Power conversion system

Abstract

Provided is a power conversion system that is capable of transmitting power with high efficiency over a wide voltage range and that is capable of achieving both stable control of transmitted power and responsiveness. [Solution] A control device 106a executes, in accordance with the magnitude of a control variable D, either discontinuous current mode phase control for controlling the period during which both the AC voltages on the primary side and the secondary side of an isolation transformer 102 are at zero voltage by controlling the phase of an edge of a drive pulse, or continuous current mode phase control for controlling the period δ during which the AC voltages on the primary side and the secondary side of an isolation transformer 102 are at opposite polarities by controlling the phase of an edge of a drive pulse, and in so doing, controls the power or current transmitted via the isolated DC / DC converter to change linearly with respect to the input control variable over the entire range including the control range of the discontinuous current mode and the control range of the continuous current mode. Input Control Variables to generate the control variables.

Description

[Technical field]

[0001] The present invention relates to a power conversion system that uses an isolated DC / DC converter. [Background technology]

[0002] 7 is a circuit diagram showing a configuration example of a power conversion system 100 using an isolated DC / DC converter 110. The isolated DC / DC converter 110 has an isolated transformer 102 whose primary and secondary windings are electrically insulated from each other. A series inductor 104a is connected to the primary winding of the isolated transformer 102. This series inductor 104a is the leakage inductance of the primary winding of the isolated transformer 102 or an external inductance added to this leakage inductance. Note that when only the leakage inductance is used for power transmission, the external inductance is not necessary. A similar series inductor 104b is also connected to the secondary winding of the isolated transformer 102.

[0003] The first bridge circuit 111 supplies a primary AC voltage v to the primary winding of the isolation transformer 102. 1 The first bridge circuit 111 is a full bridge circuit in which switching elements 101a and 101b connected in series and switching elements 101c and 101d connected in series are connected in parallel. In this example, each of the switching elements 101a to 101d is made of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and a diode connected in inverse parallel to the MOSFET. A capacitor 103a is connected in parallel to the first bridge circuit 111. A primary side DC voltage E 1 In the first bridge circuit 111, a primary AC voltage v 1 will be output.

[0004] The second bridge circuit 112 supplies a secondary AC voltage v to the secondary winding of the isolation transformer 102. 2 The second bridge circuit 112 is a bridge circuit in which, like the first bridge circuit 111, switching elements 101e and 101f connected in series are connected in parallel with switching elements 101g and 101h connected in series. A capacitor 103b is connected in parallel to the second bridge circuit 112. The second bridge circuit 112 is connected in parallel with a secondary side DC voltage E 2 In the second bridge circuit 112, a secondary AC voltage v 2 will be output.

[0005] The DC voltage detection unit 107a detects the primary side DC voltage E 1 The DC voltage detector 107b is a circuit for detecting the secondary DC voltage E 2 This is a circuit that detects the above.

[0006] The control device 106 generates drive pulses Ga to Gd for driving the switching elements 101a to 101d of the first bridge circuit 111, respectively, and drive pulses Ge to Gh for driving the switching elements 101e to 101h of the second bridge circuit 112, respectively.

[0007] The drive circuit section 105a drives the switching elements 101a to 101d with drive pulses Ga to Gd generated by the control device , and the drive circuit section 105b drives the switching elements 101e to 101h with drive pulses Ge to Gh generated by the control device .

[0008] The control device 106 detects the primary side DC voltage E 1 and the secondary side DC voltage E detected by the DC voltage detection unit 107b2 Based on this, the phases of the edges of the drive pulses Ga to Gh for driving the switching elements 101a to 101h are controlled, and the power transmission of the isolated DC / DC converter 110 is controlled.

[0009] An example of the operation of the power conversion system 100 will be described below with reference to the waveform diagram of Fig. 8. In the power conversion system 100, the first bridge circuit 111 and the second bridge circuit 112 are connected to a primary side AC voltage v 1 and the secondary AC voltage v 2 In the following explanation, the terms phase angle or phase difference are used, which refers to the primary AC voltage v 1 and the secondary AC voltage v 2 It means the relative length of various periods expressed as 2π for one period (one wavelength) of the secondary DC voltage E 2 and the secondary AC voltage v 2 means a voltage value converted to the primary side. In other words, when the number of turns of the primary winding of the insulating transformer 102 is n1 and the number of turns of the secondary winding is n2, the voltage value (voltage value converted to the primary side) obtained by multiplying the actual secondary DC voltage by the coefficient n1 / n2 is the secondary DC voltage E 2 Secondary AC voltage v 2 The same is true for the primary side DC voltage E. In the following description, the low voltage side and the high voltage side refer to the side where the low voltage is generated and the high voltage is generated, out of the primary side and the secondary side of the isolated DC / DC converter 110. For example, 1 and the secondary DC voltage E converted to the primary side 2 Between 1 <E 2 If the relationship is such that the primary side is the low-pressure side and the secondary side is the high-pressure side, E 1 >E 2 If the above relationship exists, the primary side is the high-pressure side and the secondary side is the low-pressure side.

[0010] In the example of operation in Figure 8, the primary DC voltage E 1 and secondary DC voltage E 2 Between 1 <E 2Therefore, the primary side is the low voltage side, and the secondary side is the high voltage side. In this operation example, the control device 106 controls the ±E 1 The primary AC voltage v of a square wave with a duty ratio of 50% 1 is output to the first bridge circuit 111, and ±E 2 and a duty ratio of 50%, and the primary AC voltage v 1 The secondary AC voltage v of a square wave delayed by a phase angle δ with respect to 2 is output to the second bridge circuit 112. Note that the duty ratio may be slightly deviated from 50%. In this way, the primary side AC voltage v 1 For the secondary AC voltage v 2 When the phase of the input signal lags, power is transferred from the primary side to the secondary side in the isolated DC / DC converter 110. The operation of this power transfer will be described below.

[0011] In the isolated DC / DC converter 110, the primary AC voltage v 1 and the secondary AC voltage v 2 The voltage difference between the leakage inductance l of the isolation transformer 102 and the external inductance L aux The inductance L=l+L aux , and a current i satisfying the following equation (1.1) flows in the primary winding of the isolation transformer 104. In addition, a current corresponding to this current i (a current the same as current i when the turns ratio between the primary and secondary sides of the isolation transformer 102 is 1) flows in the secondary winding of the isolation transformer 104. di / dt=(v 1 (t)-v 2 (t)) / L ……(1.1)

[0012] In this example, the primary AC voltage v 1 During the period of phase angle δ from the rising edge of and the primary side AC voltage v 1 During the period of phase angle δ from the falling edge of 1 and the secondary AC voltage V 2Therefore, during this period, a larger voltage difference is applied to the inductance L than during other periods, and the time gradient of the current i becomes larger as shown in FIG.

