In the past few years, pollution in the power supply system has significantly increased. The primary reason is that non-linear loads are constantly increasing among residential, commercial, and industrial users. Therefore, power supply distortion is caused by high-order harmonic currents occurring in the public power grid. Single phase and three-phase APC UPS power supplies are used to protect, supply clean and uninterrupted electrical energy free from interference from the public power grid, thereby improving the quality of electrical energy supplied to important loads such as computers, medical equipment, industrial process control, etc. In addition, it is necessary for the UPS system to manipulate the input current to reduce its total harmonic distortion (TH), which is beneficial for improving power factor. The three-phase parallel type uninterruptible power supply system has been applied in harmonic suppression and reactive power compensation, but the output voltage and input current cannot be controlled together. Single phase and three-phase APC UPS systems have been proposed, and the output voltage and input current can be controlled together,. In the literature, when comparing UPS with filtering function with backup, online, and online interactive topology structures, some of its advantages become apparent. Therefore, the primary advantage of dual inverters is their rated power, which is approximately 10% -20% of the total power of the UPS system. Series parallel compensation single-phase UPS has been proposed, which can achieve high-quality input current and output voltage. This article proposes a similar single-phase UPS structure that can also be achieved in output parallel conditioning. The UPS system consists of two single-phase PWM converters to perform the function of an active filter. As a series active power filter, it completes the phase synchronization between the sine current source and the input voltage. Another, as a parallel active power filter, it makes the sine voltage source in phase with the input voltage and supplies a sine voltage with low total harmonic distortion to the load. Select the repetitive manipulation algorithm to generate the reference input current and output voltage. The input current of the reference is obtained through an algorithm based on synchronous rotating coordinate system, and the output voltage of the reference is obtained through single-phase PLL based on instantaneous active power theory. Phase detection is completed through a single-phase phase-locked loop. According to the theory of instantaneous active power, a single-phase phase-locked loop (P-PLL) is used to construct a two-phase stop coordinate system, in which a virtual orthogonal voltage needs to be generated, which is 90 ° different from the measured mains voltage. Describe and analyze the control algorithm of UPS system in synchronous rotating coordinate system and the active power flow of the entire APC UPS system. The mathematical analysis and simulation results have verified the development of the theory and proved the functionality of this UPS system.
Overview of UPS topology structure
The topology of the single-phase UPS system consists of two single-phase full bridge PW converters as shown in Figure 1. PWM converters are used for series parallel filtering at the common DC terminal. The capacitor and battery pack are connected to a common DC terminal. In addition, when the power grid occasionally malfunctions, the static switch ‘sw’ completes the quick switching function between the UPS system and the power supply. According to the control algorithm of synchronous rotating coordinate system, it is used to control the series PWM converter to make the line current amplitude close to a sine wave. Its high impedance can filter out harmonic currents generated by nonlinear loads. Operate a parallel PWM converter to function as a sine voltage source. Controlling the output voltage Vfa of APC UPS power supply and the corresponding input voltage Vsa, its low impedance can absorb the harmonic current of the load. The output voltage (V) and input current (1) are respectively controlled by the input voltage (V). This effectively eliminates harmonics and compensates for reactive power.