Power conversion device

Abstract

Provided is a power conversion device comprising: a plurality of converters that are connected in parallel with an AC circuit, are connected in parallel with a DC circuit, and perform at least one of conversion from AC power to DC power and conversion from DC power to AC power; a control circuit that controls the operation of power conversion by the plurality of converters; and a plurality of converter current detectors that each detect the magnitude of AC current flowing through each of the plurality of converters. The control circuit calculates the entire converter current total equivalent value by multiplying one converter current detection value by the number of the plurality of converters and generates a control signal for controlling the operation of the plurality of converters on the basis of the entire converter current total equivalent value. This provides the power conversion device capable of appropriately controlling the operation of the plurality of converters connected in parallel with a simpler configuration.

Description

Power Conversion Device

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

[0002] There is a power conversion device that is connected to an AC circuit and a DC circuit and performs at least one of converting AC power from the AC circuit to DC power for the DC circuit and converting DC power from the DC circuit to AC power for the AC circuit. In such a power conversion device, a plurality of converters are connected in parallel to the AC circuit and to the DC circuit. This allows the AC power from the AC circuit and the DC power from the DC circuit to be shared by the plurality of converters, and can accommodate an increase in the capacity of the power conversion device while suppressing an increase in the rated voltage and rated current required for a single converter.

[0003] In a power conversion device in which multiple converters are connected in parallel, a current detector is provided between the parallel connection point of the multiple converters and an AC circuit to detect the total AC current value flowing through the multiple converters, and the operation of the multiple converters is controlled based on the detected total AC current value. However, in a configuration in which a current detector detects a relatively large total AC current value, the configuration of the current detector becomes complicated, which is a concern as it may become a factor in increasing manufacturing costs.

[0004] Another proposed method involves providing multiple current detectors corresponding to multiple converters, detecting the AC current values ​​flowing through each converter with the multiple current detectors, and adding up the detected AC current values ​​to calculate a total AC current value. However, this configuration for calculating the total AC current value requires a circuit for calculating the total AC current value in the control circuit that controls the operation of the multiple converters. This increases the complexity of the control circuit configuration, which is also a concern as it increases manufacturing costs.

[0005] For this reason, in a power conversion device in which a plurality of converters are connected in parallel, it is desirable to be able to appropriately control the operations of the plurality of converters with a simpler configuration.

[0006] JP 2013-162679 A

[0007] The embodiments of the present invention provide a power conversion device that can appropriately control the operation of multiple converters connected in parallel with a simpler configuration.

[0008] According to an embodiment of the present invention, there is provided a power conversion device comprising: a plurality of converters connected in parallel to an AC circuit and connected in parallel to a DC circuit, and performing at least one of converting AC power in the AC circuit to DC power in the DC circuit and converting DC power in the DC circuit to AC power in the AC circuit; a control circuit for controlling the power conversion operation by the plurality of converters; and a plurality of converter current detectors provided corresponding to each of the plurality of converters, detecting the magnitude of the AC current flowing in each of the plurality of converters and inputting the detection result to the control circuit as a converter current detection value, wherein the control circuit multiplies any one of the plurality of converter current detection values ​​detected by the plurality of converter current detectors by the number of the plurality of converters to calculate a total converter current equivalent value that corresponds to the sum of the magnitudes of the AC currents flowing in each of the plurality of converters, generates a control signal for controlling the operation of the plurality of converters based on the total converter current equivalent value, and inputs the control signal to each of the plurality of converters, thereby controlling the power conversion operation by the plurality of converters.

[0009] According to an embodiment of the present invention, a power conversion device is provided that can appropriately control the operations of multiple converters connected in parallel with a simpler configuration.

[0010] 1 is a block diagram schematically showing a power conversion device according to an embodiment; FIG. 2 is a block diagram schematically showing a converter according to an embodiment; FIG. 3 is a block diagram schematically showing a control circuit according to an embodiment; FIG. 4 is a block diagram schematically showing a modified example of a power conversion device according to an embodiment; and FIG. 5 is a block diagram schematically showing a modified example of a control circuit according to an embodiment.

[0011] 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 those in reality. Even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In this specification and each drawing, elements similar to those previously described with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0012] 1 is a block diagram illustrating a power conversion device according to an embodiment. As illustrated in FIG. 1, a power conversion device 10 includes a plurality of converters 12 and a control circuit 14.

[0013] The plurality of converters 12 are provided between the AC circuit 2 and the DC circuit 4. The plurality of converters 12 are connected in parallel to the AC circuit 2 and connected in parallel to the DC circuit 4. The plurality of converters 12 perform at least one of conversion from AC power of the AC circuit 2 to DC power of the DC circuit 4 and conversion from DC power of the DC circuit 4 to AC power of the AC circuit 2.

[0014] In this way, by connecting multiple converters 12 in parallel, the AC power of the AC circuit 2 and the DC power of the DC circuit 4 can be shared among multiple converters 12, and the power conversion device 10 can accommodate an increase in capacity while suppressing an increase in the rated voltage and rated current required for one converter 12.

[0015] The AC circuit 2 is, for example, an AC power system. The AC power of the AC circuit 2 is, for example, three-phase AC power. However, the AC power of the AC circuit 2 is not limited to three-phase AC power and may be single-phase AC power or the like. The AC power of the AC circuit 2 may be any AC power. Furthermore, the AC circuit 2 is not limited to a power system and may be, for example, another AC power source or an AC load. The DC circuit 4 is, for example, a DC load. The DC circuit 4 may be, for example, a DC power source or the like.

