JPH08205547A - Output strain compensating method for power converter - Google Patents

Abstract

PURPOSE: To always minimize an output voltage strain by calculating to detect the output voltage strain corresponding to each output phase and output current polarity of a converter, and so regulating the compensating amount of the output strain at each output phase and output current polarity as to allow the calculated value to approach to zero based on the calculated value. CONSTITUTION: A compensating amount calculator 8 calculates to obtain a strain component corresponding to each element (each arm) based on a strain component estimated value, and regulates the magnitude (compensating amount) of the output amounts ΔV1 *, ΔV2 * at compensators 51, 52 correspondingly to the elements in response to the components. The compensators 51, 52 form signals relative to the output current polarities, add them to a voltage command V* to cancel the voltage strain ΔV, thereby compensating the output voltage strain. Accordingly, the output voltage strain of a power converter is so automatically compensated as to become minimum at each phase and each output current polarity, thereby preventing a torque ripple and power source harmonic waves.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling a device such as an AC electric motor or an AC power supply by a power converter such as a pulse width modulation inverter (hereinafter referred to as a PWM inverter), and particularly to a converter. The present invention relates to a control method for a power converter that can always appropriately compensate for distortion included in an output voltage and can always keep torque ripple from an electric motor and harmonics flowing out to a power supply circuit to a minimum.

[0002]

2. Description of the Related Art In a PWM inverter, switching between a positive side and a negative side of the inverter is performed according to a pulse width modulation signal (hereinafter referred to as a PWM signal) obtained by comparing a voltage command (sine wave) and a carrier wave (triangular wave). The elements are alternately turned on and off and the output voltage is controlled according to the voltage command by changing the pulse width of the output voltage. At this time, in order to prevent both elements from being turned on at the same time and causing a DC short circuit, a period (hereinafter, referred to as dead time) in which both elements are turned off at the time of on / off change is provided in consideration of the turn-off time of the elements. However, during this period, the inverter output voltage depends on the polarity of the output current and does not follow the above-mentioned PWM signal, so that output voltage distortion occurs.

Due to this output distortion, the electric motor driven by the inverter generates torque ripple, and the control accuracy of torque and speed deteriorates. Since this output voltage distortion is related to the polarity of the output current, there is known a method of adding a compensation signal according to the output current polarity to the voltage command and suppressing the output voltage distortion by feedforward control.

Further, a method of detecting the output voltage of the inverter, comparing the output voltage with a voltage command, correcting the pulse width of the PWM signal according to the difference, and suppressing the output voltage distortion by feedback control (for example, Japanese Patent Laid-Open No. Sho 60). -82066) is known.

[0005]

In the former output voltage distortion compensation method described above, the magnitude (compensation amount) of the compensation signal is the time obtained by subtracting the element turn-off time from the dead time (hereinafter referred to as the effective dead time). Set according to. However, the turn-off time changes due to variations in element characteristics, element current, and element temperature. Further, in the driver circuit for controlling the ON / OFF of each element, the ON / OFF of each element may be changed due to the variation of the signal transfer characteristics of the photocoupler that insulates the control circuit low potential side from the main circuit high potential side.
Since the off period varies, the effective dead time varies from the reference value, and the appropriate value of the compensation amount differs for each element (each output phase and each output current polarity). For this reason, in the conventional method, the compensation becomes incomplete, and in some cases, the output current contains a harmful DC component, which causes problems such as torque ripple of the electric motor or DC bias magnetization of the power transformer.

Further, in the latter compensation method, it is necessary to newly provide a voltage detector capable of detecting even a minute DC voltage with high accuracy in order to suppress the above-mentioned DC component, and a detection circuit and its signal processing operation are required. Becomes complicated.

An object of the present invention is to solve the above problems, automatically control the compensation amount for each element (each arm) to an optimum value, and to always minimize the output voltage distortion. To provide compensation law.

[0008]

In order to achieve the above object, the output voltage distortion of a power converter for converting direct current into alternating current or alternating current into direct current is controlled by pulse width modulation control of the switching elements constituting each arm. In an output distortion compensation method of a power converter that corrects an output voltage by a signal according to an output current of the converter to perform compensation, based on an output voltage command value and an output current value of the converter. Of output voltage distortion corresponding to each output phase and output current polarity of the detector, and the amount of output distortion compensation for each output phase and output current polarity so that the calculated value approaches zero based on this calculated value Is to adjust.

