Power conversion device and inductor current control method for power conversion device

Abstract

A power conversion device (100) comprises a plurality of power conversion units (U) connected in parallel and a control unit (99) for controlling the power conversion units (U), and converts input DC power into DC power having a target voltage and outputs the DC power having the target voltage. The control unit (99) comprises: a first current control unit (40) that, on the basis of an inductor current (IL) and an inductor current command value (IL**), generates a first duty ratio (Dccm) of a control signal (So) that controls a plurality of switching elements so as to cause the current (IL) to flow through an inductor (5) in a continuous current mode; a second current control unit (41) that, on the basis of the current command value (IL**), generates a second duty ratio (Ddcm) of the control signal (So) that controls the elements so as to cause the current (IL) to flow through the inductor (5) in a discontinuous current mode; and a duty ratio selection unit (42) that sets either of the duty ratios (Dccm, Ddcm) corresponding to the current modes as the duty ratio of the control signal (So).

Description

Power conversion device and inductor current control method for power conversion device

[0001] The present disclosure relates to a power conversion device and an inductor current control method for a power conversion device.

[0002] Power conversion devices such as DC-DC converters that convert input voltages to target output voltages must output a distortion-free output voltage. As the output power capacity of power conversion devices increases, multi-phase configurations in which multiple DC-DC converters are connected in parallel are used.

[0003] The power conversion device disclosed in Patent Document 1 does not have a multiphase configuration, but is equivalent to a DC-DC converter with one phase. The power conversion device of Patent Document 1 converts DC power input from a battery via an input-side filter circuit into DC power with a target output voltage using a power conversion circuit, and supplies the DC power with the target output voltage to a load via an output-side filter circuit. When controlling the power conversion circuit, the power conversion device of Patent Document 1 calculates a feedforward term for a continuous current mode and a feedforward term for a discontinuous current mode to suppress output voltage distortion due to changes in current mode, selects one of them as the feedforward term, and controls the switching elements of the power conversion circuit using a control circuit based on a drive signal generated based on the selected feedforward term. The power conversion circuit of Patent Document 1 also includes an input-side switching circuit, a reactor (inductor), a transformer, and an output-side switching circuit.

[0004] When the power conversion device of Patent Document 1 is configured as a multi-phase device, the power conversion circuits are connected in parallel. The operation and stop of each of the parallel-connected power conversion circuits is controlled by a control circuit. The number of phases of the power conversion device is switched by the operation and stop of the multiple power conversion circuits.

[0005] Japanese Patent Application Laid-Open No. 2015-035921

[0006] Factors that distort the output voltage of a power conversion device with an inductor as its power conversion circuit, such as the power conversion device of Patent Document 1, include fluctuations in the input voltage, fluctuations in the output load, and switching the number of phases. When the input voltage fluctuates, the ripple of the inductor current fluctuates. When the output load fluctuates, the DC component of the inductor current, which is the current flowing through the inductor, fluctuates. When the number of phases is switched, the DC component of the inductor current fluctuates. These fluctuations cause a change in the current mode of the inductor current. The current mode of the inductor current is broadly classified into continuous current mode (CCM) and discontinuous current mode (DCM). Continuous current mode is an operating mode in which current always flows, while discontinuous current mode is a current mode with a zero-current period. It is known that a change in the current mode degrades the response of the power conversion circuit to a current command value.

[0007] In the power conversion device of Patent Document 1, a feedback duty ratio is generated by a PI (Proportional-Integral) calculation unit for current control, and is added to either the duty ratio for continuous current mode or the duty ratio for discontinuous current mode to generate a duty ratio for PWM (Pulse Width Modulation) control. When the feedback term is shared, output voltage distortion occurs due to accumulated error of the integrator of the previous current mode when the current mode changes, and output voltage distortion occurs due to inability to detect the average current in discontinuous current mode.

[0008] Furthermore, when the power conversion device of Patent Document 1 is configured as a multi-phase device, the detected output current is used for the feedforward calculation, so when the number of phases is switched, overcompensation occurs due to the feedforward term, resulting in distortion of the output voltage.

[0009] The present disclosure aims to reduce output voltage distortion when switching the number of phases in a power conversion device with a multi-phase configuration.

[0010] A power conversion device according to the present disclosure includes a plurality of power conversion units connected in parallel and a control unit for controlling the plurality of power conversion units, converting DC power input from an input terminal into DC power of a target voltage and outputting it from an output terminal. Each power conversion unit includes a plurality of PWM-controlled switching elements, an inductor arranged closer to the output terminal than the plurality of switching elements, and an inductor current output device that outputs an inductor current that detects or estimates a current flowing through the inductor. The control unit includes a command control unit that outputs an inductor current command value that causes the inductor current of each power conversion unit to track, and a current control unit that generates a control signal for controlling the corresponding plurality of switching elements for each power conversion unit. The current control section for each power conversion unit includes: a first current control section that generates, based on the inductor current and an inductor current command value, a first duty ratio of a control signal that controls the plurality of switching elements to flow an inductor current that is in a continuous current mode where current flows continuously through the inductor; a second current control section that generates, based on the inductor current command value, a second duty ratio of a control signal that controls the plurality of switching elements to flow an inductor current that is in a discontinuous current mode where current flows intermittently through the inductor; and a duty ratio selection section that selects either the first duty ratio or the second duty ratio corresponding to the current mode of the continuous current mode or the discontinuous current mode as a selected duty ratio and determines the selected duty ratio as the duty ratio of the control signal.

[0011] According to the power conversion device of the present disclosure, each power conversion unit connected in parallel is controlled by a control signal having a duty ratio corresponding to the current mode of the inductor current, that is, the continuous current mode and the discontinuous current mode, thereby reducing output voltage distortion when switching the number of phases, which is the number of operating power conversion units.

[0012] 7 is a diagram illustrating a configuration of a power conversion device according to a first embodiment. FIG. 17 is a diagram illustrating a configuration of an inverter circuit of FIG. 1. FIG. 17 is a diagram illustrating a first example of a transformer and a rectifier circuit of FIG. 1. FIG. 17 is a diagram illustrating a first example of an inductor current output device of FIG. 1. FIG. 17 is a diagram illustrating a second example of an inductor current output device of FIG. 1. FIG. 17 is a diagram illustrating a third example of an inductor current output device of FIG. 1. FIG. 17 is a diagram illustrating a configuration of a control unit of FIG. 1. FIG. 17 is a diagram illustrating an example of a hardware configuration that realizes the function of the control unit of FIG. 7 by digital calculation. FIG. 17 is a diagram illustrating an example of an output of a control signal to each unit of FIG. 1. FIG. 17 is a diagram illustrating the sign of a phase input current output from each unit of FIG. 1. FIG. 17 is a diagram illustrating the sign of a primary-side current output from each unit of FIG. 1. FIG. 17 is a diagram illustrating the sign of an inductor current output from each unit of FIG. 1. FIG. 17 is a diagram illustrating the sign of a phase output current output from each unit of FIG. 1. FIG. 17 is a diagram illustrating a duty ratio. FIG. 17 is a diagram illustrating a first example of a duty ratio characteristic according to the first embodiment. FIG. 17 is a diagram illustrating a second example of a duty ratio characteristic according to the first embodiment. FIG. 17 is a flowchart illustrating an example of a control method for a power conversion device according to the first embodiment. FIG. 17 is a flowchart illustrating a first example of step S05 of FIG. 17. FIG. 17 is a flowchart illustrating a second example of step S05 of FIG. 17. FIG. 17 is a flowchart illustrating the processing steps of step S05 of FIG. 17. FIG. 2 is a diagram showing a second example of the transformer and rectifier circuit of FIG. 1. FIG. 3 is a diagram showing a third example of the transformer and rectifier circuit of FIG. 1. FIG. 4 is a diagram showing a fourth example of the transformer and rectifier circuit of FIG. 1. FIG. 2 is a diagram showing control signals output to the rectifier circuits of FIGS. 21 to 23. FIG. 24 is a diagram showing the configuration of control signals corresponding to FIGS. 21 and 23. FIG. 25 is a diagram showing the configuration of control signals corresponding to FIG. 22. FIG. 26 is a diagram showing the configuration of another power conversion unit according to embodiment 1. FIG. 27 is a diagram showing the configuration of yet another power conversion unit according to embodiment 1. FIG. 28 is a diagram showing the main parts of another current control unit according to embodiment 1.

[0013] First Embodiment. FIG. 1 is a diagram illustrating the configuration of a power conversion device according to a first embodiment. FIG. 2 is a diagram illustrating the configuration of the inverter circuit of FIG. 1, and FIG. 3 is a diagram illustrating a first example of the transformer and rectifier circuit of FIG. 1. FIGS. 4 to 6 are diagrams illustrating first to third examples of the inductor current output device of FIG. 1, respectively. FIG. 7 is a diagram illustrating the configuration of the control unit of FIG. 1, and FIG. 8 is a diagram illustrating an example of a hardware configuration that realizes the function of the control unit of FIG. 7 through digital calculation. FIG. 9 is a diagram illustrating an example of the output of control signals to each unit of FIG. 1. FIG. 10 is a diagram illustrating the signs of phase input currents output from each unit of FIG. 1, and FIG. 11 is a diagram illustrating the signs of primary-side currents output from each unit of FIG. 1. FIG. 12 is a diagram illustrating the signs of inductor currents output from each unit of FIG. 1, and FIG. 13 is a diagram illustrating the signs of phase output currents output from each unit of FIG. 1. FIG. 14 is a diagram illustrating duty ratios, and FIGS. 15 and 16 are first and second examples of duty ratio characteristics according to the first embodiment, respectively. FIG. 17 is a flowchart illustrating an example of a control method for the power conversion device according to the first embodiment. FIG. 18 is a flowchart showing a first example of step S05 in FIG. 17 , and FIG. 19 is a flowchart showing a second example of step S05 in FIG. 17 . FIG. 20 is a flowchart showing the processing steps of step S05 in FIG. 17 . FIGS. 21 to 23 are diagrams showing second to fourth examples of the transformer and rectifier circuit of FIG. 1 , respectively. FIG. 24 is a diagram showing control signals output to the rectifier circuits of FIGS. 21 to 23 . FIG. 25 is a diagram showing the configuration of control signals corresponding to FIGS. 21 and 23 , and FIG. 26 is a diagram showing the configuration of control signals corresponding to FIG. 22 . Power conversion device 100 of embodiment 1 is a multi-phase power conversion device that includes multiple power conversion units U connected in parallel and a control unit 99 that controls the multiple power conversion units U, and converts DC power input from input terminals 23 a, 23 b into DC power of a target voltage and outputs the converted power from output terminals 24 a, 24 b.

