Power supply device for electric vehicle

A resonant inverter of a power supply for electric vehicle includes a first resonant capacitor and a switching element cutting off a current flowing in a resonant circuit and generates first alternating-current power from direct-current power. The transformer is included in a part of the resonant circuit, supplies the first alternating-current power generated by the resonant inverter to a first winding, and supplies second alternating-current power after conversion of the first alternating-current power to a load from a second winding. A control unit confines a difference between a resonant frequency of the resonant circuit and a switching frequency of the switching element to a predetermined range to cause that a current flowing in switching of the switching element to at least the first winding or the second winding is equal to or less than a predetermined value and to cause the resonant inverter to perform soft switching.

TECHNICAL FIELD

Embodiments of the present invention relate to a power supply for an electric vehicle. Priority is claimed to Japanese Patent Application No. 2017-212151, filed Nov. 1, 2017, the content of which is incorporated herein by reference.

BACKGROUND ART

There are power supplies for electric vehicles that include resonant inverters. Values of resonant frequencies of resonant circuits of the resonant inverters are determined mainly depending on capacitances of capacitors and inductances of transformers. When semiconductor switching elements cutting off currents flowing in the resonant circuits of the resonant inverters are caused to perform soft switching, actual resonant frequencies of the resonant circuits are set to be higher than frequencies for cutting off the semiconductor switching elements (switching frequencies) periodically. When the actual resonant frequencies of the resonant circuits are lower than the switching frequencies, the semiconductor switching elements cut off the currents in a state in which currents exceeding a predetermined value flow, and therefore operate through hard switching for switching an operation state while the currents flow. When power amounts supplied to loads from power supply for electric vehicles vary, values of the resonant frequencies vary. Therefore, an unintended increase in a power loss in the power supply for electric vehicles occurs in some cases.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

An objective of the present invention is to provide a power supply for an electric vehicle capable of inhibiting an increase in a power loss occurring due to a variation in a power amount supplied to a load.

Solution to Problem

According an embodiment of the present invention, a power supply for an electric vehicle includes a resonant inverter, a transformer, an influence inhibitor, and a control unit. The resonant inverter includes a first resonant capacitor included in a resonant circuit and a switching element that cuts off a current flowing in the resonant circuit, is supplied with direct-current power from a power supply, and generates first alternating-current power from the direct-current power through resonance of the resonant circuit and periodic switching of the switching element. The transformer includes at least a first winding and a second winding mutually electrically insulated and magnetically coupled, is included in a part of the resonant circuit, supplies first alternating-current power generated by the resonant inverter to the first winding, and supplies second alternating-current power after the conversion of the first alternating-current power from the second winding to a load. The control unit confines a difference between a resonant frequency of the resonant circuit and a switching frequency of the switching element to a predetermined range to cause that a current flowing in switching of the switching element to at least the first winding or the second winding is equal to or less than a predetermined value and to cause the resonant inverter to perform soft switching.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a power supply for electric vehicle according to embodiments will be described with reference to the drawings. In the following description, the same reference signs are given to configurations that have identical or similar functions. Then, repeated description of these configurations will be omitted in some cases.

A power supply for electric vehicle1according an embodiment is an example of a power supply for electric vehicle. In the present specification, “soft switching” is a method of driving a switching element that switches between a conductive state and a cutoff state in a state in which a current flowing in a switching element at the time of switching is equal to or less than a predetermined minute value (a predetermined value) in a switching element used to convert power. In the “soft switching,” for example, a current flowing in a switching element at the time of switching is about 0 A (amperes). By driving a switching element through soft switching, it is possible to inhibit occurrence of a loss in the switching element. On the other hand, a method of driving a switching element that performs switching in a state in which a current flowing in a switching element at the time of switching exceeds a predetermined value is referred to as “hard switching.” In the present specification, “connection” includes electric connection.

First Embodiment

FIG. 1Ais a diagram illustrating an overall configuration of a power supply for electric vehicle according to a first embodiment. The power supply1for electric vehicle is connected in series to a current path between a current collector CC supplied with power from an overhead wire (feeder) F (not illustrated) and a wheel W (not illustrated) grounded via a line R (not illustrated). A pole that has substantially the same potential as a pole on the side of the line R and the wheel W inFIG. 1Ais indicated as a ground pole.

The power supply1for electric vehicle includes, for example, a power conversion circuit2, a resonant inverter3, a transformer4, a rectifier5(rectifier circuit), a control unit6, and a current detector7(a first current detector). Reference sign Z denotes a load.

The power conversion circuit2is connected to the rear stage of the current collector CC and converts power collected by the current collector CC into direct-current power with a predetermined voltage. The resonant inverter3to which a direct current is input is connected to the rear stage of the power conversion circuit2. For example, the power conversion circuit2may convert an alternating-current power received by the current collector CC serving as an alternating-current direct-current power converter into direct-current power or may convert first direct-current power collected by the current collector CC serving as a direct-current voltage converter into second direct-current power. In the following description, a case in which the current collector CC receives the first direct-current power will be described as an example.

The resonant inverter3converts the second direct-current power which is an output of the power conversion circuit2into first alternating-current power and outputs the first alternating-current power. For example, a frequency of the first alternating-current power accords with a switching frequency of switching elements32aand32bto be described below. A pair of primary-side terminals of the transformer4are connected to a pair of output terminals of the resonant inverter3.

The transformer4includes at least a primary winding41(a first winding) and a secondary winding42(a second winding) mutually electrically insulated and magnetically coupled. The transformer4is included in a resonant circuit and the first alternating-current power generated by the resonant inverter3is supplied to the primary-side terminal connected to the primary winding41. The transformer4converts the first alternating-current power output from the resonant inverter3into second alternating-current power in accordance with a winding ratio between the primary winding41and the secondary winding42and supplies the secondary alternating-current power after the conversion from a secondary-side terminal connected to the secondary winding42. The rectifier5is connected to the pair of secondary-side terminals of the transformer4.

The rectifier5performs full wave rectification on the secondary alternating-current power output by the transformer4. For example, the rectifier5includes diodes51aand52athat form an upper arm and diodes51band52bthat form a lower arm. The diodes51aand51bare connected in series and the diodes52aand52bare connected in series. A load Z is connected to the rear stage of the rectifier5and power rectified by the rectifier5is supplied to the load Z. A filter (not illustrated) that removes a high frequency component (noise) from the output of the rectifier5and outputs the component from which the high frequency component is removed to the load Z may be connected. Further, when a load is an alternating-current load, a power conversion circuit (not illustrated) may be connected between an output unit of the rectifier5and an input unit of a load.

