Power conversion device and power supply system

Abstract

This power conversion device is connected to a DC bus to which a first DC power supply is connected and an AC grid to which a second DC power supply is connected via a power conditioner, converts the DC power of the DC bus and the AC power of the AC grid to each other, and controls the operation of the power conditioner on the basis of the voltage of the DC bus.

Description

Power conversion device, power supply system

[0001] The present invention relates to a power conversion device and a power supply system using the same.

[0002] Conventionally, a power conversion device is connected between a DC power source such as a solar panel or a storage battery and a commercial power system, and converts the DC power output from the DC power source into AC power that matches the frequency and phase of the power system and inputs it to the power system, thereby connecting the DC power source and the power system. For example, in Patent Document 1, there is described a power conversion device that converts DC power generated by a fuel cell into AC power, which includes a boost converter circuit that boosts the output voltage of the fuel cell, an inverter circuit that converts the output voltage of the boost converter circuit into AC power and connects it to the power system, a buck converter circuit that converts the output power of the boost converter circuit and supplies it to an internal load, and a controller. Thereby, the fuel cell, the power system, and the internal load are interconnected, enabling power input and output between them.

[0003] International Publication No. 2011 / 099280

[0004] DC power sources such as solar panels and storage batteries can have their output fluctuate depending on the solar radiation state and the charge state. Also, there may be cases where another power conversion device is further connected between the DC power source and the power conversion device to connect a DC power source such as a solar panel or a storage battery, or a load. In such cases, the DC power input to the power conversion device connected to the power system may exceed the rating of the power conversion device, which may hinder the operation of the power conversion device. The power conversion device described in Patent Document 1 cannot adequately handle such cases.

[0005] In view of the above problems, an object of the present invention is to provide a technology capable of suppressing an increase in DC power input to a power conversion device for grid connection and an accompanying rise in DC voltage.

[0006] The power conversion device according to the present invention is connected to a DC bus to which a first DC power supply is connected and to an AC grid to which a second DC power supply is connected via a power conditioner, and converts between the DC power of the DC bus and the AC power of the AC grid, and controls the operation of the power conditioner based on the voltage of the DC bus. The power supply system according to the present invention comprises a first DC power supply that supplies DC power, a DC bus to which the first DC power supply is connected, a second DC power supply that supplies DC power, a power conditioner that converts the DC power supplied from the second DC power supply into AC power, an AC grid to which the second DC power supply is connected via the power conditioner, and a power conversion device that converts between the DC power of the DC bus and the AC power of the AC grid, wherein the power conversion device controls the operation of the power conditioner based on the voltage of the DC bus.

[0007] According to the present invention, it is possible to suppress the increase in DC power input to a power converter for grid connection and the resulting rise in DC voltage.

[0008] A diagram showing an example configuration of a power supply system according to the first embodiment of the present invention. A control block diagram showing details of the power converter in the power supply system. An explanatory diagram of the operation of the AC voltage command correction unit. A diagram showing an example configuration of a power supply system according to the second embodiment of the present invention.

[0009] (First Embodiment) Figure 1 is a diagram showing an example configuration of a power supply system according to the first embodiment of the present invention. The power supply system 1 of this embodiment is connected to a commercial power grid 2 and transmits power obtained by power generation to the power grid 2, and when there is a shortage of power generated, it receives power supplied from the power grid 2 and supplies it to the load. The power supply system 1 comprises a grid connection power converter 10, a DC bus 20, a DC power supply 21, a storage battery 22, converters 23 and 24, a DC load 25, a power converter 30, an AC grid 40, a DC power supply 41, a power conditioner (PCS) 42, and an AC load 43.

[0010] The grid-connected power converter 10 is connected between the power system 2 and the DC bus 20. It converts the DC power of the DC bus 20 into AC power and outputs it to the power system 2, and also converts the AC power supplied from the power system 2 into DC power and outputs it to the DC bus 20. The power input and output direction of the grid-connected power converter 10 changes according to the power supply and demand state of the entire DC system, which is composed of each device connected to the DC bus 20. That is, if there is a power surplus in the entire DC system, the grid-connected power converter 10 converts the DC power of the DC bus 20 into AC power and outputs it to the power system 2. On the other hand, if there is a power shortage in the entire DC system, the grid-connected power converter 10 converts the AC power of the power system 2 into DC power and outputs it to the DC bus 20. This power input and output is achieved by the grid-connected power converter 10 controlling the voltage of the DC bus 20. Examples of this voltage control methods include PI control and droop control. For example, a GFL (Grid Following) type inverter is used in the grid-connected power converter 10.