[0014] DC power input to the power conversion device 100 is input from a DC source 19 via an input filter 17. A positive terminal (not shown) of the DC source 19 and an input terminal 23a of the power conversion device 100 are connected via a positive wiring 21a, and a negative terminal (not shown) of the DC source 19 and an input terminal 23b of the power conversion device 100 are connected via a negative wiring 22a. The input filter 17 is connected to the positive wiring 21a and the negative wiring 22a. DC power output from the power conversion device 100 is supplied to a load 20 via an output filter 18. An output terminal 24a of the power conversion device 100 and a positive terminal (not shown) of the load 20 are connected via a positive wiring 21b, and an output terminal 24b of the power conversion device 100 and a negative terminal (not shown) of the load 20 are connected via a negative wiring 22b.

[0015] FIG. 1 shows an example in which four power conversion units U are provided corresponding to four phases, i.e., phases 1 to 4. That is, the power conversion device 100 shown in FIG. 1 is an example in which the number of phases is four. Where appropriate, the reference symbol U is used collectively for the power conversion units, and U1 to U4 are used when distinguishing between them. The power conversion units U corresponding to phases 1 to 4 are power conversion unit U1 to power conversion unit U4, respectively. Where appropriate, the power conversion units U1 to U4 corresponding to phases 1 to 4 will be simply referred to as power conversion units U1 to U4 of phases 1 to 4. A capacitor 7 is connected between positive wiring 21b and negative wiring 22b from the positive-side junction and negative-side junction where the outputs of the power conversion units U join to output terminals 24a, 24b. That is, the positive-side junction and the negative-side junction where the outputs of the power conversion units U are joined are provided between the output terminals 27, 28 of the power conversion units U and the connection points with the positive-side wiring 21 b and the negative-side wiring 22 b of the capacitor 7. The power conversion device 100 of the first embodiment converts the DC voltage of the DC source 19 into an arbitrary target DC voltage and supplies it to the load 20.

[0016] The DC source 19 is, for example, a battery, a DC power supply and other battery systems such as solar cells, a power supply that rectifies AC voltage to generate DC voltage, a DC power distribution network, etc. The load 20 is, for example, a DC load, an AC load via an inverter, etc. The AC load via an inverter is a device in which an inverter that converts DC voltage to AC voltage and an AC load such as a motor that is powered by the inverter are connected.

[0017] The input filter 17 includes at least one of a smoothing capacitor, a normal mode filter, and a common mode filter. The output filter 18 includes at least one of a smoothing capacitor, a normal mode filter, and a common mode filter.

[0018] The power conversion unit U will now be described. The configuration of the power conversion unit U is shown in FIG. 1 for the power conversion unit U1. An example will be described in which the power conversion units U2 to U4 have the same configuration. The power conversion unit U is, for example, an isolated DC-DC converter including an inverter circuit 2, a transformer 3, a rectifier circuit 4, an inductor 5, and a capacitor 6, arranged in this order from the input terminals 25 and 26 side. The inverter circuit 2 includes a plurality of PWM-controlled switching elements, and the inductor 5 is arranged closer to the output terminals 24a and 24b than the plurality of switching elements. The power conversion unit U includes input terminals 25 and 26 to which DC power is input, and output terminals 27 and 28 to which converted DC power having a target voltage is output. The input terminals 25 and 26 of each power conversion unit U are connected to the input terminals 23a and 23b of the power conversion device 100, respectively. The output terminals 27 and 28 of each power conversion unit U are connected to the output terminals 24a and 24b of the power conversion device 100, respectively. The wiring from the positive terminal of the DC source 19 to the positive side of the inverter circuit 2 is denoted by 21a, and the wiring from the negative terminal of the DC source 19 to the negative side of the inverter circuit 2 is denoted by 22a. The wiring from the positive terminal of the load 20 to the positive side of the rectifier circuit 4 is denoted by 21b, and the wiring from the negative terminal of the load 20 to the negative side of the rectifier circuit 4 is denoted by 22b.

[0019] 2 , inverter circuit 2 converts input DC power into AC power, transformer 3 outputs AC power insulated from the AC power, and rectifier circuit 4 converts the AC power output from transformer 3 into DC power. Therefore, the primary side of transformer 3 is connected to the output terminals (connection points nd1 and nd2) of inverter circuit 2, and the secondary side of transformer 3 is connected to input terminals 65a, 65b, and 65c of rectifier circuit 4. Positive output terminal 66a of rectifier circuit 4 is connected to positive output terminal 27 of power conversion unit U via positive wiring 21b, to which inductor 5 is connected. Negative output terminal 66b of rectifier circuit 4 and negative output terminal 28 of power conversion unit U are connected via negative wiring 22b. Capacitor 6 is connected in parallel with load 20 between positive wiring 21b and negative wiring 22b.

[0020] As shown in FIG. 2 , the inverter circuit 2 includes upper arm switching elements Qa1 and Qa3 connected to the positive wiring 21a and lower arm switching elements Qa2 and Qa4 connected to the negative wiring 22a, forming a full-bridge circuit. The legs, each formed by connecting the upper arm and the lower arm in series, are a series body formed by connecting the switching elements Qa1 and Qa2 in series, and a series body formed by connecting the switching elements Qa3 and Qa4 in series. The connection points between the upper arm and the lower arm are connected to AC wiring. The connection point nd1 between the switching elements Qa1 and Qa2 is connected to AC wiring 61a. The connection point nd2 between the switching elements Qa3 and Qa4 is connected to AC wiring 61b.

[0021] FIG. 1 illustrates an example in which the switching elements Qa1 to Qa4 are MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) each having a transistor Tr and a diode Di. The diode Di may be a parasitic diode of the MOSFET or a separate diode. The drains d of the switching elements Qa1 and Qa3 are connected to a positive wiring 21a, and the sources s of the switching elements Qa2 and Qa4 are connected to a negative wiring 22a. The source s of the switching element Qa1 and the drain d of the switching element Qa2 are connected at a connection point nd1, and the source s of the switching element Qa3 and the drain d of the switching element Qa4 are connected at a connection point nd2. The cathode of the diode Di is connected to the drains d of the switching elements Qa1 to Qa4, and the anode of the diode Di is connected to the sources s of the switching elements Qa1 to Qa4. A control signal So output from a control unit 99 is input to the gates g, which are control terminals of the switching elements Qa1 to Qa4.

[0022] 2 shows an example in which a control signal So corresponding to the power conversion unit U1, i.e., control signal So1, is input. As shown in FIG. 1, control signal So1 is input to the inverter circuit 2 of power conversion unit U1, control signal So2 is input to the inverter circuit 2 of power conversion unit U2, control signal So3 is input to the inverter circuit 2 of power conversion unit U3, and control signal So4 is input to the inverter circuit 2 of power conversion unit U4. Control signals So11, So21, So31, and So41 are input to the gates g of switching elements Qa1 to Qa4 in power conversion unit U1, respectively. The symbol So is used for the control signals collectively, and So1, So2, So3, and So4 are used to distinguish them according to the power conversion unit U to which they are input. Furthermore, So11, So21, So31, and So41 are used to distinguish them according to the switching elements Qa1 to Qa4 of the power conversion unit U1 to which they are input. Similarly, as shown in FIG. 9, when distinguishing based on the switching elements Qa1 to Qa4 of the input power conversion unit U2, So12, So22, So32, and So42 are used; when distinguishing based on the switching elements Qa1 to Qa4 of the input power conversion unit U3, So13, So23, So33, and So43 are used; and when distinguishing based on the switching elements Qa1 to Qa4 of the input power conversion unit U4, So14, So24, So34, and So44 are used.

[0023] The switching elements Qa1 to Qa4 are not limited to MOSFETs. For example, they may be configured with an insulated gate bipolar transistor (IGBT) as a transistor Tr and a diode Di connected in anti-parallel to the IGBT, or they may be configured with bipolar transistors. The semiconductor material of the switching elements Qa1 to Qa4 is not limited to silicon (Si), but may also be a wide bandgap semiconductor material with a wider bandgap than silicon, such as silicon carbide (SiC), gallium nitride (GaN), or gallium oxide (Ga2O3). That is, the switching elements Qa1 to Qa4 may be Si-MOSFETs, Si-IGBTs, SiC-MOSFETs, SiC-IGBTs, GaN power transistors, Ga2O3 power transistors, or the like. When the switching elements Qa1 to Qa4 are IGBTs, the drain d and source s are replaced with collector and emitter. When the switching elements Qa1 to Qa4 are bipolar transistors such as GaN power transistors or Ga2O3 power transistors, the control terminal gate g is replaced with the base, and the drain d and source s are replaced with the collector and emitter. By using wide bandgap semiconductor materials for the switching elements Qa1 to Qa4, an inverter circuit with high voltage resistance, good heat dissipation, and high-speed switching can be obtained.

[0024] Although the switching elements Qa1 to Qa4 are symbolically represented as a single element, they may be connected in multiple parallel or multiple series to increase the current capacity or withstand voltage. When connected in multiple parallel or multiple series, the switching elements Qa1 to Qa4 may be configured as a mixture of the aforementioned Si-IGBTs, SiC-MOSFETs, etc.

[0025] FIG. 3 shows a first example of the transformer 3 and rectifier circuit 4. The transformer 3 shown in FIG. 3 is a center-tapped transformer. The transformer 3 includes a primary winding 63 and a secondary winding 64. The primary winding 63 is connected between AC wiring 61a and AC wiring 61b. One end of the secondary winding 64 is connected to an input terminal 65a of the rectifier circuit 4 via AC wiring 62a. The other end of the secondary winding 64 is connected to an input terminal 65b of the rectifier circuit 4 via AC wiring 62b. The middle end of the secondary winding 64 is connected to an input terminal 65c of the rectifier circuit 4 via AC wiring 62c. The rectifier circuit 4 shown in FIG. 3 includes two diodes Di. The anode of the first diode Di is connected to the input terminal 65a, and the cathode of the first diode Di is connected to the output terminal 66a. The anode of the second diode Di is connected to the input terminal 65b, and the cathode of the second diode Di is connected to the output terminal 66a. The input terminal 65c and output terminal 66b of the rectifier circuit 4 are connected by the negative wiring 22b. That is, the intermediate potential of the transformer 3 is the negative potential of the rectifier circuit 4. The primary winding 63 and the secondary winding 64 have windings Np and Ns, respectively. The transformer turns ratio n of the transformer 3 is Np / Ns.

