Control method of bidirectional resonant power conversion device

Abstract

To stabilize an output within a large input voltage range in a LLC resonant power conversion device.SOLUTION: In an LLC bidirectional resonant power conversion device which makes a first switch circuit performing a rectangular conversion and a second switch circuit performing a rectification a half-bridge structure and can perform a bidirectional conversion, the second switch circuit is made OFF without synchronization and rectification, and is made ON for a predetermined time only with ON / OFF of the second switch circuit being delayed for a predetermined time with respect to ON / OFF of the first switch circuit when a conversion frequency becomes a preset frequency.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an output voltage control of a bidirectional resonant DC power supply device, and more particularly to a control method for an LLC type bidirectional resonant power conversion device for stabilizing a wide input voltage or a wide variable range of output voltage. [Background technology]

[0002] In recent years, there has been a growing demand for higher power output in DC power supplies, and there is a demand for higher efficiency. Therefore, resonant power supplies, especially LLC type, which are relatively efficient and capable of reducing noise, have been attracting attention. However, since resonant power supplies control the output by frequency control, it is difficult to achieve a wide input voltage or wide output voltage range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-017179 Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, Patent Document 1 proposes that, for a three-phase LLC system or a single-phase LLC system using a first switch circuit in a full-bridge configuration, a delay time is applied to the on / off of the first switch circuit and the second switch circuit, and the output is controlled by controlling the delay time. This means that the input voltage range can be expanded.

[0005] However, this method is difficult to apply to a single-phase LLC resonant power supply with a simple half-bridge circuit, which is widely used. [Means for solving the problem]

[0006] In view of the above, the LLC type resonant power conversion device of the present invention includes a first switch circuit connected to a first DC voltage and combining a plurality of switch elements, a second switch circuit connected to a second DC voltage and combining a plurality of switch elements, a first resonant circuit in which a first resonant capacitor, a first resonant reactor, and a primary winding of a transformer are connected in series, and a second resonant circuit in which a second resonant capacitor, a second resonant reactor, and a secondary winding of the transformer are connected in series, and the LLC type bidirectional resonant power conversion device converts a first DC voltage to a second DC voltage by varying the on / off frequency of the first switching circuit, wherein a diode is connected in parallel to each of the switch elements, the first switch circuit converts the first DC voltage into a rectangular wave, and the second switch circuit rectifies the rectangular wave by the parallel diode of each switch element without turning it on and off, and when the on / off frequency of the first switch circuit drops to a predetermined value that is near the resonant frequency of the first resonant circuit or the second resonant circuit, the on / off of the second switch circuit is delayed by a first predetermined time compared to the on / off of the first switch circuit, and the on period is limited to a second predetermined time.

[0007] The maximum and minimum conversion frequencies are determined in advance, and the minimum frequency is set to a value slightly higher than the resonant frequency of the first or second resonant circuit. Specifically, when the input voltage is low and the load is large, the output voltage falls below the target value and approaches the minimum frequency. Therefore, when the conversion frequency reaches the minimum frequency, the second switch circuit is turned on for a predetermined time with respect to the first switch circuit being turned on and off, and is turned on for a short time.

[0008] Furthermore, it is preferable to use three LLC type resonant power conversion devices of the present invention, with the primary winding and / or secondary winding of the transformer connected in a Y-connection, and the on / off operation of the switch circuit of each power conversion device being a three-phase LLC type with a phase difference of 120°, and to connect the neutral point of the Y-connection to one side of a DC power source via a reactor. Effect of the Invention

[0009] In this way, when the conversion frequency becomes the preset minimum frequency and the on / off of the second switch circuit is delayed by a predetermined time from the on / off of the first switch circuit, the output voltage rises according to the delay time. Therefore, even if the input voltage drops, the output voltage can be maintained at a desired voltage, and the allowable range of the input voltage can be substantially expanded. [Brief description of the drawings]

