Development of AC Stabilized Power Supply Using Instantaneous Comparison Method
Precision electronic instruments and equipment are widely used in households, industrial production, office automation, experimental research, communication engineering, medical care and other fields, and are generally powered by urban power grids. The rated voltage of the urban power grid is single-phase 220V, which is an artificially stipulated ideal voltage. Since the voltage at the head end of the power supply line from the transformer is (220+10%) V and the voltage at the end is (220-10%) V, electrical equipment is required to have a certain ability to resist grid voltage fluctuations. Although most electrical equipment has the ability to resist power supply voltage fluctuations, according to statistics, power supply voltage fluctuations are one of the causes of electrical equipment failures. Therefore, these electrical equipment need to use regulated power supplies to ensure their normal operation.
The stabilized power supply is a device that stabilizes the grid voltage. It has been used in my country for many years, such as: the sliding contact type of the servo motor driving the voltage regulating transformer, the variable reactor type, and the magnetic saturation automatic voltage stabilized power supply.
In principle, the above-mentioned regulated power supply samples the grid voltage, compares them, and adjusts them using a servo motor or a non-contact switch to stabilize the output of the AC voltage. This kind of regulated power supply generally has poor voltage regulation effect, and the accuracy is 1%~0.5%.
The current AC regulated power supply mainly has the following problems:
(1) The use of nonlinear reactors often brings harmonics, which does not improve the quality of the grid voltage waveform, and some have additional waveform distortion that causes harmonic pollution to the grid.
(2) The sampling time and actuator action time are too long.
These two links have a great impact on the performance of the voltage stabilizer. The sampling method generally adopts effective value or average value sampling, which takes at least several cycles; while the servo motor generally takes several seconds to tens of seconds to perform adjustment actions, which is too long and harmful to There is no improvement in the voltage waveform. These voltage stabilization methods have no time to respond and implement the fast-changing disturbances in the grid voltage, such as surges, sags, pulse disturbances, and high-frequency disturbances, which cause disturbances to pass through the voltage stabilization device and reach the electrical equipment, which cannot affect electrical equipment. If the protective effect is not achieved, it may also cause the electrical equipment to malfunction or even be damaged.
It can be seen that when the grid voltage changes and interferes, the output voltage of the regulated power supply can quickly return to the vicinity of the rated value, and the sinusoidal AC voltage with good waveform and stable amplitude will be provided to the electrical equipment, which will ensure its safe and normal operation. There are great benefits.
2. Instantaneous comparison of AC voltage regulation methods
The following introduces a new method of AC voltage stabilization that can improve the shortage of the above-mentioned AC voltage stabilization power supply, that is, using the instantaneous comparison method-waveform repair technology to make an AC voltage stabilization power supply.
Grid voltage uin=rated voltage uS+⊿u
Grid voltage uin+control voltage uC=output voltage uout
Among them, the rated voltage uS is the voltage in the ideal state artificially specified, and ⊿u is the deviation of the grid voltage from the rated voltage. Regardless of the size, as long as the deviation from the rated voltage can be superimposed by the artificially manufactured control voltage uC and the grid voltage uin. If the artificial control voltage uC is equal to -⊿u, when ⊿u changes, -⊿u also changes accordingly, and the input voltage uin and the control voltage uC are superimposed to be equal to the rated voltage uS. In the urban power grid, the effective value of single-phase rated voltage is 220V.
For the change caused by the input voltage, the input voltage is first sampled, and the ratio coefficient is 1/A,
uin/A=(uS+⊿u1)/A = uS/A+⊿u1/A
Artificially create a reference voltage ur, which has the same frequency and phase as the grid voltage, the effective value is US/A, and the waveform is good. The difference between the sampling value of the input voltage uin and ur is ⊿u1/A, that is, uin—ur=⊿u1/A, and then the voltage difference and power are amplified by β times. Let β=A, then the amplified value is ⊿u1, and then superimpose ⊿u1 into the circuit in reverse through the coupling transformer. At this time, the output voltage is equal to the rated voltage, that is, uout=uS=Aur=βur. At this time, since β is an amplification factor, the performance of uout is only related to ur. ur is a real voltage generated artificially, which can be obtained by analog or digital circuits, and has good performance indicators. The stability of ur also determines the stability of the output voltage.
