JP2000287456A - Waveform generator for pwm inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent thermal breakdown of transistors by making configuration so as not to turn the output transistor elements on, if an on-pulse width for the output transistor elements computed in a waveform generating part is smaller than a detection delay time of an overcurrent protecting circuit. SOLUTION: In a waveform generating part 6, this apparatus compares a signal wave with a carrier wave and computes an on-pulse width for each output transistor, and compares the computed on-pulse width with the detection delay time of an overcurrent protecting circuit to be determined by a time constant, circuit constant, etc. If the computed on-pulse width >= the detection delay time of the current protecting circuit is satisfied, the computed on-pulse width is outputted as it is, to turn to the next waveform computation. If the computed on-pulse width < the detected delay time of the current protecting circuit is satisfied, it returns to the next waveform computation, without outputting an on-pulse. Consequently, it becomes possible to prevent thermal breakdown of the transistors caused by short overcurrent pulses applied several times successively when a load is grounded, since operation of the transistors can be stopped by one pulse, when a current equal to or larger than an overcurrent protection level flows in the transistors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a PWM inverter waveform generator for driving an induction motor or the like.

[0002]

2. Description of the Related Art Conventionally, this type of waveform generator is as follows.

FIG. 1 is a circuit example of a conventional PWM inverter waveform generator.

In FIG. 1, reference numeral 1 denotes an AC voltage power supply;
Is a converter, 3 is a smoothing capacitor, 4 is an inverter, 5 is a motor, and 6 is a waveform generator.

[0005] U, V, W, X,
It has 6 output transistors, Y and Z.
Is switched by a command from the waveform generation section of FIG.

In general, the waveform generator 6 outputs a driving waveform of each output transistor based on a comparison result between a signal wave and a carrier wave and a short-circuit prevention time (dead time) of the upper and lower elements of the inverter.

FIG. 5 shows an example of a driving waveform of each output transistor based on a result of comparison between a signal wave (sine wave) and a carrier wave (triangular wave).

In the actual driving waveform, a time (dead time) during which no output is output from both the upper and lower transistors is provided in order to prevent a short circuit between the upper and lower elements. However, in order to explain the principle, no dead time is provided. (0 μS).

[0009]

In FIG. 5 described above,
There may be pulses where the output transistor drive time is very short.

[0010] Looking at one transistor driving waveform, there is a point where a pulse having a short driving time is continuously applied.

On the other hand, the inverter section 4 usually has a built-in overcurrent protection circuit (not shown).
If the output section of this section is grounded for some reason and an overcurrent flows through the transistors of the inverter section, the driving of all the transistors is stopped to prevent the transistors from being destroyed.

Normally, however, this overcurrent protection circuit has several tens μS to 10 μS to prevent malfunction due to noise or the like.
The detection delay time of the order is set.

For this reason, when a waveform as shown in FIG. 5 is applied in a state where the output section of the inverter section 4 is grounded for some reason, even if an overcurrent flows due to a ground fault, the overcurrent protection function is not performed. There will be timings that do not work.

Next, the relationship between the overcurrent and the thermal destruction of the output transistor will be described.

Generally, if the temperature inside the transistor before the overcurrent flows is not so high, the temperature inside the transistor does not rise enough to cause thermal destruction with a very short single-pulse overcurrent.

Therefore, the inverter overcurrent protection circuit is set with a detection delay time within a range where the semiconductor will not be thermally damaged even if an overcurrent flows within a certain temperature condition range, and a malfunction due to noise or the like will occur. Is generally prevented.

That is, the overcurrent protection function reliably operates for the overcurrent that continues for the overcurrent protection detection delay time,
The transistor can be protected before the temperature rises enough to thermally destroy the transistor due to overcurrent.

However, the overcurrent protection does not work when short overcurrent pulses are applied continuously so that the overcurrent protection function does not work.

In this case, a temperature rise due to an overcurrent is accumulated in the transistor, which eventually leads to thermal destruction.

That is, as shown in FIG. 5, when an overcurrent flows at a timing at which pulses having a short drive time are continuously applied, there is a problem that the transistor is thermally destroyed.

[0021] The present invention provides a waveform generator that prevents thermal destruction of a transistor.

