed power supplies 107a and 107b includes a power supply that can be connected to a DC system via a DC output terminal, such as a combination of a DC power source like a solar power generation system or a storage battery and a DC / DC converter. Each of the DC loads 108a to 108c includes equipment that operates by receiving DC voltage, such as lighting equipment and air conditioning equipment. A DC load may also be a group of multiple pieces of equipment used by a single customer. The number of DC distributed power supplies and DC loads connected to the DC system 103 is also arbitrary.

[0025] The DC system voltage Vdc of DC system 103 fluctuates depending on the supply and demand balance of the load and power supply, or the power flow conditions, but it must always be maintained within a certain quality standard in order for the DC load to operate normally. Although this quality standard is not currently clearly defined, it is reasonable to assume that it will be defined in the future as DC power distribution expands. In this embodiment, the voltage value of the DC system voltage Vdc needs to be controlled within a predetermined management range.

[0026] Thus, the power distribution system 10 for AC / DC hybrid power distribution is connected to multiple power sources and multiple loads, and it is necessary to manage the voltage quality of both the AC system 102 and the DC system 103 within a certain standard even in the face of moment-to-moment changes in power flow conditions. As will become clear from the following description, the power converter 100 according to this disclosure is characterized by its ability to simultaneously manage the voltage quality of both the AC system 102 and the DC system 103 with a single unit, thereby improving the flexibility of the equipment connected to the AC / DC hybrid power distribution system.

[0027] Figure 2 is a block diagram illustrating an example of the internal configuration of the power converter 100 according to Embodiment 1 shown in Figure 1. The configuration and operation of the power converter 100 will be explained using Figure 2.

[0028] As shown in Figure 2, the power converter 100 comprises a bidirectional AC / DC converter 201, a first bidirectional DC / DC converter 202, a second bidirectional DC / DC converter 203, and a control device 200.

[0029] The bidirectional AC / DC converter 201, the first bidirectional DC / DC converter 202, and the second bidirectional DC / DC converter 203 are connected to a common DC bus 205. A capacitor 207 for voltage smoothing is connected to the DC bus 205.

[0030] The bidirectional AC / DC converter 201 is further connected to the AC system 102. The bidirectional AC / DC converter 201 is configured to include at least one semiconductor switching element (not shown), and is configured to perform bidirectional AC / DC conversion between the AC system 102 and the DC bus 205 by the on / off operation (switching operation) of the semiconductor switching element. For example, the bidirectional AC / DC converter 201 can be configured as a single-phase full-bridge (when the AC system 102 is single-phase) or a three-phase full-bridge (when the AC system 102 is three-phase).

[0031] The first bidirectional DC / DC converter 202 is further connected to the DC system 103. The first bidirectional DC / DC converter 202 is configured to include at least one semiconductor switching element (not shown), and is configured to perform bidirectional DC / DC conversion between the DC system 103 and the DC bus 205 by the on / off operation (switching operation) of the semiconductor switching element. For example, the first bidirectional DC / DC converter 202 can be configured as a buck-boost chopper or a DAB (Dual Active Bride) configuration.

[0032] The second bidirectional DC / DC converter 203 is further connected to a power storage device 206. The power storage device 206 may consist of a device capable of storing power, such as a rechargeable battery and / or a large-capacity capacitor. The second bidirectional DC / DC converter 203 is configured to include at least one semiconductor switching element (not shown), and the on / off operation (switching operation) of the semiconductor switching element is configured to perform bidirectional DC / DC conversion between the DC bus 205 and the power storage device 206. For example, the second bidirectional DC / DC converter 203 may be configured in a step-up / step-down chopper configuration or a DAB (Dual Active Bride) configuration, similar to the first bidirectional DC / DC converter 202.

[0033] In this disclosure, the circuit configurations of the bidirectional AC / DC converter 201, the first bidirectional DC / DC converter 202, and the second bidirectional DC / DC converter 203 are not particularly limited and can be appropriately selected according to whether the AC system 102 is three-phase or single-phase, and the magnitude of the rated voltages of the AC system 102, DC system 103, and DC bus 205.

[0034] On the AC system 102 side of the bidirectional AC / DC converter 201, a sensor 210 is provided to detect the AC system voltage Vac and AC system current Iac. On the DC bus 205, a sensor 220 is provided to detect the DC bus voltage Vdcbus and DC bus current Idcbus flowing through the DC bus 205. On the DC system 103 side of the first bidirectional DC / DC converter 202, a sensor 230 is provided to detect the DC system voltage Vdc and DC system current Idc, in addition to the sensor 210 provided. Furthermore, on the power storage device 206 side of the second bidirectional DC / DC converter 203, a sensor 240 is provided to detect the output voltage Vbat of the power storage device 206. The detected values ​​from sensors 210 to 240, i.e., the measured values ​​of each current and each voltage, are input to the control device 200.

[0035] The control device 200 controls the power conversion of each of the bidirectional AC / DC converters 201, the first bidirectional DC / DC converter 202, and the second bidirectional DC / DC converter 203. Specifically, the power conversion is controlled by on / off control of the semiconductor switching elements included in each converter.

[0036] Figure 3 shows a block diagram illustrating an example of the hardware configuration of the control device 200. Figure 3 also shows an example of the control device 200 being configured by a computer.

[0037] Referring to Figure 3, the control device 200 includes one or more input converters 90, one or more sample-and-hold (S / H) circuits 91, a multiplexer (MUX) 92, an A / D (Analog-to-Digital) converter 93, one or more CPUs 94, a RAM (Random Access Memory) 95, a ROM (Read Only Memory) 96, one or more input / output interfaces (I / F) 97, an auxiliary storage device 98, and a bus 99 that interconnects the above components.

[0038] The input converter 90 has an auxiliary transformer (not shown) for each input channel. Each auxiliary transformer converts, for example, detection signals indicating measured values ​​such as voltage, current, and temperature from each sensor (for example, sensors 210 to 240 in Figure 2) into signals with a voltage level suitable for subsequent signal processing. A sample-and-hold circuit 91 is provided for each input converter 90. The sample-and-hold circuit 91 samples and holds the signal representing the quantity of electricity received from the corresponding input converter 90 at a specified sampling frequency.

[0039] The multiplexer 92 sequentially selects signals held by multiple sample-and-hold circuits 91. The A / D converter 93 converts the signals selected by the multiplexer 92 into digital values. Note that by providing multiple A / D converters 93, A / D conversion may be performed in parallel for detection signals from multiple input channels.

[0040] The CPU 94 controls the entire control unit 200 and performs arithmetic processing according to the program. The RAM 95, which is volatile memory, and the ROM 96, which is non-volatile memory, are used as the main memory of the CPU 94. The ROM 96 stores programs and setting values ​​for signal processing. The auxiliary storage device 98 is a non-volatile memory with a larger capacity than the ROM 96, and stores programs and sensor detection data.

[0041] The input / output interface 97 is an interface circuit for communication between the CPU 94 and external devices. Control signals (e.g., gate signals, described later) can be output to the bidirectional AC / DC converter 201, the first bidirectional DC / DC converter 202, and the second bidirectional DC / DC converter 202 via the input / output interface 97. In addition, the control device 200 can receive command values, setting inputs, etc., from outside via the input / output interface 97.

[0042] Unlike the example in Figure 3, it is also possible to configure at least a portion of the control device 200 using circuits such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit).

[0043] For example, the functions of each block described in the block diagrams below can be configured based on the computer illustrated in Figure 3, or at least a part of it can be configured using circuits such as FPGAs or ASICs. Furthermore, at least a part of the functions of each functional block can also be configured using analog circuits.

[0044] Referring again to Figure 2, each of the bidirectional AC / DC converter 201, the first bidirectional DC / DC converter 202, and the second bidirectional DC / DC converter 203 is controlled by the control device 200. Specifically, the control device 200 generates gate signals corresponding to on / off control signals for the semiconductor switching elements (not shown) of each converter so that power conversion is performed to control electrical quantities such as voltage, current, or power according to command values, as will be described later.

[0045] The control device 200 controls the power conversion by the bidirectional AC / DC converter 201 so that the bidirectional AC / DC converter 201 manages the voltage of the AC system 102 (AC system voltage Vac). The control device 200 also controls the power conversion of the first bidirectional DC / DC converter 202 so that the first bidirectional DC / DC converter 202 manages the voltage of the DC system 103 (DC system voltage Vdc). Furthermore, the control device 200 controls the power conversion by the second bidirectional DC / DC converter 203 so that the second bidirectional DC / DC converter 203 manages the voltage of the DC bus 205 (DC bus voltage Vdcbus).

