Multiphase LLC resonant converter circuit

Abstract

A multiphase LLC resonant converter circuit (10) is provided with: first to third LLC resonant converters each provided with: a series circuit (S1-S3) of a first switch and a second switch, the series circuit being connected in parallel to a DC power source; a high-frequency transformer (T1-T3) provided with a primary winding and a secondary winding; and a resonance circuit including a resonance reactor (Lr1-Lr3) connected between a connection point between the first switch and the second switch and one end of the primary side winding, a resonance capacitor (Cr1-Cr3) having one end connected to the other end of the primary side winding, and a divided resonance capacitor (Cn1-Cn3) having one end connected to a connection point between the primary side winding and the resonance capacitor. The multiphase LLC resonant converter circuit (10) is further provided with: a first neutral line (N1) connecting the other end of the resonant capacitor; a neutral line reactor (Ln) connected between the first neutral line and a power line of the DC power supply; and a second neutral line (N2) connecting the other ends of the divided resonant capacitors.

Description

Technical Field

[0001] The present invention relates to a multi-phase LLC resonant converter circuit for converting a first DC voltage of a DC power supply into a second DC voltage and outputting the second DC voltage. Background Art

[0002] Conventionally, as a converter circuit for converting a first DC voltage of a DC power supply into a second DC voltage and outputting the converted voltage, a multi-phase (N-phase) LLC resonant converter circuit is known (see Patent Document 1). In this circuit, a plurality (N) of LLC resonant converters are connected in parallel to a DC power supply, and switches of each LLC resonant converter are turned on and off so that the resonant current of the resonant circuit connected to the primary winding of the high-frequency transformer of each LLC resonant converter has a phase difference of 360° / N.

[0003] The LLC resonant converter is preferably designed so that when the voltage value of the DC power supply is rated (for example, 380V), the switching frequency of the switch on and off becomes near the resonant frequency of the resonant circuit. On the other hand, when the voltage value of the DC input voltage is reduced (for example, reduced to 300V), if the boost action is performed by reducing the switching frequency of the switch, the circuit loss increases and the efficiency decreases. Considering that under the same output power, if the voltage value of the DC input voltage is reduced, the value of the DC input current increases in inverse proportion to it, so the efficiency naturally decreases to a certain extent. However, in reality, the peak value of the resonant current flowing through the resonant circuit increases to a value greater than the increase in the value of the DC input current. Most of the unnecessary current that increases the resonant current is a third harmonic current with a frequency three times the switching frequency.

[0004] Fig.11 A conventional multi-phase LLC resonant converter circuit 13 is shown. The circuit has both a first neutral line N1 connected to a power line of a DC power source Vin and a floating second neutral line N2 (see Patent Documents 1 and 2). The conventional multi-phase LLC resonant converter circuit 13 can naturally balance the resonant currents ir1, ir2, and ir3 flowing through the resonant circuits 41, 42, and 43 in the multi-phase operation mode, and can switch from the multi-phase operation mode to the single-phase operation mode.

[0005] In the conventional multi-phase LLC resonant converter circuit 13, when the DC input voltage Vin of the DC power source 30 is rated (for example, 380 V), Fig.12 As shown in (a), the resonant current ir (ir1, ir2, ir3) of each phase flowing through the series resonant circuits 41, 42, 43 becomes a substantially sinusoidal wave. Fig.12As shown in (b), the value of the neutral line current in flowing through the neutral line N1 is substantially zero. However, when the DC input voltage Vin of the DC power supply 30 is reduced from the rated value (for example, 380 V) (for example, to 300 V), if a step-up operation is performed by reducing the switching frequency of the switch, as shown in FIG. Fig.13 As shown in (a), since the third harmonic component is generated in the resonant current ir (ir1, ir2, ir3), the effective value of the resonant current ir increases. In addition, Fig.13 As shown in (b), a third harmonic current flows through the first neutral line N1 as a neutral line current in.

[0006] Furthermore, in the conventional multi-phase LLC resonant converter circuit 13 , the resonant frequency changes when switching from the multi-phase operation mode to the single-phase operation mode.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent No. 6696617

[0010] Patent Document 2: Japanese Patent Application Publication No. 2021-153382 Summary of the invention

[0011] Problems to be solved by the invention

[0012] One aspect of the present invention provides a multi-phase LLC resonant converter circuit, which, in a multi-phase operation mode, can suppress an increase in resonant current during a boost operation when a DC input voltage is lower than a rated value and the generation of a third harmonic current flowing through a neutral line, and does not change the resonant frequency when switching from the multi-phase operation mode to the single-phase operation mode.

[0013] Means for solving problems

[0014] A multi-phase LLC resonant converter circuit according to one embodiment of the present invention is a multi-phase LLC resonant converter circuit for converting a first DC voltage of a DC power supply into a second DC voltage for output, and is provided with first to Nth (N is an integer greater than 2) LLC resonant converters, and the first to Nth NLLC resonant converters are respectively provided with: a series circuit connected in parallel with the DC power supply, in which a first switch and a second switch are connected in series; a high-frequency transformer having a primary winding and a secondary winding; a resonant circuit having a resonant inductor connected between a connection point between the first switch and the second switch and one end of the primary winding, a resonant capacitor having one end connected to the other end of the primary winding, and a split resonant capacitor having one end connected to a connection point between the primary winding and the resonant capacitor; and a rectifier circuit for rectifying the output of the secondary winding. The multi-phase LLC resonant converter circuit also includes: a first neutral line, connecting the other ends of the resonant capacitors of the first to Nth LLC resonant converters to each other; a neutral line inductor, connected between the first neutral line and a power line of either the positive pole or the negative pole of the DC power supply; a second neutral line, connecting the other ends of the split resonant capacitors of the first to Nth LLC resonant converters to each other; and an output capacitor, connected in parallel to the output side of the rectifier circuit of the first to Nth LLC resonant converters, and used to output a second DC voltage at both ends. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 : is a circuit diagram showing the configuration of a multi-phase LLC resonant converter circuit according to the first embodiment.

