Active drive system and method

Abstract

The present invention provides an active drive system and method, the system comprising: an active drive circuit and a main control chip, a drive push-pull circuit, a drive resistor, and a driven device connected in sequence, the active drive circuit is also connected to the main control chip, the drive resistor, and the driven device respectively; the active drive circuit is used to control the switching speed of the driven device in the third stage of the turn-on process and the switching speed of the third stage of the turn-off process. The scheme realizes staged control of the device switching process by detecting different stages of the device switching process, so as to reduce current overshoot, voltage overshoot and subsequent oscillation.

Description

Technical Field

[0001] The present invention belongs to the field of drive technology, and in particular relates to an active drive system and method. Background Art

[0002] With the continuous development of power electronics technology, the performance of Si (silicon)-based power electronic devices has been brought to the limit of its material properties, becoming a bottleneck for power electronics technology to pursue high efficiency, high frequency and high power density. In order to achieve technological breakthroughs, a new generation of semiconductor devices represented by SiC (silicon carbide) has developed rapidly in the past decade. Compared with silicon-based materials, silicon carbide materials have performance advantages in bandgap width, breakdown field strength, thermal conductivity, electron drift velocity, etc. Among them, SiC MOSFET devices are increasingly used in power electronic systems due to their excellent structural characteristics. However, the faster switching speed of SiC MOSFET also brings challenges to power electronic systems. Due to the higher voltage and current change rate of SiC MOSFET, as well as the inherent stray inductance and parasitic capacitance in the circuit, SiC MOSFET will have higher voltage, current spikes and oscillations during the switching process. These overshoot and oscillation processes increase the voltage and current stress of SiC MOSFET, aggravate the electromagnetic interference of the system, threaten the safe operation of the system, and increase the switching loss of the device. In order to better utilize the performance advantages of SiC MOSFET, these problems need to be solved.

[0003] There are currently several main solutions to the problems of voltage, current spikes and oscillations as well as electromagnetic interference. First, the stray inductance in the circuit can be reduced by optimizing the circuit design (such as PCB board layout and busbar structure) to reduce the impact of high voltage and current change rates, but the optimization effect of this method is limited. Secondly, the overall switching speed of SiC MOSFET can be directly reduced by increasing the resistance of the drive resistor, adding additional gate capacitance, and adding a buffer circuit to reduce voltage, current spikes and oscillations, but this type of solution not only sacrifices the switching speed of SiC MOSFET, but also greatly increases the switching loss of SiC MOSFET, and cannot give full play to the performance advantages of SiC MOSFET. Therefore, technicians proposed another more optimized driving scheme - active driving scheme. Its principle is to perform fine control on the switching process of SiC MOSFET in stages, and to increase the switching speed of the device as much as possible in the stage without affecting the voltage, current spikes and oscillations, and to appropriately reduce the switching speed of the device in the stage affecting the voltage, current spikes and oscillations. This control scheme optimizes the compromise curve between the switching speed and switching loss of the device. Compared with the scheme of directly reducing the switching speed overall, it can greatly reduce the switching loss while maintaining the same voltage, current spike and oscillation levels, and can better play the advantages of SiC MOSFET.

[0004] In the existing active drive schemes, the phased control design mostly follows the phased processing method suitable for Si devices. However, the switching process of SiC devices is different from that of Si devices, especially the influencing factor of current overshoot during the turn-on process. The original scheme cannot optimize the compromise curve of switching loss and switching speed of SiC MOSFET. Summary of the invention

[0005] The purpose of the embodiments of this specification is to provide an active drive system and method.

[0006] To solve the above technical problems, the embodiments of the present application are implemented in the following ways:

[0007] In a first aspect, the present application provides an active driving system, the system comprising: an active driving circuit and a main control chip, a driving push-pull circuit, a driving resistor, and a driven device connected in sequence, the active driving circuit is also connected to the main control chip, the driving resistor, and the driven device respectively;

[0008] The active drive circuit is used to control the switching speed of the driven device in the third stage of the turn-on process and the third stage of the turn-off process.

[0009] In one embodiment, the active driving circuit is used to control the switching speed of the driven device in the third stage of the turn-on process and the switching speed of the driven device in the third stage of the turn-off process through closed-loop feedback.

[0010] In one of the embodiments, the active drive circuit includes a current change rate sampling module, a turn-on process active drive module, and a turn-off process active drive module;

[0011] The current change rate sampling module is respectively connected to the turn-on process active driving module and the turn-off process active driving module;

[0012] The active driving module in the turn-on process and the active driving module in the turn-off process are respectively connected to the main control chip and the driven device.

[0013] In one embodiment, the current change rate sampling module includes a current change rate sampling element, a first resistor R1 and a second resistor R2;

[0014] One end of the output port of the current change rate sampling element is connected to one end of the first resistor R1, and the other end of the output port of the current change rate sampling element is grounded;

[0015] The other end of the first resistor R1 and one end of the second resistor R2 are connected to a node, the node is respectively connected to the turn-on process active driving module and the turn-off process active driving module, and the other end of the second resistor R2 is grounded.