It can be seen from the above analysis that the essence of the instantaneous comparison AC voltage stabilization method is: to use the input voltage and the reference voltage for instantaneous comparison to find out the deficiency of the waveform, and to improve and repair the input voltage waveform by controlling the superposition of the voltage, so as to achieve stability. output voltage purpose. The power quality of the output voltage is determined by ur, with good waveform and stable amplitude; while the input voltage only provides energy for the internal operation of the power supply and stable voltage output, and a stable output voltage with high power is obtained by using a low-power control voltage. In this way, the output energy is provided by the grid, and the control voltage is only used to repair the fluctuating part of the grid that deviates from the rated voltage.
Similarly, when the input voltage is constant and the output voltage changes due to changes in the load, the output voltage is sampled, and the control voltage uC2 is adjusted in a similar way to change the control voltage uC2 to maintain the output voltage stability without affecting the input voltage.
For the consideration of economy in the implementation of the scheme, in order to simplify the circuit, the acquisition of the control voltage uC1 and the acquisition of the control voltage uC2 are combined in a specific circuit to obtain the functional block diagram shown in Figure 3 .
The comparison value of the input voltage and the reference voltage and the comparison value of the output voltage and the reference voltage are added by the adder, and then amplified by the voltage and power amplifier circuit, and the control voltage uC is obtained by the coupling transformer, which is superimposed between the input voltage and the output voltage . The control voltage uC is mainly used to repair the waveform, adjust the power supply voltage, and at the same time play the role of isolating the input power supply and the load.
3. Comparison with conventional regulated power supplies
Compared with the regulated power supply made by the conventional principle, the regulated power supply made by the above principle has the following characteristics:
(1) Fast response. Due to the use of high-speed linear electronic devices, instantaneous sampling and instantaneous execution, the control response speed is extremely fast, and the adjustment can be completed within milliseconds, so that the output voltage can quickly return to the vicinity of the rated voltage. Therefore, it has the function of suppressing high-frequency interference and noise, and has the effect of purifying millisecond-level interference, which is impossible for ordinary regulated power supplies.
(2) Wide application range of input voltage. The input voltage can vary by 30%~50% or more, and it can be adjusted symmetrically. The wider the range, the more repair energy needs to be provided. The value of the control voltage is mainly determined by the demand. From an economical and practical point of view, it is advisable to take (8~10)%.
(3) High accuracy of voltage regulation. Depending on the generation method of the reference voltage, the voltage stabilization effect can reach 1%, 0.1%, 0.01%. Voltage regulators with different precisions are suitable for occasions with different requirements. 1% is used for general voltage stabilization requirements; 0.1% is used for laboratories or important industrial equipment; 0.01% can be used for instrument verification.
(4) It has the characteristics of green power supply. This method first corrects the waveform of the grid voltage to a good sine wave, and then supplies power to the load. The amount of repair energy depends on the need. Since the essence of this method is to correct the grid waveform, the distortion of the corrected waveform is generally less than 1% to 0.5%, so this voltage stabilization method is green.
(5) It has certain environmental protection properties. If the input voltage does not change, the output voltage changes due to the different nature of the load, and the corresponding change of the control voltage is used within a certain harmonic range to keep the output voltage constant. Since the control voltage has an isolation effect and does not affect the input voltage, this voltage stabilizing method is environmentally friendly to a certain extent.
(6) High work efficiency. The working principle of this power supply is that low power controls high power, and it has high efficiency. The capacity of the output voltage is mainly taken from the grid, and the control voltage is generally the part where the grid voltage deviates from the rated voltage, so it only needs to consume the power of manufacturing the control power supply, so the efficiency is extremely high.