[0026] 4 shows examples of the inductor 5 and the capacitor 6. As described above, one end of the inductor 5 is connected to the positive output terminal 66a of the rectifier circuit 4, and the other end is connected to one end of the capacitor 6 via the positive wiring 21b. The other end of the capacitor 6 is connected to the negative wiring 22b.

[0027] Next, the input information Sin used for controlling the power conversion device 100 will be described. The input information Sin includes, for example, an input voltage Vin and an input current Iint of DC power input to the power conversion device 100, an output voltage Vo and an output current Iot of DC power output from the power conversion device 100, a phase input current Iin input to the power conversion unit U, a primary current Ip of the transformer 3, an inductor current IL of the inductor 5, and a phase output current Io output from the power conversion unit U. Note that some of the exemplified input information Sin is not used in the control described below. The input voltage Vin is, for example, the output voltage of the DC source 19 detected by the voltage detector 14a. The input current Iint is, for example, the output current of the DC source 19 detected by the current detector 15a.

[0028] The output voltage Vo is the voltage of the capacitor 7 detected by, for example, the voltage detector 14b. The output current Iot is the current output from the capacitor 7 detected by, for example, the current detector 15b. The phase input current Iin is the current in the positive wiring 21a connected from the input terminal 25 to the inverter circuit 2 detected by, for example, the current detector 8. The primary current Ip is the current in the AC wiring 61a detected by, for example, the current detector 9. The inductor current IL is the current in the inductor 5 output by, for example, the inductor current output device 12. The phase output current Io is the current in the positive wiring 21b from the capacitor 6 to the output terminal 27 detected by, for example, the current detector 13.

[0029] The inductor current output device 12 outputs the inductor current IL, which is obtained by detecting or estimating the current flowing through the inductor 5. FIGS. 4 to 6 show first to third examples of the inductor current output device 12. The inductor current output device 12 shown in FIG. 4 is an example of the current detector 10. In this case, the inductor current IL is the current in the positive wiring 21b up to the output side of the inductor 5, i.e., the connection point of the capacitor 6, detected by the current detector 10, which is the inductor current output device 12. The inductor current output device 12 shown in FIG. 5 is an example of the first current estimation circuit 11. In this case, the inductor current IL is a current estimated based on the phase input current Iin or the primary side current Ip. More specifically, the first current estimation circuit 11 estimates the inductor current IL by dividing the excitation current Im flowing through the excitation inductance Lm by the product of the detected value of the phase input current Iin or the primary side current Ip and the transformer turns ratio n of the transformer 3. The excitation current Im is calculated based on the excitation inductance Lm of the transformer 3, the input voltage Vin, and the duty ratio D of the control signal So, which will be described later. The inductor current output device 12 shown in Fig. 6 is an example of the second current estimation circuit 11 and the voltage detector 16. In this case, the inductor current IL is estimated by integrating the value of the inductor voltage VL of the inductor 5, which is detected by the voltage detector 16.

[0030] The input information Sin output from each of the power conversion units U1 to U4 and input to the control unit 99 will now be described. As shown in FIG. 10 , phase input currents Iin1, Iin2, Iin3, and Iin4 are output from the current detectors 8 of the power conversion units U1, U2, U3, and U4, respectively. Where appropriate, the phase input currents are generally designated as Iin, and when distinguishing between them by power conversion unit U, Iin1, Iin2, Iin3, and Iin4 are used. As shown in FIG. 11 , primary side currents Ip1, Ip2, Ip3, and Ip4 are output from the current detectors 9 of the power conversion units U1, U2, U3, and U4, respectively. Where appropriate, the primary side currents are generally designated as Ip, and when distinguishing between them by power conversion unit U, Ip1, Ip2, Ip3, and Ip4 are used. As shown in FIG. 12 , inductor currents IL1, IL2, IL3, and IL4 are output from the inductor current output devices 12 of the power conversion units U1, U2, U3, and U4, respectively. As appropriate, the sign of the inductor current is collectively referred to as IL, and IL1, IL2, IL3, and IL4 are used when distinguishing between the inductor currents according to the power conversion unit U. As shown in Fig. 13 , phase output currents Io1, Io2, Io3, and Io4 are output from the current detectors 13 of the power conversion units U1, U2, U3, and U4, respectively. As appropriate, the sign of the phase output current is collectively referred to as Io, and Io1, Io2, Io3, and Io4 are used when distinguishing between the inductor currents according to the power conversion unit U.

[0031] Next, the configuration and functions of the control unit 99 will be described using FIGS. 7 and 8 . The control unit 99 includes a processor 50 such as a central processing unit (CPU), a memory 51 that exchanges data with the processor 50, and an input / output interface that inputs and outputs signals between the processor 50 and the outside in order to control the power conversion units U1 to U4. The input / output interface includes an input circuit 52 that inputs signals between the processor 50 and the outside, and an output circuit 53 that outputs signals between the processor 50 and the outside. The processor 50 may include an application-specific integrated circuit (ASIC), an integrated circuit (IC), a digital signal processor (DSP), a field programmable gate array (FPGA), various signal processing circuits, and the like. Furthermore, the processor 50 may include multiple devices of the same type or different types, each of which may share the responsibility for executing various processes. The memory 51 may include a random access memory (RAM) that can read and write data from and to the processor 50, a read-only memory (ROM) that can read data from the processor 50, and the like. The functions of the voltage control unit 31, the phase shedding control unit 32, and the plurality of current control units 33, which are functional blocks of the control unit 99 described below, are realized by the processor 50 and the memory 51 shown in Fig. 8. The functional blocks of the control unit 99 are realized by the processor 50 executing a program stored in the memory 51. Furthermore, the plurality of processors 50 and the plurality of memories 51 may cooperate to execute each function.

[0032] The input circuit 52 includes, for example, an AD (analog-digital) converter 54 that converts the analog signals of the phase input current Iin, primary current Ip, phase output current Io, and inductor current IL output from the current detectors 8, 9, and 13 and inductor current output device 12 provided in the power conversion units U1 to U4 into digital signals. The input circuit 52 also includes an AD converter 54 that converts the analog signals of the input voltage Vin, output voltage Vo, input current Iint, and output current Iot output from the voltage detectors 14a and 14b and current detectors 15a and 15b into digital signals. Note that FIG. 8 illustrates only one AD converter 54. The output circuit 53 includes a switching element drive circuit 55 that outputs a control signal So for driving the switching elements Qa1 to Qa4 of the power conversion units U1 to U4. The switching element drive circuit 55 outputs a digital control signal Sod with a changed voltage value. Note that the same symbols are used before and after AD conversion.

[0033] The control unit 99 controls the output voltage of the power conversion device 100 and the current of the power conversion units U1 to U4 based on, for example, voltage information such as the input voltage Vin and output voltage Vo of the power conversion units U1 to U4, and current information, i.e., input information Sin, of each of the power conversion units U1 to U4. The currents used in the control described below may be phase input currents Iin1 to Iin4 input to the inverter circuit 2, primary currents Ip1 to Ip4 of the transformer 3, or inductor currents IL1 to IL4 of the inductor 5. Furthermore, overvoltages and overcurrents may be detected based on voltage and current information detected by the voltage detectors 14a and 14b and current detectors 8, 9, 13, 15a, and 15b, and the entire power conversion device 100 or at least one power conversion unit may be stopped and protected at a protection threshold. A temperature sensor may be provided to input temperature information or a threshold may be used for protection.

[0034] The control unit 99 outputs a control signal So for driving the switching elements Qa1 to Qa4 of the power conversion units U1 to U4. The switching elements Qa1 to Qa4 are power semiconductor elements of the inverter circuit 2 and are arranged on the primary side of the transformer 3, and therefore are primary-side switching elements. An example in which the switching elements Qb1 to Qb4 are used in the rectifier circuits 4 of the power conversion units U1 to U4 (see FIGS. 21 to 23) will be described later. When the switching elements Qb1 to Qb4 are used in the rectifier circuits 4 of the power conversion units U1 to U4, the control unit 99 also outputs a control signal So for driving the switching elements Qb1 to Qb4 of the power conversion units U1 to U4. The switching elements Qb1 to Qb4 are power semiconductor elements of the rectifier circuit 4 and are arranged on the secondary side of the transformer 3, and therefore are secondary-side switching elements. The control signal So is generated using a triangular wave comparison method such as PWM (Pulse Width Modulation) control. The secondary side switching elements Qb1 to Qb4 may be synchronously rectified in order to reduce conduction loss equivalent to the forward voltage VF of the diodes.

[0035] The control unit 99 may be configured to shift the carrier phases of the triangular waves to control the power conversion units U1 to U4. The operation of shifting the phases of multiple power conversion units U to cancel out ripples in the output current Iot is called interleaving. Interleaving allows the input filter 17 and output filter 18 to be miniaturized. There are various interleaving methods, but interleaving can be achieved by controlling the operation or stopping of multiple power conversion units U. For example, four carrier phases may be operated with a shift of approximately 45 degrees. Two carrier phases may be shifted by approximately 90 degrees, and four power conversion units U1 to U4 may be operated with two carrier phases. One of the four power conversion units U1 to U4 may be stopped, and three may be operated with their carrier phases shifted by approximately 60 degrees each. Two of the four power conversion units U1 to U4 may be stopped, and two may be operated with their carrier phases shifted by approximately 90 degrees. The aforementioned "approximately 45 degrees" refers to 40 degrees or more and 50 degrees or less, and preferably 44 degrees or more and 46 degrees or less. The same applies to phase angles with other numerical values. The phase shift angle may be any angle that can suppress ripples in the output current Iot. A sawtooth wave carrier may be used instead of the triangular wave carrier used for PWM switching control.