[0016] In one of the embodiments, the turn-on process active driving module includes a current change rate integration unit, a current value judgment unit, and a turn-on process driving voltage compensation unit connected in sequence;

[0017] The current change rate integration unit includes: an operational amplifier, a third resistor R3, a fourth resistor R4, an integration capacitor C1, an integration parallel resistor R f , analog switch;

[0018] One end of the third resistor R3 is connected to the current change rate sampling module, and the other end of the third resistor R3 is connected to the input inverting terminal of the operational amplifier; one end of the fourth resistor R4 is connected to the input non-inverting terminal of the operational amplifier, and the other end of the fourth resistor R4 is grounded; the integral capacitor C1 and the integral parallel resistor R f , the analog switch is connected across the input inverting terminal and the output terminal of the operational amplifier; the control terminal of the analog switch is connected to the main control chip;

[0019] The current value judgment unit includes: a first comparator, a first threshold voltage V ref1 , a fifth resistor R5;

[0020] The positive input terminal of the first comparator is connected to the output terminal of the operational amplifier, and the negative input terminal of the first comparator is connected to the first threshold voltage Vref1 The output terminal of the first comparator is connected to one end of a fifth resistor R5;

[0021] The turn-on process driving voltage compensation unit includes: a first diode D1, a sixth resistor R6, a first controllable device S1, and a second controllable device S2;

[0022] The base of the first controllable device S1 is connected to the other end of the fifth resistor R5, the emitter of the first controllable device S1 is connected to the drain of the second controllable device S2, the collector of the first controllable device S1 is connected to one end of the sixth resistor R6, the other end of the sixth resistor R6 is connected to the cathode of the first diode D1, and the anode of the first diode D1 is respectively connected to the gate of the driven device and the driving resistor; the gate of the second controllable device S2 is connected to the main control chip, and the source of the second controllable device S2 is grounded.

[0023] In one embodiment, the first controllable device S1 is an NPN transistor, and the second controllable device S2 is an N-channel enhancement MOSFET.

[0024] In one of the embodiments, the shutdown process active driving module includes a current change rate judgment unit and a shutdown process driving voltage compensation unit;

[0025] The current change rate judgment unit includes: a second comparator, a second threshold voltage V ref2 , a seventh resistor R7;

[0026] The positive input terminal of the second comparator is connected to the current change rate sampling module, and the negative input terminal of the second comparator is connected to the second threshold voltage V ref2 The output terminal of the second comparator is connected to one end of a seventh resistor R7;

[0027] The shutdown process driving voltage compensation unit includes: a third controllable device S3, a fourth controllable device S4, a fifth controllable device S5, an eighth resistor R8, a ninth resistor R9, a tenth resistor R 10 , a second diode D2;

[0028] The base of the fourth controllable device S4 is connected to the other end of the seventh resistor R7, the emitter of the fourth controllable device S4 is connected to the drain of the fifth controllable device S5, the source of the fifth controllable device S5 is grounded, and the gate of the fifth controllable device S5 is connected to the main control chip; the collector of the fourth controllable device S4 is connected to one end of the eighth resistor R8, and the collector of the fourth controllable device S4 is also connected to the drain of the fifth controllable device S5 through the tenth resistor R 10 Pull up to positive power supply V GG The other end of the eighth resistor R8 is connected to the base of the third controllable device S3, and the collector of the third controllable device S3 is connected to the positive power supply V GGThe emitter of the third controllable device S3 is connected to one end of the ninth resistor R9, the other end of the ninth resistor R9 is connected to the anode of the second diode D2, and the cathode of the second diode D2 is connected to the gate G of the driven device.

[0029] In one embodiment, the third controllable device S3 is a PNP transistor, the fourth controllable device S4 is an NPN transistor, and the fifth controllable device S5 is an N-channel enhancement MOSFET.

[0030] In a second aspect, the present application provides an active driving method, using the active driving system of the first aspect, the method comprising:

[0031] When the main control chip receives the turn-on signal for turning on the driven device, the main control chip sends a high level signal to the driving push-pull circuit and the second controllable device S2 and sends a disconnection signal to the analog switch, so that the current change rate integration unit integrates during the current rising process of the driven device being turned on;

[0032] If the output voltage of the current change rate integration unit is greater than the first threshold voltage V ref1 When , the first comparator flips and outputs a high level signal to control the first controllable device S1 to turn on, and the turn-on process driving voltage compensation unit starts to work to lower the gate voltage of the driven device and reduce the switching speed of the third stage of the turn-on process of the driven device;

[0033] After the first preset time, the main control chip sends a shutdown signal to the second controllable device S2;

[0034] When the main control chip receives a shutdown signal to disconnect the driven device, the main control chip sends a low level signal to the driving push-pull circuit and a high level signal to the fifth controllable device S5; and sends a conduction signal to the analog switch to clear the output voltage of the current change rate integration unit;

[0035] If the output voltage of the current change rate sampling module is greater than the second threshold voltage V ref2 , the second comparator flips and outputs a high level, controls the fourth controllable device S4 to turn on, and drives the voltage compensation unit to start working during the shutdown process to increase the gate voltage of the driven device and reduce the switching speed of the third stage of the shutdown process of the driven device;

[0036] When the output voltage of the current change rate sampling module is lower than the second threshold voltage V ref2 , the second comparator flips again and outputs a low level, controlling the fourth controllable device S4 to turn off;

[0037] After the second preset time period, the main control chip sends a low level signal to the fifth controllable component S5.

[0038] It can be seen from the technical solution provided in the above embodiments of this specification that:

[0039] The active drive system is a closed loop, which realizes stage-by-stage control of the device switching process by detecting different stages of the device switching process.

[0040] The device current action and switching phase can be identified by detecting the device current change rate and its integral.

