Power conversion system and control method

Abstract

This power conversion system distributes power by using an AC-line bus and a DC-line bus. The power conversion system comprises a power converter and a controller. The power converter is provided between the AC-line bus and the DC-line bus, and is capable of performing conversion between AC power and DC power. The controller controls the power converter in a control mode which includes a DC-AC conversion mode in which AC power can be supplied to the AC-line bus and an AC-DC conversion mode in which the AC power supplied to the AC-line bus is converted into DC power having a desired DC voltage.

Description

Power Conversion System and Control Method

[0001] Embodiments of the present invention relate to a power conversion system and a control method.

[0002] The power conversion system distributes power using an AC system bus and a DC system bus connected to the AC system bus via a power converter. In such a power conversion system, it has been required to implement the adjustment of the AC power supplied to the AC system bus and the adjustment of the DC voltage of the DC system bus in a simpler manner.

[0003] Japanese Patent Application Laid-Open No. 2001-161098

[0004] An object of the present invention is to provide a power conversion system and a control method capable of adjusting the AC power supplied to the AC system bus and the DC voltage of the DC system bus connected to the AC system bus via a power converter in a simpler manner.

[0005] The power conversion system of the embodiment distributes power using an AC system bus and a DC system bus. The power conversion system includes a power converter and a controller. The power converter is provided between the AC system bus and the DC system bus and can mutually convert AC power and DC power. The controller controls the power converter by a control mode including an AC-DC conversion mode capable of supplying AC power to the AC system bus and an AC-DC conversion mode for converting the AC power supplied to the AC system bus into DC power with a desired DC voltage.

[0006] Schematic diagram of the power conversion system of the embodiment. Schematic diagram of the power conversion system of the embodiment. Schematic diagram of the power conversion system of the embodiment. Schematic diagram of the controller of the embodiment. Schematic diagram of the d-axis AC voltage control unit of the embodiment. Schematic diagram of the q-axis AC voltage control unit of the embodiment. Diagram illustrating the basic settings for ACAVR control of the embodiment. Diagram illustrating the generation of DC current command values ​​of the embodiment. Diagram illustrating the DCAVR operating mode of the embodiment. Diagram illustrating the DCAVR operating mode of the embodiment. Diagram illustrating the APR operating mode of the embodiment. Diagram illustrating the APR operating mode of the embodiment. Diagram illustrating cases where the APR operating mode of the embodiment is restricted. Diagram illustrating cases where the APR operating mode of the embodiment is restricted. Diagram illustrating the charging of the battery of the embodiment. Diagram illustrating the charging of the battery of the embodiment. Diagram illustrating the CVCF operating mode of the embodiment. Diagram illustrating the CVCF operating mode of the embodiment. Diagram illustrating an example of the configuration of the controller of the power conversion system according to the embodiment.

[0007] The power conversion system and control method of the embodiment will be described below with reference to the drawings. In the following description, components having the same or similar functions will be denoted by the same reference numerals. Duplication of these components may be omitted. Electrical connection may simply be referred to as "being connected." In the description of the embodiment, when representing AC in a stationary coordinate system, a-phase, b-phase, and c-phase are used, and when representing it in a rotating coordinate system, mutually orthogonal dq-axis coordinate systems are used. The coordinate system is not limited to this and may be changed as appropriate. In the description of the embodiment, constant voltage constant frequency control is referred to as CVCF control, and its control state is referred to as CVCF operation.

[0008] (First Embodiment) The power conversion system 1 of the embodiment will be described with reference to Figure 1A. Figure 1A is a schematic diagram of the power conversion system 1 of the embodiment.

[0009] The power conversion system 1 distributes power using an AC bus ACBUS and a DC bus DCBUS. During normal operation, AC power with adjusted AC voltage is supplied to the AC bus ACBUS. The AC bus ACBUS is connected to the system PS via a circuit breaker SA. The system PS may be a power distribution network or power distribution equipment capable of supplying AC power. The power distribution equipment may include phase-shifting power generation equipment, substations, etc., which are not shown.

[0010] The power conversion system 1 includes, for example, a generator 2, a transformer 3, power converters 4 and 5, storage batteries 6 and 7, and controllers 8 and 9.

[0011] The generator 2 generates alternating current (AC) power by receiving power around its shaft, for example, from a prime mover. More specifically, the generator 2 generates multiphase AC power with three or more phases. In the following explanation, a three-phase AC with a phase, b phase, and c phase will be used as an example. Alternatively, the generator may generate multiphase AC with other configurations. The generator 2 is connected to the AC system bus ACBUS via a circuit breaker SB.

[0012] The transformer 3 has windings with a predetermined turns ratio, for example, with the primary and secondary sides insulated from each other, and converts the voltage of the three-phase AC power through electromagnetic coupling. For example, the primary winding of the transformer 3 is connected to the AC system bus ACBUS via a circuit breaker SE. The secondary winding of the transformer 3 is connected to the AC load 3L.

[0013] Power converters 4 and 5 are power conversion devices that mutually convert AC power and DC power through control. The AC sides of power converters 4 and 5 are connected to the AC power bus ACBUS via circuit breakers SC. The DC sides of power converters 4 and 5 are connected to DC loads 4L and 5L via DC power buses DCBUS. For example, if the AC power bus ACBUS is three-phase AC, power converters 4 and 5 form a bridge circuit including three legs. IGBTs (Insulated Gate Bipolar Transistors), OSFETs, etc., can be used as semiconductor switching elements forming power converters 4 and 5. The number of semiconductor switching elements forming power converters 4 and 5, the circuit configuration, the number of stages in the bridge circuit, etc., can be appropriately selected according to the conditions of the AC side and the DC side.

[0014] The storage batteries 6 and 7 store a portion of the DC power generated by the power converters 4 and 5 during the charging cycle and discharge the DC power during the discharge cycle. This makes the stored power available for use, for example, power conversion by the power converters 4 and 5. The storage batteries 6 and 7 are each connected to the DC power bus DCBUS via the circuit breaker SD.

