Isolated DC-DC converter, its control method, and power conversion system
The isolated DC-DC converter addresses the issues of circuit size and cost by using a switching unit and control unit to adjust voltages during preparatory operations, achieving efficient and rapid capacitor voltage control.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- OMRON CORP
- Filing Date
- 2021-11-02
- Publication Date
- 2026-06-23
Smart Images
Figure 0007877660000001 
Figure 0007877660000002 
Figure 0007877660000003
Abstract
Description
Technical Field
[0001] The present invention relates to an isolated DCDC converter, a control method thereof, and a power conversion system.
Background Art
[0002] A conventional isolated DCDC converter includes switching circuits each composed of a plurality of switches on both sides of a transformer for electrical isolation, and smoothing capacitors are provided outside them respectively. When there is a potential difference between the pair of smoothing capacitors, there is a problem that a large current flows during the operation of the DCDC converter and components are damaged. To solve this problem, it is necessary to adjust the voltages of the pair of smoothing capacitors as an operation before starting operation. For example, during discharge, the voltage of the smoothing capacitor is reduced by connecting it to a charge-consuming resistor via a switch. Also, during charging, it was connected to a charge-consuming resistor via a switch to prevent inrush current.
[0003] For example, Patent Document 1 discloses a power conversion device and a control method that can start operation without generating an excessive current in the components constituting the DC / DC converter even when there is a voltage difference between two capacitors. This power conversion device includes an isolated DC / DC converter that converts one DC power into another DC power via AC power. The isolated DC / DC converter includes a first capacitor connected to a first conduction path of one DC power, a second capacitor connected to a second conduction path of the other DC power, and a first current limiting circuit that suppresses the current flowing through a third conduction path of the AC power. Specifically, in the power conversion device of Patent Document 1, as a preliminary charge before starting operation, when there is a potential difference between the input smoothing section and the output smoothing section, the switch of the current limiting circuit is turned off, and current flows through the current limiter and is controlled to be limited.
[0004] Furthermore, Patent Document 2 discloses a control circuit for an isolated DC / DC converter that safely charges the capacitor voltage while suppressing inrush current during pre-charging, without providing a current detection sensor or an overcurrent prevention circuit. This control circuit for the isolated DC / DC converter performs voltage control according to the deviation between the first capacitor voltage and the second capacitor voltage. Based on the result of the voltage control, it generates gate signals for multiple semiconductor switch elements provided in the isolated DC / DC converter. Specifically, the control circuit for the isolated DC / DC converter in Patent Document 2 performs voltage control according to the voltage deviation between the input smoothing section and the output smoothing section as pre-charging before starting operation, determines the phase difference, and controls multiple semiconductor switch elements to prevent overcurrent from flowing. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2017-118806 [Patent Document 2] Japanese Patent Publication No. 2021-078274 [Overview of the Initiative] [Problems that the invention aims to solve]
[0006] However, conventional isolated DC-DC converters require the inclusion of charge-dissipating resistors and switches, which increases the circuit size and thus the circuit cost.
[0007] Furthermore, the power conversion device described in Patent Document 1 required the provision of a current limiting circuit, which resulted in increased circuit size and increased circuit costs.
[0008] Furthermore, the control circuit for the isolated DC / DC converter described in Patent Document 2 had the problem that the control sequence of the control circuit was complex, resulting in a long processing time when implemented in a microcomputer or the like.
[0009] The object of the present invention is to solve the above problems and to provide an isolated DC-DC converter, a control method thereof, and a power conversion system that can control the voltage of a smoothing capacitor in a relatively short time within a predetermined operating time, with a simpler configuration compared to the conventional technology, during the preparatory operation before the operation of the isolated DC-DC converter. [Means for solving the problem]
[0010] An isolated DC-DC converter according to one aspect of the present invention is: A first smoothing section including a first capacitor for smoothing the input voltage, A switching unit comprising an isolation transformer, an inductor, a switching circuit on the primary side of the isolation transformer, and a switching circuit on the secondary side of the isolation transformer, wherein the switching unit switches the smoothed voltage to convert it into power to a predetermined output voltage, A second smoothing unit including a second capacitor for smoothing the power-converted output voltage, An isolated DC-DC converter comprising the switching unit and a control unit that controls preparatory operations before starting operation, In the preparatory operation before starting operation, the control unit controls the switching unit to adjust the input voltage and the output voltage based on the input voltage and the output voltage so that the inductor current flowing through the inductor is less than a predetermined upper limit. [Effects of the Invention]