[0016] The control circuit 14 controls the power conversion operation of the multiple converters 12. The control circuit 14 controls the power conversion operation of the multiple converters 12 by inputting the same control signal to each of the multiple converters 12 and causing the multiple converters 12 to perform substantially the same operation. Therefore, the rated outputs of the multiple converters 12 are, for example, substantially the same. In other words, the magnitude of the DC power and the magnitude of the AC power output by each of the multiple converters 12 are substantially the same.

[0017] The power conversion device 10 further includes a filter circuit 16. The filter circuit 16 is provided between the AC circuit 2 and parallel connection points PP1 to PP3 on the AC sides of the multiple converters 12, and suppresses noise (e.g., harmonic components) generated on the AC sides of the multiple converters 12 as the multiple converters 12 convert power. In other words, the filter circuit 16 suppresses noise superimposed on the AC power supplied from the AC circuit 2 to the multiple converters 12 and on the AC power supplied from the multiple converters 12 to the AC circuit 2. In this way, the filter circuit 16 makes the AC power between the multiple converters 12 and the AC circuit 2 closer to a sine wave, for example.

[0018] For example, when the AC power of the AC circuit 2 is three-phase AC power, the filter circuit 16 has three filter units corresponding to each phase of the three-phase AC power of the AC circuit 2. The filter units are, for example, series-connected elements in which a resistor, a reactor, and a capacitor are connected in series. The three filter units (series-connected elements) are, for example, star-connected between each phase of the three-phase AC power of the AC circuit 2. However, the configuration of the filter circuit 16 is not limited to this, and any configuration that can appropriately suppress noise generated on the AC sides of the multiple converters 12 may be used.

[0019] Moreover, the power conversion device 10 further includes AC voltage detectors 20a to 20c, filter current detectors 22a to 22c, a DC voltage detector 24, a plurality of converter current detectors 26a to 26c, and a plurality of reactors 27a to 27c.

[0020] The AC voltage detectors 20a to 20c detect the magnitude of the AC voltage of the AC circuit 2 and input the detection results as AC voltage detection values ​​to the control circuit 14. For example, when the AC power of the AC circuit 2 is three-phase AC power, the AC voltage detectors 20a to 20c detect the magnitude of the phase voltage of each phase of the three-phase AC power of the AC circuit 2 and input the detected value of the magnitude of the phase voltage of each phase to the control circuit 14 as the AC voltage detection value.

[0021] The filter current detectors 22a to 22c detect the magnitude of the AC current flowing through the filter circuit 16 and input the detection results as filter current detection values ​​to the control circuit 14. For example, when the AC power of the AC circuit 2 is three-phase AC power, the filter current detectors 22a to 22c detect the magnitude of the AC current flowing through each of the three filter units of the filter circuit 16 and input each detection value to the control circuit 14 as a filter current detection value.

[0022] The DC voltage detector 24 detects the magnitude of the DC voltage of the DC circuit 4 and inputs the detection result to the control circuit 14 as a DC voltage detection value.

[0023] The multiple converter current detectors 26a to 26c are provided corresponding to the multiple converters 12, respectively. In other words, the multiple converter current detectors 26a to 26c are provided between the multiple converters 12 and parallel connection points PP1 to PP3 on the AC sides of the multiple converters 12. The multiple converter current detectors 26a to 26c detect the magnitude of the AC current flowing through each of the multiple converters 12 and input the detection results as converter current detection values ​​to the control circuit 14. For example, when the AC power of the AC circuit 2 is three-phase AC power, the multiple converter current detectors 26a to 26c detect the magnitude of the line current of each phase of the three-phase AC current flowing through the converter 12 and input the detected value of the magnitude of the line current of each phase to the control circuit 14 as the converter current detection value.

[0024] The multiple reactors 27a to 27c are provided in series with the converter current detectors 26a to 26c between the parallel connection points PP1 to PP3 and the multiple converters 12, respectively. The multiple reactors 27a to 27c suppress current changes due to switching of the multiple converters 12, while suppressing current imbalances due to variations in the characteristics of the multiple converters 12 that operate in response to the same control signal.

[0025] The control circuit 14 generates control signals based on the input system voltage detection value, filter current detection value, DC voltage detection value, and multiple converter current detection values ​​corresponding to the multiple converters 12, and controls the power conversion operation of the multiple converters 12 by inputting the generated control signals to the multiple converters 12. The generated control signals control the on / off of the multiple switching elements 33a to 33c, 34a to 34c, 35a to 35c, and 36a to 36c, and the control circuit 14 inputs the same control signal to the multiple converters 12.

[0026] 2 is a block diagram illustrating a converter according to an embodiment. As illustrated in FIG. 2, the converter 12 includes a positive potential terminal 30a, a negative potential terminal 30b, a neutral terminal 30c, multiple AC terminals 31a-31c, two charge storage elements 32a and 32b, multiple switching elements 33a-33c, 34a-34c, 35a-35c, and 36a-36c, and multiple rectifying elements 37a-37c, 38a-38c, 39a-39c, and 40a-40c.

[0027] The converters 12 are connected to the DC circuit 4 via a positive potential terminal 30a and a negative potential terminal 30b. The positive potential terminal 30a is connected to a high potential terminal of the DC circuit 4. The negative potential terminal 30b is connected to a low potential terminal of the DC circuit 4. In this way, the multiple converters 12 are connected in parallel to the DC circuit 4.

