JPH0465564B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a device for converting direct current into an arbitrary voltage waveform, and more particularly to a device suitable for direct current to alternating current conversion. Prior art Let f ₁ (x) and f ₂ (x) be functions of the transformation x, and let a be a constant, f ₁ (x) = af ₂ (x)... (1) ^x0 ₀ f ₁ (x)・dx = ^x0 ₀ af ₂ (x)・dx=a ^x0 ₀ f ₂ (x)・dx…… (2) If equation (1) holds, regardless of the value of x ₀
Equation (2) holds true. Furthermore, when equation (2) holds regardless of the value of x ₀ , equation (1) holds. This is known as a mathematical theory. In equation (2), ^x0 ₀ f ₁ (x)dx
and ^x0 ₀ f ₂ (x) dx are 0 of f ₁ (x) and f ₂ (x), respectively.
is the area from to x ₀ . Therefore, regardless of the value of x ₀ , if the area from 0 to x ₀ is equal, then f ₁ (x) and
f ₂ (x) is the same function, ie, the same waveform. Further, the constant a is a coefficient representing the amplitude of the waveform regardless of the waveform of the function, and is also a coefficient representing a multiple of the area. Based on the above idea, when obtaining the specific voltage waveform 1 shown in FIG. 1 using the conventional method, a rectangular wave control pulse train shown in (2) was formed. That is, any function af ₂ (θ)
In order to obtain waveform 1, a function f ₁ approximated to waveform 1
The rectangular wave control pulse train 2 was determined so as to obtain (x). By the way, in order to obtain the rectangular wave control pulse train 2 shown in FIG. 1 using the conventional method, it was necessary to prepare integral waveforms 3, 4, 5, and 6 shown in FIG. 2.
Waveform 3 in FIG. 2 is the integral value of waveform 1 in FIG. 1, ie af ₁ (θ)·dθ, and waveform 4 is the integral value of rectangular wave control pulse train 2 in _FIG. )・dθ, waveform 5 is a value obtained by shifting waveform 3 in the positive direction by a constant value α, that is, af ₁ (θ)・dθ+α, and waveform 6
is a value obtained by shifting waveform 3 in the negative direction by a constant value α, that is, af ₁ (θ)·dθ−α. When forming the control pulse train 2 in FIG. 1 based on the four waveforms 3, 4, 5, and 6 in FIG. let As is clear from the above, the conventional method requires many integral waveforms, making the conversion complicated. In addition, in order to continuously change the output voltage, it is necessary to change the value of the coefficient a continuously, and in order to achieve this control, it is necessary to change the value of the coefficient a continuously, regardless of whether analog technology or digital technology is used. The control system is relatively complex and expensive. OBJECT OF THE INVENTION Therefore, an object of the present invention is to provide a device that can easily convert direct current into any voltage waveform. Composition of the Invention To achieve the above object, the present invention is a device for converting a DC voltage into a specific voltage waveform, which is formed so as to sequentially send out unit rectangular waves at a constant cycle, and in which the unit rectangular waves are a unit rectangular wave generating circuit having means for changing the pulse width of the unit rectangular wave, and a digital circuit for obtaining a control pulse train in which the unit rectangular wave is distributed so as to obtain an integral waveform approximately equal to the integral waveform of the specific voltage waveform. a memory that stores signals in advance; a logic circuit that sends out the control pulse train based on the output of the unit rectangular wave generation circuit and the digital signal obtained from the memory; and the control that is sent out from the logic circuit. a switching circuit that intermittents the DC voltage in response to a pulse train;
The present invention relates to a device for converting direct current into an arbitrary voltage waveform, comprising means for controlling means for changing the pulse width of the unit rectangular wave generation circuit when changing the voltage of the specific voltage waveform. Effects of the Invention According to the present invention, a control pulse train is formed by the logic of a unit rectangular wave sent out at a constant cycle from a unit rectangular wave generation circuit and a digital signal sent out from a memory, and based on this A specific voltage waveform is obtained by intermittent DC voltage. Also, by changing the pulse width of the unit rectangular wave, the voltage of the specific voltage waveform is changed. Therefore, various specific voltage waveforms having different voltage values can be easily obtained. Embodiment FIGS. 3 and 4 show a method of converting direct current into an arbitrary voltage waveform according to an embodiment of the present invention. The specific voltage waveform 7 in FIG. 3 is the same as the waveform 1 in FIG. 1, and shows the 0 to 90 degree section of the waveform of sin θ + 0.5 sin 3 θ. The control pulse train 8 is for obtaining a specific voltage waveform 7,
Consists of pulses P ₁ to P ₁₃ . Pulse P ₁ , P ₂ , P ₈ ~
P ₁₃ is a unit rectangular wave with a height h and a width w, but pulses P ₃ and P ₇ are collective waves of two unit rectangular waves and have a width 2w, as is clear from the division by dotted lines. Further, pulses P ₄ and P ₆ are collective waves of three unit rectangular waves and have a width of 3w, and pulse P ₅ is a collective wave of 10 unit rectangular waves and has a width of 10w.