[0013] Therefore, the power P transmitted from the primary side to the secondary side is the primary side AC voltage v 1 and the secondary AC voltage v 2 It depends on the phase difference δ between the primary AC voltage v 1 and the secondary AC voltage v 2 If the fundamental wave angular frequency is ω, the transmission power P from the primary side to the secondary side is given by the following equation (1.2). P =(E 1 E 2 / (ωL))δ(1-(δ / π)) ……(1.2)

[0014] Therefore, the control device 106 controls the phases of the edges of the drive pulses Ga to Gh for driving the switching elements 101a to 101h, thereby controlling the primary AC voltage v 1 and the secondary AC voltage v 2 By controlling the period (phase angle δ) during which the polarities are opposite, the transmission power P between the primary side and the secondary side is controlled.

[0015] In this example, in order to increase the transmission power P, the primary AC voltage v 1 and the secondary AC voltage v 2 If the phase difference δ between the primary side AC voltage v and the secondary side AC voltage v is increased, the peak value of the current i flowing through the isolation transformer 104 becomes excessive. One method for solving this problem is the continuous current mode phase control. 1 and the secondary AC voltage v 2 This is phase control that reduces the peak value of current i by modulating the pulse width of one of the two.

[0016] FIG. 9 is a waveform diagram showing an example of the operation of the continuous current mode phase control. In this operation example, the high-voltage secondary AC voltage v 2 is the primary AC voltage v on the low voltage side 1During the period of phase angle δ from the rising edge of 1 and maintains a voltage of opposite polarity, and then maintains zero voltage for a period of phase angle φ, after which the primary side AC voltage v 1 In other words, in the continuous current mode phase control, the high-voltage secondary AC voltage v, which occurs with a phase angle δ lag, 2 The pulse width is shortened by the phase angle φ (to zero voltage).

[0017] In this way, the current i flowing through the isolation transformer 104 changes with a large time gradient during the period of phase angle δ, and then changes with a smaller time gradient during the period of phase angle φ than the previous period, reaching a peak value, thereby making it possible to prevent the peak value from becoming excessive.

[0018] 9, the control device 106 controls the period (phase angle δ) during which the AC voltages on the primary and secondary sides of the isolation transformer 102 are in opposite polarity, thereby controlling the transmission power P between the primary and secondary sides. This transmission power P is expressed by the following equation. P =(E 1 E 2 / (ωL))((π-φ)(2δ+φ)-2δ 2 ) / (2π) …(1.3)

[0019] The above-described continuous current mode phase control has a problem. 1 and the secondary AC voltage v 2 This is a problem in that reverse power is generated, which is transmitted in the opposite direction to the transmission direction determined by the phase relationship with the inverter. This generates reactive power.

[0020] For example, in the operation example of Figure 9, the primary AC voltage v 1 For the secondary AC voltage v 2 The phase of the primary side AC voltage v is delayed, and the direction of power transmission is from the primary side to the secondary side. However, in the phase control of the continuous current mode, the primary side AC voltage v 1The polarity of the current i flowing through the isolation transformer 104 is reversed within a period of phase angle δ starting from the rising edge (or falling edge) of the primary side AC voltage v 1 and the secondary AC voltage v 2 The reverse power P is transmitted from the secondary side to the primary side, which is the opposite direction of the transmission direction determined by the phase relationship with b This reverse power P b is the power P transmitted from the primary side to the secondary side before the polarity reversal of the current i occurs during the period of phase angle δ. f and offset each other.

[0021] In this way, in the phase control of the continuous current mode, the reverse power P b This causes a problem of a corresponding decrease in transmission efficiency. This problem occurs particularly when the DC voltage difference between the primary and secondary sides is large or when the load is light, and causes an increase in conduction loss (deterioration in the efficiency of power transmission).

[0022] One solution to this problem of continuous current mode phase control is discontinuous current mode phase control. This is a method of controlling the primary side AC voltage v 1 and the secondary AC voltage v 2 The generation of reverse power is avoided by generating a period in which both of the first and second inputs are at zero voltage.

[0023] FIG. 10 is a waveform diagram showing an example of phase control operation in discontinuous current mode. In this operation example, the primary side AC voltage v 1 and the secondary AC voltage v 2 After both of them change from the voltage of the first polarity (positive polarity in this example) to zero voltage at the same time, they both maintain zero voltage for the period of phase angle γ, and then the primary AC voltage v on the low voltage side 1 changes to a voltage of the second polarity (negative polarity in this example) opposite to the first polarity, and then, with a phase angle φ-δ behind, the high-voltage secondary AC voltage v 2 changes to a voltage of the second polarity. Then, the primary AC voltage v 1 and the secondary AC voltage v2 follows a waveform similar to that described above and changes from a voltage of the second polarity to a voltage of the first polarity.

[0024] In this operation example, the primary AC voltage v 1 is a voltage of the first or second polarity, and the secondary AC voltage v 2 During the phase angle φ-γ period when the voltage is zero, the current i flowing through the isolation transformer 102 increases, and the primary side AC voltage v 1 and the secondary AC voltage v 2 During the period when both of these terminals have the same polarity, the current i flowing through the isolation transformer 102 decreases and becomes zero. This operation is repeated.

[0025] Then, during the period of phase angle γ after the current i flowing through the isolation transformer 102 decreases and becomes zero, the primary side AC voltage v 1 and the secondary AC voltage v 2 The voltage at both ends becomes zero, and the change in the current i flowing through the insulating transformer 102 stops, and no polarity reversal occurs. As a result, no reverse power occurs.