[0036] FIG. 7 shows functional blocks within the control unit 99. The control unit 99 has a voltage control function, a phase number switching function, and a phase current control function. More specifically, the control unit 99 includes a current control unit 33 (33u1 to 33u4) for each phase, i.e., each power conversion unit U; a phase shedding control unit 32 having a current command generation unit 37 that generates a current command value for each phase and a stop signal generation unit 38 that generates a phase stop signal GB that stops the operation of each phase; and a voltage control unit 31 that generates an output current command value Iot*. The phase shedding control unit 32 outputs an inductor current command value IL** that tracks the inductor current IL for each power conversion unit U, and can therefore also be referred to as a command control unit that outputs the inductor current command value IL**. The current control unit 33 generates a control signal So for each power conversion unit U, controlling the corresponding multiple switching elements Qa1 to Qa4. In FIG. 7, the inductor current command values ​​IL1** to IL4** enclosed in long dashed squares are collectively represented by the inductor current command value IL**, the phase stop signals GB1 to GB4 enclosed in dashed squares are collectively represented by the phase stop signal GB, and the inductor currents IL1 to IL4 enclosed in dashed circles are collectively represented by the inductor current IL.

[0037] The voltage control unit 31 generates an output current command value Iot*, which is a command value for the output current Iot, based on the output voltage Vo and the output voltage command value Vo*. When generating the output current command value Iot*, the voltage control unit 31 converts, for example, an error voltage between the output voltage command value Vo* and the detected value of the output voltage Vo, which is the voltage of the capacitor 7, into the current of the capacitor 7, i.e., the capacitor current, using a compensator. The voltage control unit 31 then adds the capacitor current and the value of the output current Iot detected by the current detector 15b to calculate a total current command value for each phase, i.e., the output current command value Iot*. Note that the value of the output current Iot may be an estimated value instead of the detected value detected by the current detector 15b, or the output current value may not be used. The compensator may be, for example, a proportional (P) controller, an integral (PI) controller, a proportional-integral-differential (PID) controller, a Type-2 compensator, a Type-3 compensator, or any other compensator that can adjust the gain characteristic or phase characteristic of the open-loop characteristics.

[0038] The phase shedding control unit 32 generates a current command value for each phase and phase stop signals GB1 to GB4 based on the total current command value for each phase, i.e., the output current command value Iot*. Examples of the current command values ​​for each phase include inductor current command values ​​IL1** to IL4**. Where appropriate, the inductor current command values ​​are generally labeled IL**, and when distinguished by power conversion unit U, IL1**, IL2**, IL3**, and IL4** are used. The phase stop signals are generally labeled GB, and when distinguished by power conversion unit U, GB1, GB2, GB3, and GB4 are used. The total current command value for each phase, i.e., the output current command value Iot*, is equal to the sum of the inductor current command values ​​IL1** to IL4**. When the phase stop signal GB is turned on (enabled), the primary-side switching elements Qa1 to Qa4 are turned off, i.e., the inverter circuit 2 is stopped. Furthermore, if the secondary side has the switching elements Qb1 to Qb4, when the phase stop signal GB is turned on (enabled), the secondary side switching elements Qb1 to Qb4 are turned off, that is, the rectifier circuit 4 is stopped.

[0039] The phase stop signal GB may be turned on when the current command value of each phase, i.e., the inductor current command value IL**, becomes equal to or less than a preset threshold, or may be turned on when the total current command value, i.e., the output current command value Iot*, becomes equal to or less than a preset threshold. The threshold of the phase stop signal GB may be set to maximize the efficiency of the power conversion device 100, or to be less than the maximum temperature of the power conversion device 100, or to be an operation time that has a significant impact on the life of the power conversion device 100. When the phase stop signal GB is turned on, the current command value that is turned on, i.e., the inductor current command value IL**, is set to zero, and the total current command value of each phase, i.e., the output current command value Iot*, is set to the sum of the current command values ​​of each phase, i.e., the inductor current command values ​​IL**.

[0040] The current control unit 33 includes a CCM current control unit (continuous current mode current control unit) 40, a DCM current control unit (discontinuous current mode current control unit) 41, a duty ratio selector 42, a PWM generator 43, and a switching element drive circuit 55. The digital calculation functions of the current control unit 33 are realized by the CCM current control unit 40, the DCM current control unit 41, the duty ratio selector 42, and the PWM generator 43. Where appropriate, the current control units are collectively referred to as 33, and when distinguishing them by power conversion unit U, the reference numerals 33u1, 33u2, 33u3, and 33u4 are used.

[0041] The CCM current control unit 40 generates a duty ratio Dccm, which is a first duty ratio of the control signal So that controls the multiple switching elements Qa1 to Qa4 of the inverter circuit 2, based on the inductor current IL and the inductor current command value IL**, so as to flow the inductor current IL, which is a continuous current mode in which current flows continuously through the inductor 5. Since the CCM current control unit 40 generates the first duty ratio (duty ratio Dccm) of the control signal So, it can also be called a first current control unit. The DCM current control unit 41 generates a duty ratio Ddcm, which is a second duty ratio of the control signal So that controls the multiple switching elements Qa1 to Qa4 of the inverter circuit 2, based on the inductor current command value IL**, so as to flow the inductor current IL, which is a discontinuous current mode in which current flows intermittently through the inductor 5. Since the DCM current control unit 41 generates the second duty ratio (duty ratio Ddcm) of the control signal So, it can also be called a second current control unit. The duty ratio selection unit 42 selects one of a first duty ratio (duty ratio Dccm) and a second duty ratio (duty ratio Ddcm) corresponding to the current mode, either the continuous current mode or the discontinuous current mode, as the selected duty ratio, and determines the selected duty ratio as the duty ratio D of the control signal So. Furthermore, when the number of operating power conversion units U, i.e., the number of operating phases, is changed, the duty ratio selection units 42 of the power conversion units U that continue to operate and the power conversion units U that start to operate determine the selected duty ratios. The selected duty ratio is the duty ratio D output from the duty ratio selection unit 42. The duty ratio selection unit 42 of the power conversion unit U that starts to operate outputs, for example, the duty ratio D before the operation was stopped.

[0042] The duty ratio D will now be explained. FIG. 14 shows the pulse of the control signal Sod, which is a digital signal. The duty ratio D is obtained by dividing the high period Th, which is the period during which the control signal Sod is at a high voltage (digital value 1), by the switching period Tsw of the control signal Sod. In other words, the duty ratio D is expressed as Th / Tsw. The duty ratio D of the control signal So, which is a digital signal whose voltage value has been changed, is also expressed as Th / Tsw.

[0043] The voltage control unit 31 generates an output current command value Iot*, which is a command value for the target voltage, using an output voltage command value Vo*, which is a command value for the target voltage, and the value of the output voltage Vo, which is the voltage of the DC power output from the output terminals 24a and 24b of the power conversion device 100, detected by the voltage detector 14a. The PWM generation unit 43 generates a digital control signal Sod that controls the multiple switching elements Qa1 to Qa4 of the inverter circuit 2 by PWM control, based on the duty ratio D output from the duty ratio selection unit 42 and the phase stop signal GB output from the phase shedding control unit 32. The PWM generation unit 43 outputs the control signal Sod to stop the inverter circuit 2 when the phase stop signal GB is valid, i.e., indicating a stop, and does not output the control signal Sod to operate the inverter circuit 2 when the phase stop signal GB is invalid, i.e., indicating a non-stop. The switching element drive circuit 55 changes the voltage value of the control signal Sod, which is a digital signal that has been input, and outputs the control signal So, which is a digital signal with the changed voltage value.

[0044] The operation of the power conversion device 100 according to the first embodiment will be described with reference to FIGS. 17 to 20. In step S01, the control unit 99 acquires the output voltage command value Vo* (output voltage command value acquisition step). In step S02, the control unit 99 acquires input information Sin (input information acquisition step). In step S03, the control unit 99 calculates the output current command value Iot* using the voltage control unit 31 (output current command value calculation step). In step S04, the control unit 99 calculates the inductor current command value IL** and the phase stop signal GB using the phase shedding control unit 32 (command calculation step). In step S05, the control unit 99 executes a processing step for each power conversion unit U (power conversion unit processing step). After executing step S05, the control unit 99 terminates the processing. Note that in FIGS. 17 to 20, the power conversion units are simply referred to as units. The command calculation step can also be referred to as a command output step, since the inductor current command value IL** is calculated and the command value is output. Fig. 18 is a flowchart expanded into a first example of step S05, and Fig. 19 is a flowchart expanded into a second example of step S05. Step S05 shown in Fig. 18 is for processing multiple power conversion units U in parallel, while step S05 shown in Fig. 19 is for processing multiple power conversion units U in sequence. Figs. 18 and 19 show a case where the number of power conversion units U is four, i.e., the number of phases is four.

[0045] The flowchart of FIG. 18 will now be described. Steps S01 to S04 are the same as those of FIG. 17, and therefore will not be described again. The power conversion unit processing step of step S05 includes steps S06a to S06d and step S07. In step S06a, the control unit 99 executes the processing step for power conversion unit U1 (first power conversion unit processing step). In step S06b, the control unit 99 executes the processing step for power conversion unit U2 (second power conversion unit processing step). In step S06c, the control unit 99 executes the processing step for power conversion unit U3 (third power conversion unit processing step). In step S06d, the control unit 99 executes the processing step for power conversion unit U4 (fourth power conversion unit processing step). In step S07, the control unit 99 determines whether the processing steps for all power conversion units U have been completed. If there are any processing steps that have not yet been completed, step S07 continues. If the processing steps for all power conversion units U have been completed, the control unit 99 ends the processing.

[0046] The flowchart of FIG. 19 will now be described. Steps S01 to S04 are the same as those of FIG. 17, and therefore will not be described again. The power conversion unit processing step of step S05 includes steps S06a to S06d. In step S06a, the control unit 99 executes the processing step for power conversion unit U1 (first power conversion unit processing step). After step S06a, in step S06b, the control unit 99 executes the processing step for power conversion unit U2 (second power conversion unit processing step). After step S06b, in step S06c, the control unit 99 executes the processing step for power conversion unit U3 (third power conversion unit processing step). After step S06c, in step S06d, the control unit 99 executes the processing step for power conversion unit U4 (fourth power conversion unit processing step). After executing step S06d, the control unit 99 ends the processing.

[0047] FIG. 20 illustrates the specific processing of step S05. The units Ux illustrated in FIG. 20 represent the respective power conversion units U, with x representing the ordinal number of the power conversion unit U. If the power conversion apparatus 100 includes four power conversion units U, x is 1, 2, 3, or 4. In step S11, the control unit 99 acquires the inductor current command value IL** and the phase stop signal GB of the power conversion unit Ux (command acquisition step). In step S12, the control unit 99 acquires the input information Sin of the power conversion unit Ux (unit input information acquisition step). In step S13, the control unit 99 generates the duty ratio Dccm, which is the first duty ratio, using the CCM current control unit 40 of the power conversion unit Ux, to prepare for control using the first duty ratio (first control step). In step S14, the control unit 99 generates the duty ratio Ddcm, which is the second duty ratio, using the DCM current control unit 41 of the power conversion unit Ux, to prepare for control using the second duty ratio (second control step).