[0046] Next, the control functions of the control device 200 for the bidirectional AC / DC converter 201, the first bidirectional DC / DC converter 202, and the second bidirectional DC / DC converter 203 will be explained in detail using Figures 4 to 6. It is also possible to configure the control functions of the bidirectional AC / DC converter 201, the first bidirectional DC / DC converter 202, and the second bidirectional DC / DC converter 203 to be executed by individual control devices. In this case, the control device 200 in Figure 3 corresponds to a collection of these individual control devices.

[0047] Figure 4 is a block diagram illustrating the control function of the bidirectional AC / DC converter 201 by the control device 200.

[0048] As shown in Figure 4, the control unit 310 of the bidirectional AC / DC converter 201 includes deviation calculation units 311 and 313, control calculation units 312 and 314, duty cycle conversion unit 315, and PWM control unit 316. The control unit 310 controls the AC system voltage Vac according to the AC system voltage command value Vacref in order to maintain it within the control range in accordance with quality standards.

[0049] The AC system voltage command value Vacref can be set arbitrarily as long as it provides an effect of managing the AC system voltage Vac. However, in Embodiment 1, it is set as a sinusoidal voltage with a rated frequency (typically 50 Hz or 60 Hz) and rated voltage amplitude. The AC system voltage command value Vacref may be set internally in the control device 200, or it may be input to the control device 200 from an external source.

[0050] The deviation calculation unit 311 calculates the AC voltage deviation ΔVac by subtracting the measured value Vacm (sensor 210) of the AC system voltage Vac from the AC system voltage command value Vacref. The control calculation unit 312 calculates the AC current command value Iaccom, which indicates the AC current waveform to be output from the power converter 100 (bidirectional AC / DC converter 201) to the AC system 102, by performing a control calculation using the AC voltage deviation ΔVac as input.

[0051] Here, a positive value of the AC current command value Iaccom indicates the direction of current from the bidirectional AC / DC converter 201 to the AC system 102. Conversely, a negative value of the AC current command value Iaccom indicates the direction of current from the AC system 102 to the bidirectional AC / DC converter 201.

[0052] The deviation calculation unit 313 calculates the AC current deviation ΔIac by subtracting the measured value Iacm (sensor 210) of the AC system current Iac from the AC current command value Iaccom. The control calculation unit 314 calculates the AC voltage command value Vaccom, which indicates the AC voltage waveform to be output from the power converter 100 (bidirectional AC / DC converter 201) to the AC system 102, by performing a control calculation using the AC current deviation ΔIac as input.

[0053] In the example shown in Figure 4, the control calculation units 312 and 314 calculate the AC current command value Iaccom and the AC voltage command value Vaccom by proportional-integral (PI) control of proportional gains K11 and K12 and integral gains (K11 / T11) and (K12 / T12). However, the control calculation by the control calculation units 312 and 314 may also apply proportional (P) control or proportional-integral-derivative (PID) control, and any other method can be used.

[0054] The duty cycle conversion unit 315 normalizes the AC voltage command value Vaccom from the control calculation unit 314 by dividing the measured value Vdcbusm of the DC bus voltage Vdcbus by (1 / 2) to an AC waveform with an amplitude of (Vdcbus / 2) = 1.0. This allows the duty cycle of the semiconductor switching element at each switching period to be determined by comparing it with a carrier composed of a periodic waveform (such as a triangular wave) with an amplitude of 1.0.

[0055] The PWM control unit 316 generates a gate signal (pulse pattern) for on / off control of the switching element (not shown) included in the bidirectional AC / DC converter 201, according to a comparison between the carrier (not shown) and the normalized AC voltage command value Vaccom.

[0056] For example, if the AC system 102 supplies three-phase AC and the bidirectional AC / DC converter 201 is composed of a three-phase inverter, the AC system voltage command value Vacref is individually set for each of the three phases (U-phase, V-phase, and W-phase) to have a phase difference of 120°. Furthermore, the measured value Vacm of the AC system voltage Vac, the AC current command value Iaccom, the measured value Iacm of the AC system current Iac, and the AC voltage command value Vaccom are determined for each of the three phases (U-phase, V-phase, and W-phase). Then, the semiconductor switching elements (not shown) constituting the U-phase arm of the three-phase inverter are turned on and off according to the gate signals generated according to the comparison between the AC voltage command value Vaccom of the U-phase and the carrier. The on / off control of the semiconductor switching elements for the V-phase and W-phase is controlled similarly.

[0057] Alternatively, the AC system voltage command value Vacref and the measured AC system voltage Vacm, as well as the AC current command value Iaccom and the measured AC system current Iacm, can be converted using a three-phase / two-phase rotational coordinate transformation (e.g., dq transformation) to obtain the converted values ​​(e.g., d-axis and q-axis values). In this case, the AC voltage command value Vaccom, which corresponds to the command value for PWM control, needs to be converted to a three-phase AC value by an inverse two-phase / three-phase transformation.

[0058] Figure 7 shows a block diagram illustrating the rotational coordinate transformation applicable to Figure 4. As shown in Figure 7, the coordinate transformation unit 340 transforms the three-phase electrical quantity Euvw using a rotation angle θ to perform a rotational coordinate transformation (three-phase / two-phase transformation), and outputs the transformed two-phase electrical quantity Edq. The electrical quantity Euvw is the AC value of the voltage, current, or power of each of the three phases (U phase, V phase, W phase), and the electrical quantity Edq is the DC value of the voltage, current, or power of each of the two transformed phases (d axis, q axis).

[0059] In response, the coordinate transformation unit 350 outputs the three-phase electrical quantity Euvw by performing a rotational coordinate transformation (two-phase / three-phase transformation) on the two-phase electrical quantity Edq using the rotation angle θ.

[0060] The rotation angle θ used in the rotational coordinate transformation is obtained by integrating the angular velocity ω (ω = 2π·f) which is proportional to the AC frequency f of the electric quantity, and is therefore expressed by the following equation (1) with respect to the passage of time t.

[0061]

number

[0062] Referring again to Figure 4, in a modified example in which a rotational coordinate transformation is applied to Figure 4, the AC system voltage (measured value) Vacm and AC system current (measured value) Iacm are output to the coordinate transformation unit 340, and the output values ​​(d-axis value and q-axis value) of the coordinate transformation unit 340 are input to the deviation calculation units 311 and 313.

[0063] In this modified example, the AC system voltage command value Vacref is also given by the d-axis value (Vacref_d) and the q-axis value (Vacref_q), and the square root of the sum of their squares (√(Vacref_d) 2 +Vacref_q 2 The amplitude of the AC system voltage command value can be defined by ). The frequency of the AC system voltage command value can be determined by f in equation (1) in the coordinate transformation unit 350. In Embodiment 1, f in equation (1) can be a constant value of 50 [Hz] or 60 [Hz].

[0064] Furthermore, the control calculation units 312 and 314 also calculate the AC current command value Iaccom and the AC voltage command value Vaccom using the d-axis and q-axis values. The AC voltage command value Vaccom output from the control calculation unit 314 is then converted inversely to three-phase by the coordinate transformation unit 350, and then input to the duty cycle conversion unit 315 to obtain the AC voltage command value Vaccom (three-phase) corresponding to the command value for PWM control. Thus, it is stated for confirmation that the control process in Figure 4 encompasses both control involving rotational coordinate transformation and control targeting instantaneous AC values ​​without rotational coordinate transformation.

[0065] The control unit 310 can control the AC system voltage Vac so that the AC voltage deviation ΔVac becomes zero, that is, so that it matches the AC system voltage command value Vacref, by repeating the control process shown in Figure 4. As a result, it becomes possible to maintain the AC system voltage Vac within the control range that conforms to the quality standards. In this way, the control unit 310 can realize one embodiment of the "first control" of the bidirectional AC / DC converter 201 for managing the voltage quality of the AC system 102.

[0066] Figure 5 is a block diagram illustrating the control function of the first bidirectional DC / DC converter 202 by the control device 200.

[0067] As shown in Figure 5, the control unit 320 of the first bidirectional DC / DC converter 202 includes deviation calculation units 321, 323, control calculation units 322, 324, duty cycle conversion unit 325, and PWM control unit 326. The control unit 320 controls the DC system voltage Vdc according to the DC system voltage command value Vdcref in order to maintain it within a control range in accordance with quality standards.

[0068] The DC system voltage command value Vdcref can be set arbitrarily as long as it provides an effect of managing the DC system voltage Vdc, but in Embodiment 1, it is set to a constant value equivalent to the rated voltage of the DC system 103. The DC system voltage command value Vdcref may be set internally in the control device 200, or it may be input to the control device 200 from an external source.

