p.8
System Stability and Performance Analysis
What happens to the AC filter inductance during the simulation?
It is set to deviate from normal 0.005 H to 0.0065 H to simulate parameter perturbations.
p.6
Robust Inner Loop Control
What equations define the errors of the observed and actual values?
{ e_d(t) = w_d(t) - ˆw_d(t), e_q(t) = w_q(t) - ˆw_q(t) }
p.7
Simulation Results and Validation
What are the rated parameters of the AC subgrid in the simulation?
Rated frequency of 50 Hz and AC voltage RMS of 380 V.
p.7
Robust Inner Loop Control
How does a large cut-off frequency affect disturbance suppression?
It improves disturbance suppression but increases sensitivity to noise.
p.3
Flexible Power Sharing Control
What is the purpose of the droop coefficients in the interlinking converter control scheme?
To realize proportional power sharing of the distributed generators (DGs) corresponding to their rated output.
p.1
Flexible Power Sharing Control
What does the outer loop power control of ILC aim to achieve?
Flexible power sharing of distributed generations (DGs) in the hybrid microgrid.
p.8
Disturbance Observer Implementation
What is the significance of the observed disturbance in the system?
It indicates the system's response to high-frequency noise and the robustness of the proposed control.
p.8
Dynamic Response Improvement
What does the AC frequency response indicate in the context of control strategies?
It shows the effectiveness of the control strategy under varying conditions.
p.3
System Stability and Performance Analysis
What relationship is established for the frequency in the microgrid?
The frequency is unique in the microgrid and can be expressed as a function of the rated and actual active power outputs of the DGs.
p.1
Robust Inner Loop Control
How does the improved robust inner loop control enhance the system?
By suppressing external disturbances and improving dynamic response.
p.6
Dynamic Response Improvement
What is the significance of the transfer functions T F_1(s) and T F_2(s)?
They depict current fluctuations with and without disturbance suppression control.
p.2
Interlinking Converter (ILC) Control Scheme
What are the components of the ILC structure?
Converter voltage and current, AC bus voltage, DC side current and voltage, equivalent resistance, filter inductance, and filter capacitor.
p.2
Robust Inner Loop Control
What is a significant challenge in microgrid control models?
The lack of accurate control models due to system parameter uncertainties and detection technology limitations.
p.1
Interlinking Converter (ILC) Control Scheme
What is the main focus of the paper regarding the interlinking converter (ILC)?
To present a comprehensive control scheme for the ILC in a hybrid AC/DC microgrid.
p.9
Interlinking Converter (ILC) Control Scheme
What is the main focus of the paper by LIU et al.?
A comprehensive control scheme for an interlinking converter in a hybrid AC/DC microgrid.
p.2
Hybrid AC/DC Microgrid Structure
What role does the ILC play in a hybrid AC/DC microgrid?
It facilitates power exchange and support between AC and DC subgrids.
p.3
Power Management Strategies
What does the regulation parameter λ represent in the power sharing scheme?
It represents the ratio of sharing between AC and DC distributed generators, allowing for flexible load power sharing.
p.1
Hybrid AC/DC Microgrid Structure
What advantages does a hybrid AC/DC microgrid have over traditional AC microgrids?
Less energy conversion and lower power loss.
p.9
System Stability and Performance Analysis
What is the consequence of AC filter inductance deviation in traditional PI control?
It results in instability and mess in power sharing.
p.2
Robust Inner Loop Control
What is the impact of classic feedback control in microgrids?
It often sacrifices nominal performance to achieve better robustness against disturbances.
p.2
Hybrid AC/DC Microgrid Structure
What is the proposed control scheme for the ILC in a hybrid AC/DC microgrid?
A combination of outer loop flexible power sharing control and improved robust inner loop control.
p.5
Interlinking Converter (ILC) Control Scheme
What do G sd (s) and G sq (s) represent in the ILC model?
They are the actual transfer functions in the d-axis and q-axis, respectively.
p.4
Flexible Power Sharing Control
What is the significance of the regulation parameter λ in the proposed control scheme?
It adjusts power sharing among AC and DC subgrids based on different management objectives.
p.9
System Stability and Performance Analysis
What issue arises with traditional PI control when system parameters change?
The voltage and frequency of the AC/DC bus lose stability and become abnormal.
p.7
Disturbance Observer Implementation
What issue does the proposed disturbance observer link address?
