ENERGY CONVERTER AND CURRENT DETECTION CIRCUIT

Abstract

An energy converter (1) with a coil comprises a detection coil (Ld) magnetically coupled to the coil, a detection resistor (Rd) and a detection capacitor (Cd) connected in series with each other and in parallel with the detection coil (Ld), and a detection circuit (4) which detects a current flowing through the coil based on a voltage across the detection capacitor (Cd).

Description

BACKGROUND OF THE INVENTIONThe present invention relates to a method for detecting a current flowing through a coil provided in an energy converter.PRIOR ARTA current detection circuit is known in which a coil provided in an energy converter is connected in parallel to a detection resistor and a detection capacitor connected in series with each other, and a detection circuit is connected to both terminals of the detection capacitor. The detection circuit detects a current flowing through the coil based on a drop voltage of a direct current (DC) resistance component of the coil obtained by a voltage across the detection capacitor, and corrects the detected current based on an error between the voltage across the detection capacitor and the voltage drop. JP 2000-193 687 is a prior art related to the current detection circuit described above.However, in the above-described current detection circuit, the detection capacitor is directly connected to the coil. For this reason, in detecting the current flowing through the coil based on the voltage drop of the DC resistance component of the coil, it is necessary to balance a reference potential of the detection circuit based on the voltage across the detection capacitor or balance the voltage across the detection capacitor based on the reference potential of the detection circuit. Accordingly, the manufacturing cost may increase as much as the cost of adding a function to balance the reference potential of the detection circuit or the voltage across the detection capacitor to the detection circuit. In addition, since the voltage drop is a relatively small value, the voltage drop is easily affected by quantization errors in the detection circuit when an analog value of the voltage drop is converted into a digital value. This can reduce the detection accuracy of the current.The present invention is directed, in part, to reducing the manufacturing cost of an energy converter while improving the detection accuracy of a current flowing through a coil provided in the energy converter.SUMMARYAccording to an aspect of the present invention, an energy converter including a coil includes a detection coil magnetically coupled to the coil, a detection resistor and a detection capacitor connected in series with each other and in parallel with the detection coil, and a detection circuit that detects a current flowing through the coil based on a voltage across the detection capacitor.According to another aspect of the present invention, a current detection circuit for detecting a current flowing through a coil provided in an energy converter includes a detection coil magnetically coupled to the coil, a detection resistor and a detection capacitor connected in series with each other and in parallel with the detection coil, and a detection circuit that detects a current flowing through the coil based on a voltage across the detection capacitor.Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.BRIEF DESCRIPTION OF THE FIGURESFor an understanding of the invention and the objects and advantages thereof, reference is made to the following description of the embodiments taken in conjunction with the accompanying figures, in which: FIG. 1 is a diagram showing an example of an energy converter according to an embodiment; FIG. 2 is an illustration showing an example of a smoothing coil, a core, and a detection coil; FIG. 3 is a diagram showing a first modification of the power converter according to the embodiment; FIG. 4 is a diagram showing a second modification of the power converter according to the embodiment; FIG. 5 is a diagram showing a third modification of the power converter according to the embodiment; FIG. 6 is a diagram showing a fourth modification of the power converter according to the embodiment; FIG. 7 is a diagram showing a fifth modification of the power converter according to the embodiment; and FIG. 8 is a diagram showing a sixth modification of the power converter according to the embodiment.DETAILED DESCRIPTION OF THE EMBODIMENTSAn embodiment will be described in detail below with reference to the figures.FIG. 1 is a diagram showing an example of an energy converter according to the present embodiment.An energy converter 1 illustrated in FIG. 1 is an active clamp-forward converter that converts a DC output from a power supply B into a specific DC current and supplies the specific DC current to a load.The power converter 1 includes switches Q 1, Q 2, capacitors Cp, Cs, a transformer T, diodes Do 1, Do 2, a smoothing coil Lo, a smoothing capacitor Co, a control circuit 2, and a current detection circuit 3. A drain terminal of the switch Q 1 is connected to one terminal of the capacitor Cp, a source terminal of the switch Q 2, and one terminal of a primary coil Lp 1 of the transformer T. A source terminal of the switch Q 1 is connected to the other terminal of the capacitor Cp and a negative terminal of the power supply line B. A drain terminal of the switch Q 2 is connected to a positive terminal of the power supply B and the other terminal of the primary coil Lp 1 via the capacitor Cs. A cathode terminal of the diode Do 1 is connected to a cathode terminal of the diode Do 2. The cathode terminal of the diode Do 1 is also connected to one terminal of the smoothing capacitor Co and one terminal of the load via the smoothing coil Lo. An anode terminal of the diode Do 1 is connected to a terminal of a secondary coil Lp 2 of the transformer T. An anode terminal of the diode Do 2 is connected to the other terminal of the secondary coil Lp 2, the other terminal of the smoothing capacitor Co, and the other terminal of the load.The control circuit 2 is composed of, for example, a central processing unit (CPU), a multi-core CPU, or a programmable package such as a field programmable gate array (FPGA) or a programmable logic device (PLD).When the power converter 1 