[0026] In this operation example, the power P transmitted from the primary side to the secondary side depends on the peak value of the current i flowing through the isolation transformer 102. The peak value of the current i depends on the length of the period of phase angle φ-γ. Therefore, the control device 106 controls the period of phase angle γ during which both the AC voltages on the primary side and secondary side of the isolation transformer 102 are zero voltage, and also controls the phase angles φ and γ, thereby controlling the transmission power P between the primary side and the secondary side. This transmission power P is expressed by the following equation. P =(E 1 E 2 / (ωL))(A(1-A)(π-γ) 2 ) / (2π) …(1.4) In this equation (1.4), A is given by the following equation: A =Low side DC voltage / High side DC voltage<1……(1.5)

[0027] The above-mentioned continuous current mode phase control can transmit a certain amount of power or more in a wide voltage range, but reverse power may occur, which may result in a decrease in power transmission efficiency. On the other hand, discontinuous current mode phase control can avoid the occurrence of reverse power, but has the problem that it is difficult to transmit a certain amount of power or more in a wide voltage range, including when the voltage difference between the primary side and the secondary side is small.

[0028] Therefore, Patent Document 1 discloses a power conversion system that performs discontinuous current mode phase control, which controls the phase of the edge of a drive pulse to control the period during which both AC voltages on the primary and secondary sides of an isolation transformer are at zero voltage, or continuous current mode phase control, which controls the phase of the edge of a drive pulse to control the period during which the AC voltages on the primary and secondary sides of an isolation transformer are at opposite polarities, depending on the magnitude of a control variable. [Prior art documents] [Patent documents]

[0029] [Patent Document 1] JP 2024-82491 A Summary of the Invention [Problem to be solved by the invention]

[0030] According to the power conversion system disclosed in Patent Document 1, discontinuous current mode phase control or continuous current mode phase control is performed depending on the magnitude of the control variable, making it possible to transmit power with high efficiency over a wide voltage range. However, the power conversion system disclosed in Patent Document 1 has the following problems.

[0031] Fig. 11 is a diagram illustrating the power transmission characteristics in the power conversion system disclosed in Patent Document 1. In Fig. 11, the horizontal axis is the control variable D, and the vertical axis is the transmission power P of the power conversion system. In this operation example, in the range (a) of 0≦D≦π, phase control in discontinuous current mode is performed according to the control variable D. Also, in the range (c) of π≦D≦3π / 2, phase control in continuous current mode is performed according to the control variable D.

[0032] As illustrated in FIG. 11, in the range (a) where the phase control of the discontinuous current mode is performed, the change in the transmission power P relative to the control variable D is gradual. Therefore, in this range (a), if the control gain of the transmission power P is low, the response tracking performance is reduced. On the other hand, in the range (c) where the phase control of the continuous current mode is performed, the change in the transmission power P relative to the control variable D is steep. Therefore, in this range (c), if the control gain of the transmission power P is set high, the stability is reduced. Thus, in the power conversion system of Patent Document 1, stability is reduced when the control gain is set high in accordance with the range (a), and response tracking performance is reduced when the control gain is set low in accordance with the range (c), making it difficult to achieve both stability and response tracking performance.

[0033] The present invention has been made in consideration of the circumstances described above, and has an object to provide a power conversion system that is capable of transmitting power with high efficiency over a wide voltage range, and that is capable of achieving both stable control of the transmitted power and responsiveness. [Means for solving the problem]

[0034] A power conversion system according to one aspect of the present invention includes an isolated DC / DC converter including an isolation transformer, a first bridge circuit and a second bridge circuit connected to a primary side and a secondary side of the isolation transformer, respectively, and each including at least one switching element, a DC voltage detection unit that detects both a primary side DC voltage applied to the first bridge circuit and a secondary side DC voltage applied to the second bridge circuit, a control device that generates drive pulses for each of the switching elements of the first bridge circuit and the second bridge circuit based on the primary side DC voltage and the secondary side DC voltage detected by the DC voltage detection unit and a control variable, and a control device that drives the switching elements of the first bridge circuit and the second bridge circuit based on the drive pulses. and a drive circuit unit which operates in a manner such that the power or current transmitted via the isolated DC / DC converter changes linearly with respect to an input control variable over an entire range including a range of control variables in which the discontinuous current mode phase control is performed and a range of control variables in which the continuous current mode phase control is performed, the control device controls a discontinuous current mode phase control in which a period during which both of the AC voltages on the primary side and the secondary side of the isolation transformer are zero voltage by controlling a phase of an edge of the drive pulse, or a continuous current mode phase control in which a period during which the AC voltages on the primary side and the secondary side of the isolation transformer are opposite in polarity by controlling a phase of an edge of the drive pulse, in accordance with a magnitude of the control variable, The input control variables to generate the control variable.

[0035] In a preferred embodiment, the control device calculates a control variable by an inverse function of a function relating the control variable to the power or current transmitted through the isolated DC / DC converter. The input control variables to generate the control variable.

[0036] In another preferred embodiment, the controller is adapted to: The input control variablesto generate a first controlled variable, and using an inverse function of a function relating the controlled variable to the power or the current in the continuous current mode, The input control variables to generate a second control variable, and if the first control variable falls within a range of control variables for which the phase control in the discontinuous current mode is to be executed, execute the phase control in the discontinuous current mode based on the first control variable, and if the second control variable falls within a range of control variables for which the phase control in the continuous current mode is to be executed, execute the phase control in the continuous current mode based on the second control variable. Effect of the Invention

[0037] According to the power conversion system of one aspect of the present invention, the control device executes discontinuous current mode phase control or continuous current mode phase control according to the magnitude of the control variable, so that the power transmission between the primary side and the secondary side of the isolated DC / DC converter can be executed with high efficiency over a wide voltage range. Also, according to the power conversion system, the power or current transmitted through the isolated DC / DC converter changes linearly with respect to the input control variable over the entire range including the range of the control variable in which the discontinuous current mode phase control is executed and the range of the control variable in which the continuous current mode phase control is executed. Input Control Variables Since the control variables are generated by performing a transformation on the above, it is possible to achieve both stability in the control of the transmission power and response tracking ability. [Brief description of the drawings]

[0038] [Figure 1] 1 is a circuit diagram showing a configuration of a power conversion system according to an embodiment of the present invention. [Diagram 2] 4 is a waveform diagram showing an example of an operation of discontinuous current mode phase control executed in the power conversion system. FIG. [Diagram 3] 4 is a waveform diagram showing an example of an operation of phase control in a continuous current mode executed in the power conversion system. FIG. [Figure 4] 4 is a waveform diagram showing an example of the overall operation of the power conversion system. FIG. [Diagram 5] 4 is a diagram illustrating an example of current transmission characteristics in the power conversion system. FIG. [Figure 6] FIG. 2 is a block diagram showing a configuration of a control device of the power conversion system. [Figure 7] 1 is a circuit diagram showing a configuration example of a power conversion system. [Figure 8] 3 is a waveform diagram showing basic operating waveforms of the power conversion system. FIG. [Figure 9] 4 is a waveform diagram showing an example of an operation of phase control in a continuous current mode in the power conversion system. FIG. [Figure 10] 4 is a waveform diagram showing an example of an operation of phase control in a discontinuous current mode in the power conversion system. FIG. [Figure 11] 1 is a diagram illustrating an example of power transmission characteristics in the power conversion system disclosed in Patent Document 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a circuit diagram showing a configuration of a power conversion system 100a according to an embodiment of the present invention. In this power conversion system 100a, the control device 106 in the conventional power conversion system (Fig. 7) is replaced with a control device 106a.