It suppresses high-frequency measurement noise.
p.4
Robust Inner Loop Control
What is the purpose of the improved inner loop robust control strategy?
To enhance the robust stability of the microgrid under external or internal disturbance impacts.
p.4
Disturbance Observer Implementation
Why is a first-order disturbance adopted in the ILC modeling?
Because low frequency components dominate system response, and high-order disturbances complicate engineering implementation.
p.7
Robust Inner Loop Control
What happens to the overshoot of the unit-step response of TF1 compared to TF2?
TF1 has almost zero overshoot, while TF2 has an overshoot of -0.5.
p.7
Simulation Results and Validation
What simulation platform was used to validate the proposed control scheme?
PSCAD/EMTDC simulation platform.
p.2
Flexible Power Sharing Control
How does the proposed outer loop control strategy differ from existing literature?
It realizes autonomous power balance based on a deduced balance state equation.
p.3
Robust Inner Loop Control
How does the balance state equation (6) contribute to the interlinking converter's function?
It allows the ILC to manage flexible active power flow between AC and DC subgrids while maintaining stability.
p.1
Disturbance Observer Implementation
What is the role of the disturbance observer in the inner loop control?
To force the converter current to track the reference value with no steady error.
p.6
Dynamic Response Improvement
What parameters are analyzed to understand the dynamic performance of the disturbance suppression strategy?
The unit-step responses of the transfer functions T F_1(s) and T F_2(s).
p.5
Robust Inner Loop Control
What does the equation ˆ w d (s) = g d s + g d · w d (s) represent?
It depicts the relationship between the observed and actual values of the resultant disturbance term w d.
p.9
Hybrid AC/DC Microgrid Structure
What is the significance of the proposed control scheme for practical microgrid applications?
It addresses issues that cannot be effectively solved by traditional technical methods.
p.7
Robust Inner Loop Control
What is the purpose of the disturbance suppression control in the interlinking converter?
To eliminate perturbations and quickly track the reference current value.
p.4
Flexible Power Sharing Control
What is the role of ILCs in steady state within a hybrid microgrid?
ILCs work in a coordinated way to share power and maintain frequency/voltage.
p.6
Robust Inner Loop Control
What happens to the error terms as time approaches infinity?
The errors converge to zero: lim t → ∞ e_d(t) = 0 and lim t → ∞ e_q(t) = 0.
p.5
Interlinking Converter (ILC) Control Scheme
How are the resultant disturbance terms w d and w q defined?
They are caused by lumped disturbances and the intermediate variables U d 1 and U q 1.
p.4
Robust Inner Loop Control
What is the function of the reactive power PI control in the ILC?
It maintains the AC bus voltage at rated levels by supplying reactive power to the AC subgrid.
p.6
Dynamic Response Improvement
What does the equation ∆i_d(s) represent?
The current fluctuation caused by the disturbance w_d(s).
p.4
System Stability and Performance Analysis
What does the nominal ILC model in the synchronous d-q reference frame represent?
It describes the dynamics of the ILC considering the d and q axis components.
p.6
Robust Inner Loop Control
What is the purpose of the disturbance observers in the control scheme?
To exponentially converge to the system's actual status, eliminating measurement noise.
p.5
Interlinking Converter (ILC) Control Scheme
What are the intermediate variables in the nominal ILC model?
U d 1 and U q 1, defined as U d 1 = E d − U d − ωL n i q and U q 1 = E q − U q + ωL n i d.
p.4
Dynamic Response Improvement
What happens to the DC bus voltage when there is a sudden increase in DC load?
There is a drop in DC bus voltage, generating a positive difference value.
p.6
Dynamic Response Improvement
What does the disturbance suppression link G_c(s) do?
It eliminates the perturbation of w_d on i_d, allowing accurate tracking of the reference value.
p.7
System Stability and Performance Analysis
How does the proposed disturbance suppression control compare to traditional PI control?
It results in smaller transients in AC frequency and voltage during disturbances.
p.5
Robust Inner Loop Control
What is the role of G Q (s) and G M (s) in the DOL design?
They are first-order filters used to observe the resultant disturbance terms while avoiding high-frequency noise.
p.6
System Stability and Performance Analysis
What is the effect of the first-order disturbance on the system?
It influences the dynamic performance and stability of the microgrid system.
p.8
Interlinking Converter (ILC) Control Scheme
What is the purpose of the interlinking converter in the system?
