Skip to content

3 phase online ups uninterruptible power supply electrical Circuit knowledge

Provide knowledge of UPS uninterruptible power supply, understand the classification of UPS uninterruptible power supply and UPS electrica Circuit, etc.

Menu
  • Home
Menu
Figure 4 - Test waveforms considering the presence of harmonics in the mains voltage

Application of 12-phase rectifier and passive and active filter in UPS

Posted on June 11, 2022June 11, 2022 by admin

Most of the SCR polyphase phase-controlled rectifiers used in three-phase high-power power frequency UPS use 12-phase rectifiers or 12-phase rectification + 11th harmonic passive filters, which have become a typical power frequency UPS circuit mode, which can Meet the requirements of the national standard GB/T 7260.3 for the harmonic content of the mains input current. However, due to the birth of the new international harmonic standard IEC 61000-3-4, 12-phase rectification or 12-phase rectification + 11th harmonic passive filter can no longer meet the basic requirements of this standard. Driven by the development of active filter technology in power electronics technology, the power frequency rectification method of 6-phase rectifier + power active filter has been applied in high-power power frequency UPS. The international standard IEC61000-3-4 harmonic standard is shown in Table 1.

Table 1 - International Standard IEC61000-3-4 Harmonic Standard
Table 1 – International Standard IEC61000-3-4 Harmonic Standard

The total current harmonic distortion of the 12-phase phase-controlled rectifier is 10%, which meets the standard, but the single harmonics such as the 11th harmonic (H11) and the 13th harmonic (H13) are more than twice the standard value, even if Using 12-phase rectification + 11th harmonic (H11) passive filter method can make the mains input power factor reach 0.90, but the effect is not ideal. However, the method of 6-phase rectification + power active filter can well meet the standard requirements shown in Table 1. The principle circuit of the series power active filter plus passive filter is shown in Figure 1. Since the 6-phase rectifier used in UPS is a capacitor filter and a harmonic source with the nature of a voltage source, in order to reduce the capacity of the active filter and reduce the cost, a series of active filters and LC passive filters are generally used. filter method to use. In this way of use, the capacity of the series power active filter is only 2% to 3% of the UPS capacity. A 20kV·A UPS can only use a 0.45kV·A series-type power active filter. The series-type power active filter has the following three functions in the circuit:

Figure 1 - Principle circuit of series power active filter plus passive filter
Figure 1 – Principle circuit of series power active filter plus passive filter

①It is equivalent to a harmonic isolator, which can isolate the harmonic voltage of the mains power supply from the load;
②It can prevent the harmonic current caused by the nonlinear load from flowing to the mains power supply, so that the power factor of the mains input is close to 1;

③Improve the performance of the passive filter, thereby avoiding the “harmonic resonance amplification phenomenon” that may be formed with the mains impedance. The main function of the LC passive filter in the circuit is to eliminate the harmonics in the input current of the mains and compensate for the reactive power required by the load.

The circuit shown in Figure 1 is tested, and the waveforms shown in Figure 2 to Figure 4 are obtained. Figure 2 shows the waveform obtained from the test when the mains voltage contains 1% harmonics and no other loads are connected at the same time. This test shows that when the active filter does not work, the mains input current contains 10% harmonic components. When the active filter is started and put into operation, the input current of the mains becomes a sine wave (a test performed by replacing the mains with a diesel generator set), and the terminal voltage waveform ual of the passive filter is still a sine wave. Therefore, The waveform of the current iF flowing into the passive filter is naturally also a sine wave. The waveform shown in Figure 3 indicates that if the series active filter does not start, the mains input current contains harmonic components; when the series active filter is started and put into operation, the mains input current becomes a sine wave.

Figure 2 - The mains voltage contains 1% harmonic components, the test waveform at no-load
Figure 2 – The mains voltage contains 1% harmonic components, the test waveform at no-load
Figure 3 - Test waveform with nonlinear 6-phase rectifier load
Figure 3 – Test waveform with nonlinear 6-phase rectifier load

Figure 4 is the test waveform when considering the harmonics in the mains voltage. At this time, when the series active filter is started and put into operation, the voltage on the load no longer contains harmonic components, and the mains input current is also a sine wave, while avoiding the resonance amplification of the fourth harmonic.

Figure 4 - Test waveforms considering the presence of harmonics in the mains voltage
Figure 4 – Test waveforms considering the presence of harmonics in the mains voltage

Read more: Common UPS uninterruptible power supply classification and characteristics

Recent Posts

  • Comparison of multi-superrectifier characteristics and the influence of load dual-input PF
  • Application of 12-phase rectifier and passive and active filter in UPS
  • Influence of Input Transformer Connection on Harmonic Current
  • What is a 12-phase diode rectifier with transformer injected harmonics?
  • The working principle of the harmonic type SCR phase-controlled 12-phase rectifier

Categories

  • Basic knowledge of IGBT three-phase SPWM inverter
  • Basic knowledge of uninterruptible power supply
  • SCR polyphase phase controlled power frequency rectifier and three-phase boost single switch SPWM PFC rectifier

Tags

AC filter circuit backup UPS Basic circuit of single-phase PWM inverter Basic structure of IGBT Cascade superposition of independent DC power supply Compensation for the influence of dead zone Composition of three-phase full-bridge SPWM inverter computer power Control method of the three-phase four-leg inverter current crest factor Development of inverter technology Double Fourier series analysis High frequency UPS industrial frequency UPS influence of dead zone on output voltage Influence of unbalanced load on DC input current fluctuation Instantaneous space current phasor control method using hysteresis comparator Inverter technology mains grid nature of the load Power frequency UPS power supply quality issues Precautions for using SCR PWM technology SCR multi-phase phase controlled rectifier SCR power switch time single phase capacitor filter rectifier space flux linkage phasor SPWM control SPWM control method SPWM modulation waveform SPWM soft-switching inverter technology Synchronous SPWM modulation The third generation UPS Three-phase half-bridge inverter Thyristor rectifier Transformer in UPS Two-level SPWM inverter Types of spwm multilevel inverters UPS applications Use gate resistance to control IGBT switch Various control methods of ups Working principle of the three-phase four-leg inverter Working principle of three-phase full-bridge SPWM inverter Working principle of three-phase half-bridge SPWM inverter
ups uninterruptible power supply is a UPS power supply that contains energy storage devices, which can be classified according to the characteristics of transformers and the structure of ups electrical circuit.