An inverter circuit control method for realizing adaptive dead time optimization

Abstract

The present application discloses an inverter circuit control method for realizing adaptive dead time optimization, which relates to the field of inverter circuits. The method takes into account that the switching speed of a power tube is affected by the size of the load, and determines that the modulation wave of one power tube in a bridge arm is a reference waveform according to the direction of the load current, and the modulation wave of another power tube is a waveform after adjusting the offset voltage of the reference waveform, and the offset voltage is related to the size of the load current; thereby, the modulation waves of the upper tube and the lower tube matching the load current can be generated and then the drive signal can be generated, so that the dead time can be accurately adjusted according to the load current, the diode freewheeling loss and the output capacitor loss can be effectively reduced, and the waveform quality of the inverter output current can be improved, and no additional hardware structure is required, which is easy to implement and particularly outstanding in high switching frequency and high power applications.

Description

Technical Field

[0001] The present application relates to the field of inverters, and in particular to an inverter circuit control method for realizing adaptive dead time optimization. Background Art

[0002] Inverter circuits are widely used in the field of motor control. The typical circuit structure of a three-phase bridge inverter driving a three-phase load ABC is as follows: Figure 1 As shown, there are multiple parallel bridge arms in the inverter circuit, and each bridge arm has two power tubes, respectively called the upper tube and the lower tube. The inverter circuit needs to control the switching of each power tube during operation. In order to prevent the upper tube and the lower tube of the same bridge arm from being turned on at the same time (called bridge arm direct-on), when controlling the switching of each power tube on and off, there will be a period of time when both the upper tube and the lower tube of the same bridge arm are turned off, which is called the dead time. During the dead time, both the upper tube and the lower tube of the same bridge arm are turned off, but the current is not immediately cut off due to the resistive and inductive load, but is continued through the reverse-connected freewheeling diodes at both ends of the power tube, which causes output voltage loss, known as the dead time effect, affecting the performance of the inverter circuit.

[0003] At present, most of the dead time is a fixed time set by experience. Whether the dead time is set reasonably seriously affects the performance of the inverter circuit. Moreover, with the advancement of power semiconductor technology, SiC MOSFET with high switching frequency and high power level has been more and more widely used. Higher switching frequency can improve the power density of the inverter and reduce the output current distortion. However, since the switching speed of SiC MOSFET varies with the load size, when it is applied to the inverter, the actual switching speed of SiC MOSFET varies within a fundamental wave cycle, especially the turn-off speed varies, which will aggravate the dead time effect and affect the performance of the inverter circuit: when the dead time is set longer, when the turn-off time of SiC MOSFET becomes shorter with the load, there will be an extra dead time, which will increase the diode freewheeling loss; when the dead time is set shorter, when the turn-off time of SiC MOSFET becomes longer with the load, the output capacitor loss will increase due to the short dead time, and it may even cause the bridge arm to pass through and damage the power tube. Summary of the invention

[0004] In view of the above problems and technical requirements, the present application proposes an inverter circuit control method for realizing adaptive dead time optimization. The technical solution of the present application is as follows:

[0005] An inverter circuit control method for realizing adaptive dead time optimization, the inverter circuit control method comprising for any bridge arm in the inverter circuit:

[0006] Collect the magnitude and direction of the load current flowing through the load connected to the bridge arm, with the direction of the load current flowing from the midpoint of the bridge arm to the load as the positive direction;

[0007] According to the direction of the load current, the modulation wave of one power tube in the bridge arm is determined to be the reference waveform, and the modulation wave of the other power tube is the waveform after the reference waveform is adjusted with an offset voltage, and the offset voltage is related to the magnitude of the load current;

[0008] An upper tube driving signal is generated based on the carrier and the modulation wave of the upper tube, and a lower tube driving signal is generated based on the carrier and the modulation wave of the lower tube. The upper tube of the bridge arm is controlled according to the upper tube driving signal, and the lower tube of the bridge arm is controlled according to the lower tube driving signal.

[0009] A further technical solution is to determine, according to the direction of the load current, that the modulation wave of one power tube in the bridge arm is the reference waveform, and the modulation wave of the other power tube is the waveform after adjusting the offset voltage of the reference waveform, including:

[0010] When the load current is in the positive direction, the modulation wave of the upper tube in the bridge arm is determined to be the reference waveform, and the modulation wave of the lower tube is the waveform after adding an offset voltage to the reference waveform;

[0011] When the load current is in the negative direction, the modulation wave of the lower tube in the bridge arm is determined to be the reference waveform, and the modulation wave of the upper tube is the waveform obtained by reducing the offset voltage from the reference waveform.

