JP2014176226A - Dc/dc converter and distributed power supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a loss in a DC/DC converter using a phase shift scheme, and to provide a distributed power supply system including such a DC/DC converter.SOLUTION: Provided is an insulated-type DC/DC converter 101 comprising a control unit 3 for operating a bridge circuit 1 by a phase shift scheme and operating the bridge circuit 1 so that a constant current flows in a transformer T1 in a partial resonance stage, and a reactor Ls1 for inductance adjustment inserted in an electric path coupling the bridge circuit 1 and the transformer T1. When a partial resonance is caused to occur by a combined inductance of inductance possessed by the reactor Ls1 and leakage inductance of the transformer T1 and a capacitor present in parallel to a semiconductor switching element Q2, the combined inductance is a value which causes a duration of time until the capacitor voltage is reduced to zero and a duration of time until a current flowing in the transformer T1 is reduced to zero to match each other.

Description

  The present invention relates to a DC / DC converter, and more particularly to a DC / DC converter used for charging / discharging a storage battery and a distributed power supply system using the same.

In recent years, consumers such as ordinary households and offices have increased interest in distributed power supply systems that do not depend only on commercial power. For example, in a distributed power supply system using solar power generation, a configuration in which a solar power generation panel and a chargeable / dischargeable storage battery are combined in addition to a commercial power supply system is used (see, for example, Patent Document 1). In such a distributed power supply system, since different types and different voltages of power sources such as a commercial power source (AC), a photovoltaic power generation panel (DC), and a storage battery (DC) are used, a conversion device (AC / DC conversion or DC / DC conversion) and a common DC bus voltage. A DC / DC converter used for a storage battery can perform bidirectional operations of charging and discharging.
Usually, the voltage of the DC bus is further converted into alternating current by an inverter device and supplied to a load in a consumer.

JP2012-161189A

  In a DC / DC converter, switching loss occurs when a semiconductor switch element constituting an internal circuit is originally turned on / off. As a control method for reducing such switching loss, a phase shift method is adopted. On the other hand, in the conventional distributed power supply system as described above, for example, the bidirectional DC / DC converter connected to the storage battery changes the charge / discharge current in small increments in an attempt to maintain the DC bus voltage at a constant value. . However, such a small change in the charging / discharging current may cause a recirculation in the DC / DC converter or may interfere with zero volt switching which is an effect of the phase shift method. In either case, a loss occurs as a circuit, which is not preferable.

  The present invention has been made to solve such a problem, and an object thereof is to reduce the loss of a DC / DC converter using a phase shift method. It is another object of the present invention to provide a distributed power supply system including such a DC / DC converter.

  (1) The present invention is an insulation type DC / DC converter including a bridge circuit constituted by semiconductor switch elements and a transformer connected to the bridge circuit, and operates the bridge circuit by a phase shift method. A control unit that operates the bridge circuit so that a constant current flows through the transformer at the stage of resonance, and an inductor for adjusting inductance that is inserted in an electric circuit that connects the bridge circuit and the transformer. Yes, when partial resonance occurs due to the combined inductance of the inductance of the reactor and the leakage inductance of the transformer and the capacitance existing in parallel with the semiconductor switch element, the combined inductance is used until the voltage of the capacitance disappears. The time and flow to the transformer Flow is a value to match each other the time and to is eliminated.

  In the above-described DC / DC conversion apparatus, by determining the combined inductance in this way, the time until the voltage of the capacitance disappears can coincide with the time until the current flowing through the transformer disappears. That is, an appropriate partial resonance condition is prepared, and the loss of the DC / DC converter can be reduced.

(2) Further, the present invention is an insulation type DC / DC converter including a bridge circuit constituted by semiconductor switch elements and a transformer connected to the bridge circuit, and operates the bridge circuit by a phase shift method. A control unit that operates the bridge circuit so that a constant current flows through the transformer at the stage of partial resonance, and the partial resonance is caused by a leakage inductance of the transformer and a capacitance that exists in parallel to the semiconductor switch element. When this occurs, the leakage inductance is a value that makes the time until the voltage of the capacitance disappears coincides with the time until the current flowing through the transformer disappears.
Also in this case, similarly to the above, the time until the capacitance voltage disappears and the time until the current flowing through the transformer disappears can be made to coincide with each other. That is, an appropriate partial resonance condition is prepared, and the loss of the DC / DC converter can be reduced.

