JP3446348B2 - Control method and control device for power converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting an AC power supply into an AC of a required frequency, and particularly to a control method suitable for a DC intermediate circuit of the converter having a large-capacity smoothing capacitor. Regarding the control device.

[0002]

2. Description of the Related Art Recently, a system using a voltage-type inverter has been put into practical use in an electric motor control system such as a rolling mill drive and a power control system such as pumped storage power generation. The main circuit of this inverter is connected to a first converter (converter) for converting alternating current to direct current and to this through a direct current circuit,
A second converter (inverter) for converting direct current to alternating current, and a direct current circuit provided with a large-capacity smoothing capacitor. In this device, the volume ratio of the smoothing capacitor to the whole converter is large, and this downsizing is essential for downsizing the converter.

One of the functions of the capacitor is to suppress the fluctuation of the DC voltage due to the disagreement of the power transfer between the first converter and the second converter. Therefore, if the fluctuation of the DC voltage can be reduced separately, the capacitor capacity can be reduced and the size can be reduced. Therefore, conventionally, 1) the current of the first converter is controlled according to the output value of the voltage controller that controls the DC voltage to a predetermined value, and the DC voltage is controlled to be constant. (For example, Japanese Patent Laid-Open No. 61-109491 is available.) 2) The current command value of the second converter is added to the current command value of the first converter, and the second conversion is performed by feedforward control. The current of the first converter is controlled in synchronization with the change in the current of the converter. (For example, there is one disclosed in Japanese Patent Laid-Open No. 3-245793).

[0004]

In the above method 1), the current of the first converter is controlled on the basis of the fluctuation of the DC voltage accompanying the change of the current of the second converter. For this reason,
There is a current control delay in the first converter with respect to the second converter, which results in a fluctuation of the DC voltage.

On the other hand, in the method of 2) above, the mismatch (time delay) of the alternating current between both converters can be eliminated. However, as will be described later, based on the operation of the converter itself, there is a difference between the alternating current and the direct current. Since there is a response delay, it is still impossible to minimize the fluctuation of the DC voltage. An object of the present invention is to reduce the smoothing capacitor capacity by compensating for the above-mentioned DC current response delay, minimizing the fluctuation of the DC voltage, and reducing the smoothing capacitor capacity in a power converter provided with a large-capacity smoothing capacitor in a DC intermediate circuit. is there.

[0006]

The above object is to convert AC into DC (forward conversion) by a plurality of semiconductor switching elements.
A converter, comprising <br/> a converter for converting (inverse transform) direct current into alternating current, the direct current terminals of both transducers are connected to each other, between its positive and negative terminals are connected to the smoothing capacitor, wherein both The converter is a power converter controlled by a current controller that controls each AC current, and the current of the converter that performs the forward conversion operation with respect to the current fluctuation on the AC side of the converter that performs the inverse conversion operation. This is achieved by making the response control from the controller faster than the current controller of the converter that performs the inverse conversion operation.

[0007]

The response control from the current controller of the converter performing the forward conversion operation to the current fluctuation on the AC side of the converter performing the inverse conversion operation is made faster than that of the current controller of the converter performing the inverse conversion operation. Thus, the alternating current of the converter operating in the forward conversion operation is controlled prior to that of the converter operating in the reverse conversion operation. Thereby, the response delay of the DC current described above is compensated, and the DC output current of the converter that performs the forward conversion operation can be matched as much as possible to the change of the DC input current of the converter that performs the inverse conversion operation.
The DC voltage fluctuation can be minimized and the smoothing capacitor capacity can be reduced.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. Reference numerals 1 and 4 are converters (referred to as first and second converters) each including a semiconductor element for converting alternating current to direct current (converter) or converting direct current to alternating current (inverter). A smoothing capacitor 6 is connected between the positive and negative terminals and suppresses the fluctuation of the DC voltage. The AC power supply 2 and the AC side of the converter 1 are connected via a reactor 3 for reducing ripple current, the AC side of the converter 4 is connected to an AC electric motor 5, and the AC motor 5 is connected to the converter 4
AC power of variable voltage and variable frequency output from is supplied.