[0015] Controllers 8 and 9 control, for example, the power conversion performed by power converters 4 and 5. Details of this will be described later.

[0016] The power conversion system 1 shown in Figure 1A is an example in which power converters 4 and 5, storage batteries 6 and 7, and controllers 8 and 9 are configured redundantly.

[0017] Referring to Figure 2, an example of the configuration of the controller 8 in this embodiment will be described. Figure 2 is a diagram of the configuration of the controller 8 in this embodiment. It is preferable that the controller 9 also have a similar configuration to the controller 8. The controller 8 will be described below as a representative example.

[0018] The controller 8 includes a d-axis AC voltage control unit 81 (ACAVRd), a q-axis AC voltage control unit 82 (ACAVRq), a DC voltage control unit 83 (DCACR), a redundant configuration control unit 84, a current control unit 85 (ACR), an output level setting unit 86 (VBL), a two-phase to three-phase conversion unit 87 (DQ / abc), a three-phase to two-phase conversion unit 88 (abc / DQ), and a reference phase generation unit 89. The d-axis AC voltage control unit 81 (ACAVRd) and the q-axis AC voltage control unit 82 (ACAVRq) are sometimes collectively referred to as the AC voltage control unit (ACAVR).

[0019] The d-axis AC voltage control unit 81 generates a d-axis current command (Idref) to adjust the d-axis component of the AC voltage output by the power converter 4 (CONV) using the d-axis AC voltage command, the detected d-axis voltage Vd_lpf, etc. The q-axis AC voltage control unit 82 generates a q-axis current command (Iqref0) to adjust the q-axis component of the AC voltage output by the power converter 4 using the q-axis AC voltage command, the detected q-axis voltage Vq_lpf, etc. The DC voltage control unit 83 generates a q-axis current command (Iqref) to adjust the DC voltage output by the power converter 4 using the output value (q-axis current command (Iqref0)) from the q-axis AC voltage control unit 82. The redundant configuration control unit 84 adjusts the current command value output to the subsequent stage according to the setting (CMD_MS) of whether to set one of the redundant power converters 4 or 5 as the master or slave. For example, when power converter 4 is set as the master, the redundant configuration control unit 84 uses the output values ​​(q-axis current command (Iqref)) from the preceding d-axis AC voltage control unit 81 and DC voltage control unit 83. In contrast, when power converter 4 is set as the slave, the redundant configuration control unit 84 uses a fixed value instead of the output values ​​from the preceding d-axis AC voltage control unit 81 and DC voltage control unit 83. This fixed value may define the magnitude of the current flowing from the slave power converter to the master power converter.

[0020] The current control unit 85 adjusts the voltage output by the power converter 4 by performing current control using the output value of the redundant configuration control unit 84 and the detected AC current value. For example, the current control unit 85 performs proportional-integral calculations for each component of the dq axis so that the difference between the output value of the redundant configuration control unit 84 and the detected AC current value is eliminated. The current control unit 85 may also be configured to include non-interference control. General methods can be applied to this non-interference control.

[0021] The output level setting unit 86 adds a reference output level to the output value from the current control unit 85 and outputs the result. The output level setting unit 86 adjusts the reference output level according to the setting (CMD_CVCF) of whether or not to use the power converter 4 in CVCF operation mode. For example, when the power converter 4 is used in CVCF operation mode, the output level setting unit 86 uses the reference value as is for the reference output level (gain 1x), and when the power converter 4 is used in a mode other than CVCF operation mode, it uses a value obtained by reducing the reference value by a predetermined ratio for the reference output level (gain less than 1x). The same procedure may also be followed in the case of constant voltage control, which will be described later, as in the case of the CVCF operation mode described above.

[0022] The two-phase to three-phase conversion unit 87 uses the reference phase θ0 to convert the dq-axis voltage component output by the output level setting unit 86 into three-phase axis components using the reference phase θ0.

[0023] The three-phase two-phase conversion unit 88 uses the reference phase θ0 to convert the three-phase axial components of the detected AC current value and AC voltage value (Vac_fbk) into dq-axis components, respectively, using the reference phase θ0. The three-phase two-phase conversion unit 88 may also perform low-pass filter processing on the result of the above conversion. In this embodiment, the value of the signal after filtering is sometimes called the detected value. The three-phase two-phase conversion unit 88 is an example of a conversion unit that converts the AC voltage and AC current of the AC power bus ACBUS into DC flow rates (Vd_lpf, Vq_lpf) on two mutually orthogonal axes (dq axis).

[0024] The reference phase generation unit 89 generates a reference phase θ0 to be supplied to the two-phase to three-phase conversion unit 87 and the three-phase to two-phase conversion unit 88 using the detected AC voltage value (Vac_fbk), the DC flow rate (Vd_lpf, etc.) supplied from the three-phase to two-phase conversion unit 88, the self-propulsion signal, or AC phase information supplied from an external source. The AC phase information supplied from an external source may be obtained from a paired controller 9 in a redundant configuration. The configuration shown in the figure is an example when Vd_lpf is used.

[0025] As described above, the AC voltage control unit (ACAVR) may perform, for each of the two mutually orthogonal axes, a first voltage control using DC flow rate based on AC voltage and a second voltage control using DC flow rate based on AC current, in a predetermined order.

[0026] Next, the generation of the current command value in the embodiment will be explained with reference to Figures 3A to 5.

[0027] (Regarding the generation of d-axis current command values) First, the generation of d-axis current command values ​​will be explained. Figure 3A is a schematic diagram of the d-axis AC voltage control unit 81 of the embodiment. As shown in Figure 3A, the d-axis AC voltage control unit 81 comprises a subtractor 811, a PI calculator 812, a subtractor 813, and a PI calculator 814.

