Ultrahigh voltage direct current generator and voltage adjusting method
Technical Field
The invention belongs to the technical field of extra-high voltage, and particularly relates to an extra-high voltage direct current generator and a voltage adjusting method.
Background
Since the construction of the ultra-high voltage transmission and transformation project in China, the voltage grade of the transmission line is gradually improved, and the voltage grade of the corresponding high-voltage measuring equipment and the transmission equipment is also gradually improved. Before the equipment is delivered or put into operation formally, some voltage-resistant insulation tests or calibration tests and the like need to be completed so as to detect whether the delivery parameters of the high-voltage equipment can meet the requirements or not, whether virtual standard parameters exist or not and the like.
To test these extra-high voltage devices, extra-high voltage dc generators are needed to test these devices. Most of existing ultrahigh-voltage direct-current generators control a single chip microcomputer to output an analog voltage through a DA chip through a digital potentiometer, the analog voltage adjusts PWM through PID voltage regulation control to control the output size of direct-current voltage, then the analog voltage is converted into alternating current through IGBT bridge type inversion to be supplied to a medium-frequency high-voltage transformer, then the alternating current is rectified through medium-frequency voltage doubling to output direct-current high-voltage, and the direct-current high-voltage is sampled and transmitted to the single chip microcomputer to be processed and then displayed on a display screen.
At present, the resolution output by the DA chip is limited, so that the step-up step length is large, namely when the digital knob steps by one grid, the high-voltage is likely to change greatly, the voltage is increased in a step manner, and the damage to a power module and a power tube is great. When the voltage regulation speed of the direct-current high-voltage generator is high, the power module is damaged, high-voltage mutation is caused, and the high-voltage generator has considerable harm to tested high-voltage equipment liquid. Specifically, the output voltage of the current ultra-high voltage direct current generator basically exceeds 1000kV, the amplitude of the output high voltage cannot be too large, and the requirement on boosting is relatively high. At present, a direct current generator basically controls analog voltage output by adjusting a DA chip through a single chip microcomputer, and the resolution of most of the existing DA digital-to-analog conversion chips is 16 bits (a small number is 24 bits), so that the fineness adjustment range is large, namely, the step size is large, the voltage of a bus is greatly changed, and finally the high-voltage is boosted too fast. Increasing the resolution of DA chips helps to solve the problem of large steps, but, limited by technology and cost, the resolution of current mainstream DA digital-to-analog conversion chips is still 16 bits (a few are 24 bits).
Therefore, it is necessary to develop an extra-high voltage dc generator suitable for the detection of devices above 1000 kV.
Disclosure of Invention
Aiming at the defect that the output of the output voltage is larger due to the fact that the existing ultrahigh-voltage direct-current generator controls the output of the analog voltage through a DA chip, the invention provides the ultrahigh-voltage direct-current generator which improves the adjustment precision and reduces the output voltage step, and is particularly suitable for large equipment with the grade of more than 1000 kV. The invention also provides a method for regulating the voltage of the extra-high voltage direct current generator.
In order to achieve the purpose, the invention adopts the following technical scheme: an extra-high voltage direct current generator, comprising:
a reference voltage unit;
a first stage voltage adjustment unit;
a second stage voltage regulating unit;
a power voltage regulating unit;
a control unit;
the reference voltage unit generates reference voltage, the first-stage voltage regulating unit receives the reference voltage and outputs first regulating voltage to the second-stage voltage regulating unit under the control of the control unit, and the second-stage voltage regulating unit outputs second regulating voltage to the power voltage regulating unit under the control of the control unit.
Compared with the one-stage voltage regulation in the prior art, the ultra-high voltage direct current generator has greatly increased precision, thereby being capable of outputting voltage more gently. For example, in the prior art, a 16-bit resolution DA digital-to-analog conversion chip is adopted, and the invention adopts two serially connected 16-bit resolution DA digital-to-analog conversion chips, so that the adjustment precision is 216Increase to 232。
As a refinement, the reference voltage unit generates a constant reference voltage. The reference voltage may be 2.5V.
