POWER CONVERSION DEVICE, THREE-PHASE POWER CONVERSION SYSTEM AND CONTROL METHOD FOR IT

Abstract

A power conversion device that converts AC power to DC power or DC power to AC power, wherein the power conversion device comprises a multi-stage circuit in which several power conversion cells (103) are connected in series, the multi-stage circuit comprising a primary control circuit (105) which includes a voltage control that controls the output voltages of the power conversion cells and is configured to output a command value of a system current calculated by the voltage control, and the power conversion cell (103) comprising a secondary control circuit (104) which includes a current sensing means that senses the system current and a current control that controls the system current based on the command value of the system current output by the primary control circuit (105).In addition, a communication line connecting the primary control circuit (105) and the secondary control circuit (104) is connected in a daisy-chain type.

Description

Technical field

[0001] The present invention relates to a power conversion device, a three-phase power conversion system and a control method therefor. State of the art

[0002] For a power conversion device connected to a high-voltage AC system (such as a 3-phase 6.6 kV system), a configuration has conventionally been proposed (see PTL 1) in which power conversion cells consisting of low-voltage power devices and passive components are connected in series (also referred to as a multi-stage series connection).

[0003] An AC-DC converter, which converts AC power from the high-voltage AC system into DC power, is required to control a system current so that it provides a required power factor (e.g., power factor 1). If the AC-DC converter connected to the system is configured by a multi-stage series connection, it becomes necessary that each power converter cell be controlled so that the entire circuit behaves like an AC-DC converter.

[0004] For this reason, the multi-stage series circuit is controlled by a primary control circuit, on which controls for DC voltage control, system current control and the like are mounted, and a secondary control circuit that controls the power device contained in each of the power converter cells, the primary control circuit and the secondary control circuit generally being connected by a communication line.

[0005] Furthermore, system current control requires controlling the system current to a sine wave with an operating frequency of 50 Hz or 60 Hz, in accordance with harmonic suppression guidelines. Therefore, the current control calculation frequency is often set at 10 kHz or higher. In multi-stage series circuits, it is also necessary to provide current control in the primary control circuit and to transmit a duty cycle (on-time ratio) of the power device contained in each power converter cell, along with a gate signal pattern command, to the secondary control circuit via the communication line. As described above, the current control calculation frequency is generally 10 kHz or higher, and consequently, the communication frequency must also be set to 10 kHz or higher to ensure stable current control. List of literature on patent literature

[0006] PTL 1: JP 2014-207728 A Summary of the invention: Technical problem

[0007] To align the communication frequency between the primary and secondary control circuits with the current control calculation frequency, a high-speed communication method is required. Generally, the higher the communication speed, the more expensive the communication method becomes. However, it is also conceivable to use a cost-effective, low-speed communication method to reduce the cost of the power conversion device. If the communication frequency is set lower than the current control calculation frequency, the current control output will not be reflected in the control signal of each power converter cell, and the current control may become unstable, especially if the system voltage or load power changes suddenly.Therefore, one challenge is to achieve stable system current control in a case where a low-cost, low-speed communication method is used to reduce the cost of the power conversion device.

[0008] The present invention was developed accordingly to solve the problems described above, and one object of the present invention is to provide a power conversion device, a three-phase power conversion system and a control method therefor, which are capable of reducing the cost of a communication system of a multi-stage series circuit. Solution to the problem

[0009] To achieve the above-described problem, a power conversion device according to the present invention is a power conversion device that converts AC power to DC power or DC power to AC power, wherein the power conversion device comprises a multi-stage circuit in which several power conversion cells are connected in series, wherein the multi-stage circuit includes a primary control circuit comprising a voltage control that controls the output voltages of the power conversion cells and is configured to output a command value of a system current calculated by the voltage control, and each of the power conversion cells comprises a secondary control circuit comprising a current sensing means that senses the system current and a current control that controls the system current based on the command value of the system current.which is output by the primary control circuit. Further aspects of the present invention are described in the following embodiments. Advantageous effects of the invention

