Power converter and method for controlling the inductor current of the power converter

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

Technical Field

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

Background Art

[0002] A power converter such as a DC-DC converter that converts an input voltage to a target output voltage is required to output an undistorted output voltage. In addition, as the output power capacity of power converters increases, a multi-phase configuration in which a plurality of DC-DC converters are connected in parallel is used.

[0003] The power converter disclosed in Patent Document 1 does not have a multi-phase configuration, but corresponds to a DC-DC converter with one phase. The power converter of Patent Document 1 converts direct-current power input from a battery via an input-side filter circuit into direct-current power of a target output voltage by a power conversion circuit, and supplies the direct-current power of the target output voltage to a load via an output-side filter circuit. When controlling the power conversion circuit, in order to suppress output voltage distortion caused by changes in current mode, the power converter of Patent Document 1 obtains a feedforward term for continuous current mode and a feedforward term for discontinuous current mode, selects one of them as the feedforward term, and controls the switching element of the power conversion circuit by 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 converter of Patent Document 1 is configured in a multi-phase arrangement, a plurality of power conversion circuits are connected in parallel. The operation and stop of each of the plurality of parallel-connected power conversion circuits are controlled by a control circuit. The number of phases of the power converter is switched by the operation and stop of the plurality of power conversion circuits.

Prior Art Literature

Patent Literature

[0005] [Patent Document 1] Japanese Patent Publication No. 2015-035921 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In power converters equipped with an inductor, such as the power converter described in Patent Document 1, factors that cause distortion in the output voltage include fluctuations in the input voltage, fluctuations in the output load, and switching of 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; and when the number of phases is switched, the DC component of the inductor current fluctuates. These fluctuations change 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 is always flowing, while discontinuous current mode is a current mode that has a zero-current period. It is known that when the current mode changes, the response of the power converter circuit to the current command value deteriorates.

[0007] The power converter described in Patent Document 1 generates a feedback duty cycle using a current control PI (Proportional-Integral) calculation unit, which is then added to either the duty cycle for continuous current mode or the duty cycle for discontinuous current mode to generate the duty cycle for PWM (Pulse Width Modulation) control. The commonality of the feedback term leads to output voltage distortion due to the cumulative error of the integrator for the previous current mode when the current mode changes, and output voltage distortion due to the inability to detect the average current when the current discontinuous mode is in operation.

[0008] Furthermore, when the power converter described in Patent Document 1 is configured in a multi-phase configuration, the detected output current is used in the feedforward calculation. As a result, when the number of phases is switched, the feedforward term overcompensates, causing distortion of the output voltage.

[0009] This disclosure aims to reduce output voltage distortion during phase switching in a multi-phase power converter. [Means for solving the problem]

[0010] The power conversion device according to this disclosure comprises a plurality of power conversion units connected in parallel, and a control unit that controls the plurality of power conversion units, and converts DC power input from the input terminal into DC power of a target voltage and outputs it from the output terminal. Each power conversion unit comprises a plurality of PWM-controlled switching elements, an inductor positioned on the output terminal side of the plurality of switching elements, and an inductor current outputter that detects or estimates the current flowing through the inductor and outputs the inductor current. The control unit comprises a command control unit that outputs an inductor current command value that tracks the inductor current of each power conversion unit, and a current control unit that generates a control signal for controlling the corresponding plurality of switching elements for each power conversion unit. Each power conversion unit's current control unit includes: a first current control unit that generates a first duty cycle for a control signal that controls multiple switching elements to flow an inductor current in a continuous current mode, where 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 cycle for a control signal that controls multiple switching elements to flow an inductor current in a discontinuous current mode, where current flows intermittently through the inductor, based on the inductor current command value; and a duty cycle selection unit that selects either the first duty cycle or the second duty cycle corresponding to the current modes of continuous current mode and discontinuous current mode as the selected duty cycle, and determines the selected duty cycle as the duty cycle of the control signal. [Effects of the Invention]

[0011] According to the power conversion device of this disclosure, each power conversion unit connected in parallel is controlled by a control signal with a duty cycle corresponding to the current modes of the inductor current continuous mode and current discontinuous mode, thereby reducing output voltage distortion when switching the number of phases, which is the number of power conversion units in operation. [Brief explanation of the drawing]

[0012] [Figure 1] This diagram shows the configuration of the power conversion device according to Embodiment 1. [Figure 2] This diagram shows the configuration of the inverter circuit shown in Figure 1. [Figure 3] This figure shows a first example of the transformer and rectifier circuit shown in Figure 1. [Figure 4] This figure shows a first example of an inductor current output device. [Figure 5] This figure shows a second example of the inductor current output device shown in Figure 1. [Figure 6] This figure shows a third example of the inductor current output device shown in Figure 1. [Figure 7] This diagram shows the configuration of the control unit shown in Figure 1. [Figure 8] This figure shows an example of a hardware configuration in which the functions of the control unit shown in Figure 7 are realized by digital calculations. [Figure 9] This figure shows an example of the output to each unit in the control signal shown in Figure 1. [Figure 10] This figure illustrates the signs of the phase input currents output from each unit in Figure 1. [Figure 11] This diagram illustrates the signs of the primary currents output from each unit in Figure 1. [Figure 12] This figure illustrates the sign of the inductor current output from each unit in Figure 1. [Figure 13] This figure illustrates the signs of the phase output currents output from each unit in Figure 1. [Figure 14] This is a diagram explaining duty cycle. [Figure 15]FIG. 1 is a diagram showing a first example of duty ratio characteristics according to the first embodiment. [Figure 16] FIG. 2 is a diagram showing a second example of duty ratio characteristics according to the first embodiment. [Figure 17] FIG. 3 is a flowchart showing an example of a control method for the power converter according to the first embodiment. [Figure 18] FIG. 4 is a flowchart showing a first example of step S05 in FIG. 17. [Figure 19] FIG. 5 is a flowchart showing a second example of step S05 in FIG. 17. [Figure 20] FIG. 6 is a flowchart showing processing steps of step S05 in FIG. 17. [Figure 21] FIG. 7 is a diagram showing a second example of the transformer and rectifier circuit in FIG. 1. [Figure 22] FIG. 8 is a diagram showing a third example of the transformer and rectifier circuit in FIG. 1. [Figure 23] FIG. 9 is a diagram showing a fourth example of the transformer and rectifier circuit in FIG. 1. [Figure 24] FIG. 10 is a diagram showing control signals output to the rectifier circuits of FIGS. 21 to 23. [Figure 25] FIG. 11 is a diagram showing a configuration of a control signal corresponding to FIGS. 21 and 23. [Figure 26] FIG. 12 is a diagram showing a configuration of a control signal corresponding to FIG. 22. [Figure 27] FIG. 13 is a diagram showing a configuration of another power conversion unit according to the first embodiment. [Figure 28] FIG. 14 is a diagram showing a configuration of still another power conversion unit according to the first embodiment. [Figure 29] FIG. 15 is a diagram showing main parts of another current control unit according to the first embodiment. MODE FOR CARRYING OUT THE INVENTION

