DAB type bidirectional isolated DC / DC converter and control method thereof

Abstract

To improve the efficiency of a DAB system bidirectional insulation type DC / DC converter, which has one end connected in series and the other end connected in parallel, on the whole device.SOLUTION: A DAB system bidirectional insulation type DC / DC converter comprises a primary-side DC power supply DC1, a secondary-side DC power supply DC2, and a first unit to an (m)th (m: an integer equal to or larger than 2) unit connected between the primary-side DC power supply DC1 and secondary-side DC power supply DC2. Primary-side DC capacitors C1 of the first unit to the (m)th unit are connected to the primary-side DC power supply DC1 in series. Secondary-side DC capacitors C2 of the first unit to the (m)th unit are connected to the secondary-side DC power supply DC2 in parallel. A balance control part which controls voltage balance of the primary-side DC capacitors controls primary-side DC capacitor voltages of the respective units so that they are not uniform, but deviate.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to voltage balance control on the series-connected side of a dual active bridge (DAB) type bidirectional isolated DC / DC converter in which DC power is converted to AC power by an inverter, isolated by a transformer, and converted back to DC by another inverter, in a circuit configuration in which one end is connected in series and the other end is connected in parallel. [Background technology]

[0002] Figure 1 shows the circuit configuration used in this invention. This circuit configuration consists of m DAB converters. Since the input and output sides of a DAB converter are insulated, multiple converters can be connected in series and parallel. In addition to converting and isolating high-current DC power by connecting them in parallel, bidirectional conversion from high-voltage power to low-voltage, high-current power, or vice versa, can be performed by connecting one end in series as shown in Figure 1. Here, the series-connected side on the left side of Figure 1 is defined as the primary side, and the parallel-connected side on the right side is defined as the secondary side.

[0003] The problem in this case is the balance of the series-connected primary capacitor voltage. Causes of imbalance include copper loss and iron loss in the high-frequency transformer, and variations in conduction loss and switching loss in the switching elements. In units with large losses, the primary DC capacitor voltage is discharged, causing the voltage balance to be disrupted, and the voltage burden is concentrated on units with small losses, causing problems such as unit overheating, destruction of elements due to switching surges, and destruction of parts due to overvoltage.

[0004] To address this issue, Patent Documents 1 and 2 disclose a method for controlling the balance of the primary side DC capacitor voltage. Patent Document 1 is a method for a two-unit configuration, while Patent Document 2 is a method for a configuration with more than two units, which detects the imbalance of the primary side DC capacitor voltage and adjusts the phase difference of the AC output voltage of each DAB unit accordingly, thereby maintaining the balance of the primary side DC capacitor voltage. In addition, the current responsibility of each unit is equalized, which prevents overheating, damage, and shortened lifespan due to current concentration in a specific unit.

[0005] Fig. 11 shows a block diagram of a balance control for the primary side DC capacitor voltages connected in series as disclosed in Patent Documents 1 and 2. There are m DAB units, and Fig. 11 shows the control block for the kth unit.

[0006] The low-pass filter LPF removes ripples and noises with a frequency twice that of the fundamental wave from the primary DC capacitor voltage Vdc1k of the kth unit. The primary DC capacitor voltage average value Vdc1avg is a value obtained by dividing either the total of the primary DC capacitor voltages Vdc11 to Vdc1m or the primary DC voltage Vdc1 by the number m of units. When voltage control is applied to the primary DC voltage Vdc1, the command value may be a value obtained by dividing the command value by the number m of units.

[0007] The subtractor 1 subtracts the primary side DC capacitor voltage average value Vdc1avg from the primary side DC capacitor voltage Vdc1k of the kth unit to which the low pass filter LPF is applied, to obtain the primary side voltage deviation of the kth unit.

[0008] Amplifier 2 amplifies the primary side voltage deviation and outputs the phase θkb of the kth unit. As an example, the following two amplifiers are used in combination for this amplifier 2. Proportional amplifier P1 outputs a value proportional to the primary side voltage deviation. First-order lag filter 2a with gain amplifies the low-frequency components of the primary side voltage deviation. First adder 2b adds the outputs of the above two amplifiers and outputs the phase θkb. Second adder 3 adds a phase command value θ*, which is provided separately, to the phase θkb, and outputs the phase difference command value θk of the kth unit.

