Analysis of controller bandwidth interactions for vector-controlled VSC connected to very weak AC grids

Question

1. What have the authors contributed in "Abstract—stability assessment of conventional vector current control (vcc) of voltage-source converters (vscs) in weak grids" ?

2. What can be used to amend the stability definition in Section V.C?

3. What is the effect of the PLL on the stability of the VSC?

4. What are the practical recommendations arising from this research?

Accepted Answer

In this paper, a small signal model is derived to quantify the maximum active power transfer in a very weak grid across a much wider range of controller bandwidths than has previously been investigated.. Robustness of the stability bubble under different SCRs is investigated and dynamic performance considerations are introduced to form a reduced operating region with good transient performance.

Accepted Answer

The power transfer requirements and dynamic performance constraints for a given application can be used to amend the stability definition in Section V.C and the acceptable dynamic performance definition in Section V.D.

Accepted Answer

At high 𝜔PLL, the VSC behaves as a grid-following converter i.e. the controller reference frame is synchronized to transient changes in the PCC voltage phase via the PLL.

Accepted Answer

Practical recommendations arising from this research include the avoidance of intermediate PLL bandwidths (approx. 5 – 30 Hz), which offer poor stability, and the implementation of customized control tunings for inverting and rectifying operation.

Accepted Answer

A linearized model using full state-space representations of each component of the AC grid, VSC and controller is used to quantify the small signal stability limits.

Accepted Answer

This method for development of the stability bubble and dynamic performance region can also be used as a valuable tool for controller design and tuning.

Accepted Answer

As discussed in [24], a slower ICL with respect to the PLL is destabilizing in both power directions due to the impact on the negativereal-part of the input-admittance.

Accepted Answer

The boundaries between stability and instability are determined by linear bisection, giving the inverting and rectifying active power transfer limits for that controller configuration.

Accepted Answer

The methodology to determine this power transfer limit for any given set of controller parameters isbased on conventional eigenvalue analysis of the state space model.

Accepted Answer

Impedance modelling can fully substitute state space small signal modelling [25], [26] and so can be used to independently reproduce the results of Section IV.

Accepted Answer

The d- and q-axis current references for the inner current loop are produced from PI control of the active power and AC voltage magnitude errors, respectively,Δicdref c =FP(s) ΔPref c − ΔP cf (13)Δicqref c =FU(s) ΔUref c − ΔU cf (14)Where ΔPcf is the filtered active power at the PCC, ΔU cf is the filtered AC voltage magnitude at the PCC, FP(s) = kp-P + ki-P/s (where kp-P and ki-P are the APL proportional and integral gains, respectively) and FU(s) = kp-U + ki-U/s (where kp-U and ki-U are the AVL proportional and integral gains, respectively).

Accepted Answer

This analysis can therefore be used to investigate dynamic performance, and the sensitivity of transient performance to controller tuning, without the requirement for protracted time-domain simulations.

Accepted Answer

At each operating point, the maximum active power (measured at the PCC) that can be exchanged between the grid and the VSC whilst maintaining stability is calculated in both inverting and rectifying modes.

Accepted Answer

In inverting mode (Fig. 7(a)), stability is almost independent of APL bandwidth, but in rectifying mode a fast APL causes significant instability, particularly when the ICL is slow.

Accepted Answer

This therefore validates the active power transfer and controller bandwidth interaction results that were produced with the state-space small signal model and shows that the impedance model is equally valid for stability analysis.

Accepted Answer

For clarity, ki-U is plotted as the proxy for AVL bandwidth in Fig. 9 due to the impracticalities, discussed in Section IV, of directly specifying the bandwidth in the small signal model.

Analysis of controller bandwidth interactions for vector-controlled VSC connected to very weak AC grids

Chat with Paper

AI Agents for this Paper

Most frequently asked questions

1. What have the authors contributed in "Abstract—stability assessment of conventional vector current control (vcc) of voltage-source converters (vscs) in weak grids" ?

2. What can be used to amend the stability definition in Section V.C?

3. What is the effect of the PLL on the stability of the VSC?

4. What are the practical recommendations arising from this research?

5. What is the simplest way to quantify the small signal stability limits?

6. What can be used for controller design and tuning?

7. What is the effect of a slower ICL with respect to the PLL?

8. How are the boundaries between stability and instability determined?

9. What is the method to determine the power transfer limit for any given set of controller parameters?

10. Can Impedance modelling be used to substitute state space small signal modelling?

11. what is the d- and q-axis current reference for the inner current loop?

12. What can be used to investigate dynamic performance?

13. What is the maximum power that can be exchanged between the grid and the VSC?

14. What is the difference between inverting and rectifying mode?

15. What is the impedance model for small signal modeling?

16. Why is ki-U plotted as the proxy for AVL bandwidth in Fig?

Figures

Citations

Stability Analysis of the Grid-Connected Inverter Considering the Asymmetric Positive-Feedback Loops Introduced by the PLL in Weak Grids

New Perspectives on Stability of Decoupled Double Synchronous Reference Frame PLL

Optimal Controller Design for Transient Stability Enhancement of Grid-Following Converters Under Weak-Grid Conditions

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

Stability Analysis of a Weak-Grid-Connected Voltage-Sourced Rectifier Considering the Phase-Locked Loop Dynamics

References

Impedance-Based Stability Criterion for Grid-Connected Inverters

Input filter considerations in design and application of switching regulators.

A phase tracking system for three phase utility interface inverters

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

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

Related Papers (5)

Parameter Design Oriented Analysis of the Current Control Stability of the Weak-Grid-Tied VSC

Analysis and Damping Control of Small-Signal Oscillations for VSC Connected to Weak AC Grid During LVRT

Large Signal Synchronizing Instability of PLL-Based VSC Connected to Weak AC Grid

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

Control of Power Electronic Converters in Distributed Power Generation Systems: Evaluation of Current Control Structures for Voltage Source Converters operating under Weak Grid Conditions