As a refinement, the control unit.
As a modification, the first-stage voltage regulating unit and the second-stage voltage regulating unit are the same.
As an improvement, the first-stage voltage regulating unit comprises a digital-to-analog conversion chip and an operational amplifier circuit.
As an improvement, the digital-to-analog conversion chip is connected with the reference voltage unit through a pin, and the digital-to-analog conversion chip is connected with the control unit through a serial data interface, a clock and a chip pin.
As an improvement, the extra-high voltage dc generator further includes a voltage-current transmitting unit, where the voltage-current transmitting unit converts a voltage signal into a current signal and transmits the current signal to the power voltage regulating unit. In the actual detection process, a low-voltage analog signal generated by the DA chip through the operational amplifier unit needs to be sent into the power voltage regulating unit through a cable, and a certain distance is certainly reserved between the second regulating voltage signal and the power voltage regulating unit. After the voltage is subdivided by two stages, the signal is weak, the transmission line is too long, the external influence on the signal is large, and the stability of high-voltage output is not facilitated. When the structure layout is carried out, the distance between the circuit board and the power voltage regulating unit is shortened as much as possible on the premise of not causing interference to the circuit board; the cables from the control signals to the control power modules adopt multilayer shielded cables and are made of high-temperature-resistant and low-temperature-resistant materials; the voltage control signal is converted to a current signal by the transducer. The practical operation mode is to convert a voltage signal of 0-5V into a current signal of 4-20mA, which has been verified in practical production, and the effect is obvious: even when the power voltage regulating unit can not be close to the second voltage regulating signal part in structural design, the influence caused by properly extending the distance of the cable is small, and therefore the output precision is guaranteed.
As an improvement, the extra-high voltage dc generator further includes a detection unit in communication connection with the control unit, and the detection unit includes a 24-bit high-precision AD analog-to-digital conversion chip. Since the accuracy of the DA output is improved by one level, the resolution of the sampled voltage signal is high. If the accuracy of the DA output is improved alone, and no feedback signal is used for controlling the DA output, the output voltage is unstable, and the deviation is large. A24-bit high-precision AD analog-to-digital conversion chip adopts a principle of a sigma-delta A/D conversion mode, has 24-bit error-free code rate, has a linear error smaller than 0.0015 percent, and can reach 23-bit effective resolution. Can carry out accurate reading to the feedback signal of measurement like this, feed back to DA output chip simultaneously, adjust output voltage, make voltage can stable output to do not receive external disturbance, have certain assurance to the extra-high voltage stability and the accuracy of whole equipment output simultaneously.
As an improvement, the output end of each stage of voltage regulating unit passes through a multi-stage operational amplifier unit to add a calculus circuit, and the calculus circuit is adjusted to realize the conversion of waveforms.
As an improvement, the power voltage regulating unit is controlled by subdivided analog voltage, so that a subdivided analog voltage rising curve is a smooth rising curve, the impact on the power voltage regulating unit is greatly reduced, the damage rate of the power voltage regulating unit is reduced rarely, then the power voltage regulating unit is inverted into alternating voltage in a bridge mode through an IGBT, and high-voltage direct current output is generated through an intermediate frequency transformer and an intermediate frequency voltage-multiplying rectifying unit.
An extra-high voltage direct current generator voltage regulation method, comprising:
step one, generating a reference voltage;
step two, regulating the reference voltage once and outputting a first regulated voltage which is 1/2 times of the reference voltageMWherein M is the minimum resolution of the first-stage voltage regulating unit;
step three, carrying out secondary regulation on the first regulation voltage and outputting a second regulation voltage, wherein the second regulation voltage is 1/2 of the first regulation voltageNWherein, N is the minimum resolution of the second-stage voltage regulating unit;
and step four, outputting the second regulating voltage to a power voltage regulating unit for voltage regulation.
