Power converter and power conversion system

Abstract

To provide a power conversion device that can discharge the charge of a capacitor without increasing costs or size. [Solution] A power conversion device 10 comprising a main circuit section 11 and a control section 12, wherein the main circuit section 11 comprises a first bridge circuit 14, a first resonant circuit 15, a transformer Tr, a second resonant circuit 16, a second bridge circuit 17, and a smoothing circuit 18 including a capacitor C12, and the control section 12 performs charge discharge control to dissipate the charge of the capacitor C12 in the main circuit section 11, and during charge discharge control, the control section 12 performs freewheel control to control the first switching elements Q1 to Q4 so that a freewheel current flows through the first bridge circuit 14, frequency modulation control to modulate the switching frequencies of the second switching elements Q5 to Q8, and phase shift control to modulate the phase difference between the second switching elements Q5 and Q6 of the third leg and the second switching elements Q7 and Q8 of the fourth leg.

Description

Technical Field

[0001] The present invention relates to a power conversion device and a power conversion system.

Background Art

[0002] In recent years, in line with the popularization of electric vehicles, the development of charging devices for charging the batteries of electric vehicles, V2H (Vehicle to Home) systems for supplying the battery power of electric vehicles to household loads, distributed power systems combining solar power generation devices and stationary energy storage devices, etc. has been progressing. As the power conversion devices included in these devices and systems, current resonance type DC / DC converters with a small number of components and capable of high-efficiency power conversion, for example, CLLC type DC / DC converters, are used (see, for example, Patent Document 1).

[0003] The CLLC type DC / DC converter includes a primary side circuit (primary side capacitor, primary side bridge circuit, primary side resonance circuit), a transformer, a secondary side circuit (secondary side capacitor, secondary side bridge circuit, secondary side resonance circuit), and a control unit. The CLLC type DC / DC converter is connected to an electric vehicle via the cable part and connector part of the power transmission device, and supplies the electric vehicle with the terminal voltage of the secondary side capacitor as the output voltage.

[0004] On the other hand, in the CHAdeMO standard, which is the charging standard for electric vehicles, insulation diagnosis of the cable part and connector part is required in the charging / discharging start sequence. During the insulation diagnosis, the DC / DC converter charges the secondary side capacitor to raise the terminal voltage of the secondary side capacitor to a predetermined voltage value (for example, 450 [V]). After the insulation diagnosis, the DC / DC converter discharges the charge of the secondary side capacitor to lower the terminal voltage to a predetermined voltage value (for example, 0 [V]), and then starts the charging / discharging of the electric vehicle.

[0005] Conventional power converters (CLLC type DC / DC converters) require an additional charge discharge circuit, consisting of multiple cement resistors, to discharge the charge from the secondary capacitor after insulation diagnosis. This additional charge discharge circuit in conventional power converters leads to increased costs and larger size of the device. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-97849 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention has been made in view of the above circumstances, and its objective is to provide a power conversion device and a power conversion system that can discharge the charge of a capacitor without increasing costs and size. [Means for solving the problem]

[0008] To solve the above problems, the power conversion device according to the present invention is Primary terminal and secondary terminal, A main circuit section is provided between the primary terminal and the secondary terminal, A control unit that controls the main circuit section, A current-resonant type power converter equipped with, The main circuit section is, A first bridge circuit is connected to the primary terminal, and includes a first leg and a second leg connected in parallel, each leg including an upper arm and a lower arm connected in series, each arm including a first switching element, A first resonant circuit, which includes a first resonant inductor and a first resonant capacitor and is connected to the first bridge circuit, A transformer including a primary coil and a secondary coil, wherein the primary coil is connected to the first resonant circuit, A second resonant circuit, which includes a second resonant inductor and a second resonant capacitor and is connected to the secondary coil, A second bridge circuit is connected to the second resonant circuit, including a third and fourth leg connected in parallel, each leg including an upper arm and a lower arm connected in series, each arm including a second switching element, The system includes a smoothing circuit that includes a capacitor for smoothing the output of the second bridge circuit, and outputs the terminal voltage of the capacitor as the output voltage from the secondary side terminal, The control unit, The first switching element and the second switching element are controlled to discharge the charge stored in the capacitor, and charge discharge control is performed to consume the charge in the main circuit section. The control unit during charge discharge control, Recirculation control controls the first switching element so that a recirculating current flows through the first bridge circuit, Frequency modulation control for modulating the switching frequency of the second switching element, The present invention is characterized by performing phase shift control that modulates the phase difference between the second switching element of the third leg and the second switching element of the fourth leg.

[0009] In this configuration, the capacitor's charge is discharged by flowing a return current through the first bridge circuit, eliminating the need for an additional charge discharge circuit and thus avoiding increased costs and size of the device. Furthermore, while there is a risk of surge voltage generation in the second switching element during charge discharge control in the second bridge circuit, this configuration allows for control of the current flowing through the current path of the second switching element by performing frequency modulation control and phase shift control, thereby suppressing the surge voltage generated in the second switching element.

