JP2001320881A - Controller for power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power converter controller which can be composed of a small number of components and facilitates the improvement of reliability. SOLUTION: A circuit employs a photocoupler 4 in order to detect a DC voltage with which a smoothing capacitor 3 is charged. By correcting the detected voltage value Ed with a correction factor Kn given by a correction factor memory unit 52 for the control, a reference voltage necessary for detecting the variation in characteristics is obtained from a voltage of an AC power supply 1 when a detection error caused by aging change etc., and observed in the detection characteristics of the photocoupler 4 is corrected. The correction factor Kn is calculated by a correction factor calculation unit 59 at predetermined timings at any time and re-written in the correction factor memory unit 52 and up-to-dated. With this constitution, as high precision can be secured even if the photocouler 4 is employed as a DC voltage detector, the number of components can be reduced by employing the photocoupler 4, so that a power converter which is low in cost and high in reliability can be obtained easily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter control device, and more particularly to a control device for detecting a DC voltage of a power converter by an optical coupling device.

[0002]

2. Description of the Related Art For example, in an apparatus such as an inverter apparatus that converts AC power received from a commercial power system into DC power and uses it, control according to the converted DC voltage may be required. At this time, it is necessary to electrically isolate the power system and the control system. For this reason, a power converter control device that detects a DC voltage using an optical coupling element (photocoupler) is conventionally known. .

[0003] In such a case, a linear characteristic is required for the optical coupling element used therein, and as a result, a change in the characteristic becomes a problem. Therefore,
For example, in Japanese Patent Application Laid-Open No. 58-89071, in order to correct a detection error of an optical coupling element due to a change over time, a DC voltage is detected by a first photocoupler and a temperature change or a change over time is detected by a second photocoupler. A method is proposed in which corresponding values are detected and added to obtain a DC voltage having no error.

[0004]

The prior art described above does not consider the increase in the number of components, and has problems in cost reduction, miniaturization, and improvement in reliability. That is, in the prior art, two pairs of optical coupling elements and their associated circuit elements are used to correct a detection error due to aging (also referred to as aging). There is a problem in increasing the size and miniaturization, and the increase in the number of elements leaves room for improvement in reliability.

It is an object of the present invention to provide a power converter control device capable of reducing the number of components and easily improving reliability.

[0006]

According to the present invention, an object of the present invention is to provide a power converter of a type in which a DC voltage output from a forward power converter is detected by an optical coupling element and the forward power converter is controlled. The control device according to claim 1, further comprising: a correction coefficient calculating unit that calculates a change in the detection characteristic of the optical coupling element based on the AC voltage input to the forward conversion unit, and sequentially updates and sets the correction coefficient. This is achieved by correcting the detected value of the DC voltage with the correction coefficient set, and controlling the output DC voltage of the forward power conversion unit.

At this time, the forward power conversion section is constituted by a circuit in which a circuit in which a diode is connected in reverse parallel to a switching element is bridge-connected as each arm, and the correction coefficient calculating means turns off the switching element of the forward power conversion section. In this case, the correction coefficient may be calculated based on a DC voltage that appears when the AC voltage is full-wave rectified by the diode.

Further, at this time, the correction coefficient calculating means includes:
An initial value of the DC voltage may be held, and a change in the detection characteristic of the optical coupling element may be calculated by comparing the initial value with the DC voltage detected at the present time.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a power converter control device according to the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 shows an embodiment of the present invention, in which 1 is an AC power supply, 2 is a forward power conversion unit, 3 is a smoothing capacitor,
Is an optical coupling element, 5 is a forward converter control circuit, 6 is a current detector, 7 is a reverse power converter, and 8 is an AC motor.

The forward power conversion section 2 is a three-phase bridge connection in which an inverse parallel connection circuit of an IGBT (insulated gate bipolar transistor) and a diode is used as one arm.
IGBT of each arm is PWM (Pulse Width Modulation)
The control serves to convert AC power supplied from the AC power supply 1 into DC power of an arbitrary predetermined voltage E.

The smoothing capacitor 3 functions to smooth the output voltage of the forward power conversion unit 2 so that the DC power of the voltage E with smoothed pulsation is supplied to the reverse power conversion unit 7. . Therefore, the forward power converter 2, the smoothing capacitor 3, and the reverse power converter 7 constitute a main circuit of the inverter device.