[0040] The elements of the power conversion system 100a other than the control device 106a are similar to those of the conventional power conversion system (FIG. 7). That is, the isolated DC / DC converter 110 includes an isolated transformer 102, and a first bridge circuit 111 and a second bridge circuit 112, each of which includes at least one switching element and are connected to the primary side and secondary side of the isolated transformer 102, respectively. A DC voltage detection unit 107a detects a primary side DC voltage E 1 The DC voltage detector 107b detects the secondary DC voltage E 2The drive circuit unit 105a drives the switching elements 101a to 101d of the first bridge circuit 111 based on drive pulses Ga to Gd generated by the control device 106a, and the drive circuit unit 105b drives the switching elements 101e to 101h of the second bridge circuit 112 based on drive pulses Ge to Gh generated by the control device 106a.

[0041] The control device 106a includes a conversion unit 121. The conversion unit 121 converts an input control variable I DC The input control variable I DC is, for example, a command value for the power or current to be transmitted by the isolated DC / DC converter 110.

[0042] In a preferred embodiment, the input control variable I DC is provided to the control device 106a from a higher-level device that controls the power conversion system 100a. In another preferred embodiment, the control device 106a controls the input control variable I DC Determine.

[0043] The control device 106a uses this input control variable I DC and the primary side DC voltage E detected by the DC voltage detection units 107a and 107b. 1 and secondary DC voltage E 2 Based on this, driving pulses Ga to Gh for driving the switching elements of the first bridge circuit 111 and the second bridge circuit 112 are generated.

[0044] As described above, the continuous current mode phase control can transmit a certain amount of power or more in a wide voltage range, but there is a problem that the power transmission efficiency decreases due to the occurrence of reverse power. On the other hand, the discontinuous current mode phase control can avoid the occurrence of reverse power, but there is a problem that it is difficult to transmit a certain amount of power or more in a wide voltage range including a case where the voltage difference between the primary side and the secondary side is small. Therefore, if only one of the continuous current mode phase control and the discontinuous current mode phase control is performed, it is difficult to transmit power with high efficiency in a wide voltage range. Therefore, in this embodiment, both the continuous current mode phase control and the discontinuous current mode phase control are executed by the control device 106a.

[0045] In addition, as mentioned above, in the phase control of the continuous current mode, the primary side AC voltage v 1 and the secondary AC voltage v 2 The phase angle δ of the phase lag between the primary side and the secondary side, and the phase angle φ of the period during which the AC voltage on the high side remains at zero voltage, are the objects of operation. On the other hand, in discontinuous current mode phase control, the primary side AC voltage v 1 and the secondary AC voltage v 2 There is no phase lag (phase angle δ) between them, and the phase angle γ during the period when both the AC voltages on the low-voltage side and the high-voltage side maintain zero voltage and the phase angle φ during the period when the AC voltage on the high-voltage side maintains zero voltage are the objects of manipulation. Moreover, in this case, since one of the phase angles γ and φ depends on the other, the actual object of manipulation is only one of the phase angles γ and φ. Therefore, in this embodiment, a single control variable D is associated with the object of manipulation of the phase control in the discontinuous current mode, and the same control variable D is associated with the object of manipulation of the phase control in the continuous current mode, so that the phase control in the discontinuous current mode or the phase control in the continuous current mode is performed according to the magnitude of the control variable D.

[0046] Specifically, in this embodiment, the control device 106a controls the phases of the edges of the driving pulses Ga to Gh to control the primary side AC voltage v 1 and the secondary AC voltage v 2By controlling the phase of the edges of the driving pulses Ga to Gh, the primary side AC voltage v 1 and the secondary AC voltage v 2 The transmission of power P between the primary side and the secondary side of the isolated DC / DC converter 110 is controlled by executing continuous current mode phase control that controls the period during which the polarity of the input current I is reversed in accordance with the magnitude of the control variable D.

[0047] The control variable D can take a value between 0 and 3π / 2. When the control variable D is a value greater than or equal to 0 and less than or equal to π, the controller 106a performs phase control in discontinuous current mode. When the control variable D is a value greater than or equal to π and less than or equal to 3π / 2, the controller 106a performs phase control in continuous current mode.

[0048] In this embodiment, the larger the control variable D, the larger the transmission power P between the primary side and the secondary side, but the relationship between the control variable D and the transmission power P is as shown in Fig. 11. That is, in the range (a) where the phase control of the discontinuous current mode is performed, the change in the transmission power P relative to the control variable D is gentle, but in the range (c) where the phase control of the continuous current mode is performed, the change in the transmission power P relative to the control variable D is steep. For this reason, if the control variable D is given to the control device 106a to perform phase control, it is difficult to achieve both stability in the control of the transmission power and response tracking ability.

[0049] Therefore, in this embodiment, the conversion unit 121 converts the power or current transmitted via the isolated DC / DC converter 110 into the input control variable I over the entire range including the range of the control variable D in which the phase control in the discontinuous current mode is performed and the range of the control variable D in which the phase control in the continuous current mode is performed. DC The conversion unit 121 performs a conversion on the input control variable IDC so that the input control variable IDC changes linearly with respect to the input control variable D, thereby generating a control variable D. The conversion unit 121 will be described in detail later.

[0050] The phase control in this embodiment will be described in detail below. The case where power is transmitted from the primary side to the secondary side of the isolated DC / DC converter 110 will be described below. The case where the primary side is the low voltage side and the secondary side is the high voltage side will be described below.