[0069] The deviation calculation unit 321 calculates the DC voltage deviation ΔVdc by subtracting the measured value Vdcm (sensor 230) of the DC system voltage Vdc from the DC system voltage command value Vdcref. The control calculation unit 322 calculates the DC current command value Idccom, which indicates the DC current value to be output from the power converter 100 (first bidirectional DC / DC converter 202) to the DC system 103, by performing a control calculation using the DC voltage deviation ΔVdc as input.

[0070] Here, a positive value of the DC current command value Idccom indicates the direction of current from the first bidirectional DC / DC converter 202 to the DC system 103. Conversely, a negative value of the DC current command value Idccom indicates the direction of current from the DC system 103 to the first bidirectional DC / DC converter 202.

[0071] The deviation calculation unit 323 calculates the DC current deviation ΔIdc by subtracting the measured value Idcm (sensor 230) of the DC system current Idc from the DC current command value Idccom. The control calculation unit 324 calculates the DC voltage command value Vdccom, which indicates the DC voltage value to be output from the power converter 100 (first bidirectional DC / DC converter 202) to the DC system 103, by performing a control calculation using the DC current deviation ΔIdc as input.

[0072] In the example shown in Figure 5, the control calculation units 322 and 324 calculate the DC current command value Idccom and the DC voltage command value Vdccom by proportional-integral (PI) control of proportional gains K21 and K22 and integral gains (K21 / T21) and (K22 / T22). However, the control calculation by the control calculation units 322 and 324 may also apply proportional (P) control or proportional-integral-derivative (PID) control, and any other method can be used.

[0073] The duty cycle conversion unit 325 converts the DC voltage command value Vdccom from the control calculation unit 324 into a duty cycle by dividing it by the measured value Vdcbusm of the DC bus voltage Vdcbus.

[0074] The PWM control unit 326 generates a gate signal (pulse pattern) for on / off control of a semiconductor switching element (not shown) included in the first bidirectional DC / DC converter 202, according to a comparison between a carrier (not shown) similar to that of the PWM control unit 316 and a normalized DC voltage command value Vdccom.

[0075] The control unit 320 can control the DC system voltage Vdc to make the DC voltage deviation ΔVdc zero, that is, to match the DC system voltage command value Vdcref, by repeating the control process shown in Figure 5. In this way, it becomes possible to maintain the DC system voltage Vdc within a control range that conforms to the quality standards. The control unit 320 can realize one embodiment of the "second control" of the first bidirectional DC / DC converter 202 for managing the voltage quality of the DC system 103.

[0076] As shown in Figure 4, when the bidirectional AC / DC converter 201 performs AC system voltage control, and as shown in Figure 5, when the first bidirectional DC / DC converter 202 performs DC system voltage control, in order to appropriately maintain the AC system voltage Vac and DC system voltage Vdc while responding to fluctuations in supply and demand conditions within the AC system 102 and DC system 103, it is necessary to supply adjustment power from the DC bus 205 to the AC system 102 and DC system 103 to compensate for the fluctuating supply and demand difference.

[0077] The regulating power is supplied from the stored charge of capacitor 207 connected to DC bus 205, but the increase or decrease in the charge of capacitor 207 due to the exchange of regulating power will cause fluctuations in the DC bus voltage Vdcbus. If the DC bus voltage Vdcbus rises or falls excessively, there is a concern that the power conversion operation of the bidirectional AC / DC converter 201 and / or the first bidirectional DC / DC converter 202 may become overmodulated and power conversion may not be possible, or that the capacitor 207 may be overcharged and exceed its withstand voltage, potentially causing damage to the equipment.

[0078] Therefore, although there are no quality standards for the DC bus voltage Vdcbus, such as for the AC system voltage Vac and DC system voltage Vdc, that are necessary for the normal operation of the load, it is necessary to manage it within a certain range from the viewpoint of stabilizing the control operation of the power converter 100. In the power converter 100 according to this embodiment, the DC bus voltage is controlled by power conversion between the DC bus 205 and the power storage device 206 using the charge and discharge power of the power storage device 206 by the second bidirectional DC / DC converter 203.

[0079] Figure 6 is a block diagram illustrating the control function of the second bidirectional DC / DC converter 203 by the control device 200.

[0080] As shown in Figure 6, the control unit 330 of the second bidirectional DC / DC converter 203 includes deviation calculation units 331 and 333, control calculation units 332 and 334, duty cycle conversion unit 335, and PWM control unit 336. The control unit 330 controls the DC bus voltage Vdcbus according to the DC bus voltage command value Vdcbusref.

[0081] The DC bus voltage command value Vdcbusref can be set arbitrarily as long as it does not destabilize the operation of the power converter 100, but it can be set to a constant value equivalent to the rated voltage of the DC bus 205, for example. The DC system voltage command value Vdcref may be set internally in the control device 200, or it may be input to the control device 200 from an external source.

[0082] The deviation calculation unit 331 calculates the DC bus voltage deviation ΔVdcbus by subtracting the measured value Vdcbusm (sensor 220) of the DC bus voltage Vdcbus from the DC bus voltage command value Vdcbusref. The control calculation unit 332 calculates the bus current command value Idcbuscom to be output from the second bidirectional DC / DC converter 203 to the DC bus 205 by performing a control calculation using the DC bus voltage deviation ΔVdcbus as input. A positive value of the bus current command value Idcbuscom indicates the discharge direction of the power storage device 206, i.e., the current direction from the second bidirectional DC / DC converter 203 to the DC bus 205. Conversely, a negative value of the bus current command value Idcbuscom indicates the charging direction of the power storage device 206, i.e., the current direction from the DC bus 205 to the second bidirectional DC / DC converter 203.

[0083] The deviation calculation unit 333 calculates the DC bus current deviation ΔIdcbus by subtracting the measured value Idcbusm (sensor 220) of the DC bus current Idcbus from the bus current command value Idcbuscom. The control calculation unit 334 calculates the output voltage command value Vdcbuscom from the second bidirectional DC / DC converter 203 to the DC bus 205 by performing a control calculation using the DC bus current deviation ΔIdcbus as input.

[0084] In the example shown in Figure 6, the control calculation units 332 and 334 calculate the bus current command value Idcbuscom and the output voltage command value Vdcbuscom by proportional-integral (PI) control of proportional gains K31 and K32 and integral gains (K31 / T31) and (K32 / T32). However, the control calculations performed by the control calculation units 332 and 334 may also be performed using proportional (P) control or proportional-integral-derivative (PID) control, or any other method.

[0085] The duty cycle conversion unit 335 converts the output voltage command value Vdcbuscom from the control calculation unit 334 into a duty cycle by dividing it by the measured value Vbatm (sensor 240) of the output voltage Vbat of the power storage device 206.

[0086] The PWM control unit 336 generates a gate signal (pulse pattern) for on / off control of a switching element (not shown) included in the second bidirectional DC / DC converter 203, according to a comparison between a carrier (not shown) similar to that of the PWM control units 316 and 326 and a normalized output voltage command value Vdcbuscom.

[0087] The control unit 330 can control the DC bus voltage Vdcbus to make the DC bus voltage deviation ΔVdcbus zero, that is, to match the DC bus voltage command value Vdcbusref, by repeating the control process shown in Figure 6. This makes it possible to maintain the DC bus voltage Vdcbus within a voltage range that does not destabilize the operation of the power converter 100. In this way, the control unit 330 can realize one embodiment of the "third control" of the second bidirectional DC / DC converter 203 for controlling the voltage of the DC bus 205 within a certain range.

[0088] Furthermore, the control function provided by the second bidirectional DC / DC converter 203 can be arranged as follows.

[0089] Firstly, a dead zone, as shown in Figure 15, can be introduced into the calculation of the DC bus voltage deviation ΔVdcbus by the deviation calculation unit 331.

[0090] Figure 15 is a conceptual diagram illustrating a modified example of the calculation of the DC bus voltage deviation in the control function of the second bidirectional DC / DC converter.

[0091] Figure 15 shows a graph with the measured value Vdcbusm (DC bus voltage Vdcbus) on the horizontal axis and the DC bus voltage deviation ΔVdcbus on the vertical axis, with Vdcbusm = Vdcbusref (horizontal axis) and ΔVdcbus = 0 (vertical axis) as the origin.

[0092] As shown in FIG. 15, when Vdcbusref-Vdz1 < Vdcbusm < Vdcbusref+Vdz2, the deviation calculation unit 331 calculates ΔVdcbus = 0. Thereby, a dead band 360 including the DC bus voltage command value Vdcbusref can be provided in the calculation of the DC bus voltage deviation ΔVdcbus. That is, inside the dead band 360, ΔVdcbus is calculated as 0 even if Vdcbusm ≠ Vdcbusref.

