JP2024154458A - Three-phase AC/DC converter - Google Patents

Abstract

To provide a three-phase AC/DC converter that is lower in cost, smaller in size, longer in service life, and easier in control than the conventional devices.SOLUTION: A three-phase AC-DC converter 1A includes: a first PFC unit 21A to which a first phase power is input; a second PFC unit 22A to which second phase power is input; a third PFC unit 23A to which third phase power is input; and a three-phase LLC converter unit 3A having a first input terminal, a second input terminal, and a third input terminal, each connected to the PFC units 21A, 22A, 23A on a one to-one basis. The PFC units 21A, 22A, 23A each include a capacitor for removing high-frequency noise generated by control of the switching elements. The three-phase LLC converter unit 3A includes transformers Tr1, Tr2, Tr3, each connected to the first input terminal, the second input terminal, and the third input terminal.SELECTED DRAWING: Figure 1

Description

The present invention relates to a three-phase AC/DC conversion device that converts power supplied from a three-phase AC power source into a desired DC power.

There is a demand for quick chargers for electric vehicles that are more powerful, smaller, and less expensive than conventional ones. Such quick chargers will be able to charge the large-capacity batteries installed in recent electric vehicles in a short period of time. Furthermore, the realization of such quick chargers is expected to lead to the further spread of electric vehicles.

High-output quick chargers are often configured with a three-phase AC/DC converter, which has a smaller current value per phase compared to a single-phase AC/DC converter. A three-phase AC/DC converter usually includes a PFC (Power Factor Correction) section that converts the input AC voltage into a DC intermediate voltage (sometimes called a link voltage, bus voltage, etc.) while improving the power factor, and a DC/DC converter section that converts the intermediate voltage and outputs the desired DC power. A small, highly efficient current-resonant DC/DC converter is often used as the DC/DC converter section.

A conventional three-phase AC/DC conversion device is described in Patent Document 1. As shown in FIG. 6, this AC/DC conversion device includes a PFC section consisting of a three-phase bridge type PWM rectification (inverter) circuit with an input reactor provided for each phase, an LLC section consisting of a single-phase bridge type LLC converter, and a smoothing capacitor C provided between them. In this three-phase AC/DC conversion device, an intermediate voltage is generated by smoothing the rectified output of the PFC section with the smoothing capacitor C.

The smoothing capacitor C is usually composed of a film capacitor for absorbing high-frequency switching noise generated in the PFC section, and a large-capacity electrolytic capacitor for removing low-frequency ripple caused by the frequency of the AC power supply (for example, commercial frequencies of 50 Hz/60 Hz).

When the AC power supply is a three-phase 200V system, the intermediate voltage is about 380 to 400V. In this case, smoothing capacitor C is made up of a large number (for example, 10 or more) of electrolytic capacitors that have high voltage resistance and can handle high ripples. In general, such electrolytic capacitors have a larger capacitance per unit volume than film capacitors for high-frequency switching noise, and are suitable for removing low-frequency ripples caused by commercial frequencies. However, they are expensive, large, have a short life, and do not have high environmental resistance. Therefore, in order to realize the above-mentioned quick charger, it is necessary to solve the problems of high cost, large size, and short life that come with using electrolytic capacitors. Note that this problem becomes more important the higher the voltage input from the AC power supply.

Furthermore, another conventional three-phase AC/DC conversion device is known from Patent Document 2. As shown in FIG. 7, this three-phase AC/DC conversion device is composed of a boost chopper section (a total of three boost chopper sections) and a DC/DC converter section (a total of three DC/DC converter sections) provided for each phase. The boost chopper section includes a diode bridge rectifier circuit, and the DC/DC converter section is a forward type converter.

In this three-phase AC/DC conversion device, the ripple contained in the intermediate voltage is removed to some extent in the DC/DC converter section. However, it is not completely removed, so it is necessary to configure the smoothing capacitors provided in the output section of the boost chopper section and the DC/DC converter section with high-capacity electrolytic capacitors that are expensive, large, and have a short life. In other words, this three-phase AC/DC conversion device has the same problems as the three-phase AC/DC conversion device shown in Figure 6.

A conventional three-phase AC/DC conversion device that can solve this problem is described in Patent Document 3. As shown in FIG. 8, this three-phase AC/DC conversion device is composed of a primary converter unit provided for each phase (three primary converter units in total), a high-frequency transformer provided for each phase (three high-frequency transformers in total), and a common secondary converter.

In this three-phase AC/DC conversion device, the primary converter unit is configured as a non-smooth DC stage that links low frequency (commercial frequency) and high frequency by a non-smooth DC link capacitor Cd, and is not configured to use a smooth DC link. Therefore, with this three-phase AC/DC conversion device, it is said that it is possible to eliminate the need for a large-capacity electrolytic capacitor.

JP 2018-183037 A Japanese Patent Application Publication No. 10-304663 JP 2019-169991 A

However, in the conventional three-phase AC/DC conversion device shown in Figure 8, the primary converter unit, which is made up of a combination of a PFC circuit and a full-bridge inverter circuit, is subjected to a complex control unique to this circuit called phase-shift pulse-width modulation control. Under this control, the PFC circuit operates in DCM (discontinuous conduction mode). For this reason, this three-phase AC/DC conversion device has a large peak current and low efficiency, making it unsuitable for high-power applications.

