Digital Current Control of a Voltage Source Converter With Active Damping of LCL Resonance

Abstract

Inductance-capacitor-inductance (LCL)-filters installed at converter outputs offer higher harmonic attenuation than L-filters, but careful design is required to damp LCL resonance, which can cause poorly damped oscillations and even instability. A new topology is presented for a discrete-time current controller which damps this resonance, combining deadbeat current control with optimal state-feedback pole assignment. By separating the state feedback gains into deadbeat and damping feedback loops, transient overcurrent protection is realizable while preserving the desired pole locations. Moreover, the controller is shown to be robust to parameter uncertainty in the grid inductance. Experimental tests verify that fast well-damped transient response and overcurrent protection is possible at low switching frequencies relative to the resonant frequency. Index Terms-Electromagnetic interference (EMI), inductance-capacitor-inductance (LCL)-filter, voltage source converters (VSCs).

Stability Analysis of Three-Phase PWM Converter with LCL Filter by Means of Nonlinear Model

“…An another solution is the active damping which is realized by modifying the control algorithm. Methods proposed in the literature differ in number of additional sensors and complexity of control algorithms [5][6][7][8]. Although the results presented in the papers show that the stability margins can be enlarged by the active damping, most of these methods have some restrictions and drawbacks such as a very complicated and unreliable parameter tuning and poor robustness against parameters variations.…”

LCL-resonance damping strategies for grid-connected inverters with LCL filters: a comprehensive review

“…In total, there are 18 kinds of state feedback as shown in (6) where P, I and D stand for proportional, integral and derivative feedback, respectively. The number of states participating in the pole-placement can be 2, 3 or 4 [42][43][44][45][46][47][48][49].…”

“…Filter-based AD improves stability by adding a digital filter next to the current controller [11][12][13][14][15][16]. For feedbackbased AD, the state used for feedback can be the capacitor current [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], the capacitor voltage [33][34][35][36], the inverterside current [37], the grid current [38][39][40][41] or a combination of multiple states [42][43][44][45][46][47][48][49][50]. Among the feedback-based AD methods, proportional feedback of capacitor current is widely studied during last decade due to its simple implementation.…”

Active Damping Method Using Grid-Side Current Feedback for Active Power Filters with LCL Filters

“…By considering u i as an additional state and u 1 as a new input, this delay can be taken into account in the state-space model by rearranging the state equation [19]. The augmented discrete-time state-space model is then given by:…”

“…Another important work in this area was done in [18] by introducing the concept of a "virtual resistor", in which the differential of the capacitor current was fed back to the reference of the converter-side current to simulate a real damping resistor. Unlike these single state feedback methods, complete state information was used in [19] and [20] for current control. All of these methods require extra sensors to measure additional states in order to achieve the necessary damping, which increases hardware costs and reduces system reliability.…”