Igbt module inverter circuit diagram design (1)The essence of solar photovoltaic power generation is that under the illumination of sunlight, the solar array (ie, the PV module square array) converts the solar energy into electrical energy, and the output direct current is converted into the alternating current that the user can use after passing through the inverter. The conventional photovoltaic power generation system is an inverter circuit composed of a power FET MOSFET. However, as the voltage increases, the on-resistance of the MOSFET increases. In some high-voltage and large-capacity systems, the MOSFET may increase the switching loss due to its on-state resistance. In practical projects, IGBT inverters have gradually replaced power FET MOSFETs because IGBTs have large on-state currents, high forward-reverse configuration voltages, and voltage control to turn them on or off. The IGBT is more advantageous in the system of medium and high voltage capacity. Therefore, the use of IGBT to form a switching device for the key circuit of solar photovoltaic power generation helps to reduce the unnecessary loss of the entire system and achieve the best working condition. In practical projects, IGBT inverters have gradually replaced power FET MOSFETs.
How IGBT inverter worksThe inverter is a key component in the solar photovoltaic system because it is the necessary process to convert the direct current into the alternating current that the user can use, and is the only way to connect the solar energy and the user. Therefore, to study the process of solar photovoltaic power generation, it is necessary to focus on the inverter circuit. As shown in Fig. 2(a), it is a relatively simple push-pull inverter circuit composed of a power FET MOSFET. The neutral tap of the transformer is connected to the positive pole of the power supply, and one end of the MOSFET is connected to the negative pole of the power supply. The alternating operation of tubes Q1 and Q2 finally outputs AC power, but the disadvantage of this circuit is that the ability to carry inductive loads is poor, and the efficiency of the transformer is also low, so there are some conditional restrictions on application. A full-bridge inverter circuit composed of an insulated gate bipolar transistor IGBT is shown in Fig. 2(b). The phase between Q1 and Q2 is 180° out of phase, and the value of the output AC voltage varies with the output of Q1 and Q2. Q3 and Q4 are simultaneously turned on to form a freewheeling circuit, so the waveform of the output voltage is not affected by the inductive load, so the shortcomings of the push-pull inverter circuit composed of the MOSFET are overcome, so the full bridge inverter composed of the IGBT is used. The application of the circuit is more extensive.
The insulated gate bipolar transistor IGBT is equivalent to adding a P+ region under the drain of the MOSFET. Compared with the MOSFET, there is one more PN junction. When a negative voltage is applied between the collector and the emitter of the IGBT, the PN junction In the reverse bias state, no current flows between the collector and the emitter, so the IGBT has higher voltage resistance than the MOSFET. Also due to the existence of the P+ region, the IGBT is in a low-resistance state when turned on, so the current capacity of the IGBT is larger relative to the MOSFET.
IGBT inverter circuit designThe pre-stage DC-DC converter part of the inverter circuit adopts the PIC16F873 single-chip microcomputer as the control core, and the DC-AC part of the latter stage adopts the high-performance DSP chip TMS320F240 as the full-bridge inverter circuit of the control core. In order to improve the efficiency of the solar photovoltaic inverter, it can be done by reducing the inverter loss, in which the drive loss and switching loss are the key targets. The key to reducing the drive loss depends on the gate characteristics of the power switch IGBT. The key to reducing the switching loss depends on the control mode of the power switch IGBT. Therefore, the following solutions are proposed for the characteristics of drive loss and switching loss.
1, the drive circuit
The driving circuit converts the signal output by the main control circuit into a driving signal required by the inverter circuit, that is, it is a bridge between the main controller and the inverter, so the design of the driving circuit performance is crucial of. The EXB841 integrated circuit is used to form the gate drive circuit of the IGBT. As shown in Figure 3, the EXB841 has a fast response speed, which can reduce the drive loss by controlling the resistance of its gate and improve its working efficiency. The EXB841 has an overcurrent protection circuit inside, which reduces the design of the external circuit and makes the circuit design simpler and more convenient. Compared with the typical EXB841 application circuit, a resistor Rg is connected in series with the gate of the IGBT. This is to reduce the oscillation before and after the control pulse. The selection of the appropriate Rg resistance has a significant impact on the IGBT drive. . Based on the EXB841 typical application circuit, this circuit optimizes the series resistor on the IGBT gate so that its resistance changes as needed during the turn-on and turn-off of the IGBT.
