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The active filter developed by Dumarsing as an advanced power quality management product integrates the cutting-edge technologies including power electronics technology, digital control technology, and digital signal processing technology, thus featuring high technological content. The core of the product is composed of two parts: power electronic converter circuit and harmonic detection algorithm. The key technology of the power electronic converter circuit is the selection and implementation of topology structure.
The traditional topology in active power filter is two-level topology, characterized by AC-side port only outputting high and low-voltage levels (with the midpoint of converter DC side as the reference point). Another type of novel topology is three-level topology, characterized by AC-side port outputting 3 levels: high voltage, low voltage and neutral voltage (with the midpoint of converter DC side as the reference point). Through comparison of two-level and three-level topology, the two-level topology has the advantage of relatively simple and easy to implement control algorithm, and the disadvantage of the inverter switching device withstanding high voltage, larger stress, and greater loss, and the high frequency harmonic components in the output waveform are rather high, bringing difficulty to the design of switch filter, and lead to higher losses on magnetic components. The three-level solution solves the problem in the two-level solution, so that the system efficiency can be significantly improved, but the control algorithms are relatively complex, and more switching devices are required (but as the voltage withstood by single switch device is reduced by half, the cost of single device declines, so the three-level solution will not significantly increase the system costs).
Our active filter has the following functions during normal operation: eliminate harmonic current generated by non-linear loads, compensate reactive power of backward load and operate as dummy resistor to avoid resonance damage.

The active filter collects current on the DC line using current transformer, after sampling, processes the obtained current signals by harmonics separation algorithm to obtain the harmonic reference signal as modulated signal, and then compare with the triangular wave to obtain the switch signal. The switch signals are used to control the single-phase bridge, according to the principles of technology, reverse connected with the switch signals of the upper and lower bridge arms, so that the harmonic currents with magnitude equal to and direction opposite with the harmonic signal to counteract the online harmonic currents. This is the feedforward control section. Then the online current harmonic components after the filter access points are fed back as the controller input to adjust the feedforward control error.

◆ Three-level inverter circuit;
◆ Modular design;
◆ Three compensation modes: harmonic, reactive and unbalanced load;
◆ Work efficiency >97%, low loss;
◆ Small size, innovative wall/rack-mounted, space-saving;
◆ 3DSP + CPLD digital control methods;
◆ 2nd ~50th orders of harmonics are simultaneously compensated, and can be specified the number of order of compensation;
◆ Two algorithm modes: fast FFT and instantaneous reactive power
◆ Multi-function LCD monitor system, and with PC-end enhancement software.

◆ Harmonic current filter-its main function are harmonic currents absorption and micro-quantitative reactive power compensation.
◆ Slow start electromagnetic contactor bank - suppress the surge current possibly caused during charge by the DC capacitor.
◆ High-frequency inductance capacitor bank - as the power transmission interface between the electric element power converters and power systems, as well as provide the reactive power compensation capabilities to the backward power load.
◆ IGBT power converter - The main functions are to convert the energy supplied by the power system into harmonic compensating current source, and feedback to the power system, and achieve the functions of reducing the harmonic.
◆ DC capacitor bank - Store the energy from the power system in the capacitor bank.

Efficient filtering capabilities

The active filter is product for dynamic filtering of the harmonic currents. Its technical advantages are thorough filtering effect, effectively filtering out higher harmonics, and effectively suppressing resonance, so that the filtering capability is the key parameter of active filter product. Our active filter can filter out 2nd ~50th order harmonic current and for harmonic current less than 50th order, can complete the filtered once for all; and can customize the selection of filtering for harmonic current system within 50th order. Such technology has two advantages:

Product Features:

