JPH0570386B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter device that converts DC voltage to AC voltage, and particularly relates to an inverter device suitable for converting DC voltage obtained from solar cells or fuel cells into AC voltage close to a sine wave. It is something.

Recently, various systems for effectively utilizing solar energy have been studied. As one of these, power supply systems are being developed that convert solar energy into electricity and supply it to consumers.When using solar cells in this type of system,
It is necessary to convert the DC voltage obtained from the solar cells into AC voltage using an inverter device. Further, a power supply system using fuel cells is also being researched, but this system also requires an inverter device. A conventionally known inverter device generates high frequency pulses whose pulse width is modulated in a sinusoidal waveform by turning DC voltage on and off with a switching element, and obtains a sinusoidal AC voltage by passing this high frequency pulse through a filter circuit. Some use pulse width modulation (PWM). However, this inverter requires a filter with a large power capacity in order to pass high-frequency pulses with high peak values through the filter circuit, which has the drawback of increasing power loss in the filter and lowering conversion efficiency.

Therefore, as seen in JP-A No. 56-86077,
By creating a plurality of currents having waveforms obtained by cutting both ends of a rectangular wave into a pulse shape, and superimposing the plurality of currents with a predetermined phase difference, the average value of the whole becomes stable. An inverter device has been proposed that outputs a waveform output having a shape.

However, in order to make the output waveform closer to a sine wave with this inverter device, it is necessary to create and synthesize a large number of currents that have a waveform in which both ends of a rectangular wave are pulsed and cut, making the device configuration complicated. There was a problem.

In addition, in this inverter device, no matter how many currents are combined, the output waveform is trapezoidal, so the deviation from the sine wave becomes large at the top of the output waveform, and the high frequency components increase accordingly. There was a problem. An object of the present invention is to provide an inverter device that can efficiently convert the DC voltage of a battery unit such as a solar cell or a fuel cell into a sinusoidal AC voltage with a simple configuration.

The present invention relates to an inverter device that converts a DC voltage obtained from a battery unit into a substantially sinusoidal low-frequency AC voltage. A step waveform generation circuit generates a low frequency step waveform voltage that changes in a stepwise manner along the direction of the step waveform voltage; , a voltage synthesis circuit that superimposes a high-frequency pulse voltage on a stepped waveform voltage, and a filter circuit that converts the output voltage of the voltage synthesis circuit into a substantially sinusoidal AC voltage. The high frequency pulse voltage superimposed on each part of the step waveform voltage is pulse width modulated so as to correspond to the difference between each part of the step waveform voltage and each part of the AC voltage waveform to be converted.

As described above, a step waveform voltage that changes stepwise along the sine waveform of the AC voltage to be converted is generated, and the difference between each part of this step waveform voltage and each part of the AC voltage waveform to be converted is By superimposing a correspondingly pulse width-modulated high-frequency pulse voltage on each part of the stepped waveform voltage, an AC voltage waveform that approximates a sine wave can be obtained. The harmonic components of the input voltage to the filter circuit can be reduced compared to a pulse width modulation method in which a sinusoidal AC voltage is obtained by passing the obtained high-frequency pulse through a filter circuit.

In addition, by generating a step waveform voltage that approximates a sine wave voltage and superimposing a pulse voltage on this step waveform voltage, a high frequency pulse can also be superimposed on the top of the step waveform voltage. Compared to the case where the waveform is approximated by a trapezoidal waveform, the input waveform of the filter circuit can be made closer to a sine wave, and the harmonic components of the input voltage of the filter circuit can be reduced. Therefore, an AC output voltage without waveform distortion and with few harmonic components can be obtained.

Furthermore, as mentioned above, if a step waveform voltage that approximates a sine wave is obtained and a high frequency pulse voltage is superimposed on this step waveform voltage, there is no need to provide many circuits to generate high frequency pulses. , the circuit configuration of the inverter device can be simplified.

