JPH10164884A - Inverter control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inverter control apparatus by which the limit of an inverter can be applied without lowering the running performance of an elevator, which can be made small and lightweight and whose costs can be lowered. SOLUTION: The temperature of a cooling fin is measured by a temperature sensor 18, and whether the temperature exceeds an upper-limit value or not is judged by a temperature judgment means 20. When the temperature is at the upper-limit value or lower, a maximum permissible current with reference to the temperature is computed by a maximum-permissible-current computing means 21, and the maximum permissible current and an inverter output current are compared by a carrier-frequency change means 22. As a result, when the inverter output current exceeds the maximum permissible current, a signal 22a which is used to lower a carrier frequency is output. A carrier-signal generation circuit 15 outputs a carrier signal whose frequency is normally, e.g. 10kHz. When a signal 22a from the carrier-frequency change means 22 is input, the frequency of the carrier signal is changed to 5kHz so that the inverter output current does not exceed the maximum permissible current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an inverter control device that drives an induction motor and performs speed control.

[0002]

2. Description of the Related Art In recent years, with the advance of control technology, many industrial machines have become AC motors driven by inverters, and efforts have been made to improve performance and reduce costs.

Hereinafter, the application will be described by taking an elevator apparatus as an example. By the way, in order to reduce the cost of the inverter device,
Although it is necessary to appropriately select the capacity of the inverter, the inverter applied to the elevator control is selected so that its output current does not exceed the maximum allowable current of the inverter. This maximum allowable current is defined by the carrier frequency of the PWM control and the junction temperature of the semiconductor element such as the IGBT constituting the inverter main circuit or the upper limit of the cooling fin temperature. As shown in FIG. Conventionally, the carrier frequency is fixed in terms of motor noise and response characteristics (for example, 10 k).
Hz), and in calculating the cooling fin temperature, the following factors, which allow for a design margin, were considered under the strictest conditions.

Ambient temperature Elevator duty cycle Loss characteristics of semiconductor elements Cooling fin efficiency Cooling fan power supply conditions (frequency, voltage drop, etc.) Operating conditions (loading exceeding rating, low speed operation, governor test, etc.)

[0005]

That is, in an elevator, the output current of the inverter greatly differs depending on the load condition of the car, the driving direction, acceleration or deceleration, etc. (the maximum current occurs when accelerating an unloading or decelerating a unloading). ) However, conventionally, semiconductor elements are selected so that the output current value does not exceed the maximum permissible current at any time. As a result, the size and cost of the inverter are increased more than necessary.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has as its object to reduce the cost by reducing the size and weight of the inverter by making it possible to apply the limit of the inverter without lowering the running performance. It is.

[0007]

The present invention is characterized by temperature detecting means for detecting the cooling fin temperature of the inverter and maximum allowable current calculating means for calculating the maximum allowable current of the inverter based on the cooling fin temperature. And a carrier frequency changing means for lowering the carrier frequency of the PWM control when the output current of the inverter exceeds the maximum allowable current.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the temperature of a cooling fin is detected by a temperature detecting means, and when the temperature is equal to or lower than an upper limit value, a maximum allowable current for the temperature is calculated by a maximum allowable current calculating means. Then, the maximum allowable current is compared with the output current of the inverter by the carrier frequency changing means. If the output current exceeds the maximum allowable current, a signal for lowering the carrier frequency is output. The carrier signal generating circuit normally outputs a carrier signal having a frequency of, for example, 10 kHz. However, when a signal is input from the carrier frequency changing unit, the frequency of the carrier signal is reduced, and the output current does not exceed the maximum allowable current. To do.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of the present invention.
Is a three-phase AC power supply, 2 is a converter for converting the AC power supply to DC, 3 is a smoothing capacitor for smoothing the output of this converter, 4 is an inverter for converting the output of the converter 2 to AC of variable voltage and variable frequency, and 5 is an inverter 4 is a current detector that detects the output current of each phase of the output of 4 and outputs it as a detection signal 5a; 6 is an induction motor that is fed by the inverter 4 and drives the elevator; and 7 outputs the actual speed of the car as a speed feedback signal 7a. Speed detector, 8 is a sheave of a hoist driven by the induction motor 6, 9 is a main rope wound around the sheave 8, 10 is a basket connected to the main rope 9, 11
Is also a counterweight, and 12 is an ideal speed command signal 12a.
The speed command generator 13 outputs a speed command signal 12
a and the car speed feedback signal 7a and the current command signal 13
a, an ACR (current regulator); 15, a carrier signal generating circuit for generating a carrier signal of 10 kHz, and outputting a carrier signal of 5 kHz based on a signal 22a to be described later; and 16, a PWM signal Circuit, 1
Reference numeral 7 denotes a base drive circuit, and reference numeral 18 denotes a temperature sensor such as a thermistor for detecting a cooling fin temperature of the inverter.

