Classification and characteristics of AC power supply AC regulated power supply
Basic principle and composition of AC power supply At present, in power plants, so-called primary load industrial and mining enterprises and some substations, continuous and reliable power consumption is the basic condition for the safe operation of motors. All use the auxiliary contact of the working power switch to start the backup power input directly (or via a low-voltage, time-delay relay). This method has no phase frequency detection, and the success rate of power switching is low or the switching time is long. The permissible range of values is damaged by shock, especially with some
Basic principle and composition of AC power supply
At present, in power plants, so-called primary load industrial and mining enterprises, and some substations, the continuous and reliable power consumption is the basic condition for the safe operation of the motor. Auxiliary contact directly (or via low-voltage, time-delay relay) starts the backup power supply input, this method has no phase frequency detection, the success rate of power switching is low or the switching time is long, and the motor reset current is too large and it is easy to exceed the allowable value range and be damaged by impact , especially in some occasions where high-power motors and high-voltage motors are used, because the voltage decays slowly after the motor is powered off, if the backup power is turned on without checking the synchronization conditions when the residual voltage is large, the starting/standby transformer and the motor will have It may be damaged by severe impact. If the residual voltage drops to a certain level (such as between 20[[%]]-40[[%]]Un), then put in the backup power supply. Due to the long power-off time, The speed of the electric motor drops greatly, and the self-starting of the motors in groups causes the busbar to continue to lose pressure seriously, and some auxiliary machines are bound to withdraw.
In order to solve the above problems, this device will automatically track and monitor the frequency, voltage and phase of the power supply at both ends of the switch for a long time during normal power consumption. At the same time, use an appropriate mathematical model (not only consider the current phase difference and frequency difference, but also consider the change rate of the future phase difference and frequency difference) combined with the preset time before the switch is to be closed, calculate the phase difference and frequency of the closing point in the future. The difference is compared with the preset allowable phase difference and frequency difference, and when the conditions are met, it will send out a closing and tripping pulse signal.
Classification and characteristics of AC regulated power supply
A power supply that can provide a stable voltage and frequency is called an AC stable power supply. At present, the work done by most domestic manufacturers is to stabilize the AC voltage. The following is a brief description of the classification characteristics of some AC regulated power supplies in the market.
Parameter adjustment (resonance) type stabilized power supply, the basic principle of voltage stabilization is LC series resonance, and the magnetic saturation stabilizer that appeared in the early days belongs to this category. Its advantages are: simple structure, no many components , The reliability is quite high, the voltage regulation range is quite wide, and the anti-interference and anti-overload capabilities are strong. The disadvantages are: high energy consumption, high noise, bulky and high cost. The parametric voltage stabilizer developed on the basis of the principle of magnetic saturation and the "magnetic amplifier adjustable electronic AC voltage stabilizer" (ie, Type 614) that has become popular in my country in the 1950s are AC voltage stabilizers of this type.
Auto-coupling (transformation ratio) adjustment type 1. Mechanical voltage regulation type, that is, the servo motor drives the carbon brush to move on the winding sliding surface of the autotransformer, changing the ratio of Vo to Vi to realize the adjustment and stability of the output voltage. This kind of voltage regulator can be from hundreds of watts to several kilowatts. It is characterized by simple structure, low cost, and small output waveform distortion; however, the sliding contact of the carbon brush is easy to generate electric sparks, causing the brush to be damaged or even burned to failure; and the voltage adjustment speed is slow. 2. Change the tap type, make the autotransformer into multiple fixed taps, and use relays or thyristors (solid-state relays) as 10 switches to automatically change the tap position, thereby realizing the stability of the output voltage. The advantages of this type of voltage regulator are simple circuit, wide range of voltage regulation (130V-280V), high efficiency (≥95[%]), and low price. The disadvantage is that the accuracy of voltage regulation is low (±8～10[%]) and the working life is short. It is suitable for powering air conditioners in households.
High-power compensation type—purification type voltage stabilizer (including precision type voltage stabilizer), which uses compensation links to stabilize the output voltage, and is easy to realize microcomputer control. Its advantages are good anti-interference performance, high precision of voltage regulation (≤±1[%]), fast response (40~60ms), simple circuit and reliable operation. The disadvantages are: there is low-frequency oscillation phenomenon when there are nonlinear loads such as computers and program-controlled switches; the input side current distortion is large, and the source power factor is low; the output voltage has a phase shift with respect to the input voltage. Units with high requirements for anti-interference function are suitable for use in cities. When the computer is powered, a voltage stabilizer about 2-3 times the total power of the computer must be used. Because of the advantages of voltage stabilization, anti-interference, fast response, moderate price, etc., it is widely used.
Switching AC regulated power supply is used in high-frequency pulse width modulation technology. The difference from general switching power supply is that its output must be an AC voltage with the same frequency and phase as the input side. Its output voltage waveforms include quasi-square wave, trapezoidal wave, sine wave, etc. The uninterruptible power supply (UpS) on the market removes the storage power supply and charger, which is a voltage regulator of a switching AC regulated power supply. Good performance, strong control function, easy to realize intelligence, it is a very promising AC regulated power supply. However, because of its complex circuit and high price, promotion is slow.
