JP3097070B2 - Inverter control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control circuit, and more particularly, to an inverter control circuit configured to supply its output to a system.

[0002]

2. Description of the Related Art An inverter configured to convert DC power into AC power and supply the AC power to a system is provided with a control circuit for preventing waveform distortion due to a change in an output current flowing into the system. I have.

[0003] As shown in FIG. 2, the above-mentioned inverter has a DC power supply 1 and a main converter 2 having four switching elements connected in a bridge and converting DC power from the DC power supply 1 into AC power. And an AC filter 3 for converting an AC current by the AC power into a sine wave, and a system 10 is connected so that the AC power is supplied.

[0004] The above-described inverter control circuit includes:
An inverter output current detector for detecting an output current of the inverter and outputting a value corresponding to the inverter output current;
An inverter output voltage detector 5 that detects the output voltage and outputs an inverter output voltage corresponding value, and a PLL circuit 11 that inputs the inverter output voltage corresponding value and creates a reference signal corresponding thereto. A differential amplifier for inputting the reference signal and the inverter output current corresponding value and generating a control signal for matching the inverter output current corresponding value to the reference signal; And a PWM control circuit 13 for generating a PWM control signal for controlling the two switching elements.

The PWM control signal is converted into a drive signal for driving the switching element by a drive circuit (not shown), and the drive signal is input to a drive input terminal of each switching element. It becomes.

In the above-described inverter control circuit, the time until the reference signal is input to one input terminal of the differential amplifier 12 and the value corresponding to the inverter output current are input to the other input terminal of the differential amplifier 12. Since the generated control signal may become unstable due to the difference between the time and the time required to perform the operation, a resistor R and a capacitor C may be connected between the output terminal of the differential amplifier 12 and one input terminal. Are connected in parallel to prevent the control signal from becoming unstable due to the time difference described above.

[0007]

In the conventional inverter control circuit described above, the reference signal is delayed by utilizing the charging and discharging time of the capacitor C of the integrating circuit of the differential amplifier 12 to stabilize the control signal. However, since the charge and discharge time of the capacitor C changes depending on the amplitude of the reference signal,
When the amplitude of the reference signal is small, that is, when the output current of the inverter is small, the charging / discharging time becomes long, so that an appropriate control signal cannot be created.
As shown by the broken line, there is a problem that the power factor and efficiency of the inverter are reduced.

[0008]

In order to solve the above problems, the present invention detects an output current of an inverter configured to convert DC power from a DC power supply into AC power and to supply the AC power to a system. An inverter output current detector for outputting a corresponding value of an inverter output current, a system current detector for detecting a system current flowing into the system and outputting a system current corresponding value, and an inverter for detecting an output voltage of the inverter. An inverter output voltage detector for outputting an output voltage corresponding value, and inputting the system current corresponding value and the inverter output voltage corresponding value to a control circuit of a switching element constituting the inverter, and each of them is provided at a predetermined period. To calculate the time difference between the zero cross points, and when this time difference is greater than the sampling period,
And a phase correction circuit for generating a correction signal corresponding to the time difference , the correction signal and the inverter output voltage corresponding value, and a system current pair corresponding to the inverter output voltage corresponding value.
A PLL circuit for generating a reference signal having a corresponding phase difference, and a difference for inputting the reference signal and the inverter output current corresponding value and generating a control signal for matching the inverter output current corresponding value to the reference signal. And a PWM for receiving the control signal and controlling the switching element
And a PWM control circuit for generating a control signal.

[0009]

According to the present invention, the phase correction circuit samples the system current corresponding value and the inverter output voltage corresponding value at a constant period, and calculates the time difference between the respective zero cross points.
Is larger than the sampling period, a correction signal corresponding to the time difference is created, and the inverter output voltage is generated by the PLL circuit.
Since the reference signal having the phase difference of the system current corresponding value with respect to the pressure corresponding value is created, even if the amplitude of the reference signal changes, the reference signal is adjusted in accordance with the time difference of the zero cross point, An appropriate control signal can be generated by the differential amplifier.

[0010]

Embodiments will be described below with reference to embodiments.

FIG. 1 is a block diagram of a control circuit for an inverter according to the present invention. Parts having the same functions as in FIG. 2 are denoted by the same reference numerals, and the following description is omitted.