[0009] The phase command value θ* may be given by feedback control of the DC current or voltage, or may be calculated from the power command value P*, the primary DC capacitor voltage Vdc1k of the kth unit, and the secondary DC capacitor voltage Vdc2k of the kth unit.

[0010] Here, when the phase θkb, phase command value θ*, and phase difference command value θk are positive, the phase of the AC side voltage V1k leads the phase of the AC side voltage V2k, and power is transmitted from the primary side to the secondary side. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2018-98834 A [Patent Document 2] JP 2015-6066 A Summary of the Invention [Problem to be solved by the invention]

[0012] However, even if the m units shown in Figure 1 are identically designed, there may be cases where differences in copper loss and conduction loss occur between each unit due to variations in the characteristics of components such as transformers and switching elements within the units.

[0013] The technologies of Patent Documents 1 and 2 are effective from the viewpoint of equalizing voltage and current duties. However, they cause currents of approximately the same magnitude to pass through units with large copper losses and conduction losses. From the viewpoint of efficiency, it is preferable to pass a large current through units with small losses. Units with large copper losses and conduction losses also generate a lot of heat. By reducing the current flowing through units with large losses, the heat duties can be made closer to equal.

[0014] For the reasons described above, in a DAB type bidirectional isolated DC / DC converter in which one end is connected in series and the other end is connected in parallel, the challenge is to improve the efficiency of the entire device. [Means for solving the problem]

[0015] The present invention has been devised in view of the above-mentioned problems in the related art, and one aspect thereof is a DAB type bidirectional isolated DC / DC converter including a primary side DC power supply, a secondary side DC power supply, and a first unit to an m-th unit (m: an integer of 2 or more) connected between the primary side DC power supply and the secondary side DC power supply, the first unit to the m-th unit being connected in series between a positive electrode and a negative electrode of the primary side DC power supply, secondary side DC capacitors of the first unit to the m-th unit being connected in parallel between a positive electrode and a negative electrode of the secondary side DC power supply, and secondary capacitors of the first unit to the m-th unit being connected to the primary side DC capacitors of the first unit to the m-th unit, respectively. The power supply system includes a first inverter of the m-th unit, second inverters of the first unit to the m-th unit connected to the secondary side DC capacitors of the first unit to the m-th unit, respectively, transformers of the first unit to the m-th unit having primary windings connected to the AC sides of the first inverters of the first unit to the m-th unit and secondary windings connected to the AC sides of the second inverters of the first unit to the m-th unit, respectively, and a balance control unit that controls the voltage balance of the primary side DC capacitors, wherein the balance control unit controls the primary side DC capacitor voltages of each unit so that they are not equal but a deviation occurs.

[0016] In one aspect, the balance control unit controls the primary side DC capacitor voltage of the kth unit (k=an integer from 1 to m) to be smaller than the primary side DC capacitor voltage average value if the loss of the kth unit is larger than the unit loss average value, and controls the primary side DC capacitor voltage of the kth unit to be larger than the primary side DC capacitor voltage average value if the loss of the kth unit is smaller than the unit loss average value.

[0017] In another aspect, the balance control unit controls the primary side DC capacitor voltage of the kth unit (k=an integer from 1 to m) to be smaller than the primary side DC capacitor voltage average value if the temperature detection value of the kth unit is higher than the unit temperature average value, and controls the primary side DC capacitor voltage of the kth unit to be larger than the primary side DC capacitor voltage average value if the temperature detection value of the kth unit is lower than the unit temperature average value.

[0018] In another aspect, the balance control unit includes a low-pass filter that extracts a DC component of the primary side DC capacitor voltage of the kth unit (k=an integer from 1 to m), a first subtractor that subtracts a primary side DC capacitor voltage average value from an output of the low-pass filter and outputs the result as a primary side voltage deviation of the kth unit, a second subtractor that subtracts an unbalance voltage command value of the kth unit from the primary side voltage deviation of the kth unit, a first amplifier that amplifies the output of the second subtractor and outputs the result as the phase of the kth unit, and a second adder that adds a phase command value to the phase of the kth unit and outputs the result as a phase difference command value of the kth unit.

[0019] In one aspect of the present invention, the balance control section sets the unbalance voltage command value of each unit to a fixed value determined in advance in accordance with a loss of each unit.