The control unit6includes, for example, a storage unit61, a central processing unit (CPU)62, a driving unit63, and a current value acquisition unit64. The storage unit61, the CPU62, the driving unit63, and the current value acquisition unit64are connected via a bus. The storage unit61includes a semiconductor memory. The CPU62includes a processor that executes a desired process in accordance with a software program. The driving unit63generates a control signal of the resonant inverter3under the control of the CPU62. The current value acquisition unit64acquires a detection result of the current detector7. For example, the CPU62of the control unit6causes the driving unit63to control the resonant inverter3based on a detection result of the current detector7acquired by the current value acquisition unit64. Hereinafter, processes performed by the CPU62, the driving unit63, and the current value acquisition unit64will be simply described together as a process of the control unit6in some cases. In this case, instead of the above description, for example, the control unit6controls the resonant inverter3based on a detection result of the current detector7in the following description. The control unit6controls the entire power supply1for electric vehicle in addition to the above description.

Here, an example of the resonant inverter3according to the embodiment will be described. The resonant inverter3includes, for example, capacitors31aand31b, switching elements32aand32b, a resonant reactor33, a control frequency adjustment unit35, and a drive circuit36.

The capacitors31aand31bare connected in series to form a filter capacitor. A pair of first ends of the capacitors31aand31bconnected in series are connected to the first pole of an output terminal of the power conversion circuit2and second ends thereof are connected to a second pole of an output terminal of the power conversion circuit2. For example, capacitances of the capacitors31aand31bmay be the same and characteristics may be uniform.

The switching elements32aand32bare connected in series. The switching element32ais connected to the first pole of the output terminal of the power conversion circuit2to form a so-called upper arm. The switching element32bis connected to the second pole of the output terminal of the power conversion circuit2to form a so-called lower arm. The switching elements32aand32bare, for example, insulated gate bipolar transistors (IGBTs), injection enhanced gate transistors (IEGTs), or metal-oxide-semiconductor field-effect transistors (MOSFETs) which can be applied to self-excited control. For example, the switching elements32aand32bare switched between a conductive state and a cutoff state at a timing generated by the control frequency adjustment unit35.

The control frequency adjustment unit35receives a control signal from the driving unit63of the control unit6, adjusts a frequency of a control pulse supplied to the drive circuit36, and supplies the control pulse with the adjusted frequency to the drive circuit36. For example, the control frequency adjustment unit35includes a transmitter (not illustrated) and a divider capable of changing a division ratio. The control frequency adjustment unit35adjusts the division ratio under the control of the control unit6and generates a control pulse with a pre-decided frequency. The frequency is a frequency selected from a plurality of pre-decided frequency candidates. The control frequency adjustment unit35sets the above frequency as a switching frequency at which the switching elements32aand32bare controlled.

The drive circuit36supplies a gate signal corresponding to the control pulse supplied from the control frequency adjustment unit35to the switching elements32aand32b. The switching elements32aand32bswitch between a conductive state and a cutoff state based on the gate signal supplied from the drive circuit36.

As described above, the control frequency adjustment unit35can adjust a difference between the resonant frequency of the resonant circuit and the switching frequency of the switching elements32aand32bin accordance with the switching of the switching frequency. In the following description, the control frequency adjustment unit35is assumed to select a frequency fLwith a relatively low frequency and a frequency fHhigher than the frequency fLas the switching frequency. The control frequency adjustment unit35is an example of an influence inhibition unit.

The resonant reactor33is connected between a connection point of the switching elements32aand32band the first end of the primary side terminal of the transformer4. The second end of the primary side terminal of the transformer4is connected to the connection point (middle point) of the capacitors31aand31b. When necessary inductance of the transformer4is satisfied, the resonant reactor33may be omitted.

The control unit6causes the current detector7to detect a current flowing in the transformer4. The current detector7illustrated inFIG. 1Adetects a current flowing in the primary winding of the transformer4. For example, when supply (output) of power from the transformer4is stopped, an influence of the stopping of the supply of the power has an influence on the primary side of the transformer4in some cases. The control unit6inhibits the influence by controlling gate voltages of the switching elements32aand32bin accordance with a detection current value of the current flowing in the primary winding of the transformer4.

For example, the control unit6according to the embodiment adjusts the switching frequency of the resonant inverter3based on the detection current value of a current flowing in the primary winding of the transformer4. The details thereof will be described below.

The resonant inverter3illustrated inFIG. 1Ais an example of a half bridge type voltage inverter. The resonant inverter3is not limited to the resonant inverter illustrated inFIG. 1Aand may be, for example, a full bridge type voltage inverter or current inverter.

A process of adjusting the switching frequency according to the embodiment will be described with reference toFIGS. 1B to 1D.FIG. 1Bis a flowchart illustrating a process of adjusting a switching frequency according to the embodiment.

The current detector7detects a current of the primary winding of the transformer4. The CPU62of the control unit6causes the current value acquisition unit64to acquire current values detected by the current detector7and records the current values as time-series data in the storage unit61(step S11). The CPU62of the control unit6determines whether the acquired current value is greater than a threshold ITH(step S12). For example, the threshold ITHis determined using a rated current value or the like of the resonant inverter3as a standard. The value of the threshold ITHis set to a value equal to or less than the rated current of the resonant inverter3and greater than a variation width of a load current at normal times.

When the current value is greater than the value of the threshold ITH, the control unit6adjusts the value of the switching frequency to a value lower than the value before the adjustment (step S13). For example, the control unit6sends a control signal for designating the frequency fLas the switching frequency to the control frequency adjustment unit35so that the switching frequency generated by the control frequency adjustment unit35is adjusted. A value of the switching frequency in this case may be a pre-decided value. A lower limit of the switching frequency may be set and the value of the switching frequency may be adjusted gradually in pre-decided steps until the switching frequency reaches the lower limit. Thus, the series of processes illustrated in the drawing ends.

When the current value is equal to or less than the threshold ITH, the control unit6adjusts the value of the switching frequency so that the value is higher than a value before the adjustment (step S14). For example, the control unit6sends a control signal for designating the frequency fHas the switching frequency to the control frequency adjustment unit35so that the switching frequency generated by the control frequency adjustment unit35is adjusted. A value of the switching frequency in this case may be a pre-decided value within a frequency range in which switching of the switching elements32aand32bis soft switching. An upper limit of the switching frequency at which the switching of the switching elements32aand32bis the soft switching may be set and the control unit6may adjust the value of the switching frequency in a range in which the switching frequency reaches the upper limit. The control unit6may adjust the value of the switching frequency gradually in pre-decided steps so that the value of the switching frequency is close to the upper limit. A series of processes illustrated in the drawing ends.

FIG. 1Cis a diagram illustrating the process of adjusting the switching frequency according to the embodiment. A timing chart is illustrated inFIG. 1C, where examples of changes in the switching frequency and a current value detected by the current detector7are depicted. ITHdenotes a threshold used to determine the current value. For example, the control unit6can select one of the frequencies fHand fLas a switching frequency (fs).