(3) In the DC / DC converter of (1) or (2), the storage battery is charged from the bridge circuit via the transformer and the synchronous rectifier circuit, and conversely, the synchronous rectifier circuit, the transformer, and the A bi-directional configuration in which power is supplied to the DC bus via a bridge circuit can also be used.
In this case, the loss of the DC / DC converter used for charging / discharging the storage battery can be reduced.

(4) Moreover, in the DC / DC converter of (3) above, the control unit may perform the following control.
(A) When the voltage of the DC bus rises and becomes equal to or higher than the charging start threshold value, the charging operation of the storage battery is started, and when the voltage of the DC bus falls and falls below the charging stop threshold value, the charging operation of the storage battery is stopped. When the bus voltage drops and falls below the discharge start threshold, the storage battery starts to discharge, and when the DC bus voltage rises above the discharge stop threshold, the battery has a function to stop discharging. Adjust the average output current,
(B) The charge stop threshold value and the discharge stop threshold value are values between the charge start threshold value and the discharge start threshold value, and the control unit controls the charging current of the storage battery to a constant value in the charging operation, and in the discharging operation. The discharge current of the storage battery is controlled to a constant value.
In this case, since the charging current of the storage battery is constant, the current flowing through the transformer at the time of partial resonance is constant. The time until the combined capacitance of the parasitic capacitance of the semiconductor switch element and the capacitance existing in parallel with the semiconductor switch disappears and the time until the current flowing through the transformer disappears for the current value. The combined inductance for the partial resonance condition to be made is determined. Therefore, the constant current control of charging / discharging and the operation of the phase shift type bridge circuit can be combined to reduce the loss of the DC / DC converter. Details will be described later.

(5) In the DC / DC converter of (3) or (4), the capacitance is, for example, a composite value of the parasitic capacitance of the semiconductor switch element and the capacitance of the snubber capacitor connected in parallel.
In this case, the required capacitance can be made by the snubber capacitor.

(6) Moreover, the distributed power supply system of this invention is connected to a power generator installed in a consumer, a converter connected to the power generator and supplying output to the DC bus, a storage battery, a storage battery, and a DC bus. And the DC / DC conversion device according to any one of (3) to (5), which supplies an output to the device.
In this case, it is possible to provide a distributed power supply system in which the loss of the DC / DC converter is reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the loss of the DC / DC converter using a phase shift system can be reduced. In addition, a distributed power supply system including such a DC / DC converter can be provided.

1 is a connection diagram illustrating a configuration example of a distributed power supply system according to an embodiment of the present invention. It is a figure which shows an example of charging / discharging operation | movement of a DC / DC converter. It is a figure which shows an example of the threshold voltage for charging / discharging operation | movement in a DC / DC converter. It is an example of the internal circuit diagram of the DC / DC converter for storage batteries. It is a flowchart which shows the procedure of the electric power supply operation | movement by a DC / DC converter. For example, it is a graph showing signals, voltages, currents, and the like of each part of a DC / DC converter that performs a charging operation. FIG. 5 is a circuit diagram (time t2 to t3) in which a part of FIG. 4 is extracted. FIG. 5 is a circuit diagram (time t3 to t4) in which a part of FIG. 4 is extracted.

<< Configuration example of distributed power supply system >>
FIG. 1 is a connection diagram illustrating a configuration example of a distributed power supply system according to an embodiment of the present invention. Here, a case where a distributed power supply system including solar power generation and a storage battery is installed in a consumer will be described as an example.

  In FIG. 1, a distributed power supply system 201 includes a storage battery 106, a bidirectional DC / DC converter 101 for the storage battery 106, a photovoltaic power generation panel 102, and outputs from the photovoltaic power generation panel 102. DC / DC converter 103 that performs control), AC / DC converter 105 for commercial AC power supply 104 (for example, AC 100V), and DC / AC converter 107 for load 108 (for example, AC 100V). I have. The DC bus 151 serves as a common line for three types of power supplies (solar power generation panel 102, storage battery 106, and commercial AC power supply 104).

The photovoltaic power generation panel 102 can supply power to the load 108 via the DC / DC conversion device 103 and the DC / AC conversion device (inverter device) 107. Although not shown in FIG. 1, the output of the DC / AC converter 107 can be sold by grid connection.
Further, the DC power generated in the solar power generation panel 102 can be used for charging the storage battery 106 via the DC / DC conversion device 103 and the DC / DC conversion device 101. Further, the storage battery 106 can be charged from the commercial AC power supply 104 via the AC / DC converter 105 and the DC / DC converter 101.