[0028] The converter 12 is connected to the AC circuit 2 via a plurality of AC terminals 31 a to 31 c. When the AC power of the AC circuit 2 is three-phase AC power, the converter 12 has three AC terminals 31 a to 31 c corresponding to the respective phases of the three-phase AC power of the AC circuit 2. When the AC power of the AC circuit 2 is single-phase AC power, the converter 12 has two AC terminals. In this way, the number of AC terminals may be set appropriately depending on the AC power of the AC circuit 2.

[0029] The AC terminal 31a is connected to the AC circuit 2 via a parallel connection point PP1. The AC terminal 31b is connected to the AC circuit 2 via a parallel connection point PP2. The AC terminal 31c is connected to the AC circuit 2 via a parallel connection point PP3. As a result, the multiple converters 12 are connected in parallel to the AC circuit 2.

[0030] The potential of the neutral terminal 30c is set to a potential intermediate between the potential of the positive potential terminal 30a and the potential of the negative potential terminal 30b, for example, to a potential that is substantially half the potential of the positive potential terminal 30a and the potential of the negative potential terminal 30b.

[0031] The charge storage element 32a is provided between the positive potential terminal 30a and the neutral terminal 30c. The charge storage element 32b is provided between the neutral terminal 30c and the negative potential terminal 30b. The capacitances of the pair of charge storage elements 32a, 32b are substantially the same. This allows the potential of the neutral terminal 30c to be set to a potential that is substantially half the potential of the positive potential terminal 30a and the negative potential terminal 30b.

[0032] However, the method for setting the potential of the neutral terminal 30c is not limited to the above, and any method may be used that can appropriately set the potential to an intermediate potential between the positive potential terminal 30a and the negative potential terminal 30b. Furthermore, the potential of the neutral terminal 30c is not limited to a potential that is exactly half the potential of the positive potential terminal 30a and the negative potential terminal 30b, and may include, for example, manufacturing errors due to variations in the capacitance of the charge storage elements 32a, 32b. The potential of the neutral terminal 30c may be set to an intermediate potential between the positive potential terminal 30a and the negative potential terminal 30b, and may be any potential that allows the converter 12 to appropriately perform power conversion.

[0033] The multiple switching elements 33a to 33c, 34a to 34c, 35a to 35c, and 36a to 36c each have a pair of main terminals and a control terminal. The multiple switching elements 33a to 33c, 34a to 34c, 35a to 35c, and 36a to 36c each have an on state and an off state. The on state is a state in which current flows between the pair of main terminals. The off state is a state in which current flow between the pair of main terminals is blocked. The multiple switching elements 33a to 33c, 34a to 34c, 35a to 35c, and 36a to 36c switch between the on state and the off state depending on the voltage between the pair of main terminals and the voltage at the control terminal. The off state does not necessarily have to be a state in which no current flows between the pair of main terminals, but may also be a state in which a weak current flows between the pair of main terminals within a range that does not affect the operation of the converter 12. The switching elements 33a to 33c, 34a to 34c, 35a to 35c, and 36a to 36c are each formed of a self-extinguishing element such as a gate turn-off thyristor (GTO) or an insulated gate bipolar transistor (IGBT). The control terminal is, for example, a gate terminal.

[0034] The switching elements 33a and 34a are connected in series between the positive potential terminal 30a and the negative potential terminal 30b so that, when the switching element 33a is in the ON state, a current flows from the positive potential terminal 30a to the AC terminal 31a, and, when the switching element 34a is in the ON state, a current flows from the AC terminal 31a to the negative potential terminal 30b. The connection point of the switching elements 33a and 34a is connected to the AC terminal 31a.

[0035] The switching elements 35a and 36a are connected in series between the connection point of the switching elements 33a and 34a and the neutral terminal 30c. The switching elements 35a and 36a are connected in series so that when they are turned on, the directions of current flow are opposite to each other.

[0036] The switching elements 33b and 34b are connected in series between the positive potential terminal 30a and the negative potential terminal 30b so that, when the switching element 33b is in the ON state, a current flows from the positive potential terminal 30a to the AC terminal 31b, and when the switching element 34b is in the ON state, a current flows from the AC terminal 31b to the negative potential terminal 30b. In other words, the switching elements 33b and 34b are provided in parallel with the switching elements 33a and 34a. The connection point of the switching elements 33b and 34b is connected to the AC terminal 31b.

[0037] The switching elements 35b and 36b are connected in series between the connection point of the switching elements 33b and 34b and the neutral terminal 30c. The switching elements 35b and 36b are connected in series so that when they are turned on, the directions of current flow are opposite to each other.

[0038] The switching elements 33c and 34c are connected in series between the positive potential terminal 30a and the negative potential terminal 30b so that when the switching element 33c is in the ON state, a current flows from the positive potential terminal 30a to the AC terminal 31c, and when the switching element 34c is in the ON state, a current flows from the AC terminal 31c to the negative potential terminal 30b. In other words, the switching elements 33c and 34c are provided in parallel with the switching elements 33a and 34a and the switching elements 33b and 34b. The connection point of the switching elements 33c and 34c is connected to the AC terminal 31c.

[0039] The switching elements 35c and 36c are connected in series between the connection point of the switching elements 33c and 34c and the neutral terminal 30c. The switching elements 35c and 36c are connected in series so that when they are turned on, the directions of current flow are opposite to each other.

[0040] The rectifying element 37a is connected in anti-parallel to the switching element 33a. The rectifying element 38a is connected in anti-parallel to the switching element 34a. The rectifying element 39a is connected in anti-parallel to the switching element 35a. The rectifying element 40a is connected in anti-parallel to the switching element 36a.