[0010] According to the present invention, it is possible to reduce the costs of the multi-stage series communication system. Brief description of the drawings [ Fig. 1] Fig. Figure 1 is a diagram illustrating an example of a circuit configuration of a power conversion device according to a first embodiment. [ Fig. 2] Fig. Figure 2 is a diagram illustrating an example of a circuit configuration of an AC-DC converter contained in a power converter cell according to the first embodiment. [ Fig. 3A] Fig. Figure 3A is a diagram illustrating an example of a control block of a primary control circuit according to the first embodiment. [ Fig. 3B] Fig. Figure 3B is a diagram illustrating an example of a control block of a secondary control circuit according to the first embodiment. [ Fig. 4] Fig. Figure 4 is a flowchart illustrating an example of the control of a current control switch included in each secondary control circuit according to the first embodiment. [ Fig. 5] Fig. Figure 5 is a diagram illustrating an example of each waveform of the power conversion device according to the first embodiment. [ Fig. 6] Fig. Figure 6 is a diagram illustrating an example of a circuit configuration of a power conversion device according to a second embodiment. [ Fig. 7] Fig. Figure 7 is a diagram illustrating an example of a circuit configuration of a power conversion device according to a third embodiment. [ Fig. 8] Fig. Figure 8 is a diagram illustrating an example of a circuit configuration of a power conversion device according to a fourth embodiment. [ Fig. 9A] Fig. Figure 9A is a diagram illustrating a control outline of a power conversion device of a comparative example. [ Fig. 9B] Fig. Figure 9B is a diagram illustrating a control outline of a power conversion device according to the present embodiment. Description of the embodiments

[0011] Embodiments of the present invention are described below with reference to the drawings and the like. <Erste Ausführungsform>

[0012] Fig. Figure 1 is an example of a circuit configuration of a power conversion device 100 according to the first embodiment. The power conversion device 100 receives power from a single-phase AC system 101 and comprises an AC choke 102, several power conversion cells 103 (first to Nth power conversion cells 103), secondary control circuits 104 (first to Nth secondary control circuits 104) that control the power conversion cells 103, and a primary control circuit 105 that controls the entire power conversion device 100. Furthermore, the primary control circuit 105 and the secondary control circuits 104 are connected via communication lines 110 in a daisy-chain configuration.

[0013] The power conversion device 100 is a power conversion device that converts alternating current power into direct current power or direct current power into alternating current power, wherein the power conversion device comprises a multi-stage circuit in which several power conversion cells 103 are connected in series, wherein the multi-stage circuit comprises a primary control circuit 105 (primary control device) which includes a voltage control 303 (see Fig. 3A) includes which controls the output voltages of the power converter cells 103, and is configured to output a command value of a system current calculated by the voltage control 303, and each of the power converter cells 103 includes a secondary control circuit 104 (secondary control device) which includes a current sensing means (current sensor 108) that senses the system current, and a current control 305 (see Fig. 3B), which controls the system current based on the command value of the system current output by the primary control circuit.

[0014] The power converter cell 103 further comprises an AC-DC converter 106, a smoothing capacitor 107 connected to a DC section, a current sensor 108 that detects a system current, and a voltage sensor 109 that detects a DC section voltage.

[0015] In particular, the power conversion device 100 comprises a power converter cell 103_1, a secondary control circuit 104_1 that controls the power converter cell 103_1, a power converter cell 103_2 up to an Nth power converter cell 103_N (N is a natural number) having configurations similar to those of the power converter cell 103_1, secondary control circuits 104_2 to 104_N that control the respective power converter cells 103_2 to 103_N, and a primary control circuit 105 that controls the entire power conversion device 100.

[0016] The power converter cells 103_1 to 103_N further comprise AC-DC converters 106_1 to 106_N, smoothing capacitors 107_1 to 107_N connected to the DC section, current sensors 108_1 to 108_N that detect system currents, and voltage sensors 109_1 to 109_N that detect DC section voltages.

[0017] The primary control circuit 105 and the secondary control circuit 104_1 are connected via a communication line 110_1, and the secondary control circuit 104_1 and the secondary control circuit 104_2 are connected via a communication line 110_2. The primary control circuit 105 and each of the secondary control circuits 104_1 to 104_N are connected in a so-called daisy-chain configuration.

