1 Introduction
Intelligent Power Module (IPM) has been widely used in the field of power electronics because of its advantages of fast switching speed, low loss, low power consumption, multiple protection functions, strong anti-interference ability, no need to take anti-static measures, and small size. Taking PM200DSA060 IPM as an example, the design of IPM application circuit and its application in single-phase inverter are introduced.
2 IPM structure
IPM consists of high-speed, low-power IGBT, optimized gate driver and protection circuit. Among them, IGBT is the combination of GTR and MOSFET to drive GTR, so IPM has the advantages of high current density, low saturation voltage, high withstand voltage, high input impedance of MOSFET, high switching frequency and low driving power.
According to the configuration of the internal power supply circuit. There are many types of IPM. For example, PM200DSA060 IPM is type D (with two IGBT integrated inside). Its internal functional block diagram is shown in figure 1, and its internal structure is shown in figure 2. There are drive and protection circuits in it. The protection functions include undervoltage lockout protection, overheating protection, overcurrent protection and short circuit protection of the control power supply. When any of these protection functions acts, IPM will output fault signal FO.
The internal circuit of IPM does not include signal isolation circuit, self-protection function and anti-interference surge absorption circuit. In order to ensure the security and reliability of IPM, some peripheral circuits need to be designed by themselves.
Design of 3 IPM external drive circuit
The external driving circuit of IPM is the interface between the internal circuit of IPM and the control circuit. A good external driving circuit is of great significance to the operation efficiency, reliability and security of the system composed of IPM.
As can be seen from the internal structure diagram of IPM, the device itself contains the driving circuit. Therefore, it is only necessary to provide PWM signals that meet the requirements of driving power supply, driving circuit power supply and electrical isolation devices to prevent interference. However, IPM has strict requirements on the output voltage of the driving circuit: the driving voltage range is 13.5V- 16.5V, below which undervoltage protection will occur, while above 16.5V, internal components may be damaged. The frequency of the driving signal is 5 Hz ~ 20 kHz, which requires electrical isolation devices to prevent interference: the isolation voltage of the driving power supply is at least 2 times (2 vces) of the reverse withstand voltage between IPM poles; The driving current reaches19ma-26ma; The filter capacitance at the output of the driving circuit should not be too large, because when the parasitic capacitance exceeds 100pF, noise interference may trigger the internal driving circuit by mistake.
Figure 3 shows a typical high-reliability IPM external drive circuit scheme. The PWM signal from the control circuit is limited by R 1.
Flow, and then isolated and amplified by high-speed optical coupler, and then connected to the IPM internal drive circuit to control the switch tube to work, and the FO signal is also isolated and output by optical coupler. Among them, the control power supply end of each switching tube adopts an independent isolated regulated 15V power supply, and is connected with a 1 decoupling capacitor (not shown in the figure) to filter out the * * * mode noise. Select R 1 according to the output current of the control circuit. If PWM is generated by DSP, the resistance of R 1 can be 330ω. R2 is selected according to the driving current of IPM. On the one hand, it should be as small as possible to avoid picking up noise from high impedance IPM; on the other hand, it should have enough reliability to control IPM, and it can be selected from 2kΩ to 6.8kΩ. C 1 is 0. 1μF filter capacitor between two terminals and ground, and the requirement for PWM isolated optocoupler is TPLH.
The external interface circuit in Figure 3 is directly fixed on the PCB, close to the input pin of the module, to reduce noise and interference, and the wiring distance on the PCB should be appropriate to avoid potential change caused by interference during switching.
In addition, considering that strong current may cause interference from external driving circuit to IPM leads, filter capacitors can be added between pins 1 ~ 4, 3 ~ 4 and 4 ~ 5 according to the interference situation.
Design of IPM protection circuit
Because the protection circuit provided by IPM itself does not have self-protection function. Therefore, it is necessary to convert the internal FO signal into a control signal through the auxiliary circuit of peripheral hardware or software to block IPM and close IPM to realize protection.
4. 1 hardware
When IPM fails, FO outputs low level and reaches the hardware circuit through high-speed optocoupler. Turn off PWM output to protect IPM. The specific hardware connection mode is: a three-state transceiver with a control terminal (such as 74HC245) is set in front of the PWM interface circuit, the PWM signal is sent to the IPM interface circuit after passing through the three-state transceiver, and the fault output signal FO of IPM is output to the NAND gate through optical coupling isolation, and then sent to the enabling terminal OE of the three-state transceiver. When IPM works normally, the output of NAND gate is low, and the 3-state transceiver is gated; When IPM fails, the output of NAND gate is high, and all outputs of 3-state transceiver are set to high impedance state, thus blocking the control signals of each IPM, turning off IPM and realizing protection.
