【正文】 lex power system under consideration are given in the αβ domain, as described in references [1], [3] and [5], as follows: depicts the time variation of p and q for the plex single phase power system under consideration. In this figure PAV and QAV respectively are the average values of the active and reactive power. The instantaneous power factor, Ф, is defined as: It is important to point out that the values of p, q and Ф in Eqs (7) and (8) are instantaneous values. The pqr theory is introduced in reference [3], where the current, voltage and power equations are projected in pqr rotating frame of reference. shows the voltage ponents in both of the fixed αβ and rotating pq frame of reference for a single phase power system. The raxis is considered to be identical to the zero axis, hence the voltage transformation equation from the fixed frame of reference αβ to the rotating frame of reference pqr, can be written as: The currents in the rotating frame of reference, ip, iq and ir are related to the currents in the stationary frame of reference, iα and iβ by similar equations as the voltage equations in . Moreover, the following relations can be derived in the pqr rotating frame of reference: 3 DERIVATION OF REFERENCE CURRENT EXPRESSIONS FOR THE ACTIVE FILTER In this section instantaneous expressions for the reference currents for an active power filter to pensate for the harmonic distortion or reactive power or both in the single phase power system under investigation are derived. Because of the symmetry of the plex voltage and current vectors trajectories, , the average value of the active and reactive powers for both of the real and imaginary/fictitious phases can be evaluated from as follows: According to reference [1], the instantaneous expressions for the active and reactive power in the real phase of the single phase power system under analysis are given as: The real phase average value, fundamental and ripple ponents of the active and reactive power are extracted from Eqs (12) and (13) and are depicted in Fig .7 and respectively. The real phase current, iα, can be derived from as follows: In , p~ and q~ respectively are the ripple active and reactive power ponents. Reference current for the active filter of the single phase system under consideration can assume different expressions depending on the special requirements of pensating for the reactive power or filtering the distortion harmonics. Three special cases are listed below: i) Reference current for distortion harmonic filtering and reactive power pensation ii) Reference current for average reactive power pensation iii) Reference current harmonic distortion pensation 4 EXPERIMENTAL RESULTS A test rig was set up to verify the theoretical derivations above. An active power filter is implemented with the current reference of Eq.(15) used as an input to the filter and the digital signal processing of the voltages and currents is implemented using a 32 bit floating point DSP, TMS 320C31. The configuration of the experimental setting is shown in . The nonlinear of the single phase power system under experimentation is a diode bridge rectifier with an RL load connected to the dc side. The ac to dc converter is rated at 25 kVA. An inductor, L, with a value of mH and a capacitor with a value of 10,000 181。F are used as dc output filter.. The output current of the active power filter is controlled by a hysteresis parator to confine the switching frequency to 15 kHz. shows the waveforms of the load current, the pensating current of the active power filter and the supply current. It is clear that active power filter performed its task of pensating for the harmonic distortion as the supply current is converted to a pseudosinusoidal waveform from its original square shape waveform. The top waveform in shows the original supply current waveform and the bottom waveform shows the supply current wave form after the implementation of the active power filter. The middle wave form is the pensating current of the active power filter. 5 CONCLUSIONS A novel strategy, orthogonal transformation technique, is used to yield reference current expressions for the active power filter of a single phase power supply feeding a solid state power converter, in terms of the supply voltage and current. The power active filter control strategy could pensate for either the harmonic distortion of the supply current or the reactive power or both. Experimental results demonstrated the effectiveness of the novel active power filter control strategy. 6 REFERENCES 1. Akagi, H., Kanazawa, Y. and Nabae, A., Generalized Theory of the Instantaneous Reactive Power in Three Phase Circuits, Proceedings IPEC83 Conference, Tokyo (J8), Sept. 1983, pp 13751386. 2. Dobrucky, B., Analysis and Modelling of Power Semiconductor in Steady and Transient States, PhD Thesis, University of Zilina, Slovak Republic, 1985. 3. Kim, H. and Akagi, H., The Instantaneous Power Theory on the Rotating pqr Reference Frame, Proceeding of PEDS’99 Conference, . 4. Kim, H., Blaabjerg, F., BakJensen, B. and Choi J., Novel Instantaneous Compensation Theory in Three Phase Systems, Proceedings of EPE’01 Conference, Graz (Austria), . 5. Akagi, H., Kanazawa and Nabae, Instantaneous reactive Power Compensators Comprising Switching Devices Without Energy Storage Components, IEEE Transactions on AI, , 1984, , pp 625630. Power System Harmonic Fundamental Considerations: Tips and Tools for Reducing Harm