[0013] First Embodiment Figure 1 is a diagram showing the configuration of a power converter according to Embodiment 1. Figure 2 is a diagram showing the configuration of the inverter circuit in Figure 1, and Figure 3 is a diagram showing a first example of the transformer and rectifier circuit in Figure 1. Figures 4 to 6 are diagrams showing the first to third examples of the inductor current output devices in Figure 1, respectively. Figure 7 is a diagram showing the configuration of the control unit in Figure 1, and Figure 8 is a diagram showing an example of a hardware configuration that realizes the functions of the control unit in Figure 7 by digital calculations. Figure 9 is a diagram showing an example of output to each unit in the control signal in Figure 1. Figure 10 is a diagram explaining the sign of the phase input current output from each unit in Figure 1, and Figure 11 is a diagram explaining the sign of the primary side current output from each unit in Figure 1. Figure 12 is a diagram explaining the sign of the inductor current output from each unit in Figure 1, and Figure 13 is a diagram explaining the sign of the phase output current output from each unit in Figure 1. Figure 14 is a diagram explaining the duty cycle, and Figures 15 and 16 are diagrams showing the first and second examples of duty cycle characteristics according to Embodiment 1, respectively. Figure 17 is a flowchart showing an example of a control method for a power converter according to Embodiment 1. Figure 18 is a flowchart showing the first example of step S05 in Figure 17, and Figure 19 is a flowchart showing the second example of step S05 in Figure 17. Figure 20 is a flowchart showing the processing steps of step S05 in Figure 17. Figures 21 to 23 show the second to fourth examples of the transformer and rectifier circuit in Figure 1, respectively. Figure 24 shows the control signals output to the rectifier circuits in Figures 21 to 23. Figure 25 shows the configuration of the control signals corresponding to Figures 21 and 23, and Figure 26 shows the configuration of the control signals corresponding to Figure 22. The power converter 100 of Embodiment 1 is a multi-phase power converter that 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, and converts DC power input from input terminals 23a and 23b into DC power of a target voltage and outputs it from output terminals 24a and 24b.

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

[0015] Figure 1 shows an example with four power conversion units U corresponding to four phases, i.e., phases 1 to 4. In other words, the power conversion device 100 shown in Figure 1 is an example where there are four phases. Where appropriate, the power conversion units are generally denoted as U, and U1 to U4 are used to distinguish them. The power conversion units U corresponding to phases 1 to 4 are power conversion units U1 to U4, respectively. Where appropriate, power conversion units U1 to U4 corresponding to phases 1 to 4 are simply referred to as power conversion units U1 to U4 of phases 1 to 4. A capacitor 7 is connected between the positive wiring 21b and the negative wiring 22b from the positive and negative confluence points where the outputs of each power conversion unit U merge to the output terminals 24a and 24b. In other words, the positive and negative confluence points where the outputs of each power conversion unit U merge are located between the output terminals 27 and 28 of each power conversion unit U and the connection points with the positive wiring 21b and negative wiring 22b of the capacitor 7. The power conversion device 100 of Embodiment 1 converts the DC voltage of the DC source 19 to a 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 produce DC voltage, a DC power distribution network, etc. The load 20 is, for example, a DC load, an AC load via an inverter, etc. An AC load via an inverter is a device in which an inverter that converts DC voltage to AC voltage is connected to an AC load such as a motor that is powered by this inverter.

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

[0018] The power conversion unit U will now be described. The configuration of power conversion unit U is shown in power conversion unit U1 in Figure 1. An example of a similar configuration for power conversion units U2 to U4 will also be described. Power conversion unit U is an isolated DC-DC converter equipped with an inverter circuit 2, a transformer 3, a rectifier circuit 4, an inductor 5, and a capacitor 6, arranged sequentially from the input terminals 25 and 26. The inverter circuit 2 is equipped with multiple PWM-controlled switching elements, and the inductor 5 is positioned on the output terminals 24a and 24b side of the multiple switching elements. Power conversion unit U is equipped with input terminals 25 and 26 into which DC power is input, and output terminals 27 and 28 that output DC power of the converted target voltage. 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 symbol for the positive wiring from the positive terminal of the DC source 19 to the positive wiring of the inverter circuit 2 is denoted as 21a, and the symbol for the negative wiring from the negative terminal of the DC source 19 to the negative wiring of the inverter circuit 2 is denoted as 22a. The symbol for the positive wiring from the positive terminal of the load 20 to the positive wiring of the rectifier circuit 4 is denoted as 21b, and the symbol for the negative wiring from the negative terminal of the load 20 to the negative wiring of the rectifier circuit 4 is denoted as 22b.

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

[0020] The inverter circuit 2, as shown in Figure 2 for example, comprises upper arm switching elements Qa1 and Qa3 connected to positive wiring 21a, and lower arm switching elements Qa2 and Qa4 connected to negative wiring 22a, forming a full-bridge circuit. The legs formed by the series connection of the upper and lower arms are series units of switching elements Qa1 and Qa2 connected in series, and switching elements Qa3 and Qa4 connected in series. The connection point between the upper and lower arms is connected to the AC wiring. The connection point nd1 between switching elements Qa1 and Qa2 is connected to AC wiring 61a. The connection point nd2 between switching elements Qa3 and Qa4 is connected to AC wiring 61b.

[0021] Figure 1 shows an example of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) having transistors Tr and diodes Di as switching elements Qa1 to Qa4. Diode Di may be a parasitic diode of the MOSFET or a diode of a separate element. The drains d of switching elements Qa1 and Qa3 are connected to the positive wiring 21a, and the sources s of switching elements Qa2 and Qa4 are connected to the negative wiring 22a. The source s of switching element Qa1 and the drain d of switching element Qa2 are connected at connection point nd1, and the source s of switching element Qa3 and the drain d of switching element Qa4 are connected at connection point nd2. The cathode of diode Di is connected to the drains d of switching elements Qa1 to Qa4, and the anode of diode Di is connected to the sources s of switching elements Qa1 to Qa4. The control signal So output from the control unit 99 is input to the gate g, which is the control terminal of switching elements Qa1 to Qa4.

[0022] Figure 2 shows an example where the control signal So, i.e., control signal So1, corresponding to power conversion unit U1 is input. As shown in Figure 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 code for the control signals is generally So, and when distinguishing by the power conversion unit U to which they are input, So1, So2, So3, and So4 are used. Furthermore, when distinguishing by the switching elements Qa1 to Qa4 of the power conversion unit U1 to which they are input, So11, So21, So31, and So41 are used. Similarly, as shown in Figure 9, when distinguishing by the switching elements Qa1 to Qa4 of the input power conversion unit U2, So12, So22, So32, and So42 are used; when distinguishing by the switching elements Qa1 to Qa4 of the input power conversion unit U3, So13, So23, So33, and So43 are used; and when distinguishing by 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, but may also consist of, for example, an IGBT (Insulated Gate Bipolar Transistor) and a diode Di connected in antiparallel to the IGBT, or they may consist of a bipolar transistor. The semiconductor material of the switching elements Qa1 to Qa4 is not limited to Si (Silicon), but may also be a wide-bandgap semiconductor material with a wider bandgap than Si, such as silicon carbide (SiC), gallium nitride (GaN), or gallium oxide (Ga2O3). In other words, the switching elements Qa1 to Qa4 may be Si-MOSFETs, Si-IGBTs, SiC-MOSFETs, SiC-IGBTs, GaN power transistors, Ga2O3 power transistors, etc. When the switching elements Qa1 to Qa4 are IGBTs, drain d and source s should be read as collector and emitter. When the switching elements Qa1 to Qa4 are bipolar transistors such as GaN power transistors and Ga2O3 power transistors, the control terminal gate g is read as the base, and the drain d and source s are read as 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 capabilities can be obtained.