[0041] It is clarified that the time for the active driving circuit to adjust the turn-on speed of the driven device in the turn-on process is the third stage of the turn-on process, that is, the voltage drop stage, and the time for the active driving circuit to adjust the turn-off speed of the driven device in the turn-off process is the third stage of the turn-off process, that is, the current drop stage.

[0042] In order to increase the speed of connecting and disconnecting the active drive circuit, the active drive circuit is controlled by a transistor when connected and by a MOSFET when disconnected, so that the auxiliary circuit can be turned on and off as quickly as possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0044] Figure 1 A circuit diagram of the active drive system provided for this application;

[0045] Figure 2 The circuit schematic diagram of the active drive module for the turn-on process provided in this application;

[0046] Figure 3 The circuit schematic diagram of the active drive module for the shutdown process provided by this application;

[0047] Figure 4 Schematic diagram of the switching process of the driven device, the driving push-pull voltage waveform, etc. provided in this application;

[0048] Figure 5 A schematic diagram of the process of activating the active drive system provided for this application;

[0049] Figure 6 A schematic diagram of a process for shutting down an active drive system provided in this application. DETAILED DESCRIPTION

[0050] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below in conjunction with the drawings in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this specification.

[0051] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0052] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present application description without departing from the scope or spirit of the present application. Other embodiments derived from the present application description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0053] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0054] Unless otherwise specified, "parts" in this application are all calculated by mass.

[0055] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0056] Reference Figure 1 , which shows a circuit diagram of an active drive system applicable to the embodiment of the present application. The active drive scheme is characterized by adjusting the gate (or gate electrode) driving conditions (such as driving voltage, driving current, driving resistance) of the fully controlled semiconductor device at different switching stages to achieve separate control of different stages of its switching process, which helps to optimize the compromise curve of overshoot, oscillation and loss in the device switching process.

[0057] like Figure 1 As shown, the active drive system may include:

[0058] An active driving circuit and a main control chip, a driving push-pull circuit, a driving resistor, and a driven device connected in sequence, wherein the active driving circuit is also connected to the main control chip, the driving resistor, and the driven device respectively;

[0059] The active drive circuit is used to control the switching speed of the driven device in the third stage of the turn-on process and the switching speed of the third stage of the turn-off process. Specifically, the main control chip can send control signals to the drive push-pull circuit and the active drive circuit. Exemplarily, the main control chip can adopt a programmable logic chip such as CPLD (Complex Programmable Logic Device) and FPGA (Field-Programmable Gate Array).

[0060] The push-pull circuit drives the resistor R G The gate of the driven device Q is charged and discharged to achieve the effect of controlling the on and off of the driven device Q.

[0061] The driven device Q can be a voltage-controlled semiconductor device, such as SiC MOSFET (SiC Metal-Oxide-Semiconductor Field-Effect Transistor), SiC IGBT (SiC Insulated Gate Bipolar Transistor), SiMOSFET (Silicon Metal-Oxide Semiconductor Field-Effect Transistor), Si IGBT (Silicon Insulated Gate Bipolar Transistor), etc.

[0062] In the embodiment of the present application, an active driving circuit is used to control the switching speed of the driven device in the third stage of the turn-on process and the third stage of the turn-off process, so as to reduce current overshoot, voltage overshoot and subsequent oscillation.

[0063] In one embodiment, the active driving circuit is used to control the switching speed of the driven device in the third stage of the turn-on process and the switching speed of the driven device in the third stage of the turn-off process through closed-loop feedback.

[0064] In the embodiments of the present application, closed-loop feedback is used to control the switching speed of the driven device in the third stage of the turn-on process and the switching speed in the third stage of the turn-off process, thereby avoiding the defects of the open-loop solution in that it has poor adaptability to different working conditions and parameters and needs to consider the application conditions and perform complex parameter calculations before setting the control parameters.

[0065] In one embodiment, continue to refer to Figure 1 , the active drive circuit includes a current change rate sampling module, a turn-on process active drive module, and a turn-off process active drive module;

[0066] The current change rate sampling module is respectively connected to the turn-on process active driving module and the turn-off process active driving module;

[0067] The active driving module in the turn-on process and the active driving module in the turn-off process are respectively connected to the main control chip and the driven device.

[0068] Specifically, the output of the current change rate sampling module is used as both an input signal of the active drive module in the turn-on process and an input signal of the active drive module in the turn-off process.

[0069] In one embodiment, Figure 2 , 3 As shown, the current change rate sampling module includes a current change rate sampling element and a first resistor R1 and a second resistor R2;

[0070] One end of the output port of the current change rate sampling element is connected to one end of the first resistor R1, and the other end of the output port of the current change rate sampling element is grounded;

[0071] The other end of the first resistor R1 and one end of the second resistor R2 are connected to a node ( Figure 2 and Figure 3 As shown in the node ①), the node is connected to the active driving module of the turn-on process and the active driving module of the turn-off process respectively, and the other end of the second resistor R2 is grounded.

[0072] Specifically, the current change rate sampling element may be a Rogowski coil or a parasitic inductance of a lead in a circuit, etc., which is used to sample the change rate of the drain-source current of the driven device Q.

[0073] The first resistor R1 and the second resistor R2 are output voltage proportional voltage dividing resistors, which are used to divide the proportional voltage of the output voltage.

[0074] In one embodiment, Figure 2 As shown, the turn-on process active driving module includes a current change rate integration unit, a current value judgment unit, and a turn-on process driving voltage compensation unit which are connected in sequence.