[0010] In the aforementioned power converter, The control unit during the frequency modulation control, The switching frequency can be modulated in accordance with the terminal voltage such that the switching frequency decreases as the terminal voltage decreases.

[0011] In the power conversion device, The control unit during the phase shift control can be configured to modulate the phase difference according to the switching frequency so that the phase difference decreases as the switching frequency decreases.

[0012] In the power conversion device, The control unit during the charge discharge control starts the frequency modulation control and the phase shift control from the start point of the charge discharge control. When the switching frequency is included in a preset frequency band, the phase difference is modulated by the phase shift control. When the switching frequency is not included in the frequency band, the phase difference can be fixed.

[0013] In order to solve the above problems, a power conversion system according to the present invention includes a power conversion device according to the present invention, a power transmission device having one side connected to the secondary side terminal of the power conversion device and the other side connected to a vehicle equipped with a battery, and performing power transmission between the power conversion device and the battery, and is a power conversion system including: The power transmission device includes a connector portion connected to the vehicle, a cable portion connecting the connector portion and the secondary side terminal, and a power transmission control unit that performs insulation diagnosis of the connector portion and the cable portion in a state where the connector portion is connected to the vehicle. The control unit of the power conversion device is characterized in that during the insulation diagnosis, the capacitor is charged to raise the output voltage to a predetermined set voltage value, and after the insulation diagnosis is completed, the charge discharge control is started.

[0014] The power conversion system includes a stationary energy storage device, It can be further configured to include a power conditioner device having a function of performing a charge / discharge operation of the energy storage device and a function of supplying a DC voltage to the primary side terminal of the power conversion device.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a power conversion device and a power conversion system capable of discharging the charge of a capacitor without causing an increase in cost and size.

Brief Description of the Drawings

[0016] [Figure 1] It is a block diagram of a power conversion system according to the first embodiment. [Figure 2] It is a circuit diagram of a power conversion device according to the first embodiment. [Figure 3] It is a diagram showing the time change of the voltage (or command value) during insulation diagnosis and charge discharge control. [Figure 4] (A) It is a diagram showing the relationship between the switching frequency and the terminal voltage. (B) It is a diagram showing the relationship between the phase shift amount and the switching frequency. (C) It is a diagram showing the time change of the reflux current. [Figure 5] It is a waveform diagram of the control signal of the switching element during charge discharge control. [Figure 6] (A) It is a diagram showing the current flow during the mode 4 period. (B) It is a diagram showing the current flow during the mode 1 period. [Figure 7] (A) It is a diagram showing the current flow during the mode 2 period. (B) It is a diagram showing the current flow during the mode 3 period. [Figure 8] It is a block diagram of a power conversion system according to the second embodiment.

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of a power conversion device and a power conversion system according to the present invention will be described with reference to the accompanying drawings.

[0018] [First Embodiment] Figure 1 shows a power conversion system 1A according to a first embodiment of the present invention. The power conversion system 1A includes a first power conversion device 10, a second power conversion device 20, and a power transmission device 30 according to the present invention. The power conversion system 1A is, for example, a V2H (Vehicle to Home) system.

[0019] In the power conversion system 1A, the first power converter 10 is connected to an AC power source 2 via a second power converter 20, and to an electric vehicle 3 (corresponding to the "vehicle" in this invention) via a power transmission device 30. The AC power source 2 is, for example, a commercial power grid. The electric vehicle 3 is an electric vehicle compliant with the CHAdeMO standard and is equipped with a rechargeable battery.

[0020] The second power converter 20 performs AC / DC conversion, which converts AC voltage to DC voltage, and DC / AC conversion, which converts DC voltage to AC voltage. The second power converter 20 is, for example, a bidirectional PFC (power factor correction) converter.

[0021] The power transmission device 30 is compliant with the CHAdeMO standard and performs power transmission and information communication between the electric vehicle 3 and the first power converter 10. The power transmission device 30 includes a connector section connected to the electric vehicle 3, a cable section connecting the connector section and the first power converter 10, and a power transmission control section. The power transmission device 30 may also include a storage section for housing the connector section when it is not connected to the electric vehicle 3.

[0022] The power transmission control unit of the power transmission device 30 communicates with the electric vehicle 3 (for example, via CAN communication) and obtains information from the electric vehicle 3, such as the remaining battery charge and charge / discharge conditions. The power transmission control unit also communicates with the first power converter 10 and transmits, for example, a command value (external command value) related to the output voltage of the first power converter 10 to the first power converter 10. Furthermore, in the charge / discharge start sequence, the power transmission control unit performs insulation diagnosis of the cable and connector sections to diagnose whether there are any abnormalities such as short circuits in the cable and connector sections.