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

[0025] A first example of transformer 3 and rectifier circuit 4 is shown in Figure 3. Transformer 3 shown in Figure 3 is a center-tapped transformer. 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 the input terminal 65a of the rectifier circuit 4 via AC wiring 62a. The other end of the secondary winding 64 is connected to the input terminal 65b of the rectifier circuit 4 via AC wiring 62b. The middle of the secondary winding 64 is connected to the input terminal 65c of the rectifier circuit 4 via AC wiring 62c. The rectifier circuit 4 shown in Figure 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 potential at the midpoint of the transformer 3 is the negative potential of the rectifier circuit 4. The primary winding 63 and the secondary winding 64 are Np and Ns, respectively. The transformer turns ratio n of the transformer 3 is Np / Ns.

[0026] An example of inductor 5 and capacitor 6 is shown in Figure 4. As previously mentioned, one end of 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 capacitor 6 via positive wiring 21b. The other end of capacitor 6 is connected to negative wiring 22b.

[0027] Next, the input information Sin used to control the power converter 100 will be described. The input information Sin includes, for example, the input voltage Vin and input current Iint of the DC power input to the power converter 100, the output voltage Vo and output current Iot of the DC power output from the power converter 100, the phase input current Iin input to the power conversion unit U, the primary side current Ip of the transformer 3, the inductor current IL of the inductor 5, and the phase output current Io output from the power conversion unit U. Note that some of the input information Sin exemplified above will not be used in the control described later. 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, for example, the voltage across capacitor 7 detected by voltage detector 14b. The output current Iot is, for example, the current output from capacitor 7 detected by current detector 15b. The phase input current Iin is, for example, the current in the positive wiring 21a connected from input terminal 25 to inverter circuit 2 detected by current detector 8. The primary current Ip is, for example, the current in AC wiring 61a detected by current detector 9. The inductor current IL is, for example, the current of inductor 5 output by inductor current output 12. The phase output current Io is, for example, the current in the positive wiring 21b from capacitor 6 to output terminal 27 detected by current detector 13.

[0029] The inductor current outputter 12 outputs the inductor current IL, which is the detected or estimated current flowing through the inductor 5. Figures 4 to 6 show the first to third examples of the inductor current outputter 12. The inductor current outputter 12 shown in Figure 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, as detected by the current detector 10, which is the inductor current outputter 12. The inductor current outputter 12 shown in Figure 5 is an example of the first current estimation circuit 11. In this case, the inductor current IL is the 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 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 cycle D of the control signal So, which will be described later. The inductor current output device 12 shown in Figure 6 is an example of a second current estimation circuit 11 and 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 detected by the voltage detector 16.

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

[0031] Next, the configuration and function of the control unit 99 will be described using Figures 7 and 8. The control unit 99 is equipped with a processor 50 such as a CPU (Central Processing Unit), a memory 51 for exchanging data with the processor 50, and an input / output interface for inputting and outputting signals between the processor 50 and the outside world in order to control the power conversion units U1 to U4. The input / output interface consists of an input circuit 52 for inputting signals between the processor 50 and the outside world, and an output circuit 53 for outputting signals between the processor 50 and the outside world. The processor 50 may be an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), and various signal processing circuits. In addition, multiple devices of the same type or different types may be provided as the processor 50, and each process may be performed separately. The memory 51 is equipped with RAM (Random Access Memory) configured to allow reading and writing of data from the processor 50, ROM (Read Only Memory) configured to allow reading of data from the processor 50, etc. The functional blocks of the control unit 99, described later, namely the voltage control unit 31, the phase shedding control unit 32, and the multiple current control units 33, are implemented by the processor 50 and memory 51 shown in Figure 8. The functional blocks of the control unit 99 are implemented by the processor 50 executing a program stored in the memory 51. Alternatively, multiple processors 50 and multiple memory units 51 may work together to execute each function.

[0032] The input circuit 52 includes an analog-to-digital (AD) converter 54 that converts the phase input current Iin, primary current Ip, phase output current Io, and inductor current IL of the analog signals output from the current detectors 8, 9, 13 and inductor current output 12 of the power conversion units U1 to U4 into digital signals. The input circuit 52 also includes an AD converter 54 that converts the input voltage Vin, output voltage Vo, input current Iint, and output current Iot of the analog signals output from the voltage detectors 14a, 14b and current detectors 15a, 15b into digital signals. Note that only one AD converter 54 is shown in Figure 8. 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 control signal So of the digital signal with a changed voltage value. Note that the same sign is used before and after the AD conversion.

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

[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 located on the primary side of the transformer 3, so they are primary-side switching elements. An example in which the switching elements Qb1 to Qb4 are used in the rectifier circuit 4 of the power conversion units U1 to U4 (see Figures 21 to 23) will be described later, but when the switching elements Qb1 to Qb4 are used in the rectifier circuit 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 located on the secondary side of the transformer 3, so they 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 switching elements Qb1 to Qb4 may be synchronously rectified to reduce conduction losses due to the forward voltage VF of the diodes.

[0035] The control unit 99 may be configured to shift the carrier phase of the triangular wave in order to control the power conversion units U1 to U4. The operation of shifting the phases of multiple power conversion units U to cancel out the ripple of the output current Iot is called interleaving operation. Interleaving operation makes it possible to miniaturize the input filter 17 and the output filter 18. There are various methods for interleaving, but it can be achieved by controlling the operation or stopping of multiple power conversion units U. For example, the four carrier phases may be shifted by approximately 45 degrees and operated. Alternatively, two carrier phases may be shifted by approximately 90 degrees, and the four power conversion units U1 to U4 may be operated with these two carrier phases. Alternatively, one of the four power conversion units U1 to U4 may be stopped, and the carrier phases of the remaining three may be shifted by approximately 60 degrees each and operated. Alternatively, two of the four power conversion units U1 to U4 may be stopped, and the remaining two may be operated with their carrier phases shifted by approximately 90 degrees. The aforementioned "approximately 45 degrees" refers to a range of 40 degrees to 50 degrees, preferably 44 degrees to 46 degrees. The same applies to the other phase angles indicated. Furthermore, the phase shift angle should be such that it can suppress the ripple of the output current Iot. In addition, a sawtooth wave carrier may be used as the triangular wave carrier for PWM switching control.

