A method for improving overload capacity of a network construction converter based on valve machine joint control and a driving circuit

Abstract

The application relates to a network-constructing converter overload capacity improvement method and a driving circuit based on valve machine joint control, and belongs to the technical field of power device overload performance improvement. The method is based on the active heat control theory of a power device: by improving the gate driving signal of an IGBT, the voltage drop between the collector and the emitter can be reduced V ce The active gate driving technology is applied to the on-state stage of the IGBT, and the switching loss of the power device can be greatly reduced by combining the scheme of reducing the switching frequency, the running state of the IGBT device is judged according to the junction temperature monitored by the IGBT device, the gate driving voltage of the device is adjusted V ge , and the switching frequency is reduced f sw The overcurrent capacity is improved, and the overload capacity of the network-constructing converter is finally improved.

Description

TECHNICAL FIELD

[0001] The application relates to a valve machine joint control-based network construction converter overload capacity improvement method and a driving circuit, and belongs to the technical field of power device overload performance improvement. BACKGROUND

[0002] Power converters have been widely used in many power fields, such as renewable energy systems, industrial motor drives, and power transmission. Although the wide bandgap semiconductor technology develops rapidly, IGBT is still the core device of today's high-power power converter due to its mature industrial chain, low cost and high reliability. With a large number of high-proportion renewable energy and high-proportion power electronic equipment accessing the power system, network construction converters have the advantages of active support capability of self-construction of voltage / frequency, control capability of flexible adaptation to island and weak power grid, and the importance in the power system is increasingly prominent. At the same time, due to the sharp fluctuation of renewable energy (such as wind power and photovoltaic) output affected by weather, the rapid response characteristics of network construction converters will cause the power change rate of the power grid to increase sharply. As the core switching device of network construction converters, the current-carrying capacity of IGBT directly determines the upper limit of the instantaneous power output of the device. Taking the case of power grid frequency drop as an example, if the network construction converter needs to output 1.5 times the rated power for a short time, it requires IGBT to withstand 2 times or even multiple times the rated current for a short time. Therefore, in the scenes of high fluctuation load, weak power grid operation, multi-machine parallel connection and extreme environment, which cause the power of the converter to be frequently adjusted, temporarily improving the current-carrying capacity of the key device IGBT has become a problem to be solved.

[0003] At present, the solutions to improve the current-carrying capacity of IGBT mainly include the following aspects. First, multiple IGBTs are connected in parallel to realize the improvement of the current-carrying capacity of the converter valve. This method adjusts the gate drive signal or increases the buffer filter device under the premise of realizing device current sharing, and connects a corresponding number of IGBT devices according to the current-carrying capacity; second, improve the heat conduction (heat dissipation capacity) efficiency to reduce the junction temperature, allowing IGBT to operate safely at a higher current, thereby improving the current-carrying capacity of the IGBT device; third, introduce wide bandgap semiconductor devices such as SiC, which can realize the improvement of the current-carrying capacity of the converter valve by using the higher current density of silicon carbide devices in high-frequency and high-temperature scenes.

[0004] The above three schemes can improve the current-carrying capacity of the power device to some extent, but still have some defects, such as precise current sharing control for multiple IGBTs, parasitic parameter difference easy to cause high-frequency oscillation, and nonlinear rise of expansion cost; the optimization of heat dissipation is limited by material cost and physical limit, and cannot break through the upper limit of current density; the wide bandgap device fusion faces the problems of high cost of SiC and time sequence coordination of mixed switches. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a network configuration converter overload capacity improvement method and driving circuit based on valve machine joint control, which links the network configuration converter control in an overload scenario to the current-carrying capacity of an IGBT power device.

[0006] Term explanation:

[0007] IGBT (Insulated Gate Bipolar Transistor), an insulated gate bipolar transistor, is a composite full-control voltage-driven power semiconductor device composed of a BJT (bipolar transistor) and a MOSFET (insulated gate field effect transistor), which has both the high input impedance of a MOSFET and the low on-state voltage drop of a BTJ.

[0008] At present, as the core switching device of a network configuration converter, the current-carrying capacity of an IGBT directly determines the upper limit of the instantaneous power output of the device. Taking the case of a sudden drop in grid frequency as an example, if the network configuration converter needs to output 1.5 times the rated power for a short time, the IGBT needs to withstand 2 times or even multiple times the rated current in a short time. Therefore, in the scenarios of high fluctuation load, weak grid operation, multi-machine parallel operation and extreme environment, which cause frequent power regulation of the converter, temporarily improving the current-carrying capacity of the IGBT, the key device of the converter, plays a crucial role in improving the overload capacity of the network configuration converter.