Note that the interval between the rising points of each pulse is also set to an integral multiple of the unit interval of the rising points, and in this embodiment, the distance from 0 degrees to the rising edge of the first pulse _P1 is 6 degrees,
The rising interval between P ₁ and P ₂ is 6 degrees, the rising interval between P ₂ and P ₃ is 4 degrees, and the rising interval between P ₃ and P ₄ is 6 degrees, and so on. It is set. Note that the minimum rising unit interval corresponds to the case of a collective wave, and coincides with the pulse width w. The control pulse train 8 set in this way becomes a control signal for the switching element for intermittent direct current, and when the switching element turns on and off in response to the control pulse train 8 shown in FIG. 3, its output voltage waveform also follows the control pulse train. By passing the smoothing circuit,
A waveform that approximates the specific voltage waveform 7 in FIG. 3 can be obtained. The control pulse train 8 shown in FIG. 3 is formed by the method shown in FIG. 4. In FIG. 4, waveform 9 is an integral value of specific voltage waveform 7 of FIG. 3, and waveform 10 is an integral value of control pulse train 8 of FIG. In short, the integral waveform 10 of the control pulse train 8 is determined to approximate the integral waveform 9 of the specific voltage waveform 7, and the control pulse train 8 is determined to be a unit rectangular wave and/or
Alternatively, the width and distribution of each pulse P ₁ to P ₁₃ are determined so as to form a collective wave thereof. Next, how closely does a waveform consisting of an array of unit rectangular waves approximate the waveform of a given arbitrary function? Also, if the width of the unit rectangular wave is changed, only the amplitude changes and the waveform hardly changes. I will explain about it. The functions of waveform 1 in FIG. 1 and waveform 7 in FIG. 3 are both sinθ+0.5sin3θ. The rectangular wave control pulse trains that approximate this are 2 in Figure 1 and 8 in Figure 3, and the amplitudes of each harmonic when the waveforms of pulse trains 2 and 8 are expanded into a Foury series are shown in Table a.
and b. Furthermore, Table c shows values obtained by expanding the waveform into a Foury series when the width of each unit rectangular wave of the control pulse train 8 in FIG. 3 is halved. Table d shows the values when the width of the unit rectangular wave is reduced to 1/10 in the same way. Furthermore, if the width of the unit rectangular wave is halved or 1/10, the aggregate wave is completely divided into unit rectangular waves so that the dotted line portion of the aggregate wave pulses P ₃ to _{P 7} becomes the rising edge of the unit rectangular wave. Ru. The values shown in Table b are the values when the width of the unit rectangular wave, that is, w, is set to 2 degrees in phase.If this width is made smaller and the arrangement of the unit rectangular waves is subdivided, the approximation will be even better. .

[Table] The amplitudes of harmonics in this table are expressed as a ratio of 100 to the amplitude of the first harmonic, and the remaining third to 27th harmonics. Therefore, tables a, b, c, d
The amplitudes of the first harmonics in Tables a and b are not necessarily equal; if the amplitudes of the first harmonics in Tables a and b are set to 100, the amplitude of the first harmonics in Table c is 49.9, and the amplitude of the first harmonics in Table d is The amplitude of is 10. Each harmonic component of the conventional control pulse train 2 shown in Table a and the control pulse train 8 according to the present invention shown in Table b
As is clear from the comparison with the harmonic components of , the two are extremely similar. That is, by the method of the present invention, it is possible to obtain a specific voltage waveform with almost the same accuracy as the conventional method. Also, as is clear from the comparison between Table b showing the case where the width w of the unit rectangular wave is 100%, Table c showing the case where the width is 50%, and Table d showing the case where the width is 10%, Even if the width of the unit rectangular wave is changed, the proportion of harmonic components does not change. Therefore, it is possible to keep the waveform approximate and change only the amplitude, that is, the output voltage. This effect occurs because the unit rectangular waves are arranged and their rising phases are fixed. Although the control pulse train 2 in FIG. 1 and the control pulse train 8 in FIG. 3 are shown up to 90 degrees,
If the waveform between 180 degrees is made symmetrical about 90 degrees, even harmonics will not occur. FIG. 5 shows a conversion circuit according to an embodiment in which the control pulse train is simplified to simplify the explanation, and FIG. 6 is a diagram showing the states of each part in FIG. 5. In FIG. 5, 11 is an integral voltage input terminal, which in this embodiment is a terminal that supplies a DC voltage corresponding to the input voltage of the inverter. The voltage supplied from this input terminal 11 is sent to a sawtooth wave generation circuit 12, and then supplied to an integrating capacitor 14 via an operational amplifier 13, where it is integrated. Since a discharging transistor 15 is connected in parallel to the capacitor 14, the transistor 15 is turned on and off.