[0023] The first power converter 10 is a current-resonant CLLC type DC / DC converter. As shown in Figure 2, the first power converter 10 comprises primary terminals T1 and T2 and secondary terminals T3 and T4, a main circuit section 11, and a control section 12 that controls the main circuit section 11. The first power converter 10 can switch between forward power transmission from the primary terminals T1 and T2 to the secondary terminals T3 and T4, and reverse power transmission from the secondary terminals T3 and T4 to the primary terminals T1 and T2.

[0024] The primary terminals T1 and T2 are connected to the DC side of the second power converter 20. The secondary terminals T3 and T4 are connected to the power transmission device 30. In this embodiment, the voltage between the primary terminals T1 and T2 is defined as V1, and the voltage between the secondary terminals T3 and T4 is defined as V2.

[0025] The main circuit section 11 includes a first smoothing circuit 13, a first bridge circuit 14, a first resonant circuit 15, a transformer Tr, a second resonant circuit 16, a second bridge circuit 17, and a second smoothing circuit 18 (corresponding to the "smoothing circuit" of the present invention).

[0026] The first smoothing circuit 13 includes a capacitor C11 connected between the primary terminals T1 and T2. The capacitor C11 consists of at least one capacitor and reduces input ripple during forward power transmission and output ripple during reverse power transmission. The first smoothing circuit 13 may be provided between the first power converter 10 and the second power converter 20.

[0027] The first bridge circuit 14 is a full bridge circuit including a first leg and a second leg connected in parallel, and an upper arm and a lower arm connected in series to each leg. The upper arm of the first leg includes a switching element Q1, the lower arm of the first leg includes a switching element Q2, the upper arm of the second leg includes a switching element Q3, and the lower arm of the second leg includes a switching element Q4. Diodes D1 to D4 are connected in parallel in reverse direction to the current path of switching elements Q1 to Q4, and capacitors C1 to C4 are also connected in parallel. Switching elements Q1 to Q4 correspond to the "first switching element" of the present invention.

[0028] Switching elements Q1 to Q4 are power semiconductor switching elements capable of switching at high frequencies, and may be IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistors). The same applies to switching elements Q5 to Q8, which will be described later. Diodes D1 to D4 are freewheeling diodes, and may be built-in diodes of switching elements Q1 to Q4, external diodes, or both. The same applies to diodes D5 to D8, which will be described later. Capacitors C1 to C4 are partial resonant capacitors, and may be parasitic capacitors of switching elements Q1 to Q4, external capacitors, or both. The same applies to capacitors C5 to C8, which will be described later.

[0029] The collector (or drain) terminals of switching elements Q1 and Q3, i.e., the high-voltage connection points of the first and second legs, are connected to the primary terminal T1. The emitter (or source) terminals of switching elements Q2 and Q4, i.e., the low-voltage connection points of the first and second legs, are connected to the primary terminal T2. The connection point between the emitter (or source) terminal of switching element Q1 and the collector (or drain) terminal of switching element Q2, and the connection point between the emitter (or source) terminal of switching element Q3 and the collector (or drain) terminal of switching element Q4, are connected to the first resonant circuit 15.

[0030] The first resonant circuit 15 includes a first resonant inductor (induction coil, sometimes simply called a coil) Lr1 and a first resonant capacitor (sometimes called a capacitor) Cr1. The first resonant inductor Lr1 and the first resonant capacitor Cr1 form a series resonant circuit together with the excitation inductance of the transformer Tr during forward power transmission. The excitation inductance of the transformer Tr is omitted from the illustration as it is included in the primary coil N1 of the transformer Tr, but it may be composed of a coil with a separate core.

[0031] The arrangement of the first resonant inductor Lr1 and the first resonant capacitor Cr1 is arbitrary, as long as they are connected to the primary coil N1 of the transformer Tr to form a series resonant circuit. For example, the first resonant inductor Lr1 and the first resonant capacitor Cr1 may be arranged separately on the primary and secondary sides of the transformer Tr. Also, the first resonant inductor Lr1 may be the leakage inductance of the transformer Tr, a coil with an individual core, or both. The first resonant capacitor Cr1 may be an individual capacitor, the parasitic capacitance of switching elements Q1 to Q4, or both. The same applies to the second resonant inductor Lr2 and the second resonant capacitor Cr2, which will be described later.

[0032] The transformer Tr consists of one or more high-frequency isolation transformers. The primary coil (primary winding) N1 of the transformer Tr is connected to the first bridge circuit 14 via the first resonant circuit 15. The secondary coil (secondary winding) N2 of the transformer Tr is connected to the second bridge circuit 17 via the second resonant circuit 16.

[0033] The second resonant circuit 16 includes a second resonant inductor Lr2 and a second resonant capacitor Cr2. The second resonant inductor Lr2 and the second resonant capacitor Cr2 form a series resonant circuit together with the excitation inductance of the transformer Tr during reverse power transmission. The excitation inductance of the transformer Tr is omitted from the illustration as it is included in the secondary coil N2 of the transformer Tr, but it may be composed of a coil with a separate core.