[0011] The DC power supply 21 is connected to the DC bus 20 via a converter 23 and outputs a predetermined DC power to the converter 23. The converter 23 performs a voltage conversion on the DC power input from the DC power supply 21 and outputs it to the DC bus 20. For example, solar power generation can be used as the DC power supply 21.

[0012] The battery 22 is a rechargeable secondary battery connected to the DC bus 20 via a converter 24. When charging the battery 22, DC power supplied from the DC power supply 21 or the grid-connected power converter 10 is input to the battery 22 via the DC bus 20 and the converter 24. On the other hand, when discharging the battery 22, the DC power output from the battery 22 is output to the DC bus 20 via the converter 24. The converter 24 is a device capable of bidirectional DC voltage conversion between the DC bus 20 and the battery 22, and can be used by switching between boost and buck operations. The charging and discharging of the battery 22 is switched according to, for example, the charge state (SOC) of the battery 22 or the power supply and demand state of the entire DC system.

[0013] The DC load 25 is a device that consumes DC power supplied via the DC bus 20 and acts as a load on the DC system. For example, motors and various pumps driven by a DC power supply are connected to the DC bus 20 as DC loads 25. The amount of power consumed by the DC load 25 may vary depending on its operating state.

[0014] The power converter 30 is connected between the DC bus 20 and the AC grid 40. It converts the DC power of the DC bus 20 into AC power and outputs it to the AC grid 40, and also converts the AC power of the AC grid 40 into DC power and outputs it to the DC bus 20. In other words, the power converter 30 converts between the DC power of the DC bus 20 and the AC power of the AC grid 40. The power input and output direction in the power converter 30 changes according to the power supply and demand state of the entire AC system, which is composed of each device connected to the AC grid 40. That is, if there is a power surplus in the entire AC system, the power converter 30 converts the AC power of the AC grid 40 into DC power and outputs it to the DC bus 20. On the other hand, if there is a power shortage in the entire AC system, the power converter 30 converts the DC power of the DC bus 20 into AC power and outputs it to the AC grid 40.

[0015] The power converter 30 can arbitrarily control the voltage, frequency, and phase of the AC power in the AC grid 40. To achieve this, the power converter 30 uses, for example, a GFM (Grid Forming) inverter. Details of the power converter 30 will be described later.

[0016] The DC power supply 41 is connected to the AC grid 40 via the PCS 42 and outputs a predetermined amount of DC power to the PCS 42. The PCS 42 converts the DC power input from the DC power supply 41 into AC power and outputs it to the AC grid 40. For example, solar power generation can be used as the DC power supply 41. Alternatively, a rechargeable secondary battery may be used as the DC power supply 41. In this case, the PCS 42 can also charge the DC power supply 41, which is a secondary battery, by converting the AC power from the AC grid 40 into DC power and outputting it to the DC power supply 41. Furthermore, a combination of solar power generation and a secondary battery may be used to configure the DC power supply 41. For example, a GFL type inverter can be used as the PCS 42.

[0017] Furthermore, the PCS 42 has a well-known voltage rise suppression function. This voltage rise suppression function suppresses the voltage rise of the AC grid 40 by limiting the power supply from the DC power source 41 by suppressing the output of the PCS 42 itself when the voltage of the AC grid 40 is above a predetermined value. Generally, power conditioners for connecting solar power generation equipment to the power grid have such a voltage rise suppression function to prevent the connection point voltage from rising and exceeding a predetermined upper limit.

[0018] The AC load 43 is a device that consumes AC power supplied via the AC grid 40 and acts as a load on the AC system. For example, AC motors and various industrial or household electrical appliances are connected to the AC grid 40 as AC loads 43. Similar to the DC load 25, the amount of power consumed by the AC load 43 may vary depending on its operating state.