[0036] Figure 7 shows the functional blocks within the control unit 99. The control unit 99 includes a voltage control function, a phase number switching function, and a phase current control function. More specifically, the control unit 99 includes a phase shedding control unit 32 having current control units 33 (33u1 to 33u4) for each phase, i.e., each power conversion unit U, a current command generation unit 37 that generates current command values ​​for each phase, and a stop signal generation unit 38 that generates a phase stop signal GB to stop 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, so it can also be called a command control unit that outputs an inductor current command value IL**. The current control unit 33 generates a control signal So for each power conversion unit U that controls a corresponding number of switching elements Qa1 to Qa4. In Figure 7, the inductor current command values ​​IL1** to IL4** enclosed in long dashed rectangles are collectively represented by the inductor current command value IL**, the phase stop signals GB1 to GB4 enclosed in dashed rectangles 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 the output current command value Iot*, which is the 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, for example, uses a compensator to convert the 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, and calculates the total current command value for each phase, i.e., the output current command value Iot*, by adding the capacitor current and the value of the output current Iot detected by the current detector 15b. 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 at all. The compensator can be any type that can adjust the gain characteristics or phase characteristics of the open-loop characteristics, such as a P (Proportional) controller, PI (Integral) controller, PID (Proportional-Integral-Differential) controller, Type-2 compensator, Type-3 compensator, etc.

[0038] The phase shedding control unit 32 generates the current command values ​​for each phase and the phase stop signals GB1 to GB4 from the total current command value for each phase, i.e., the output current command value Iot*. As an example of the current command values ​​for each phase, the inductor current command values ​​IL1** to IL4** are used. The sign of the inductor current command values ​​is generally IL**, and if distinguished by the power conversion unit U, IL1**, IL2**, IL3**, and IL4** are used. The sign of the phase stop signals is generally GB, and if distinguished by the 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** for each phase. 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 stops. Furthermore, if there are switching elements Qb1 to Qb4 on the secondary side, when the phase stop signal GB is turned on (enabled), the switching elements Qb1 to Qb4 on the secondary side turn off, which means that the rectifier circuit 4 stops.

[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**, falls below a preset threshold, or when the total current command value, i.e., the output current command value Iot*, falls below a preset threshold. The threshold for the phase stop signal GB may be set to a threshold that maximizes the efficiency of the power converter 100, a threshold that keeps the power converter 100 below its maximum temperature, or an operating time that significantly affects the lifespan of the power converter 100. When the phase stop signal GB is turned on, the current command value that was 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 comprises 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 cycle selection unit 42, a PWM generation unit 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 cycle selection unit 42, and the PWM generation unit 43. The current control unit is generally designated as 33, and when distinguished by the power conversion unit U, 33u1, 33u2, 33u3, and 33u4 are used.

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

[0042] Let's explain the duty cycle D. Figure 14 shows the pulse of the control signal Sod for a digital signal. The duty cycle D is obtained by dividing the high-voltage period Th, which is the period during which the control signal Sod is at a high voltage (digital value of 1), by the switching period Tsw of the control signal Sod. In other words, the duty cycle D is expressed as Th / Tsw. Similarly, the duty cycle D of the control signal So for 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 the command value for the output current Iot of the DC power output from output terminals 24a and 24b, using the output voltage command value Vo*, which is the command value for the target voltage, and the value of the output voltage Vo detected by the voltage detector 14a, which is the voltage of the DC power output from output terminals 24a and 24b of the power converter 100. The PWM generation unit 43 generates a digital signal control Sod that controls multiple switching elements Qa1 to Qa4 of the inverter circuit 2 by PWM control, based on the duty cycle D output from the duty cycle selection unit 42 and the phase stop signal GB output from the phase shedding control unit 32. The PWM generation unit 43 outputs a control signal Sod that stops the inverter circuit 2 when the phase stop signal GB is valid, i.e., indicates a stop, and does not output a control signal Sod that operates the inverter circuit 2 when the phase stop signal GB is invalid, i.e., indicates a non-stop. The switching element drive circuit 55 changes the voltage value of the input digital signal control Sod and outputs a digital signal control So with the changed voltage value.

[0044] The operation of the power converter 100 of Embodiment 1 will be explained using Figures 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 the 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 the processing steps for each power conversion unit U (power conversion unit processing step). After executing step S05, the control unit 99 terminates processing. Note that in Figures 17 to 20, the power conversion unit is simply referred to as a unit. The command calculation step calculates the inductor current command value IL** and outputs that command value, so it can also be called the command output step. Figure 18 is a flowchart expanded to the first example of step S05, and Figure 19 is a flowchart expanded to the second example of step S05. Step S05 shown in Figure 18 is the case where multiple power conversion units U are processed in parallel, and step S05 shown in Figure 19 is the case where multiple power conversion units U are processed sequentially. Figures 18 and 19 show the case where the number of power conversion units U is 4, i.e., there are 4 phases.

[0045] Let's explain the flowchart in Figure 18. Steps S01 to S04 are the same as in Figure 17, so we won't repeat the explanation. The power conversion unit processing step in step S05 includes steps S06a to S06d and step S07. In step S06a, the control unit 99 executes the processing step of power conversion unit U1 (first power conversion unit processing step). In step S06b, the control unit 99 executes the processing step of power conversion unit U2 (second power conversion unit processing step). In step S06c, the control unit 99 executes the processing step of power conversion unit U3 (third power conversion unit processing step). In step S06d, the control unit 99 executes the processing step of power conversion unit U4 (fourth power conversion unit processing step). In step S07, the control unit 99 determines whether all processing steps of power conversion unit U have been completed. If there are processing steps that have not yet been completed, it continues in step S07. If all processing steps of power conversion unit U have been completed, it terminates.

[0046] Let's explain the flowchart in Figure 19. Steps S01 to S04 are the same as in Figure 17, so we won't repeat the explanation. The power conversion unit processing step in 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 step S06d, the control unit 99 terminates processing.

[0047] Figure 20 shows the specific processing of step S05. The unit Ux shown in Figure 20 is each power conversion unit where x is the ordinal number of the power conversion unit U. If the power conversion device 100 has four power conversion units U, then x is one of 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 first duty cycle, duty cycle Dccm, using the CCM current control unit 40 of the power conversion unit Ux, and prepares for control using the first duty cycle (first control step). In step S14, the control unit 99 generates the second duty cycle, duty cycle Ddcm, using the DCM current control unit 41 of the power conversion unit Ux, and prepares for control using the second duty cycle (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** from the command acquisition step (current mode determination step). The determination in the current mode determination step is made based on the relationship between the duty cycle Dccm and the duty cycle Ddcm. Specifically, if Dccm ≤ Ddcm, it is determined to be a continuous current mode, and if Dccm > Ddcm, it is determined to be a discontinuous current mode. If the current mode determination step determines that it is a continuous current mode, the process proceeds to step S16; if the current mode determination step determines that it is a discontinuous current mode, the process proceeds to step S17. In step S16, the control unit 99 sets the duty cycle Dccm to the duty cycle D using the duty cycle selection unit 42 (first duty cycle setting step). In step S17, the control unit 99 sets the duty cycle Ddcm to the duty cycle D using the duty cycle selection unit 42 (second duty cycle setting step). Specifically, if Dccm ≤ Ddcm, it is determined to be a continuous current mode, and the duty cycle Dccm is set to duty cycle D. If Dccm > Ddcm, it is determined to be a discontinuous current mode, and the duty cycle Ddcm is set to duty cycle D. In other words, the smaller value of the duty cycle is set to duty cycle 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 cycle selection steps.