[0034] The second bridge circuit 17 is a full bridge circuit that includes a third leg and a fourth leg connected in parallel, and an upper arm and a lower arm connected in series with each leg. The upper arm of the third leg includes a switching element Q5, the lower arm of the third leg includes a switching element Q6, the upper arm of the fourth leg includes a switching element Q7, and the lower arm of the fourth leg includes a switching element Q8. Diodes D5 to D8 are connected in parallel in reverse direction to the current path of switching elements Q5 to Q8, and capacitors C5 to C8 are also connected in parallel. Switching elements Q5 to Q8 correspond to the "second switching element" of the present invention.

[0035] The collector (or drain) terminals of switching elements Q5 and Q7, i.e., the high-voltage connection points of the third and fourth legs, are connected to the secondary terminal T3. The emitter (or source) terminals of switching elements Q6 and Q8, i.e., the low-voltage connection points of the third and fourth legs, are connected to the secondary terminal T4. The connection point between the emitter (or source) terminal of switching element Q5 and the collector (or drain) terminal of switching element Q6, and the connection point between the emitter (or source) terminal of switching element Q7 and the collector (or drain) terminal of switching element Q8, are connected to the second resonant circuit 16.

[0036] The second smoothing circuit 18 includes a capacitor C12 (corresponding to the "capacitor" of the present invention) connected between the secondary terminals T3 and T4. The capacitor C12 consists of at least one capacitor and reduces output ripple during forward power transmission and input ripple during reverse power transmission. The terminal voltage of capacitor C12 is the voltage V2 between the secondary terminals T3 and T4.

[0037] The control unit 12 controls the switching elements Q1 to Q8 to turn on and off. The control unit 12 may be composed of digital circuits such as a microprocessor or a digital signal processor, analog circuits, or a combination of digital and analog circuits. The control unit 12 further includes a detection unit. The detection unit detects at least the terminal voltage of capacitor C12, and further detects the current value and / or voltage value necessary for control.

[0038] During forward power transmission, the control unit 12 operates the first bridge circuit 14 as a drive circuit and the second bridge circuit 17 as a synchronous rectifier circuit or a diode rectifier circuit. Specifically, during forward power transmission, the control unit 12 performs frequency control to modulate the switching frequency of the switching elements Q1 to Q4 of the first bridge circuit 14 according to the input / output characteristics of the LLC method, and performs phase difference control to modulate the phase difference between the first leg and the second leg as needed.

[0039] During reverse power transmission, the control unit 12 operates the second bridge circuit 17 as a drive circuit and the first bridge circuit 14 as a synchronous rectifier circuit or a diode rectifier circuit. Specifically, during reverse power transmission, the control unit 12 performs frequency control to modulate the switching frequency of the switching elements Q5 to Q8 of the second bridge circuit 17 according to the input / output characteristics of the LLC method, and, if necessary, performs phase difference control to modulate the phase difference between the third leg and the fourth leg.

[0040] Furthermore, the control unit 12 performs charge discharge control to discharge the charge stored in capacitor C12 and consume the charge in the main circuit unit 11, while neither forward nor reverse power transmission is being performed. In this embodiment, the control unit 12 performs charge discharge control after insulation diagnosis by forward power transmission in the charge discharge start sequence.

[0041] Figure 3 shows the time variation of the external command value, operation command value, and output voltage V2 during insulation diagnosis and charge discharge control. The external command value is the command value of the output voltage V2 transmitted from the power transmission device 30 to the control unit 12. The operation command value is the command value of the output voltage V2 generated by the control unit 12 based on the external command value. The output voltage V2 is the voltage between the secondary terminals T3 and T4, and in this embodiment, it is the terminal voltage of the capacitor C12. During insulation diagnosis, the control unit 12 controls the switching elements Q1 to Q8 to turn them on and off so that the voltage value (detected value) of the output voltage V2 approaches the operation command value (output voltage control during forward power transmission). During charge discharge control, the control unit 12 does not generate an operation command value, but controls the switching elements Q1 to Q8 to turn them on and off so that the output voltage V2 becomes 0[V]. Note that an operation command value may also be generated during charge discharge control so that the output voltage V2 becomes 0[V].

[0042] At time t1, the power transmission device 30 starts an insulation diagnosis and transmits an external command value (command value = voltage value X1 [V]) to the control unit 12. Upon receiving the external command value, the control unit 12 raises the operation command value to the voltage value X1 at a predetermined slope and switches the switching elements Q1 to Q8 on and off to raise the output voltage V2 according to the operation command value. The voltage value X1 is, for example, 150 [V].