[0028] The subtractor 811 subtracts the detected d-axis voltage value Vd_lpf from the d-axis voltage upper limit command Vdref_H to obtain the first d-axis voltage deviation. The PI arithmetic unit 812 performs a proportional-integral operation on the first d-axis voltage deviation. The PI arithmetic unit 812 limits the result of the proportional-integral operation on the first d-axis voltage deviation using an attached limiter. The lower limit of the limiter is the current (-Ilim). The upper limit of the limiter is set to an external command value or a fixed value (Q=0). The output of the PI arithmetic unit 812 is limited between the lower limit current (-Ilim) and the upper limit of the limiter.

[0029] The subtractor 813 subtracts the detected d-axis voltage value Vd_lpf from the d-axis voltage lower limit command Vdref_L to obtain the second d-axis voltage deviation. The PI arithmetic unit 814 performs a proportional-integral operation on the second d-axis voltage deviation and outputs the d-axis current command Idref. The PI arithmetic unit 814 limits the result of the proportional-integral operation on the second d-axis voltage deviation using an attached limiter. The lower limit of the limiter is the output value of the PI arithmetic unit 812. The upper limit of the limiter is the current (+Ilim). The output of the PI arithmetic unit 814 is limited to between the lower limit of the limiter and the upper limit of the limiter, which is the current (+Ilim).

[0030] Note that setting the reactive power Q to 0 is equivalent to setting the d-axis current component to 0. When specifying the upper limit of the limiter, it is best to decide whether to simply set the d-axis current command Id to 0 (reactive power command Qref to 0) or to determine it based on the calculation result using the active power command Pref, the d-axis voltage component Vd, and the q-axis voltage component Vq, depending on the power factor requirement. Note that PI calculators 812 and 814 are assumed to each have a positive gain.

[0031] Next, the generation of the q-axis current command value will be explained. Figure 3B is a schematic diagram of the q-axis AC voltage control unit 82 of the embodiment. As shown in Figure 3B, the q-axis AC voltage control unit 82 includes a subtractor 821, a PI arithmetic unit 822, a subtractor 823, a PI arithmetic unit 824, and a divider 825.

[0032] The subtractor 821 subtracts the detected q-axis voltage value Vq_lpf from the q-axis voltage upper limit command Vqref_H to obtain the second q-axis voltage deviation. The PI arithmetic unit 822 performs a proportional-integral operation on the second q-axis voltage deviation. The PI arithmetic unit 822 limits the result of the proportional-integral operation on the second q-axis voltage deviation using an attached limiter. The lower limit of the limiter is the current (-Ilim). The upper limit of the limiter is the result obtained by dividing the external command value (Pref) by the detected q-axis voltage value Vq_lpf. The output of the PI arithmetic unit 822 is limited between the lower limit current (-Ilim) and the upper limit of the limiter (q-axis current reference Iqref1). This upper limit (q-axis current reference Iqref1) is determined by the calculation result of the divider 825. The divider 825, for example, divides the external command Pref by the q-axis voltage detection value Vq_lpf to obtain the q-axis current reference Iqref1.

[0033] The subtractor 823 subtracts the detected q-axis voltage value Vq_lpf from the q-axis voltage lower limit command Vqref_L to obtain the second q-axis voltage deviation. The PI arithmetic unit 824 performs a proportional-integral operation on the second q-axis voltage deviation and outputs the q-axis current command Iqref. The PI arithmetic unit 824 limits the result of the proportional-integral operation on the second q-axis voltage deviation using an attached limiter. The lower limit of the limiter is the output value of the PI arithmetic unit 822. The upper limit of the limiter is the current (+Ilim). The output of the PI arithmetic unit 824 is limited to between the lower limit of the limiter and the upper limit of the limiter, which is the current (+Ilim). The PI arithmetic units 822 and 824 are assumed to each have a positive gain.

[0034] When specifying the upper limit of the limiter mentioned above, it is advisable to determine, based on the power factor requirements, whether to simply determine the d-axis current command Id based on the ratio of the active power command Pref and the d-axis voltage component Vd, to set the reactive power command Qref to 0, or to determine it based on the calculation result of the d-axis voltage component Vd and the q-axis voltage component Vq.

[0035] As described above, the AC voltage control unit (ACAVR) performs AC voltage control for each of the two mutually orthogonal axes. For example, a first voltage control using DC flow rate based on AC voltage is performed by subtractor 821 and PI arithmetic unit 822, and a second voltage control using DC flow rate based on AC current is performed by subtractor 823 and PI arithmetic unit 824, in a predetermined order.

[0036] The functions and other features of the power conversion system 1 described above will be explained in detail below.

[0037] (Basic Functions of ACAVR Control) The basic functions of the ACAVR control of this embodiment will be explained with reference to Figure 4. Figure 4 is a diagram illustrating the basic settings for the ACAVR control of this embodiment. The graph shown in Figure 4 shows an example of the ACAVR characteristics (characteristic example) that define the q-axis current reference Iqref1 of the output value of the ACAVR control. According to this characteristic example of ACAVR control, when the q-axis current reference Iqref1 is within the range from its lower limit (-Ilim1) to its upper limit (+Ilim1), and the q-axis voltage reference Vqref is within the range from its lower limit (Vqref_L) to its upper limit (Vqref_H), the value of the q-axis current reference Iqref1 corresponding to the operating point that falls within the above range is determined. The q-axis current reference Iqref has a limited lower and upper limit. Therefore, values ​​smaller than its lower limit (-Ilim1) or larger than its upper limit (+Ilim1) are not output. The q-axis voltage reference Vqref has a lower limit (Vqref_L) and an upper limit (Vqref_H) defined relative to the rated voltage. This ensures that it will never be smaller than the lower limit (Vqref_L) or larger than the upper limit (Vqref_H). In the characteristic example of the embodiment, the operating point is defined on the q-axis current reference Iqref1 corresponding to the power command Pref. Therefore, the q-axis current reference Iqref1 is output regardless of the q-axis voltage.