Furthermore, in the conventional three-phase AC/DC conversion device shown in FIG. 8, the outputs of each phase are simply added in the secondary converter, so that an imbalance between the phases may occur. In order to eliminate this imbalance, complex individual control of each phase is required. It is known that the imbalance between the phases occurs due to variations in the characteristics of the circuit elements provided for each phase, such as the high-frequency transformer, coil Lb, and capacitor Cr, particularly variations in the characteristics of the high-frequency transformer and coil Lb.

The present invention was made in consideration of these circumstances, and aims to provide a three-phase AC/DC conversion device that is lower cost, smaller, has a longer life, and is easier to control than conventional devices.

In order to solve the above problems, the three-phase AC/DC conversion device according to the present invention converts first-phase power, second-phase power, and third-phase power supplied from a three-phase AC power source into desired DC power, and is a three-phase LLC converter having a first PFC section to whose input terminal the first-phase power is input, a second PFC section to whose input terminal the second-phase power is input, a third PFC section to whose input terminal the third-phase power is input, a first input terminal connected to the output terminal of the first PFC section, a second input terminal connected to the output terminal of the second PFC section, and a third input terminal connected to the output terminal of the third PFC section. and a control unit that controls at least the first PFC unit, the second PFC unit, and the third PFC unit, each of which includes a switching element that is turned on and off by the control unit at a frequency higher than the frequency of the three-phase AC power supply, and a capacitor for removing noise caused by the control, and the three-phase LLC converter unit includes a first insulating transformer connected to the first input terminal, a second insulating transformer connected to the second input terminal, and a third insulating transformer connected to the third input terminal.

In the above configuration, i.e., in which the output terminal of the first PFC section provided in the first phase is connected to the first input terminal of the three-phase LLC converter section, the output terminal of the second PFC section provided in the second phase is connected to the second input terminal of the three-phase LLC converter section, and the output terminal of the third PFC section provided in the third phase is connected to the third input terminal of the three-phase LLC converter section, harmonics six times the frequency of the three-phase AC power supply are superimposed on the output of the three-phase LLC converter section. Therefore, with this configuration, it becomes possible to absorb low-frequency ripple with an output capacitor with a smaller capacity than the capacitor used to remove low-frequency ripple in conventional intermediate voltages.

It is preferable that the first PFC section, the second PFC section, and the third PFC section are mutually neutral-connected, and that the three primary coils and the three secondary coils constituting the first isolation transformer, the second isolation transformer, and the third isolation transformer are mutually neutral-connected.

According to the above configuration, i.e., the first PFC section, the second PFC section, and the third PFC section are connected to each other at their neutral points, and the three primary coils and three secondary coils constituting the first insulating transformer, the second insulating transformer, and the third insulating transformer are each connected to each other at their neutral points, the imbalance between the phases in the first PFC section, the second PFC section, the third PFC section, and the three-phase LLC converter section is autonomously eliminated or mitigated. Therefore, according to this configuration, it is not necessary to perform complex individual control for each phase, or to perform special control to link the first PFC section, the second PFC section, and the third PFC section with the three-phase LLC converter section.

When the three-phase AC power supply is a commercial AC power supply, it is preferable that the on/off control frequency is 10 kHz or higher and the capacitor is a film capacitor or a ceramic capacitor. Film capacitors and ceramic capacitors are lower cost, smaller, have a longer life, and have better environmental resistance than electrolytic capacitors.

The first PFC section, the second PFC section, and the third PFC section are preferably each an interleaved PFC circuit. With this configuration, the frequency of the harmonics superimposed on the output of the three-phase LLC converter section is multiplied by n (where n is the number of stages in the PFC circuit), making it possible to absorb low-frequency ripples with a smaller capacity output capacitor, and making it possible to miniaturize the entire three-phase AC/DC conversion device.

The control unit may perform on/off control of the first PFC unit, the second PFC unit, and the third PFC unit based on the effective value of the voltage at each output terminal. With this configuration, it becomes possible to perform control without being affected by fluctuations in the voltage at the output terminal of each PFC unit, specifically, low-frequency ripples caused by the frequency of the three-phase AC power supply.

The present invention provides a three-phase AC/DC conversion device that is lower cost, smaller, has a longer life, and is easier to control than conventional devices.

1 is a circuit diagram showing a three-phase AC/DC conversion device according to a first embodiment of the present invention. FIG. 11 is a circuit diagram showing a three-phase AC/DC conversion device according to a second embodiment of the present invention. FIG. 11 is a circuit diagram showing a three-phase AC/DC conversion device according to a third embodiment of the present invention. FIG. 13 is a circuit diagram showing a three-phase AC/DC conversion device according to a modified example of the present invention. FIG. 11 is a circuit diagram showing a three-phase AC/DC conversion device according to another modified example of the present invention. FIG. 1 is a circuit diagram showing a conventional three-phase AC/DC conversion device. FIG. 1 is a circuit diagram showing another conventional three-phase AC/DC conversion device. FIG. 11 is a circuit diagram showing yet another conventional three-phase AC/DC conversion device.

