Electric power conversion device

Abstract

To provide an electric power conversion device capable of more stably supplying power to a load also in a single operation.SOLUTION: An electric power conversion device comprises: a main circuit part that converts DC power supplied from a DC power supply into AC power corresponding to a load, and supplies the AC power after the conversion to the load; and a control device that controls an operation of the conversion to the AC power from the DC power by the main circuit part. The control device includes: a voltage control device that calculates a voltage command value for outputting AC voltage of a constant magnitude in accordance with a voltage reference from the main circuit part; and an overcurrent suppression control part that determines a reduction ratio of the voltage command value calculated by the voltage control device on the basis of the magnitude of AC current of the AC power supplied to the load from the main circuit part. The overcurrent suppression control part reduces the magnitude of the AC voltage output from the main circuit part by inputting the reduction ratio at the suppression into the voltage control device when an absolute value of the magnitude of the AC current is a set value or larger.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] FIELD An embodiment of the present invention relates to a power conversion device. [Background technology]

[0002] 2. Description of the Related Art There are power conversion devices that convert DC power into AC power and supply the AC power to a load. In some cases, such power conversion devices perform stand-alone operation in which they supply power to a load independently without being connected to a power grid.

[0003] In a power conversion device that performs an isolated operation, an overcurrent stop due to an inrush current of a load tends to occur more easily than in a power conversion device that is connected to a power grid. In addition, in a power conversion device that performs an isolated operation, it may be difficult to stably control the output voltage due to noise superimposed on the output voltage. For this reason, it is desirable for a power conversion device that performs an isolated operation to be able to supply power to a load more stably. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-143075 A [Patent Document 2] Patent No. 5938068 Summary of the Invention [Problem to be solved by the invention]

[0005] An embodiment of the present invention provides a power conversion device that can supply power to a load more stably even in an isolated operation. [Means for solving the problem]

[0006] According to an embodiment of the present invention, there is provided a power conversion device that performs an isolated operation for independently supplying power to a load without being interconnected with a power grid, the power conversion device including: a main circuit unit that converts DC power supplied from a DC power source into AC power corresponding to a load and supplies the converted AC power to the load; a control device that controls an operation of converting DC power to AC power by the main circuit unit; a current detector that detects a magnitude of the AC current of the AC power supplied from the main circuit unit to the load; and a voltage detector that detects a magnitude of the AC voltage of the AC power supplied from the main circuit unit to the load. The control device includes a voltage controller that calculates a voltage command value for outputting an AC voltage of a certain magnitude according to a voltage reference from the main circuit unit; and a control signal that generates a control signal for controlling an operation of the main circuit unit based on the voltage command value and inputs the generated control signal to the main circuit unit. and an overcurrent suppression control unit which determines a reduction rate of the voltage command value calculated by the voltage controller, based on the magnitude of the AC current detected by the current detector. The voltage controller calculates the voltage command value based on the magnitude of the AC voltage detected by the voltage detector, the voltage reference, and the reduction rate. When the absolute value of the magnitude of the AC current is less than a set value, the overcurrent suppression control unit inputs the reduction rate during normal operation to the voltage controller, and when the absolute value of the magnitude of the AC current is equal to or greater than the set value, the overcurrent suppression control unit inputs the reduction rate during suppression to the voltage controller, thereby reducing the magnitude of the AC voltage output from the main circuit unit compared to when the reduction rate during normal operation is input to the voltage controller. Effect of the Invention

[0007] According to an embodiment of the present invention, a power conversion device capable of supplying power to a load more stably even in an isolated operation is provided. [Brief description of the drawings]

[0008] [Figure 1] 1 is a circuit diagram illustrating a power conversion device according to an embodiment of the present invention; [Diagram 2]FIG. 1 is a circuit diagram illustrating a converter according to an embodiment. [Diagram 3] FIG. 2 is a block diagram illustrating a control device according to the embodiment. [Figure 4] 2 is a block diagram illustrating an overcurrent suppression control unit according to an embodiment of the present invention; FIG. [Diagram 5] FIG. 2 is a block diagram illustrating a voltage controller according to an embodiment. [Figure 6] 6(a) to 6(c) are block diagrams each showing a schematic example of the operation of the control device according to the embodiment.

[0009] Each embodiment will be described below with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as in reality. Even when the same part is shown, the dimensions and ratios of each part may be different depending on the drawing. In this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

[0010] FIG. 1 is a circuit diagram that illustrates a power conversion device according to an embodiment. As shown in Fig. 1, the power conversion device 10 includes a main circuit unit 12 and a control device 14. The main circuit unit 12 is connected to a DC power source 2 and a load 4. The DC power source 2 is, for example, another power conversion device that converts AC power supplied from a power system into DC power. The DC power source 2 may be, for example, a distributed power source that outputs DC power, such as a solar panel. The DC power source 2 may be any device that can supply DC power to the main circuit unit 12. More specifically, the load 4 is an AC load.

[0011] The main circuit unit 12 converts the DC power supplied from the DC power source 2 into AC power corresponding to the load 4, and supplies the converted AC power to the load 4. The power conversion device 10 performs an independent operation in which it supplies power from the main circuit unit 12 to the load 4 independently, without being connected to a power grid.

[0012] The main circuit unit 12 includes, for example, a plurality of converters 20 and a plurality of transformers 22. The plurality of converters 20 includes, for example, a pair of DC input terminals 20a, 20b and a pair of AC output terminals 20c, 20d. The plurality of transformers 22 includes a primary winding 22a and a secondary winding 22b.

[0013] A pair of DC input terminals 20a, 20b of each of the converters 20 is connected to the DC power source 2. In other words, a pair of DC input terminals 20a, 20b of each of the converters 20 is connected in parallel. Thus, DC power supplied from the DC power source 2 is input to each of the converters 20.

[0014] A pair of AC output terminals 20c, 20d of each of the multiple converters 20 is connected to a primary winding 22a of each of the multiple transformers 22. More specifically, one AC output terminal 20c of the converter 20 is connected to one end of the primary winding 22a, and the other AC output terminal 20d of the converter 20 is connected to the other end of the primary winding 22a. In this case, the number of the multiple transformers 22 is the same as the number of the multiple converters 20.

[0015] The converters 20 convert the DC power supplied from the DC power source 2 into AC power, and output the converted AC power to a primary winding 22a of a transformer 22 connected thereto.

[0016] In each of the multiple transformers 22, the secondary winding 22b is magnetically coupled to the primary winding 22a. The number of the multiple secondary windings 22b is the same as the number of the multiple primary windings 22a. However, the number of the multiple secondary windings 22b does not necessarily have to be the same as the number of the multiple primary windings 22a.

