250 W Grid Connected Microinverter Enabling new generation of PV systems 250 W microinverter for PV applications 2 • Key features: • 250 W power capability • Output voltage Vout= 230Vac 50Hz -240Vac 60Hz • High conversion efficiency (>94%, 93.5% CEC) • MPPT efficiency (99%) • Decoupled control of active and reactive power • Overcurrent and anti-islanding protection • Galvanic isolation between the panel and the grid • Key products: • STM32F103ZE (32-bit microcontroller) • STB18N65M5, STH180N10F3-2 (power MOSFETs) • PM8834, L6390 (MOSFET drivers) System evaluation board order code: STEVAL-ISV003V1(*) • STPSC606, STPS1545C, STTH12R06 (diodes) • SMBJ (EOS surge protection) • ST3232EB (RS-232 interface) (*) Available at the end of Q1 2012 250 W microinverter: block diagram 3 250 W microinverter: DC-DC section Electrical Specs • Vin= 18V to 55V • Pout= 250W • Vmppt= 20V to 40V • fsw = 35kHz 4 The topology Vin L1 + • Iin=7,6A (nominal) STTH12R06 Vout + • Vout= 370Vdc to 430Vdc • Iout= 0.65A (nominal) Max Efficiency DC-DC converter 97.4% STH180N10F3-2 PM8834 MOSFETs driver L2 HF transformer STTH12R06 STH180N10F3-2 32-bit MCU STM32F ISOLATED INTERLEAVED BOOST CONVERTER 250 W microinverter: DC-AC section Electrical Specs The topology • Vin= 370Vdc to 430Vdc • fsw1= 17kHz (high frequency leg) STPS1545C • fsw2= 50Hz (low frequency leg) •Vin (nominal) = 380 V STPSC606 STB18N65M5 STB18N65M5 • Vout= 230Vac / 240Vac • fout= 50Hz / 60Hz L6390 + PM8834 • Iout = 1.1 A/ 1.06A [ E f f i c % i e n c y + Vin Max conversion efficiency 94.1% L6390 + PM8834 Vout MOSFETs drivers MOSFETs drivers ~ Microinverter Efficiency STPS1545C ] 96 94 92 90 88 86 84 82 STPSC606 STB18N65M5 STB18N65M5 32-bit MCU 0 50 100 150 200 250 300 STM32F Output Power [W] HIGH FREQUENCY LEG MIXED FREQUENCY INVERTER LOW FREQUENCY LEG 5 250 W microinverter: MPPT algorithm The MPPT “Perturb and Observe” algorithm STM32F and MPPT DC Sense V(k), I(k) DC: Duty cycle value C: Duty cycle step value V(k): input voltage P(k): Power k4 DC Vsense STM32F Microcontroller 6 P(k)=V(k)*I(k) MPPT k3 k2 Isense NO A/D converter YES k1 Duty cycle calculation NO Previous Power and Input voltage value register P(k)>P(k-1) V(k)>V(k-1) YES NO V(k)<V(k-1) k0 YES MPPT controller DC=DC-C DC=DC+C DC=DC-C DC=DC+C MPPT is reached following PV panel curve 250 W microinverter: grid connection The PARK transformation q β The DQ-Phase Locked Loop (PLL) structure Vd is controlled to zero with a PI regulator→ GRID ANGLE θe KNOWN STM32F Vgrid Microcontroller d θe α FROM Vα and Vβ (grid voltage and 90°phase shifted voltage on stationary frame) TO Vd and Vq (two voltage components on rotating DQ reference frame) ADVANTAGES of DQ-PLL • Vd, Vq, Id, Iq are constants in DQ reference frame: standard PI regulators for their control ensure zero steady state error • Decoupled control of active P and reactive Q power 7 250 W microinverter: smart communication Communication section Power Line Communication AC bus Microinverter ST75xx: STarGRID power line networking SoC the most integrated and flexible solution for smart grid applications and smart metering Wireless Communication Local monitoring & control Remote monitoring & control •STM32W RF MCUs (ZigBee®) •SPZB32W ZigBee® modules •Bluetooth® modules Data concentrator To the AC Grid Enabling onsite or remote monitoring of PV system 8