JP2019201455A - Resonance-type converter and program - Google Patents

Abstract

To provide a resonance-type converter in which the variation of a resonance frequency can be determined in a short time.SOLUTION: The resonance-type converter includes a switching circuit which is connected to a coil via a resonance circuit, and converts a voltage inputted to the switching circuit and outputs the voltage. The resonance-type converter includes a detection unit that detects values of current flowing through the switching circuit at two or more time points within the same resonance period, and a determination unit that determines the variation of a resonance frequency on the basis of the current values at two or more time points detected by the detection unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a resonant converter and a program.

  There is known a resonance type power converter including a bridge circuit having a plurality of switching elements to which DC power is input, a transformer, a current detection circuit for detecting a current value flowing through at least one switching element, and a control circuit. (For example, Patent Document 1).

  In the resonant power converter described in Patent Document 1, when the detection value of the current detection circuit is greater than zero at the timing when the control circuit outputs a control signal for turning on the switching element, the resonant power converter operates abnormally. It is assumed that it is determined.

JP 2017-184599 A

  However, the resonant power converter of Patent Document 1 determines that the resonant power converter operates abnormally when the detection value of the current detection circuit is greater than zero at the timing when the control circuit outputs a control signal for turning on the switching element. Therefore, there is a problem that determination in a short time becomes difficult.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a resonant converter and a program that can determine the fluctuation of the resonant frequency in a short time.

  A resonant converter according to an aspect of the present disclosure is a resonant converter that includes a switching circuit connected to a coil through a resonant circuit, converts the voltage input to the switching circuit, and outputs the converted voltage. A detection unit that detects current values at two or more time points flowing in the switching circuit within a cycle, and a determination unit that determines a fluctuation in resonance frequency based on current values at two or more time points detected by the detection unit.

  According to one aspect of the present disclosure, it is possible to provide a resonance type converter that can determine a change in resonance frequency in a short time.

FIG. 3 is a circuit diagram schematically illustrating a configuration example of a resonant converter according to the first embodiment. FIG. 3 is a block diagram schematically showing a configuration example of a control circuit. It is explanatory drawing regarding the AD conversion process in a control circuit. It is explanatory drawing regarding a resonance period. It is explanatory drawing regarding control of a switching element, and the waveform of an electric current. It is a flowchart which shows the process of the control part which concerns on Embodiment 1 (determination of the fluctuation | variation of the resonant frequency). It is a flowchart which shows the process of the control part which concerns on Embodiment 2 (a drive frequency is fluctuated and it adapts to a resonant frequency).

[Description of Embodiment of the Present Invention]
First, embodiments of the present disclosure will be listed and described. Moreover, you may combine arbitrarily at least one part of embodiment described below.

(1) A resonant converter according to an aspect of the present disclosure is a resonant converter that includes a switching circuit connected to a coil via a resonant circuit, converts a voltage input to the switching circuit, and outputs the converted voltage. A detection unit that detects current values at two or more time points flowing through the switching circuit within the same resonance period, and a determination unit that determines fluctuations in resonance frequency based on current values at two or more time points detected by the detection unit; Is provided.

  In this aspect, since the fluctuation of the resonance frequency is determined based on the current values at two or more time points detected within the same resonance period, the determination can be performed in a short time.

(2) Of the detected current values of two or more time points, it is preferable that at least two current value detection time points are symmetrical with respect to the midpoint of the half cycle in the resonance period.

  In this aspect, in the detected current values at two or more time points, the detection time points of at least two current values are symmetric with respect to the midpoint of the half cycle of the resonance cycle, so that the variation in the resonance frequency is accurately determined. be able to.

(3) A configuration in which the determination unit determines that the resonance frequency has fluctuated when the two current values at which the detection time points are symmetric differ from the midpoint of the half cycle in the resonance cycle by a predetermined value or more. preferable.

  In this aspect, when the two current values whose detection time points are symmetrical with respect to the midpoint of the resonance period are different from each other by a predetermined value or more, it is determined that the resonance frequency has changed. In other words, it is possible to accurately determine the fluctuation of the resonance frequency.

(4) The detection unit increases a time difference between the two detection time points according to the extension of the resonance period, and currents at two detection time points that are symmetrical with respect to a midpoint of the half cycle in the resonance period. A configuration for detecting the value is preferable.

  In this aspect, the difference in detection time is increased in accordance with the extension of the resonance period, and two current values that are symmetric with respect to the midpoint of the half period in the resonance period are detected. Variation can be determined.