[0019] The configuration of the power supply system 1 described above is just one example, and other configurations are also possible. For example, multiple DC power supplies 21, batteries 22, and DC loads 25 can be connected to the DC bus 20, or multiple DC power supplies 41 and AC loads 43 can be connected to the AC grid 40. It is also possible to connect multiple converters 23 and 24 in parallel between the DC bus 20 and the DC power supplies 21 and batteries 22, or to connect multiple power conditioners 42 in parallel between the AC grid 40 and the DC power supply 41. Furthermore, it is possible to connect an AC power source such as a generator to the AC grid 40. In addition to these, the power supply system 1 can be realized with any configuration as long as a power converter 30 is connected between the DC bus 20 and the AC grid 40.

[0020] Figure 2 is a control block diagram showing the details of the power converter 30 in the power supply system 1. As shown in Figure 2, the power converter 30 includes an inverter control device 31, an inverter 32, a filter 33, a DC voltage sensor 34, a current sensor 35, and an AC voltage sensor 36.

[0021] The inverter 32 is configured, for example, using a three-phase full-bridge circuit, and operates in accordance with the control of the inverter control device 31 to convert the DC power input from the DC bus 20 into AC power and output it to the AC grid 40 via the filter 33. It also converts the AC power input from the AC grid 40 via the filter 33 into DC power and outputs it to the DC bus 20.

[0022] The filter 33 removes unwanted high-frequency components from the AC power output from the inverter 32 or input from the AC grid 40.

[0023] The DC voltage sensor 34 measures the voltage value of the DC power input and output between the DC bus 20 and the inverter 32 (the DC voltage value of the DC bus 20). The current sensor 35 measures the current value of the AC power input and output between the AC grid 40 and the inverter 32. The AC voltage sensor 36 measures the voltage value of the AC power input and output between the AC grid 40 and the inverter 32 (the AC voltage value of the AC grid 40). The measurement results from the DC voltage sensor 34, the current sensor 35, and the AC voltage sensor 36 are input to the inverter control device 31 as measured values ​​of voltage and current for the DC power and AC power input and output to the power converter 30 (DC voltage measurement value Vdc, AC current measurement value Iout, and AC voltage measurement value Vout), respectively.

[0024] The inverter control device 31 has the following functional blocks: a power calculation unit 311, an AC voltage command correction unit 312, a reactive power command unit 313, a first voltage command generation unit 314, an angular frequency command generation unit 315, a phase command generation unit 316, a current command generation unit 317, a current command constraint unit 318, a current control unit 319, and a main circuit control unit 320. The inverter control device 31 is configured, for example, by a microcomputer, and these functional blocks can be realized by executing a predetermined program on the microcomputer. Alternatively, some or all of these functional blocks may be realized using hardware circuits such as logic ICs or FPGAs.

[0025] The power calculation unit 311 calculates the active power P and reactive power Q, which represent the active and reactive components of the AC power actually input and output to the power converter 30, from the AC current measurement value Iout and AC voltage measurement value Vout obtained from the current sensor 35 and the AC voltage sensor 36, respectively.

[0026] The AC voltage command correction unit 312 corrects the AC voltage command value V0 (for example, V0 = 200V) input from an external source based on the DC voltage measurement value Vdc obtained from the DC voltage sensor 34. The correction result of the AC voltage command value V0 is then output as the corrected AC voltage command value Vref. Details of the method by which the AC voltage command correction unit 312 corrects the AC voltage command value V0 will be described later.

[0027] The reactive power command unit 313 generates a command value for the reactive component of the AC power input and output to the power converter 30 based on the AC voltage measurement value Vout obtained from the AC voltage sensor 36, and outputs this command value as a reactive power command Q*. Specifically, the reactive power command unit 313 generates the reactive power command Q* by multiplying the difference (Vref - Vout) between the corrected AC voltage command value Vref input from the AC voltage command correction unit 312 and the AC voltage measurement value Vout by a predetermined proportional gain KQ.