[0010] [Figure 1] A circuit diagram of a resonant power converter according to a first embodiment of the present invention. [Diagram 2] Voltage and current waveforms of each switch when the second switch circuit is delayed at low input voltage, heavy load, and light load in the circuit of Figure 1 [Diagram 3] Voltage and current waveforms of each switch when the circuit of FIG. 1 is operated in accordance with the second embodiment of the present invention [Figure 4] Circuit diagram when the control of the second embodiment of the present invention is applied to a three-phase LLC system DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0011] The circuit diagram shown in FIG. 1 is a bidirectional power converter with a general LLC type conversion section. Specifically, one end of a DC voltage VDC1 is connected to a first switch circuit 11 consisting of a switch element Q1 and a switch element Q2 connected in series, and a connection point between the switch elements Q1 and Q2 is connected to one end of a first resonant circuit 13 in which a first resonant capacitor Cs1, a first resonant reactor Ls1, and a primary winding P1 of a transformer 15 are connected in series, and the other end of the first resonant circuit 13 is connected to the other end of the DC voltage VDC1. Furthermore, a second resonant circuit 16 in which one end of a secondary winding S1 of the transformer 15, a second resonant reactor Ls2, and a second resonant capacitor Cs2 are connected in series is connected to a connection point between a switch element Q3 and a switch element Q4. Furthermore, the other end of the second resonant circuit 16 is connected to the other end of the secondary winding S1 of the transformer 15 and one terminal of the capacitor Cf2. The other end of the second switch circuit 12 is connected to the other terminal of the capacitor Cf2. The switch elements Q1 to Q4 in the present embodiment 1 use field effect transistors (MOSFETs: Metal Oxide Semiconductor Field Effect Transistors) having parasitic diodes in anti-parallel. Furthermore, the resonant frequencies of the first resonant circuit 13 and the second resonant circuit 16 are set to the same value.

[0012] A power conversion device 10 configured as shown in Fig. 1 (hereinafter referred to as the power conversion device 10 of the present invention) operates as a resonant power conversion device that receives a DC voltage VDC1 as an input and generates a DC voltage VDC2 across a capacitor Cf2. Furthermore, the power conversion device 10 of Fig. 1 also operates as a resonant power conversion device that receives a DC voltage VDC2 as an input and outputs a DC voltage VDC1. That is, the power conversion device 10 of the present invention is a bidirectional resonant power conversion device. The following operation will be described in detail as a resonant power conversion device that receives a DC voltage VDC1 as an input and outputs a DC voltage VDC2.

[0013] The basic output control of the power conversion device 10 of the present invention is performed by variable frequency control that adjusts the conversion frequency, similar to a general LLC type resonant power supply. The maximum and minimum conversion frequencies are set in advance, and generally, the maximum frequency is set under the condition of output stabilization at light load, and the minimum frequency is determined by the minimum input voltage and maximum output power. The minimum frequency is set so as not to be lower than the resonant frequency of the first resonant circuit 13 when converting from the DC voltage VDC1 to the DC voltage VDC2, and is set so as not to be lower than the resonant frequency of the second resonant circuit 16 when converting from the DC voltage VDC2 to the DC voltage VDC1. The switching elements Q1 and Q2 are alternately turned on and off with a dead time in between. Similarly, the switching elements Q3 and Q4 are alternately turned on and off with a dead time in between. Furthermore, the first resonant reactor Ls1 and the second resonant reactor Ls2 may use the leakage inductance of the primary winding and secondary winding of the transformer 15.

[0014] A voltage detection / frequency modulation 101 detects a DC voltage VDC2, determines a conversion frequency according to the difference with a reference voltage (not shown), and generates a drive signal FD. Based on the drive signal FD, a driver 103 generates a drive signal VG1 for the switch element Q1 and a drive signal VG2 for the switch element Q2 of the first switch circuit 11, and turns each switch element on and off.

[0015] Here, when the DC voltage VDC1 decreases and / or the current flowing through the load RL1 increases, the frequency of the drive signal FD decreases, and the second switch circuit 12 does not operate until it approaches the minimum frequency, so that a period Tc1 during which no power is supplied to the secondary side is generated, as shown in FIG. 2(a), and the operation is the same as that of the conventional LLC method. During a period Tc1 in which the first switch circuit 11 is on but does not supply power to the secondary side, a current flows through the path of the DC voltage VDC1 → switch element Q1 → first resonant circuit 13 → DC power supply VDC1. However, since the second switch circuit is off, no energy is released via the transformer 15 and a large amount of energy is stored in the first resonant circuit 13.

[0016] When the DC voltage VDC1 further decreases and / or the load RL1 becomes heavier and the conversion frequency reaches a preset minimum frequency, the on / off of the second switch circuit 12 is phase-delayed from the on / off of the first switch circuit 11. Here, if there is no period Tc1 during which the first switch circuit 11 does not supply power to the load, the energy stored in the first resonant circuit 13 increases. Next, when the on / off of the first switch circuit is reversed, the smoothing capacitor Cf2 is charged via a diode connected in parallel to the switch element Q4. Since the increased energy is stored in the first resonant circuit 13, the output voltage becomes higher. As a result, the output voltage can be maintained at a desired voltage even when the input voltage is low, resulting in a wider input voltage range.

