JP2646481B2 - Inverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention smoothly changes an inverter device that performs variable control (hereinafter referred to as PWM control) of an AC voltage by changing the width of a voltage pulse to be supplied, and particularly switches a modulation unit smoothly. The present invention relates to such an inverter device.

[Prior art] Conventionally, when controlling an inverter, the electrical angle is 0 ° to 18 °.
90 ゜ at high potential of 0 ゜ and 270 at low potential of 180 ゜ to 360 ゜
Modulation means for adding a switching pulse for inverting the original potential in ゜ (hereinafter referred to as first modulation means)
Alternatively, modulation means (hereinafter referred to as second modulation means) for adding a switching pulse for inverting the original phase potential at electrical angles of 0 ° and 180 ° as a continuous pulse pair of a high potential pulse and a low potential pulse as a switching pulse. Was used.

The first modulating means is widely used because the output is proportional to the pulse width and the control is easy, but the switching element for performing PWM control has a characteristic that the cycle of repetition of a conduction state and a cutoff state is limited due to its characteristic, The pulse width of the pulse cannot be smaller than a predetermined value. As a result, the upper limit of the output voltage of PWM control is determined, and when the fundamental frequency is about 75 Hz,
90% is the limit.

On the other hand, a modulator capable of controlling a high voltage exceeding the voltage control range of the first modulator can be controlled by the second modulator up to about 99% of the output at the same basic frequency as described above.

[Problems to be solved by the invention]

The voltage control is generally used because the advantage of the first modulation means is superior. However, if the two modulation means are switched and the second modulation means is applied to a region exceeding the voltage upper limit of the first modulation means. It is desirable because it leads to capacity enhancement.

However, in the conventional means, the first modulation means for adding a switching pulse to the electric angles 90 ° and 270 ° and the electric angles 0 ° and 18 ° are used.
It does not switch smoothly with the second modulating means that adds a switching pulse to 0 °, and large transient fluctuations occur. This effect causes a temporary increase in motor current and torque fluctuation in applications where an induction motor is connected to the load of the inverter device. This transient fluctuation also affects the input current of the inverter device, resulting in a steep current disturbance.

[Means for solving the problem]

For the phase potential output, which has a high potential between 0 ° and 180 ° and a low potential between 180 ° and 360 °, electrical angles of 90 ° and 27 °
A first modulation means for applying a switching pulse to invert the original potential to 0 °, and a phase for setting a high potential between 0 ° and 180 ° and a low potential between 180 ° and 360 °. A second modulating means for adding a switching pulse to the potential output to invert the original potential to a predetermined width before and after the electrical angle of 0 ° and a predetermined width before and after the electrical angle of 180 °, and An inverter device having switching means for switching between the first modulation means and the second modulation means and variably controlling an AC voltage, wherein the switching means switches from the first modulation means to the second modulation means. At the time of switching, the electrical angle of the phase potential is 0 ° or 180 °.
゜, the waveforms of the respective phase potentials are connected, and the second modulating means narrows the width of the switching pulse added immediately after the switching, and when switching from the second modulating means to the first modulating means. Is an electrical angle 0 ° of the phase potential or
At 180 °, the waveforms of the respective phase potentials are connected, and the second modulating means narrows the width of the switching pulse added immediately before switching.

[Action]

As described above, the fundamental wave components of the output voltage are made to coincide with each other when the modulation means is switched. However, the voltage waveform subjected to the PWM control originally contains many harmonic components.
The transient fluctuation caused by switching between the first modulation means and the second modulation means according to the present invention is caused by the difference in harmonic components included in the two modulation means. Therefore, in both the case of switching from the first modulating means to the second modulating means and the case of switching from the second modulating means to the first modulating means, an electric angle of 0 ° or 180 ° is added to the phase angle output together. By narrowing the pulse width of the switching pulse of the second modulating means, it is possible to smoothly switch the harmonic components.