converts the direct current output from the power supply B into the predetermined direct current and supplies the predetermined direct current to the load, the switches Q 1, Q 2 are alternately and repeatedly turned on and off by the control circuit 2 so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current.First, when the switch Q 1 is turned on (when the switch Q 1 is in the on state and the switch Q 2 is in the off state), a current flows from the power supply B to the primary coil Lp 1, and a current flows from the secondary coil Lp 2 to the load through the diode Do 1 and the smoothing coil Lo.Then, when the switch Q 1 is turned off (when the switches Q 1, Q 2 are in the off state (dead time)), a current flows from the primary coil Lp 1 to the capacitor Cp to charge the capacitor Cp. When the voltage across the capacitor Cp reaches a total voltage of a voltage of the power supply B and a voltage across the capacitor Cs, a current flows from the primary coil Lp 1 into the capacitor Cs through a body diode of the switch Q 2 to charge the capacitor Cs. On one side of the load, the current continuously flows from the diode Do 1 to the load through the smoothing coil Lo. Note that the energy stored in the primary coil Lp 1 is dissipated by charging the capacitors Cp, Cs, so that the transformer T is gradually demagnetized in a magnetic saturation state. In addition, when the switch Q 1 is turned off, the voltage across the capacitor Cp is 0 [V], so that switching loss is reduced.Then, when the switch Q 2 is turned on (when the switch Q 1 is in the off state and the switch Q 2 is in the on state), a current flows from the primary coil Lp 1 into the capacitor Cs through the switch Q 2 to charge the capacitor Cs. In addition, on the side of the load, a current flows from the diode Do 2 to the load through the smoothing coil Lo. Note that the energy stored in the primary coil Lp 1 is further dissipated by charging the capacitor Cs, so that the transformer T is gradually demagnetized in the magnetic saturation state. In addition, when the switch Q 2 is turned on, a current flows through the body diode of the switch Q 2, so that the switching losses are reduced. While the switch Q 2 is in the on state, the direction of the current is reversed and the capacitor Cs is discharged.Then, when the switch Q 2 is turned off (when the switches Q 1, Q 2 are in the off state (dead time)), a current flows from the capacitor Cp to the power supply B through the primary coil Lp 1, that is, the capacitor Cp is discharged. After the capacitor Cp is discharged, a current flows from the body diode of the switch Q 1 through the primary coil Lp 1 to the power supply B. In addition, on the load side, the current continuously flows from the diode Do 2 through the smoothing coil Lo to the load.Thereafter, the switches Q1 and Q2 are alternately and repeatedly turned on and off. Note that when the switch Q 1 is turned on, the current flows through the body diode of the switch Q 1, and thus the switching loss is reduced.The current detection circuit 3 includes a detection coil Ld, a detection resistor Rd, a detection capacitor Cd, and a detection circuit 4.The detection coil Ld is wound around a core Cre of the smoothing coil Lo, and thus the detection coil Ld is magnetically coupled to the smoothing coil Lo. Note that in a case where the number of turns of the smoothing coil Lo is represented as N 1 and the number of turns of the detection coil Ld is represented as N 2, a turn ratio N 2 / N 1 is preferably equal to or greater than 0.3 and equal to or less than 10. Moreover, the turns ratio N 2 / N 1 is preferably equal to or greater than 1 and equal to or less than 10. Thus, a voltage across the detection capacitor Cd increases by setting the turns ratio n to a relatively large value, so that the voltage across the detection capacitor Cd is not easily affected by a quantization error in the detection circuit 4 when an analog value is converted to a digital value in the voltage across the detection capacitor Cd. This can improve the detection accuracy of the current.The detection resistor Rd and the detection capacitor Cd are connected in series with each other and in parallel with the detection coil Ld. That is, one terminal of the detection capacitor Cd is connected to one terminal of the detection coil Ld via the detection resistor Rd, and the other terminal of the detection capacitor Cd is connected to the other terminal of the detection coil Ld and a reference potential of the detection circuit 4 (e.g., a ground of the power converter 1).The detection circuit 4 detects the current flowing through the smoothing coil Lo based on the voltage across the detection capacitor Cd (difference between an electric potential at the one terminal of the detection capacitor Cd and the reference potential of the detection circuit 4).For example, a voltage across the smoothing coil Lo is represented as VL, the current flowing through the smoothing coil Lo is represented as iL, an inductance of the smoothing coil Lo is represented as L, the voltage across the detection capacitor Cd is represented as Vc, a capacitance of the detection capacitor Cd is represented as C, a voltage across the detection resistor Rd is represented as Vr, a resistance of the detection resistor Rd is represented as R, a current flowing through the detection capacitor Cd and the detection resistor Rd is represented as is, a ratio of the number of turns of the detection coil Ld to the number of turns of the smoothing coil Lo is represented as n, and a Laplace operator is represented as s. In this case, a voltage VLd across the detection coil Ld is expressed by the following equation: where VLd=n×VL=s×n×L×iL is satisfied, Vc=is / (s×C) is satisfied, and Vr=R×is is satisfied. Accordingly, the above-described equation is expressed by the following equation:When this equation is solved for the current is, the current is is expressed by the following equation:The voltage Vr is thus expressed by the following equation:Thus, the voltage Vc of the detection capacitor Cd is expressed by the following Equation 1.Here, a cut-off frequency fc in a filter circuit formed of the detection resistor Rd and the detection capacitor Cd is expressed by the following equation: fc=1 / (2π×R×C). When the resistance R of the