Heikki Tuusa

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

A vector controlled current-source PWM rectifier with a novel current damping method

Three-phase current-type pulse width modulation (PWM) rectifiers are becoming increasingly popular as the front-end converter unit in power electronic systems due to tighter electromagnetic compatibility (EMC) regulations. In this paper the control of the current source PWM rectifier in the synchronously rotating reference frame is discussed. A control system is presented in which the active and reactive power are independently controlled with real and imaginary axis components of the supply current vector. A new damping method for supply current oscillations is introduced. The method operates in an open-loop manner and is very suitable for microcontroller implementation since the calculation power demand is low. Furthermore, it is shown that in the synchronously rotating coordinates, where the sinusoidal variables appear as DC quantities, the compensation of the reactive power drawn by the supply filter can be done very easily. The proposed control methods are realized using a single-chip Motorola MC68HC916Y1 microcontroller. The experimental tests show excellent performance in both steady state and transient conditions.

Comparison of Simple Control Strategies of Space-Vector Modulated Indirect Matrix Converter Under Distorted Supply Voltage

This paper concerns the effect of symmetric supply voltage harmonics in a space-vector modulated three-phase indirect matrix converter (IMC). The IMC is modulated using indirect space-vector modulation. The effect of symmetric supply harmonics on load voltages and currents is analyzed using space-vector presentation. The measurement and simulation results with distorted supply voltages are compared to the results with pure sinusoidal supply voltage. Four simple control methods of IMC are tested in simulations and measurements: 1) open-loop control without measurements (Method I); 2) calculation of modulation index using measured supply voltages (Method II); 3) closed-loop control of output currents (Method III); and 4) combination of Methods II and III, i.e., closed-loop output current control with supply voltage measurement (Method IV). All the methods are easy to implement and do not require complicated computing. It is noted that Methods II and IV, where modulation index is calculated using measured supply voltage magnitudes, can produce more sinusoidal load currents than Methods I and III, which suppose ideal supply conditions

vector-controlled PWM current-source-inverter-fed induction motor drive with a new stator current control method

In this paper, the control of the pulsewidth-modulated current-source-inverter-fed induction motor drive is discussed. The vector control system of the induction motor is realized in a rotor-flux-oriented reference frame, where only the measured angular rotor speed and the dc-link current are needed for motor control. A new damping method for stator current oscillations is introduced. The method operates in an open-loop manner and is very suitable for microcontroller implementation, since the calculation power demand is low. Also, the stator current phase error caused by the load filter is compensated without measurement of any electrical variable. With the proposed control methods the motor current sensors can be totally eliminated since the stator current measurements are not needed either for protection in the current-source-inverter-fed drives. The proposed control methods are realized using a single-chip Motorola MC68HC916Y1 microcontroller. The experimental tests show excellent performance in both steady-state and transient conditions.

A novel open-loop control method for a current-source active power filter

This paper presents a new control system for a current-source active power filter. The harmonic current compensation is realized using only a feedforward control of the load currents. The LC filter resonance of the converter is damped in an open-loop manner using the dynamic equations of the supply filter. The benefits of the proposed control system are that it is simple and straightforward, the number of measurements and sensors can be minimized, and also that the LC filter size can be optimized according to proper harmonic distortion level of the supply currents without care about the stability issues of the closed-loop system. This usually leads to reduction of the filter size. Also, the changes in fundamental current components of the active filter can be effectively realized when the active power filter can also be used as a fast reactive power compensator. The control system also includes the calculation delay compensation of the digital control system. The control system is realized using a single-chip Motorola MPC555 microcontroller. The tests with the prototype show effective current harmonic compensating performance of the nonlinear loads.

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.

Realization of a three-phase indirect matrix converter with an indirect vector modulation method

This paper presents the simulation and measurement results of a three-phase 5 kVA vector modulated indirect matrix converter (IMC). Functionally the IMC is very similar to the direct matrix converter (DMC) but it has separate line and load bridges. The indirect vector modulation method (IVM) is presented using space vector theory instead of conventional matrix form. Most research on IMC modulation has been done using triangular wave voltage command modulation (TVM). However, microcontroller technology is nowadays more flexible and multifunctional than analog technology. For microcontrollers vector modulation is more appropriate than TVM. Thus, the IVM with microcontroller was used instead of conventional TVM with analog technology. The benefits of the IMC are sinusoidal input current waveform, very low input current distortion and controllable input power factor. Simulations and measurements confirmed these benefits. Measured efficiency of the IMC prototype was 0.97.

Space vector modulation and control of a unidirectional three-phase/level/switch VIENNA I rectifier with LCL-type AC filter

This paper presents a novel three-level space vector modulation method applied to a vector controlled VIENNA I rectifier with LCL-type AC filter. The principle modulation algorithm operation, basic assumptions and restrictions due to the main circuit are analysed in case of conventional L filter. Then the analysis is extended to include the LCL filter. On the basis of the key equations derived from the system examined, the vector control system is realised. The theoretical analysis of the proposed modulation technique and vector control system is verified by Simplorer and Matlab Simulink simulations, taking into consideration the total harmonic line current distortion, the losses in the active and passive components, delays and switching transients of the semiconductor devices. The rectifier system is designed to operate at a nominal DC link output power of 50 kW, DC link voltage 650 V and applied switching frequency 3.5 kHz. The LCL filter is designed so that the total harmonic line current distortion is 1% while the rectifier current distortion is 4%.

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.

Comparison of three series hybrid active power filter topologies

The most common problem arising in the supply network is current harmonics. They may cause harmonics in the supply voltage and create problems, for example, in the distribution network. Active and passive filters are the traditional way of filtering currents. However, both of these have some disadvantages, namely resonance and tuning problems in passive filters and lack of high power switches in active filters. Research has recently been done to combine active and passive filters. These combinations are called hybrid filters and their purpose is to work efficiently without the disadvantages characteristic of the active and passive filter used alone. This paper presents a comparison of three hybrid filter topologies. All hybrid filters included in the comparison are based on a series active power filter. The comparison between filters is made according to their capability to filter current harmonics in the case of nonlinear load at different operating conditions.