[0075] The current change rate integration unit includes: an operational amplifier, a third resistor R3, a fourth resistor R4, an integration capacitor C1, an integration parallel resistor R f , analog switch;

[0076] One end of the third resistor R3 is connected to the current change rate sampling module (one end of the third resistor R3 is connected to the current change rate sampling module Figure 2 The other end of the third resistor R3 is connected to the inverting input terminal of the operational amplifier; one end of the fourth resistor R4 is connected to the non-inverting input terminal of the operational amplifier, and the other end of the fourth resistor R4 is grounded; the integral capacitor C1, the integral parallel resistor R f , the analog switch is connected across the input inverting terminal and the output terminal of the operational amplifier; the control terminal of the analog switch is connected to the main control chip (not shown in the figure).

[0077] The current value judgment unit includes: a first comparator, a first threshold voltage V ref1 , a fifth resistor R5;

[0078] The positive input terminal of the first comparator is connected to the output terminal of the operational amplifier, and the negative input terminal of the first comparator is connected to the first threshold voltage V ref1 The output end of the first comparator is connected to one end of the fifth resistor R5.

[0079] The turn-on process driving voltage compensation unit includes: a first diode D1, a sixth resistor R6, a first controllable device S1, and a second controllable device S2;

[0080] The base of the first controllable device S1 is connected to the other end of the fifth resistor R5, the emitter of the first controllable device S1 is connected to the drain of the second controllable device S2, the collector of the first controllable device S1 is connected to one end of the sixth resistor R6, the other end of the sixth resistor R6 is connected to the cathode of the first diode D1, and the anode of the first diode D1 is connected to the gate G of the driven device Q and the driving resistor R G The gate of the second controllable device S2 is connected to the main control chip, and the source of the second controllable device S2 is grounded.

[0081] Specifically, the first controllable device S1 is controlled to be on and off by the output of the first comparator in the current value judgment unit, and the second controllable device S2 is controlled to be on and off by the main control chip.

[0082] In order to ensure the rapidity of switching on and off of the active drive circuit, the first controllable device S1 selects an NPN transistor, and the second controllable device S2 selects an N-channel enhancement MOSFET.

[0083] It can be understood that GND in the figure is a reference ground, and generally the source of the driven device Q is used as the reference ground.

[0084] It can also be understood that the output end of the driving push-pull circuit can be driven by the driving resistor R G Connected to the gate G of the driven device Q.

[0085] In one embodiment, Figure 3 As shown, the shutdown process active driving module includes a current change rate judgment unit and a shutdown process driving voltage compensation unit;

[0086] The current change rate judgment unit includes: a second comparator, a second threshold voltage V ref2 , a seventh resistor R7;

[0087] The positive input terminal of the second comparator is connected to the current change rate sampling module (the positive input terminal of the second comparator is connected to Figure 3The negative input terminal of the second comparator is connected to the second threshold voltage V ref2 The output terminal of the second comparator is connected to one end of a seventh resistor R7;

[0088] The shutdown process driving voltage compensation unit includes: a third controllable device S3, a fourth controllable device S4, a fifth controllable device S5, an eighth resistor R8, a ninth resistor R9, a tenth resistor R 10 , a second diode D2;

[0089] The base of the fourth controllable device S4 is connected to the other end of the seventh resistor R7, the emitter of the fourth controllable device S4 is connected to the drain of the fifth controllable device S5, the source of the fifth controllable device S5 is grounded, and the gate of the fifth controllable device S5 is connected to the main control chip; the collector of the fourth controllable device S4 is connected to one end of the eighth resistor R8, and the collector of the fourth controllable device S4 is also connected to the drain of the fifth controllable device S5 through the tenth resistor R 10 Pull up to positive power supply V GG The other end of the eighth resistor R8 is connected to the base of the third controllable device S3, and the collector of the third controllable device S3 is connected to the positive power supply V GG The emitter of the third controllable device S3 is connected to one end of the ninth resistor R9, the other end of the ninth resistor R9 is connected to the anode of the second diode D2, and the cathode of the second diode D2 is connected to the gate G of the driven device.

[0090] Specifically, the on-off of the fourth controllable device S4 is controlled by the output of the second comparator in the current change rate judgment unit, and the on-off of the fifth controllable device S5 is controlled by the main control chip.

[0091] In order to ensure the rapidity of switching on and off of the active drive circuit, the third controllable device S3 selects a PNP transistor, the fourth controllable device S4 selects an NPN transistor, and the fifth controllable device S5 selects an N-channel enhancement MOSFET.

[0092] The present application also discloses an active driving method, which comprises:

[0093] When the main control chip receives the turn-on signal to turn on the driven device, the main control chip sends a high level signal to the driving push-pull circuit and the second controllable device S2 and sends a disconnection signal to the analog switch, and the current change rate integration unit integrates the current rising process when the driven device is turned on;

[0094] If the output voltage of the current change rate integration unit is greater than the first threshold voltage V ref1When , it indicates that the turn-on process of the driven device enters the third stage, the first comparator flips, outputs a high-level signal, controls the first controllable device S1 to turn on, and the turn-on process driving voltage compensation unit starts to work to lower the gate voltage of the driven device and reduce the switching speed of the third stage of the turn-on process of the driven device;

[0095] After the first preset time, the main control chip sends a shutdown signal to the second controllable device S2;

[0096] When the main control chip receives a shutdown signal to disconnect the driven device, the main control chip sends a low level signal to the driving push-pull circuit and a high level signal to the fifth controllable device S5; and sends a conduction signal to the analog switch to clear the output voltage of the current change rate integration unit;

[0097] If the output voltage of the current change rate sampling module is greater than the second threshold voltage V ref2 , indicating that the shutdown process of the driven device enters the third stage, the second comparator flips, outputs a high level, controls the fourth controllable device S4 to turn on, and the shutdown process drives the voltage compensation unit to start working to increase the gate voltage of the driven device and reduce the switching speed of the third stage of the shutdown process of the driven device;

[0098] When the output voltage of the current change rate sampling module is lower than the second threshold voltage V ref2 , the second comparator flips again and outputs a low level, controlling the fourth controllable device S4 to turn off;

[0099] After the second preset time period, the main control chip sends a low level signal to the fifth controllable component S5.