[0020] In another aspect, the balance control unit sets the unbalance voltage command value of the kth unit to a value obtained by amplifying the value obtained by subtracting the temperature detection value of the kth unit from the unit temperature average value.

[0021] In another aspect, the balance control section sets the unbalance voltage command value of the kth unit to a value determined based on the phase of the kth unit.

[0022] In one aspect, the balance control unit is characterized in that a parameter used when determining the unbalance voltage command value of the kth unit from the phase of the kth unit is made variable based on a power command value or a phase command value. Effect of the Invention

[0023] According to the present invention, it is possible to improve the efficiency of the entire device in a DAB type bidirectional isolated DC / DC converter in which one end is connected in series and the other end is connected in parallel. [Brief description of the drawings]

[0024] [Figure 1] This diagram shows a DAB type bidirectional isolated DC / DC converter in which the primary side is connected in series and the secondary side is connected in parallel. [Diagram 2] FIG. 2 is a block diagram showing a balance control unit for a primary-side DC capacitor voltage in the first embodiment. [Diagram 3] A diagram showing the relationship between the primary side DC capacitor voltage and the passing power of each unit. [Figure 4] FIG. 11 is a block diagram showing a balance control unit for a primary-side DC capacitor voltage in the second embodiment. [Diagram 5] FIG. 11 is a block diagram showing a balance control unit for a primary-side DC capacitor voltage in the third embodiment. [Figure 6] FIG. 13 is a block diagram showing a balance control unit for a primary-side DC capacitor voltage in the fourth embodiment. [Figure 7] FIG. 13 is a diagram showing the influence of the primary side DC capacitor voltage when transmitting power from the primary side to the secondary side. [Figure 8] FIG. 13 is a diagram showing the influence of the primary side DC capacitor voltage when transmitting power from the secondary side to the primary side. [Figure 9] FIG. [Figure 10] FIG. [Figure 11] FIG. 1 is a block diagram showing a conventional primary-side DC capacitor voltage balance control unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, first to fourth embodiments of the DAB type bidirectional isolated DC / DC converter according to the present invention will be described in detail with reference to Figs.

[0026] [Embodiment 1] The present invention is premised on being applied to the circuit in Fig. 1. With the left side of Fig. 1 being the primary side and the right side being the secondary side, the primary sides of m DAB units are connected in series and the secondary sides are connected in parallel. The first to m-th units are connected between the primary side DC power supply DC1 and the secondary side DC2.

[0027] Primary side DC capacitors C1 of the first to m-th units are connected in series across the primary side DC power supply DC1. First and second switching elements S1 and S2 are connected in series across the primary side DC capacitor C1 of each unit. Third and fourth switching elements S3 and S4 are connected in series across the primary side DC capacitor C1 of each unit. The first to fourth switching elements S1 to S4 form a first inverter.

[0028] Secondary side DC capacitors C2 of the first to m-th units are connected in parallel across the secondary side DC power supply DC2. Fifth and sixth switching elements S5 and S6 are connected in series across the secondary side DC capacitor C2 of each unit. Seventh and eighth switching elements S7 and S8 are connected in series across the secondary side DC capacitor C2 of each unit. The fifth to eighth switching elements S5 to S8 form a second inverter.

[0029] One end of a reactor L1 is connected to the connection point of the first and second switching elements S1 and S2. One end of a reactor L2 is connected to the connection point of the third and fourth switching elements S3 and S4. One end of a reactor L3 is connected to the connection point of the fifth and sixth switching elements S5 and S6. One end of a reactor L4 is connected to the connection point of the seventh and eighth switching elements S7 and S8.

[0030] A primary winding of the transformer Tr is connected between the other end of the reactor L1 and the other end of the reactor L2. A secondary winding of the transformer Tr is connected between the other end of the reactor L3 and the other end of the reactor L4. The first inverter, the second inverter, and the transformer Tr form one unit. In the first embodiment, the system includes first to m-th units (m: an integer of 2 or more).

[0031] 1, the reactors L1 to L4 are connected in series between the first inverter, the second inverter and the transformer Tr, but the reactors L1 to L4 may be replaced by the leakage inductance of the transformer Tr, or both the reactors L1 to L4 and the leakage inductance of the transformer Tr may be used.