[0048] In step S15, the control unit 99 determines the current mode of the inductor current IL corresponding to the inductor current command value IL** in the command acquisition step (current mode determination step). The determination in the current mode determination step is made based on the magnitude relationship between the duty ratio Dccm and the duty ratio Ddcm. Specifically, if Dccm≦Ddcm, the current mode is determined to be continuous, and if Dccm>Ddcm, the current mode is determined to be discontinuous. If the current mode determination step determines the current mode to be continuous, the process proceeds to step S16. If the current mode determination step determines the current mode to be discontinuous, the process proceeds to step S17. In step S16, the control unit 99 sets the duty ratio Dccm to the duty ratio D using the duty ratio selection unit 42 (first duty ratio setting step). In step S17, the control unit 99 sets the duty ratio Ddcm to the duty ratio D using the duty ratio selection unit 42 (second duty ratio setting step). Specifically, if Dccm≦Ddcm, it is determined that the mode is continuous current mode, and the duty ratio Dccm is set to duty ratio D. If Dccm>Ddcm, it is determined that the mode is discontinuous current mode, and the duty ratio Ddcm is set to duty ratio D. In other words, a small duty ratio is set to duty ratio D. In step S18, the control unit 99 determines the phase stop signal GB using the PWM generation unit 43 (stop signal determination step). Steps S15 to S17 are duty ratio selection steps.

[0049] In the stop signal determination step of step S18, if the phase stop signal GB indicates stop, the process proceeds to step S19, but if the phase stop signal GB does not indicate stop, i.e., indicates non-stop, the process proceeds to step S20. In step S19, the control unit 99 outputs a control signal So that stops the power conversion unit Ux from the PWM generation unit 43 and the switching element drive circuit 55, thereby stopping the power conversion unit Ux (power conversion unit stopping step). In step S20, the PWM generation unit 43 and the switching element drive circuit 55 output a control signal So that operates the power conversion unit Ux, thereby driving the power conversion unit Ux at a duty ratio D (power conversion unit driving step). After step S19 or step S20, the control unit 99 ends the process.

[0050] The CCM current control unit 40 of the power conversion unit U includes a feedback controller 44 that calculates a feedback duty ratio Dccmb using a PI controller or the like based on the difference between the inductor current command value IL** and the detected inductor current IL, a feedforward controller 45 that calculates a feedforward duty ratio Dccmb using the output voltage Vo or the like, and an adder 46 that adds the feedback duty ratio Dccmb and the feedforward duty ratio Dccmbf to generate a duty ratio Dccm for continuous current mode. Note that instead of a PI controller, a P controller, PID controller, Type-2 compensator, Type-3 compensator, or the like that can adjust the gain or phase characteristics of open-loop characteristics may be used. The duty ratio Dccm for continuous current mode when a PI controller is used can be expressed by equation (1).

[0051] Here, IL** is the inductor current command value, IL is the value of the inductor current, Kp is the proportional gain of the PI controller, Ki is the integral gain of the PI controller, n is the turns ratio of the transformer, Vin is the input voltage, and Vo is the output voltage.

[0052] When a PI controller is applied, the CCM current control unit 40 performs the calculation of equation (1), and therefore receives the input voltage Vin as well as the output voltage Vo.

[0053] The DCM current control unit 41 of the power conversion unit U includes a feedforward controller 47 that uses the inductor current command value IL**. The feedforward controller 47 generates a duty ratio Ddcm for the discontinuous current mode. Equation (7) can be used to determine the duty ratio Ddcm.

[0054] Next, we will explain how to generate the duty ratio Ddcm. When feedback control is applied in discontinuous current mode, distortion occurs in the output voltage Vo due to the inability to detect the average value of the inductor current IL. Furthermore, when the power conversion unit U starts and stops, i.e., when the phase starts and stops, the power conversion unit U enters discontinuous current mode (DCM), which changes the dynamics of the controlled system, i.e., the multiple power conversion units U. Due to the effects of DCM, a current controller designed for continuous current mode (CCM), i.e., a current controller that does not take DCM into account, reduces the control margin and becomes unstable. This causes the output voltage Vo to rise, triggering overvoltage protection or current protection. Therefore, a control system that can accommodate DCM during startup and shutdown is required. DCM is known to behave like a resistor. In other words, the controlled system has no dynamics and can be controlled in an open loop.

[0055] In the control of the power conversion unit U in DCM, the inductor current IL is reset to zero every control period, allowing for free control of the input and output power of the power conversion device 100. The input power Pin of the power conversion unit U in the first embodiment in DCM can be expressed as in equation (2).

[0056] Here, Fsw is the switching frequency, which can be expressed by equation (3) using the switching period Tsw of the switching elements Qa1 to Qa4: Fsw=(1 / Tsw) (3)

[0057] Furthermore, Vin is the input voltage, Iin is the phase input current, n is the transformer turns ratio of the transformer 3, Lf is the inductance of the inductor 5, which is a smoothing inductor, Vo is the output voltage, Lm is the excitation inductance of the transformer 3, and Da is the duty ratio. Da = 2Ddcm. In the case of a transformer with a low excitation inductance Lm, if the excitation inductance Lm is ignored as infinite, an error will occur in the duty ratio Ddcm, resulting in a large deviation between the inductor current command value IL** and the actual inductor current IL. In contrast, by taking the excitation inductance Lm into consideration, the deviation between the inductor current command value IL** and the actual inductor current IL is reduced, enabling good current response. As a result, by taking the excitation inductance Lm into consideration, switching between continuous current mode and discontinuous current mode can be performed appropriately.

[0058] By dividing equation (2) by the input voltage Vin, the phase input current Iin is obtained as shown in equation (4).

[0059] Equation (4) is solved for the duty ratio Da. In addition, if the loss of the power conversion unit U is assumed to be sufficiently small and negligible, the phase input current Iin can be approximated as in equation (5). Iin ≈ IL × Vo / Vin (5)

[0060] If the inductor current IL of the phase, i.e., the power conversion unit U, is taken as the inductor current command value IL**, it can be expressed as in equation (6). Here, taking into account the loss of the power conversion unit U, the phase output current Io may be converted into the inductor current command value IL**.

[0061] Here, the inductor current command value IL** is used instead of the value of the inductor current IL because the current average value of the inductor current IL cannot be sampled or estimated during DCM. From equation (6), the duty ratio Ddcm during DCM can be expressed as equation (7).

[0062] From equation (7), the degree of freedom in controlling the duty ratio Ddcm by the inductor current command value IL** can be improved, and therefore, the power conversion unit U can be controlled in a feedforward manner.

[0063] In this case, the duty ratio Ddcm for the discontinuous current mode may be calculated using a table or the like, or the inductance Lf, the excitation inductance Lm, and the switching frequency Fsw may be varied depending on the input voltage Vin, the output voltage Vo, the phase input current Iin, and the phase output current Io.

[0064] 15 and 16 show duty ratio characteristics 71a and 71b, which are characteristics of the duty ratio Dccm in continuous current mode, and duty ratio characteristics 72a and 72b, which are characteristics of the duty ratio Ddcm in discontinuous current mode. As a comparative example, FIGS. 15 and 16 show duty ratio characteristics 73a and 73b, which are characteristics of the duty ratio Ddcm in discontinuous current mode when the exciting inductance Lm is not taken into consideration. In FIGS. 15 and 16, the horizontal axis represents the inductor current IL, and the vertical axis represents the duty ratio D. The difference between FIGS. 15 and 16 is the difference in the duty ratio Dccm in continuous current mode. Here, the duty ratio Dccm shown in FIGS. 15 and 16 is the feedforward duty ratio Dccmf, which can be expressed by equation (8): Dccmf=nVo / 2Vin (8)

[0065] FIG. 15 shows the case where the duty ratio Dccm is 0.27, and FIG. 16 shows the case where the duty ratio Dccm is 0.38. When the transformer turns ratio n of the transformer 3 is 2, the input voltage Vin is 100 (arbitrary units), and the output voltage Vo is 27 (arbitrary units), the duty ratio Dccm is 0.27 according to equation (8). When the transformer turns ratio n of the transformer 3 is 2, the input voltage Vin is 100 (arbitrary units), and the output voltage Vo is 38 (arbitrary units), the duty ratio Dccm is 0.38 according to equation (8). Therefore, the difference between FIG. 15 and FIG. 16 is also the difference in the input voltage Vin and the output voltage Vo. In both the continuous current mode and the discontinuous current mode, the optimal duty ratios Dccm and Ddcm change as the input voltage Vin and the output voltage Vo change.

[0066] 15 and 16, the duty ratio Dccm in the continuous current mode is constant with respect to the inductor current IL, whereas the duty ratio Ddcm in the discontinuous current mode varies depending on the inductor current IL. Here, the feedforward duty ratio Dccmf in the continuous current mode is given by equation (8), which is the equation enclosed by the parentheses "( " and ")" in equation (1) and the equation to the right of the "+" on the right. The difference between the characteristics of the duty ratio Dccm and the duty ratio Ddcm is also clear from the equations for the feedforward duty ratio Dccmf in the continuous current mode and the duty ratio Ddcm in the discontinuous current mode. Because the discontinuous current mode occurs when the inductor current IL is low, it is sufficient to select the smaller of the duty ratio Dccm in the continuous current mode or the duty ratio Ddcm in the discontinuous current mode.

[0067] 15 and 16, duty ratio characteristics 72a and 72b are obtained when the excitation inductance Lm is taken into account when calculating the duty ratio Ddcm for the discontinuous current mode, while duty ratio characteristics 73a and 73b are obtained when the excitation inductance Lm is not taken into account. As can be seen from FIGS. 15 and 16, the duty ratio Ddcm for the discontinuous current mode is larger when the excitation inductance Lm is not taken into account than when the excitation inductance Lm is taken into account. As a result, when compared with the duty ratio Dccm for the continuous current mode, the control unit of the comparative example that does not take the excitation inductance Lm into account may determine that the discontinuous current mode is the continuous current mode, even if the actual current mode is the discontinuous current mode, based on the magnitude relationship between the duty ratio Dccm and the duty ratio Ddcm. Current mode mismatches cause distortion in the output voltage Vo. Therefore, by taking the excitation inductance Lm into account, it is possible to further suppress distortion in the output voltage Vo.