[0041] Rectifying element 37b is connected in anti-parallel to switching element 33b. Rectifying element 38b is connected in anti-parallel to switching element 34b. Rectifying element 39b is connected in anti-parallel to switching element 35b. Rectifying element 40b is connected in anti-parallel to switching element 36b.

[0042] The rectifying element 37c is connected in anti-parallel to the switching element 33c. The rectifying element 38c is connected in anti-parallel to the switching element 34c. The rectifying element 39c is connected in anti-parallel to the switching element 35c. The rectifying element 40c is connected in anti-parallel to the switching element 36c.

[0043] The direction of current flowing through the rectifying elements 37a to 37c, 38a to 38c, 39a to 39c, and 40a to 40c is opposite to the direction of current flowing between pairs of main terminals of the switching elements 33a to 33c, 34a to 34c, 35a to 35c, and 36a to 36c. The rectifying elements 37a to 37c, 38a to 38c, 39a to 39c, and 40a to 40c are so-called freewheeling diodes.

[0044] In this example, the converter 12 is a so-called neutral-point switching three-level converter. In this case, the converter 12 is capable of bidirectional conversion, that is, conversion from AC power in the AC circuit 2 to DC power in the DC circuit 4 and conversion from DC power in the DC circuit 4 to AC power in the AC circuit 2. However, the configuration of the converter 12 is not limited to this. The converter 12 may be a two-level converter, etc. The converter 12 is not limited to a configuration capable of bidirectional conversion from AC to DC and DC to AC, but may be configured to perform only AC to DC conversion or only DC to AC conversion. The converter 12 may be configured in any way that is capable of performing at least one of conversion from AC power in the AC circuit 2 to DC power in the DC circuit 4 and conversion from DC power in the DC circuit 4 to AC power in the AC circuit 2.

[0045] 3 is a block diagram schematically illustrating a control circuit according to an embodiment. As illustrated in FIG. 3, the control circuit 14 includes, for example, a multiplier 50, a dq converter 51, a current controller 52, an adder 53, a dq converter 54, a reactive power controller 55, a DC voltage controller 56, a dq converter 57, adders 58 and 59, an inverse dq converter 60, a control signal generator 61, an overcurrent detector 62, an imbalance detector 63, and an OR circuit 64.

[0046] Any one of the plurality of converter current detection values ​​detected by the plurality of converter current detectors 26 a to 26 c is input to the multiplier 50. The multiplier 50 multiplies the input converter current detection value by the number N of the plurality of converters 12 to calculate a value equivalent to the total of all converter currents, which corresponds to the total value of the magnitude of the AC currents flowing through each of the plurality of converters 12. The multiplier 50 inputs the calculated value equivalent to the total of all converter currents to a dq converter 51 and an adder 53.

[0047] The dq converter 51 performs a dq transformation (Park transformation) on the value equivalent to the sum of all converter currents, which is a three-phase AC current signal, to calculate a d-axis signal equivalent to the sum of all converter currents and a q-axis signal equivalent to the sum of all converter currents from the value equivalent to the sum of all converter currents. The d-axis signal equivalent to the sum of all converter currents represents the active current component of the AC current flowing through the multiple converters 12. The q-axis signal equivalent to the sum of all converter currents represents the reactive current component of the AC current flowing through the multiple converters 12. The dq converter 51 inputs the calculated d-axis signal equivalent to the sum of all converter currents and q-axis signal equivalent to the sum of all converter currents to the current controller 52.

[0048] The adder 53 receives an input of the total equivalent value of all converter currents, as well as the filter current detection values ​​detected by the filter current detectors 22a to 22c. The adder 53 adds the filter current detection values ​​to the input total equivalent value of all converter currents to calculate an AC current equivalent value that corresponds to the magnitude of the AC current in the AC circuit 2. The adder 53 inputs the calculated AC current equivalent value to a dq converter 54.

[0049] The dq converter 54 performs a dq transformation (Park transformation) on the AC current equivalent value, which is a three-phase AC current signal, to calculate an AC current equivalent q-axis signal from the AC current equivalent value. The AC current equivalent q-axis signal represents a reactive current component of the AC current in the AC circuit 2. The dq converter 54 inputs the calculated AC current equivalent q-axis signal to the reactive power controller 55.

[0050] The reactive power controller 55 receives the AC current equivalent q-axis signal as input, and also receives a command value (not shown) representing the magnitude of the reactive current supplied (flowed out) from the multiple converters 12 to the AC circuit 2. The reactive power controller 55, for example, calculates the difference between the reactive current command value and the AC current equivalent q-axis signal, and performs proportional control or proportional-integral control on the calculated difference to calculate a q-axis current command value representing the reactive current component output from the multiple converters 12 so that the AC current equivalent q-axis signal approaches the reactive current command value. The reactive current command value is set to zero, for example. This allows the operation of the multiple converters 12 to be controlled so that the magnitude of the reactive current supplied (flowed out) from the multiple converters 12 to the AC circuit 2 becomes zero. The reactive power controller 55 inputs the calculated q-axis current command value to the current controller 52.

[0051] The DC voltage controller 56 receives an input of a detected DC voltage value detected by the DC voltage detector 24. The DC voltage controller 56 also receives an input of a command value (not shown) representing the magnitude of the DC voltage to be supplied from the multiple converters 12 to the DC circuit 4. The DC voltage controller 56, for example, calculates a difference between the command value of the DC voltage and the detected DC voltage value, and performs proportional control or proportional-integral control on the calculated difference to calculate a d-axis current command value representing an active current component to be output from the multiple converters 12 so that the detected DC voltage value approaches the command value of the DC voltage. This allows the operation of the multiple converters 12 to be controlled so that the magnitude of the DC voltage supplied from the multiple converters 12 to the DC circuit 4 is substantially constant according to the command value. The DC voltage controller 56 inputs the calculated d-axis current command value to the current controller 52.

