JP2000116145A - Resonance-type power conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resonance-type power conversion apparatus which uses resonance by an LC resonance circuit, which commutates a power conversion part, and whose power conversion efficiency is made satisfactory when load is low. SOLUTION: In this power conversion apparatus, an LC resonance circuit 8 is constituted in such a way that switching elements 81a, 81b,..., 81n are connected in series with respective series circuits by capacitors 6a, 6b,..., 6n for resonance and by reactors 7a, 7b,..., 7n for resonance. Then, the switching elements 81a, 81b,..., 81n in an LC resonance circuit 8 are selectively turned on and off, on the basis of the effective value of an output current which is detected by a current sensor 18, so that the peak value of a resonance current is changed over.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance type power converter which is provided between a load such as an AC motor or an AC rotating machine and a DC power supply to perform power conversion.

[0002]

2. Description of the Related Art The applicant of the present invention has previously proposed a resonance type power conversion device that performs a collective commutation by switching a three-phase main switching element to zero voltage by using a set of a resonance capacitor and a resonance reactor. (Japanese Patent Application No. 9-328992).
FIG. 18 shows the configuration of this resonance type power converter. The DC voltage Vs of the DC voltage source 1 is converted into an AC voltage by the power converter 2. The power conversion unit 2 includes main switching elements (for example, IGBTs) 3a to 3f serving as self-turn-off switching elements between the positive bus and the negative bus.
Phase, V phase, W phase). Further, anti-parallel diodes (flywheel diodes) 4a to 4f are connected to the main switching elements 3a to 3f, respectively. One arm is composed of one main switching element and one flywheel diode connected in anti-parallel to the main switching element, and the one connected to the positive bus is connected to the upper arm and the negative bus. Is the lower arm.

In the power converter 2, the main switching elements 3a and 3b, the main switching elements 3c and 3d, and the main switching elements 3e and 3f are controlled to be turned on and off with a phase shift of 120 °, and a load (for example, an AC rotating machine). ) 5 to output an AC voltage. Also,
A resonance capacitor 6 and a resonance reactor 7 are connected in series between the positive bus and the negative bus. The resonance capacitor 6 and the resonance reactor 7 constitute an LC resonance circuit 8, and when the main switching elements of the upper and lower arms between the positive bus and the negative bus are both turned on to perform zero voltage switching, It resonates and a resonance current flows.

A reactor 9 is connected in series with the DC voltage source 1.
And a voltage clamping circuit 10 having a voltage clamping reactor 11 differentially connected to the reactor 9 is provided. Reactor 9 is equivalent to the reactor component of the AC rotating machine as load 5, and both main switching elements of the upper and lower arms between the positive bus and the negative bus are turned on to short-circuit between the positive bus and the negative bus. At this time, a short circuit between the DC voltage source 1 and the power converter 2 is prevented to prevent an overcurrent from flowing through each main switching element. The voltage clamp circuit 10 includes a voltage clamp reactor 11 and a diode 12, and clamps a voltage between a positive bus and a negative bus to (1 + 1 / n) Vs.
The DC voltage source 1 regenerates power. The ratio between the number of turns of the voltage clamping reactor 11 and the number of turns of the reactor 9 is n (1 <n).

In addition, the main switching elements 3a to 3
3f is switching-controlled by the control unit 13.
The control unit 13 includes a gate signal generation circuit 14 for generating a gate signal (PWM signal) for the upper arm and the lower arm for each of the U phase, the V phase, and the W phase, and between the positive bus and the negative bus, that is, between the upper and lower arms. a voltage detection circuit 15 for detecting a voltage V _PN, the main switching element 3a~3f the processing control circuit 16 that performs for switching control, the main switching device 3 based on a control signal from the control circuit 16
It is composed of a drive circuit 17 for driving a to 3f.

In the above configuration, the switching operation of the power converter 2 will be described with reference to the signal waveform diagram shown in FIG. 19, taking the main switching elements 3a and 3b as an example. As a state before performing this switching, the main switching element 3a is turned on, the main switching element 3b is turned off,
It is assumed that a current is supplied from the main switching element 3a to the load side.