[0011] Accordingly, according to one aspect of the present invention, in the preparation operation before the operation of the isolated DC-DC converter, the voltage of the smoothing capacitor can be controlled in a relatively short time within a predetermined operating time with a simpler configuration compared to the conventional technology. [Brief explanation of the drawing]
[0012] [Figure 1] This is a block diagram showing an example configuration of a power conversion system according to the embodiment. [Figure 2]Figure 1 is a circuit diagram showing an example configuration of an isolated DC-DC converter 2. [Figure 3] Figure 2 is a flowchart showing the pre-operation preparation process performed by the control unit 10. [Figure 4A] Figure 2 shows the timing charts for each signal in an isolated DC-DC converter 2, illustrating an example of operation when the inductor current IL is continuous due to boost switching and synchronous rectification is performed. [Figure 4B] Figure 2 shows the timing charts for each signal in an isolated DC-DC converter 2, illustrating an example of operation when the inductor current IL is continuous due to boost switching and there is no synchronous rectification. [Figure 5A] Figure 2 shows the timing charts for each signal in an isolated DC-DC converter 2, illustrating an example of operation when the inductor current IL is discontinuous during boost switching and synchronous rectification is performed. [Figure 5B] Figure 2 shows the timing charts for each signal in an isolated DC-DC converter 2, illustrating an example of operation when the inductor current IL is discontinuous during boost switching and there is no synchronous rectification. [Figure 6] Figure 2 shows the timing chart of the inductor current IL in the isolated DC-DC converter 2 when the inductor current IL is at its maximum value during boost switching and the inductor current IL is continuous. [Figure 7] Figure 2 shows the timing chart of the inductor current IL in the isolated DC-DC converter 2 when the inductor current IL is at its maximum value during boost switching and is discontinuous. [Figure 8A] Figure 2 shows the timing charts for each signal in an isolated DC-DC converter 2, illustrating an example of operation when the inductor current IL is continuous due to step-down switching and synchronous rectification is enabled. [Figure 8B] Figure 2 shows the timing charts for each signal in an isolated DC-DC converter 2, illustrating an example of operation when the inductor current IL is continuous due to step-down switching and there is no synchronous rectification. [Figure 9A]In the isolated DCDC converter 2 of FIG. 2, this is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-down switching and there is synchronous rectification. [Figure 9B] In the isolated DCDC converter 2 of FIG. 2, this is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-down switching and there is no synchronous rectification. [Figure 10] In the isolated DCDC converter 2 of FIG. 2, this is a timing chart of the inductor current IL when the inductor current IL is at its maximum value in step-down switching and the inductor current IL is continuous. [Figure 11] In the isolated DCDC converter 2 of FIG. 2, this is a timing chart of the inductor current IL when the inductor current IL is at its maximum value in step-down switching and the inductor current IL is discontinuous. [Figure 12] This is a flowchart showing the pre-charge control process (outline control flow) executed by the control unit 10 of FIG. 2. [Figure 13] This is a diagram showing a table of charge and discharge control modes executed by the switching unit 9 of FIG. 2. [Figure 14A] This is a flowchart showing the first part of the pre-charge control process (detailed control flow) executed by the control unit 10 of FIG. 2. [Figure 14B] This is a flowchart showing the second part of the pre-charge control process (detailed control flow) executed by the control unit 10 of FIG. 2. [Figure 14C] This is a flowchart showing the third part of the pre-charge control process (detailed control flow) executed by the control unit 10 of FIG. 2. [Figure 15] This is a simulation result of the isolated DCDC converter 2 of FIG. 2 and is a timing chart of each signal. [Figure 16] This is a block diagram showing a configuration example of a power conversion system according to a modified example.
Embodiments for Carrying Out the Invention
[0013] Embodiments and modified examples of the present invention will be described below with reference to the drawings. The same or similar components are denoted by the same reference numerals.
[0014] (Embodiment) Figure 1 is a block diagram showing an example configuration of a power conversion system according to an embodiment. In Figure 1, the power conversion system according to the embodiment comprises, for example, a battery 1 mounted on an electric vehicle (EV), an isolated DC-DC converter 2 having an isolation transformer that converts the DC voltage from the battery 1 to a predetermined DC voltage, and a DC-AC inverter device 3 that converts the DC voltage from the isolated DC-DC converter 2 to an AC voltage by switching and outputs it to a power system or a load 4. Here, the power system or load 4 is the power system 4 during grid-connected operation and the load 4 during standalone operation.
[0015] In Figure 1, when the battery 1 is discharged, the isolated DC-DC converter 2 converts the DC voltage output from the battery 1 to AC voltage (DCAC), then converts the AC voltage back to DC voltage (ACDC) and outputs it, thus forming a so-called step-up / step-down converter. The DC-AC inverter 3 converts the DC voltage to AC voltage and outputs it to the power system 4 during grid-connected operation and to the load 4 during standalone operation.