[0009]

The output voltage distortion can be regarded as a kind of inverter internal voltage drop. From this, it is possible to assume a model in which a disturbance (distortion component) acts on the transmission path from the voltage command (sinusoidal wave) to the inverter output voltage, which causes distortion to be added to the output voltage. Therefore, in the present invention, a compensation signal according to the output current polarity is added to the voltage command to cancel the distortion component, and each element (each arm) is supported based on the voltage command and the output current according to the principle of the disturbance observer. The distortion component (compensation residual component) to be estimated is estimated, and the compensation amount corresponding to each element (each arm) is controlled so that each component approaches zero to minimize the output voltage distortion.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a voltage control type PWM inverter will be described with reference to FIG.
1 is a PWM that outputs an output voltage proportional to the voltage command v **
In the inverter, the block 1D shows that the above-mentioned output voltage distortion ΔV is generated according to the output current polarity, and this acts as a disturbance on the output voltage. Reference numeral 2 is a motor driven by the inverter 1 and reference numeral 3 is a rotating magnetic field. The voltage command values V _d * and V _q * of the coordinate system are set to the voltage command value V * of the stator coordinate system (3 in FIG.
The coordinate converter for converting into one of the phase components), 4 is a current detector for detecting the inverter output current, and 5 is a current detector.
Reference numerals 1 and 52 denote compensators for outputting a compensation signal ΔV * according to the polarity of the output current and adding the compensation signal ΔV * to the voltage command V *, capable of individually adjusting the compensation amounts corresponding to the positive and negative polarities of the output current. Three phases are provided for each phase, but only one phase is shown and the others are omitted. 6 is a coordinate converter for converting the output current i into quantities i _d and i _q of the rotating magnetic field coordinate system, and 7 is an output voltage distortion component (compensation residual component) based on V _d *, V _q * and i _d , i _q. ) Is a distortion component estimator, 8 calculates the distortion component corresponding to each element (each arm) based on the distortion component estimated value,
It is a compensation amount calculator that adjusts the magnitude (compensation amount) of the output amounts ΔV ₁ * and ΔV ₂ * of the compensators 51 and 52 corresponding to each element according to each component.

Next, the operation of this system will be described. Since the configurations of the part numbers 1 to 4 and 6 are well known in the related art, an outline will be described here.

As described above, the output voltage distortion due to the dead time is generated when the distortion component related to the output current polarity acts on the inverter output voltage as shown by the block 1D in the broken line in FIG. At this time, the distortion component can be regarded as a disturbance acting on the output voltage. From this, the compensators 51 and 52 generate a signal related to the output current polarity and add it to the voltage command V * to cancel the voltage distortion ΔV, thereby compensating the output voltage distortion.

When the magnitude (compensation amount) of the compensation signal is the same as that of the distortion component, the compensation effect is the largest, and the distortion component remains even if it is larger or smaller than that. Conventionally, due to the reason described in the above-mentioned “problem to be solved” section, the amount of compensation becomes excessive and insufficient, and output distortion remains.

The present invention addresses this problem with part numbers 51,5.
The solution is to add 2, 7, and 8. First, the mechanism of output distortion and the principle of the present invention will be described below. FIG. 2 is a diagram for explaining the mechanism of generation of output distortion. The illustrated PWM signal is generated by a known method according to the magnitude relationship between the voltage command value V ** and the carrier wave c. Here, only one output phase is shown as a representative. The positive side (P side) element and the negative side (N side) element of the corresponding phase are alternately turned on and off according to the PWM signal, but at the time of this switching, both elements are turned on at the same time so that a DC short circuit does not occur. In consideration of the turn-off time of the device, a dead time period _Td is set in which both devices are turned off at the same time. This relationship is as indicated by the ON / OFF signals shown in the figure.

Therefore, the actual inverter output voltage is
As shown in the figure, when the output current i is “positive”, the P
After the side element ON / OFF signal changes to OFF, it changes to negative with a delay of the turn-off time T _p of the P side element, and
It changes to "positive" with a delay of the dead time _Td from the time when the N-side element on / off signal changes to off.