When the main switching element 3b is turned on at time t ₁ in FIG. 19, the short circuit occurs between the positive bus and the negative bus, that is, the upper and lower arms, and the resonance capacitor 6, the resonance reactor 7, the main switching element 3a , 3
A resonance path is formed by b, and a resonance current starts to flow.
At this time, since the resonance current and the load current i _L flow in the same direction, a current in which the load current i _L and the resonance current are superimposed flows through the main switching element 3a, and the main switching element 3b
, A resonance current flows.

Thereafter, the resonance current becomes the reverse polarity, the absolute value of the resonance current becomes larger than the load current i _L , and the voltage _VPN between the upper and lower arms becomes a negative voltage (from time t _{2 to} time t _{2 in} FIG. 19).
At time ₃ ), current flows through the flywheel diodes 4a and 4b. Therefore, the main switching element 3
The collector-emitter voltages a and 3b are negative. In the period of t ₃ from the t _2, the main switching element 3a
When an off signal is applied to the gate terminal of the IGBT, zero voltage switching can be performed, and no switching loss occurs.

When the resonance current gradually decreases and the flywheel diode 4a turns off, the load current starts flowing through the flywheel diode 4b (t _{3 in} FIG. 19).
Time). At this time, the constant current flowing through the reactor 9 is
Since the current flows through the resonance capacitor 6, the resonance reactor 7, and the flywheel diode 4b, the resonance capacitor 6 is charged, and the potential of the positive electrode of the resonance capacitor 6 increases. When the voltage _VPN between both ends of the resonance capacitor 6 and the resonance reactor 7 becomes (1 + 1 / n) times the DC voltage Vs of the DC voltage source 1, the voltage _VPN is clamped to this value, and A current starts to flow in a voltage clamp circuit 10 including a clamp reactor 11 and a voltage clamp diode 12, and power is regenerated in the DC voltage source 1.

[0010]

In the above configuration, the resonance current needs to be larger than the output current in order to perform zero voltage switching of the main switching element. Therefore, the peak value of the resonance current is set to be larger than the peak value of the output current at the time of the maximum load. However,
If the peak value of the resonance current is set to be larger than the peak value of the output current at the maximum load, a large resonance current is generated even when the output current at the low load is small, so that the power conversion efficiency at the low load deteriorates. There's a problem. Such a problem is not limited to the above-described batch commutation method using one LC resonance circuit, but also occurs in a method that performs commutation by providing an LC resonance circuit for each phase.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a resonance type power converter that can improve power conversion efficiency even at a low load.

[0012]

In order to achieve the above object, the invention according to claim 1 is provided with a means for changing a peak value of a resonance current based on information indicating an output current of a power converter. It is characterized by: According to the present invention, the power conversion efficiency at the time of a low load can be improved by changing the peak value of the resonance current.

In this case, information indicating the output current includes:
The effective value of the output current described in claim 2, the instantaneous value of the output current described in claim 3, the average value of the input current of the power conversion unit described in claim 4, or the power described in claim 5. The information may be information indicating the torque of the load connected to the conversion unit. The means for changing the peak value may be such that the product of the capacitance and the inductance in the LC resonance circuit is kept constant and the ratio between the two is changed. According to the present invention, since the product of the capacitance and the inductance in the LC resonance circuit is fixed, the peak value of the resonance current can be changed without changing the resonance cycle.

The means for changing the peak value selectively connects the series circuit of the resonance capacitor and the resonance reactor in the LC resonance circuit to the upper and lower arms selectively in parallel. Can be configured as Specifically, the switching means provided in the series circuit can be selectively turned on and off, and the series circuit can be selectively connected in parallel to the upper and lower arms.

In this case, the capacitance and the inductance are set to different values and the product of the two is made constant for each series circuit as in the ninth aspect of the present invention, or as in the ninth aspect of the present invention, If the capacitance and the inductance have the same value in any of the series circuits, the peak value of the resonance current can be changed without changing the resonance period.

[0016] The means for changing the peak value may be a capacitance in the LC resonance circuit such that the main switching element is switched during a period when the resonance current is a negative current. Can be changed. According to the present invention, the peak value of the resonance current can be changed by changing the capacitance, and the switching of the main switching element is performed when the resonance current is a negative current. Can be reduced.