[0018] In the multi-stage series circuit, the voltage of the AC system 101 is also divided by the power converter cells 103_1 to 103_N, resulting in different potentials. If the communication lines are connected in a daisy-chain configuration, secondary control circuits with small potential differences can be connected to each other, so that the dielectric strength of the communication lines 110_1 to 110_N can be lower than the voltage of the AC system 101.

[0019] Although in Fig. 1 not every one of the power converter cells 103_i to 103_N every one of the secondary control circuits 104_1 to 104_N in Fig. 1 includes (see the square dashed frame in Fig. 1) This is simply because the latter are described separately for the sake of simplicity, so that each of the secondary control circuits 104_1 to 104_N can also be integrated into a corresponding power converter cell of the power converter cells 103_1 to 103_N. Furthermore, the secondary control circuit 104_N and the primary control circuit 105 can also be connected by a communication line in a so-called ring configuration. Using the ring configuration allows for duplicated communication lines, which further improves reliability.

[0020] Fig. Figure 2 further shows a diagram illustrating an example of a circuit configuration of the AC-DC converter 106 contained in the power converter cell 103 according to the first embodiment.

[0021] The AC-DC converter 106 is formed by a full bridge circuit comprising switching elements S1 to S4. For this purpose, the secondary control circuit 104 and the AC-DC converter 106 transmit and receive a control signal, such as a gate drive pattern, via a signal line 201. Furthermore, the power converter cells 103_1 to 103_N have Fig. 1 configurations that are similar to those of the power converter cell 103 from Fig. 2 are similar, so their description is omitted below.

[0022] Although IGBTs are used as switching elements in Fig. 2. The present embodiment is not limited to the use of the aforementioned full-bridge circuit, and other switching elements, such as MOSFETs, can also be used. Furthermore, the circuit method is not limited to the aforementioned full-bridge circuit, and other circuit types, such as a dead-pole circuit, can also be used.

[0023] Next, the operation of the power conversion device 100 will be described with reference to Fig. 1 and Fig. 2 described.

[0024] The power converter cells 103_1 to 103_N operate as a common single-phase AC-DC converter. In particular, while the DC voltage of each of the power converter cells 103_1 to 103_N is controlled to a predetermined value, the system current of the AC system 101 is controlled so that it has a sinusoidal waveform.

[0025] Each of the power converter cells 103_1 to 103_N can output a specific voltage (an average voltage obtained by multiplying the DC voltage by the duty cycle) between AC system-side terminals of the full bridge circuit by controlling the duty cycle of each of the switching elements S1 to S4, i.e., control the system current by controlling the voltage applied to the AC choke 102.

[0026] Although not described in detail in the present embodiment, a voltage equalization control can also be provided to equalize the DC voltages of the power converter cells 103_1 to 103_N, and the present embodiment can be used regardless of whether the voltage equalization control is provided. Furthermore, any other control method not described in the present embodiment can also be used in the present invention.

[0027] Fig. Figure 3A shows a diagram illustrating an example of the primary control circuit 105 according to the first embodiment. The primary control circuit 105 comprises a PLL circuit 301, a current command value scheduler 302, a voltage control 303, and a duty cycle scheduler 304.

[0028] A system voltage sensing value Vu, acquired by a voltage sensor (not shown), is further input to the primary control circuit 105. Additionally, the system voltage sensing value is input to the PLL circuit 301, and the amplitude, frequency f, and phase θ of the system voltage are acquired. These acquired values ​​are then input to the current command scheduler 302. Furthermore, the frequency f and phase θ are transmitted to each of the secondary control circuits 104_1 to 104_N. It should be noted that PLL is an abbreviation for phase-locked loop.