A feature of the present invention is that an inverter 10
A system current detector 6 for detecting a system current flowing into the inverter and outputting a system current corresponding value, and providing the system current corresponding value and an inverter output voltage corresponding value from the inverter output voltage detector 5 to an inverter control circuit. And a phase correction circuit 14 that samples each of them at a fixed cycle, calculates a time difference between the zero cross points, and creates a correction signal corresponding to the time difference.

The phase correction circuit 14 receives a system current corresponding value and an inverter output voltage corresponding value and samples each at a fixed cycle, so that the time difference between the zero cross points is larger than the sampling cycle. If possible, a correction signal corresponding to this time difference can be created.

The sampling cycle is determined on the basis of an allowable phase difference between the output of the inverter and the system and an allowable variation range of the power factor and efficiency with respect to a load variation. Output cycle 3
It is preferable to set it to half or more.

The correction signal is input to a PLL circuit 11 together with a value corresponding to the inverter output voltage from the inverter output voltage detector 5, and a reference signal having a phase difference corresponding to the correction signal is generated by the PLL circuit 11. Therefore, the reference signal corresponds to the phase difference between the system current corresponding value and the inverter output voltage corresponding value.

Then, the reference signal is input to a differential amplifier 12 together with a value corresponding to the inverter output current from the inverter output current detector 4, and the differential amplifier 12 matches the value corresponding to the inverter output current with the reference signal. Since the control signal is generated such that the inverter output current corresponding value matches the system current corresponding value.

Therefore, the control signal is transmitted to the PWM control circuit 1
3, a PWM control signal for controlling the switching element of the main converter 2 is generated, and converted into a drive signal for driving the switching element by a drive circuit (not shown). Is driven, the phase of the output current of the inverter can be made to match the phase of the system current, the output current of the inverter decreases, and the charging and discharging time of the capacitor C of the integrating circuit of the differential amplifier 12 increases. Therefore, even if a difference occurs between the phase of the output current of the inverter and the phase of the system current, a control signal that reduces the difference can be created.

Using the inverter control circuit of the present invention, the inverter was operated to change the load, and its power factor and efficiency were measured. The results were as shown by the solid lines in FIGS. 3 and 4.

FIGS. 3 and 4 show that the inverter control circuit of the present invention does not decrease in power factor and efficiency even when the load is changed.

[0020]

As described above, in the inverter control circuit according to the present invention, even if a difference occurs between the phase of the output current of the inverter and the phase of the system current due to the integration circuit of the differential amplifier, the difference causes a difference in power. Since the rate and efficiency do not decrease, it is suitable for an inverter control circuit configured to supply the inverter output to the system.

[Brief description of the drawings]

FIG. 1 is a block diagram of a control circuit of an inverter according to the present invention.

FIG. 2 is a block diagram of a conventional inverter control circuit.

FIG. 3 is a diagram comparing a power factor of a control circuit of the present invention with respect to a load change and a power factor of a conventional control circuit.

FIG. 4 is a diagram comparing the efficiency of the control circuit of the present invention with respect to load fluctuation and the efficiency of a conventional control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Main conversion part 3 AC filter 4 Inverter output current detector 5 Inverter output voltage detector 6 System current detector 10 System 11 PLL circuit 12 Differential amplifier 13 PWM control circuit 14 Phase correction circuit

Claims (1)

(57) [Claims] An inverter configured to convert a DC power from a DC power supply into an AC power and to supply the AC power to a system, to detect an output current of the inverter and to output an inverter output current corresponding value; A system current detector that detects a system current flowing into the system and outputs a system current corresponding value, and an inverter output voltage detector that detects an output voltage of the inverter and outputs an inverter output voltage corresponding value. The system current corresponding value and the inverter output voltage corresponding value are input to a control circuit of a switching element constituting the inverter, and each is sampled at a constant cycle to calculate a time difference between respective zero cross points. When the time difference is larger than the sampling period
And a phase correction circuit for generating a correction signal corresponding to the time difference , the correction signal and the inverter output voltage corresponding value, and a system current pair corresponding to the inverter output voltage corresponding value.
A PLL circuit for generating a reference signal having a corresponding phase difference, and a difference for inputting the reference signal and the inverter output current corresponding value and generating a control signal for matching the inverter output current corresponding value to the reference signal. And a PWM for receiving the control signal and controlling the switching element
And a PWM control circuit for generating a control signal.