In this case, the timing for switching the main switching element may be changed in accordance with the change in the capacitance. In the invention according to claim 11 or 12, the means for changing the peak value is configured to selectively connect a plurality of resonance capacitors in the LC resonance circuit to reduce the capacitance as in the invention described in claim 13. It can be configured to vary.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 1 shows a configuration of a resonance type power converter according to one embodiment of the present invention. Note that the basic configuration of the resonance type power conversion device in this embodiment is the same as that shown in FIG. 18, and that the components denoted by the same reference numerals as those shown in FIG. 18 are equivalent or identical. Is shown. Reactor 9 shown in FIG. 18 includes a DC voltage source 1 and a power conversion unit 2 when a short circuit occurs between a positive bus and a negative bus.
A short-circuit prevention circuit 9 is shown in FIG.

In this embodiment, the LC resonance circuit 8
6n and resonance elements 7a, 7b,... 7n are connected to respective series circuits by switching elements (for example, IGBTs) 81a, 81n.
.. 81n are connected in series. Further, a current sensor 18 is provided on any output line from the power converter 2 to the load 5. And the control circuit 1
6 controls the switching elements 81a, 81b,... 81n in the LC resonance circuit 8 selectively on and off based on the effective value of the output current detected by the current sensor 18 to switch the peak value of the resonance current.

Hereinafter, the switching of the peak value of the resonance current will be described. Now, the capacitance of the resonance capacitor in the LC resonance circuit 8 is Cr, the inductance of the resonance reactor is Lr, and the peak value of the resonance current is I.
rp, the resonance period is Tr, and the initial voltage of the resonance capacitor is Vo, the resonance period Tr and the peak value Ir of the resonance current
p is represented by Expressions 1 and 2.

[0021]

## EQU1 ## Tr = 2π × (Lr × Cr) ^1/2

[0022]

[Number 2] Irp = Vo × (Cr / Lr ) 1/2 here, Tr = 4μs, when the Vo = 100V, Ir
p, Lr, and Cr have the relationship shown in FIG.
Is constant and Cr / Lr is changed, the resonance period T
The peak value Irp of the resonance current can be changed while r is constant.

In this type of resonance type power converter,
Assuming that the resonance current flows evenly in three phases, the peak value of the resonance current needs to be at least three times the current flowing through the main switching element for switching. And the current sensor 18
The effective value of the detected output current by an I _load, M
Is a coefficient for a safety margin, the required peak value Irp of the resonance current is expressed by Expression 3.

[0024]

Irp = M × I _load × 2 ^1/2 × 3 Therefore, the peak value I of the resonance current obtained by the equation (3)
By selectively turning on and off the switching elements 81a, 81b,... 81n in the LC resonance circuit 8 based on the rp, the peak value of the resonance current can be switched.

Here, I _load is information indicating the output current of the power conversion unit 2, and as this information, the instantaneous value i _load of the output current can be used. In this case, as shown in FIG. 3, current sensors 19a to 19c are provided on each output line from the power conversion unit 2 to the load 5, and the current sensors 19a to 19c are provided.
The peak value Irp of the resonance current is obtained from Equation 4 from the instantaneous value i _load of the output current detected by に よ っ て 19c.

[0026]

Irp = M × i _load × 3 As the information indicating the output current of the power converter 2, an average value Ia of the input current of the power converter 2 can be used. In this case, if the input / output power of the power conversion unit 2 is stored, Equation 5 is established.

[0027]

Vs × Ia / 3 = I _load × Vs / _2/2 ^1/2 where Vs is the voltage of the DC voltage source 1 and Vs / 2 indicates the amplitude of the output voltage. From Equations 5 and 3, the peak value Irp of the resonance current is obtained by Equation 6.

[0028]

Irp = M × Ia × 4 The input current of the power converter 2 is L as shown in FIG.
A current sensor 20 provided on the positive bus between the C resonance circuit 8 and the power conversion unit 2 or a current sensor 21 provided between the short circuit prevention circuit 9 and the LC resonance circuit 8 as shown in FIG. Alternatively, as shown in FIG.
And a current sensor 22 provided between the short circuit prevention circuit 9.