[0038] For example, if the q-axis voltage Vq_lpf is within the range of the lower limit (Vqref_L) to the upper limit (Vqref_H), the first q-axis voltage deviation of the subtractor 821's calculation result becomes positive. As a result, the calculation result of the PI arithmetic unit 822 sticks to the upper limit of the limiter (assuming Iqref0), and the q-axis current reference Iqref0 is output from the PI arithmetic unit 822. Also, in the above case, the second q-axis voltage deviation of the subtractor 823's calculation result becomes negative. As a result, the calculation result of the PI arithmetic unit 824 sticks to the lower limit of the limiter, and the q-axis current reference Iqref0 of the same value as above is output from the PI arithmetic unit 824. Note that the upper limit of the PI arithmetic unit 822's limiter may take a different value from Iqref0 due to an external command (Pref), etc., but due to the above action, that value is propagated to the subsequent stage.

[0039] The above explanation pertains to the basic operation of the q-axis AC voltage control unit 82, but the same applies to the basic operation of the d-axis AC voltage control unit 81.

[0040] (Regarding the generation of q-axis current command values ​​for DC voltage control) Next, the generation of d-axis current command values ​​for DC voltage control will be explained. Figure 5 is a schematic diagram of the DC voltage control unit 83 of the embodiment. As shown in Figure 5, the DC voltage control unit 83 includes a subtractor 831, a PI arithmetic unit 832, a subtractor 833, a PI arithmetic unit 834, and multipliers 835 and 836.

[0041] The subtractor 831 subtracts the detected DC voltage value Vdc_lpf from the DC voltage lower limit command Vdcref_L to obtain the first DC voltage deviation. The multiplier 835 multiplies the first DC voltage deviation by (-1) to reverse the sign of the first DC voltage deviation. The PI arithmetic unit 832 performs a proportional-integral operation on the first DC voltage deviation whose sign has been reversed. The PI arithmetic unit 832 limits the result of the proportional-integral operation on the first DC voltage deviation whose sign has been reversed using an attached limiter. The lower limit of the limiter is the current (-Ilim). The upper limit of the limiter is the output value of the q-axis AC voltage control unit 82 (q-axis current reference Iqref1). The output of the PI arithmetic unit 832 is limited to between the lower limit current (-Ilim) and the upper limit of the limiter.

[0042] The subtractor 833 subtracts the detected DC voltage value Vdc_lpf from the DC voltage upper limit command Vdcref_H to obtain the second DC voltage deviation. The multiplier 836 multiplies the second DC voltage deviation by (-1) to invert the sign of the second DC voltage deviation. The PI arithmetic unit 834 performs a proportional-integral operation on the second DC voltage deviation with the sign inverted and outputs the DC current command Iqref. The PI arithmetic unit 834 limits the result of the proportional-integral operation on the second DC voltage deviation with the sign inverted using an attached limiter. The lower limit of the limiter is the output value of the PI arithmetic unit 832. The upper limit of the limiter is the current (+Ilim). The output of the PI arithmetic unit 834 is limited to between the lower limit of the limiter and the upper limit of the limiter, which is the current (+Ilim). Furthermore, PI calculators 832 and 834 are assumed to each have a positive gain on their own. In the case of the DC voltage control unit 83, since it combines multipliers 835 and 836 that multiply by (-1), the proportional-integral operation on the first DC voltage deviation and the second DC voltage deviation effectively results in a negative gain.

[0043] For example, if the voltage Vdc_lpf of the DC bus DCBUS is within the range of the lower limit (Vdcref_L) to the upper limit (Vdcref_H) of the DC voltage, the first DC voltage deviation of the subtractor 831 calculation result becomes negative. The multiplier 835 inverts the sign, making it positive. As a result, the calculation result of the PI calculator 832 sticks to the upper limit of the limiter, and the q-axis current reference Iqref0, which depends on the output value of the preceding q-axis AC voltage control unit 82, is output from the PI calculator 832. Also, in the above case, the second DC voltage deviation of the calculation result of the subtractor 833 becomes positive. The multiplier 836 inverts the sign, making it negative. As a result, the calculation result of the PI calculator 824 sticks to the lower limit of the limiter, and the q-axis current reference Iqref0 with the same value as above is output from the PI calculator 834. As described above, the upper limit of the PI calculator 832 may depend on the output value of the preceding q-axis AC voltage control unit 82. In this case as well, due to the above mechanism, that value is propagated to the subsequent stage.

[0044] The controller 8 controls power conversion according to the following operation modes. Hereinafter, the details of each operation mode provided in the controller 8 will be described in order.

[0045] (DCAVR operation mode) Referring to FIGS. 6A and 6B, an example of the implementation of the DCAVR operation mode will be described. FIGS. 6A and 6B are diagrams for explaining the DCAVR operation mode of the embodiment. FIG. 6A shows the ACAVR characteristics in the DCAVR operation mode, and FIG. 6B shows the DCAVR characteristics in the DCAVR operation mode.

[0046] The DCAVR operation mode is an operation mode in which the AC power supplied to the AC system bus ACBUS is converted into DC power of a desired DC voltage to stabilize the DC voltage. For example, when the circuit breakers SA or SB are closed, the generator 2 or another system (PS) capable of supplying AC power is connected to the AC system bus ACBUS in the DCAVR operation mode. Further, the power converter 4 (converter) is connected by closing the circuit breaker SC. In the DCAVR operation mode, the controller 8 operates the power converter 4 as a converter, converts the AC power supplied from the generator 2 or another system PS by the power converter 4, and controls it so that the DC voltage becomes constant. Note that the above control of the DC voltage becomes effective when the battery 6 is in the disconnected state or when the control target voltage exceeds the voltage of the connected battery 6. As described above, in this operation mode, constant voltage control of the DC voltage is performed. For example, the allowable fluctuation range of the voltage control command value of the DC voltage is set to be 0 or smaller than a predetermined value. The relationship in the case where the allowable fluctuation range is set to 0 is shown in the following equation.

[0047] DC rated voltage (DC voltage command) = Vdcref_H = Vdcref_L

[0048] The above equation is an example in the case where the allowable fluctuation range of the voltage control command value of the DC voltage is set to 0, and both the upper limit value Vdcref_H and the lower limit value Vdcref_L are set to a predetermined DC rated voltage.