[0068] Note that if the power conversion unit U does not use a transformer 3, it is not necessary to consider the excitation inductance Lm. If the power conversion unit U uses a transformer 3, the DCM current control unit 41 generates the duty ratio Ddcm based on equation (8) that takes the excitation inductance Lm into consideration. The power conversion device 100 of the first embodiment, when using the transformer 3 for the power conversion unit U, controls the power conversion unit U using a control signal So of the duty ratio D corresponding to the current modes of the inductor current IL, namely, the continuous current mode and the discontinuous current mode. This reduces output voltage distortion when switching the number of phases, which is the number of phases at which the power conversion unit operates. Furthermore, the power conversion device 100 of the first embodiment can achieve a high-speed control response without increasing the capacitance of the output-side capacitors 6 and 7.

[0069] 1 and 7 show four power conversion units U connected in parallel, but the number of power conversion units U is not limited thereto, and a configuration in which at least two or more power conversion units U are connected in parallel may also be used. Furthermore, the inputs may be connected in series and the outputs in parallel, or the inputs may be connected in series and the outputs in series, or the inputs may be connected in parallel and the outputs in series. An example has been described in which the power conversion units U1 to U4 have the same configuration. Here, an example has been described in which the power conversion unit U is an isolated DC-DC converter, so the power conversion units U1 to U4 may each have a different configuration as long as they are isolated DC-DC converters.

[0070] Regarding capacitor 6, since the interleaved operation described above can reduce the size of the filter capacitor, multiple capacitors 6 in phases 1 to 4 may be integrated into a single capacitor Co. Similarly, multiple inductors 5 in phases 1 to 4 may be integrated into a single capacitor Co, like a coupled inductor, to reduce the size of the inductor 5. The inverter circuit 2 may be a half-bridge circuit or a three-phase circuit. Furthermore, the inverter circuit 2 may be a multi-level circuit, such as a three-level circuit, in addition to a two-level system.

[0071] While FIG. 3 illustrates a first example of the transformer 3 and rectifier circuit 4, the present invention is not limited to this example. FIGS. 21 to 23 illustrate second and third examples of the transformer 3 and rectifier circuit 4. Differences from the first example of the transformer 3 and rectifier circuit 4 illustrated in FIG. 3 will be mainly described. The second example of the transformer 3 and rectifier circuit 4 illustrated in FIG. 21 will be described. The transformer 3 illustrated in FIG. 21 is a center-tapped transformer and is the same as the transformer 3 illustrated in FIG. 3. The rectifier circuit 4 illustrated in FIG. 21 is an example including two switching elements Qb1 and Qb2 and an inductor 67. The switching elements Qb1 and Qb2 are the same as the switching element Qa1, etc., described above. One end of the secondary winding 64 is connected to an input terminal 65a of the rectifier circuit 4 via AC wiring 62a. The other end of the secondary winding 64 is connected to an input terminal 65b of the rectifier circuit 4 via AC wiring 62b. The middle of the secondary winding 64 is connected to an input terminal 65c of the rectifier circuit 4 via AC wiring 62c. The drain d of the switching element Qb1 is connected to the input terminal 65a, and the source s of the switching element Qb1 is connected to the output terminal 66b. The drain d of the switching element Qb2 is connected to the input terminal 65b, and the source s of the switching element Qb2 is connected to the output terminal 66b. One end of the inductor 67 is connected to the input terminal 65c, and the other end of the inductor 67 is connected to the output terminal 66a. The output terminal 66a of the rectifier circuit 4 is connected to the outer positive side wiring 21b, and the output terminal 66b of the rectifier circuit 4 is connected to the outer negative side wiring 22b. The intermediate potential of the transformer 3 becomes the positive side potential of the rectifier circuit 4 via the inductor 67. As mentioned above, the signs of the positive side wiring and negative side wiring inside the rectifier circuit 4 are the same as the signs of the positive side wiring and negative side wiring outside the rectifier circuit 4, 21b and 22b.

[0072] 21 shows an example in which the control signal So corresponding to the power conversion unit U1, i.e., the control signal Soa1, is input. As shown in FIG. 24, the switching element drive circuits 55 of the current control units 33 corresponding to the power conversion units U1 to U4 in the control unit 99 each include a first drive unit 56 and a second drive unit 57. The first drive unit 56 outputs the control signal So for the inverter circuit 2, and the second drive unit 57 outputs the control signal So for the rectifier circuit 4. Similar to the control signals So1, So2, So3, and So4 in FIG. 1, the control signal Soa1 is input to the rectifier circuit 4 of the power conversion unit U1, the control signal Soa2 is input to the rectifier circuit 4 of the power conversion unit U2, the control signal Soa3 is input to the rectifier circuit 4 of the power conversion unit U3, and the control signal Soa4 is input to the rectifier circuit 4 of the power conversion unit U4.

[0073] Control signals Soa11 and Soa21 are input to gates g of switching elements Qb1 and Qb2 in power conversion unit U1, respectively. As with the control signals input to inverter circuit 2, the symbols of control signals input to rectifier circuit 4 are collectively referred to as So, and Soa1, Soa2, Soa3, and Soa4 are used when distinguishing between signals according to the power conversion unit U to which they are input. Furthermore, Soa11 and Soa21 are used when distinguishing between signals according to the switching elements Qb1 and Qb2 of power conversion unit U1 to which they are input (see FIG. 25 ). Similarly, when distinguishing based on the switching elements Qb1 and Qb2 of the input power conversion unit U2, Soa12 and Soa22 are used, when distinguishing based on the switching elements Qb1 and Qb2 of the input power conversion unit U3, Soa13 and Soa23 are used, and when distinguishing based on the switching elements Qb1 and Qb2 of the input power conversion unit U4, Soa14 and Soa24 are used (see Figure 25).

[0074] A third example of the transformer 3 and rectifier circuit 4 shown in FIG. 22 will be described. The rectifier circuit 4 shown in FIG. 22 includes four switching elements Qb1 to Qb4 and an inductor 67. The four switching elements Qb1 to Qb4 form a full-bridge circuit. The transformer 3 shown in FIG. 22 differs from the transformers 3 shown in FIGS. 3 and 21 in that the AC wiring 62c is not drawn from the middle of the secondary winding 64. One end of the secondary winding 64 is connected to the input terminal 65a of the rectifier circuit 4 via the AC wiring 62a. The other end of the secondary winding 64 is connected to the input terminal 65b of the rectifier circuit 4 via the AC wiring 62b. The full-bridge circuit formed by the four switching elements Qb1 to Qb4 has a configuration similar to that of the inverter circuit 2 shown in FIG. 2. The upper-arm switching elements Qb1 and Qb3 are connected to the positive-side wiring 21b, which is connected to the inductor 67, and the lower-arm switching elements Qb2 and Qb4 are connected to the negative-side wiring 22b. The leg in which the upper arm and the lower arm are connected in series is a series body in which switching element Qb1 and switching element Qb2 are connected in series, and a series body in which switching element Qb3 and switching element Qb4 are connected in series. The connection point between the upper arm and the lower arm is connected to the AC wiring. The connection point nd3 between switching element Qb1 and switching element Qb2 is connected to the AC wiring 62a. The connection point nd4 between switching element Qb3 and switching element Qb4 is connected to the AC wiring 62b.

[0075] 22 shows an example of MOSFETs each having a transistor Tr and a diode Di, similar to the switching elements Qa1 to Qa4. The drains d of the switching elements Qb1 and Qb3 are connected to the positive wiring 21b to which the inductor 67 is connected, and the sources s of the switching elements Qb2 and Qb4 are connected to the negative wiring 22b. The source s of the switching element Qb1 and the drain d of the switching element Qb2 are connected at a connection point nd3, and the source s of the switching element Qb3 and the drain d of the switching element Qb4 are connected at a connection point nd4. A control signal So output from the control unit 99 is input to the gates g, which are the control terminals of the switching elements Qb1 to Qb4.

[0076] 22 shows an example in which the control signal So corresponding to the power conversion unit U1, i.e., the control signal Soa1, is input. The second drive unit 57 of the switching element drive circuit 55 outputs the control signal So for the rectifier circuit 4. Similar to the control signals So1, So2, So3, and So4 in FIG. 1, the control signal Soa1 is input to the rectifier circuit 4 of the power conversion unit U1, the control signal Soa2 is input to the rectifier circuit 4 of the power conversion unit U2, the control signal Soa3 is input to the rectifier circuit 4 of the power conversion unit U3, and the control signal Soa4 is input to the rectifier circuit 4 of the power conversion unit U4.

[0077] Control signals Soa11, Soa21, Soa31, and Soa41 are input to the gates g of the switching elements Qb1 to Qb4 in the power conversion unit U1, respectively. The signs of the control signals are as explained in the second example of the transformer 3 and the rectifier circuit 4. However, because the number of switching elements in the rectifier circuit 4 is increased to four, the section relating to the switching elements Qb1 to Qb4 is expanded. When distinguishing between the switching elements Qb1 to Qb4 of the power conversion unit U1 to which the signals are input, Soa11, Soa21, Soa31, and Soa41 are used (see FIG. 26). Similarly, when distinguishing based on the switching elements Qb1 to Qb4 of the input power conversion unit U2, Soa12, Soa22, Soa32, and Soa42 are used; when distinguishing based on the switching elements Qb1 to Qb4 of the input power conversion unit U3, Soa13, Soa23, Soa33, and Soa43 are used; and when distinguishing based on the switching elements Qb1 to Qb4 of the input power conversion unit U4, Soa14, Soa24, Soa34, and Soa44 are used.

[0078] A fourth example of the transformer 3 and rectifier circuit 4 shown in FIG. 23 will be described. The rectifier circuit 4 shown in FIG. 23 is an example including two switching elements Qb1 and Qb2 and two inductors 67a and 67b. The transformer 3 in FIG. 23 is the same as the transformer 3 in FIG. 22. One end of the inductors 67a and 67b is connected to the positive side wiring 21b, the other end of the inductors 67a and 67b is connected to the drains d of the switching elements Qb1 and Qb2, and the sources s of the switching elements Qb1 and Qb2 are connected to the negative side wiring 22b. A connection point nd5 between the other end of the inductor 67a and the drain d of the switching element Qb1 is connected to the AC wiring 62a. A connection point nd6 between the other end of the inductor 67b and the drain d of the switching element Qb2 is connected to the AC wiring 62b. As in the second example of the transformer 3 and rectifier circuit 4, a control signal So output from the control unit 99 is input to the gates g, which are control terminals of the switching elements Qb1 and Qb2.

