JP6976145B2 - Power converter - Google Patents

Description

The present invention relates to a power conversion device.

Conventionally, a power conversion device in which the output sides of a plurality of isolated DC-DC converters are connected in series has been known (Patent Document 1). In the invention according to Patent Document 1, a high voltage output power is obtained from a low voltage power source by the above configuration.

Japanese Unexamined Patent Publication No. 2011-125175

In general, the efficiency of a DC-DC converter is high when operating at rated power, whereas when the output power of the power supply on the input side fluctuates or when the power required on the output side fluctuates, the efficiency of the DC-DC converter increases. It is known to decrease. In the power conversion device according to Patent Document 1, all DC-DC converters are operated in the same manner by synchronously driving switching elements provided on the primary side of each DC-DC converter. Therefore, when the power conversion device according to Patent Document 1 operates in a state other than the rated power, the efficiency of all the DC-DC converters operates in a low state, so that the efficiency of the entire power conversion device becomes low. There is a problem.

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

In the power conversion device according to one aspect of the present invention, an output terminal configured by connecting the output units of a plurality of converters in series and an output sharing ratio of the plurality of converters are set based on the amount of power output from the output terminals. A setting circuit for controlling the operation of the power conversion circuit and a control circuit for controlling the operation of the power conversion circuit based on the output sharing ratio set by the setting circuit are provided. The plurality of 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) is smaller than the minimum load voltage required for the load connected to the output terminal to operate, and the maximum voltage output by each converter is multiplied by N. The value is greater than the maximum load voltage allowed for the load to operate.

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

FIG. 1 is a block diagram of a power conversion device according to the 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 sharing ratio and the time ratio. FIG. 4 is a graph showing the relationship between efficiency and output power. FIG. 5 is a block diagram of the power conversion device according to the 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 is a forward type circuit system. FIG. 8 shows a flyback type circuit system. FIG. 9 is 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 are designated by the same reference numerals and the description thereof will be omitted.

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

The input unit of the converter 1a and the input unit 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 unit of the converter 1a and the output unit of the converter 1b are connected in series to form an output terminal. A load 7 is connected to the output terminal.

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

The sensor 10 acquires the amount of electric power output from the output terminal to the load 7. The determination circuit 11 determines the amount of electric power acquired by the sensor 10. For example, the determination circuit 11 can determine whether or not the amount of electric power acquired by the sensor 10 is insufficient.

The setting circuit 12 sets the output sharing ratio of the converter 1a and the converter 1b based on the result determined by the 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 electric power output by the converter 1a and the converter 1b to the load 7. When the power output by the converter 1a to the load 7 is larger than the power output by 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 by the converter 1a to the load 7 is less than the power output by the converter 1b to the load 7, the output sharing ratio of the converter 1a is lower than the output sharing ratio of the converter 1b.

The control circuit 13 controls the operations of the converter 1a and the 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 element 8a to 8d, 9a to 9d) described later, a transformer (isolation transformer 3), and a rectifier circuit (rectifier circuit 4). 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 8a to 8d and 9a to 9d is an element that converts the 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 referred to as a second DC power below. Further, the DC power input from the DC power supply 6 may be referred to as a first DC power below. The power conversion circuit converts the first DC power input from the DC power supply 6 into the second DC power. Further, the output unit of the converter 1a and the output unit of the converter 1b output the second DC power converted by the power conversion circuit.

The determination circuit 11, the setting circuit 12, and the control circuit 13 include a programmed processing device such as a processing device including an electric circuit. Further, the determination circuit 11, the setting circuit 12, and the control circuit 13 include devices such as an application specific integrated circuit (ASIC) 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 voltage after boosting becomes (Ns / Np) Vin. Here, Np is the number of turns of the primary winding of the isolation transformer 3. Ns is the number of turns of the secondary winding of the isolation transformer 3. Also in the converter 1b, the number of turns of the primary winding of the 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 rectifier circuit 4. The voltage rectified by the rectifier circuit 4 is hereinafter referred to as voltage Vrec1. The voltage rectified by the rectifier circuit 4 in the converter 1b is hereinafter referred to as voltage Vrec2.