[0009] The reason why there is a close relationship between the IGBT device level and the network configuration system level is that this relationship is reflected in the fact that the power loss of the IGBT directly affects the junction temperature T j , which restricts the overall performance and reliability of the entire network configuration system. By changing the parameters at the device level, such as reducing the switching frequency f sw and improving the gate drive voltage V ge , the application can effectively reduce the junction temperature and thus have a beneficial effect on the network configuration system. The following specifically analyzes and describes the losses at the device level.

[0010] As a high-efficiency power switching device, IGBT is widely used in fields such as frequency converters, electric vehicle drive systems and renewable energy inverters. However, IGBT generates significant power loss during operation, leading to thermal stress and device aging. The total power loss of IGBT is mainly divided into switching loss and conduction loss. These losses directly affect the junction temperature of the device, thus restricting the overall performance of the system.

[0011] Traditional methods manage heat through passive cooling (such as air cooling or water cooling), but cannot dynamically respond to load changes. This invention proposes an active thermal control strategy that optimizes switching losses and conduction losses in real time by adjusting the switching frequency and gate drive voltage, respectively, to achieve more precise thermal management.

[0012] Total power loss of IGBT ( P total It can be decomposed into switching losses ( P sw ) and on-state loss ( P cond The two most important components are switching loss and conduction loss. Switching loss is the transient loss generated by the IGBT during turn-on and turn-off. It mainly originates from the charge storage effect inside the device and the charging / discharging process of parasitic capacitance. Switching loss is closely related to the switching frequency, load current, and DC bus voltage. In high-frequency applications, switching loss often accounts for a large proportion of the total loss. Conduction loss, on the other hand, is the steady-state loss generated by the IGBT in the on state. It is mainly composed of saturation voltage drop (…). V ce ) and conduction current ( I t The ohmic losses caused by the switching voltage (IGBT) constitute the total power loss. On-state losses are related to the duty cycle and gate drive voltage, and are often more significant in low-frequency or high-load applications. In addition, the total IGBT losses may also include smaller reverse recovery losses and drive losses, but these are usually included in the switching losses. Therefore, the total power loss can be expressed as:

[0013] P total =P sw +P cond

[0014] Switching losses include turn-on losses ( E on ) and shutdown loss ( E off Energy values ​​are usually obtained directly from datasheets, and average switching losses can be calculated as follows:

[0015] P sw =( E on + E off )× f sw

[0016] In the formula, E on This represents the energy loss during a single activation. E off This represents the energy loss during a single shutdown. f swRepresentative switching frequency.

[0017] On-state loss P cond The power loss of IGBT during conduction (i.e. when the gate drive signal is high), mainly due to the saturation voltage drop between the collector and the emitter V ce The product of the current flowing through the IGBT power device I c , P cond Can be calculated as:

[0018] P cond = V ce × I t

[0019] In the formula, V ce It is not a constant value, at different gate drive voltages, with I c A certain nonlinear relationship, for example, FF50R12RT4 produced by Infineon, V ce With I c The relationship shown in Figure 1 , can be modeled as:

[0020] V ce = V ce0 + r ce· I t

[0021] In the formula, V ce0 Represent the threshold voltage, the typical value is 0.8-1.2V, often affected by V ge ; r ce Represent the equivalent on-resistance, the typical value is a few mΩ, often affected by temperature T j , V ge Therefore, combined with P cond Calculation formula and V ce Calculation formula, can be written as:

[0022]

[0023] Total loss P total It can be written as:

[0024]

[0025] The above formula shows that reducing the switching frequency... f sw This can effectively reduce switching losses, thereby reducing total losses. Simultaneously, with increasing switching frequency... f sw The reduction in the number of turn-on and turn-off cycles, on the same time scale, will increase the proportion of on-state time, meaning that the proportion of on-state loss in total loss will increase to some extent. Meanwhile, in Figure 1 In this process, by appropriately increasing the gate drive voltage V ge (For clarity, V is used in the diagram) GE To replace V ge ), can effectively reduce V ce In improving V ge Meanwhile, the current flowing through the IGBT power device remains constant, thus effectively reducing the IGBT's conduction losses. This achieves a dual reduction in both switching and conduction losses of the IGBT device. These changes directly lead to a reduction in total losses, thereby lowering the IGBT's junction temperature. T j Lowering the junction temperature helps alleviate thermal stress, prevent device aging and failure, and improve the short-term current carrying capacity of the IGBT.