Then, the control circuit 16 performs control for switching the peak value of the resonance current based on the information indicating the output current of the power converter 2 described above. FIG. 7 shows a control process in that case. First, a detection value detected by any of the above-described current sensors is input (step 101), and based on the detected value, a peak of a required resonance current is obtained using the above-described mathematical expression corresponding to the current sensor. The value Irp is obtained (Step 102), and the switching elements 81a to 81n in the LC resonance circuit 8 are selectively turned on / off so that the peak value of the resonance current by the LC resonance circuit 8 becomes Irp (Step 103). By repeatedly executing this control process, it is possible to improve the power conversion efficiency when the load 5 is high and when the load 5 is low.

The resonance capacitors 6a, 6b,... 6n in the LC resonance circuit 8 and the resonance reactors 7a, 7
For b,... 7n, those having different values of capacitance and inductance for each series circuit and having a constant product of both can be used. By doing so, it is possible to switch only the peak value of the resonance current while keeping the resonance period Tr constant. For example, when there are four series circuits, and the peak value Irp of the resonance current by each series circuit is 50
A, 100A, 150A, and 200A, and the switching elements connected to the respective series circuits are S1, S2, S
3, S4, the required resonance current peak value I
rp, the switching element S1, as shown in FIG.
By turning on and off S2, S3, and S4, the peak value of the resonance current can be switched to a desired value.

The resonance capacitors 6a, 6b,.
n and the inductance values of the resonance reactors 7a, 7b,... 7n may be the same. In this case, the resonance current flowing through the main switching element is the sum of the resonance currents of the respective series circuits. Therefore, assuming that the peak value Irp of the resonance current of the respective series circuits is 50 A, the switching element S1 shown in FIG. , S2, S3, S
By turning on and off 4, the peak value of the resonance current can be switched to a desired value.

Further, as shown in FIG. 10, a resonance capacitor 61 whose capacitance can be varied and a resonance reactor 71 whose inductance can be varied may be used. For example, as the resonance capacitor 61,
As shown in an embodiment of FIG. 13 to be described later, the capacitance is made variable by selectively connecting a plurality of capacitors by switching elements, and the plurality of reactors are similarly selectively connected by switching elements in the resonance reactor 71. By doing so, the reactance can be made variable.

Further, the peak value Irp of the resonance current can be changed by the voltage of the DC voltage source 1 as can be seen from the equation (2). An embodiment in this case is shown in FIG.
The voltage of the DC voltage source 1 can be made variable by, for example, selectively connecting a plurality of power supplies in series by switching means. Although not shown, also in this embodiment, a current sensor similar to that shown in FIGS. 1, 3 to 6 is provided, and a control circuit is provided based on a detection value detected by the current sensor. The control for varying the voltage of the DC voltage source 1 is performed by the control unit 16.

Here, if the voltage of the DC voltage source 1 is made variable, the voltage input to the power converter 2 also changes. Therefore, the modulation rate of the power converter 2 is changed according to the voltage change. Needs to be corrected. Alternatively, as shown in FIG. 12, a switching element 82 is provided in the LC resonance circuit 8, and when charging the resonance capacitor 6, the voltage of the DC voltage source 1 is changed and the switching element 82 is turned on to switch the resonance capacitor 6. After charging and after charging,
If the switching element 82 is turned off and the voltage of the DC voltage source 1 is restored, the voltage input to the power converter 2 can be kept unchanged.

In the embodiment shown in FIGS. 1, 3 to 6, the LC resonance circuit 8 is configured to change both the capacitance of the resonance capacitor and the inductance of the resonance reactor. Even if only the capacitance is changed, the peak value of the resonance current can be changed. An embodiment in this case is shown in FIG. A plurality of capacitors 61a, 61b,... 61n are connected in parallel, and each of the capacitors is constituted by a switching element (indicated by a switch symbol in the figures, a semiconductor switching element as in FIGS. 1, 3 to 6). 83n are connected. Although not shown, in this embodiment, FIG.
A current sensor similar to that shown in FIGS. 3 to 6 is provided, and the control circuit 16 controls the switching elements 83a, 8a based on the detection value detected by the current sensor.
.. 83n are switched on and off to switch the peak value of the resonance current.