[0029] Additionally, a total DC voltage command value ΣVdc* for the power converter cells 103_1 to 103_N is externally input into the primary control circuit 105, and DC voltage sensing values ​​Vdc_1 to Vdc_N, detected by voltage sensors 109_1 to 109_N contained in the respective power converter cells 103_1 to 103_N, are input into the primary control circuit 105 by the respective secondary control circuits 104_1 to 104_N. These values ​​are then input into the voltage controller 303, and a system current amplitude command value Iu* is calculated, for example, by a PID controller contained in the voltage controller 303. It should be noted that P represents proportional control, I represents integral control, and D represents differential control.

[0030] The system current amplitude command value Iu* is entered into the current command value planner 302. The current command value planner 302 then calculates a system current instantaneous command value iu* for the communication cycle using the entered system current amplitude command value Iu* and the phase θ / frequency f, and transmits the calculated system current instantaneous command value iu* to each of the secondary control circuits 104_1 to 104_N.

[0031] The amplitude, phase θ, and frequency f of the system voltage, as well as the DC voltage sensing values ​​Vdc_1 to Vdc_N, are entered into the duty cycle scheduler 304. The duty cycle scheduler 304 then calculates the duty cycle assignment command values ​​duty_1* to duty_N* for the respective power converter cells 103_1 to 103_N for the communication cycle based on the amplitude, phase θ, and frequency f of the system voltage, and transmits the calculated duty cycle assignment command values ​​duty_1* to duty_N* to the secondary control circuits 104_1 to 104_N.

[0032] That is, the primary control circuit 105 of Fig. 3A calculates a current command value of a system current (system current amplitude command value Iu*) and duty cycle command values ​​(duty cycle assignment plan command values ​​duty_1* to duty_N*) for the communication cycle between the primary control circuit 105 and the secondary control circuits 104, and outputs the calculated values ​​to the secondary control circuits 104. The primary control circuit 105 also calculates the current command value (system current amplitude command value Iu*) and the duty cycle command values ​​(duty cycle assignment plan command values ​​duty_1* to duty_N*) such that a secondary control circuit 104 always enables the current control 305.

[0033] Fig. Figure 3B further shows a diagram illustrating an example of a control block of the secondary control circuit 104 according to the first embodiment. Although the secondary control circuit 104_1 is already shown in Fig. As illustrated in Figure 3, the same applies to each of the secondary control circuits 104_2 to 104_N.

[0034] The secondary control circuit 104 further comprises a current control 305, a current control switch 306, a PWM pulse generator 307 and a current instant command value generator 308. Fig. Figure 3 illustrates, as an example, the secondary control circuit 104_1, which is contained in the power converter cell 103_1. The other secondary control circuits have the same configuration, so their description is omitted below.

[0035] The system current instantaneous value plan command value iu* and the duty cycle assignment plan command value duty_1*, which are output by the primary control circuit 105, the system current detection value iu, which is detected by the current sensor 108_1, the frequency f and the phase θ are first entered into the secondary control circuit 104_1.

[0036] In the secondary control circuit 104_1, a system current instant command value iu*' is then calculated by the current instant command value generator 308 using the system current instant command value plan command value iu*, the frequency f and the phase θ, and a system current deviation iuerr is calculated from the system current instant command value iu*' and the system current detection value iu and entered into the current control 305.

[0037] The system current deviation iuerr and the duty cycle assignment plan command value duty_1* are also input into the current control switch 306. If the duty cycle assignment plan command value duty_1* is -1, 0, or 1, and the system current deviation iuerr is less than a predetermined threshold, the current control switch 306 outputs a current control blocking signal to the current controller 305. Conversely, if the duty cycle assignment plan command value duty_1* is not -1, 0, or 1, a current control enable signal is output to the current controller 305. Furthermore, if the duty cycle assignment plan command value duty_1* is -1, 0, or 1, and the system current deviation iuerr is greater than or equal to the predetermined threshold, a current control enable signal is output to the current controller 305. This will be explained later with reference to Fig. 4 described in detail.

[0038] For example, while receiving the enable signal, the current controller 305 performs calculations using PID control to determine a duty cycle control amount Δduty_1*. Conversely, while receiving the block signal, the PID calculations are stopped, and the duty cycle control amount Δduty_1 is output as zero. This output duty cycle control amount Δduty_1 is then added to the duty cycle assignment plan command value duty_1* and fed into the PWM pulse generator 307 as a duty cycle output duty_1.