[0100] The circuit principle and working process of the proposed active driving circuit are described in detail below.

[0101] like Figure 4 The figure shows the voltage waveform of the driving push-pull circuit and the control signal waveform of the key controllable devices (i.e. S1, S2, S4, S5) in the compensation unit (including the driving voltage compensation unit in the turn-on process and the driving voltage compensation unit in the turn-off process) during the switching process of the driven device. GG Vss is the positive voltage for driving the push-pull circuit, and Vss is the negative voltage for driving the push-pull circuit. The driving circuit designed for SiC MOSFET is generally designed to be V GG is 20V, Vss is -4 to -6V.

[0102] Generally, the turn-on and turn-off processes of SiC MOSFET are divided into four stages: the turn-on process is divided into four stages: turn-on delay, current rise, voltage drop, and gate voltage continues to rise; the turn-off process is divided into four stages: turn-off delay, voltage rise, current drop, and gate voltage continues to drop. Figure 4 As shown, at time t0, the output voltage of the push-pull circuit increases to the positive driving voltage V GG , the gate voltage of the driven device begins to rise until its gate voltage reaches the threshold voltage V at time t1 TH , threshold voltage V TH The size of is related to the device itself and the operating temperature. This period of time (i.e., t0-t1) is called the turn-on delay. From t1 to t2, as the gate voltage of the driven device increases, the current of the driven device also increases until the current of the driven device reaches the circuit load current. At this time, the gate voltage value of the driven device is called the Miller platform voltage V miller , Miller platform voltage V miller The size of is related to the output characteristics of the driven device and the actual load current. This stage (i.e., t1 to t2) is called the device current rising stage. From t2 to t3, the device gate voltage remains basically unchanged and remains at the Miller platform voltage V miller At the same time, the device drain-source voltage continues to drop to the conduction voltage drop. This stage (i.e., t2-t3) is called the device voltage drop stage. In the fourth stage, the device gate voltage continues to rise to the driving positive voltage V GG The turn-on process ends here. The four stages of the turn-off process correspond to the turn-on process. At t5, the output voltage of the push-pull circuit is reduced to the negative voltage V SS , the device gate voltage begins to decrease, and at t6 the device gate voltage drops to the Miller platform voltage V miller This stage (i.e., t5 to t6) is the turn-off delay stage. From t6 to t7, the device gate voltage remains basically unchanged, maintaining at the Miller platform voltage V miller At the same time, the device drain-source voltage continues to rise to the bus voltage. This stage (i.e., t6-t7) is called the device voltage rising stage. From t7 to t8, as the device gate voltage decreases, the device current also decreases until the device gate voltage drops to the threshold voltage V TH , and the device current returns to zero. This stage (i.e., t7-t8) is called the device current falling stage. In the final stage, the device gate voltage continues to drop to the negative driving voltage V SS , the shutdown process ends here.

[0103] In the actual switching process, high voltage and current change rate mainly appear in the second and third stages of the turn-on process and the second and third stages of the turn-off process. The current spike in the turn-on process mainly appears in the third stage. There are two main reasons for this. The first is the reverse recovery current generated by the anti-parallel diode of the corresponding converter device in the circuit topology. The second is the junction capacitance charging current during the voltage increase of the converter device diode. These two parts of current are superimposed on the channel current of the driven device to form a current spike, which increases the switching loss of the device. The intensity of the subsequent voltage oscillation also depends on the voltage change speed in the third stage. Therefore, in most active drive schemes, the gate voltage, drive current or drive resistance in the second and third stages are changed to appropriately reduce the switching speed of these two stages to reduce the current spike and oscillation. However, the reverse recovery characteristics of the anti-parallel diode of SiC MOSFET are not obvious. The current spike in the third stage of the SiC MOSFET turn-on process is mainly caused by the voltage change process in the third stage. Therefore, it is only necessary to appropriately reduce the speed of the third stage to reduce the current spike and oscillation process, and the switching speed of the first, second and fourth stages can be increased as much as possible. The voltage spike and oscillation during the shutdown process mainly depend on the current change speed in the third stage. Therefore, the speed of the third stage needs to be appropriately reduced to reduce the voltage spike and oscillation process. The switching speeds of the first, second and fourth stages can be increased as much as possible.

[0104] In order to realize the separate control of the switching speed at different stages of the switching process, it is necessary to detect and identify the stages of the switching process. It should be noted that there are drastic current changes in the process that needs to be identified. Considering the voltage drop formed by the parasitic inductance in the line due to the current change, the detected voltage is the superposition of the actual device voltage and the parasitic inductance voltage drop. Therefore, the detected voltage has inherent errors, which is not conducive to the detection and accurate identification of the stages of the switching process. This is also one of the shortcomings of the closed-loop active drive circuit based on voltage detection. Therefore, the present application identifies the different stages of the switching process based on the current change rate.