[0026] Traditional methods manage heat through passive cooling (such as air cooling or water cooling), but cannot dynamically respond to load changes. While existing technologies offer some thermal control and management methods at the power device level, they lack integrated control strategies for specific scenarios of grid-connected converters. This prevents coordinated control between the valve side (IGBT device level) and the machine side (system level), leading to a sharp rise in IGBT junction temperature under overload conditions and limiting the converter's instantaneous power output capability. Based on these problems, this invention proposes a "valve-machine coordinated control" strategy. This method combines IGBT device-level thermal control (valve-side control) with the system-level power response of the grid-connected converter (machine-side control) to achieve dynamic thermal management and improved overload capacity. Specifically, by improving… V ge Reduce conduction losses and reduce f sw Reduce switching losses while ensuring stable system voltage / frequency support, and avoid device aging and system failure caused by overload.

[0027] The technical solutions of the present application are as follows:

[0028] A network construction converter overload capacity improvement method based on valve machine joint control, the steps are as follows:

[0029] (1) Collecting various electrical parameters in the network construction converter by using voltage and current sensors, realizing control of the network construction converter under normal working conditions, and inputting the current flowing through the IGBT I t as a characterization of the junction temperature of the reaction device; T j ;

[0030] (2) In order to avoid the adverse effects of current glitches and fluctuations on control, set the opening current threshold I up and the closing current threshold I down in the current hysteresis comparator, and input the reference current I ref in the network construction converter as a signal quantity of active heat control;

[0031] (3) When the network construction converter operates in an overload condition, the power device IGBT needs to withstand a larger current, and the reference current I ref exceeds the opening current threshold I up set by the hysteresis control, and the active heat control is started, which realizes the double reduction of switching loss and on-state loss by reducing the system switching frequency f sw and improving the gate drive voltage V ge , thereby reducing the device junction temperature T j , supporting the power device IGBT to pass through a larger current in a short time, and improving the overload capacity of the network construction converter;

[0032] (4) When the network construction converter returns to the normal condition, I ref and is lower than the closing current threshold I down set by the hysteresis control, the active heat control is ended, and the switching frequency f sw and the gate drive voltage V ge return to the normal state.

[0033] According to the present application, preferably, in step (1), the electrical parameters include three-phase voltage at the outlet of the converter U t and three-phase current at the outlet of the converterI t , i.e. the current flowing through the power device IGBT and the PCC point voltage U s .

[0034] According to the present application, preferably, in step (2), the turn-on current threshold I up and the turn-off current threshold I down The relationship is as follows:

[0035]

[0036] In the formula: I N I denotes the rated current passing through the device under normal working conditions; α K denotes the upper threshold coefficient of the current hysteresis loop; β K denotes the lower threshold coefficient of the current hysteresis loop, when the inner loop control reference current I ref is greater than I up , the active thermal control is turned on; when the inner loop control reference current I ref is less than I down , the active thermal control is turned off.

[0037] According to the present application, preferably, in step (3), the gate drive voltage V ge is switched from 15V to 20V.

[0038] A drive circuit applied to a network converter overload capacity improvement method based on valve machine joint control, comprising a voltage conversion circuit, a voltage switching circuit and a gate drive circuit, the voltage switching circuit and the gate drive circuit are both connected with an upper computer, controlled by the upper computer, and the gate drive circuit output end is connected with an IGBT converter valve;

[0039] The voltage conversion circuit is used for receiving input 15V DC voltage, converting the 15V voltage input by the switching power supply into 15V, 20V and -4V three-level DC voltages, respectively used for device turn-on and turn-off.

[0040] The voltage switching circuit is used for receiving 15V and 20V DC voltages output by the voltage conversion circuit, using the given 0 / 5V control signal output by the upper computer to realize the active switching of the turn-on voltage 15 / 20V.

[0041] The gate drive circuit receives -4V off voltage output by the voltage conversion circuit and 15 / 20V on voltage output by the voltage switching circuit, and simultaneously receives the PWM signal given by the upper computer, and outputs the IGBT drive signal with the drive voltage amplitude being switchable at any time.

[0042] The upper computer is used for sending the PWM signal and 0 / 5V voltage switching signal, and the upper computer gives the signal to the gate drive circuit to drive the IGBT device to turn on and off.