As a result, the pulse width of the output voltage has an error with respect to the PWM signal. The error voltage due to this is generated in a pulse shape every PWM signal cycle T _PWM ,
The average value V _{ep for} each PWM cycle is expressed by _Equation 1.

[0017]

[Equation 1]

The same is true when i is "negative", and this average value V _eN is expressed by equation 2.

[0019]

[Equation 2]

As described above, the error voltage changes into a substantially square wave shape according to the sign of i as shown in the figure.

Further, as described above, if the actual ON / OFF signal given to each element is delayed from the ON / OFF signal shown in the figure due to the transmission delay of the photocoupler, an error voltage is further added. That is, when i is “positive”, the actual output voltage is the falling delay ΔT _{OFP of} the P-side element photocoupler and the above-mentioned T _p from the time when the illustrated P-side element ON / OFF signal changes to “OFF”. Changes to a negative value after the addition time of, and from the time when the illustrated N-side element ON / OFF signal changes to “OFF”, it is delayed by the addition time of the rise delay ΔT _ONP of the T _d and P-side element photocouplers. Change to "positive". As a result, the error voltage V _ep ′ is expressed by _Equation 3.

[0022]

(Equation 3)

The same applies when i is "negative".

[0024]

[Equation 4]

[0025] Thus, depending on the output current polarity, when i is “positive”, it is related to the P-side element, and when i is “negative”, it is related to the N-side element.
_eP 'and V _eN ' are individually generated. Therefore, in order to compensate for this error voltage (output voltage distortion), compensation is made individually for each phase and for each positive and negative of the output current polarity,
And it is necessary to set each compensation amount individually.

Therefore, according to the present invention, the appropriate value of each compensation amount is obtained as follows, and the compensation is individually performed using these values. FIG. 3 shows output voltage distortions (compensation residuals, which correspond to −V _eP ′ and −V _eN ′ in the case of non-compensation) corresponding to each phase and output current polarity, and their current coordinate conversion amounts. (The contents of conversion will be described later). The converted value of each voltage distortion has the relationship shown in the figure. here,

[0027]

(Equation 5)

The combined value Y of the respective converted values in the period ~ is shown in equation 6.

[0029]

[Equation 6] Period: F (ωt) · X ₁ + I (ωt) · X ₄ + J (ωt) · X ₅ = Y ₁ (ωt) Period: F (ωt) · X ₁ + I (ωt) · X ₄ + K (ωt) ・ X ₆ = Y ₂ (ωt) Period: F (ωt) ・ X ₁ + H (ωt) ・ X ₃ + K (ωt) ・ X ₆ = Y ₃ (ωt) Period: G (ωt) ・ X ₂ + H (ωt) ・ X ₃ + K (ωt) ・ X ₆ = Y ₄ (ωt) period: G (ωt) ・ X ₂ + H (ωt) ・ X ₃ + J (ωt) ・ X ₅ = Y ₅ (ωt) period : G (ωt) · X ₂ + I (ωt) · X ₄ + J (ωt) · X ₅ = Y ₆ (ωt) (Equation 6) Here, paying attention to the variation of each conversion value, The relational expression for the difference between the integrated values of the first half 30 ° and the latter half 30 ° is expressed by Equation 7.

[0030]

[Expression 7] Period: ΔF · X ₁ + ΔI · X ₄ + ΔJ · X ₅ = ΔY ₁ Period: ΔF · X ₁ + ΔI · X ₄ + ΔK · X ₆ = ΔY ₂ Period: ΔF · X ₁ + ΔH · X ₃ + ΔK · X ₆ = ΔY ₃ Period: ΔG · X ₂ + ΔH · X ₃ + ΔK · X ₆ = ΔY ₄ Period: ΔG · X ₂ + ΔH · X ₃ + ΔJ · X ₅ = ΔY ₅ Period: ΔG · X ₂ + ΔI · X ₄ + ΔJ · X ₅ = ΔY ₆ (Equation 7) Here, ΔF to ΔK are constants, and ΔY _{1 to} ΔY ₆ can be calculated and detected by the method described later. Therefore, it is possible to determine the respective compensation residue X ₁ to X ₆ than the number 7, by modifying the amount of compensation by adding them to the previous compensation amount of the compensator 51, phase and output current It is possible to perform compensation for each polarity. The above is the principle of the present invention.

