Using Power Integrated Modules to Design High Energy Efficiency and High Reliability Solar Inverters

As energy and environmental issues become increasingly prominent, solar energy develops rapidly as a clean and renewable energy source, and solar power generation facilities proliferate, of which inverters are essential. ON Semiconductor's Power Integrated Module (PIM) solutions provide energy-efficient, high-reliability inverter designs.


Solar Inverter, Uninterruptible Power Supply (UPS) and Energy Storage System (ESS) Architecture

In battery-powered operation, UPS, ESS, and solar inverters consist of DC-DC converters and DC-AC inverters, and the solutions enjoy a high degree of similarity and versatility. As shown in Figure 1, 20 to 200kVA string solar inverters include boost inductors, boost modules, DC bus capacitors, inverter modules, AC filter inductors and capacitors, while 20 to 50kVA UPS/ESS include input Filtering, Power Factor Correction (PFC), Rectifiers, DC Bus Capacitors, Inverter Modules, Filter Inductors and Capacitors. UPSs provide backup power in the event of a power outage or unstable power supply and are widely used to power critical components in countless applications such as telecommunications and data centers, various industrial facilities, and more. ESSs are increasingly being deployed in conjunction with renewable energy sources to ensure uninterrupted power supply and facilitate grid modernization.

Figure 1: Typical block diagram of a solar inverter/UPS/ESS

Solar Inverter/UPS/ESS Solutions and Trends

Due to the need for higher energy efficiency, inverter modules are commonly used in multi-level structures in typical applications, especially 3-level (NPC or T-NPC) inverters are popular because 3-level is more than 2-level The inverter is more energy efficient, with lower current total harmonic distortion (THD), lower input leakage current, and smaller output filtering closer to an ideal sine wave. Of course, due to the increase in the number of IGBTs, drivers, and auxiliary power supplies, the cost of the bill of materials (BOM) and the complexity of the control scheme will also increase. ON Semiconductor provides a PIM solution, which adopts a multi-string inverter structure without power frequency transformers, and optimizes the chipset and layout to reduce losses and achieve high-frequency switching, high energy efficiency and high power density.

Typical 3-level inverter topology

TNPC, NPC, and ANPC are three typical 3-level inverter topologies. TNPC achieves low switching losses, NPC has been widely used in the past, and ANPC has the advantage of low parasitic inductance. The three-level solution provided by ON Semiconductor covers output power from 20kW to 220kW, and uses different packages of Q0, Q1, and Q2 for users in different power segments to choose. The Q0 and Q1 packages are used for boost modules up to 25kW and 40kW and inverter modules up to 15kW and 20kW, respectively. The Q2 package has a copper substrate for enhanced heat dissipation and is used for 1500V inverter modules up to 220kW and 1100V inverter modules up to 90kW.

Table 1: Typical 3-level inverter topology


Recommended Boost and Inverter Modules and PIM Selection Guide

Table 2 lists the boost and inverter modules currently offered by ON Semiconductor. These modules all integrate high-speed IGBTs, Si/SiC diodes for energy-efficient, compact designs, built-in thermistors for high reliability, and solder/press-fit pins for easy installation. PIM_OPN Product Description Package Package Selection Boost Module
NXH80B120H2Q0SG Q0PACK / Dual Boost / 1200V,
40A IGBT and SiC diode
Number of MPPTs: 2
IGBT rated current: 41A
SiC Diode Rating: 3X5A PIM Q0 Solder Pins
NXH80B120L2Q0SG Q0PACK/Dual boost/1200V,
40A IGBT and Si diode PIM Q0 soldering pins
NXH100B120H3Q0SG/PG Q0PACK/Dual boost/1200V,
40A IGBT and SiC diode
Number of MPPTs: 2
IGBT rated current: 50A
SiC Diode Rating: 2X10A PIM Q0 Solder Lead/Press-Fit Lead
NXH240B120H3Q1PG Q1PACK / 3-channel boost /
1200V IGBT and SiC diode
Number of MPPTs: 3
IGBT rated current: 68A
SiC Diode Rating: 4X5A PIM Q1 Press Pin Inverter Module
NXH80T120L2Q0 S2G Q0PACK / 80A TNPC Inverter
3-phase inverter maximum total power: 30kVA
Number of modules in a 3-phase inverter: 3 PIM Q0 solder pins
NXH160T120L2Q1PG/SG Q1PACK / 160A TNPC inverter
3-phase inverter maximum total power: 6kVA
Number of modules in a 3-phase inverter: 3 PIM Q1 press-fit pins/solder pins
NXH160T120L2Q2F2SG Q2PACK /160A TNPC inverter
3-phase inverter maximum total power: 90kVA
Number of modules in a 3-phase inverter: 3 PIM Q2 solder pins
NXH25T120L2Q1PG Q1PACK / 25A TNPC Inverter
3-phase inverter maximum total power: 10kVA
Number of modules in a 3-phase inverter: 1 PIM Q1 Press-fit pins/solder pins
NXH450N65L4Q2F2SG Q2PACK / 1100V System INPC Inverter
3-phase inverter maximum total power: 140kVA
Number of modules in a 3-phase inverter: 3 PIM Q2 Soldering Pins Table 2: Recommended Boost and Inverter Modules