[0105] The current change rate sampling element in the above current change rate sampling module may be a Rogowski coil or parasitic inductance of a lead in a circuit.

[0106] Among them, the Rogowski coil is an induction coil, and the magnitude of its output voltage is proportional to the rate of change of the current of the current-carrying conductor passing through it, which can be expressed by the following formula:

[0107]

[0108] Among them, v Mis the output voltage of the Rogowski coil, M is the mutual inductance between the Rogowski coil and the current-carrying conductor passing through it, and di / dt is the current change rate in the measured current-carrying conductor. The drain-source current of the driven device Q can be made to pass through the Rogowski coil through structural design, so that the Rogowski coil can correctly reflect the current change rate of the drain-source current of the driven device Q.

[0109] The device current change rate information can also be obtained by measuring the voltage across a small section of parasitic inductance in the circuit that is connected in series with the drain and source of the device. The relationship between the inductor voltage and current can be expressed by the following formula:

[0110]

[0111] Among them, v L is the voltage across the parasitic inductance of the lead being measured, L S is the inductance value of the parasitic inductance of the lead being measured, di / dt is the rate of change of the current flowing through the lead inductance. Since the selected lead inductance is in series with the device channel, it can be considered that the di / dt here is the rate of change of the device drain-source current.

[0112] Figure 2 and Figure 3 The first resistor R1 and the second resistor R2 of the current change rate sampling module are output voltage-dividing resistors for proportionally adjusting the output voltage of the current change rate sampling element. The output voltage of the current change rate sampling module can be expressed as:

[0113]

[0114] For the turn-on process active drive module, the moment when the turn-on process drive voltage compensation unit needs to be connected is moment t2. The current action that needs to be detected and identified is whether the current of the driven device reaches the load current. Therefore, the current change rate information obtained by the current change rate sampling module must be processed to obtain information that can reflect the actual device load current and make a judgment. Here, the current change rate integration unit can be used to integrate the collected current change rate information to obtain the output voltage value of the current change rate integration unit that can reflect the actual device current value. Taking the Rogowski coil as the current change rate sampling module as an example, the advantage of the Rogowski coil is that it is electrically isolated from the main circuit, which can reduce the impact on the main circuit. For the convenience of explanation, it is stipulated here that the direction of the driven device channel current i flowing from the drain to the source is set to the positive direction of the current (such as Figure 1 As shown), when the forward current value increases, the output voltage v of the Rogowski coil M is a negative value, the output voltage of the current change rate integration unit can be expressed as:

[0115]

[0116] From the above formula, we can know that the output voltage of the current change rate integration unit is in a certain proportional relationship with the actual current value i. Therefore, the output voltage of the current change rate integration unit can be used to reflect the current value of the actual device. The threshold voltage V of the first comparator is designed according to the proportional relationship between the actual current value and the output voltage of the current change rate integration unit. ref1 , so that when the actual current value of the device reaches the load current value, the first comparator flips and jumps from a low level to a high level. In addition, the role of the analog switch in the current change rate integration unit is to clear the output voltage of the current change rate integration unit during the device shutdown process, so as to ensure that the output voltage of the current change rate integration unit starts from zero every time the device is turned on, and to avoid the output voltage drift after the integrator has been working for a long time. Therefore, each time the device needs to be turned on, the analog switch is also disconnected synchronously to allow the current change rate integration unit to integrate normally. When the device needs to be turned off, the analog switch is closed synchronously to realize the integration output voltage clearing, and the analog switch is controlled by the main control chip.

[0117] Reference below Figure 2 , Figure 4 and Figure 5 The working process of turning on the active drive circuit is described in detail. In the initial stage, the main control chip receives a signal from the host computer to turn on the driven device Q. The main control chip sends a high-level signal to the drive push-pull circuit and the second controllable device S2, so that the output voltage of the drive push-pull circuit jumps from the output negative voltage to the output positive voltage. The second controllable device S2 is turned on, and the analog switch is disconnected at the same time to allow the current change rate integration unit to integrate normally. The driven device Q starts to turn on, and after the turn-on delay stage, its device current begins to rise. At this time, the device current change rate will be sampled by the current change rate sampling module, and integrated by the current change rate integration unit. The output voltage of the current change rate integration unit rises synchronously with the device current. When the device current reaches the load current, that is, the output voltage v1 of the current change rate integration unit reaches the first threshold voltage V of the first comparator. ref1 , the first comparator flips and outputs a high-level signal. At this time, the first controllable device S1 is also turned on. The turn-on process drives the voltage compensation unit to start working, pulling down the gate voltage of the driven device Q. The steady-state value of the voltage after pulling down can be expressed as:

[0118]

[0119] By reducing the gate voltage in this stage, the switching speed of the third stage of device opening can be reduced, that is, the voltage change rate in the voltage drop stage, which correspondingly reduces the current overshoot and subsequent oscillation. After the first preset time, the main control chip can control the second controllable device S2 to turn off, disconnecting the influence of the opening process driving voltage compensation unit on the device gate. The first preset time does not need to accurately determine the stage of the device opening action, and can be set by experience or actual conditions, and only needs to be slightly longer than the duration of the third stage of the device (that is, within Figure 4 Before or after the t3 moment shown, the second controllable device S2 is turned off by the main control chip). At this point, the entire process of the active drive module is completed. It should be noted that the conduction time of the analog switch is the t5 moment when the main control chip sends a device shutdown signal, which is also controlled by the main control chip.