detection resistor Rd and the capacitance C of the detection capacitor Cd are set such that the cut-off frequency fc is sufficiently smaller than a switching frequency of the power converter 1, the condition is satisfied that s×C×R>>1. Then, the "1" in the denominator of the above Equation 1 can be ignored, so that Equation 1 is converted to the following Equation 2.That is, in the detection circuit 4, the current iL flowing through the smoothing coil Lo is obtained by substituting the voltage Vc across the detection capacitor Cd into the above-described equation 2. Note that the turns ratio n, the inductance L, the capacitance C, and the resistance R each have a predetermined value.Since the detection coil Ld is magnetically coupled to the smoothing coil Lo, the smoothing coil Lo and the detection capacitor Cd are electrically disconnected (isolated) from each other after the power converter 1 in the embodiment. This can arbitrarily set a reference potential of the detection capacitor Cd regardless of the smoothing coil Lo. Therefore, when the other terminal (reference potential) of the detection capacitor Cd is connected to the reference potential of the detection circuit 4, the current iL flowing through the smoothing coil Lo is detected from the voltage Vc across the detection capacitor Cd without calculating the reference voltage of the detection circuit 4 or the voltage across the detection capacitor Cd. As a result, the power converter 1 does not need to have a function of canceling the reference potential of the detection circuit 4 or the voltage across the detection capacitor Cd, so that an increase in the manufacturing cost of the power converter 1 is suppressed. In addition, the current iL flowing through the smoothing coil Lo does not need to be corrected after the detection, so that an increase in the detection time of the current iL is suppressed.The current detection circuit 3 may be configured to detect a current flowing through the primary coil Lp 1 or the secondary coil Lp 2 having a core. When the current detection circuit 3 detects the current flowing through the primary coil Lp 1 or the secondary coil Lp 2, the detection coil Ld is formed by being wound around the core of the primary coil Lp 1 or the secondary coil Lp 2. In the above-described equation 2, when the detection circuit 4 detects the current flowing through the primary coil Lp 1 or the secondary coil Lp 2 based on the voltage across the detection capacitor Cd, the turns ratio n represents a ratio of the number of turns of the detection coil Ld to the number of turns of the primary coil Lp 1 or the secondary coil Lp 2, and the inductance L represents an inductance of the primary coil Lp 1 or the secondary coil Lp 2.In FIGS. 2A to 2D, an example of the smoothing coil Lo, the detection coil Ld, and the core Cre are shown, respectively. FIG. 2A is a perspective view showing a multilayer printed circuit board (PCB) Sb on which the power converter 1 is mounted, the smoothing coil Lo, and the core Cre. FIG. 2B is a cross-sectional view showing the multilayer printed circuit board Sb, the smoothing coil Lo, and the detection coil Ld. FIG. 2C shows an example of the core Cre, and FIG. 2D shows another example of the core Cre.The smoothing coil Lo illustrated in FIGS. 2A and 2B is formed of plate-shaped conductors L 1, L 2 each having a C shape. The plate-shaped conductor L 1 is disposed on one main surface (a surface facing a positive side in the Z direction) of the multilayer printed circuit board Sb, and the plate-shaped conductor L 2 is disposed on the other main surface (a surface facing a negative side in the Z direction) of the multilayer printed circuit board Sb. For example, one terminal of the plate-shaped conductor L 1 is connected to a wiring pattern on the one main surface of the multilayer printed circuit board Sb by soldering, and the other terminal of the plate-shaped conductor L 1 is connected to one terminal of the plate-shaped conductor L 2 via a conductor in the multilayer printed circuit board Sb. The other terminal of the plate-shaped conductor L 2 is connected to a wiring pattern on the other main surface of the multilayer printed circuit board Sb by soldering. Thus, the plate-shaped conductor L 1 and the plate-shaped conductor L 2 are connected in series with each other, and form the smoothing coil Lo of two turns. Note that the smoothing coil Lo may be formed of only the plate-shaped conductor L 1 or only the plate-shaped conductor L 2. That is, the smoothing coil Lo is disposed on at least one of the main surfaces of the multilayer printed circuit board Sb on which the power converter 1 is mounted.Moreover, the detection coil Ld illustrated in FIG. 2B is an accumulated coil formed of a wiring pattern disposed on an inner layer of the multilayer printed circuit board Sb such that the detection coil Ld faces the smoothing coil Lo in a thickness direction (Z direction) of the multilayer printed circuit board Sb. In FIG. 2B, the detection coil Ld is formed of the wiring pattern that rotates four times in a spiral shape; however, the number of turns is not limited to four. Note that the detection coil Ld may be disposed on at least one of the main surfaces of the multilayer printed circuit board Sb. That is, the detection coil Ld is disposed relative to the smoothing coil Lo in the thickness direction of the multilayer printed circuit board Sb. In addition, the detection coil Ld is not limited to a configuration in which the detection coil Ld is disposed on the one inner layer of the multilayer printed circuit board Sb. The detection coil Ld may be formed by connecting winding patterns each formed on a corresponding plurality of inner layers in series. Moreover, the detection coil Ld may be formed of a conductive wire or the like, and the detection coil is not limited to the wiring pattern. The printed circuit board on which the energy converter 1 is mounted does not have to consist of a multilayer printed circuit board.The core Cre shown in FIG. 2A is composed of a magnetic body Cre1 having an E-shape and a magnetic body Cre2 having an I-shape. Three through holes H 1 to H 3 are arranged in the Y direction in the multilayer printed circuit board Sb. The through hole H 2 is located inside the smoothing coil Lo, and the through holes H 1, H 3 