[0049] In the stop signal determination step S18, if the phase stop signal GB indicates a stop, the process proceeds to step S19; otherwise, if the phase stop signal GB does not indicate a stop, i.e., does not indicate a 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 via the PWM generation unit 43 and the switching element drive circuit 55, and stops the power conversion unit Ux (power conversion unit stop 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, and drives the power conversion unit Ux with a duty cycle D (power conversion unit drive step). After step S19 or after step S20, the control unit 99 terminates processing.

[0050] The CCM current control unit 40 of the power conversion unit U includes a feedback controller 44 that calculates a feedback duty cycle 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 cycle Dccmf using the output voltage Vo or the like, and an adder 46 that adds the feedback duty cycle Dccmb and the feedforward duty cycle Dccmf to generate a duty cycle Dccm for the current continuous mode. Note that any controller that can adjust the gain characteristics or phase characteristics of the open-loop characteristics, such as a P controller, PID controller, Type-2 compensator, or Type-3 compensator, is acceptable instead of a PI controller. The duty cycle Dccm for the current continuous mode when a PI controller is applied can be expressed by equation (1).

[0051]

number

[0052] When a PI controller is applied, the CCM current control unit 40 performs the calculation in equation (1), so both the output voltage Vo and the input voltage Vin are input.

[0053] The DCM current control unit 41 of the power conversion unit U is equipped with a feedforward controller 47 that uses the inductor current command value IL**. The feedforward controller 47 generates a duty cycle Ddcm for the current discontinuous mode. The duty cycle Ddcm can be calculated using equation (7).

[0054] Next, we will explain how to generate the duty cycle Ddcm. When feedback control is applied in current discontinuous mode, distortion occurs in the output voltage Vo because the average value of the inductor current IL cannot be detected. Also, during startup and shutdown of the power conversion unit U, i.e., during phase startup and shutdown, the system enters current discontinuous mode (DCM), and consequently, the dynamics of the controlled object, i.e., multiple power conversion units U, change. Due to the influence of DCM, current controllers designed for current continuous mode (CCM), i.e., current controllers that do not consider DCM, experience a decrease in control margin and become unstable. As a result, the output voltage Vo rises, and overvoltage protection or current protection is activated. Therefore, a control system that can handle DCM during startup and shutdown is necessary. DCM is known to behave like a resistive characteristic. That is, there is no dynamics in the controlled object, and it can be controlled in an open loop.

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

number

[0056] Here, Fsw is the switching frequency, and it 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 transformer 3, Lf is the inductance of the smoothing inductor 5, Vo is the output voltage, Lm is the excitation inductance of transformer 3, and Da is the duty cycle. Da = 2Ddcm. In the case of a transformer with a low excitation inductance Lm, if the excitation inductance Lm is ignored by treating it as infinite, an error will occur in the duty cycle Ddcm, resulting in a large discrepancy between the inductor current command value IL** and the actual inductor current IL. In contrast, by considering the excitation inductance Lm, the discrepancy between the inductor current command value IL** and the actual inductor current IL is reduced, enabling a good current response. As a result, by considering the excitation inductance Lm, the switching between current continuous mode and current discontinuous mode is performed appropriately.

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

number

[0059] Solve equation (4) for the duty cycle Da. In addition, assuming that the losses of the power conversion unit U are sufficiently small and negligible, the phase input current Iin can be approximated as shown in equation (5). Iin≒IL×Vo / Vin ···(5)

[0060] If we denote the phase, i.e., the inductor current IL of the power conversion unit U, as the inductor current command value IL**, then it can be expressed as in equation (6). Here, considering the losses of the power conversion unit U, the phase output current Io may be converted to the inductor current command value IL**.

number

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

number

[0062] From equation (7), the degree of freedom to control the duty cycle Ddcm by the inductor current command value IL** is improved, making it possible to control the power conversion unit U in feedforward mode.

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

[0064] Figures 15 and 16 show duty cycle characteristics 71a and 71b, which represent the characteristics of the duty cycle Dccm in continuous current mode, and duty cycle characteristics 72a and 72b, which represent the characteristics of the duty cycle Ddcm in discontinuous current mode. As a comparative example, Figures 15 and 16 also show duty cycle characteristics 73a and 73b, which represent the characteristics of the duty cycle Ddcm in discontinuous current mode without considering the excitation inductance Lm. In Figures 15 and 16, the horizontal axis is the inductor current IL, and the vertical axis is the duty cycle D. The difference between Figure 15 and Figure 16 is the difference in the duty cycle Dccm in continuous current mode. Here, the duty cycle Dccm shown in Figures 15 and 16 is the feedforward duty cycle Dccmf, and the feedforward duty cycle Dccmf can be expressed by equation (8). Dccmf = nVo / 2Vin ... (8)

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

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

[0067] Figures 15 and 16 show that when calculating the duty cycle Ddcm for the current discontinuous mode, the duty cycle characteristics 72a and 72b are when the excitation inductance Lm is considered, while the duty cycle characteristics 73a and 73b are when the excitation inductance Lm is not considered. As can be seen from Figures 15 and 16, the duty cycle Ddcm for the current discontinuous mode is larger when the excitation inductance Lm is not considered compared to when the excitation inductance Lm is considered. As a result, when compared with the duty cycle Dccm for the current continuous mode, the control unit in the comparative example where the excitation inductance Lm is not considered may mistakenly judge the current discontinuous mode as a continuous current mode based on the relative magnitudes of the duty cycles Dccm and Ddcm. This mismatch in current modes causes distortion in the output voltage Vo. Therefore, by considering the excitation inductance Lm, it is possible to further suppress the distortion of the output voltage Vo.

[0068] Furthermore, if the power conversion unit U does not use transformer 3, it is not necessary to consider the excitation inductance Lm. When the power conversion unit U uses transformer 3, the DCM current control unit 41 generates a duty cycle Ddcm based on equation (8) that takes the excitation inductance Lm into consideration. In the power conversion device 100 of Embodiment 1 when transformer 3 is used in the power conversion unit U, the power conversion unit U is controlled by a control signal So of the duty cycle D corresponding to the current modes of the inductor current IL, which are the current modes of the current continuous mode and current discontinuous mode. This reduces the output voltage distortion when switching the number of phases, which is the number of times the power conversion unit operates. In addition, the power conversion device 100 of Embodiment 1 can achieve a high-speed control response without increasing the capacity of the output side capacitors 6 and 7.