[0093] On the other hand, outside the dead band 360 (regions where Vdcbusm < Vdcbusref-Vdz1, or Vdcbusm > Vdcbusref+Vdz2), the deviation calculation unit 331 calculates the DC bus voltage deviation ΔVdcbus by reflecting the voltage difference (Vdcbusref - Vdcbusm).

[0094] For example, when Vdcbusm < Vdcbusref-Vdz1, ΔVdcbus = (Vdcbusref - Vdz1) - Vdcbusm = (Vdcbusref - Vdcbusm) - Vdz1 can be calculated (ΔVdcbus > 0). On the other hand, when Vdcbusm > Vdcbusref+Vdz2, ΔVdcbus = (Vdcbusref + Vdz2) - Vdcbusm = (Vdcbusref - Vdcbusm) + Vdz2 can be calculated (ΔVdcbus < 0). As described above, outside the dead band 360, by calculating the deviation between the measured value Vdcbusm (DC bus voltage) and the boundary value of the dead band 360, it is possible to prevent the control from becoming unstable due to abrupt change of the DC bus voltage deviation ΔVdcbus.

[0095] The electric power for eliminating the DC bus voltage deviation ΔVdcbus, that is, the electric power for controlling the DC bus voltage Vdcbus to the DC bus voltage command value Vdcbusref, is secured by discharging or charging of the power storage device 206. Therefore, by providing the dead band 360 as shown in FIG. 15 to calculate the DC bus voltage deviation ΔVdcbus, it is possible to avoid an operation in which the power storage device 206 repeats a small amount of charging and discharging. Thereby, deterioration of the power storage device 206 can be prevented.

[0096] Note that the dead zone 360 ​​may be symmetrical (Vdz1=Vdz2) or asymmetrical (Vdz1≠Vdz2) in Figure 15.

[0097] Secondly, considering that the DC bus voltage Vdcbus fluctuates in response to the supply of adjustment power for appropriately maintaining the AC system voltage Vac and DC system voltage Vdc as described above, it is preferable that the control response speed of the DC bus voltage Vdcbus by the control unit 330 be higher than both the control response speed of the AC system voltage Vac by the control unit 310 and the control response speed of the DC system voltage Vdc by the first bidirectional DC / DC converter 202 (control unit 320).

[0098] For example, the difference in control response speed (high / low) mentioned above can be achieved by adjusting the proportional gains K11 (Figure 4), K21 (Figure 5), and K31 (Figure 6). As an example, with respect to the gain crossover angular frequency of the loop transfer function obtained by combining the characteristics of the controller (control unit 310, 320, 330) and the response characteristics of the controlled objects (bidirectional AC / DC converter 201, first bidirectional DC / DC converter 202, second bidirectional DC / DC converter 203), the values ​​of the proportional gains K11 (Figure 4), K21 (Figure 5), and K31 (Figure 6) can be set so that the gain crossover angular frequency of DC bus voltage control (Figure 6) is higher than the gain crossover angular frequencies of AC system voltage control (Figure 4) and DC system voltage control (Figure 5).

[0099] In this way, by speeding up the control of the DC bus voltage Vdcbus using the charge and discharge power of the power storage device 206 through power conversion by the second bidirectional DC / DC converter 203, large fluctuations in the DC bus voltage Vdcbus associated with the supply of regulated power can be suppressed, thereby stabilizing the control operation of the power converter 100.

[0100] Furthermore, the setting of the dead zone in the calculation of the DC bus voltage deviation ΔVdcbus, as described above, and the setting of the high or low control response speed between the control units 310 and 330 can be applied in combination.

[0101] As described above, according to the power conversion device of Embodiment 1, the bidirectional AC / DC converter 201 performs AC system voltage control, the first bidirectional DC / DC converter 202 performs DC system voltage control, and the second bidirectional DC / DC converter 203 performs DC bus voltage control. This allows for power conversion between the AC system 102 and the DC system 103 while simultaneously managing the voltage quality of both systems with a single power conversion device. This enables the realization of an independent AC / DC hybrid power distribution system that is not dependent on the voltage supplied from the commercial power grid.

[0102] Furthermore, adjustment power to respond to fluctuations in supply and demand conditions within the AC system 102 and DC system 103 can be autonomously supplied to the AC system 102 and / or DC system 103 via the DC bus 205 by discharging or charging the power storage device 206. Therefore, another advantage of the power converter according to Embodiment 1 is that there is no need to provide separate power storage devices for compensation in the AC system 102 and DC system 103, and the adjustment power for voltage management can be shared between the AC system 102 and DC system 103 and supplied to the entire distribution system 10.

[0103] Embodiment 2. Embodiment 2 describes a configuration that adds an additional control function to the AC system voltage control in the bidirectional AC / DC converter 201, in addition to the configuration of Embodiment 1. In the following, only the part concerning the additional control function will be described, and the other elements will not be repeated as they are equivalent to those described in Embodiment 1.

[0104] In this specification, among power sources connected to a grid, a power source that has the effect of maintaining the grid voltage will be referred to as a "voltage source type power source," and a power source that does not have the effect of maintaining the grid voltage itself but supplies current in a phase synchronized with the grid voltage generated by another power source will be referred to as a "current source type power source." The control of the power converter 100 according to Embodiment 1 corresponds to the power converter 100 behaving as a "voltage source type power source" for both the AC grid 102 and the DC grid 103.

[0105] In Embodiment 1, an example was described in which the AC system voltage command value Vacref for AC system voltage control is set as a sine wave with the rated voltage amplitude and rated frequency of the AC system 102. This type of power converter operation is generally called the CVCF (Constant Voltage Constant Frequency) method.

[0106] Here, we consider a case where, under the control of the AC system voltage by the bidirectional AC / DC converter 201, another voltage source power supply is connected to the AC system 102. In this case, if a voltage phase difference occurs between the bidirectional AC / DC converter 201 and the other voltage source power supply, a crosscurrent corresponding to that phase difference will occur. Note that crosscurrent refers to the power flowing between one power supply and another power supply.

[0107] Once a crosscurrent occurs, the bidirectional AC / DC converter 201, when operating in CVCF mode, lacks a function to resolve the voltage phase difference that has occurred between it and other voltage source power supplies. As a result, the crosscurrent condition persists, and depending on the magnitude of the crosscurrent, there is a possibility of overcurrent occurring.

[0108] When the bidirectional AC / DC converter 201 of Embodiment 1 is operated in a CVCF manner, the effect of managing the voltage of the AC system 102 is obtained, but in cases where there are other voltage source type power supplies in the AC system 102, coordinated operation to suppress crosscurrent is difficult. For this reason, in actual operation, there is a problem that other power supplies that can be connected to the same AC system 102 are limited to "current source type power supplies". Embodiment 2 describes a control method to solve this problem.

[0109] Figure 8 is a block diagram illustrating an example of the internal configuration of a power converter according to Embodiment 2. As shown in Figure 8, the power converter 100X according to Embodiment 2 differs from the power converter 100 according to Embodiment 1 in that it includes a control device 200X instead of a control device 200.

[0110] The control device 200X obtains the measured value of the active power Pac output from the bidirectional AC / DC converter 201 to the AC system 102 from the AC system voltage Vac and AC system current Iac. The measured value of the active power Pac can be obtained by averaging the product of the measured values ​​of the AC system voltage Vac and AC system current Iac (sensor 210) at regular intervals. Alternatively, the measured value of the active power Pac may be obtained by inputting the measured value from sensor 210 to the control device 200X.

[0111] The active power Pac represents the total three-phase active power output from the bidirectional AC / DC converter 201 to the AC system 102. A Pac > 0 (positive value) indicates the power direction output from the bidirectional AC / DC converter 201 to the AC system 102, while a Pac < 0 (negative value) indicates the power direction input from the AC system 102 to the bidirectional AC / DC converter 201.

[0112] Figure 9 is a block diagram illustrating the control functions added to the power converter according to Embodiment 2.

[0113] In addition to the functions of the control units 310 to 330 shown in Figures 4 to 6, the control unit 200X further includes the function of the control unit 400 for droop control, as shown in Figure 9. The hardware configuration of the control unit 200X can be the same as that of the control unit 200.

[0114] In Embodiment 2, an active power command value Pacref is set, which indicates the active power Pac to be output from the bidirectional AC / DC converter 201 to the AC system 102. The active power command value Pacref can be set arbitrarily and may be stored in the control device 200X as a predetermined constant value, or a value set by the user of the power converter 100X may be input from outside the control device 200X.