The specific implementation is as follows: Rg2 and VD1 are connected in series and then connected in parallel with Rg1. When the IGBT is turned on, the positive voltage is output from the 3rd leg of the EXB841 in the driving circuit, VD1 is turned on, and Rg1 and Rg2 work together because the total resistance after paralleling is less than The sub-resistance of a branch, so the value of the total resistance Rg connected in series on the gate is smaller than the values of Rg1 and Rg2, so that the switching time and switching loss decrease as the total resistance decreases, thereby reducing the drive. loss. When the IGBT is turned off, the 5 pin of the EXB841 inside the driving circuit is turned on, the 3 pin is not turned on, and the emitter of the IGBT provides a negative voltage, so that the VD1 in series with Rg2 is turned off, Rg1 works, and Rg2 does not work. The value of the total resistance Rg on the gate is the resistance of Rg1, so that when the IGBT is turned off, the resistance between the gates is not too small, which leads to mis-conduction of the device, thereby improving the working efficiency.
2, soft switching DC-DC converter circuit
For switching losses, soft switching technology is used. Soft switching technology is relative to hard switching. The traditional switching method is called hard switching. The so-called soft switching technology is that the semiconductor switch has a short time when it is turned on or off, so that the current flowing through the switch is added or added. The voltage of the switch is small, almost zero, which reduces switching losses. The essence is to reduce the volume and weight of the transformer and the filter by increasing the switching frequency, thereby greatly increasing the power density of the converter, reducing the audio noise of the switching power supply, thereby reducing the switching loss. When the IGBT power switch is turned on, the voltage applied to both ends is zero, which is called zero voltage switch. When the IGBT is turned off, the current flowing through it is zero, which is called zero current switch. Since the IGBT has a certain switching loss, the phase-shifted full-bridge zero-voltage zero-current PWM soft-switching converter (shown in Figure 4) is used. The structure is simple and there is no lossy component, which reduces the influence of the IGBT tail current, thereby reducing the switch. Loss increases the efficiency of the inverter.
Q1～Q4 are 4 IGBT power switch tubes, where Q1 and Q3 are super forearms, Q2 and Q4 are lagging arms, Q1 and Q3 lead one phase of Q2 and Q4, when Q1 and Q4 are turned off, and Q2 and Q3 are turned on. The voltage across the UAB is equal to the voltage across V1, and the capacitor C1 is charged by the supply voltage V1. When Q3 is turned on to off, capacitor C3 is charged, and inductor L1 releases energy, causing capacitor C1 to resonate and discharge until the voltage on capacitor C1 is zero, so that Q1 has a zero-voltage conduction condition. The zero voltage conduction principle of the forearm Q3. When Q1 and Q4 are turned on and Q2 and Q3 are turned off, the voltage across AB is equal to the voltage across V1, and capacitor C3 is in the charging state. When Q1 and Q4 are continuously turned on, inductor L2 and capacitor C8 resonate. Therefore, the capacitor C8 is charged. When Q1 is turned on to off, capacitor C1 is charged, so that C3 starts to discharge, the voltage across AB decreases, so that C8 is resonantly discharged, C8 continues to discharge, and finally diode D7 continues to flow, and the driving pulse of Q4 continues to drop until Zero, and finally completed the zero current shutdown of Q4. Similarly, the zero current turn-off principle of the lag arm Q2 can be known.
Therefore, it can be said that the super-arms Q1 and Q3 complete the zero voltage conduction and turn-off through the parallel capacitors C1 and C3, respectively, thereby reducing the switching loss; the lag arms Q2 and Q4 discharge the C8 through the auxiliary circuit, so that the transformer flows through The primary current is reduced to zero to complete zero current turn-on and turn-off.
The general circuit waveform close to the square wave part indicates that its output contains more harmonic components, which will cause unnecessary additional loss of the system. Figure 5 is an improved circuit using IGBT, the waveform is very close to sine wave, ideal sine wave The total harmonic distortion is zero, but it is difficult to achieve such a level in real life, so it basically meets the requirements. At the same time, since the PIC16F873 single-chip microcomputer has a multi-channel PWM generator and has a better output sine wave, it is verified. The feasibility of the design has achieved the desired results.