To manage power flow between DC and AC sources and loads.
p.2
Disturbance Observer Implementation
What is the purpose of a disturbance observer in control systems?
To suppress transient fluctuations and improve dynamic performance under disturbances.
p.4
Power Management Strategies
How does the ILC operate based on the reference active power?
When P_ref > 0, active power flows from AC to DC subgrid; when P_ref < 0, it flows from DC to AC subgrid.
p.6
Flexible Power Sharing Control
What is the role of the compensation control in the current inner loop control?
To eliminate the influence of resultant disturbance terms on the microgrid system.
p.7
Power Management Strategies
What does the ILC do during load demand increases in the simulation?
Transfers power from the AC to DC subgrid to achieve proportional power sharing.
p.5
Robust Inner Loop Control
What is the purpose of the disturbance observer link (DOL)?
To track the resultant disturbance terms w d and w q and improve the dynamic response of the control system.
p.4
Disturbance Observer Implementation
What challenges do transient disturbances pose to the hybrid microgrid?
They break the instantaneous power balance state and cause fluctuations in the inner loop current reference.
p.5
Robust Inner Loop Control
What is the effect of the first-order filter on the converter current?
It allows low-frequency dynamics to be close to 1 while attenuating high-frequency dynamics to nearly 0.
p.8
Robust Inner Loop Control
How does disturbance suppression control compare to traditional PI control?
It shows better performance in terms of active power, reactive power, AC frequency, and AC voltage.
p.8
Power Management Strategies
What load conditions were maintained in Case 1 of the simulation?
A load of 40 kW and 40 kVar.
p.1
Interlinking Converter (ILC) Control Scheme
What are the two main components of the control scheme for the ILC?
Outer loop flexible power sharing control and improved robust inner loop control.
p.9
Power Management Strategies
What happens to the output power of the distributed generators (DGs) when one DG quits operation?
The output power of the remaining DGs and the transfer power by the interlinking converter is proportionally reallocated.
p.2
Hybrid AC/DC Microgrid Structure
What is the function of the Point of Common Coupling (PCC) in a microgrid?
It allows the utility grid to provide power support to the microgrid.
p.3
Dynamic Response Improvement
What is the role of the PI control in the active power control structure of the ILC?
To eliminate steady-state error for the reference command of the ILC.
p.1
Hybrid AC/DC Microgrid Structure
What is the expected future preference for microgrid types?
Hybrid AC/DC microgrid, as it can meet the needs of both AC and DC loads efficiently.
p.3
Interlinking Converter (ILC) Control Scheme
How are the droop characteristics of the AC bus of the ILC expressed?
As a function of the actual and rated active power outputs of the droop-controlled DGs.
p.5
Interlinking Converter (ILC) Control Scheme
What is the significance of the disturbance terms w ed (s) and w eq (s)?
They represent the lumped disturbance terms that include external disturbances and system parameter uncertainties.
p.4
System Stability and Performance Analysis
What does the balance state equation indicate about flexible power sharing?
It relies on coefficients k_ac, k_dc, and λ, requiring proportional DG outputs in each subgrid.
p.9
Robust Inner Loop Control
What advantage does the improved disturbance suppression control provide?
It significantly improves the system’s robust stability under system parameter perturbations.
p.3
Flexible Power Sharing Control
What happens when λ is taken as 1 in the power sharing scheme?
Globally proportional power sharing according to different DG capacities is realized.
p.3
Dynamic Response Improvement
What is the significance of the active power droop characteristics in the DC subgrid?
They describe how the actual DC bus voltage relates to the rated values and active power outputs of the DGs.
p.2
Flexible Power Sharing Control
What is the significance of the active power droop characteristics in droop-controlled DGs?
They enable load power sharing and eliminate the need for fast communication links.
p.3
Distributed Generation (DG) Integration
What is the effect of feeder resistances in the DC subgrid?
They cause a difference in DG terminal voltages, which can be compensated using the virtual compensation resistance method.
p.1
System Stability and Performance Analysis
What is a significant challenge in managing power in hybrid AC/DC microgrids?
Coordinating AC frequency droop characteristics and DC voltage droop characteristics.
p.1
Power Management Strategies
What is a key requirement for effective power sharing among distributed generations?
A proper power sharing scheme that aligns with the requirements of the hybrid microgrid.
p.1
Flexible Power Sharing Control
What is the significance of droop control in hybrid AC/DC microgrids?
It allows for independent operation of distributed generators without communication.
