A Study On Detection A Way Of Reactive Harmonic Current

With the development of Power Electronics technology, many kinds of large power capacity switching components are widely used. On one hand, they made Power energy transformation and application conveniently, on the other hand , they lead to the serious reactive power and harmonic current pollution in the power system. It has been a key project in power electronics application technology to study the active power filters to compensate the reactive power and harmonic current pollution caused by power converters. However, surveying the last 30 years studying achievements, we can find that the research jobs are mainly focused on three-phase current tracking parallel active power filters. At the same time, reactive and harmonic current detection method which decides the current tracking active power filter's dynamic compensation characteristics has some demerits .For example ,an excellent method to detect the reactive and harmonic current quickly and exactly has not been found up to the present when the mainline voltage and the load current are both distorted .As a result, the reactive and harmonic current detection method based on ac power theory and the voltage tracking active power filter without the need of current detection control have been snidied systematically in this dissertation . These studies have important significance for the active power filters early industrialization and application. The main studying contents and achievements in this dissertation are presented asfollows.Based on the analysis of the selective harmonic elimination PWM mathematical model, an equivalent Newton iteration solving method about the switching angles nonlinear transcendental equation set is presented. The algorithmic convergence time is enormously reduced and the algorithmic convergence ability is highly increased.Traditional AC averaged power theory, instantaneous reactive power theory and the relative reactive and harmonic current detection methods are systematically studied. Then it is revealed that the reactive and harmonic current detection method based on the instantaneous reactive power theory is the same as the method based on the averaged power theory in the essence under the condition of mainline voltage and load current are both distorted.According to the ultimate goal of AC mainline reactive compensation and harmonic suppression, a new optimized pulse modulation detection method for reactive and harmonic current based on the averaged power theory is presented . The mathematical model of this method is established and the detection current realization is studied. Simulation and experiment results manifest that the proposed method has many advantages. Firstly it dose not need multipliers for signal modulation. Secondly the detection precision is only related to the synchronization phase but not to the amplitude of the mainline voltage because that it uses the optimized pulses synchronous with the mainline voltage as modulation signals. Thirdly it decreases the requirement of the input low pass filter and eliminates the error resulting from the direct component and even harmonics of load current. The most significant merit is that it can eliminate the effect of a few low order odd harmonics and the detecting circuit is easy to be implemented. This method overcomes some disadvantages of the traditional methods.