  On the other hand, by discharging the storage battery 106, electric power can be supplied to the load 108 via the DC / DC conversion device 101 and the DC / AC conversion device 107. The DC / DC conversion apparatus 101 performs a charging operation when the storage battery 106 can be charged and charging is necessary. At this time, the voltage of the DC bus 151 is converted into a voltage suitable for charging the storage battery 106. Further, the DC / DC converter 101 performs a discharging operation when the storage battery 106 can be discharged and discharge is necessary. At this time, the voltage of the storage battery 106 is converted into the voltage of the DC bus 151.

  The storage battery 106 is a rechargeable secondary battery, for example, a lead battery, a lithium ion battery, a redox flow battery, a NAS battery, a Ni-Cd battery, a Ni-MH battery, an electric double layer capacitor, a lithium ion capacitor, or A molten salt battery can be used.

  The combined capacity 109 of the DC bus 151 by the DC / DC converter 101, the DC / DC converter 103, the AC / DC converter 105, and the DC / AC converter 107 is 9 mF, for example. The combined capacity 109, the generated power of the photovoltaic power generation panel 102 via the DC / DC converter 103, the supply power of the commercial AC power supply 104 via the AC / DC converter 105, and the power consumption of the load 108, the storage battery A slope of voltage rise and voltage drop of the DC bus 151 at the time of charging and discharging 106 is determined.

  In addition, although FIG. 1 demonstrated the case where the electric power generating apparatus installed in a consumer was the solar power generation panel 102, other power supplies, such as a wind power generation, may be sufficient.

<< DC bus voltage and charge / discharge >>
Next, the relationship between the change in the voltage of the DC bus 151 and the charge / discharge of the storage battery 106 will be described.
FIG. 2 is a diagram illustrating an example of a charge / discharge operation centered on the DC / DC converter 101. In the figure, the lower limit value of the voltage Vdc of the DC bus 151 is 160V, for example, and the upper limit value is 190V. Here, it is assumed that the power consumption of the load 108 is constant.

  When the power generation amount of the photovoltaic power generation panel 102 increases and the voltage Vdc of the DC bus 151 increases to reach 190 V, the DC / DC conversion device 101 starts charging the storage battery 106 (timing t1). As a result, surplus power generated by the photovoltaic power generation panel 102 is supplied to the storage battery 106, and the voltage Vdc of the DC bus 151 decreases. At this time, the current in the storage battery 106 is −30 A, that is, a charging current of 30 A flows from the DC bus 151 to the storage battery 106. The numerical value of 30A is only an example.

  Thereafter, for example, when the charge amount of the storage battery 106 is large, when the voltage Vdc of the DC bus 151 decreases and reaches 175 V, the DC / DC converter 101 stops charging the storage battery 106 (timing t2). The integral value of the charging current is calculated by the product of 30A and the time from timing t1 to timing t2. Thereafter, when the voltage Vdc of the DC bus 151 rises again to reach 190 V, the DC / DC converter 101 starts charging the storage battery 106 again (timing t3). Similarly, when the voltage Vdc of the DC bus 151 decreases to reach 175 V, the DC / DC converter 101 stops charging the storage battery 106.

  On the other hand, the DC / DC converter 101 starts discharging the storage battery 106 when the power generation amount of the photovoltaic power generation panel 102 decreases and the voltage Vdc of the DC bus 151 decreases to 160 V (timing t11). Thereby, the shortage of the generated power of the photovoltaic power generation panel 102 is supplied to the DC bus 151, and the voltage Vdc of the DC bus 151 increases. At this time, the current in the storage battery 106 is 30 A, that is, a discharge current of 30 A flows from the storage battery 106 to the DC bus 151.

  Thereafter, for example, when the discharge amount of the storage battery 106 is large, when the voltage Vdc of the DC bus 151 increases and reaches 175 V, the DC / DC converter 101 stops discharging the storage battery 106 (timing t12). The integrated value of the discharge current is calculated by the product of 30A and the time from timing t11 to timing t12. Thereafter, when the voltage Vdc of the DC bus 151 decreases again to reach 160 V, the DC / DC converter 101 starts discharging the storage battery 106 again (timing t13). Similarly, when the voltage Vdc of the DC bus 151 increases and reaches 175 V, the DC / DC converter 101 stops discharging the storage battery 106.

  Further, the DC / DC converter 103 for the photovoltaic power generation panel 102 suppresses the output so that the voltage of the DC bus 151 does not exceed a predetermined upper limit value, for example, 195 V, when the voltage of the DC bus 151 rises to 190 V or more. Take control.