Below, an embodiment of a three-phase AC/DC conversion device according to the present invention will be described with reference to the attached drawings.

[First embodiment]
1 shows a three-phase AC/DC converter 1A according to a first embodiment of the present invention. The three-phase AC/DC converter 1A converts power supplied from a three-phase AC power source 10 into a desired DC power and supplies it to a load 20. As shown in the figure, the three-phase AC/DC converter 1A includes a first PFC section 21A, a second PFC section 22A, a third PFC section 23A, and a three-phase LLC converter section 3A. In addition, the three-phase AC/DC converter 1A also includes an input terminal T1 connected to a first phase of the three-phase AC power source 10, an input terminal T2 connected to a second phase of the three-phase AC power source 10, an input terminal T3 connected to a third phase of the three-phase AC power source 10, an output terminal T4 connected to one end of the load 20, and an output terminal T5 connected to the other end of the load 20. In this embodiment and second and third embodiments described later, the three-phase AC power source 10 is a three-phase 200V commercial AC power source, and the load 20 is a battery for driving an electric vehicle.

The first PFC section 21A is composed of a bridgeless totem-pole PFC circuit capable of high-frequency switching, and includes a coil L1, a first switching element Q1 and a second switching element Q2, a first diode D1 and a second diode D2, and a non-smoothing capacitor C1. The bridgeless rectifier circuit has less element conduction loss than a diode bridge rectifier circuit, and is highly efficient because there is no loss due to the reverse recovery time of the diode. It also has a PFC (power factor correction) function, making it suitable for high-output AC/DC conversion devices of about kW or more.

The coil L1 has one end connected to the input terminal T1 and the other end connected to the switching elements Q1 and Q2. One end of the coil L1 can be said to be the "input end" of the first PFC section 21A.

The switching elements Q1 and Q2 are composed of IGBTs (Insulated Gate Bipolar Transistors), which are a type of power semiconductor switching element. A diode serving as an FWD (Free Wheeling Diode) is connected in inverse parallel to the switching elements Q1 and Q2, but this may be built into the switching elements Q1 and Q2 or may be attached externally.

The first switching element Q1 has a collector connected to node Vp1 and an emitter connected to the other end of the coil L1. The second switching element Q2 has a collector connected to the other end of the coil L1 and an emitter connected to node Vn1. In other words, the switching elements Q1 and Q2 are connected in series and provided between nodes Vp1 and Vn1.

The switching elements Q1 and Q2 are controlled to be turned on and off by a control unit (not shown) at a high frequency in the range of 10 kHz to several hundred kHz, which is sufficiently higher than the commercial frequency. The control unit controls the switching elements Q1 and Q2 to be turned on and off via an appropriate drive circuit (not shown) while referring to the current or voltage of each part detected by a detection circuit (not shown).

The first diode D1 has a cathode connected to node Vp1 and an anode connected to the neutral point N. The second diode element D2 has a cathode connected to the neutral point N and an anode connected to node Vn1. In other words, the diodes D1 and D2 are connected in series and arranged in the opposite direction between nodes Vp1 and Vn1. The connection point of the diodes D1 and D2 can be said to be the "other input end" of the first PFC section 21A.

The non-smoothing capacitor C1 is a capacitor selected to absorb high-frequency switching noise generated by the on-off control of the switching elements Q1 and Q2, and has one end connected to the node Vp1 and the other end connected to the node Vn1. As the name "non-smoothing" makes clear, the non-smoothing capacitor C1 is not intended for smoothing. In other words, the non-smoothing capacitor C1 is not intended to remove low-frequency ripples caused by the commercial frequency. For this reason, in this embodiment, a film capacitor that is smaller, lower cost, has a longer life, and has better environmental resistance than an electrolytic capacitor is used as the non-smoothing capacitor C1, rather than a large-capacity electrolytic capacitor that has been used to remove low-frequency ripples in the intermediate voltage in conventional three-phase AC/DC conversion devices. However, a ceramic capacitor or the like can also be used instead. As a result of using such a capacitor as the non-smoothing capacitor C1, the intermediate voltage generated across both ends of the non-smoothing capacitor C1, i.e., between the nodes Vp1 and Vn1, may include low-frequency ripples. In addition, both ends of the non-smoothing capacitor C1 can be considered the "output terminals" of the first PFC section 21A.

The second PFC unit 22A and the third PFC unit 23A are the same as the first PFC unit 21A, except that they are connected to input terminals T2 and T3 instead of input terminal T1, and to nodes Vp2, Vn2, Vp3, and Vn3 instead of nodes Vp1 and Vn1.

The connection points of the diodes D1 and D2 constituting each of the PFC units 21A, 22A, and 23A are connected to each other at the neutral point N. In other words, the PFC units 21A, 22A, and 23A are neutral-point connected to each other at the other input terminal.

