Current Error Based Compensations for VSC Current Control in Weak Grids for Wind Farm Applications

Question

1. How much power can be transferred by using the classical vector control?

2. What are the contributions in "Current error based compensations for vsc current control in weak grids for wind farm applications" ?

3. How can the proposed current compensation improve stability performance?

4. How can compensation regulations be applied to a weak AC grid?

Accepted Answer

By using the classical vector control, the maximum power transferring capability will be less than 1 p.u. when SCR is lower than 1.5 and decrease to 0.63 p.u. as SCR drops to 1.

Accepted Answer

In this paper, a current error based compensation control is proposed for VSC integration to weak AC grid with closed-loop current regulation.

Accepted Answer

Based on frequency domain analysis, the proposed active current compensation can significantly improve stability performance by enhancing the system damping in addition to reactive power compensation.

Accepted Answer

Compensation regulations can be applied by taking advantage of the small-signal linear relationship between active and reactive current against converter angle and voltage magnitude, respectively.

Accepted Answer

Once the voltage returns to its nominal values in approximately 0.12 s after clearance, the VSC also resumes to its pre-fault operational state.

Accepted Answer

Power ramp test using the proposed control is performed with a lumped VSC model representing a cluster of 10 wind turbines each rated at 6 MW and SCR = 1.

Accepted Answer

In this paper, a current error based compensation control is proposed for VSC integration to weak AC grid with closedloop current regulation.

Accepted Answer

Taking advantage of the current loop, the VSC continues controlling the AC current and the maximum instant current overshoot is approximately 0.3 p.u. for the case of SCR = 1 and well regulated under 1.1 p.u. thereafter.

Accepted Answer

since the proposed compensations do not involve any internal modification of PLL itself, they can still be used to enhance system damping with different PLL implementations.

Accepted Answer

Considering (1), the plant of VSC current (connecting to ideal stiff grid) in d-q reference frame can be ideally considered as a first-order process 1/Lls, where R assumed to be negligible for the most adverse case and simplicity as well.

Accepted Answer

For linearization concern, the PWM control is therefore modeled as a first order process of a time constant of half switching cycle as the high frequency switching harmonics can be reasonably ignored for the dynamic analysis.

Accepted Answer

By adding the proposed control of active current with angle compensation only, the corresponding root locus of the main poles shown in Fig. 6(c) reveals that the main poles are kept within the left plane even when the grid is very weak as the SCR goes as small as 1.

Accepted Answer

Comparing with gain scheduling control with 8 additional control parameters based on conventional vector control [10], the proposed control, with similar purposes, involves only 3 control parameters – one set of PI parameters for angle compensation and one proportional for magnitude compensation, which is easier to implement.

Accepted Answer

The converter power rating at 6 MW, SCR at 1 p.u. for illustration of a very adverse case (excluding transformer impedance), L1, Rl, C, and transformer inductance at 0.2 p.u., 0.001 p.u. and 0.1 p.u. respectively.

Accepted Answer

An angular error compensation control strategy is therefore proposed to eliminate the angular error and more importantly, improve the damping of the overall system.

Accepted Answer

It can be seen from Fig. 3 that, significant angular error are induced when the output power has reached more than approximately 0.65 per unit, which gives rise to the failure of power delivery or vice versa.

Accepted Answer

Time domain simulations show that the proposed control can significantly increase the power transferring capability of a VSC generation from weak grid point.

Current Error Based Compensations for VSC Current Control in Weak Grids for Wind Farm Applications

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Most frequently asked questions

1. How much power can be transferred by using the classical vector control?

2. What are the contributions in "Current error based compensations for vsc current control in weak grids for wind farm applications" ?

3. How can the proposed current compensation improve stability performance?

4. How can compensation regulations be applied to a weak AC grid?

5. How long does the VSC return to its pre-fault operational state?

6. How many wind turbines are used in the proposed control?

7. How is the current error based compensation proposed?

8. What is the maximum instant current overshoot for the case of SCR = 1?

9. How can the proposed compensations be used to enhance system damping?

10. What is the way to consider the VSC current in a d-q reference?

11. What is the simplest way to model the PWM control?

12. What is the root locus of the main poles in Fig. 6(c)?

13. What is the way to compare gain scheduling with conventional vector control?

14. How many p.u. is the transformer inductance?

15. What is the angular error compensation strategy?

16. What is the angular error in the output power?

17. How can a VSC control be improved?

Figures

Citations

Stability Control for Wind in Weak Grids

Coordinated Control Strategy of PMSG and Cascaded H-Bridge STATCOM in Dispersed Wind Farm for Suppressing Unbalanced Grid Voltage

Impact of Grid Strength and Impedance Characteristics on the Maximum Power Transfer Capability of Grid-Connected Inverters

Self-Adjustable Step-Based Control Algorithm for Grid-Interactive Multifunctional Single-Phase PV-Battery System Under Abnormal Grid Conditions

A Double-PLLs-Based Impedance Reshaping Method for Extending Stability Range of Grid-Following Inverter Under Weak Grid

References

Synchronverters: Inverters That Mimic Synchronous Generators

Voltage-Sourced Converters in Power Systems

Voltage-Sourced Converters in Power Systems : Modeling, Control, and Applications

Power-Synchronization Control of Grid-Connected Voltage-Source Converters

Analysis of D-Q Small-Signal Impedance of Grid-Tied Inverters

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