Reference numeral 19 denotes a microcomputer, a temperature determining means 20 for determining whether or not the cooling fin temperature is below the upper limit, and a maximum allowable current for calculating the maximum allowable current of the inverter based on the actually measured temperature of the cooling fin. It comprises a calculating means 21 and a carrier signal changing means 22 for outputting a signal 22a for changing the carrier frequency when the output current of the inverter exceeds the maximum allowable current value. The signal 20a is an operation stop signal output when the measured temperature of the cooling fin exceeds the upper limit.

In the above configuration, the speed command generator 1
When the speed command 12a is output from 2, the current command generator 13 generates a current command signal 13a corresponding to the torque required by the induction motor 6 so that the elevator car 10 follows the speed command 12a. This current command signal 13
“a” is compared with a detection signal 5 a detected by the current detector 5, the deviation thereof is amplified by the ACR 14, and pulse width modulation is performed by the PWM circuit 15 by comparison with a carrier signal. The base drive circuit 16 controls a switching element such as a transistor constituting an inverter according to the pulse width modulation signal, and moves the elevator car 10 up and down by following a speed command.

On the other hand, during this time, the temperature of the cooling fins of the inverter is detected at the temperature 18, and the temperature judging means 20 judges whether the temperature exceeds the upper limit. If the value exceeds the upper limit, the signal 20a is output, and the operation of the elevator is stopped. If the value is less than the upper limit, the maximum allowable current for the temperature at that time is calculated by the maximum allowable current calculating means 21. Then, the maximum allowable current is compared with the output current of the inverter by the carrier frequency changing means 22, and as a result, when the output current of the inverter exceeds the maximum allowable current, a signal 22a is output, which is usually set to 10 kHz. Change the carrier frequency to 5 kHz.

The procedure for changing the carrier frequency, which is executed by software in the microcomputer 19, will be described with reference to the flowchart of FIG.

First, in step S1, the temperature of the cooling fin is detected, and in step S2, it is determined whether the temperature is equal to or lower than the upper limit. If the temperature exceeds the upper limit, an operation stop signal is output in step S3, and the operation of the elevator is stopped until the temperature becomes equal to or lower than the upper limit.

If the temperature of the cooling fin is below the upper limit,
In step S4, it is confirmed whether or not the elevator has already started operation, and in step S5, the maximum allowable current at that temperature is obtained. For the calculation of this maximum allowable current,
Each time, it is also possible to actually calculate by an estimation calculation. However, as shown in FIG. 4, since the relationship between the cooling fin temperature and the maximum allowable current at that time is known in advance, this relationship is stored in a memory in advance. By storing it, it can be easily calculated. Then, the maximum allowable current is compared with the actual output current of the inverter in step S6, and it is determined which is larger in step S7. Although the example of FIG. 1 shows an example in which the comparison is made using the current command signal 13a as the output current of the inverter, it may be compared with the detection signal 5a. As a result of the comparison, if the output current is smaller, there is no possibility that the temperature of the cooling fin will exceed the upper limit during the current operation. Therefore, it is determined whether or not the carrier frequency is 10 kHz in step S8.
If so, continue driving.

On the other hand, as shown in FIG. 3, for example, when the output current exceeds the maximum allowable current during acceleration,
Since there is a possibility that the junction temperature may exceed the upper limit value, at that time, the carrier frequency is set to 5 kHz by step S10.
In step S11, this state is maintained for a fixed time (a time corresponding to the acceleration time). As a result, as shown in FIG. 3, at least during this acceleration, the maximum allowable current becomes larger than the output current, and the temperature of the cooling fins, that is, the junction temperature of the semiconductor element, can be prevented from exceeding the upper limit.