[0043] At time t2, the power transmission device 30 transmits an external command value (command value = voltage value X2 [V]) to the control unit 12. Upon receiving the external command value, the control unit 12 raises the operation command value to the voltage value X2 at a predetermined rate and switches the switching elements Q1 to Q8 on and off to raise the output voltage V2 according to the operation command value. The control unit 12 generates the operation command value such that the time during which the operation command value becomes the voltage value X2 is secured for a predetermined time (for example, 1 second). The output voltage V2 rises in accordance with the operation command value and reaches the voltage value X2. The voltage value X2 is, for example, 450 [V].

[0044] At time t3, the power transmission device 30 completes the insulation diagnosis and transmits an external command value (command value = 0[V]) to the control unit 12. Upon receiving the external command value of 0[V], the control unit 12 starts charge discharge control.

[0045] At time t4, when the output voltage V2, i.e., the terminal voltage of capacitor C12, drops to 0[V], the control unit 12 terminates the charge discharge control. Note that the terminal voltage of capacitor C12 at the end of the charge discharge control does not need to be 0[V]; it can be any voltage value up to, for example, 150[V].

[0046] During charge discharge control, the control unit 12 performs freewheel control, which controls switching elements Q1 to Q4 so that a freewheel current flows through the first bridge circuit 14; frequency modulation control, which modulates the switching frequencies of switching elements Q5 to Q8; and phase shift control, which modulates the phase difference between the third leg (switching elements Q5 and Q6) and the fourth leg (switching elements Q7 and Q8).

[0047] During recirculation control, the control unit 12 keeps switching elements Q1 and Q3 continuously off while keeping switching elements Q2 and Q4 continuously on during the period from time t3 to time t4. As a result, recirculation current flows through the first bridge circuit 14 via switching elements Q2 and Q4.

[0048] Incidentally, in the second bridge circuit 17 during charge discharge control, it is necessary to suppress surge voltages generated in the switching elements Q5 to Q8. Surge voltages are generated particularly when the switching elements Q5 to Q8 are turned off and depend on the terminal voltage of capacitor C12 and the current flowing through the current paths of the switching elements Q5 to Q8. For this reason, the control unit 12 during charge discharge control controls the current according to the terminal voltage of capacitor C12 by performing frequency modulation control and phase shift control on the second bridge circuit 17, thereby suppressing surge voltages generated in the switching elements Q5 to Q8.

[0049] Fig. 4(A) shows the relationship between the switching frequency of the switching elements Q5 to Q8 and the terminal voltage of the capacitor C12 during frequency modulation control. Fig. 4(B) shows the relationship between the phase shift amount and the switching frequency during phase shift control. Fig. 4(C) shows the time change of the reflux current during reflux control.

[0050] The control unit 12 starts frequency modulation control and phase shift control at the time t3 when the charge discharge control starts. The control unit 12 that has started frequency modulation control acquires the voltage value of the terminal voltage of the capacitor C12 at a predetermined cycle, and determines the switching frequency of the switching elements Q5 to Q8 based on the voltage value of the terminal voltage.

[0051] As shown in Fig. 4(A), when the terminal voltage of the capacitor C12 is X2 [V] (for example, 450 [V]), the control unit 12 sets the switching frequency to f2 [kHz], and decreases the switching frequency as the terminal voltage decreases. When the terminal voltage is 0 [V], the switching frequency is set to f1 [kHz] (where the resonance frequency < f1 < f2). That is, the control unit 12 decreases the switching frequency in response to the decrease in the terminal voltage of the capacitor C12 from the start point of the charge discharge control.

[0052] In this embodiment, the switching frequency is denoted as f(V), and the terminal voltage of the capacitor C12 is denoted as V C12 Then, when C12 V ≧ Vth, the control unit 12 determines f(V) based on the following equation (1), and when C12 V < Vth, the control unit 12 determines f(V) based on the following equation (2). Vth is an arbitrary voltage value set within a range greater than 150 [V] and less than 450 [V].

[0053]

Equation

[0054]

Equation

[0055] In this embodiment, equation (1) is set as a quadratic function of the terminal voltage of capacitor C12, and equation (2) is set as a cubic function of the terminal voltage V C12 of capacitor C12. However, if the switching frequency f(V) can be decreased as the terminal voltage V C12 decreases, equations (1) and / or (2) can be changed as appropriate.

[0056] The control unit 12 that determines the switching frequency by frequency modulation control determines the phase shift amount of the phase shift control based on the switching frequency. The phase shift amount is the phase difference between the third leg (switching elements Q5, Q6) and the fourth leg (switching elements Q7, Q8). The phase shift amount (phase difference) is an angle with respect to one cycle (= 360 [°]) of the switching frequency, and has a value [°] in the range from 0 [°] to a maximum of 180 [°].

[0057] As shown in FIG. 4(B), the control unit 12 fixes the phase shift amount to θ2 when the switching frequency of the switching elements Q5 to Q8 is f4 [kHz] or more, and fixes the phase shift amount to θ1 (where θ1 < θ2) when the switching frequency is less than f3 [kHz] (however, f3 < f4). When the switching frequency is less than f4 and more than f3, the control unit 12 decreases the phase shift amount as the switching frequency decreases. θ2 is, for example, 145 [°], and θ1 is, for example, 0 [°]. That is, the control unit 12 starts the phase shift control from the start point of the charge discharge control, and modulates the phase shift amount when the switching frequency is included in a preset frequency band (when it is less than f4 and more than f3).

