MOSFET thermal protection method based on current and time integration

Abstract

According to the MOSFET thermal protection method based on current and time integration, a group of current and time relations are obtained in an offline calibration mode; the working time of different segments can be realized by setting a plurality of counters, each counter is respectively mapped to different current intervals, the formula of the counter is J = summa 0Pdt = summa 0I2Rdt, and the counter is used as table look-up input to obtain a target sustainable working current; comparing the obtained target current with an actual working phase current, and if the actual current is greater than a sustainable working current value, progressively decreasing the torque according to a preset gradient until the torque is 0; if the actual current is smaller than the sustainable working current value, the torque is progressively increased according to the preset gradient until the torque is equal to the torque instruction. The method is simple and convenient to implement, avoids complex operation, reduces the load rate of the MCU execution cycle, does not need simulation, is completely completed through rack calibration data, is high in estimation precision, and effectively prevents the MOSFET from being damaged.

Description

Technical Field

[0001] The invention relates to the fields of MOSFET thermal protection and inverter thermal protection, and in particular to a MOSFET thermal protection method based on current and time integration. Background Art

[0002] Generally, the overheat protection of MOSFET mainly uses junction temperature estimation, which is estimated by calculating MOSFET loss and tau model. The main disadvantage is that the loss calculation is relatively complicated and many factors need to be considered, especially when combined with multiple modulation modes. If the loss calculation is inaccurate, the accuracy of junction temperature estimation will be greatly affected. In addition, the complexity of the algorithm will also increase the load rate of the MCU execution cycle, especially on some low-end MCUs, which makes it more difficult to implement. Summary of the invention

[0003] The object of the present invention is to provide a MOSFET thermal protection method based on current and time integration, comprising the following steps:

[0004] 1) Obtain a set of current and time relationships through offline calibration;

[0005] 2) For different working time segments, it can be achieved by setting multiple counters, each counter is mapped to a different current interval, and the counter formula is:

[0006] J represents the heat generated by the power P during the action time t, and I is the effective value of the phase current;

[0007] The counter is used as the table lookup input of step 1) to obtain the target sustainable working current;

[0008] 3) Compare the target current obtained in step 2) with the actual working phase current. If the actual current is greater than the sustainable working current value, the torque decreases according to the preset gradient until the torque is 0; if the actual current is less than the sustainable working current value, the torque increases according to the preset gradient until it is equal to the torque command.

[0009] Furthermore, several power levels are defined in step 1), namely, maximum torque (load shedding for 10 seconds), peak torque (load shedding for 30 seconds), short-time power (load shedding for 2 minutes), and rated power (load shedding for 60 minutes).

[0010] Furthermore, based on the above power ranges, the working current that meets the duration is calibrated and recorded in a two-dimensional array.

[0011] Furthermore, for the stall condition under peak torque, a correction factor may be added.

[0012] Compared with the prior art, the MOSFET thermal protection method based on current and time integration of the present invention has the following beneficial effects: 1) The implementation method is simple, avoiding complex calculations and reducing the load rate of the MCU execution cycle.

[0013] 2) No simulation is required, and it is completely completed by bench calibration data, with high estimation accuracy, which effectively prevents MOSFET damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic flow chart of the method of the present invention. DETAILED DESCRIPTION

[0015] See also Figure 1 , a MOSFET thermal protection method based on current and time integration, comprising the following steps:

[0016] 1) Obtain a set of current and time relationships through offline calibration. For air-cooled systems, the junction temperature of the MOS tube is mainly affected by the rotation speed and initial temperature. Define several power levels, namely maximum torque (duration of 10 seconds to reduce load), peak torque (duration of 30s to reduce load), short-time power (duration of 2 minutes to reduce load), and rated power (duration of 60 minutes to reduce load). If the duration of different powers is linear, the power levels can be divided more finely. According to the above power segments, calibrate the working current that meets the duration and record it in a two-dimensional array. For the stall condition under peak torque, because the output current needs to be smaller at this time, a correction factor can be added.

[0017] 2) For the working time of different segments, it can be achieved by setting multiple counters, each counter is mapped to a different current interval. For example, when the actual current is between the short-time current and the peak current, the counters of the short-time current, the peak current and the maximum current need to be incremented. The step size of each counter can also be set separately. Although the design logic is clear, it requires more counters, the code implementation is more complicated, and it is easy to make mistakes. A more preferred method is to provide a simple counter.

[0018] For pure resistance R, power P = I 2 R.

[0019] The current I is the effective value of the phase current.

[0020]

[0021] J represents the heat generated by the power P within the time t. The formula actually integrates the power P, and the essence of integration is accumulation, so the formula can be equivalent to a counter. The coefficient in front is the square of the current, which is equivalent to dynamically adjusting the step size of the counter. This method is easier to implement. Use the counter as the table input of step 1) to obtain the target sustainable working current.

[0022] 3) Compare the target current obtained in step 2) with the actual working phase current. If the actual current is greater than the sustainable working current value, the torque decreases according to the preset gradient until the torque is 0; if the actual current is less than the sustainable working current value, the torque increases according to the preset gradient until it is equal to the torque command.

[0023] The present invention estimates the sustainable target current under various working conditions by integrating the current flowing through the MOSFET and the square of the action time, and compares it with the actual current. When the actual current is larger, the load is reduced, otherwise it is restored. The method is very simple to implement and is completely completed by calibration, avoiding problems such as complex loss calculation and insufficient MCU computing power, and plays a good protective role on the MOSFET.

[0024] Compared with the prior art, it has the following advantages:

[0025] 1) The implementation method is simple, avoiding complex calculations and reducing the load rate of the MCU execution cycle.

[0026] 2) No simulation is required, and it is completely completed by bench calibration data, with high estimation accuracy, which effectively prevents MOSFET damage.

[0027] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0028] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A MOSFET thermal protection method based on current and time integration, characterized in that: The following steps are involved: 1) Obtain a set of current and time relationships through offline calibration; 2) For different working time segments, it can be achieved by setting multiple counters, each counter is mapped to a different current interval, and the counter formula is: J represents the heat generated by the power P during the action time t, and I is the effective value of the phase current; The counter is used as the table lookup input of step 1) to obtain the target sustainable working current; 3) Compare the target current obtained in step 2) with the actual working phase current. If the actual current is greater than the sustainable working current value, the torque is decreased according to a preset gradient until the torque is 0; If the actual current is less than the sustainable working current value, the torque increases according to the preset gradient until it is equal to the torque command.

2. The MOSFET thermal protection method based on current and time integration according to claim 1, characterized in that: In step 1), several power levels are defined, namely, maximum torque (10 seconds load reduction), peak torque (30 seconds load reduction), short-time power (2 minutes load reduction), and rated power (60 minutes load reduction).

3. The MOSFET thermal protection method based on current and time integration according to claim 1, characterized in that: According to the above power ranges, the working current that meets the duration is calibrated and recorded in a two-dimensional array.

4. The MOSFET thermal protection method based on current and time integration according to claim 1, characterized in that: For stall conditions at peak torque, a correction factor can be added.

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