In the following, a method for calculating and detecting the current coordinate conversion amount Y of the output voltage distortion (compensation residual amount) and the operation of the entire system will be described with reference to FIG.

In the coordinate converter 6, the output current i is converted into the rotating magnetic field coordinate system by using the phase reference signal common to the coordinate converter 3. The conversion formula is shown in Equation 8.

[0033]

(Equation 8)

Next, the operation of the distortion component estimator 7 for detecting the above Y (ωt) will be described. The estimator has the following two functions and performs the following operations corresponding to each of them.

One is an output voltage command component V which is orthogonal to the output power fundamental wave component vector based on V _d *, V _q *, i _d and i _q.
It is a function to calculate ⊥ * and output current component i⊥ (variation component other than fundamental wave component). The reasons for converting various quantities into current coordinates and calculating the component orthogonal to the output current vector in this way are as follows: 1) The output voltage distortion (compensation residual component) is related to the variation of the primary resistance value of the motor. Since the quantity can be identified, highly accurate compensation becomes possible.

2) Since the amount related to the output voltage distortion can be detected as a ripple waveform having a constant shape regardless of the inverter output power factor, the voltage distortion (excess or shortage of compensation amount) can always be detected with high accuracy and high accuracy. Compensation is possible.

To clarify the concept of calculation, a vector diagram of the output voltage command and the output current is shown in FIG. V * is the output voltage command vector, i is the output current vector, i ^- is the output current fundamental wave component vectors, i ^- a in the orthogonal V *
The components V⊥ * and i⊥ of i and i are expressed by Equations 9 and 10.

[0038]

[Equation 9] V⊥ * = | V * | sin (θ 1 + θ 2) = (i - d · V q * -i - q · V d *) / | i - | ... ( number 9)

[0039]

[Equation 10]

Another function of the estimator 7 is to output voltage distortion component based on V⊥ *, i⊥ thus obtained.
It is a function of calculating a component Y (ωt) orthogonal to the i vector of (compensation residual amount). The calculation model is shown in FIG. Reference numeral 71 is a model that represents the voltage command of the inverter to the output current of the motor, 72 is a motor model that represents the input voltage to the output current of the motor as a transfer function, and Δv ⊥ is the output voltage distortion component (the speed electromotive force component is also a DC Although it is included as a component, it is erased by the operation described later, so this is ignored here), Δv ⊥ * is this compensation component (without velocity electromotive force component), 73 is based on V ⊥ * and i ⊥ Is a disturbance observer for estimating the output voltage distortion component (Δv⊥−Δv⊥ *) ^ = Y (ωt) according to Equation 11, and is composed of an inverse model 74 of the motor. It should be noted that although a filter for cutting high frequencies is appropriately provided for the observer output, it is not shown.

[0041]

[Formula 11] (Δv⊥−Δ⊥ *) ^ = V⊥ * − (Rσ ^ + Lσ ^ · s) i⊥ (Formula 11) where Rσ ^: composite value of the primary and secondary resistances of the motor (Reference value) Lσ ^: Combined value of the primary and secondary leakage inductances of the motor (reference value) Δv⊥−Δv⊥ * (= Y (ωt)) detected by the above is input to the compensation amount calculator 8. , X _{1 to} X ₆ are calculated based on the equation 7. First, this Y signal is applied to each of the above-mentioned periods.
Since it is necessary to separate the signal into
Seek in 1. FIG. 6 shows this logical relationship. Signals (p _u , p _u depending on the polarity of the output currents ( _iu , _iv , _iw ) of each phase)
based on p _v , p _w ), each period according to the illustrated relationship ~
Separate.

Further, in the separator 81, the first half 3 of each period
Obtain the integration interval classification signal that separates 0 ° and the latter half 30 °,
Both discrimination signals are given to the calculator 82. The calculator 82 outputs the Y signal in the first half 30 of each period according to the integration interval classification signal.
And the latter half of 30 ° are integrated respectively, and the difference between the two is calculated to obtain ΔY _{1 to} ΔY ₆ in Equation 7 sequentially for each period. Then, ΔY _{1 to} ΔY ₆ are changed from each period depending on the period classification signal.
Are stored in the storage element corresponding to. This calculation is repeated for each cycle of the output current, and new ΔY _{1 to} ΔY are sequentially obtained.
Updated to Y ₆ .

