JP2019097273A - Power conversion device - Google Patents

Abstract

[Problem] To provide a power conversion device that operates efficiently. [Solution] The power conversion device includes an output terminal configured by connecting the output sections of multiple converters 1a, 1b in series, a setting circuit 12 that sets the output sharing rates of the multiple converters 1a, 1b based on the amount of power output from the output terminal, and a control circuit 13 that controls the operation of the power conversion circuit based on the output sharing rates set by the setting circuit 12. (Selected Figure)

Description

  The present invention relates to a power converter.

  DESCRIPTION OF RELATED ART Conventionally, the power converter device which connected the output side of several insulation type DC-DC converters in series is known (patent document 1). The invention which concerns on patent document 1 has obtained the output electric power of high voltage from the power supply of low voltage by the said structure.

JP 2011-125175 A

  In general, the efficiency of the DC-DC converter is higher when operating at the rated power, but when the output power of the power supply on the input side fluctuates or the power required on the output side fluctuates, It is known to decline. The power conversion device according to Patent Document 1 operates all DC-DC converters in the same manner by synchronously driving switching elements provided on the primary side of each DC-DC converter. For this reason, when operating in a state other than rated power, the power conversion device according to Patent Document 1 operates in a state in which the efficiency of all DC-DC converters is low, so the efficiency of the entire power conversion device decreases. There is a problem of

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power converter that operates efficiently.

  The power conversion device according to one aspect of the present invention sets the output sharing ratio of the plurality of converters based on the output terminal configured by connecting the output portions of the plurality of converters in series and the amount of power output from the output terminal. And a control circuit that controls the operation of the power conversion circuit based on the output sharing ratio set by the setting circuit.

  According to the present invention, a power converter that operates efficiently is realized.

FIG. 1 is a block diagram of a power conversion device according to a first embodiment of the present invention. FIG. 2 is a time chart showing each output according to the first embodiment of the present invention. FIG. 3 is a graph showing the relationship between the output share ratio and the duty ratio. FIG. 4 is a graph showing the relationship between efficiency and output power. FIG. 5 is a block diagram of a power conversion device according to a second embodiment of the present invention. FIG. 6 is a block diagram of a power conversion device according to another embodiment of the present invention. FIG. 7 shows a forward type circuit system. FIG. 8 shows a flyback type circuit system. FIG. 9 shows an LLC type circuit system. FIG. 10 shows a phase shift full bridge type circuit system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same parts will be denoted by the same reference numerals and the description thereof will be omitted.

First Embodiment
The power converter according to the first embodiment will be described with reference to FIG. As shown in FIG. 1, the power converter includes a converter 1a and a converter 1b. The power converter further includes a sensor 10, a determination circuit 11, a setting circuit 12, and a control circuit 13.

  The input portion of the converter 1a and the input portion of the converter 1b are connected in parallel to form an input terminal. A DC power supply 6 is connected to the input terminal. On the other hand, the output portion of converter 1a and the output portion of converter 1b are connected in series to constitute an output terminal. The load 7 is connected to the output terminal.

  Although the converter 1a and the converter 1b are isolated DC-DC converters, they are not limited to this. The load 7 is an energy storage device such as, for example, a battery, but is not limited thereto.

  The sensor 10 acquires the amount of power output from the output terminal to the load 7. The determination circuit 11 determines the amount of power acquired by the sensor 10. For example, the determination circuit 11 can determine whether the amount of power acquired by the sensor 10 is insufficient.

  Setting circuit 12 sets the output sharing ratio of converter 1 a and converter 1 b based on the result determined by determination circuit 11. In other words, the setting circuit 12 sets the output sharing ratio of the converter 1a and the converter 1b based on the amount of power output from the output terminal. The output sharing ratio is the ratio of the power that converter 1 a and converter 1 b output to load 7. When the power output from the converter 1a to the load 7 is larger than the power output from the converter 1b to the load 7, the output sharing ratio of the converter 1a is higher than the output sharing ratio of the converter 1b. On the other hand, when the power output from converter 1a to load 7 is smaller than the power output from converter 1b to load 7, the output sharing ratio of converter 1a is lower than the output sharing ratio of converter 1b.

