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In this paper, a novel configuration of the back-to-back (BTB) converter interconnecting two synchronous AC grids is proposed. The feature of this BTB converter configuration is the substantially reduced capacity compared with the exchanged power between the two grid partitions. Unlike the conventional full-capacity BTB converters, the capacity of the proposed BTB converter in this paper is around...
In this paper, an improved voltage balancing method of modular multilevel converters (MMCs) is proposed. This method divides sub-modules in same arm into several groups which voltage balancing is based on. The voltage balancing between groups is based on the sorting result of group sub-module average voltage and the voltage balancing within group is based on the sorting result of sub-module voltages...
Aimed at the problems of larger torque ripple and non-constant inverter switch frequency in the direct torque control for asynchronous motor, this article puts forward a new idea. In same words, the idea is that the traditional PI controller is replaced by speed controller of sliding mode variable structure (SMVS). What's more, according to the mathematical models of induction motor in synchronous...
Ideally, the inner (the upper or lower arm) current of a modular multilevel converter (MMC) is assumed to be the sum of a dc component and an ac component of the fundamental frequency. However, this current is usually distorted and the peak/RMS value of it is increased compared with the theoretical result. This is because ac current flows through the submodule (SM) capacitors and the capacitor voltages...
Power electronic transformer acts as a key component of the future automation in smart grid, which is the replacement of conventional distribution transformers by a power transformer. In this paper , the optimum design of a power electronic transformer(PET) based on topology of Modular multilevel converter (M2C). M2C is an emerging and highly attractive topology intended for high- or medium-voltage...
The droop method has been widely used in the parallel operation of inverters. The coefficients of the droop controller influence the transient response and stability of the wireless paralleled inverters system. However, the conventional phasor representation of sinusoidal signals is constrained by the quasi-stationary assumption, which is generally acceptable for the steady-state or slow-acting analysis...
Modular multilevel converter (MMC) is a highly attractive and promising topology especially for high voltage applications. In this paper, the dead time effect introduced by the real power switches on the performance of MMC is analyzed. The results show that the dead time will deteriorate the output voltage and is very harmful to the buffer inductors. To alleviate the effect of the dead time, an improved...
This paper deals with parallel operation of 400Hz inverters in ground power units (GPU) for airplanes. For high-power 400-Hz inverters, the modulation frequency ratio is fairly low, which causes difficulties to the parallel operation. To reach low THD content in output voltage, resonant controllers are used for control of each 400-Hz inverter in the paralleled GPUs. With resonant controllers, very...
Based on conventional droop control scheme, a novel active and reactive power sharing method is proposed for parallel operation of 400-Hz inverters. Compared with the existing methods, the proposed solution employs the single-loop resonant controller which ensures good voltage regulation. Moreover, the feedback sensors of the output currents are also removed by implementing it in a software routine,...
For voltage source inverter based 50 Hz or 60 Hz power supplies, it is conventionally assumed that double-loop control with an inner current-loop performs better than single-loop methods. However, this paper analyzes the role of the inner current-loop in double-loop digital control of 400 Hz inverter under low switching frequency condition. The results show that the inclusion of an inner current-loop...
This paper presents an advanced voltage control method for voltage-controlled current source inverter(VC-CSI) with nonlinear loads. The proposed technique adopts the proportional sinusoidal signal integrator (PSSI) controller to achieve a rather good voltage tracking ability under nonlinear load conditions, which can be implemented directly in the stationary alphabeta frame with no need of the rotating...
For voltage source inverter (VSI) based power supply with small filter inductor, the current ripple of the power switch is large especially under light load conditions. The dead-time effect in this situation is analyzed in this paper. The results show that the dead-time effect is eliminated at most zero-crossing instants of the current. Conventional dead-time compensation methods either average voltage...
This paper studied the control of current source inverter (CSI) used in direct-drive wind power generation system, where CSI serves as the actuator of the control and optimization of the system besides the grid inverter. This function of CSI is realized through the control of CSI dc terminal voltage Vdc. Two factors which exert restrictions on the control of Vdc were analyzed. The first one is the...
Static power converters are used for many applications, like frequency converters for motors, uninterruptible power supplies(UPS's), general power supplies, and also with ground power units(GPU) for airplanes. This paper analyses the performance of high power static 400 Hz supply system. In such a system, the topology is a three single- phase H-bridge inverter with a multi-limb output transformer...
Wind power generation system operates in variable speed constant frequency condition. If the wind turbine is under controlled working around the optimal tip-speed ratio, the wind turbine can achieve relatively high conversion efficiency, and generated energy can be obviously increased, then propeller regulation can be simplified. Current source inverter (CSI) is adopted as the inverter of direct-drive...
In this paper, the different influences of three-limb and multi-limb transformer with Star-Star or Delta-Star connection, three-limb filter inductor, multi-limb filter inductor and position of the LC filter in a three-phase PWM inverter have been analyzed in detail in stationary dq0 frame. The analysis show that three-phase transformer with different limb numbers and connection types have different...
The current source back-to-back converters have been largely neglected because of the slow transient response and low power factor, which is mainly resulted from a fixed PWM pattern and a poor control method. However, current source converters have intrinsic advantages such as the high reliability and the inherent current limiting capability. Due to these advantages, more and more people have been...
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