Mikko Routimo

Comparison of Voltage-Source and Current-Source Shunt Active Power Filters

In recent years, active power filters have been widely studied. The research has mainly concentrated on voltage-source active filters, but some attention has also been paid to an alternative-to current-source active filters. Since voltage-source pulsewidth modulation (PWM) technology is widely used in industrial applications, this has also been more common in active filter use. In addition, current-source technology has been said to have drawbacks compared to voltage-source systems, such as high on-state losses in the PWM bridge and inefficient inductive energy storage element on the dc side of the bridge. In the paper, the two active filter topologies are compared. First, the main circuits and space-vector modulation techniques used are studied and the digital control systems are presented. The filtering performances of the systems with different kinds of nonlinear load are examined and finally the power losses of the active filters are studied. The comparison is based on measurements with the prototypes built. The results clearly show the properties of the active filters examined. In addition, the results prove that current-source active filters also offer a considerable choice for harmonic filtering

LCL Type Supply Filter for Active Power Filter - Comparison of an Active and a Passive Method for Resonance Damping

First-order L type supply Alters do not always offer sufficient attenuation of switching ripple currents in voltage- source active power filter applications. By using third-order LCL filters the level of the switching frequency current components can be reduced more effectively. However, because of the resonance phenomenon of the supply filter and the active filter wide operating bandwidth, the use of the LCL filter in the active filter applications is challenging. This paper compares an active and a passive method for LCL filter resonance damping, assesses their suitability for the active power filter application and presents their benefits and drawbacks. The passively damped LCL filter utilizes a control system designed for an active filter with a first-order L type filter, while the active damping method examined is based on the cascaded control of the mains side inductor and the capacitor currents. First, the frequency responses of the transfer function models are examined and second, the topologies are studied through experimental tests. The results presented show that both topologies filter the harmonics effectively and the switching ripple is attenuated. The active method requires more current sensors, while additional damping resistors are needed in the passively damped system. However, there are only slight differences both in the filtering results and the power losses.

A novel simple prediction based current reference generation method for an active power filter

This paper presents a novel current reference generation method for an active power filter. The method is simple and it uses data collected in previous periods to generate a current reference prediction. This is used as a reference at the stationary operating point of the load. Because in transient state the prediction no longer holds true, a computational control delay compensation method is used instead. Changing the algorithm according to the operating point guarantees effective harmonic compensation both in stationary and dynamic state. In this paper the proposed reference generation technique is applied to the control of a voltage source shunt active power filter. The system performance and efficiency are examined through measurements.

Current sensorless control of a voltage-source active power filter

The performance of a conventional shunt active filter is heavily dependent on the accurate current sensing and complicated control algorithm. This paper presents a voltage source active power filter control method that does not require any current sensors. The proposed control system is moreover very simple because it compensates the load current harmonics by operating as a sinusoidal voltage source. This paper presents the operating principles and space-vector control of the system. The system performance and power losses are studied with laboratory measurements and the results are compared to a conventional shunt active filter. The test results show effective, high efficiency current harmonic compensating performance.

A novel control method for wideband harmonic compensation

In this paper a novel control method for wideband harmonic compensation with a voltage source shunt active power filter is presented. The effective filtering of the low order harmonics is achieved with an active filter together with a simple computational control delay compensation method. The filtering performance with high order harmonics is improved with a small passive high pass filter connected parallel to the active filter. The control system is presented and the system performance examined through a transfer function model. The measurement results are presented and compared to other methods. The benefits of the proposed system can be clearly seen in the results.

Wideband harmonic compensation with a voltage-source hybrid active power filter

In this paper a voltage-source hybrid active power filter is examined. Wideband harmonic compensation is achieved by improving the active power filter performance with two methods. Filtering of the low order harmonies is improved with a simple computational control delay compensation method applied to the control system, while the high order harmonics are filtered with a small passive high pass filter connected parallel to the active filter. The control system is presented and the system performance examined with measurements at various operating points. The power losses caused by the hybrid filter system are presented and they are compared to the losses of a voltage-source shunt active filter. The benefits of the proposed system can be clearly seen in the results.

Flicker compensation with combined active and passive filters

This paper concentrates on a solution for the voltage flicker problem caused by a resistance spot welding plant. Repetitive voltage changes causing the flicker are difficult to compensate, since the welding currents are high, and the length of the welding period, the delay time between the cycles, and the amplitude of the currents may vary. The solution presented in this paper is the use of an active filter together with fixed reactive power compensator capacitor banks. The simulation and measurement results presented show that voltage fluctuations and flicker levels can be greatly reduced. The dynamics of the combination is found to be fast enough to compensate the rapid variations in the reactive power of the plant. In the solution proposed the use of the passive filter provides a great reduction to the active filter ratings compared to the situation with the active filter as the only compensator. Further benefit is smoothed instantaneous active power drawn from the mains.

A Simple Prediction Based Current Reference Generation Method for a Four-Wire Active Power Filter

This paper presents a simple prediction based current reference generation method for a four-wire active power filter. In the steady state the current reference is generated according to data collected during the previous period. However, during the transient state of the load the prediction is no longer valid. Thus, in order to maintain the effective harmonic filtering performance a computational control delay compensation method is used instead. The proposed method is verified by experimental tests in a laboratory with a microcontroller controlled four-wire active power filter prototype