[0028] The first voltage command generation unit 314 generates a first voltage command E*, which is a voltage command value for the AC power input and output to the power converter 30, using the reactive power Q obtained by the power calculation unit 311 and the reactive power command Q* output from the reactive power command unit 313. Specifically, the first voltage command generation unit 314 generates a first voltage command E* based on the corrected AC voltage command value Vref by PI control of the deviation (Q* - Q) between the reactive power command Q* and the reactive power Q.

[0029] The angular frequency command generation unit 315 generates a command value for the angular frequency of the AC power input to and output from the power converter 30 based on the active power P obtained by the power calculation unit 311 and the active power command P0 input from an external source, and outputs this command value as the angular frequency command ω*. Specifically, the angular frequency command generation unit 315 calculates a value obtained by multiplying the difference between the active power command P0 and the active power P (P0-P) by the reciprocal of a predetermined proportional gain, 1 / KP, and calculates an angular frequency deviation Δω with pseudo-inertia by performing first-order lag and first-order lead compensation on this value. Then, by adding the angular frequency deviation Δω to the rated angular frequency ω0 (for example, 2π × 50 Hz), the angular frequency command ω* is generated.

[0030] The phase command generation unit 316 generates a phase command θ*, which is a command value for the phase of the AC power input and output to the power converter 30, based on the angular frequency command ω* output from the angular frequency command generation unit 315. Specifically, the phase command generation unit 316 generates the phase command θ* by integrating the angular frequency command ω*. This makes it possible to obtain the phase command θ* based on the angular frequency command ω*. Note that the phase command θ* may also be the remainder when the value obtained by integrating the angular frequency command ω* is divided by 2π.

[0031] The current command generation unit 317 generates a current command I* for the AC power input and output to the power converter 30 based on a first voltage command E* based on a corrected AC voltage command value Vref generated by the first voltage command generation unit 314, a phase command θ* based on an angular frequency command ω* obtained by the phase command generation unit 316, and an AC voltage measurement value Vout from the AC voltage sensor 36. Specifically, it calculates the deviation between the value obtained by dq-converting the AC voltage measurement value Vout based on the phase command θ* and the first voltage command E*, and calculates the current command I* based on this deviation and the impedance of the filter 33. As a result, the current command generation unit 317 can generate a current command I* for the AC power of the AC grid 40 based on an angular frequency command ω* generated by the angular frequency command generation unit 315 and a corrected AC voltage command value Vref generated by the first voltage command generation unit 314.

[0032] The current command constraint unit 318 restricts the current command I* generated by the current command generation unit 317 so that the current command I* remains below a predetermined limit value if the current command I* exceeds a predetermined limit value. If it is not necessary to keep the current command I* below a limit value, the current command constraint unit 318 may be omitted.

[0033] The current control unit 319 generates a voltage command V* for the AC power input and output to the power converter 30, based on the current command I* generated by the current command generation unit 317 and further constrained as necessary by the current command constraint unit 318, and the AC current measurement value Iout from the current sensor 35. Specifically, the current control unit 319 calculates the difference between the value obtained by dq-converting the AC current measurement value Iout based on the phase command θ* and the current command I*, and calculates the voltage command V* based on this difference.

[0034] The main circuit control unit 320 controls the operation of the inverter 32 based on the voltage command V* generated by the current control unit 319 and the phase command θ* determined by the phase command generation unit 316. At this time, the main circuit control unit 320 generates gate signals for each switching element of the inverter 32 by performing PWM control based on the voltage command V* and the phase command θ*, and outputs these gate signals to the inverter 32. As a result, the inverter 32 is driven so that the voltage and phase of the AC power output from the inverter 32 to the AC grid 40, or input from the AC grid 40 to the inverter 32, change according to the voltage command V* and the phase command θ*, thereby enabling mutual power conversion between DC power and AC power.

[0035] As a result, the power converter 30 can operate between the DC bus 20 and the AC grid 40 while virtually possessing inertia.

[0036] Next, the details of the method for correcting the AC voltage command value V0 by the AC voltage command correction unit 312 will be described below with reference to Figure 3. Figure 3 is an explanatory diagram of the operation of the AC voltage command correction unit 312.

