What kind of structure UPS is used is the primary factor that users should consider when choosing. Therefore, to understand the structural form and performance characteristics of various types of UPS, and correctly evaluate its advantages and disadvantages, it must become a UPS manufacturer, operator and user. Concerns.
First, the backup structure (including backup square wave and backup sine wave) UPS
When the utility power is normal, the inverter does not work, and the mains voltage is directly sent to the load after being intelligently regulated, so it has the following characteristics:
1: The conventional output electrical performance index depends on intelligent voltage regulation, the index is relatively poor, 220Vac ± 10%, but can meet the load requirements;
2: In the process of power failure and recovery of the mains, there is a switching process of the output voltage, which can be controlled within 10ms, and does not affect the load supply;
3: The inverter is only put into operation when the mains supply is abnormal. When the mains is normal, it is in the backup state. Therefore, the output capability of the whole machine is strong.
Second, online interactive UPS
Its working process is similar to the backup type, generally intelligent structure, controlled by MCU, and there is no essential difference between the backup type. The difference is that the bidirectional converter replaces the backup inverter and charger. When the utility power is normal, AC/DC Change to charge the battery. When the mains is abnormal, the DC/AC supplies power to the load. It also has the characteristics of simple backup circuit, high reliability and strong output capability. When the mains battery is switched, the switching time of the output voltage is also short (generally less than 4ms), which is suitable for small power UPS users.
Three, three port UPS
It has a power frequency inductor L connected in series in the main circuit, and the inverter also works in both directions. The relationship between input and output voltage is Uin-UL=Uout, and there is a phase difference between the three. By changing the amplitude and phase of the current in the inverter, the magnitude and phase of the voltage across the inductor L can be varied to maintain the output voltage stable during the input voltage change. The special structure determines its characteristics:
1: The inverter is in online working mode, monitoring and participating in the adjustment of the output voltage at any time to ensure the output voltage is stable. When the commercial power is out of pressure, the output voltage switching time is the input switching switch action time when the power is off, and the output capability is strong. The steady state accuracy is good, but the input voltage range is small.
2: Since the input and output voltages are adjusted by changing the phase relationship, the input power factor is low, when the input voltage is high and light load is inductive, the input voltage is low and the load is capacitive.
3: Because the input voltage of the input has a phase difference, the UPS bypass will be interrupted, so the three-port type can only be used for small power UPS users.
Four, double conversion online (according to the structure can be classified into high frequency line UPS and power frequency line UPS):
The first converter (AC/DC) is usually a rectified or controlled rectifier circuit that converts AC to DC and charges the battery while providing DC power of 100% load power to the second converter, the second converter (DC/AC) is an inverter that converts DC power into AC power that meets the load requirements. When the mains voltage is lost, DC power is supplied by the battery. Double-conversion online UPS is widely used, especially for high-power UPS. It is mostly used in this form. Its characteristics are as follows:
1: On-line sine wave output UPS, because the online UPS is powered by the UPS inverter when the mains supply is normal or during the mains supply interruption. Because of this, this fundamentally completely eliminates the influence of any voltage fluctuations and interference from the mains on the load operation, and truly realizes the interference-free regulated power supply to the load. Obviously this is not something that can be solved by any kind of anti-interference AC power supply. At present, online UPS sold on the market, when the external mains voltage varies from 180V to 250V, its output voltage stability accuracy is generally 220V ± 3%, and the sine wave operating frequency stability is 50HZ ± 1%. Even higher. The waveform distortion is in the range of <3%. When the mains supply is interrupted, the online UPS can achieve true uninterrupted (zero-off) power supply to the load.
2: The online UPS has excellent output voltage transient characteristics compared to the backup UPS. Generally, when the load is 0~50%, 50~100% load or 100%~50%, when the load is 50%~0, the output voltage varies by ≤5%, and the duration of this change is generally less than 100ms. The online UPS generally adopts PWM pulse width modulation technology of about 20kHZ, so the noise is relatively small, and the general noise is less than 50dB.
3: In the control circuit design of the power frequency online UPS, due to the use of input transformers, output transformers and optocoupler devices, the "strong" drive section and the "weak" control line are isolated from the electrical angle. As a result, the reliability of the line work has been greatly improved. This UPS technology is mature and the failure rate is generally low. Therefore, medium and large UPS (generally 6k or more) users should use the power frequency online UPS. For general small system UPS users can use high frequency online UPS, because high frequency online UPS uses high frequency conversion technology, the cost is relatively low, but the reliability is slightly worse than the power frequency online UPS, EMI interference is larger.
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