A voltage controller (7) outputs an AC current command value i _d1 * (amplitude command value) of the converter 1 in accordance with the difference between the DC voltage command value V _dc * of the DC circuit and its detected value V _dc. AV
R), 8 is an adder for adding a second current command value i _d2 * described later to the AC current command value i _d1 * of the converter 1, and 9 is an adder 8
Amplitude proportional to the output value, the AC alternating current command value of the power supply and second voltage having the same phase i _s * AC current command calculator that outputs (instantaneous value command), 10 i _s * and AC transducer 1 Current detection value i
current controller for outputting an input voltage command value Vc * of the converter 1 in accordance with the difference _s (ACR1), 11 is a pulse width for pulse-width control the AC input voltage V _c of the converter 1 in accordance with the V _c * It is a modulator (PWM).

Reference numeral 12 is a speed detector (PG) for detecting the rotation speed ω _r of the electric motor 5, and 13 is an output current command value i of the converter 4 in accordance with the difference between the speed command value ω _r1 * and the speed detection value ω _{r. t1} *
Speed controller to output (torque current command value of the electric motor 5) (ASR), 14 is i _t1 * Based on the output current instantaneous value command i _M vector calculator for outputting a * (VEC.C), 15
Is a current controller (ACR2) that outputs the output voltage command value V _M * of the converter 4 according to the difference between i _M * and the output current detection value i _M ,
Reference _numeral 16 is a pulse width modulator (PWM) that controls the pulse width of the AC output voltage V _M of the converter 4 according to V _M *.

Reference numeral A in the broken line is a portion directly related to the present invention, 17 is a delay device (DEL1) for delaying the target speed command value ω _r * and outputting a delay signal ω _r1 * of the speed command value, and 18 is A delay device (DE that delays the target speed command value ω _r * at a time different from the delay time of the delay device 17 and outputs the delayed signal ω _r2 * (DE
L2) and 19 are model speed controllers (MASR1) that output a model current signal i _t2 * according to the difference between ω _r2 * and ω _r , 2
0 represents the integrated value of the difference between _it2 * and _it1 * as the model speed controller 1
9 adjuster for feeding back to the input of the (REG1), 21 is a multiplier to apply the product of i _t2 * and omega _r in adder 8.

Next, the overall operation will be described. The configuration excluding the element numbers 17 to 21 of A in the broken line is well known as a speed control device for an AC electric motor using a PWM control converter and a PWM control inverter. That is, the converter 4 and the control elements 12-16 associated therewith are associated with the motor 5
The motor-side PWM inverter that controls the speed of the converter, and the converter 1 and the control elements 6 to 11 related thereto are
A PWM converter on the power supply side is configured to control the power supply power factor to 1.0 while keeping the DC circuit voltage constant.

In the following, the operation and problems of the conventional method will be described first, and then the overall operation including the characteristic elements 17 to 21 of the present invention will be described.

(1) Operation and Problems of Conventional System The operation and problems of the conventional system except the element numbers 17 to 21 will be described. AC input current i _s of the transducer 1 in accordance with operation of the voltage controller 7 is controlled according to the fluctuation of the DC voltage V _dc of the smoothing capacitor. Now, the output of the converter 4 is ω _r *
If the increased by a sudden change, since the V _dc is reduced by increasing the DC current i _I of the transducer 4, i _s in accordance with operation of the voltage controller 7 is controlled in an increasing direction. i _s is V _s and V _c
Flows as a result of adding the difference of 3 to the reactor 3. Therefore, according to the operation of the current controller 10, according to the current deviation, V _c
By controlling the i _s can be controlled so as to coincide with the command value i _s *.

By the way, when the converter 1 performs the forward conversion operation (operation of converting AC to DC), it is necessary to control V _c so as to be lower than V _s by the voltage drop of the reactor 3. At this time, the converter 1 given by the product of V _c and i _s
The input power P _c of P _s does not increase in proportion to i _s , even though i _s is controlled to increase.

FIG. 2 shows the above situation. That is, during the period in which i _s changes, the power output P _s (=
V _s · i _s) is proportional to i _s but, P _c is not proportional to i _s. This is the voltage drop L _s (d _is / in reactor 3
The power P _c reaching the converter 1 in order to produce d _t ) is given by

[0017]

[Equation 1]

As a result, as shown in FIG. 2, generally P _c <P _s
Is. Especially when d _is / d _t is large, a period (dead time) in which P _c does not increase occurs in the changing period of i _s . Therefore, the DC output current i _c of the converter 1 given by the equation 2 has a delay with respect to i _s .

