The principle and structure of Solar Power Inverter

The principle and structure of Solar Power Inverter




Usually converted into DC to AC power the process is called rectification, phase-controlled rectifier is the most common AC - DC conversion process; while the DC into AC power to transform the process is called inverter, which is the reverse process of rectification . In the inverter circuit, in accordance with the nature of the load different inverter. And the power inverter is divided into active and passive inverter. If the exchange side of the circuit, on receiving the AC power to DC can be through the direct - the exchange of transformation, inverse becomes the AC power delivered to the same frequency AC power grid back up, called the active inverter. The corresponding device is called the active inverter to control the angle is greater than 90 ° phase-controlled rectifier is a common active inverter. And the DC can be transformed to the exchange of electrical energy directly to the non-load power supply circuit, known as passive inverter circuit, also known as converters.



Inverter types of inverter-excited, self-encouragement inverter, pulse width modulation (PWM) inverter. Reed inverter in which he need for external AC voltage source, to provide thyristor rectifier voltage. Excited mainly used in high-power inverter-grid situations; for less than 1MW photovoltaic power generation systems, mainly in inverter mode and self-motivation. And self-encouragement inverter does not require an external AC voltage source, rectifier voltage from the inverter part of the storage components (such as capacitors) to provide or to be off by increasing the rectifier valve (such as MOSFET or IGBT) of the resistance value to achieve. The output voltage is pulse modulated and self-motivation is known as pulse inverter. This cycle, by increasing the power inverter switching frequency of the pulse, to reduce the voltage and current harmonics content; harmonic content was proportional to the frequency and pulse switch. Currently, grid-connected inverter output There are two main control modes: voltage mode control mode and current-mode control mode. Voltage-control mode based on the principle of output voltage as the controlled quantity, the system output and the power grid voltage in phase with the frequency of the voltage signal, the entire system is equivalent to a small resistance controlled voltage source; current-mode control mode is the principle of to the output inductor current as the controlled target, the system output and the power grid voltage current in phase with the same frequency signal, the entire system is equivalent to a large resistance controlled current source.



At present, solar inverters have been a variety of topologies, the most common for single-phase half-bridge, full bridge, and Heric (Sunways patent) inverter, as well as for three-phase six-pulse bridge and the midpoint of pliers bit (NPC) inverter. A typical solar inverter framework is generally a four-switch full-bridge topology.



In essence, in order to maintain a low harmonic and power loss minimum, high-side IGBT inverter uses pulse-width modulation (PWM), low-side IGBT Zeyi 60Hz frequency conversion current direction. By allowing the use of high-side IGBT above 20kHz or 20kHz frequency and PWM modulation scheme 50/60Hz, output inductors L1 and L2 can be done at the instance of a very small, and still be able to efficiently filter the harmonic components. And standards with fast speed compared to planar devices, switching speed of 20kHz ultra-fast channel-type IGBT can provide the lowest total conduction losses and switching power loss. Similarly, for low-voltage side switching circuit, working in the standard 60Hz rate of IGBT can offer the lowest power loss.



The design of the switch technology has the following advantages: by allowing high-pressure side and low-side IGBT independently optimized to achieve very high efficiency; high-pressure side, with the package, there is no soft-recovery diode freewheeling time, thus eliminating unnecessary switching losses; low side IGBT's switching frequency is only 60Hz, so these IGBT conduction losses are the main factors; no cross-conduction, because any point in time switches have occurred in the right corner on the two devices (Q1 and Q4 or Q2 and Q3); there is no bus through this possibility, because the bridge will never be the same side of the IGBT switches in a complementary manner; jumper low-side IGBT of the same package, ultra-fast, soft recovery diodes are optimized to allow continued flow and reverse-recovery period The loss to a minimum.



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