[0052] The current controller 52 calculates the difference between the input d-axis current command value and the d-axis signal equivalent to the sum of all converter currents, and performs proportional control or proportional-integral control on the calculated difference to calculate a control amount of the active component of the AC voltage output from the multiple converters 12 in order to bring the d-axis signal equivalent to the sum of all converter currents closer to the d-axis current command value. The current controller 52 inputs the calculated control amount of the active component to the adder 58.

[0053] The current controller 52 calculates the difference between the input q-axis current command value and the q-axis signal equivalent to the sum of all converter currents, and performs proportional control or proportional-integral control on the calculated difference to calculate a control amount of the reactive component of the AC voltage output from the multiple converters 12 in order to make the q-axis signal equivalent to the sum of all converter currents approach the q-axis current command value. The current controller 52 inputs the calculated control amount of the reactive component to the adder 59.

[0054] The AC voltage detection values ​​detected by the AC voltage detectors 20 a to 20 c are input to the dq converter 57. The dq converter 57 performs a dq transformation (Park transformation) on the AC voltage detection values, which are three-phase AC voltage signals, to calculate an AC voltage d-axis signal and an AC voltage q-axis signal from the AC voltage detection values. The dq converter 57 inputs the calculated AC voltage d-axis signal to an adder 58, and inputs the calculated AC voltage q-axis signal to an adder 59.

[0055] The adder 58 adds the control amount of the active component to the AC voltage d-axis signal, thereby calculating voltage command values ​​of the active components of the AC voltages output from the multiple converters 12. The adder 58 inputs the calculated voltage command values ​​of the active components to the inverse dq converter 60.

[0056] The adder 59 adds the control amount of the reactive component to the AC voltage q-axis signal, thereby calculating voltage command values ​​of the reactive components of the AC voltages output from the multiple converters 12. The adder 59 inputs the calculated voltage command values ​​of the reactive components to the inverse dq converter 60.

[0057] The inverse dq converter 60 performs an inverse dq transform (inverse Park transform) on the input active component voltage command value and reactive component voltage command value, and calculates voltage command values ​​of the three-phase AC voltage signals to be output from the multiple converters 12, based on the active component voltage command value and reactive component voltage command value. The inverse dq converter 60 inputs the calculated voltage command values ​​of the three-phase AC voltage signals to the control signal generator 61.

[0058] Based on the input voltage command value, the control signal generator 61 generates control signals for controlling the operation of the plurality of converters 12. For example, the control signal generator 61 compares the voltage command value with a triangular waveform carrier signal to generate, as control signals, pulse signals (PWM signals) for switching the on and off states of the plurality of switching elements 33 a to 33 c, 34 a to 34 c, 35 a to 35 c, and 36 a to 36 c.

[0059] The control signal generator 61 inputs the generated control signal to each of the multiple converters 12. This makes it possible to control the power conversion operation of the multiple converters 12. For example, in this example, the command value of the reactive current is set to, for example, zero. This makes it possible to control the operation of the multiple converters 12 so that the magnitude of the reactive current supplied (flowing out) from the multiple converters 12 to the AC circuit 2 is substantially constant according to the command value of the reactive current, and so that the magnitude of the DC voltage supplied from the multiple converters 12 to the DC circuit 4 is substantially constant according to the command value of the DC voltage.

[0060] A plurality of converter current detection values ​​detected by the plurality of converter current detectors 26 a to 26 c are input to the overcurrent detector 62. Based on the plurality of converter current detection values, the overcurrent detector 62 detects overcurrents in the AC currents flowing through the plurality of converters 12. The overcurrent detector 62 inputs an overcurrent detection signal to an OR circuit 64 when any of the plurality of converter current detection values ​​becomes equal to or greater than a threshold value.

[0061] The overcurrent detection signal is, for example, a signal that goes low when each of the multiple converter current detection values ​​is below a threshold, and goes high when any of the multiple converter current detection values ​​is equal to or greater than a threshold. The low state is, in other words, a low voltage state corresponding to a digital signal "0." The high state is, in other words, a high voltage state corresponding to a digital signal "1."

[0062] A plurality of converter current detection values ​​detected by the plurality of converter current detectors 26 a to 26 c are input to the unbalance detector 63. The unbalance detector 63 detects an imbalance among the plurality of converter current detection values, and inputs an imbalance detection signal to an OR circuit 64 when an imbalance is detected.

[0063] The imbalance detector 63 detects imbalance, for example, by comparing the converter current detection values ​​of two adjacent converters 12. For example, assume that there are four converters 12, numbered first through fourth. In this case, the imbalance detector 63 calculates, for example, the difference between the converter current detection value of the first converter and the converter current detection value of the second converter, the difference between the converter current detection value of the second converter and the converter current detection value of the third converter, and the difference between the converter current detection value of the third converter and the converter current detection value of the fourth converter, and detects an imbalance in the multiple converter current detection values ​​when any of the absolute values ​​of these differences exceeds a threshold. The imbalance detection signal is, for example, low when no imbalance is detected and high when an imbalance is detected.