The three-phase LLC converter section 3A includes a fifth switching element Q5, a sixth switching element Q6, a seventh switching element Q7, an eighth switching element Q8, a ninth switching element Q9, and a tenth switching element Q10, a first resonant coil Lr1, a second resonant coil Lr2, and a third resonant coil Lr3, a first resonant capacitor Cr1, a second resonant coil Cr2, and a third resonant coil Cr3, a first high-frequency isolation transformer (hereinafter simply referred to as the "transformer") Tr1, a second transformer Tr2, and a third transformer Tr3.

The switching elements Q5, Q6, Q7, Q8, Q9, and Q10 are composed of IGBTs. Diodes serving as FWDs are connected in inverse parallel to the switching elements Q5, Q6, Q7, Q8, Q9, and Q10, but these may be built into the switching elements Q5, Q6, Q7, Q8, Q9, and Q10 or may be externally attached.

The fifth switching element Q5 has a collector connected to node Vp1 and an emitter connected to one end of the first resonant coil Lr1. The sixth switching element Q6 has a collector connected to one end of the first resonant coil Lr1 and an emitter connected to node Vn1. In other words, the switching elements Q5 and Q6 are connected in series and provided between nodes Vp1 and Vn1. The collector of the fifth switching element Q5 and the emitter of the sixth switching element Q6 can be said to be the "first input end" of the three-phase LLC converter section 3A.

The first resonant coil Lr1 has one end as described above and the other end connected to one end of the primary winding that constitutes the first transformer Tr1. Note that the primary winding of the first transformer Tr1 shown in FIG. 1 includes an excitation inductance.

The primary winding constituting the first transformer Tr1 has one end as described above and the other end connected to one end of the first resonant capacitor Cr1. The secondary winding constituting the first transformer Tr1 has one end and the other end connected to the other ends of the secondary windings constituting the other transformers Tr2 and Tr3.

The first resonant capacitor Cr1 has one end as mentioned above and the other end connected to the other ends of the other resonant capacitors Cr2 and Cr3.

In this embodiment, the first resonant coil Lr1, the first transformer Tr1 (excitation inductance), and the first resonant capacitor Cr1 form a series resonant circuit. This series resonant circuit is the first phase of the three-phase LLC converter section 3A, and is therefore the "first resonant circuit." The first resonant circuit is driven by switching elements Q5 and Q6.

The switching elements Q7 and Q8, the second resonant coil Lr2, the second resonant capacitor Cr2, and the second transformer Tr2 are common to the switching elements Q5 and Q6, the first resonant coil Lr1, the first resonant capacitor Cr1, and the first transformer Tr1, except that they are connected to nodes Vp2 and Vn2 instead of Vp1 and Vn1. The collector of the seventh switching element Q7 and the emitter of the eighth switching element Q8 can be said to be the "second input terminal" of the three-phase LLC converter section 3A. The series resonant circuit formed by the second resonant coil Lr2, the second transformer Tr2, and the second resonant capacitor Cr2 can be said to be the "second resonant circuit". The second resonant circuit is driven by the switching elements Q7 and Q8.

The switching elements Q9 and Q10, the third resonant coil Lr3, the third resonant capacitor Cr3, and the third transformer Tr3 are the same as the switching elements Q5 and Q6, the first resonant coil Lr1, the first resonant capacitor Cr1, and the first transformer Tr1, except that they are connected to nodes Vp3 and Vn3 instead of Vp1 and Vn1. The collector of the ninth switching element Q9 and the emitter of the tenth switching element Q10 can be said to be the "third input terminal" of the three-phase LLC converter section 3A. The series resonant circuit formed by the third resonant coil Lr3, the third transformer Tr3, and the third resonant capacitor Cr3 can be said to be the "third resonant circuit". The third resonant circuit is driven by the switching elements Q9 and Q10.

As mentioned above, the primary windings of the transformers Tr1, Tr2, and Tr3 are connected to each other via the resonant capacitors Cr1, Cr2, and Cr3. In other words, the primary windings of the transformers Tr1, Tr2, and Tr3 are neutral-connected by a Y connection.

As mentioned above, the secondary windings of the transformers Tr1, Tr2, and Tr3 are directly connected to each other. In other words, the secondary windings of the transformers Tr1, Tr2, and Tr3 are also neutral-connected by a Y connection.

The three-phase LLC converter section 3A further includes a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a seventh diode D7, and an eighth diode D8, and an output capacitor C2.

The third diode D3 has a cathode connected to the output terminal T4 and an anode connected to one end of the secondary winding that constitutes the first transformer Tr1. The fourth diode D4 has a cathode connected to one end of the secondary winding that constitutes the first transformer Tr1 and an anode connected to the output terminal T5. In other words, the diodes D3 and D4 are connected in series and arranged in the opposite direction between the output terminals T4 and T5.

Diodes D5 and D6 are the same as diodes D3 and D4, except that they are connected to the secondary winding of the second transformer Tr2 instead of the secondary winding of the first transformer Tr1. Diodes D7 and D8 are the same as diodes D3 and D4, except that they are connected to the secondary winding of the third transformer Tr3 instead of the secondary winding of the first transformer Tr1.