The inverter device of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the basic configuration of the present invention, in which 1 is a battery unit of a solar cell, and 2 is a DC voltage obtained from battery unit 1.
a step waveform generation circuit that receives E _d as an input and generates a low frequency step waveform voltage V _S that changes stepwise along a waveform close to the waveform of the alternating current voltage e ₀ to be converted;
3 is a high frequency generator that receives the DC voltage E _d as input and outputs a high frequency pulse that needs to be superimposed on the step waveform voltage V _S in order to approximate the waveform of the AC voltage e ₀ to be converted _. This is a pulse generation circuit. 4 is a voltage synthesis circuit that superimposes the high-frequency pulse voltage V _P on the stepped waveform voltage V _S , and 5 is a filter circuit that shapes the high-frequency pulse superimposed waveform obtained from the voltage synthesis circuit 4 and converts it into a sinusoidal AC voltage waveform _e0 . It is.

The stepped waveform generation circuit 2 is a type of pulse amplitude modulation (PAM) circuit, which generates rectangular wave voltages with various peak values obtained by turning on and off the DC voltage E _d using switching elements such as thyristors, transistors, and field effect transistors. Figure 2B is obtained by synthesizing
The sinusoidal AC voltage to be converted as shown in e is a stepped waveform voltage that changes stepwise along a waveform close to ₀ .
Outputs V _S. To obtain this stepped waveform voltage V _S, for example, as shown in FIG. 2B, a sine wave AC voltage e ₀
The period of each half cycle of the appropriate number of periods T ₁ to T ₇
(T ₁ = T ₇ , T ₂ = T ₆ , T ₃ = T ₅ ) and lasts from the end time t ₁ of the first period T ₁ to the end time t ₆ of the sixth period T ₆ Wave voltage υ _S1 and second period T ₂
A square wave voltage υ _S2 that lasts from the end time t ₂ of the fifth period T ₅ to the end time t ₅ of the third period T 3 and from the end time t ₃ of the third period T ₃ to the end time t ₄ of the fourth period T ₄ This can be obtained by generating a square wave voltage υ _S3 that lasts until 2000, and then superimposing these square wave voltages υ _S1 to υ _S3 having different generation times and widths. Also, the pulse width
A square wave pulse with a peak value of A ₁ at T ₂ and a pulse width of
A square wave pulse with a peak value of A ₂ at T ₃ and a pulse width of
A square wave pulse with a peak value of A ₃ (>A ₂ >A ₁ ) at T ₄ ,
A square wave pulse with a pulse width of T ₅ and a peak value of A ₂ ,
Similarly, the stepped waveform voltage V _S can be obtained by sequentially generating rectangular wave pulses having a pulse width of T ₆ and a peak value of A ₁ at times t ₁ to _{t 5} . By inverting the polarity of the voltage and doing the same thing, it is possible to obtain a stepped waveform voltage that approximates the negative half cycle of the sinusoidal AC voltage e ₀ .
Regardless of which method is used to obtain the stepped waveform voltage V _S , this voltage V _S does not need to change exactly along the waveform of the AC voltage e ₀ to be converted, but must be close to the AC voltage e ₀ . Any material that changes along the waveform may be used.

The high frequency pulse generating circuit 3 is a pulse width modulation (PWM) circuit, and this circuit synchronizes with the stepped waveform generating circuit 2 to generate the above T ₁ , T ₂ ,...T _{7 .}
each period (these periods are the step waveform generation circuit 2
is set within. ), the pulse width is modulated such that the width of each pulse corresponds to the difference between the area inside the waveform of the AC sinusoidal voltage e ₀ and the area inside the waveform of the stepwise waveform voltage _VS. A high frequency pulse V _p as shown in A is generated. The frequency of this high-frequency pulse voltage V _p is set to approximately 100 times the frequency of the AC voltage e ₀ to be converted.

The voltage synthesis circuit 4 superimposes the high frequency pulse voltage V _p on the stepped waveform voltage V _S to generate a voltage having a waveform as shown in FIG. 3. When the outputs of the stepped waveform generation circuit 2 and the high frequency pulse generation circuit 3 are obtained from an output transformer,
The voltage combining circuit can be constructed by connecting the secondary windings of the output transformers of both circuits in series. Furthermore, the stepped waveform voltage V _S and the high-frequency pulse voltage V _p can also be combined directly or via a semiconductor element.