When only the capacitance in the LC resonance circuit 8 is changed as in this embodiment, the resonance period Tr changes as can be seen from Expression 1. In this case, by switching the main switching element in the power conversion unit 2 when the resonance current is a negative current, the switching loss can be reduced. That is, FIG.
[Mathematical formula-see original document] For n = 0, 1, 2,..., The relationship between the time Tsw from the start of resonance to the switching of the main switching element and the resonance period Tr is expressed by Expression 7. In addition, when the resonance current is a negative current (when the sine wave has a half of the resonance waveform), switching of the main switching element can be performed.

[0037]

(2n + 1) / 2 × Tr <Tsw <(n + 1) × Tr Since the resonance period Tr varies with the capacitance as shown in Expression 2, a plurality of capacitors 61a and 61b are provided so as to satisfy Expression 7. , 61n are selectively connected.

FIG. 15 shows a control process of the control circuit 16 in this embodiment. Note that FIG. 15 is shown as detailed processing of step 103 in FIG.
The capacitance Cr in the LC resonance circuit 8 is represented by C
Switching control is performed in three stages of (0), C (1), and C (2). Note that C (0) <C (1) <C (2), and
Thresholds Ith (1), I for switching the capacitance
th (2) is set so that Ith (1) <Ith (2).

In steps 201 and 202, the peak value Irp of the resonance current obtained in step 102 in FIG. 7 is compared with threshold values Ith (1) and Ith (2).
When Irp is greater than Ith (2) and Cr is C
When it is determined that the condition is not (2) (step 2
In 03), the switching element (SW) in the LC resonance circuit 8 is turned on / off so that Cr becomes C (2) (step 204).

If Irp is larger than Ith (1),
When it is smaller than th (2) and it is determined that Cr is not C (1) (step 205),
The switching element in the LC resonance circuit 8 is turned on / off so that r is set to C (1) (step 206). If Irp is smaller than Ith (1),
When it is determined that the value is not (0) (step 2
In step 07), the switching elements in the LC resonance circuit 8 are turned on and off so that Cr becomes C (0) (step 208).

In the above embodiment, the time Tsw from the start of resonance to the switching of the main switching element is set to be constant.
The time Tsw may be changed according to the change in the capacitance Cr in the resonance circuit 8. in this case,
As shown in FIG. 16, if the switching of the main switching element is performed during a period in which the resonance current becomes a negative current for the first time, it is possible to reduce the loss due to the resonance current which occurs until the switching is performed. .

The configuration of the LC resonance circuit 8 shown in FIG. 13 can be variously modified. For example, as shown in FIG. 17A, the switching element may not be connected to one capacitor 61a, and may be always connected to the resonance reactor 7. Also, as shown in FIG.
61n may be connected in series, and the switching elements 83a, 83b,... 83n may be connected in parallel to respective capacitors. Also in this case, FIG.
As shown in (c), one capacitor 61a may not be provided with a switching element. FIG.
As shown in (c), the capacitors 61a, 61b, 61
c, 61d and 61e are connected in a bridge shape, and the switching elements 83a, 83b, 83c and 83d are connected to a capacitor 6
You may make it connect in parallel with 1a, 61b, 61c, 61d. Also in this case, the switching element may not be provided in the capacitor 61c as shown in FIG.

Also, in the embodiments shown in FIGS. 1, 3 to 6, the switching elements are not provided in all of the series circuits including the resonance capacitor and the resonance reactor, and one of the series circuits is always connected to the positive bus. You may make it connect to a negative bus. Further, the switching element in the various embodiments described above is not limited to the IGBT, but may be another semiconductor element.

Further, the present invention is not limited to the above-described batch commutation method using one LC resonance circuit 8, and is also applicable to a system in which an LC resonance circuit is provided for each phase to perform commutation. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a resonance type power converter according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a capacitance, an inductance, and a peak value of a resonance current in an LC resonance circuit.

FIG. 3 is a diagram showing a modification of the resonance type power converter shown in FIG.

FIG. 4 is a diagram showing another modification of the resonance type power converter shown in FIG.

FIG. 5 is a diagram showing another modification of the resonance type power converter shown in FIG.

FIG. 6 is a diagram showing another modification of the resonance type power converter shown in FIG.

FIG. 7 is a flowchart showing a control process by a control circuit 16 shown in FIG. 1;

FIG. 8 is a chart showing a pattern in which switching elements S1, S2, S3, and S4 are turned on and off with respect to a peak value Irp of a resonance current.