In this way, diodes D3, D4, D5, D6, D7, and D8 form a three-phase diode bridge rectifier circuit of the three-phase LLC converter section 3A.

The output capacitor C2 is a smoothing capacitor selected to smooth the voltage after rectification by the three-phase diode bridge rectifier circuit composed of diodes D3, D4, D5, D6, D7, and D8, and has one end connected to the output terminal T4 and the other end connected to the output terminal T5. In this embodiment, an electrolytic capacitor is used as the output capacitor C2, but a film capacitor can also be used instead.

The control unit (not shown) is composed of an MPU (Micro Processing Unit), DSP (Digital Signal Processor), etc. The control unit is configured to control the on/off of the switching elements Q1 and Q2 that constitute the PFC units 21A, 22A, and 23A, and the switching elements Q5, Q6, Q7, Q8, Q9, and Q10 that constitute the three-phase LLC converter unit 3A, based on the intermediate voltage (the voltage between nodes Vp1 and Vn1).

Specifically, the control unit detects the input voltages of each PFC unit 21A, 22A, 23A, i.e., the voltages at input terminals T1, T2, T3, and the output voltages of each PFC unit 21A, 22A, 23A, i.e., intermediate voltages Vp1-Vn1, Vp2-Vn2, Vp3-Vn3, using a detection circuit (not shown), and provides a phase difference of 120° for each phase and performs PWM control of switching elements Q1 and Q2 in an opposing manner so that the intermediate voltage becomes the desired voltage. By controlling in this way, each phase can be controlled with the same duty, simplifying the control. The control unit detects the output voltage (voltage between output terminals T4-T5) of the three-phase LLC converter unit 3A and the output current supplied to the load 20 using a detection circuit (not shown), and controls the switching elements Q5, Q6, Q7, Q8, and Q9, Q10 in a back-to-back arrangement with a phase difference of 120° between each set, and frequency-modulates each set at the same frequency with a duty of 50% so that the output current becomes the desired current value. Because the three-phase LLC converter unit 3A is a current-resonant type, the control unit can drive the switching elements Q1, Q2, Q5, Q6, Q7, Q8, Q9, and Q10 at a high frequency (within the range of 10 kHz to several hundreds of kHz).

As mentioned above, the intermediate voltage may contain low-frequency ripples due to the commercial frequency. In other words, the intermediate voltage is not a stable DC voltage. For this reason, the control unit samples the intermediate voltage at a period that is sufficiently short relative to the multiplication of the commercial frequency, and performs control based on the effective value calculated from the group of values obtained by this sampling.

The three-phase AC/DC conversion device 1A according to this embodiment allows the capacitance of the capacitors used to be smaller than in the past (ultimately, completely eliminating electrolytic capacitors except for those used to counter momentary power outages in the three-phase AC power source 10) for the following reasons.

By turning on and off the switching elements Q5 and Q6 connected to the first PFC section 21A provided in the first phase, the switching elements Q7 and Q8 connected to the second PFC section 22A provided in the second phase, and the switching elements Q9 and Q10 connected to the third PFC section 23A provided in the third phase at frequencies sufficiently higher than the commercial frequency, the high-frequency switching noise generated is removed by the non-smoothing capacitor C1, and the low-frequency ripple of the commercial frequency contained in the intermediate voltage is converted to six times higher harmonics by the three-phase diode bridge rectifier circuit (D3, D4, D5, D6, D7, D8) in the subsequent stage. The capacity of the non-smoothing capacitor C1 required to remove the high-frequency switching noise is significantly smaller than the capacity of the smoothing capacitor required to remove the low-frequency ripple. In addition, the capacity of the output capacitor C2 required to remove the ripple that has been made six times higher in frequency is smaller than the capacity of the smoothing capacitor required to remove the low-frequency ripple in the PCF sections 21A, 22A, and 23A. As a result, the capacity of the capacitors used throughout the three-phase AC/DC conversion device 1A is small.

Furthermore, the three-phase AC/DC conversion device 1A according to this embodiment simplifies control for the following reasons:

Because the three PFC units 21A, 22A, and 23A are mutually neutral-connected, the imbalance between the phases in the PFC units 21A, 22A, and 23A is autonomously eliminated or mitigated. In addition, because the three primary coils and three secondary coils constituting the transformers Tr1, Tr2, and Tr3 are mutually neutral-connected, the imbalance between the phases in the three-phase LLC converter unit 3A is also autonomously eliminated or mitigated. For this reason, there is no need to perform complex individual control for each phase or special control to link the PFC units 21A, 22A, and 23A and the three-phase LLC converter unit 3A.

[Second embodiment]
2 shows a three-phase AC/DC conversion apparatus 1B according to a second embodiment of the present invention. Three-phase AC/DC conversion apparatus 1B differs from three-phase AC/DC conversion apparatus 1A in that it includes PFC units 21B, 22B, and 23B instead of PFC units 21A, 22A, and 23A, but is the same as three-phase AC/DC conversion apparatus 1A in other respects.

The first PFC section 21B is configured as a bridge PWM rectification (inverter) type PFC circuit that is capable of bidirectional operation and has a small number of components, and includes a coil L1, a first switching element Q1, a second switching element Q2, and a non-smoothing capacitor C1.