[0051] FIG. 2 is a waveform diagram showing an example of phase control in discontinuous current mode. In FIG. 2, / Gb, / Gd, / Gf, and / Gh represent the level inversion waveforms of the drive pulses Gb, Gd, Gf, and Gh. The same applies to the other waveform diagrams (FIGS. 3 and 6). In the example of FIG. 2, the control device 106a detects a peak point P 1 (P 2 ) before and after the inflection point Q 11 and Q 12 (Q 21 and Q 22 The phase of the edge of the drive pulse is controlled so that the current values ​​of the two electrodes match.

[0052] Specifically, the control device 106a controls the low-voltage primary AC voltage v 1 and the high-voltage secondary AC voltage v 2 The first differential voltage (E in the example of Figure 2) between 1 -0>0) occurs in the first period T1 (phase angle φ-γ), and the time integral of the first differential voltage in the first period T1 (phase angle φ-γ) occurs in the first period T2 (phase angle φ-γ) in which the first differential voltage occurs in the first period T1 (phase angle φ-γ) in which the first differential voltage occurs in the first period T2 (phase angle φ-γ) 1 and the high-voltage secondary AC voltage v 2 A first differential voltage and a second differential voltage of the opposite polarity (E 1 -E 2 The phases of the edges of the driving pulses Ga to Gh are controlled so that the sum of this and the time integral of the second differential voltage in the second period T2 (phase angle π-φ) in which (<0) occurs becomes zero. That is, in the example of FIG. 2, the phases of the edges of the driving pulses Ga to Gh are controlled so that the following equation (2.1) is satisfied. E 1 (φ-γ)+(E 1 -E 2 )(π-φ)=0 ……(2.1) In addition, the primary DC voltage E 1 and secondary DC voltage E 2Strictly speaking, it varies with time, but since the time constant is large, it is considered to be a constant voltage in the above equation (2.1).

[0053] This control reduces the primary AC voltage v 1 and the secondary AC voltage v 2 The current i of the isolation transformer 102 generated by the difference voltage between the primary side AC voltage v 1 and the secondary AC voltage v 2 becomes zero at the start timing of the third period T3 (period of phase angle γ) in which both become zero voltage, and the occurrence of reverse power is avoided.

[0054] Above, the current i reaches a positive peak point P 1 The phase control of the edges of the driving pulses Ga to Gh in the period before and after the timing when the negative peak point P 2 The same applies to the phase control of the edges of the driving pulses Ga to Gh in the periods before and after the timing when the pulses occur.

[0055] One object of this embodiment is to perform phase control of the driving pulses Ga to Gh based on a single control variable D not only in the continuous current mode but also in the discontinuous current mode. For this reason, in this embodiment, in the discontinuous current mode, the phase angle γ is determined based on the control variable D, and the phase angle φ is made dependent on this phase angle γ. Specifically, this is as follows.

[0056] Solving the above equation (2.1) for φ gives the following equation (2.2). φ(γ) =(1-(E 1 / E 2 ))π+(E 1 / E 2 )γ =(1-A)π+Aγ ……(2.2) Here, A is as shown in the above formula (1.5).

[0057] Furthermore, the control variable D in the discontinuous current mode is related to the phase angle γ as follows: D=π-γ ……(2.3)

[0058] When a control variable D, where 0≦D≦π, is given, the control device 106a determines the phase angle γ from the control variable D according to equation (2.3), and determines the phase angle φ from the phase angle γ according to equation (2.2).

[0059] Above, the phase control of the discontinuous current mode is performed for the primary side AC voltage v 1 and the secondary AC voltage v 2 The explanation was focused on the change in the differential voltage between the primary side AC voltage v 1 and the secondary AC voltage v 2 The following explains each of the changes in the above.

[0060] In the phase control of the discontinuous current mode, the control device 106a controls the primary side AC voltage v of the isolation transformer 102. 1 or secondary AC voltage v 2 A first period T1 during which one side (specifically, the low-voltage side) of the primary side is at a first polarity (positive polarity in the example of FIG. 2) and the other side (specifically, the high-voltage side) is at zero voltage, and a first period T2 during which the primary side AC voltage v 1 and the secondary AC voltage v 2 A second period T2 in which both of the primary side AC voltage v 1 and the secondary AC voltage v 2 and a third period T3 during which both are at zero voltage are sequentially generated, and the third period T3 is decreased according to the magnitude of the control variable D (see the above formula (2.3)).

[0061] In addition, in the phase control of the discontinuous current mode, the control device 106a calculates the primary side AC voltage v 1 and the secondary AC voltage v 2 and the time integral of the difference voltage v during the second period T2. 1 and the secondary AC voltage v 2 The phases of the edges of the driving pulses Ga to Gh are controlled so that the sum of these and the time integral of the difference voltage becomes zero (see formula (2.1) above).

[0062] Next, a specific example of phase control of the edges of the drive pulse in the discontinuous current mode will be described. In the following description, unless otherwise specified, the phase angle is the phase of the rising edges of the drive pulses Ga and / Gb in FIG. 2 (phase angle θ 12 = 0) as the reference position (starting point). In other words, the phase angle θ 34 is the phase angle of the rising edge of the drive pulses Gc and / Gd relative to the reference position, and the phase angle θ 56 is the phase angle of the rising edge of the driving pulses Ge and / Gf relative to the reference position, and the phase angle θ 78 is the phase angle of the rising edge of the drive pulses Gg and / Gh relative to the reference position.

[0063] In the operation example of Figure 2, the primary AC voltage v 1 The falling edge of the primary side AC voltage v to zero voltage (the beginning of the third period T3) occurs due to the rising edges of the driving pulses Gc and / Gd. 1 The falling edge of the driving pulses Gc and / Gd to zero voltage has a phase angle π-γ. Therefore, the phase angle θ 34 is calculated using the following formula (2.4): θ 34 =π-γ =π-π+D =D ……(2.4)

[0064] In addition, the secondary AC voltage v 2 The rising edge of the secondary AC voltage v to zero voltage (the beginning of the third period T3) occurs due to the rising edges of the driving pulses Ge and / Gf. 2 The falling edge of the driving pulses Ge and / Gf to zero voltage has a phase angle -γ. Therefore, the rising edge of the driving pulses Ge and / Gf has a phase angle θ 56 is calculated using the following formula (2.5): θ 56 =-γ =D-π ……(2.5)

[0065] In addition, the secondary AC voltage v 2The falling edge from zero voltage (the beginning of the second period T2) of the secondary side AC voltage v 2 The falling edge from zero voltage of 56 +π+φ. Therefore, the phase angle θ of the rising edges of the drive pulses Gg and / Gh 78 is calculated using the following formula (2.6): θ 78 =θ56+π+φ =D-π+π+φ =D-π+π+π-AD =π+(1-A)D ……(2.6) The above is the phase control in the discontinuous current mode in this embodiment.