  For example, when the power generation amount of the solar power generation panel 102 increases, the voltage Vdc of the DC bus 151 increases to reach 190 V, and charging of the storage battery 106 is started (timing t21), the power generation amount of the solar power generation panel 102 Is very large, the voltage Vdc of the DC bus 151 further rises to reach 195V. Then, the DC / DC converter 103 stops the MPPT control of the photovoltaic power generation panel 102 and controls the voltage Vdc of the DC bus 151 not to exceed 195 V. Specifically, the DC / DC conversion device 103 receives from the photovoltaic power generation panel 102. The current is limited (timing t22). Then, when the power generation amount of the photovoltaic power generation panel 102 decreases and the output voltage decreases from 195 V, the DC / DC conversion device 103 resumes MPPT control.

  Further, the AC / DC converter 105 performs output suppression control so that the voltage of the DC bus 151 does not exceed a predetermined upper limit value, for example, 193 V, when the voltage of the DC bus 151 rises to 193 V or more, which is greater than 190 V.

  For example, when the power generation amount of the solar power generation panel 102 increases, the voltage Vdc of the DC bus 151 increases to reach 190 V, and charging of the storage battery 106 is started (timing t31), the power generation amount of the solar power generation panel 102 Is very large, the voltage Vdc of the DC bus 151 further rises to reach 193V. Then, AC / DC converter 105 stops the constant current control, and controls voltage Vdc of DC bus 151 not to exceed 193V. Specifically, the current received from commercial AC power supply 104 is limited (timing t32). And the AC / DC converter 105 will restart constant current control, if the electric power generation amount of the photovoltaic power generation panel 102 reduces and an output voltage falls from 193V.

As described above, the limit threshold that is the voltage at which the AC / DC converter 105 starts the output suppression control is made smaller than the limit threshold that is the voltage at which the DC / DC converter 103 starts the output suppression control. The use of natural energy using the photovoltaic panel 102 can be prioritized.
The DC / DC converter 101, the DC / DC converter 103, the AC / DC converter 105, and the DC / AC converter 107 increase the voltage of the DC bus 151 when the voltage of the DC bus 151 increases to 200V. Judge that it is rising abnormally and stop operation.

  In the above operation, the charging current and discharging current of the storage battery 106 are constant at 30A. In this distributed power supply system 201, the charging current and the discharging current can be set to a constant current. Both the on loss of the semiconductor switch and the copper loss of the reactor in the DC / DC converter 101 are both proportional to the square of the current. In particular, when an IGBT is used as the semiconductor switch, the circuit can be operated with a small on-resistance by setting the current as large as 30A. Therefore, the efficiency of the DC / DC converter 101 is improved by setting the current value that minimizes the total loss of the on-loss and the copper loss of the reactor while taking into account the rated capacity of the DC / DC converter 101. Can do.

  Note that the voltage Vdc of the DC bus 151 is not limited to a positive voltage, and may be a negative voltage. In the case of a negative voltage, the “rising” of the voltage means, for example, that the magnitude of the voltage changes in the direction from −180 V to −190 V, and the “decreasing” of the voltage, for example, in the direction from −190 V to −180 V. This means that the magnitude of the voltage changes.

FIG. 3 is a diagram illustrating an example of a threshold voltage for charge / discharge operation in the DC / DC conversion apparatus 101. In the figure, the charge start voltage VdcH is 190V, the charge / discharge stop voltage VdcS is 175V, and the discharge start voltage VdcL is 160V.
The charge stop voltage and the discharge stop voltage may be different from the above. That is, the charge stop voltage and the discharge stop voltage may be any voltage between the charge start voltage VdcH and the discharge start voltage VdcL.

In the example illustrated in FIG. 3, the charge stop voltage and the discharge stop voltage are median values of the charge start voltage VdcH and the discharge start voltage VdcL.
The DC / DC converter 101 starts the charging operation when the voltage Vdc of the DC bus 151 rises and becomes equal to or higher than the charge start threshold, that is, equal to or higher than the charge start voltage VdcH, and the voltage Vdc of the DC bus 151 decreases and falls below the charge stop threshold. That is, when the charge / discharge stop voltage VdcS or less is reached, the charging operation is stopped.