[0017] The secondary windings 22b of the multiple transformers 22 are connected in series. One end of the multiple secondary windings 22b connected in series is connected to one terminal of the load 4. The other end of the multiple secondary windings 22b connected in series is connected to the other terminal of the load 4. In this manner, the power conversion device 10 (main circuit unit 12) is connected to the load 4 via the secondary windings 22b of the multiple transformers 22.

[0018] The multiple converters 20 convert the DC power supplied from the DC power source 2 into AC power and output the converted AC power to a primary winding 22a of a transformer 22. The multiple transformers 22 serially combine the AC power (voltage) output from the multiple converters 20 via a secondary winding 22b. The voltage across both ends of the multiple secondary windings 22b connected in series (the voltage input to the load 4) is the sum of the voltages output from each of the multiple secondary windings 22b. The multiple transformers 22 supply the combined AC power to the load 4.

[0019] The multiple converters 20 convert, for example, DC power supplied from the DC power source 2 into single-phase AC power. The main circuit unit 12 supplies single-phase AC power to the load 4, for example, by serially combining the AC powers output from the multiple converters 20 using secondary windings 22b of the multiple transformers 22. The main circuit unit 12 is, for example, a power conversion device having a transformer series multiplexing configuration using the multiple converters 20 and the multiple transformers 22. The AC power of the load 4 is, for example, single-phase AC power.

[0020] However, the AC power of the load 4 may be three-phase AC power or the like. The main circuit unit 12 may be configured to supply three-phase AC power to the load 4 by providing, for example, a plurality of converters 20 and a plurality of transformers 22 for three phases.

[0021] The control device 14 controls the operation of the main circuit unit 12. More specifically, the control device 14 controls the operation of converting DC power to AC power by the main circuit unit 12. The control device 14 controls the operation of each of the multiple converters 20 to convert DC power to AC power.

[0022] The main circuit unit 12 further has voltage detectors 30, 32 and a current detector 34. The voltage detector 30 detects the magnitude of the DC voltage of the DC power supplied from the DC power source 2 to the main circuit unit 12 (each converter 20), and inputs a detection signal indicating the detection result of the magnitude of the DC voltage to the control device 14. The voltage detector 32 detects the magnitude of the AC voltage of the AC power supplied from the main circuit unit 12 to the load 4, and inputs a detection signal indicating the detection result of the magnitude of the AC voltage to the control device 14. The current detector 34 detects the magnitude of the AC current of the AC power supplied from the main circuit unit 12 to the load 4, and inputs a detection signal indicating the detection result of the magnitude of the AC current to the control device 14.

[0023] FIG. 2 is a circuit diagram illustrating a converter according to an embodiment. As shown in FIG. 2, each converter 20 includes a number of switching elements 40, a number of rectifying elements 42, and a charge storage element 44.

[0024] Each converter 20 has, for example, four full-bridge-connected switching elements 40 and four rectifier elements 42 connected in anti-parallel to each switching element 40. Both ends of the four switching elements 40 are connected to a pair of DC input terminals 20a, 20b. A connection point between two switching elements 40 connected in series is connected to an AC output terminal 20c. A connection point between two other switching elements 40 connected in series is connected to an AC output terminal 20d.

[0025] Each switching element 40 has a pair of main terminals and a control terminal. The control terminal is used to switch between an ON state in which a current flows between the main terminals and an OFF state in which substantially no current flows between the main terminals. Each switching element 40 is, for example, a self-extinguishing element such as a GTO (Gate Turn Off thyristor) or an IGBT (Insulated Gate Bipolar Transistor). The control terminal is, for example, a gate terminal. Each rectifying element 42 is, for example, a diode.

[0026] The charge storage element 44 is connected between the pair of DC input terminals 20a, 20b. In other words, the charge storage element 44 is connected in parallel to each switching element 40. The charge storage element 44 suppresses, for example, fluctuations in the DC voltage input to the pair of DC input terminals 20a, 20b. The charge storage element 44 is, for example, a capacitor.

[0027] Each converter 20 converts the DC power supplied from the DC power source 2 into AC power by switching of each switching element 40. In this example, each converter 20 converts the DC power supplied from the DC power source 2 into single-phase AC power by switching of each switching element 40.

[0028] Each converter 20 further includes a current detector 46. The current detector 46 detects the magnitude of the AC current of the AC power output from the converter 20, and inputs a detection signal indicating the detection result of the magnitude of the AC current to the control device 14. In other words, the current detector 46 detects the magnitude of a part of the AC current of the AC power supplied from the main circuit unit 12 to the load 4.

[0029] The control device 14 controls the operation of each of the multiple converters 20 converting DC power into AC power based on detection signals input from each of the voltage detectors 30, 32, the current detector 34, and each current detector 46. The control device 14 generates control signals for controlling the switching of each switching element 40 of each converter 20 based on each detection signal, and controls the operation of each converter 20 by inputting the generated control signals to each converter 20. In other words, the control device 14 controls the operation of the main circuit unit 12 based on each detection signal.

[0030] FIG. 3 is a block diagram illustrating a control device according to the embodiment. As shown in FIG. 3, the control device 14 includes a calculator 50, a filter circuit 51, a voltage controller 52, and an inverse dq transformation circuit 53.

[0031] A detection signal indicating the magnitude of the AC voltage of the main circuit unit 12 detected by the voltage detector 32 is input to the calculator 50. The calculator 50 multiplies the input detection signal by a predetermined coefficient to standardize (normalize) the detected magnitude of the AC voltage of the main circuit unit 12, and inputs the normalized magnitude of the AC voltage of the main circuit unit 12 to the filter circuit 51.

[0032] The filter circuit 51 performs a process of suppressing noise superimposed on the input AC voltage of the main circuit unit 12. Then, the filter circuit 51 inputs the AC voltage of the main circuit unit 12 after the noise suppression process to the voltage controller 52.

[0033] The filter circuit 51 is, for example, a bandpass filter that transmits frequency components in a predetermined bandwidth including the fundamental frequency of the AC voltage of the main circuit unit 12 and attenuates frequency components outside the bandwidth. The fundamental frequency of the AC voltage of the main circuit unit 12 is, for example, 50 Hz or 60 Hz.

[0034] The filter circuit 51 suppresses, for example, noise superimposed on the AC voltage due to switching of the switching element 40 of each converter 20. The bandwidth of the filter circuit 51 may be set, for example, so as to suppress noise due to switching of the switching element 40. In other words, the filter circuit 51 attenuates the switching frequency component of the switching element 40 superimposed on the AC voltage of the main circuit unit 12. The switching frequency of the switching element 40 is higher than the fundamental frequency of the AC voltage. Therefore, the filter circuit 51 is not limited to a band-pass filter, and may be, for example, a low-pass filter that passes frequency components equal to or lower than the fundamental frequency of the AC voltage and attenuates frequency components higher than the fundamental frequency of the AC voltage. The filter circuit 51 may be configured in any manner that can appropriately suppress noise superimposed on the AC voltage of the main circuit unit 12.