  Control circuit 13 controls the operation of converter 1a and converter 1b. More specifically, the control circuit 13 controls the operation of the power conversion circuit based on the output sharing ratio set by the setting circuit 12. The power conversion circuit is a bridge circuit (full bridge circuit 2) composed of switching elements (each switching elements 8a to 8d and 9a to 9d) described later, a transformer (insulation transformer 3), and a rectification circuit (rectification circuit 4) It consists of The control circuit 13 controls the on / off states of the switching elements 8a to 8d and 9a to 9d of the full bridge circuit 2 related to the converter 1a and the converter 1b. Each of the switching elements 8 a to 8 d and 9 a to 9 d is an element that converts DC power input from the DC power supply 6. The DC power converted by the switching elements 8a to 8d and 9a to 9d may be hereinafter referred to as second DC power. Further, the DC power input from the DC power supply 6 may be hereinafter referred to as first DC power. The power conversion circuit converts the first DC power input from the DC power supply 6 into second DC power. Moreover, the output part of the converter 1a and the output part of the converter 1b output 2nd direct-current power converted by the power conversion circuit.

  The determination circuit 11, the setting circuit 12, and the control circuit 13 include programmed processing devices such as processing devices including electrical circuits. Also, the decision circuit 11, the setting circuit 12, and the control circuit 13 include devices such as application specific integrated circuits (ASICs) and circuit components arranged to perform the described functions.

  Next, an operation example of the converter 1a will be described. As shown in FIG. 1, when the voltage input from the DC power supply 6 is the input voltage Vin, the input voltage Vin is boosted by the isolation transformer 3. The boosted voltage is (Ns / Np) Vin. Here, Np is the number of turns of the primary side winding of the insulating transformer 3. Ns is the number of turns of the secondary side winding of the isolation transformer 3. Also in converter 1b, the number of turns of the primary winding of isolation transformer 3 is Np, and the number of turns of the secondary winding is Ns.

  The voltage boosted by the isolation transformer 3 is rectified by the rectification circuit 4. The voltage rectified by the rectifier circuit 4 is hereinafter referred to as a voltage Vrec1. In the converter 1b, the voltage rectified by the rectifier circuit 4 is hereinafter referred to as a voltage Vrec2.

  In the present embodiment, the control circuit 13 controls the on / off states of the switching elements 8a to 8d, so that the voltage Vrec1 is a PWM voltage of (Ns / Np) Vin. This PWM voltage is smoothed by the output filter circuit 5 to output a DC output voltage Vout1. Similarly, in converter 1b, a DC output voltage Vout2 is output.

  In the present embodiment, the converter 1a is designed to perform soft switching operation. In this case, it is the conduction loss that causes the efficiency of the converter 1a to deteriorate. As shown in FIG. 2, when the current Irec1 output from the rectifier circuit 4 is always a positive value (that is, when the converter 1a is in the current continuous mode), the factor to increase the conduction loss is the duty ratio D1 and , And the ripple component of the current I rec1. The duty ratio D1 is the ratio of the on time to one cycle of the on / off states of the switching elements 8a to 8d in the converter 1a. Further, the duty ratio D2 described later is a ratio of the on time to one cycle of the on / off state of each of the switching elements 9a to 9d in the converter 1b. The current continuous mode is a mode in which current flows continuously. The converter 1b is also designed to perform soft switching operation.

  As the duty ratio D1 decreases, the time ratio at which the converter 1a outputs power decreases. Thus, the power output from converter 1a is reduced. Further, as the duty ratio D1 decreases, in the full bridge circuit 2, the time during which the return current that does not contribute to the power output from the converter 1a flows increases. In the step-up converter in which Np <Ns, the current flowing through full bridge circuit 2 is larger than the current flowing through rectification circuit 4, so the ratio of conduction loss of full bridge circuit 2 to the entire conduction loss is high. Become. That is, an increase in time during which the return current flows in the full bridge circuit 2 causes an increase in conduction loss, which lowers the efficiency of converter 1a.