4.2 Software
When the IPM fails, the FO output is low, and the FO signal is transmitted to the controller for processing through high-speed optical coupling. After the processor confirms, the PWM control signal of IPM is turned off by interruption or software, so as to achieve the protection purpose. For example, in the system based on DSP control, the protection of IPM is realized by using the power-driven protection pin (PDPINT) interrupt in the event manager. Usually, the multi-channel PWM generated by 1 event manager can control multiple IPMs, and each switch tube can output FO signal. The FO signal of each switch tube passes through the AND gate. When any switch tube fails, it outputs a low level, and the AND gate outputs a low level to connect this pin to PDPINT. Because the DSP is interrupted when PDPINT is low, all the event manager output pins are set to high impedance state by hardware, thus achieving the protection purpose.
The above two schemes use IPM fault output signal to block the control signal channel of IPM. Thus, it makes up for the deficiency of IPM's own protection and effectively protects the equipment.
Design of 5 IPM buffer circuit
In IPM application, the DI/DT, DV/DT and instantaneous power consumption caused by the superposition of high-frequency switching process and parasitic inductance of power loop will have a great impact on the device and easily damage the device. Therefore, in order to change the switching trajectory of the device, control all kinds of transient overvoltage, reduce the switching loss of the device and protect the safe operation of the device, it is necessary to set up a buffer circuit (that is, an absorption circuit).
Figure 4 shows three commonly used IPM buffer circuits. Fig. 4(a) shows a snubber circuit composed of a single non-inductive capacitor. It is effective for transient voltage and low cost, and is suitable for low power IPM. Fig. 4(b) shows a snubber circuit composed of RCD, which is suitable for high-power IPM. The snubber diode d can clamp the transient voltage. So as to suppress parasitic oscillation that may be caused by parasitic inductance of the bus. Its RC time constant should be designed as l/3 of the switching period, that is, τ=T/3= 1/3f. Fig. 4(c) shows a buffer circuit composed of a P-type RCD and an N-type RCD. Suitable for high power IPM. Its function is similar to the snubber circuit shown in Figure 4(b), and its loop inductance is smaller. If the snubber circuit shown in Figure 4(a) is used together, the stress of snubber diode can be reduced and the snubber effect is better.
In fig. 4(c), when the IGBT is turned off, the load current charges the snubber capacitor through the snubber diode, and at the same time, the collector current gradually decreases. Because the voltage across the capacitor will not change suddenly, the voltage rise rate dv/dt of IGBT collector is effectively limited. It also prevents the collector voltage and collector current from reaching the maximum at the same time. When the IGBT is turned on, the energy stored in the bus inductance and stray inductance of the IGBT collector in the circuit and its components is stored in the buffer capacitor at this time. When IGBT is turned on. The collector bus inductance and other stray inductance effectively limit the collector current rise rate di/dt of IGBT. It also prevents the collector voltage and collector current from reaching the maximum at the same time. At this time, the buffer capacitor discharges through the external resistor and IGBT switch, and its stored switching energy is also dissipated on the external resistor and the resistors inside the circuit and components. So ... The switching loss caused by IGBT operation is transferred to the snubber circuit, and finally dissipated in the form of heat on the related resistors, thus protecting the safe operation of IGBT.
The resistance value and capacitance value in fig. 4(c) are selected according to the empirical data: for example, the capacitance value of PM200DSA060 is 0.22μF-0.47μF, the voltage withstand value is 1. 1.5 times that of IGBT, the resistance value is10Ω ~ 20Ω, and the resistance power is p = fc. The diode is a fast recovery diode. So as to ensure the reliability of the buffer circuit. The package buffer circuit shown in fig. 4 can be selected according to the power.
In addition, as bus inductance, stray inductance in snubber circuit and its components has great influence on IPM, especially for high-power IPM, the smaller the better. To reduce these inductions, we need to start from many aspects: DC buses should be as short as possible; The buffer circuit should be as close to the module as possible; Low inductance polypropylene electrodeless capacitor, fast buffer diode matched with IPM and non-inductive bleeder resistor are selected.
Application of 6 IPM in single-phase full-bridge inverter
The single-phase full-bridge inverter circuit shown in Figure 5 is mainly composed of inverter circuit and control circuit. The inverter circuit comprises an inverter full bridge and a filter circuit, wherein the inverter full bridge completes the conversion from DC to AC, and the filter circuit filters out harmonic components to obtain the required AC; The control circuit completes the control of the switching tube in the inverter bridge and realizes some protection functions.
The full bridge of the inverter in the figure consists of four switching tubes and four freewheeling diodes, and the switching tubes are turned on and off at high frequency during operation. At the moment of switching, the voltage and current of the switch tube become larger, the loss is large, and the junction temperature rises. In addition, the parasitic inductance, oscillation and noise of the power circuit also easily lead to the instantaneous damage of the switch tube. In the past, the protection circuit and driving circuit of the switch tube were usually designed with discrete components, which led to huge and unreliable circuits.
The author uses a pair of PM200DSA060 dual-unit IPM modules to replace the combination of V 1, D 1, V2, D2 and V3, D3, V4 and D4 in the figure respectively to form a full-bridge inverter circuit, and uses DSP to control IPM to complete the design and debugging of 20kW and 230V inverters, and adopts the above driving circuit and Figure 4(c). The design practice shows that IPM can simplify the system hardware circuit, shorten the system development time, improve the reliability, reduce the volume and improve the protection ability.