The reverse power converter 7 is controlled by a control circuit (not shown), so that AC power of a desired voltage and a desired frequency is supplied to an AC motor 8 such as an induction motor which is a load. The DC voltage E is further controlled by the forward power conversion unit 2 at this time.

The optical coupling element 4 is also called a photocoupler, and has a DC voltage E output from the forward power converter 2.
As an analog signal having a linear input / output characteristic with respect to the voltage E in a state of being electrically isolated from the main circuit, and supplying this analog signal to the forward converter control circuit 5 as a detected voltage value Ed. Work.

The forward converter control circuit 5 controls the forward power converter 2 so that a DC voltage of a predetermined voltage E can be obtained in the smoothing capacitor 3, and is supplied from the DC voltage detector 4. A predetermined gate pulse P for PWM control is generated in accordance with the detected voltage Ed, and the IG of the
It works to supply to BT.

The current detector 6 detects an AC current supplied from the AC power supply 1 to the forward power converter 2, and detects a detected current value Is.
To the forward conversion unit control circuit 5. Next, the forward conversion unit control circuit 5 will be described in more detail.

As described above, the forward converter control circuit 5 controls the forward power converter 2 so that a DC voltage of a predetermined voltage E can be obtained in the smoothing capacitor 3. At this time, In general, the optical coupling element 4 used as a DC voltage detector is inevitable with time in its input / output characteristics. For example, when viewed over a period of 5 to 10 years, a difference between the voltage detection value Ed and the DC voltage E Causes a considerable error from the initial value.

Therefore, in the forward converter control circuit 5 according to this embodiment, the voltage detection value Ed is not used for control as it is, but is input to the multiplier 51 first, where it is given from the correction coefficient storage 52. The forward power converter 2 is controlled by the corrected voltage detection value Edc by being multiplied by a predetermined correction coefficient Kn.

At this time, the predetermined correction coefficient Kn
Is updated at any time as described later in accordance with a temporal change appearing in the input / output characteristics of the optical coupling element 4, and is updated as described later. Therefore, according to this embodiment, Voltage detection value E corresponding to DC voltage E always accurately
Control by dc will be obtained.

As a result, according to the above-described embodiment, there is no danger of a change with time due to the use of the optical coupling element 4 as the DC voltage detector. Therefore, high reliability can be easily maintained while suppressing the number of components. can do.

The corrected voltage detection value Edc output from the multiplying unit 51 is firstly deviated from the DC voltage command value Ed ^* by the comparing unit 53, and then the deviation is calculated by the PI (proportional to the voltage control system). Integral) compensation 54 is given, and becomes the current command value Is ^* for the forward power conversion unit 2.

Next, the current command value Is ^* is compared with the comparison value 55
, A deviation from the detected current value Is supplied from the current detector 6 is obtained.
Compensation 56 is given, and becomes output voltage command value Vb ^* for forward power conversion unit 2.

The output voltage command value Vb ^* is compared in magnitude with the carrier signal Cr by the comparator 57, and a PWM pulse is generated by the pulse generator 58 from the comparison result. 2 will be supplied.

As a result, feedback control is obtained in which the DC voltage E output from the forward power converter 2 converges to a voltage value equal to the DC voltage command value Ed ^* . Therefore, a DC voltage of the desired voltage E can always be supplied to the reverse power converter 7, and the AC motor 8 can always be controlled accurately.

Next, the operation of rewriting the predetermined correction coefficient Kn in the correction coefficient storage section 52 will be described. As described above, in the forward conversion unit control circuit 5, the correction coefficient Kn set in the correction coefficient storage unit 52 is updated in accordance with the temporal change appearing in the input / output characteristics of the optical coupling element 4. The updating process is executed by the correction coefficient calculating unit 59.

Therefore, the correction coefficient calculating section 59 must first detect a change in the input / output characteristics of the optical coupling element 4. To this end, the relationship between the DC voltage E to be detected and the voltage detection value Ed is determined. Need to know how has changed from the initial state.

