Central inverters are a type of inverter used in solar modules to convert DC power from solar panels into AC power.
Solar Inverter
Inverters are vital pieces of equipment for any solar system. There are different types of inverters including Central inverters, micro inverters, and power optimizers. Inverters are used to convert the power produced by solar panels into (AC) power which can be directly used by home appliances or connected to the grid. The solar panels initially produce electricity as a direct current (DC). Inverters convert the raw DC power into AC power that can be used for equipment. It additionally monitors and controls the PV system performance.
Types of Solar inverters
There are two main types of inverters: central inverters and micro-inverters.Central inverters (also called string inverters) connect a string of PV panels and convert the DC electricity into AC. A single string- term used for solar panels connected in series - usually has a maximum of about ten solar panels. Multiple strings are combined in parallel and the output is passed through the inverter.
In addition, they are more suitable for the utility sized solar PV systems. Large arrays of solar panels are all connected to one combiner box and from there all the DC power is directed to the central inverter.However, the approach of micro-inverters is quite different; a single inverter is attached to each solar panel. Each micro-inverter converts DC into AC current and the output of each panel is combined and sent to the grid or battery bank.
What are the advantages and disadvantages of central inverters compared to the string and micro inverters?
The main advantages of Central inverters include the following:
Credibility due to presence for long time and use in the market.
Lower costs
Ability to produce much higher power
Reliability: as central inverters are placed in protective environments
The main disadvantages of Central inverters include the following:
Potential for a single point of failure even if a single panel is shaded or fails due to some other reason, it will affect the performance of the entire system.
Higher risk factor because of the produced DC voltage of high rating, which could be life threatening to both the operators and owners.
Higher replacement cost
Products and reference designs of Central inverter
DC relay power stage
The connection of each voltage bus is equipped with a relay to protect the system. The DC relay disconnects the battery management system from the central inverter controller to prevent over-charging and over-discharging of battery banks. DC relay power stage includes Solenoid drivers、N-channel MOSFETs, the corresponding products are DRV110、CSD18531Q5A
DC/DC input current & voltage sense
Accurate and high speed sensory data of the various power busses in the solar inverter is required to effectively control the power electronics and help ensure operational safety. Isolated sensory techniques are routinely used due to the high voltages involved. DC/DC input current & voltage sense includes General-purpose op amps、Precision op amps (Vos<1mV)、Comparators, the corresponding products are TLV9052、OPA2335、LM2901AV
DC/DC converter
The first power stage in an inverter is used to generate a stable internal DC voltage suitable for the operation of the inversion stage. FETs must be sized appropriately, and matching dedicated gate drivers are used to ensure proper driving and operational efficiency. DC/DC converter includes Isolated gate drivers、Half-bridge drivers、Low-side drivers、PWM controllers、LLC controllers、Flyback controllers、Isolated DC/DC converters & modules、N-channel MOSFETs、SR & load share controllers, the corresponding products are ISO5851、SM72295、UCC27511、UCC28C52、UCC25600、UCC28740、DCH010505S、CSD18514Q5A、UCC24630
DC/DC logic
Communication between the DC/DC power processor and the host controller need to be functionally isolated to help ensure immunity against common mode transients. DC/DC logic includes Inverting buffers & drivers、AND gates、Noninverting buffers & drivers、Ethernet PHYs, the corresponding products are SN74LVC1G14、SN74LVC08A、SN74LVC1G126、DP83848I
DC/DC output current & voltage sense
Accurate and high speed sensory data of the various power busses in the solar inverter is required to effectively control the power electronics and help ensure operational safety. Isolated sensory techniques are routinely used due to the high voltages involved. DC/DC output current & voltage sense includes General-purpose op amps、Precision op amps (Vos<1mV)、Comparators, the corresponding products are LM2904BA、OPA2188、LM2901AV
DC/DC self-diagnostics/monitoring
A temperature sensor is required to monitor the FETs as they are prone to self-heating under load. This temperature sensor can be used as a simple thermal switch or provide the information back to the host controller DSP, so the power output can be throttled instead of a complete shut-off. DC/DC self-diagnostics/monitoring includes Digital temperature sensors、Temperature switches、Analog temperature sensors, the corresponding products are TMP1075、TMP302、LMT87
DC/DC analog front end
To ensure tight control loops on the DC/DC and DC/AC stages, the DSP requires high accuracy data from the various analog sensors across the system. Dedicated analog filters and amplifiers help reduce noise and properly scale signals regardless of the ADC used. DC/DC analog front end includes General-purpose op amps、Precision op amps (Vos<1mV)、Precision ADCs、Precision DACs (≤10 MSPS), the corresponding products are LM2904BA、LMV321A、OPA2206、ADS124S06、DAC8564
DC/DC wired interface
