Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Outline ü Introduction to distributed power generation and renewable energy systems ü World energy scenario (including renewable energy) ü Outlook on wind and photovoltaic energy ü Integrating renewable energy sources with the future power system ü Wind systems ü Photovoltaic systems Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Distributed power generation ü ü Relatively small generating units and storage technologies Either be interconnected with the electric grid or isolated from the grid in "stand- alone" Marco Liserre ü ü Provide electric capacity and/or energy at or near consumer sites to meet specific customer needs The location value is important to the economics and operation liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Renewable energy systems Source: Billman, Advances in Solar Energy submission, 1/8/99 Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) World energy consumption ü The growth of energy demand in 2007 remained high despite high energy prices ü China has surpassed the EU Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) World energy production ü The relative market share of oil is decreasing respect coal and gas Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Renewable Energy scenario ü In 2007 the world renewable energy production share has been calculated as 19 %. ü However 16 % is due to hydraulic energy production, hence wind and photovoltaic (the most promising renewable sources) energy production is still very modest. ü The goal of the European Community is to reach 20 % in 2020, however the EU-27 energy is only 17% of world energy. ü USA with 22% of energy share may adopt similar goals under the pressure of public opinion concerned by environmental problems (in California the goal is 20 % in 2010). Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Renewable Energy scenario ü However the policies of Asia and Pacific countries, with 35% of energy share, will be probably more important in the future energy scenario. ü In fact countries like China and India require continuously more energy (China energy share increases 1 point every year from 2000). ü The need for more energy of the emerging countries and the environmental concerns of USA and EU will drive the increase of the renewable energy production: the importance of renewable energy sources in the future energy scenario is not anymore under discussion ! ü The needed technology is available and it benefits of continuous improvement due to academic and industrial research activity ü Knowledge transfer to industry on the basis of international conferences and workshops and educational programs. Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Renewable Energy scenario ü Wind energy – highest development ü Solar energy – next highest development ü Wave energy – largely unexplored ü Tidal energy – largely unexplored ü Small hydro (<10 MW), 47 GW used, 180 GW untapped (70% in developing countries). Oldest technology (not covered) ü Biomass 18 GW used (2000), largely unexplored. Used in CHP Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind energy üBigger and more efficient ! ü 3. 6 -6 MW prototypes running (Vestas, GE, Siemens Wind, Enercon) üDanish Vestas and Siemens Wind stand for over 40% of the worldwide market ü 2 MW WT are still the "best seller" on the market! Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind energy ü Wind energy can benefit of huge investments in research and education. ü Some of the most relevant goals of the research can be briefly summarized as: ü to increase the power production of each wind turbine (over 5 MW), ü to increase the penetration of small wind turbine systems (under 50 k. W) ü to create wind plants (preferably off-shore) that can behave similarly to standard oil & gas power plants respect to the grid (due to wind forecast and proper control strategies). ü Educational investments are mainly done by universities to prepare a future category of engineers for the wind industry but also by leader wind companies that want to form highly specialized engineers through specific Ph. D programs Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Photovoltaic energy ü The cost of PV electricity will reach the break-even point soon in many countries Optimistic ! Silicon shortage has slowed the price reduction Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Photovoltaic energy ü Despite the silicium shortage in the last years the PV industry is growing at more than 30% ü PV Module technology is also developing fast toward higher efficiency and lower cost of 4 -5 €/Wp, expected 3€/Wp in 5 years. From experience 7%/year fall ü String technology is dominating. Multi-string for residential applications ü Mini-central three-phase inverters 8 -15 k. W are emerging for modular configuration in medium and high power systems (commercial roof-tops) ü Central inverters are available for plants up to MW range (1 MW – SMA) ü Reliability is increased now 5 years but extended 20 years (not free!) ü Increase functionality available (built-in logger, communication, grid support, etc) ü Cost is still high (400 - 500€/k. Wp) and high efforts are done in order to reduce it to 250 -300 €/k. Wp in the next 5 years by: ü mass production ü better topologies with fewer components ü design-to-cost ü PV electricity cost is expected to reach the break-even cost around 2015 where mass PV penetration is expected Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Photovoltaic energy