WO1984004214A1

WO1984004214A1 - Inverter apparatus

Info

Publication number: WO1984004214A1
Application number: PCT/JP1984/000176
Authority: WO
Inventors: Hideaki Tada; Osamu Miyazaki; Masayuki Katto
Original assignee: Mitsubishi Electric Corp
Priority date: 1983-04-08
Filing date: 1984-04-07
Publication date: 1984-10-25
Also published as: JPS59188393A; DE3490167T1

Abstract

A inverter apparatus is employed to convert power from a commercial power source (1) into AC power of variable frequency and variable voltage by an inverter circuit (8), so that an AC motor (4) can operate at variable speed. The inverter apparatus is provided with a detection means (5) which detects the magnitude of current supplied to the AC motor (4), and a control device (16) which is supplied with an output from the detection means and an operating frequency signal from the AC motor (4). The control device is used to shut off the output of the inverter circuit (8) according to an inverted limit-time overcurrent shut-off characteristic corresponding to the operating frequency of the AC motor (4), to prevent the AC motor (4) from overheating, particularly during low-speed operation.

Description

- Specification

Title of invention

Inverter device

Technical field

The present invention relates to an inverter device capable of protecting a driven AC motor from overcurrent. Background Technology ·

As a method for protecting an AC motor driven by an inverter device, for example, an induction motor against overcurrent, conventionally, as shown in Fig. 1, an overcurrent relay with anti-time characteristic is used. Protection schemes have been adopted. '

In the figure, (1) is a commercial AC power supply, (2) is an inverter device, (3) is an overcurrent relay having an output contact (S a) with anti-time characteristic, and (4) is an induction motor. It is.

Ie, detects the over current of the induction motor 'machine ⁽⁴⁾ of the primary winding of the inverse time characteristics are connected in series overcurrent relay (3) to by Ri induction motor (4), the overcurrent继By sending the output contact signal (S) of the electric device (3) to the inverter device (2) and shutting off the output of the inverter device (2), the time limit for the reciprocal time limit is increased. It is intended to obtain a current cutoff characteristic, that is, a characteristic in which the operating time is shortened as the current increases.

In general, induction motors have a built-in self-cooling fan, and the self-cooling effect can be obtained by rotating the rotor. Here, the induction motor is converted to an inverter. When variable speed operation is performed by the device, the overcurrent capability of the induction motor naturally decreases due to the reduction of the self-cooling effect, especially when the rotational speed changes in the low frequency range. Therefore, it was difficult to accurately protect the induction motor with the above-mentioned protection method using an overcurrent relay having a time limit characteristic with a constant current.

Disclosure of the invention

The present invention has been made in order to eliminate the drawbacks of the conventional protection method, and has a means to have an anti-time cutoff characteristic suitable for each operating frequency of an AC motor such as an induction motor. By providing this, it is intended to provide complete protection against overcurrent of the induction machine. Brief description of drawings

Fig. 1 is a diagram of the principle of the conventional device, Fig. 2 is a schematic diagram of the essential parts of one embodiment of the present invention, Fig. 3 is a general structure diagram showing an embodiment of the present invention, and Fig. ⁴ is It is a diagram that flows the operation port of the micro computer.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below with reference to FIGS.

First, the principle of the present invention will be described. In FIG. 2, (5) shows a current transformer (hereinafter referred to as G) that detects the DC current that is the reference of the three-phase AC current flowing through the induction motor (4). ), (6) is a microprocessor for computing, and (7) is a read-only processor. One memory (hereinafter abbreviated as ROM). The other parts are the same as those shown in Fig. 1, and the description is omitted.

The current signal (SN) detected by the CT (5) is sent to the micro-processor (6), and the current signal (SN) is sent to the micro-processor (6). Time integration. The time-integrated current value was equal to the value given by the ROM ( ⁷ ) force. Outputs the signal (SS) that shuts off the output of the circuit ( ⁸ ). The operating frequency is given to the address of R 0 M), and the value corresponding to the overcurrent capability of the induction motor ( ⁴ ) at each operating frequency stored in advance is the operating frequency. According to the signal (SF), it is output from R0M (7) to the processor (6) of the microphone port, so that accurate overcurrent protection of the induction motor can be performed. -Next, a specific embodiment of the present invention will be described with reference to FIG. In the figure, (1) is a commercial current power supply, (2) is the inverter device according to the present invention,) is a three-phase induction motor driven by the inverter device, (5) is a current transformer (CT) as a detecting means for detecting the current flowing through the DC bus (9), and (8) is a well-known method consisting of a transistor, a diode, and a power. An inverter circuit of £ 10) is a converter that converts the AC (three-phase AC) of the power supply (1) to DC, (1 is a smoothing capacitor, and (12) is a DC The current detection circuit averages the current detected by C Τ (5), converts it to a level, and sends it to the operating point adjuster). W) is an A-D converter that converts the analog signal into a digital signal, (15) is a frequency setting circuit that arbitrarily sets the operating frequency of the induction motor (4), (16) is a control circuit, A micro-computer with a built-in micro-processor (6) and R0M) shown in Fig. 2 M5L8004 9-XXX P type manufactured by Co., Ltd. is used.