[0037] Figure 3(a) shows an example of how the voltage in the DC bus 20 changes over time. In Figure 3(a), the horizontal axis represents the passage of time, and the vertical axis represents the measured DC voltage Vdc obtained by measuring the voltage of the DC bus 20. Figure 3(a) shows the case where the power converter 10 for grid connection controls the voltage of the DC bus 20 by droop control, and the voltage of the DC bus 20 gradually increases over time.

[0038] In the power supply system 1 shown in Figure 1, the sum of the power supplied to the DC bus 20 by each device connected to the DC bus 20, excluding the grid-connected power converter 10, is denoted as Pdc, and the upper limit power that the grid-connected power converter 10 outputs to the power system 2 is denoted as Plimit. If the outputs of converters 23, 24, and 30 to the DC bus 20 are P23, P24, and P30, respectively, and the power consumption of the DC load 25 is P25, then Pdc = P23 + P24 + P30 - P25. In Figure 3(a), during the period up to time t, the power Pdc of the DC system is less than or equal to the upper limit power Plimit of the grid-connected power converter 10. At this time, the voltage of the DC bus 20 changes between a minimum value Vl and a maximum value Vu. The minimum value Vl and the maximum value Vu can be determined from the DC voltage range that can be input to each device connected to the DC bus 20. For example, the minimum value Vl may be set to a value lower than the highest value of the lower limit of the DC voltage input range of each device connected to the DC bus 20, and the maximum value Vu may be set to a value higher than the lowest value of the upper limit of the DC voltage input range. On the other hand, during the period after time t, the power Pdc of the DC system exceeds the upper limit power Plimit of the grid-connected power converter 10. At this time, the voltage of the DC bus 20 rises above the maximum value Vu and at a higher rate of increase than during the period up to time t. Such a voltage change of the DC bus 20 may occur, for example, when the power generated by the DC power sources 21 and 41 exceeds the upper limit power Plimit that can be output from the grid-connected power converter 10 to the power system 2, and the power consumed by the DC load 25 and AC load 43 and the charging power of the storage battery 22 cannot absorb this excess power.

[0039] Figure 3(b) shows an example of the relationship between the DC voltage measurement value Vdc input to the AC voltage command correction unit 312 and the corrected AC voltage command value Vref output from the AC voltage command correction unit 312. In Figure 3(b), the horizontal axis represents the DC voltage measurement value Vdc measured by the DC voltage sensor 34 and input to the AC voltage command correction unit 312, and the vertical axis represents the corrected AC voltage command value Vref output from the AC voltage command correction unit 312.

[0040] When the measured DC voltage Vdc is between the aforementioned minimum value Vl and a predetermined threshold Vth, the AC voltage command correction unit 312 outputs the AC voltage command value V0 input from an external source as the corrected AC voltage command value Vref. In other words, in the DC power of the DC bus 20, the voltage range between Vl and Vth corresponds to a dead zone in which the AC voltage command correction unit 312 does not operate.

[0041] Furthermore, when the measured DC voltage Vdc exceeds the threshold Vth, the AC voltage command correction unit 312 corrects the AC voltage command value V0 to be larger than the original value and outputs the corrected AC voltage command value Vref. At this time, as shown in Figure 3(b), the larger the measured DC voltage Vdc, the larger the corrected AC voltage command value Vref. That is, the larger the amount of the measured DC voltage Vdc exceeds the threshold Vth, the greater the correction amount for the original AC voltage command value V0, so that the corrected AC voltage command value Vref becomes larger. When the AC voltage command value V0 is the aforementioned maximum value Vu, the correction amount for the original AC voltage command value V0 is adjusted so that a predetermined value Vpcs is output as the corrected AC voltage command value Vref. This predetermined value Vpcs corresponds to the voltage of the AC grid 40 when the PCS 42 connected to the AC grid 40 in the power supply system 1 in Figure 1 exerts the aforementioned voltage rise suppression function to limit the power supply from the DC power supply 41 and suppress the voltage rise of the AC grid 40. Furthermore, the correction amount relative to the original AC voltage command value V0 may be adjusted so that the PCS42 outputs a voltage at which it stops operation due to overvoltage detection, which is set as a predetermined value Vpcs.