[0035] The voltage controller 52 receives the AC voltage of the main circuit unit 12 after noise suppression, and also receives a voltage reference for the AC voltage of the main circuit unit 12. Based on the AC voltage of the main circuit unit 12 input from the filter circuit 51 and the voltage reference, the voltage controller 52 calculates a voltage command value for the d-axis component of the AC voltage of the main circuit unit 12 for outputting an AC voltage of a certain magnitude according to the voltage reference from the main circuit unit 12. The voltage controller 52 is, for example, an automatic voltage regulator (AVR). The voltage controller 52 inputs the calculated voltage command value for the d-axis component to an inverse dq transformation circuit 53.

[0036] The control device 14 further includes a calculator 54 , an average value calculation circuit 55 , an overcurrent suppression control unit 56 , and a phase generation circuit 57 .

[0037] The calculator 54 receives detection signals indicating the magnitude of the AC current of each converter 20 detected by the current detectors 46 provided in each of the multiple converters 20. The calculator 54 multiplies each of the input detection signals by a predetermined coefficient to standardize (normalize) the detected magnitude of the AC current of each converter 20, and inputs the normalized magnitude of the AC current of each converter 20 to an average value calculation circuit 55.

[0038] The average value calculation circuit 55 calculates the average value of the magnitude of the normalized AC currents of each of the multiple converters 20 input from the calculator 54 , and inputs the calculated average value to the overcurrent suppression control unit 56 .

[0039] The overcurrent suppression control unit 56 determines the reduction rate of the voltage command value of the d-axis component calculated by the voltage controller 52 based on the input average value, and inputs the determined reduction rate to the voltage controller 52 .

[0040] The phase generation circuit 57 receives the setting of the frequency of the AC voltage output from the main circuit unit 12. In other words, information on the fundamental frequency of the AC voltage output from the main circuit unit 12 is input to the phase generation circuit 57. Based on the input frequency setting, the phase generation circuit 57 calculates the phases sin θ and cos θ of the AC voltage output from the main circuit unit 12, and inputs the calculated phases sin θ and cos θ to the inverse dq transformation circuit 53.

[0041] The inverse dq transformation circuit 53 receives the voltage command value of the d-axis component from the voltage controller 52, and the phases sin θ and cos θ from the phase generation circuit 57, as well as the voltage command value of the q-axis component of the AC voltage of the main circuit unit 12. The voltage command value of the q-axis component is set to a constant value, for example. The voltage command value of the q-axis component is 0, for example.

[0042] The inverse dq transformation circuit 53 performs an inverse dq transformation (inverse Park transformation) based on the input voltage command value of the d-axis component, the voltage command value of the q-axis component, and the phases sin θ and cos θ to transform the voltage command value in the rotating coordinate system into a voltage command value in the orthogonal two-axis coordinate system. The inverse dq transformation circuit 53 outputs the converted voltage command value as a reference voltage command value.

[0043] The control device 14 further includes calculators 60, 61, a divider 62, a plurality of subtractors 63a-63n, a plurality of limiters 64a-64n, a control signal generating circuit 65, calculators 66, 67, and a bias magnetism suppression control unit 68. The plurality of subtractors 63a-63n and the plurality of limiters 64a-64n are provided corresponding to the plurality of converters 20, respectively. The number of the plurality of subtractors 63a-63n and the number of the plurality of limiters 64a-64n is the same as the number of the plurality of converters 20.

[0044] A detection signal indicating the magnitude of the DC voltage of the DC power supply 2 detected by the voltage detector 30 is input to the calculator 60. The calculator 60 standardizes (normalizes) the magnitude of the detected DC voltage by multiplying the input detection signal by a predetermined coefficient, and inputs the standardized magnitude of the DC voltage of the DC power supply 2 to a divider 62.

[0045] The reference voltage command value calculated by the inverse dq transformation circuit 53 is input to the calculator 61. The calculator 61 multiplies the input reference voltage command value by a predetermined coefficient, and inputs the multiplied voltage command value to the divider 62.

[0046] Divider 62 divides the reference voltage command value input from calculator 61 by the magnitude of the DC voltage of DC power supply 2 input from calculator 60, thereby correcting the reference voltage command value in accordance with the magnitude of the DC voltage of DC power supply 2. Divider 62 inputs the corrected reference voltage command value to each of a plurality of subtractors 63a to 63n.

[0047] Similar to the calculator 54, the calculator 66 multiplies each of the multiple detection signals detected by the current detectors 46 provided in each of the multiple converters 20 by a predetermined coefficient, thereby standardizing (normalizing) the magnitude of the detected AC current of each converter 20, and inputs the normalized magnitude of the AC current of each converter 20 to the bias magnetization suppression control unit 68.

[0048] A detection signal indicating the magnitude of the AC current in the main circuit unit 12 detected by the current detector 34 is input to the calculator 67. The calculator 67 multiplies the input detection signal by a predetermined coefficient to standardize (normalize) the detected magnitude of the AC current in the main circuit unit 12, and inputs the normalized magnitude of the AC current in the main circuit unit 12 to the bias magnetism suppression control unit 68.

[0049] The magnetic bias suppression control unit 68 controls the operation of the multiple converters 20 so that the DC current component flowing through the multiple transformers 22 becomes zero, thereby calculating correction values ​​for the voltage command values ​​for suppressing magnetic bias in the cores of the multiple transformers 22. The magnetic bias suppression control unit 68 calculates correction values ​​for the multiple voltage command values ​​corresponding to the multiple converters 20, respectively, based on the magnitude of the AC current of the multiple converters 20 input from the calculator 66 and the magnitude of the AC current of the main circuit unit 12 input from the calculator 67. The magnetic bias suppression control unit 68 inputs the calculated correction values ​​to multiple subtractors 63a to 63n corresponding to the multiple converters 20, respectively.

[0050] The multiple subtractors 63a to 63n subtract the correction value input from the bias magnetization suppression control unit 68 from the reference voltage command value input from the divider 62, and correct the reference voltage command value to generate multiple voltage command values ​​corresponding to the multiple converters 20. The multiple subtractors 63a to 63n input the generated voltage command values ​​to the multiple limiters 64a to 64n.

[0051] The limiters 64a to 64n set upper and lower limits for the voltage command value. When the input voltage command value is equal to or greater than the upper limit value, the limiters 64a to 64n limit the voltage command value to the upper limit value. When the input voltage command value is equal to or less than the lower limit value, the limiters 64a to 64n limit the voltage command value to the lower limit value. The limiters 64a to 64n input the processed voltage command value to the control signal generating circuit 65.