Through the comparison and analysis of the device, the improvement and optimization of the circuit, the integrated circuit EXB841 itself contains an overcurrent protection circuit, which solves the requirements of the IGBT on the driver circuit part, and reduces the design of the external circuit, so that the whole The design process is simple and convenient. The soft switching technology solves the problem of excessive current flowing through the IGBT during turn-on and turn-off, and the drive loss and switching loss of the whole system are greatly reduced. The output waveform is a relatively stable sine wave, thereby improving the overall system. Work efficiency.
The following figure shows the internal structure of the M57962L driver. The optocoupler is used for electrical isolation. The optocoupler is fast. It is suitable for high-frequency switching operation. The primary side of the optocoupler has series current limiting resistor (about 185 Ω), which can be 5 V. The voltage is applied directly to the input side. It uses a dual power supply structure, integrated with 2 500 V high isolation voltage optocoupler and overcurrent protection circuit, overcurrent protection output signal terminal and TTL level compatible input interface, drive electrical signal delay up to 1.5 Us.
Igbt module inverter circuit diagram Daquan (six igbt module inverter circuit design schematic diagram detailed) When the M57962L is used alone to drive the IGBT. There are three points that should be considered. First of all. The maximum current rate of change of the driver should be set within the limits of the minimum RG resistance, because for many IGBTs, when RG is used too large, td(on) (on-delay time) is increased, td(off) (cut-off delay time), tr (rise time) and switching loss, this loss should be avoided as much as possible in high frequency applications (over 5 kHz). Also. The loss of the drive itself must also be considered.
If the loss of the drive itself is too large, it will cause the drive to overheat and cause damage. Finally, when the M57962L is used to drive large-capacity IGBTs, its slow turn-off will increase losses. The cause of this phenomenon is that the current flowing to the gate of the M57962L through the Gres (reverse transfer capacitor) of the IGBT cannot be absorbed by the driver. Its impedance is not low enough, this slow turn-off time will become slower and requires a larger snubber capacitor to apply the driver circuit of the M57962L design as shown below.
Circuit Description: Power supply decoupling capacitors C2 ~ C7 use aluminum electrolytic capacitors, the capacity is 100 uF / 50 V, R1 resistance value is 1 kΩ, R2 resistance value is 1.5kΩ, R3 is 5.1 kΩ, power supply uses positive and negative l5 V power supply module Connected to the 4th and 6th pins of the M57962L respectively, the logic control signal IN is input to the driver M57962L via the l3 pin. The bidirectional voltage regulator Z1 is selected to be 9.1 V, Z2 is 18V, and Z3 is 30 V. The gate and emitter of the IGBT are prevented from breakdown and the drive circuit is damaged. The diode adopts the fast recovery FR107 tube.
The IR2110 drives the IGBT circuit as shown. The circuit adopts the bootstrap driving mode, VD1 is the bootstrap diode, and C1 is the bootstrap capacitor. When the power is turned on, Cy is charged by VDt when VT2 is turned on. This circuit is suitable for driving smaller capacity IGBTs. For the IR2110, there is a protection function to turn off the driver when the supply voltage is low. The bootstrap drive mode dominates the turn-on voltage of the VT2, so a lower voltage protection is a necessary condition. If the IGBT is driven when the driving voltage is low, the IGBT is thermally damaged. VD1 selects ERA38-06, ERB38-06 and other diodes with high speed and withstand voltage greater than 600V.
An insulated gate bipolar transistor (IGBT) is a device in which a MOSFET is combined with a bipolar transistor. The utility model has the advantages that the power MOSFET is easy to drive, the control is simple, the switching frequency is high, and the power transistor has low on-voltage, large on-state current and small loss.
