 1. non-isolated photovoltaic grid-connected inverter 1.1 PV grid system photovoltaic power generation is increasing year by year, the contribution of the world's energy,Grid tie inverter, and this for all to see. IEA PVPS data show that in 2009, the project members install photovoltaic capacity the 6.2GW (installed worldwide about 7GW up and), of which more than 95% for the grid system, as shown in Figure 1. Figure 1 photovoltaic power generation of the world's energy contribution increases every year Data source: IEA PVPS, BS EN 60904-3-1993 Power Systems Programme of the International Energy 1,power inverter.2 photovoltaic power generation system photovoltaic power generation system consists of a photovoltaic cell array and inverter (Figure 2). Which grid-connected inverter system performance and cost of power generation plays an important role in the decision. in accordance with transformer and grid-connected inverter can be divided into isolated and non-isolated, including: power frequency isolation grid inverter, high frequency isolation grid inverter, non-isolated grid inverter (single-stage and multi-stage). -frequency isolation grid inverter (Figure 3) with electrical isolation and eliminate the current DC component, etc., but a large volume weight of high prices, only 94% -96% of the efficiency of the system.  the high frequency isolation grid inverter (Figure 4) with electrical isolation, size,power inverter, weight, cost reduction and other advantages, but the efficiency of the system is only 90% -95%. non-isolated and non-isolated single-stage grid-connected inverter is divided into grid inverters and two non-isolated grid inverter. Single-stage non-isolated grid inverter is suitable for higher PV voltage and power; while the two non-isolated grid inverter is suitable for a wide voltage range of the PV array, they have a maximum efficiency of 98.8%, small size, weight lightweight, low cost, but its drawback is that there is an electrical connection between the battery plates and grid. Figure 2 the composition of the photovoltaic power generation system structure Figure 3-frequency isolation grid inverter diagram electrical connections for leakage current flow path is a high-efficiency non-isolated PV grid inverter applications biggest obstacle. The leakage current is generated the parasitic capacitance 150nF/kWp, caused by the switching frequency common-mode voltage source. Mostly used the circuit structure SPWM modulation strategy. Figure 4 high frequency isolation grid inverter 2. non-isolated and grid-connected inverter commonly used circuit topology the past, we often bipolar SPWM modulated full-bridge grid inverters (its topology in Figure 5), because its efficiency is not high, often used in low power situations, and there is no patent barriers. http://www.gridtieinverter.de/ Figure 5 Bipolar SPWM modulation full-bridge inverter grid Billiton here we want to introduce several patented topology. 2.1 Sunways company's patented topology (Figure 6) single-phase two series: AT 2700/3000/3600/4500/5000: single-phase single-stage series: NT 2500/3700/4200/5000; the three-phase two series: Three-phase IxIT 10000/11000/12000. the 6 Sunways patented topology the company's patented topology 2,www.12vgridtiepowerinverters.com.2 SMA (Figure 7) single the phase two Series: SB3000TL/4000TL/5000TL; single-phase single-stage series: SMC6000TL / 7000TL / 8000TL / 9000TL / 10000TL / 11000Tlo the Company Figure 7SMA patented topology 2,Grid tie inverter.3 half-bridge topology level SPWM half bridge two patent barriers, they have been widely adopted; Unipolar SPWM electric Pingban bridge. 3. improved full-bridge non-isolated photovoltaic grid-connected inverter The single-phase grid first look at the analysis of the leakage current of the inverter model (Figure 8) is how to solve the problem of single-phase grid-connected inverter leakage current. filter branch: the network access filter, EMI filter and the grid parasitic dominated play a leading role in the common mode current loop impedance; parasitic branch: parasitic capacitance constituted by the mid-point of the bridge arm, influence from the common mode current loop impedance: by single-phase grid analysis of the leakage current of the inverter model (Figure 9) summarized two ways to eliminate leakage current: (1) in a symmetrical circuit and parasitic parameters under the premise that meet Figure 8 single-phase grid-connected inverter leakage current analysis model single-phase grid analysis of the leakage current of the inverter model VCM-DM: 0), the the VCM voltage produced by the SPWM switching mode for the constant value; the SPWM switching mode VCM voltage of (2) for the high-frequency time-varying circuit parameters matching makes VCM + VCM-DM = consto. full bridge class single-phase grid inverter leakage current suppression techniques include: (1), under the premise of a symmetrical circuit and parasitic parameters (i.e., meet the VCM-DM: O) SPWM switching mode generated V voltage is a constant value. common circuit are the following: full bridge circuit with AC bypass links; full bridge circuit with DC bypass links; full bridge circuit with the DC side of the bypass clamp; improved functionality and efficiency optimization-based full-bridge circuit. join a controllable switch and a two-way clamp divider capacitor branch. theoretical analysis and experimental research 4.1 circuit structure and driver timing the main circuit structures of SPWM and drive timing work modal for the current positive half cycle and current negative half-cycle. voltage clamp work freewheeling stage midpoint voltage with the grid voltage fluctuations, enhance the midpoint voltage or lower midpoint voltage. loss analysis and calculation of 4.2 power devices PV voltage 500V power 5kW level, for example (Figure 10), we study the following experimental conditions. input voltage :340-700VDG PV parasitic capacitance: 2 × 0.1 u F grid: 220V/50Hz network access filter: 4mH +6.6 u F power: 1kW switching frequency: 20kHz form of circuit experiment listed below: A: Haric B: H5 C: H6 D: Optimized H5  the 10 power device loss analysis and calculation Figure the 11 experimental A: Haric 5. conclusion non-isolated PV grid inverter appliances with high efficiency, small size, light weight, etc.; according to bridge non-isolated photovoltaic grid-connected inverter leakage current analysis model, we can draw two to suppress the switching frequency leakage current ways; |
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