FIG. 9 is a table showing another pattern for turning on and off the switching elements S1, S2, S3, and S4 with respect to the peak value Irp of the resonance current.

FIG. 10 is a diagram showing a configuration of a resonance type power converter according to another embodiment of the present invention.

FIG. 11 is a diagram showing a configuration of a resonance type power converter according to another embodiment of the present invention.

FIG. 12 is a diagram showing a modification of the resonance type power converter shown in FIG.

FIG. 13 is a diagram showing a configuration of a resonance type power converter according to another embodiment of the present invention.

FIG. 14 is an explanatory diagram for explaining switching timing of a main switching element when a resonance period Tr is fixed.

15 is a flowchart showing a control process by a control circuit 16 shown in FIG.

FIG. 16 is an explanatory diagram for explaining switching timing of a main switching element when a resonance period Tr is made variable.

FIG. 17 is a diagram showing a modification of the LC resonance circuit 8 shown in FIG.

FIG. 18 is a diagram showing a configuration of a resonance-type power conversion device previously proposed by the present applicant.

FIG. 19 is a waveform chart for explaining the operation of the resonance type power converter shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC voltage source, 2 ... Power conversion part, 3a-3f ... Main switching element, 4a-4f ... Flywheel diode, 5 ... Load, 6, 6a-6n, 61, 61a-61n
... Resonant capacitors, 7, 71 ... Resonant reactor, 8
... LC resonance circuit, 9 ... Reactor (short circuit prevention circuit), 1
0: Voltage clamp circuit, 11: Reactor for voltage clamp, 12: Diode, 13: Control unit, 14: Gate signal generation circuit, 15: Voltage detection circuit, 16: Control circuit, 1
7 Drive circuit, 18-22 Current sensor, 81a-
81n, 82, 83a to 83n: switching elements.

Claims (13)

[Claims] 1. A resonance type power converter in which upper and lower arms in a power converter are short-circuited to generate resonance by an LC resonance circuit, and at the time of the resonance, a main switching element of the power converter is switched to perform commutation. The apparatus according to claim 1, further comprising means for changing a peak value of a resonance current based on information indicating an output current of the power conversion unit. 2. The resonance type power converter according to claim 1, wherein the information indicating the output current is an effective value of the output current. 3. The resonance type power converter according to claim 1, wherein the information indicating the output current is an instantaneous value of the output current. 4. The resonance type power conversion device according to claim 1, wherein the information indicating the output current is an average value of an input current of the power conversion unit. 5. The resonance type power converter according to claim 1, wherein the information indicating the output current is information indicating a torque of a load connected to the power converter. 6. The method according to claim 1, wherein the means for changing the peak value changes a ratio between a capacitance and an inductance of the LC resonance circuit while keeping the product constant. 4. A resonance type power converter according to any one of the above. 7. The LC resonance circuit has a plurality of series circuits in which a resonance capacitor and a resonance reactor are connected in series, and the means for changing the peak value includes: connecting the plurality of series circuits to the upper and lower arms. The resonant power converter according to any one of claims 1 to 5, wherein the power converter is selectively connected in parallel to the power converter. 8. The plurality of series circuits are provided with switching means, respectively, and the means for changing the peak value selectively turns on / off the switching means in the plurality of series circuits. The resonance type power converter according to claim 7, wherein 9. The system according to claim 7, wherein the capacitance of the resonance capacitor connected in series and the inductance of the resonance reactor have different values for each series circuit, and the product of the two is constant. Or the resonance type power converter according to 8. 10. The resonance type power supply according to claim 7, wherein the capacitance of the resonance capacitor connected in series and the inductance of the resonance reactor have the same value in all the series circuits. Conversion device. 11. The means for changing the peak value, wherein the switching of the main switching element is performed during a period when the resonance current is a negative current.
The resonance type power converter according to any one of claims 1 to 5, wherein the capacitance in the resonance circuit is changed. 12. The resonance type electric power according to claim 11, wherein the means for changing the peak value changes timing for switching the main switching element in accordance with the change in the capacitance. Conversion device. 13. The LC resonance circuit has a plurality of resonance capacitors, and the means for changing the peak value changes the capacitance by selectively connecting the plurality of resonance capacitors. The resonance type power converter according to claim 11 or 12, wherein