In an initial stage illustrated in the drawing, switching of the switching elements32aand32bis soft switching in a state in which the current value detected by the current detector7is lower than the threshold ITH. In this case, the control unit6selects the frequency fHas the switching frequency. The control unit6identifies the state of the resonant inverter3at a predetermined period. Time t1and time t2illustrated in the drawing are timings defined at the predetermined period. A time (predetermined period) from time t1to time t2is sufficiently longer than the switching period of the switching elements32aand32b(a period defined based on the frequencies fHand fL).

It is assumed that the current value detected by the current detector7is higher than the threshold ITHuntil time t1. When time t1comes, the control unit6identifies that the current value detected by the current detector7is greater than the threshold ITHand selects the frequency fLas the switching frequency. For example, based on a result indicating that the control unit6identifies that the current value at the time of switching of the resonant inverter3is greater than the threshold ITH, the control unit6determines that the switching of the switching elements32aand32bis hard switching and automatically sets the value of the switching frequency of the resonant inverter3to the frequency fL. Thus, the switching of the switching elements32aand32btransitions from the hard switching to the soft switching. The control unit6keeps the value of the switching frequency at the frequency ft, until time t2which is a subsequent detection time.

For example, it is assumed that the current value detected by the current detector7is less than the threshold ITHuntil time t2. When time t2comes, the control unit6identifies that the current value detected by the current detector7is less than the threshold ITHand selects the frequency fHas the switching frequency.

The control unit6keeps the value of the switching frequency at the frequency fHuntil a subsequent detection time.

A frequency selected by the control unit6when the value of the switching frequency is lowered may be a pre-decided value, as described above, or may be a value calculated based on the current frequency and a difference value decided in advance so that the difference value is lowered by a predetermined amount from a current frequency.

FIG. 1Dis a diagram illustrating the process of adjusting the switching frequency according to the embodiment. In (a) to (c) ofFIG. 1D, three timing charts in which conditions are mutually different are depicted. For example, in the timing chart of (a) ofFIG. 1D, an example of a situation in which the switching of the switching elements32aand32bis established as soft switching in a state in which the control unit6selects the frequency fHas the switching frequency is depicted. A control period in this case is T1.

At the uppermost stage and the second state of the timing chart in (a) ofFIG. 1D, gate signals (32aand32b) of the switching elements32aand32bare depicted, respectively. In the drawing, notation of a guard time between the gate signals is omitted. The switching elements32aand32benter a conductive state when signal levels of the gate signals are at an H level and enter a cutoff state when the signal levels of the gate signals are at an L level. At third to fifth stages of the timing chart in (a) ofFIG. 1D, illustrated waveforms of waveforms (I32aand I32b) of currents flowing in the switching elements32aand32band a waveform (I33) of a current flowing in the resonant reactor33are depicted. The capacitors31aand31bare equally charged and respective terminal voltages are assumed to be substantially equal. The waveform (I33) of the current flowing in the resonant reactor33is equivalent to the current (I33) flowing in the primary winding of the transformer4. The waveform (I33) of the current flowing in the resonant reactor33is an example of a waveform of a load current.

From time t10to time t12, the control unit6controls the switching elements32aand32bsuch that the switching element32aenters the conductive state and the switching element32benters the cutoff state. During this period of time, the current I32aflows for a period of time from the conductive state of the switching element32ato a half of a resonant period of the resonant circuit. However, when this period of time has passed, the switching element32aenters a reverse bias and the flow of a current stops (time t11). Time t11to time t12is a period of time in which no current flows. Since the switching element32bis in the cutoff state from time t10to time t12, the waveform of the current I33shown at the fifth stage has the same form as the waveform of the current I32a.

From time t12to time t14, the control unit6controls the switching elements32aand32bsuch that the switching element32benters the conductive state and the switching element32benters the cutoff state. The waveform of each signal from time t12to time t14is generated so that polarity is different from that of a current waveform from time t10to time t12and the waveform is similar to the waveform of each signal from time t10to time t12described above. The current I32bis detected as a signal that has negative polarity by the current detector7.

As described above, the current I32aand the current I32bare substantially 0 at a time point of time t11at which the switching element32aenters the cutoff state and time t13at which the switching element32benters the cutoff state. In a period of time from time t14to time t15, the switching element32acontrolled in the conductive state causes the current I32ato flow. After time t16, repetition is performed similarly. The waveform depicted in (a) ofFIG. 1Dis a waveform in a case in which the switching of the switching elements32aand32bis established as soft switching.

In the timing chart of (b) ofFIG. 1D, an example related to a state in which the control unit6selects the frequency fLas the switching frequency is depicted. In this case, as in the case of (a) ofFIG. 1D, an example of a situation in which the switching of the switching elements32aand32bis established as the soft switching is also depicted. Times t20, t21, t22, t23, t24, and t25indicate times that pass in the described sequence and correspond to the above-described times t10,01, t12, t13, t14, and t15. A control period in the case illustrated in (b) ofFIG. 1Dis T2longer than T1. When a resonant condition of a resonant circuit is the same as the resonant condition in the case of (a) ofFIG. 1D, the length of a period of time in which a current flows is the same as the length in the case of (a) ofFIG. 1Dand the length of a period of time in which no current flows is longer than the length in the case of (a) ofFIG. 1D.

On the other hand, in the timing chart of (c) ofFIG. 1D, an example of a situation in which a resonant condition of a resonant circuit is different from the resonant condition in the case of (a) ofFIG. 1Dand a period of time in which a current flows is longer than the period of time in the case of (a) ofFIG. 1Dis depicted. The case of (c) ofFIG. 1Dexemplifies a state in which the control unit6selects the frequency fHas a switching frequency as in the case of (a) ofFIG. 1D. Here, for the waveform illustrated in the drawing, an example of a situation in which the switching of the switching elements32aand32bis not established as the soft switching is depicted. Times t30, t32, t34, and t36indicate times that pass in the described sequence and correspond to the above-described times t10, t12, t13, t14, and t16. Times t31, t33, and t35indicate times later than times t32, t34, and t36. A control period in the case illustrated in (c) ofFIG. 1Dis T3equal to T1.

From time t30to time t32, the control unit6controls the switching elements32aand32bsuch that the switching element32aenters the conductive state and the switching element32benters the cutoff state similarly to the case of (a) ofFIG. 1D. For the waveform of the current I32ain (c) ofFIG. 1D, a time point of time t32is focused on. In the case of this instance, even when the switching element32atransitions to the cutoff state at time t32, the resonant reactor33causes a current to flow in the same direction as that of the current I32aby an action of the resonant circuit from time t32to time t31. Due to the electromotive force, potentials on the side of the switching elements32aand32bof the resonant reactor33increase.