[0049] In DCAVR operation mode, DCAVR control takes precedence over ACAVR control. The q-axis AC voltage control unit 82 is positioned before the DC voltage control unit 83 for DCAVR control. In DCAVR operation mode, DCAVR control by the subsequent DC voltage control unit 83 takes precedence over ACAVR control by the q-axis AC voltage control unit 82.

[0050] For example, the ACAVR characteristics shown in Figure 6A represent an example of characteristics that define the q-axis current reference Iqref1 of the output value. This characteristic example is the same as that for the basic operation described above. In this characteristic example, the q-axis voltage reference Vqref is defined between the lower limit (Vqref_L) and the upper limit (Vqref_H) based on the rated voltage. As a result, the q-axis voltage Vq will never be smaller than its lower limit (Vqref_L) or larger than its upper limit (Vqref_H). In this characteristic example, the operating point is defined on the q-axis current reference Iqref1 corresponding to the power command Pref. Therefore, the q-axis current reference Iqref1 is output regardless of the q-axis voltage.

[0051] The DCAVR characteristics shown in Figure 6B illustrate an example of the characteristics that define the q-axis current reference Iqref2 of the output value. According to this example of DCAVR characteristics, when the q-axis current reference Iqref2 is within the range of its lower limit (-Ilim2) to its upper limit (+Ilim2), the value of the q-axis current reference Iqref2, which depends on the DC load, is determined within the above range. The q-axis current reference Iqref has a limited lower and upper limit. Therefore, values ​​smaller than the lower limit (-Ilim2) or larger than the upper limit (+Ilim2) will not be output. The q-axis voltage reference Vqref is defined by the rated voltage. For example, it is desirable that the lower limit (Vqref_L) and the upper limit (Vqref_H) be set to the same values ​​as the rated voltage.

[0052] In this characteristic example, the calculation results related to the ACAVR characteristics do not affect the calculations for DCAVR control. DCAVR control generates a command value (e.g., Iqref2) for performing DC voltage control.

[0053] (APR Operation Mode) An example of implementing the APR operation mode will be described with reference to Figures 7A to 7D. Figures 7A and 7B are diagrams illustrating the APR operation mode of the embodiment. Figures 7C and 7D are diagrams illustrating cases where the APR operation mode of the embodiment is limited. Figures 7A and 7B show examples of APR operation characteristics in which power commands are reflected during APR control mode. The characteristics shown in Figures 7A and 7B are an example of a case in which the operating point becomes a position dependent on a specific current value during APR operation (APR operation mode).

[0054] The APR operating mode is an operating mode that controls the active power supplied to the AC power bus ACBUS when a generator 2, which maintains a constant AC voltage on the AC power bus ACBUS, is connected to the AC power bus ACBUS. For example, the case where the AC voltage on the AC power bus ACBUS is constant will be explained. Under the conditions of the APR operating mode, the controller 8 sets the d-axis current command Id_ref, which defines the reactive power, to 0, and sets the q-axis current command Iq_ref to a desired value according to the power consumed by the load 3L etc. connected to the AC power bus ACBUS. Under this setting, the controller 8 controls the active power supplied to the AC power bus ACBUS from the power grid PS etc. At this time, the controller 8 can supply the power consumed on the AC side by transferring energy from the battery 6 connected to the DC power bus DCBUS to the AC power bus ACBUS. The controller 8 can adjust the amount of power supplied by the generator 2 and the amount of power supplied by the battery 6 according to the set value of the q-axis current command Iq_ref.

[0055] As described above, in this embodiment, the voltage of the AC system bus ACBUS is maintained constant by the operation of the generator 2 or another system (PS). In this case, for example, if the detected value Vq_lpf of the q-axis voltage is within the range from the lower limit value Vqref_L to the upper limit value Vqref_H of the q-axis voltage reference (within the range of Vqref_L < Vq_lpf < Vqref_H), the operating point in this case is at a position that depends on the value of a predetermined current command Iqref1(Pref). In other words, the q-axis current command Iq_ref can be controlled by setting Iqref1(Pref). Note that the value of this current command Iqref1(Pref) may be made changeable according to the user's operation.

[0056] On the other hand, as described above, in this embodiment, since the action of the generator 2 or another system (PS) is weak, there may be a case where the voltage of the AC system bus ACBUS cannot be maintained constant. In such a case, the controller 8 may be made to perform constant voltage control.

[0057] FIGS. 7C and 7D show characteristic examples when the reflection of the power command is restricted during the APR control mode. The characteristics shown in FIGS. 7C and 7D are an example when the AC voltage exceeds the allowable AC voltage range.

[0058] During the APR operation mode, the q-axis voltage Vq_lpf may tend to deviate in a direction exceeding the range from Vqref_L to Vqref_H. In such a case, it is advisable to limit the adjustment of the power supply amount using the Pref command (power command). For example, in order to stabilize the AC voltage, for example, the q-axis voltage Vq_lpf may be controlled (restricted) to the upper limit value Vqref_H. In such a situation, even if the Pref command of the APR control mode is input, the power control (constant current control) by the APR operation mode is not prioritized, and the control for constant AC voltage (constant voltage control) is performed.

[0059] As shown in FIG. 7C, upper and lower limit values of an allowable voltage command for an alternating current voltage (q-axis voltage Vq) are set to different values. For example, it is preferable to set an upper limit value (Vqref_H) and a lower limit value (Vqref_L) of the allowable voltage command for the q-axis voltage Vq to provide a width in the voltage allowable range. If the q-axis voltage Vq_lpf is within the above voltage allowable range, current control works effectively. For example, q-axis current commands Iq_ref1 and Iq_ref2 become equal, and the value can be controlled by setting it to Iqref1(Pref). When DCAVR control is prioritized in the APR operation mode, as shown in FIG. 7D, it is a case where a detected value of the direct current voltage (Vdc_lpf) exceeds an allowable direct current voltage command value width (when Vdc_lpf > Vdcref_H or Vdc_lpf < Vdcref_L).