For this purpose, it is necessary to determine that the DC voltage E is correct, and to compare the voltage detection value Ed detected by the optical coupling element 4 with the DC voltage E which is determined to be correct. Therefore, a reference DC voltage E is required.

Here, regarding the AC power supply 1, this is usually a commercial power system of a general electric power company, and its voltage is strictly controlled, so that the change with time can be practically ignored.

Then, assuming that the DC voltage E is extracted under a specific condition that a proportional relationship is established with respect to the voltage of the AC power supply 1, if the DC voltage E at this time is taken out,
Can be regarded as always showing a constant value, and can be used as a reference DC voltage E.

Therefore, in this embodiment, as a specific condition at this time, the PWM operation of the forward power conversion unit 2 is stopped, and the current of the forward power conversion unit 2 is only the charge / discharge current of the smoothing capacitor 3. It is something that is to be when it is.

As described above, each arm of the forward power conversion unit 2 is composed of an IGBT and a diode connected in anti-parallel to the IGBT. Therefore, when the PWM operation is stopped, It becomes equivalent to a phase full-wave rectifier diode circuit, and is in a state of generating a DC voltage obtained by full-wave rectification of the AC by the AC power supply 1.

At this time, assuming that the current of the forward power converter 2 is only the charging / discharging current of the smoothing capacitor 3,
The DC voltage E at this time is substantially equal to the peak value of the AC voltage of the AC power supply 1, which can be regarded as a constant value as long as the AC voltage of the AC power supply 1 does not change. It can be a value.

Hereinafter, the updating process of the correction coefficient Kn by the correction coefficient calculating section 59 will be described in detail with reference to FIG. FIG. 2 shows a correction request interrupt task executed when the correction request interrupt signal IRQ1 (FIG. 1) is generated. According to this, the correction coefficient Kn is calculated every time the correction request interrupt signal IRQ1 is generated. Is updated. At this time, the voltage detection value E obtained from the optical coupling element 4 in the initial state is
Under d, the control conditions of each section are set so that the correction coefficient Kn becomes 1.

When the task shown in FIG. 2 is started, first, in step S1, the PWM pulses for the forward power converter 2 and the reverse power converter 7 are turned off to stop the switching operation.

As a result, the forward power converter 2 is in a state equivalent to a diode rectifier circuit, and a state in which the AC full-wave rectified voltage supplied from the AC power supply 1 is charged in the smoothing capacitor 3. Then, the reverse power conversion unit 7 stops the operation of supplying the reverse conversion power to the AC motor 8.

Next, in step S2, it is determined from the signal of a speed detector such as an encoder (not shown) that the AC motor 8 as a load has completely stopped, and the influence of the back electromotive force of the AC motor 8 and the like is determined. Confirm that is gone.

As a result of the processing in steps S1 and S2,
Since the reverse power conversion unit 7 and the AC motor 8 are equivalent to being separated from the smoothing capacitor 3, when the smoothing capacitor 3 is used as a voltage source, the load becomes an infinite resistance. As a result, the smoothing capacitor 3 is almost charged to the peak value of the voltage of the AC power supply 1.

Then, since the output voltage of the forward power conversion unit 2 at this time is derived from the voltage of the AC power supply 1, there is no change with time, and as described above, the voltage value can be regarded as a fixed value that has already been set. . Therefore, using this as the reference voltage,
If the detection is performed by the optical coupling element 4 and the detection result is compared with the initial value, the change in the detection characteristic of the optical coupling element 4 from the initial value, that is, the change with time can be calculated quantitatively.

Therefore, in the next step S3, as shown in FIG. 3, the voltage value detected at this time is changed to the detected voltage value Ed.
From this and the initial value Eda of the detected voltage value, the correction coefficient Kn is calculated as follows. Here, first, although the smoothing capacitor 3 is almost charged to the peak value of the voltage of the AC power supply 1 as described above, a ripple component appears in the voltage, although slightly, in reality.