[0115] Referring to Figure 9, the control unit 400 includes a deviation calculation unit 410, a control calculation unit 420, and a frequency command value setting unit 440.

[0116] The deviation calculation unit 410 calculates the active power deviation ΔPac by subtracting the measured value of active power Pac Pacm from the active power command value Pacref. The control calculation unit 420 calculates the frequency deviation Δf by performing a control calculation using the active power deviation ΔPac as input.

[0117] For example, the control calculation unit 420 can be configured with a feedback loop consisting of an integrator 422, a gain multiplier 424, and a subtractor 430 to provide a so-called virtual synchronous generator function (or grid forming control function). The transfer function of the integrator 422 is expressed as "1 / (M·s)" using the constant of inertia M, and the gain multiplier 424 multiplies the frequency deviation Δf, which is the output value of the integrator 422, by the damping coefficient D and inputs it to the subtractor 430. The subtractor 430 subtracts the output value of the gain multiplier 424 from the active power deviation ΔPac and uses this as the input to the integrator 422.

[0118] As is well known, by performing feedback control calculations using the inertia constant M and braking coefficient D in the rotational motion of a synchronous generator, a relationship can be established between the deviation of the active power Pac (ΔPac) and the deviation of the frequency of the AC system 102 (Δf) that simulates the rotational speed fluctuation characteristics of a synchronous generator that has conventionally played the role of a voltage source type power supply in a power system.

[0119] Furthermore, the calculation method used by the control calculation unit 420 to calculate the frequency deviation Δf from the active power deviation ΔPac is not limited to the example shown in Figure 9, but can be arbitrarily set to include simple proportional (P) control calculations or the application of first-order lag calculations.

[0120] The frequency command value setting unit 440 generates a frequency command value fref by adding the rated frequency fn of the AC system 102 and the frequency deviation Δf calculated by the control calculation unit 420.

[0121] The frequency command value fref is reflected in the frequency of the AC system voltage command value Vacref for the control unit 310 in Figure 4. Alternatively, in the control unit 310 to which the rotational coordinate transformation described in Figure 7 is applied, the frequency command value fref is reflected in the frequency f in equation (1) for calculating the rotation angle θ.

[0122] By setting such a frequency command value fref, the frequency of the AC voltage output from the bidirectional AC / DC converter 201 to the AC system 102 can be changed according to the active power deviation ΔPac. In other words, the control unit 400 can realize one embodiment of "first droop control".

[0123] As a result, in Embodiment 2, active power-frequency droop control, in which the frequency of the AC system voltage Vac changes according to the deviation between the active power Pac and the active power command value Pacref, is performed in addition to the AC system voltage control in Embodiment 1 (Figure 4). As a result, compared to Embodiment 1, in which a CVCF method is applied and the AC system voltage Vac is controlled with fref = fn fixed, Embodiment 2 can be made to eliminate the crosscurrent caused by the voltage phase difference between the bidirectional AC / DC converter 201 and other power sources connected to the AC system 102. The principle will be explained below.

[0124] As an example, consider a case where the phase of the output voltage from the bidirectional AC / DC converter 201 to the AC system 102 leads the phase of the output voltage of "another voltage source power supply" connected to the AC system 102. In this case, a lateral flow of active power occurs from the bidirectional AC / DC converter 201 to the other voltage source power supply.

[0125] Under these circumstances, the bidirectional AC / DC converter 201 outputs more active power Pac than the active power command value Pacref that it should output. Therefore, in the control system shown in Figure 9, the active power deviation ΔPac < 0 (Pacref - Pacm < 0). At this time, the frequency deviation Δf determined by droop control also becomes a negative value, and it is understood that the frequency command value fref is calculated to be lower than the rated frequency fn.

[0126] As a result, if the output voltage phase of the bidirectional AC / DC converter 201 is leading in phase with respect to other voltage source power supplies, the droop control in Figure 9 acts to decrease the frequency command value fref (decelerate the generator). This reduces the frequency of the output voltage of the bidirectional AC / DC converter 201, and as it becomes lower than the frequency of the output voltage of the other voltage source power supplies, the voltage phase difference that had occurred decreases, and the crosscurrent is eliminated.

[0127] Conversely, if the output voltage phase of the bidirectional AC / DC converter 201 lags behind the other voltage source power supply, the droop control in Figure 9 acts to increase the frequency command value fref (increase the generator speed). As a result, the frequency of the output voltage of the bidirectional AC / DC converter 201 increases, and when it becomes higher than the frequency of the output voltage of the other voltage source power supply, the voltage phase difference that had occurred decreases, and the crosscurrent is eliminated. In this way, the droop control in Figure 9 enables the bidirectional AC / DC converter 201 and the other voltage source power supply to autonomously synchronize their frequencies and phases.

[0128] Thus, according to the power converter of Embodiment 2, by adding active power-frequency droop control (Figure 9), the frequency is autonomously synchronized with "other voltage source power supplies" connected to the AC system 102, thereby obtaining the effect of suppressing crosscurrent in addition to the effect of Embodiment 1. As a result, parallel operation with other voltage source power supplies to the AC system 102 is permitted, and the degree of freedom of the power supply configuration within the AC system 102 can be increased. Furthermore, by keeping the relay 111 in the ON state in the configuration of Figure 1, it is possible to operate in conjunction with the commercial power system (external AC system 104). That is, in the configuration of Figure 1, switching between interconnection with the commercial power system (AC system 104) and independent operation is possible by turning the relay 111 on and off.

[0129] Referring again to Figure 8, in Embodiment 2, the active power-frequency droop control (Figure 9) can be combined with control that manages the charge level of the power storage device 206 connected to the second bidirectional DC / DC converter 203. Hereinafter, the charge level of the power storage device 206 will be referred to as SOC (State of Charge). SOC represents the current charge level as a percentage, with a full charge of the power storage device 206 being 100 (%).

[0130] Referring again to Figure 8, the control device 200X acquires the State of Charge (SOC) information of the power storage device 206. The SOC information can be acquired at predetermined intervals or in response to predetermined triggers. For example, in the configuration shown in Figure 3, the SOC information is input to the control device 200 using the input / output interface 97.

[0131] The State of Charge (SOC) of the power storage device 206 has a pre-set upper control value Sc1 to prevent overcharging and a lower control value Sc2 to prevent over-discharging. For example, Sc1 can be set to 80%, and Sc2 to 20%. The upper control value Sc1 and the lower control value Sc2 may be changeable by the user.

[0132] In the power converter described in the first embodiment, by the control functions shown in FIGS. 4 to 6, control is executed to autonomously supply electric power that compensates for fluctuations in power supply and demand within the AC system 102 and within the DC system 103 from the power storage device 206 via the DC bus 205. However, since this control is performed independently of the SOC of the power storage device 206, the power storage device 206 may experience a state where the discharge state continues for a long time resulting in insufficient SOC, or a state where the charge state continues for a long time resulting in excessive SOC.

[0133] Accordingly, the control device 200X according to the second embodiment can further execute SOC management control for controlling the SOC of the power storage device 206 within a range from the control lower limit value Sc2 to the control upper limit value Sc1 by using the active power command value Pac used for the droop control in FIG. 9.

[0134] FIG. 10 is a flowchart illustrating the process of SOC management control according to the second embodiment. The control process shown in FIG. 10 can be repeatedly executed every time the control device 200X acquires the SOC information of the power storage device 206.

[0135] As shown in FIG. 10, the control device 200X compares the acquired SOC of the power storage device 206 with the control upper limit value Sc1 in step (hereinafter simply referred to as "S") 110. Further, in S120, the SOC of the power storage device 206 is compared with the control lower limit value Sc2.

[0136] When Sc2 < SOC < Sc1, that is, when both S110 and S120 are determined as NO, the control device 200X sets the active power command value Pacref to the default value Pac0 in S130. The default value Pac0 corresponds to a predetermined constant value exemplified in FIG. 9 or an input value from the outside of the control device 200X.

[0137] In contrast, when SOC>Sc1 (when YES is determined in S110), the control device 200X sets the active power command value Pacref to be higher than the default value Pac0 through S140. Accordingly, compared with the default value Pac0, the active power command value Pacref changes in a direction that increases the active power Pac supplied from the bidirectional AC / DC converter 201 to the AC system 102.

[0138] When the active power command value Pacref increases, the frequency command value fref increases in accordance with the droop control shown in Fig. 9. As a result, the output voltage phase of the bidirectional AC / DC converter 201 becomes an advanced phase with respect to other voltage-type power supplies or the external AC system 104, and consequently the active power Pac output from the bidirectional AC / DC converter 201 to the AC system 102 increases. An increase in the active power Pac acts in a direction to lower the DC bus voltage Vdcbus, therefore, under the control of the second bidirectional DC / DC converter 203 by the control unit 330 in Fig. 6, active power for restoring (increasing) the DC bus voltage Vdcbus is supplied by discharge of the power storage device 206. Along with such a control operation, the SOC of the power storage device 206 decreases, whereby the SOC that has exceeded the upper control limit Sc1 can be returned to be equal to or lower than the upper control limit Sc1.