[0016] Figure 2 is a circuit diagram showing an example configuration of the isolated DC-DC converter 2 of Figure 1. In Figure 2, the isolated DC-DC converter 2 has the following configuration between each pair of terminals T11, T12; T13, T14: (1) Switches SW1 and SW2 controlled by the control unit 10, (2) A voltage detection unit 11 detects the voltage V1 between terminals T11 and T12 and outputs the detected voltage V1 to the control unit 10, (3) The first smoothing section is a smoothing capacitor C1, (4) A switching unit 9 including switching circuits 7, 8, an inductor L, an isolation transformer TR having a primary winding L1 and a secondary winding L2, and a current detection unit 13, (5) The second smoothing section is a smoothing capacitor C2, (6) A voltage detection unit 12 detects the voltage V2 between terminals T13 and T14 and outputs the detected voltage V2 to the control unit 10, It is composed of the following features.
[0017] Here, terminal T11 is connected via switch SW1 to one end of the voltage detection unit 11, one end of the smoothing capacitor C1, and one end of the switching circuit 7. Terminal T12 is connected via switch SW2 to the other end of the voltage detection unit 11, the other end of the smoothing capacitor C1, and the other end of the switching circuit 7. Terminal T13 is connected to one end of the voltage detection unit 12, one end of the smoothing capacitor C2, and one end of the switching circuit 8. Terminal T14 is connected to the other end of the voltage detection unit 12, the other end of the smoothing capacitor C2, and the other end of the switching circuit 8.
[0018] Switching circuit 7 includes four switching elements Q1 to Q4, each consisting of reverse-conducting diodes D1 to D4 connected in parallel in a bridge configuration, and is made up of MOSFETs, for example. It switches the input DC voltage according to gate control signals Sg1 to Sg4, which are PWM signals from control unit 10, and outputs an AC voltage. Switching circuit 8 also includes four switching elements Q5 to Q8, each consisting of reverse-conducting diodes D5 to D8 connected in parallel in a bridge configuration, and is made up of MOSFETs, for example. It switches the input DC voltage according to gate control signals Sg5 to Sg8, which are PWM signals from control unit 10, and outputs an AC voltage.
[0019] The connection point between the source of switching element Q1 and the drain of switching element Q3 in switching circuit 7 is connected to the connection point between the source of switching element Q2 and the drain of switching element Q4 in switching circuit 7 via the current detection unit 13, inductor L, and the primary winding L1 of transformer TR. Furthermore, the connection point between the source of switching element Q5 and the drain of switching element Q7 in switching circuit 8 is connected to the connection point between the source of switching element Q6 and the drain of switching element Q8 in switching circuit 8 via the secondary winding L2 of transformer TR.
[0020] In the isolated DC-DC converter 2 configured as described above, the DC voltage output from the battery 1 is input to the switching unit 9 via terminals T11, T12, switches SW1, SW2, voltage detection unit 11, and smoothing capacitor C1. The switching unit 9 is controlled by the control unit 10, converts the input DC voltage to an AC voltage, then converts the converted AC voltage back to a DC voltage, and outputs it via smoothing capacitor C2, voltage detection unit 12, and terminals T13, T14. Here, switches SW1 and SW2 are turned on when the battery 1 is being charged or discharged, and turned off when not in operation. Smoothing capacitors C1 and C2 each smooth the input DC voltage to minimize the ripple before outputting it. Note that smoothing capacitor C1 requires rapid discharge after the isolated DC-DC converter 2 stops operating, while smoothing capacitor C2 has a larger capacitance than smoothing capacitor C1 and does not require rapid discharge after the isolated DC-DC converter 2 stops operating.
[0021] The voltage detection unit 11 detects the voltage V1 across the smoothing capacitor C1 and outputs it to the control unit 10. The voltage detection unit 12 also detects the voltage V2 across the smoothing capacitor C2 and outputs it to the control unit 10. Furthermore, the current detection unit 13 detects the inductor current IL flowing through the inductor L and outputs it to the control unit 10. The control unit 10 controls switches SW1 and SW2, and based on the detected voltages V1 and V2 and the inductor current IL, generates and outputs gate control signals Sg1 to Sg8 for switching elements Q1 to Q8, thereby operating the isolated DC-DC converter 2 as a bidirectional converter during normal operation, and before starting operation, it performs the "preparation process before starting operation" shown in Figure 3.
[0022] Figure 3 is a flowchart showing the pre-operation preparation process performed by the control unit 10 in Figure 2.
[0023] In step S1 of Figure 3, a fault diagnosis process is performed. Specifically, switches SW1 and SW2 are turned off, and the voltage V1 of the smoothing capacitor C1 is charged to the voltage Va required for fault diagnosis. Next, in step S2, an insulation diagnosis process is performed. Specifically, switches SW1 and SW2 are turned off, and the voltage V1 of the smoothing capacitor C1 is charged to the voltage Vb required for insulation diagnosis. Furthermore, in step S3, a voltage adjustment process is performed before connecting to the battery 1. Specifically, switches SW1 and SW2 are turned off, and the voltage V1 of the capacitor C1 is discharged (Figure 13) to a voltage below the voltage of the battery 1. In step S4, a voltage adjustment process is performed before operation of the DC-AC inverter device 3. Specifically, switches SW1 and SW2 are turned on, and the voltage V2 of the capacitor C2 is charged (Figure 13) to the voltage Vc required for operation of the DC-AC inverter device 3.