[0043] According to the application, the voltage conversion circuit adopts the DC-DC isolation circuit, the voltage switching circuit adopts the LTC4416 chip, and the gate drive circuit adopts the SLM343 drive chip.

[0044] According to the application, the output mode switching relationship of the voltage switching circuit is:

[0045]

[0046] Wherein, V normal The normal drive voltage required for driving the IGBT is generally 15V under normal circumstances, V limit The maximum drive voltage for driving the IGBT is generally determined according to the Datasheet in the technical manual, and for example, the maximum drive voltage of the IGBT FF5012RT4 is 20V. V limit Generally, 20V is selected, S 1 and S 2 are respectively V normal and V limit The output states of the two are 0 or 1 according to the limiting condition in the above formula.

[0047] The application proposes a new concept of "valve-machine joint control", which links the overcurrent capability of the power electronic power device and the overload performance of the network type converter, and builds a scheme for realizing the performance improvement of the network type converter by adjusting the amplitude V ge , switching frequency f sw of the power device drive signal.

[0048] The application has the advantages that:

[0049] The application is based on the active heat control theory of the power device: the amplitude of the IGBT gate drive signal is improved to reduce the voltage drop between the collector and the emitter V ceThe active gate drive technology is applied to the on-state stage of the IGBT, and the switching loss of the power device can be greatly reduced by combining the scheme of reducing the switching frequency, the running state of the device is judged according to the junction temperature monitored by the IGBT device, and the gate drive voltage of the device is adjusted V ge , the switching frequency is reduced f sw The overcurrent capability is improved, and finally the overload capability of the network type converter is improved. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 The graph of the saturation voltage drop of the active gate drive voltage and the current of the IGBT power device is provided for the application;

[0051] Figure 2 The valve machine joint control block diagram of the application is provided for the application;

[0052] Figure 3 The method flow chart of the application is provided for the application;

[0053] Figure 4 The device life comparison chart of the active heat control device with / without the application example 1 is provided for the application;

[0054] Figure 5 The current hysteresis loop chart of the application example 1 is provided for the application;

[0055] Figure 6 The IGBT active heat control current hysteresis characteristic analysis of the application example 1 is provided for the application;

[0056] Figure 7 The SLM343 drive chip structure chart of the application example 1 is provided for the application;

[0057] Figure 8 The LTC4416 chip switching principle diagram of the application example 1 is provided for the application;

[0058] Figure 9 The overall principle diagram of the LTC4416 chip drive circuit of the application example 1 is provided for the application;

[0059] Figure 10 The switching voltage waveform chart of the application example 1 is provided for the application. DETAILED DESCRIPTION

[0060] The application will be further described below through examples and in conjunction with the drawings, but is not limited thereto.

[0061] Example 1:

[0062] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0063] The present embodiment provides a method for improving overload capacity of network-constructing converter based on valve machine joint control, as shown in Figure 3 , the steps are as follows:

[0064] (1) Collecting various electrical parameters in the network-constructing converter by using voltage and current sensors, including three-phase voltage at the outlet of the converter U t , three-phase current at the outlet of the converter I t , current flowing through the power device IGBT and PCC point voltage U s , realizing control under normal working condition of the network-constructing converter, and taking the current flowing through the IGBT I t as a characteristic quantity of the device junction temperature T j ;

[0065] (2) In order to avoid the adverse effects of current glitches and fluctuations on control, set the opening current threshold I up and the closing current threshold I down in the current hysteresis comparator, and input the reference current in the network-constructing converter I ref as the signal quantity of active thermal control into the current hysteresis comparator;

[0066] Suppose that in the network-constructing converter, under normal working condition, the converter operates at rated power, and the rated current can be defined as I N , at this time, the current flowing through the power device IGBT is recorded as I t , at this time, the current reference value of the control inner loop is I ref , after considering glitches or slight amplitude fluctuations, the real-time interval of the IGBT control inner loop current I ref is 0.95 I ref ~ 1.05 I ref(Considering a 5% fluctuation range between the upper and lower limits), the upper limit of the current hysteresis is set to... I up The lower limit of the current hysteresis is set to I down .when I ref Greater than I up When active thermal control is activated; when I ref Less than I down At that time, active thermal control is turned off. Assume:

[0067]

[0068] In the formula: α This represents the upper threshold coefficient for current hysteresis. According to specific engineering standards and technical specifications, the converter is generally required to operate continuously at 110% of its rated current; therefore, in this embodiment... α Take 1.1; β This represents the lower threshold coefficient of the current hysteresis loop. According to the hysteresis control principle of the control system, the recovery threshold must be lower than the start-up threshold to avoid oscillation. Classical control theory suggests that the hysteresis bandwidth should be 5-20% of the set value; in this embodiment... beta take At 0.95, the constraints in the above formula are satisfied. This design is to avoid oscillations caused by frequent switching near the threshold, ensuring both control stability and the smooth exit of the thermal control state.