For the DC-DC boost module, one MPPT channel can support a maximum photovoltaic (PV) input of about 25A (two PV panels in parallel). Each module has different MPPT numbers, IGBT rated current, and SiC diode rated value. The number of MPPTs required by the application and the power of each MPPT should be selected with appropriate modules and number of modules.

For the application of 1100V maximum DC bus, the corresponding 3-level DC-AC inverter module should be selected according to the inverter power level required by the application. For smaller power inverter requirements, such as 10kVA, ON Semiconductor provides a three-in-one solution that integrates a, b, and c three phases into one Q1 package.

In addition, in response to the recent rapidly growing demand for 1500V photovoltaic power plants, ON Semiconductor will also launch 1500V three-level inverters and boost modules. Compared with the mainstream 1200V wafers in the market, its 1000V IGBT wafers have thinner linings. bottom area, so the on-resistance is smaller and losses are significantly reduced. For single-phase inverters, ON Semiconductor will launch a module using H6.5 topology, which greatly reduces the common mode current compared with the widely used H-bridge topology to meet the safety requirements for grid connection without an isolation transformer. Considering the demand for increasing battery energy storage for households in the future, bidirectional power flow is considered when selecting wafers, which can send electricity to the grid, or take electricity from the grid and store it in the battery. When the power factor is 1 or -1, it can be highly efficient. run.

When choosing a PIM, you should first know the application requirements, such as rated power and voltage, whether a boost module is required, whether to use 3-phase or single-phase, and what topology to use, then work with the application engineer to calculate the number of modules required, and use the simulation software Calculate losses and maximum junction temperature.

Practical Design Examples

Figure 2 is a circuit diagram of a 60kW solar inverter product. Taking the 1100V three-phase inverter as an example, the red block diagram shows a DC boost module, which is used to boost the lower photovoltaic panel input voltage to the higher DC bus capacitor voltage, and the blue block diagram shows the TNPC three The level inverter module realizes the energy conversion from DC to AC.

Figure 2: Solar inverter circuit (1100 V three-phase inverter)


In addition, some passive devices such as electrolytic capacitors, film capacitors, common mode inductors, AC filter inductors, DC filter inductors, and AC relays are also used. The electrolytic capacitor supports the stability of the DC bus voltage, the film capacitor is used to absorb the peak voltage generated when the IGBT is switched, and the common mode inductor provides high impedance in the common mode loop to suppress common mode interference EMI and common mode loss.

To design an 80kW system, assuming that 4 Q0 boost modules NXH80B120H2Q0SG and 3 Q2Pack inverter modules NXH160T120L2Q2F2S1G are selected, the power of each MPPT is: 80/8 =10kW, and the PV current is:

10kW/600V=16.67A, the power of each inverter module is: 80/3=26.67kW. Then, the following system condition parameters are input through the simulation software to calculate the energy efficiency and evaluate the junction temperature of the IGBT and diode.

Figure 3: Design example of an 80 kW system


The simulation results show that the system energy efficiency of this design is more than 98%, and the loss and thermal performance are good, so it is feasible.

Gate Drive Circuit Design Considerations

The turn-on and turn-off of the IGBT needs to charge and discharge the cge circuit. In photovoltaic applications, control signals and high-voltage circuits need to be isolated. When laying out the board, the gate drive circuit should be placed as close to the PIM module as possible to reduce the stray inductance of the drive loop, because higher stray inductance may cause gate voltage oscillation. When choosing the gate resistance value Rg, a compromise needs to be made between switching losses and voltage and current stress. In addition, designers need to pay attention to the common-mode transient immunity (CMTI) parameters of the isolation chip.

Summarize

The world is turning to renewable energy sources such as solar energy to replace traditional energy sources to solve increasingly prominent energy and environmental problems. ON Semiconductor offers a variety of 3-level inverter modules and booster modules with optimized power semiconductor devices and package designs to provide more than 98% energy efficiency and high reliability in solar inverters, UPS and ESS systems, And provide a variety of gate drivers used with power modules to optimize system performance, supplemented by rapid and in-depth technical support to help customers win business opportunities and expand business.