[0032] The voltage of the primary DC power supply DC1 is Vdc1, the voltage of the secondary DC power supply DC2 is Vdc2, the primary DC capacitor voltages of the primary DC capacitor C1 of the 1st to mth units are Vdc11 to Vdc1m, the secondary DC capacitor voltages of the secondary DC capacitor C2 of the 1st to mth units are Vdc21 to Vdc2m, the primary AC voltage of the kth unit is V1k, the secondary AC voltage of the kth unit is V2k, the primary AC current of the kth unit is i1k, and the secondary AC current of the kth unit is i2k, where k is an integer from 1 to m.

[0033] Fig. 2 shows a balance control section that controls the voltage balancer of the primary side DC capacitor of the kth unit in the circuit configuration of Fig. 1. In Fig. 2, as in Fig. 11, the phase difference command value θk of the kth unit is calculated.

[0034] The low-pass filter LPF removes ripples and noises with a frequency twice that of the fundamental wave from the primary DC capacitor voltage Vdc1k of the kth unit. The primary DC capacitor voltage average value Vdc1avg is a value obtained by dividing either the total of the primary DC capacitor voltages Vdc11 to Vdc1m or the primary DC voltage Vdc1 by the number m of units. When voltage control is applied to the primary DC voltage Vdc1, the command value may be a value obtained by dividing the command value by the number m of units.

[0035] The subtractor 1 subtracts the primary side DC capacitor voltage average value Vdc1avg from the primary side DC capacitor voltage Vdc1k of the kth unit to which the low pass filter LPF is applied, to obtain the primary side voltage deviation of the kth unit.

[0036] The second subtractor 4 subtracts the unbalanced voltage command value ΔVdc1k* of the primary side DC capacitor of the kth unit from the primary side voltage deviation of the kth unit. In the present embodiment 1, the unbalanced voltage command value ΔVdc1k* is a fixed value. The output of the second subtractor 4 is input to the amplifier 2.

[0037] The amplifier 2 amplifies the output of the second subtractor 4 and outputs the phase θkb of the AC output voltage of the kth unit. As an example, the following two amplifiers are used in combination for the amplifier 2 in this example. The proportional amplifier P1 outputs a value proportional to the output of the second subtractor 4. The first-order lag filter 2a with gain amplifies the low-frequency components of the output of the second subtractor 4. The first adder 2b adds the outputs of the above two amplifiers and outputs the phase θkb of the kth unit. The second adder 3 adds a phase command value θ*, which is provided separately, to the phase θkb and outputs the phase difference command value θk of the kth unit.

[0038] The phase command value θ* may be given by feedback control of the DC current or voltage, or may be calculated from the power command value P*, the primary DC capacitor voltage Vdc1k of the kth unit, and the secondary DC capacitor voltage Vdc2k of the kth unit.

[0039] Here, when the phase θkb, phase command value θ*, and phase difference command value θk are positive, the phase of the AC side voltage V1k leads the phase of the AC side voltage V2k, and power is transmitted from the primary side to the secondary side.

[0040] In the present invention, the primary side DC capacitor voltage of each unit is not made equal but a deviation is generated, thereby creating a difference in the power passing through each unit. First, the operation will be explained.

[0041] Figure 3 shows the series side (primary side) extracted from the circuit in Figure 1. Consider the case where the primary side DC capacitor voltage Vdc1k of the kth unit is excessive, and the primary side DC capacitor voltage Vdc1m of the mth unit is insufficient. In this case, since each unit is connected in series, the current flowing from the primary side DC power supply DC1 to each unit is equal. Therefore, the power exchanged between the kth unit and the primary side DC power supply DC1 is greater than the power of the other units, and the power exchanged between the mth unit and the primary side DC power supply DC1 is less than the power of the other units.

[0042] Here, we assume that the capacitor voltage balance control is operating normally and the primary-side DC capacitor voltage remains constant. In order for the capacitor voltage to be constant, when each unit receives power from the primary-side DC power supply DC1, the received power is transmitted as is to the secondary side, and when each unit sends power to the primary-side DC power supply DC1, it receives the same amount of power from the secondary side. Therefore, due to the functioning of the capacitor voltage balance control, the kth unit has a higher passing power than the other units, and the mth unit has a lower passing power than the other units.