[0069] In Figures 1 and 7, four power conversion units U are shown in parallel. However, this does not limit the number of power conversion units U; a configuration in which at least two or more power conversion units U are connected in parallel is also acceptable. 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. In addition, an example in which power conversion units U1 to U4 have similar configurations has been described. Here, an example in which power conversion units U are isolated DC-DC converters has been described, so power conversion units U1 to U4 may have different configurations as long as they are isolated DC-DC converters.

[0070] Furthermore, since the filter capacitor 6 can be miniaturized by the interleaved operation described above, multiple capacitors 6 in phases 1 to 4 may be integrated and configured as capacitor Co. Similarly, multiple inductors 5 in phases 1 to 4 may be integrated and miniaturized, similar to a coupled inductor. The inverter circuit 2 may be a half-bridge circuit or a three-phase circuit. In addition, the inverter circuit 2 may be a multi-level system such as a three-level system, rather than a two-level system.

[0071] Figure 3 shows a first example of the transformer 3 and rectifier circuit 4, but the invention is not limited to this example. Figures 21 to 23 show second and third examples of the transformer 3 and rectifier circuit 4. The differences from the first example of the transformer 3 and rectifier circuit 4 shown in Figure 3 will be mainly explained. The second example of the transformer 3 and rectifier circuit 4 shown in Figure 21 will be explained. The transformer 3 shown in Figure 21 is a center-tapped transformer and is the same as the transformer 3 shown in Figure 3. The rectifier circuit 4 shown in Figure 21 is an example equipped with two switching elements Qb1 and Qb2 and an inductor 67. Switching elements Qb1 and Qb2 are the same as the switching elements Qa1 etc. mentioned above. One end of the secondary winding is connected to the input terminal 65a of the rectifier circuit 4 via AC wiring 62a. The other end of the secondary winding 64 is connected to the input terminal 65b of the rectifier circuit 4 via AC wiring 62b. The middle of the secondary winding 64 is connected to the input terminal 65c of the rectifier circuit 4 via AC wiring 62c. The drain d of switching element Qb1 is connected to input terminal 65a, and the source s of switching element Qb1 is connected to output terminal 66b. The drain d of switching element Qb2 is connected to input terminal 65b, and the source s of switching element Qb2 is connected to output terminal 66b. One end of inductor 67 is connected to input terminal 65c, and the other end of inductor 67 is connected to output terminal 66a. Output terminal 66a of rectifier circuit 4 is connected to the outer positive side wiring 21b, and output terminal 66b of rectifier circuit 4 is connected to the outer negative side wiring 22b. The potential in the middle of transformer 3 is the positive side potential of rectifier circuit 4 via inductor 67. As mentioned above, the signs of the positive and negative side wiring inside rectifier circuit 4 are the same as the signs of the positive and negative side wiring outside rectifier circuit 4, 21b and 22b.

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

[0073] Control signals Soa11 and Soa21 are input to the gates g of switching elements Qb1 and Qb2 in power conversion unit U1, respectively. The code of the control signals input to the rectifier circuit 4 is generally So, similar to the control signals input to the inverter circuit 2, and Soa1, Soa2, Soa3, and Soa4 are used when distinguishing by the input power conversion unit U. Furthermore, Soa11 and Soa21 are used when distinguishing by the switching elements Qb1 and Qb2 of the input power conversion unit U1 (see Figure 25). Similarly, Soa12 and Soa22 are used when distinguishing by the switching elements Qb1 and Qb2 of the input power conversion unit U2, Soa13 and Soa23 are used when distinguishing by the switching elements Qb1 and Qb2 of the input power conversion unit U3, and Soa14 and Soa24 are used when distinguishing by the switching elements Qb1 and Qb2 of the input power conversion unit U4 (see Figure 25).

[0074] A third example of the transformer 3 and rectifier circuit 4 shown in Figure 22 will be described. The rectifier circuit 4 shown in Figure 22 is an example equipped with four switching elements Qb1 to Qb4 and an inductor 67. The four switching elements Qb1 to Qb4 constitute a full-bridge circuit. The transformer 3 in Figure 22 differs from the transformer 3 in Figures 3 and 21 in that the AC wiring 62c is not drawn out 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 composed of the four switching elements Qb1 to Qb4 has the same configuration as the inverter circuit 2 shown in Figure 2. The switching elements Qb1 and Qb3 of the upper arm are connected to the positive side wiring 21b to which the inductor 67 is connected, and the switching elements Qb2 and Qb4 of the lower arm are connected to the negative side wiring 22b. The leg formed by connecting the upper and lower arms in series is a series unit in which switching elements Qb1 and Qb2 are connected in series, and a series unit in which switching elements Qb3 and Qb4 are connected in series. The connection point between the upper and lower arms is connected to the AC wiring. The connection point nd3 between switching elements Qb1 and Qb2 is connected to the AC wiring 62a. The connection point nd4 between switching elements Qb3 and Qb4 is connected to the AC wiring 62b.

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

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

[0077] The gates g of switching elements Qb1 to Qb4 in the power conversion unit U1 are input to control signals Soa11, Soa21, Soa31, and Soa41, respectively. The codes of the control signals are as described in the second example of the transformer 3 and rectifier circuit 4. However, since the number of switching elements in the rectifier circuit 4 has increased to four, the part concerning switching elements Qb1 to Qb4 is extended. When distinguishing by 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 Figure 26). Similarly, when distinguishing by the switching elements Qb1 to Qb4 of the input power conversion unit U2, Soa12, Soa22, Soa32, and Soa42 are used; when distinguishing by the switching elements Qb1 to Qb4 of the input power conversion unit U3, Soa13, Soa23, Soa33, and Soa43 are used; and when distinguishing by 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 Figure 23 will be described. The rectifier circuit 4 shown in Figure 23 is an example that includes two switching elements Qb1 and Qb2 and two inductors 67a and 67b. The transformer 3 in Figure 23 is the same as the transformer 3 in Figure 22. One end of inductors 67a and 67b is connected to the positive wiring 21b, the other end of inductors 67a and 67b is connected to the drains d of switching elements Qb1 and Qb2, and the sources s of switching elements Qb1 and Qb2 are connected to the negative wiring 22b. The connection point nd5 between the other end of inductor 67a and the drain d of switching element Qb1 is connected to the AC wiring 62a. The connection point nd6 between the other end of inductor 67b and the drain d of switching element Qb2 is connected to the AC wiring 62b. The gate g, which is the control terminal of switching elements Qb1 and Qb2, receives a control signal So output from the control unit 99, similar to the second example of the transformer 3 and rectifier circuit 4.

[0079] The switching elements Qb1 to Qb4 are not limited to MOSFETs, but may also be the switching elements described in Switching Elements Qa1 to Qa4. By using wide-bandgap semiconductor materials for switching elements Qb1 to Qb4, an inverter circuit with high voltage resistance, good heat dissipation, and high-speed switching capabilities can be obtained. Although switching elements Qb1 to Qb4 are symbolically represented as one, they may be arranged in multiple parallel or multiple series configurations to increase current capacity or voltage resistance. In the case of multiple parallel or multiple series configurations, switching elements Qb1 to Qb4 may be a mixed configuration of Si-IGBTs, SiC-MOSFETs, etc., as described above.