[0016] Figure 2 (a) is a timing chart showing a waveform of a resonant current when a voltage (300 V) of a DC power supply is boosted in the multi-phase LLC resonant converter circuit according to the first embodiment. Figure 2 (b) is a timing chart showing the waveform of the neutral line current when the voltage (300 V) of the DC power supply is stepped up.

[0017] Figure 3 The graph plots the effective value of the resonant current for the value of the DC input voltage (rated: 380 V) when the DC input voltage is boosted in the multi-phase LLC resonant converter circuit of the first embodiment (solid line) and the conventional example (dashed line).

[0018] Figure 4 The inductance ratio L is plotted when the capacitance division ratio α = 0.5. n / L r The resonant frequency change rate f during single-phase operation r2 / f r1Graph of the relationship.

[0019] Figure 5 (a) is a transient waveform of the output voltage and the resonant current of each phase when switching from three-phase operation to single-phase operation in a multi-phase LLC resonant converter circuit of a conventional example. Figure 5 (b) shows transition waveforms of the output voltage and the resonant current of each phase when the multi-phase LLC resonant converter according to the first embodiment switches from a three-phase operation to a single-phase operation.

[0020] Figure 6 (a) is a transient waveform of the output voltage and the resonant current of each phase when switching from single-phase operation to three-phase operation in a multi-phase LLC resonant converter circuit of a conventional example. Figure 6 (b) shows transition waveforms of the output voltage and the resonant current of each phase when the multi-phase LLC resonant converter according to the first embodiment switches from a single-phase operation to a three-phase operation.

[0021] Figure 7 : is a circuit diagram showing the configuration of a multi-phase LLC resonant converter circuit according to the second embodiment.

[0022] Figure 8 This is a diagram showing a structure in which a resonant reactor and a neutral line reactor used in a multi-phase LLC resonant converter circuit according to a second embodiment are magnetically coupled via a dedicated magnetic core.

[0023] Fig. 9 The diagram shows a structure in which a resonant reactor and a neutral line reactor used in a multi-phase LLC resonant converter circuit according to a modification of the second embodiment are magnetically coupled via a five-leg core.

[0024] Fig.10 This is a graph in which the winding increase rate ρ0 of the first embodiment and the winding increase rate ρ of the second embodiment are plotted with respect to the capacitance division ratio α.

[0025] Fig.11 : is a circuit diagram showing the structure of a multi-phase LLC resonant converter circuit of a conventional example.

[0026] Fig.12 (a) is a timing chart showing the waveform of the resonant current when the voltage of the DC power supply is the rated voltage (380 V) in a multi-phase LLC resonant converter circuit of a conventional example. Fig.12 (b) is a timing chart showing the waveform of the neutral line current when the voltage of the DC power supply is the rated voltage (380 V).

[0027] Fig.13(a) is a timing chart showing the waveform of the resonant current when a voltage (300 V) of a DC power supply is boosted in a multi-phase LLC resonant converter circuit of a conventional example. Fig.13 (b) is a timing chart showing the waveform of the neutral line current when the voltage (300 V) of the DC power supply is stepped up. DETAILED DESCRIPTION

[0028] The following is a reference Figure 1 The multi-phase LLC resonant converter circuit according to the embodiment of the present invention will be described in detail. The present invention is not limited to the embodiment described below.

[0029] (First Embodiment)

[0030] Figure 1 : is a circuit diagram showing the configuration of a multi-phase LLC resonant converter circuit 10 according to the first embodiment. Here, the configuration of the multi-phase LLC resonant converter circuit 10 in which the number of phases N=3 (three-phase LLC resonant converter circuit) will be described.

[0031] The multi-phase LLC resonant converter circuit 10 includes a first series circuit S1, a second series circuit S2, and a third series circuit S3, which are connected in parallel to a DC power supply 30 having a DC voltage value Vin. In the first series circuit S1, a first switch Q11 and a second switch Q12 are connected in series. In the second series circuit S2, a first switch Q21 and a second switch Q22 are connected in series. In the third series circuit S3, a first switch Q31 and a second switch Q32 are connected in series.

[0032] In the first embodiment, N-channel MOSFETs are used for the switches Q11 , Q12 , Q21 , Q22 , Q31 , and Q32 , but other switching elements may be used.

[0033] One end of the first resonant reactor Lr1 is connected to a connection point between the first switch Q11 and the second switch Q12 of the first series circuit S1. One end of the second resonant reactor Lr2 is connected to a connection point between the first switch Q21 and the second switch Q22 of the second series circuit S2. One end of the third resonant reactor Lr3 is connected to a connection point between the first switch Q31 and the second switch Q32 of the third series circuit S3.

[0034] The other end of the first resonant reactor Lr1 is connected to one end of the primary winding Lp1 of the first high-frequency transformer T1, one end of the first resonant capacitor Cr1 is connected to the other end of the primary winding Lp1 of the first high-frequency transformer T1, and one end of the first split resonant capacitor Cn1 is connected to the connection point between the primary winding Lp1 of the first high-frequency transformer T1 and the first resonant capacitor Cr1, thereby forming a first resonant circuit 41. The first high-frequency transformer T1 includes a magnetic core, a primary winding Lp1, and a secondary winding Ls1. The primary winding Lp1 and the secondary winding Ls1 are insulated from each other.

[0035] The other end of the second resonant reactor Lr2 is connected to one end of the primary winding Lp2 of the second high-frequency transformer T2, one end of the second resonant capacitor Cr2 is connected to the other end of the primary winding Lp2 of the second high-frequency transformer T2, and one end of the second split resonant capacitor Cn2 is connected to the connection point between the primary winding Lp2 of the second high-frequency transformer T2 and the second resonant capacitor Cr2, thereby forming a second resonant circuit 42. The second high-frequency transformer T2 includes a magnetic core, a primary winding Lp2, and a secondary winding Ls2. The primary winding Lp2 and the secondary winding Ls2 are insulated from each other.

