Power Conversion Device

Abstract

To individually measure delay of signal transmission due to an insulation element which insulates a control signal to be transmitted for each conversion cell without adding the insulation element in a central controller in a power conversion device constituted of a plurality of conversion cells.SOLUTION: Each of a plurality of conversion cells 111, 112 and 113 includes a plurality of insulation elements for causing each cell controller 108 to mutually transmit signals between each cell controller and a central controller 107. The central controller 107 individually calculates delay time of signal transmission due to the insulation element by individually reciprocating a pulse signal between the cell controllers 108 of the plurality of conversion cells 111, 112 and 113 and itself.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device including a plurality of conversion cells that perform power conversion. [Background technology]

[0002] A power conversion device such as a multi-cell converter is known, which includes multiple conversion cells that perform power conversion, each connected in series via a pair of input terminals or a pair of output terminals. In this type of power conversion device, each conversion cell operates at a different potential. For this reason, each conversion cell is provided with multiple isolation elements so that a central control device that controls the entire power conversion device can transmit control signals to and from each conversion cell.

[0003] It is known that the multiple isolation elements that transmit control signals have component-specific delay times. In addition, delay times accumulate depending on the number of isolation elements through which the control signal passes, and the delay times may differ for each conversion cell. These delay times cause discrepancies in the operation timing of each conversion cell, which can cause malfunctions under certain conditions, so delay compensation is necessary. To perform this delay compensation, it is necessary to calculate the delay time of signal transmission between the central control unit and each conversion cell.

[0004] In Patent Document 1, in a configuration consisting of a main control unit (control unit) and multiple conversion cells individually connected to this main control unit, the main control unit transmits a signal simultaneously to the multiple conversion cells (see Figure 4 of Patent Document 1), and the simultaneously transmitted signal is looped back to the multiple conversion cells, measuring the error in the transmission and reception time difference of each conversion cell and performing delay compensation.

[0005] However, in the configuration shown in Patent Document 1, it is necessary to individually connect the main control unit and the multiple conversion cells, and it is necessary to provide many insulating elements on the main control unit side, which increases the cost of the insulating elements.

[0006] In contrast, Patent Documents 2 and 3 disclose a configuration in which multiple converter cells are connected in a daisy chain, thereby reducing the number of isolation elements provided in the main control unit (central control device), and thereby reducing costs. In Patent Documents 2 and 3, a dummy signal is sent from the central control device to multiple converter cells connected in a daisy chain, and the delay time until the signal returns is measured, thereby measuring the total delay time. The measured total delay time is then converted into a delay time based on a ratio according to the position of the converter cell relative to the central control device, and this delay time is used to compensate for the delay time accumulated in each converter cell. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-32342

[0008] [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-24393

[0009] [Patent Document 3] Japanese Patent Application Publication No. 2019-140772 Summary of the Invention [Problem to be solved by the invention]

[0010] In Patent Documents 2 and 3, the delay time of each conversion cell is individually compensated for by assuming that the delay times of multiple isolation elements are the same. Therefore, it is necessary to select components with small individual differences as the isolation elements to be applied. In this case, the required performance of the isolation elements is high, which results in high costs.

[0011] The present disclosure aims to measure the signal transmission delay caused by isolation elements that isolate and transmit control signals in a power conversion device composed of multiple conversion cells individually for each conversion cell without adding additional isolation elements to a central control device. [Means for solving the problem]

[0012] A power conversion device according to one aspect of the present disclosure comprises a plurality of conversion cells each including a DC / DC converter, each of which is connected in series via a pair of input terminals or a pair of output terminals and has a cell control device that controls each of the plurality of conversion cells; and a central control device that transmits control signals between each of the cell control devices of the plurality of conversion cells, wherein each of the plurality of conversion cells has a plurality of isolation elements for transmitting signals between the cell control devices and the central control device, and the central control device and one of the cell control devices of the plurality of conversion cells individually transmits a pulse signal back and forth between the other, thereby calculating the signal transmission delay time caused by the isolation elements for each conversion cell.

[0013] In a preferred embodiment, each of the cell control devices of the plurality of conversion cells has a signal reply means for generating and transmitting a pulse signal having the same pulse width as the pulse signal received from the central control device, and the central control device has a signal generating means for generating and transmitting a pulse signal having a pulse width corresponding to each of the plurality of conversion cells, a pulse discrimination means for discriminating the pulse width of the pulse signal received from the plurality of conversion cells, a time measuring means for measuring, for each of the plurality of conversion cells, the time from when the signal generating means transmits a pulse signal having a pulse width corresponding to that conversion cell to when a pulse signal having the same pulse width is discriminated by the pulse discrimination means, and a delay measuring means for calculating a differential time indicating the difference between the time measured by the time measuring means and the time required for discrimination by the pulse discrimination means.