are located outside the smoothing coil Lo. Three protrusions of the magnetic body Cre 1 are inserted into the corresponding through holes H 1 to H 3, respectively, and connected to the magnetic body Cre 2 to form the core Cre.As illustrated in FIG. 2C, in the core Cre, when the magnetic body Cre 1 and the magnetic body Cre 2 are joined to each other, at least one of the three protrusions of the magnetic body Cre 1 may be shortened so that a distal end of the protrusion does not come into contact with the magnetic body Cre 2 forming a gap AG.Alternatively, as illustrated in FIG. 2D, in the core Cre, the gap AG may be formed by connecting the three protrusions of the magnetic body Cre 1 to the magnetic body Cre 2 through a spacer S.In addition, there may also be no gap in the core Cre.The present invention is not limited to the above-described embodiment, and may be improved or modified within the scope of the present invention.The power converter 1 of the embodiment is not limited to the active clamp-forward converter, and may be another converter.< Modification>FIG. 3 is a diagram showing a first modification of the power converter 1 according to the embodiment. In FIG. 3, the same components as in FIG. 1 are denoted by the same reference numerals and may not be described again.The energy converter 1 shown in FIG. 3 is a non-insulated step-down converter which converts a direct current output of the current supply B into a predetermined direct current and supplies the predetermined direct current to the load.That is, the power converter 1 illustrated in FIG. 3 includes the switch Q 1, the diode Do 2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2, and the current detection circuit 3. The source terminal of the switch Q 1 is connected to the cathode terminal of the diode Do 2 and to the one terminal of the smoothing capacitor Co and the one terminal of the load via the smoothing coil Lo. The anode terminal of the diode Do 2 is connected to the negative terminal of the power supply line B, the other terminal of the smoothing capacitor Co, and the other terminal of the load. Note that the configuration and operation of the current detection circuit 3 illustrated in FIG. 3 are identical to those of the current detection circuit 3 illustrated in FIG. 1, so the description of the configuration and operation is omitted. Moreover, a voltage across the load is lower than a voltage of the power supply B, and therefore, even when the load is composed of a battery, no current flows from the load to the power supply B through the body diode of the switch Q 1.When the power converter 1 converts the direct current output from the power supply B into the predetermined direct current and supplies the predetermined direct current to the load, the switch Q 1 is repeatedly turned on and off by the control circuit 2 shown in FIG. 3 so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current. When the switch Q 1 is turned on, a current flows from the power supply B to the load via the switch Q 1 and the smoothing coil Lo. In addition, when the switch Q 1 is turned off, the current continuously flows from the diode Do 2 to the load via the smoothing coil Lo.Also in the power converter 1 illustrated in FIG. 3, when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have a function of canceling a reference potential of the detection circuit 4 or a voltage across the detection capacitor Cd, so that the increase in the manufacturing cost of the power converter 1 is suppressed. Moreover, also in the power converter 1 illustrated in FIG. 3, the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not so easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. Thereby, the detection accuracy of the current can be improved. Also in the power converter 1 shown in FIG. 3, the current iL flowing through the smoothing coil Lo does not need to be corrected after detection, so that the prolongation of the detection time of the current iL is suppressed.< Modification>FIG. 4 is a diagram showing a second modification of the power converter 1 according to the embodiment. In FIG. 4, the same components as in FIG. 1 are denoted by the same reference numerals and may not be described again.The power converter 1 shown in FIG. 4 is an insulated forward converter that converts a direct current output from the power supply B into a predetermined direct current and supplies the predetermined direct current to the load.That is, the power converter 1 illustrated in FIG. 4 includes the switch Q 1, the transformer T, the diodes Do 1, Do 2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2, and the current detection circuit 3. Note that in the insulated type flow converter illustrated in FIG. 4, a circuit configuration for resetting the transformer T is omitted. In addition, the structure and operation of the current detection circuit 3 shown in FIG. 4 are the same as those of the current detection circuit 3 shown in FIG. 1, so that the description of the structure and operation will be omitted.When the power converter 1 converts the direct current output from the power supply B into the predetermined direct current and supplies the predetermined direct current to the load, the switch Q 1 is repeatedly turned on and off by the control circuit 2 shown in FIG. 4 so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current. When the switch Q 1 is turned on, a current flows from the power supply B to the primary coil Lp 1, and a current flows from the secondary coil Lp 2 of the transformer T to the load via the diode Do 1 and the smoothing coil Lo. Then, when the switch Q 1 is turned off, the current continuously flows from the diode Do 2 to the load via the smoothing coil Lo.Also in the power converter 1 illustrated in FIG. 4, when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have a function of canceling a reference potential of the detection circuit 4 or a voltage across the detection capacitor Cd, so that the increase in the manufacturing cost of the power converter 1 is suppressed. Moreover, also in the power converter 1 illustrated in FIG. 4, the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not so easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. Thereby, the detection accuracy of the current can be improved. Also in the power converter 1 shown in FIG. 4, the current iL flowing through the smoothing coil Lo does not need to be corrected after detection, so that the prolongation of the detection time of the current iL is suppressed.