[0139] Conversely, when SOC<Sc2 (when NO is determined in S110 and YES is determined in S120), the control device 200X sets the active power command value Pacref to be lower than the default value Pac0 through S150. Accordingly, compared with the default value Pac0, the active power command value Pacref changes in a direction that decreases the active power Pac supplied from the bidirectional AC / DC converter 201 to the AC system 102.

[0140] When the active power command value Pacref decreases, the frequency command value fref decreases according to the droop control shown in Figure 9. As a result, the output voltage phase of the bidirectional AC / DC converter 201 lags behind other voltage source power supplies or the external AC system 104, and the active power Pac output from the bidirectional AC / DC converter 201 to the AC system 102 decreases. Since the decrease in active power Pac acts to increase the DC bus voltage Vdcbus, the control unit 330 in Figure 6 controls the second bidirectional DC / DC converter 203, and the active power required to restore (decrease) the DC bus voltage Vdcbus flows into the power storage device 206 and is used for charging. With this control operation, the SOC of the power storage device 206 increases, allowing the SOC, which has fallen below the control lower limit value Sc2, to return to above the control lower limit value Sc2.

[0141] The increase in the active power command value Pacref in S140 (Pacref-Pac0) and the decrease in the active power command value Pacref in S150 (Pac0-Pacref) can be set arbitrarily. For example, a predetermined constant value can be set as the increase (S140) or decrease (S150). Alternatively, the increase (S140) or decrease (S150) can be set in proportion to the excess amount relative to the control upper limit value Sc1 (SOC-Sc1) or the deficit amount relative to the control lower limit value Sc2 (Sc2-SOC).

[0142] The control process shown in Figure 10 enables the realization of one embodiment of the "first charge amount management control," which variably sets the active power command value Pacref according to the SOC of the power storage device 206 to prevent overcharging and over-discharging. Note that the setting logic for the active power command value Pacref according to the SOC of the power storage device 206 in the "first charge amount management control" is not limited to the content shown in Figure 10, and any setting logic to prevent overcharging and over-discharging can be applied.

[0143] Thus, the power converter according to Embodiment 2 can be further provided with a function to variably set the active power command value Pacref in the droop control shown in Figure 9 according to the SOC of the power storage device 206. This makes it possible to achieve SOC management control to prevent overcharging and over-discharging of the power storage device 206, in addition to the effects described above in Embodiment 2. The SOC management control in Embodiment 2 is equivalent to managing the SOC of the power storage device 206 by utilizing the supply and demand adjustment capacity of other power sources connected within the AC system 102.

[0144] Embodiment 3. Embodiment 3 describes a configuration that adds an additional control function to the DC system voltage control in the first bidirectional DC / DC converter 202, in addition to the configuration of Embodiment 1. In the following, only the part concerning the additional control function will be described, and the other elements will not be repeated as they are equivalent to those described in Embodiment 1.

[0145] In Embodiment 1, an example was described in which the DC system voltage command value Vdcref for DC system voltage control is set to a constant value equivalent to the rated voltage of the DC system 103. Here, assuming a situation in which another voltage source type power supply is connected to the DC system 103, if there is a difference between the output voltage of the first bidirectional DC / DC converter 202 and the output voltage of the other voltage source type power supply, a crosscurrent corresponding to the voltage difference will occur.

[0146] Once a crosscurrent occurs, when the first bidirectional DC / DC converter 202 is operated by the control described in Embodiment 1, there is no function to eliminate the voltage difference that has occurred between it and other voltage source type power supplies. As a result, the state in which the crosscurrent occurs will continue, and depending on the magnitude of the crosscurrent, there is a possibility that an overcurrent may occur.

[0147] Thus, when the bidirectional AC / DC converter 201 is operated to maintain the DC system voltage Vdc at a constant voltage, as in Embodiment 1, the effect of managing the voltage of the DC system 103 is obtained. However, in cases where there are other voltage source type power supplies within the DC system 103, coordinated operation to suppress crosscurrent becomes difficult. For this reason, in actual operation, there is a problem that other power supplies that can be connected to the same DC system 103 are limited to "current source type power supplies". Embodiment 3 describes a control method to solve this problem.

[0148] Figure 11 is a block diagram illustrating an example of the internal configuration of a power conversion device according to Embodiment 3.

[0149] As shown in Figure 11, the power converter 100Y according to Embodiment 3 differs from the power converter 100 according to Embodiment 1 in that it includes a control device 200Y instead of a control device 200.

[0150] The control device 200Y acquires the measured value of DC power Pdc, which is output to the DC system 103 from the first bidirectional DC / DC converter 202, from the DC system voltage Vdc and DC system current Idc. The measured value of DC power Pdc can be obtained by averaging the product of the measured values ​​of DC system voltage Vdc and DC system current Idc (sensor 230) at regular intervals. Alternatively, the measured value of DC power Pdc may be acquired by inputting the measured value from sensor 230 to the control device 200X.

[0151] The DC power Pdc represents the power output from the first bidirectional DC / DC converter 202 to the DC system 103. A Pdc > 0 (positive value) indicates the power output direction from the first bidirectional DC / DC converter 202 to the DC system 103, while a Pdc < 0 (negative value) indicates the power input direction from the DC system 103 to the first bidirectional DC / DC converter 202.

[0152] Figure 12 is a block diagram illustrating the control functions added to the power converter according to Embodiment 3.

[0153] In addition to the functions of the control units 310 to 330 shown in Figures 4 to 6, the control unit 200Y also has the function of the control unit 500 for droop control, as shown in Figure 12. The hardware configuration of the control unit 200Y can be the same as that of the control unit 200.

[0154] In Embodiment 3, a DC power command value Pdcref is set, which indicates the DC power Pdc to be output from the first bidirectional DC / DC converter 202 to the DC system 103. The DC power command value Pdcref can be set arbitrarily and may be stored in the control device 200Y as a predetermined constant value, or a value set by the user of the power converter 100Y may be input from outside the control device 200Y.

[0155] Referring to Figure 12, the control unit 500 includes a deviation calculation unit 510, a control calculation unit 520, and a voltage command value setting unit 530.

[0156] The deviation calculation unit 510 calculates the DC power deviation ΔPdc by subtracting the measured value Pdcm of DC power Pdc from the DC power command value Pdcref. The control calculation unit 520 calculates the DC voltage deviation ΔV by performing a control calculation using the DC power deviation ΔPdc as input.

[0157] In the example shown in Figure 12, the control calculation unit 520 is composed of a first-order lag element (K4 / (1+s·T4)). However, the calculation method for calculating the DC voltage deviation ΔV from the DC power deviation ΔPdc is not limited to the example shown in Figure 12, and can be arbitrarily set, such as by applying a simple proportional (P) control calculation.

[0158] The voltage command value setting unit 530 generates a DC system voltage command value Vdcref by adding the rated voltage Vn of the DC system 102 and the voltage deviation ΔV calculated by the control calculation unit 520. As a result, in Embodiment 3, power-voltage droop control, in which the DC system voltage Vdc changes according to the deviation between the DC power Pdc and the DC power command value Pdcref, is performed in addition to the DC system voltage control in Embodiment 1 (Figure 6).

[0159] As a result, in Embodiment 1, where Vdcref is fixed to Vn and the DC system voltage Vdc is controlled to a constant voltage, Embodiment 3 has the effect of eliminating crosscurrent caused by the voltage difference between the first bidirectional DC / DC converter 202 and other power sources connected to the DC system 103. The principle will be explained below.

[0160] As an example, consider a case where the output voltage from the first bidirectional DC / DC converter 202 to the DC system 103 is higher than the output voltage of the "other voltage source type power supply" connected to the DC system 103. In this case, a crosscurrent occurs from the first bidirectional DC / DC converter 202 to the other voltage source type power supply.

[0161] Under these circumstances, the first bidirectional DC / DC converter 202 outputs a DC power Pdc greater than the DC power command value Pdcref that it should output. Therefore, in the control system shown in Figure 12, the DC power deviation ΔPdc < 0 (Pdcref - Pdcm < 0). At this time, the voltage deviation ΔV determined by droop control also becomes negative, and it is understood that the DC system voltage command value Vdcref is calculated to be lower than the rated voltage Vn.