[0080] Up to this point, we have described an example in which each power conversion unit U of the power conversion device 100 is equipped with a transformer 3, but each power conversion unit U of the power conversion device 100 does not necessarily have to be equipped with a transformer 3. An example of a power conversion unit U without a transformer 3 will be described. Figure 27 is a diagram showing the configuration of another power conversion unit according to Embodiment 1, and Figure 28 is a diagram showing the configuration of yet another power conversion unit according to Embodiment 1. The power conversion unit U in Figure 27 and the power conversion unit U in Figure 28 are equipped with an inverter circuit 2, an inductor 5, and a capacitor 6. The inverter circuit 2 in Figure 27 is equipped with switching elements Qa1 and Qa2 that constitute a half bridge. The inverter circuit 2 in Figure 28 is equipped with switching elements Qa1 to Qa4 that constitute a full bridge.

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

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

[0083] Up to this point, we have described an example in which multiple power conversion units U are controlled by PWM duty cycle control, but the system is not limited to this example. The control of multiple power conversion units U by the control unit 99 may be performed not by PWM duty cycle control, but by frequency control using PFM (Pulse Frequency Modulation) control, or by constant on-time (or constant off-time) control. The pulse widths of the control signals So1 to So4 output by the inverter circuit 2 located on the primary side of the transformer 3 may be controlled to output symmetrical pulses, or asymmetrical pulses may be output for soft switching, etc.

[0084] When extending the control of multiple power conversion units U by the control unit 99 to other control methods including PWM control, the switching frequency Fsw is varied. In PFM control, the switching frequency Fsw is changed while keeping the pulse duration Th (see Figure 14) constant. Here, we will describe an example where the duty cycle D of the PWM control is determined first, and then the switching frequency Fsw is changed, rather than just PFM control. In current continuous mode, the output voltage Vo does not change even if the switching frequency Fsw changes. Therefore, the duty cycle Dccm is uniquely determined by the input voltage Vin, output voltage Vo, and transformer turns ratio n, using the feedforward duty cycle Dccmf of equation (1) above, i.e., equation (8). In current continuous mode, the output voltage Vo does not change even if 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, but the switching frequency Fsw may be set to the value that minimizes the loss of the power converter 100, for example. In other words, a table may be created showing the switching frequency Fsw that minimizes the losses of the power converter 100 according to the input voltage Vin, output voltage Vo, and output power, and the switching frequency Fsw may be varied when the duty cycle DCcm is changed.

[0085] In current discontinuity mode, the switching frequency Fsw may be varied to satisfy equation (2) described above. That is, the input power Pin must remain the same even if the duty cycle Da or the switching frequency Fsw is changed. Equation (2) can be rearranged to equation (9).

number

[0086] Here, the relationship between the switching frequency Fsw and the switching period Tsw is given 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 cycle Da has a lower limit value Damin, and the duty cycle Da becomes smaller than the lower limit value Damin, the switching frequency Fsw needs to be changed. Note that this lower limit value Damin is a lower limit set for a certain purpose, and the control unit 99 can also be set to a value less than the lower limit value Damin. Since the duty cycle Da is 2Ddcm, the duty cycle D in the current discontinuous mode has a lower limit value Dmin, and if the duty cycle D becomes smaller than the lower limit value Dmin, the switching frequency Fsw needs to be changed. Note that this lower limit value Dmin is a lower limit set for a certain purpose, and the control unit 99 can also be set to a value less than the lower limit value Dmin.

[0087] Here, if we let the current switching frequency be Fsw, the duty cycle Ddcm calculated in step S14 of Figure 20 be Dmin, then the new switching frequency Fswa corresponding to the determined duty cycle Ddcm can be calculated as shown in equation (10).

number

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

[0089] This section describes the control unit 99 when the switching frequency Fsw is varied in the control of multiple power conversion units U by the control unit 99. In this case, the control unit 99 has a switching frequency changing unit 80 added to the current control unit 33 corresponding to each power conversion unit U. Figure 29 shows the main part of the current control unit 33. Figure 29 is a diagram showing the main part of another current control unit according to Embodiment 1. The switching frequency changing unit 80 includes a switching frequency table 81 for selecting the switching frequency Fsw1 that minimizes the loss of the power converter 100 according to the input voltage Vin, output voltage Vo, and output power in the current continuous mode, a switching frequency calculation unit 82 for calculating the switching frequency Fswa that keeps the input power Pin the same even if the duty cycle Da is changed in the current discontinuous mode, and a switching frequency output unit 83 that outputs a switching frequency Fswo which is one of the switching frequencies Fsw1 and Fswa corresponding to the current continuous mode and current discontinuous mode. In Figure 29, the initial switching frequency input to the switching frequency changing unit 80 is shown as the switching frequency Fsw. In continuous current mode, the switching frequency changing unit 80 outputs the switching frequency Fsw1 as the switching frequency Fswo. In discontinuous current mode, the switching frequency changing unit 80 outputs the switching frequency Fswa as the switching frequency Fswo.

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

[0091] As described above, the power conversion device 100 of Embodiment 1 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. It converts the DC power input from input terminals 23a and 23b into DC power of a target voltage and outputs it from output terminals 24a and 24b. Each power conversion unit U includes a plurality of PWM-controlled switching elements Qa1 to Qa4, an inductor 5, and an inductor current outputter 12 that outputs an inductor current IL which is detected or estimated to be the current flowing through the inductor 5 located on the output terminals 24a and 24b side of 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** which tracks the inductor current IL of each power conversion unit U, and a current control unit 33 that generates a control signal So for each power conversion unit U that controls the corresponding plurality of switching elements Qa1 to Qa4. Each power conversion unit U's current control unit 33 includes: a first current control unit (CCM current control unit 40) that generates a first duty cycle (duty cycle Dccm) of a control signal So that controls multiple switching elements Qa1 to Qa4 to flow an inductor current IL, which is a continuous current mode, based on the inductor current IL and the inductor current command value IL**; a second current control unit (DCM current control unit 41) that generates a second duty cycle (duty cycle Ddcm) of a control signal So that controls multiple switching elements Qa1 to Qa4 to flow an inductor current IL, which is a discontinuous current mode, based on the inductor current command value IL**; and a duty cycle selection unit 42 that selects either the first duty cycle (duty cycle Dccm) or the second duty cycle (duty cycle Ddcm) corresponding to the current modes of continuous current mode and discontinuous current mode as the selected duty cycle (duty cycle D), and determines the selected duty cycle (duty cycle D) as the duty cycle of the control signal So.In the power conversion device 100 of Embodiment 1, each power conversion unit U connected in parallel is controlled by a control signal So with a duty cycle D corresponding to the current mode of the inductor current IL, which is the current mode of the continuous mode and the current discontinuous mode. Therefore, the output voltage distortion during phase switching, which is the number of phases in which the power conversion unit U operates, can be reduced.