On the other hand, from time t32to time t34, the switching element32benters the conductive state, but an excessive current flows in the switching element32bdue to the electromotive force in some cases. For example, a current from time t32to time t31is greater than a current value of a waveform generated by the original resonant circuit in a state in which there is no electromotive force in some cases. Since the same event also subsequently occurs, an instantaneous value (an absolute value), an effective value, and an average value of the current I33are together greater than in the case in which the soft switching is established. Depending on a condition, a peak value is also greater than in the case in which the soft switching is established in some cases.

An example of the foregoing waveform is illustrated, but when there is a resonant circuit in the state illustrated in (c) ofFIG. 1D, the control unit6can realize a state in which the soft switching is established by extending the control period to T2, as illustrated in (b) ofFIG. 1D.

According to the embodiment, a range in which the value of the load current flowing from the power supply1for electric vehicle to the load Z varies includes a predetermined range related to an increase in a conversion loss of power without an intention when desired measures to inhibit an influence of the variation in the value of the load current are not taken. When an individual difference of characteristics of the capacitor, the resonant reactor, and the transformer used in the power supply1for electric vehicle exceeds a desired range, the value of an actual resonant frequency deviates from a designed value and a conversion loss in the resonant inverter3increases in some cases. The control unit6of the power supply1for electric vehicle according to the embodiment confines a difference between the switching frequency and the resonant frequency of the resonant circuit to a predetermined range so that a current flowing in the switching elements32aand32bis equal to or less than a predetermined value when the switching elements32aand32bof the resonant inverter3are switched and causes the switching elements32aand32bof the resonant inverter3to perform the soft switching. Thus, a state in which the switching of the switching elements32aand32bis the soft switching is kept by adjusting the switching frequency so that the switching elements32aand32bare switched. Thus, the resonant inverter3can reduce a switching loss of the switching elements32aand32b. When the value of the resonant frequency of the resonant inverter3deviates from the designed value and the value of the resonant frequency and the value of the switching frequency at which the switching elements32aand32bare switched do not satisfy the condition that the resonant inverter is configured, the switching of the switching elements32aand32bbecomes the hard switching. By applying the resonant inverter3on this condition in accordance with the foregoing method, it is possible to bring about a state in which the switching elements32aand32bare caused to perform the soft switching, and thus it is possible to reduce the switching loss of the switching elements32aand32b.

The control unit6can optimize the value of the switching frequency, and thus it is possible to achieve simplicity of a cooling system of the resonant inverter3and realize miniaturization and weight reduction. The optimization process for the value of the switching frequency by the control unit6may be performed by the control frequency adjustment unit35. A threshold for determining a current value flowing in the transformer4may be determined in advance within a range of a current value at which the hard switching is not performed in the switching elements32aand32b.

In this way, the control unit6has a function of varying the value of the switching frequency of the resonant inverter3, and thus the switching of the switching elements32aand32bcan transition to the soft switching by changing the value of the switching frequency of the switching elements32aand32beven when the switching of the switching elements32aand32bis the hard switching without matching between the value of the resonant frequency of the resonant inverter3and the value of the switching frequency at which the switching elements32aand32bare switched.

The load Z according to the embodiment may include a power storage unit electrically connected in parallel to the load Z. In this case, when a potential of the power storage unit becomes higher than a potential output by the rectifier5in the charging, supply of power from the rectifier5to the load Z is stopped. In this way, in addition to a case in which the load Z is cut off by a mechanical switch or the like, the supply of the power from the rectifier5to the load Z is stopped in some cases. According to the embodiment, even when the load Z includes a power storage unit in a configuration, as described above, it is possible to inhibit an influence of the stopping of the supply of the power.

(First Modified Example of First Embodiment)

The resonant inverter3according to the first embodiment adjusts the switching frequency of the resonant inverter to a pre-decided switching frequency in a fixed or semi-fixed manner. Instead of this, in a first modified example, an instance in which a switching frequency of a resonant inverter is adjusted to an optimized frequency will be described.

In the case of the resonant inverter, by forming a current waveform as a waveform closer to a sinusoidal wave, it is possible to further improve efficiency. Accordingly, the control unit6finds an upper limit of the resonant frequency at which the switching of the switching elements32aand32bis the soft switching, forms a waveform of a current flowing to the primary side of the transformer4as a waveform closer to a sinusoidal wave, and outputs the waveform.

For example, the power supply1for electric vehicle includes the current detector7that detects a current flowing in the primary winding41of the transformer4. The control unit6finds a switching frequency at which switching of the resonant inverter3is the soft switching from a range of the switching frequency allowed for control in which the switching elements32aand32bare caused to switch periodically based on a current value detected by the current detector7. Further, the control unit6selects a higher switching frequency.

According to the foregoing first modified example, in addition to the same advantageous effects as those of the first embodiment, it is possible to optimize the switching frequency and cause a waveform of an output voltage to come close to a sinusoidal wave by causing the control unit6to find a switching frequency higher than the frequency at which the switching of the switching elements32aand32bof the resonant inverter is the soft switching. For example, in a case in which a period of time obtained by adding a dead timing for inhibiting the hard switching to a semi-period corresponding to the resonant frequency of the resonant circuit matches a semi-period of the switching frequency, a feasible highest frequency is achieved.

(Second Modified Example of First Embodiment)

The resonant inverter3according to an embodiment is an example of a half bridge type voltage inverter. The resonant inverter3is not limited to the resonant inverter illustrated inFIG. 1A. Instead of this, for example, a full bridge type voltage inverter or current inverter may be used. In the case of the current inverter, the control unit6can measure a voltage instead of measuring a current, as described above, and can perform the control similarly based on the voltage.

Second Embodiment

A second embodiment will be described in detail with reference to the drawings.FIG. 2is a diagram illustrating an overall configuration of a power supply for electric vehicle according to the second embodiment. The embodiment is different from the first embodiment illustrated inFIG. 1A, as described above, in that there are a plurality of output systems of the transformer4. Hereinafter, this point will be described mainly in detail.

A power supply for electric vehicle1A includes, for example, the power conversion circuit2, the resonant inverter3, a transformer4A, a rectifier5-1(a rectification circuit), a rectifier5-2(a rectification circuit), a control unit6A, the current detector7, a current detector8-1(a second current detector), and a current detector8-2(a third current detector).

The transformer4A includes at least the primary winding41, a secondary winding42(a second winding), and a third winding43(a third winding) mutually electrically insulated and magnetically coupled. The transformer4A converts an alternating-current voltage output from the resonant inverter3in accordance with a winding ratio between the first winding41and the second winding42and supplies second alternating-current power after the conversion from a secondary-side terminal connected to the secondary winding42. The rectifier5-1is connected to a second-side terminal of the transformer4A.

The transformer4A converts the alternating-current power output from the resonant inverter3in accordance with a winding ratio between the first winding41and the third winding43and supplies third alternating-current power after the conversion from a third-side terminal connected to the third winding43. The rectifier5-2is connected to the third-side terminal of the transformer4A.