< Modification>FIG. 5 is a diagram showing a third modification of the power converter 1 according to the embodiment. In FIG. 5, the same components as in FIG. 1 are denoted by the same reference numerals and may not be described again.The energy converter 1 shown in FIG. 5 is an insulated push-pull converter which converts a direct current output of the current supply B into a specific direct current and supplies the specified direct current to the load.That is, the power converter 1 illustrated in FIG. 5 includes the switches Q 1, Q 2, the transformer T, the diodes Do 1, Do 2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2, and the current detection circuit 3. the source terminal of the switch Q 1 is connected to the negative terminal of the power supply B, and the drain terminal of the switch Q 1 is connected to the one terminal of the primary coil Lp 1 of the transformer T. The source terminal of the switch Q 2 is connected to the negative terminal of the power supply B, and the drain terminal of the switch Q 2 is connected to the other terminal of the primary coil Lp 1 of the transformer T. The cathodic terminal of diode Do1 is connected to the cathodic terminal of diode Do2. The cathode terminal of the diode Do 1 is also connected to the one terminal of the smoothing capacitor Co and the one terminal of the load via the smoothing coil Lo. The anode terminal of the diode Do 1 is connected to the one terminal of the secondary coil Lp 2 of the transformer T. The anode terminal of the diode Do 2 is connected to the other terminal of the secondary coil Lp 2. A center tap of the secondary coil Lp 2 is connected to the other terminal of the smoothing capacitor Co and the other terminal of the load. Note that the configuration and operation of the current detection circuit 3 illustrated in FIG. 5 are identical to those of the current detection circuit 3 illustrated in FIG. 1, so the description of the configuration and operation is omitted.When the power converter 1 converts the direct current output from the power supply B into the predetermined direct current and supplies the predetermined direct current to the load, the switches Q 1, Q 2 are alternately and repeatedly turned on and off by the control circuit 2 shown in FIG. 5, so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current. When the switch Q 2 is turned off and the switch Q 1 is turned on, a current flows from the power supply B to the primary coil Lp 1 via the center tap of the primary coil Lp 1, and a current flows from the secondary coil Lp 2 to the load via the diode Do 1 and the smoothing coil Lo. When the switch Q 1 is turned off and the switch Q 2 is turned on, a current flows from the power supply B to the primary coil Lp 1 through the center tap of the primary coil Lp 1, and a current flows from the secondary coil Lp 2 to the load through the diode Do 2 and the smoothing coil Lo.Also in the power converter 1 illustrated in FIG. 5, when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have a function of canceling a reference potential of the detection circuit 4 or a voltage across the detection capacitor Cd, so that the increase in the manufacturing cost of the power converter 1 is suppressed. Moreover, also in the power converter 1 illustrated in FIG. 5, the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not so easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. Thereby, the detection accuracy of the current can be improved. Also in the power converter 1 shown in FIG. 5, the current iL flowing through the smoothing coil Lo does not need to be corrected after detection, so that the prolongation of the detection time of the current iL is suppressed.< Modification>FIG. 6 is a diagram showing a fourth modification of the power converter 1 according to the embodiment. In FIG. 6, the same components as in FIG. 1 are denoted by the same reference numerals and may not be described again.The energy converter 1 shown in FIG. 6 is an insulated half-bridge converter which converts a direct current output of the current supply B into a specific direct current and supplies the specific direct current to the load.That is, the power converter 1 illustrated in FIG. 6 includes the switches Q 1, Q 2, a capacitor Cr, the transformer T, the diodes Do 1, Do 2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2, and the current detection circuit 3. The source terminal of the switch Q 2 is connected to the other terminal of the primary coil Lp 1 and to the negative terminal of the power supply B via the capacitor Cr. The cathode terminal of the diode Do 1 is connected to the cathode terminal of the diode Do 2. The cathode terminal of the diode Do 1 is also connected to the one terminal of the smoothing capacitor Co and the one terminal of the load via the smoothing coil Lo. The anode terminal of the diode Do 1 is connected to the one terminal of the secondary coil Lp 2 of the transformer T. The anode terminal of the diode Do 2 is connected to the other terminal of the secondary coil Lp 2. The center tap of the secondary coil Lp 2 is connected to the other terminal of the smoothing capacitor Co and the other terminal of the load. Note that the configuration and operation of the current detection circuit 3 illustrated in FIG. 6 are identical to those of the current detection circuit 3 illustrated in FIG. 1, so the description of the configuration and operation is omitted.In addition, when the power converter 1 converts the direct current output from the power supply B into the predetermined direct current and supplies the predetermined direct current to the load, the switches Q 1, Q 2 are alternately and repeatedly turned on and off by the control circuit 2 illustrated in FIG. 6, so that a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current.First, when the switch Q 1 is turned on (when the switch Q 1 is in the on state and the switch Q 2 is in the off state), a current flows from the power supply B to the primary coil Lp 1 through the switch Q 1, and a current flows from the secondary coil Lp 2 to the load through the diode Do 1 and the smoothing coil Lo.Then, when the switch