  Further, the DC / DC converter 101 starts the discharge operation when the voltage Vdc of the DC bus 151 decreases and becomes equal to or lower than the discharge start threshold, that is, equal to or lower than the discharge start voltage VdcL, and the voltage Vdc of the DC bus 151 increases to stop the discharge. The discharge operation is stopped when the threshold value is exceeded, that is, the charge / discharge stop voltage VdcS or more.

<< Details of DC / DC Converter for Storage Battery >>
FIG. 4 is an example of an internal circuit diagram of the DC / DC converter 101 for the storage battery 106. In the figure, a DC / DC converter 101 includes, as main components, a bridge circuit (full bridge circuit) 1 on the DC bus 151 side, a current doubler circuit 2 as a synchronous rectifier circuit on the storage battery 106 side, A transformer T1 which is in the middle and achieves insulation from each other, and a control unit 3 including a CPU and other control center functions and a PWM circuit are provided.

  Specifically, the bridge circuit 1 connected to the DC bus 151 includes four semiconductor switches Q1, Q2, Q3, and Q4, and snubber capacitors C1, C2, C3, and C4 connected in parallel to each of them. Yes. The semiconductor switches Q1 to Q4 are switched by the control unit 3. The bridge circuit 1 is connected to the primary winding Np of the transformer T1 via an inductance adjusting reactor Ls1 as shown in the figure. That is, the reactor Ls1 is inserted in the electric circuit connecting the bridge circuit 1 and the transformer T1. An electrolytic capacitor Cd1 is connected between the two lines of the DC bus 151. The voltage Vdc between the two lines of the DC bus 151 is detected by the voltage sensor 4, and the control unit 3 grasps the voltage Vdc based on the detection output.

  On the other hand, the current doubler circuit 2 is connected to the secondary winding Ns of the transformer T1, and includes two semiconductor switch elements QA and QB, reactors L1 and L2, and an electrolytic capacitor Cd2, which are as shown in the figure. It is connected. The voltage Vb generated at both ends of the storage battery 106 is detected by the voltage sensor 6, and the control unit 3 grasps the voltage Vb of the storage battery 106 based on the detection output. The current (charge / discharge current) Ib of the storage battery 106 is detected by the current sensor 5, and the control unit 3 grasps the current Ib based on the detected output.

  The control unit 3 measures the charging time and discharging time of the storage battery 106. Control unit 3 determines whether to start and stop the charging operation and discharging operation of storage battery 106 based on voltage Vdc. Based on the charging time and discharging time of the storage battery 106, and the voltage Vb and current Ib of the storage battery 106, the control unit 3 calculates the remaining amount of charge of the storage battery 106, for example, the state of charge (SOC). Then, the control unit 3 determines whether to start and stop the charging operation and discharging operation of the storage battery 106 based on the calculated charging rate. The voltage Vb of the storage battery 106 when no current flows through the storage battery 106 and the charging rate have a predetermined correspondence relationship.

  Based on the charging time and discharging time of the storage battery 106, and the voltage Vb and current Ib of the storage battery 106, the control unit 3 controls the electromotive force of the storage battery 106, that is, the current flowing through the internal resistance r of the storage battery 106 from the terminal voltage of the storage battery 106. The voltage value from which the voltage component due to is excluded is calculated. And the control part 3 calculates | requires the charging rate of the storage battery 106 from the electromotive force of the storage battery 106 by referring the correspondence memorize | stored beforehand.

  In addition, the control unit 3 switches the semiconductor switches Q1 to Q4, QA, and QB of the bridge circuit 1 and the current doubler circuit 2 based on the charging rate of the storage battery 106 and the voltage Vdc of the DC bus 151. Thereby, for example, in the discharging operation of the storage battery 106, the voltage Vb of the storage battery 106 is boosted and supplied to the DC bus 151, and in the charging operation of the storage battery 106, the voltage Vdc of the DC bus 151 is stepped down and supplied to the storage battery 106. The

  The DC / DC conversion apparatus 101 performs constant current charging as the charging operation of the storage battery 106 and performs constant current discharging as the discharging operation of the storage battery 106. That is, the control unit 12 controls the current flowing into the storage battery 106 in the charging operation to a constant value, and controls the current flowing out of the storage battery 106 in the discharging operation to a constant value. This constant value is, for example, a value preset by the user, that is, a predetermined value. The charge / discharge current is determined by the current flowing through the transformer T1. Therefore, the control unit 3 controls the bridge circuit 1 and the current doubler circuit 2 so that a desired constant current flows through the transformer T1.

