JPH0538158A - Dc power supply device - Google Patents

Abstract

PURPOSE:To control, the load current with high degree of accuracy by making an output signal of a sample hold circuit as a signal proportional to the load current. CONSTITUTION:A signal proportional to the primary current of a transformer 5 measured by a current measuring equipment 9 is inputted to a sample hold circuit 83 through an absolute value circuit 81. The sample hold circuit 83 makes the output of a pulse generator 82 as a sample signal to make sample hold action, and the output is outputted to a current controller through a low pass filter 84. The sample signal from the pulse generator 82 is outputted to just an intermediate section of the leading edge and trailing edge of ON command of a power transistor, so that a dc component of the output voltage of the sample hold circuit 83 corresponds to the load current, an error-caused in accordance with a period when the primary current of the transformer 5 reaches O is eliminated, and a signal proportion to the load current having high degree of accuracy is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention temporarily rectifies a commercial AC power source as a DC power source apparatus requiring a low voltage, large current and highly accurate current control, such as an alumite plating power source. The present invention relates to a direct-current power supply device that converts its output into high-frequency alternating current by an inverter, converts this alternating current into a predetermined voltage, and then rectifies it to obtain direct current.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a DC power supply device of this type. In this figure, the DC power obtained by rectifying the power supplied from the commercial frequency three-phase power supply 1 distributed from the power system by the rectifier 2 is converted into a square wave single-phase AC power of several kHz by the inverter 4, This AC is stepped down to an appropriate voltage by the transformer 5 and rectified by the rectifier 6 to supply a DC current to the load 7.

The current flowing through the load 7 must be controlled to a predetermined current value with high precision, and therefore the inverter 4
Output current is measured by the current measuring device 9 and input to the control device 4, which is rectified inside the control device 4 to obtain a control signal proportional to the current flowing through the load 7, and this and the load current are designated. A difference signal from the setting signal is input to a current regulator (not shown), and an output signal of the current regulator is used as a control signal to generate an ON command signal for the power transistor forming the inverting 4 by pulse generation.

The smoothing capacitor 3 removes the pulsating current component contained in the DC voltage input to the inverter 4. As the current measuring device 9, a Hall CT, which is a current measuring device having excellent frequency characteristics, is used because it has a square wave with a frequency of several kHz, which is much higher than the commercial frequency. FIG. 4 is a waveform diagram showing the voltage and current waveforms of the respective parts of FIG. In this figure, A is an ON command signal for the power transistors 41 and 44 of the four power transistors forming the inverter 4, and B is an ON command signal for the power transistors 42 and 43. Off when low. C is the output voltage of the inverter 4, D is the same output current, E is the load voltage which is the voltage across the terminals of the load 7, and F is the load current flowing through the load 7.

Since the frequency of the pulsating current component of the terminal voltage E of the load 7 is twice the frequency of the output voltage of the inverter 4, it is 10 kHz.
Since it is a high frequency component that exceeds, the impedance of the load 7 is mainly the inductance component for this frequency, and therefore the load current F is, for example, in the period between time points t ₁ and t _{2 in the} figure. Load voltage E is 0
When the load voltage E is 0, which is a period between the time points t ₂ and t ₃ , it linearly decreases.

Along with this, the output current D of the inverter 4 becomes a trapezoidal waveform, and all the power transistors 4
It is 0 when 1, 42, 43 and 44 are off. The load current F is not 0 even in this off period,
The two rectifying elements 61, 62 of the rectifier 6 are in the ON state at the same time, and the currents of the two windings on the secondary side of the transformer 5 cancel each other.

FIG. 5 is a partial circuit diagram showing the output side circuit of the inverter 4 of FIG. 3 and a part of the control device. In this figure, the current signal measured by the current measuring device 9 is converted into a positive signal by the absolute value circuit 81, which is a full-wave rectifier in the control device 8, and a pulsating flow component is generated by the low-pass filter 82. Only the DC component is output after being removed and input to a current regulator (not shown). Illustration of the circuits after this is omitted.

FIG. 6 is a waveform diagram showing the waveforms of the voltages and currents of the respective parts of FIG. 5, and the same reference numerals are given to the same voltages and currents as in FIG. G is an output signal of the absolute value circuit 81. In this figure, the load current F and the output signal G of the absolute value circuit 81 are similar during the period between the time points t ₁ and t ₂ . On the other hand, during the period between the time points t ₂ and t ₃ , although the load current F is not 0, the absolute value circuit 81
Since the output signal G of the signal is 0, the DC voltage value which is the output signal of the low-pass filter 82 from which the pulsating flow component of this signal is removed is the time t with respect to the DC component of the load current F.
Period between ₂ and time t ₃ (t ₃ -t ₂₎ is higher in the smaller value larger. That is, the error is generated that is substantially proportional to the period (t ₃ -t _2).

