Phase Angle Of Output Voltage Research Articles

PMSG Wind turbine grid-connected pre-synchronization technology based on virtual impedance

With the integration of large-scale wind power, the inertia of the whole grid system is reduced. Therefore, virtual synchronous machine (VSG) technology has become a new strategy for wind power integration. In view of the fact that the VSG grid connected control of permanent magnet direct drive wind turbine does not consider the constraints of grid connection conditions, a scheme combining VSG technology with pre synchronization technology is proposed in this paper. VSG technology is still used in the PWM control of grid connected inverter. However, considering that there is no deviation between the phase angle of output voltage and the phase angle of grid voltage, it is impossible to judge whether the grid connection conditions are met or not when there is no deviation between the phase angle of output voltage and that of grid voltage.

Parallel Control of Converters with Energy Storage Equipment in a Microgrid

The converter in a microgrid uses the active power and reactive power (PQ) control strategy when connected to the grid. In the case of failure of large power grid, the converters are required to be connected in parallel under the condition of island to provide power to the load. In this paper, a new control method for the parallel operation of converters based on V/F control is proposed. The V/F control is used to ensure the output voltages have the same amplitude and frequency, then the converters will only produce circulating current caused by phase angle inconsistency. The phase angle self-synchronization strategy is proposed to make sure the phase angle of output voltage of all converters in the system are consistent. First, a large inductor is added to the end of the converter to ignore the line reactance, through this, the measured voltage at the terminal of the converter roughly equals to the voltage of the load, thus, every converter has the same reference of phase angle. Using the proposed phase angle self-synchronization strategy allows the output voltage of every converter to have the same phase angle, so that there is no circulating current between converters, and the power is evenly distributed among the converters. The simulation verification was carried out on the Power Simulation (PSIM) simulation platform, and the experimental verification was implemented on the hardware experimental platform. Both results demonstrate the effectiveness of the proposed strategy. This method is highly reliable and easy to implement, and the circulating current can be reduced effectively.

A communication-free economical-sharing scheme for cascaded-type microgrids

This paper proposes an economical-sharing scheme without the needs of any communications for islanded AC microgrids (MGs) fed by cascaded inverters. The output voltage phase angle of each distributed generator (DG) is regulated by its corresponding incremental cost. Then the equal incremental principle used to guarantee the economic optimality is realized by synchronization conditions. In addition, a modification method is introduced with considering the capacity constraints. Stability analysis of the proposed method is carried out, and the conditions for economic optimality and stability are obtained. Because the communications are not needed, the advantages in cost and reliability are obvious. Simulations and experiments are implemented to verify the effectiveness of the proposed scheme.

Voltage conditioner & power flow controller based on bipolar matrix-reactance choppers

Voltage amplitude is one of the most important parameters of electrical energy, particularly from the viewpoint of sensitive loads connected to the grid. The dynamic state in a power grid (voltage sags/swells/interrupts) originating from dynamic loads, uncontrolled power flow, switching effects, adverse weather condition, etc., might cause defects in sensitive loads and financial losses. The annual damages in Europe due to voltage perturbations is estimated at 10billion €. This paper presents a three-phase voltage conditioner and power flow controller without DC energy storage unit for the control of phase and voltage amplitude. In comparison to conventional solutions, such as DVR or UPFC, the power electronic AC/AC converter is based on a bipolar matrix-reactance chopper. The main aim of this paper is to analyse the basic properties of the presented solution, especially from the point of view of the ability to compensate voltage sag/swell and interruption and to control phase shift in bidirectional power flow control. The studies have been carried out on a three phase system with passive and active load (two-source system). On the basis of the authors’ research, it can be stated that the described solution gives the possibility to compensate deep voltage sag (50% of nominal voltage), overvoltages (up to 150% of nominal voltage) and single phase interruption. Simultaneously the solution allows independent control of the phase angle of output voltage in the range±π/3. The paper presents an operational description, theoretical analysis, simulation and the experimental test results of a 1kVA laboratory model using a conventional PWM control strategy.

A dual programmable AC to DC rectifier using three-phase matrix converter topology—analysis aspects

Three-phase matrix converter-based dual AC to DC rectifier is reported in the literature. But these reports only indicate that dual DC output voltages with fixed value are possible by setting the desired AC output voltage phase angle leading by 30 degrees and output frequency zero in the model. Detailed modeling studies using SIMULINK reveal that with the frequency of desired AC output voltage set to zero, as the AC output voltage phase angle is varied from 0 to + $$\pi $$ and 0 to $$-\pi $$ , dual DC output voltages in multitude of combinations are possible such as (a) both voltages positive and unequal, (b) both voltages positive and equal, (c) any one voltage zero and the other positive, (d) any one voltage positive and the other negative with unequal modulus value, (e) any one voltage positive and the other negative with equal modulus value, (f) any one voltage zero and the other negative, (g) both voltages negative and unequal, (h) both voltages negative and equal. This paper provides a detailed insight into this finding with a mathematical derivation for the dual DC output voltage magnitude. Theoretical finding is confirmed by model simulation.

系統連系自励式変換器の運転位相制御方式の検討

As increasing installation of renewable energies which are accompanied by self-commutated power converters, installed capacity of the converters cannot be negligible as compared to the total generation capacity. Those self-commutated converters trade active power with adjusting their output voltage phase angle according to the voltage at the point of commoncoupling (pcc). Therefore, increasing installation of the self-commutated power converters may result in reducing a synchronizing torque of the power system. The tendency is remarkable in a microgrid where the rate of converter-based generation is high. The synchronizing torque is supplied by traditional synchronous generators inherently because, at some disturbance, their inertias make phase differences among their terminal voltages and they can trade active power by the phase differences. In order to keep the synchronizing torque under high penetration of renewables, a concept of Virtual Synchronous Machine was proposed. The VSM emulates a conventional synchronous generator and realizes the power trade among them. This paper deals with a controller of self-commutated converter like the VSM. Instead of applying the same characteristics of the conventional synchronous generator, the phase angle of the output voltage is adjusted as lead or lagged to the pcc voltage in order to trade the active power. The effectiveness of the control is verified in a microgrid system model where the rotating generator and self-commutated converter have almost same rated capacity. The effectiveness of the controller is verified from the viewpoint of frequency control through some simulation studies.

Design of an Autonomous Control for Parallel-Connected Uninterruptible Power Supplies

This paper proposes an autonomous control for parallel-connected uninterruptible power supply (UPS) systems based on electrical power system interrelations. The controllable variables are the output voltage phase angle and magnitude. Relation between active current and output voltage phase angle is derived from a synchronous machine model. Electrical power systems suggest that voltage regulation and reactive current can be proportionally related to yield another control equation. The resulted control scheme is very simple and only requires an output current measurement to provide a voltage reference signal locally in synchronism with other UPSs without communication signal exchange. A small-signal model represents the entire system and constitutes proof of its stability. Feasibility is confirmed by an experimental setup with three UPSs connected in parallel with different output power ratings. In the experiments, voltage limiters (1%) are employed and three cases are verified. Under all conditions, the results show excellent performance in terms of stability, and active and reactive load sharing.

Effects of phase locking on modulation characteristics

An advanced differential equation for phase angle of output voltage, when an unmodulated or modulated oscillator is locked to a modulated or unmodulated external driving signal, respectively, is solved by analog computer. Suppression of the modulation rate is verified experimentally and applied to noise reduction of an avalanche oscillator.