(5) Preferably, the detection unit detects a current value at two or more time points flowing through the switching circuit within a period in which any one of the switching elements in the switching circuit is turned on.

  In this aspect, since current values at two or more time points flowing through the switching circuit are detected within a period in which any of the switching elements in the switching circuit is turned on, these current values can be reliably detected.

(6) When the current value detected before the midpoint of the half cycle in the resonance cycle is larger than the current value detected after the midpoint of the half cycle in the resonance cycle, the switching element in the switching circuit When the drive frequency is increased and the current value detected before the midpoint of the half cycle in the resonance cycle is smaller than the current value detected after the midpoint of the half cycle in the resonance cycle, A configuration including a control unit that performs switching control of the switching element by reducing the driving frequency of the switching element is preferable.

  In this aspect, switching is performed by increasing or decreasing the driving frequency of the switching element based on the magnitude relationship between the current value detected before the midpoint of the half cycle and the current value detected after the midpoint of the half cycle. Since the control is performed, even when the resonance frequency varies, the drive frequency of the switching element can be controlled to adapt to the varied resonance frequency.

(7) A program according to an aspect of the present disclosure detects a current value at two or more time points in the same resonance cycle flowing in the switching circuit of the resonance converter in a computer, and based on the detected current values at two or more time points, A process for determining the fluctuation of the resonance frequency is executed.

  In this aspect, it is possible to cause the computer to determine the fluctuation of the resonance frequency in a short time based on the current values at two or more time points detected within the same resonance period.

[Details of the embodiment of the present invention]
The present invention will be specifically described with reference to the drawings showing the embodiments thereof. A resonant converter according to an embodiment of the present disclosure will be described below with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to the claim are included.

(Embodiment 1)
Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a circuit diagram schematically illustrating a configuration example of a resonant converter 1 according to the first embodiment. The resonant converter 1 according to the present embodiment is a full-wave rectifying full-bridge LLC resonant DC / DC converter, and is mounted on a hybrid vehicle, an electric vehicle, or the like.

  Resonant converter 1 includes an input terminal pair 10A to which a direct voltage is applied and an output terminal pair 10B to which a DC / DC converted voltage is output. A DC power supply 4 is connected to the input terminal pair 10A, and a load 5 is connected to the output terminal pair 10B. The DC power supply 4 and the load 5 are, for example, an HV battery and an auxiliary battery, and a voltage of several hundred volts output from the HV battery is applied to the input terminal pair 10A. The resonant converter 1 performs DC / DC conversion of the input voltage to a voltage of several V to several tens V, and outputs the DC / DC converted voltage from the output terminal pair 10B to, for example, an auxiliary battery or an in-vehicle load. . The input / output voltage is an example.

  The resonant converter 1 includes a switching circuit 11 that converts a DC voltage input to the input terminal pair 10 </ b> A into an AC voltage by DC / AC conversion, a resonance circuit 12 that resonates by the DC / AC converted AC voltage, and an AC voltage. Includes a transformer 13 that transforms the AC voltage, a rectifier circuit 14 that full-wave rectifies the AC voltage transformed by the transformer 13, and a smoothing capacitor 15 that smoothes the DC voltage that has been full-wave rectified.

  The switching circuit 11 is a full bridge circuit that converts a DC voltage input to the input terminal pair 10A into an AC voltage by switching control. The switching circuit 11 includes a first leg 11A in which a positive switching element Q11 and a negative switching element Q12 are connected in series, and a positive switching element Q21 and a negative switching element Q22 connected in series. The first leg 11A and the second leg 11B are connected in parallel.

  The switching elements Q11, Q12, Q21, and Q22 are power devices such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). These switching elements Q11, Q12, Q21, and Q22 will be described as n-channel MOSFETs.

  As shown in FIG. 1, each of the switching elements Q11, Q12, Q21, and Q22 has a parasitic capacitance and a parasitic diode. In addition, you may provide a capacitive element separately in the drain and source | sauce of switching element Q11, Q12, Q21, Q222.

  The drains of the switching elements Q11 and Q21 are connected to the positive terminal of the input terminal pair 10A. The sources of the switching elements Q11 and Q21 are connected to the drains of the switching elements Q12 and Q22, respectively, and the sources of the switching elements Q12 and Q22 are connected to the negative terminal of the input terminal pair 10A.