[0058] In this embodiment, when the phase shift amount is Δθ, the control unit 12 determines Δθ based on the following equation (3) when the switching frequency is less than f4 and more than f3.

[0059]

Equation

[0060] As shown in Figure 4(C), the return current flowing through the primary coil N1 of the transformer Tr and the first bridge circuit 14 becomes a current with a large absolute value over time, within the range of ±Y[A]. This is because when the switching frequency decreases due to frequency modulation control, the impedance decreases, and the current flowing through the current paths of switching elements Q5 to Q8 increases. Similarly, when the amount of phase shift decreases due to phase shift control, the current flowing through the current paths of switching elements Q5 to Q8 also increases.

[0061] When the terminal voltage of capacitor C12 is high, that is, when the switching frequency is high and the phase shift is large, the current flowing through the current paths of switching elements Q5 to Q8 becomes small. As described above, the surge voltage depends on the terminal voltage of capacitor C12 and the current flowing through the current paths of switching elements Q5 to Q8, so in this embodiment, the surge voltage generated in switching elements Q5 to Q8 can be suppressed.

[0062] Figure 5 shows the control timing of switching elements Q1 to Q8 during charge discharge control. The control unit 12 repeatedly performs control of modes 1 to 4 during charge discharge control. Switching elements Q1 to Q8 are turned on when the control signals for switching elements Q1 to Q8 shown in Figure 5 are high level (H) and turned off when they are low level (L).

[0063] For simplicity, Figure 5 omits the description of dead time. In actual control, there is a time for soft switching and a pass-through prevention time (for example, a pass-through prevention time for switching elements Q5 and Q6) when the upper and lower arms of the same leg switch from off to on (for example, from the turn-off of switching element Q6 to the turn-on of switching element Q5, or from the turn-off of switching element Q5 to the turn-on of switching element Q6). The same applies to switching elements Q7 and Q8. The on-duty cycle of switching elements Q5 to Q8 decreases by the dead time, for example from 50%, or the off-duty cycle of switching elements Q5 to Q8 increases by the dead time, for example from 50%.

[0064] The control signals for switching element Q1 and switching element Q3 are always at a low level. On the other hand, the control signals for switching element Q2 and switching element Q4 are always at a high level. The control signals for switching element Q5 and switching element Q6 have a phase difference of 180°, excluding the dead time, and the control signals for switching element Q8 and switching element Q7 also have a phase difference of 180°, excluding the dead time. The on-duty cycle of switching elements Q5 to Q8 is set to 50%, excluding the dead time.

[0065] If the period of the switching frequency is T, the ON timing of the control signal of switching element Q8 is delayed by △T compared to the ON timing of the control signal of switching element Q5. Similarly, the ON timing of the control signal of switching element Q7 is delayed by △T compared to the ON timing of the control signal of switching element Q6. The period of the switching frequency T is calculated as T = 1 / f(V), and △T is calculated as △T = (△θ / 360) × T. f(V) is the switching frequency determined by frequency modulation control, and △θ is the phase shift amount determined by phase shift control.

[0066] Figures 6 and 7 show the current flow during each mode period in the control timing diagram of Figure 5. Figure 6(A) shows the current flow during mode 4, Figure 6(B) shows the current flow during mode 1, Figure 7(A) shows the current flow during mode 2, and Figure 7(B) shows the current flow during mode 3. Note that the currents shown in Figures 6 and 7 are the discharge current (resonant current) and the recirculation current, and the excitation current is not shown. Also, the currents during the on / off state of switching elements Q5 to Q8 (transient currents) are not shown.

[0067] During mode 4, switching elements Q5 and Q8 are in the off state, and switching elements Q6 and Q7 are in the on state. As shown in Figure 6(A), the terminal voltage of capacitor C12 is applied to the second bridge circuit 17. The discharge current (resonant current) of capacitor C12 flows through switching element Q7, second resonant capacitor Cr2, secondary coil N2, second resonant inductor Lr2, and switching element Q6. In the first bridge circuit 14, a return current flows through switching elements Q2 and Q4.

[0068] During mode 1, switching elements Q5 and Q7 are ON, and switching elements Q6 and Q8 are OFF. As shown in Figure 6(B), in the second bridge circuit 17, the discharge current (resonant current) of capacitor C12 continues to flow through switching elements Q5 and Q7, but gradually decreases to zero. The return current of the first bridge circuit 14 continues to flow through switching elements Q2 and Q4, but similar to the discharge current, gradually decreases to zero.