[0043] From the above, if the capacitor voltage balance control is operating, the passing power of the unit can be increased by increasing the primary side DC capacitor voltage, and the passing power of the unit can be decreased by decreasing the primary side DC capacitor voltage.

[0044] In the first embodiment, a balance control is applied to the primary side DC capacitor voltage to keep the voltage constant, while an unbalanced voltage command value is given to the balance control to generate a deviation.

[0045] If the loss of a unit is larger than the unit loss average value, the primary DC capacitor voltage of that unit is controlled to be smaller than the primary DC capacitor voltage average value, and if the loss of a unit is smaller than the unit loss average value, the primary DC capacitor voltage of that unit is controlled to be larger than the primary DC capacitor voltage average value. The unit loss average value is calculated by dividing the total loss of each unit by the number of units m.

[0046] This operation will be explained using Fig. 2. Consider the case where an unbalanced voltage command value ΔVdc1k* of the primary side DC capacitor of the positive k-th unit is given in a state where the primary side DC capacitor voltages are balanced at Vdc1k=Vdc1avg.

[0047] At this time, the value input to the amplifier 2 becomes negative, the phase θkb is also negative, the primary side AC voltage lags behind the secondary side AC voltage, and power is transmitted from the secondary side to the primary side. This power is charged to the primary side DC capacitor C1, and the primary side DC capacitor voltage Vdc1k of the kth unit increases.

[0048] This operation continues until the primary side DC capacitor voltage Vdc1k of the kth unit increases to Vdc1avg+ΔVdc1k*. Therefore, the control block in Fig. 2 can increase the primary side DC capacitor voltage of the kth unit by the unbalance voltage command value ΔVdc1k* from the primary side DC capacitor voltage average value Vdc1avg.

[0049] The method of giving the unbalance voltage command value ΔVdc1k* differs depending on the embodiment. In the present embodiment 1, the unbalance voltage command value ΔVdc1k* is a fixed value. To determine the fixed value, an efficiency measurement test or a measurement of the winding resistance of the transformer is performed to obtain the loss of the unit, and the fixed value is determined in advance according to this loss.

[0050] For units with large losses, the primary side DC capacitor voltage can be lowered and the power passing through the unit can be reduced by setting the unbalance voltage command value ΔVdc1k* to a negative value. For units with small losses, the primary side DC capacitor voltage can be raised and the power passing through the unit can be increased by setting the unbalance voltage command value ΔVdc1k* to a positive value. This makes it possible to reduce losses throughout the equipment.

[0051] In a configuration in which multiple DAB bidirectional isolated DC / DC converters are connected at one end in series and the other end in parallel, a deviation occurs in the balance of the primary side DC capacitor voltages according to the first embodiment, but by increasing the primary side DC capacitor voltage of a unit with small loss, the passing power of that unit increases, and by decreasing the primary side DC capacitor voltage of a unit with large loss, the transmission power of that unit decreases. This allows large power to pass through units with small loss, making it possible to reduce losses in the entire device.

[0052] In the first embodiment, the above effect is achieved by measuring the loss of the unit in advance. Since a fixed value is used for control, the stability is the highest.

[0053] [Embodiment 2] Fig. 4 shows a balance control unit for controlling the voltage balance of the primary side DC capacitors in the present embodiment 2. Fig. 4 adds the following to Fig. 2.

[0054] The temperature detector 5 detects the temperature detection value Tk of the kth unit. The third subtractor 6 subtracts the temperature detection value Tk of the kth unit from the average temperature value Tavg of each unit to obtain the difference from the average unit temperature. The average temperature value Tavg is the sum of T1 to Tm divided by the number of units m.

[0055] The second proportional amplifier P2 amplifies the output of the third subtractor 6. The output of the second proportional amplifier P2 becomes the unbalance voltage command value ΔVdc1k* of the primary side DC capacitor of the kth unit.

[0056] If the unit temperature detection value is higher than the unit temperature average value Tavg, the primary side DC capacitor voltage is controlled to be smaller than the primary side DC capacitor voltage average value Vdc1avg, and if the unit temperature detection value is lower than the unit temperature average value Tavg, the primary side DC capacitor voltage is controlled to be larger than the primary side DC capacitor voltage average value Vdc1avg.