  FIG. 5 is a flowchart showing the procedure of power supply operation by the DC / DC converter 101. In the figure, in the stop mode (step S1), the DC / DC conversion device 101 stops the charging operation and the discharging operation of the storage battery 106, and in the charging mode (step S4), the DC / DC conversion device 101 performs the charging operation of the storage battery 106. In the discharge mode (step S8), the DC / DC converter 101 performs the discharge operation of the storage battery 106.

For example, the control unit 3 of the DC / DC converter 101 measures the voltage Vb of the storage battery 106 in the stop mode, that is, when the charging operation and the discharging operation are stopped.
Further, for example, the control unit 3 calculates the remaining amount of electricity stored in the storage battery 106 based on the voltage Vb of the storage battery 106 measured in the stop mode. And the control part 3 does not start charge operation or discharge operation irrespective of the voltage Vdc of the DC bus 151, when the calculated remaining power storage amount satisfies a predetermined condition.

  Specifically, the control unit 3 determines the voltage Vdc of the DC bus 151 in the stop mode (step S1) (step S2), and the voltage Vdc is larger than the charging start voltage VdcH (in step S2). YES), when the remaining amount of the storage battery 106, for example, the charging rate is equal to or less than a predetermined value (YES in step S3), the mode is changed to the charging mode (step S4).

  Next, in the charging mode (step S4), the controller 3 determines the voltage Vdc of the DC bus 151 (step S5), and continues the charging mode until the voltage Vdc reaches the charge / discharge stop voltage VdcS (step S5). NO), when the voltage Vdc reaches the charge / discharge stop voltage VdcS (YES in step S5), a transition is made to the stop mode (step S1).

  The control unit 3 determines the voltage Vdc of the DC bus 151 in the stop mode (step S1) (step S2), and the voltage Vdc is equal to or lower than the charge start voltage VdcH and lower than the discharge start voltage VdcL. (NO in step S2 and YES in step S6) When the remaining amount of the storage battery 106, for example, the charging rate is equal to or greater than a predetermined value (YES in step S7), transition to the discharge mode (step S8).

  Next, in the discharge mode (step S8), the control unit 3 determines the voltage Vdc of the DC bus 151 (step S9), and continues the discharge mode until the voltage Vdc reaches the charge / discharge stop voltage VdcS (step S9). NO), when the voltage Vdc reaches the charge / discharge stop voltage VdcS (YES in step S9), a transition is made to the stop mode (step S1).

  On the other hand, even when the voltage Vdc is higher than the charging start voltage VdcH (YES in step S2), the control unit 12 charges when the remaining amount of the storage battery 106, for example, the charging rate is higher than a predetermined value (NO in step S3). The stop mode is continued without changing to the mode (step S1).

  Further, even when the voltage Vdc is less than the discharge start voltage VdcL (YES in Step S6), the control unit 3 determines that the remaining amount of the storage battery 106, for example, the charging rate is less than a predetermined value (NO in Step S7). The stop mode is continued without transitioning to the discharge mode (step S1).

<< Details of Operation of DC / DC Converter >>
Next, details of the operation of the DC / DC converter 101 will be described.
FIG. 6 is a graph illustrating signals, voltages, currents, and the like of the respective units of the DC / DC conversion apparatus 101 that performs a charging operation, for example. In order from the top, the relationship between the sawtooth wave, which is the basis of switching, and the threshold, the gate signal of the semiconductor switch Q1, the gate signal of the semiconductor switch Q2, the gate signal of the semiconductor switch Q3, the gate signal of the semiconductor switch Q4, 1 of the transformer T1 The voltage of the secondary winding (T1 voltage), the primary winding current (T1 current) of the transformer T1, the gate signal of the semiconductor switch QA, the gate signal of the semiconductor switch QB, the current IL1 flowing through the reactor L1, and the reactor L2 A flowing current IL2 and a current Ib of the storage battery 106 are shown.

  As indicated by the gate signals of the semiconductor switches Q1 to Q4, the control unit 3 operates the bridge circuit 1 by the phase shift method. By such switching, a current (T1 current) as shown in the figure flows through the transformer T1, and a generally stable current Ib is supplied to the storage battery 106 through the rectification / smoothing operation by the current doubler circuit 2 on the secondary side of the transformer T1. Can be supplied. The semiconductor switch Q1 and the semiconductor switch Q2 are alternately turned on, but there is a delay time DT1 when switching. Similarly, the semiconductor switch Q3 and the semiconductor switch Q4 are alternately turned on, but there is a delay time DT2 when switching.