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

In this embodiment, the converter 1a is designed to operate in soft switching. 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 for increasing the conduction loss is the time ratio D1. , Is a ripple component of the current Irec1. The time ratio D1 is the ratio of the on-time to one cycle of the on-off state of each of the switching elements 8a to 8d in the converter 1a. The time ratio D2, which will be described later, is the ratio of the on-time to one cycle of the on / off states of the switching elements 9a to 9d in the converter 1b. The continuous current mode is a mode in which current flows continuously. The converter 1b is also designed to operate in soft switching.

The lower the time ratio D1, the lower the time ratio at which the converter 1a outputs power. As a result, the power output by the converter 1a is reduced. Further, as the time ratio D1 becomes lower, the time for the reflux current that does not contribute to the power output by the converter 1a increases in the full bridge circuit 2. In the step-up converter in which Np <Ns, the current flowing through the full bridge circuit 2 is larger than the current flowing through the rectifier circuit 4, so that the conduction loss of the full bridge circuit 2 accounts for a large proportion of the total conduction loss. Become. That is, an increase in the time during which the reflux current flows in the full bridge circuit 2 causes an increase in conduction loss and reduces the efficiency of the converter 1a.

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

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

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

[Number 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 for the load 7 to operate. 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 the equation (2) is established.

[Number 2]
(Ns / Np) Vin <Vload_min ... (2)

From the above equations (1) and (2), it can be seen that power cannot be output from the DC power supply 6 to the load 7 with only one of the converter 1a and the converter 1b. In the present embodiment, since the output unit of the converter 1a and the output unit of the converter 1b are connected in series, the output current Iout is common to the converter 1a and the converter 1b. Even if the converter 1a tries to output the maximum power, (Ns / Np) Vin is less than the minimum load voltage Vload_min, so that the converter 1b needs to be operated in order to output the power to the load 7. As shown in FIG. 3, when the converter 1b starts to operate, the time ratio D2 increases, but the output voltage Vout1 of the converter 1a with respect to the load voltage Voltage is constant, so that the output sharing ratio does not change. When the time 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.

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

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

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

When the time ratio D1 is fixed at 0.99, there is a difference in the output sharing ratio. It can be seen that the conversion efficiency is improved in a wide output power operating range as shown in FIG. 4 when the difference in the output sharing ratio is changed according to the output power. The Var shown in FIG. 4 is a variable.

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

The power conversion device according to the first embodiment includes a plurality of converters (converter 1a and converter 1b). The output unit of the converter 1a and the output unit of the converter 1b are connected in series to form an output terminal. The sensor 10 acquires the amount of electric power supplied to the load 7 from the output terminal. The setting circuit 12 sets the output sharing ratio of the converter 1a and the converter 1b based on the amount of electric 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. As described above, the power conversion device can operate efficiently as a whole by controlling the power output by the converter 1a and the converter 1b based on the output sharing ratio.

Further, in the present embodiment, a region in which the converter 1a operates in the current continuous mode and a region in which the converter 1b operates in the current discontinuous mode coexist. Since the conversion efficiency of the 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, the control circuit 13 adjusts the power output from the converter 1b having the lower output sharing ratio among the converter 1a and the converter 1b. As a result, the power conversion device can reduce the power control load, so that it 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 having the lowest output sharing ratio.

Further, among the converter 1a and the converter 1b, the on / off state of the switching element of the converter 1a having a high output sharing ratio is constant regardless of the power output by the converter 1b having a low output sharing ratio. As a result, the converter 1a having a high output sharing ratio always operates efficiently, so that 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 having the highest output sharing ratio may be constant regardless of the power output by the other converters.