[0014] In another preferred aspect, the central control device has a signal reply means for generating and transmitting a pulse signal having the same pulse width as the pulse signal received from the cell control devices of the plurality of conversion cells, and each of the cell control devices of the plurality of conversion cells has a signal generating means for generating and transmitting a pulse signal having a pulse width corresponding to the conversion cell, a pulse discrimination means for discriminating the pulse width of the pulse signal received from the central control device, a time measuring means for measuring the time from when the signal generating means transmits a pulse signal having a pulse width corresponding to the conversion cell to when a pulse signal having the same pulse width is discriminated by the pulse discrimination means, and a delay measuring means for calculating a differential time indicating the difference between the time measured by the time measuring means and the time required for discrimination by the pulse discrimination means.

[0015] In a preferred embodiment, the central control unit and the cell control units of the plurality of conversion cells are cascade-connected by the insulating elements.

[0016] In another preferred embodiment, the central control unit and the cell control units of the plurality of converter cells are connected in a one-to-multiple manner by the insulating elements. [Effects of the Invention]

[0017] According to one aspect of the present disclosure, even if there are individual differences in the isolation elements, the delay time of the isolation elements can be measured individually for each conversion cell. This allows the use of inexpensive isolation elements with individual differences in delay time. Furthermore, there is no need to add an isolation element to the central control unit to measure the delay in signal transmission. Furthermore, there is no need to make the signal wiring lengths equal in each section, and the signal wiring lengths can be minimized in each section, thereby reducing the cost of signal wiring. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a circuit diagram showing a configuration of a power conversion device according to a first embodiment of the present disclosure. [Figure 2] 4 is a timing chart showing the operation of the embodiment. [Figure 3] 4 is a timing chart showing the operation of the embodiment. [Figure 4] FIG. 4 is a circuit diagram showing the configuration of a power conversion device according to a second embodiment of the present disclosure. [Figure 5] 4 is a timing chart showing the operation of the embodiment. [Figure 6] FIG. 10 is a circuit diagram showing the configuration of a power conversion device according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that "DC" and "AC" are abbreviations for "Direct Current" and "Alternative Current," respectively.

[0020] First Embodiment The power conversion device 1 shown in FIG. 1 is a multi-cell converter including a plurality of (three in this example) converter cells 111, 112, and 113 and a central control device 107 that controls the power conversion operation of each of the converter cells 111, 112, and 113. Each of the converter cells 111, 112, and 113 is a cell converter that boosts or lowers a DC voltage input from a common DC path and outputs the DC voltage. Each of the converter cells 111, 112, and 113 has an isolated DC / DC converter and a pair of terminals p and q. Note that while FIG. 1 does not explicitly show a path for supplying power for driving, a power supply voltage is supplied to drive circuits 104a and 104b, the central control device 107, a cell control device 108, and the like, which will be described later, from a power supply unit (not shown).

[0021] 1, the pair of terminals p and q are output terminals connected to the output side of the isolated DC / DC converter 100. Of the pair of terminals p and q, the first terminal p is a terminal on the high potential side, and the second terminal q is a terminal on the low potential side.

[0022] Each of the multiple conversion cells 111, 112, and 113 has a pair of terminals p and q, and is connected in series via the pair of terminals p and q. The first terminal p of each of the multiple conversion cells 111, 112, and 113 is connected to the second terminal q of one of the adjacent conversion cells, and the second terminal q of each of the multiple conversion cells 111, 112, and 113 is connected to the first terminal p of the other adjacent conversion cell. Of the multiple conversion cells connected in series via the pair of terminals p and q, the first terminal p of the conversion cell located on the highest potential side (in this example, the conversion cell 111) is electrically connected to the high-potential end of a load (not shown). On the other hand, of the multiple conversion cells connected in series via the pair of terminals p and q, the second terminal q of the conversion cell located on the lowest potential side (in this example, the conversion cell 113) is electrically connected to the low-potential end of a load (not shown).

[0023] The isolated DC / DC converter 100 boosts or lowers a DC voltage input from a DC path common to multiple conversion cells 111, 112, and 113, and outputs the DC voltage from a pair of terminals p and q. The isolated DC / DC converter 100 includes a transformer 102, a primary side circuit 100a, and a secondary side circuit 100b. The transformer 102 has a primary side coil and a secondary side coil, and is a transformer that magnetically couples the primary side coil and the secondary side coil. The primary side circuit 100a and the secondary side circuit 100b are magnetically coupled by the transformer 102.