[0092] Furthermore, the inductor current control method for the power converter of Embodiment 1 includes a plurality of power conversion units U connected in parallel, each having an inductor 5 and controlled by a control unit 99. These units convert DC power input from input terminals 23a and 23b into DC power of a target voltage and output it from output terminals 24a and 24b. The method controls the inductor current IL, which is the current flowing through the inductor 5 in the power converter 100. 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 positioned on the output terminals 24a and 24b side of the plurality of switching elements Qa1 to Qa4, and an inductor current output device 12 that outputs the detected or estimated inductor current IL. The inductor current control method for the power converter of Embodiment 1 includes a command output step, a first current control step, a second current control step, and a duty cycle selection step. The command output step outputs an inductor current command value IL** for each power conversion unit U, which tracks the inductor current IL. The first current control step generates a first duty cycle (duty cycle Dccm) for the control signal So that controls multiple switching elements Qa1 to Qa4 to flow an inductor current IL, resulting in a continuous current mode, based on the inductor current IL and the inductor current command value IL** for each power conversion unit U. The second current control step generates a second duty cycle (duty cycle Ddcm) for the control signal So that controls multiple switching elements Qa1 to Qa4 to flow an inductor current IL, resulting in a discontinuous current mode, based on the inductor current command value IL** for each power conversion unit U. The duty cycle selection step selects either the first duty cycle (duty cycle Dccm) or the second duty cycle (duty cycle Ddcm) corresponding to the current modes of continuous current mode and discontinuous current mode for each power conversion unit U, as the selected duty cycle (duty cycle D), and determines the selected duty cycle (duty cycle D) as the duty cycle of the control signal So.In the inductor current control method of the power conversion device in Embodiment 1, each power conversion unit U connected in parallel is controlled by a control signal So with a duty cycle D corresponding to the current mode of continuous current mode and current discontinuous current mode in the inductor current IL. Therefore, the output voltage distortion during phase switching, which is the number of phases in which the power conversion unit U operates, can be reduced.

[0093] While this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in the embodiments are not limited to the application of any particular embodiment, but can be applied individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are conceivable within the scope of the technology disclosed in this specification. For example, these may include modifying, adding, or omitting at least one component, or even extracting at least one component and combining it with a component from another embodiment. [Explanation of Symbols]

[0094] 3...Transformer, 5...Inductor, 12...Inductor current output, 14b...Voltage detector, 23a, 23b...Input terminals, 24a, 24b...Output terminals, 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 cycle selector, 99...Control unit, 100...Power converter, D...Duty cycle (selected duty cycle), Dccm...Duty cycle (first duty cycle), Ddcm...Duty cycle (second duty cycle), 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...I 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, a control unit that controls the plurality of power conversion units, which converts DC power input from an input terminal into DC power of a target voltage and outputs it from an output terminal, Each of the aforementioned power conversion units is: It comprises a plurality of PWM-controlled switching elements, an inductor positioned 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 the current flowing through the inductor. The control unit, A command control unit that outputs an inductor current command value that tracks the inductor current for each power conversion unit, Each of the power conversion units includes a current control unit that generates control signals for controlling a corresponding number of switching elements. The current control unit for each power conversion unit is: A first current control unit generates a first duty cycle of the control signal that controls a plurality of switching elements to flow an inductor current in a continuous current mode, based on the inductor current and the inductor current command value, A second current control unit generates a second duty cycle of the control signal that controls a plurality of switching elements to flow an inductor current in a current discontinuity mode, in which current flows intermittently through the inductor, based on the inductor current command value. The system includes a duty cycle selection unit that selects one of the first duty cycle and the second duty cycle corresponding to the current modes of the current continuous mode and the current discontinuous mode as the selected duty cycle, and determines the selected duty cycle as the duty cycle of the control signal. Power converter.

2. The control unit, The power converter includes a voltage control unit that generates an output current command value, which is a command value for the output current of the DC power output from the output terminal, using an output voltage command value, which is a command value for the target voltage, and the output voltage value of the DC power output from the output terminal of the power converter detected by a voltage detector. The number of times the power conversion unit operates is defined as the number of operating phases. The command control unit, Based on the output current command value, For each of the power conversion units, a stop signal to stop the operation of the power conversion unit and the inductor current command value of the power conversion unit are output. When the number of operating phases is changed, the duty cycle selection unit of the power conversion unit determines the selected duty cycle. The power conversion device according to claim 1.

3. The duty cycle selection unit selects the smaller of the first duty cycle and the second duty cycle. A power conversion device according to claim 1 or claim 2.

4. Multiple switching elements constitute an inverter circuit that converts DC power input from the input terminal into AC power. A power conversion device according to claim 1 or claim 2.

5. The plurality of switching elements constitute an inverter circuit that converts DC power input from the input terminal into AC power. The power conversion device according to claim 3.

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

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

8. The second current control unit is Based on the inductor current command value, the input voltage of the DC power input from the input terminal, the output voltage of the DC power output from the output terminal, the inductance of the inductor, the excitation inductance of the transformer, the turns ratio of the transformer, and the switching frequency of the switching element, the second duty cycle of the control signal is generated. The power conversion device according to claim 6.

9. The second current control unit is Based on the inductor current command value, the input voltage of the DC power input from the input terminal, the output voltage of the DC power output from the output terminal, the inductance of the inductor, the excitation inductance of the transformer, the turns ratio of the transformer, and the switching frequency of the switching element, the second duty cycle of the control signal is generated. The power conversion device according to claim 7.

10. A method for controlling the inductor current of a power converter, wherein a power converter has multiple power conversion units connected in parallel, each having an inductor and controlled by a control unit, and converts DC power input from an input terminal into DC power of a target voltage, which is output from an output terminal, and controls the inductor current which flows through the inductor, Each of the aforementioned power conversion units is: The system comprises a plurality of switching elements controlled by PWM by a control signal from the control unit, an inductor positioned on the output terminal side of the plurality of switching elements, and an inductor current output device that outputs the detected or estimated inductor current. Each of the aforementioned power conversion units includes a command output step that outputs an inductor current command value that tracks the inductor current, For each power conversion unit, a first current control step generates a first duty cycle of the control signal that controls a plurality of switching elements to flow an inductor current that results in a continuous current mode in which current flows continuously through the inductor, based on the inductor current and the inductor current command value. For each power conversion unit, a second current control step is provided to generate a second duty cycle of the control signal that controls a plurality of switching elements to flow an inductor current in a current discontinuity mode, based on the inductor current command value, such that current flows intermittently through the inductor. The process includes a duty cycle selection step for each power conversion unit, in which one of the first duty cycle and the second duty cycle corresponding to the current mode of the current continuous mode and the current discontinuous mode is selected as the selected duty cycle, and the selected duty cycle is determined as the duty cycle of the control signal. A method for controlling the inductor current of a power converter.

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