(L7) is a control circuit (a modulation circuit that generates a pulse width modulation signal (PWM) according to the output signal from 1Θ). (18) is a protection circuit that generates a predetermined shutoff signal (SS) according to an output cutoff command from the control circuit. appear.

a is a base drive circuit for controlling the inverter circuit (8), which outputs a signal for controlling the base current of the transistor. (20) indicates a three-phase bus.

Next, the operation of the device will be described with reference to Fig. 4. The control circuit s operates according to the program shown in Fig. 4. Immediately after the start 60), the operation of setting the flag only once every 16 times is performed. Then, an operation (33) of reading the current flowing through the induction motor (4) is performed. This reading operation (33 is performed on the signal detected by 0Τ (5) as shown in FIG. 3). Then, the operation of averaging the current values obtained by 16 readings is performed (3¾. Then, the operation ^ of subtracting the current value corresponding to 5% from the average current value is performed ^). This is because the protection operation is performed when the current value that is the reference value of the protection operation is 105% or more. Next, after operation (34), a determination operation 65) is performed to determine whether the answer is negative. -If the answer is negative, the induction motor ( ⁴ ) has stopped and the operation (36) is performed to determine whether the value of the integrating counter is 0. The operation of determining whether there is a lag is performed (37), and if there is a lag, the operation of subtracting 1 is decremented ( ³⁸ ) and the operation ends (100). .

Action (If the result in step ³ is a positive value, perform the action (3S) to determine whether it is a current equivalent to 100% of the reference value, and do not exceed 100%. In this case, the operation (40) for reading the operating frequency (SF) is performed, and the operation for determining the addition / subtraction of the integrated counter (41) is performed, where the addition / subtraction differs depending on the operating frequency (SF). Therefore, as the frequency (SF) becomes smaller, even if the current value is smaller, the addition is performed.

Then, in the case of addition, an operation (referring to the data of R 0 M (7)) is performed next by the judgment operation ^. The result of the judgment operation ω

If it is determined that the value is 100% or more,

R 0 動作 Operation ( ⁴ ) referring to the data in (7). After the operation that refers to the data of R0M (7) ( ⁴³ ) (44), the operation to determine whether there is a flag (5) is performed, and if it is, the operation ends immediately. (100), and if there is, then the operation of adding the data of ROM (a) to the integration counter is performed ( ⁴⁶ ), and as a result, the integration counter is over-performed. The operation to determine the united force is performed (the operation is performed. If the operation is not overflow, the operation is terminated (丄 00). If the operation is overpowered, the operation is completed. The lock inhibit operation ( ⁴⁸ ) is performed, and then

O PI For confirmation again, the operation of determining whether the accumulated power counter is overflow or not ( ⁹ ) is performed, and if it is done through the overpass, the above-mentioned interface will be used. When the release operation of the lock prohibition is performed, the operation ends (100), and when the operation is over-flow, the protection operation (51) is performed.

First, the operation of setting the flag once every 16 times (3D is performed, but the control circuit aa performs many other control operations such as the control of the modulation circuit (L7). Only once in 16 times is the main switch for such overcurrent protection performed.

In the above-described embodiment, since the CT (5) is provided on the DC bus (9) in the inverter device (2), each of the transistors included in the inverter circuit (8) is provided. Although it has the effect of protecting the transistor as well, it goes without saying that it is good to insert it into the three-phase bus (0) after the inverter circuit (8).

As described above, according to the present invention, overcurrent and disconnection characteristics during the time limit corresponding to the operating frequency of the AC motor can be obtained, so that complete protection of the AC motor during the inverter operation is achieved. Is possible.

Claims

_ The scope of the claims

1. An inverter circuit that converts AC power of variable frequency and variable voltage by an inverter circuit and operates the AC motor at a variable speed, the current value given to the AC motor. And a control device to which a detection output of the detection means and an operating frequency signal of the AC motor are inputted, and which has an anti-time cutoff characteristic corresponding to the frequency at each of the operating frequencies. An inverter device characterized in that the output of the AC power is cut off by an output cutoff command signal of the control device.

2. The inverter device according to claim 1, wherein the detection means is provided in a circuit for supplying DC power to the inverter circuit.

3. The control circuit is a micro-processor for calculation and a read-only memory (ROM) that stores the current value corresponding to the overcurrent capability of the AC motor for each operating frequency. ). The inverter device according to claim 1, further comprising a microphone opening computer having the following.