[0017] However, in a normal LLC system, the minimum operating frequency is set so that there is a period Tc1. When the switch element Q3 is turned on during the period Tc1, the transformer 15 is excited in the reverse direction from the DC power source VDC2 via the second switch circuit 12 and the second resonant circuit 16, and the energy stored in the first resonant circuit 13 is reduced. Furthermore, when the load current decreases, the period Tc1 is extended, and a current may flow (reverse flow) from the capacitor Cf2 to the secondary winding S1 of the transformer 15 via the switch element Q3. When this occurs, the charge stored in the capacitor Cf2 is released, and in the worst case, the resonant reactor Ls1 is excited in the reverse direction. In this operation, as shown in FIG. 2(b), ZVS (Zero Volt Switching) or ZCS (Zero Current Switching) of each switch element cannot be achieved. In addition, the output power also decreases, and the effect of operating the second switch circuit 12 is lost.

[0018] The above operation is shown as voltage and current charts in Figures 2(a) and 2(b). Each waveform shows the control voltage of each switch element (Q1, Q2, Q3, Q4) and the current flowing through the main terminal. In Figure 2(a), switch elements Q1 and Q2 turn on and off reciprocally, and each current flows as a typical LLC type current. In the control method of the present invention, switch elements Q3 and Q4 are normally off, so that rectification is performed by parasitic diodes connected in anti-parallel to each switch element. Specifically, this corresponds to the Q3 current and Q4 current in Figure 2(a).

[0019] Next, in Fig. 2(b), the switching element Q3 is turned on and off with a delay of a period Ta from the switching element Q1, and the switching element Q4 is turned on and off with a delay of a period Tb from the switching element Q2. When operated in this manner, the switching element Q3 is also turned on during the period Tc1 in which no current is supplied to the output shown in Fig. 2(a). At this timing, the smoothing capacitor Cf2 cannot be charged from the second switch circuit 12, and instead the smoothing capacitor Cf2 inversely excites the transformer 15 via the second switch circuit 12. When the discharge current to the smoothing capacitor Cf2 becomes larger than the charging current, the voltage of the smoothing capacitor Cf2 drops, i.e., the output voltage drops.

[0020] Therefore, as shown in FIG. 3, the signals for driving the switch elements Q3 and Q4 may be set to turn off the second switch circuit during periods Tc1 and Tc2. By operating in this manner, the second switch circuit 12 is turned on with a delay of the preset periods Td1 and Td2 from the first switch circuit 11, thereby making it possible to avoid a problem in which the voltage of the smoothing capacitor Cf2 drops. During periods Te1 and Te2 when current is being supplied to the output, power is supplied to the output via a parasitic diode of the switch element of the second switch circuit, so it is not necessary to turn on the switch element of the second switch circuit during periods Td1 and Td2. However, since the voltage drop during rectification is small under heavy load, turning on the switch element of the second switch circuit during period Td2 increases efficiency.

[0021] 3, the switching element Q3 is turned on in period Te1, then turned off for period Tc1, and then turned on for period Tg1. Similarly, the switching element Q4 is turned on in period Te2, then turned off for period Tc2, and then turned on for period Tg2. This means that as long as the charging current and discharging current of the smoothing capacitor Cf2 by the second switch circuit 12 are not the same, the effect of the present invention can be expected even if the switching element Q3 is turned on again in period Tg1 or Tg2. The present invention functions sufficiently even if the switching element Q3 is not turned on again in period Tg1 and period Tg2.

[0022] Furthermore, even if the primary winding P1 and secondary winding S1 of the transformer 15 have the same number of turns, the inductance may change because the positions when wound on the bobbin are different. This causes the operation to change when moved in both directions, so the same characteristics cannot be obtained in both directions with the same control. To avoid this, it is a good idea to adjust the capacitance of the resonant capacitors Cs1 and Cs2 so that they produce the same characteristics. EXAMPLES

[0023] This method can also be applied to circuits that operate multiple units in parallel in a multi-phase manner, as long as the rectifier circuit on the output side of the LLC type resonant power conversion device is synchronously rectified. For example, in a so-called three-phase LLC DC / DC converter, as shown in Figure 4, three LLC resonant power conversion devices are connected in parallel on the input and output sides, and the phase of the on / off cycle of each resonant power conversion device is shifted by 120° to turn the switch circuit on and off.The output voltage can be adjusted by delaying the on timing of the primary side switch circuit and the secondary side switch circuit.