  In the DC / DC conversion device 101 that operates the bridge circuit 1 by the phase shift method, the parasitic capacitance in each of the semiconductor switch elements (Q1 to Q4) and the combined capacitance of the snubber capacitors (C1 to C4) connected in parallel (= C), and the combined inductance (= Ls) of the inductance of the inductor Ls1 for adjusting the inductance and the leakage inductance of the transformer T1 causes partial resonance. The parasitic capacitance of the semiconductor switch elements (Q1 to Q4) is determined to be a substantially constant value for each element. The snubber capacitors (C1 to C4) are for adjusting the capacitance component value and have a constant value.

  That is, in the DC / DC conversion device 101 that operates the bridge circuit 1 by the phase shift method, partial resonance occurs during switching of the semiconductor switch. Therefore, for example, the partial resonance will be described by focusing on the times t2 to t3 to t4 in FIG.

  FIG. 7 is a circuit diagram in which a part of FIG. 4 is extracted. From time t2 to t3, the semiconductor switches Q1 and Q3 are on (the semiconductor switches Q2 and Q4 are off). At this time, a current flows as shown by a thick line in the figure by the energy accumulated in the leakage inductance in the reactor Ls1 and the primary winding Np of the transformer T1. This current contributes to charging. On the other hand, the voltage Vdc remains in the snubber capacitors C2 and C4 connected in parallel to the semiconductor switches Q2 and Q4 that are turned off, respectively.

  FIG. 8 is a circuit diagram of the same circuit portion as FIG. 7, but shows a state at times t3 to t4. When the semiconductor switch Q1 turns off from the state of FIG. 7, the snubber capacitor C1 in the short-circuited state has no voltage, and the semiconductor switch Q1 turns from on to off by zero volt switching. In FIG. 8, only the semiconductor switch Q3 is on during the time period from time t3 to t4, and the other semiconductor switches Q1, Q2, and Q4 are off.

At this time, the current flows as indicated by the bold line in the figure. The combined capacitance of the parasitic capacitance of the semiconductor switch element Q2 and the snubber capacitor C2, and the combined inductance of the inductance of the reactor Ls1 and the leakage inductance of the primary winding Np are in a partial resonance state. When the time reaches t4, the semiconductor switch element Q2 is turned on. To achieve zero volt switching at this time, the voltage of the snubber capacitor C2 needs to be zero.
On the other hand, as described above, the current flowing through the transformer T1 during charging exhibits a constant behavior every cycle since the charging current of the storage battery 106 is constant. Therefore, at the instant (time t3) when the constant current for charging the storage battery 106 shifts to the state of partial resonance, the current value I _NP flowing through the transformer T1 becomes a constant value (in each cycle) (see T1 current in FIG. 6). ).

Here, when the voltage of the snubber capacitor C2 is V _C2 ,
V _C2 = Vdc−I _NP × (Ls / 2C) ^1/2 (1)
It is. Meanwhile, the time partial resonance occurs can be determined as the time t _VC2 for the voltage V _C2 of the snubber capacitor C2 becomes zero. Here, the voltage Vdc is determined as a control set value, the current I _NP is constant, and the combined capacitance C is also a fixed value.
On the other hand, the time t _NP until the current I _NP becomes 0 is ¼ of the resonance period,
t _NP = 2π × (2LsC) ^1/2 × (1/4) (2)
It is.

Here, if the current I _NP at the start of partial resonance changes instead of a constant current, and the voltage V _C2 becomes zero before a quarter of the resonance period has elapsed, the resonance at that time The remaining current flows back through the parasitic diode of the semiconductor switch element Q2, resulting in a circuit loss. When the voltage V _C2 does not reach zero, at time t4, a switching loss due to the voltage V _C2 and the current flowing through the semiconductor switch element Q2 occurs, resulting in a circuit loss.

Although minimizing the circuit loss leads to an improvement in efficiency, the current I _NP is constant in the DC bus voltage control described above. Therefore, the value of the combined inductance Ls is determined so that the time t _VC2 and the time t _NP coincide with each other, and the inductance of the reactor Ls1 necessary for that is determined. Since the reactor Ls1 is provided for inductance adjustment, a necessary value can be prepared. It is also possible to consider a circuit in which the reactor Ls1 is not provided and the inductance component of the primary circuit is only the leakage inductance of the transformer T1.