A sawtooth wave V _A shown in FIG. 6 is generated in synchronization with the off period. 16 is an output frequency instruction voltage input terminal, and the instruction voltage supplied therefrom is converted into a frequency signal by the V-F converter 17, and pulses are generated at a period corresponding to the instructed frequency. The output pulse of the V-F converter 17 is input to the counter 18 as a clock pulse and is also input to the base of the transistor 15. In the example shown in Figure 6, 18 pulses are generated at a period of θ _s = 20° during the period from 0° to 360°, and 18
Sawtooth waves V _A are generated. A voltage comparator 19 generates a comparison output between the control voltage V _R applied from the control voltage input terminal 20 and the sawtooth wave V _A. As is clear from V _P in FIG. 6, this embodiment generates a comparison output V _P that is at a high level during a period in which the sawtooth wave V _A is lower than the control voltage _VR . That is, the period θ _{s is} from 0° to 360° in Figure 6.
18 unit rectangular wave pulse outputs V _P are generated.
Therefore, in the embodiment shown in FIG. 5, the unit rectangular wave generating circuit 2
1 is configured. 22 is a memory, which outputs the unit rectangular wave in Fig. 6.
Based on V _P , the control pulse trains V ₁ and V ₂ of FIG.
It stores digital signals for forming . As is clear from the address column in Figure 6, this memory 22 has a total of 19 addresses from 0 to 18.
A reset signal is stored in address 18, and a reset signal for counter 18 is generated from line _M4 at the moment of switching to address 18.
The address switches to zero. In addition, each address 0 to 18
stores 4-bit data as shown by M- _M4 in FIG. 6, and this data is read out through four output lines _M1 - _M4 corresponding to the 4-bits. memory 1
Data reading from 1 is performed using the same clock as the period θ _s of the sawtooth wave V _A . That is, the addresses are sequentially designated by the counter 18. 23 and 24 are the first pulses for obtaining the control pulse train.
and a second AND circuit, one input terminal of the first AND circuit is connected to the comparator 19,
The other input terminal is the first output line of the memory 22.
_One input terminal of the second AND circuit 24 is connected to the comparator 19, and the other input terminal is connected to the second output line _M2 of the memory 22. The outputs of M ₁ to M ₄ in Figure 6 are θ _s = 20
A low level L or high level H output is sent out in each division period. Therefore, when the AND circuits 23 and 24 calculate the AND of the output V _P of the comparator 19 in FIG. 6 and the memory outputs M ₁ and M ₂ , the first and second control pulse trains V ₁ , V ₂ is obtained. The first and second control pulse trains V ₁ and V ₂ are
Since it is obtained based on the unit rectangular wave indicated by V _P , it is a pulse train in which unit rectangular waves are arranged. Transistors Q ₁ , Q ₂ , Q ₃ , and Q ₄ in FIG. 5 constitute a bridge inverter, which cuts the voltage of the DC power supply E intermittently. The output of the first AND circuit 23 is coupled to the bases of transistors _Q1 and _{Q4, and the output of the first AND circuit 23 is coupled to the bases of transistors Q1 and Q4} .
The output of AND gate 24 is connected to transistors Q ₂ and Q ₃
is coupled to the base of output terminals 25, 2 in response to the control pulse trains V ₁ and V ₂ of FIG.
6, an output voltage indicated by V ₀ in FIG. 6 is obtained.
The output voltage V ₀ can be made into a waveform approximating a sine wave by the smoothing circuit or the smoothing effect of the load itself. The output line M ₃ of the memory 22 is coupled to the base of a transistor 28 which is connected in parallel to the resistor 27 of the control voltage input terminal 20 line. Therefore, when the outputs shown in FIG. 6 are sequentially generated from the memory output line _M3 , the transistor 28 is turned on and off accordingly, and the value of the control voltage _VR changes. Therefore, it becomes possible to change the width of the output pulse at a specific position. Note that when there is no need to change the control voltage _VR , the value of the memory output line _M3 is always kept constant. Since the circuit of FIG. 5 has a comparator 19, by changing the control voltage _VR ,
The magnitude of the output voltage V ₀ can be adjusted.