ü The most relevant goals of photovoltaic energy are 40% cost reduction of photovoltaic panels and of the power converter stage in 5 years and the increase of the efficiency of both and the reliability of the latter considerably. ü These goals are driving the research towards several directions such as: ü maximum power extraction algorithms, ü advanced anti-islanding algorithms for higher safety levels ü higher efficiency of the power converter (98 % efficiency is the goal for transformerless topologies) Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Power system evolution ü Active distribution grids with a significant amount of medium-scale and small-scale generators (ranging from hundreds of k. W to tens of MW), involving both conventional and renewable technologies, together with storage systems and flexible high-voltage transportation systems connecting those grids with lower cost and ROW (Right Of Way) restrictions. The importance of storage in the overall scenario is crucial Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Smart micro-grids (SMG) ü Within active grids, generators and loads can both play a role as operators in electricity markets ü Distribution grids have to be equipped with protection systems and real-time control systems leading to smart micro-grids (SMG) usually operated in connection to distribution grids but with the capability of automatically switching to a stand-alone operation if faults occur in the main distribution grid, and then re-connected to the grid. ü The safe operation in any condition (grid-connected or stand-alone) relies also on good simulation tools to predict the behavior of the overall system considering the specific operation of the renewable energy sources. Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Information Technology Networking The operation of a SMG can result in higher availability and quality compared with strictly hierarchical management of power generation and distribution. The security of the system can be improved by the ability of feeding final users, reacting to demand variations in a short time by redispatching energy thanks to smart systems. This allows to reduce risks and consequences of black-outs, avoiding the increase of the global production. Photovoltaic systems highly integrated in the buildings Marco Liserre Hydrogen distribution network liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Information Technology Networking problems. . . Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Information Technology Networking possible solutions. . . Color-based indication of grid status Automated Demand Response from Dr. Peter Palensky’s contribution to IEEE – IECON 2008 Panel Discussion Session On Industrial Electronics for Renewable Energy Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind systems Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems Doubly-fed induction generator - wounded rotor Ø Ø Ø Limited speed range (-30% to +20%, typical) Small-scale power converter (Less power losses, price) Complete control of active Pref and reactive power Qref Need for slip-rings Need for gear Ø Producers: Vestas, Gamesa, NEG Micon, GE Wind, Nordex, REpower Systems, DEWind Ø Power range: 0. 85 MW to 4. 2 MW Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems Induction generator - Squirrel cage rotor Ø Ø Ø Full speed range No brushes on the generator Complete control of active and reactive power Proven technology Full-scale power converter Need for a gear Ø Mainly for low power stand-alone Ø Producers: Verteco (converter rated for 50% power), Neg Micon, Siemens Ø Power range: 0. 66 MW to 3. 6 MW Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems Synchronous generator - External magnetized Ø Ø Ø Ø Full speed range Possible to avoid gear (multi-pole generator) Complete control of active and reactive power Small converter for field Need of slip-rings Full scale power converter Multi-pole generator may be big and heavy inverter or diode-bridge + chopper Ø Producers: Enercon, Largey, Ø Power range: 0. 6 MW to 4. 5 MW Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems Synchronous generator - Permanent magnets Ø Ø Ø Ø Full speed range Possible to avoid gear (multi-pole generator) Complete control of active and reactive power Brushless (reduced maintenance) No power converter for field (higher efficiency) Full scale power converter Multi-pole generator big and heavy Permanent magnets needed inverter or diode-bridge + chopper Ø Producers: Largey, Mitsubishi, Pfleiderer Wind Energy Ø Power range: 0. 6 MW to 4. 5 MW Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) SG Example 1 20 k. W mini-WT multipolar permanent magnet synchronous generator with axial flux produced by JONICA IMPIANTI (JIMP) Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) SG Example 2 from “Wind. Blatt 02/03” WT Enercon 300 k. W multipolar synchronous generator installed in Antartica Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) SG Example 3 Multibrid WT 5 MW multipolar synchronous generator (Multi) with ibrid gear (brid) for offshore applications Prokon Nord synchronous generator with permanet magnets surface mounted and radial flux Marco Liserre 3 k. V NPC converter from Alstom or ABB liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Trends 2002 no gear-box - Power electronics is now in wind turbines - Direct-driven genertaor market share is growing Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems control Basic power conversion and control: Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems control Basic demands: Electrical: • Interconnection (conversion, synchronization) • Overload protection • Active and reactive power control Mechanical: • Power limitation (pitch) • Maximum energy capture • Speed limitation/control • Reduce acoustical noise Control loops with different bandwidth Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems control - Controllers (internal) - Modulation - Overall system control Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems control Control of permanent magnet synchronous generator system Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems control Control of synchronous generator system - Control of active and reactive power Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems control Control of doubly-fed induction generator system Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Detailed example Operating range Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Wind turbine systems control Control of doubly-fed induction generator system (generator-side) - Complete control of active and reactive power Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Detailed example Basic power flow Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Photovoltaic systems Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) PV Inverter Topologies • PV dc voltage typical low for string inverters boost needed for low power • For high power (>100 k. W) central PV inverters w/o boost, typical threephase FB topologies with LV-MV trafo • Galvanic isolation necessary in some countries • LF/HF transformer (cost-volume issue) • A large variety of topologies • The optimal topology is not matured yet as for drives • Transformerless topologies having higher efficiency are emerging and the grid regulations are changing in order to allow them Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) PV inverters with boost converter and isolation On low frequency (LF) side Boosting inverter with LF trafo based on boost converter On high frequency (HF) side Boosting inverter with HF trafo based on FB boost converter [2] Both technologies are on the market! Efficiency 93 -95% Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Transformerless PV inverters with boost • FB inverter + boost • Typical configuration • Efficiency >95% • Leakage current problem • Safety issue Marco Liserre • Time sharing configuration • Efficiency > 96% • Extra diode to bypass boost when Vpv > Vg • Boost with rectified sinus reference liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Frequency analysis of voltage to earth Vpe for FB with UP and BP PWM switching VAB, VPE and IPE for FB-UP Spectrum of voltage to earth Spectrum of leakage current Based on ICp and VCp and different frequencies the leakage capacitance was calculated at: Cp=13. 6 n. F (7. 06 n. F/k. Wp). Cp is useful in high-frequency analysis and in damping resonances Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from Hbridge FB with Bipolar PWM Switching q S 1 + S 4 and S 2 + S 3 are switched complementary at high frequency (PWM) q No 0 output voltage possible q The switching ripple in the current equals 1 x switching frequency large filtering needed q Voltage across filter is bipolar high core losses q No common mode voltage VPE free for high frequency low leakage current q Max efficiency 96. 5% due to reactive power exchange L 1(2)<-> Cpv during freewheeling and due to the fact that 2 switched are simultaneously switched every switching q This topology is not suited to transformerless PV inverter due to low efficiency! Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from H-bridge FB with Unipolar PWM Switching q q q q Leg A and Leg B are switched with high frequency with mirrored sinusoidal reference Two 0 output voltage states possible: S 1 and S 2 = ON and S 3 and S 4 = ON The switching ripple in the current equals 2 x switching frequency lower filtering needed Voltage across filter is unipolar low core losses VPE has switching frequency components high leakage current and EMI Max efficiency 98% due to no reactive power exchange L 1(2)<-> Cpv during freewheeling This topology is not suited to transformerless PV inverter due to high leakage! Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from H-bridge FB with Hybrid PWM Switching q Leg A is switched with grid low frequency and Leg B is switched with high PWM frequency q Two 0 output voltage states possible: S 1 and S 2 = ON and S 3 and S 4 = ON q The switching ripple in the current equals 1 x switching frequency high filtering needed q Voltage across filter is unipolar low core losses q VPE has square wave variation at grid frequency high leakage current and EMI q High efficiency 98% due to no reactive power exchange L 1(2)<-> Cpv during freewheeling and due to lower frequency switching in one leg. q This topology is not suited to transformerless PV inverter due to high leakage! Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from H-bridge H 5 (SMA)– ηmax=98% q Extra switch in the dc link to decouple the PV generator from grid during zero voltage q Two 0 output voltage states possible: S 5 = OFF, S 1 = ON and S 5 = OFF, S 3 = ON q The switching ripple in the current equals 1 x switching frequency high filtering needed q Voltage across filter is unipolar low core losses q VPE is sinusoidal with grid frequency component low leakage current and EMI q High max. efficiency 98% due to no reactive power exchange as reported by Photon Magazine for SMA Sunny. Boy 4000/5000 TL single-phase Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from H-bridge HERIC (Sunways)-ηmax=98% q Two 0 output voltage states possible: S+ and D- = ON and S- and D+ = ON q The switching ripple in the current equals 1 x switching frequency high filtering needed q Voltage across filter is unipolar low core losses q VPE is sinusoidal has grid frequency component low leakage current and EMI q High efficiency 98% due to no reactive power exchange as reported by Photon Magazine for Sunways AT series 2. 