As a method of measuring a load current without such an error, a shunt is directly connected to the load circuit, and a terminal voltage of the shunt is isolated from the load circuit to the control device. There is a method of inputting it to the control device via a current divider, but the problem is that a large current shunt with a load current of several thousand amps is expensive as described above, and a measurement error increases with a shunt with poor high-frequency characteristics. As a result, it is necessary to use a shunt with excellent frequency characteristics, so there is a problem that the shunt becomes more expensive. Therefore, as a method of measuring a direct current of such a large current, a signal proportional to the load current is obtained by measuring and rectifying the alternating current on the output side of the inverter 4, that is, the primary side of the transformer 5 as described above. The method of obtaining is common.

[0010]

As described above, the method of measuring the AC current on the output side of the inverter 4 of the DC power supply device and obtaining the signal proportional to the load current from this is inexpensive, but the inverter 4 is constructed. There is a problem that the measurement error of the load current increases substantially in proportion to the period when all the power transistors are turned off and the output current becomes zero.

An object of the present invention is to solve such a problem and adopt a method of measuring the current on the output side of the inverter, which is an inexpensive load current measuring method, and has a high level of measurement error related to the off period. It is an object of the present invention to provide a DC power supply device that can obtain an accurate load current measurement value.

[0012]

In order to solve the above-mentioned problems, according to the present invention, a rectifier for obtaining a direct current from a commercial frequency AC power supply, and an output of the rectifier is input to output a square wave AC of a predetermined frequency. An inverter, a control device that controls the output of the inverter, a transformer that converts the output voltage of the inverter, and a rectifier that rectifies the secondary output of the transformer, and the control device measures the output current of the inverter. In the DC power supply device for controlling the output current of the rectifier by controlling the waveform width of the square wave by inputting the output signal of the current measuring device, the control device is the input signal of the current measuring device. An absolute value circuit for full-wave rectifying the output signal to obtain an absolute value signal, and a pulse signal at an intermediate point between the rising time and the falling time of the inverter ON command signal. Pulse generator for outputting a signal, and a sample and hold circuit samples and holds the output signal of the absolute value circuit a pulse signal output from the pulse generator as a sample signal, the sample
It is assumed that the output signal of the hold circuit is a signal that is proportional to the load current, and that the pulse generator uses at least one ON command signal of the inverter as an input signal.

[0013]

In the structure of the present invention, an absolute value circuit for full-wave rectifying the output signal of the current measuring device as an input signal to obtain an absolute value signal, an intermediate time point between the rising time and the falling time of the ON command signal of the inverter. The control device is equipped with a pulse generator that outputs a pulse signal to the controller and a sample-hold circuit that holds the output signal of the absolute value circuit using the pulse signal output by this pulse generator as the sample signal. Assuming that the signal is a signal proportional to the load current, the load current has a sawtooth waveform that increases linearly when the ON command signal is not 0 and decreases linearly when the ON command signal is 0. The output signal of the absolute value circuit at the sampling time determined by the sample signal of becomes the average value in the period when the ON command signal is not 0,
This value is proportional to the average value of the load current in the same period. Further, the output signal of the absolute value circuit is 0 during the period when the ON command signal is 0, but the load current is not 0 and its average value is the same as the average value when it is not 0. Since the sample value is held also during this period, the output signal of the sample and hold circuit becomes a signal proportional to the load current regardless of the pulse width of the ON command signal.

Further, when the ON command signal of the inverter is used as the input signal of the pulse generator for generating the sample signal, the circuit which issues the sample signal at a time point just between the rising time and the falling time of the ON command signal. Can be easily manufactured. Further, almost the same operation can be obtained even when only one of the two ON command signals is used instead of using all of them.

[0015]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is a partial circuit diagram of a DC power supply device showing an embodiment of the present invention, and the same circuit elements as those in FIG. In this figure, a signal proportional to the primary current of the transformer 5 measured by the current measuring device 9 is converted from a negative component into a positive component by the absolute value circuit 81 in the control device 8 and input to the sample and hold circuit 83. .
The sample and hold circuit 83 uses the pulse signal output from the pulse generator 82 as a sample signal to sample the value of the above-mentioned input signal at that time, hold it until the next sample signal, and output that value. This output signal is input to a current regulator (not shown) through the low pass filter 84.