[0042] In the power conversion device 30 of this embodiment, in the AC voltage command correction unit 312 of the inverter control device 31, by performing the control as described above, based on the voltage of the DC bus 20, the operation of the PCS 42 connected to the AC grid 40 is controlled. Specifically, when the voltage of the AC grid 40 is equal to or higher than a predetermined value, the PCS 42 has a voltage increase function of suppressing its own output and restricting the power supply from the DC power source 41 to suppress the voltage increase of the AC grid 40. When the measured DC voltage value Vdc exceeds a predetermined threshold value Vth, the AC voltage command correction unit 312 corrects the AC voltage command value V0 so that the corrected AC voltage command value Vref increases as the measured DC voltage value Vdc increases according to the graph in FIG. 3(b). As a result, the voltage command V* generated by the current control unit 319 changes according to the corrected AC voltage command value Vref, and based on this voltage command V*, the main circuit control unit 320 controls the operation of the inverter 32, so that the power conversion device 30 operates such that the voltage of the AC grid 40 approaches the corrected AC voltage command value Vref. As a result, the voltage increase function of the PCS 42 works and the power supply from the DC power source 41 is restricted, so that the power supply from the AC grid 40 side to the DC bus 20 side can be reduced, and the voltage increase of the DC bus 20 can be suppressed.

[0043] According to the first embodiment of the present invention described above, the following effects can be obtained.

[0044] (1) The power conversion device 30 is connected to a DC bus 20 to which a DC power source 21 is connected and an AC grid 40 to which a DC power source 41 is connected via a PCS 42, and converts the DC power of the DC bus 20 and the AC power of the AC grid 40 with each other, and controls the operation of the PCS 42 based on the voltage of the DC bus 20. By doing so, it is possible to suppress an increase in the DC power input from the DC bus 20 to the system connection power conversion device 10 and an accompanying increase in the DC voltage.

[0045] (2) The power converter 30 includes an inverter 32 that converts DC power to AC power, a main circuit control unit 320 that controls the operation of the inverter based on an AC voltage command value V0 input from an external source, and an AC voltage command correction unit 312 that corrects the AC voltage command value V0 based on a DC voltage measurement value Vdc obtained by measuring the voltage of the DC bus 20. The PCS 42 has a voltage rise suppression function that suppresses a voltage rise in the AC grid 40 by limiting the power supply from the DC power source 41 when the voltage of the AC grid 40 is above a predetermined value. The main circuit control unit 320 controls the operation of the inverter 32 based on the AC voltage command value Vref corrected by the AC voltage command correction unit 312. The AC voltage command correction unit 312 corrects the AC voltage command value V0 so that the voltage rise suppression function is activated in the PCS 42 when the DC voltage measurement value Vdc satisfies predetermined conditions. Specifically, when the measured DC voltage Vdc exceeds a predetermined threshold Vth, the AC voltage command correction unit 312 corrects the AC voltage command value V0 so that the corrected AC voltage command value Vref increases as the measured DC voltage Vdc increases. In this way, when the measured DC voltage Vdc reaches the maximum value Vu of the DC bus 20's voltage control range, the voltage rise suppression function of the PCS 42 limits the power supply from the DC power supply 41, thereby suppressing the voltage rise of the DC bus 20.

[0046] (3) The power converter 30 includes a first voltage command generation unit 314 that generates a first voltage command E* based on an AC voltage command value Vref corrected by an AC voltage command correction unit 312, an angular frequency command generation unit 315 that generates an angular frequency command ω* for AC power based on an active power command P0 input from an external source, a phase command generation unit 316 that generates a phase command θ* based on the angular frequency command ω*, a current command generation unit 317 that generates a current command I* for AC power based on the phase command θ* and the first voltage command E*, and a current control unit 319 that generates a voltage command V* for AC power based on the current command I* generated by the current command generation unit 317. The main circuit control unit 320 uses the phase command θ* and the voltage command V* generated by the current control unit 319 to control the operation of the inverter 32 based on the corrected AC voltage command value Vref.