As an improvement of the voltage regulation method of the extra-high voltage dc generator, in the fourth step, the second regulated voltage is converted into a current signal by the current transducer and then transmitted to the power voltage regulation unit.
As an improvement of the voltage regulation method of the extra-high voltage direct current generator, M is equal to N.
The ultrahigh voltage direct current generator has the advantages that: the two-stage voltage regulating units connected in series replace the existing one-stage voltage regulating mode, and output voltage is regulated by increasing the number of digital-to-analog conversion chips instead of improving the precision of the digital-to-analog conversion chips, so that the output voltage is more precise and stable.
Drawings
Fig. 1 is a block diagram of an extra-high voltage dc generator according to a first embodiment of the present invention.
Fig. 2 is a schematic circuit diagram of a voltage regulating unit of an extra-high voltage dc generator according to a first embodiment of the present invention.
Detailed Description
The technical solutions of the embodiments of the present invention will be explained and explained below with reference to the drawings of the embodiments of the present invention, but the embodiments described below are only preferred embodiments of the present invention, and are not all embodiments. Other embodiments obtained by persons skilled in the art without any inventive work based on the embodiments in the embodiment belong to the protection scope of the invention.
Referring to fig. 1 and 2, an extra high voltage dc generator according to a first embodiment of the present invention includes:
a reference voltage unit;
a first stage voltage adjustment unit;
a second stage voltage regulating unit;
a power voltage regulating unit;
a control unit;
the reference voltage unit generates reference voltage, the first-stage voltage regulating unit receives the reference voltage and outputs first regulating voltage to the second-stage voltage regulating unit under the control of the control unit, and the second-stage voltage regulating unit outputs second regulating voltage to the power voltage regulating unit under the control of the control unit.
Compared with the one-stage voltage regulation in the prior art, the ultra-high voltage direct current generator has greatly increased precision, thereby being capable of outputting voltage more gently. For example, in the prior art, a 16-bit resolution DA digital-to-analog conversion chip is adopted, and the invention adopts two serially connected 16-bit resolution DA digital-to-analog conversion chips, so that the adjustment precision is 216Increase to 232。
In this embodiment, the reference voltage unit generates a constant reference voltage. The reference voltage may be 2.5V.
In this embodiment, the control unit.
In this embodiment, the first-stage voltage regulating unit and the second-stage voltage regulating unit are the same.
In this embodiment, the first-stage voltage adjusting unit includes a digital-to-analog conversion chip and an operational amplifier circuit.
In this example, the numberThe analog-to-digital conversion chip adopts an AD5543 chip, the AD5543 chip is a 16-bit resolution digital-to-analog conversion chip, and the current output type is adopted, so that the voltage can be output only through an operational amplifier circuit on the output side, as shown in a device U2 in fig. 2. The AD5543 chip U1 communicates with the single chip microcomputer through a serial data interface, provides high-speed and three-wire microcontroller compatibility input by using a Serial Data Input (SDI), a Clock (CLK) and a Chip Selection (CS) pin, and the VREF pin is connected with a reference voltage unit, so that after the chip passes through an external operational amplifier module, the minimum resolution which can be achieved is the reference voltage and 216Is the regulation principle of a single-stage voltage regulation unit.
In this embodiment, the output end of each stage of voltage regulating unit passes through the multistage operational amplifier unit to add the calculus circuit, and the conversion of waveforms is realized by adjusting the calculus circuit.