[0069] During mode 2, switching elements Q5 and Q8 are ON, and switching elements Q6 and Q7 are OFF. As shown in Figure 7(A), the terminal voltage of capacitor C12 is applied to the second bridge circuit 17. The discharge current (resonant current) of capacitor C12 flows through switching element Q5, second resonant inductor Lr2, secondary coil N2, second resonant capacitor Cr2, and switching element Q8. In the first bridge circuit 14, a reverse return current flows through switching elements Q2 and Q4, opposite to the current during mode 4.

[0070] During mode 3, switching elements Q5 and Q7 are in the off state, while switching elements Q6 and Q8 are in the on state. As shown in Figure 7(B), in the second bridge circuit 17, the discharge current (resonant current) of capacitor C12 continues to flow through switching elements Q6 and Q8, but gradually decreases to zero. The return current of the first bridge circuit 14 continues to flow through switching elements Q2 and Q4, but similar to the discharge current, gradually decreases to zero.

[0071] As described above, in the power conversion system 1A according to this embodiment, the control unit 12 of the first power conversion device 10 performs freewheeling control on the first bridge circuit 14 and frequency modulation control and phase shift control on the second bridge circuit 17 when controlling the charge discharge of capacitor C12. In the first power conversion device 10, an additional charge discharge circuit for discharging the charge of capacitor C12 is not required, thus avoiding increased costs and size of the device, and furthermore, surge voltages generated in switching elements Q5 to Q8 can be suppressed.

[0072] [Second Embodiment] Figure 8 shows a power conversion system 1B according to a second embodiment of the present invention. The power conversion system 1B includes a first power conversion device 10, a power transmission device 30, a power conditioner device 40, and an energy storage device 50. The power conversion system 1B is, for example, a distributed power supply system.

[0073] The power conversion system 1B has the same configuration as the power conversion system 1A of the first embodiment, except that it includes a power conditioner device 40 and an energy storage device 50 instead of the second power conversion device 20 of the first embodiment.

[0074] The power conditioner unit 40 is connected to the first power converter 10, the energy storage device 50, the AC power supply 2, and the solar power generation device 4. The power conditioner unit 40 performs AC / DC conversion to convert AC voltage to DC voltage, DC / AC conversion to convert DC voltage to AC voltage, and DC / DC conversion to boost or step down DC voltage for output. For example, the power conditioner unit 40 charges and discharges the energy storage device 50, extracts DC voltage from the solar power generation device 4, and supplies AC voltage to a load connected to the AC power supply 2 (for example, a household load).

[0075] The energy storage device 50 is a stationary energy storage device installed and used in a predetermined location, and includes at least one rechargeable battery configured to be rechargeable and dischargeable, and a battery management system for managing the rechargeable battery. For example, a lithium-ion rechargeable battery is used as the rechargeable battery, but a rechargeable battery other than a lithium-ion rechargeable battery may also be used.

[0076] In the power conversion system 1B according to this embodiment, similar to the first embodiment, the control unit 12 of the first power conversion device 10 performs freewheeling control on the first bridge circuit 14 and frequency modulation control and phase shift control on the second bridge circuit 17 when controlling the charge discharge of capacitor C12. As a result, the first power conversion device 10 does not require an additional charge discharge circuit to discharge the charge of capacitor C12, thereby avoiding increased costs and size of the device, and further suppressing surge voltages generated in switching elements Q5 to Q8.

[0077] Although embodiments of the power conversion device and power conversion system according to the present invention have been described above, the present invention is not limited to the above embodiments.

[0078] The power conversion device according to the present invention is a current-resonant type power conversion device comprising a primary terminal and a secondary terminal, a main circuit section provided between the primary terminal and the secondary terminal, and a control section for controlling the main circuit section, wherein the main circuit section includes a first bridge circuit connected to the primary terminal, each leg including a first leg and a second leg connected in parallel, each leg including an upper arm and a lower arm connected in series, each arm including a first switching element, a first resonant circuit connected to the primary terminal, each including a first resonant inductor and a first resonant capacitor, a transformer including a primary coil and a secondary coil, the primary coil connected to the first resonant circuit, a second resonant circuit connected to the secondary coil, each including a second resonant inductor and a second resonant capacitor, and a third leg and a fourth leg connected in parallel, each leg including an upper arm connected in series The circuit includes a second bridge circuit, which includes a frame and a lower arm, each arm including a second switching element, and is connected to a second resonant circuit; and a smoothing circuit, which includes a capacitor for smoothing the output of the second bridge circuit, and outputs the terminal voltage of the capacitor as the output voltage from the secondary terminal. The control unit controls the first and second switching elements and performs charge discharge control to discharge the charge stored in the capacitor and consume the charge in the main circuit section. During charge discharge control, the control unit performs freewheel control to control the first switching element so that a freewheel current flows through the first bridge circuit; frequency modulation control to modulate the switching frequency of the second switching element; and phase shift control to modulate the phase difference between the second switching element of the third leg and the second switching element of the fourth leg. The configuration can be changed as appropriate.