[0047] (4) The power supply system 1 includes a DC power supply 21 that supplies DC power, a DC bus 20 to which the DC power supply 21 is connected, a DC power supply 41 that supplies DC power, a PCS 42 that converts the DC power supplied from the DC power supply 41 into AC power, an AC grid 40 to which the DC power supply 41 is connected via the PCS 42, and a power converter 30 that converts the DC power of the DC bus 20 and the AC power of the AC grid 40 into each other. The power converter 30 controls the operation of the PCS 42 based on the voltage of the DC bus 20. The power supply system 1 also includes a grid-connection power converter 10 that is connected between the DC bus 20 and the commercial power grid 2 and converts the DC power of the DC bus 20 into AC power and outputs it to the power grid 2. In this way, the power supply system 1 can suppress the increase in DC power input from the DC bus 20 to the grid-connection power converter 10 and the resulting rise in DC voltage.

[0048] (Second Embodiment) FIG. 4 is a diagram showing a configuration example of a power supply system according to the second embodiment of the present invention. The power supply system 1A of the present embodiment is different from the power supply system 1 of FIG. 1 described in the first embodiment in that the power supply system 1A does not have the system connection power conversion device 10 and is not connected to the power system 2.

[0049] Note that the power supply system 1A of the present embodiment corresponds to a state where the operation of the system connection power conversion device 10 is stopped or off-grid in the power supply system 1 of FIG. 1. Further, in the power supply system 1 of FIG. 1, the power supply system 1A of the present embodiment may be realized by switching the connection destination of the system connection power conversion device 10 from the power system 2 to the AC grid 40 and operating the system connection power conversion device 10 as the power conversion device 30.

[0050] Each device in the power supply system 1A of this embodiment operates in the same manner as in the first embodiment. For example, the power converter 30 converts between the DC power of the DC bus 20 and the AC power of the AC grid 40, similar to the first embodiment. In this embodiment as well, the power converter 30 has the configuration shown in Figure 2, and in the AC voltage command correction unit 312, when the DC voltage measurement value Vdc exceeds a predetermined threshold Vth, the AC voltage command value V0 is corrected according to the graph in Figure 3(b) so that the corrected AC voltage command value Vref increases as the DC voltage measurement value Vdc increases. As a result, the voltage command V* generated by the current control unit 319 changes according to the corrected AC voltage command value Vref, and the main circuit control unit 320 controls the operation of the inverter 32 based on this voltage command V*, so that the power converter 30 operates so that the voltage of the AC grid 40 approaches the corrected AC voltage command value Vref. As a result, the voltage boosting function of the PCS 42 activates, limiting the power supply from the DC power supply 41. This reduces the power supply from the AC grid 40 to the DC bus 20, thereby suppressing the voltage rise on the DC bus 20. Depending on the power consumption of the AC load 43, the DC power supplied from the DC power supply 21 via the DC bus 20 is converted to AC power by the power converter 30 and output to the AC load 43 via the AC grid 40. Therefore, the power on the DC bus 20 is consumed on the AC grid 40 side, making it possible to suppress the voltage rise on the DC bus 20.

[0051] According to the second embodiment of the present invention described above, the power supply system 1A includes an AC load 43 connected to an AC grid 40. The power converter 30 converts DC power supplied from a DC power source 21 via a DC bus 20 into AC power and outputs it to the AC load 43 via the AC grid 40. In this way, in the power supply system 1A, when the power generated by the DC power source 21 is excessive, the power rise of the DC bus 20 can be suppressed.

[0052] In the first and second embodiments described above, the AC voltage command correction unit 312 of the power converter 30 may also correct the AC voltage command value V0 based on the time change of the DC voltage measurement value Vdc. Specifically, the AC voltage command correction unit 312 may correct the AC voltage command value V0 to be larger than the original value when the DC voltage measurement value Vdc exceeds the threshold Vth, as described above, or instead when the time derivative value Vdc' of the DC voltage measurement value Vdc exceeds a predetermined threshold Vth', and output the correction result as the corrected AC voltage command value Vref. In this case, similar to the case where the AC voltage command value V0 is corrected based on the DC voltage measurement value Vdc, it is preferable to increase the corrected AC voltage command value Vref as the time derivative value Vdc' increases. In this way, when the voltage of the DC bus 20 changes sharply, it is possible to start limiting the power supply from the DC power source 41 earlier and reliably suppress the voltage rise of the DC bus 20.