  The resonance circuit 12 is an LC resonance circuit 12 that resonates with an alternating voltage that is DC / AC converted by the switching circuit 11. The resonance circuit 12 includes a circuit in which a resonance capacitor C1 and a resonance inductor Lr are connected in series, and one end of the circuit is connected to a connection portion (connection node) between the two switching elements Q11 and Q12 constituting the first leg 11A. The other end is connected to one end of the primary coil 131 of the transformer 13.

  The exciting inductor Lm related to the primary coil 131 constituting the transformer 13 also constitutes a part of the resonance circuit 12. The resonant inductor Lr may be replaced by a leakage inductor of the primary coil 131 that constitutes the transformer 13. Moreover, although the example which comprises the LLC resonant circuit 12 by the exciting inductor Lm of the primary coil 131 was demonstrated, you may connect another inductor to the primary coil 131 in parallel.

  The transformer 13 includes a primary coil 131 and a secondary coil 132 that are magnetically coupled. One end of the primary coil 131 is connected to the other end of the resonance circuit 12 in which a resonance capacitor C1 and a resonance inductor Lr are connected in series.

  One end of the resonance capacitor C1 is connected to the connection of the switching elements Q11 and Q12, the other end of the resonance capacitor C1 is connected to one end of the resonance inductor Lr, and the other end of the resonance inductor Lr is the primary coil 131. Connected to one end. The other end portion of the primary coil 131 is connected to a connection portion (connection node) between the two switching elements Q21 and Q22 constituting the second leg 11B.

  When an AC voltage DC / AC converted by the switching circuit 11 is applied to the primary coil 131, an alternating magnetic flux is generated in the primary coil 131, and the primary coil 131 and the secondary coil are electromagnetically induced by the alternating magnetic flux. An alternating voltage transformed according to the turn ratio of 132 is generated in the secondary coil 132. Both ends of the secondary coil 132 are connected to the rectifier circuit 14. That is, the AC voltage generated in the secondary coil 132 is output to the rectifier circuit 14 with its polarity inverted at a predetermined cycle.

  The rectifier circuit 14 is, for example, a full-wave rectifier circuit (double-wave rectifier circuit, bridge rectifier circuit, or the like) such as a diode bridge. Alternatively, the rectifier circuit 14 uses two rectifying switching elements and complementarily turns on and off the two rectifying switching elements according to the period of the AC voltage generated in the secondary coil 132. It's okay.

  The DC voltage rectified by the rectifier circuit 14 is a voltage having a pulsating current component (pulsating current voltage), and this pulsating current voltage is charged and discharged by the smoothing capacitor 15 to remove the pulsating current component. To be smoothed. The DC voltage smoothed by the smoothing capacitor 15 is applied to the load via the output terminal pair 10B.

  Resonant converter 1 includes a current detection unit 2 that detects a current flowing through switching circuit 11 and a control circuit 3 that controls ON / OFF of switching elements Q11, Q12, Q21, and Q22 (switching control).

  The current detection unit 2 is a current sensor using, for example, a Hall element or a shunt resistor. The current value flowing through the switching circuit 11 detected by the current detection unit 2 is output to the control circuit 3 as an analog value.

  In connection between the current detection unit 2 and the control circuit 3, the wiring connected to the output terminal of the current detection unit 2 is branched into two, and each branched wiring is connected to the control circuit 3.

  The control circuit 3 sends gate signals to the gate terminals of the switching elements Q11, Q12, Q21, and Q22 so that the driving frequency of the switching elements Q11, Q12, Q21, and Q22 becomes the resonance frequency of the resonance circuit 12 described later. For example, output is performed at a duty ratio of 50% having a dead time.

  Of the two output terminals 36 provided in the control circuit 3, one output terminal 36 (Vg1) is connected to the gate terminals of the switching element Q11 of the first leg 11A and the switching element Q22 of the second leg 11B. .

  The other output terminal 36 (Vg2) is connected to the gate terminals of the switching element Q12 of the first leg 11A and the switching element Q21 of the second leg 11B.

  Although details will be described later, the control unit 35 alternately outputs gate signals at the two output terminals 36, whereby a current from the DC power source flows in the order of Q11, the resonance circuit 12, the primary coil 131, and Q22. , Q21, primary coil 131, resonant circuit 12, and Q12 are switched in this order. By switching in this way, an alternating voltage is output from the switching circuit 11, and an alternating current whose polarity is reversed at a predetermined period flows through the primary coil 131.