Q 1 is turned off (when the switches Q 1, Q 2 are in the off state (dead time)), a current flows from the other terminal of the primary coil Lp 1 to one terminal of the primary coil Lp 1 through the capacitor Cr and the body diode of the switch Q 2, and the current continuously flows from the secondary coil Lp 2 to the load through the diode Do 1 and the smoothing coil Lo.Then, when the switch Q 2 is turned on (when the switch Q 1 is in the off state and the switch Q 2 is in the on state), a current flows from the one terminal of the capacitor Cr to the other terminal of the capacitor Cr through the primary coil Lp 1 and the switch Q 2, and a current flows from the secondary coil Lp 2 to the load through the diode Do 2 and the smoothing coil Lo. Note that when the switch Q 2 is turned on, the current flows through the body diode of the switch Q 2, and thus the switching losses are reduced.Then, when the switch Q 2 is turned off (when the switches Q 1, Q 2 are in the off state (dead time)), a current flows from the negative terminal of the power supply B to the positive terminal of the power supply B through the capacitor Cr, the primary coil Lp 1, and the body diode of the switch Q 1, and the current continuously flows from the secondary coil Lp 2 to the load through the diode Do 2 and the smoothing coil Lo.Thereafter, the switches Q1 and Q2 are alternately and repeatedly turned on and off. Note that when the switch Q 1 is turned on, the current flows through the body diode of the switch Q 1, and thus the switching loss is reduced.Also in the power converter 1 illustrated in FIG. 6, when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have a function of canceling a reference potential of the detection circuit 4 or a voltage across the detection capacitor Cd, so that the increase in the manufacturing cost of the power converter 1 is suppressed. Moreover, also in the power converter 1 illustrated in FIG. 6, the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not so easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. Thereby, the detection accuracy of the current can be improved. Also in the power converter 1 shown in FIG. 6, the current iL flowing through the smoothing coil Lo does not need to be corrected after detection, so that the prolongation of the detection time of the current iL is suppressed.< Modification>FIG. 7 is a diagram showing a fifth modification of the power converter 1 according to the embodiment. Note that in FIG. 7, the same components as in FIG. 1 are denoted by the same reference numerals and may not be described again.The power converter 1 shown in FIG. 7 is a full-bridge insulated converter that converts a direct current output from the power supply B into a predetermined direct current and supplies the predetermined direct current to the load.That is, the power converter 1 illustrated in FIG. 7 includes the switches Q 1, Q 2, switches Q 3, Q 4, the transformer T, the diodes Do 1, Do 2, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2, and the current detection circuit 3. The drain terminal of the switch Q 1 is connected to the positive terminal of the power supply B and a drain terminal of the switch Q 3. The source terminal of the switch Q 1 is connected to the one terminal of the primary coil Lp 1 of the transformer T and the drain terminal of the switch Q 2. The source terminal of the switch Q 2 is connected to the negative terminal of the power supply B and a source terminal of the switch Q 4. A source terminal of the switch Q 3 is connected to the other terminal of the primary coil Lp 1 and a drain terminal of the switch Q 4. The cathode terminal of the diode Do 1 is connected to the cathode terminal of the diode Do 2. The cathode terminal of the diode Do 1 is also connected to the one terminal of the smoothing capacitor Co and the one terminal of the load via the smoothing coil Lo. The anode terminal of the diode Do 1 is connected to the one terminal of the secondary coil Lp 2 of the transformer T. The anode terminal of the diode Do 2 is connected to the other terminal of the secondary coil Lp 2. The center tap of the secondary coil Lp 2 is connected to the other terminal of the smoothing capacitor Co and the other terminal of the load. Note that the configuration and operation of the current detection circuit 3 shown in FIG. 7 are identical to those of the current detection circuit 3 shown in FIG. 1, so the description of the configuration and operation is omitted.When the power converter 1 converts the direct current output from the power supply B into the predetermined direct current and supplies the predetermined direct current to the load, the switches Q 1, Q 4 are turned on and the switches Q 2, Q 3 are turned off, and then the switches Q 1, Q 4 are turned off and the switches Q 2, Q 3 are turned on by the control circuit 2 illustrated in FIG. 7, and this switching operation is repeated until a voltage across the smoothing capacitor Co reaches a target voltage and a current detected by the current detection circuit 3 reaches a target current. When the switches Q 1, Q 4 are turned on (when the switches Q 1, Q 4 are in the on state and the switches Q 2, Q 3 are in the off state), a current flows from the positive terminal of the power supply B to the negative terminal of the power supply B through the switch Q 1, the primary coil Lp 1, and the switch Q 4, and a current flows from the secondary coil Lp 2 to the load through the diode Do 1 and the smoothing coil Lo. When the switches Q 2, Q 3 are turned on (when the switches Q 1, Q 4 are in the off state and the switches Q 2, Q 3 are in the on state), a current flows from the positive terminal of the power supply B to the negative terminal of the power supply B through the switch Q 3, the primary coil Lp 1, and the switch Q 2, and a current flows from the secondary coil Lp 2 to the load through the diode Do 2 and the smoothing coil Lo.Also in the power converter 1 illustrated in FIG. 7, when the detection circuit 4 detects the current flowing through the smoothing coil Lo, the power converter 1 does not need to have a function of canceling a reference potential of the detection circuit 4 or a voltage across the detection capacitor Cd, so that the increase in the manufacturing cost of the power converter 1 is suppressed. Moreover, also in the power converter 1 illustrated in FIG. 7, the voltage across the detection capacitor Cd increases as the turns ratio n increases, so that the voltage across the detection capacitor Cd is not so easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. Thereby, the detection accuracy of the current can be improved. Also in the power converter 1 shown in FIG. 7, the current iL flowing through the smoothing coil Lo does not need to be corrected after detection, so that the prolongation of the detection time of the current iL is suppressed.