[0120] For the active drive module in the shutdown process, the time when the process drive voltage compensation unit needs to be connected is the start time t7 of the shutdown current drop phase. Therefore, it is possible to directly determine whether the device has entered the device current drop phase based on the device current change rate. According to the previous definition of the positive direction of the device current and the output voltage direction of the current change rate sampling module, when the device channel current decreases, the output voltage of the current change rate sampling module is positive. Therefore, the second threshold voltage V ref2 is a positive voltage greater than zero. When the output voltage of the current change rate sampling module exceeds the second threshold voltage V ref2 When the second comparator flips, it changes from low level to high level, and the fourth controllable device S4 is turned on. When the device current decreases, the output voltage of the current change rate sampling module is lower than the second threshold voltage V ref2 , the second comparator flips again, jumping from a high level to a low level, and the fourth controllable device S4 is turned off.

[0121] Reference below Figure 3 , Figure 4 and Figure 6 The working process of shutting down the active drive circuit is described in detail. In the initial stage, the main control chip receives a signal from the host computer to shut down the driven device Q. Therefore, the main control chip sends a low-level signal to the drive push-pull circuit and a high-level signal to the fifth controllable device S5, and the fifth controllable device S5 is turned on. The output voltage of the drive push-pull circuit jumps from the output positive voltage to the output negative voltage. The driven device Q begins to shut down. After the shutdown delay stage and the voltage rise process, its device current begins to decrease. At this time, the output voltage of the current change rate sampling module reaches the second threshold voltage V of the second comparator. ref2 , the second comparator flips and outputs a high level. At this time, the fourth controllable device S4 is turned on, and the shutdown process drives the voltage compensation unit to start working, pulling up the gate voltage of the driven device Q. The pulled-up voltage can be expressed as:

[0122]

[0123] By increasing the gate voltage in this stage, the switching speed of the third stage of device shutdown, that is, the current change rate in the current drop stage, can be reduced, and the voltage overshoot and subsequent oscillation are correspondingly reduced. At t8, the device current drop stage ends, and the output voltage of the current change rate sampling module is lower than the second threshold voltage V of the second comparator. ref2 , the second comparator flips again and outputs a low level. At this time, the fourth controllable device S4 is turned off, and the shutdown process drives the voltage compensation unit to work. After the second preset time, the main control chip can turn off the fifth controllable device S5, which can be any time before the driven device is turned on again. However, for the sake of reliability, the fifth controllable device S5 can be turned off after the fourth controllable device S4 is turned off. At this point, the entire process of the active drive circuit in a shutdown process ends.

[0124] In order to adapt to the fast switching action during the operation of SiC MOSFET and improve the effect of the closed-loop active drive system, the comparator, current change rate integration unit, analog switch, and controllable device used in the circuit must have the characteristics of high frequency and fast response speed. This embodiment provides a set of feasible device selection schemes. The comparator can use the LT1711 comparator of Linear Technology; the operational amplifier in the current change rate integration unit can use the AD4817 operational amplifier of Analog Devices; the analog switch can use the TMUX1101 of Texas Instruments; the controllable devices S1 and S4 can use the CPH3205 NPN transistor of ON Semiconductor; the controllable devices S2 and S5 can use the BSS214NW N-channel enhancement MOSFET of Infineon; and the controllable device S3 can use the CPH3105 PNP transistor of ON Semiconductor.

[0125] The active drive system provided in the embodiment of the present application is a closed loop, and realizes stage-by-stage control of the device switching process by detecting different stages of the device switching process.

[0126] The embodiment of the present application realizes the identification of the device current action and the switching stage by detecting the device current change rate and its integral.

[0127] The embodiment of the present application clarifies that the active drive circuit adjustment time of the turn-on process is the third stage of the turn-on process, that is, the voltage drop stage, and the active drive circuit adjustment time of the turn-off process is the third stage of the turn-off process, that is, the current drop stage.

[0128] In order to improve the speed of the active drive circuit in the embodiment of the present application, the active drive circuit is controlled by a transistor when connected and by a MOSFET when disconnected, so that the auxiliary circuit can be turned on and off as quickly as possible.

[0129] It should be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of further restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0130] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