[0024] Figure 4A is a timing chart of each signal showing an example of operation in the isolated DC-DC converter 2 of Figure 2 when the inductor current IL is continuous due to boost switching and synchronous rectification is performed. Figure 4B is a timing chart of each signal showing an example of operation in the isolated DC-DC converter 2 of Figure 2 when the inductor current IL is continuous due to boost switching and synchronous rectification is not performed. Note that when each gate control signal Sg1 to Sg8 is 1 (high level), each switching element Q1 to Q8 is turned on, while when each gate control signal Sg1 to Sg8 is 0 (low level), each switching element Q1 to Q8 is turned off, and so on.
[0025] Figures 4A and 4B show the inductor current IL when the switching elements Q1 to Q8 of switching circuits 7 and 8 are driven by gate control signals Sg1 to Sg8, respectively. Tdead is the dead time Tdead set for each switching element Q1 to Q8 to prevent shoot-through current. Tφ is the phase shift amount, which will be described in detail later. As is clear from comparing Figures 4A and 4B, the gate control signals Sg5 to Sg8 differ depending on whether synchronous rectification is present or not.
[0026] Figure 5A is a timing chart of each signal showing an example of operation in the isolated DC-DC converter 2 of Figure 2 when the inductor current IL is discontinuous during boost switching and synchronous rectification is performed. Figure 5B is a timing chart of each signal showing an example of operation in the isolated DC-DC converter 2 of Figure 2 when the inductor current IL is discontinuous during boost switching and synchronous rectification is not performed.
[0027] Figures 5A and 5B show the inductor current IL when the switching elements Q1 to Q8 of switching circuits 7 and 8 are driven by gate control signals Sg1 to Sg8, respectively. Tdead is the dead time Tdead set to prevent shoot-through current in each switching element Q1 to Q8. As is clear from comparing Figures 5A and 5B, the gate control signals Sg5 to Sg8 differ depending on whether synchronous rectification is present or not.
[0028] Figure 6 is a timing chart of the inductor current IL in the isolated DC-DC converter 2 of Figure 2, when the inductor current IL is at its maximum value during boost switching and the inductor current IL is continuous.
[0029] In Figure 6, the currents ΔI1, ΔI2, ΔI3, on-times Ton, Ton2, and off-time Toff are expressed by the following equations.
[0030] ΔI1 = (Vin × Ton) / L ΔI² = (Vin - Vout) · Toff / L ΔI3 = -(Vin + Vout)·Ton² / L Ton = Tφ - Ton² Ton2 ={-(Toff·Vout)+(Tφ+Toff)·Vin} (Vout + 2·Vin) Toff = T / 2 - Tφ
[0031] Here, Vin is the input voltage, Vout is the output voltage, and L is the inductance of the inductor L.
[0032] Figure 7 is a timing chart of the inductor current IL in the isolated DC-DC converter 2 of Figure 2 when the inductor current IL is at its maximum value during boost switching and when the inductor current IL is discontinuous.
[0033] In Figure 7, the current ΔI1, on-time Ton, and off-time Toff1 are expressed by the following equations. Note that the theoretical formula for the maximum current differs depending on whether the inductor current IL is continuous or discontinuous, but for the sake of simplifying calculations, the theoretical formula for discontinuous current is used as a guideline for the maximum current.
[0034] ΔI1=(Vin·Ton) / L Ton=Tφ-Tdead Toff1 = (Vin·Ton) / (Vout-Vin)
[0035] Figure 8A is a timing chart of each signal showing an example of operation in the isolated DC-DC converter 2 of Figure 2 when the inductor current IL is continuous with step-down switching and synchronous rectification is performed. Figure 8B is a timing chart of each signal showing an example of operation in the isolated DC-DC converter 2 of Figure 2 when the inductor current IL is continuous with step-down switching and synchronous rectification is not performed.
[0036] Figures 8A and 8B show the inductor current IL when the switching elements Q1 to Q8 of switching circuits 7 and 8 are driven by gate control signals Sg1 to Sg8, respectively. Tdead is the dead time Tdead set for each switching element Q1 to Q8 to prevent shoot-through current. Tφ is the phase shift amount, which will be described in detail later. As is clear from comparing Figures 8A and 8B, the gate control signals Sg5 to Sg8 differ depending on whether synchronous rectification is present or not.
[0037] Figure 9A is a timing chart of each signal showing an example of operation in the isolated DC-DC converter 2 of Figure 2 when the inductor current IL is discontinuous during step-down switching and synchronous rectification is performed. Figure 9B is a timing chart of each signal showing an example of operation in the isolated DC-DC converter 2 of Figure 2 when the inductor current IL is discontinuous during step-down switching and synchronous rectification is not performed.