In the computing unit 83, these ΔY
X _{1 to} X ₆ are calculated based on _{1 to} ΔY ₆ . This calculation can be performed using a known method. Required X ₁ ~
X ₆ is added to the cumulative adder 84, and X _{1 to} X ₆ are added to each compensation amount up to that point to correct the compensation amount. According to the corrected compensation amount, the output amounts ΔV ₁ * of the compensators 51 and 52,
The magnitude of ΔV ₂ * is adjusted. As described above, the compensation amount for each phase and each output current polarity is individually controlled to a value that minimizes the output voltage distortion.

In the above embodiment, V _d *, V _q *, i
A component orthogonal to the output current fundamental wave vector of the inverter output voltage and output current is obtained based on _d and _iq , and the output voltage distortion component Y is detected based on these components. By changing the order of this operation, the d-axis and q-axis components of the output voltage distortion are first estimated based on V _d *, V _q * and i _d , i _q ,
Next, the distortion component Y can be detected even if the component orthogonal to the output current fundamental wave vector of the output voltage distortion is obtained based on these. The difference lies in the calculation contents of the distortion component estimator 7, and will be described below.

FIG. 7 shows a model of the calculation contents. In the figure, 71 'is a model that represents the voltage command of the inverter to the output current of the motor, and 72' is a motor model that represents the input voltage to the output current of the motor as a transfer function.
ΔV _d and ΔV _q are the d-axis and q-axis components of the output voltage distortion ΔV,
ΔV _d * and ΔV _q * are the d-axis and q-axis components of the compensation signal ΔV *,
Reference numeral 73 'is a disturbance observer for estimating the output voltage distortion components ΔV _d -ΔV _d * and ΔV _q -ΔV _q * according to the equation 12 based on V _d *, V _q * and i _d , i _q. Model 74 '
Etc.

[0046]

[Number 12] _{(ΔV d -ΔV d *) ^} = V d * - (Rσ ^ + Lσ ^ · s) i d (ΔV _q −ΔV _q *) ^ = V _q * − (Rσ ^ + Lσ ^ · s) i _q (Equation 12) Then, a component (Δv⊥−Δv⊥ *) orthogonal to the output current fundamental wave vector of the distortion component is calculated according to Equation 13.

[0047]

[Number 13] (Δv⊥-Δv⊥ *) ^ = {i d - · (ΔV q -ΔV q *) ^ - i q - · (ΔV d - ΔV d *) ^} / | i - | ... ( (Equation 13) The result of this operation is the same as Equation 11 in the previous embodiment. Therefore, also in this embodiment, the same operation as in the above embodiment can be performed.

In the above embodiment, the compensators 51 and 52 obtain the compensation signals ΔV ₁ * and ΔV ₂ * based on the detected value (instantaneous value of each phase) of the inverter output current.
The phase of the output current of each phase is calculated according to the equation 14 based on the coordinate conversion values i _d and i _q of the output current, and based on this, the polarity of the output current of each phase (for the U phase, the phase θ is −π / 2 ≦ θ ≦ π
It is also possible to determine ΔV ₁ * and ΔV ₂ * from this by discriminating the positive period during the period of / 2 and the negative period during the period of π / 2 <θ <3π / 2).

[0049]

∠i _u = ω ₁ t * + δ ∠i _v = ω ₁ t * + δ-2π / 3 ∠i _w = ω ₁ t * + δ + 2π / 3 (Equation 14) where δ = tan ⁻¹ (i _q / _id ) In this case, even if the output current of each phase may change in a complicated manner in the vicinity of its polarity change, i _d ,
Since the compensation signal is stably obtained by removing the ripple component of i _q and then using it for the calculation, the compensation can be performed with higher accuracy.

In the above embodiment, the output voltage distortion component is estimated based on the voltage command values V _d *, V _q * and the current detection values i _d , i _q in the rotating magnetic field coordinate system, and the compensation signal ΔV is estimated accordingly. Although * is adjusted, the output voltage distortion component can be estimated based on the voltage command value V * of the stator coordinate system and the current detection value i, and ΔV * can be adjusted accordingly.