[0019]

## EQU00002 ## i _c = P _c / V _dc ( _Equation 2) Since there is a change delay (dead time) in i _c with respect to i _s , even if voltage control has a high response. The fluctuation of DC voltage cannot be suppressed sufficiently.

On the other hand, the converter 4 outputs a required current i _M according to the torque of the electric motor. i _M is the converter output voltage V
The difference between _M and the motor speed electromotive force e _M flows as a result of acting on the motor leakage inductance L _M. Current controller 15
Controlling V _M in accordance with the operation of 1 and controlling i _M so as to match the command value i _M * is the same as in the case of the converter 1 described above.

However, since the converter 4 performs an inverse conversion operation (operation of converting direct current into alternating current), when increasing i _M , V _M is higher than e _M by a voltage drop of the leakage inductance L _M. There is a need to.

Therefore, the output power P _I of the converter 4 is given by
, The motor output P _M by the amount corresponding to the second term on the right side.
Get bigger.

[0023]

[Equation 3]

FIG. 3 shows the relationship between P _I and P _M during the increasing period of i _M. Since the DC input current i _I is expressed by Equation 4, i _I changes similarly to P _I. Therefore, there is no delay in the response of the direct current to the alternating current as in the converter 1. Rather, since the change (rate of increase) of i _I is large, the DC voltage fluctuation is promoted.

[0025]

Equation 4] _{i I = P I / V dc} ... ( Equation 4) Figure 4 shows the variation of P _c and P _I in the case of synchronously controlled i _s and i _M as in the conventional method is there. Since the difference between the two during the current change period (hatched portion) is supplied by the capacitor 6, the DC voltage fluctuates (decreases) due to the discharge of the capacitor. Since the capacitor capacity is determined so that the voltage fluctuation is within the allowable value, a large capacity is required.

(2) Principle and operation of the present invention The fluctuation of the DC voltage is proportional to the integral value of the difference between i _c and i _I. Therefore, by way of the present invention, i _s as shown in FIG. 5
Is controlled prior to i _{M so} that the area of the hatched portion in the figure becomes small. This is the principle of the present invention. The part within the broken line in FIG. 1 is the part for performing this control.

Next, the operation of the present invention will be described in order when the current does not change and when it changes. At the time of no change, the output values ω _r1 * and ω _r2 * of the delay devices 17 and 18 are the same, and the speed controller 13 and the model speed controller 19
The outputs i _t1 * and i _t2 * of are also in agreement. If i _t1 *,
In the part where i _t2 * does not match, the difference between the two is fed back to the input of the controller 19 via the adjuster 20, so this difference is controlled to zero. I _t2 * and ω in the multiplier 21
_The multiplication value i _d2 * is multiplied by _r and added to the adder 8.
i _d2 * is a current command value for controlling i _c to match i _I. The control principle of i _d2 * will be described below.

If the converter loss is ignored, the output P _I of the second converter matches the motor output P _M when the current does not change, and therefore, the following equation 5 is established.

[0029]

Equation 5] _{P I = V dc · i I} = ω r · τ ... ( 5) for respectively proportional electric motor torque and the rotational speed and i _t1 * and speed detection value omega _r, 6 is established.

[0030]

[Equation 6]

Here, k, k ': proportional constants.

That is, P _I and i _I are given by the product of ω _r and i _t1 *. From the above, since i _t1 * = i _t2 *, i _d2 * is P
It is a value proportional to _I and i _I.

On the other hand, when neglecting the converter loss, P _c coincides with P _s when the current does not change, and therefore, the equation 7 is established.

[0034]

(7) P _c = V _dc · i _c = P _s = 3 | V _s │ | i _s │ (in the case of power source power factor = 1.0) (Equation 7) Since │i _s │ is proportional to i _d2 *, _Equation 8 holds and P _c , i
_c is controlled in proportion to i _d2 *.

[0035]

[Equation 8]

As described above, i _d2 * proportional to P _I , i _I
As a result of controlling P _c and i _c according to
The DC voltage is kept constant.