[0079] The switching elements Qb1 to Qb4 are not limited to MOSFETs, and may be the switching elements described for the switching elements Qa1 to Qa4. By using wide bandgap semiconductor materials for the switching elements Qb1 to Qb4, an inverter circuit with high voltage resistance, good heat dissipation, and high-speed switching can be obtained. Although the switching elements Qb1 to Qb4 are symbolically shown as a single element, they may be connected in multiple parallel or multiple series to increase the current capacity or withstand voltage. When connected in multiple parallel or multiple series, the switching elements Qb1 to Qb4 may be configured as a mixture of the aforementioned Si-IGBTs, SiC-MOSFETs, etc.

[0080] Up to now, an example has been described in which each power conversion unit U of the power conversion device 100 includes a transformer 3. However, each power conversion unit U of the power conversion device 100 does not necessarily have to include a transformer 3. An example of a power conversion unit U not including a transformer 3 will be described. FIG. 27 is a diagram showing the configuration of another power conversion unit according to embodiment 1, and FIG. 28 is a diagram showing the configuration of yet another power conversion unit according to embodiment 1. The power conversion unit U of FIG. 27 and the power conversion unit U of FIG. 28 include an inverter circuit 2, an inductor 5, and a capacitor 6. The inverter circuit 2 of FIG. 27 includes switching elements Qa1 and Qa2 that form a half bridge. The inverter circuit 2 of FIG. 28 includes switching elements Qa1 to Qa4 that form a full bridge.

[0081] The inverter circuit 2 in FIG. 27 has the same configuration as the switching elements Qa1 and Qa2 of the inverter circuit 2 shown in FIG. 2. A connection point nd1, at which the source s of the switching element Qa1 and the drain d of the switching element Qa2 are connected, is connected to one end of the inductor 5 via an AC wiring 61a. The other end of the inductor 5 is connected to an output terminal 27 via a positive side wiring 21b. The inductor 5 and capacitor 6 in FIG. 27 have the same configuration as the inductor 5 and capacitor 6 in FIG. 4. In FIG. 27, the negative side wiring 22a connected to the input terminal 26 and the negative side wiring 22b connected to the output terminal 28 are connected to each other. The power conversion unit U in FIG. 27 outputs a DC output voltage Vo from output terminals 27 and 28, which is obtained by stepping down a DC input voltage Vin input from input terminals 25 and 26.

[0082] The inverter circuit 2 of FIG. 28 has the same configuration as the switching elements Qa1 to Qa4 of the inverter circuit 2 shown in FIG. 2. A connection point nd1, at which the source s of the switching element Qa1 and the drain d of the switching element Qa2 are connected, is connected to one end of the inductor 5 via AC wiring 61a. The other end of the inductor 5 is connected to the output terminal 27 via the positive side wiring 21b. A connection point nd2, at which the source s of the switching element Qa3 and the drain d of the switching element Qa4 are connected, is connected to one end of the capacitor 6 via the AC wiring 61b. The AC wiring 61b and the negative side wiring 22b are connected to each other. One end of the capacitor 6 is connected to the AC wiring 61b and the negative side wiring 22b, and the other end of the capacitor 6 is connected to the positive side wiring 21b. The power conversion unit U of FIG. 28 has a configuration in which a half bridge of the switching elements Qa3 and Qa4 is added to the power conversion unit U of FIG. 27. The power conversion unit U in Fig. 28 can output a positive or negative output voltage Vo from output terminals 27, 28 by changing the potential of one end of capacitor 6 connected to output terminal 28 to either a positive side potential input from input terminal 25 or a negative side potential input from input terminal 26. Furthermore, by combining the operation of a half bridge of switching elements Qa1, Qa2 and a half bridge of switching elements Qa3, Qa4, the power conversion unit U in Fig. 28 can output a DC output voltage Vo from output terminals 27, 28, which is boosted from a DC input voltage Vin input from input terminals 25, 26.

[0083] Up to now, an example has been described in which the multiple power conversion units U are subjected to duty control using PWM control, but this is not limiting. The control of the multiple power conversion units U by the control unit 99 may be PFM (Pulse Frequency Modulation) control, which controls frequency, or constant on-time (or constant off-time) control, instead of duty control using PWM control. The pulse widths of the control signals So1 to So4 output by the inverter circuit 2 arranged on the primary side of the transformer 3 may be controlled to output symmetrical pulses, or asymmetrical pulses may be output for soft switching or the like.

[0084] When the control of the multiple power conversion units U by the control unit 99 is expanded to include other control methods, including PWM control, the switching frequency Fsw is varied. In PFM control, the switching frequency Fsw is varied while maintaining a constant pulse high period Th (see FIG. 14 ). Here, an example is described in which, instead of PFM control, the duty ratio D for PWM control is first determined and then the switching frequency Fsw is varied. In continuous current mode, the output voltage Vo does not change even when the switching frequency Fsw changes. Therefore, the feedforward duty ratio Dccmf in the above-described equation (1), i.e., equation (8), uniquely determines the duty ratio Dccm based on the input voltage Vin, the output voltage Vo, and the transformer turns ratio n. In continuous current mode, the output voltage Vo does not change even when the switching frequency Fsw changes, so it is not necessary to determine the switching frequency Fsw for the purpose of controlling the output voltage Vo. However, the switching frequency Fsw may be set to a value that minimizes the loss of the power conversion device 100, for example. That is, a table may be created of the switching frequency Fsw that minimizes the loss of the power conversion device 100 according to the input voltage Vin, output voltage Vo, and output power, and the switching frequency Fsw may be varied when the duty ratio Dccm is changed.

[0085] In the discontinuous current mode, the switching frequency Fsw may be varied so as to satisfy the above-mentioned equation (2). In other words, even if the duty ratio Da or the switching frequency Fsw is changed, the input power Pin must remain the same. Equation (2) can be rearranged to obtain equation (9).

[0086] Here, the relationship between the switching frequency Fsw and the switching period Tsw is expressed by Equation (3), so the switching period Tsw in Equation (2) is expressed in terms of the switching frequency Fsw. Equation (9) is in the form of multiplying the first equation, Da^2 / Fsw, by the remaining equations. For example, if the duty ratio Da has a lower limit Dmin, and the duty ratio Da becomes smaller than the lower limit Dmin, the switching frequency Fsw needs to be changed. Note that this lower limit Dmin is a lower limit set for a certain purpose, and the control unit 99 can set it to a value less than the lower limit Dmin. Since the duty ratio Da is 2Ddcm, the duty ratio D in the discontinuous current mode has a lower limit Dmin, and if the duty ratio D becomes smaller than the lower limit Dmin, the switching frequency Fsw needs to be changed. Note that this lower limit Dmin is a lower limit set for a certain purpose, and the control unit 99 can set it to a value less than the lower limit Dmin.

[0087] Here, assuming that the current switching frequency is Fsw, the duty ratio Ddcm calculated in step S14 of FIG. 20 is Ddcm, and the lower limit value Dmin of the duty ratio Ddcm is Dmin, a new switching frequency Fswa corresponding to the determined duty ratio Ddcm can be calculated as shown in equation (10).

[0088] In equation (10), when the duty ratio Ddcm is greater than the lower limit Dmin, max(Dmin^2, Ddcm^2) is Ddcm^2, and Fswa = Fsw. Therefore, when the duty ratio Ddcm is greater than the lower limit Dmin, the new switching frequency Fswa is maintained as the switching frequency Fsw. When the duty ratio Ddcm is smaller than the lower limit Dmin, max(Dmin^2, Ddcm^2) is Dmin^2, and Fswa = Dmin^2 / Ddcm^2 × Fsw.

[0089] A control unit 99 will be described when the control unit 99 varies the switching frequency Fsw in its control of multiple power conversion units U. In this case, the control unit 99 includes a current control unit 33 corresponding to each power conversion unit U and a switching frequency change unit 80 added to the current control unit 33. FIG. 29 illustrates a main portion of the current control unit 33. FIG. 29 is a diagram illustrating a main portion of another current control unit according to the first embodiment. The switching frequency change unit 80 includes a switching frequency table 81 for selecting a switching frequency Fsw1 that minimizes the loss of the power conversion device 100 in accordance with the input voltage Vin, output voltage Vo, and output power in continuous current mode, a switching frequency calculation unit 82 for calculating a switching frequency Fswa that maintains the input power Pin constant even when the duty ratio Da in discontinuous current mode is changed, and a switching frequency output unit 83 that outputs a switching frequency Fswo, which is either the switching frequency Fsw1 or the switching frequency Fswa corresponding to the continuous current mode or the discontinuous current mode. In FIG. 29, the initial switching frequency input to the switching frequency change unit 80 is indicated as the switching frequency Fsw. In the continuous current mode, the switching frequency changer 80 outputs the switching frequency Fsw1 as the switching frequency Fswo, and in the discontinuous current mode, the switching frequency changer 80 outputs the switching frequency Fswa as the switching frequency Fswo.

[0090] The switching frequency Fswo is input to the PWM generation unit 43. The PWM generation unit 43 generates a digital control signal Sod that controls the multiple switching elements Qa1 to Qa4 of the inverter circuit 2 by PWM control based on the switching frequency Fswo, the duty ratio D selected by the duty ratio selection unit 42, and the phase stop signal GB. The switching element drive circuit 55 outputs a digital control signal So that is a digital control signal obtained by changing the voltage value of the digital control signal Sod. The control signal So output from the current control unit 33 has a duty ratio D and switching frequency Fsw that correspond to the continuous current mode and the discontinuous current mode.