The rectifier5-1and the rectifier5-2perform full wave rectification on the alternating-current power output by the transformer4A as in the above-described rectifier5.

The current detector8-1and a load Z-1are provided on the rear stage of the rectifier5-1illustrated inFIG. 2. The load Z-1is supplied with the second alternating-current power (output1). The current detector8-1detects a load current (a second load current) flowing from the rectifier5-1to the load Z-1. Similarly, the current detector8-2and a load Z-2are provided on the rear stage of the rectifier5-2. The load Z-2is supplied with the third alternating-current power (output2). The current detector8-2detects a load current (a third load current) flowing from the rectifier5-2to the load Z-2.

A filter (not illustrated) that removes a high frequency component (noise) from the output of the rectifier5-1and outputs the component from which the high frequency component is removed to the load Z-1may be connected to the rear stage of the rectifier5-1. Further, a filter (not illustrated) that removes a high frequency component (noise) from the output of the rectifier5-2and outputs the component from which the high frequency component is removed to the load Z-2may be connected to the rear stage of the rectifier5-2.

The control unit6A corresponds to the above-described control unit6. The control unit6A includes a current value acquisition unit64A instead of the current value acquisition unit64of the above-described control unit6. The current value acquisition unit64A corresponds to the above-described current value acquisition unit64. The current value acquisition unit64A acquires detection results of the current detector7, the current detector8-1, and the current detector8-2. For example, the CPU62of the control unit6causes the driving unit63to control the resonant inverter3based on the detection results of the current detector7, the current detector8-1, and the current detector8-2acquired by the current value acquisition unit64. For example, the control unit6A calculates a load current based on the detection results of the current detector7, the current detector8-1, and the current detector8-2. When at least the load current exceeds a predetermined value, the control unit6A sets a relatively low switching frequency.

A process of adjusting a switching frequency according to the embodiment will be described with reference toFIG. 1Bdescribed above.

In the embodiment, three current detectors, the current detectors7,8-1, and8-2, are included. The current detectors7,8-1, and8-2each detect a current flowing in the winding of the transformer4A at each position. The control unit6A acquires current values detected by the foregoing three current detectors and records the current values as time-series data in the storage unit61(step S11).

For example, the control unit6A determines whether one of the acquired current values is greater than the threshold (step S12).

When the current value is greater than the threshold, the control unit6A adjusts the switching frequency to a relatively low switching frequency (step S13) and the series of processes illustrated in the drawing ends.

When all the current values are each equal to or less than the threshold, the control unit6A adjusts the switching frequency to a relatively high switching frequency (step S14) and the series of processes illustrated in the drawing ends.

By repeating the foregoing processes, the control unit6A can apply a scheme according to the embodiment even when the transformer4A has a plurality of secondary-side systems. The scheme can be applied not only in the case of the secondary winding and the third winding illustrated inFIG. 2but also in a case in which more windings such as a fourth winding are included. The scheme according to the first embodiment may be applied to the adjustment of the current value.

When the loads Z-1and Z-2are connected to the plurality of secondary-side systems of the transformer4A as in the embodiment, for example, supply of power is stopped in some cases due to occurrence of a variation in power consumption of the loads Z-1and Z-2of any system. In primary-side change of combined inductance of the transformer4A, when there is a system in which the foregoing supply of the power is stopped, the inductance of the winding of the system is apparently invalidated. As a result, the combined inductance in the primary-side change of the transformer4A is greater than in a state in which the output of the system is valid. At this time, since the resonant frequency of the resonant circuit is lowered, there is a possibility of the resonant inverter3transitioning from the soft switching to the hard switching. For example, by causing the control unit6A to determine that a current of any system is less than a given value using the current detectors8-1and8-2included in each system and changing the switching frequency of the resonant inverter through the foregoing process, it is possible to inhibit the hard switching.

According to the embodiment, in addition to the same advantageous effects as those of the first embodiment, the control unit6A of the power supply1A for electric vehicle adjusts at least one of the resonant frequency of the resonant circuit and the switching frequency so that a difference between the resonant frequency of the resonant circuit and the switching frequency falls within a predetermined range when any load current detected by each current detector is equal to or less than a predetermined value in the switching. Thus, even when the output of any system is stopped and the hard switching is performed without matching between the resonant frequency of the resonant inverter and the switching frequency, the power supply1A for electric vehicle can keep the soft switching by adjusting the switching frequency and inhibits an increase in a switching loss as in the first embodiment.

The control unit6A adjusts at least one of the value of the resonant frequency of the resonant circuit and the value of the switching frequency so that the values of the second load current and the third load current flowing through the switching of the switching elements32aand32bare equal to or less than a predetermined value, and thus it is possible to keep the soft switching of the switching elements32aand32b.

Third Embodiment

A third embodiment will be described in detail with reference to the drawings.FIG. 3Ais a diagram illustrating an overall configuration of a power supply for electric vehicle according to the third embodiment. The embodiment is different from the second embodiment illustrated inFIG. 2, as described above, in a configuration of capacitors. Hereinafter, this point will be described mainly in detail.

A power supply for electric vehicle1B includes, for example, the power conversion circuit2, a resonant inverter3B, the transformer4A, the rectifier5-1, the rectifier5-2, a control unit6B, the current detector7, the current detector8-1, and the current detector8-2.

The capacitors31aand31b(a first resonant capacitor) are mutually connected in series. A first end of the pair of capacitors31aand31bconnected in series is connected to a first pole of the output terminal of the power conversion circuit2and a second end thereof is connected to a second pole of the output terminal of the power conversion circuit2.

The capacitors31cand31d(a second resonant capacitor) are mutually connected in series. A first end of the pair of capacitors31cand31bconnected in series is connected to the first pole of the output terminal of the power conversion circuit2and a second end thereof is connected to the second pole of the output terminal of the power conversion circuit2. A connection point (a middle point) of the capacitors31cand31dis connected to a connection point (a middle point) of the capacitors31aand31band the second end of the primary-side terminal of the transformer4A. The pair of capacitors31cand31dis combined with the pair of capacitors31aand31bto form a filter capacitor. In the following description, the capacitors31a,31b,31c, and31dare collectively referred to as the capacitors31in some cases.

Further, in the pair of capacitors31cand31dconnected in series, the contactor34aassociated with the capacitor31cand the contactor34bassociated with the capacitor31dare provided. The contactor34ais connected in series to the capacitor31cand is disposed between the middle point and the first pole of the output terminal of the power conversion circuit2. The contactor34bis connected in series to the capacitor31dand is disposed between the middle point and the second pole of the output terminal of the power conversion circuit2. The contactors34aand34bmay be able to open or close a circuit such as a semiconductor switching element.