[0057] In the second embodiment, the unit temperature is measured and compared with the average value, and the unbalance voltage command value ΔVdc1k* is determined based on the result. A unit with small loss has a lower unit temperature than the surroundings, the unbalance voltage command value ΔVdc1k* is set to a positive value, the primary side DC capacitor voltage increases, and the passing power increases. A unit with large loss has a higher unit temperature, the unbalance voltage command value ΔVdc1k* is set to a negative value, the primary side DC capacitor voltage decreases, the passing power decreases, and heat generation is suppressed.

[0058] In the second embodiment, the loss of the entire device can be suppressed without measuring the unit loss in advance. Also, the temperature of each unit can be made uniform, and the shortening of the life span of a specific unit can be prevented.

[0059] In the second embodiment, by using a temperature detection means, the same effects as those of the first embodiment are achieved. In addition to eliminating the need for prior loss measurement, the temperature of each unit can be made uniform, preventing a reduction in the life span of a specific unit.

[0060] [Embodiment 3] Fig. 5 shows a balance control unit for controlling the voltage balance of the primary side DC capacitor in the present embodiment 3. In the present embodiment 3, the unbalanced voltage command value ΔVdc1k* is set to a value determined based on the phase θkb. Fig. 5 adds the following to Fig. 2.

[0061] The gain-added first-order lag filter 7 cuts out the high-frequency components with phase θkb and amplifies the low-frequency components. The gain-added first-order lag filter 7 is set to G2 / (1+sT2) as shown in Fig. 5. The output of the gain-added first-order lag filter 7 becomes the unbalance voltage command value ΔVdc1k* of the primary side DC capacitor of the kth unit.

[0062] As mentioned above, in a unit with large losses, the primary side DC capacitor is discharged and the voltage drops. For this reason, the phase θkb becomes negative due to balance control, and power is transferred from the secondary side to the primary side to compensate for the discharged charge.

[0063] In the third embodiment, this operation is detected and a negative unbalance voltage command value ΔVdc1k* is set for the unit with large loss to reduce the unit passing power.

[0064] Conversely, in a unit with small losses, the primary side DC capacitor voltage increases, so the phase θkb becomes positive for discharge and power is transmitted from the primary side to the secondary side. The unbalance voltage command value ΔVdc1k* is set to positive, allowing the unit passing power to be increased.

[0065] In the third embodiment, the same effect as in the second embodiment can be obtained without providing a separate temperature detection means.

[0066] As described above, according to the third embodiment, the same effects as those of the first and second embodiments can be obtained. Moreover, in the third embodiment, the above effects are realized by using the phase θkb. Therefore, there is no need to measure loss in advance or to use a temperature detection means.

[0067] [Embodiment 4] Fig. 6 shows a balance control unit for controlling the voltage balance of the primary side DC capacitor in the present embodiment 4. In the present embodiment 4, the parameters used when determining the unbalanced voltage command value ΔVdc1k* from the phase θkb in the embodiment 3 are made variable based on the power command value P* or the phase command value θ*. Fig. 6 adds the following to Fig. 5.

[0068] The gain adjustment unit 8 outputs a unique positive value for the power command value P*, and outputs a small value if the power command value P* is positive, and outputs a large value if the power command value P* is negative. A phase command value θ* can also be used instead of the power command value P*.

[0069] This gain adjustment unit 8 can be a linear function consisting of offset and gain, or it can be a quadratic or higher function or a table. The output of this gain adjustment unit 8 becomes the gain G2 of the parameter G2 / (1+sT2) of the first-order lag filter 7 with gain that amplifies the low-frequency component of the phase θkb.

[0070] In the fourth embodiment, the unbalance voltage command value ΔVdc1k* is determined based on the phase θkb, as in the third embodiment. However, in the fourth embodiment, the gain G2 is changed according to the power command value P*. The necessity for this will be explained with reference to Figs. 7 and 8.

[0071] 7 shows a state in which the power command value P* is positive, power is transmitted from the primary side DC power supply DC1 to the units, and the units transmit power from the primary side to the secondary side. Here, consider the case in which the primary side DC capacitor voltage Vdc1k of the kth unit is larger than those of the other units.