The coil L1 has one end connected to the input terminal T1 and the other end connected to the switching elements Q1 and Q2. One end of the coil L1 can be said to be the "input end" of the first PFC section 21B.

The switching elements Q1 and Q2 are composed of IGBTs. A diode serving as a FWD is connected in inverse parallel to the switching elements Q1 and Q2, but this may be built into the switching elements Q1 and Q2 or may be attached externally.

The first switching element Q1 has a collector connected to node Vp1 and an emitter connected to the other end of the coil L1. The second switching element Q2 has a collector connected to the other end of the coil L1 and an emitter connected to node Vn1. In other words, the switching elements Q1 and Q2 are connected in series and provided between nodes Vp1 and Vn1. The emitter of the second switching element Q2 can be said to be the "other input end" of the first PFC section 21B.

The switching elements Q1 and Q2 are controlled to be turned on and off by a control unit (not shown) at a high frequency in the range of 10 kHz to several hundred kHz, which is sufficiently higher than the commercial frequency.

The non-smoothing capacitor C1 is a capacitor selected to absorb high-frequency switching noise generated by the on/off control of the switching elements Q1 and Q2, and has one end connected to node Vp1 and the other end connected to node Vn1. In this embodiment, a film capacitor is used as the non-smoothing capacitor C1, but a ceramic capacitor or the like can also be used instead. Both ends of the non-smoothing capacitor C1 can be said to be the "output ends" of the first PFC section 21B.

The second PFC unit 22B and the third PFC unit 23B are the same as the first PFC unit 21B, except that they are connected to input terminals T2 and T3 instead of input terminal T1, and to nodes Vp2, Vn2, Vp3, and Vn3 instead of nodes Vp1 and Vn1.

The emitters of the second switching elements Q2 constituting each of the PFC units 21B, 22B, and 23B, i.e., nodes Vn1, Vn2, and Vn3, are connected to each other at the neutral point N. In other words, the PFC units 21B, 22B, and 23B are connected to each other at the neutral point at the other input terminal.

The three-phase AC/DC conversion device 1B of this embodiment provides the same effects as the first embodiment.

[Third Example]
3 shows a three-phase AC/DC conversion apparatus 1C according to a third embodiment of the present invention. Three-phase AC/DC conversion apparatus 1C differs from three-phase AC/DC conversion apparatus 1A in that it includes PFC units 21C, 22C, and 23C instead of PFC units 21A, 22A, and 23A, but is the same as three-phase AC/DC conversion apparatus 1A in other respects.

The first PFC section 21C is configured as a two-stage interleaved totem-pole PFC circuit, and includes a first coil L1, a second coil L2, a first switching element Q1, a second switching element Q2, a third switching element Q3, and a fourth switching element Q4, a first diode D1, a second diode D2, and a non-smoothing capacitor C1.

The first coil L1 has one end connected to the input terminal T1 and the other end connected to the switching elements Q1 and Q2. The second coil L2 has one end connected to the input terminal T1 and the other end connected to the switching elements Q3 and Q4. One end of the coils L1 and L2 can be said to be the "input end" of the first PFC section 21C.

The switching elements Q1, Q2, Q3, and Q4 are composed of IGBTs. Diodes serving as FWDs are connected in inverse parallel to the switching elements Q1, Q2, Q3, and Q4, but these may be built into the switching elements Q1, Q2, Q3, and Q4 or may be externally attached.

The first switching element Q1 has a collector connected to node Vp1 and an emitter connected to the other end of the first coil L1. The second switching element Q2 has a collector connected to the other end of the first coil L1 and an emitter connected to node Vn1. In other words, the switching elements Q1 and Q2 are connected in series and provided between nodes Vp1 and Vn1.

The third switching element Q3 has a collector connected to node Vp1 and an emitter connected to the other end of the second coil L2. The fourth switching element Q4 has a collector connected to the other end of the second coil L2 and an emitter connected to node Vn1. In other words, the switching elements Q3 and Q4 are connected in series and provided between nodes Vp1 and Vn1.

The switching elements Q1, Q2, Q3, and Q4 are controlled to be turned on and off by a control unit (not shown) at a high frequency in the range of 10 kHz to several hundred kHz, which is sufficiently higher than the commercial frequency.

The first diode D1 has a cathode connected to node Vp1 and an anode connected to the neutral point N. The second diode element D2 has a cathode connected to the neutral point N and an anode connected to node Vn1. In other words, the diodes D1 and D2 are connected in series and arranged in the opposite direction between nodes Vp1 and Vn1. The connection point of the diodes D1 and D2 can be said to be the "other input end" of the first PFC section 21C.

The non-smoothing capacitor C1 is a capacitor selected to absorb high-frequency switching noise generated by the on/off control of the switching elements Q1, Q2, Q3, and Q4, and has one end connected to node Vp1 and the other end connected to node Vn1. In this embodiment, a film capacitor is used as the non-smoothing capacitor C1, but a ceramic capacitor or the like can also be used instead. Both ends of the non-smoothing capacitor C1 can be said to be the "output ends" of the first PFC section 21C.