[0052] A plurality of voltage command values ​​corresponding to the plurality of converters 20 are input to the control signal generating circuit 65, and a carrier signal is also input to the control signal generating circuit 65. The carrier signal is, for example, a triangular wave signal having a frequency higher than the frequency of the AC voltage output from the main circuit unit 12 (each converter 20). In other words, the carrier signal is a carrier wave.

[0053] The control signal generating circuit 65 generates a control signal for controlling the switching of each switching element 40 of each converter 20 by comparing the voltage command value with the carrier signal. For example, the control signal generating circuit 65 generates a control signal for turning on the switching element 40 when the voltage command value is larger than the carrier signal, and for turning off the switching element 40 when the voltage command value is smaller than the carrier signal. The control signal generating circuit 65 controls the operation of each converter 20 by inputting the generated control signal to each converter 20. For example, the control signal generating circuit 65 generates a control signal (pulse signal) for controlling the switching of each switching element 40 of each converter 20 by PWM (Pulse Width Modulation) control.

[0054] In this way, the control signal generating circuit 65 generates a control signal for controlling the operation of the main circuit unit 12 based on the voltage command value calculated by the voltage controller 52. More specifically, the control signal generating circuit 65 generates a control signal for controlling the operation of the main circuit unit 12 based on the voltage command value calculated by the voltage controller 52 and subjected to predetermined processing by the inverse dq transformation circuit 53, the calculator 61, the divider 62, the plurality of subtractors 63a to 63n, and the plurality of limiters 64a to 64n. The control signal generating circuit 65 inputs the generated control signal to the main circuit unit 12, thereby controlling the operation of the main circuit unit 12 based on the voltage command value. The control signal generating circuit 65 controls the operation of the main circuit unit 12 based on the voltage command value so as to output an AC voltage of a certain magnitude according to a voltage reference based on the voltage command value.

[0055] FIG. 4 is a block diagram illustrating an overcurrent suppression control unit according to the embodiment. As shown in FIG. 4, the overcurrent suppression control unit 56 includes an absolute value calculator 70, a detection circuit 71, a delay circuit 72, and a switching circuit 73.

[0056] The absolute value calculator 70 calculates the absolute value of the average value of the magnitudes of the AC currents of the multiple converters 20 input from the average value calculation circuit 55 , and inputs the calculated absolute value to a detection circuit 71 .

[0057] The absolute value of the average value of the magnitude of the AC current of the multiple converters 20 and a set value of the operation level of the overcurrent suppression control are input to the detection circuit 71. The set value of the operation level of the overcurrent suppression control is set to a value that can suppress an overcurrent of the AC current output from each converter 20.

[0058] The detection circuit 71 detects whether or not the absolute value of the average value of the magnitude of the AC currents of the multiple converters 20 inputted is equal to or greater than a set value of the operation level of the overcurrent suppression control. The detection circuit 71 inputs an output signal representing the detection result, whether or not the absolute value of the average value is equal to or greater than the set value, to the delay circuit 72.

[0059] The output signal has, for example, a detection state indicating that the absolute value of the average value is equal to or greater than a set value, and a non-detection state indicating that the absolute value of the average value is less than the set value. For example, the detection circuit 71 has a high state (a state corresponding to a logical "1") as the detection state, and a low state (a state corresponding to a logical "0") as the non-detection state. However, the detection state and non-detection state are not limited to the above, and may be any state that can indicate whether the absolute value of the average value is equal to or greater than a set value.

[0060] The delay circuit 72 performs a process of delaying the timing of switching the output signal input from the detection circuit 71 from a detection state to a non-detection state. The delay circuit 72 is, for example, an off-delay circuit that delays the timing of switching from a high state to a low state. The delay circuit 72 inputs the processed output signal to a switching circuit 73.

[0061] The switching circuit 73 switches the reduction rate of the voltage command value of the d-axis component to be input to the voltage controller 52 in response to the output signal input from the delay circuit 72. When the output signal input from the delay circuit 72 is in the non-detection state, the switching circuit 73 inputs the reduction rate for normal operation to the voltage controller 52. When the output signal input from the delay circuit 72 is in the detection state, the switching circuit 73 inputs the reduction rate for suppression to the voltage controller 52.

[0062] The reduction rate during normal operation is, for example, “1.” The reduction rate during suppression is, for example, “0.5.” In other words, the reduction rate is a coefficient for the voltage command value of the d-axis component.

[0063] In this way, for example, when the absolute value of the average value of the magnitudes of the AC currents of the multiple converters 20 is less than the set value of the operation level of the overcurrent suppression control, the overcurrent suppression control unit 56 inputs the reduction rate during normal operation to the voltage controller 52 so that the voltage command value of the d-axis component calculated based on the AC voltage of the main circuit unit 12 and the voltage reference is input as is to the inverse dq transformation circuit 53. Then, for example, when the absolute value of the average value of the magnitudes of the AC currents of the multiple converters 20 is equal to or greater than the set value of the operation level of the overcurrent suppression control, the overcurrent suppression control unit 56 inputs the reduction rate during suppression to the voltage controller 52 so that the voltage command value of the d-axis component calculated based on the AC voltage of the main circuit unit 12 and the voltage reference is input to the inverse dq transformation circuit 53 in a state reduced based on the reduction rate during suppression.

[0064] As a result, when an inrush current or the like occurs in the load 4, for example, the AC voltage output from each converter 20 can be temporarily lowered, and it is possible to prevent an overcurrent from occurring in the AC current output from each converter 20. As a result, it is possible to prevent the main circuit unit 12 from stopping operation due to the occurrence of an overcurrent, for example, and it is possible to make it easier to continue the operation of the main circuit unit 12.

[0065] FIG. 5 is a block diagram illustrating a voltage controller according to an embodiment. As shown in FIG. 5, the voltage controller 52 includes a voltage soft-start circuit 80, a multiplier 81, a subtractor 82, an effective value detection circuit 83, a multiplier 84, an arithmetic unit 85, a switching circuit 86, an adder 87, and a limiter 88.

[0066] The voltage soft start circuit 80 enables a soft start operation to be performed, such as when the main circuit section 12 starts to operate, to gradually increase the magnitude of the AC voltage output from the main circuit section 12 (each converter 20).

[0067] The voltage soft start circuit 80 has an integrator 80a. A fixed value of a voltage soft start coefficient is set in the integrator 80a. The integrator 80a also receives the reduction rate of the voltage command value of the d-axis component input from the overcurrent suppression control unit 56, and a switching signal for switching between execution and stop of the soft start operation.