When the contactors34aand34bare closed, the capacitors31cand31dare electrically connected in parallel to the capacitors31aand31band the capacitance of the capacitor31increases compared to the case of the pair of capacitors31aand31b. By connecting the capacitor31cin parallel to the capacitor31aand connecting the capacitor31din parallel to the capacitor31b, it is possible to lower the value of the resonant frequency by the increase in the capacitance of the capacitor31. For example, by reducing the capacitance of the capacitors31cand31dwith respect to the capacitance of the capacitors31aand31b, it is possible to use the capacitors31cand31dto minutely adjust the resonant frequency. Alternatively, the capacitance of each capacitor31may be the same.

The control unit6B corresponds to the above-described control units6and6A. The control unit6B includes, for example, the storage unit61, the CPU62, the driving unit63, the current value acquisition unit64A, and a switch driving unit65. The storage unit61, the CPU62, the driving unit63, the current value acquisition unit64A, and the switch driving unit65are connected via a bus. The switch driving unit65sends a control signal to the contactors34aand34bto switch an open state and a closed state of a contact point of the contactors34aand34b. For example, processes performed by the CPU62, the driving unit63, the current value acquisition unit64, and the switch driving unit65will be simply described collectively as a process of the control unit6B in some cases. When at least the load current is greater than a predetermined value, the control unit6B opens the contactors34aand34bto release the parallel connection of the capacitors31cand31d.

A process of adjusting a switching frequency according to the embodiment will be described with reference toFIG. 3B.FIG. 3Bis a flowchart illustrating the process of adjusting the switching frequency according to the embodiment.

The control unit6B acquires current values detected by the current detector7and records the current values as time-series data in the storage unit61(step S31). The control unit6B determines whether the acquired current value is greater than a threshold (step S32).

When the current value is greater than the threshold, the control unit6B opens the contactors34aand34b(switches) (step S33) and ends the series of processes illustrated in the drawing.

When the current value is equal to or less than the threshold, the control unit6B closes the contactors34aand34b(switches) (step S34) and ends the series of processes illustrated in the drawing.

For example, by repeating the foregoing processes, the control unit6B can inhibit the hard switching by changing the resonant frequency of the resonant inverter.

As described above, when the current value in the switching of the resonant inverter3B is greater than a given value, the control unit6B determines that the switching is the hard switching and automatically lowers the switching frequency of the resonant inverter. Thus, the switching transitions from the hard switching to the soft switching.

In the embodiment, the following control is also possible. Even in the embodiment, as in the second embodiment, there is a possibility of the resonant inverter3B transitioning from the soft switching to the hard switching.

FIG. 3Cis a diagram illustrating the process of adjusting the switching frequency according to the embodiment. The timing chart illustrated inFIG. 3C, in the timing chart, a current value detected by the current detector7, a state of a closer, and an example of a change in the resonant frequency of the resonant circuit are depicted.

At the initial state illustrated in the drawing, the switching of the switching elements32aand32bis the soft switching in a state in which the current value detected by the current detector7is less than the threshold ITH. In this case, the control unit6B selects a frequency f1as the resonant frequency. The control unit6identifies the state of the resonant inverter3at a predetermined period. A time t1and a time t2illustrated in the drawing are timings regulated at the predetermined period. A time (a predetermined period) from time t1to time t2is sufficiently longer than a switching period (a period regulated based on a resonant frequency f1and a resonant frequency f2) of the switching elements32aand32b. The resonant frequency f1is assumed to be lower than the resonant frequency f2.

It is assumed that the current value detected by the current detector7transitions to a state higher than the threshold ITHuntil time t1. When time t1comes, the control unit6identifies the transition of the current value detected by the current detector7to the state higher than the threshold ITH. The control unit6selects the resonant frequency f1as a switching frequency. For example, the control unit6B identifies that the current value of any system is greater than the threshold ITHby using the current detectors7,8-1, and8-2included in each system. When the current value is greater than pre-decided threshold ITH, the control unit6B determines that the switching of the switching elements32aand32bis the hard switching and controls the contactors34aand34bto an open state based on a determination result. The control unit6B raises the resonant frequency of the resonant circuit of the resonant inverter by automatically setting the value of the switching frequency of the resonant inverter3to the frequency f1, and thus it is possible to inhibit the state of the hard switching from being kept (time t2). The process after time t2refers to the above description.

According to the embodiment, the contactors34aand34bthat release the parallel connection to the capacitors31aand31b(a first parallel resonant capacitor) of the capacitors31cand31d(a second parallel resonant capacitor) of the resonant inverter3are included. The control unit6B controls the contactors34aand34bwhen the load current is greater than a predetermined value. Thus, in addition to the same advantageous effects as those of the first embodiment, it is possible to adjust the resonant frequency of the resonant circuit by changing the capacitance of the capacitor31even under the condition that the supply of the power of any power system of the secondary-side system of the transformer4A is stopped, the matching between the resonant frequency of the resonant inverter3B and the switching frequency is collapsed, and the switching becomes the hard switching. Thus, it is possible to keep the soft switching and inhibit an increase in a switching loss.

The disposition of the contactors34aand34bis not limited to the foregoing instance. For example, the contactors34aand34bor the like releasing the parallel connection may be provided in one or both of the capacitors31aand31band the capacitors31cand31dof the resonant inverter3. Here, when the contactors are provided in both of the capacitors, the control unit6B performs control such that at least one of the pair of capacitors31aand31band the pair of capacitors31cand31dis connected to the primary side of the transformer4A. Thus, for example, by setting the capacitance of the pair of capacitors31aand31band the capacitance of the pair of capacitors31cand31dto different values, it is possible to set the number of switching stages of the resonant frequency to at least three stages.

Fourth Embodiment

A fourth embodiment will be described in detail with reference to the drawings.FIG. 4Ais a diagram illustrating an overall configuration of a power supply for electric vehicle according to the fourth embodiment. The embodiment is different from the second embodiment illustrated inFIG. 2in that capacitors are included in an output side of the transformer4A. Hereinafter, this point will be described mainly in detail.

A power supply for electric vehicle1C includes, for example, the power conversion circuit2, the resonant inverter3, the transformer4A, the rectifier5-1, the rectifier5-2, a control unit6C, the current detector7, a capacitor9-1(a parallel capacitor), and a capacitor9-2(a parallel capacitor).

The capacitor9-1is connected in parallel to the second winding42of the transformer4A. The capacitor9-1is a parallel circuit of the second winding42of the transformer4. The capacitor9-2is connected in parallel to the third winding43of the transformer4A. The capacitor9-2is a parallel circuit of the third winding42of the transformer4.

As described above, in the power supply1C for electric vehicle, the capacitors9-1and9-2are added to an output side of the transformer4A, compared to the second embodiment. The capacitors9-1and9-2are an example of an influence inhibitor.