The second PFC unit 22C and the third PFC unit 23C are the same as the first PFC unit 21C, except that they are connected to input terminals T2 and T3 instead of input terminal T1, and to nodes Vp2, Vn2, Vp3, and Vn3 instead of nodes Vp1 and Vn1.

The connection points of the diodes D1 and D2 constituting each of the PFC units 21C, 22C, and 23C are connected to each other at the neutral point N. In other words, the PFC units 21C, 22C, and 23C are neutral-point connected to each other at the other input terminal.

As described above, in the first and second embodiments, the intermediate voltage may include ripples at a frequency equal to the commercial frequency. On the other hand, in this embodiment, in which the PFC units 21C, 22C, and 23C are totem-pole PFC circuits of a two-stage interleaved system, the intermediate voltage may include ripples at a frequency twice the commercial frequency. For this reason, in this embodiment, harmonics at 12 times (=2×6 times) the commercial frequency are superimposed on the voltage after rectification by the three-phase diode bridge rectifier circuit (D3, D4, D5, D6, D7, and D8). As a result, according to the three-phase AC/DC conversion device 1C of this embodiment, it is possible to absorb low-frequency ripples with an output capacitor C2 with a smaller capacity than the output capacitor C2 used in the first and second embodiments, and thus the three-phase AC/DC conversion device 1C can be made even smaller.

[Modification]
Although the first, second and third embodiments of the three-phase AC/DC conversion device according to the present invention have been described above, the configurations of the present invention are not limited to these.

For example, the three-phase AC/DC conversion device according to the present invention may include a three-phase LLC converter unit 3D in which the primary windings constituting each of the transformers Tr1, Tr2, and Tr3 of the three-phase LLC converter unit 3D are neutral-point connected by a delta connection, and the secondary windings of each of the transformers Tr1, Tr2, and Tr3 are neutral-point connected by a delta connection, as in the three-phase AC/DC conversion device 1D shown in Fig. 4. Alternatively, the three-phase AC/DC conversion device according to the present invention may include a three-phase LLC converter unit 3E in which the primary windings constituting each of the transformers Tr1, Tr2, and Tr3 of the three-phase LLC converter unit 3E are neutral-point connected by a delta-Cr connection, and the secondary windings of each of the transformers Tr1, Tr2, and Tr3 are neutral-point connected by a Y connection, as in the three-phase AC/DC conversion device 1E shown in Fig. 5. In other words, in the present invention, the three primary windings and three secondary windings that make up the transformers Tr1, Tr2, and Tr3 of the three-phase LLC converter section can each be neutral-connected in any manner.

The resonant coils Lr1, Lr2, Lr3 and resonant capacitors Cr1, Cr2, Cr3 that make up the three-phase LLC converter section may be placed at any position on the primary side. However, the resonant coil Lr1, the resonant capacitor Lr1, and the primary winding of the first transformer Tr1 must be connected in series. The same applies to the resonant coils Lr2, Lr3, the resonant capacitors Cr2, Cr3, and the transformers Tr2, Tr3.

The resonant coils Lr1, Lr2, and Lr3 constituting the three-phase LLC converter section may be the leakage inductances of the transformers Tr1, Tr2, and Tr3. In other words, in the present invention, the leakage inductances of the transformers Tr1, Tr2, and Tr3 can be used as the resonant coils Lr1, Lr2, and Lr3.

The three-phase LLC converter section may also include a synchronous rectifier circuit composed of switching elements instead of the three-phase diode bridge rectifier circuit (D3, D4, D5, D6, D7, D8). Alternatively, the three-phase LLC converter section may include a boost control circuit in which some of the diodes (D3, D5, D7, or D4, D6, D8) are replaced with switching elements.

In addition, the switching elements Q5, Q6, Q7, Q8, Q9, and Q10 that make up the three-phase LLC converter section may have an external capacitor connected in parallel for partial resonance.

The first PFC section, the second PFC section, and the third PFC section may be any circuit that combines a PFC circuit (power factor correction circuit) capable of high-frequency conversion with a non-smoothing capacitor. For example, the switching element Q1 and the diode D2 that constitute the PFC sections 21A, 22A, and 23A of the first embodiment may be interchanged. The PFC sections 21C, 22C, and 23C of the third embodiment may be an interleaved PFC circuit with three or more stages. The PFC sections 21A, 22A, and 23A of the first embodiment and the PFC sections 21C, 22C, and 23C of the third embodiment may further include a coil located between the connection point of the diodes D1 and D2 and the neutral point N.

Furthermore, the first PFC section, the second PFC section, and the third PFC section do not have to be neutral-point connected. For example, the other input terminals of the first PFC section, the second PFC section, and the third PFC section may be connected to the negative pole of the three-phase AC power supply.

The first PFC section, the second PFC section, the third PFC section and the three-phase LLC converter section may also include switching elements Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9 and Q10 configured with any power semiconductor switching element other than an IGBT (e.g., MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) etc.). Of course, in the present invention, any type of power semiconductor switching element other than Si (Silicon) based (e.g., SiC (Silicon Carbide) based, GaN (Gallium Nitride) based, etc.) can also be used.