[0036] The other end of the third resonant reactor Lr3 is connected to one end of the primary winding Lp3 of the third high-frequency transformer T3, one end of the third resonant capacitor Cr3 is connected to the other end of the primary winding Lp3 of the third high-frequency transformer T3, and one end of the third split resonant capacitor Cn3 is connected to the connection point between the primary winding Lp3 of the third high-frequency transformer T3 and the third resonant capacitor Cr3, thereby forming a third resonant circuit 43. The third high-frequency transformer T3 includes a magnetic core, a primary winding Lp3, and a secondary winding Ls3. The primary winding Lp3 and the secondary winding Ls3 are insulated from each other.

[0037] The other end of the first resonant capacitor Cr1 , the other end of the second resonant capacitor Cr2 , and the other end of the third resonant capacitor Cr3 are connected to each other through the first neutral line N1 .

[0038] First neutral line N1 is connected to a power line on the negative electrode side of DC power supply 30 via neutral line reactor Ln. Alternatively, first neutral line N1 may be connected to a power line on the positive electrode side of DC power supply 30 via neutral line reactor Ln.

[0039] The other end of the first split resonant capacitor Cn1 , the other end of the second split resonant capacitor Cn2 , and the other end of the third split resonant capacitor Cn3 are connected to each other through the floating second neutral line N2 .

[0040] The resonant reactors Lr1, Lr2, and Lr3 are set to have equal inductance values ​​L rWhen the resonant reactors Lr1, Lr2, and Lr3 do not utilize magnetic coupling as in the second embodiment described later, the leakage inductance of the high-frequency transformers T1, T2, and T3 can also be utilized. The resonant capacitors Cr1, Cr2, and Cr3 are set to have equal electrostatic capacitance αC. r The split resonant capacitors Cn1, Cn2, and Cn3 are set to have equal electrostatic capacitance (1-α)C. r Here, α is the division ratio of the electrostatic capacitance of the resonant capacitors Cr1, Cr2, Cr3 and the divided resonant capacitors Cn1, Cn2, Cn3, and is a parameter having a value of 0<α<1. Inductance value L r and electrostatic capacitance C r The inductance value L of the neutral line reactor Ln is determined by the desired resonant frequency. n Will be described later.

[0041] The high-frequency transformers T1, T2, and T3 can use high-frequency transformers of the same specifications. The primary windings Lp1, Lp2, and Lp3 have the same number of turns Np and are set to the same inductance value L. p The secondary windings Ls1, Ls2, and Ls3 are set to have equal turns Ns and equal inductance L. s The ratio of the number of turns Np of the primary winding Lp to the number of turns Ns of the secondary winding Ls may be determined according to the ratio of the DC input voltage Vin to the DC output voltage Vo.

[0042] The cathode of the first rectifier diode D1a is connected to the negative side of the secondary winding Ls1 of the first high-frequency transformer T1, and the cathode of the second rectifier diode D1b is connected to the positive side of the secondary winding Ls1 of the first high-frequency transformer T1. The first rectifier circuit 51 is composed of the first rectifier diode D1a and the second rectifier diode D1b. The neutral point of the secondary winding Ls1 of the first high-frequency transformer T1 is connected to one end of the output capacitor Co, and the anodes of the first rectifier diode D1a and the second rectifier diode D1b are connected to the other end of the output capacitor Co, so that the AC voltage output at both ends of the secondary winding Ls1 is full-wave rectified and smoothed.

[0043] The cathode of the third rectifier diode D2a is connected to the negative side of the secondary winding Ls2 of the second high-frequency transformer T2, and the cathode of the fourth rectifier diode D2b is connected to the positive side of the secondary winding Ls2 of the second high-frequency transformer T2. The second rectifier circuit 52 is composed of the third rectifier diode D2a and the fourth rectifier diode D2b. The neutral point of the secondary winding Ls2 of the second high-frequency transformer T2 is connected to one end of the output capacitor Co, and the anodes of the third rectifier diode D2a and the fourth rectifier diode D2b are connected to the other end of the output capacitor Co, so that the AC voltage output at both ends of the secondary winding Ls2 is full-wave rectified and smoothed.

[0044] The cathode of the fifth rectifier diode D3a is connected to the negative side of the secondary winding Ls3 of the third high-frequency transformer T3, and the cathode of the sixth rectifier diode D3b is connected to the positive side of the secondary winding Ls3 of the third high-frequency transformer T3. The third rectifier circuit 53 is composed of the fifth rectifier diode D3a and the sixth rectifier diode D3b. The neutral point of the secondary winding Ls3 of the third high-frequency transformer T3 is connected to one end of the output capacitor Co, and the anodes of the fifth rectifier diode D3a and the sixth rectifier diode D3b are connected to the other end of the output capacitor Co, so that the AC voltage output at both ends of the secondary winding Ls3 is full-wave rectified and smoothed.

[0045] In addition, although the rectifying circuits 51 , 52 , and 53 use rectifying diodes as an example, any configuration is acceptable as long as the output voltages of the secondary windings Ls1 , Ls2 , and Ls3 can be rectified.

[0046] The first LLC resonant converter is composed of a first series circuit S1, a first resonant circuit 41, a first high-frequency transformer T1, and a first rectifier circuit 51. Similarly, the second LLC resonant converter is composed of a second series circuit S2, a second resonant circuit 42, a second high-frequency transformer T2, and a second rectifier circuit 52, and the third LLC resonant converter is composed of a third series circuit S3, a third resonant circuit 43, a third high-frequency transformer T3, and a third rectifier circuit 53.

[0047] The outputs of the first to third LLC resonant converters are connected in parallel to both ends of the output capacitor Co, and output a DC output voltage Vo.