FIG. 7 shows this voltage adjustment. When the control voltage V _R moves to the top of the sawtooth wave V _A in FIG. 7A, the output voltage V ₀ in FIG. 7B is obtained, and V _R
If is located in the middle of V _A , the output voltage in Figure 7C
V ₀ is obtained. As is clear from the comparison between B and C in Figure 7, in the case of the maximum output voltage, a collective wave of two unit rectangular waves is included, and when the output voltage is lowered below this, the collective wave contains two unit rectangular waves. Split into square waves. Figure 7C shows the output when the rising phase of each unit rectangular wave is fixed and the falling phase is controlled, and Figure 7D shows the output when the rising phase of each unit rectangular wave is fixed and the rising phase is controlled. shows the output of Even with the method of fixing the falling phase in FIG. 7D,
It is possible to obtain the same effect as the method of fixing the rising phase layer. As is clear from the above, this embodiment has the following advantages. (a) As shown in FIG. _{6 ,} the control pulse train is formed by arranging unit rectangular waves, so the control pulse train can be easily obtained. (b) Since the interval between the rising points of the unit rectangular waves is set to an integral multiple of the unit interval θ _s , it is easy to form the control pulse train and control the switching of the inverter. (c) The rising phase of each unit rectangular wave is always constant regardless of the output voltage and output frequency, and the interval between the rising points is an integral multiple of θ _s . It can be configured very easily using analog technology. Furthermore, the pulse width after the rise can be easily controlled, and the output voltage V ₀ can be adjusted without changing the waveform. (d) Since this embodiment is configured to supply the DC voltage of the inverter power supply E to the input terminal 11, it is possible to limit fluctuations in the inverter output voltage due to fluctuations in the inverter input voltage. That is, when the input voltage decreases, for example, the input voltage of the integrating capacitor 14 also decreases, and the slope of the sawtooth wave V _A shown in FIG. 6 becomes gentler. As a result,
The pulse width of the inverter output voltage becomes wider. However, since the input voltage has decreased and the amplitude of the output pulse has become smaller, the area of the output pulse remains approximately constant, and there is substantially no variation in the output voltage or variation in the harmonic components. Such an operation also occurs when the inverter power supply E supplies a pulsating voltage. Therefore, there is a great advantage that voltage fluctuations including input voltage pulsations do not appear on the output side. (e) Since the width of a specific pulse can be controlled by switching the level of the control voltage V _R using the memory output line M ₃ , control that improves the approximation to a sine wave can be easily achieved. Modifications Although the embodiments of the present invention have been described above, the present invention is not limited thereto, and for example, the following modifications are possible. (A) In FIG. 5, the voltage V _R supplied from the control voltage input terminal 20 to the comparator 19 may be used as a constant reference voltage, and the voltage supplied from the input terminal 11 may be used as the output voltage command voltage. That is, the width of the inverter output pulse may be changed by changing the slope of the sawtooth wave V _A in FIG. 6 according to the output voltage. (B) The voltage at the terminal 11 or 20 may be supplied based on the detection of the output voltage of the inverter, and closed loop control may be performed. (C) The pulse width of only the unit rectangular wave selected from the pulse train of the output V _P of the comparator 19 may be changed to improve waveform approximation.

[Brief explanation of drawings]

Figure 1 is a waveform diagram showing a specific voltage waveform in a conventional conversion method and a control pulse train to obtain it.
FIG. 2 is a waveform diagram showing a method for forming the control pulse train of FIG. 1; FIG. Fig. 4 is a waveform diagram showing the principle for obtaining the control pulse train shown in Fig. 3, Fig. 5 is a circuit showing a conversion device according to an embodiment of the present invention, and Fig. 6 is a waveform diagram showing the states of each part in Fig. 5. 7 are waveform diagrams showing adjustment of the output voltage. 7...Specific voltage waveform, 8...Control pulse train, 21...
Unit rectangular wave generation circuit, 22...Memory, 23, 24
...AND circuit, E...DC power supply, _Q1 to _Q4 ...transistor.

Claims (1)

[Scope of Claims] 1. A device for converting a DC voltage into a specific voltage waveform, the device being formed to sequentially send out unit rectangular waves at a constant cycle, and comprising means for changing the pulse width of the unit rectangular waves. and a digital signal for obtaining a control pulse train in which the unit rectangular waves are distributed so as to obtain an integral waveform substantially equal to the integral waveform of the specific voltage waveform. a logic circuit that sends out the control pulse train based on the output of the unit rectangular wave generation circuit and the digital signal obtained from the memory; and a logic circuit that sends out the control pulse train in response to the control pulse train sent out from the logic circuit. A device for converting direct current into an arbitrary voltage waveform, comprising a switching circuit for intermittent direct current voltage, and means for controlling means for changing the pulse width of the unit rectangular wave generation circuit when changing the voltage of the specific voltage waveform.