[0024] The primary circuit 100a includes a capacitive element 103a, a primary full-bridge circuit 120a, and a drive circuit 104a. The primary circuit 100a may include a reactor 106a connected in series to the primary coil of the transformer 102.

[0025] The primary full-bridge circuit 120a includes a primary first half-bridge circuit in which a switching element 101a serving as a primary first upper arm and a switching element 101b serving as a primary first lower arm are connected in series, and a primary second half-bridge circuit in which a switching element 101c serving as a primary second upper arm and a switching element 101d serving as a primary second lower arm are connected in series. The primary coil of the transformer 102 (or a series circuit of the primary coil and the reactor 106a) is connected between the intermediate connection point of the switching elements 101a and 101b and the intermediate connection point of the switching elements 101c and 101d.

[0026] The secondary side circuit 100b includes a capacitive element 103b, a secondary side full bridge circuit 120b, and a drive circuit 104b. The secondary side circuit 100b may include a reactor 106b connected in series to the secondary side coil of the transformer 102. The secondary side circuit 100b and the secondary side full bridge circuit 120b have the same configuration as the primary side circuit 100a and the primary side full bridge circuit 120a.

[0027] The multiple primary-side switching elements 101a, 101b, 101c, and 101d are driven by a primary-side drive circuit 104a. The multiple secondary-side switching elements 101e, 101f, 101g, and 101h in the secondary-side full-bridge circuit 120b are driven by a secondary-side drive circuit 104b.

[0028] Specific examples of the primary-side and secondary-side switching elements include semiconductor switching elements such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors). The drive circuits 104a and 104b are also referred to as GDUs (Gate Driver Units).

[0029] The isolated DC / DC converter 100 is a power conversion circuit known as a DAB (Dual Active Bridge) converter, which has a primary-side full-bridge circuit 120a provided on the primary side of a transformer 102 and a secondary-side full-bridge circuit 120b provided on the secondary side of the transformer 102. The DAB converter transmits power between the primary side and the secondary side by applying a voltage to the leakage inductance of the transformer 102 or to reactors 106a and 106b connected in series to the transformer 102. The transmitted power is controlled by the phase difference between the output voltage output from two intermediate connection points of the primary-side full-bridge circuit 120a and the output voltage output from two intermediate connection points of the secondary-side full-bridge circuit 120b. The power transmitted from the secondary side to the primary side is expressed by the following simplified equation (1): P=(V1·V2·Φ(1-Φ / π)) / (ω·L) ……(1)

[0030] In equation (1), P is the transmitted power, V1 is the amplitude of the primary output voltage, V2 is the amplitude of the secondary output voltage, L is the transformer leakage inductance or the inductance of the external reactor, Φ is the phase difference between V1 and V2, π is the constant of the circumference of a circle, and ω (= 2πf) is the angular frequency of the switching of each switching element. f is the switching frequency of each switching element. Note that equation (1) above applies when the switching duty ratio of each switching element is 50% (when V1 and V2 are square waves (including approximate square waves) with a duty ratio of 50%). Note that because the circuit configuration of a DAB converter is symmetrical, the reference phase for the phase difference of the output voltage can be on either the secondary side or the primary side.

[0031] In this embodiment, the primary circuits 100a of the multiple converter cells 111, 112, and 113 are connected in parallel to each other and have the same reference potential. On the other hand, the secondary circuits 100b of the multiple converter cells 111, 112, and 113 are connected in series to each other and have different reference potentials for each converter cell.

[0032] In the power conversion device 1 shown in FIG. 1, the central control device 107 supplies a plurality of control signals that define the timing at which the waveform of the output voltage V1 starts to repeat to each of the primary side circuits 100a in which the reference potentials of the plurality of conversion cells 111, 112, and 113 are equal.

[0033] The secondary-side circuits 100b of the multiple converter cells 111, 112, and 113 each include a cell control device 108 and a drive circuit 104b. The power conversion device 1 also includes multiple isolation elements 105a, 105b, 105c, 105d, 105e, and 105f that are provided for each of the multiple converter cells 111, 112, and 113 and transmit transmit / receive signals to a corresponding converter cell among the multiple converter cells 111, 112, and 113. This allows electrically isolated transmit / receive signals to be transmitted / received to each of the internal circuits (cell control devices 108 and drive circuits 104b) that operate at different reference potentials for each converter cell.