[0048] The multi-phase LLC resonant converter circuit 10 includes a control circuit 60 connected to gates of switches Q11, Q12, Q21, Q22, Q31, and Q32 to control ON and OFF of the switches Q11, Q12, Q21, Q22, Q31, and Q32.

[0049] The control circuit 60 generates a first resonant current ir1 flowing through the first resonant circuit 41 by alternately turning on and off the first switch Q11 and the second switch Q12 of the first series circuit S1. The control circuit 60 generates a second resonant current ir2 flowing through the second resonant circuit 42 by alternately turning on and off the first switch Q21 and the second switch Q22 of the second series circuit S2. The control circuit 60 generates a third resonant current ir3 flowing through the third resonant circuit 43 by alternately turning on and off the first switch Q31 and the second switch Q32 of the third series circuit S3.

[0050] The control circuit 60 generates resonant currents ir1 , ir2 , ir3 having the predetermined frequency f by controlling the gate signals for turning on and off the switches Q11 , Q12 , Q21 , Q22 , Q31 , Q32 at the predetermined frequency f.

[0051] The control circuit 60 has a multi-phase operation mode and a single-phase operation mode. The multi-phase operation mode enables all of the first, second, and third LLC resonant converters of the multi-phase LLC resonant converter circuit 10 to operate. The single-phase operation mode enables any one of the first, second, and third LLC resonant converters of the multi-phase LLC resonant converter circuit 10 to operate and stops the operations of the other LLC resonant converters.

[0052] In the multi-phase operation mode, the control circuit 60 controls the on / off of all switches Q11, Q12, Q21, Q22, Q31, Q32 of the series circuits S1, S2, S3 so that the resonant currents ir1, ir2, ir3 flowing through the resonant circuits 41, 42, 43 have a phase difference of 360° / 3=120°.

[0053] Resonant frequency f in multi-phase operation mode r1 The resonant frequency of the resonant circuits 41 , 42 , and 43 is expressed as in Formula 1.

[0054] [Number 1]

[0055]

[0056] As shown in equation 1, the resonant frequency f in multi-phase operation mode r1 It does not depend on the split ratio α and the neutral line reactor Ln. In the multi-phase operation mode, the predetermined frequency f, which is the switching frequency for turning the switch on and off, is obtained from the resonant frequency f of Formula 1. r1 Just set it.

[0057] As a result, resonant currents ir1 , ir2 , and ir3 are generated which flow through the series resonant circuits 41 , 42 , and 43 .

[0058] When the DC input voltage Vin of the DC power supply 30 is at a rated value (e.g., 380 V) in the multi-phase operation mode, the resonant currents ir1, ir2, and ir3x having a phase difference of 120° mutually cancel each other out, so the current ir1+ir2+ir3 is generally substantially zero. Fig.12 (a) Similarly, the neutral line current in flowing through the first neutral line N1 is the same as that shown in the conventional example. Fig.12 (b) Likewise.

[0059] When the DC input voltage Vin of the DC power supply 30 is lower than the rated value (for example, 300 V) in the multi-phase operation mode, if the switching frequency f is lower than fr1 to perform the boost operation, for example, in the conventional example, a voltage having the following characteristics is generated in the first neutral line N1: Fig.13 (b) shows a neutral line current in having a third harmonic component. In this regard, as in the first embodiment, by connecting a neutral line inductor Ln between the first neutral line N1 and the power line on the negative side (or positive side) of the DC power supply 50, the generation of the neutral line current in having a third harmonic component can be suppressed. Figure 2 Showing this situation, Figure 2 (a) is the resonant current ir flowing through a resonant circuit during the boost operation. Figure 2 (b) is the neutral line current in flowing through the first neutral line N1 during the voltage step-up operation.

[0060] In this way, Figure 2 In the first embodiment shown in (b), the neutral line current in flowing through the first neutral line N1 during the voltage step-up operation is Fig.13 Compared with the neutral line current in flowing through the first neutral line N1 during the boost operation in the conventional example shown in (b), the magnitude of the neutral line current in can be suppressed. Figure 2 In the first embodiment shown in (a), the resonant current ir flowing through one resonant circuit during the step-up operation is Fig.13 In the conventional example shown in (a), the magnitude of the harmonic component can be suppressed compared to the resonant current ir flowing through one resonant circuit during the step-up operation.

[0061] Figure 3 When the DC input voltage Vin is below the rated value (380V), Fig.11 The structure of the conventional example shown (dashed line) and Figure 1 The diagram is a comparison of the effective values ​​of the resonant current ir (ir1, ir2, ir3) flowing through any of the resonant circuits 41, 42, 43 in the configuration (solid line) of the first embodiment shown in FIG. n =L r / 3). According to Figure 3It can be seen that in the first embodiment, the increase in the effective value of the resonant current can be suppressed compared to the conventional example.

[0062] The control circuit 60 controls the on / off of the first switch and the second switch of any one of the series circuits of the first, second, and third LLC resonant converters in the single-phase operation mode, and controls the first switch and the second switch of the other two LLC resonant converters to be turned off. Here, consider the case where the control circuit 60 controls the on / off of the first switch Q11 and the second switch Q12 of the series circuit S1 of the first LLC resonant converter in the single-phase operation mode, and controls the first switch Q21, Q31 and the second switch Q22, Q32 of the series circuits S2, S3 of the second and third LLC resonant converters to be turned off.

[0063] Resonant frequency f in single-phase operation mode r2 The resonant frequency based on the resonant circuit 41, the resonant capacitors Cr2, Cr3, the divided resonant capacitors Cn2, Cn3, and the neutral line reactor Ln is expressed as in Expression 2.

[0064] [Number 2]

[0065]

[0066] In the single-phase operation mode, the switching frequency f of the switches Q11 and Q12 of the first series circuit S1 is turned on and off according to the resonant frequency f of formula 2. r2 Just set it.

