Verification of current sensorless control for single-phase NPC multilevel inverter

Abstract

The current control is becoming a challenging task for switched mode power supplies, while current sensorless control solutions can avoid the instantaneous current measurements that has been applied for mostly used power factor correction topologies. However, multilevel type of converters haven't been considered to use with current sensorless control (CSC). Hereby, the CSC is applied to three level neutral point clamped converter, where special volt-second balance is applied to inductor in order to keep average inductor's current value to track the reference signal during both discontinuous and continuous current modes. The explanation of post-fitting and pre-fitting current trajectories is done that are necessary for proper transition between voltage levels. Experimental results have confirmed the theoretical model. Keywords-sensorless control; current control; pulse width modulation inverters978-1-4799-6301-0/15/$31.00 ©2015 IEEE

Bidirectional single-loop current sensorless control applied to NPC multi-level converter considering conduction losses

“…This type of control utilises only one control loop with feedback from the output capacitor voltage and does not use any current feedback signal as it is assumed that inductor's volt-second balance is perfectly calculated and inductor's current follows the reference signal (see Figure 1 (c)). Since that time the CSC has been applied to multiple type of PFC topologies: single switch PFC (diode bridge and boost converter) [38,39], interleaved [40,41], bridgeless [42,43], half-bridge [44][45][46], full-bridge [47,48] and also neutral-point clamped multi-level converter (NPC MLC) [49,50]. Several recently published papers have been devoted to different type of three-phase converter topologies operated under CSC [51][52][53] that makes evidence of CSC use in high power applications.…”

Current sensorless control for half‐bridge based AC/DC PFC converter with consideration of conduction losses

“…There are current sensorless approaches for three-phase converters reported before that utilize DC link current sensor, which allows to estimate phase currents based on state of switches if measured at right instant within the period [23,[26][27][28]. In contrast, the single-loop CSC defined in various articles contains only single voltage control loop (Figure 1(b)) to control the AC/DC converter, but current control is replaced with mathematical block without the PI regulator [32][33][34][35]. However, current control was implemented as in traditional scheme, where current control loop based on PI regulator was used to form the current shape ( Figure 1(a)), while voltage control loop was used to stabilize DC bus voltage [31].…”

“…The interleaved PFC with phase-shedding function has also been evaluated in [37]. Several other approaches were dedicated to implementation of CSC with bridgeless [38], half-bridge [21,39], and even multilevel type of converters [34,40]. The last one is challenging because of problem of proper volt-second balance during transition between different voltage levels, where it was proposed to use pre-fitting and post-fitting current matching trajectories.…”

“…However, current control was implemented as in traditional scheme, where current control loop based on PI regulator was used to form the current shape ( Figure 1(a)), while voltage control loop was used to stabilize DC bus voltage [31]. In contrast, the single-loop CSC defined in various articles contains only single voltage control loop (Figure 1(b)) to control the AC/DC converter, but current control is replaced with mathematical block without the PI regulator [32][33][34][35]. Thus, CSC allows simplifying the control scheme and the transfer function of the converter.…”

“…This impose limitations on power density and efficiency of converter utilizing those CSC methods. The discontinuous conduction mode (DCM) was studied by BS [44] FB [42] MLC [34] This work HB derived [35] FB derived [29] FB derived [30] FB derived [45] Fixed Fsw authors in [41] because half-bridge converter topology inherits higher voltage swing applied to the input inductor, which causes rapid rising and falling slopes of the inductor current, resulting in longer duration of DCM that should not be neglected. Further, boost converter and topologies derived from it feature high linearity of the input characteristic and thus provide 'self-PFC' functionality when operate in DCM with average current control [46,47], which is the case for the CSC proposed.…”