FIG. 8 shows another embodiment based on this concept.
Will be explained. Reference numeral 1 is a PWM inverter, 2 is an electric motor, 4 is a current detector, and 5 is a compensator, which are the same as those in the above embodiment. Reference numeral 9 is a disturbance observer that estimates the output voltage distortion component ΔV−ΔV * according to the equation 15 based on the voltage command value V * and the current detection value i, and is composed of an inverse model 91 of the electric motor.

[0052]

[Equation 15] (ΔV−ΔV *) ^ = V * − (Rσ ^ + Lσ ^ · s) i (Equation 15) The arithmetic unit 10 follows the equation 16 to obtain a component (Δv⊥) orthogonal to the output current vector of the distortion component. −Δv⊥ *) is calculated.

[0053]

[Equation 16]

This calculated value is the same as the output value of the distortion component estimator 7 in the above embodiment. Therefore, the same operation can be performed based on this calculated value. The present embodiment can also be applied to the case where the coordinate converters 3 and 6 in the above embodiment are not provided.

The present invention may be applied only in the range where the output frequency of the power converter is low, and may not be applied in the high range. In this case, since the frequency of the distortion component is low, the calculation cycle can be lengthened and the load of microcomputer calculation can be reduced. The above can also be performed in the adjustment operation before the actual operation.

The above embodiment is an example in which the present invention is applied to a system for compensating the output voltage distortion by correcting the voltage command value V * with the compensation signal ΔV *. However, the pulse width controlled according to V * It can be applied to a system in which the pulse width of the modulation signal is modified by ΔV *, and it is clear that the same effect can be obtained.

The present invention can be applied not only to an inverter for driving a motor but also to a converter connected to an AC power source, and can reduce output voltage distortion and reduce power source harmonics.

[0058]

According to the present invention, the output voltage distortion of the power converter can be automatically compensated so as to be minimized for each phase and output current polarity, and torque ripple and power supply harmonics can be prevented.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a pulse width modulation inverter showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining a mechanism of generation of output voltage distortion of an inverter.

FIG. 3 is a diagram for explaining the principle of the present invention.

FIG. 4 is a diagram for explaining the concept of calculation contents related to the present invention.

FIG. 5 is a diagram for explaining the contents of calculation related to the present invention.

FIG. 6 is a diagram for explaining the contents of calculation related to the present invention.

FIG. 7 is a diagram for explaining the contents of calculation related to the present invention.

FIG. 8 is a pulse width modulation inverter configuration diagram showing another embodiment of the present invention.

[Explanation of symbols]

1 ... Pulse width modulation inverter, 4 ... Current detector, 7 ... Distortion component estimator, 8 ... Compensation amount calculator, 51, 52 ... Compensator.

Claims (5)

[Claims] 1. An output voltage distortion of a power converter for converting a direct current into an alternating current or an alternating current into a direct current by controlling a pulse width modulation of a switching element forming each arm, and a signal corresponding to an output current of the converter. In the output distortion compensation method of the power converter that corrects the output voltage by performing the compensation, the output voltage command value and the output current value of the converter are used to correspond to each output phase and output current polarity of the converter. Output voltage distortion is calculated and detected, and the amount of output distortion compensation for each output phase and output current polarity is adjusted so that the calculated value approaches zero based on this calculated value. Converter output distortion compensation method. 2. The output distortion compensation method for a power converter according to claim 1, wherein a rotational coordinate conversion amount or a stator coordinate amount is used for the output voltage command value and the output current value of the converter. 3. The component according to claim 1, wherein a component orthogonal to the output current vector of the output voltage distortion is obtained based on the output voltage command value and the output current value of the converter, and each output phase and the output are obtained based on the calculated value. Output voltage distortion corresponding to each current polarity is calculated and detected, and the output distortion compensation amount is adjusted for each output phase and each output current polarity based on the calculated value. Distortion compensation method. 4. The output distortion compensation method for a power converter according to claim 1, wherein the output distortion compensation amount is adjusted only in a range in which the output frequency of the converter is equal to or lower than a predetermined value. 5. The output distortion compensation method for a power converter according to claim 1, wherein the adjustment amount of the output distortion compensation is performed in an adjustment operation before the actual operation of the converter.