[0038] Figures 9A and 9B show the inductor current IL when the switching elements Q1 to Q8 of switching circuits 7 and 8 are driven by gate control signals Sg1 to Sg8, respectively. Tdead is the dead time Tdead set to prevent shoot-through current in each switching element Q1 to Q8. As is clear from comparing Figures 9A and 9B, the gate control signals Sg5 to Sg8 differ depending on whether synchronous rectification is present or not.
[0039] Figure 10 is a timing chart of the inductor current IL in the isolated DC-DC converter 2 of Figure 2, when the inductor current IL is at its maximum value during step-down switching and the inductor current IL is continuous.
[0040] In Figure 10, the currents ΔI1, ΔI2, ΔI3, on-times Ton, Ton2, and off-time Toff are expressed by the following equations.
[0041] ΔI1 = (Vin - Vout) · Ton / L ΔI² = -(Vout·Toff) / L ΔI3 = -(Vin + Vout)·Ton² / L Ton = Tφ - Ton² Ton2 ={-(Vout·T)+(2·Tφ·Vin)} / (4·Vin) Toff = T / 2 - Tφ
[0042] Figure 11 is a timing chart of the inductor current IL in the isolated DC-DC converter 2 of Figure 2, when the inductor current IL is at its maximum value during step-down switching and the inductor current IL is discontinuous.
[0043] In Figure 11, the current ΔI1, on-time Ton, and off-time Toff1 are expressed by the following equations. Note that the theoretical formula for the maximum current differs depending on whether the inductor current IL is continuous or discontinuous, but for the sake of simplifying calculations, the theoretical formula for discontinuous current is used as a guideline for the maximum current.
[0044] ΔI1 = (Vin - Vout) · Ton / L Ton=Tφ-Tdead Toff1 = (Vin - Vout) · Ton / Vout
[0045] Figure 12 is a flowchart showing the pre-charging control process (overview control flow) executed by the control unit 10 in Figure 2.
[0046] Here, the phase shift amount Tφ in step-down mode is expressed by the following equation.
[0047] Tφ = Ton + Tdead Ton = (ILtarget·L) / (Vin-Vout)
[0048] Here, ILtarget is the target current value flowing through the inductor L.
[0049] Furthermore, the phase shift amount Tφ in boost mode is expressed by the following equation.
[0050] Tφ = Ton + Tdead Ton = (ILtarget·L) / Vin
[0051] In step S11 of the pre-charging process (overview flow) in FIG. 12, the switching unit 9 is operated at the minimum phase shift amount Tφmin in the step-down mode. Next, in step S12, the switching unit 9 is operated in step-down switching (step-down mode) with a phase shift amount Tφ at which the inductor current IL reaches the maximum value ILmax according to the voltage difference between the input voltage Vin and the output voltage Vout (Tφ calculated with ILtarget = ILmax). Then, in step S13, it is determined whether the voltage of the smoothing capacitor (when C1 discharges to 150V, it is the voltage of the input capacitor; otherwise, it is the voltage of the output capacitor) is within the target value setting range. When YES, the pre-charging process is terminated, while when NO, the process proceeds to step S14. In step S14, it is determined whether the switching unit 9 is operating in step-down switching (step-down mode). When YES, the process proceeds to step S15, while when NO, the process proceeds to step S16. In step S15, it is determined whether the calculation result Tφ of the phase shift amount Tφ at which the inductor current IL reaches the maximum value ILmax is less than Tφmax (the upper limit value of the phase shift amount Tφ). When YES, the process returns to step S12, while when NO, the process proceeds to step S16. In step S16, according to the input voltage Vin, the switching unit 9 is operated in boost switching (boost mode) with a phase shift amount Tφ at which the inductor current IL reaches the maximum value ILmax.
[0052] Note that in the pre-charging process of FIG. 12, the following processes are omitted from the actual operation process for description. (1) Soft start process to make the current increase gradually. (2) Charging standby process to standby at the minimum output (zero) so that recharging can start immediately when the voltage changes by a predetermined amount or more after charging is completed.
[0053] In the pre-charge control process configured as described above, it can be used in each of the processes S1 to S4 in the preparation process before the operation start in FIG. 3. The voltage of the smoothing capacitor for which the voltage is to be adjusted (for example, when the voltage of C1 discharge is 150V, it is the voltage of the input capacitor) is switched by the switching unit 9 at the phase shift amount Tφ at which the inductor current IL becomes the maximum value ILmax until it falls within the target voltage range in the step-down switching (step-down mode) (S11). During the operation in the step-down switching (step-down mode) (YES in step S14), if Tφ < Tφmax (YES in S15), in step S12, the switching unit 9 is operated in the step-down switching (step-down mode) at the phase shift amount Tφ at which the inductor current IL becomes the maximum value ILmax according to the voltage difference between the input voltage Vin and the output voltage Vout. On the other hand, when the switching unit 9 is not operating in the step-down switching (step-down mode) (NO in step S14), or even when operating in the step-down switching (step-down mode) (YES in step S14) but Tφ ≧ Tφmax (NO in S15), in step S16, the switching unit 9 is operated in the boost switching (boost mode) at the phase shift amount Tφ at which the inductor current IL becomes the maximum value ILmax according to the input voltage Vin.