[0072] The current flowing from the primary DC power supply DC1 to each unit is equal, and the kth unit receives more power from the primary DC power supply DC1 than the other units. This makes the primary DC capacitor voltage Vdc1k of the kth unit more likely to increase. If the primary DC capacitor voltage Vdc1k of the kth unit increases and the balance control response is not fast enough to increase the amount of power transmitted to the secondary side, the primary DC capacitor voltage Vdc1k of the kth unit will continue to increase, and the voltage balance of the primary DC capacitor will be completely destroyed.

[0073] On the other hand, if the primary side DC capacitor voltage Vdc1m of the mth unit is smaller than those of the other units, the primary side DC capacitor voltage Vdc1m of the mth unit is more likely to decrease, and if the balance control response is not fast enough, it will drop to zero. In this way, when the power command value P* is positive, the voltage balance of the primary side DC capacitors is likely to become unstable. Therefore, in this embodiment 4, when the power command value P* is positive, the gain G2 is reduced and the unbalanced voltage command value is reduced.

[0074] Figure 8 shows a state in which the power command value P* is negative. Power is transmitted from the secondary side of the unit to the primary side, and from the unit to the primary-side DC power supply DC1. If the primary-side DC capacitor voltage Vdc1k of the kth unit is larger than that of the other units, the power transmitted to the primary-side DC power supply DC1 also increases, so the primary-side DC capacitor voltage Vdc1k of the kth unit tends to decrease.

[0075] Furthermore, when the primary side DC capacitor voltage Vdc1m of the mth unit is smaller than those of the other units, the power transmitted to the primary side DC power supply DC1 also decreases, suppressing the decrease in the primary side DC capacitor voltage Vdc1m of the mth unit.

[0076] Therefore, when the power command value P* is negative, the voltage balance of the primary side DC capacitor becomes stable. This means that imbalance is less likely to occur, and the effect of reducing loss in the entire device, which is the target of the present invention, decreases. Therefore, in the fourth embodiment, when the power command value P* is negative, the gain G2 is increased to encourage the occurrence of imbalance.

[0077] As described above, the fourth embodiment has the same effects as the first to third embodiments. In addition, it is possible to improve the instability of the primary side DC capacitor voltage balance when the direction of power transmission is from the series side (primary side) to the parallel side (secondary side), which is a problem in the third embodiment. In addition, it is possible to prevent a decrease in the loss reduction effect when the direction of power transmission is from the parallel side (secondary side) to the series side (primary side).

[0078] The effect of the third embodiment is shown by a simulation. Figure 9 shows a configuration of two DAB units under the simulation conditions. Power is transmitted from the primary side in series to the secondary side in parallel, and the first unit increases the copper loss of the high-frequency transformer.

[0079] A simulation waveform is shown in Fig. 10. In this waveform, the ripple of the operating frequency on the DAB AC side is removed by a filter. At time 0 seconds, the third embodiment is enabled. Before time 0 seconds, Vdc11=Vdc12, and the primary side DC capacitor voltages Vdc11 and Vdc12 are balanced.

[0080] When the third embodiment is enabled, the primary side DC capacitor voltage Vdc12 of the second unit with small copper loss increases, but the deviation remains constant and stable. Of the secondary side DC currents Idc21 and Idc22, Idc22 is larger from before time 0 seconds, but by enabling the third embodiment, Idc22 increases further, and the passing power can be concentrated in the unit with small loss.

[0081] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims. [Explanation of symbols]

[0082] LPF: Low-pass filter 1...First subtractor 2…Amplifier 2a…First-order lag filter with gain 2b...First adder P1…1st proportional amplifier 3...Second adder 4...Second subtractor 5. Temperature detector 6…Third subtraction period P2: Second proportional amplifier 7...First-order lag filter with gain 8…Gain adjustment section

Claims

1. A DAB bidirectional isolated DC / DC converter including a primary side DC power supply, a secondary side DC power supply, and first to m-th units (m: an integer of 2 or more) connected between the primary side DC power supply and the secondary side DC power supply, primary side DC capacitors of the first unit to the mth unit connected in series between a positive electrode and a negative electrode of the primary side DC power supply; secondary-side DC capacitors of the first unit to the mth unit connected in parallel between a positive electrode and a negative electrode of the secondary-side DC power supply; First inverters of the first unit to the m unit connected to the primary side DC capacitors of the first unit to the m unit, respectively; second inverters of the first unit to the m unit connected to the secondary side DC capacitors of the first unit to the m unit, respectively; Transformers of the first unit to the m unit, each having a primary winding connected to an AC side of the first inverter of the first unit to the m unit, and a secondary winding connected to an AC side of the second inverter of the first unit to the m unit, a balance control unit for controlling a voltage balance of the primary side DC capacitor; Equipped with The balance control unit is A DAB bidirectional isolated DC / DC converter, characterized in that the primary side DC capacitor voltage of each unit is controlled to a value obtained by adding an unbalance voltage command value of each unit to an average primary side DC capacitor voltage value.