[0064] When an overcurrent detection signal is input from the overcurrent detector 62 or an imbalance detection signal is input from the imbalance detector 63, the OR circuit 64 inputs a stop command to the control signal generator 61. For example, when at least one of the overcurrent detection signal and the imbalance detection signal becomes high, the OR circuit 64 switches its output to high to input a stop command to the control signal generator 61.

[0065] The control signal generator 61 stops the power conversion operation by the multiple converters 12 by stopping the input of control signals to the multiple converters 12 in response to the input of the stop command from the OR circuit 64. In other words, the control signal generator 61 stops the power conversion operation by the multiple converters 12 in response to at least one of the detection of an overcurrent in any of the multiple converters 12 and the detection of an imbalance in the multiple converter current detection values.

[0066] As described above, in the power conversion device 10 according to this embodiment, the control circuit 14 calculates a total converter current equivalent value corresponding to the sum of the magnitudes of the AC currents flowing through each of the multiple converters 12 by multiplying any one of the multiple converter current detection values ​​detected by the multiple converter current detectors 26a to 26c by the number N of the multiple converters 12, and generates a control signal for controlling the operation of the multiple converters 12 based on the total converter current equivalent value, and controls the power conversion operation by the multiple converters 12 by inputting the generated control signal to each of the multiple converters 12.

[0067] As a result, in the power conversion device 10, it is possible to prevent the configuration of the current detector from becoming complicated compared to a configuration in which a current detector is provided between the AC circuit 2 and the parallel connection points PP1 to PP3 on the AC side of the multiple converters 12 and detects the total AC current value flowing through the multiple converters 12. In the power conversion device 10, the configuration of the multiple converter current detectors 26a to 26c is simplified, and it is possible to prevent an increase in manufacturing costs due to the complexity of the current detector configuration.

[0068] Furthermore, in the power conversion device 10, the configuration of the control circuit 14 can be simplified compared to a configuration in which a total AC current value is calculated by adding together multiple converter current detection values ​​detected by multiple converter current detectors 26a-26c. Calculating a total AC current value by adding together multiple converter current detection values ​​requires, for example, multiple adder circuits corresponding to the number of times the multiple converter current detection values ​​are added. In contrast, in the power conversion device 10, a value equivalent to the total of all converter currents can be calculated using only a single multiplier 50. Therefore, in the power conversion device 10, the configuration of the control circuit 14 can be simplified, and an increase in manufacturing costs associated with a more complex configuration of the control circuit 14 can be suppressed.

[0069] In this way, the power conversion device 10 according to this embodiment can appropriately control the operation of the multiple converters 12 connected in parallel with a simpler configuration, and can suppress increases in manufacturing costs that would otherwise accompany a more complex configuration.

[0070] Furthermore, in the power conversion device 10, the control circuit 14 generates control signals for controlling the operation of the multiple converters 12 based on the DC voltage detection value detected by the DC voltage detector 24 and the value equivalent to the total of all converter currents so that the magnitude of the DC voltage supplied from the multiple converters 12 to the DC circuit 4 is constant according to the command value. This makes it possible to supply DC power with a DC voltage of a substantially constant magnitude to the DC circuit 4.

[0071] In the power conversion device 10, the control circuit 14 calculates an AC current equivalent value corresponding to the magnitude of the AC current in the AC circuit 2 based on the total equivalent value of all converter currents, and generates a control signal for controlling the operation of the multiple converters 12 based on the AC current equivalent value and the total equivalent value of all converter currents so that the magnitude of the reactive current supplied (flowing out) from the multiple converters 12 to the AC circuit 2 is a constant magnitude corresponding to a command value. This makes it possible to control the magnitude of the reactive current supplied (flowing out) to the AC circuit 2 to a magnitude corresponding to the command value. For example, the magnitude of the reactive current supplied (flowing out) from the multiple converters 12 to the AC circuit 2 can be made substantially zero.

[0072] In the power conversion device 10, the control circuit 14 detects an overcurrent in the AC current flowing through the multiple converters 12 based on multiple converter current detection values, and stops the power conversion operation of the multiple converters 12 in response to the detection of an overcurrent in any of the multiple converters 12. This makes it possible to appropriately detect an overcurrent in the AC current flowing through the multiple converters 12 even when controlling the operation of the multiple converters 12 based on a value equivalent to the total of all converter currents. This makes it possible, for example, to prevent failures of each device in the power conversion device 10 and further improve the reliability of the power conversion device 10. Furthermore, the overcurrent detection can be performed using a relatively simple circuit that, for example, compares multiple converter current detection values ​​with a threshold value, thereby preventing the configuration of the control circuit 14 from becoming complicated.

[0073] In the power conversion device 10, the control circuit 14 detects an imbalance between the multiple converter current detection values ​​based on the multiple converter current detection values, and stops the power conversion operation of the multiple converters 12 in response to the detected imbalance between the multiple converter current detection values. This allows for appropriate detection of an imbalance between the multiple converter current detection values ​​even when controlling the operation of the multiple converters 12 based on a value equivalent to the total of all converter currents. This makes it possible to detect, for example, an operational abnormality between the multiple converters 12 and prevent widespread failure of each device in the power conversion device 10 due to an operational abnormality between the multiple converters 12, thereby further improving the reliability of the power conversion device 10. Furthermore, the imbalance can be detected using a relatively simple circuit that compares the multiple converter current detection values, for example, and the configuration of the control circuit 14 can be kept from becoming too complicated.