[0069] If the upper threshold of the hysteresis current is set too high, it will reduce the sensitivity of the active thermal control activation, decrease the device's heat dissipation time, and in severe cases, cause thermal breakdown of the device. If the upper threshold of the hysteresis current is set too low, it may cause the active thermal control to be falsely activated. If the lower threshold of the hysteresis current is set too high, it may cause the active thermal control to be turned off while the device is still in overcurrent operation, which will cause thermal breakdown and damage to the device over a long period of time. If the lower threshold of the hysteresis current is set too low, it may reduce the sensitivity of the active thermal control shutdown, which will reduce the device's thermal breakdown and damage over a long period of time. f sw and high V ge Under certain driving voltage conditions, power quality deterioration and damage to the IGBT gate oxide layer can occur. The current hysteresis in this embodiment is as follows: Figure 5 As shown, Figure 6 The diagram shows the hysteresis characteristic analysis of the IGBT active thermal control current, simulating the start-up and shutdown of active thermal control when the current changes.

[0070] (3) When the grid-type converter operates under overload conditions, the power devices IGBTs need to withstand a larger current, and the reference current is required.I ref Exceeding the turn-on current threshold set by the hysteresis control I up , starting active thermal control, which reduces the system switching frequency f sw and raises the gate drive voltage V ge , achieving double reduction of switching loss and on-state loss, thereby reducing the device junction temperature T j , supporting the power device IGBT to pass a larger current in a short time, improving the overload capacity of the network converter;

[0071] (4) When the network converter returns to normal operating conditions, I ref Lower than the turn-off current threshold set by the hysteresis control I down , end active thermal control, restore switching frequency f sw and gate drive voltage V ge to normal state.

[0072] Figure 2 The overall control block diagram of the valve machine joint control proposed in the embodiment is shown, and the control block diagram will be analyzed and described in detail below.

[0073] The hardware basis of the system is the main circuit of the network converter, including the DC side voltage source U dc , IGBT converter valve array, filter and grid link, U t representing the three-phase voltage at the outlet of the converter; I t representing the three-phase current at the outlet of the converter, i.e. the current flowing through the power device IGBT; L f representing the filter inductance; U s representing the PCC point voltage; Z g representing the grid-side impedance; U g representing the grid-side voltage. By real-time acquisition of the current flowing through the IGBT device I t , the basic data for subsequent valve machine joint control is provided. This design changes the power device from a passive protection object to an active sensing unit.

[0074] The system uses the classic abc / dqCoordinate transformation technology converts three-phase time-domain signals into DC signals for easier control. Voltage U s and current I t After coordinate transformation, power calculation is performed in a synchronously rotating coordinate system to obtain the active power. P g and reactive power Q g This step not only provides feedback signals for the upper-level power control, but more importantly, it provides power reference data for the active thermal control module.

[0075] As a core feature of grid-type converters, the system drives frequency regulation through active power deviation. P - f (Sag), to achieve synchronous control with the power grid. The synchronous control link uses a transfer function. H syn ( s Process the power deviation signal and compare it with the nominal frequency. omega n The superposition produces the system phase angle theta g Reactive power control is achieved through the transfer function. H q ( s Adjust voltage amplitude command U t The design parameters of these two control loops directly affect the overcurrent characteristics of the system. Because grid-connected converters actively support the voltage frequency during grid disturbances, this can lead to excessive output current. (Based on voltage amplitude commands...) U t and PCC point voltage U s Voltage outer loop control is performed, and after passing through the current limiting stage, the voltage is generated. I ref , and the current sensor collected I t After calculating the deviation, inner-loop control is performed to generate the modulation signal. S g After being sent to the drive module, a gate drive signal is generated to drive each IGBT device to achieve overall closed-loop control.