[0068] The fixed value of the voltage soft start coefficient is set to, for example, "1". The reduction rate of the voltage command value of the d-axis component is set to, for example, the upper output limit of the integrator 80a. The lower output limit of the integrator 80a is set to, for example, "0". For example, when the reduction rate of the voltage command value of the d-axis component is set to "1" (reduction rate during normal operation), the integrator 80a gradually increases the output from "0" to "1". And, for example, when the reduction rate of the voltage command value of the d-axis component is set to "0.5" (reduction rate during suppression), the integrator 80a limits the output to "0.5".

[0069] When the switching signal is in a state representing the execution of the soft start operation, the integrator 80a performs the process of gradually increasing the output as described above. When the switching signal is in a state representing the stop of the soft start operation, the integrator 80a outputs, for example, zero. The switching signal is input to the integrator 80a from, for example, another control unit in the control device 14 or an external controller.

[0070] The integrator 80a inputs its output signal to a multiplier 81 and a multiplier 84. The multiplier 81 receives the output signal of the integrator 80a and a voltage reference of the AC voltage of the main circuit unit 12. The multiplier 81 corrects the voltage reference by multiplying the output signal of the integrator 80a. The multiplier 81 inputs the corrected voltage reference to a subtractor 82 and an adder 87.

[0071] In this way, by multiplying the voltage reference by the output signal of the integrator 80a and correcting the voltage reference, during the soft start period in which the integrator 80a (voltage soft start circuit 80) gradually increases the magnitude of the output signal, the magnitude of the corrected voltage reference also gradually increases. When the reduction rate of the voltage command value of the d-axis component becomes the reduction rate during suppression, the magnitude of the corrected voltage reference is also reduced based on the reduction rate during suppression. This temporarily reduces the AC voltage output from the main circuit unit 12, and suppresses the occurrence of an overcurrent in the AC current output from each converter 20.

[0072] The effective value detection circuit 83 receives the AC voltage of the main circuit unit 12 after noise suppression processing has been performed by the filter circuit 51. The effective value detection circuit 83 calculates the effective value of the input AC voltage of the main circuit unit 12, and inputs the calculated effective value to the subtractor 82.

[0073] The subtractor 82 calculates the difference between the corrected voltage reference input from the multiplier 81 and the effective value of the AC voltage of the main circuit unit 12 input from the effective value detection circuit 83. The voltage reference of the AC voltage of the main circuit unit 12 input to the multiplier 81 is, for example, a voltage reference representing the effective value of the AC voltage output from the main circuit unit 12. In other words, the subtractor 82 calculates the difference between the effective value of the AC voltage to be output from the main circuit unit 12 and the effective value of the current AC voltage of the main circuit unit 12 detected by the voltage detector 32. The subtractor 82 inputs the calculated difference to the multiplier 84.

[0074] The multiplier 84 corrects the difference by multiplying the difference input from the subtractor 82 by the output signal of the integrator 80a. The multiplier 84 inputs the corrected difference to the calculator 85.

[0075] The calculator 85 calculates a correction value of the AC voltage based on the inputted corrected difference for outputting an AC voltage having a magnitude according to the voltage reference from the main circuit unit 12. The calculator 85 calculates the correction value from the difference, for example, by a proportional integral calculation (PI control, PD control, PID control, etc.). However, the calculation of the calculator 85 is not limited to this, and any calculation that can appropriately calculate a correction value may be used. The calculator 85 inputs the calculated correction value to the switching circuit 86.

[0076] The correction value calculated by the calculator 85 is input to the switching circuit 86, and a switching signal for switching between execution and stop of the voltage control operation by the voltage controller 52 is also input. When the switching signal is in a state representing execution of the voltage control operation, the switching circuit 86 inputs the correction value input from the calculator 85 to the adder 87. On the other hand, when the switching signal is in a state representing stop of the voltage control operation, the switching circuit 86 inputs, for example, "0" to the adder 87. The switching signal is input to the switching circuit 86 from, for example, another control unit in the control device 14 or an external controller.

[0077] A switching signal for switching between execution and stop of the voltage control operation is input to the switching circuit 86 and also to the calculator 85. For example, the calculator 85 calculates a correction value when the switching signal is in a state representing execution of the voltage control operation, and does not calculate a correction value when the switching signal is in a state representing stop of the voltage control operation.

[0078] The adder 87 adds the input from the switching circuit 86 to the corrected voltage reference input from the multiplier 81, and inputs the addition result to the limiter 88. More specifically, when the switching signal is in a state representing the execution of the voltage control operation, the adder 87 adds the correction value input from the switching circuit 86 to the voltage reference input from the multiplier 81, and inputs the addition result to the limiter 88. This makes it possible to correct the voltage reference so that an AC voltage having a magnitude according to the voltage reference is output from the main circuit unit 12. Then, when the switching signal is in a state representing the stop of the voltage control operation, the adder 87 adds "0" to the voltage reference input from the multiplier 81, and inputs the addition result to the limiter 88. In other words, when the switching signal is in a state representing the stop of the voltage control operation, the adder 87 inputs the voltage reference input from the multiplier 81 as it is to the limiter 88.

[0079] The limiter 88 sets an upper limit and a lower limit for the voltage reference input from the adder 87. When the voltage reference input from the adder 87 is equal to or greater than the upper limit, the limiter 88 limits the voltage reference to the upper limit, and when the voltage reference input from the adder 87 is equal to or less than the lower limit, the limiter 88 limits the voltage reference to the lower limit. The limiter 88 outputs the processed voltage reference as a voltage command value for the d-axis component of the AC voltage of the main circuit unit 12.

[0080] For example, as described above, based on the AC voltage of the main circuit unit 12 input from the filter circuit 51 and the voltage reference, the voltage controller 52 calculates a voltage command value of the d-axis component of the AC voltage of the main circuit unit 12 for outputting an AC voltage having a magnitude according to the voltage reference from the main circuit unit 12. However, the method of calculating the voltage command value by the voltage controller 52 is not limited to the above, and any calculation method capable of appropriately calculating the voltage command value may be used.

[0081] 6(a) to 6(c) are block diagrams each showing a schematic example of the operation of the control device according to the embodiment. FIG. 6( a ) shows an example of the absolute value of the average value of the magnitude of the AC currents of the multiple converters 20 calculated by the absolute value calculator 70 of the overcurrent suppression control unit 56 . FIG. 6B illustrates an example of an output signal input from the delay circuit 72 of the overcurrent suppression control unit 56 to the switching circuit 73. As shown in FIG. FIG. 6(c) shows an example of a voltage command value of the d-axis component of the AC voltage of the main circuit unit 12 outputted from the voltage controller 52. In FIG.