The control unit6C corresponds to the above-described control unit6. The control unit6C includes, for example, the storage unit61, the CPU62, the driving unit63, the current value acquisition unit64, and a switch driving unit66. The storage unit61, the CPU62, the driving unit63, the current value acquisition unit64, and the switch driving unit66are connected via a bus. For example, processes performed by the CPU62, the driving unit63, the current value acquisition unit64, and the switch driving unit66will be simply described collectively as a process of the control unit6B in some cases. The switch driving unit66will be described later. The control unit6C according to the embodiment may not be required to include a function of adjusting a switching frequency of the resonant inverter3.

As described above, the capacitors9-1and9-2are provided on the output side of the transformer4A. Thus, when supply of power of any system among a plurality of secondary-side systems of the transformer4A is stopped, an alternating current flows to the capacitors9-1and9-2provided in the system and inductance of the winding of the transformer4A is thus validated. Therefore, a resonant frequency of the resonant inverter3is not changed.

According to the embodiment, a load Z-1is connected to the secondary winding42of the transformer4A via the rectifier5-1and a load Z-2is connected to the third winding43via the rectifier5-2. The power supply1C for electric vehicle further includes the capacitor9-1which is a parallel circuit connected in parallel to the secondary winding42of the transformer4A and the capacitor9-2which is a parallel circuit connected in parallel to the third winding43. Thus, even when supply of power to the load of any system is stopped, an alternating current flows to the capacitors9-1and9-2provided in the system, the soft switching is thus kept, and it is possible to inhibit an increase of a switching loss occurring due to a variation in power consumed by the load of each system of the transformer4A. In the foregoing configuration, it can be unnecessary to detect output stop by the control unit6C.

It is enough for the capacitors9-1and9-2to be provided only in the system in which a stop state of power supply occurs.

(Modified Example of Fourth Embodiment)

The capacitors9-1and9-2according to the embodiment are connected and fixed to the secondary side of the transformer4A. On the other hand, the capacitors9-1and9-2according to a modified example are appropriately connected to the secondary side of the transformer4A.

FIG. 4Bis a diagram illustrating a configuration of a capacitor according to the modified example of the fourth embodiment. The capacitor9-1illustrated inFIG. 4Bincludes, for example, a capacitor body9aand a contactor9bconnected in series to the capacitor body9a. For example, the contactor9bmay open or close a circuit such as a semiconductor switching element.

The switch driving unit66of the control unit6C according to the modified example sends a control signal to the contactor9bprovided in each of the capacitors9-1and9-2to switch an open state and a closed state of a contact point of the contactor9b. For example, when a current value detected by the current detector7is greater than a pre-decided value (the threshold ITH) as inFIG. 3Bdescribed above, the control unit6C opens the contactor9b. When the current value detected by the current detector7is equal to or less than the pre-decided value (the threshold ITH), the control unit6C closes the contactor9b.

In this way, the control unit6C identifies that the hard switching occurs and performs control such that the resonant frequency is lowered when a current value is greater than the threshold based on the current value detected by the current detector7.

According to the foregoing modified example, in addition to the same advantageous effects as those of the fourth embodiment, it is not necessary to connect the capacitor9-1and the like to the transformer4A normally and the control unit6C makes connection when it is detected that the hard switching occurs. Since the capacitor9-1and the like becomes a load of the transformer4A, a loss in the capacitor9-1or the like occurs in the connection. According to the modified example, it is not necessary connect the capacitor9-1or the like to the transformer4A normally and it is possible to reduce a switching loss compared to the case of the normal connection. The capacitors9-1and9-2and the switch driving unit66of the control unit6C are examples of the influence inhibitor.

Fifth Embodiment

A fifth embodiment will be described in detail with reference to the drawings.FIG. 5Ais a diagram illustrating an overall configuration of a power supply for electric vehicle according to the fifth embodiment. The embodiment is different from the fourth embodiment in that a resistor10-1and the like are included in place of the capacitor9-1and the like of the fourth embodiment. Hereinafter, this point will be described mainly in detail.

A power supply for electric vehicle1D includes, for example, the power conversion circuit2, the resonant inverter3, the transformer4A, the rectifier5-1, the rectifier5-2, a control unit6D, the current detector7, a resistor10-1(a parallel resistor), and a resistor10-2(a parallel resistor).

The resistors10-1and10-2are electric resistors.

While the capacitors9-1and9-2are provided on the secondary side of the transformer4A in the fourth embodiment, the power supply1D for electric vehicle according to the embodiment includes the resistors10-1and10-2in place of these capacitors compared to the fourth embodiment. The other points are the same as those of the fourth embodiment.

Compared to the second embodiment, in the power supply1D for electric vehicle according to the embodiment, the resistors10-1and10-2are added to the output side of the transformer4A. The resistors10-1and10-2are examples of an influence inhibitor.

The control unit6D corresponds to the above-described control unit6C. The control unit6D includes a switch driving unit67instead of the switch driving unit66of the control unit6C described above. The switch driving unit67corresponds to the switch driving unit66described above. The switch driving unit67will be described below. The control unit6D according to the embodiment is not required to have a function of adjusting a switching frequency of the resonant inverter3.

As described above, the resistors10-1and10-2are provided on the output side of the transformer4A. Thus, even when supply of power of any system among a plurality of secondary-side systems of the transformer4A is stopped, an alternating current flows to the resistors10-1and10-2provided in the system and inductance of the winding of the transformer4A is thus validated. Therefore, a resonant frequency of the resonant inverter3is not changed.

According to the embodiment, a load is connected to the secondary winding42of the transformer4A via the rectifier5-1and the rectifier5-1and a load is connected to the third winding43via the rectifier5-2and the rectifier5-2. The power supply1D for electric vehicle further includes the resistor10-1which is a parallel circuit connected in parallel to the secondary winding42of the transformer4A and the resistor10-2which is a parallel circuit connected in parallel to the third winding43. Thus, even when supply of power to the load of any system is stopped, the soft switching is thus kept, and it is possible to inhibit an increase of a switching loss occurring due to a variation in power consumed by the load of each system of the transformer4A. In the foregoing configuration, it can be unnecessary to detect output stop by the control unit6D.

It is enough for the resistors10-1and10-2to be provided only in the system in which a stop state of power supply occurs.

(Modified Example of Fifth Embodiment)

The resistors10-1and10-2according to the embodiment are connected and fixed to the secondary side of the transformer4A. On the other hand, the resistors10-1and10-2according to a modified example are appropriately connected to the secondary side of the transformer4A.

FIG. 5Bis a diagram illustrating the resistor according to a modified example of the fourth embodiment. The resistor10-1illustrated inFIG. 5Bincludes a resistor body10aand a contactor10bconnected in series to the resistor body10a. For example, the contactor10bmay open or close a circuit such as a semiconductor switching element.