[0067] Here, when switching from the three-phase operation mode to the single-phase operation mode, if the condition that the resonant frequency does not increase is considered (f r2 ≦f r1 ), then equation 3 is obtained by equation 1 and equation 2.

[0068] [Number 3]

[0069]

[0070] In particular, by setting the condition (f r2 =f r1 ), when switching between the three-phase operation mode and the single-phase operation mode, the resonant frequency does not change, so the transient characteristics during switching can be improved.

[0071] [Number 4]

[0072]

[0073] If the inductance ratio of the neutral line reactor Ln and the resonant reactor Lr is L n / L r =λ, then Equation 4 is shown as Equation 5.

[0074] [Number 5]

[0075]

[0076] If Formula 5 is transformed into a form regarding the split ratio α, it becomes as shown in Formula 6.

[0077] [Number 6]

[0078]

[0079] By making the inductance ratio of the neutral line reactor Ln and the resonant reactor Lr n / L r =λ and the split ratio α is set as in equation 5 or equation 6. When the three-phase operation mode and the single-phase operation mode are switched, the resonant frequency does not change (f r2 =f r1 ).

[0080] Figure 4 The inductance ratio L between the neutral line reactor Ln and the resonant reactor Lr when α=0.5 is shown. n / L r The change rate f of the resonant frequency when switching from the three-phase operation mode to the single-phase operation mode r2 / f r1 According to the relationship between Figure 4 It can be seen that when α = 0.5, at L n / L r =1 / 3, the change rate of the resonant frequency f r2 / f r1 =1, that is, the resonant frequency does not change, at L n / L r >1 / 3, it becomes f r2 / f r1 <1, the increase of the resonant frequency is suppressed.

[0081] Figure 5 (a) is Fig.11 The illustrated conventional multi-phase LLC resonant converter circuit 13 shows transient waveforms of the DC output voltage Vo and the resonant currents ir1 , ir2 , and ir3 of each phase when switching from the three-phase operation mode to the single-phase operation mode is performed at a fixed frequency. Figure 5 (b) shows the multi-phase LLC resonant converter circuit 10 (α=0.5, L n =L r / 3) when switching from three-phase operation mode to single-phase operation mode at a fixed frequency, the transient waveforms of the DC output voltage Vo and the resonant currents ir1, ir2, and ir3 of each phase. The conditions for switching from three-phase operation to single-phase operation are fixed using an operating frequency of f = 69.4kHz and an electrostatic capacitance C of the output capacitor Co. o =1000μF, equivalent series resistance =18mΩ, output current Io =12.5A (at output voltage Vo =48.0V, output power Po =600W).

[0082] exist Figure 5 In the case of the conventional example shown in (a), immediately after switching from three-phase to single-phase, the output voltage Vo and the resonant current ir1 both have large overshoots, and the average value of the output voltage Vo after stabilization rises to 51.5V. Figure 5 In the case of the first embodiment shown in (b), the overshoot of the output voltage Vo and the resonant current ir1 immediately after switching from three phases to single phase is small, and the average value of the output voltage Vo after stabilization remains at 48.0V.

[0083] Figure 6 (a) Shown in Fig.11 The illustrated conventional multi-phase LLC resonant converter circuit 13 shows transient waveforms of the DC output voltage Vo and the resonant currents ir1 , ir2 , and ir3 of the respective phases when switching from the single-phase operation mode to the three-phase operation mode is performed at a fixed frequency. Figure 6 (b) shows the multi-phase LLC resonant converter circuit 10 (α=0.5, L n =L r / 3) when switching from the single-phase operation mode to the three-phase operation mode at a fixed frequency, the transient waveforms of the DC output voltage Vo and the resonant currents ir1, ir2, and ir3 of each phase. The conditions for switching from single-phase operation to three-phase operation are the operating frequency f=79.8kHz of the prior art example, the operating frequency f=69.4kHz of the first embodiment, and the electrostatic capacitance C of the output capacitor Co. o =1000μF, equivalent series resistance =18mΩ, output current Io =12.5A (at output voltage Vo =48.0V, output power Po =600W).

[0084] exist Figure 6 In the case of the conventional example shown in (a), the average output voltage after stabilization drops to 45.3 V. Figure 6 In the case of the first embodiment shown in (b), the average value of the output voltage after stabilization remains at 48.0 V.

[0085] Therefore, in Fig.11In the LLC resonant converter circuit 13 of the conventional example shown in FIG. 1 , an operation of the operating frequency f based on feedback control is required when switching the number of phases. Figure 1 In the LLC resonant converter circuit 10 according to the embodiment shown, the operation of the operating frequency f based on feedback control when switching the number of phases can be eliminated. Therefore, the LLC resonant converter circuit 10 according to the embodiment is suitable for use in a DC converter (DCX) that is expected to replace a commercial frequency transformer such as a pole transformer, for example.

[0086] Here, consider the case where the resonant inductors Lr1, Lr2, Lr3 and the neutral line inductor Ln are wound on a core of the same specification. If the number of turns of the resonant inductors Lr1, Lr2, Lr3 is N r , set the number of turns of the neutral line reactor Ln to N n , set the turns ratio to Nn / N r =n(=√λ), then Formula 2 can be rewritten as Formula 7.

[0087] [Number 7]

[0088]

[0089] Therefore, under the following condition of equation 8, f r2 =f r1 .

[0090] [Number 8]

[0091]

[0092] Furthermore, if Expression 8 is transformed into an expression related to the division ratio α, it becomes Expression 9.

[0093] [Number 9]

[0094]

[0095] Here, for example, when α=0.5 is adopted, n=1 / √3=0.577 may be used.

[0096] In addition, as the magnetic core, for example, a tripod magnetic core can be used, and the reactors Lr1 , Lr2 , Lr3 , and Ln can be wound around the middle leg of the tripod magnetic core. However, other methods may be used.