The main circuit of the full-bridge inverter consists of main components such as power switch IGBT and intermediate frequency transformer. As shown in Figure 1, the fast recovery diodes VD1~VD4 are connected in parallel with lGBT1~IGBT4 in reverse, and the reverse current generated by the load is applied to protect the IGBT. . IGBT1 and IGBT4 are a group, IGBT2 and IGBT3 are a group, each group of IGBTs is turned on and off at the same time. When the excitation pulse signal drives IGBT1, IGBT4 and IGBT2, IGBT3 in turn, the inverter main circuit converts DC high voltage to 20 kHz. The AC voltage is sent to the intermediate frequency transformer and output by the step-down rectification filter.
One of the major drawbacks of full-bridge inverters is the problem of biasing the IF transformer. Under normal operating conditions, the power switching device has the same conduction pulse width in the first half of the working period and the second half of the working cycle, and the saturation voltage drop is equal, and the front and rear half cycles alternately. There is no remanence in the transformer core. However, if the IGBT drive circuit output pulse width is asymmetrical or other reasons, the positive and negative half-cycle imbalance will occur. At this time, the magnetic core in the transformer will accumulate residual magnetism in a certain half-cycle, and a “unidirectional bias” phenomenon occurs. With a few pulses, the unidirectional flux of the transformer can be saturated, the transformer loses its function, and it is equivalent to a short circuit. This is extremely dangerous for IGBTs and can cause an explosion.
Another disadvantage of bridge circuits is that they are prone to shoot-through. The straight-through phenomenon means that the IGBTs of the same bridge overlap in the conduction period of the front and rear half cycles, and the main circuit board path, the huge addition current instantaneously passes through the IGBT.
In view of the above two shortcomings, from the perspective of driving, the designed driving circuit must satisfy the four-way driving waveform completely symmetrical, strictly limit the maximum working pulse width, and ensure that the dead time is sufficient.
For a full-bridge inverter with hard-switching trigger mode, the four-way drive circuit is identical, but the circuits must be isolated from each other on the circuit to prevent interference or false triggering. The four-way drive signals are divided into two groups according to the trigger phase. in contrast. Figure 3 shows a gate drive circuit. The rectifier bridges B1 and B2 and the electrolytic capacitors C1 and C2 form a rectification and filtering circuit to provide +25V and -15V DC drive voltages for the drive circuit. The function of the optocoupler 6N137 is to achieve isolation between the control circuit and the main circuit and to transmit the PWM signal. The resistor R1 and the Zener diode VS1 form a PWM sampling signal, and the resistor R2 limits the optocoupler input current. Resistors R3 and R4 and voltage regulators VS3 and VS4 form a 5.5V optocoupler level limiting circuit, respectively, which provide driving levels for the optocoupler and MOSFET Q3. Q3 operates under the optocoupler control state. The MOSFETs Q1 and Q2 form a push-pull amplifier circuit, and the amplified output signal is input to the IGBT gate to provide a gate drive signal. When the control signal is input, the optocoupler U is turned on, Q3 is turned off, and Q2 is turned on to output the +15V driving voltage. When the control signal is zero, the optocoupler U is turned off, Q3 and Q1 are turned on, and the output voltage is -15V. When the IGBT is turned off, the gate is provided with a negative bias to improve the anti-interference ability of the lGBT. The voltage regulators VS3 to VS6 limit the input voltage of Q2 and Q1 to -10V and +15V respectively, preventing Q1 and Q2 from entering deep saturation and affecting the response speed of the MOS tube. The resistors R6 and R7 and the capacitor C0 are Q1 and Q2 to form a bias network. The capacitor C0 is for accelerating the rising current of the drain current of the Q2 tube when it is turned on, providing an overshoot current to the gate, and accelerating the gate conduction.
The IGBT gate withstand voltage is generally around ±20V, so the gate is voltage-protected at the output of the driver circuit, the parallel resistor Rge and the reverse series limiting regulator.
The gate series resistance Rg has a great influence on the IGBT turn-on process. Rg is small to speed up the turn-off speed and reduce the turn-off loss, but too small will cause the di/dt to be too large, resulting in a large collector voltage spike. According to the specific requirements of this design, Rg selects 4.7Ω.
The parasitic inductance of the gate wiring and the parasitic capacitance between the gate and the emitter will generate an oscillating voltage, so the gate lead should be transmitted by twisted pair and driven as short as possible, preferably not exceeding 0.5 m. Reduce the wiring inductance.