Inverter structure and working principle

The inverter is composed of two major parts: semiconductor power devices and inverter drive and control circuits. Due to the development of microelectronics and power electronics technology, new high-power semiconductor devices and drive and control circuits have emerged, and now the inverter mostly uses various advanced and easy-to-control high-power devices such as insulated gate transistors, power field-effect tubes, MOS controller thyristors and intelligent power modules. The control circuit is also developed from the original analog integrated circuit to be controlled by microcontroller or digital signal processor, which makes the inverter develop in the direction of systemization, full control, energy saving and multi-functionalization.

Basic structure of inverter

The inverter structure consists of an input circuit, a main inverter circuit, an output circuit, an auxiliary circuit, a control circuit and a protection circuit.

The input circuit is responsible for providing DC input voltage; the main inverter circuit completes the inverting procedure by the action of semiconductor switching devices; the output circuit mainly compensates and corrects the frequency, phase and amplitude of voltage and current of the AC output from the main inverter circuit to meet certain standards; the control circuit provides pulse signals to the main inverter circuit and controls the opening and closing of semiconductor devices; the box helper circuit converts the DC voltage from the input circuit into a DC voltage suitable for the operation of the control circuit, and also includes a series of detection circuits.

Basic working principle of inverter circuit

The inverter works similar to a switching power supply, through an oscillation chip, or a specific circuit, which controls the oscillation signal output, the signal is amplified to drive the field effect tube to switch continuously, so that after the DC input, after this switching action, a certain AC characteristic is formed, and after correction, a sine wave AC similar to the kind on the grid can be obtained. The inverter is a power investigation device that is necessary for stand-alone PV systems that use AC loads. An important factor in inverter selection is the magnitude of the DC voltage set. The output of an inverter can be divided into two categories: DC output and AC output. For the DC output, the inverter is called a converter, which is a conversion of DC voltage to DC voltage, so that it can provide the voltage required to work with DC loads of different voltages. For AC output, what needs to be considered is not only the output power and voltage, but also its waveform and frequency. At the input side, attention must be paid to the DC voltage required by the inverter and the variation of the surge voltage it can withstand.

The control of the inverter can use logic circuits or special control chips, or general-purpose microcontrollers or DSP chips, etc., to control the gate drive circuit of the power switching tubes. The inverter output can have a certain voltage regulation capability. Taking the bridge inverter as an example, if the peak AC bus rated voltage of the inverter output is designed to be 10%~20% lower than its DC bus rated voltage (the purpose is to make it have a certain voltage regulation capability), then the inverter output by PWM modulation can have a margin of 10%~20% adjustment to the higher amplitude, and the adjustment to the lower value is not restricted, but only needs to reduce the PWM open duty cycle can be reduced. Therefore, the inverter input DC voltage fluctuation range of a 15% ~ 20%, up as long as the device voltage allows it is not limited, just adjust the output pulse width can be (equivalent to chopper). When the battery or photovoltaic battery output voltage is low, the inverter internal configuration of the boost circuit, boost can use the switching power supply mode boost can also use the DC charge pump principle boost. The inverter uses the output transformer to step up the voltage, that is, the inverter voltage matches the battery or photovoltaic cell array voltage, and the inverter outputs a lower AC voltage, which is then stepped up by the industrial frequency transformer and sent to the transmission line. It should be noted that whether it is a transformer or an electronic circuit that boosts the voltage, some energy is lost. The optimal inverter operating mode is to match the DC input voltage with the voltage required by the transmission line, and the DC power only passes through a layer of inverter link to reduce the losses in the conversion link, which is generally more than 90% efficient. The energy lost in the inverter link is converted to energy in the form of heat from power tubes and transformers. The heat is detrimental to the operation of the inverter and threatens the safety of the device, and this heat should be discharged from the device using heat sinks, fans, etc. Inverter loss usually includes two parts: conduction loss and switching loss. MOSFET tube switching frequency is higher, the conduction impedance is larger, the inverter composed of more work in the child ten to hundreds of kilohertz frequency, while the 1GBT conduction voltage drop is relatively small, the switching loss is larger, the switch face rate in the child dry to tens of dry hertz between, generally choose the number of ten kilohertz below, the switch is not the ideal switch, in its opening process In its opening process, the current has a rising process, the voltage at the end of the tube has two drops over and, the voltage and current crossover process loss is the opening loss. The loss in the process of voltage and current crossover is the turn-on loss. The turn-off loss is the crossover loss in the opposite direction of voltage and current crossover. To reduce the inverter's proposed consumption is mainly to reduce the opening loss, the new please report type switching inverter, in the voltage or current over the zero point of the implementation of the opening or closing, so as to reduce the switching loss.

Single-phase voltage type inverter circuit

A voltage source inverter is a device that converts DC energy into AC energy according to a control voltage and is a common type of inverter technology. There are various ways to obtain AC energy from a DC source, but there should be at least two power switching devices. Single-phase inverters have three circuit topologies: push-pull, half-bridge and full-bridge, which have different circuit structures but similar operating principles. The circuit uses semiconductor power devices with switching characteristics, and the control circuit periodically sends a switching pulse control signal to the power devices to control multiple power devices to turn on and off, and then through the transformer coupling step-up or step-down, shaping and filtering output to meet the requirements of

After the transformer coupling step-up or step-down, the shaping and filtering output meets the required AC power.

Three Phase Inverter

The capacity of single-phase inverters is generally below 100 kV. A due to the limitations of power switching device capacity, neutral line current, grid load balancing requirements and the nature of the power load. The three-phase inverter is divided into three-phase voltage source inverter and three-phase current source inverter according to the nature of DC power supply.