JPH0811067Y2 - Inverter control circuit - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a control circuit for an inverter controlled by PWM.

(Problems to be Solved by Prior Art and Invention) FIG. 4 is a block diagram illustrating a conventional inverter control circuit. In the figure, the direct current of the direct current input DC is converted into alternating current by the inverter circuit INV, and the sine wave alternating current is output to the alternating current output AC by the alternating current filter ACFIL including the inductor L and the capacitor C. In this DC-AC conversion, the current signal Ic of the capacitor C of the AC filter ACFIL is added to the output voltage signal Vac to detect these detection signals Vac and Ic.
And the reference sine wave Vr are compared and amplified by the comparison and amplification circuit AMP, and the sine wave signal V _s obtained is input to the PWM generation circuit PWM.
The PWM signal V _pwm is obtained and input to the driver circuit DR1 that generates a signal for controlling the switching element (not shown) of the inverter circuit INV, and the output thereof controls the switching element. When this control technology is applied, AC filter ACFIL L
C series resonance can be suppressed, AC filter ACFIL can be designed easily, and the gain of the feedback loop can be kept constant up to the high frequency range, making it very suitable for controlling the output voltage waveform of the inverter INV. ing.

However, with the conventional technology, the current signal Ic of this capacitor C is
Increase the feedback amount of the
When the gain of P is increased, the ripple superimposed on the sine wave signal V _s of the output of the comparison and amplification circuit AMP becomes large, and the rising and falling slopes become larger than the slope of the carrier triangular wave. As shown in FIG. 6C, the PWM signal is generated at a frequency higher than the carrier frequency, and the stable operation of the main switching element cannot be performed.

Further, it will be described in detail with reference to FIG. In the figure, (A), (B) and (C) show the waveforms when the gain of the comparison and amplification circuit AMP is increased in order, and (a) is a part of the sine wave signal V _s (for example, 50 Hz). Waveform,
(B) is a PWM control carrier triangular wave (for example, 2 KHz). A PWM signal (C) is generated at X ₁ and X ₂ where the sine wave signal (a) and the carrier triangular wave (b) intersect.
However, as shown in FIG. 7C, when the gain of the comparison amplifier circuit AMP is increased, the ripple (due to high frequency vibration due to PWM control) superimposed on the sine wave signal V _s is increased, and the carrier triangular wave (b). During the half cycle of
An intersection with the sine wave signal (a) is generated according to the vibration of the ripple, and the PWM signal (C) appears randomly as shown in FIG. 7C, which makes the control of the inverter INV unstable.

An object of the present invention is to provide a stable inverter control circuit in order to solve the above problems.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention adds a current signal of a capacitor forming an AC filter to an output voltage signal of an inverter, and compares and amplifies this signal with a reference sine wave. Comparator amplifier, PWM generator circuit to generate PWM signal and
In an inverter control circuit including a driver circuit that drives a main switching element of an inverter with a signal from the PWM generation circuit, between the PWM generation circuit and the driver circuit, an output from the PWM generation circuit and a carrier triangular wave An inclusive or circuit that inputs signals of the same frequency in synchronization with each other, an output obtained by inverting the output from the inclusive or circuit, and a signal of the same frequency in synchronization with the carrier triangular wave are provided. The gist of the invention is an inverter control circuit characterized in that a signal shaping circuit having a flip-flop is provided.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings. Needless to say, the embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the invention.

FIG. 1 is a block diagram showing an embodiment of the present invention.
As in the past, the DC of the DC input DC is converted to the inverter circuit INV
Is converted into alternating current with and is output to alternating current output AC as a sine wave with alternating current filter ACFIL. The output voltage signal Vac and the current Ic of the capacitor C of the AC filter ACFIL are added and input to the comparison and amplification circuit AMP. Further, the reference sine wave V _r is input to the comparison amplification circuit AMP, and the sine wave signal V _s is output. This sine wave signal V _s generates a PWM signal V _pwm by the PWM generation circuit PWM, inputs the PWM signal V ′ _pwm shaped by the signal shaping circuit N to the driver circuit DRI, and drives the inverter circuit by the driver circuit DRI. PWM control of INV switching element. In this embodiment, only one signal shaping circuit N is provided at the rising slope and falling slope of the carrier triangular wave (b) described in the conventional example of FIG. 5A, that is, in one cycle of the carrier triangular wave (b). Shape to output the PWM signal of.