  The control unit 35 performs switching control by a soft switching method. All switching elements Q11, Q12, Q31, and Q32 are turned off in the dead time for switching the conduction state. When the conduction state is switched, charging and discharging of the parasitic capacitances of the switching elements Q11 and Q22 are performed. The control unit 35 switches the switching elements Q11 and Q22 to the on state at the timing when the voltage across the switching elements Q11 and Q22 becomes zero during the charge / discharge process. By performing switching at the timing, soft switching that can reduce switching loss is realized.

  FIG. 2 is a block diagram schematically showing a configuration example of the control circuit 3. FIG. 3 is an explanatory diagram regarding AD conversion processing in the control circuit 3.

  An analog value based on the current value output from the current detection unit 2 is input to the control circuit 3. The control circuit 3 is connected to the sample hold unit 341 that samples and holds an input analog value (sample and hold), and the current value (analog value) output from the sample hold unit 341 by AD conversion. , An AD conversion unit 351 for converting into a digital value is included. These sample hold unit 341 and AD conversion unit 351 constitute an AD converter 34.

  The control circuit 3 switches to the first input terminal 31, the second input terminal 32, and any one of these input terminals 31, 32, and switches any one of the switched input terminals 31, 32. And a connection switching unit 33 that connects the sample holding unit 341 to the sample hold unit 341. Each of the first input terminal 31 and the second input terminal 32 is connected to a wiring branched in two from the wiring connected to the output terminal of the current detection unit 2.

  The control circuit 3 includes a storage unit such as a CPU (Central Processing Unit) or MPU (Micro Processing Input Terminal Unit), a ROM (Read Only Memory) or a RAM (Random Access Memory), and a control unit including a clock unit having a timing function. 35 (microcomputer). The control unit 35 functions as the AD conversion unit 351 by executing the program stored in the storage unit. Although details will be described later, the control unit 35 may function as a detection unit that detects a current value by executing a program stored in the storage unit based on the current value output from the current detection unit 2. Good. Further, the control unit 35 functions as a determination unit that determines the variation of the resonance frequency by executing the program stored in the storage unit, and based on the determination, the switching elements Q11, Q12, and Q21 of the switching circuit 11. , Q22 is controlled.

  The sample hold unit 341 is configured to sample an analog value based on a control signal from the control unit 35. The sample hold unit 341 includes, for example, a capacitor, and holds an analog value input using the capacitor.

  The control unit 35 performs switching control of the connection switching unit 33 in conjunction with the output of a control signal for sampling the analog value in the sample hold unit 341. That is, when the analog value input from the first input terminal 31 is sampled and held, the connection switching unit 33 switches to the first input terminal 31 and connects the first input terminal 31 and the sample hold unit 341.

  When sampling and holding an analog value input from the second input terminal 32, the connection switching unit 33 switches to the second input terminal 32 and connects the second input terminal 32 and the sample hold unit 341.

  As shown in FIG. 3, analog values are input to the AD converter 34 included in the control circuit 3 from the two channels of the first input terminal 31 (1ch) and the second input terminal 32 (2ch). When the AD converter 34 converts the input analog value into a digital signal, the sample and hold of the analog value by the sample hold unit 341 and the AD conversion by the control unit 35 are sequentially performed.

  Sample and hold of the sample hold unit 341 are performed by hardware processing, and AD conversion by the control unit 35 is performed by software processing. As an example, the sample and hold processing time of the sample hold unit 341 is 10 μsec, and the AD conversion processing time by the control unit 35 is 500 μsec. That is, in order to convert an input analog value into a digital value, a time (510 μse = 10 + 500) obtained by adding these processing times is required.

  The control unit 35 controls the sampling of the analog value input from the second input terminal 32 (2ch) before the AD conversion of the analog value input from the first input terminal 31 (1ch) is completed. Output a signal.

  In FIG. 3A, the control unit 35 determines that the end of the analog value sample and hold processing at the second input terminal 32 is substantially the same as the end of the analog value AD conversion at the first input terminal 31. A control signal for sampling an analog value from the two input terminals 32 (2ch) is output. By outputting the control signal in this way, the analog value input from the first input terminal 31 (1ch) is input from the second input terminal 32 (2ch) even before the AD conversion is completed. Analog values can be obtained, ie sampled and held.