Several wired interfaces may be used for a variety of use cases. RS-485, Ethernet and CAN may be used to communicate from the main controller to the power supplies and meters. The host controller is the heart of the central inverter system, providing information and communication among various components of the system. The controller regulates the output of renewable energy sources, protects the system from over-charging/over-discharging and manages voltage and current paths. DC/DC wired interface includes Isolated RS-485 transceivers、Isolated CAN transceivers、RS-485 & RS-422 transceivers、Ethernet PHYs、RS-232 transceivers, the corresponding products are ISO1410、ISO1050、SN65LBC184、DP83822IF、MAX3221
DC/DC power digital processing
The power stages in the stationary energy storage system are controlled by a DSP. The bi-directional DC/DC converter uses a DSP-based solution to more efficiently convert power between the battery bank and the high voltage DC bus. Dedicated DSPs for the application will have sufficient MIPS or accelerators, as well as performance for a communications layer. DC/DC power digital processing includes C2000 real-time microcontrollers、MSP430 microcontrollers, the corresponding products are TMS320F280049C、MSP430FR5969
DC/DC host logic
Communication between the DC/DC power processor, DC/AC power processor and the host controller need to be functionally isolated to help ensure immunity against common mode transients. DC/DC host logic includes Inverting buffers & drivers、AND gates、Noninverting buffers & drivers, the corresponding products are SN74LVC1G14、SN74AHC1G08、SN74LVC126A
DC/AC inverter
The DC/AC power stage converts the AC power source voltage to a high DC voltage to be used by the DC/DC stage. The DC/AC power stage also needs to invert the high voltage DC bus to usable AC power when discharging of the battery bank occurs. DC/AC inverter includes Isolated gate drivers、Low-side drivers、PWM controllers、Power factor correction (PFC) controllers、LLC controllers、Half-bridge drivers、Flyback controllers、Isolated DC/DC converters & modules、N-channel MOSFETs、SR & load share controllers, the corresponding products are ISO5451、UCC27624、TL2844B、UCC28056、UCC25600、SM72295、UCC28740、LM5160、CSD18531Q5A、UCC24630
DC/AC logic
Communication between the DC/AC power processor and the host controller need to be functionally isolated to help ensure immunity against common mode transients. DC/AC logic includes Inverting buffers & drivers、AND gates、Noninverting buffers & drivers, the corresponding products are SN74LVC1G14、SN74AHC1G08、SN74LVC1G126
DC/AC power digital processing
The power stages in the stationary energy storage system are controlled by a DSP. The bi-directional DC/AC inverter uses a DSP-based solution to more efficiently convert power between the high voltage DC bus and AC energy sources and correct the power factor. Dedicated DSPs for the application will have sufficient MIPS or accelerators, as well as performance for a communications layer. DC/AC power digital processing includes C2000 real-time microcontrollers、MSP430 microcontrollers, the corresponding products are TMS320F280049C、MSP430FR5969
AC relay power stage
The connection of each voltage bus is equipped with a relay to protect the energy storage system. The AC relay disconnects AC power sources from the controller to ensure protection for the system in the event of a fault. AC relay power stage includes Solenoid drivers、N-channel MOSFETs, the corresponding products are DRV110、CSD18514Q5A
Grid current & voltage sense
Accurate and high speed sensory data of the grid power bus in a stationary energy storage system is required to help ensure operational safety and effectively correct the power factor of the system's AC output. Isolated sensory techniques are routinely used due to the high voltages involved. Grid current & voltage sense includes General-purpose op amps、Precision op amps (Vos<1mV)、Comparators, the corresponding products are LM2904BA、OPA4206、LM2901AV
DC/AC analog front end
To ensure tight control loops on the DC/DC and DC/AC stages, the DSP requires high accuracy data from the various analog sensors across the system. Dedicated analog filters and amplifiers help reduce noise and properly scale signals regardless of the ADC used. DC/AC analog front end includes General-purpose op amps、Precision op amps (Vos<1mV)、Precision ADCs、Precision DACs (≤10 MSPS), the corresponding products are TLV9052、OPA2188、ADS8556、DAC8564
DC/AC self-diagnostics/monitoring
A temperature sensor is also required to monitor the FETs as they are prone to self-heating while under load. This temperature sensor can be used as a simple thermal switch, or provide the information back to the DSP, so the inverter can throttle back its power output rather than shut off. DC/AC self-diagnostics/monitoring includes Digital temperature sensors、Temperature switches、Analog temperature sensors, the corresponding products are TMP1075、TMP302、LMT84
DC/AC wired interface
Several wired interfaces may be used for a variety of use cases. RS-485, Ethernet and CAN may be used to communicate from the main controller to the power supplies and meters. The host controller is the heart of the central inverter system, providing information and communication among various components of the system. The controller regulates the output of renewable energy sources, protects the system from over-charging/over-discharging and manages voltage and current paths. DC/AC wired interface includes Isolated RS-485 transceivers、Isolated CAN transceivers、RS-485 & RS-422 transceivers、Ethernet PHYs、RS-232 transceivers, the corresponding products are THVD1500、DP83822IF、TRS3243E
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