A Novel Repetitive Control Enhanced Phase-Locked Loop for Synchronization of Three-Phase Grid-Connected Converters
Abstract
:1. Introduction
- A novel filtering stage is proposed based on RC that enables faster settling times than that of the QT1-PLL designed according to [10], while maintaining the ability of complete disturbance rejection when the grid frequency is nominal.
- To the authors’ knowledge, this proposed PLL is the first to offer instantaneous partial compensation of the phase angle difference in the events of grid phase jump.
- Validation of the proposed PLL effectiveness was done on a group of comprehensive experiments, with a set of frequencies around and including the nominal.
- The filtering stage of the proposed PLL is provided in a MATLAB code fit for implementation in simulations or on a digital control device.
2. Low Voltage Grid Disturbances and Their Influence on Phase Locked Loop Synchronization
2.1. Grid Voltage Vector Tracking
2.2. SRF-PLL Small-Signal Model
3. Description of the Proposed PLL and Design Guidelines
3.1. Enhancement of SRF-PLL with Repetitive Control Based Filter
3.2. Phase and Frequency Tracking Ability of the Proposed PLL
3.3. Stability Analysis of RCE-PLL
- The roots being in the left half-plane of the complex plane. This stability condition can be fulfilled with appropriate controller parameter selection using Equation (15).
- For all frequencies below the Nyquist frequency (), the following equation should be applicable:
3.4. Optimal Value of Parameter K
4. Main Results
4.1. Experiment Setup and Testing Methodology
- Phase jump;
- Voltage sag;
- Voltage harmonics; and
- Frequency step and ramp change.
- Voltage sag with grid frequency variation;
- Voltage harmonics with grid frequency variation;
- DC offset; and
- Random noise.
4.2. Transient Behavior of Selected Algorithms
4.2.1. Phase Jump
4.2.2. Voltage Sag
4.2.3. Voltage Harmonics
4.2.4. Frequency Ramp and Step Change
4.3. Steady-State Behavior of Selected Algorithms
4.3.1. Voltage Sag with Grid Frequency Variation
4.3.2. Voltage Harmonics with Grid Frequency Variation
4.3.3. DC Offset
4.3.4. Measured Noise
4.4. Summary
5. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Acronyms and Symbols
RES | Renewable Energy Sources |
DSP | Digital Signal Processor |
FPGA | Field Programmable Gate Arrays |
FGVVPA | Fundamental Grid Voltage Vector Phase Angle |
FGVVF | Fundamental Grid Voltage Vector Frequency |
PLL | Phase-Locked Loop |
PCC | Point of Common Coupling |
SRF-PLL | Synchronous Reference Frame Phase-Locked Loop |
DDSRF-PLL | Decoupled Double SRF-PLL |
MAF | Moving Average Filter |
MAF-PLL | Moving Average Filter based SRF-PLL |
QT1-PLL | Quasi-Type 1 PLL |
SOGI | Second-Order Generalized Integrator |
PI | Proportional-Integral |
PID | Proportional-Integral-Derivative |
PR | Proportional-Resonant |
LF | Loop Filter |
PD | Phase Detector |
VCO | Voltage-Controlled Oscillator |
LPF | Low Pass Filter |
BPF | Band Pass Filter |
RC | Repetitive Control |
RCF | Repetitive Control Filter |
RCE-PLL | Repetitive Control Enhanced SRF-PLL |
h | Order of harmonic |
Voltages in natural reference frame (abc) | |
Voltages in the stationary reference frame (αβ) | |
Voltages in the synchronous reference frame (dq) | |
DC voltage in natural reference frame | |
Voltage components in stationary reference frame that are consequence of DC voltages in natural reference frame | |
Voltage components in synchronous reference frame that are consequence of DC voltages in natural reference frame | |
Voltage amplitude of h-th positive (+) or negative (−) sequence harmonic | |
Fundamental frequency | |
Initial phase angle of h-th positive (+) or negative (−) sequence harmonic | |
Phase angle of h-th positive (+) or negative (−) sequence harmonic | |
Instantaneous phase angle of the synchronous reference frame vector | |
Positive fundamental grid voltage vector phase angle | |
Estimated angle of the positive fundamental grid voltage vector | |
p | Laplace complex variable |
ωn | Natural frequency |
ζ | Damping ratio |
kp | Proportional gain |
Ti | Integral time constant |
K | Gain of repetitive controller |
T | Delay time of repetitive controller |
Ts | Sampling time |
N | Closest integer ratio between delay time T and sampling period Ts |
ωff | Expected fundamental frequency |
Δω | Fundamental frequency correction signal |
e(p) | Error signal |
Filtered error signal | |
