Single-phase PV Inverter Research Articles

Small-Signal Stability Analysis of Three-Phase Four-Wire System Integrated With Single-Phase PV Inverters Considering Phase to Phase Coupling

Small-Signal Stability Analysis of Three-Phase Four-Wire System Integrated With Single-Phase PV Inverters Considering Phase to Phase Coupling

Framework to assess the stable operation of commercially available single-phase inverters for photovoltaic applications in public low voltage networks

This paper presents a framework to assess the grid compatibility of single-phase inverters connected to public low voltage network, which is characterized by a stable operation at reasonable emission. The assessment is based on considering emission, immunity and stability. The state of the art for commercially available devices relies only on the classical, impedance-based stability analysis based on the Nyquist criterion. However, experiences have shown that this is not sufficient for a statement towards the stable operation of an inverter, since the stable operation can also be affected by other factors than the network impedance, e.g. a background voltage distortion. Exemplary laboratory measurements of two commercially available single-phase PV inverters are presented to validate the statement by showing that despite the impedance-based stability criterion is met, inverters can still trip in presence of a high background voltage distortion. The paper concludes that the immunity of the inverter with regard to the voltage distortion at the point of connection (PoC) is additionally of importance for its stable operation.

Small-Signal Stability Analysis of Three-Phase Four-Wire System Integrated With Single-Phase PV Inverters Considering Phase to Phase Coupling Effect Under Asymmetric Grid

Small-Signal Stability Analysis of Three-Phase Four-Wire System Integrated With Single-Phase PV Inverters Considering Phase to Phase Coupling Effect Under Asymmetric Grid

Improving Voltage Regulation and Unbalance in Distribution Networks Using Peer-to-Peer Data Sharing Between Single-Phase PV Inverters

This paper proposes a novel reactive power-based control strategy for single-phase PV inverters (PVIs) to simultaneously improve voltage unbalance (VU) and voltage regulation (VR) in low-voltage distribution networks. The proposed strategy relies on communication links between neighboring PVIs to exchange limited data. In this strategy, each PVI finds communication paths between itself and the closest neighboring ones connected to other phases. Then, using the obtained paths and the maximum and the minimum voltage magnitude of the grid, PVIs improve both VU and VR at the same time. The performance of the proposed control strategy is evaluated by various simulation studies using the IEEE European low-voltage test feeder and considering different operational conditions. In addition, the impacts of moving clouds and a failure in the communication links have been assessed. The simulation results exhibit that using the proposed control strategy, the voltage magnitude of all the nodes will remain within the allowed limits and at the same time, the phase voltage unbalance factor will be also significantly improved.

Supraharmonic emission from a three-phase PV system connected to the LV grid

Existing international standards address harmonic orders up to the 40th or 50th (at 2 or 2.5 kHz for a 50 Hz network). Modern converters effectively suppress components within that range, but they also tend to shift emission to higher frequencies. Recently reported cases of disturbances in modern distribution grids specifically attributed to supraharmonics (harmonic components within the 2–150​ kHz range) have drawn interest in associated research. Grid-connected PV systems utilizing PWM-controlled inverters inject supraharmonic currents into the distribution network at their point of connection. Comprehension of their electrical behavior, including their impact on grid supraharmonic levels, can be achieved through extensive simulation studies. In this paper, a three-phase PV system is simulated using models successfully already developed for single phase PV inverters that increase simulation speed by avoiding time-consuming procedures. Current and voltage waveforms as well as supraharmonic levels are presented. The simulation results are compared with real measurements obtained from an operating small rooftop PV system and evaluated. Additional simulations are carried out using different values for system parameters and their respective impact on supraharmonic levels is assessed. Moreover, this paper presents real supraharmonics’ measurements from a grid-connected 8kWp PV system.

Control of power converter used for electric vehicle DC charging station with the capability of balancing distribution currents and reactive power compensation

The global interest in electric cars aims to achieve sustainability in the transportation sector and reduce dependence on conventional cars that mainly depend on fossil fuels, the main source of emissions polluting the environment. However, the electric cars required electric fast chargers to charge the batteries with high currents in order to make the electric cars competitive with conventional cars that required a short time for filling fuel. Single-phase electric chargers make the distribution feeders with unbalanced currents as the single-phase loads and single-phase PV inverters. In the case of the unbalanced operation, one of the three phases may reach its maximum limit before other phases which leads to disconnect the transformer and thereby inefficient and unreliable system operation. This paper presents a control scheme for a three-phase, four-leg power converter that can be used as a fast charger for electric cars. Moreover, it can be used for balancing grid currents and for reactive power compensation. This will avoid frequent interruptions of distribution transformers due to unbalanced operation and reactive power loads. The distribution feeder considered to evaluate the control scheme consists of single-phase loads and inverters in addition to the proposed converter. The converter controls the charging power effectively and balancing the feeder currents. Moreover, during off charging time which is a possible manner for the charging station when the EV battery is fully charged the converter is effectively used for unbalanced mitigation and reactive power compensation. The simulated results show the effectiveness of the proposed control scheme.