[0066] 3 is a waveform diagram showing an example of phase control in the continuous current mode in this embodiment. In this embodiment, in the continuous current mode as well as in the discontinuous current mode, the peak point P 1 (P 2 ) before and after the inflection point Q 11 and Q 12 (Q 21 and Q 22 The phase of the edge of the drive pulse is controlled so that the current values ​​of the two electrodes match.

[0067] Specifically, the control device 106a controls the primary AC voltage v of the isolation transformer 102. 1 and the secondary AC voltage v 2 The first differential voltage (E in the example of Figure 3) between 1 -0>0) occurs in a fifth period T5 (phase angle φ), and the primary AC voltage v of the isolation transformer 102 is expressed as 1 and the secondary AC voltage v 2 A first differential voltage and a second differential voltage of the opposite polarity (E 1 -E 2The phase of the edge of the drive pulse is controlled so that the sum of this and the time integral of the second differential voltage in a sixth period T6 (phase angle π-δ-φ) in which (<0) occurs becomes zero. That is, in the example of Figure 3, the phase of the edges of the drive pulses Ga to Gh is controlled so that the following equation (3.1) is satisfied. E 1 φ+(E 1 -E 2 )(π-δ-φ)=0 ……(3.1)

[0068] Above, the current i reaches a positive peak point P 1 We have explained the phase control of the edge of the drive pulse in the period before and after the timing when the negative peak point P 2 The same applies to the phase control of the edges of the driving pulses Ga to Gh in the periods before and after the timing when the pulses occur.

[0069] As already described, in this embodiment, in both the discontinuous current mode and the continuous current mode, the phase of the driving pulses Ga to Gh is controlled based on a single control variable D. Therefore, in this embodiment, in the continuous current mode, the phase angle δ is determined based on the control variable D, and the phase angle φ is made to depend on this phase angle δ. Specifically, this is as follows.

[0070] Solving the above equation (3.1) for φ gives the following equation (3.2). φ(δ) =(1-(E 1 / E 2 ))(π-δ) =(1-A)(π-δ) ……(3.2)

[0071] Also, in continuous current mode, we relate the control variable D to the phase angle δ by D = δ + π ……(3.3)

[0072] In this embodiment, when a control variable D where π≦D≦3π / 2 is given, the control device 106a calculates the phase angle δ from the control variable D according to equation (3.3), and calculates the phase angle φ from the phase angle δ according to equation (3.2).

[0073] By performing such control, continuity of the change in the waveform of the current i flowing through the isolation transformer 102 during mode transition between the discontinuous current mode and the continuous current mode is ensured.

[0074] Above, the phase control of the continuous current mode is performed for the primary side AC voltage v 1 and the secondary AC voltage v 2 The explanation was focused on the change in the differential voltage between the primary side AC voltage v 1 and the secondary AC voltage v 2 The following explains each of the changes in the above.

[0075] The control device 106a controls the primary AC voltage v of the isolation transformer 102 in the continuous current mode phase control. 1 and the secondary AC voltage v 2 The fourth period T4 (phase angle δ) in which the polarity of the primary AC voltage v 1 or secondary AC voltage v 2 A fifth period T5 (phase angle φ) in which one side (specifically, the low-voltage side) is at the first polarity and the other side (specifically, the high-voltage side) is at zero voltage, and the primary side AC voltage v 1 and the secondary AC voltage v 2 and a sixth period T6 (phase angles π-δ-φ) in which both of the first and second polarities are the first polarity are sequentially generated, and the fourth period T4 is increased in accordance with the magnitude of the control variable D.

[0076] In addition, in the phase control of the continuous current mode, the control device 106a calculates the primary side AC voltage v 1 and the secondary AC voltage v 2 The time integral of the difference voltage between the primary side AC voltage v during the sixth period T6 1 and the secondary AC voltage v 2 The phase of the edge of the drive pulse is controlled so that the sum of the time integral of the difference voltage between the two becomes zero (see equation (3.1)).

[0077] Next, a specific example of phase control of the edges of the driving pulses Ga to Gh in the continuous current mode will be described. In the operation example of FIG. 3, the primary side AC voltage v 1The polarity reversal of the primary side AC voltage v (the beginning of the fourth period T4) occurs at the rising edge of the driving pulses Gc and / Gd. 1 The polarity reversal of the driving pulses Gc and / Gd has a phase angle θ 34 is calculated using the following formula (3.4): θ 34 = pi ……(3.4)

[0078] In addition, the secondary AC voltage v 2 The rise of the secondary AC voltage v to zero voltage (the beginning of the fifth period T5) occurs due to the rising edges of the driving pulses Ge and / Gf. 2 The rising edge of the driving pulses Ge and / Gf to zero voltage has a phase angle δ. Therefore, the phase angle θ 56 is calculated using the following formula (3.5): θ 56 = δ =D-π ……(3.5)

[0079] In addition, the secondary AC voltage v 2 The fall from zero voltage (the beginning of the sixth period T6) occurs at the rising edge of the driving pulses Gg and / Gh. 2 The falling edge from zero voltage of 56 +π+φ. Therefore, the phase angle θ of the rising edges of the drive pulses Gg and / Gh 78 is calculated using the following formula (3.6): θ 78 =θ 56 +π+φ =D-π+π+φ =D+φ =D+(1-A)(2π-D) =AD+2π(1-A) =(D-2π)A ……(3.6) The above is the phase control in the continuous current mode in this embodiment.

[0080] Fig. 4 is a waveform diagram showing an example of the overall operation of the power conversion system 100a. The operation of this embodiment can be summarized as follows with reference to Fig. 4 and the above-mentioned Fig. 11.