  Therefore, the control circuit 13 controls the on / off states of the switching elements 8a to 8d so that the duty ratio D1 becomes constant at 0.95 or more. Further, the control circuit 13 controls the on / off states of the switching elements 9a to 9d so that the duty ratio D2 becomes lower than the duty ratio D1. Thus, the control circuit 13 controls the duty ratios D1 and D2 to adjust the power output from the converter 1a and the converter 1b. In general, a power conversion device provided with a plurality of converters often equalizes load sharing. That is, a general power conversion device adjusts the power output from each converter while changing the duty ratio D under the condition of D = D1 = D2.

  On the other hand, the control circuit 13 controls the on / off states of the switching elements 8a to 8d so that the duty ratio D1 becomes constant at 0.95 or more. As a result, in converter 1a, since duty ratio D1 is always 0.95 or more, the time when the return current flows in full bridge circuit 2 becomes short. This reduces the conduction loss and improves the overall efficiency of the power converter. On the other hand, since control circuit 13 controls duty ratio D2 to be lower than duty ratio D1, as shown in FIG. 2, the frequency of time during which current Irec2 of converter 1b becomes zero increases. In other words, the frequency at which converter 1b is in the current discontinuous mode is increased. As a result, a part of the switching elements of the full bridge circuit 2 related to the converter 1b can not operate by soft switching, and the switching loss increases. In addition, since the current Irec2 becomes discontinuous, the time in which the converter 1b can output power is shortened, and the power output from the converter 1b is reduced. Since the relative loss ratio increases in this manner, the efficiency of converter 1 b alone decreases. The current discontinuous mode is a mode in which current flows discontinuously.

  Here, the load 7 according to the present embodiment operates at a voltage represented by equation (1).

[Equation 1]
Vload_min <Vload <Vload_max (1)
Here, Vload is a load voltage. Vload_min is the minimum load voltage. The minimum load voltage is a voltage required when the load 7 operates. Vload_max is the maximum load voltage. The maximum load voltage is a voltage allowed when the load 7 operates.

  Further, in the present embodiment, the relationship represented by equation (2) is established.

[Equation 2]
(Ns / Np) Vin <Vload_min (2)

  From the above equations (1) and (2), it can be understood that power can not be output from the DC power supply 6 to the load 7 by only one of the converter 1a and the converter 1b. In the present embodiment, since the output portion of the converter 1a and the output portion of the converter 1b are connected in series, the output current Iout is common to the converter 1a and the converter 1b. Since (Ns / Np) Vin does not reach the minimum load voltage Vload_min even when the converter 1a tries to output the maximum power, it is necessary to operate the converter 1b in order to output power to the load 7. As shown in FIG. 3, when the converter 1b starts to operate, although the duty ratio D2 increases, the output voltage Vout1 of the converter 1a with respect to the load voltage Vload is constant, so the output sharing ratio does not change. When the duty ratio D2 further increases, the output voltage Vout2 increases, and when the condition represented by the equation (3) is satisfied, the converter 1b shifts from the current discontinuous mode to the current continuous mode.

[Equation 3]
(Ns / Np) Vin × (D1 + D2)> Vload (3)

  When converter 1b shifts from the discontinuous current mode to the continuous current mode, the output sharing ratio becomes equal to the ratio of time ratio D1 to time ratio D2.

  Next, referring to FIG. 4, the duty ratio D1 is fixed at 0.99, and the conversion efficiency with respect to the output power when the duty ratio D2 is changed, and the duty ratio D is changed as D = D1 = D2. The result of comparing the conversion efficiency with the output power in the case will be described. The output power is power output from the converter 1a and the converter 1b.

  When the duty ratio D1 is fixed to 0.99, a difference occurs in the output sharing ratio. When the difference of the output sharing ratio is changed according to the output power, it is understood that the conversion efficiency is improved in a wide output power operation range as shown in FIG. Note that Var shown in FIG. 4 is a variable.

  As described above, according to the power conversion device of the first embodiment, the following effects can be obtained.