[0076] The most direct consequence of overcurrent is that the IGBT, a power device that withstands high current, will overheat in a short period of time. After the junction temperature rises to a certain level, it will cause thermal breakdown of the IGBT, the core switching device in the grid converter, ultimately leading to the collapse of the grid converter system.

[0077] Therefore, the embodiment proposes a valve machine joint control based network construction converter overload capacity improvement method, wherein the active thermal control module is an important part of the entire valve machine joint control system. Since the network construction converter is in the normal condition and then in the overload condition, the reference current in the control is first increased to a certain value according to the actual overcurrent requirement I ref , I t In order to follow the change of I ref , the stability of closed-loop control is realized after the PI regulator, therefore, the active thermal control module needs to use the reference current I ref as the input, and the active thermal control is realized after the current hysteresis comparator. I ref Specifically, the reference current value after the change is calculated, which can be expressed as: abc / dq

[0078]

[0079] I dref and I qref are the field current reference and the line current reference generated by the outer loop control respectively. d q

[0080] The specific scheme of the active thermal control is to reduce the switching frequency f sw and improve the gate drive voltage V ge , which simultaneously reduces the switching loss and on-state loss of the IGBT. The loss reduction means that the junction temperature T j of the IGBT will be reduced, and the IGBT can withstand longer overload current, which reduces the risk of thermal breakdown and improves the reliability of the device in the overload condition of the network construction converter.

[0081] The entire valve machine joint control system realizes the deep integration of the device driving stage, the system control stage and the thermal management: in the normal condition, the system operates according to the standard control logic of the network construction converter; when the overcurrent risk or thermal stress is detected, the active thermal control module immediately intervenes, and realizes the active thermal control by dynamically adjusting the device gate drive voltage and reducing the system level switching frequency. This design concept changes the traditional "protection after failure" to "prevention before risk", which significantly improves the reliability and continuous power supply capacity of the system, and is especially suitable for the application scenarios of the network construction converter in microgrid, new energy access and other high requirements for power supply continuity.​​​

[0082] This device-level optimization has positive impacts on grid-forming system level in multiple aspects. First, reducing junction temperature allows the converter to output higher power temporarily under high fluctuation load or weak grid environment, enhancing the system's fast response characteristics, such as providing active support when the grid frequency drops, maintaining voltage / frequency stability, and avoiding system collapse. Second, in multi-machine parallel or extreme environmental scenarios, device-level thermal management improves the overall system reliability and efficiency, reduces the risk of downtime due to overload, and extends the life of the equipment. Figure 4 The power device thermal characteristics of grid-forming converters under abnormal conditions such as faults or frequency drops are compared. When the system experiences a power surge, the temperature-time curves of the power device are given under two conditions: with active thermal control turned on and without active thermal control. According to the Figure 4 It can be seen that, with active thermal control turned on, the IGBT device can withstand higher current for a longer period of time before reaching the thermal breakdown temperature limit, so turning on active thermal control can significantly improve the life of the device. In addition, the valve-machine co-control strategy ensures the coordination of device-level optimization and system-level control (such as PCC power regulation), achieving seamless integration from the micro (device thermal balance) to the macro (grid support), thereby improving the adaptability and robustness of the grid-forming converter. In summary, through device-level loss reduction, not only is the junction temperature directly controlled, but also the system's instantaneous power limit and stability are indirectly improved, solving the limitations of traditional passive cooling methods.

[0083] In the valve-machine co-control strategy, to avoid the problem of frequent false starts of thermal control caused by glitches, oscillations, and many other factors, current hysteresis control is used, and the principle of current hysteresis control is as follows:

[0084] The core principle of current hysteresis control is state memory and double threshold judgment: the system uses two different thresholds, and the controller "remembers" the current state, and only changes the state when the current crosses the threshold in the corresponding direction. This design creates a "safe interval" between the two thresholds, i.e. the hysteresis width, when the reference current I ref When the current fluctuates within this interval, the control state remains unchanged, effectively avoiding the problem of frequent switching caused by noise or small fluctuations near the threshold in single-threshold control.

[0085] The main advantages of hysteresis control can be summarized as follows: First, it has strong anti-interference capability, preventing false triggering when the noise amplitude is less than the hysteresis width. Second, it avoids frequent switching, reducing controller fatigue and system oscillation. Third, current hysteresis control is simple to implement, requiring only comparison operations, resulting in low computational load and fast response. Especially in IGBT thermal control applications, hysteresis control can find the optimal balance between protection safety and system efficiency: a high threshold ensures protection is activated only when necessary, while a low threshold ensures protection is deactivated promptly when the current returns to normal. This "intelligent switch with memory" characteristic makes it an ideal choice for power device protection.