[0037]

[Equation 9]

When P _I = P _c is not satisfied due to a control calculation error, the output value i _d1 * of the voltage controller 7 causes i _d2 *.
Error is compensated and corrected so that V _dc becomes constant. Next, the operation when the current changes will be described. The change in current occurs when ω _r * is changed and when the load torque of the motor changes. For the i _t1 * is changed by fluctuation omega _r by the torque change, then i _t2 * by the action of the regulator 20 is controlled so as to coincide with i _t1 *, the result proportional to i _t1 * Then i _d2 * changes. During this time, the control delay caused by adjuster 20, i _d2 * because i _t1 * to but with a delay, if at gentle as compared with when the change in i _t1 * is of the practical problems (DC voltage Fluctuation) does not occur.

The present invention is applicable to the cases described below. The output values ω _r1 * and ω _r2 * of the delay devices 17 and 18 have different delay amounts. As described above, since it is necessary to control the current of the converter 1 in advance, the delay amount of ω _r2 * is set smaller than that of ω _r1 * by the amount of advance control. Therefore, when ω _r * is changed, ω _r2 * changes first, and then ω _r1 * changes.

Therefore, i _t2 * changes earlier than i _t1 *, and i _s is controlled prior to i _M. As a result, the response delay of i _c is compensated according to the above-mentioned principle, and the fluctuation of the DC voltage is suppressed. As described above, according to the present invention, the capacitance of the capacitor can be reduced.

In the above embodiment, the case where the converter 1 carries out the forward conversion operation and the converter 4 carries out the inverse conversion operation is targeted.
As in the case of performing regenerative operation, the converter 4 performs forward conversion operation,
When the converter 1 performs the inverse conversion operation, the change of P _I , i _I has a delay with respect to P _C , i _c , contrary to the above embodiment.
Therefore, in this case, the delay amount of the delay device 18 is set to the delay device 1
It is necessary to set it larger than 7. When the electric operation and the regenerative operation are switched from moment to moment, each operation is discriminated and the delay amount of the delay device 18 is changed.

FIG. 6 shows another embodiment of the present invention in consideration of the above, and the element numbers 13, 14, 17, 19, 2 in the figure are shown.
0 and 21 are the same as those in FIG. In this embodiment, FIG.
The control elements newly added and changed to the control configuration of are as follows.

22 is a target speed command value ω _r * and its detected value ω
second model speed controller for outputting a signal i _t3 * corresponding to the difference between _r (MASR2), 23 is an integral value of the difference between the i _t3 * and i _t1 * to the input of the second model speed controller 22 Feedback regulator (REG2), 24 polar discriminator for discriminating the positive and negative polarities of _{i t3 * (DISC), 18} ' is a delay unit with a delay amount varies depending on the polarity of the i _t3 * (DEL3).

The operation of the newly added components will be described below. Since the difference between _it1 * and _it3 * is fed back to the input of the model speed controller 22 via the adjuster 23, both _it1 * and _it3 * match when the current does not change. There is. If ω _r * changes in this state,
Since the model to the speed controller 22 that omega _r * is input directly without delay, i _t3 * Other i _t1 *, i _t2 * changes earlier than any. Therefore, the polarity change of i _t1 * can be detected in advance by i _t3 *. Electric operation when i _t1 * polarity is positive, because if negative corresponding to regenerative operation, to predict the i _t3 * future operation mode from the polarity (or any electric / regeneration is selected) You can

Therefore, the discriminator 24 discriminates the polarity,
Based on this result, the delay amount of the delay device 18 'is changed according to the above-mentioned relationship. That is, the amount of delay is changed to be smaller than that of the delay device 17 in the case of electric operation (i _t3 * is positive), and to be larger in the case of regenerative operation (i _t3 * is negative).