In this embodiment, the extra-high voltage dc generator further includes a voltage-current transmitting unit, where the voltage-current transmitting unit converts a voltage signal into a current signal and transmits the current signal to the power voltage regulating unit. In the actual detection process, a low-voltage analog signal generated by the DA chip through the operational amplifier unit needs to be sent into the power voltage regulating unit through a cable, and a certain distance is certainly reserved between the second regulating voltage signal and the power voltage regulating unit. After the voltage is subdivided by two stages, the signal is weak, the transmission line is too long, the external influence on the signal is large, and the stability of high-voltage output is not facilitated. When the structure layout is carried out, the distance between the circuit board and the power voltage regulating unit is shortened as much as possible on the premise of not causing interference to the circuit board; the cables from the control signals to the control power modules adopt multilayer shielded cables and are made of high-temperature-resistant and low-temperature-resistant materials; the voltage control signal is converted to a current signal by the transducer. The practical operation mode is to convert a voltage signal of 0-5V into a current signal of 4-20mA, which has been verified in practical production, and the effect is obvious: even when the power voltage regulating unit can not be close to the second voltage regulating signal part in structural design, the influence caused by properly extending the distance of the cable is small, and therefore the output precision is guaranteed.
In this embodiment, the extra-high voltage dc generator further includes a detection unit in communication connection with the control unit, and the detection unit includes a 24-bit high-precision AD analog-to-digital conversion chip. Since the accuracy of the DA output is improved by one level, the resolution of the sampled voltage signal is high. If the accuracy of the DA output is improved alone, and no feedback signal is used for controlling the DA output, the output voltage is unstable, and the deviation is large. A24-bit high-precision AD analog-to-digital conversion chip adopts a principle of a sigma-delta A/D conversion mode, has 24-bit error-free code rate, has a linear error smaller than 0.0015 percent, and can reach 23-bit effective resolution. Can carry out accurate reading to the feedback signal of measurement like this, feed back to DA output chip simultaneously, adjust output voltage, make voltage can stable output to do not receive external disturbance, have certain assurance to the extra-high voltage stability and the accuracy of whole equipment output simultaneously.
In the embodiment, the power voltage regulating unit is controlled by subdivided analog voltage, so that a subdivided analog voltage rising curve is a curve which rises smoothly, the impact on the power voltage regulating unit is reduced greatly, the damage rate of the power voltage regulating unit can be reduced rarely, then the power voltage regulating unit is inverted into alternating voltage in a bridge mode through an IGBT, and high-voltage direct current output is generated through the intermediate-frequency transformer and the intermediate-frequency voltage-multiplying rectifying unit.
The ultrahigh-voltage direct-current generator of the first embodiment of the invention has the beneficial effects that: the two-stage voltage regulating units connected in series replace the existing one-stage voltage regulating mode, and output voltage is regulated by increasing the number of digital-to-analog conversion chips instead of improving the precision of the digital-to-analog conversion chips, so that the output voltage is more precise and stable, and the power voltage regulating unit and tested equipment are effectively protected.
An extra-high voltage direct current generator voltage regulation method, comprising:
step one, generating a reference voltage;
step two, regulating the reference voltage once and outputting a first regulated voltage which is 1/2 times of the reference voltageMWherein M is the minimum resolution of the first-stage voltage regulating unit;
step three, carrying out secondary regulation on the first regulation voltage and outputting a second regulation voltage, wherein the second regulation voltage is 1/2 of the first regulation voltageNWherein, N is the minimum resolution of the second-stage voltage regulating unit;
and step four, outputting the second regulating voltage to a power voltage regulating unit for voltage regulation.
As an improvement of the voltage regulation method of the extra-high voltage dc generator, in the fourth step, the second regulated voltage is converted into a current signal by the current transducer and then transmitted to the power voltage regulation unit.
As an improvement of the voltage regulation method of the extra-high voltage direct current generator, M is equal to N.
As an improvement of the voltage regulation method of the extra-high voltage direct current generator, a high-precision AD conversion chip is adopted to accurately read a measured feedback signal and feed the feedback signal back to the single chip microcomputer and the DA output chip.
While the invention has been described with reference to specific embodiments thereof, it will be understood by those skilled in the art that the invention is not limited thereto but is intended to cover all modifications and equivalents as may be included within the spirit and scope of the invention. Any modification which does not depart from the functional and structural principles of the invention is intended to be included within the scope of the following claims.