[0082] As shown in Figures 6(a) to 6(c), when the absolute value of the average value of the magnitude of the AC currents of the multiple converters 20 is less than the set value of the operating level of the overcurrent suppression control, the reduction rate during normal operation is input from the overcurrent suppression control unit 56 to the voltage controller 52, and a voltage command value for the d-axis component of the AC voltage of the main circuit unit 12 for outputting an AC voltage of a magnitude according to the voltage reference from the main circuit unit 12 is output from the voltage controller 52 (timing t0 to t1 in Figures 6(a) to 6(c)).

[0083] When the detection circuit 71 detects that the absolute value of the average value of the magnitude of the AC current of the multiple converters 20 is equal to or greater than the set value of the operation level of the overcurrent suppression control, the output signal of the detection circuit 71 switches from a non-detection state to a detection state, and the reduction rate during suppression is input from the overcurrent suppression control unit 56 to the voltage controller 52. When the reduction rate during suppression is input from the overcurrent suppression control unit 56 to the voltage controller 52, the output signal of the integrator 80a of the voltage controller 52 is limited according to the reduction rate during suppression, so that the voltage command value of the d-axis component of the AC voltage of the main circuit unit 12 output from the voltage controller 52 is also limited according to the reduction rate during suppression. For example, when the reduction rate during suppression is set to "0.5", the voltage command value of the d-axis component of the AC voltage of the main circuit unit 12 is also limited from 1 pu (per unit) to 0.5 pu according to the reduction rate during suppression (timing t1 in FIG. 6(a) to FIG. 6(c)). In this case, for example, the effective value of the AC voltage output from the main circuit unit 12 drops from 1 pu to 0.5 pu.

[0084] As the AC voltage output from the main circuit unit 12 decreases, the AC current of the multiple converters 20 decreases, and when the absolute value of the average value of the magnitude of the AC current of the multiple converters 20 becomes less than the set value of the operation level of the overcurrent suppression control, the detection circuit 71 detects that it is less than the setting, and the output signal of the detection circuit 71 switches from a detection state to a non-detection state (timing t2 in Figures 6(a) to 6(c)).

[0085] On the other hand, even if the output signal of the detection circuit 71 switches from a detection state to a non-detection state, the state in which the reduction rate during suppression is input from the overcurrent suppression control unit 56 to the voltage controller 52 is continued for a predetermined period from the timing of the switch from the detection state to the non-detection state due to the processing of the delay circuit 72 (timings t2 to t3 in Figures 6(a) to 6(c)).

[0086] When a predetermined period of time has elapsed from the timing at which the output signal of the detection circuit 71 switches from the detection state to the non-detection state, the output signal of the delay circuit 72 also switches from the detection state to the non-detection state, and the normal reduction rate is input from the overcurrent suppression control unit 56 to the voltage controller 52 (timing t3 in Figures 6(a) to 6(c)).

[0087] When the reduction rate input to the voltage controller 52 is switched from the reduction rate during suppression to the reduction rate during normal operation, the output signal of the integrator 80a of the voltage controller 52 gradually increases from a value corresponding to the reduction rate during suppression to a value corresponding to the reduction rate during normal operation. This causes the voltage command value of the d-axis component of the AC voltage of the main circuit unit 12 to also gradually increase (timings t3 to t4 in FIG. 6(a) to FIG. 6(c)).

[0088] As described above, in the power conversion device 10 according to the present embodiment, the control device 14 includes the voltage controller 52, the overcurrent suppression control unit 56, and the control signal generation circuit 65. The voltage controller 52 calculates a voltage command value for causing the main circuit unit 12 to output an AC voltage of a certain magnitude according to a voltage reference. The control signal generation circuit 65 generates a control signal for controlling the operation of the main circuit unit 12 based on the voltage command value, and controls the operation of the main circuit unit 12 based on the voltage command value by inputting the generated control signal to the main circuit unit 12. The overcurrent suppression control unit 56 determines the reduction rate of the voltage command value calculated by the voltage controller 52 based on the magnitude of the AC current detected by the current detector 46.

[0089] The voltage controller 52 calculates a voltage command value based on the magnitude of the AC voltage detected by the voltage detector 32, the voltage reference, and the reduction rate. When the absolute value of the magnitude of the AC current is less than a set value, the overcurrent suppression control unit 56 inputs the reduction rate during normal operation to the voltage controller 52, and when the absolute value of the magnitude of the AC current is equal to or greater than the set value, the overcurrent suppression control unit 56 inputs the reduction rate during suppression to the voltage controller 52, thereby reducing the magnitude of the AC voltage output from the main circuit unit 12 compared to when the reduction rate during normal operation is input to the voltage controller 52.

[0090] As a result, in the power conversion device 10 according to the present embodiment, even when an inrush current occurs, for example, when starting to supply power to the load 4, the magnitude of the AC voltage output from the main circuit unit 12 is reduced, thereby making it possible to suppress an overcurrent of the AC current supplied from the main circuit unit 12 to the load 4. For example, it is possible to realize a state in which an equivalent system impedance exists and a voltage drop occurs due to an inrush current of the load 4.

[0091] The control device 14 stops the operation of the main circuit unit 12, for example, when the magnitude of the AC current of the AC power supplied from the main circuit unit 12 to the load 4 becomes equal to or greater than an overcurrent detection level. The overcurrent detection level is set, for example, higher than the operation level of the overcurrent suppression control. Therefore, the power conversion device 10 according to this embodiment can suppress, for example, a stop of operation caused by an overcurrent in the main circuit unit 12. Therefore, the power conversion device 10 according to this embodiment can supply power to the load 4 more stably even in an isolated operation not connected to the power grid.

[0092] In the power conversion device 10 according to this embodiment, the control device 14 further includes a filter circuit 51 that performs processing to suppress noise superimposed on the AC voltage detected by the voltage detector 32. The voltage controller 52 calculates a voltage command value based on the magnitude of the AC voltage after the processing to suppress noise has been performed by the filter circuit 51.

[0093] This makes it possible to prevent noise (ripple) superimposed on the magnitude of the detected AC voltage from making the calculation result of the voltage command value unstable and making it difficult to stably control the output voltage when calculating the voltage command value based on the magnitude of the AC voltage detected by the voltage detector 32. Therefore, even in the case of isolated operation without being connected to the power grid, power can be supplied to the load 4 more stably.

[0094] In the power conversion device 10 of this embodiment, the voltage controller 52 has an integrator 80a that performs a process to gradually increase the output, and by multiplying the output signal of the integrator 80a by a voltage reference and correcting the voltage reference, it is possible to perform a soft start operation that gradually increases the magnitude of the AC voltage output from the main circuit unit 12, and by setting the reduction rate to the output upper limit of the integrator 80a, when the reduction rate during suppression is input from the overcurrent suppression control unit 56, the magnitude of the AC voltage output from the main circuit unit 12 is reduced more than when the reduction rate during normal operation is input.