[0034] 1, a central control device 107 and cell control devices 108 of a plurality of converter cells 111, 112, and 113 are cascade-connected by isolation elements. The central control device 107 supplies a transmission / reception signal common to the plurality of converter cells 111, 112, and 113 to the plurality of cascade-connected isolation elements 105e, 105c, and 105a. Here, information included in the transmission signal transmitted by the central control device 107 to the plurality of converter cells 111, 112, and 113 is, for example, drive signal information for the switching elements of each cell.

[0035] When the reference phase of the phase difference of the output voltage of the DAB converter is set to the secondary side, the transmission signal transmitted by the central control device 107, which includes drive signal information for the secondary side switching elements, may be a signal shared by the multiple converter cells 111, 112, and 113. The transmission signal common to the multiple converter cells 111, 112, and 113 is supplied from the converter cell 113 with the lowest potential to the converter cell 111 with the highest potential among the multiple converter cells 111, 112, and 113.

[0036] In the power conversion device 1 shown in FIG. 1, the central control device 107 receives signals transmitted from the plurality of conversion cells 111, 112, and 113 via the cascaded isolation elements 105b, 105d, and 105f, respectively.

[0037] Here, the signals received by the central control device 107 from each of the multiple conversion cells 111, 112, and 113 are, for example, digital signals obtained by converting voltage information of the capacitance element 103b of each conversion cell, current information of the secondary coil of the transformer 102, etc., or digital signals such as abnormality detection information of the secondary circuit.

[0038] The received signal returned from the plurality of converter cells 111, 112, 113 to the central control unit 107 is transmitted from the converter cell 111 with the higher potential to the converter cell 113 with the lower potential among the plurality of converter cells 111, 112, 113.

[0039] Each of the isolation elements 105a, 105b, 105c, 105d, 105e, and 105f may be composed of a single isolation element or a plurality of cascade-connected isolation elements. Specific examples of the isolation elements 105 include an isolation transformer, a pulse transformer, a digital isolator, and an isolation amplifier. The isolation elements 105 may also be optical isolators such as photocouplers.

[0040] Each of the isolation elements 105a, 105b, 105c, 105d, 105e, and 105f has a different delay time T(105a), T(105b), T(105c), T(105d), T(105e), and T(105f) due to individual differences in the components used.

[0041] Hereinafter, a method for measuring the delay time of each of the converter cells 111, 112, and 113 in the first embodiment will be described with reference to Fig. 2. Fig. 2 is a timing chart showing an example of operating waveforms for individually measuring the delay of the central control device 107 of the power conversion device and each of the converter cells 111, 112, and 113 in the first embodiment.

[0042] In this embodiment, the central control unit 107 individually sends pulse signals back and forth between multiple conversion cells 111, 112, and 113, and uses the transmission signal S107 sent to the multiple conversion cells 111, 112, and 113 and the reception signals R107_111, R107_112, and R107_113 received from the multiple conversion cells 111, 112, and 113 to measure the signal transmission delay time caused by the isolation elements between the central control unit 107 and each conversion cell 111, 112, and 113 individually for each conversion cell.

[0043] For example, when the central control device 107 and each cell control device 108 are initialized, even if the transmission / reception signals between the central control device 107 and the multiple conversion cells 111, 112, and 113 are used for delay measurement, this does not affect the operation of the power conversion device 1.

[0044] The central control device 107 generates a plurality of pulse signals having pulse widths corresponding to the plurality of converter cells 111, 112, and 113 as transmission signals, and transmits the signals to the plurality of converter cells 111, 112, and 113. In this embodiment, the pulse width corresponding to the converter cell 111 is set to a first specified value PW1, the pulse width corresponding to the converter cell 112 is set to a second specified value PW2, and the pulse width corresponding to the converter cell 113 is set to a third specified value PW3. In this way, the central control device 107 in this embodiment functions as a signal generating means that generates and transmits pulse signals having pulse widths corresponding to the plurality of converter cells.

[0045] The transmission signal S107 from the central control unit 107 is delayed by the delay time of each isolation element each time it passes through an isolation element, and is finally received by the cell control unit 108 of each converter cell. For example, the received signal R108_111 received by the cell control unit 108 of the converter cell 111 with the highest potential arrives at the cell control unit 108 delayed by a delay time TDF(111), which is the sum of the delay times T(105a), T(105c), and T(105e) of the three isolation elements. The delay times T(105a), T(105c), and T(105e) of the isolation elements are each unknown. Similarly, the received signal R108_112 received by the cell control unit 108 of the converter cell 112 with the second highest potential arrives at the cell control unit 108 delayed by a delay time TDF(112), which is the sum of the delay times T(105c) and T(105e) of the two isolation elements. Furthermore, the reception signal R108_113 received by the cell control device 108 of the conversion cell 113 with the lowest potential reaches the cell control device 108 with a delay time TDF(113) equal to the delay time T(105e) of one insulating element.