The filter circuit 5 is composed of an inductance, a capacitor, etc., and removes harmonic components from the output of the voltage synthesis circuit 4, and outputs a sinusoidal AC voltage. When the superimposed waveform shown in FIG. 3 passes through the filter circuit 5, the high-frequency pulse portion fills the stepped portion of the stepped waveform, so the output voltage has a waveform close to a sine wave as shown by the solid line in FIG. e ₀ can be obtained, and a sinusoidal AC voltage with less waveform distortion can be obtained.

As mentioned above, if we obtain a step-like waveform voltage V _S that changes along a waveform close to that of a sine-wave AC voltage, and then make it approximate to a sine-wave AC voltage waveform by superimposing a high-frequency pulse on it, we can generate a high-frequency The peak value of the pulse can be lowered, and the frequency of the high-frequency pulse can be increased. Therefore, a filter circuit with a small capacity can be used, and power loss in the filter circuit can be reduced. Generally, the power loss of a filter is approximately constant with respect to changes in its load factor, so if the power loss can be reduced as described above, the power loss at low load factors can be significantly reduced. , economical.

In the above explanation, the half cycle of the sine wave AC voltage is divided into seven periods T ₁ to _{T 7} , but this number of divisions is arbitrary, and increasing the number of divisions (the number of stages of the stepped waveform) will make the sine wave more Of course, you can get closer.

Furthermore, it is possible to adjust the converted AC voltage value by controlling the width of the high-frequency pulse, and by controlling the width of each step of the stepped waveform in coordination with the width of the high-frequency pulse. The AC voltage value can also be adjusted.

As described above, according to the present invention, a step waveform voltage that changes stepwise along a sine waveform is generated, and the difference between each part of the step waveform voltage and each part of the AC voltage waveform to be converted is By superimposing a correspondingly pulse width-modulated high-frequency pulse voltage on each part of the stepped waveform voltage, an AC voltage waveform that approximates a sine wave was obtained. Compared to a pulse width modulation method in which a sinusoidal AC voltage is obtained by passing the obtained high-frequency pulse through a filter circuit, harmonic components of the input voltage to the filter circuit can be reduced. Furthermore, according to the present invention, a high-frequency pulse can also be superimposed on the top of the stepped waveform voltage, so the input voltage waveform of the filter circuit can be made into a more sinusoidal wave than when a sine wave is approximated by a trapezoidal waveform. It is possible to obtain an AC output voltage with less waveform distortion and less harmonic components.

Furthermore, according to the present invention, a stepped waveform voltage that approximates a sine wave is obtained and a high frequency pulse voltage is superimposed on this stepped waveform voltage, so it is not necessary to provide a large number of circuits for generating high frequency pulses. Therefore, the circuit configuration of the inverter device can be prevented from becoming complicated.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic configuration of the present invention, Fig. 2 A and B are waveform diagrams for explaining the operation of the inverter shown in Fig. 1, and Fig. 3 shows the filter circuit in the inverter shown in Fig. 1. FIG. 3 is a waveform diagram showing the waveform of an input voltage. DESCRIPTION OF SYMBOLS 1... Battery unit, 2... Staircase waveform generation circuit, 3... High frequency pulse generation circuit, 4... Voltage synthesis circuit, 5... Filter circuit.

Claims (1)

[Scope of Claims] 1. In an inverter device that converts a DC voltage obtained from a battery unit into a substantially sinusoidal low-frequency AC voltage, the DC voltage is input and a step is applied along a waveform close to the waveform of the AC voltage to be converted. a high-frequency pulse generation circuit that receives the DC voltage as an input and generates a high-frequency pulse voltage that is superimposed on each part of the stepped waveform voltage; a voltage synthesis circuit that superimposes the high-frequency pulse voltage on the step waveform voltage; and a filter circuit that converts the output voltage of the voltage synthesis circuit into a substantially sinusoidal alternating voltage; The inverter device is characterized in that the high frequency pulse voltage to be converted is pulse width modulated so as to correspond to the difference between each part of the stepped waveform voltage and each part of the AC voltage waveform to be converted.