[0095] This enables a soft start operation and can suppress a sudden rise in the AC voltage supplied from the main circuit unit 12 to the load 4. For example, it is possible to make it difficult for an inrush current to occur when starting to supply power to the load 4. By setting the reduction rate to the upper output limit of the integrator 80a, it is possible to appropriately reduce the magnitude of the AC voltage output from the main circuit unit 12 in response to the input of the reduction rate during suppression, while suppressing, for example, the configuration of the voltage controller 52 from becoming complicated.

[0096] In the power conversion device 10 according to this embodiment, the overcurrent suppression control unit 56 includes a detection circuit 71, a delay circuit 72, and a switching circuit 73. The detection circuit 71 detects whether the absolute value of the magnitude of the AC current is equal to or greater than a set value, and outputs an output signal having a detection state indicating that the absolute value is equal to or greater than the set value, and a non-detection state indicating that the absolute value is less than the set value. The delay circuit 72 performs processing to delay the timing of switching the output signal from the detection state to the non-detection state. The switching circuit 73 inputs a reduction rate during normal operation to the voltage controller 52 when the output signal input from the delay circuit 72 is in the non-detection state, and inputs a reduction rate during suppression to the voltage controller 52 when the output signal input from the delay circuit 72 is in the detection state.

[0097] In this way, by delaying the timing of switching the output signal from the detection state to the non-detection state in the delay circuit 72, the period of the reduction rate during suppression input to the voltage controller 52 can be lengthened, the magnitude of the AC voltage output from the main circuit unit 12 can be more appropriately reduced, and the overcurrent of the AC current supplied from the main circuit unit 12 to the load 4 can be more appropriately suppressed. In addition, it is also possible to prevent the operation of the control device 14 from becoming unstable due to an AC current detection error or the like that occurs when the output signal of the delay circuit 72 immediately returns from the non-detection state to the detection state after switching from the detection state to the non-detection state.

[0098] In the above embodiment, the control device 14 has the filter circuit 51, the voltage controller 52, and the overcurrent suppression control unit 56. For example, the control device 14 may be configured to have only the voltage controller 52 and the overcurrent suppression control unit 56, without the filter circuit 51. The voltage controller 52 may calculate a voltage command value based on the magnitude of the AC voltage after the noise suppression process is performed by the filter circuit 51, for example, the magnitude of the AC voltage as it is detected by the voltage detector 32, or the magnitude of the AC voltage after normalization by the calculator 50.

[0099] Moreover, the control device 14 may be configured to have, for example, the filter circuit 51 and the voltage controller 52, without the overcurrent suppression control unit 56. In this case as well, as described above, it is possible to suppress the calculation result of the voltage command value from becoming unstable due to noise superimposed on the magnitude of the detected AC voltage, and it is possible to supply power to the load 4 more stably even in the case of an isolated operation not connected to the power grid.

[0100] In the above embodiment, the main circuit unit 12 has a plurality of converters 20 and a plurality of transformers 22. The configuration of the main circuit unit 12 is not limited to this, and may be any configuration capable of converting DC power supplied from the DC power source 2 into AC power corresponding to the load 4 and supplying the converted AC power to the load 4.

[0101] In the above embodiment, the voltage controller 52 calculates a voltage command value of the d-axis component of the AC voltage of the main circuit unit 12. The voltage command value calculated by the voltage controller 52 is not limited to the voltage command value of the d-axis component, and may be any voltage command value for outputting an AC voltage of a certain magnitude from the main circuit unit 12 according to a voltage reference.

[0102] In the above embodiment, the overcurrent suppression control unit 56 determines the reduction rate of the voltage command value based on the absolute value of the average value of the magnitudes of the AC currents of the multiple converters 20. The overcurrent suppression control unit 56 is not limited to this, and may determine the reduction rate of the voltage command value based on, for example, the magnitude of the AC current of the AC power supplied from the main circuit unit 12 to the load 4 detected by the current detector 34. The magnitude of the AC current used to determine the reduction rate by the overcurrent suppression control unit 56 is related to the magnitude of the AC current of the AC power supplied from the main circuit unit 12 to the load 4, and may be any magnitude of AC current that can appropriately determine the reduction rate of the voltage command value.

[0103] The present embodiment includes the following aspects. (Appendix 1) A power conversion device that performs an isolated operation to independently supply power to a load without being connected to a power grid, a main circuit unit that converts DC power supplied from a DC power source into AC power corresponding to a load and supplies the converted AC power to the load; a control device for controlling an operation of converting DC power to AC power by the main circuit unit; a current detector that detects the magnitude of an AC current of the AC power supplied from the main circuit unit to the load; a voltage detector that detects a magnitude of an AC voltage of the AC power supplied from the main circuit unit to the load; Equipped with The control device includes: a voltage controller that calculates a voltage command value for outputting an AC voltage of a constant magnitude from the main circuit unit according to a voltage reference; a control signal generating circuit that generates a control signal for controlling an operation of the main circuit unit based on the voltage command value, and inputs the generated control signal to the main circuit unit, thereby controlling the operation of the main circuit unit based on the voltage command value; an overcurrent suppression control unit that determines a reduction rate of the voltage command value calculated by the voltage controller based on the magnitude of the AC current detected by the current detector; having the voltage controller calculates the voltage command value based on the magnitude of the AC voltage detected by the voltage detector, the voltage reference, and the reduction rate; The overcurrent suppression control unit inputs the reduction rate during normal operation to the voltage controller when the absolute value of the magnitude of the AC current is less than a set value, and inputs the reduction rate during suppression to the voltage controller when the absolute value of the magnitude of the AC current is equal to or greater than the set value, thereby reducing the magnitude of the AC voltage output from the main circuit unit compared to when the reduction rate during normal operation is input to the voltage controller.

[0104] (Appendix 2) The control device further includes a filter circuit that performs processing to suppress noise superimposed on the AC voltage detected by the voltage detector, 2. The power conversion device according to claim 1, wherein the voltage controller calculates the voltage command value based on a magnitude of the AC voltage after the noise suppression process is performed by the filter circuit.

[0105] (Appendix 3) The voltage controller has an integrator that performs a process of gradually increasing an output, and by multiplying the voltage reference by an output signal of the integrator and correcting the voltage reference, a soft-start operation can be performed to gradually increase the magnitude of the AC voltage output from the main circuit unit, and by setting the reduction rate to an upper limit of the output of the integrator, when the reduction rate during suppression is input from the overcurrent suppression control unit, the magnitude of the AC voltage output from the main circuit unit is lower than when the reduction rate during normal operation is input. The power conversion device described in Appendix 1 or 2.