< Modification>FIG. 8 is a diagram showing a sixth modification of the power converter 1 according to the embodiment. Note that in FIG. 8, the same components as in FIG. 1 are denoted by the same reference numerals and may not be described again.The power converter 1 illustrated in FIG. 8 is an active clamp-forward converter that converts a DC output of a high-voltage battery BH into a predetermined DC voltage and supplies the predetermined DC voltage to a low-voltage battery BL.That is, the power converter 1 illustrated in FIG. 8 includes the relays Re 1, Re 2, a smoothing capacitor Cb, the switches Q 1, Q 2, the capacitor Cs, the transformer T, the switches Q 5, Q 6, the smoothing coil Lo, the smoothing capacitor Co, the control circuit 2, and the current detection circuit 3. The drain terminal of the switch Q 1 is connected to the source terminal of the switch Q 2 and the one terminal of the primary coil Lp 1 of the transformer T, and the source terminal of the switch Q 1 is connected to a negative terminal of the high voltage battery BH and to one terminal of the smoothing capacitor Cb via the relay Re 1. The drain terminal of the switch Q 2 is connected to a positive terminal of the high voltage battery BH via the capacitor Cs and the relay Re 2. The drain terminal of the switch Q 2 is also connected to the other terminal of the primary coil Lp 1 and the other terminal of the smoothing capacitor Cb via the capacitor Cs. A drain terminal of the switch Q 5 is connected to a drain terminal of the switch Q 6. The drain terminal of the switch Q 5 is also connected to the one terminal of the smoothing capacitor Co and a positive terminal of the low voltage battery BL via the smoothing coil Lo. A source terminal of the switch Q 5 is connected to one terminal of the secondary coil Lp 2 of the transformer T, the other terminal of the smoothing capacitor Co, and a negative terminal of the low voltage battery BL. A source terminal of the switch Q 6 is connected to the other terminal of the secondary coil Lp 2.The current detection circuit 3 illustrated in FIG. 8 includes the detection coil Ld, the detection resistor Rd, the detection capacitor Cd, the detection circuit 4, and the offset resistors R 1, R 2.The detection coil Ld is wound around the core Cre of the smoothing coil Lo.The detection resistor Rd and the detection capacitor Cd are connected in series with each other and in parallel with the detection coil Ld.The offset resistors R1, R2 are connected in series with each other between a constant voltage power supply Pvc and a reference potential of the detection circuit 4. A node between the offset resistors R 1, R 2 is connected to a node between the detection coil Ld and the detection capacitor Cd. Thus, a total voltage of a voltage across the detection capacitor Cd and a voltage across the offset resistor R 2 is supplied to the detection circuit 4. That is, due to the offset resistors R 1, R 2, the voltage across the detection capacitor Cd is shifted by a difference between an electric potential at the node between the offset resistors R 1, R 2 and the reference potential of the detection circuit 4, and the voltage of the detection capacitor Cd after the shift is input to the detection circuit 4. The detection circuit 4 substitutes the voltage Vc across the detection capacitor Cd that has been calculated into the above-described equation 2 to obtain the current iL flowing through the smoothing coil Lo. Accordingly, while the current flowing in a forward direction through the smoothing coil Lo is detected based on a voltage higher than the electric potential at the node between the offset resistors R 1, R 2 of the voltage input to the detection circuit 4, the current in a reverse direction flowing through the smoothing coil Lo is detected based on a voltage lower than the electric potential at the node between the offset resistors R 1, R 2 of the voltage input to the detection circuit 4.In the energy converter 1 shown in FIG. 8, the electrical potential at the smoothing capacitor Cb is equal to zero before starting up the energy converter 1. Prior to a normal operation in which the direct current output from the high voltage battery BH is converted into the predetermined direct current and the predetermined direct current is input to the low voltage battery BL, the relays Re 1, Re 2 are placed in an electrically disconnected state by the control circuit 2, and the smoothing capacitor Cb is charged in advance by power supplied from the low voltage battery BL. Thereafter, the relays Re 1, Re 2 are placed in an electrically connected state by the control circuit 2, and the current is supplied from the high voltage battery BH to the low voltage battery BL. In this operation, when the relays Re 1, Re 2 are changed from the electrically disconnected state to the electrically turned on state, a relatively large inrush current is suppressed from flowing from the high voltage battery BH into the smoothing capacitor Cb.For example, it is assumed that a direction in which current flows from the high voltage battery BH to the low voltage battery BL is defined as a forward direction, and a direction in which current flows from the low voltage battery BL to the high voltage battery BH is defined as a backward direction. Further, a range of an input voltage of the detection circuit 4 for analog-to-digital conversion thereof is defined as a range from 0 [V] to 5 [V], and the electric potential at the node between the offset resistors R 1, R 2 is defined as 2.5 [V]. The voltage across the detection capacitor Cd after the offset is represented as Vc.In this case, first, the relays Re1, Re2 are turned off by the control circuit 2, and the switch Q1 is continuously turned off, and the switches Q2, Q5, Q6 are repeatedly