[0097] In the polyphase LLC resonant converter circuit 10 according to the first embodiment, the first neutral line N1 is connected to the negative (or positive) electrode of the DC power supply 30 via the neutral line reactor Ln, so that the operation of switching between the polyphase operation mode and the single-phase operation mode can be performed. Further, the neutral line reactor Ln exhibits a high impedance value with respect to the AC current of the high-frequency component. Therefore, during the boost operation in the polyphase operation mode, the high-order harmonic components such as the third harmonic contained in the resonant currents ir1, ir2, and ir3 flowing through the resonant circuits 41, 42, and 43 are suppressed, the increase in the effective value is suppressed, and the high-order harmonic components such as the third harmonic contained in the neutral line current in flowing from the first neutral line N1 via the neutral line reactor Ln to the negative (or positive) electrode of the DC power supply 30 can be suppressed.

[0098] In the first embodiment, the three-phase LLC resonant converter circuit with the number of phases N = 3 has been described. However, it may also have a structure such as a polyphase LLC resonant converter circuit including N LLC resonant converters with N = 2 or N > 3. In this case, during the polyphase operation mode, it is operated by the control circuit 60 so that the phase difference of the resonant currents ir of the respective LLC resonant converters becomes 360° / N. Further, the control circuit 60 can be made to operate so that N1 (N1 < N) of the N LLC resonant converters operate and the operation of N - N1 LLC resonant converters is stopped. The so-called "controlling the ON and OFF of the first switch and the second switch of the first LLC resonant converter at a second frequency corresponding to the second resonant frequency based on the resonant circuit and the neutral line reactor, and setting the first switch and the second switch of the second to the Nth LLC resonant converters to OFF" in this specification may also mean that the "first LLC resonant converter" is a plurality of LLC resonant converters. For example, it may be possible to control the two switches of four LLC resonant converters at the second frequency and set the remaining two switches to OFF. Alternatively, it may be possible to control two or three switches of six LLC resonant converters at the second frequency and set the remaining four or three switches to OFF.

[0099] Further, during the single-phase operation mode, it is only necessary to operate only any one of the N LLC resonant converters with N = 2 or N > 3. In this case, the operation can also be performed in the same manner as the single-phase operation mode of the polyphase LLC resonant converter circuit 10 according to the first embodiment.

[0100] (Second Embodiment)

[0101] Figure 7 It is a circuit diagram showing the structure of the polyphase LLC resonant converter circuit 10A according to the second embodiment.

[0102] The multi-phase LLC resonant converter circuit 10A is Figure 1 The first embodiment shown is different in that three neutral line reactors, namely, a first neutral line reactor Ln1, a second neutral line reactor Ln2, and a third neutral line reactor Ln3, are connected in series. Only the differences will be described here, and description of the common points will be omitted.

[0103] like Figure 7 , 8 As shown, the first neutral line inductor Ln1 is magnetically coupled to the first resonant inductor Lr1 through the first magnetic core Tn1, the second neutral line inductor Ln2 is magnetically coupled to the second resonant inductor Lr2 through the second magnetic core Tn2, and the third neutral line inductor Ln3 is magnetically coupled to the third resonant inductor Lr3 through the third magnetic core Tn3.

[0104] exist Figure 8 In the embodiment, a tripod core is used as a magnetic core, and each reactor is wound around a leg in the middle of the tripod cores Tn1, Tn2, and Tn3. An air gap is provided near the center of the leg in the middle of the tripod cores Tn1, Tn2, and Tn3.

[0105] As Figure 8 A variation of Fig. 9 In FIG. 1 , a five-legged core Tn is used as a core, and each reactor is wound around three legs on the center side. The three legs on the center side of the five-legged core Tn have air gaps near the center of each leg. In the case where the number of phases N is other than 3, a core with (N+2) legs can be used, and a similar structure can be set. In addition, the core can be used according to the intended use state. Figure 8 , 9 Any core other than the cores shown in FIG.

[0106] exist Figure 8 , 9 In the figure, for convenience, the first neutral line reactor Ln1 and the first resonant reactor Lr1, the second neutral line reactor Ln2 and the second resonant reactor Lr2, and the third neutral line reactor Ln3 and the third resonant reactor Lr3 are separately represented. In fact, in order to improve the mutual coupling, the first neutral line reactor Ln1 and the first resonant reactor Lr1, the second neutral line reactor Ln2 and the second resonant reactor Lr2, and the third neutral line reactor Ln3 and the third resonant reactor Lr3 are set to be stacked (re-wound) or bifilar wound (bifilar wound) respectively to set to a strong coupling state.

[0107] By setting Figure 8 , 9The structure can reduce the number of magnetic cores compared to the case where dedicated magnetic cores are used for each of the resonant inductors Lr1, Lr2, Lr3 and the neutral line inductor Ln as in the first embodiment.

[0108] In the second embodiment, the resonance frequency f of the three-phase operation mode is r3 In terms of the fundamental wave of the resonant current ir1, ir2, ir3, the phase difference is 120°, and the fundamental wave component of the current in flowing through the neutral line N1 is zero. Since the self-inductance of the neutral line reactors Ln1, Ln2, Ln3 and the mutual inductance of the resonant reactors Lr1, Lr2, Lr3 and the neutral line reactors Ln1, Ln2, Ln3 can be ignored, it is as shown in equation 10 in the same way as in the first embodiment.

[0109] [Number 10]

[0110]

[0111] In contrast, the third harmonic current superimposed on the resonant current ir1, ir2, ir3 becomes the same phase in each phase, and the current superimposed on the third harmonic current of each phase flows through the neutral line N1 and the neutral line reactors Ln1, Ln2, Ln3. Therefore, the third harmonic current generates components of the self-inductance of the neutral line reactors Ln1, Ln2, Ln3 and the mutual inductance of the resonant reactors Lr1, Lr2, Lr3 and the neutral line reactors Ln1, Ln2, Ln3.