  In FIG. 3B, the control unit 35 samples the analog value input from the first input terminal 31 (1ch) and immediately after finishing the hold process, the analog value sample input from the second input terminal 32 (2ch). And a control signal for sampling the analog value so as to start the hold process.

  After the analog value sample and hold process input from the second input terminal 32 (2ch) is completed, the analog value AD conversion of the second input terminal 32 is completed. It will be started later. By outputting the control signal in this manner, the second input terminal 32 (before the AD conversion of the analog value input from the first input terminal 31 (1ch) is completed as in FIG. 3A. 2ch) can be obtained, that is, sampled and held.

  Therefore, when two analog values are acquired in succession, the connection switching unit 33 switches to one of the input terminals connected to the sample and the hold, so that the AD conversion unit 351 finishes the AD conversion process. Even so, the second analog value can be acquired. The number of input terminals 31 and 32 is not limited to two, and the number of input terminals 31 and 32 may be three or more.

  FIG. 4 is an explanatory diagram relating to the resonance period. FIG. 5 is an explanatory diagram regarding the control of the switching element and the waveform of the current. In FIG. 4, the horizontal axis represents time (t), and the vertical axis represents current (A), which represents one cycle of the alternating current output from the switching circuit 11. FIG. 5 shows a timing chart in which the horizontal axis represents time, and the vertical axis represents gate signals output to the switching elements Q11, Q12, Q21, and Q22.

  In the storage unit of the control unit 35 (microcomputer), the resonance frequency by the resonance circuit 12 is stored. The resonance frequency (f [Hz]) is determined by the capacitance (C [F]) of the resonance capacitor C1 constituting the resonance circuit 12 and the inductance (L [H]) of the resonance inductor Lr (f = 1 / {2π (L * C) ^ (1/2)}). Therefore, the resonance period (T [s]) that is the reciprocal of the resonance frequency is obtained by multiplying the square root of the value obtained by multiplying the capacitance of the resonance capacitor C1 by the inductance of the resonance inductor Lr by 2π, as shown in FIG. Value (2π (L * C) ^ (1/2)).

  The half cycle of the resonance period is the difference between the zero crossing point where the positive and negative polarities are reversed in one resonance cycle and the time point of the zero crossing (zero crossing at the start and end of the resonance cycle) located before and after that point. It becomes time by. The middle point (vertex) in the first half cycle is the time when the time obtained by multiplying the resonance cycle (T) by 0.25 (T × 0.25) has elapsed from the time of zero crossing when one resonance cycle starts. .

  The control unit 35 determines the drive frequency of the switching elements Q11, Q12, Q21, and Q22 in the switching circuit 11 so as to match the resonance frequency of the resonance circuit 12. In the two output terminals 36, the control unit 35 alternately outputs a gate signal to one output terminal 36 (Vg1) and the other output terminal 36 (Vg2), and is connected to one output terminal 36 (Vg1). Q11 and Q22 and Q12 and Q21 connected to the other output terminal 36 (Vg2) are turned on and off alternately, that is, complementarily. When the control unit 35 switches the output of the gate signal from one output terminal 36 (Vg1) to the other output terminal 36 (Vg2), the one of the output terminal 36 (Vg1) and the other output terminal 36 (Vg2). A dead time during which no gate signal is output is set to any output terminal 36.

  In the timing chart of FIG. 5, current waveforms in three states based on fluctuations in the resonance frequency are also shown in the current output from the switching circuit 11 when the gate signal is output to one output terminal 36 (Vg1). Yes. The fluctuation of the resonance frequency occurs due to, for example, aging deterioration of the resonance capacitor C1 or the resonance inductor Lr constituting the resonance circuit 12.

  The middle point between the start time when the output of the gate signal is started and the end time when the output of the gate signal is finished in one output of the gate signal to one output terminal 36 (Vg1), that is, in one switching, is This corresponds to the midpoint of a half cycle at the resonance frequency.

  The control unit 35 determines the output period of the gate signal, that is, the drive period of the switching elements Q11, Q12, Q21, and Q22 based on the resonance frequency stored in the storage unit. Based on the driving cycle, the time point of the midpoint of the half cycle at the resonance frequency is specified.