Take the 300 VA output power supply as an example: if the grid voltage fluctuates by +10%, you only need to control the +10% power fluctuation. The efficiency is 300/(300+100)=75%. And the higher the efficiency of the method for making the control power supply, the higher the working efficiency of the whole machine.
Take the inverter method as an example: to make a 0.01% high-stability power supply, due to the AC/DC, DC/AC conversion and the limitation of the efficiency of the power amplifier device, the overall efficiency is below 30% without other losses. When using the instantaneous comparison method to make a regulated power supply of the same power, it is only necessary to make the power of the control power supply for repairing 10% fluctuations. Even if the control power supply is manufactured using the inverter method, the power consumed is only equivalent to that of the inverter method. 1/10. Obviously, when making a high-stability regulated power supply, the efficiency of using the instantaneous comparison method is much higher than that of the regulated power supply using the inverter method.
(7) Do not use low-frequency filter devices such as large inductance and large capacitance, small size, light weight, good output waveform, and the general waveform distortion is 1%~0.5%.
(8) This voltage regulator can be cascaded with other voltage regulators, and the narrower the stability accuracy range is set, the smaller the energy consumption will be. For example, when the stability accuracy of the pre-stage regulator is 2%, if it is necessary to output 5000 VA of power, it only needs to manufacture a 100 VA control power supply, and the stability can reach more than 0.1%.
(9) A fast protection circuit can be used. When the instantaneous short-circuit fault occurs at the load end, the control power supply will quit working immediately. At this time, the coupling transformer is equivalent to a reactor (the coupling transformer is a transformer that introduces the control power supply), which has the function of limiting the growth of the short-circuit current. After the fault is eliminated, the control power supply will resume work by itself.
4. apply effects
Initially, a compensating stabilized power supply was developed using this control method. The main idea is to control the grid voltage with negative feedback, with a stability of 0.1%, a waveform distortion of 1%, and a power of 100VA. Due to the limited selection of devices at that time, the protection speed could not keep up with other problems, this kind of regulated power supply could not be popularized and applied. Afterwards, the original design scheme, device selection, fast protection input circuit, etc. were optimized by using instantaneous comparison and waveform repair technology. After several improvements and tests, the 300VA output power AC stabilized power supply made for the verification of electric energy meters has practical functions, and the actual measurement reaches the following indicators:
When the input grid voltage changes by +10%, measured with a digital voltmeter, the maximum output voltage stability does not exceed +0.03%/3 minutes, and the output waveform distortion is <0.5%.
The regulated power supply has the following characteristics:
(1) The circuits are all composed of analog devices, which are easy to select and cheap;
(2) The working principle of the power supply is that low power controls high power, and has high efficiency. Only need to make 30 VA control power to achieve 300VA power output;
(3) The output power tube does not need a combined tube. When the output power of the whole machine is 300VA, since only 30VA control power is needed, only a pair of high-power tubes can be used for output, and no air-cooled heat dissipation is required;
(4) Strong anti-interference ability. During the test, the three-phase electric welding operation is carried out on the same power supply line in the same room of the power supply, and the output voltage does not jump;
(5) The regulated power supply independently produced by the assistant according to this design has the same technical indicators, which shows that the design method is very consistent.
5. in conclusion:
Instantaneous comparison method - waveform repair technology The basic principle of making a regulated power supply is to compare the sampling value of the input voltage with the reference voltage to find out the deficiency of the waveform, and then improve and repair the input voltage waveform and stabilize the amplitude by changing the control voltage , to achieve the purpose of output voltage stability. Its essence is to use a low-power control power supply to obtain a large-capacity stable voltage output. It is an AC voltage stabilization method that integrates green, environmental protection, purification, high efficiency and high efficiency. The AC regulated power supply developed by using this technology has the characteristics of low cost, high index, low cost, and easy control, and can also be expanded to a high-power regulated power supply according to needs.
Using this voltage stabilization method can provide high-quality AC stabilized voltage power supply for scientific research, computer room, medical equipment, industrial automation equipment, communication equipment, lighting system, audio-visual equipment and other equipment.