[0046] The cell control device 108 of each conversion cell generates signals S108_111, S108_112, S108_113 which have the same pulse width as the signals R108_111, R108_112, R108_113 received from the central control device 107 and are delayed by the pulse width determination time TJ, and transmits these signals to the central control device 107. In this way, the cell control device 108 of each conversion cell functions as a signal return means which generates and transmits a pulse signal having the same pulse width as the pulse signal received from the central control device 107. The process by which the cell control device 108 generates a transmission signal based on the received signal will be described in detail later. The pulse width determination time TJ is a known value preset in the cell control device 108 and is greater than any of the first specified value PW1, the second specified value PW2, and the third specified value PW3.

[0047] Signals S108_111, S108_112, and S108_113 transmitted from the cell control devices 108 of the multiple converter cells 111, 112, and 113 are delayed by the delay time of each isolation element each time they pass through an isolation element, and are finally received by the central control device 107. For example, the signal S108_111 transmitted from the cell control device 108 of the converter cell 111 with the highest potential is delayed by a delay time TDB(111), which is the sum of the delay times T(105b), T(105d), and T(105f) of the three isolation elements, and arrives at the central control device 107 as signal R107_111. The delay times T(105b), T(105d), and T(105f) of the isolation elements are each unknown. Furthermore, the signal S108_112 transmitted from the cell control device 108 of the converter cell 112 with the second highest potential is delayed by a delay time TDB(112), which is the sum of the delay times T(105d) and T(105f) of the two insulating elements, and arrives as signal R107_112 at the central control device 107. Furthermore, the signal S108_113 transmitted from the cell control device 108 of the converter cell 113 with the lowest potential is delayed by a delay time TDB(113), which is equal to the delay time T(105f) of one insulating element, and arrives at the central control device 107 as signal R107_113.

[0048] The central control device 107 receives signals transmitted from the cell control devices 108 of the plurality of conversion cells 111, 112, and 113, performs signal determination based on the pulse width of the received signals, and generates signal determination flags F107_111, F107_112, and F107_113 at a timing delayed by a pulse width determination time TJ from the timing of reception from the cell control device 108. Here, the signal determination flag F107_111 corresponds to the conversion cell 111, the signal determination flag F107_112 corresponds to the conversion cell 112, and the signal determination flag F107_113 corresponds to the conversion cell 113. For example, when the central control device 107 detects the pulse width of the first specified value PW1 corresponding to the conversion cell 111, it generates the signal determination flag F107_111. In this way, the central control device 107 in this embodiment functions as a pulse determination means for determining the pulse width of pulse signals received from the plurality of conversion cells.

[0049] The central control unit 107 measures count values ​​C107_111, C107_112, C107_113 from the rising edge of the transmission signal (pulse signal) S107 to the multiple conversion cells 111, 112, 113 to the count values ​​C107_111, C107_112, C107_113 of each signal determination flag F107_111, F107_112, F107_113 that it has generated based on the signals R107_111, R107_112, R107_113 received from the multiple conversion cells 111, 112, 113.

[0050] In this embodiment, the count value corresponding to the conversion cell 111 is designated as C107_111, the count value corresponding to the conversion cell 112 is designated as C107_112, and the count value corresponding to the conversion cell 113 is designated as C107_113. For example, the central control device 107 measures the count value C107_111 by measuring the time from the rising edge of a pulse having a pulse width of the first specified value PW1 that it has generated to the signal determination flag F107_111 that it has generated using a counter or the like. In this way, the central control device 107 in this embodiment functions as a time measurement means that measures, for each of the multiple conversion cells, the times C107_111, C107_112, and C107_113 from when the signal generating means transmits a pulse signal having a pulse width corresponding to the conversion cell to when the pulse determining means discriminates a pulse signal having the same pulse width.