[0039] The PWM pulse generator 307 further generates gate signals for controlling the switching elements S1 to S4 (see Fig. 2) based on the input duty cycle output duty_1, it inputs the gate signals via a gate drive circuit (not shown) into the switching elements S1 to S4.

[0040] That means the secondary control circuit 104 in Fig. 3B determines whether the current control 305 is enabled or disabled based on the deviation (system current deviation iuerr) between the current command value (system current instantaneous value plan command value iu*) received by the primary control circuit 105, the current sensing value (system current sensing value iu) received by the current sensing device (current sensor 108), and the duty cycle command value (e.g., duty cycle assignment plan command value duty_1*) received by the primary control circuit 105.

[0041] With the above configuration, at the normal time when the system current instantaneous value plan command value iu* and the system current sensing value iu are essentially equal, one of the power converter cells 103_1 to 103_N performs system current control accordingly. This is because the power converter cells 103_1 to 103_N share a common system current, so if the current control is performed simultaneously, the current control can become unstable due to sensing errors of the current sensor 108_1 to 108_N or the like.

[0042] On the other hand, in an emergency situation where, due to a sudden change in system voltage or load power, the duty cycle output of the power converter cell controlling the system current at that time is stuck at its upper or lower limit, and a deviation occurs between the instantaneous system current command value iu* and the system current sensing value iu, control is implemented such that other power converter cells autonomously begin current control. Therefore, this control can stably control the system current regardless of the communication frequency between the primary control circuit 105 and each of the secondary control circuits 104_1 to 104_N. Furthermore, this allows for the use of a cost-effective, low-speed communication scheme, thereby reducing the cost of the power converter device 100 without compromising the stability of the control.

[0043] Fig. Figure 4 shows a flowchart illustrating an example of the control of the current control switch 306, which is included in each of the secondary control circuits 104_1 to 104_N according to the first embodiment. Only the secondary control circuit 104_1 is described below, omitting the description of the secondary control circuits 104_2 to 104_N, which have the same configuration as the secondary control circuit 104_1.

[0044] The current control switch 306. starts a series of processes to determine whether the current control should be enabled or disabled (step S401).

[0045] The current control switch 306 then determines whether the entered duty cycle assignment plan command value duty_1* is -1, 0 or 1 (step S402).

[0046] If NO is identified in step S402, the current control switch 306 enables the current control (step S406).

[0047] If, however, YES is identified in step S402, the current control switch 306 then determines whether an absolute value of a system current deviation iuerr, which is a difference between the system current instantaneous value plan command value iu* and the system current sensing value iu, is less than the threshold value (step S403).

[0048] If YES is identified in step S403, the current control switch 306 blocks the current control (step S404).

[0049] If NO is identified in step S403, the current control switch 306 determines whether the duty cycle can be controlled based on the polarities of the system current sensing value iu and the system current deviation iuerr and the duty cycle output duty_1 (step S405).

[0050] If NO is identified in step S405, the power control switch 306 then performs a control operation to enable power control during the planned period and to lock power control during the other period (step S404).

[0051] If, however, YES is identified in step S405, the current control switch 306 enables current control (step S406). It should be noted that the planned period is a period scheduled for each power converter cell 103 to perform control, and corresponds to the periods T1, T2, T3,... in Fig. 5 corresponds to.

[0052] The sequence of processes then ends (step S407).

[0053] According to the above control sequence, the system current can be controlled by one power converter cell 103 at normal times, and the system current can be controlled by several power converter cells 103 only when the system current deviation becomes greater than or equal to the threshold value.

[0054] Fig. Figure 5 further shows a diagram illustrating an example of each waveform of the power conversion device 100 according to the first embodiment. The waveform is extracted for a communication cycle Tctrl within a cycle of the AC system 101, representing a period during which the system current sensing value iu increases in the positive direction from zero, and assuming that the Fig. The first illustrated direction is defined as positive. Furthermore, it illustrates Fig. 5 duty cycle outputs duty_1, duty_2 and duty_3 for three power converter cells.

