SAPF for the Inter-harmonics on Grid Network Compensation
International Journal of Grid and Distributed Computing
Using SAPF (shunt active power filter) has been proved as an effective way for harmonic compensation. In practical applications, the performance of SAPF will be impacted by interharmonics and non-periodic disturbances. This paper analyzed the CPT (conservative power theory) definition of power theory and the application method for SAPF. Repetitive controller and PI controller were used as a combination way for the harmonic and inter-harmonic compensation. By the EID (equivalent
... nt input-disturbance) controller, the performance for non-periodic interference suppression of SAPF can be improved. By simulation with MATLAB, the models of SAPF system, repetitive controller and EID controller were built. Through the computer simulation method, we can verify the designed system performance. unbalance and waveform is distorted. Detection method based on p-q-r power theory, of which the zero power is defined  , can be used for the detection of three-phase unbalanced system. Harmonic and reactive current detection problems can be solved by universal instantaneous power theory and its improved algorithm when the three-phase voltage is unbalance and waveform is distorted [15, 16] . FBD method was proposed by Fryze, and improved by Buchholz and Dpenbrock. By separating the current with concept of equivalent conductance, the physical meaning of the current component was discussed. And compared to the traditional instantaneous power definition, without coordinate transformation, FBD method was characterized by a relatively simple algorithm [17, 18] . The instantaneous power was defined by CPT (conservative power theory) in the three phase unbalance and distortion system  . Compared to the p-q power theory and FBD power theory, the unbalanced and distortion current is more accurately expressed by CPT theory [20, 21] . But it needs further study for the grid with inter-harmonics situation. The periodic reference signal or the periodic interference signal will be controlled by repetitive control method. And when it combined with PI control, or predictive control, the PWM converter can get better control performance for current. But repetitive control performance for non-periodic signal or non-periodic interference signal is poor. Therefore, it is important to improve the control system for better non-periodic control performance. There are two ways to improve the performance, HORC (high-order repetitive controller)  and adaptive repetitive controller . Though the control performance can be improved by these methods, the complexity of the system will be increased, and it will be difficult to achieve system stability. If we consider the non-periodic signals as interference, the disturbance observer can be used to improve the non-periodic control performance of repetitive controller. EID (equivalent input disturbance) observer  is different with the usual disturbance observer, which is not based on the inverse system theory, but based on an active disturbance rejection method. This method is simple to implement and can be used for repeatedly controller to improve the non-periodic disturbance rejection performance. In this paper, the model of three-level SAPF was built. SAPF directive harmonic current detection method under the inter-harmonic environment based on the definition of CPT power theory was studied. Both the repetitive control and PI control was used for the grid current harmonics and inter-harmonics compensation. By introducing EID controller improves the SAPF control performance for non-periodic signal interference. Analysis of the designed system stability and sensitivity of the issue, gives a suitable inter-harmonics environment SAPF system design methodology. Simulation and experiment show that the designed system can accurately detect harmonic, inter-harmonic content, effective on the grid to compensate harmonics and inter-harmonics. Mathematic Model of Three-level SAPF on Virtual Flux Oriented The main circuit topology of SAPF is a diode-clamped three-level inverter. Three kinds of switch state can be obtained by four switches of each phase leg from threelevel converter, which is shown in Figure 1 (a) .