[0051] Here, the delay time T(111) between the central control unit 107 and the conversion cell 111, the delay time T(112) between the central control unit 107 and the conversion cell 112, and the delay time T(113) between the central control unit 107 and the conversion cell 113 can be expressed by the following equation (2). T(111)=T(105a)+T(105b)+T(105c)+T(105d) +T(105e)+T(105f) =TDF(111)+TDB(111) =C107_111-2TJ T(112)=T(105c)+T(105d)+T(105e)+T(105f) =TDF(112)+TDB(112) =C107_112-2TJ T(113)=T(105e)+T(105f) =TDF(113)+TDB(113) =C107_113-2TJ ……(2)

[0052] Therefore, the central control device 107 individually measures delay times T(111), T(112), and T(113) from the central control device 107 to the multiple conversion cells 111, 112, and 113 by subtracting the time related to the judgment (pulse width judgment time TJ × 2 times) from the count values ​​C107_111, C107_112, and C107_113 corresponding to each of the multiple conversion cells 111, 112, and 113. In this way, the central control device 107 in this embodiment functions as delay measurement means that calculates a differential time indicating the difference between the time measured by the time measurement means and the time required for judgment by the pulse discrimination means.

[0053] Then, the central control unit 107 uses the measured individual delay times T(111), T(112), and T(113) from the central control unit 107 to the multiple conversion cells 111, 112, and 113 to compensate for the delay as compensation time for the control signals that the central control unit 107 supplies to each of the primary side circuits 100a of the multiple conversion cells 111, 112, and 113, thereby compensating for the delay time of each of the multiple conversion cells 111, 112, and 113 individually.

[0054] Furthermore, for example, the central control device 107 can convert the measured individual delay times T(111), T(112), and T(113) from the central control device 107 to the multiple conversion cells 111, 112, and 113 into digital values ​​and transmit them via isolation elements to the cell control devices 108 of the multiple conversion cells 111, 112, and 113. The cell control devices 108 of the multiple conversion cells 111, 112, and 113 can compensate for the delay times individually by using these individual delay times T(111), T(112), and T(113) to perform delay compensation on the control signals generated by the cell control device 108 as compensation times.

[0055] Hereinafter, the pulse width determination method in the cell control device 108 and the central control device 107 will be described with reference to FIG.

[0056] The cell control device 108 and the central control device 107 each detect the beginning of a pulse of a received signal (in FIG. 3, the rising edge of the pulse of signals R108_111 and R107_111) and count up to the end of the pulse (in FIG. 3, the falling edge of the pulse of signals R108_111 and R107_111) using a counter or the like. The cell control device 108 and the central control device 107 compare the measured count value with a predetermined specified value (in the example of FIG. 3, a first specified value PW1) to generate a corresponding pulse (in FIG. 3, a pulse having the same width as the count value) or a flag. These pulses and flags are generated by the cell control device 108 and the central control device 107 after a predetermined pulse width determination time TJ has elapsed since the beginning of the received pulse was detected.

[0057] Second Embodiment FIG. 4 is a diagram illustrating the configuration of a power conversion device according to a second embodiment. In the second embodiment, the same components as those in the above-described embodiment are denoted by the same reference numerals, and the description of the same components and operations as those in the above-described embodiment will be omitted by citing the above description. In the power conversion device 2 shown in FIG. 4, a central control device 107 and a cell control device 108 of a plurality of converter cells 111, 112, and 113 are connected in a one-to-multiple manner via isolation elements. Specifically, the central control device 107 distributes a transmission signal common to the plurality of converter cells 111, 112, and 113 and supplies the signal to a plurality of isolation elements 105a, 105c, and 105e. In the power conversion device 2, the central control device 107 individually receives signals transmitted from the plurality of converter cells 111, 112, and 113 via a plurality of isolation elements 105b, 105d, and 105f.

[0058] 5 is a timing chart showing an example of operational waveforms for individually measuring the delay times of the central control device 107 and each of the converter cells 111, 112, and 113 of the power conversion device in the second embodiment. In the second embodiment, the same reference numerals as those in the above-described embodiment are used, and the description of the same configurations and operations as those in the above-described embodiment will be omitted by citing the above description. In this example, similar to the first embodiment, the central control device 107 uses received signals received from the multiple converter cells 111, 112, and 113 to individually measure the delay times of the central control device 107 and each of the converter cells 111, 112, and 113.

[0059] The signal transmitted from the central control device 107 is delayed by the delay time of the isolation elements provided in each of the converter cells 111, 112, and 113, and is received by the cell control device 108. For example, the signal received by the cell control device 108 of the converter cell 111 is delayed by the delay time T (105a) of one isolation element.

[0060] The transmission signal S107 from the cell control device 108 is delayed by the delay time of the isolation elements provided in each of the conversion cells 111, 112, and 113, and is received by the central control device 107. For example, the signal S107 transmitted from the cell control device 108 of the conversion cell 111 is received by the central control device 107 as a signal R108_111 delayed by the delay time T (105b) of one isolation element.

[0061] In this embodiment, the delay times of the central control unit 107 and the conversion cells 111, 112, and 113 can be measured and compensated for individually in the same manner as in the first embodiment.