  Based on the output from the current detection unit 2, the control unit 35 determines current values (i1, i2) at two time points (first time point and second time point) that are contrasted with respect to the midpoint of the half cycle at the resonance frequency. ) Is detected. Contrast with the midpoint of the half cycle is, for example, the time when a predetermined time is added to and subtracted from the time (T / 4 [sec]) of the midpoint of the half cycle of the resonance cycle (T [sec]) It becomes. This predetermined time is a time obtained by multiplying the resonance period (T [sec]) by a value smaller than 0.25, that is, a time shorter than a quarter of the resonance period.

  Alternatively, the predetermined time is shorter than a quarter of the resonance period and is a period in which any one of the switching elements Q11, Q12, Q21, and Q22 is on, that is, a period other than the dead time. It is desirable to be set as follows. By detecting the current value during the period when any of the switching elements Q11, Q12, Q21, Q22 is on, the current value can be detected stably.

  For example, when the predetermined time is a time for multiplying the resonance period by 0.125, the first time point is a time (T × 0) obtained by multiplying the resonance point by 0.125 with respect to the middle point of the half cycle. .125) is subtracted. The second time point is a time point obtained by adding a time (T × 0.125) obtained by multiplying the resonance period by 0.125 to the time point at the midpoint of the half cycle.

  That is, two time points obtained by adding and subtracting a predetermined time (± predetermined time) with respect to the time point of the midpoint of the half cycle within the same resonance period are set as two time points symmetrical to the midpoint of the half cycle. The control unit 35 detects the current value at these two time points. Therefore, two time points symmetrical with respect to the midpoint of this half cycle correspond to two time points within the same resonance period.

  When setting two time points (first time point and second time point) that are contrasted with the midpoint of the half cycle at the resonance frequency as a reference (time point of the midpoint), the control unit 35 sets the time point of the midpoint of the half cycle. On the other hand, a predetermined time for addition and subtraction is stored in the storage unit.

  The waveform of the current described in the upper stage is a state where the resonance frequency does not fluctuate. In a state where the resonance frequency is not fluctuating, current values (i1) at two time points (first time point and second time point) which are contrasted with the midpoint of the half cycle at the resonance frequency as a reference (time point of the midpoint). , I2) are substantially the same value (i1≈i2).

  The waveform of the current described in the middle stage is in a changed state due to a decrease (decrease) in the resonance frequency. In a state where the resonance frequency has decreased and fluctuated, the current value (i1 ′) detected at the first time point before the midpoint of the half cycle at the resonance frequency is the time of the midpoint of the half cycle at the resonance frequency. It becomes smaller than the current value (i2 ′) at the second time point detected later (i1 ′ <i2 ′).

  The waveform of the current described in the lower stage is in a state of fluctuation as the resonance frequency increases (rises). In a state in which the resonance frequency has increased and fluctuated, the current value (i1 ″) detected at the first time before the midpoint of the half cycle at the resonance frequency is the midpoint of the half cycle at the resonance frequency. It becomes larger than the current value (i2 ″) at the second time point detected later (i1 ″> i2 ″).

  The control unit 35 determines the fluctuation of the resonance frequency by comparing the current values at the first time point and the second time point which are contrasted with respect to the midpoint of the half cycle at the resonance frequency.

  The control unit 35 may determine a predetermined time to be added and subtracted from the time point of the midpoint of the half cycle according to the length of the resonance frequency. That is, the control unit 35 may be set to increase the predetermined time in accordance with the extension of the resonance frequency.

  By extending the predetermined time according to the expansion of the resonance frequency, it is possible to accurately determine the fluctuation of the resonance frequency based on the difference in the current value between the first time point and the second time point.

  In setting two time points symmetrical with respect to the midpoint of the half cycle, the same predetermined time is added to and subtracted from the time point of the midpoint of the half cycle. However, the present invention is not limited to this. The predetermined time to be added and the predetermined time to be subtracted from the middle point of the half cycle do not have to be completely the same value, and a range in which a predetermined accuracy can be ensured in determining fluctuations in the resonance frequency. Thus, the predetermined time to be added and the predetermined time to be subtracted may be different values.

  Or, the current is detected at a plurality of time points before the midpoint of the half cycle, and based on the detected current values at the plurality of time points, The current value at the first time point may be derived. Similarly, the current is detected at a plurality of times after the midpoint of the half cycle, and based on the detected current values at the plurality of times, a time after the midpoint of the half cycle is detected. The current value at the second time point may be derived.

  FIG. 6 is a flowchart showing the processing of the control unit 35 according to the first embodiment (determining the variation of the resonance frequency). The control unit 35 of the control circuit 3 starts switching control for the switching circuit 11 based on the resonance frequency stored in the storage unit in response to an operation start instruction or the like.