[0055] During the period T1, the power converter cell 103_1 performs current control, and the power converter cells 103_2 and 103_3 do not perform switching and current control, since the duty-time outputs duty_2 and duty_3 of the power converter cells 103_2 and 103_3 are 0.

[0056] Since duty_1, which defines the upper limit, reaches 1 at the boundary between period T1 and period T2, the power converter cell 103_2 performs current control from period T2 onwards, so that the duty cycle output duty_1 of the power converter cell 103_1 is 1 and the duty cycle output duty_3 of the power converter cell 103_3 is 0.

[0057] At this time, a power converter cell normally always performs current control in period T2 as well as in period T1. However, this illustrates Fig. 5 a case in which the system current detection value iu exceeds the system current instantaneous value plan command value iu* during the period T2 due to some factors.

[0058] Accordingly, during period T2, while power converter cell 103_2 controls the system current, the duty cycle output duty_2 is controlled to increase in order to suppress the current. However, when the duty cycle output duty_2 reaches its upper limit, the system current can no longer be controlled, and thus the deviation between the system current sensing value iu and the system current instantaneous value scheduled command value iu* increases; that is, the system current deviation iuerr. When the system current deviation iuerr becomes greater than or equal to the threshold value, power converter cell 103_3, which was scheduled to control the system current during period T3, autonomously begins to control the current.

[0059] That is, if the deviation between the current command value and the current sensing value obtained by the current sensing means of the secondary control circuit 104 is greater than or equal to a predetermined value, the two or more secondary control circuits 104 release the respective current controls 305.

[0060] Consequently, the system current sensing value iu is controlled so that it again follows the system current instantaneous value plan command value iu*. Accordingly, the above control allows stable system current control even in a state where no communication exists from the primary control circuit 105. <Zweite Ausführungsform>

[0061] In the second embodiment of the present invention, the primary control circuit 105 and the secondary control circuits 104_1 to 104_N are connected in a so-called star configuration by communication lines in the first embodiment. Differences from the first embodiment are described below, and descriptions of points similar to those of the first embodiment are omitted.

[0062] Fig. Figure 6 shows a diagram illustrating an example of a circuit configuration of a power conversion device 100B according to the second embodiment. In the second embodiment, the primary control circuit 105 and the secondary control circuits 104_1 to 104_N are connected by communication lines 601 in a star configuration rather than a daisy-chain configuration.

[0063] In particular, the primary control circuit 105 and the secondary control circuit 104_1 are connected by a communication line 601_1, the primary control circuit 105 and the secondary control circuit 104_2 by a communication line 601_2, and the primary control circuit 105 and the secondary control circuit 104_N by a communication line 601_N.

[0064] Thus, in the configuration of the second embodiment, signals can be simultaneously transmitted from the primary control circuit 105 to the secondary control circuits 104_1 to 104_N, thereby increasing the communication frequency and the voltage control frequency or reducing the dead time of the control. However, since the primary control circuit 105 and each of the secondary control circuits 104_1 to 104_N are connected on a one-to-one basis, a voltage withstand capability is required between the primary control circuit 105 and each of the secondary control circuits 104_1 to 104_N that is higher than or equal to the system voltage of the AC system 101. <Dritte Ausführungsform>

[0065] In the third embodiment, the functions of the primary control circuit 105 in the first and second embodiments are provided for each of the secondary control circuits 104_1 to 104_N, thus eliminating the need for the separately provided primary control circuit 105. Differences from the first and second embodiments are described below, and descriptions of points similar to those of the first and second embodiments are omitted.