Firstly, for system with particularly huge capacity of harmonic currents, the Dumarsing active filter and passive filter can form into hybrid filters, among which the passive filter is used to filter out high-capacity and stable low harmonic current, and the active filter is used to filter out the changing and complex high harmonic current and suppress resonance of harmonic current;
Secondly, the optional filtering can be customized in light of the distribution characteristics of the harmonic current frequency of the system to ensure better filtering effect and system stability within fixed capacity.
Meanwhile, the active filter belongs to large power electronics products. The work efficiency (i.e. operation loss) of the product is closely related to the electricity demand. The Dumarsing active filter uses three-level inverter circuit program to reduce the internal IGBT losses, so that the system efficiency is improved significantly. This control algorithm is relatively complicated, but the Dumarsing Electrical active filter keeps work efficiency stably at 97%, which is 2% higher compared with conventional efficiency of 95% of the active filter.
Original 3DSP + CPLD multi-CPU control system
The active filter adopts the harmonic current technology of dynamic compensation, and completes the full motion of detection, analysis and compensation of harmonic current using software algorithms. The software algorithms are burned in DSP (CPU). Compared with double DSP control system of conventional active filter, our active filter uses innovation 3DSP+CPLD multi-CPU control system. In this multi-CPU system, CPLD is the main processor, and the 3 CPUs are co-processors. The CPLD is used mainly to control tasks of three CPUs e.g. simultaneous initiating of data sampling, synchronized processing of data, control of inverter current and generation of PWM timing. Each CPU performs the task of testing one-phase harmonic current, and sends the test results to the CPLD for processing. The system using multiple CPUs for parallel work mainly has the following two advantages:
(1) The computing speed can be exponentially increased, i.e. exponential increase in the harmonic compensation rate;
(2) The increased number of CPUs leads to larger data volume of the software algorithms available.
The active filter mainly includes the following two types of typical algorithm modes: the fast Fourier transform (FFT) and instantaneous reactive mode, and these two algorithms have their respective apparent advantages and disadvantages. The core of the FFT-based digital analysis is how to extract the fundamental component and harmonic component from the currents. Its principle is that the signals in one period are decomposed through FFT to obtain amplitude and phase of different orders of harmonics. The advantages of this method are: the amplitude and phase for each order of harmonics can be obtained once for all, and the number of order for harmonics necessary to be compensated and the proportion of compensation can be freely selected. Its main drawback is that a period of sampling data must be obtained for calculating the content for each order of harmonics. The error signals have to be reconstructed, requiring complex computation and causing great delay. On the other hand, the harmonic extraction method is based on Fourier analysis, the compensated waveform must be subject to cycling change, otherwise greater error will be caused, which also limits the use of the product. The core idea of the detection method based on instantaneous power theory is to extract the current harmonic components using the relationship between the voltage and current in the system. This harmonic detection method may be completely free of delay when only detecting reactive current. When detecting harmonic currents, certain delay exists as the composition of the detected harmonic and the used filter are different, but such delay does not exceed one power frequency period. However, the instantaneous power theory is put forward based on three-phase balance system. According to the existing theory, the three-phase currents can not be independently detected and controlled in the three-phase four-wire system.
The two types listed below are the mainstream algorithms for active filter. Currently, most manufacturers select use of the fast Fourier transform. Thanks to the patented technology of Dumarsing Electrical of hardware system with 3DSP+CPLD multi-CPU parallel connection supporting massive data and the harmonic current detection methods, the Dumarsing Electric active filter can support both algorithms of fast Fourier transform and instantaneous reactive power, our engineers use both algorithms respectively to detect the actual filtering effect during commissioning machine for users on site, and select the algorithm with the best filtering effect in light of the actual situation.

High stability and reliability, high management efficiency, and high engineering efficiency

One major advantage of Dumarsing active filter lies in its modular structure. Compared with conventional two-level active filter, it has advantages of high reliability, high management efficiency, and high engineering efficiency. Our typical active filter modules are in capacities: 25A, 35A, 50A, 60A, and 100A. The active filter system is constructed with multiple active filter modules, so that when any module fails, the remaining modules can sustain normal operation, thereby reducing the single failure points of the system, reflecting the advantages of high stability; any failed module in the system can be directly replaced with active filter module, while the normal operation of remaining modules can support the filtering requirements of users, and minimize the inability to meet the user’s demand caused by such failure.
The loss of filter demand reflects the advantage of high management efficiency; our modular active filter for harmonic compensation capacities weighs only 16kg-40kg, easily handled and installed manually, and free of requirements for cranes, forklifts and other construction machinery. The filters have wide range of module capacities, allow flexible combination and configuration to optimize system capacity, and can be mounted either by wall mounting and rack mounting, reflecting the advantages of high engineering efficiency. The filters are based on three-level inverter circuit technology, the internal switches and other components have smaller volumes than the conventional active filters. The entire unit has the world smallest volume among its kind, thus the space resources can be better used.

Human-Computer Interaction of Information

The human-computer interaction (HCI) of information is an important function of the active filter, and the human-computer information interaction is the carrier for user to understand the system filtering effect, and the machine operation state. The Dumarsing Electric HCI information consists of two parts: the LCD front-desk monitoring system and the PC-end enhancer software self-contained in the active filter. In addition to voltage, current, and total harmonic current distortion (THDi) data routinely read by the monitoring system before and after filtering, our active filter monitoring system also read the orders harmonics spectrum comparison and waveform control graphics before and after filtering, allowing the users to understand the filtering effect of the active filter more intuitively.
In addition to the front-desk monitoring system, our active filters can display filtering information and machine operation in the computer system through the PC-end enhancement software, so that the users understand better the information on human-computer interaction. The Dumarsing Electric is the first manufacturer of imported active filter providing PC-end enhancement software.