[0060] Also, by setting a command value for the active power command Pref to supply direct current power to the storage battery 6, it becomes possible to perform a charging operation of the storage battery 6.

[0061] (Charging of the battery 6 in APR operation mode) The charging of the battery 6 in APR operation mode will be explained with reference to Figures 8A and 8B. Figures 8A and 8B are diagrams for explaining the charging of the battery 6 in the embodiment. Figure 8A shows the ACAVR characteristics used during charging of the battery 6, and Figure 8B shows an example of the DCAVR characteristics used during charging of the battery 6. The examples shown in Figures 8A and 8B are examples of cases in which DC voltage control is performed by setting the power command Pref when charging the battery 6. Figure 8A shows an example in which the voltage of the AC power bus ACBUS is controlled to a constant level by the generator 2, etc. In this case, Iqref1 is output based on the power command Pref set by the user. At this time, the power command Pref becomes the command value (power command) of the power flowing into the battery 6. By adjusting the magnitude of the power command Pref, excessive current during charging of the battery 6 can be suppressed. Figure 8B shows an example where the voltage of the storage battery 6 is below the lower limit of the DC voltage tolerance range, Vdcref_L. In this case, the lower limit of the DC voltage range, Vdcref_L, is set as the target voltage, and Iqref1 is set as the upper limit of the current that can be supplied during charging. Charging of the storage battery 6 is then performed within the range of Iqref1.

[0062] (Regarding CVCF operating mode) The CVCF operating mode will be explained with reference to Figures 9A and 9B. Figures 9A and 9B are diagrams for explaining the CVCF operating mode of the embodiment. Figure 9A shows the ACAVR characteristics when the CVCF operating mode is applied, and Figure 9B shows an example of the DCAVR characteristics when the CVCF operating mode is applied. The examples shown in Figures 9A and 9B are examples of when the CVCF operating mode is implemented.

[0063] Unlike the other operating modes described above, the CVCF operating mode is based on the assumption that the generator 2 and external power systems (PS) are not connected during normal operation. The CVCF operating mode allows control to set the dq-axis AC voltage Vdq, which defines the AC system voltage, to a value corresponding to the rated AC voltage. For example, in order to maintain the AC voltage (Vdq) at the rated voltage during CVCF operation mode, both the upper limit Vdcref_H and the lower limit Vdcref_L are set to the rated voltage to limit the operating range of the q-axis voltage command.

[0064] Vqref_H = Vqref_L = (rated voltage)

[0065] An example of the operating point at this time is shown in Figure 9A. As shown in this figure, since CVCF control is being performed, the control is performed based on predetermined set values ​​and does not follow current command values ​​(Idref, Iqref), etc., which change depending on the control state. In this CVCF operating mode, the power required by the load 3L, etc., is supplied from the battery 6. Also, as shown in the characteristic diagram in Figure 9B, according to the subsequent DC voltage control unit 83, the operation in CVCF operating mode is the same as the operation in constant voltage control mode, which takes precedence over APR operating mode, and Iqref2 = Iqref1 is applied as long as it is within the DC voltage tolerance range.

[0066] Although two power converters 4 and 5 are connected in parallel as in the embodiment, only one power converter is required to be set to CVCF operation mode. For example, by controlling one power converter 4 in CVCF operation mode as described above, and operating the other power converter 5 in APR operation mode, power control of the grid becomes possible.

[0067] For example, when the controller 8 generates AC power by controlling the power converter 4 using the CVCF control, it is preferable to disconnect the AC power supply that provides the reference AC from the AC power bus.

[0068] As described above, the power conversion system 1 distributes power using an AC bus ACBUS and a DC bus DCBUS. The power conversion system 1 comprises a power converter 4 and a controller 8. The power converter 4 is installed between the AC bus ACBUS and the DC bus DCBUS and is capable of converting AC power and DC power to each other. The controller 8 controls the power converter 4 with control modes that include a DC-AC conversion mode capable of supplying AC power to the AC bus ACBUS and an AC-DC conversion mode that converts the AC power supplied to the AC bus ACBUS into DC power of a desired DC voltage. This makes it possible to adjust the AC power supplied to the AC bus ACBUS and the DC voltage of the DC bus DCBUS connected to the AC bus ACBUS via the power converter in a simpler way.

[0069] Furthermore, the controller 8 may select a DC-AC conversion mode when the AC voltage of the AC power bus ACBUS deviates from a predetermined range, and generate and output AC power from the power converter 4 using constant voltage control or CVCF control.

[0070] The controller 8 performs the following processing using at least the q-axis AC voltage control unit 82 and the DC voltage control unit 83. The q-axis AC voltage control unit 82 generates a current command for adjusting the AC voltage of the AC power bus ACBUS. The DC voltage control unit 83 may generate a DC current command based on the generated current command.

[0071] The DC voltage control unit 83 performs voltage control on one of the two orthogonal axes, for example, the q-axis. For example, the subtractor 831 and the PI arithmetic unit 832 use the calculation result of the q-axis AC voltage control unit 82 as a limit value and perform a third voltage control using DC flow rate based on AC voltage. The subtractor 833 and the PI arithmetic unit 834 perform a fourth voltage control using DC flow rate based on AC current. The order in which the third and fourth voltage control are performed is predetermined and should be performed in that predetermined order.

[0072] (First Modification) A first modification of the embodiment will now be described. The power conversion system 1 shown in Figure 1 was an example of a redundant configuration. In this modification, instead, an example is shown in which the redundant components have been removed. The power conversion system 1A shown in Figure 1B is the power conversion system 1 with the redundant components removed. In the power conversion system 1A, the power converter 5, the storage battery 7, and the controller 9 have been removed from the power conversion system 1. Thus, except for matters related to the redundant configuration, the description of the embodiment above can be referred to.