For this reason, the detection voltage value Ed and the initial value Eda
Also, as shown in FIG. 3, since the waveform changes sinusoidally during one AC cycle, it is necessary to perform sampling at the same timing for each AC cycle. Therefore, in this embodiment, as shown in the figure, the voltage is taken in at the time Tm when the voltage value reaches the maximum value, the detected voltage value Ed at this time is set to Ed (Tm), and the initial value Eda is set to Eda (Tm). And

In FIG. 3, the solid line is the detected voltage value Eda,
Since the dashed line is the initial value Eda, this figure shows a case where the time-dependent change appears as a decrease in the detection sensitivity. Therefore, when the magnitude of the time-dependent change is represented by ΔEd, as shown in FIG. Downward, that is, a negative value -ΔEd.

At this time, the time Tm at which the DC voltage becomes maximum
Can be easily obtained by measuring the elapsed time from the zero-cross signal of the AC voltage, so that there is no problem in sampling.

Accordingly, the correction coefficient Kn is the ratio between the detected voltage value Eda and the initial value Eda. Therefore, the calculation of the correction coefficient Kn in step S3 can be obtained by executing the following equation (1). Kn = Eda (Tm) / Ed (Tm) (1) Then, the correction coefficient Kn previously stored in the correction coefficient storage unit 52 is sequentially updated by the correction coefficient Kn obtained in step S3. It goes.

As a result, the corrected voltage value Edc output from the multiplication unit 51 is expressed by the following equation (2). Edc = Kn × Ed (2) Here, when the timing reaches Tm, the optical coupling element 4
When the voltage value Ed (Tm) including the detection error due to the change with time of the correction is corrected, the following expression (3) is obtained from the expressions (1) and (2).

Edc = Eda (Tm) / Ed (Tm) × Ed = Eda (Tm) (3) According to the equation (3), the initial value Ed of the maximum detection voltage is obtained.
a (Tm) becomes equal to the corrected voltage Edc of the voltage detector 4, and thus the validity of the method of calculating the correction coefficient Kn according to this embodiment can be understood. Then, steps S1, S
2. When the routine of S3 ends, the correction request task of FIG. 2 ends.

Here, the correction coefficient Kn is calculated from the detected value sampled at the time Tm at which the rectified voltage becomes maximum. However, the correction coefficient Kn may be sampled and corrected at the minimum timing. What is necessary is just to make it the same timing.

At this time, the correction coefficient Kn may be calculated from a value obtained by averaging the detection values sampled a plurality of times. In this case, although the calculation is delayed, the influence of a disturbance element such as noise may be caused. Can be eliminated,
Accurate correction can always be obtained, and a greater effect can be expected for improving reliability.

The correction coefficient Kn calculated as described above
Is rewritten in the memory as a new correction coefficient Kn in the correction coefficient storage unit 52, a correction request task is generated again, and is held in the memory until the task is completed, and the corrected voltage value Edc is stored in the voltage command value Ed. ^In contrast, ^* is used as a negative feedback value, so that the voltage control system can be controlled without being affected by aging.

The correction coefficient Kn calculated at this time is
Is not limited to a change in the characteristics of the optical coupling element 4 due to a change with time, needless to say, also corresponds to a change in the characteristics due to other causes. Therefore, according to this embodiment,
In any case, accurate control is always possible.

Next, the frequency and timing of executing the correction request interrupt task, that is, the correction request interrupt signal IRQ1
The frequency and timing of occurrence of will be described. First, the correction request interrupt signal IRQ1 may be generated at any timing. For example, the correction request interrupt signal IRQ1 may be periodically generated at a predetermined cycle.

Here, from the viewpoint of maintaining the correct operation state, the frequency of generation of the correction request interrupt signal IRQ1 has never been higher so that the change with time does not become too large. However, in this case, since the operation of the AC motor 8 as the load must be stopped, the operation can be performed only when the operation of the load can be stopped due to the restriction due to the operating conditions of the load.

Therefore, in general, at the time of periodic maintenance and the like, the correction request interruption task may be executed when the operation of the load is forcibly stopped. On the other hand, if there is no restriction on stopping the load,
It can be executed irregularly as needed.

By the way, in the case of a power converter for an elevator or an escalator, the operation of the car or the step is stopped at night or on a holiday, so that the above-described correction request interruption task should be executed during that period. In terms of timing, there is no influence on the normal operation, and in this case, even if the present invention is applied, there is no possibility that the service is reduced.