〔Example〕

FIG. 1 shows a three-phase AC output waveform of an inverter to which the present invention is applied. U, V, and W indicate phase potential waveforms of each phase, U0 indicates a phase voltage of an AC device connected to a load, and U0 and The superimposed broken line indicates the fundamental wave component included in the phase voltage. Ux indicates the difference voltage between the phase voltage U0 and the fundamental wave component for intuitively estimating the dominant component of the harmonic, and Uh indicates the phase voltage waveform separately for the first modulating means and the second modulating means. Is expanded into a ferry series, and the waveforms of the harmonic components obtained by resynthesizing only the fifth and seventh harmonics having a high content ratio among the harmonic components obtained, and X and Y are switching points of each modulation means. . In FIG. 1, a, which represents the pulse width,
b is a pulse width corresponding to the pulse width described in FIGS. 2 and 3, and the pulse width Δt is a pulse width according to the present invention. FIG. 2 shows an output waveform of the first modulating means for performing the highest variable voltage control in normal control. a indicates the switching pulse width added to the electrical angles of 90 ° and 270 °. FIG. 3 shows a second example used to extend the voltage control range.
2 shows an output waveform of the modulation means. b is the electrical angle 0 ° and 180
The switching pulse added to ゜ has the same pulse width. FIG. 4 shows a state in which the first modulation means shown in FIG. 2 is simply switched to the second modulation means shown in FIG. 3, and the switching pulse of each modulation means is in a steady state. In order to maintain the timing.

In FIG. 1, even if the switching is synchronized with the electrical angle of 0 ° or 180 °, the switching timing is possible every 60 ° when the modulating means is switched equally in each phase by three-phase alternating current. Now, assuming that the switching is completed at 0 ° of the U phase, the switching is performed at the 180 ° position of the V phase 60 ° before. The 180-degree timing of the V phase is made narrower than the width of the normal switching pulse of the second modulation means as shown by the oblique line U in FIG. That is, switching is performed with a pulse width narrower by Δt than b in FIG. For U0 and Ux, the state of the timing change is also indicated by hatching. In order for the first modulating means and the second modulating means to match the fundamental wave, the pulse width of the second modulating means is theoretically 694 .mu.S while the pulse width of the first modulating means is 240 .mu.S. At this time, the pulse width changed in order to shift the harmonic components smoothly is approximately 300.
μS. This makes it possible to control the harmonic components as indicated by the arrow in Uh in FIG. The arrow from Uh to the direction from X to Y is the case of switching from the first modulation means to the second modulation means, and the direction from Y to X is the second direction.
Switching from the first modulation means to the first modulation means,
In both cases, the pulse width of the switching pulse added to the second modulation means is changed. In the case of switching at an electrical angle of 0 °, illustration of the same principle is omitted.

〔The invention's effect〕

If the first modulation means and the second modulation means are used merely by switching when the voltage control range is expanded by the PWM control, the transient fluctuation of the output current or torque generated when the modulation means is switched may reduce the capacity of the inverter device. This may be a factor to be evaluated, and there is a possibility that a peripheral device may malfunction or an inverter device may be a noise source due to a steep change of the input current.

The present invention solves the above-mentioned problem by directly controlling the waveform with a value calculated in advance, and can suppress the transient fluctuation with the shortest time measure. As a result, the control performance of the inverter device can be fully utilized, and the capability evaluation of the device can be properly performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a three-phase AC output waveform of an inverter to which the present invention is applied, FIG. 2 is a diagram showing normal PWM control (output waveform of a first modulation means), and FIG. 3 is a voltage control range. FIG. 4 is a diagram showing a PWM control (output waveform of the second modulating means) in the case where the width of the signal is expanded, and FIG. 4 is a waveform diagram showing a conventional switching method between the first modulating means and the second modulating means. U, V, W ... phase potential waveform of each phase, U0 ... phase voltage waveform on the load side, Ux ... difference voltage waveform between phase voltage U0 and fundamental wave component, Uh ...
… A waveform of a harmonic component obtained by resynthesizing only the fifth and seventh harmonics,
a, b… Pulse width, X, Y… Switching point of each modulation means.

Claims (1)

(57) [Claims] 1. An original electric potential is inverted to an electric angle of 90 ° and 270 ° for a phase electric potential output of a high electric potential between 0 ° and 180 ° and a low electric potential between 180 ° and 360 °. A first modulation means for applying a switching pulse so as to apply a phase pulse output having a high potential between 0 ° and 180 ° and a low potential between 180 ° and 360 °. A second modulating means for adding a switching pulse so as to invert the original potential to a predetermined width before and after the center and a predetermined width before and after the electric angle of 180 °, and the first modulation means and the second modulation means. A switching means for switching between the first modulation means and the second modulation means, the switching means comprising: a switching means for switching between the first modulation means and the second modulation means. Connect each phase potential waveform at 0 ° or 180 ° electrical angle, Second modulating means so as to narrow the width of the switching pulse to be added immediately after the switching, also during switching to the first modulating means from the second modulating means, said phase potential of the electrical angle 0 ° or 18
At 0 °, the waveform of each phase potential is connected, and the second
Wherein the modulation means reduces the width of a switching pulse added immediately before switching.