Four-Switch Single-Phase Common-Ground PV Inverter With Active Power Decoupling

This letter presents a transformerless single-phase PV inverter, which combines with common-ground and active power decoupling techniques. The leakage current is eliminated and bulky electrolytic capacitors are removed, thus improving the system safety and reliability. In addition, it needs only four switches and can be implemented conveniently by a commercial H-bridge module. The validity of the inverter is verified with a 2-kW prototype.

Optimization Design and Control of Single-Stage Single-Phase PV Inverters for MPPT Improvement

Due to the inherent double-frequency (2 f 0) ripple in single-stage single-phase photovoltaic grid-connected inverters, the maximum power point tracking (MPPT) will inevitably be affected. To improve the MPPT performances, a passive LC power decoupling circuit with a robust second-order sliding-mode control (SOSMC) is thus proposed in this article. With the passive LC decoupling path, the double-frequency pulsation on the dc link is effectively cancelled out. Thus, the MPPT accuracy is significantly enhanced, and the utilization of a small dc-link capacitor becomes possible. However, resonance between the LC circuit and the main dc-link capacitor may appear, which can be damped through an active damping method. Additionally, the proposed SOSMC ensures good steady-state, dynamic performance (voltage fluctuation and settling time), and the robustness of the dc-link voltage, which is also beneficial to MPPT control in terms of high accuracy and fast dynamics. The systematic design of SOSMC is presented, and a detailed parameter optimization design of LC decoupling circuit is discussed. Experimental tests are performed on a 2.5-kW single-stage single-phase grid-connected inverter, and the results validate the effectiveness of the proposed strategy.

The Essence of the Little Box Challenge-Part B: Hardware Demonstrators & Comparative Evaluations

In order to expedite the development of power electronic systems towards higher power density and efficiency at a lower cost of implementation, Google and IEEE initiated the Google Little Box Challenge (GLBC) aiming for the worldwide smallest 2 kVA/450 VDC/230 VAC single-phase PV inverter with η > 95% CEC weighted efficiency and an air-cooled case temperature of less than 60 °C by using latest power semiconductor technology and innovative topological concepts. This paper, i.e. Part B of a discussion of The Essence of the Little Box Challenge, presents the hardware implementations and novel control concepts of two GaN-based inverter systems selected by the authors to counter the challenge: (i) Little Box 1.0 (LB 1.0), a H-bridge inverter with two interleaved bridge-legs both operated with Triangular Current Mode (TCM) modulation which features a power density of 8.18 kW/dm 3 (134 W/in 3 ) and a nominal efficiency of 96.4% and (ii) Little Box 2.0 (LB 2.0), an inverter topology with single bridgeleg DC/|AC| buck-stage operated with constant frequency PWM and a subsequent |AC|/AC H-bridge unfolder, which features a remarkable power density of 14.8 kW/dm 3 (243 W/in 3 ) and a nominal efficiency of 97.4% Implemented using latest GaN power semiconductor technology, Zero Voltage Switching (ZVS) throughout the AC period and a variable switching frequency in the range of 200 kHz-1 MHz in order to shrink the size of filter passives, the LB 1.0 was ranked among the top 10 out of 100+ teams actively participating in the GLBC. The LB 2.0 is the result of further research and considers lessons learned from the GLBC and achieves despite moderate 140 kHz constant frequency PWM and hard-switching around the peak of the AC output current a higher power density ρ and a higher efficiency η. For both implemented prototypes experimental results are provided to confirm that all GLBC technical requirements are met. The experimental results include steady-state and step-response waveforms, EMI and ground current measurements, as well as efficiency and operating temperature measurements. The reason for the ηρ-performance improvement of LB 2.0 over LB 1.0 are then discussed in detail. Furthermore, the solutions of other GLBC finalists are described and then compared to the performance achieved with the hardware prototypes presented in this paper. This leads to findings of general importance and provides key guideline for the future development of ultracompact power electronic converters.