The control unit may be configured as a single control unit that collectively controls the first PFC unit, the second PFC unit, the third PFC unit, and the three-phase LLC converter unit, or may be configured as multiple control units that share and control these units. Furthermore, the control unit may control the first PFC unit, the second PFC unit, and the third PFC unit in any manner. For example, the control unit may control them using a PWM method, or may control them using a PFM method.

The control unit may increase or decrease the output by phase shift control that shifts by a predetermined amount the timing for turning on and off the switching elements Q5, Q7, and Q9 that constitute the upper arm of the three-phase LLC converter unit and the timing for turning on and off the switching elements Q6, Q8, and Q10 that constitute the lower arm, or may increase or decrease the output by changing the duty of the switching elements Q5, Q6, Q7, Q8, Q9, and Q10.

The control unit may also obtain the effective value of the intermediate voltage by detecting the intermediate voltage through a low-pass filter circuit. Alternatively, the control unit may calculate the effective value of the intermediate voltage based on the peak value of the intermediate voltage detected through a peak-hold circuit. Note that the capacitor used in the low-pass filter circuit or peak-hold circuit may be sufficiently small and of small capacity compared to the capacitor that smoothes the intermediate voltage in the main circuit (PFC unit) because the signals handled are small signals.

In addition, the control unit may perform control based on, for example, the time average value of the intermediate voltage of each phase (i.e., three average values) rather than the effective value of the intermediate voltage of each phase, or may perform control based on a further average of the time average value of the intermediate voltage of each phase (i.e., one average value).

The control unit may also have a function of individually controlling the output voltage of the PFC unit of each phase (for example, the first PFC unit 21A, the second PFC unit 22A, and the third PFC unit 23A in the first embodiment) when the imbalance between the phases is about to exceed the range that can be eliminated (mitigated) by the above-mentioned imbalance elimination (mitigation) function, or when it has exceeded the range, thereby making the imbalance at a level that can be eliminated (mitigated).

In addition, each element shown in Figures 1 to 5 is merely a symbol indicating a function, and for example, switching elements Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, and Q10 may be the same or different elements connected in series or in parallel. Also, each of transformers Tr1, Tr2, and Tr3 may be a single-phase winding transformer, or may be composed of multiple transformers connected in series or in parallel. Alternatively, transformers Tr1, Tr2, and Tr3 may be a coupled transformer composed of one or multiple transformers with a three-phase coil. The same applies to the other elements.

The three-phase AC power supply that supplies power to the three-phase AC/DC conversion device according to the present invention is not limited to a 200V commercial AC power supply. For example, the three-phase AC power supply may be another 200V AC power supply, or may be a 400V AC power supply, etc.

In addition, the load to which power is supplied by the three-phase AC/DC conversion device according to the present invention is not limited to the drive battery of an electric vehicle. For example, the load may be another storage battery in a distributed power source, or a DC load, etc.

1A, 1B, 1C, 1D, 1E Three-phase AC/DC converter 21A, 21B, 21C First PFC section 22A, 22B, 22C Second PFC section 23A, 23B, 23C Third PFC section 3A, 3D, 3E Three-phase LLC converter section 10 Three-phase AC power supply 20 Load

Claims (6)

A three-phase AC/DC conversion device that converts first phase power, second phase power, and third phase power supplied from a three-phase AC power source into desired DC power,
a first PFC unit having an input terminal to which the first phase power is input;
a second PFC unit having an input terminal to which the second phase power is input;
a third PFC unit having an input terminal to which the third phase power is input;
a three-phase LLC converter unit having a first input terminal connected to an output terminal of the first PFC unit, a second input terminal connected to an output terminal of the second PFC unit, and a third input terminal connected to an output terminal of the third PFC unit;
a control unit that controls at least the first PFC unit, the second PFC unit, and the third PFC unit,
the first PFC unit, the second PFC unit, and the third PFC unit each include a switching element that is on/off controlled by the control unit at a frequency higher than a frequency of the three-phase AC power supply, and a capacitor for removing noise generated by the control,
a first isolation transformer connected to the first input terminal, a second isolation transformer connected to the second input terminal, and a third isolation transformer connected to the third input terminal. the first PFC section, the second PFC section, and the third PFC section are connected to each other at a neutral point;
2. The three-phase AC/DC conversion device according to claim 1, wherein the three primary coils and the three secondary coils constituting the first isolation transformer, the second isolation transformer and the third isolation transformer are respectively connected to each other at their neutral points. 3. The three-phase AC/DC conversion device according to claim 2, wherein the frequency of the on/off control is 10 kHz or more. 3. The three-phase AC/DC conversion device according to claim 2, wherein the capacitor is a film capacitor or a ceramic capacitor. 5. The three-phase AC/DC conversion device according to claim 1, wherein the first PFC section, the second PFC section, and the third PFC section are each an interleaved PFC circuit. 5. The three-phase AC/DC conversion device according to claim 1, wherein the control unit performs the on/off control in the first PFC unit, the second PFC unit, and the third PFC unit based on an effective value of a voltage at each of the output terminals.

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