[0074] Fig. 4 is a block diagram schematically illustrating a modified example of the power conversion device according to the embodiment. As illustrated in Fig. 4, in the power conversion device 10a, the DC voltage detector 24 of the above embodiment is replaced with a DC current detector 28. The DC current detector 28 detects the magnitude of the DC current flowing through the DC circuit 4 and inputs the detection result to the control circuit 14a as a DC current detection value. Note that components that are substantially the same in function and configuration as those of the above embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

[0075] 5 is a block diagram illustrating a modified example of the control circuit according to the embodiment. As shown in FIG. 5, in a control circuit 14 a, the DC voltage controller 56 of the above embodiment is replaced with a DC current controller 66.

[0076] The DC current controller 66 receives an input of a DC current detection value detected by the DC current detector 28. The DC current controller 66 also receives an input of a command value (not shown) representing the magnitude of the DC current to be supplied from the multiple converters 12 to the DC circuit 4. The DC current controller 66, for example, calculates a difference between the DC current command value and the DC current detection value, and performs proportional control or proportional-integral control on the calculated difference to calculate a d-axis current command value representing an active current component to be output from the multiple converters 12 so that the DC current detection value approaches the DC current command value. This allows the operation of the multiple converters 12 to be controlled so that the magnitude of the DC current supplied from the multiple converters 12 to the DC circuit 4 is substantially constant according to the command value. The DC current controller 66 inputs the calculated d-axis current command value to the current controller 52.

[0077] In the power conversion device 10a, the control circuit 14a generates control signals for controlling the operation of the multiple converters 12 based on the DC current detection value detected by the DC current detector 28 and a value equivalent to the total current of all converters so that the magnitude of the DC current supplied from the multiple converters 12 to the DC circuit 4 is constant according to the command value. This makes it possible to supply DC power of a substantially constant magnitude to the DC circuit 4.

[0078] In this way, the control circuit may generate a control signal based on the DC voltage detection value and the value equivalent to the total of all converter currents so that the magnitude of the DC voltage supplied from the multiple converters 12 to the DC circuit 4 is a constant magnitude corresponding to the command value, or may generate a control signal based on the DC current detection value and the value equivalent to the total of all converter currents so that the magnitude of the DC current supplied from the multiple converters 12 to the DC circuit 4 is a constant magnitude corresponding to the command value.

[0079] However, the method of generating the control signal by the control circuit is not limited to the above. The method of generating the control signal by the control circuit may be any method that can appropriately generate control signals for controlling the operation of the multiple converters 12 based on a value equivalent to the total of all converter currents. For example, the control circuit may generate the control signal so that the magnitude of the effective value of the active current supplied to the AC circuit 2 is a constant magnitude corresponding to a command value, or may generate the control signal so that the magnitude of the effective value of the AC voltage supplied to the AC circuit 2 is a constant magnitude corresponding to a command value.

[0080] The configuration of the control circuit is not limited to the above. For example, if the AC power of the AC circuit 2 is single-phase AC power, the dq converters 51, 54, and 57 can be replaced with another controller or the like. The control circuit may be configured in any way that can appropriately generate control signals for controlling the operation of the multiple converters 12 based on a value equivalent to the total current of all the converters. The configuration of the control circuit may be set appropriately depending on the type of AC power of the AC circuit 2, the method of generating the control signal, etc.

[0081] This embodiment includes the following aspects: (Supplementary Note 1) A power conversion device comprising: a plurality of converters connected in parallel to an AC circuit and connected in parallel to a DC circuit, and performing at least one of converting AC power of the AC circuit to DC power of the DC circuit and converting DC power of the DC circuit to AC power of the AC circuit, a control circuit controlling the power conversion operation of the plurality of converters, and a plurality of converter current detectors provided corresponding to the plurality of converters, respectively, detecting a magnitude of an AC current flowing through each of the plurality of converters and inputting the detection result to the control circuit as a converter current detection value, wherein the control circuit calculates a total converter current equivalent value corresponding to a sum of the magnitudes of the AC currents flowing through each of the plurality of converters by multiplying any one of the plurality of converter current detection values ​​detected by the plurality of converter current detectors by the number of the plurality of converters, generates a control signal for controlling the operation of the plurality of converters based on the total converter current equivalent value, and controls the power conversion operation of the plurality of converters by inputting the control signal to each of the plurality of converters.

[0082] (Supplementary Note 2) The power conversion device according to Supplementary Note 1, further comprising a DC voltage detector that detects a magnitude of the DC voltage of the DC circuit and inputs the detection result to the control circuit as a DC voltage detection value, wherein the control circuit generates the control signal based on the DC voltage detection value and the value equivalent to the total of all converter currents so that the magnitude of the DC voltage supplied from the plurality of converters to the DC circuit is a constant magnitude corresponding to a command value.

[0083] (Supplementary Note 3) The power conversion device according to Supplementary Note 1, further comprising a DC current detector that detects a magnitude of a DC current flowing in the DC circuit and inputs the detection result to the control circuit as a DC current detection value, wherein the control circuit generates the control signal based on the DC current detection value and the value equivalent to the total of all converter currents so that the magnitude of the DC current supplied from the plurality of converters to the DC circuit is a constant magnitude corresponding to a command value.

[0084] (Supplementary Note 4) The power conversion device according to any one of Supplementary Notes 1 to 3, wherein the control circuit calculates an AC current equivalent value corresponding to the magnitude of the AC current in the AC circuit based on the total equivalent value of all converter currents, and generates the control signal based on the AC current equivalent value and the total equivalent value of all converter currents so that the magnitude of the reactive current supplied from the plurality of converters to the AC circuit is a constant magnitude corresponding to a command value.

