Comparative Performance of UPQC Control System Based on PI-GWO, Fractional Order Controllers, and Reinforcement Learning Agent

Round 1

Reviewer 1 Report

In the manuscript, authors have presented an architecture of Unified Power Quality Conditioner (UPQC) and its performance. The manuscript is written well however there are a few minor comments:

1. The manuscript includes implemntation using Matlab/Simulink. Please comment on the practical implementation and resource requirements for the implementation of UPQC.

2. Please provide definitations of the performnace indicators: stationary error, voltage ripple, and DF. And also, what other performance indicators can be used to evaluate the performance?

 

Author Response

Dear reviewer, thanks for your recommendations.

1. The UPQC system hardware implementation is presented in Appendix A and contains the follows main blocks.

            The series active filter which includes the next components:

• Series voltage inverter;
• Sinusoidal type filter that includes the LSF inductances, the CSF capacitors, respectively, the RSF damping resistors;
• Single-phase transformers connecting to the network;
• Three-phase contactors used to connect the voltage inverter to its load (single-phase transformers) or to short-circuit the secondaries of single-phase transformers to remove the series active filter from the circuit;
• Hall effect voltage transducers used to measure the phase voltages at the output of the inverter or to measure the phase voltages of the three-phase distribution network.

            The APF which includes the next components:

• Parallel voltage inverter;
• Sinusoidal type filter that includes the LpF inductances, the CpF capacitors, respectively, the RpF damping resistors;
• Coupling coils used to interface the APF to mains or to help smooth the current waveform;
• Hall effect current transducers for measuring the currents generated by the APF;
• Hall effect current transducers for measuring the currents absorbed by the nonlinear load;
• Resistors for limiting the charging current of the capacitors in the DC intermediate circuit;
• Three-phase contactors used for connecting the APF to the mains or short-circuiting the load current limiting resistors.

            DC intermediate circuit is common to the two active filters, both the series and the parallel one, and contains the following components: high-capacity capacitors with middle plug for connecting the neutral wire of the three-phase distribution network and voltage transducer for measuring V_DC voltage.

            To create the power circuits, the latest generation components from Semikron were used, capable of working on high switching frequencies. The system involves the acquisition and processing in real time of a number of 11 voltages and 9 currents, for these using Hall effect transducers, with fast response. The implementation of the control algorithms was achieved by using two control hardware boards, for each separate filter, with the help of DSPIC33FJ256MC710 type DSPs.

2.  

Voltage stationarry error represents the absolute value of the difference between reference V_DCref voltage and measured V_DC voltage.

Voltage ripple is defined as follows [23]:

(23)

where: the number of samples is denoted as N, V_DC represents the voltage in DC intermediate circuit, and the reference voltage is denoted as V_DCref = 700V.

            The following briefly describes the method of calculating the DF of a signal, in case of our application, a one-dimensional signal. For this we use the box-counting method. Thus, for the analysed one-dimensional signal we find a square that encompasses of it, in which the length of one side is considered the unit of measurement. The chosen square must contain all the non-zero values of the signal, and the size chosen for the scale is preferable to be power of 2 for quick calculation.

            In addition, the unit of measurement is repeatedly divided by 2 until the value obtained decreases below a predefined threshold. This form of division is of the form 1/2k, where k represents the current step. On the other axis the division is of the form , where n_k represents the total number of domains that are occupied by the signal at the given scale.

            For each sequence at the current step, the values obtained on the two axes following the procedure described above can be considered as the coordinates of a point M_k(x,y), and the representation is in Cartesian system but with log coordinates. Using these values, the coordinates of the sequences of points M₁, M₂, ...,M_n are calculated sequentially at each step k (until reaching values over the chosen threshold). The slope of the line closest to the points M₁, M₂, ...,M_n, provides the DF of the initial signal. Using the following Matlab command “[n,r] = boxcount(signal,'slope')” the vectors corresponding to the two dimensions in the algorithm described above are obtained.

            With the following Matlab commands: “df = -diff(log(n))./diff(log(r))” and “['DF = 'num2str(mean(df(1:length(df)))) '+/- 'num2str(std(df(1:length(df))))])” the coordinates of the points Mk and the slope of the line closest to the points M₁, M₂, ...,M_n i.e. DF are obtained in logarithmic coordinates [31].

            Another important indicator of the performance of an APF in a UPQC-type system is the THD. Both THD current and THD voltage for the most efficient (PI controller with RL-TD3 agent) and the least efficient (PI controller) of the presented controllers will be presented by FFT analysis. For this, both a nonlinear load presented above which is highly polluting in terms of harmonics, containing switching elements but no filters, and a 100kW/10Kvar RLC linear load are considered.

THD current is described by the next expression [32]:

(24)

where: I_N represents the RMS value of the harmonic N and I_RMS represents RMS value of the fundamental of the signal.

Author Response File: Author Response.pdf

Reviewer 2 Report

I note that the similarity cross reference report on your paper returns a value of more 30% where (7% Ref 01 and 4% Ref 02). I suggest to revise the paper thoroughly to reduce the overall similarity.

Ref 01 : Comparative Performance of UPQC Control System Based on 

PI-GWO, Fractional Order Controllers, and Reinforcement Learning Agent.

 

Ref 02: Improved Control Strategy of Unified Power Quality Conditioner Using Fractional Order Controller and Particle Swarm Optimization.

Author Response

Dear reviewer, thanks for your recommendations.

            We specify that Ref 01 is the current article, and Ref 02 is an article by the same authors. In the current article, as presented, a substantial development of the results from the previous article is achieved.

            The similarity comes from the description of the UPQC system, which is used as a benchmark. In the revised version we tried to reduce the degree of similarity, but if it did not decrease enough, we consider it necessary to send us the similarity report to make the necessary corrections.

Author Response File: Author Response.pdf