  The power converter according to the first embodiment includes a plurality of converters (a converter 1a and a converter 1b). The output part of the converter 1a and the output part of the converter 1b are connected in series to constitute an output terminal. The sensor 10 acquires the amount of power supplied to the load 7 from the output terminal. The setting circuit 12 sets the output sharing ratio of the converter 1 a and the converter 1 b based on the amount of power acquired by the sensor 10. Then, the control circuit 13 controls the operation of the power conversion circuit based on the output sharing ratio set by the setting circuit 12. That is, the control circuit 13 controls the on / off states of the switching elements 8a to 8d and 9a to 9d based on the output sharing ratio set by the setting circuit 12. Thus, the power conversion device can operate efficiently as a whole by controlling the power output from the converter 1a and the converter 1b based on the output share ratio.

  Further, in the present embodiment, the region in which converter 1 a operates in the continuous current mode and the region in which converter 1 b operates in the discontinuous current mode coexist. Since the conversion efficiency of converter 1a operating in the current continuous mode is high and the output sharing ratio is also high, the power conversion device can operate efficiently as a whole.

  Further, control circuit 13 adjusts the power output from converter 1 b having a lower output sharing ratio among converter 1 a and converter 1 b. Thus, the power conversion device can reduce the power control load, and thus can operate efficiently as a whole. When there are three or more converters, the control circuit 13 may adjust the power output from the converter with the lowest output sharing ratio.

  Further, among the converter 1a and the converter 1b, the on / off states of the switching elements of the converter 1a having a high output sharing ratio are constant regardless of the power output from the converter 1b having a low output sharing ratio. Thus, the converter 1a having a high output sharing ratio always operates efficiently, and the efficiency of the entire power conversion device is improved. When there are three or more converters, the on / off state of the switching element of the converter with the highest output sharing ratio may be constant regardless of the power output from the other converters.

  The converter 1 a and the converter 1 b have an isolation transformer 3. It is preferable that the excitation inductance of the isolation transformer 3 related to the converter 1 b having a low output sharing ratio is smaller than the excitation inductance of the isolation transformer 3 related to the converter 1 a having a high output sharing ratio. As a result, the excitation current is increased, and the region in which the soft switching is established in the current discontinuous mode is expanded. This improves the efficiency of the entire power conversion device in the low power region. In order to obtain the excitation current necessary for the soft switching to be established, it is preferable that the output capacitances of the switching elements 9a to 9d related to the converter 1b be as low as possible.

  Converter 1a and converter 1b are isolated DC-DC converters. Further, the input parts of converter 1a and converter 1b are connected in parallel, and the output parts of converter 1a and converter 1b are connected in series. Thereby, the isolation transformer 3 is dispersed, and the converter can be miniaturized. Further, since the heat generation density of the insulating transformer 3 is reduced, the total volume can be reduced in size, and a high step-up ratio can be obtained. Furthermore, the power conversion device changes the output sharing ratio of converter 1a and converter 1b according to the power output from converter 1a and converter 1b. Thus, the power conversion device can minimize the number of converters operating at an operating point where conversion efficiency is low. Since the output sharing ratio of the converter operating at the operating point where the conversion efficiency is low is low, the power conversion device as a whole can operate more efficiently than the case where the output sharing ratio is equalized.

  In particular, in the low power region operating in the current discontinuous mode when the output sharing ratio is equalized, the number of converters operating in the current discontinuous mode is reduced by causing the power conversion device to have a difference in the output sharing ratio. Therefore, the efficiency of the power conversion device is improved. Moreover, in the area | region which operate | moves in electric current continuous mode when output sharing ratio is equalized, by making a power conversion device have a difference in output sharing ratio, higher output is obtained, while all the converters operate in electric current continuous mode. Since the sharing ratio converter can operate in the highest efficiency region, the efficiency of the power conversion device is improved.