[0054] FIG. 13 is a diagram showing a table of charge / discharge control modes executed by the switching unit 9 in FIG. 2. As is clear from FIG. 13, the isolated DCDC converter 2 has the following four control modes. The voltage is an example during operation. (1) C1 charge 150V: The input voltage Vin becomes the voltage V2, the output voltage Vout becomes the voltage V1, and the switches SW1 and SW2 are off and disconnected from the battery 1, and it is an operation mode for charging the smoothing capacitor C1. (2) C1 charge 450V: The input voltage Vin becomes the voltage V2, the output voltage Vout becomes the voltage V1, and the switches SW1 and SW2 are off and disconnected from the battery 1, and it is an operation mode for charging the smoothing capacitor C1. (3) C1 discharge 150V: The input voltage Vin becomes voltage V1, the output voltage Vout becomes voltage V2, and with switches SW1 and SW2 off, the device operates disconnected from battery 1, discharging from the smoothing capacitor C1. (4) C2 charging 280V: The input voltage Vin becomes voltage V1, the output voltage Vout becomes voltage V2, and the device operates with switches SW1 and SW2 turned on and connected to battery 1. This is the operating mode in which DC power is discharged from battery 1.
[0055] Note that the "Voltage Target Upper Limit Reached Setting" in Figure 13 corresponds to the process in step S31 of Figure 14B. Also, the "Voltage Target Lower Limit Reached Setting" in Figure 13 corresponds to one step within step S32 of Figure 14B. Note that Figure 13 includes charge and discharge items because the timing charts differ for charging and discharging. Figures 4A, 4B, 5A, 5B, 8A, 8B, 9A, and 9B above show the patterns during discharge. During charging, the primary and secondary sides are swapped, and the gate control signals Sg1, Sg2, Sg3, Sg4, Sg5, Sg6, Sg7, Sg8 during discharge become the gate control signals Sg5, Sg6, Sg7, Sg8, Sg1, Sg2, Sg3, Sg4, respectively, during charging. In other words, the corresponding gate control signals Sg in the timing charts differ between charging and discharging.
[0056] Figures 14A to 14C are flowcharts of the pre-charge control process (detailed control flow) executed by the control unit 10 in Figure 2. In Figures 14A to 14C, an example of operation of "C1 charge 150V" from the operation modes in Figure 13 is described below. In this example, the smoothing capacitor is C1, and its output voltage is V1. As is clear from Figure 13, in C1 discharge or C2 charge, the smoothing capacitor is C2, and its output voltage is V2.
[0057] In step S21 of FIG. 14A, first, an initial setting process is executed. Specifically, set C1 charging 150V in the control mode, set "step-down" in the parameters Bb and Bbnext respectively, and set "charging" in the charge-discharge mode. Also, set the C2 voltage (V2) in the input voltage Vin, set the C1 voltage (V1) in the output voltage Vout, and set a predetermined current start value ILstart in the current target value ILtarget.
[0058] Next, in step S22, it is determined whether the parameter Bb is "step-down". If YES, the process proceeds to step S23; if NO, the process proceeds to step S41 in FIG. 14C. In step S23, a Tφ step-down upper limit determination process is executed. Specifically, it is determined whether Vin - Vout < ILtarget × L / (Tφmax - Tdead). If YES, the process proceeds to step S27; if NO, the process proceeds to step S24. Here, Tφmax is the maximum value of the phase shift amount Tφ.
[0059] In step S24, the phase shift amount Tφ is set to the step-down calculated value. Specifically, set Ton to ILtarget × L / (Vin - Vout), and set the phase shift amount Tφ to Ton + Tdead. Next, in step S25, the current target value ILtarget is updated. Specifically, set the target value ILtarget of the inductor current IL to ILtarget + ILstep. However, when ILtarget > ILmax (the upper limit value of the inductor current IL), set the target value ILtarget of the inductor current IL to ILmax. Then, in step S26, set "step-down" in the parameter Bbnext, and proceed to step S29 in FIG. 14B.
[0060] In step S27, set the phase shift amount Tφ to the step-down upper limit value Tmaxbu. In step S28, after setting "boost" in the parameter Bbnext, proceed to step S29 in FIG. 14B.