[0112] Here, the number of turns of the resonant reactors Lr1, Lr2, and Lr3 is assumed to be N. r In addition, for comparison with the first embodiment, the total number of turns of the neutral line reactors Ln1, Ln2, and Ln3 is assumed to be N. n That is, let the number of turns of each neutral line reactor Ln1, Ln2, Ln3 be N n / 3, then the turns ratio of each resonant reactor Lr1, Lr2, Lr3 and the neutral line reactor Ln1, Ln2, Ln3 is (N n / 3) / N r =n / 3. If the self-inductance of each neutral line reactor Ln1, Ln2, Ln3 is l n , then by considering the self-inductance and mutual inductance, the resonant inductance value L of each resonant reactor for the third harmonic current rt As shown in formula 11.

[0113] [Number 11]

[0114]

[0115] Here, k is the coupling coefficient between the resonant reactor winding and the neutral line reactor winding. In this way, the inductance value of the resonant reactor Lr can be increased for the third harmonic.

[0116] The total neutral line inductance L of three series-connected neutral line reactors for the third harmonic current in three-phase operation mode nt As shown in formula 12.

[0117] [Number 12]

[0118]

[0119] Note that the resonant reactor is considered to be connected in parallel, and the total inductance value L for the third harmonic current is t As shown in formula 13.

[0120] [Number 13]

[0121]

[0122] On the other hand, the total inductance value L for the third harmonic current in the first embodiment is t As shown in formula 8.

[0123] [Number 14]

[0124]

[0125] The total inductance value L of the second embodiment for the third harmonic current t The condition for the total inductance to be larger than that of the first embodiment is obtained as shown in Expression 15 by comparing Expression 13 and Expression 14.

[0126] [Number 15]

[0127] n<k

[0128] …(Equation 15)

[0129] That is, in the case where the coupling coefficient is k to 1 and the turns ratio n<1 (n / 3<1 / 3=0.333) in the strong coupling, the total inductance value of the second embodiment becomes larger than the total inductance value of the first embodiment for the third harmonic current. In other words, in the case where the turns ratio n<1 (n / 3<1 / 3=0.333), for the third harmonic current, even if the total number of turns of the neutral line reactors Ln1, Ln2, and Ln3 of the second embodiment is set smaller than the number of turns Nn of the neutral line reactor Ln of the first embodiment, the total inductance value of the second embodiment can be made substantially equal to the total inductance value of the first embodiment.

[0130] Next, consider the total resonant inductance value L in single-phase operation mode. rt1By considering the self-inductance and mutual inductance of Lr1, the total resonant inductance value L in single-phase operation rt1 As shown in formula 16.

[0131] [Number 16]

[0132]

[0133] Similarly, consider the total neutral line inductance L in single-phase operation mode. nt1 The total neutral line inductance value L during single-phase operation nt1 For Ln1, both self-inductance and mutual inductance are considered, and for Ln2 and Ln3, only self-inductance is considered, as shown in Formula 17.

[0134] [Number 17]

[0135]

[0136] Therefore, the resonant frequency f in single-phase operation mode is r4 For the resonant reactor Lr, the total inductance value L including the mutual inductance is also used. rt1 , thus as shown in Equation 18.

[0137] [Number 18]

[0138]

[0139] In the single-phase operation mode, the switching frequency f at which the switches Q11 and Q12 of the first series circuit S1 are turned on and off is calculated according to the resonant frequency f of equation 18. r4 Just set it.

[0140] According to equation 15, the condition that the resonant frequency does not change when switching from the three-phase operation mode to the single-phase operation mode (f r4 =f r3 ) and obtain equation 19.

[0141] [Number 19]

[0142]

[0143] If equation 19 is solved for n / 3, equation 20 is obtained. Here, the coupling coefficient is set to k=1 (close coupling).

[0144] [Number 20]

[0145]

[0146] Therefore, by setting the turns ratio to the value n / 3 obtained from equation 20 using the adopted split ratio α, the resonant frequency f in the three-phase operation mode is r3 and the resonant frequency f in single-phase operation mode r4Become equal (f r4 =f r3 For example, when the split ratio α=0.5 is adopted, by setting the turns ratio n / 3=0.138, the resonant frequency does not change when switching between the three-phase operation mode and the single-phase operation mode (f r4 =f r3 ).

[0147] If equation 20 is transformed into an equation regarding the split ratio α, it becomes equation 21.

[0148] [Number 21]

[0149]

[0150] By setting the split ratio α to the value obtained from equation 21 using the adopted turns ratio n / 3 or n, the resonant frequency f in the three-phase operation mode is r3 and the resonant frequency f in single-phase operation mode r4 Become equal (f r4 =f r3 ).

[0151] Here, if the total number of turns N of the neutral line reactors Ln1, Ln2, and Ln3 in the second embodiment is n The total number of turns of the resonant reactors Lr1, Lr2, and Lr3 is 3N r The ratio of is the winding increase rate ρ, then the winding increase rate ρ is expressed as formula 22 through formula 20.

[0152] [Number 22]

[0153]

[0154] On the other hand, if the number of turns Nn of the neutral line reactor Ln and the total number of turns 3N of the resonant reactors Lr1, Lr2, and Lr3 are equal when magnetic coupling is not used as in the first embodiment, r The ratio of is set as the winding increase rate ρ0, then the winding increase rate ρ0 is expressed as Formula 23 through Formula 8.

[0155] [Number 23]

[0156]

[0157] Fig.10This is a graph plotting the winding increase rate ρ in the second embodiment of equation 22 and the winding increase rate ρ0 in the first embodiment of equation 23 with respect to the split ratio α. Thus, in the range of the split ratio α>0.25, the winding increase rate ρ in the second embodiment becomes smaller than the winding increase rate ρ0 in the first embodiment (ρ<ρ0), that is, the number of turns of the neutral line reactor is reduced in the side using magnetic coupling as in the second embodiment compared to the side not using magnetic coupling as in the first embodiment.