[0053] The present invention is not limited to the embodiments or modifications described above, and can be implemented using any components without departing from its spirit. Furthermore, each embodiment or modification may be adopted individually, or multiple embodiments may be adopted in any combination. In other words, the present invention can achieve the effects described above by arbitrarily combining the features of each embodiment.

[0054] The embodiments and modifications described above are merely examples, and the present invention is not limited to these, as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0055] 1, 1A...Power supply system 2...Power grid 10...Power converter for grid connection 20...DC bus 21...DC power supply 22...Battery 23, 24...Converter 25...DC load 30...Power converter 31...Inverter control device 32...Inverter 33...Filter 34...DC voltage sensor 35...Current sensor 36...AC voltage sensor 40...AC grid 41...DC power supply 42...Power conditioner (PCS) 43...AC load 311...Power calculation unit 312...AC voltage command correction unit 313...Reactive power command unit 314...First voltage command generation unit 315...Angular frequency command generation unit 316...Phase command generation unit 317...Current command generation unit 318...Current command constraint unit 319...Current control unit 320...Main circuit control unit

Claims

1. A power conversion device connected to a DC bus to which a first DC power supply is connected, and to an AC grid to which a second DC power supply is connected via a power conditioner, which converts between the DC power of the DC bus and the AC power of the AC grid, wherein the power conversion device controls the operation of the power conditioner based on the voltage of the DC bus.

2. A power conversion device according to claim 1, comprising: an inverter that converts DC power to AC power; a main circuit control unit that controls the operation of the inverter based on an AC voltage command value input from an external source; and an AC voltage command correction unit that corrects the AC voltage command value based on a DC voltage measurement value obtained by measuring the voltage of the DC bus, wherein the power conditioner has a voltage rise suppression function that limits the power supply from the second DC power source to suppress a voltage rise in the AC grid when the voltage of the AC grid is above a predetermined value; the main circuit control unit controls the operation of the inverter based on the AC voltage command value corrected by the AC voltage command correction unit; and the AC voltage command correction unit corrects the AC voltage command value so that the voltage rise suppression function is performed in the power conditioner when the DC voltage measurement value satisfies predetermined conditions.

3. A power conversion device according to claim 2, wherein the AC voltage command correction unit corrects the AC voltage command value such that the corrected AC voltage command value increases as the DC voltage measurement value increases when the DC voltage measurement value exceeds a predetermined first threshold.

4. A power conversion device according to claim 2, wherein the AC voltage command correction unit corrects the AC voltage command value such that the corrected AC voltage command value increases as the amount of time change of the DC voltage measurement exceeds a predetermined second threshold.

5. A power conversion device according to claim 2, comprising: a first voltage command generation unit that generates a first voltage command based on the AC voltage command value corrected by the AC voltage command correction unit; an angular frequency command generation unit that generates an angular frequency command for the AC power based on an active power command input from an external source; a phase command generation unit that generates a phase command based on the angular frequency command; a current command generation unit that generates a current command for the AC power based on the phase command and the first voltage command; and a current control unit that generates a voltage command for the AC power based on the current command generated by the current command generation unit, wherein the main circuit control unit controls the operation of the inverter based on the corrected AC voltage command value using the phase command and the voltage command generated by the current control unit.

6. A power supply system comprising: a first DC power supply for supplying DC power; a DC bus to which the first DC power supply is connected; a second DC power supply for supplying DC power; a power conditioner for converting DC power supplied from the second DC power supply into AC power; an AC grid to which the second DC power supply is connected via the power conditioner; and a power converter for mutually converting DC power from the DC bus and AC power from the AC grid, wherein the power converter controls the operation of the power conditioner based on the voltage of the DC bus.

7. A power supply system according to claim 6, further comprising a grid-connection power converter connected between the DC bus and the commercial power grid, which converts the DC power of the DC bus into AC power and outputs it to the power grid.

8. The power supply system according to claim 6, further comprising an AC load connected to the AC grid, wherein the power converter converts DC power supplied from the first DC power source via the DC bus into AC power and outputs it to the AC load via the AC grid.

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