[0061] In step S29 of Figure 14B, a PWM signal including gate control signals Sg1 to Sg8 is generated with the set phase shift amount Tφ and output to the switching unit 9 to drive and operate it. Next, in step S30, the data for parameter Bbnext is set to parameter Bb, and in step S31, a voltage target value upper limit determination process is executed. Specifically, it is determined whether V1 ≥ V1max, and if YES, the process proceeds to step S32, while if NO, the process returns to step S22 in Figure 14A. In step S32, a capacitor charging standby process is executed. Specifically, the capacitor voltage of the output voltage Vout (voltage V1 when C1 is charged at 150V) is within the target voltage range, and after controlling the switching unit 90 to operate with the minimum phase shift amount Tφ (output current zero), the process returns to step S22 in Figure 14A.
[0062] In step S41 of Figure 14C, the input / output voltage difference upper limit determination process is performed. Specifically, it is determined whether Vin-Vout > (ILmax + ILmargin) × L / (Tφmax - Tdead). If YES, the process proceeds to step S42; otherwise, it proceeds to step S43. Here, ILmargin is a predetermined margin value of the inductor current IL. Next, in step S42, the output of the PWM signal is stopped for a predetermined period of time, and then the process returns to step S21 of Figure 14A.
[0063] In step S43, the phase shift amount Tφ is set to the boosted calculated value. Specifically, the ON period Ton is set to ILtarget × L / Vin, and the phase shift amount Tφ is set to Ton + Tdead. Next, in step S44, the boost limit determination process for the phase shift amount Tφ is executed, specifically determining whether Tφ > Tφmaxbo. If YES, the process proceeds to step S46; otherwise, it proceeds to step S45. Here, Tφmaxbo is the boost limit value for the phase shift amount Tφ. In step S45, the current target value ILtarget is updated. Specifically, ILtarget is incremented by a predetermined step value ILstep, however, if ILtarget > ILmax, the maximum inductor current value ILmax is set to ILtarget. In step S46, after setting the boost limit value Tφmaxbo for the phase shift amount Tφ, the process returns to step S29.
[0064] The pre-charge control process configured as described above can be used in each process S1 to S4 of the pre-operation preparation process shown in Figure 3. In the smoothing capacitor charging process in steps S21 to S31 and S41 to S46, the switching unit 9 is operated with a phase shift amount Tφ such that the inductor current IL reaches its upper limit until the output voltage of the smoothing capacitor reaches the target voltage range. Once the output voltage of the smoothing capacitor reaches the upper limit of the target voltage range, the smoothing capacitor charging control process in step S32 is executed. In this smoothing capacitor charging control process, the output voltage of the smoothing capacitor is within the target voltage range, and the switching unit 9 is operated with the minimum phase shift amount Tφ (output current zero). If the output voltage of the smoothing capacitor reaches the lower limit of the target voltage range in this state, the process returns to the smoothing capacitor charging process.
[0065] Figure 15 shows the simulation results of the isolated DC-DC converter 2 in Figure 2, and is a timing chart of each signal. For the sake of the simulation, the inventors performed the verification using a two-phase interleaved configuration.
[0066] As is clear from the phase shift amounts φ1 and φ2 in Figures 15(a) and (b), the phase shift amount Tφ gradually increases, switches to boost when it reaches the upper limit of the buck voltage, and gradually increases from the lower limit of the boost voltage. Also, the voltage V2 in Figure 15(c) stops when it reaches the target value. Furthermore, the inductor currents IL1 and IL2 in Figures 15(d) and (e) are 90 degrees apart from each other, and the current gradually increases, but operates to stay below 10A, and the current becomes almost zero when the voltage V2 reaches the target value. Figure 15(f) shows the buck-boost flag BFF, where BFF=0 indicates buck voltage and BFF=1 indicates boost voltage.
[0067] Furthermore, the control unit 10 monitors the inductor current value detected by the current detection unit 13 and determines the current upper limit, allowing the inductor current IL to flow up to the current upper limit, thus enabling a faster discharge.
[0068] As described above, according to this embodiment, by executing the pre-charge control process shown in Figure 12 or Figures 14A to 14C, the control unit 10 controls the switching unit 9 to adjust the input voltage and output voltage based on the input voltage and output voltage so that the inductor current IL flowing through the inductor L is less than a predetermined upper limit value.Therefore, in an isolated DC-DC converter, the voltage of the smoothing capacitor can be controlled in a relatively short time within a predetermined operating time with a simpler configuration compared to the conventional technology.
[0069] (modified version) Figure 16 is a block diagram showing an example configuration of a modified power conversion system. The modified power conversion system in Figure 16 differs from the power conversion system in Figure 1 in the following ways. (1) The system further comprises a solar cell 5 and a DC-DC converter 6. Here, the output terminal of the DC-DC converter 6 is connected in parallel to the connection point between the isolated DC-DC converter 2 and the DC-AC inverter device 3. The differences are explained below.
[0070] In Figure 16, the DC voltage related to the DC power generated by the solar cell 5 is converted to a predetermined DC voltage by the DC-DC converter 6, and then charged to the storage battery 1 via the isolated DC-DC converter 2, or output to the load 4 via the DC-AC inverter 3.