[0162] As a result, if the output voltage of the first bidirectional DC / DC converter 202 is higher than the output voltage of the other voltage source power supply, the droop control in Figure 12 acts to decrease the DC system voltage command value Vdcref. As a result, when the output voltage of the first bidirectional DC / DC converter 202 decreases, the voltage difference with the output voltage of the other voltage source power supply decreases, and the droop current is eliminated.

[0163] Conversely, if the output voltage of the first bidirectional DC / DC converter 202 is lower than the output voltage of the other voltage source power supply, the droop control in Figure 12 acts to increase the DC system voltage command value Vdcref. As a result, when the output voltage of the first bidirectional DC / DC converter 202 increases, the voltage difference that had occurred decreases, and the crosscurrent is eliminated. In this way, the droop control in Figure 12 enables the first bidirectional DC / DC converter 202 and the other voltage source power supply to autonomously match their output voltages.

[0164] By setting such a DC system voltage command value Vdcref, the DC voltage value output from the first bidirectional DC / DC converter 202 to the DC system 103 can be changed according to the DC power deviation ΔPdc. In other words, the control unit 500 can realize one embodiment of "second droop control".

[0165] Thus, according to the power conversion device of Embodiment 3, by adding power-voltage droop control (Figure 12), the output voltage is autonomously matched with "other voltage source power supplies" connected to the DC system 103, thereby obtaining the effect of suppressing lateral current in addition to the effect of Embodiment 1. This improves the tolerance for parallel operation with other voltage source power supplies to the DC system 103, and thus increases the degree of freedom in the power supply configuration within the DC system 103.

[0166] Referring again to Figure 11, in Embodiment 3, the power-voltage droop control (Figure 12) can be combined with the SOC management control of the power storage device 206 described in Embodiment 2. Specifically, the control device 200Y according to Embodiment 3 can further perform SOC management control to control the SOC of the power storage device 206 within a range from the lower control limit Sc2 to the upper control limit Sc1, using the DC power command value Pdcref used in the droop control in Figure 12.

[0167] The SOC of the power storage device 206, as well as its control upper limit value Sc1 and control lower limit value Sc2, are the same as those described in Embodiment 2, and thus detailed description will not be repeated. Similar to the control device 200X, the control device 200Y can acquire the SOC information of the power storage device 206 at a predetermined fixed cycle or in response to a predetermined trigger.

[0168] FIG. 13 is a flowchart illustrating the SOC management control process according to Embodiment 3. The control process shown in FIG. 13 can be repeatedly executed every time the control device 200Y acquires the SOC information of the power storage device 206.

[0169] As shown in FIG. 13, the control device 200Y compares the acquired SOC of the power storage device 206 with the control upper limit value Sc1 through S210 similar to S110 (FIG. 10). Further, through S220 similar to S120 (FIG. 10), the SOC of the power storage device 206 is compared with the control lower limit value Sc2.

[0170] When Sc2 < SOC < Sc1, that is, when both S210 and S220 make a NO determination, the control device 200Y sets the DC power command value Pdcref to the default value Pdc0 through S230. The default value Pdc0 corresponds to a predetermined fixed value exemplified in FIG. 12 or an input value from outside the control device 200Y.

[0171] In contrast, when SOC > Sc1 (when a YES determination is made in S210), the control device 200Y sets the DC power command value Pdcref to be higher than the default value Pdc0 through S240. As a result, compared with the default value Pdc0, the DC power command value Pdcref changes in a direction that increases the DC power Pdc supplied from the first bidirectional DC / DC converter 202 to the DC system 103.

[0172] When the DC power command value Pdcref increases, the DC system voltage command value Vdcref increases in accordance with the droop control shown in FIG. 12. As a result, the output voltage of the first bidirectional DC / DC converter 202 becomes higher than the output voltages of other voltage-source power supplies in the DC system 103, and consequently the DC power Pdc output from the first bidirectional DC / DC converter 202 to the DC system 103 increases. An increase in DC power Pdc acts in a direction that lowers the DC bus voltage Vdcbus, therefore, under the control of the second bidirectional DC / DC converter 203 by the control unit 330 in FIG. 6, power for restoring (increasing) the DC bus voltage Vdcbus is supplied by discharging of the power storage device 206. Along with such a control operation, the SOC of the power storage device 206 decreases, whereby the SOC that has exceeded the upper control limit value Sc1 can be returned to be equal to or lower than the upper control limit value Sc1.

[0173] Conversely, when SOC < Sc2 (when a negative determination is made in S210 and a positive determination is made in S220), the control device 200Y sets the DC power command value Pdcref to be lower than the default value Pdc0 in step S250. As a result, compared with the default value Pdc0, the DC power command value Pdcref changes in a direction that reduces the DC power Pdc supplied from the first bidirectional DC / DC converter 202 to the DC system 103.

[0174] When the DC power command value Pdcref decreases, the DC system voltage command value Vdcref decreases in accordance with the droop control shown in FIG. 12. As a result, the output voltage of the first bidirectional DC / DC converter 202 becomes lower than the output voltages of other voltage-source power supplies in the DC system 103, and consequently the DC power Pdc output from the bidirectional AC / DC converter 201 to the DC system 103 decreases. A decrease in DC power Pdc acts in a direction that increases the DC bus voltage Vdcbus, therefore, under the control of the second bidirectional DC / DC converter 203 by the control unit 330 in FIG. 6, power for restoring (decreasing) the DC bus voltage Vdcbus flows into the power storage device 206 and is used for charging. Along with such a control operation, the SOC of the power storage device 206 increases, whereby the SOC that has fallen below the lower control limit value Sc2 can be returned to be equal to or higher than the lower control limit value Sc2.

[0175] The increase in the DC power command value Pdcref in S240 (Pdcref-Pdc0) and the decrease in the DC power command value Pdcref in S250 (Pdc0-Pdcref) can be set arbitrarily. For example, a predetermined constant value can be set as the increase (S240) or decrease (S250). Alternatively, the increase (S240) or decrease (S250) can be set in proportion to the excess amount relative to the control upper limit Sc1 (SOC-Sc1) or the deficit amount relative to the control lower limit Sc2 (Sc2-SOC).

[0176] The control process shown in Figure 13 enables the implementation of one embodiment of the "second charge amount management control," which variably sets the DC power command value Pdcref according to the SOC of the power storage device 206 to prevent overcharging and over-discharging. Note that the setting logic for the DC power command value Pdcref according to the SOC of the power storage device 206 in the "second charge amount management control" is not limited to the content shown in Figure 13, and any setting logic to prevent overcharging and over-discharging can be applied.

[0177] Thus, the power converter according to Embodiment 3 can be further provided with a function to variably set the DC power command value Pdcref in the droop control shown in Figure 12 according to the State of Charge (SOC) of the power storage device 206. This makes it possible to achieve SOC management control to prevent overcharging and over-discharging of the power storage device 206, in addition to the effects described above in Embodiment 3. The SOC management control in Embodiment 3 is equivalent to managing the SOC of the power storage device 206 by utilizing the supply and demand adjustment capacity of other power sources connected within the DC system 103.

[0178] Embodiment 4. The active power-frequency droop control for the AC system 102 according to Embodiment 2 and the power-voltage droop control for the DC system 103 according to Embodiment 3 can be performed without interfering with each other, provided that the control accuracy of the DC bus voltage Vdcbus by the second bidirectional DC / DC converter 203 is maintained. Therefore, it is possible to perform both the droop control according to Embodiment 2 and the droop control according to Embodiment 3 simultaneously.

[0179] Figure 14 is a block diagram illustrating an example of the internal configuration of a power conversion device according to Embodiment 4.

[0180] As shown in Figure 14, the power converter 100Z according to Embodiment 4 differs from the power converter 100 according to Embodiment 1 in that it includes a control device 200Z instead of a control device 200.

[0181] The control device 200Z, like the control device 200X, is capable of acquiring measured values ​​of active power Pac, and like the control device 200Y, it is capable of acquiring measured values ​​of DC power Pdc.

[0182] Furthermore, in addition to the functions of the control units 310 to 330 shown in Figures 4 to 6, the control device 200Z also has the functions of the control unit 400 shown in Figure 9 according to Embodiment 2 and the functions of the control unit 500 shown in Figure 12 according to Embodiment 3. The hardware configuration of the control device 200Z can also be the same as that of the control device 200. The details of the control units 400 and 500 are the same as those described in Embodiments 2 and 3, so a detailed explanation will not be repeated.