FIG. 2 is a waveform diagram showing the voltage and current waveforms of the respective portions of FIG. 1, and the same voltage and current as those in FIGS. 4 and 6 are designated by common reference numerals. H is the output signal of the pulse generator 82, and I is the output signal of the sample and hold circuit 83. The input signals of the pulse generator 82 are ON command signals A and B.
And the input signal is used to generate the output signal H. Time t _m at which the first pulse of the output signal H is emitted
Is the rising time t ₁ and the falling time t of the ON signal A.
It is set exactly in the middle of ₂ . That is, t _m = (t ₁
+ T ₂ ) / 2 holds. Output signal G of absolute value circuit 81
Is sampled at the sampling time t _m , this value becomes the average value of the trapezoidal waveform. In addition, as described above, the load current F is not 0 even during the period in which the current between the time points t ₂ and t ₃ is 0, and the trapezoidal shape of a downward-sloping trapezoid, which is contrary to the period between the time points t ₁ and t ₂ , is obtained. It is a waveform and its average value is the same as the average value of the period between time points t ₁ and t ₂ . Therefore, the DC component of the output signal I of the sample and hold circuit 83, which is obtained by continuing the value held by the sample and hold circuit 83 until the next sample signal, coincides with that of the load current F, and the transformer 5 The error that occurs according to the period when the primary current becomes zero is eliminated, and a highly accurate signal proportional to the load current can be obtained.

It is also possible to use only one ON command signal as the input signal of the pulse generating circuit 81 for generating the pulse at the time point t _m . Since the frequency of the output of the inverter 4 is as high as several kHz as described above, the change in the DC component of the load current is slight during one cycle, and even if the cycle of the sample signal is doubled and the hold period is doubled. The error of the obtained signal with respect to the DC component of the load current is negligible. In any case, various kinds of input signals and circuit systems of the pulse generating circuit 81 are conceivable, but all of them can be easily manufactured by the conventional electronic circuit technology. It does not matter which circuit method is adopted as long as it does not violate.

[0018]

As described above, the present invention has an absolute value circuit that takes an absolute value of an input signal, a pulse generator that outputs a pulse signal at an intermediate point of an ON command signal, and a pulse that this pulse generator outputs. If the controller is equipped with a sample and hold circuit that samples the output signal of the absolute value circuit using the signal as a sample signal and holds it until the next sample signal, and if the output signal of this sample and hold circuit is a signal that is proportional to the load current, A value corresponding to an intermediate value of the rising portion of the load current is sampled. Since this value is a signal proportional to the average value of the load current, that is, the DC component, the period of 0 of the ON command signal. It is possible to obtain a control signal which is proportional to the load current with high accuracy. As a result, it is possible to obtain an effect that the DC power supply device can control the load current with high accuracy.

Further, when the input signal of the pulse generator for generating the sample signal is an ON command signal, a circuit which issues the sample signal at an intermediate time point between the rising time point and the falling time point of the ON command signal can be easily manufactured. can do. Further, it is possible to obtain a signal corresponding to the load current having substantially no problem even when only one of the two ON command signals is used instead of using all of them.

[Brief description of drawings]

FIG. 1 is a partial circuit diagram of a DC power supply device showing an embodiment of the present invention.

FIG. 2 is a waveform diagram showing voltage and current waveforms at various parts in FIG.

FIG. 3 is a circuit diagram showing a DC power supply device.

FIG. 4 is a waveform diagram showing the waveforms of the voltage and current of each part in FIG.

FIG. 5 is a partial circuit diagram of a conventional DC power supply device.

FIG. 6 is a waveform diagram showing voltage and current waveforms of various parts in FIG.

[Explanation of symbols]

4 inverter 41 Power Transistor 42 Power transistor 43 Power transistor 44 power transistor 5 transformer 6 rectifier 7 load 8 control device 81 Absolute value circuit 82 pulse generator 83 Sample and hold circuit 9 Current measuring device

Claims (2)

[Claims] 1. A rectifier for obtaining direct current from a commercial frequency alternating current power supply,
An inverter that receives the output of the rectifier and outputs a square wave alternating current of a predetermined frequency, a control device that controls the output of the inverter, a transformer that converts the output voltage of the inverter, and a secondary output of the transformer. A DC power supply device comprising a rectifier for rectifying, wherein the control device receives an output signal of a current measuring device for measuring an output current of the inverter and controls a waveform width of the square wave to control an output current of the rectifier. In the above, the control device is an absolute value circuit that obtains an absolute value signal by full-wave rectifying the output signal of the current measuring device, which is the input signal, between the rising time point and the falling time point of the ON command signal of the inverter. A pulse generator that outputs a pulse signal at a time point, and an output of the absolute value circuit using the pulse signal output by the pulse generator as a sample signal Sample and a sample-and-hold circuit for holding the DC power supply apparatus characterized by a signal proportional to the output signal of the sample-and-hold circuit to the load current issue. 2. The DC power supply device according to claim 1, wherein the pulse generator receives at least one ON command signal of the inverter as an input signal.