The switch driving unit67of the control unit6D according to the modified example sends a control signal to the contactor10bprovided in each of the resistors10-1and10-2to switch an open state and a closed state of a contact point of the contactor10b. For example, when a current value detected by the current detector7is greater than a pre-decided value (the threshold), the control unit6D according to the modified example opens the contactor10b. When the current value detected by the current detector7is equal to or less than the pre-decided value (the threshold), the control unit6D closes the contactor10b.

In this way, the control unit6D identifies that the hard switching occurs and performs control such that the resonant frequency is lowered when a current value is greater than the threshold based on the current value detected by the current detector7.

According to the foregoing modified example, in addition to the same advantageous effects as those of the fifth embodiment, it is not necessary to connect the resistor10-1and the like to the transformer4A normally and the control unit6D makes connection when it is detected that the hard switching occurs. Since the resistor10-1and the like becomes a load of the transformer4A, a loss in the resistor10-1or the like occurs in the connection. According to the modified example, it is not necessary connect the resistor10-1or the like to the transformer4A normally and it is possible to reduce a switching loss compared to the case of the normal connection. The resistors10-1and10-2and the switch driving unit67of the control unit6C are examples of the influence inhibitor.

Sixth Embodiment

A sixth embodiment will be described in detail with reference to the drawings.FIG. 6Ais a diagram illustrating a reactor according to the sixth embodiment. The embodiment is different from the second embodiment illustrated inFIG. 2described above in a configuration of the reactor. Hereinafter, this point will be described mainly in detail.

A power supply for electric vehicle1E according to the embodiment includes, for example, the power conversion circuit2, the resonant inverter3, the transformer4A, the rectifier5-1, the rectifier5-2, a control unit6E, the current detector7, the current detector8-1, and the current detector8-2.

The resonant inverter3includes, for example, the capacitors31aand31b, the switching elements32aand32b, and the resonant reactor33.

As illustrated inFIG. 6A, the resonant reactor33according to the embodiment includes, for example, a reactor33a, a reactor33b, and a contactor33c(a second contactor).

The reactors33-1and33-2are electrically connected in series and are combined to function as the resonant reactor33.

The contactor33cis provided so that the contactor33cshort-circuits the reactor33ain a closed state.

The control unit6E corresponds to the above-described control unit6C. The control unit6E includes a switch driving unit68instead of the switch driving unit66of the control unit6C described above. The switch driving unit68corresponds to the described-above switch driving unit66. The control unit6C according to the embodiment may not be required to include a function of adjusting a switching frequency of the resonant inverter3.

The switch driving unit68of the control unit6E sends a control signal to the contactor33cprovided in the reactor33ato switch an open state and a closed state of a contact point of the contactor3c. The control unit6E opens the contactor33cto release the short-circuiting of the reactor33awhen a load current flowing through the switching of at least the switching elements32aand32bis equal to or less than a predetermined value at the time of switching of the switching elements32aand32b. When at least the foregoing load current is greater than a predetermined value, the control unit6closes the contactor33cto short-circuit the reactor33a. For example, when at least the load current is greater than the predetermined value in the switching, the control unit6E may close the contactor33cto short-circuit the reactor33a. In this case, the control unit6can exclude a period of time in which at least the load current is not switched from conditions of the control of the contactor33c.

A process of adjusting a switching frequency according to the embodiment will be described with reference toFIG. 6B.FIG. 6Bis a flowchart illustrating the process of adjusting the switching frequency according to the embodiment.

The control unit6E acquires current values detected by the current detector7and records the current values as time-series data in the storage unit61(step S61). The control unit6E determines whether the current value acquired in the switching of the load current is greater than a threshold (step S62).

When the current value is greater than the threshold, the control unit6E closes the contactor33c(a switch) (step S63) and ends the series of processes illustrated in the drawing.

When the current value is equal to or less than the threshold, the control unit6E opens the contactor33c(a switch) (step S64) and ends the series of processes illustrated in the drawing.

For example, by repeating the foregoing processes, the control unit6E can inhibit the hard switching by changing the resonant frequency of the resonant inverter.

By repeating the foregoing processes, the control unit6determines that the switching is the hard switching and automatically raises the resonant frequency of the resonant circuit when the current value in the switching of the resonant inverter3is greater than a given value. Thus, the switching transitions from the hard switching to the soft switching.

According to the embodiment, in addition to the same advantageous effects as those of the first embodiment, the hard switching can be inhibited by opening the contactor33cand releasing the short-circuiting of at least a part of the resonant reactor33when a current of at least the loads Z-1and Z-2is equal to or less than a predetermined value in switching. The reactor33a, the contactor33c, and the switch driving unit68of the control unit6E are examples of the influence inhibitor.

The control units6to6E according to the foregoing embodiments may be at least partially realized by a software functional unit or may be all realized by a hardware functional unit such as an LSI.

The power supply for electric vehicle according to at last one of the above-described embodiments includes: a resonant inverter including a first resonant capacitor included in a resonant circuit and a switching element that cuts off a current flowing in the resonant circuit, configured to be supplied with direct-current power from a power supply, and configured to generate first alternating-current power from the direct-current power through resonance of the resonant circuit and periodic switching of the switching element; a transformer including at least a first winding and a second winding mutually electrically insulated and magnetically coupled, included in a part of the resonant circuit, configured to supply first alternating-current power generated by the resonant inverter to the first winding, and configured to supply second alternating-current power after the conversion of the first alternating-current power from the second winding to a load; and an influence inhibitor configured to confine a difference between a resonant frequency of the resonant circuit and a switching frequency of the switching element to a predetermined range so that a current flowing in switching of the switching element to at least the first winding or the second winding is equal to or less than a predetermined value and causes the resonant inverter to perform soft switching. It is possible to inhibit an increase in a loss occurring due to a variation in power supplied to the load.

All the above-described embodiments have been proposed as examples and do not limit the scope of the present invention. Therefore, the embodiments can be realized in other various forms and various omissions, substitutions, and changes can be made within the scope of the present invention without departing from the gist of the present invention. The embodiments and the modifications are included in the equivalent scope as the invention described in the claims.

For example, an influence inhibitor that adjusts a difference between the resonant frequency of the resonant circuit and the switching frequency of the switching elements32aand32bmay be provided. For example, the control frequency adjustment unit35, the capacitors9-1and9-2, the resistors10-1and10-2, the reactor33a, the contactor33c, and the like are examples of the influence inhibitor. The influence inhibitor may be controlled by the control unit6such that a difference between the resonant frequency of the resonant circuit and the switching frequency of the switching elements32aand32bis confined to a predetermined range in which the current flowing in at least the first winding or the second winding is equal to or less than a predetermined value through the switching of the switching elements32aand32b, and the switching elements32aand32bare caused to perform the soft switching.

The influence inhibitor such as the control frequency adjustment unit35may be a part of the control unit6or the like.

REFERENCE SIGNS LIST