[0071] In the modified power conversion system configured as described above, the DC power generated by the solar cell 5 can be used to charge the storage battery 1 or output to the load 4. Furthermore, since the modified power conversion system includes an isolated DC-DC converter 2, it has the same effects and advantages as the power conversion system according to the embodiment. [Industrial applicability]
[0072] As described in detail above, according to the isolated DC-DC converter of the present invention, in the preparation operation before starting operation, the switching unit is controlled to adjust the input voltage and output voltage based on the input voltage and output voltage so that the inductor current flowing through the inductor is less than a predetermined upper limit. Therefore, in the isolated DC-DC converter, the voltage of the smoothing capacitor can be controlled in a relatively short time within a predetermined operating time with a simpler configuration compared to the conventional technology. [Explanation of symbols]
[0073] 1. Storage battery 2. Isolated DC-DC converter 3 DC-AC inverter device 4. Power System (or Load) 5 Solar cells 6. DC-DC converter 7,8 Switching circuits 9 Switching section 10 Control Unit 11,12 Voltage detection unit 13 Current detection unit C1, C2 Smoothing Capacitors D1~D8 Reverse Conducting General Diodes L Inductor L1 Primary winding L2 Secondary winding Q1-Q8 Switching elements SW1, SW2 switches T11~T14 terminals TR Isolation Transformer
Claims
1. A first smoothing unit including a first capacitor for smoothing the input voltage, A switching unit comprising an isolation transformer, an inductor, a switching circuit on the primary side of the isolation transformer, and a switching circuit on the secondary side of the isolation transformer, wherein the switching unit switches the smoothed voltage to convert it into power to a predetermined output voltage, A second smoothing unit including a second capacitor for smoothing the power-converted output voltage, An isolated DC-DC converter comprising the switching unit and a control unit that controls preparatory operations before starting operation, The control unit controls the switching unit in a preparatory operation before starting operation, adjusting the input voltage and the output voltage based on the input voltage and the output voltage so that the inductor current flowing through the inductor is less than a predetermined upper limit. The control unit further sets the target value of the inductor current flowing through the inductor to a predetermined upper limit during the preparatory operation before the start of operation. Based on the input voltage and output voltage, the amount of phase shift required to satisfy the target value is calculated, and it is determined whether the calculated phase shift amount has reached a predetermined upper limit of phase shift. If the calculated phase shift amount has not reached the predetermined upper limit of phase shift, the switching unit is operated in step-down switching mode, while if the calculated phase shift amount has reached the upper limit of phase shift, the switching unit is operated in step-up switching mode. Isolated DC-DC converter.
2. The aforementioned preparatory operations before starting operation are: (1) A fault diagnosis process that charges the output voltage to a voltage necessary for fault diagnosis, (2) An insulation diagnostic process that charges the output voltage to the voltage necessary for insulation diagnosis, (3) A process before connecting the first smoothing unit to the storage battery, comprising a voltage adjustment process that charges the output voltage to the rated voltage of the storage battery, (4) A voltage adjustment process to charge the output voltage to the voltage necessary for the operation of the switching unit, It is one of the following: The isolated DC-DC converter according to claim 1.
3. An isolated DC-DC converter according to claim 1 or 2, A power conversion system characterized by comprising a DC-AC inverter device that converts the output voltage output from the isolated DC-DC converter into an AC voltage.
4. A power conversion system according to claim 3, The aforementioned power conversion system, A power conversion system further comprising a DC-DC converter that converts the input voltage output from a solar cell into a predetermined output voltage and outputs it to the isolated DC-DC converter or the DC-AC inverter.
5. A first smoothing unit including a first capacitor for smoothing the input voltage, A switching unit comprising an isolation transformer, an inductor, a switching circuit on the primary side of the isolation transformer, and a switching circuit on the secondary side of the isolation transformer, wherein the switching unit switches the smoothed voltage to convert it into power to a predetermined output voltage, A second smoothing unit including a second capacitor for smoothing the power-converted output voltage, A control method for an isolated DC-DC converter comprising the switching unit and a control unit that controls preparatory operations before starting operation, The control unit includes a step of controlling the switching unit in a preparatory operation before starting operation, such that the input voltage and the output voltage are adjusted based on the input voltage and the output voltage so that the inductor current flowing through the inductor is less than a predetermined upper limit. The step of controlling the switching unit is: The control unit further sets the target value of the inductor current flowing through the inductor to a predetermined upper limit during the preparatory operation before the start of operation. Based on the input voltage and the output voltage, the system calculates the amount of phase shift required to satisfy the target value, determines whether the calculated phase shift amount has reached a predetermined upper limit of phase shift, and operates the switching unit in step-down switching mode if the calculated phase shift amount has not reached the predetermined upper limit of phase shift, while operating the switching unit in step-up switching mode if the calculated phase shift amount has reached the upper limit of phase shift, Control method for an isolated DC-DC converter.