[0062] In this embodiment, the central control device 107 can individually measure the delay time T(111) between the central control device 107 and the conversion cell 111, the delay time T(112) between the central control device 107 and the conversion cell 112, and the delay time T(113) between the central control device 107 and the conversion cell 113, according to the following equations: T(111)=T(105a)+T(105b) =C107_111-2TJ T(112)=T(105c)+T(105d) =C107_112-2TJ T(113)=T(105e)+T(105f) =C107_113-2TJ ...(3)

[0063] <Effects of the embodiment> The effects of the first and second embodiments will be described below in comparison with a comparative embodiment. First, as a comparative embodiment, the power conversion device disclosed in Patent Document 3 will be described. Note that detailed operation of this power conversion device is disclosed in Patent Document 3. Therefore, here, only the method for measuring the delay time of an insulating element in this comparative embodiment will be described.

[0064] 6 is a diagram showing the configuration of a power conversion device in a comparative example. In this comparative example, a three-phase modular multilevel converter (MMC) is used as the power conversion device 103, which is connected to a three-phase power system 201 and is configured by cascading multiple cells 205.

[0065] The central control device 207 is a device that controls the power conversion device 3. The central control device 207 is equipped with two optical transceivers 210, and transmits control signals to each cell 205 via the optical transceivers 210 and optical fiber cables 211, and also receives capacitor voltage information from each cell 205.

[0066] In this comparative example, all the cells 205 are daisy-chained from a central control unit 207 via optical fiber cables 211 .

[0067] Each cell 205 is equipped with a cell control unit 220 , and the cell control unit 220 is connected to other adjacent cell control units 220 or the central control unit 207 via two optical transceivers 210 and optical fiber cables 211 .

[0068] In this comparative example, a daisy chain connection is made using optical fiber cables, so a delay occurs before a cell control device 220 transmits a signal to another adjacent cell control device 220.

[0069] Since all cells 205 are daisy-chain connected using optical fiber cables, delays in signal transmission between cells accumulate in cells 205 that are far from the central control unit 207. Therefore, it is necessary to make the delay time from the central control unit 207 to each cell 205 equal.

[0070] The operation of the signal delay compensation method in this comparative example will be described below. In this comparative example, an optical signal transmitted from central control device 207 passes through N cells 205 and is returned to central control device 207 again.

[0071] Therefore, the central control device 207 can measure the time (total delay time) TD that an optical signal takes to pass through N cells 205.

[0072] For example, when initializing the central control device 207 and each cell control device 220, the central control device 207 can measure the total delay time TD using an optical dummy signal for delay time measurement, and optically serially transmit the digital value of TD to all cells 205. As a result, all cells 205 have information on the total delay time TD for all cells (N cells).

[0073] Also, each cell is assumed to have information (cell number K) in advance about the number of connected cells relative to the central control device 207.

[0074] Here, if the delay compensation time of the Kth cell is TB(K), then by giving TB(K) using the following equation (4), it is possible to make the signal transmission delay time from the central control device 207 to each cell 205 approximately equal. Furthermore, in the following equation (4), it is assumed that the signal transmission delay between cells is equal at each point. TB(K)=(1-K / N)·TD ……(4)

[0075] However, since the signal transmission delay between cells is caused by an isolation element consisting of the optical transceiver 210 and the optical fiber cable 211, when taking into account, for example, the individual component differences in delay time in the optical transceiver 210 and the differences in the cable length of the optical fiber cable 211, the signal transmission delay between cells may not be equal at each part.

[0076] Therefore, in the method of compensating for the delay time of the insulating elements in this comparative example, if the delay time of the insulating elements differs for each cell, the delay of each cell cannot be made equal, resulting in a discrepancy in the operation timing between cells, which may cause malfunctions depending on the conditions. Furthermore, in order to ensure the effectiveness of the method for compensating for the delay time of the isolation element in this comparative example, it would be necessary to use transceivers with small individual differences in delay time, or to make the wiring lengths of each part longer than necessary in order to make the wiring lengths of the optical fiber cables equal, which would increase costs.

[0077] In contrast, in each embodiment of the present disclosure, even if there are individual differences in the isolation elements, the delay time of the isolation elements can be compensated for individually for each converter cell. This makes it possible to apply low-cost isolation elements with large individual differences in delay time. Furthermore, there is no need to make the signal wiring lengths equal, and each section can be configured to be as short as possible. As a result, for example, it is possible to reduce the cost of the power conversion device.

