Principle and Application of Power Frequency Rectifier for Huawei ups Power Supply
The buck rectifier of UPS power supply can be divided into power frequency and high frequency, and power frequency can be divided into voltage stabilization and voltage stabilization. Following is Huawei UPS power supply in the most widely used voltage-stabilized power frequency circuit as an example for discussion. Three-phase rectifier is generally used because the fluctuation coefficient and ripple coefficient of three-phase rectifier are low. Six thyristor rectifiers are used in a three-phase thyristor bridge rectifier circuit, which requires six pulses to be controlled separately, also known as six-pulse rectifier. Three-phase full-bridge rectifier circuit works by line voltage, and the highest integer outflow voltage can be reached when the rated value of city power is 380V/220V.
UDC = 380V * 2 = 537V
Normally, the floating charge voltage (about 438 V) of 12 V * 32 batteries = 384 V is enough. Because this circuit works in accordance with the frequency (so-called power frequency) rhythm of the city electricity, it becomes a power frequency rectifier. Because the current capacity and voltage withstand of SCR can be very high, it has been widely used in medium and high power traditional double-conversion Huawei UPS power supply. Because the opening (phase) of the circuit rectifier is controllable, it has the function of output voltage stabilization. However, the function of output voltage stabilization can not be used as the basis for a wide range of changes in input power market, because there is a hidden danger of thyristor out of control under certain conditions.
For example, if the rated voltage of a battery pack is 384V and the floating charge voltage is less than 440V under normal conditions, the rectifier voltage can be guaranteed to be less than 450V even if the rated voltage of the wire rises to 135% Un in time, then the input voltage (135% Un) can be provided to the user as the advantage of converting UPS power supply, and the hidden danger will be buried in the user's use. Of course, according to the phase control principle, even if the input market voltage rises to 150% Un, the floating charge voltage of the battery can be stabilized below 440 V under normal conditions. But in case the controllable silicon runs out of control at 135% Un, then the controllable silicon rectifier will become a common diode rectifier, and the output rectifier voltage UDC will become a common diode rectifier.
UDC = 380V * 1.35 * 2 = 725V
There are two dangerous situations: one is whether the filter capacitor behind the rectifier can withstand this high voltage, otherwise it will explode undoubtedly; the other is that the original 12V battery is now turned into UB = 725/32 = 2.6V, which means that the battery is also scrapped! There are even other dangers, such as sulfuric acid injury and wounds caused by battery burst.
On the other hand, because the work of 6-pulse rectifier circuit is pulse-type, the damage to the booming input voltage of municipal electricity is very significant, so that the harmonic component of input current reaches more than 30%, and the input power factor is only about 0.8. In order to achieve the goal of "green" power supply, power factor correction must also be carried out.
Common diode rectifier does not have the function of voltage stabilization. It is generally used in low power Huawei UPS power supply circuit. Charger is set up separately.