[0091] As described above, the power conversion device 100 of the first embodiment includes a plurality of power conversion units U connected in parallel and a control unit 99 that controls the plurality of power conversion units U. The power conversion device 100 converts DC power input from the input terminals 23 a, 23 b into DC power of a target voltage and outputs the converted power from the output terminals 24 a, 24 b. Each power conversion unit U includes a plurality of PWM-controlled switching elements Qa1 to Qa4, an inductor 5, and an inductor current output unit 12 that outputs an inductor current IL that is detected or estimated as a current flowing through the inductor 5, which is disposed closer to the output terminals 24 a, 24 b than the plurality of switching elements Qa1 to Qa4. The control unit 99 includes a command control unit (phase shedding control unit 32) that outputs an inductor current command value IL** that causes the inductor current IL for each power conversion unit U to follow the inductor current IL, and a current control unit 33 that generates a control signal So for each power conversion unit U to control the corresponding plurality of switching elements Qa1 to Qa4. The current control unit 33 for each power conversion unit U includes a first current control unit (CCM current control unit 40) that generates a first duty ratio (duty ratio Dccm) of a control signal So that controls the multiple switching elements Qa1 to Qa4 to flow the inductor current IL, which is a continuous current mode in which a current flows continuously through the inductor 5, based on the inductor current IL and an inductor current command value IL**; a second current control unit (DCM current control unit 41) that generates a second duty ratio (duty ratio Ddcm) of the control signal So that controls the multiple switching elements Qa1 to Qa4 to flow the inductor current IL, which is a discontinuous current mode in which a current flows intermittently through the inductor 5, based on the inductor current command value IL**; and a duty ratio selection unit 42 that selects either the first duty ratio (duty ratio Dccm) or the second duty ratio (duty ratio Ddcm) corresponding to the current mode, the continuous current mode, or the discontinuous current mode, as a selected duty ratio (duty ratio D), and determines the selected duty ratio (duty ratio D) as the duty ratio of the control signal So.With this configuration, the power conversion device 100 of embodiment 1 controls each of the parallel-connected power conversion units U by a control signal So having a duty ratio D corresponding to the current mode of the inductor current IL, that is, the continuous current mode and the discontinuous current mode, thereby reducing output voltage distortion when switching the number of phases, which is the number of phases at which the power conversion units U operate.

[0092] Furthermore, the inductor current control method for a power conversion device according to the first embodiment includes a power conversion device 100 having a plurality of parallel-connected power conversion units U each having an inductor 5 and controlled by a control unit 99. The power conversion device 100 converts DC power input from input terminals 23 a, 23 b into DC power with a target voltage and outputs the converted DC power from output terminals 24 a, 24 b. The power conversion device 100 controls an inductor current IL, which is a current flowing through the inductor 5. Each power conversion unit U includes a plurality of switching elements Qa1 to Qa4 that are PWM-controlled by a control signal So from the control unit 99, an inductor 5 disposed closer to the output terminals 24 a, 24 b than the plurality of switching elements Qa1 to Qa4, and an inductor current output unit 12 that outputs a detected or estimated inductor current IL. The inductor current control method for a power conversion device according to the first embodiment includes a command output step, a first current control step, a second current control step, and a duty ratio selection step. The command output step outputs an inductor current command value IL** for each power conversion unit U, which causes the inductor current IL to follow the inductor current IL. The first current control step generates, for each power conversion unit U, a first duty ratio (duty ratio Dccm) of a control signal So that controls the multiple switching elements Qa1 to Qa4 to flow an inductor current IL based on an inductor current IL and an inductor current command value IL**, thereby setting the inductor current IL to a continuous current mode in which a current flows continuously through the inductor 5. The second current control step generates, for each power conversion unit U, a second duty ratio (duty ratio Ddcm) of a control signal So that controls the multiple switching elements Qa1 to Qa4 to flow an inductor current IL based on the inductor current command value IL**, thereby setting the inductor current IL to a discontinuous current mode in which a current flows intermittently through the inductor 5. The duty ratio selection step selects, for each power conversion unit U, either the first duty ratio (duty ratio Dccm) or the second duty ratio (duty ratio Ddcm) that corresponds to the current mode, the continuous current mode, or the discontinuous current mode, as a selected duty ratio (duty ratio D), and determines the selected duty ratio (duty ratio D) as the duty ratio of the control signal So.With this configuration, the inductor current control method for the power conversion device of embodiment 1 controls each parallel-connected power conversion unit U by a control signal So having a duty ratio D corresponding to the current mode of the inductor current IL, that is, the continuous current mode and the discontinuous current mode, thereby reducing output voltage distortion when switching the number of phases, which is the number of phases in which the power conversion units U operate.

[0093] Although various exemplary embodiments and examples are described in this disclosure, the various features, aspects, and functions described in the embodiments are not limited to the application of specific examples, but can be applied to the embodiments alone or in various combinations. Therefore, countless modifications not illustrated are anticipated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is modified, added, or omitted, and even cases where at least one component is extracted and combined with components of other embodiments.

[0094] 3...transformer, 5...inductor, 12...inductor current output device, 14b...voltage detector, 23a, 23b...input terminal, 24a, 24b...output terminal, 31...voltage control unit, 32...phase shedding control unit (command control unit), 33...current control unit, 33u1, 33u2, 33u3, 33u4...current control unit, 40...CCM current control unit, 41...DCM current control unit, 42...duty ratio selection unit, 99...control unit, 100...power conversion device, D...duty ratio (selected duty ratio), Dccm...duty ratio (first duty ratio), Ddcm...duty ratio (second duty ratio), Fsw...switching frequency, GB...phase stop signal, GB1, GB2, GB3, GB4...phase stop signal, IL...inductor current, IL1, IL2, IL3, IL4...inductor current, IL**...inductor current command value, IL1**, IL2**, IL3**, IL4**...inductor current command value, Iot...output current, Iot*...output current command value, Lf...inductor current inductance, Lm... excitation inductance, n... transformer turns ratio, So... control signal, So1... control signal, So11, So21, So31, So41... control signal, So2... control signal, So12, So22, So32, So42... control signal, So3... control signal, So13, So23, So33, So43... control signal, So4... control signal, So14, So24, So34, So44... control signal, Soa1... control signal, Soa11, Soa21, Soa31, Soa41 ...control signal, Soa2...control signal, Soa12, Soa22, Soa32, Soa42...control signal, Soa3...control signal, Soa13, Soa23, Soa33, Soa43...control signal, Soa4...control signal, Soa14, Soa24, Soa34, Soa44...control signal, Qa1, Qa2, Qa3, Qa4...switching element, U...power conversion unit, U1, U2, U3, U4...power conversion unit, Vin...input voltage, Vo...output voltage, Vo*...output voltage command value

Claims

1. A power conversion device comprising a plurality of power conversion units connected in parallel and a control unit for controlling the plurality of power conversion units, which converts DC power inputted from an input terminal into DC power of a target voltage and outputs the converted DC power from an output terminal, wherein each of the power conversion units comprises: a plurality of switching elements that are PWM controlled; an inductor arranged on the output terminal side of the plurality of switching elements; and an inductor current output device that outputs an inductor current that detects or estimates a current flowing through the inductor, wherein the control unit comprises: a command control unit that outputs an inductor current command value that causes the inductor current of each of the power conversion units to follow; and a current control unit that generates a control signal for each of the power conversion units to control the corresponding plurality of switching elements, wherein the current control unit for each of the power conversion units comprises: a first current control unit that generates a first duty ratio of the control signal that controls the plurality of switching elements so as to flow the inductor current that is in a current continuous mode in which current flows continuously through the inductor, based on the inductor current and the inductor current command value; a second current control unit that generates a second duty ratio of the control signal that controls a plurality of switching elements to flow an inductor current that is a discontinuous current mode in which a current flows intermittently through the inductor based on the inductor current command value; and a duty ratio selection unit that selects, as a selected duty ratio, one of the first duty ratio and the second duty ratio that corresponds to a current mode of the continuous current mode or the discontinuous current mode, and determines the selected duty ratio as the duty ratio of the control signal.

2. The power conversion device according to claim 1, wherein the control unit includes a voltage control unit that generates an output current command value that is a command value for the output current of DC power output from the output terminal using an output voltage command value that is a command value for the target voltage and an output voltage value detected by a voltage detector as the voltage of DC power output from the output terminal of the power conversion device, the number of operations of the power conversion units is defined as the number of operation phases, and the command control unit outputs, for each of the power conversion units, a stop signal that stops the operation of the power conversion unit and the inductor current command value of the power conversion unit based on the output current command value, and when the number of operation phases is changed, the duty ratio selection unit of the power conversion unit determines the selected duty ratio.

3. The power conversion device according to claim 1 or 2, wherein the duty ratio selection unit selects one of the first duty ratio and the second duty ratio, whichever has a smaller value.

4. The power conversion device according to any one of claims 1 to 3, wherein the plurality of switching elements form an inverter circuit that converts DC power input from the input terminal into AC power.

5. The power conversion device according to claim 4, wherein the power conversion unit includes a transformer between the inverter circuit and the inductor.

6. The power conversion device according to claim 5, wherein the second current control unit generates the second duty ratio of the control signal based on the inductor current command value, an input voltage of DC power input from the input terminal, an output voltage of DC power output from the output terminal, an inductance of the inductor, an excitation inductance of the transformer, a turns ratio of the transformer, and a switching frequency of the switching element.

7. An inductor current control method for a power conversion device in which a plurality of power conversion units each having an inductor and controlled by a control unit are connected in parallel, the power conversion device converting DC power inputted from an input terminal into DC power of a target voltage and outputting the converted DC power from an output terminal, the method controlling an inductor current which is a current flowing through the inductor, the power conversion unit each comprising: a plurality of switching elements PWM-controlled by a control signal from the control unit; an inductor arranged closer to the output terminal than the plurality of switching elements; and an inductor current output device which outputs the detected or estimated inductor current, the method comprising: a command output step of outputting, for each of the power conversion units, an inductor current command value which causes the inductor current to follow; and a first current control step of generating, for each of the power conversion units, a first duty ratio of the control signal which controls the plurality of switching elements based on the inductor current and the inductor current command value so as to cause the inductor current to flow in a current continuous mode in which a current flows continuously through the inductor; an inductor current control method for a power conversion device, comprising: a second current control step of generating, for each of the power conversion units, a second duty ratio of the control signal that controls a plurality of the switching elements so as to flow the inductor current that is a discontinuous current mode in which a current flows intermittently through the inductor, based on the inductor current command value; and a duty ratio selection step of selecting, for each of the power conversion units, one of the first duty ratio and the second duty ratio that corresponds to the continuous current mode or a current mode of the discontinuous current mode, as a selected duty ratio, and determining the selected duty ratio as the duty ratio of the control signal.

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