[0183] Therefore, according to the power conversion device of Embodiment 4, by adding both the active power-frequency droop control of Embodiment 2 (Figure 9) and the power-voltage droop control of Embodiment 3 (Figure 12), it is possible to suppress crosscurrents between "other voltage source power supplies" in both the AC system 102 and the DC system 103. This further improves the degree of freedom in the power supply configuration in both the AC system 102 and the DC system 103.

[0184] Furthermore, the control device 200Z, like the control devices 200X and 200Y, can acquire SOC information of the power storage device 206 at predetermined intervals or in response to predetermined triggers.

[0185] Furthermore, the control device 200Z can variably set the active power command value Pacref, used for droop control by the control unit 400 (Figure 9), according to the SOC of the power storage device 206 by applying the SOC management control shown in Figure 10. In addition, the control device 200Z can variably set the DC power command value Pdcref, used for droop control by the control unit 500 (Figure 12), according to the SOC of the power storage device 206 by applying the SOC management control shown in Figure 13.

[0186] As a result, according to the power conversion device of Embodiment 4, when the State of Charge (SOC) of the power storage device 206 falls outside the control range from the lower control limit Sc2 to the upper control limit Sc1, the SOC can be quickly restored to the control range by utilizing the supply and demand adjustment capacity of other power sources connected to both the AC system 102 and the DC system 103.

[0187] Thus, the power conversion device according to Embodiment 4 can enjoy both the effects of Embodiment 2 and the effects of Embodiment 3.

[0188] As described above in Embodiments 1 to 4, the power conversion devices 100, 100X to 100Z enable power conversion between the AC system 102 and the DC system 103 in an AC-DC hybrid power distribution system, while simultaneously managing the voltage quality of both the AC system 102 and the DC system 103. Furthermore, the introduction of droop control according to Embodiments 2 to 4 improves the flexibility of configuration of other power supply equipment within the AC system 102 and the DC system 103. It also has an effect on SOC management of the power storage device 206.

[0189] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims and not by the foregoing description, and all modifications within the meaning and scope of equivalents of the claims are intended. [Explanation of Symbols]

[0190] 10 Power distribution system, 100, 100X, 100Y, 100Z Power converter, 102 AC system, 103 DC system, 104 AC system (external), 105a, 105b, 107a, 107b Distributed power supply, 106a, 106c, 108a, 108c Load, 111 Relay, 200, 200X, 200Y, 200Z Control device, 201 Bidirectional AC / DC converter, 202 First bidirectional DC / DC converter, 203 Second bidirectional DC / DC converter, 205 DC bus, 206 Power storage device, 207 Capacitor, 210~240 Sensor, 310, 320, 330, 400, 500 Control unit, 311, 313, 321, 323, 331, 333, 410, 510 Deviation calculation unit, 312, 314, 322, 324, 332, 334, 420, 520 Control calculation unit, 315, 325, 335 Duty cycle conversion unit, 316, 326, 336 PWM control unit, 340, 350 Coordinate transformation unit, 422 Integrator, 424 Gain multiplication unit, 430 Subtraction unit, 440 Frequency command value setting unit, 530 Voltage command value setting unit, Edq Electric quantity (two phase), Euvw Electric quantity (three phase), Iac AC system current, Iacm AC system current (measured value), Iaccom AC current command value, Idccom DC current command value, Idc DC system current, Idcm DC system current (measured value), Idcbus Bus current, Idcbuscom Bus current command value, Idcbusm Bus current (measured value), Pac0, Pdc0 Default value, Pacref Active power command value, Pdc DC power, Pdcref DC power command value, Sc1 Control upper limit (SOC), Sc2 Control lower limit (SOC), Vaccom AC voltage command value, Vacref AC system voltage command value, Vdc DC system voltage, Vdcbus Bus voltage, Vdcbuscom Output voltage command value, Vdcbusm Bus voltage (measured value), Vdcbusref Bus voltage command value, Vdccom DC voltage command value, Vdcm DC system voltage (measured value), Vdcref DC system voltage command value, Vn Rated voltage, f Frequency, fn Rated frequency, fref Frequency command value.

Claims

1. A power converter connected between a three-phase or single-phase AC system requiring voltage quality control and a DC system requiring voltage quality control, A bidirectional AC / DC converter that performs power conversion between the AC system and the DC bus, A first bidirectional DC / DC converter that performs power conversion between the DC system and the DC bus, A second bidirectional DC / DC converter that performs power conversion between the power storage device and the DC bus, The system comprises the aforementioned bidirectional AC / DC converter, the first bidirectional DC / DC converter, and a control device for controlling the second bidirectional DC / DC converter. The control device is configured to perform a first control that controls the power conversion by the bidirectional AC / DC converter to control the voltage of the AC system according to an AC system voltage command value in order to manage the voltage quality of the AC system; a second control that controls the power conversion by the first bidirectional DC / DC converter to control the voltage of the DC system according to a DC system voltage command value in order to manage the voltage quality of the DC system; and a third control that controls the power conversion by the second bidirectional DC / DC converter to control the voltage of the DC bus according to a DC bus voltage command value.

2. The control device is configured to acquire measured values ​​of the active power input and output between the bidirectional AC / DC converter and the AC system. The power converter according to claim 1, wherein the control device is configured to further perform a first droop control that changes the frequency of the AC voltage output from the bidirectional AC / DC converter to the AC system according to the deviation between the command value and the measured value of the active power.

3. The control device is configured to acquire the charge amount of the power storage device, The power conversion device according to claim 2, wherein the control device is configured to further perform a first charge amount management control that sets the command value of the active power to a variable value according to the charge amount.

4. The power converter according to claim 3, wherein the control device performs the first charge amount management control such that, compared to when the charge amount is within a management range from a control lower limit to a control upper limit, when the charge amount becomes higher than the control upper limit, the command value is changed in a direction that increases the active power supplied to the AC system, and when the charge amount becomes lower than the control lower limit, the command value is changed in a direction that decreases the active power supplied to the AC system.

5. The control device is configured to acquire measured values ​​of DC power input and output between the first bidirectional DC / DC converter and the DC system. The power converter according to claim 1, wherein the control device is configured to further perform a second droop control that changes the DC voltage value output from the first bidirectional DC / DC converter to the DC system according to the deviation between the command value and the measured value of the DC power.

6. The control device is configured to acquire the charge amount of the power storage device, The power conversion device according to claim 5, wherein the control device is configured to further perform a second charge amount management control that sets the command value of the DC power to a variable value according to the charge amount.

7. The power converter according to claim 6, wherein the control device performs the second charge amount management control such that, compared to when the charge amount is within a management range from the control lower limit to the control upper limit, when the charge amount becomes higher than the control upper limit, the command value is changed in a direction that increases the DC power supplied to the DC system, and when the charge amount becomes lower than the control lower limit, the command value is changed in a direction that decreases the DC power supplied to the DC system.

8. The control device is configured to acquire measured values ​​of active power input and output between the bidirectional AC / DC converter and the AC system, and measured values ​​of DC power input and output between the first bidirectional DC / DC converter and the DC system. The power conversion device according to claim 1, wherein the control device is configured to further perform a first droop control that changes the frequency of the AC voltage output to the AC system from the bidirectional AC / DC converter according to the deviation between the command value and the measured value of the active power, and a second droop control that changes the DC voltage value output to the DC system from the first bidirectional DC / DC converter according to the deviation between the command value and the measured value of the DC power.

9. The control device is configured to acquire the charge amount of the power storage device, The power conversion device according to claim 8, wherein the control device is configured to further perform a first charge amount management control that sets the command value of the active power in a variable manner according to the charge amount, and a second charge amount management control that sets the command value of the DC power in a variable manner according to the charge amount.

10. The power converter according to claim 9, wherein the control device performs the first and second charge amount management control such that, compared to when the charge amount is within a management range from a control lower limit to a control upper limit, when the charge amount becomes higher than the control upper limit, the command value is changed in a direction that increases the active power supplied to the AC system and the DC power supplied to the DC system, and when the charge amount becomes lower than the control lower limit, the command value is changed in a direction that decreases the active power supplied to the AC system and the DC power supplied to the DC system, respectively.

11. The third control is performed according to a control calculation to bring the voltage deviation of the measured voltage of the DC bus closer to zero with respect to the DC bus voltage command value. The power conversion device according to any one of claims 1 to 10, wherein the voltage deviation is set to zero even if there is a difference between the measured voltage and the DC bus voltage command value, when the measured voltage is within a dead zone that includes the DC bus voltage command value.

12. The power converter according to any one of claims 1 to 10, wherein the control response speed of the DC bus voltage according to the DC bus voltage command value by the third control is set to be higher than both the control response speed of the AC system voltage according to the AC system voltage command value by the first control and the control response speed of the DC system voltage according to the DC system voltage command value by the second control.

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