Claims

1. An active drive system, characterized in that: The system comprises: an active driving circuit and a main control chip, a driving push-pull circuit, a driving resistor, and a driven device connected in sequence, wherein the active driving circuit is also connected to the main control chip, the driving resistor, and the driven device respectively; The active drive circuit is used to control the switching speed of the driven device in the third stage of the turn-on process and the switching speed of the third stage of the turn-off process; The active drive circuit is used to control the switching speed of the driven device in the third stage of the turn-on process and the switching speed of the third stage of the turn-off process through closed-loop feedback; The active drive circuit includes a current change rate sampling module, a turn-on process active drive module, and a turn-off process active drive module; The current change rate sampling module is connected to the turn-on process active driving module and the turn-off process active driving module respectively; The on-process active driving module and the off-process active driving module are respectively connected to the main control chip and the driven device; The switch-on process active driving module comprises a current change rate integration unit, a current value judgment unit, and a switch-on process driving voltage compensation unit connected in sequence; The current change rate integration unit includes: an operational amplifier, a third resistor R 3. The fourth resistor R 4. Integral capacitor C 1. Integral parallel resistance R f , analog switch; The third resistor R One end of 3 is connected to the current change rate sampling module, and the third resistor R The other end of 3 is connected to the input inverting end of the operational amplifier; the fourth resistor R One end of 4 is connected to the input non-inverting terminal of the operational amplifier, and the fourth resistor R The other end of 4 is grounded; the integral capacitor C 1. The integral parallel resistance R f , the analog switch is connected across the input inverting terminal and the output terminal of the operational amplifier; the control terminal of the analog switch is connected to the main control chip; The current value judgment unit includes: a first comparator, a first threshold voltage V ref1 , the fifth resistor R 5; The positive input terminal of the first comparator is connected to the output terminal of the operational amplifier, and the negative input terminal of the first comparator is connected to the first threshold voltage V ref1 The output terminal of the first comparator is connected to the fifth resistor R One end of 5 is connected; The turn-on process driving voltage compensation unit comprises: a first diode D 1. The sixth resistor R 6. The first controllable device S 1. Second controllable device S 2; The first controllable device S 1 base and the fifth resistor R 5 is connected to the other end of the first controllable device S 1 and the emitter of the second controllable device S 2, the drain connection of the first controllable device S 1 collector and the sixth resistor R 6, the sixth resistor R The other end of 6 is connected to the first diode D 1 is connected to the cathode of the first diode D 1 is connected to the gate of the driven device and the driving resistor respectively; the second controllable device S 2 is connected to the main control chip, and the second controllable device S The source of 2 is grounded.

2. The system according to claim 1, characterized in that The current change rate sampling module includes a current change rate sampling element, a first resistor R 1 and the second resistor R 2; One end of the output port of the current change rate sampling element is connected to the first resistor R 1, and the other end of the output port of the current change rate sampling element is grounded; The first resistor R 1 and the other end of the second resistor R One end of 2 is connected to a node, and the node is connected to the active drive module of the turn-on process and the active drive module of the turn-off process respectively. R The other end of 2 is grounded.

3. The system according to claim 1, characterized in that The first controllable device S 1 Using NPN transistor, the second controllable device S 2Use N-channel enhancement type MOSFET.

4. The system according to claim 1, characterized in that The shutdown process active driving module includes a current change rate judgment unit and a shutdown process driving voltage compensation unit; The current change rate judgment unit includes: a second comparator, a second threshold voltage V ref2 , the seventh resistor R 7; The positive input terminal of the second comparator is connected to the current change rate sampling module, and the negative input terminal of the second comparator is connected to the second threshold voltage V ref2 The output terminal of the second comparator is connected to the seventh resistor R One end of 7 is connected; The shutdown process driving voltage compensation unit includes: a third controllable device S 3. The fourth controllable device S 4. The fifth controllable device S 5. Eighth resistor R 8. Ninth resistor R 9. Tenth resistor R 10 , the second diode D 2; The fourth controllable device S 4 base and the seventh resistor R 7 is connected to the other end of the fourth controllable device S 4 and the emitter of the fifth controllable device S 5 is connected to the drain of the fifth controllable device S 5 has its source grounded, the fifth controllable device S 5 is connected to the main control chip; the fourth controllable device S 4 collector and the eighth resistor R 8 is connected to one end of the fourth controllable device S The collector of 4 is also connected to the tenth resistor R 10 Pull up to positive power supply V GG , the eighth resistor R The other end of 8 is connected to the third controllable device S 3 is connected to the base of the third controllable device S 3 The collector is connected to the positive power supply V GG connection, the third controllable device S 3 emitter and the ninth resistor R 9 is connected to one end of the ninth resistor R The other end of 9 is connected to the second diode D 2, the anode of the second diode is connected D The cathode of 2 is connected to the gate G of the driven device.

5. The system according to claim 4, characterized in that The third controllable device S 3 Using a PNP transistor, the fourth controllable device S 4 uses NPN transistor, the fifth controllable device S 5Use N-channel enhancement type MOSFET.

6. An active driving method, using the active driving system according to any one of claims 1 to 5, characterized in that: The method comprises: When the main control chip receives the start signal to start the driven device, the main control chip drives the push-pull circuit and the second controllable device S 2. Sending a high level signal and a disconnection signal to the analog switch, so that the current change rate integration unit integrates the current rising process when the driven device is turned on; If the output voltage of the current change rate integration unit is greater than the first threshold voltage V ref1 When the first comparator flips, it outputs a high level signal to control the first controllable device S 1 is turned on, and the turn-on process driving voltage compensation unit starts to work to pull down the gate voltage of the driven device and reduce the switching speed of the third stage of the turn-on process of the driven device; After the first preset time, the main control chip sends a signal to the second controllable device S 2. Send a shutdown signal; When the main control chip receives a shutdown signal to disconnect the driven device, the main control chip sends a low level signal to the drive push-pull circuit and to the fifth controllable device. S 5 sends a high level signal; and sends a conduction signal to the analog switch to clear the output voltage of the current change rate integration unit; If the output voltage of the current change rate sampling module is greater than the second threshold voltage of the second comparator V ref2 , the second comparator flips, outputs a high level, and controls the fourth controllable device S 4. During the turn-on and turn-off process, the driving voltage compensation unit starts to work to increase the gate voltage of the driven device and reduce the switching speed of the third stage of the turn-off process of the driven device; When the output voltage of the current change rate sampling module is lower than the second threshold voltage of the second comparator V ref2 , the second comparator flips again, outputs a low level, and controls the fourth controllable device S 4. Shut down; After the second preset time, the main control chip sends a signal to the fifth controllable device S 5 Send a low level signal.

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