Next, FIG. 2 shows an embodiment of the signal shaping circuit,
FIG. 3 shows a waveform diagram for explaining the operation of the signal shaping circuit.
In these figures, the inclusive or circuit EX
The signal V _{f of the} same frequency is input to the OR in synchronization with the PWM signal V _pwm and the carrier triangular wave, and the inverted signal of the output is input to the CP terminal of the flip-flop F / F circuit and the terminal of the flip-flop circuit F / F. Shaped PWM by inputting signal V _f to D
Obtain the signal _V'pwm . That is, the signal shaping circuit can be configured by a flip-flop circuit that inputs a digital signal of an equal frequency synchronized with the carrier triangular wave as data and uses the PWM signal as a clock. In FIG. 3, (a) is a sine wave signal, (b) is a carrier triangular wave, and (c ') is a shaped PW.
The M signal and V _f are signals of equal frequency in synchronization with the carrier triangular wave.

(Effect of the invention) The present invention adds a current signal of a capacitor that constitutes an AC filter to an output voltage signal of an inverter, compares the signal with a reference sine wave, and amplifies the signal, and a PWM generator that generates a PWM signal. In an inverter control circuit comprising a circuit and a driver circuit that drives a main switching element of an inverter with a signal from the PWM generation circuit,
Between the PWM generator circuit and the driver circuit, an output from the PWM generator circuit, an ink exclusive OR circuit that inputs a signal of the same frequency in synchronization with the carrier triangular wave, and from the ink exclusive OR circuit By providing a signal shaping circuit having an inverted output of the carrier triangle wave and a flip-flop that is synchronized with the carrier triangular wave and to which a signal of the same frequency is given, each of the rising slope and the falling slope of the carrier triangular wave is provided. In order to correct the changes in the signal of the PWM generation circuit multiple times during the period, that is, to shape so that only one PWM signal is output in one cycle of the carrier triangular wave, (a) AC filter By increasing the amount of current in the capacitor in The PWM signal generated at a frequency higher than the carrier frequency can be suppressed from being output to the driver circuit, and the current amount of the capacitor can be increased or the gain can be increased while the main switching element is operating stably. The response characteristics can be improved.

(B) The main switching element can be stably operated with respect to noise coming from the outside even if the comparison and amplification circuit malfunctions.

And so on.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a signal shaping circuit, and FIG. 3 is a waveform diagram explaining the operation of the signal shaping circuit. FIG. 4 is a block diagram showing a conventional inverter control circuit, and FIG. 5 is a waveform diagram explaining the operation of the conventional control circuit. DC …… DC input AC …… AC output INV …… Inverter circuit ACFIL …… AC filter AMP …… Comparison amplifier circuit PWM …… PWM circuit N …… Signal shaping circuit DRI …… Driver circuit

Claims (1)

[Scope of utility model registration request] 1. A comparison amplifier for adding a current signal of a capacitor forming an AC filter to an output voltage signal of an inverter, comparing the signal with a reference sine wave, and amplifying the signal, a PWM generation circuit for generating a PWM signal, and the PWM. In an inverter control circuit including a driver circuit that drives a main switching element of an inverter with a signal from a generation circuit,
Between the PWM generator circuit and the driver circuit, an output from the PWM generator circuit, an ink exclusive OR circuit that inputs a signal of the same frequency in synchronization with the carrier triangular wave, and from the ink exclusive OR circuit An inverter control circuit comprising: a signal shaping circuit having an inverted output of the above-mentioned output and a flip-flop synchronized with the carrier triangular wave and given a signal of the same frequency.