[0078] <Other embodiments> Although the first and second embodiments of the present disclosure have been described above, other embodiments of the present disclosure are also possible. For example, the following are included.

[0079] (1) In the above embodiment, the plurality of converter cells are connected in series via a pair of output terminals, but they may be connected in series via a pair of input terminals. In this case, the cell control device may be provided on the input side of the converter cell.

[0080] (2) In the above embodiment, the central control device 107 measures the delay time of signal transmission between each of the conversion cells 111, 112, and 113. However, the cell control devices 108 of each of the conversion cells 111, 112, and 113 may measure the delay time of signal transmission between each of the conversion cells 111, 112, and 113 and the central control device 107. In this embodiment, the central control device 107 is provided with a function as signal reply means for generating and transmitting a pulse signal having the same pulse width as the pulse signal received from the cell control devices 108 of the multiple conversion cells 111, 112, and 113. Furthermore, each of the cell control devices 108 of the plurality of conversion cells 111, 112, 113 is provided with the following functions: signal generation means for generating and transmitting a pulse signal having a pulse width corresponding to the conversion cell, pulse discrimination means for discriminating the pulse width of a pulse signal received from the central control device 107, time measurement means for measuring the time from when the signal generation means transmits a pulse signal having a pulse width corresponding to the conversion cell until a pulse signal having the same pulse width is discriminated by the pulse discrimination means, and delay measurement means for calculating a differential time indicating the difference between the time measured by the time measurement means and the time required for discrimination by the pulse discrimination means. In this mode as well, the same effects as those of the above embodiment can be obtained. [Explanation of symbols]

[0081] 1, 2...power conversion device, 111, 112, 113...conversion cell, 107...central control device, 105a, 105b, 105c, 105d, 105e, 105f..., 100...DC / DC converter, p, q...output terminal, 100a...primary side circuit, 100b...secondary side circuit, 101a, 101b, 101c, 101d, 101e, 101f, 101g, 101h...switching element, 102...transformer, 106a, 106b...reactor, 103a, 103b...capacitive element, 104a, 104b...drive circuit, 108...cell control device.

Claims

1. a plurality of conversion cells each including a DC / DC converter, the plurality of conversion cells being connected in series via a pair of input terminals or a pair of output terminals, and each of the conversion cells being provided with a cell control device for controlling the plurality of conversion cells; a central control unit for transmitting control signals to and from each of the cell control units of the plurality of conversion cells; each of the plurality of conversion cells includes a plurality of isolation elements for transmitting signals between each cell control device and the central control device; A power conversion device characterized in that one of the central control unit and the cell control units of the multiple conversion cells individually sends a pulse signal back and forth between the other and calculates the signal transmission delay time caused by the isolation element for each conversion cell.

2. Each of the cell control devices of the plurality of conversion cells includes: a signal reply means for generating and transmitting a pulse signal having the same pulse width as the pulse signal received from the central control device; The central control unit a signal generating means for generating and transmitting a pulse signal having a pulse width corresponding to each of the plurality of conversion cells; a pulse determining means for determining the pulse width of the pulse signals received from the plurality of conversion cells; a time measurement means for measuring, for each of the plurality of conversion cells, the time from when the signal generation means transmits a pulse signal having a pulse width corresponding to the conversion cell until when the pulse discrimination means discriminates a pulse signal having the same pulse width; a delay measuring means for calculating a differential time indicating the difference between the time measured by the time measuring means and the time required for discrimination by the pulse discriminating means; 2. The power conversion device according to claim 1, wherein each of the power conversion devices comprises:

3. The central control unit a signal reply means for generating and transmitting a pulse signal having the same pulse width as the pulse signal received from the cell control device of the plurality of conversion cells; Each of the cell control devices of the plurality of conversion cells includes: a signal generating means for generating and transmitting a pulse signal having a pulse width corresponding to the conversion cell; a pulse determining means for determining the pulse width of a pulse signal received from the central control unit; a time measurement means for measuring the time from when the signal generation means transmits a pulse signal having a pulse width corresponding to the conversion cell until when a pulse signal having the same pulse width is discriminated by the pulse discrimination means; a delay measuring means for calculating a differential time indicating the difference between the time measured by the time measuring means and the time required for discrimination by the pulse discriminating means; 2. The power conversion device according to claim 1, wherein each of the power conversion devices comprises:

4. 4. The power conversion device according to claim 1, wherein the central control device and the cell control devices of the plurality of conversion cells are cascade-connected by the insulating elements.

5. 4. The power conversion device according to claim 1, wherein the central control device and the cell control devices of the plurality of conversion cells are connected one-to-multiple by the insulating elements.

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