The Essence of the Little Box Challenge-Part A: Key Design Challenges & Solutions

In order to expedite the development of power electronic systems towards higher power density and efficiency at a lower cost of implementation, Google and IEEE initiated the Google Little Box Challenge (GLBC) aiming for the worldwide smallest 2 kVA / 450 V DC / 230 V AC single-phase PV inverter with η > 95 % CEC weighted efficiency and an air-cooled case temperature of less than 60 °C by using latest power semiconductor technology and innovative topological concepts. This paper, i.e., Part A of a discussion of The Essence of the Little Box Challenge, documents all important RD Part B is intended to convey the main findings and lessons learned from the participation in the GLBC. First, the key technical challenges of the GLBC are discussed and the technologies and concepts selected by the authors among different options are described in detail. Relevant design considerations, such as constant frequency pulse width modulation (PWM) or triangular current mode (TCM) operation of the bridge-legs, selection of power semiconductor technology, interleaving of bridge-legs, sizing of the power buffer capacitor, limitation of ground/leakage currents, etc., to achieve an ultra-compact implementation are discussed. Based on this overview, two promising inverter concepts to tackle the GLBC, (i) an H-bridge based inverter with DC-link referenced output filter and (ii) a DC/|AC| buck-stage with series-connected low-frequency (LF) |AC|/AC unfolder inverter, are then analyzed in detail. Based on the results of a multi-objective ηρ-Pareto optimization, a comparative evaluation of the performance in terms of efficiency (η) and power density (ρ) of the two considered inverter concepts is provided. It is shown that with the DC/|AC| buck-stage and |AC|/AC H-bridge unfolder inverter operated with 140 kHz PWM a power density of 14.7 kW/dm 3 (240 W/in 3 ) with a maximum efficiency of 98.1% at 2 kW output power can be achieved. These claims are then verified in Part B by means of experimental results obtained from prototype realizations and compared to the achievements of other GLBC finalists. The conclusions are of general importance and are providing key guidelines for the future development of ultra-compact power electronic converters.

Modeling and Design of Single-Phase PV Inverter with MPPT Algorithm Applied to the Boost Converter Using Back-Stepping Control in Standalone Mode

We propose a high-performance and robust control of a transformerless, single-phase PV inverter in the standalone mode. First, modeling and design of a DC-DC boost converter using a nonlinear back-stepping control was presented. The proposed converter uses a reference voltage that is generated by the Perturb and Observe (P&O) algorithm in order to extract the maximum power point (MPP) by responding accurately to varying atmospheric conditions. Another goal for using the boost converter is to raise the voltage at the input of the inverter without using a transformer in this system, thus making the system more compact and less expensive. Secondly, the single-phase H-bridge inverter was controlled by using back-stepping control in order to eliminate the error between the output voltage of the inverter and the desired value, even if there is acute load variation at the output of the inverter. The stability of the boost converter and H-bridge inverter was validated by using Lyapunov’s stability theory. Simulation results show that the proposed PV system with back-stepping controllers has a good extraction of the MPP with an efficiency of 99.93% and 1 ms of response time. In addition, the sinusoidal form of the output voltage of the inverter is fixed to 220 V and the total harmonic distortion of the output voltage was found to be less than 1%.

Development of high frequency (Supraharmonic) models of small-scale (

There is a growth of high frequency (HF) emissions in the range of 2–150kHz (also known as Supraharmonics) in electricity distribution networks, primarily due to the increasing number and capacity of AC grid connected equipment having power electronic interfaces. Although PV inverters are a major HF source in electricity distribution networks, PV inverter models that are suitable for HF emission studies are yet to be developed. To this end, a generic method that can be used to develop HF models of small-scale (<5kW), grid-tied, single-phase PV inverters using a black box approach is presented in this paper. Accordingly, HF models of three PV inverters that are commonly used in domestic and commercial installations are developed assuming standard network conditions. It is shown that these HF models are capable of successfully capturing the HF performance of the selected PV inverters under a wide range of operating conditions. The outcomes of this work are expected to broaden the knowledge pertaining to the HF emissions in the frequency range considered.

Design and Implementation of Digital Phase Locked Loop for Single-Phase Grid-Tied PV Inverters

In this article, a synchronous rotating-frame based phase-locked loop (PLL) for a single-phase PV inverter control system is presented. Detailed PLL mathematical model and the digital implementation for a single-phase PV inverter system are presented. A practical solution for transport delay based orthogonal signal generation using first-in-first-out (FIFO) circular buffer is also discussed. Details of implementation for a real-time system using digital signal processor were also described. The performance of the developed PLL was experimentally verified on a developed single-phase PV inverter prototype.

System-level reliability enhancement of DC/DC stage in a single-phase PV inverter

This paper studies the impact of modulation scheme, mission profile and PV array configuration on the reliability of a double-stage single-phase PV inverter. A single-phase double-stage inverter with two boost-based Maximum Power Point Tracker (MPPT) is considered and the reliability of dc/dc stage is estimated under different mission profiles. Furthermore, two types of PV panels with different output characteristics are considered to demonstrate the impact of PV array design on the PV converter reliability. Moreover, a phase shifted-switching scheme for the dc/dc converters and inverter is proposed to improve the overall reliability. The outcome is the PV converter reliability enhancement through suitable PV panel selection and proposed phase-shifted modulation scheme, which can be a system-level design for reliability guideline for PV converter and PV system designers.