[0086] In the design of the "valve-machine joint control" strategy, it is particularly important to ensure that the drive voltage can freely switch with the 0 / 5V control signal output by the host computer controller. In order to realize the important function of active switching of drive voltage and to adjust the conduction loss, this embodiment designs a drive circuit that can actively switch drive voltage, including a voltage conversion circuit, a voltage switching circuit and a gate drive circuit. Both the voltage switching circuit and the gate drive circuit are connected to the host computer and controlled by the host computer. The output terminal of the gate drive circuit is connected to the IGBT commutation valve.

[0087] The voltage conversion circuit is used to receive the input 15V DC voltage and convert the 15V input voltage of the switching power supply into three DC voltage levels: 15V, 20V, and -4V, which are used for turning on and off the devices, respectively.

[0088] The voltage switching circuit is used to receive the 15V and 20V DC voltages output by the voltage conversion circuit, and to actively switch the turn-on voltage to 15V / 20V by using the given 0 / 5V control signal output by the host computer.

[0089] The gate drive circuit is used to receive the -4V turn-off voltage output by the voltage conversion circuit and the 15 / 20V turn-on voltage output by the voltage switching circuit. At the same time, it receives the PWM signal given by the host computer and outputs an IGBT drive signal whose drive voltage amplitude can be switched at any time.

[0090] The host computer is used to send PWM signals and 0 / 5V voltage switching signals. The host computer sends signals to the gate drive circuit to drive the IGBT device to turn on and off.

[0091] The voltage conversion circuit uses a DC-DC isolation circuit, the voltage switching circuit uses an LTC4416 chip, and the gate drive circuit uses an SLM343 driver chip.

[0092] Figure 7This is the pinout diagram of the SLM343 chip. The SLM343 is an optocoupler-compatible single-channel isolated gate driver chip specifically designed to drive IGBT and MOSFET power devices. It features a peak output capability of 4.0A source current and 6.0A sink current, as well as a 5kV RMS enhanced isolation level. In terms of pin configuration, pins 1 and 3 are typically connected to the PWM control signal via current-limiting resistors to turn the driver on or off. Pin 6 is connected to the VCC positive power supply (14 to 40V), providing positive operating power to the IGBT output side. Pin 4 is connected to the VEE negative power supply, providing negative operating power to the output side. Pin 5 (VOUT) is the gate drive output terminal, directly connected to the gate of the IGBT or MOSFET. Pin 2 is the enable terminal and is typically left floating. This chip achieves electrical isolation between the input control circuit and the high-voltage power circuit through an isolation gate, exhibiting excellent performance such as a maximum propagation delay of 140ns and a common-mode transient immunity of 150kV / μs. It is widely used in power electronic devices such as motor drives, solar inverters, and industrial power supplies, offering higher reliability and performance compared to traditional optocoupler drivers.

[0093] Figure 8 This is a schematic diagram of a voltage switching circuit, used for intelligent switching and output between 15V and 20V power supplies.

[0094] based on Figure 7 and Figure 8 The schematic diagram of the driving circuit in this embodiment is as follows: Figure 9 As shown, Figure 9 The IGBT driver circuit system was demonstrated, employing a multi-channel isolated power supply and isolated driver design. The circuit first converts the input DC 15V into multiple isolated power supplies (15V, 20V, and -4V) through multiple isolated power supply modules. Then, an LTC4416 dual power supply switching chip automatically selects between 15V and 20V. The host computer controller not only generates two PWM control signals (PWMA and PWMB) to drive two SLM343 driver chips, but also simultaneously sends 0 / 5V control signals to the LTC4416 to control the priority or enable state of power switching, achieving active management of the power supply strategy. Each SLM343 transmits the low-voltage PWM signal from the control side to the power side via opto-isolation, amplifies it into a gate signal with sufficient drive capability, and directly connects it to the IGBT gate, achieving precise switching control of the IGBT. The entire circuit effectively isolates the control circuit from the high-voltage power circuit through multiple isolation designs (power isolation + upper and lower bridge arm isolation), preventing high-voltage interference on the power side from damaging the control side. At the same time, the host computer can actively manage the power switching strategy through control signals, and the dual-path drive design improves the reliability and intelligence of the system. Figure 10The experimental waveform diagram of the self-switching function of the driving circuit designed for this embodiment is shown in FIG. 6. At any time, the control signal is changed (the switching from 0V to 5V is shown in the figure), and the gate driving voltage is switched from 15V to 20V, which proves the feasibility of the driving scheme.