  The control unit 35 detects the current value at the first time point (S10). The control unit 35 detects the current value at the first time point that is a predetermined time before the time point of the midpoint with reference to the time point of the midpoint of the half cycle of the resonance frequency, and stores it in the storage unit.

  The control unit 35 detects the current value at the second time point (S11). The control unit 35 detects the current value at the second time point that is a predetermined time after the time point of the midpoint with reference to the time point of the midpoint of the half cycle of the resonance frequency, and stores it in the storage unit. This predetermined time is set to be shorter than a quarter of the resonance period (T) (predetermined time <(T / 4)). Therefore, the first time point and the second time point are included in the same resonance period.

  The control unit 35 determines whether or not the absolute value of the difference between the current values at the first time point and the second time point is equal to or less than a predetermined value (S12). The control unit 35 calculates a difference between the current values at the first time point and the second time point stored in the storage unit, and determines whether the absolute value of the calculated difference value is equal to or less than a predetermined value. This predetermined value is appropriately set so as to satisfy a predetermined accuracy in determining the variation of the resonance frequency. Needless to say, the absolute value being equal to or less than the predetermined value includes that the current values at the first time point and the second time point are substantially the same.

  When the absolute value of the difference between the current values at the first time point and the second time point is equal to or less than the predetermined value (S12: YES), the control unit 35 determines that the resonance frequency has not changed (S13).

  When the absolute value of the difference between the current values at the first time point and the second time point is not equal to or less than the predetermined value (S12: NO), the control unit 35 determines that the resonance frequency is fluctuating (S121).

  The control part 35 may memorize | store the determination result of S13 and S121 in a memory | storage part as log information in the drive control of the switching circuit 11. FIG. Alternatively, the control unit 35 outputs the determination result of S121, that is, the determination result that the resonance frequency has fluctuated, to an external device having a notification function, for example, and notifies that the resonance frequency has fluctuated by the external device. It may be done.

  In order to determine the fluctuation of the resonance frequency based on the current values at two or more time points detected within a half period of the resonance period in the same resonance period, that is, within one switching period of the switching elements Q11, Q12, Q21, and Q22. The determination can be performed in a short processing time.

  Since the detection time point for detecting these current values is symmetric with respect to the midpoint of the half period of the resonance period, it is possible to accurately determine the fluctuation of the resonance frequency.

  The determination of the fluctuation of the resonance frequency is performed by comparing the detected current values, that is, based on the magnitude relationship between these current values, so that the resonance frequency is not affected by the maximum value (peak value) of the current in the resonance period. Can be accurately determined.

  In the connection between the control circuit 3 and the current detection unit 2, the wiring from the current detection unit 2 is branched into two, and the two branched wirings are connected to the first input terminal 31 and the second input terminal 32 of the control circuit 3, respectively. It is connected. The control circuit 3 performs AD conversion on the analog value input from the first input terminal 31 and second input when AD converting the analog value input from the first input terminal 31 and the second input terminal 32. A process of sampling and holding an analog value input from the terminal 32 is performed in parallel. Therefore, even when the time difference between the first time point and the second time point, that is, when the sampling period is short, the current values at the first time point and the second time point can be acquired.

(Embodiment 2)
FIG. 7 is a flowchart showing the processing of the control unit 35 according to the second embodiment (fluctuating the drive frequency and adapting to the resonance frequency). The control unit 35 of the control circuit 3 of the second embodiment differs from the first embodiment in post-processing when it is determined that the resonance frequency is fluctuating. The control unit 35 performs the processes of S20 to S23 and S221 in the same manner as the processes S10 to S13 and S121 of the first embodiment.

  In the process of S22, when the absolute value of the difference between the current values at the first time point and the second time point is not equal to or less than the predetermined value (S221), the control unit 35 performs the current value at the first time point after performing the process of S221. Determines whether the current value is smaller than the current value at the second time point (S222). The current value at the first time point and the current value at the second time point are stored in the storage unit, and the control unit 35 reads the current value with reference to the storage unit and performs the comparison operation, thereby performing the first calculation. The magnitude relationship between the current value at the time point and the current value at the second time point is determined.

  When the current value at the first time point is smaller than the current value at the second time point (S222: YES), the control unit 35 decreases the drive frequency of the switching elements Q11, Q12, Q21, and Q22 of the switching circuit 11 (S223). ).