D(p) | Model of disturbances due to oscillating terms in Laplace domain |
Appendix A
functionout =fcn(in, K, N) %{ Implementation of Repetitive Control Filter Part of File : RCE-PLL Author : Filip Filipović Date : June '19 Description: Inputs - in – obtained sample, type: double - K - value of coefficient K, type: double - N - number of delays, type: int16 Output - out - filtered sample, type: double Inside function persistent variables - inputs - array of previously obtained samples type: array<double> - outputs - array of previously generated outputs type: array<double> %} % Define variables that have persistent values persistent inputs outputs; if(isempty(inputs)) inputs = zeros(1, 150); %150 is the maximum number of delays. Change outputs = zeros(1, 150); %this number if required. end % Obtaining input(output) value from N-steps ago delay_in = inputs(N); delay_out = outputs(N); % Calculation of the output out = 1/(1+K) * (in - delay_in + delay_out); % Latest samples are inserted in array to be used in next iteration inputs = [in, inputs(1:end-1)]; outputs = [out, outputs(1:end-1)];
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Oscillation Frequency (dq) | Origin (abc) |
---|---|
DC offset | |
Fundamental voltage unbalance | |
5th and/or 7th harmonic | |
11th and/or 13th harmonic | |
… | … |
Algorithm | Parameter | Value |
---|---|---|
- | Sampling time | 100 µs |
All | Execution speed | 10 kHz |
RCE-PLL | Natural frequency, ωn | 2π60 rad/s |
Damping ratio, ζ | 0.707 | |
Proportional gain, kp | 533.146 | |
Integral time, Ti | 7.04 µs | |
Delay length, N | 100 | |
Coefficient, K | 8.1 | |
Expected fundamental frequency, ωff | 2π50 rad/s | |
SRF-PLL | Natural frequency, ωn | 2π20 rad/s |
Damping ratio, ζ | 0.707 | |
Proportional gain, kp | 177.715 | |
Integral time, Ti | 63.32 µs | |
Expected fundamental frequency, ωff | 2π50 rad/s | |
MAF-PLL | Coefficient, b | 2.4 |
Proportional gain, kp | 83.333 | |
Integral time, Ti | 345.6 µs | |
MAF window length, N | 100 | |
Expected fundamental frequency, ωff | 2π50 rad/s | |
QT1-PLL | Proportional gain, kp | 92.34 |
Expected fundamental frequency, ωff | 2π50 rad/s | |
MAF window length, N | 100 |
Harmonic Order | Amplitude (%) 1 |
---|---|
5th | 6 |
7th | 5 |
11th | 3.5 |
Algorithm | SRF-PLL | MAF-PLL | QT1-PLL | RCE-PLL | |
---|---|---|---|---|---|
Number of parameters to configure | 2 | 3 | 2 | 4 | |
Complexity of implementation | low | medium | medium | high | |
Phase margin (degree) | 65 | 43.3 | 45.8 | 59.7 | |
Phase jump +30° | |||||
Settling time (cycles) | Frequency 1 | 2.35 | 4.15 | 2.2 | 1.44 |
Phase angle 2 | 1.9 | 3.6 | 1.45 | 1 | |
Maximum overshoot | Frequency (Hz) | 14 | 6.7 | 6.5 | 8.5 |
Phase angle (degree) | 30 | 30 | 30 | 20 | |
Voltage sag, Type C depth 0.7 | |||||
Settling time (cycles) | Frequency 1 | - | 1.6 | 1.25 | 0.98 |
Phase angle 2 | - | 0.95 | 0.45 | 0.55 | |
Susceptibility to frequency variation | low | low | medium | high | |
Voltage harmonics | |||||
Settling time (cycles) | Frequency 1 | - | 0.45 | 0.45 | 0.8 |
Phase angle 2 | 0.25 | 0 | 0 | 0.5 | |
Susceptibility to frequency variation | low | low | medium | high | |
Measurement disturbances | |||||
Susceptibility to measurement disturbances | high | low | medium | high | |
Ramp frequency change | |||||
Steady-state error | Frequency (Hz) | 0 | 0 | 1.09 | 0.57 |
Phase angle (degree) | 2.28 | 12.7 | 1.93 | 0.5 | |
Frequency step-change +5 Hz | |||||
Settling time (cycles) | Frequency 1 | 1.95 | 3.7 | 1.75 | 1 |
Phase angle 2 | 1.45 | 3.1 | 1.1 | 0.55 | |
Maximum overshoot | Frequency (Hz) | 1.1 | 1.75 | 0.25 | 0.2 |
Phase angle (degree) | 6.5 | 19 | 7.5 | 3 |
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Filipović, F.; Petronijević, M.; Mitrović, N.; Banković, B.; Kostić, V. A Novel Repetitive Control Enhanced Phase-Locked Loop for Synchronization of Three-Phase Grid-Connected Converters. Energies 2020, 13, 135. https://doi.org/10.3390/en13010135
Filipović F, Petronijević M, Mitrović N, Banković B, Kostić V. A Novel Repetitive Control Enhanced Phase-Locked Loop for Synchronization of Three-Phase Grid-Connected Converters. Energies. 2020; 13(1):135. https://doi.org/10.3390/en13010135
Chicago/Turabian StyleFilipović, Filip, Milutin Petronijević, Nebojša Mitrović, Bojan Banković, and Vojkan Kostić. 2020. "A Novel Repetitive Control Enhanced Phase-Locked Loop for Synchronization of Three-Phase Grid-Connected Converters" Energies 13, no. 1: 135. https://doi.org/10.3390/en13010135