M. Salo

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.

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.

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.

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.

A new control system with a control delay compensation for a current-source active power filter

In this paper, a new control system for the current-source active power filter is presented. The harmonic current compensation is realized using combined feedforward control of the load currents and closed-loop control of the supply currents. The control system includes a simple method for compensating the sampling and calculation delays of the digital control system. The compensation in the proposed method is achieved using the regular LC filter of the active power filter as an energy storage for load currents, and no additional components is needed in the main circuit. Furthermore, the calculation power demand of the compensation method is very low and is, therefore, suitable for single-chip microcontroller implementations. The proposed control system is realized using a 32-bit Motorola MPC555 microcontroller. The simulation and experimental results show effective filtering performance also for higher order harmonics of the distorted load currents.

A Novel Vector Controlled Current Source Shunt Active Power Filter with Reduced Component Voltage Stresses

Voltage stresses and power losses are a problem in active power filters. In this paper a novel topology for reducing component voltage strains and power losses in a current source shunt active power filter (CSAPF) is presented. The voltage stresses are compared with a conventional CSAPF and results are encouraging.

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.