  The upper limit of the conversion ratio of the output voltage Vout1 to the input voltage Vin may be determined regardless of the on / off states of the switching elements 8a to 8d. In this case, it is preferable that the on / off states of the switching elements 8a to 8d related to at least one converter 1a among the plurality of converters be such as to always output the maximum power. Furthermore, it is preferable that the maximum load voltage allowed when the load 7 operates is equal to or higher than the maximum output voltage that can be output with respect to the input voltage Vin of the converter 1a that always outputs the maximum power. As a result, since the converter 1a having the highest output sharing ratio always operates under the condition of high conversion efficiency, the efficiency of the entire power conversion device is improved. The input voltage Vin may be calculated based on the first DC power, and the output voltage Vout1 may be calculated based on the second DC power.

  The switching elements 8a to 8d and 9a to 9d may be semiconductor switches. In this case, it is preferable that the output capacitance of the semiconductor switch related to the converter 1b having a low output sharing ratio be smaller than the output capacitance of the semiconductor switch related to the converter 1a having a high output sharing ratio. Thereby, when the turn-on operation is hard switching in the current discontinuous mode, the switching loss is reduced, and the efficiency of the entire power conversion device in the low power region is improved.

  When the control circuit 13 controls the on / off states of the switching elements 8a to 8d related to the converter 1a to be constant and operates the converter 1a as a phase shift full bridge converter, the on time of the upper and lower sides of each bridge is 50 % Uniform. The power converter uses the pulse transformer for the drive circuit of the bridge circuit and recycles while exchanging the gate charge of the upper and lower switching elements, thereby reducing the drive power of the converter 1a, thus improving the efficiency of the power converter. Do.

Second Embodiment
Next, a second embodiment of the present invention will be described with reference to FIG. The power conversion device according to the second embodiment includes three converters 1c, 1d, 1e.

  The output voltages Voutc and Voutd of each of the converters 1c and 1d are controlled to a constant value of Vload_min / 2 or less. The power conversion device according to the second embodiment changes the output current Iout while controlling the on / off state of the switching element related to the converter 1e. In the case where the number of converters increases, in order to obtain the same effect as that of the first embodiment, the following may be performed. When the number of all converters is N (N is an integer of 3 or more), the value obtained by multiplying the maximum voltage output by each converter by (N−2) may be smaller than the minimum load voltage Vload_min. In addition, the value obtained by multiplying the maximum voltage output from each converter by N may be larger than the maximum load voltage Vload_max. Thereby, the power conversion device according to the second embodiment can operate efficiently.

  Note that the value obtained by multiplying the maximum voltage output from each converter by (N-1) may be smaller than the minimum load voltage Vload_min. Thereby, the power conversion device according to the second embodiment can operate efficiently.

  When the load 7 is a secondary battery (for example, a lithium ion battery), the maximum load voltage Vload_max is about 1.5 to 2 times the minimum load voltage Vload_min. Therefore, when the maximum voltage output from each converter is low, the value obtained by multiplying the maximum voltage by (N−2) is smaller than the minimum load voltage Vload_min. In order for the value obtained by multiplying the maximum voltage output by each converter by N to be larger than the maximum load voltage Vload_max, the N converters need to output a voltage larger than the maximum load voltage Vload_max. As the number of converters increases, the number of converters with low output sharing ratio increases, so the efficiency of the power conversion device decreases. Therefore, in order to improve the efficiency of the power converter, the number of converters is preferably about 2 to 5. However, this is not the case when the difference between the minimum load voltage Vload_min and the maximum load voltage Vload_max is small.

  While the embodiments of the present invention have been described above, it should not be understood that the statements and drawings that form a part of this disclosure limit the present invention. Various alternative embodiments, examples and operation techniques will be apparent to those skilled in the art from this disclosure.

  As shown in FIG. 6, in a power conversion device including three converters, converters of various circuit schemes can be employed. The circuit system of the converter may be, for example, a forward type shown in FIG. 7, a flyback type shown in FIG. 8, an LLC type shown in FIG. 9, or a phase shift full bridge type shown in FIG.