Impact of meteorological variations on the lifetime of grid-connected PV inverters

In this paper a grid-connected single-phase PV inverter is employed as a study case in order to investigate the effects of different meteorological conditions on the reliability analysis. The lifetime evaluation of the power modules consisting of the PV inverter is evaluated, taking into account variations on the solar irradiance and ambient temperature but also including the PV panel thermal dynamics (i.e., thermal capacitance). The mission profiles are used as the input and then translated into the thermal loading of the power switch. The Bayerer's model and Palmgren-Miner's rule are used to calculate the life consumption (LC) and B10 lifetime. The results show that the increase in irradiance generates more energy. However it strongly reduces the system lifetime. Also, the thermal dynamic of the PV panel has important impact on the lifetime prediction.

Improving performance of LVRT capability in single-phase grid-tied PV inverters by a model-predictive controller

New interconnection standards for Photovoltaic systems are going to be mandatory in some countries. Such that the next generation of PV should support a full range of operation mode like in a power plant and also support Low-Voltage Ride-Through (LVRT) capability during voltage sag fault. Since the voltage sag period is short, a fast dynamic performance along with a soft behavior of the controller is the most important issue in the LVRT duration. Recently, some methods like Proportional Resonant (PR) controllers, have been presented to control the single phase PV systems in LVRT mode. However, these methods have had uncertainties in respect their contribution in LVRT mode. In PR controllers, a fast dynamic response can be obtained by tuning the gains of PR controllers for a high bandwidth, but typically the phase margin is decreased. Therefore, the design of PR controllers needs a tradeoff between dynamic response and stability. To fill in this gap, this paper presents a fast and robust current controller based on a Model-Predictive Control (MPC) for single-phase PV inverters in other to deal with the LVRT operation. In order to confirm the effectiveness of the proposed controller, results of the proposed controller are compared with the classical PR controller. They are also implemented in a 1 kW single-phase transformerless HERIC (Highly Efficient and Reliable Inverter Concept) inverter.

A New Feed-forward Compensation Inverter Control Strategy

With the development of new energy research, photovoltaic inverter is widely used in solar photovoltaic power generation system. In this paper, a new static feedforward compensation control strategy for current loop is proposed for the shortcomings of the single-phase PV inverter in the use of the typical Ⅰ-type system in the double closed-loop control system. Through the improved Park transformation, the equivalent model of the single-phase inverter is obtained. The control equation of the current is obtained by the method of feed-forward decoupling control in the equivalent inverter model. For the interference signal in the current control equation, The static feed-forward compensation control method eliminates the interference signal present in the inner loop of the current. Through this control method, the current loop in ensuring the performance of good follow at the same time effectively improve the current loop anti-jamming performance. At the same time, current loop control and voltage outer loop control using PI control, the formation of double closed-loop control system. The simulation results show that the anti - jamming performance of the double closed-loop inverter control system with static feed-forward compensation is better, the output waveform distortion rate of the inverter is low, and the PV inverter is stable in the presence of disturbance.

Neural Network Controlled High-Step Up Based Single-Phase PV Inverter System with Improved Dynamic Response

In AC utility closed loop high step up based single phase PV inverter system is preferred because of fast dynamic response. This paper deals with comparison of dynamic response of the PI and the neural network controlled single phase PV inverter systems. The DC output from the solar cell is stepped up using a high step up converter and the output is converted into AC using an inverter. A change in the insolation is considered in the present investigation. Simulation studies are conducted using MATLAB. The closed loop control systems using the PI controller and the neural network controller are investigated and their results are compared. The Simulink model for the above system are developed and they are successfully used for simulation studies. The hardware is fabricated, tested and the practical results matches with the simulation results.

Technical assessment of centralized and localized voltage control strategies in low voltage networks

Abstract Both the electric power demand and the penetration of small-scale embedded generators (SSEGs) is rapidly increasing in LV distribution grids. These trends are expected to have significant effects on system performance, efficiency and reliability necessitating the adjustments to the current framework for power supply dispatch and delivery. This paper proposes hybrid voltage control schemes for LV distribution networks combining: (i) centralized control via the on-load tap-changer (OLTC) of secondary distribution transformers and (ii) localized control via both the real and reactive power management from single-phase PV inverters. Specific control algorithms are proposed for both the centralized and localized methods. All the possible operation sequences of the aforementioned methods are examined. The performance of the proposed approaches is investigated on four different test feeders considering the voltage magnitudes, the voltage unbalances, the total losses and the PV power utilization.

Design and Simulation of two Stages Single Phase PV Inverter operating in Standalone Mode without Batteries

Design and Simulation of two Stages Single Phase PV Inverter operating in Standalone Mode without Batteries