The converter 1a and the converter 1b have an isolation transformer 3. The exciting inductance of the isolation transformer 3 related to the converter 1b having a low output sharing ratio is preferably smaller than the exciting inductance of the insulating transformer 3 related to the converter 1a having a high output sharing ratio. As a result, the exciting current increases, and the region where soft switching is established in the current discontinuous mode expands. This improves the efficiency of the entire power converter in the low power region. In order to obtain the exciting current required for soft switching to be established, the lower the output capacitance of the switching elements 9a to 9d related to the converter 1b, the more suitable.

The converter 1a and the converter 1b are isolated DC-DC converters. Further, the input units of the converter 1a and the converter 1b are connected in parallel, and the output units of the converter 1a and the converter 1b are connected in series. As a result, the isolation transformer 3 is dispersed, and the converter itself can be miniaturized. Further, since the heat generation density of the isolation transformer 3 is reduced, the total volume can be reduced and a high step-up ratio can be obtained. Further, the power conversion device changes the output sharing ratio of the converter 1a and the converter 1b according to the power output by the converter 1a and the converter 1b. This allows the power converter to minimize the number of converters operating at operating points with low conversion efficiency. By lowering the output sharing ratio of the converter that operates at the operating point where the conversion efficiency is low, the power conversion device can operate more efficiently than the case where the output sharing ratio is made uniform as a whole.

In particular, in the low power region operating in the current discontinuous mode when the output sharing ratio is made uniform, the number of converters operating in the current discontinuous mode is reduced by making the power conversion device have a difference in the output sharing ratio. Therefore, the efficiency of the power converter is improved. Further, in the region where the output sharing ratio is made uniform and operates in the current continuous mode, the power conversion device makes a difference in the output sharing ratio, so that all the converters operate in the current continuous mode and have a higher output. Since the share ratio converter can operate in the most efficient region, the efficiency of the power converter is improved.

Further, 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 state of the switching elements 8a to 8d. In this case, it is preferable that the on / off state of the switching elements 8a to 8d related to at least one converter 1a among the plurality of converters is a state in which the maximum power is always output. Further, it is preferable that the maximum load voltage allowed when the load 7 operates is equal to or higher than the maximum 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, the converter 1a having the highest output sharing ratio always operates under the condition of high conversion efficiency, so that 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.

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

When the control circuit 13 constantly controls the on / off states of the switching elements 8a to 8d related to the converter 1a and operates the converter 1a as a phase shift type full bridge converter, the on-time above and below each bridge is 50. % Uniform. The power converter uses a pulse transformer for the drive circuit of the bridge circuit and recycles while exchanging the gate charge charges of the upper and lower switching elements, thereby reducing the drive power of the converter 1a and 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, and 1e.

The output voltages Voutc and Voutd of the converters 1c and 1d are controlled to constant values 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 according to the converter 1e. In order to obtain the same effect as that of the first embodiment when the number of converters is increased, 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) should be smaller than the minimum load voltage Vload_min. Further, it is sufficient that the value obtained by multiplying the maximum voltage output by each converter by N is larger than the maximum load voltage Vload_max. As a result, the power conversion device according to the second embodiment can operate efficiently.

The value obtained by multiplying the maximum voltage output by each converter by (N-1) may be smaller than the minimum load voltage Vload_min. As a result, 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 by each converter is low, the value obtained by multiplying the maximum voltage by (N-2) becomes 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 having a low output sharing ratio increases, so that the efficiency of the power converter decreases. Therefore, in order to improve the efficiency of the power converter, the number of converters is preferably about 2 to 5. However, this does not apply when the difference between the minimum load voltage Vload_min and the maximum load voltage Vload_max is small.

As mentioned above, embodiments of the invention have been described, but the statements and drawings that form part of this disclosure should not be understood to limit the invention. This disclosure will reveal to those skilled in the art various alternative embodiments, examples and operational techniques.

As shown in FIG. 6, in a power conversion device including three converters, converters of various circuit methods can be adopted. The circuit system of the converter may be, for example, the forward type shown in FIG. 7, the flyback type shown in FIG. 8, the LLC type shown in FIG. 9, the phase shift full bridge type shown in FIG. 10, or the like.