[0073] (Second Modification) A second modification of the embodiment will now be described. The power conversion system 1 shown in Figure 1 was an example of a redundant configuration. The power conversion system 1A shown in Figure 1B was the same as the power conversion system 1 but with the redundant components removed. In this modification, a further example is shown in which the battery 6 is omitted. The power conversion system 1B shown in Figure 1C is the same as the power conversion system 1A but with the battery 6 and circuit breaker SD removed. The power conversion system 1B excludes the explanation of charging control to the battery 6 and the explanation of APR control and CVCF control using the battery 6 as a DC power source in APR operation mode from the explanation of the power conversion system 1. Thus, except for the matters related to the above, the explanation of the embodiment above can be referred to.

[0074] Furthermore, when changing the circuit configuration from the second modified example described above to the circuit configuration of the first modified example, and generating AC power from the power converter 4 using the DC-AC conversion mode, the controller 8 may connect a DC power source (storage battery 6) to the DC side of the power converter 4.

[0075] (Examples of the configuration of the power conversion system 1 in each embodiment) Next, an example of the configuration of the controller 8 of the power conversion system 1 will be described with reference to Figure 10. Figure 10 is a diagram illustrating an example of the configuration of the controller 8 of the power conversion system 1 according to an embodiment.

[0076] The controller 8 of the power conversion system 1 includes, for example, a processing unit 8111, a communication processing unit 8121, an input / output unit 8131, and a storage unit 8141 (STRAGE). For example, the processing unit 8111, the communication processing unit 8121, the input / output unit 8131, and the storage unit 8141 are connected via a bus or the like.

[0077] The communication processing unit 8121 enables the supply of various information obtained by communicating with a higher-level device to the processing unit 8111.

[0078] The memory unit 8141 is implemented using ROM, RAM, HDD, flash memory, etc. The memory unit 8141 is allocated a memory area for storing various setting information and programs for operating the power conversion system 1, basic programs such as the OS, application programs, etc.

[0079] The input / output unit 8131 includes, for example, a current detector, a voltage detector, a relay, etc., and acquires information on the output state of the power converter (phase current, line current, phase voltage, line voltage, etc.) as input information and outputs the result of the overfrequency determination. The input / output unit 8131 may also include, for example, a display unit such as a liquid crystal display that displays various information and an operation detection unit. The above-mentioned display unit and operation detection unit may be configured as a touch panel that combines them.

[0080] The processing unit 8111 detects the reference phase and reference frequency of the AC from the AC waveform based on the line voltage, etc., and uses them for the various controls described above.

[0081] The processing unit 8111 executes a software program that includes the above-mentioned functions. By executing the software program, the processing unit 8111 performs some or all of its functions. The software program for realizing the functions of the processing unit 8111 may be stored in the storage unit 8141 in advance, or it may be downloaded to the storage unit 8141 from an external device or portable storage medium (not shown), or via a communication line.

[0082] The functions realized by the components within the power conversion system 1 described herein may be implemented in a circuit or processing circuitry. The circuit or processing circuitry may include a general-purpose processor, application-specific processor, integrated circuit, ASICs (Application Specific Integrated Circuits), FPGA (Field Programmable Gate Array), CPU (Central Processing Unit), GPU (Graphics Processing Unit), conventional circuitry, and / or combinations thereof, programmed to realize the described functions. A processor that realizes the above functions includes transistors and other circuits and is considered a circuit or processing circuitry. A processor for realizing the above functions may include, or be, a programmed processor that executes a program stored in memory, and / or a programmable device that can be reconfigured by data stored in memory. In this specification, a circuit, unit, or means is hardware programmed to realize or execute the described functions. The hardware may be any hardware disclosed herein, or any hardware known to be programmed to perform or execute the functions described herein. If the hardware is a processor that is considered to be of the type of circuit, the circuit, means, or unit is a combination of the hardware and the software used to constitute the hardware and / or the processor.

[0083] According to at least one embodiment described above, the power conversion system distributes power using an AC bus and a DC bus. The power conversion system comprises a power converter and a controller. The power converter is installed between the AC bus and the DC bus and is capable of converting AC power and DC power to each other. The controller controls the power converter by control modes including a DC-AC conversion mode that can supply AC power to the AC bus and an AC-DC conversion mode that converts the AC power supplied to the AC bus into DC power of a desired DC voltage. This makes it possible to adjust the AC power supplied to the AC bus and the DC voltage of the DC bus connected to the AC bus via the power converter in a simpler way.

[0084] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

[0085] For example, the redundant controllers 8 and 9 may be configured separately or as a single unit. In the latter case, a common processor may perform part of the processing of each unit or the aforementioned functions.

[0086] As described above, the power conversion system 1 converts the AC amount related to the AC power bus ACBUS into DC amount on the dq axis, and applies two-stage voltage control (AVR) to each. Furthermore, by adding another two-stage voltage control (AVR) to the two-stage voltage control (AVR) on the q axis, it becomes possible to handle DC voltage control as well. In addition, as in this embodiment and the first modified example, the power conversion system can be configured as a system having a storage battery 6, etc., and can be applied to systems that utilize the storage battery 6, etc.

[0087] The power conversion system 1 of this embodiment enables seamless implementation of DC voltage control (DC-AVR), power control (APR), CVCF control, and master / slave switching. Furthermore, as shown in Figure 1A of this embodiment, if the converter and battery are configured redundantly, one can be set as the master unit and the other as the slave unit. In this way, the same control is possible even with a master / slave configuration.

[0088] By applying the control method of this embodiment, PWM rectification (DC-AVR), output power control (APR), and CVCF functions can be realized with a single converter and control circuit. Furthermore, this control method seamlessly switches between the above functions by switching each command value according to the state of each circuit breaker or control transition command. More specifically, by setting upper and lower limits (limit voltages) for the d-axis voltage and q-axis voltage, power control of the AC system and CVCF operation can be implemented.