The object to which the present invention is applied is not limited to power converters for elevators and escalators, but such objects are subject to long-term product life of 20 to 30 years and aging. Therefore, a great effect can be expected by applying the present invention.

Therefore, according to the above-described embodiment, the optical coupling element 4 can be used as a DC voltage detector without a fear of a decrease in reliability, and an increase in the number of components and an increase in cost can be easily suppressed.

[0055]

According to the present invention, it is possible to sufficiently correct a decrease in the accuracy of DC voltage detection due to aging or the like, so that the power converter can be reduced in size and weight by using an optical coupling element as a voltage detector. The cost can be sufficiently reduced, and a highly reliable power converter can be provided at a low price.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a power converter control device according to the present invention.

FIG. 2 is an explanatory diagram of a correction coefficient calculation process according to an embodiment of the present invention.

FIG. 3 is a waveform diagram for explaining a principle of calculating a correction coefficient according to the present invention.

[Explanation of symbols]

Reference Signs List 1 AC power supply 2 Forward power conversion unit 3 Smoothing capacitor 4 Optical coupling element 5 Forward conversion unit control circuit 6 Current detector 7 Reverse power conversion unit 8 AC motor 51 Multiplier 52 Correction coefficient storage unit 53 Comparator 54 PI compensator 55 Comparison Unit 56 PI compensator 57 comparator 58 pulse generation circuit 59 correction coefficient calculation unit E output DC voltage value of forward power conversion unit Ed DC voltage detection value Ed (Tm) Maximum DC voltage detection value Ed ^* DC voltage command value Eda voltage detection Initial value of the value Eda (Tm) Maximum voltage value of the initial value Tm When the maximum DC voltage value is reached

Continued on the front page (72) Inventor Hiromi Inaba 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Research Laboratories Co., Ltd. In the elevator group (72) Inventor Naoto Onuma 1070 Ma, Hitachinaka-shi, Ibaraki Prefecture In the elevator group in Hitachi, Ltd. (72) Takeki Ando 1-6-6 Kanda Nishikicho, Chiyoda-ku, Tokyo F term (reference) 5H006 AA04 AA06 BB05 CA01 CB08 CC02 DA04 DB01 DC02 DC05 5H740 BA11 BB08 BB10 KK04 MM01

Claims (7)

[Claims] 1. A power converter control device of a type that detects a DC voltage output from a forward power conversion unit by an optical coupling element and controls the forward power conversion unit, wherein an AC input to the forward conversion unit is provided. Calculate the change in the detection characteristics of the optical coupling element based on the voltage, and sequentially calculate the correction coefficient,
A correction coefficient calculating means for updating and setting is provided, wherein the detection value of the DC voltage is corrected by the correction coefficient which is set to be updated, and an output DC voltage of the forward power conversion unit is controlled. Power converter control device. 2. The invention according to claim 1, wherein the forward power conversion unit is constituted by a circuit in which a circuit in which a diode is connected in reverse parallel to a switching element is bridge-connected as each arm, and the correction coefficient calculating unit includes: When the switching element of the forward power conversion unit is turned off, the diode is configured to calculate the correction coefficient on the basis of a DC voltage that appears after full-wave rectification of the AC voltage by the diode. Converter control device. 3. The optical coupling device according to claim 2, wherein the correction coefficient calculating unit holds an initial value of the DC voltage, and compares the initial value with the DC voltage detected at the present time. A control device for a power converter, wherein the control device is configured to calculate a change in a detection characteristic of the power converter. 4. The invention according to claim 1, wherein the calculation of the change in the detection characteristic of the optical coupling element by the correction coefficient calculating means is given as an average value of a plurality of calculation results. A control device for a power converter, wherein an update setting of the correction coefficient is executed based on an average value. 5. The control device for a forward power converter according to claim 1, wherein the operation of the correction coefficient calculating means is started periodically. 6. The power conversion device according to claim 1, wherein the forward power conversion unit is included in a power conversion device of an elevator or an escalator. A control device for controlling the power converter, wherein the control device calculates the correction coefficient when the operation of the elevator or the escalator is stopped. 7. The control device for a forward power converter according to claim 1, wherein the correction means has a function of holding a detection value at the start of the conversion operation.