[0022]

In order to solve the above-mentioned problems, the present invention provides a converter for converting an AC voltage power supply to a DC voltage, a smoothing capacitor connected to the output of the converter, and a DC voltage converter. In a waveform generator for a PWM inverter including an inverter circuit for converting to a phase AC voltage and a waveform generator for generating a drive signal for the inverter circuit, an ON pulse width of an output element calculated by the waveform generator is: If the output element is shorter than the detection delay time of the overcurrent protection circuit, the output element is not turned on.

Also, a converter section for converting an AC voltage power supply to a DC voltage, a smoothing capacitor connected to an output of the converter section, an inverter circuit for converting the DC voltage to a three-phase AC voltage, and a drive for the inverter circuit A waveform generating device for generating a signal, wherein the ON pulse width of the output element calculated by the waveform generating unit is within a predetermined time after the output of the inverter output of the inverter circuit is started. Is smaller than the detection delay time of the overcurrent protection circuit of the output element, the output element is not turned on.

[0024]

FIG. 1 is an example of a circuit employing a waveform generation method according to the present invention. The description of FIG. 1 is omitted because it is as described in the related art.

FIG. 2 is a flowchart for generating a waveform of the PWM inverter in the waveform generating section (first embodiment) according to the first aspect of the present invention.

The waveform generator first calculates the ON pulse width of each output transistor by comparing the signal wave with the carrier wave (S1).

Next, the "calculated ON pulse width" is compared with the "detection delay time of the overcurrent protection circuit" determined by the time constant circuit constant and the like (S2).

In the case of “calculated ON pulse width ≧ detection delay time of current protection circuit” (in the case of YES in S2), the calculated ON pulse width is output as it is, and the process returns to the next waveform calculation.

If "calculated ON pulse width <detection delay time of current protection circuit" (NO in S2), the process returns to the next waveform calculation without outputting an ON pulse.

In the present embodiment, it is described that the underground element short-circuit prevention time (dead time) of the inverter is not present (0 μS), but the “ON pulse width calculated in consideration of the dead time” is also described. The ON time calculated by comparing with the “detection delay time of the overcurrent protection circuit” determined by the time constant circuit constant, etc.
Whether to output the pulse width may be determined.

FIG. 3 shows an example of a drive waveform of each output transistor based on the flowchart of FIG.

It can be seen that short pulses are not output compared to the drive waveform of each output transistor in the prior art of FIG.

In the waveform generator configured as described above, the relationship that the transistor output element ON pulse width ≧ the detection delay time of the overcurrent protection circuit always holds.
When a current equal to or higher than the overcurrent protection level flows to the transistor due to a load ground fault, the driving can be stopped by one pulse.

For this reason, it is possible to prevent the thermal destruction of the transistor due to the application of a short overcurrent pulse or several times continuously when the load is connected to the ground.

FIG. 4 is a flowchart for generating a waveform of a PWM inverter in the waveform generating section (second embodiment) according to claim 2 of the present invention.

The waveform generator first calculates the 0N pulse width of each output transistor by comparing the signal wave with the carrier wave (S11).

Next, it is determined whether a predetermined time has elapsed after the start of the inverter output (S12).

If a predetermined time has elapsed, the calculated O
The N pulse width is output as it is (S14), and the process returns to the next waveform calculation.

If the predetermined fine interval has not elapsed, the "calculated ON pulse width" is compared with "the overcurrent protection circuit detection delay fine interval" determined by the time constant circuit constant and the like (S14).

If “calculated ON pulse width ≧ detection delay time of current protection circuit”, the calculated ON pulse width is output as it is (S13), and the process returns to the next waveform calculation.

When the calculated ON pulse width <the detection delay time of the current protection circuit, the process returns to the next waveform calculation without outputting the ON pulse.

Note that the drive waveform of each output transistor based on the flowchart of FIG. 4 becomes the waveform of FIG. 3 when the fixed time has not elapsed, and becomes the waveform of FIG. 5 after the fixed time has elapsed.

In the waveform generator having the above-described configuration, the relation that the predetermined time after the start of the inverter output is satisfied, that is, the transistor output element ON pulse width ≧ the detection delay time of the overcurrent protection circuit, is satisfied. When a current equal to or higher than the overcurrent protection level flows through the transistor due to
The drive can be stopped by a pulse, and when the load is connected continuously, a short overcurrent pulse or a continuous application of the transistor several times can prevent the thermal destruction of the transistor, as well as an inverter assembly error and load connection error. In addition, it is possible to reliably prevent the transistor from being thermally destroyed in an abnormal state in which the ground supply current flows immediately after the start of the inverter output.