[0066] Fig. Figure 7 shows a diagram illustrating an example of a circuit configuration of a power conversion device 100C according to the third embodiment. In the third embodiment, the primary control circuit 105 is omitted. By providing the functions of the primary control circuit 105 for at least one of the secondary control circuits 104_1 to 104_N, it is accordingly not necessary to prepare a housing associated with the primary control circuit 105, thus making the power conversion device 100 more compact.Furthermore, by providing the functions of the primary control circuit 105 for two or more of the secondary control circuits 104_1 to 104_N, even if the secondary control circuit is operating as the primary due to a failure or the like, another secondary control circuit can be operated as the primary, thereby allowing the operation of the power conversion device 100 to continue and improving its reliability. (These are in...) Fig. 7 communication lines between the secondary control circuits 104_1 to 104_N configured in a daisy-chain type, however, the present invention need not be limited to this, and the communication lines can also be configured in a star type, for example, as described in the second embodiment. <Vierte Ausführungsform>

[0067] In the fourth embodiment of the present invention, the power conversion device 100 in the first to third embodiments is applied to a three-phase system.

[0068] Fig. Figure 8 illustrates an example of a configuration of a power conversion device 800 according to the fourth embodiment. More precisely, it illustrates... Fig. 8. A three-phase power conversion system is described, in which the power conversion device 100 is connected to each phase of a three-phase system. The power conversion devices 100u, 100v, and 100w are each connected to the U-phase, V-phase, and W-phase of the three-phase AC system 801 (three-phase system), respectively, and the power conversion devices themselves are connected to each other at a neutral point 802. By connecting the power conversion device 100 to each phase in this way, it can be used as a three-phase power conversion system. Furthermore, the primary control circuit (not illustrated) is integrated into a single circuit without being divided among the power conversion devices 100u, 100v, and 100w, which helps to reduce the cost and size of the power conversion device 800. Fig. 8 the three-phase alternating current system 801 and the power conversion devices 100u, 100v and 100w are all connected in a Y-connection type, however, the present invention is not limited to this, and they can also be connected in a Delta-connection type.

[0069] Fig. Figure 9A also shows a diagram illustrating a control outline of a power conversion device of a comparative example. In the power conversion device of the comparative example, a main controller 205 is responsible for voltage and current control, and sub-controllers 204 are responsible for gate signal generation, thus performing control with a communication cycle (e.g., 100 µs) that is shorter than or equal to a current control cycle (calculation cycle). On the other hand, the control of the power converter according to the present embodiment has the following characteristics.

[0070] Fig.Figure 9B shows a diagram illustrating a control description of the power conversion device according to the present embodiment. Here, the primary control circuit 105 has a voltage control function, and the secondary control circuits 104 have a current control function. Normally, one secondary control circuit 104 performs current control; however, if the deviation between the detected current and the command value is large, two or more secondary control circuits 104 perform current control. By applying the control method of the present embodiment, current control can be performed within a communication cycle of milliseconds. That is, the communication cycle between the primary control circuit 105 and the secondary control circuits 104 is set to be longer than the calculation cycle of the current control 305.Furthermore, the costs of the communication system can be reduced by using a multi-stage series connection.

[0071] The present embodiment comprises, in a control method, a power conversion device that converts AC power to DC power or DC power to AC power, wherein the power conversion device comprises a multi-stage circuit in which several power conversion cells 103 are connected in series, wherein the multi-stage circuit may comprise a primary control circuit 105, which includes a voltage control 303 that controls the output voltages of the power conversion cells 103, and each of the power conversion cells 103 may include a secondary control circuit 104, the primary control circuit 105 being able to output a command value of a system current calculated by the voltage control 303, and the secondary control circuit 104 being able to detect the system current and control the system current based on the command value of the system current output by the primary control circuit.

[0072] With regard to the terms "primary" and "secondary" used in the present embodiment, the circuit (device) designated by reference numeral 104 shall also be referred to as the secondary circuit (device), although the present embodiment need not be limited to this. The circuit (device) designated by reference numeral 104 may also be referred to as the primary circuit (device), and the circuit (device) designated by reference numeral 105 may be referred to as the secondary circuit (device).