[0081] When the control variable D is within the range of 0≦D≦π, in this embodiment, the phase control of the discontinuous current mode is executed. In this discontinuous current mode, the primary side AC voltage v 1 and the secondary AC voltage v 2 There is no period (phase angle δ) during which the AC voltages on both the low-voltage side and high-voltage side maintain zero voltage as the control variable D increases. Also, in discontinuous current mode, the period during which the AC voltage on the high-voltage side maintains zero voltage (phase angle γ=π-D) decreases as the control variable D increases, and the period during which the AC voltage on the high-voltage side maintains zero voltage (phase angle φ=π-AD) decreases.

[0082] In this discontinuous current mode, no reverse power occurs, and the power P transferred between the primary and secondary sides is given by the following equation: P =((E 1 E 2 ) / (ωL))A(1-A)D 2 / (2π) ……(4.1) In this discontinuous current mode, no reverse power is generated, so power can be transmitted with little loss when the DC voltage difference between the primary and secondary sides is small or when the load is light.

[0083] When the control variable D is within the range of π≦D≦3π / 2, the phase control of the continuous current mode is executed in this embodiment. In this continuous current mode, the primary side AC voltage v 1 and the secondary AC voltage v 2 There is no period (phase angle γ) during which both are zero voltage. In the continuous current mode, when the control variable D increases, the primary side AC voltage v 1 and the secondary AC voltage v 2 The period during which the AC voltage on the high voltage side remains at zero voltage (phase angle φ=(1-A)(2π-D)) decreases.

[0084] In this continuous current mode, the primary AC voltage v 1 and the secondary AC voltage v 2 Power is transmitted during the period when the polarity is reversed, and the power P transmitted between the primary and secondary sides is given by the following equation. P =((E 1 E 2 ) / (ωL))(a(A)D 2 +b(A)D+c(A)) / (2π) …(4.2) Here, a(A), b(A), and c(A) are as follows. a(A)=-(1+A 2 ) ……(4.3) b(A) = (4A 2 -A+3)π ……(4.4) c(A)=-2(2A 2 -A+1)π 2 ……(4.5) In this continuous current mode, it is possible to transmit a certain amount of power over a wide voltage range, and it is also possible to transmit power with high efficiency even when the load is large.

[0085] As shown in FIG. 11, when the control variable D is changed from 0 to 3π / 2, the power P transmitted from the primary side to the secondary side changes continuously. When the control variable D is π (see FIG. 11(b)), the operation mode of this embodiment is at the mode boundary between the discontinuous current mode and the continuous current mode. At this mode boundary, the phase angles δ, φ, and γ calculated assuming the discontinuous current mode match the phase angles δ, φ, and γ calculated assuming the continuous current mode. Therefore, the change in the current waveform of the isolation transformer is continuous when transitioning between the discontinuous current mode and the continuous current mode.

[0086] As described above, according to this embodiment, discontinuous current mode phase control or continuous current mode phase control is performed depending on the magnitude of one control variable D, so that power can be transmitted between the primary side and the secondary side with high efficiency over a wide voltage range.

[0087] Furthermore, according to this embodiment, both the discontinuous current mode phase control and the continuous current mode phase control are executed by one control variable D, which has the effect of simplifying the control and making it stable.

[0088] Incidentally, the relationship between the control variable D and the transmission power P of the isolated DC / DC converter 110 is as exemplified in FIG. 11 above, where the change in the transmission power P relative to the control variable D is gradual in the range (a) where the phase control of the discontinuous current mode is performed, but the change in the transmission power P relative to the control variable D is steep in the range (c) where the phase control of the continuous current mode is performed. For this reason, if the control variable D is given to the control device 106a to perform phase control, it is difficult to achieve both stability in the control of the transmission power P and response tracking. Therefore, in this embodiment, the conversion unit 121 converts the power P or current I (current I in FIG. 5) transmitted via the isolated DC / DC converter 110 into the input control variable I over the entire range, as exemplified in FIG. 5. DC , which changes linearly with Input Control Variables I DC to generate the control variable D. Here, the full range means the full range including the range (a) of the control variable in which the discontinuous current mode phase control is performed and the range (c) of the control variable in which the continuous current mode phase control is performed.

[0089] 6 is a block diagram showing the configuration of the control device 106a in this embodiment. As shown in FIG 6, the control device 106a includes a conversion unit 121 provided before the phase angle calculation unit 122 and the signal generation unit 123.

[0090] Here, the phase angle calculation unit 122 calculates the above-mentioned phase angle θ based on the control variable D and the ratio A of the low-voltage side DC voltage to the high-voltage side DC voltage. 12 , θ 34 , θ 56 and θ 78 The signal generating unit 123 is a unit that generates driving pulses Ga to Gh whose phases are controlled based on the phase angle calculated by the phase angle calculating unit 122.

[0091] The conversion unit 121 calculates, by the inverse function of the function relating the control variable D to the power or current transmitted through the isolated DC / DC converter 110, Input Control Variables I DC This is a means of generating a control variable D by applying a transformation to

[0092] In FIG. 6, the conversion unit 121 includes a first conversion unit 121a, a second conversion unit 121b, and a switching unit 121c.

[0093] The first conversion unit 121a converts the control variable D to the power or current (current in this example) transmitted in the discontinuous current mode by the inverse function of the function that relates the control variable D to the power or current transmitted in the discontinuous current mode. Input Control Variables I DC to generate a first control variable D1.

[0094] The above equation (4.1) relates the control variable D to the power P transmitted in discontinuous current mode. 1 Dividing by gives us the following equation (4.1a): I =(E 2 / (ωL))A(1-A)D 2 / (2π) ……(4.1a)

[0095] Equation (4.1a) shows the function that relates the control variable D to the current I transmitted in discontinuous current mode. The inverse function of equation (4.1a) is given by D =√((ωL / E 2 )(2π / (A(1-A))I) ……(4.1b)

[0096] The first conversion unit 121a substitutes the given ratio A into this equation (4.1b) and converts the input control variable I DC The control variable D is calculated by substituting the above, and is output as the first control variable D1.

[0097] The second conversion unit 121b converts the control variable D to the power or current (current in this example) transmitted in the continuous current mode by the inverse function of the function that relates the control variable D to the power or current transmitted in the continuous current mode. Input Control Variables I DC to generate a second control variable D2.