turned on and off by the control circuit 2, so that the current in the reverse direction detected by the current detection circuit 3 reaches a target value. When the switch Q 6 is turned on (when the switches Q 1, Q 2, Q 5 are in the off state and the switch Q 6 is in the on state), a current flows from the low voltage battery BL to the secondary coil Lp 2, and a current flows from the primary coil Lp 1 through the smoothing capacitor Cb. At this time, the direction of the current flowing through the smoothing coil Lo is the reverse direction. When the switch Q 6 is turned off (when the switches Q 1, Q 6 are in the off state and the switches Q 2, Q 5 are in the on state), the transformer T is reset and the current flowing in the reverse direction through the smoothing coil Lo increases. That is, also in this case, the direction of the current flowing through the smoothing coil Lo is the reverse direction. Accordingly, the voltage input of the detection circuit 4 is lower than 2.5 [V] and equal to or higher than 0 [V], so that the detection circuit 4 detects the current flowing through the smoothing coil Lo in the reverse direction. Thereby, the smoothing capacitor Cb can be charged before the relays Re1, Re2 are put in the electrically connected state. Note that the switch Q 1 may be turned on and off in synchronization with the switch Q 6.When the voltage across the smoothing capacitor Cb is a threshold voltage (e.g., a voltage of the high voltage battery BH) or more, the control circuit 2 switches the relays Re 1, Re 2 to the electrically connected state.Then, the switches Q 5, Q 6 are alternately and repeatedly turned on and off, and the switches Q 1, Q 2 are alternately and repeatedly turned on and off by the control circuit 2, so that the voltage across the smoothing capacitor Co reaches a target voltage and the current detected by the current detection circuit 3 in the forward direction reaches a target current. When the switches Q 1, Q 6 are turned on (when the switches Q 1, Q 6 are in the on state and the switches Q 2, Q 5 are in the off state), a current flows from the high voltage battery BH to the primary coil Lp 1, and a current flows from the secondary coil Lp 2 to the low voltage battery BL via the switch Q 6 and the smoothing coil Lo. When the switch Q 2 is turned on (when the switches Q 1, Q 6 are in the off state and the switches Q 2, Q 5 are in the on state), a current flows from the primary coil Lp 1 to the capacitor Cs through the switch Q 2, so that the transformer T is gradually demagnetized in a magnetic saturation state. In addition, on one side of the low voltage battery BL, a current flows from the switch Q 5 to the low voltage battery BL via the smoothing coil Lo. Here, the voltage input to the detection circuit 4 is higher than 2.5 [V] and equal to or lower than 5 [V], and the detection circuit 4 detects the forward current / power flowing through the smoothing coil Lo.Also in the power converter 1 shown in FIG. 8, the voltage across the detection capacitor Cd increases as the wind ratio n increases, so that the voltage across the detection capacitor Cd is not so easily affected by the quantization error in the detection circuit 4 when an analog value is converted into a digital value in the voltage across the detection capacitor Cd. Thereby, the detection accuracy of the current can be improved. Also in the power converter 1 shown in FIG. 8, the current iL flowing through the smoothing coil Lo does not need to be corrected after detection, so that the prolongation of the detection time of the current iL is suppressed.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2000-193 687

[0002]

Claims

An energy converter (1) including a coil, comprising: a detection coil (Ld) magnetically coupled to the coil; a detection resistor (Rd) and a detection capacitor (Cd) connected in series with each other and in parallel with the detection coil (Ld); and a detection circuit (4) that detects a current flowing through the coil based on a voltage across the detection capacitor (Cd).The energy converter (1) according to claim 1, characterized in that the coil is a smoothing coil (Lo), by which the current flowing in the energy converter (1) is smoothed.The power converter (1) according to claim 2, characterized in that the smoothing coil (Lo) has a core (Cre), and the detection coil (Ld) is formed by being wound around the core (Cre).Energy converter (1) according to claim 3, characterised in that the core has a gap (AG).The energy converter (1) according to claim 1, characterized in that in a case where the number of turns of the coil corresponds to N1 and the number of turns of the detection coil (Ld) corresponds to N2, N2 / N1 is equal to or less than 10.The energy converter (1) according to claim 1, further comprising two offset resistors (R1, R2) connected in series with each other between a constant voltage source (Pvc) and a reference potential of the detection circuit (4), characterized in that the two offset resistors (R1, R2) offset the voltage across the detection capacitor (Cd) by a difference between an electrical potential at a node between the two offset resistors (R1, R2) and the reference potential of the detection circuit (4).The power converter (1) according to claim 2, characterized in that the smoothing coil (Lo) is disposed on at least one of the main surfaces of a circuit board on which the power converter (1) is mounted, and the detection coil (Ld) is disposed relative to the smoothing coil (Lo) in a thickness direction of the circuit board.The power converter (1) according to claim 7, characterized in that the circuit board is a multilayer circuit board (Sb), and the detection coil (Ld) is disposed on an inner layer of the circuit board as a wiring pattern.A current detection circuit (3) for detecting a current flowing through a coil provided in an energy converter (1), the current detection circuit (3) comprising: a detection coil (Ld) magnetically coupled to the coil; a detection resistor (Rd) and a detection capacitor (Cd) connected in series with each other and in parallel with the detection coil (Ld); and a detection circuit (4) that detects a current flowing through the coil based on a voltage across the detection capacitor (Cd).

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