7 – 5 k. W single-phase Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from H-bridge FB – DC Bypass (Ingeteam)-ηmax=96. 5% q Two extra switches switching with high frequency and 2 diodes bypassing the dc bus. The 4 switches in FB switch at low fsw q Two 0 output voltage states possible by “natural clamping# of D+ and Dq The switching ripple in the current equals 1 x switching frequency high filtering needed q Voltage across filter is unipolar low core losses q VPE is sinusoidal and has grid frequency component low leakage current and EMI q High max efficiency 96. 5% due to no reactive power exchange as reported by Photon Magazine for Ingeteam Ingecon Sun TL series (2. 5/3. 3/6 k. W, single-phase) Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from H-bridge REFU ηmax=98% - q Three-level output. Requires double PV voltage input in comparison with FB but it include time-shared boost q Zero voltage is achieved by shortcircuiting the grid using the biderectional switch q The switching ripple in the current equals 1 x switching frequency high filtering needed q Voltage across filter is unipolar low core losses q VPE without high frequency component low leakage current and EMI. No L in neutral! q High max efficiency 98% due to no reactive power exchange, as reported by Photon Magazine for Refu Solar Refu. Sol (11/15 k. W, three-phase) Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from Hbridge Summary • Actually both HERIC, H 5, REFU and FB-DCBP topologies are converting the 2 level FB (or HB) inverter in a 3 level one. • This increases the efficiency as both the switches and the output inductor are subject to half of the input voltage stress. • The zero voltage state is achieved by shorting the grid using higher or lower switches of the bridge (H 5) or by using additional ac bypass (HERIC or REFU) or dc bypass (FB-DCBP). • H 5 and HERIC are isolating the PV panels from the grid during zero voltage while REFU and FB-DCBP is clamping the neutral to the mid-point of the dc link. • Both REFU and HERIC use ac by-pass but REFU uses 2 switches in anti- parallel and HERIC uses 2 switches in series (back to back). Thus the conduction losses in the acbypass are lower for the REFU topology. • REFU and H 5 have slightly higher efficiencies as they have only one switching with high-frequency while HERIC and FB_DCBP have two. Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from NPC Half Bridge Neutral Point Clamped (HB-NPC)-ηmax=98% - q Three-level output. Requires double PV voltage input in comparison with FB. Typically needs boost. q Two 0 output voltage states possible: S 2 and D+ = ON and S 3 and D- = ON. For zero voltage during Vg>0, Ig<0, S 1 and S 3 switch in opsition and S 2 and S 4 for Vg<0, Ig>0 q The switching ripple in the current equals 1 x switching frequency high filtering needed q Voltage across filter is unipolar low core losses q VPE is equal –Vpv/2 without high frequency component low leakage current and EMI. No L in N! q High max efficiency 98% due to no reactive power exchange, as reported by Danfoss Solar Triple. Lynx series (10/12. 5/15 k. W) Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from NPC Conergy NPC -ηmax=96% - q Only 4 switches needed with 2 of them (S+ and S-) rated only Vpv/4 q Three-level output. Requires double PV voltage input in comparison with FB. Typically needs boost. q Two 0 output voltage states possible using the bidirectional clamping switch (S+ and S-) q The switching ripple in the current equals 1 x switching frequency high filtering needed q Voltage across filter is unipolar low core losses q VPE is equal –Vpv/2 without high frequency component low leakage current and EMI. No L in N! q High max efficiency 96. 1% due to no reactive power exchange, as reported by Conergy IPG series (2 -5 k. W single-phase) Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) High efficiency topologies derived from NPC Summary • The classical NPC and its “variant” Conergy-NPC are both three-level topologies featuring the advantages of unipolar voltage across the filter, high efficiency due to disconnection of PV panels during zero-voltage state and practical no leakage due to grounded DC link midpoint. • Due to higher complexity in comparison with FB-derived topology, these structures are typically used in three-phase PV inverters with ratings over 10 k. W (mini-central). • These topologies are also very attractive for high power in the range of hundreds of k. W) central inverters) where the advantages of multi-level inverters are even more important. Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) PV Inverter Topologies -Conclusions • The “race” for higher efficiency PV inverters has resulted in a large variety of “novel” transformerless topologies derived from H-Bridge with higher efficiency and lower CM/EMI (H 5, HERIC) • Equivalent high-efficiency can be achieved with 3 -level topologies (ex NPC) • Today more than 70% of the PV inverters sold on the market are transformerless achieving 98% max conversion efficiency and 97. 