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This paper analyzes the active power in modular multilevel converters (MMCs), and presents a novel comprehensive control scheme of low frequency operation for the arm capacitor voltages and high frequency circulating current. The inner loop of this scheme employs the arm current direct control which can control the ac side currents, dc-link current and circulating currents simultaneously; an improved...
The three-loop power virtual synchronous generator (VSG) control methods are commonly used in microgrid inverter (MGI) units to share the loads among the parallel MGI units. In order to achieve stable operation of the MGI units under paralleled or grid-connected mode, a droop synchronization controller is designed in this paper. The difference of phase and amplitude between different MGI units is...
The conventional PV systems based on the voltage inverters only inject dispatched power to the utility grid when they work at a grid-connected mode in the hydro-PV hybrid microgrid. Due to the droop method employed for load sharing between generators, as well as the enormous inertia of system. The existence of frequency steady-state error and the slow active power/frequency dynamic response are inevitable...
This paper proposes an improved power sharing control scheme to achieve the accurate power sharing control and offer an improved PCC voltage regulation capability in islanding microgrid. An enhanced virtual impedance design is assumed in the conventional droop control scheme to manage distributed generation (DG) units to export the accurate reactive power in proportion to their rating. A point of...
The resonance characteristics of ultrasonic transducer are analyzed based on the equivalent circuit of transducer and the quantitative calculation of admittance circle, and a control method of frequency tracking based on variable step length is proposed, and the limits of step switching are deduced, and the control parameters of the control method based on variable step length is designed in this...
Ripple current at twice the output frequency exists at dc side in single phase inverter due to the instantaneous power imbalance between input and output power. Neutral-point voltage waveform control method is proposed in this paper to eliminate the ripple current in E-capless full-bridge inverter. With the proposed method, the pulsation power is controlled to only flow through ac capacitors and the...
The development of an intelligent control solution for a wide range of diesel generators is discussed. Compared with most existing solutions, the advantages of the proposed solution lie in two folds: (i) The proposed control has the plug-and-play capability which is reflected by an automatic recognition procedure when it is plugged into a specific diesel generator, such that some extensive manual-tuning...
In order to deal with frequency restoration and protect the energy storage units, this paper analyses the control method of microgrid based on hierarchical control, and proposes an innovative secondary frequency control method which optimize the output of energy storage units in island mode. The simulation results show that the algorithm can make microgrid provide high stability and power quality...
Micro grid(MG) consists of a number of parallel operating inverters. The droop control strategy is commonly used in parallel-connected inverters. The conventional PI regulator for the voltage control has little effect on restraining the voltage harmonic content under the nonlinear load conditions. So an effective and reasonable control strategy for inverters must be adopted to ensure the output power...
Multiwinding transformer + H-bridge converters is a typical topology in high-voltage and high-capacity power electronic applications. Based on the analysis about the high frequency characteristics of a PWM controlled H-bridge and the high frequency equivalent model of the topology, the theoretical foundation of how carrier phase-shift control suppresses high frequency harmonics is derived, and a broader...
This paper introduces a digital multi-mode boost converter with wide range of input voltage for an energy recycling load system. The boost converter is controlled digitally with constant off- time/constant frequency hybrid pulse width modulation (PWM) control. Constant off-time control is to avoid the limit cycle oscillation and gain a high gain when the input voltage is far less than the output voltage...
In order to meet the requirements of electrolytic copper-foil, a 6.5V/50kA power supply system composed of ten power modules is developed. The power module is composed of two-leg PWM rectifier and dc/dc converter, and dc/dc converter adopts two full-wave rectifiers in parallel to enhance the output ability. In order to meet the process requirements of electrolytic copper-foil, a virtual impedance...
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