[0158] In the multi-phase LLC resonant converter circuit 10A according to the second embodiment, as in the first embodiment, the neutral line N1 is connected to the power line on the negative side (or positive side) of the DC power supply 30 via the neutral line reactors Ln1, Ln2, and Ln3, so that the operation of switching between the multi-phase operation mode and the single-phase operation mode can be performed. The neutral line reactors Ln1, Ln2, and Ln3 show a high impedance value to the AC current of the higher harmonic component, so that during the step-up operation in the multi-phase operation mode, the higher harmonic components such as the third harmonic contained in the resonant current ir1, ir2, and ir3 flowing through the resonant circuits 41, 42, and 43 are suppressed to suppress the increase in the effective value. Furthermore, the higher harmonic components such as the third harmonic contained in the neutral line current in flowing from the neutral line N1 to the power line on the negative side (or positive side) of the DC power supply 30 via the neutral line reactors Ln1, Ln2, and Ln3 can be suppressed.

[0159] Description of Reference Numerals

[0160] 10, 10A multi-phase LLC resonant converter circuit, 30 DC power supply, 41, 42, 43 resonant circuit, 51, 52, 53 rectifier circuit, Cn1, Cn2, Cn3 split resonant capacitor, Co output capacitor, Cr1, Cr2, Cr3 resonant capacitor, f switching frequency, f r1 、f r2 、f r3 、f r4 Resonant frequency, in neutral line current, ir, ir1, ir2, ir3 resonant current, Ln neutral line inductor, Lr1, Lr2, Lr3 resonant inductor, N1 first neutral line, N2 second neutral line, Q11, Q21, Q31 first switch, Q21, Q22, Q32 second switch, S1, S2, S3 series circuit, T1, T2, T3 high frequency transformer, Vin DC input voltage, Vo DC output voltage, division ratio of electrostatic capacitance of α resonant capacitor and division resonant capacitor, λ inductance ratio of neutral line inductor and resonant inductor.

Claims

1. A multi-phase LLC resonant converter circuit, which is a multi-phase LLC resonant converter circuit for converting a first DC voltage of a DC power supply into a second DC voltage for output, comprising: First to Nth LLC resonant converters, wherein, N is an integer greater than 2, and the first to Nth LLC resonant converters respectively include: a series circuit connected in parallel with the DC power supply, wherein a first switch and a second switch are connected in series; A high frequency transformer having a primary winding and a secondary winding; a resonant circuit comprising a resonant reactor connected between a connection point between the first switch and the second switch and one end of the primary winding, a resonant capacitor having one end connected to the other end of the primary winding, and a split resonant capacitor having one end connected to a connection point between the primary winding and the resonant capacitor; as well as A rectifier circuit, used for rectifying the output of the secondary winding; a first neutral line connecting the other ends of the resonant capacitors of the first to Nth LLC resonant converters to each other; A neutral line reactor connected between the first neutral line and a power line of either the positive electrode or the negative electrode of the DC power source; a second neutral line connecting the other ends of the split resonant capacitors of the first to Nth LLC resonant converters to each other; as well as An output capacitor is connected in parallel to the output side of the rectifier circuit of the first to Nth LLC resonant converters, and is used to output a second DC voltage at both ends.

2. The multi-phase LLC resonant converter circuit according to claim 1, further comprising: a control circuit, configured to control the on / off of the first switch and the second switch of the first to Nth LLC resonant converters, The control circuit comprises: a multi-phase operation mode, controlling the on / off of each of the first switch and the second switch of the first to Nth LLC resonant converters at a first frequency corresponding to a first resonant frequency based on the resonant circuit and in such a manner that the resonant current of the first frequency flowing through the series resonant circuit of the first to Nth LLC resonant converters has a phase difference of 360° / N; and In the single-phase operation mode, the first switch and the second switch of the first LLC resonant converter are controlled to be turned on and off at a second frequency corresponding to a second resonant frequency based on the resonant circuit and the neutral line reactor, and the first switch and the second switch of the second to Nth LLC resonant converters are turned off.

3. The multi-phase LLC resonant converter circuit as claimed in claim 2, wherein: A division ratio of the electrostatic capacitance of the resonant capacitor and the divided resonant capacitor and an inductance ratio of the resonant reactor and the neutral line reactor are set so that the first resonant frequency and the second resonant frequency become equal.

4. The multi-phase LLC resonant converter circuit according to any one of claims 1 to 3, wherein: The resonant inductor is the leakage inductance of the high-frequency transformer.

5. The multi-phase LLC resonant converter circuit according to any one of claims 1 to 3, wherein: The neutral line reactor comprises N reactors having equal inductance values ​​connected in series, namely, first to Nth neutral line reactors. The N pairs of the resonant inductors of the first to Nth LLC resonant converters and the first to Nth neutral line inductors are magnetically coupled through first to Nth magnetic cores, respectively.

6. The multi-phase LLC resonant converter circuit according to any one of claims 1 to 3, wherein: The neutral line reactor comprises N reactors having equal inductance values ​​connected in series, namely, first to Nth neutral line reactors. The resonant inductors of the first to Nth LLC resonant converters are magnetically coupled with the first to Nth neutral line inductors through the second to N+1th middle legs of the (N+2)-leg magnetic core, respectively.

7. The multi-phase LLC resonant converter circuit as claimed in claim 5, wherein: The resonant reactors of the first to Nth LLC resonant converters and the first to Nth neutral line reactors are stacked.

8. The multi-phase LLC resonant converter circuit as claimed in claim 5, wherein: The resonant reactors of the first to Nth LLC resonant converters and the first to Nth neutral line reactors are bifilar-wound.

9. The multi-phase LLC resonant converter circuit as claimed in claim 6, wherein: The resonant reactors of the first to Nth LLC resonant converters and the first to Nth neutral line reactors are stacked.

10. The multi-phase LLC resonant converter circuit of claim 6, wherein: The resonant reactors of the first to Nth LLC resonant converters and the first to Nth neutral line reactors are bifilar-wound.

Images