The wide use of nonlinear loads, such as front-end rectifiers connected to the power distribution systems for dc supply or inverter-based applications, causes significant power quality degradation in power distribution networks in terms of current/voltage harmonics, power factor, and resonance problems. Passive LC filters (together with capacitor banks for reactive power compensation) are simple, low-cost, and high-efficiency solutions. However, their performance strongly depends on the source impedance and can lead to unwanted resonance phenomena with the network . In addition, passive solutions are not effective for applications in which the nonlinear load exhibits fast transients.
"A number of control methods have been reported in the literature such as proportional-integral (PI) control , hysteresis control , dead-beat control , repetitive-based control , adaptive control , and nonlinear control . Also, there has been tremendous progress during the last decade in current control techniques for active power filters      including of a proportional controller plus multiple sinusoidal signal integrators , a PI controller plus a series of resonant controllers  , or vector PI (VPI) controllers . This is due to the development of powerful and fast microprocessors. "
[Show abstract][Hide abstract] ABSTRACT: This paper describes the design of a new configuration of direct power control (DPC) based on high selectivity filters (HSF) to achieve near-sinusoidal source current waveforms under different source voltage conditions. The proposed method uses the high selectivity filters instead of the classical extraction filters (low pass filters). The basic idea of the proposed DPC is to choose the best inverter voltage vector in order to minimize instantaneous active and reactive power errors using two hysteresis comparators. Their outputs associated with a switching table, control the active and reactive powers by selecting the optimal switching states of the inverter. Simulation results have proved excellent performance, and verify the validity of the proposed DPC scheme, which is much better than conventional DPC using low pass filters.
Electric Power Systems Research 03/2014; 108:113–123. DOI:10.1016/j.epsr.2013.11.006 · 1.75 Impact Factor
"Resonant controllers have been used in practical applications with good results    . They have an important saving of computational burden and complexity due to their lack of multiple Park transformations       . PR controllers can be tuned with a high bandwidth, so a fast post-sag transient response is achieved    . "
[Show abstract][Hide abstract] ABSTRACT: Power quality is a very important topic nowadays. Sensitive industrial equipment should be protected against steady-state distortions and temporary transients in the distribution lines. Typical disturbances that affect the voltage waveform quality are harmonics, imbalances and sags. This paper presents a solution to protect sensitive loads against voltage disturbances that is based on a series power line conditioner. The goal of the proposed design is that the load does not suffer considerable input voltage variations. To achieve that, a Proportional-Resonant (PR) controller and a reference generator block based on a low-gain PLL are used, which avoids a sag detection block. Furthermore, a frequency adaptation loop is included in the PR controller, which provides a proper controller operation even with utility grid frequency deviations. Finally, a hardware in the loop (HIL) test rig is used to validate the system.
Electric Power Systems Research 03/2012; 84(1):20–30. DOI:10.1016/j.epsr.2011.10.002 · 1.75 Impact Factor
", and high values of K P imply less selective filtering (which is, in fact, an interesting feature in several cases , , , , –, , , ). Thus, K P should be tuned Fig. 5. Nyquist diagrams of [K P + G PR h (z)] · P (z) (φ h = 0) for different values of K P . "
[Show abstract][Hide abstract] ABSTRACT: The following two types of resonant controllers are mainly employed to obtain high performance in voltage-source converters: 1) proportional + resonant (PR) and 2) vector proportional + integral (VPI). The analysis and design of PR controllers is usually performed by Bode diagrams and phase-margin criterion. However, this approach presents some limitations when resonant frequencies are higher than the crossover frequency defined by the proportional gain. This condition occurs in selective harmonic control and applications with high reference frequency with respect to the switching frequency, e.g., high-power converters with a low switching frequency. In such cases, additional 0-dB crossings (phase margins) appear; therefore, the usual methods for simple systems are no longer valid. In addition, VPI controllers always present multiple 0-dB crossings in their frequency response. In this paper, the proximity to the instability of PR and VPI controllers is evaluated and optimized through Nyquist diagrams. A systematic method is proposed to obtain the highest stability and avoidance of closed-loop anomalous peaks: it is achieved by the minimization of the inverse of the Nyquist trajectory distance to the critical point, i.e., the sensitivity function. Finally, several experimental tests, including an active power filter that operates at a low switching frequency and compensates harmonics up to the Nyquist frequency, validate the theoretical approach.
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