  When the current value at the first time point is not smaller than the current value at the second time point (S222: NO), the control unit increases the drive frequency of the switching elements Q11, Q12, Q21, and Q22 of the switching circuit 11. (S2221).

  As shown in FIG. 5, when the resonance frequency decreases, the current value at the first time point becomes smaller than the current value at the second time point, and when the resonance frequency increases, the current value at the first time point becomes the second time point. It becomes larger than the current value. Therefore, by reducing the drive frequency of the switching elements Q11, Q12, Q21, and Q22 according to the decrease in the resonance frequency, the drive frequency can be adapted to the resonance frequency. Similarly, by increasing the drive frequency of the switching elements Q11, Q12, Q21, and Q22 according to the increase in the resonance frequency, the drive frequency can be adapted to the resonance frequency. That is, the frequency of the alternating voltage output from the switching circuit 11 can be adapted to the fluctuating resonance frequency.

  In the present embodiment, the switching circuit 11 has been described as a full bridge circuit, but is not limited thereto. The switching circuit 11 may be a half bridge circuit. In the present embodiment, the resonant converter 1 is a full-wave rectified full-bridge LLC resonant DC / DC converter, but is not limited thereto. The resonant converter 1 may be an active clamp type resonant DC / DC converter. In the present embodiment, the resonant converter 1 is an isolated resonant converter using the transformer 13. However, the present invention is not limited to this, and may be a non-insulated resonant converter.

  In the present embodiment, the control circuit 3 connects the first input terminal 31 and the second input terminal 32 to each of the wirings from the current detection unit 2 that is bifurcated, and the analog value is determined based on the current values at the first time point and the second time point. Although the value is acquired, the present invention is not limited to this. The control circuit 3 is connected to the current detection unit 2 through a single wiring, and acquires an analog value from the current values at the first time point and the second time point according to the processing speed of the AD converter 34 included in the control circuit 3. It may be a thing.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Resonant type converter 10A Input terminal pair 10B Output terminal pair 11 Switching circuit 11A 1st leg 11B 2nd leg 12 Resonant circuit 13 Transformer 131 Primary coil 132 Secondary coil 14 Rectifier circuit 15 Smoothing capacitor 2 Current detection part (detection part)
3 Control Circuit 31 First Input Terminal 32 Second Input Terminal 33 Connection Switching Unit 34 AD Converter 341 Sample Hold Unit 35 Control Unit (Microcomputer)
351 AD converter 36 Output terminal 4 DC power supply 5 Load Q11, Q12, Q21, Q22 Switching element C1 Resonant capacitor Lr Resonant inductor Lm Exciting inductor

Claims (7)

A resonance type converter comprising a switching circuit connected to a coil via a resonance circuit, which converts and outputs a voltage input to the switching circuit,
A detection unit for detecting a current value at two or more time points flowing through the switching circuit within the same resonance period;
A resonance type converter comprising: a determination unit that determines a change in resonance frequency based on current values detected by the detection unit at two or more time points. 2. The resonant converter according to claim 1, wherein the detected current values of two or more time points are symmetrical with respect to the midpoint of the half cycle in the resonance cycle. The determination unit determines that the resonance frequency has fluctuated when the two current values at which the detection time points are symmetrical differ from the midpoint of the half cycle in the resonance cycle by a predetermined value or more. Resonant type converter. The detection unit detects a current value at two detection points that are symmetrical with respect to a midpoint of a half cycle in the resonance period by increasing a time difference between the two detection points according to the extension of the resonance period. The resonance converter according to claim 2 or 3. The detection unit detects a current value at two or more time points flowing through the switching circuit within a period in which any of the switching elements in the switching circuit is turned on. The resonant converter described. When the current value detected before the midpoint of the half cycle in the resonance cycle is larger than the current value detected after the midpoint of the half cycle in the resonance cycle, the drive frequency of the switching element in the switching circuit is Increase,
When the current value detected before the midpoint of the half cycle in the resonance cycle is smaller than the current value detected after the midpoint of the half cycle in the resonance cycle, the drive frequency of the switching element in the switching circuit is The resonant converter according to any one of claims 1 to 5, further comprising a control unit that performs switching control of the switching element by reducing the switching element. The computer detects the current value at two or more points in the same resonance period that flows through the switching circuit of the resonant converter,
A program that executes a process for determining fluctuations in resonance frequency based on detected current values at two or more time points.

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