2. The balance control unit is 2. The DAB type bidirectional isolated DC / DC converter according to claim 1, characterized in that if the loss of the kth unit (k=an integer from 1 to m) is larger than the unit loss average value, the primary side DC capacitor voltage of the kth unit is controlled to be smaller than the primary side DC capacitor voltage average value, and if the loss of the kth unit is smaller than the unit loss average value, the primary side DC capacitor voltage of the kth unit is controlled to be larger than the primary side DC capacitor voltage average value.

3. The balance control unit is 2. The DAB bidirectional isolated DC / DC converter according to claim 1, characterized in that if the temperature detection value of the kth unit (k=an integer from 1 to m) is higher than the unit temperature average value, the primary side DC capacitor voltage of the kth unit is controlled to be smaller than the primary side DC capacitor voltage average value, and if the temperature detection value of the kth unit is lower than the unit temperature average value, the primary side DC capacitor voltage of the kth unit is controlled to be larger than the primary side DC capacitor voltage average value.

4. The balance control unit is a low-pass filter that extracts a DC component of the primary-side DC capacitor voltage of the kth (k=an integer from 1 to m) unit; a first subtractor that subtracts the primary side DC capacitor voltage average value from an output of the low pass filter and outputs the result as a primary side voltage deviation of the kth unit; a second subtractor that subtracts the unbalanced voltage command value of the k-th unit from the primary side voltage deviation of the k-th unit; a first amplifier that amplifies the output of the second subtractor and outputs the amplified output as a phase of the kth unit; a second adder that adds a phase command value to the phase of the kth unit and outputs the result as a phase difference command value of the kth unit; 2. The DAB bidirectional isolated DC / DC converter according to claim 1, further comprising:

5. The balance control unit is 5. The DAB bidirectional isolated DC / DC converter according to claim 4, wherein the unbalanced voltage command value of each unit is a fixed value determined in advance in accordance with the loss of each unit.

6. The balance control unit is 5. The DAB bidirectional isolated DC / DC converter according to claim 4, wherein the unbalance voltage command value of the kth unit is an amplified value obtained by subtracting the temperature detection value of the kth unit from the unit temperature average value.

7. The balance control unit is 5. The DAB bidirectional isolated DC / DC converter according to claim 4, wherein the unbalanced voltage command value of the kth unit is a value determined based on the phase of the kth unit.

8. The balance control unit is 8. The DAB bidirectional isolated DC / DC converter according to claim 7, wherein a parameter used when determining the unbalanced voltage command value of the kth unit from the phase of the kth unit is made variable based on a power command value or a phase command value.

9. a primary side DC power supply, a secondary side DC power supply, and first to m-th units (m: an integer of 2 or more) connected between the primary side DC power supply and the secondary side DC power supplies; primary side DC capacitors of the first unit to the mth unit connected in series between a positive electrode and a negative electrode of the primary side DC power supply; secondary-side DC capacitors of the first unit to the mth unit connected in parallel between a positive electrode and a negative electrode of the secondary-side DC power supply; First inverters of the first unit to the m unit connected to the primary side DC capacitors of the first unit to the m unit, respectively; second inverters of the first unit to the m unit connected to the secondary side DC capacitors of the first unit to the m unit, respectively; Transformers of the first unit to the m unit, each having a primary winding connected to an AC side of the first inverter of the first unit to the m unit, and a secondary winding connected to an AC side of the second inverter of the first unit to the m unit, a balance control unit for controlling a voltage balance of the primary side DC capacitor; A control method for a DAB bidirectional isolated DC / DC converter comprising: The balance control unit is A control method for a DAB type bidirectional isolated DC / DC converter, characterized in that the primary side DC capacitor voltage of each unit is controlled to a value obtained by adding an unbalance voltage command value of each unit to an average primary side DC capacitor voltage value.

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