[0073] That is, there is a power conversion device that converts AC power to DC power or DC power to AC power, wherein the power conversion device comprises a multi-stage circuit in which several power converter cells 103 are connected in series, wherein the multi-stage circuit may include a secondary control circuit which includes a voltage controller 303 that controls the output voltages of the power converter cells 103 and is configured to output a command value of a system current calculated by the voltage controller 303, and each of the power converter cells 103 may include a primary control circuit which includes a current sensing means that senses the system current and a current controller 305 that controls the system current based on the command value of the system current output by the secondary control circuit. Reference symbol list 100 Power conversion device 101 Alternating current system 102 AC choke 103 Power converter cell 104 secondary control circuit (secondary control device) 105 primary control circuit (primary control device) 106 AC-DC converters 107 Smoothing capacitor 108 Current sensor (current detection device) 109 Voltage sensor 110 Communications Line 201 Signal line 301 PLL circuit 302 Current Command Value Planner 303 Voltage control 304 Duty Cycle Planner 305 Power control 306 Current control switches 307 PWM pulse generator 308 Current Moment Command Value Generator 601 Communications Line duty_1* to duty_N* each duty cycle assignment plan command value (duty cycle command value) duty_1 duty cycle output Δduty_1* duty cycle tax amount iu System current measurement value (current measurement value) iu* System current moment value plan command value (current command value) for communication cycle iu*' System current moment command value Iu* System current amplitude command value iuerr system current deviation (deviation) f frequency θ Phase S1 to S4 switching element ΣVdc* Total DC voltage command value Vdc_1 to Vdc_N DC voltage detection value QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2014-207728 A

[0006]

Claims

[1] A power conversion device that converts alternating current power to direct current power or direct current power to alternating current power, wherein the power conversion device comprises a multi-stage circuit in which several power conversion cells are connected in series, wherein the multi-stage circuit includes a primary control circuit which includes a voltage control that controls the output voltages of the power converter cells, and is configured to output a command value of a system current calculated by the voltage control, and Each of the power converter cells includes a secondary control circuit comprising a current sensing means that detects the system current and a current control that controls the system current based on the command value of the system current output by the primary control circuit. [2] The power conversion device according to claim 1, wherein the primary control circuit calculates a current command value of the system current and a duty cycle command value for a communication cycle between the primary control circuit and the secondary control circuit, and outputs the current command value and the duty cycle command value to the secondary control circuit. [3] The power conversion device according to claim 2, wherein the primary control circuit calculates the current command value and the duty cycle command value such that one of the secondary control circuits always enables the current control. [4] The power conversion device according to claim 2 or 3, wherein if a deviation between the current command value and a current sensing value obtained from the current sensing means of the secondary control circuit is greater than or equal to a predetermined value, two or more of the secondary control circuits release the respective current controls. [5] The power conversion device according to claim 4, wherein the secondary control circuits determine whether the current controls should be enabled or disabled based on deviations between the current command value received from the primary control circuit and current sensing values ​​obtained from the current sensing means and the duty cycle command value received from the primary control circuit. [6] The power conversion device according to claim 1, wherein a communication line connecting the primary control circuit and the secondary control circuit is connected in a daisy-chain type. [7] The power conversion device according to claim 1, wherein a communication line connecting the primary control circuit and the secondary control circuit is connected in a star configuration. [8] The power conversion device according to claim 1, wherein a communication cycle between the primary control circuit and the secondary control circuit is set to be longer than a calculation cycle of the current control. [9] The power conversion device according to claim 1, wherein at least one of the secondary control circuits has functions of the primary control circuit. [10] A three-phase power conversion system, wherein the power conversion device according to one of claims 1 to 3 and 6 to 9 is connected to each phase of a three-phase system. [11] A three-phase power conversion system, wherein the power conversion device according to claim 4 is connected to each phase of a three-phase system. [12] A three-phase power conversion system, wherein the power conversion device according to claim 5 is connected to each phase of a three-phase system. [13] A control method for a power conversion device that converts AC power to DC power or DC power to AC power, wherein the power conversion device comprises a multi-stage circuit in which several power conversion cells are connected in series, the multi-stage circuit comprising a primary control circuit comprising a voltage control that controls the output voltages of the power conversion cells, and each of the power conversion cells comprising a secondary control circuit, The primary control circuit outputs a command value of a system current calculated by the voltage control, and The secondary control circuit detects the system current and controls the system current based on the command value of the system current output by the primary control circuit.

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