[0098] The above equation (4.2) relates the control variable D to the power P transmitted in the continuous current mode. 1 Dividing by , we get the following equation (4.2a). I =(E 2 / (ωL))(a(A)D 2 +b(A)D+c(A)) / (2π) …(4.2a)

[0099] Equation (4.2a) shows the function that relates the control variable D to the current I transmitted in the continuous current mode. The inverse function of equation (4.2a) is given by D =(-1 / 2)(b(A) / a(A)) ±√((1 / 4)(b(A) 2 / a(A) 2 ) -((c(A) / a(A))-(2π / a(A))(ωL / E 2 )I)) …(4.2b)

[0100] The second conversion unit 121b substitutes the given ratio A into this equation (4.2b) and converts the input control variable I DC The control variable D is calculated by substituting the above, and is output as the second control variable D2.

[0101] When the first control variable D1 belongs to the range of the control variable D for which the phase control in the discontinuous current mode should be performed, that is, the range of 0≦D≦π, the switching unit 121c selects the first control variable D1 and supplies it to the phase angle calculation unit 122. As a result, the phase angle calculation unit 122 performs the phase control in the discontinuous current mode based on the first control variable D1.

[0102] Furthermore, when the second control variable D2 belongs to the range of the control variable D for which the phase control in the continuous current mode should be performed, that is, the range of π≦D≦3π / 2, the switching unit 121c selects the second control variable D2 and supplies it to the phase angle calculation unit 122. As a result, the phase angle calculation unit 122 performs the phase control in the continuous current mode based on the second control variable D2.

[0103] As described above, in this embodiment, the input control variable I is calculated by the inverse function of the function relating the control variable D to the transmitted power P or current I. DC is converted to generate the control variable D, it is possible to change the power P or the current I linearly with respect to the input control variable IDC over the entire range including the range of the control variable D in which the discontinuous current mode phase control is performed and the range of the control variable D in which the continuous current mode phase control is performed. Therefore, it is possible to achieve both stability and response tracking of the phase control.

[0104] Although one embodiment of the present invention has been described above, the present invention may have other embodiments, for example as follows.

[0105] (1) In the above embodiment, FIG. 2 and FIG. 3 show the primary side AC voltage v 1 and the secondary AC voltage v 2 1 shows an example of the relative phase relationship between the primary side AC voltage v and the drive pulses Ga to Gh for realizing such a phase relationship. However, the waveforms of the drive pulses Ga to Gh are merely examples, and even if the waveforms of the drive pulses Ga to Gh are changed, the primary side AC voltage v 1 and the secondary AC voltage v 2 The relative phase relationship of the primary AC voltage v can be made the same as that of FIG. 2 and FIG. 3. 1 and the secondary AC voltage v 2 As long as the relative phase relationships between the driving pulses Ga to Gh can be made as shown in FIGS.

[0106] (2) In the above embodiment, the operation of power transmission from the primary side to the secondary side has been described. However, in the above power conversion system 100a, power transmission from the secondary side to the primary side is also possible. In this case, the primary side AC voltage v 1 and the secondary AC voltage v 2 The isolated DC / DC converter 110 may be controlled so that the phase relationship between the

[0107] (3) In the above embodiment, the operation is described when the primary side is the low voltage side and the secondary side is the high voltage side, but the operation is similar to that of the above embodiment when the primary side is the high voltage side and the secondary side is the low voltage side. That is, when the primary side is the high voltage side and the secondary side is the low voltage side, in the description of the above embodiment, the high voltage side is referred to as the primary side AC voltage v 1 , the low voltage side is the secondary AC voltage v 2 This can be done as follows.

[0108] (4) In the above embodiment, the first bridge circuit 111 and the second bridge circuit 112 are full-bridge circuits. However, they may be half-bridge circuits.

[0109] (5) In the above embodiment, the input control variable I is calculated by the inverse function of the function relating the control variable D to the transmitted current I. DC The control variable D is generated by converting the input control variable I DC may be transformed to generate the control variable D. [Explanation of symbols]

[0110] 100, 100a...power conversion system, 106, 106a...control device, 110...isolated DC / DC converter, 102...isolated transformer, 104...series inductor, 111...first bridge circuit, 112...second bridge circuit, 101a to 101h...switching elements, 103a, 103b...capacitors, 105a, 105b...drive circuit section, 107a, 107b...DC voltage detection section, 121...conversion section, 121a...first conversion section, 121b...second conversion section, 121c...switching section, 122...phase angle calculation section, 123...signal generation section.

Claims

1. an isolated DC / DC converter including an isolation transformer, and a first bridge circuit and a second bridge circuit connected to a primary side and a secondary side of the isolation transformer, respectively, the first bridge circuit and the second bridge circuit each including at least one switching element; a DC voltage detection unit that detects both a primary side DC voltage applied to the first bridge circuit and a secondary side DC voltage applied to the second bridge circuit; a control device that generates drive pulses for the switching elements of the first bridge circuit and the second bridge circuit based on a primary side DC voltage and a secondary side DC voltage detected by the DC voltage detection unit and a control variable; a drive circuit unit that drives the switching elements of the first bridge circuit and the second bridge circuit based on the drive pulse, The control device includes: A discontinuous current mode phase control in which a period during which both the AC voltages on the primary side and the secondary side of the isolation transformer are zero voltage is controlled by controlling the phase of the edge of the drive pulse, or A continuous current mode phase control in which the period during which the AC voltages on the primary side and the secondary side of the isolation transformer have opposite polarities is controlled by controlling the phase of the edge of the drive pulse. according to the magnitude of the control variable, In this case, the control variable is generated by applying a transformation to the input control variable so that the power or current transmitted via the isolated DC / DC converter changes linearly with the input control variable over the entire range including the range of the control variable in which the discontinuous current mode phase control is performed and the range of the control variable in which the continuous current mode phase control is performed.

2. 2. The power conversion system of claim 1, wherein the control device generates the control variable by applying a transformation to the input control variable by an inverse function of a function relating the control variable to power or current transmitted through the isolated DC / DC converter.

3. 3. The power conversion system according to claim 2, wherein the control device generates a first control variable by transforming the input control variable by an inverse function of a function relating the control variable to the power or the current in the discontinuous current mode, and generates a second control variable by transforming the input control variable by an inverse function of a function relating the control variable to the power or the current in the continuous current mode, and performs the phase control of the discontinuous current mode based on the first control variable when the first control variable falls within a range of control variables for which phase control of the discontinuous current mode is to be performed, and performs the phase control of the continuous current mode based on the second control variable when the second control variable falls within a range of control variables for which phase control of the continuous current mode is to be performed.

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