By determining the combined inductance Ls in this way, the time until the voltage of the capacitance C disappears and the time until the current flowing through the transformer T1 disappears can be matched with each other. That is, appropriate partial resonance conditions are prepared, and circuit loss is particularly reduced. Thus, charging / discharging can be performed in a state in which the loss of the DC / DC converter 101 is reduced by combining the constant current control of charging / discharging and the operation of the bridge circuit of the phase shift method. Moreover, the distributed power supply system 201 including such a DC / DC converter 101 can be provided.
In addition, since the second term of the formula (1) has C in the denominator with respect to the numerator Ls, there is an advantage that the smaller the C, the smaller the Ls. The value of C can be freely set by a snubber capacitor.

  In the above description regarding the partial resonance, the semiconductor switch element Q2 is focused. However, the same applies to the other semiconductor switch elements Q1, Q3, and Q4.

For reference, examples of numerical values suitable as partial resonance conditions are as follows.
Vdc = 200V
Ib = 20A
Parasitic capacitance of semiconductor switch element: 1380pF
Snubber capacitor capacity: 500 pF
Synthetic inductance Ls = 0.38μH

  In the above-described embodiment, the reactor Ls1 is used. However, as described above, the reactor Ls1 can be omitted. In this case, partial resonance occurs due to the leakage inductance of the transformer T1 and the capacitance existing in parallel with the semiconductor switch element. Therefore, when this partial resonance occurs, the leakage inductance may be a value that makes the time until the capacitance voltage disappears coincide with the time until the current flowing through the transformer T1 disappears.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Bridge circuit 2 Current doubler circuit (synchronous rectifier circuit)
3 Control Unit 101 DC / DC Converter 106 Storage Battery 151 DC Bus C1 to C4 Snubber Capacitor Ls1 Reactor Q1 to Q4 Semiconductor Switch T1 Transformer

Claims (6)

An insulated DC / DC converter including a bridge circuit constituted by semiconductor switch elements and a transformer connected to the bridge circuit,
A control unit that operates the bridge circuit in a phase shift manner and operates the bridge circuit so that a constant current flows through the transformer at the stage of partial resonance.
An inductance adjusting reactor inserted in an electric circuit connecting the bridge circuit and the transformer,
When partial resonance occurs due to the combined inductance of the inductance of the reactor and the leakage inductance of the transformer and the capacitance existing in parallel with the semiconductor switch element, the combined inductance is the time until the voltage of the capacitance disappears. And a DC / DC converter having a value that makes the time until the current flowing through the transformer disappears agree with each other. An insulated DC / DC converter including a bridge circuit constituted by semiconductor switch elements and a transformer connected to the bridge circuit,
A control unit that operates the bridge circuit in a phase shift manner and operates the bridge circuit so that a constant current flows through the transformer at the stage of partial resonance.
When partial resonance occurs due to the leakage inductance of the transformer and the capacitance existing in parallel with the semiconductor switch element, the leakage inductance is required until the voltage of the capacitance disappears and the current flowing through the transformer disappears. The DC / DC converter is a value that makes the time of the two coincide with each other.   A bidirectional type battery that charges a storage battery from the bridge circuit via the transformer and a synchronous rectification circuit, and conversely supplies power to the DC bus via the synchronous rectification circuit, the transformer, and the bridge circuit by discharging the storage battery. Item 3. The DC / DC converter according to Item 1 or 2. The controller is
When the voltage of the DC bus rises and becomes equal to or higher than a charging start threshold value, the charging operation of the storage battery is started, and when the voltage of the DC bus falls and falls below a charging stop threshold value, the charging operation of the storage battery is stopped. The battery has a function of starting the discharge operation of the storage battery when the voltage of the DC bus falls to a discharge start threshold value or less and stops the discharge operation of the storage battery when the voltage of the DC bus rises to a discharge stop threshold value or more. And adjust the average output current with this function,
The charge stop threshold and the discharge stop threshold are values between the charge start threshold and the discharge start threshold,
The DC / DC converter according to claim 3, wherein the control unit controls a charging current of the storage battery to a constant value in the charging operation, and controls a discharging current of the storage battery to a constant value in the discharging operation. .   5. The DC / DC converter according to claim 3, wherein the capacitance is a combined value of a parasitic capacitance of the semiconductor switch element and a capacitance of a snubber capacitor connected in parallel. A power generator installed in a consumer;
A converter connected to the power generator and supplying an output to the DC bus;
The storage battery;
A distributed power supply system comprising: the DC / DC converter according to any one of claims 3 to 5, which is connected to the storage battery and supplies an output to the DC bus.

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