[0079] For example, in the above embodiment, frequency modulation control and phase shift control are started from the start of charge discharge control, but if the surge voltage generated in the switching elements Q5 to Q8 can be suppressed, frequency modulation control and / or phase shift control can be performed at any period of charge discharge control.

[0080] In the above embodiment, the control unit 12 during recirculation control is in a first state where switching elements Q1 and Q3 are in the off state and switching elements Q2 and Q4 are in the on state. However, it may also be in a second state where switching elements Q1 and Q3 are in the on state and switching elements Q2 and Q4 are in the off state, or it may alternately switch between the first and second states. Furthermore, the control unit 12 during recirculation control may be in the on state of only one of the switching elements Q1 to Q4, or it may be possible to switch between the on-state switching elements within the switching elements Q1 to Q4.

[0081] Furthermore, the power conversion system according to the present invention can be appropriately modified in configuration as long as it includes a power conversion device and a power transmission device, one end of which is connected to the secondary terminal of the power conversion device and the other end of which is connected to a vehicle equipped with a battery, and which transmits power between the power conversion device and the battery.

[0082] In the above embodiment, charge discharge control is started after the insulation diagnosis is completed, but the power conversion device of the present invention can perform charge discharge control when it is necessary to discharge the charge of the capacitor. [Explanation of Symbols]

[0083] 1A, 1B Power Conversion System 2 AC power supply 3. Electric vehicles 4. Solar power generation equipment 10. First power converter 11 Main circuit section 12 Control Unit 13 1st smoothing circuit 14. First Bridge Circuit 15 1st resonant circuit 16 Second resonant circuit 17. Second Bridge Circuit 18 Second smoothing circuit 20. Second Power Converter 30 Power transmission equipment 40 Power Conditioner Unit 50 Energy storage devices

Claims

1. Primary terminal and secondary terminal, A main circuit section is provided between the primary terminal and the secondary terminal, A control unit that controls the main circuit section, A current-resonant type power converter equipped with, The main circuit section is, A first bridge circuit is connected to the primary terminal, and includes a first leg and a second leg connected in parallel, each leg including an upper arm and a lower arm connected in series, each arm including a first switching element, A first resonant circuit, which includes a first resonant inductor and a first resonant capacitor and is connected to the first bridge circuit, A transformer including a primary coil and a secondary coil, wherein the primary coil is connected to the first resonant circuit, A second resonant circuit, which includes a second resonant inductor and a second resonant capacitor and is connected to the secondary coil, A second bridge circuit is connected to the second resonant circuit, including a third and fourth leg connected in parallel, each leg including an upper arm and a lower arm connected in series, each arm including a second switching element, The system includes a smoothing circuit that includes a capacitor for smoothing the output of the second bridge circuit, and outputs the terminal voltage of the capacitor as the output voltage from the secondary side terminal, The control unit, The first switching element and the second switching element are controlled to discharge the charge stored in the capacitor, and charge discharge control is performed to consume the charge in the main circuit section. The control unit during charge discharge control, Recirculation control controls the first switching element so that a recirculating current flows through the first bridge circuit, Frequency modulation control for modulating the switching frequency of the second switching element, The following is performed: Phase shift control is performed to modulate the phase difference between the second switching element of the third leg and the second switching element of the fourth leg. A power conversion device characterized by the following features.

2. The control unit during the frequency modulation control, The switching frequency is modulated according to the terminal voltage such that the switching frequency decreases as the terminal voltage decreases. The power conversion device according to feature 1.

3. The control unit during the phase shift control, The phase difference is modulated according to the switching frequency such that the phase difference decreases as the switching frequency decreases. The power conversion device according to feature 1.

4. The control unit during charge discharge control, The frequency modulation control and phase shift control are started from the start of the charge discharge control. If the switching frequency falls within a preset frequency band, the phase difference is modulated by the phase shift control. If the switching frequency does not fall within the frequency band, the phase difference is fixed. The power conversion device according to feature 1.

5. A power conversion device according to any one of claims 1 to 4, A power transmission device is connected on one side to the secondary terminal of the power converter and on the other side to a vehicle equipped with a battery, and performs power transmission between the power converter and the battery. A power conversion system including, The aforementioned power transmission device is The connector portion connected to the aforementioned vehicle, A cable portion connecting the connector portion and the secondary terminal, The system includes a power transmission control unit that performs insulation testing on the connector and cable while the connector is connected to the vehicle, The control unit of the power converter is During the insulation diagnosis, the capacitor is charged to raise the output voltage to a predetermined set voltage value, and after the insulation diagnosis is completed, the charge discharge control is started. A power conversion system characterized by the following features.

6. Stationary energy storage devices, The power conditioner device further includes having the function of performing charging and discharging operations on the energy storage device and the function of supplying a DC voltage to the primary terminal of the power converter. The power conversion system according to feature 5.

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