As described above, it is possible to always suppress the variation of the DC voltage even when the electric power / regeneration is switched. In the above-mentioned embodiment, the case where the PWM control converter is used for the converter 1 has been described, but the present invention is applied to the case where a well-known ignition phase control thyristor converter is used, and the same effect can be obtained. That is, the thyristor converter controls the control angle α to variably control the DC output voltage, but the control cycle is 1 power supply voltage cycle due to the commutation operation.
It is discrete as / 6 or 1/12. Therefore, from the current command (corresponding to i _d2 * in the above embodiment), the DC output current (i
There is a control delay before ₍ equivalent to _c ). Therefore, similarly to the above-described embodiment, the current command value i _d2 * of the converter 1 (thyristor converter) is controlled prior to the current command value i _t1 * of the converter 4 to compensate for the above control delay. Therefore, the fluctuation of the DC voltage can be suppressed.

In the above embodiment (FIG. 1), the converter 1
It has a reactor on the AC side, but this is not necessary. If there is a power input transformer, it can be replaced by its leakage inductance. Further, the switching elements used in the converters 1 and 4 are GTOs.
The invention is not limited to the above and can be similarly applied to the case of using an element such as a transistor or an IGBT.

In the above-described embodiment, the inconsistency in the power transfer between the converters 1 and 4 is eliminated to suppress the fluctuation of the DC voltage. However, when the power system abnormality or the internal failure of the converter is detected, these are detected. At the same time, the switching elements of the converters 1 and 4 are turned off to perform protection control.
With the turn-off of the switching element, the alternating current of the converters 1 and 4 that had been flowing until then disappears, but at this time, the inductance of the converters 1 and 4 on the alternating current side (reactor 3).
Also, the magnetic energy equivalent to (the leakage inductance of the electric motor 5) flows into the DC circuit via the diode of each converter, and the DC voltage rises.

FIG. 7 shows another embodiment of the present invention for the purpose of preventing this voltage rise. Element number 1 to 6, 11, 1
6 is the same as that of FIG. 25 is a discharge resistor, 2
6 is a switching element connected in series with the resistor 25,
This series circuit is connected across the capacitor. Reference numeral 27 denotes a protection circuit (PRO) for instructing the gate cutoff of the switching elements constituting the converters 1 and 4 and the closing of the resistor 25 into the DC circuit at the time of the above-mentioned power supply abnormality and converter failure.
T). When an abnormality is detected, the protection circuit 27 sends a command to the pulse width modulators 11 and 16, supplies an off-gate signal to the converters 1 and 4, and cuts them off. At the same time, an ON-gate signal is supplied from the same circuit to the switching element 26, and the resistor 25 is inserted in the DC circuit to prevent the DC voltage from rising due to the gate cutoff of the converter. As a result, the capacity of the capacitor 6 can be reduced.

The present invention can be applied not only to the AC motor drive converter but also to a generator control converter such as a variable speed pumped storage power generation system, and similar effects can be obtained. In a system using a wound-type induction generator, the second converter controls the generator secondary excitation. Furthermore, the present invention can be applied to an apparatus in which the second converter is connected to an AC power supply and performs power conversion between the AC power supply and the AC power supply, and the same effect can be obtained.

[0051]

According to the present invention, the fluctuation of the DC voltage due to the mismatch (control delay) of the DC current between the converter performing the forward conversion operation and the converter performing the inverse conversion operation is minimized, so that the capacitance of the smoothing capacitor is reduced. It is possible to obtain the effect that it can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a power converter to which an electric motor drive is applied in an embodiment of the present invention.

FIG. 2 is an operation characteristic diagram of a power supply side converter in a conventional power converter.

FIG. 3 is an operation characteristic diagram of a motor-side converter in a conventional power converter.

FIG. 4 is a diagram for explaining an operation and a problem in a conventional power converter.

FIG. 5 is a diagram for explaining the principle of the present invention.

FIG. 6 is a configuration diagram of a control unit showing another embodiment of the present invention.

FIG. 7 is a configuration diagram of a power converter for driving an electric motor according to another embodiment of the present invention.