Claims

1. A method for improving the overload capacity of a grid-connected converter based on valve-mechanism inter-control, characterized in that, The steps are as follows: (1) Use voltage and current sensors to collect electrical parameters in the grid-type converter to realize the control of the grid-type converter under normal operating conditions, and control the current flowing through the IGBT. I t As the junction temperature of the reaction device T j The representation quantity; (2) Set the turn-on current threshold in the current hysteresis comparator I up and turn-off current threshold I down The reference current in the grid converter I ref As a signal for active thermal control, it is input to the current hysteresis comparator; Turn-on current threshold I up and turn-off current threshold I down The relationship is as follows: In the formula: I N This indicates the rated current that the device passes under normal operating conditions; α This represents the upper threshold coefficient of the current hysteresis loop. β This represents the lower threshold coefficient of the current hysteresis loop, when the inner loop control reference current... I ref Greater than I up When this happens, active thermal control is activated; When the inner loop control reference current I ref Less than I down When this happens, active thermal control is turned off; (3) When the grid-type converter operates under overload conditions, the power devices IGBTs need to withstand a larger current, and the reference current is required. I ref Exceeding the threshold current set by the hysteresis control I up Active thermal control is activated, which reduces the system switching frequency. f sw and increase gate drive voltage V ge This achieves a dual reduction in switching losses and conduction losses, thereby lowering the device junction temperature. T j This allows the IGBT power device to carry a larger current in a short period of time, thereby improving the overload capacity of the grid converter. (4) After the grid-type converter returns to normal operating conditions, I ref Below the turn-off current threshold set by hysteresis control I down At that time, active thermal control ends and the switching frequency resumes. f sw With gate drive voltage V ge Return to normal state.

2. The method for improving the overload capacity of grid converters based on valve-mechanism inter-control as described in claim 1, characterized in that, In step (1), the electrical parameters include the three-phase voltage at the converter outlet. U t Three-phase current at converter outlet I t and PCC point voltage U s .

3. The method for improving the overload capacity of grid converters based on valve-mechanism inter-control as described in claim 1, characterized in that, In step (3), the gate drive voltage is increased. V ge This refers to switching from 15V to 20V.

4. A drive circuit applied to the method for improving the overload capacity of a grid converter based on valve-mechanism interlocking control as described in claim 1, characterized in that, It includes a voltage conversion circuit, a voltage switching circuit, and a gate drive circuit. Both the voltage switching circuit and the gate drive circuit are connected to a host computer and controlled by the host computer. The output of the gate drive circuit is connected to an IGBT commutation valve. The voltage conversion circuit is used to receive the input 15V DC voltage and convert the 15V input voltage of the switching power supply into three DC voltage levels: 15V, 20V, and -4V, which are used for turning on and off the devices, respectively. The voltage switching circuit is used to receive the 15V and 20V DC voltages output by the voltage conversion circuit, and to actively switch the turn-on voltage to 15V / 20V by using the given 0 / 5V control signal output by the host computer. The gate drive circuit is used to receive the -4V turn-off voltage output by the voltage conversion circuit and the 15 / 20V turn-on voltage output by the voltage switching circuit. At the same time, it receives the PWM signal given by the host computer and outputs an IGBT drive signal whose drive voltage amplitude can be switched at any time. The host computer is used to send PWM signals and 0 / 5V voltage switching signals. The host computer sends signals to the gate drive circuit to drive the IGBT device to turn on and off.

5. The drive circuit as described in claim 4, applied to the method for improving the overload capacity of a grid converter based on valve-mechanism interlocking control, is characterized in that... The voltage conversion circuit uses a DC-DC isolation circuit, the voltage switching circuit uses an LTC4416 chip, and the gate drive circuit uses an SLM343 driver chip.

6. The drive circuit as described in claim 5, applied to the method for improving the overload capacity of a grid converter based on valve-mechanism interlocking control, is characterized in that... The output mode switching relationship of the voltage switching circuit is as follows: in, V normal The normal drive voltage required to drive the IGBT is typically 15V. V limit This indicates the maximum driving voltage for the IGBT. S 1 and S 2 are respectively V normal and V limit According to the constraints in the above formula, the output state of cannot be 0 or 1 at the same time.

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