After a lapse of a predetermined time, it is checked in step S12 whether or not the operation has been completed. In step S5, the maximum allowable current value at the current carrier frequency is obtained again. When the carrier frequency is 5 kHz, the maximum allowable current value is large.
Proceeding to S9, the frequency is returned to 10 kHz again,
At this point, since the acceleration has been completed, the output current does not exceed the maximum allowable current.

Thus, in the present invention, the temperature of the cooling fin and the maximum allowable current at that time are constantly monitored. If the output current exceeds the maximum allowable current during acceleration or deceleration, only during the acceleration or deceleration. By lowering the carrier frequency, the output current does not exceed the maximum allowable current, and the temperature rise of the cooling fins, that is, the junction temperature of the semiconductor element is prevented.

The carrier frequency is changed from 10 kHz to 5
By lowering to kHz, motor noise is expected to increase, but the carrier frequency needs to be reduced only for a few seconds during acceleration or deceleration when the load current is large,
In addition, among these cases, such a case appears only when most of the above-described junction temperature calculation conditions are severe, and therefore, it is considered that there is almost no problem in practical use.

In the above description, the carrier frequency is set to two steps of 10 kHz and 5 kHz. However, the number of steps is further increased. If the output current exceeds the maximum allowable current even if the carrier frequency is lowered by one step, the carrier frequency is further increased. It is also possible to lower the carrier frequency by one step.

In the above embodiment, the cooling fin temperature is directly measured by a temperature sensor or the like. However, the temperature may be estimated by simulating the junction temperature of the inverter element.

In the above embodiment, when the output current of the inverter exceeds the maximum allowable current at 10 kHz, the carrier frequency is lowered for a certain period of time. For example, the maximum allowable current at 10 kHz is stored. This may be compared with the output current of the inverter (having a hysteresis), and the carrier frequency may be returned to the original value immediately after the return to 10 kHz is possible.

[0023]

According to the present invention, it is not necessary to consider an excessive design margin in the calculation of the maximum allowable current of the inverter, and in the case of the same specification, it is possible to apply a smaller inverter than before. Significant cost reduction can be achieved without reducing running performance.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of the present invention.

FIG. 2 is a flowchart showing a processing procedure for changing a carrier frequency in the present invention.

FIG. 3 is a diagram showing a relationship between an output current of an inverter and a maximum allowable current in the present invention.

FIG. 4 is a diagram showing a relationship between a temperature of a cooling fin and a maximum allowable current.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Three-phase AC power supply 2 Converter 3 Smoothing capacitor 4 Inverter 5 Current detector 6 Induction motor 10 Car 12 Speed command generator 13 Current command generator 14 ACR 15 Carrier signal generation circuit 16 PWM circuit 17 Base drive circuit 18 Temperature sensor 19 Micro Computer 20 Temperature determining means 21 Maximum allowable current calculating means 22 Carrier frequency changing means

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Hayashi 1-28-10 Sho, Ibaraki-shi, Osaka Inside Fujitec Co., Ltd.

Claims (2)

[Claims] 1. An inverter control device comprising: a converter for converting AC power to DC power; and an inverter for converting the DC power into an AC having an arbitrary variable voltage and variable frequency by PWM control and supplying power to an induction motor. Temperature detecting means for detecting the cooling fin temperature of the inverter,
Based on the cooling fin temperature detected by the temperature detecting means,
Inverter control comprising: a maximum allowable current calculating means for calculating a maximum allowable current of the inverter; and a carrier frequency changing means for lowering a carrier frequency of the PWM control when an output current of the inverter exceeds the maximum allowable current. apparatus. 2. The apparatus according to claim 1, further comprising a temperature determining means for determining a cooling fin temperature detected by said temperature detecting means, wherein the operation of the elevator or the like is stopped when the cooling fin temperature exceeds an upper limit value. Item 3. The inverter control device according to Item 1.