[Explanation of symbols]

1 ... 1st converter, 2 ... AC power supply, 3 ... Reactor, 4
... second converter, 5 ... AC motor, 6 ... smoothing capacitor, 7 ... voltage controller, 8 ... adder, 9 ... AC current command calculator, 10, 15 ... current controller, 11, 16 ... pulse width Modulator, 12 ... Speed detector, 13 ... Speed controller, 14 ...
Vector calculator, 17, 18 ... Delay device, 19 ... Model speed controller, 20 ... Regulator.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-3-128691 (JP, A) JP-A-3-190594 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02P 5/408-5/412 H02P 7/628-7/632 H02P 21/00 H02P 3/00-3/26 H02M 7/42-7/98

Claims (5)

(57) [Claims] 1. An alternating current is directly converted by a plurality of semiconductor switching elements.
A converter that converts to a current (forward conversion) and a DC to an AC
(Reverse conversion) converter, and DC terminals of both converters
Are connected to each other, and a smoothing capacitor is connected between the positive and negative terminals.
Are connected to each other, and both converters have their own alternating currents.
Control of power converter controlled by controlling current controller
In the method, when the current controller is configured to be controlled so that the input AC current command value is the AC current detection value of the converter, the AC side of the converter performing the reverse conversion operation is The AC current command value in the current controller of the converter performing the forward conversion operation is changed in advance of the AC current command value in the current controller of the converter performing the reverse conversion operation in response to the current fluctuation. Accordingly, the response from the current controller of the converter that operates the forward transform
Control is performed by the current controller of the converter that performs the inverse conversion operation.
A power converter control method characterized by being faster than ever. 2. The method according to claim 1 , wherein when the two AC current command values are calculated from a common command value via the respective delay elements, when the delay elements on the converter side that perform the forward conversion operation are used. The method of controlling a power converter, wherein the constant or the delay time is smaller than the time constant or the delay time of the delay element on the converter side that performs the inverse conversion operation. 3. A means for discriminating between electric operation and regenerative operation of the AC motor according to claim 2 , wherein time constants or delay times of the two delay elements are changed based on a signal from the discrimination means, In electric operation, the time constant or delay time of the delay element on the side of the AC motor is made larger than that of the delay element on the side of the AC power source, and in regenerative operation, the time of the delay element on the side of the AC power source is reversed. A method of controlling a power converter, wherein a constant or a delay time is set to be larger than the delay element on the side of the AC motor. 4. A converter for converting an alternating current into a direct current (forward conversion) by a plurality of semiconductor switching elements and a converter for converting a direct current into an alternating current (reverse conversion), and direct current terminals of the two converters are mutually connected. A main circuit in which a smoothing capacitor is connected between the positive and negative terminals, an AC power source is connected to the AC side of the one converter, and an AC motor is connected to the AC side of the other converter. DC voltage detecting means for detecting a DC voltage of the smoothing capacitor, and a voltage controller for outputting an amplitude command value of an AC current of the one converter in accordance with a difference between the detected DC voltage and its command value. And an AC current command calculator that outputs an AC current command value in phase with the voltage of the AC power supply at an amplitude proportional to the amplitude command value , and the AC current command value and the AC detected by the one converter. Depending on the difference in the detected current value, First outputting a voltage command value of the exchanger
Current controller, a pulse width modulator for controlling the pulse width of the AC input voltage of the one converter in accordance with the voltage command value, speed detection means for detecting the rotation speed of the AC motor, and the rotation speed. The speed controller that outputs the output current command value of the other converter according to the difference between the detected value and the command value thereof, and the AC current command value of the other converter based on the output current command value. A second vector calculator for outputting, and a voltage command value for the converter according to the difference between the AC current command value and the detected value of the AC current detected by the other converter
In the controller of the power converter comprising a current controller and a pulse width modulator for controlling the pulse width of the AC input voltage of the other converter according to the voltage command value, the target of the rotational speed of the AC motor. The speed command generating means for generating the rotation speed command value, the first delay device for delaying the target rotation speed command value by a predetermined time and outputting the rotation speed command value, and the delay time of the delay device are different from each other. A second delay device that delays the target rotation speed command value by a predetermined time and outputs a second rotation speed command value; and a difference between the second rotation speed command value and the detection value of the rotation speed. A model speed controller that outputs a model current signal according to the model speed controller; and an adjuster that feeds back an integrated value of a deviation between the model current signal and an output current command value of the speed controller to the input of the model speed controller, The model current signal is A controller for a power converter, comprising: an adder that adds to the amplitude command value that is an input of a flow current command calculator. 5. The device according to claim 4 , further comprising means for discriminating between electric operation and regenerative operation of the AC motor, and the delay times of the two delay devices are changed based on a signal from the discrimination means. Power converter control device.