[0085] (Supplementary Note 5) The power conversion device according to Supplementary Note 4 further comprises: a filter circuit provided between the parallel connection point of the AC sides of the plurality of converters and the AC circuit, for suppressing noise generated on the AC sides of the plurality of converters in conjunction with the power conversion operation of the plurality of converters; and a filter current detector that detects the magnitude of the AC current flowing through the filter circuit and inputs the detection result to the control circuit as a filter current detection value, wherein the control circuit calculates the AC current equivalent value that corresponds to the magnitude of the AC current in the AC circuit by adding the filter current detection value to the value equivalent to the total of all converter currents.

[0086] (Supplementary Note 6) The power conversion device according to any one of Supplementary Notes 1 to 5, wherein the control circuit detects an overcurrent of the AC current flowing through the plurality of converters based on the plurality of converter current detection values, and stops the power conversion operation of the plurality of converters in response to the detection of an overcurrent in any of the plurality of converters.

[0087] (Supplementary Note 7) The power conversion device according to any one of Supplementary Notes 1 to 6, wherein the control circuit detects an imbalance in the plurality of converter current detection values ​​based on the plurality of converter current detection values, and stops the power conversion operation of the plurality of converters in response to the detection of an imbalance in the plurality of converter current detection values.

[0088] Although several 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 embodied 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 within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0089] 2...AC circuit, 4...DC circuit, 10, 10a...power conversion device, 12...converter, 14, 14a...control circuit, 16...filter circuit, 20a to 20c...AC voltage detector, 22a to 22c...filter current detector, 24...DC voltage detector, 26a to 26c...converter current detector, 27a to 27c...reactor, 28...DC current detector, 30a...positive potential terminal, 30b...negative potential terminal, 30c...neutral point terminal, 31a to 31c...AC terminal, 32a, 32b...charge storage element, 33a to 33c, 34a to 34c, 35a to 35c, 36a to 36c...switching element, 37a to 37c, 38a to 38c, 39a to 39c, 40a to 40c...rectifying element, 50... Multiplier, 51... dq converter, 52... Current controller, 53... Adder, 54... dq converter, 55... Reactive power controller, 56... DC voltage controller, 57... dq converter, 58, 59... Adders, 60... Inverse dq converter, 61... Control signal generator, 62... Overcurrent detector, 63... Unbalance detector, 64... OR circuit, 66... ​​DC current controller

Claims

1. A power conversion device comprising: a plurality of converters connected in parallel to an AC circuit and in parallel to a DC circuit, and performing at least one of converting AC power in the AC circuit to DC power in the DC circuit, and converting DC power in the DC circuit to AC power in the AC circuit; a control circuit controlling the power conversion operation of the plurality of converters; and a plurality of converter current detectors provided corresponding to each of the plurality of converters, detecting the magnitude of the AC current flowing in each of the plurality of converters and inputting the detection result to the control circuit as a converter current detection value, wherein the control circuit calculates a total converter current equivalent value corresponding to the sum of the magnitudes of the AC current flowing in each of the plurality of converters by multiplying any one of the plurality of converter current detection values ​​detected by the plurality of converter current detectors by the number of the plurality of converters, generates a control signal for controlling the operation of the plurality of converters based on the total converter current equivalent value, and controls the power conversion operation of the plurality of converters by inputting the control signal to each of the plurality of converters.

2. A power conversion device according to claim 1, further comprising a DC voltage detector that detects the magnitude of the DC voltage of said DC circuit and inputs the detection result to said control circuit as a DC voltage detection value, and said control circuit generates said control signal based on said DC voltage detection value and said value equivalent to the total of all converter currents so that the magnitude of the DC voltage supplied from said plurality of converters to said DC circuit is a constant magnitude corresponding to a command value.

3. A power conversion device according to claim 1, further comprising a DC current detector that detects the magnitude of the DC current flowing in the DC circuit and inputs the detection result to the control circuit as a DC current detection value, wherein the control circuit generates the control signal based on the DC current detection value and the value equivalent to the total current of all converters so that the magnitude of the DC current supplied from the multiple converters to the DC circuit is a constant value corresponding to a command value.

4. The power conversion device according to claim 1, wherein the control circuit calculates an AC current equivalent value corresponding to the magnitude of the AC current in the AC circuit based on the total equivalent value of all converter currents, and generates the control signal based on the AC current equivalent value and the total equivalent value of all converter currents so that the magnitude of the reactive current supplied from the multiple converters to the AC circuit is a constant value corresponding to a command value.

5. A power conversion device according to claim 4, further comprising: a filter circuit provided between the parallel connection point of the AC sides of the plurality of converters and the AC circuit, for suppressing noise generated on the AC sides of the plurality of converters as a result of the power conversion operation of the plurality of converters; and a filter current detector that detects the magnitude of the AC current flowing through the filter circuit and inputs the detection result to the control circuit as a filter current detection value, wherein the control circuit calculates the AC current equivalent value that corresponds to the magnitude of the AC current in the AC circuit by adding the filter current detection value to the value equivalent to the total of all converter currents.

6. The power conversion device according to claim 1, wherein the control circuit detects overcurrents in the AC currents flowing through the plurality of converters based on the detected current values ​​of the plurality of converters, and stops the power conversion operation of the plurality of converters in response to the detection of an overcurrent in any of the plurality of converters.

7. The power conversion device according to claim 1, wherein the control circuit detects an imbalance in the plurality of converter current detection values ​​based on the plurality of converter current detection values, and stops the power conversion operation of the plurality of converters in response to the detection of an imbalance in the plurality of converter current detection values.