7% “european” (weighted) efficiency • Further improvements in the efficiency can be achieved by using Si. C Mos. Fets. ISE Fraunhofer-Freiburg reported recently 98. 5% efficiency (25% reduction in switching + conduction losses) • For 3 -phase systems the trend is to use 3 independent controlled single-phase inverters like 3 x. H 5 or 3 x. HERIC but 3 FB-SC and 3 NPC (not proprietary) are also present on the market. 3 NPC achieve higher efficiency 98% • The general trend in PV topologies is “More Switches for Lower Losses” Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Control Structure Overview Basic functions – common for all gridconnected inverters Grid current control THD limits imposed by standards Stability in case of grid impedance variations Ride-through grid voltage disturbances (not required yet!) DC voltage control Adaptation to grid voltage variations Ride-through grid voltage disturbances (optional yet) Grid synchronization Required for grid connection or reconnection after trip. Marco Liserre PV specific functions – common for PV inverters Maximum Power Point Tracking – MPPT Very high MPPT efficiency in steady state (typical > 99%) Fast tracking during rapid irradiation changes (dynamical MPPT efficiency) Stable operation at very low irradiation levels Anti-Islanding – AI as required by standards (VDE 0126, IEEE 1574, etc) Grid Monitoring Operation at unity power factor as required by standards Fast Voltage/frequency detection Plant Monitoring Diagnostic of PV panel array Partial shading detection Ancillary Support – (future? ) Voltage Control Frequency control Fault Ride-through Q compensation DVR liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Introduction to Maximum Power Point Tracking - MPPT The MPP is affected by temperature and irradiance. The task of MPPT is to track this MPP regardless of weather or load conditions so that the PV system draws maximum power from the solar array. The MPPT is a nonlinear and time-varying system that has to be solved. All algorithms are based on the fact that, looking at the power characteristic, at the left of the MPP the d. P/d. V > 0, at the right d. P/d. V < 0 and at MPP d. P/d. V = 0, MPP Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) MPPT Comparison § Most common methods: § § § Perturb&Observe – PO Incremental Conductance – IC Constant Voltage Preliminary results indicate that IC method compares favorably with PO and CV methods Still PO is preferred due to implementation simplicity Combined PO+CV is best! Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Typical control structure for dual-stage PV inverter § The MPPT is implemented in the dc-dc boost converter. § The output of the MPPT is the duty-cycle function. As the dc-link voltage VDC is controlled in the dc-ac inverter the change of the dutycycle will change voltage at the output of the PV panels, VPV as: § The dc-ac inverter is a typical current controlled voltage source inverter (VSI) with PWM and dc-voltage controller. § The power feedforward requires communication between the two stages and improves the dynamics of MPPT Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Typical control structure for single-stage PV inverter § In these topologies -which are becoming more and more popular in countries with low grid voltage (120 V) like Japan and thus the voltage from the PV array is high enough- the MPPT is implemented in the dc-ac inverter § Also in topologies with boost trafo on ac side (SMA) § The output of the MPPT is the dc-voltage reference. The output of the dcvoltage controller is the grid current reference amplitude. The power feedforward improves the dynamic response as MPPT runs at a slow sampling frequencies (typ. 1 Hz). §A PLL is used to synchronize the current reference with the grid voltage Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Practical PV inverter control implementation Dual-stage full-bridge PWM inverter with LCL filter and grid trafo • The current controller Gc can be of PI or PR (Proportional Resonant) type • Other non-linear controllers like hysteresis or predictive control can be used for current control • The dc voltage controller can be P type due to the integration effect of the typical large capacitor Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) PV Inverter Control Structures - Conclusions § § § § The most typical control structure is the current controlled voltage source inverter with PWM Typically boost dc-dc converter is required The MPPT is a necessary feature in order to extract the maximum power from a panel array at any conditions of irradiation and temperature. PO and INC are the most used ones. PO+CV is also possible According to the topology (dual- or single-stage) the MPPT is implemented in the dc-dc converter or in the dc-ac inverter PR current controller better than PI control for sinusoidal references PLL is typically required for synchronization Marco Liserre liserre@ieee. org
Overview of Distributed Power Generation Systems (DPGS) and Renewable Energy Systems (RES) Acknowledgment Part of the material is or was included in the present and/or past editions of the “Industrial/Ph. D. Course in Power Electronics for Renewable Energy Systems – in theory and practice” Speakers: R. Teodorescu, P. Rodriguez, M. Liserre, J. M. Guerrero, Place: Aalborg University, Denmark The course is held twice (May and November) every year Marco Liserre liserre@ieee. org
Скачать презентацию Overview of Distributed Power Generation Systems DPGS and
c2ceef6b9e0563ab382528c020d6d40b.ppt