[0106] (Appendix 4) The overcurrent suppression control unit, a detection circuit that detects whether or not the absolute value of the magnitude of the AC current is equal to or greater than the set value, and outputs an output signal having a detection state that indicates that the absolute value is equal to or greater than the set value, and a non-detection state that indicates that the absolute value is less than the set value; a delay circuit that delays a timing at which the output signal switches from the detection state to the non-detection state; a switching circuit that inputs the reduction rate during normal operation to the voltage controller when the output signal input from the delay circuit is in the non-detection state, and inputs the reduction rate during suppression to the voltage controller when the output signal input from the delay circuit is in the detection state; 4. The power conversion device according to claim 1, further comprising:

[0107] (Appendix 5) A power conversion device that performs an isolated operation to independently supply power to a load without being connected to a power grid, a main circuit unit that converts DC power supplied from a DC power source into AC power corresponding to a load and supplies the converted AC power to the load; a control device for controlling an operation of converting DC power to AC power by the main circuit unit; a current detector that detects the magnitude of an AC current of the AC power supplied from the main circuit unit to the load; a voltage detector that detects a magnitude of an AC voltage of the AC power supplied from the main circuit unit to the load; Equipped with The control device includes: a filter circuit that performs processing to suppress noise superimposed on the AC voltage detected by the voltage detector; a voltage controller that calculates a voltage command value for outputting an AC voltage of a constant magnitude according to a voltage reference from the main circuit unit, based on the magnitude of the AC voltage after the noise suppression process is performed by the filter circuit and a voltage reference; and a control signal generating circuit that generates a control signal for controlling an operation of the main circuit unit based on the voltage command value, and inputs the generated control signal to the main circuit unit, thereby controlling the operation of the main circuit unit based on the voltage command value; A power conversion device having the following:

[0108] Although some embodiments of the present invention have been described, 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 modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0109] 2...DC power supply, 4...load, 10...power conversion device, 12...main circuit section, 14...control device, 20...converter, 22...transformer, 30, 32...voltage detector, 34...current detector, 40...switching element, 42...rectifier element, 44...charge storage element, 46...current detector, 50...computing unit, 51...filter circuit, 52...voltage controller, 53...inverse dq conversion circuit, 54...computing unit, 55...average value calculation circuit, 56...overcurrent suppression control unit, 57...phase generation circuit, 60, 61...computing unit, 62...divider, 63a to 63n...subtractor, 64a to 64n...limiter, 65...control signal generation circuit, 66, 67...computing unit, 68...bias magnetism suppression control unit, 70...absolute value calculation unit, 71...detection circuit, 72...delay circuit, 73...switching circuit, 80...voltage soft start circuit, 81...multiplier, 82...subtractor, 83...effective value detection circuit, 84...multiplier, 85...arithmetic unit, 86...switching circuit, 87...adder, 88...limiter,

Claims

1. A power conversion device that performs an isolated operation to independently supply power to a load without being connected to a power grid, a main circuit unit that converts DC power supplied from a DC power source into AC power corresponding to a load and supplies the converted AC power to the load; a control device for controlling an operation of converting DC power to AC power by the main circuit unit; a current detector that detects the magnitude of an AC current of the AC power supplied from the main circuit unit to the load; a voltage detector that detects a magnitude of an AC voltage of the AC power supplied from the main circuit unit to the load; Equipped with The control device includes: a voltage controller that calculates a voltage command value for outputting an AC voltage of a constant magnitude from the main circuit unit according to a voltage reference; a control signal generating circuit that generates a control signal for controlling an operation of the main circuit unit based on the voltage command value, and inputs the generated control signal to the main circuit unit, thereby controlling the operation of the main circuit unit based on the voltage command value; an overcurrent suppression control unit that determines a reduction rate of the voltage command value calculated by the voltage controller based on the magnitude of the AC current detected by the current detector; having the voltage controller calculates the voltage command value based on the magnitude of the AC voltage detected by the voltage detector, the voltage reference, and the reduction rate; The overcurrent suppression control unit inputs the reduction rate during normal operation to the voltage controller when the absolute value of the magnitude of the AC current is less than a set value, and inputs the reduction rate during suppression to the voltage controller when the absolute value of the magnitude of the AC current is equal to or greater than the set value, thereby reducing the magnitude of the AC voltage output from the main circuit unit compared to when the reduction rate during normal operation is input to the voltage controller.

2. The control device further includes a filter circuit that performs processing to suppress noise superimposed on the AC voltage detected by the voltage detector, The power conversion device according to claim 1 , wherein the voltage controller calculates the voltage command value based on a magnitude of the AC voltage after the noise suppression process is performed by the filter circuit.

3. 2. The power conversion device according to claim 1, wherein the voltage controller has an integrator that performs processing to gradually increase an output, and multiplies the voltage reference by an output signal of the integrator to correct the voltage reference, thereby enabling a soft-start operation to be performed to gradually increase the magnitude of the AC voltage output from the main circuit unit, and by setting the reduction rate to an upper limit of the output of the integrator, when the reduction rate during suppression is input from the overcurrent suppression control unit, the magnitude of the AC voltage output from the main circuit unit is reduced more than when the reduction rate during normal operation is input.

4. The overcurrent suppression control unit, a detection circuit that detects whether or not the absolute value of the magnitude of the AC current is equal to or greater than the set value, and outputs an output signal having a detection state that indicates that the absolute value is equal to or greater than the set value, and a non-detection state that indicates that the absolute value is less than the set value; a delay circuit that delays a timing at which the output signal switches from the detection state to the non-detection state; a switching circuit that inputs the reduction rate during normal operation to the voltage controller when the output signal input from the delay circuit is in the non-detection state, and inputs the reduction rate during suppression to the voltage controller when the output signal input from the delay circuit is in the detection state; 2. The power converter according to claim 1, further comprising:

5. A power conversion device that performs an isolated operation to independently supply power to a load without being connected to a power grid, a main circuit unit that converts DC power supplied from a DC power source into AC power corresponding to a load and supplies the converted AC power to the load; a control device for controlling an operation of converting DC power to AC power by the main circuit unit; a current detector that detects the magnitude of an AC current of the AC power supplied from the main circuit unit to the load; a voltage detector that detects a magnitude of an AC voltage of the AC power supplied from the main circuit unit to the load; Equipped with The control device includes: a filter circuit that performs processing to suppress noise superimposed on the AC voltage detected by the voltage detector; a voltage controller that calculates a voltage command value for outputting an AC voltage of a constant magnitude according to a voltage reference from the main circuit unit, based on the magnitude of the AC voltage after the noise suppression process is performed by the filter circuit and a voltage reference; a control signal generating circuit that generates a control signal for controlling an operation of the main circuit unit based on the voltage command value, and inputs the generated control signal to the main circuit unit, thereby controlling the operation of the main circuit unit based on the voltage command value; A power conversion device having the following:

Images