[0024] The first LLC type resonant power conversion device generates on / off signals for each switch element from the output voltage using voltage detection / frequency conversion 101 and frequency detection / phase delay 102, as in Figure 1, and the second and third LLC type resonant power conversion devices distribute signals using first frequency distributor 155 and second frequency distributor 156 so that the currents flowing in the resonant circuits of each resonant power conversion device have a phase of 120°. Furthermore, either or both of the primary and secondary windings of each transformer may be Y-connected. In this case, it is even better to connect the neutral point of the Y-connection to one of the terminals of the DC power supply via an impedance element having a predetermined impedance at the conversion frequency. This reduces the impedance between the neutral point and the DC power supply, improving the current balance of each power supply device, and also increasing the effect when the switch on the output side operates. Furthermore, the same effect can be expected if the transformers of each power supply are connected in a three-phase bridge. EXAMPLES

[0025] This method can also be applied to circuits that operate multiple units in parallel in a multi-phase manner, as long as the rectifier circuit on the output side of the LLC type resonant power conversion device is synchronously rectified. For example, in a so-called three-phase LLC DC / DC converter, as shown in Figure 4, three LLC resonant power conversion devices are connected in parallel on the input and output sides, and the phase of the on / off cycle of each resonant power conversion device is shifted by 120° to turn the switch circuit on and off.The output voltage can be adjusted by delaying the on timing of the primary side switch circuit and the secondary side switch circuit. The first LLC type resonant power conversion device generates on / off signals for each switch element from the output voltage using voltage detection / frequency conversion 101 and frequency detection / phase delay 102, as in Figure 1, and the second and third LLC type resonant power conversion devices distribute signals using first frequency distributor 155 and second frequency distributor 156 so that the currents flowing in the resonant circuits of each resonant power conversion device have a phase of 120°.

[0026] Furthermore, either or both of the primary and secondary windings of each transformer may be Y-connected. In this case, it is even better to connect the neutral point of the Y-connection to one of the terminals of the DC power supply via an impedance element having a predetermined resistance value at the conversion frequency. This reduces the impedance between the neutral point and the DC power supply, improving the current balance of each power supply device. Furthermore, the same effect can be expected if the transformers of each power supply are connected in a three-phase bridge. [Explanation of symbols]

[0027] 10, 101, 102, 103 LLC type resonant power converter 100 Three-phase LLC type resonant power converter 11, 111, 121 First switch circuit 12, 112, 122 Second switch circuit 13, 113, 123 first resonant circuit 16, 116, 216 second resonant circuit 14, 114 Control circuit 15, 115, 215 transformer 101 Voltage detection, frequency modulator 102 Frequency detection and phase delay 103, 104, 153, 154 Drivers 155 First frequency divider 156 Second frequency divider VDC1 First DC power supply VDC2 Second DC power supply Q1, Q2, Q3, Q4 Switching elements Q11, Q12, Q13, Q14 Switch elements Q21, Q22, Q23, Q24 Switch elements Cf1, Cf2 capacitors Cs1, Cs2 Resonant capacitors Ls1, Ls2 Resonant reactor La,Lb Reactor RL1 load

Claims

1. a first switch circuit connected to a first DC voltage and including a combination of a plurality of switch elements; a second switch circuit connected to a second DC voltage and including a combination of a plurality of switch elements; a first resonant circuit in which a first resonant capacitor, a first resonant reactor, and a primary winding of a transformer are connected in series; a second resonant circuit in which a second resonant capacitor, a second resonant reactor, and a secondary winding of the transformer are connected in series; A bidirectional resonant power conversion apparatus of an LLC type that converts a first DC voltage into a second DC voltage by varying an on / off frequency of a first switching circuit, Each of the switch elements has a diode connected in parallel, a first switch circuit converting a first DC voltage into a square wave, a second switch circuit rectifying the square wave by a parallel diode of each switch element without turning on and off, and when an on / off frequency of the first switch circuit drops to a predetermined value that is near a resonant frequency of the first resonant circuit or the second resonant circuit, the on / off of the second switch circuit is delayed by a first predetermined time compared to the on / off of the first switch circuit, and an on period is set to a second predetermined time.

2. 2. A three-phase LLC bidirectional resonant power conversion apparatus according to claim 1, wherein the bidirectional resonant power conversion apparatuses are operated with a phase difference of 120 degrees, and the primary side and / or the secondary side of a transformer are connected in a Y-connection, and wherein a neutral point of the Y-connection and either one of a power supply is connected via a reactor.

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