Further, the circuit method of the constant operation converter in which the on / off state of the switching element is constant and the variable operation converter in which the output power is adjusted while changing the on / off state of the switching element may be different. The efficiency of the power converter is improved by combining a constant operation converter that maximizes efficiency under constant operation conditions and a variable operation converter that can maintain high efficiency even when the on / off state of the switching element changes.

1a, 1b, 1c, 1d, 1e Converter 2 Full bridge circuit 3 Isolation transformer 4 Rectifier circuit 5 Output filter circuit 6 DC power supply 7 Loads 8a to 8d, 9a to 9d Switching element 10 Sensor 11 Judgment circuit 12 Setting circuit 13 Control circuit

Claims (10)

An input unit for inputting the 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 conversion device including a plurality of converters having an output unit for output and a control circuit for controlling the operation of the converter.
An output terminal configured by connecting the output units of the plurality of converters in series,
It is equipped with a setting circuit that sets the output sharing ratio of a plurality of converters based on the amount of power output from the output terminal.
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 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 for the load connected to the output terminal to operate.
A power conversion device characterized in that a value obtained by multiplying the maximum voltage output by each of the converters by N is larger than the maximum load voltage allowed when the load operates. An input unit for inputting the 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 conversion device including a plurality of converters having an output unit for output and a control circuit for controlling the operation of the converter.
An output terminal configured by connecting the output units of the plurality of converters in series,
It is equipped with a setting circuit that sets the output sharing ratio of a plurality of converters based on the amount of power output from the output terminal.
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 are N (N is an integer of 3 or more).
The value obtained by multiplying the maximum voltage output by each converter by (N-1) is smaller than the minimum load voltage required for the load connected to the output terminal to operate.
The value obtained by multiplying the maximum voltage output by each converter by N is larger than the maximum load voltage allowed when the load operates.
A power conversion device characterized by that. The plurality of converters include a first converter that operates in a current continuous mode in which current flows continuously, and a second converter that operates in a current discontinuous mode in which current flows discontinuously.
The power conversion device according to claim 1 or 2 , 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 coexist. The power conversion device according to any one of claims 1 to 3, wherein the control circuit adjusts the power output from the converter having the lowest output sharing ratio among the plurality of converters. The power conversion circuit includes a switching element.
Any of claims 1 to 4 , wherein the on / off state of the switching element of the converter having the highest output sharing ratio among the plurality of converters is constant regardless of the power output by the other converters. The power conversion device according to item 1. 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 decided,
The on / off state of the switching element related to at least one of the plurality of converters is a state in which the maximum power is always output.
Claim 1 is characterized in that the maximum load voltage allowed when the load connected to the output terminal operates is equal to or higher than the maximum output voltage with respect to the input voltage of the converter that always outputs the maximum power. The power conversion device according to any one of 5 to 5. The plurality of converters have an isolation transformer and
Among the plurality of converters, claims 1 to 6 are characterized in that the exciting inductance of the isolation transformer of the converter having a low output sharing ratio is smaller than the exciting inductance of the insulating transformer of the converter having a high output sharing ratio. The power conversion device according to any one of the above. The power conversion circuit includes a semiconductor switch and includes a semiconductor switch.
Among the plurality of converters, claims 1 to 7 are characterized in that the output capacity of the semiconductor switch of the converter having a low output sharing ratio is smaller than the output capacity of the semiconductor switch of the converter having a high output sharing ratio. The power conversion device according to any one of the above. The power conversion circuit includes a switching element.
The plurality of converters include a constant operation converter in which the on / off state of the switching element is constant, and a variable operation converter that adjusts 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 8 , wherein the circuit system of the constant operation converter and the variable operation converter are different. The plurality of converters are isolated DC-DC converters.
The power conversion device according to any one of claims 1 to 9 , further comprising an input terminal configured by connecting the input units in parallel.

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