On the other hand, if a pulse shorter than the detection delay time of the overcurrent protection circuit is not always output, a general PWM
As a result, a voltage waveform having a large distortion is output as compared with the waveform generation method of the inverter, which may increase the noise and vibration of the driven induction motor.

However, after starting the inverter output and confirming that no overcurrent flows, switching is performed so as to drive each output transistor based on a comparison result between a general signal wave (sine wave) and a carrier wave (triangle wave). If this is the case, this increase in noise and vibration can be eliminated. Therefore, it is possible to prevent failure of the inverter due to an inverter assembly error or a load connection error, and to achieve both low noise and low vibration during normal operation.

[0046]

As described above, according to the first aspect of the present invention, at any time, the relationship of the transistor output element ON pulse width ≧ the detection delay time of the overcurrent protection circuit is satisfied. When a current equal to or higher than the overcurrent protection level flows through the transistor, the driving can be stopped by one pulse.

Therefore, it is possible to prevent the thermal destruction of the transistor due to the application of a short overcurrent pulse or several times continuously when the load is connected to the ground.

According to the second aspect of the present invention, the transistor output element O
Since the relationship of N pulse width ≧ detection delay time of the overcurrent protection circuit is established, when a current equal to or higher than the overcurrent protection level flows to the transistor due to a load ground fault, the drive can be stopped by one pulse, and when the load is continuously connected, In addition to preventing the thermal breakdown of the transistor caused by a short overcurrent pulse or being applied several times continuously, there is a mistake in inverter assembly and load connection, The transistor can be reliably prevented from thermal destruction in the flowing abnormal state.

On the other hand, when a pulse shorter than the detection delay time of the overcurrent protection circuit is not always output, a general PWM
As a result, a voltage waveform having a large distortion is output as compared with the waveform generation method of the inverter, which may increase noise and vibration of the driven induction motor.

However, after starting the inverter output and confirming that no overcurrent flows, switching is performed so as to drive each output transistor based on a comparison result between a general signal wave (sine wave) and a carrier wave (triangle wave). If this is the case, this increase in noise and vibration can be eliminated.

Therefore, it is possible to prevent failure of the inverter due to an inverter assembly error or a load connection error, and to achieve both low noise and low vibration during normal operation.

[Brief description of the drawings]

FIG. 1 is a circuit example of a waveform generator according to the present invention.

FIG. 2 is a flowchart showing a waveform generating method of the waveform generating device according to the first embodiment.

FIG. 3 is a driving waveform example of each output transistor based on the flowchart of FIG. 2;

FIG. 4 is a flowchart showing a waveform generating method of the waveform generating device according to claim 2;

FIG. 5 is a driving waveform example of each output transistor in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply voltage power supply 2 Converter part 3 Smoothing capacitor 4 Inverter part 5 Motor 6 Waveform generation part

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Tetsuo Nomoto 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Yuichi Izawa 2-5-1 Keihanhondori, Moriguchi-shi, Osaka No.5 Sanyo Electric Co., Ltd. (72) Inventor Shin Sekino 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 5H007 BB06 CA01 CB05 CC23 DB02 DB12 DC02 EA03 FA03 FA09 FA13 FA18

Claims (2)

[Claims] 1. A converter for converting an AC voltage power supply to a DC voltage, a smoothing capacitor connected to an output of the converter, an inverter circuit for converting a DC voltage to a three-phase AC voltage, and a drive for the inverter circuit. A waveform generating device for generating a signal, the waveform generating device comprising:
If the N pulse width is smaller than the detection delay time of the overcurrent protection circuit of the output element, the output element is not turned on. 2. A converter section for converting an AC voltage power supply to a DC voltage, a smoothing capacitor connected to an output of the converter section, an inverter circuit for converting the DC voltage to a three-phase AC voltage, and a drive for the inverter circuit. A waveform generator for generating a signal, wherein the ON pulse width of the output element calculated by the waveform generator is within a fixed time after the output of the inverter output of the inverter circuit is started. Is smaller than the detection delay time of the overcurrent protection circuit for the output element, the output element is not turned on.