[0089] (Note) (1) A power conversion system that distributes power using an AC bus and a DC bus comprises: a power converter provided between the AC bus and the DC bus and capable of mutually converting AC power and DC power; and a controller that controls the power conversion by the power converter using control modes including a DC-AC conversion mode capable of supplying AC power to the AC bus and an AC-DC conversion mode that converts the AC power supplied to the AC bus into DC power of a desired DC voltage. The controller may control the power converter using either the DC-AC conversion mode or the AC-DC conversion mode when the AC voltage in the AC bus is within a predetermined range. (2) The controller of the power conversion system in (1) above may select the DC-AC conversion mode when the AC voltage of the AC bus deviates from a predetermined range and generate and output AC power from the power converter using constant voltage control or CVCF control. (3) When the controller of the power conversion system described in (2) above generates AC power by controlling the power converter with the CVCF, it is preferable to disconnect the AC power supply that provides the reference AC from the AC power bus. (4) When the controller of the power conversion system described in (1) above generates AC power from the power converter using the DC-AC conversion mode, it is preferable to connect a DC power supply (for example, a storage battery) to the DC side of the power converter. (5) The controller of the power conversion system described in (1) above may include an AC voltage control unit (ACAVR) that generates a current command for adjusting the AC voltage of the AC power bus, and a DC voltage control unit (DCAVR) that generates a DC current command based on the generated current command. (6) The controller of the power conversion system described in (5) above includes a conversion unit that converts the AC voltage and AC current of the AC power bus into DC flow rates on two mutually orthogonal axes (dq axes), and the AC voltage control unit (ACAVR) may perform, for each of the two orthogonal axes, a first voltage control using the DC flow rate based on the AC voltage and a second voltage control using the DC flow rate based on the AC current, in a predetermined order.(7) The DC voltage control unit (DCAVR) of the power conversion system described in (6) above may perform, for one of the two orthogonal axes (for example, the q-axis), a third voltage control using the DC flow rate based on the AC voltage, and a fourth voltage control using the DC flow rate based on the AC current, in a predetermined order, using the calculation result of the AC voltage control unit as a limit value. (8) The control method of any of the power conversion systems described in (1) to (5) above may be to control the power converter using either a DC-to-AC conversion mode or an AC-to-DC conversion mode when the AC voltage in the AC power bus is within a predetermined range.

[0090] 1, 1A, 1B Power conversion system 2 Generator 3 Transformer 4, 5 Power converter 6, 7 Storage battery (DC power supply) 8, 9 Controller SA, SB, SC, SD, SE Circuit breaker

Claims

1. A power conversion system for distributing power using an AC bus and a DC bus, comprising: a power converter provided between the AC bus and the DC bus and capable of mutually converting AC power and DC power; and a controller that controls the power conversion by the power converter using control modes including a DC-AC conversion mode capable of supplying AC power to the AC bus and an AC-DC conversion mode that converts the AC power supplied to the AC bus into DC power of a desired DC voltage, wherein the controller controls the power converter using either the DC-AC conversion mode or the AC-DC conversion mode when the AC voltage in the AC bus is within a predetermined range.

2. The power conversion system according to claim 1, wherein the controller selects the DC-AC conversion mode when the AC voltage of the AC power bus deviates from a predetermined range, and generates and outputs AC power from the power converter by constant voltage control or CVCF control.

3. The power conversion system according to claim 2, wherein the controller disconnects the AC power supply that provides the reference AC from the AC power grid bus when generating AC power from the power converter by constant voltage control or CVCF control.

4. The power conversion system according to claim 1, wherein the controller connects a DC power source to the DC side of the power converter when generating AC power from the power converter by the DC-AC conversion mode.

5. The power conversion system according to any one of claims 1 to 4, comprising: an AC voltage control unit that generates a current command for adjusting the AC voltage of the AC power bus; and a DC voltage control unit that generates a DC current command based on the generated current command.

6. The power conversion system according to claim 5, wherein the controller includes a conversion unit that converts the AC voltage and AC current of the AC power bus into DC flow rates on two mutually orthogonal axes, and the AC voltage control unit performs, for each of the two orthogonal axes, a first voltage control using the DC flow rate based on the AC voltage and a second voltage control using the DC flow rate based on the AC current in a predetermined order.

7. The power conversion system according to claim 6, wherein the DC voltage control unit performs a third voltage control using DC flow rate based on the AC voltage and a fourth voltage control using DC flow rate based on the AC current in a predetermined order, with respect to one of the two orthogonal axes, using the calculation result of the AC voltage control unit as a limit value.

8. A control method for a power conversion system according to any one of claims 1 to 4, wherein, when the AC voltage in the AC power bus is within a predetermined range, the power converter is controlled by either a DC-AC conversion mode or an AC-DC conversion mode.

9. A control method for a power conversion system according to claim 8, wherein when the AC voltage of the AC system bus deviates from a predetermined range, the DC-AC conversion mode is selected, and AC power from the power converter is generated and output by CVCF control.

10. A control method for a power conversion system according to claim 9, wherein when generating AC power by controlling the power converter with the CVCF, the AC power source that supplies the AC to be used as a reference is disconnected from the AC power system bus.

11. A control method for a power conversion system according to claim 8, wherein when AC power is generated from the power converter by the DC-AC conversion mode, a DC power supply is connected to the DC side of the power converter.

12. A control method for a power conversion system according to claim 8, comprising generating a current command for adjusting the AC voltage of the AC power bus, and generating a DC current command based on the generated current command.

13. A control method for a power conversion system according to claim 12, wherein the AC voltage and AC current of the AC power bus are converted into DC flows on two mutually orthogonal axes, and in generating the current command, a first voltage control using the DC flow based on the AC voltage and a second voltage control using the DC flow based on the AC current are performed for each of the two orthogonal axes in a predetermined order.

14. A control method for a power conversion system according to claim 13, wherein, in generating the DC current command, the result of the second voltage control is used as a limit value for one of the two orthogonal axes, and a third voltage control using a DC flow rate based on the AC voltage and a fourth voltage control using a DC flow rate based on the AC current are performed in a predetermined order.

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