  In addition, the circuit system of the constant operation converter in which the on / off state of the switching element is constant may be different from that of the variable operation converter in which the power output is adjusted while changing the on / off state of the switching element. The efficiency of the power conversion device is improved by combining the constant operation converter in which the efficiency is maximized under the constant operation condition and the variable operation converter capable of maintaining high efficiency even if the on / off state of the switching element changes.

1a, 1b, 1c, 1d, 1e Converter 2 full bridge circuit 3 isolation transformer 4 rectification circuit 5 output filter circuit 6 DC power supply 7 load 8a to 8d, 9a to 9d switching element 10 sensor 11 determination circuit 12 setting circuit 13 control circuit

Claims (11)

An input unit for inputting a first DC power, a power conversion circuit for converting the first DC power input from the input unit into a second DC power, and the second DC power converted by the power conversion circuit A power converter comprising: a plurality of converters having an output unit for outputting; and a control circuit for controlling the operation of the converter,
An output terminal configured by connecting the output portions of the plurality of converters in series;
And a setting circuit configured to set an output sharing ratio of a plurality of converters based on the amount of power output from the output terminal.
The power conversion device, wherein the control circuit controls the operation of the power conversion circuit based on the output sharing ratio set by the setting circuit. The plurality of converters comprises a first converter operating in a current continuous mode in which current flows continuously, and a second converter operating in a current discontinuous mode in which current flows discontinuously.
The power conversion device according to claim 1, wherein a region in which the first converter operates in the current continuous mode and a region in which the second converter operates in the current discontinuous mode are mixed.   The power conversion device according to claim 1, wherein the control circuit adjusts the power output from the converter with the lowest output sharing ratio among the plurality of converters. The power conversion circuit includes a switching element,
The on / off state of the switching element related to the converter with the highest output sharing ratio among the plurality of converters is constant regardless of the power output from the other converters. The power converter according to any one of the preceding claims. The plurality of converters are N (N is an integer of 3 or more),
The value obtained by multiplying the maximum voltage output by each converter by (N−2) is smaller than the minimum load voltage required when the load connected to the output terminal operates.
The power according to any one of claims 1 to 4, wherein a value obtained by multiplying the maximum voltage output from each converter by N is larger than the maximum load voltage allowed when the load operates. Converter. The plurality of converters are N (N is an integer of 3 or more),
The value obtained by multiplying the maximum voltage output from each converter by (N-1) is smaller than the minimum load voltage required when the load connected to the output terminal operates.
The power according to any one of claims 1 to 4, wherein a value obtained by multiplying the maximum voltage output from each converter by N is larger than the maximum load voltage allowed when the load operates. Converter. The power conversion circuit includes a switching element,
The upper limit of the conversion ratio of the output voltage calculated based on the second DC power to the input voltage calculated based on the first DC power input to the input unit depends on the on / off state of the switching element. Not determined,
The on / off state of the switching element related to at least one converter among the plurality of converters is a state of always outputting the maximum power,
The maximum load voltage allowed when the load connected to the output terminal operates is equal to or greater than the maximum output voltage that can be output with respect to the input voltage of the converter that always outputs the maximum power. The power converter device as described in any one of -6. The plurality of converters include an isolation transformer,
Among the plurality of converters, the excitation inductance of the isolation transformer associated with the converter having the low output sharing ratio is smaller than the excitation inductance of the isolation transformer associated with the converter having the high output sharing ratio. The power converter device according to any one of the above. The power conversion circuit includes a semiconductor switch,
The output capacitance of the semiconductor switch associated with the converter with the low output sharing ratio among the plurality of converters is smaller than the output capacitance of the semiconductor switch associated with the converter with the high output sharing ratio. The power converter device according to any one of the above. The power conversion circuit includes a switching element,
The plurality of converters comprise a constant operation converter in which the on / off state of the switching element is constant, and a variable operation converter for adjusting the output power while changing the on / off state of the switching element,
The power conversion device according to any one of claims 1 to 9, wherein circuit configurations of the constant operation converter and the variable operation converter are different. The plurality of converters are isolated DC-DC converters,
The power converter according to any one of claims 1 to 10, further comprising an input terminal configured by connecting the input units in parallel.

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