[0012] A further technical solution is that the method for determining the offset voltage includes:

[0013] Determine the instantaneous value of the dead time T based on the load current d ;

[0014] Determine the offset voltage △u=T d *k, k is the slope of the carrier.

[0015] A further technical solution is to determine the instantaneous value of the dead time T based on the load current. d include:

[0016] According to the on-time curve of the power tube used in the inverter circuit, determine the on-time T corresponding to the load current. on , the turn-on time curve is a pre-fitted curve and reflects the change of the turn-on time of the power tube with the load current;

[0017] According to the off-time curve of the power tube used in the inverter circuit, determine the off-time T corresponding to the load current. off , the turn-off time curve is a pre-fitted curve and reflects the change of the turn-off time of the power tube with the load current;

[0018] According to the opening time T on and the off time T off Determine the instantaneous value of the dead time T d .

[0019] Its further technical solution is to, according to the opening time T on and the off time T off Determine the instantaneous value of the dead time T d Including determining T d =n*(T off -T on ), n is the margin parameter.

[0020] A further technical solution is that the method for pre-fitting the opening time curve and the closing time curve includes:

[0021] Performing a double pulse test on the power tube used in the inverter circuit to obtain test data, the test data including the on-time and off-time of the power tube under load currents of different magnitudes;

[0022] Based on the test data, a quadratic function is fitted to the relationship between the turn-on time of the power tube and the size of the load current to obtain a turn-on time curve. Based on the test data, an exponential function is fitted to the relationship between the turn-off time of the power tube and the size of the load current to obtain a turn-off time curve.

[0023] A further technical solution is that generating the upper tube driving signal and the lower tube driving signal includes:

[0024] When the carrier wave is smaller than the modulation wave of the upper tube, the upper tube drive signal is at a high level; when the carrier wave is larger than the modulation wave of the upper tube, the upper tube drive signal is at a low level, thereby generating an upper tube drive signal;

[0025] When the carrier wave is smaller than the modulation wave of the lower tube, the lower tube drive signal is at a low level; when the carrier wave is larger than the modulation wave of the upper tube, the lower tube drive signal is at a high level, thereby generating a lower tube drive signal.

[0026] A further technical solution is that the power tube used in the inverter circuit is SiC MOSFET.

[0027] The beneficial technical effects of this application are:

[0028] The present application discloses an inverter circuit control method for realizing adaptive dead time optimization. The method takes into account the influence of load size on the switching speed of the power tube, determines the modulation waves of the upper tube and the lower tube of the bridge arm respectively based on the size and direction of the load current, and then generates a driving signal for the power tube, so that the dead time can be accurately adjusted according to the load current, which can effectively reduce the diode freewheeling loss and the output capacitor loss, and improve the waveform quality of the inverter output current. The improvement effect is particularly prominent under high switching frequency and high power applications, and is particularly suitable for SiC MOSFET.

[0029] This method directly uses the current sensor of the inverter circuit to collect the load current without adding additional hardware. In addition, this method does not block the pulse of the passive tube, but only moves the rising edge of the passive tube forward and the falling edge backward. Therefore, the dead zone effect can be eliminated from the source without increasing the loss of the freewheeling diode. It can effectively suppress the dead zone effect without increasing the freewheeling loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a circuit diagram of a conventional inverter circuit.

[0031] Figure 2 Yes Figure 1 The waveform comparison of the driving waveform, gate-source voltage and bridge arm midpoint voltage of the A-phase bridge arm without considering the dead time, considering the dead time and considering the switching delay of the power tube.

[0032] Figure 3 It is a method flow chart of an inverter circuit control method according to an embodiment of the present application.

[0033] Figure 4 It is a waveform diagram of the modulation wave and the drive signal determined by the inverter circuit control method of the present application. DETAILED DESCRIPTION

[0034] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0035] The present application discloses an inverter circuit control method for realizing adaptive dead time optimization, which is used to control the power tube in the inverter circuit to perform adaptive dead time optimization to improve the circuit performance of the inverter circuit. It is particularly suitable for the case where the power tube used in the inverter circuit is SiC MOSFET. The structure of the inverter circuit can refer to Figure 1 The conventional circuit structure shown.

[0036] The design ideas of this application control method are as follows:

[0037] Please refer to Figure 2 ,by Figure 1Take the A-phase bridge arm in the inverter circuit as an example. When the dead time is not considered, the waveform of the drive signal of the upper and lower tubes of the same bridge arm in the inverter circuit is as follows: Figure 2 As shown in (a), V PWMH Represents the upper tube drive signal, V PWML Represents the lower tube drive signal, V an The ideal waveform of the midpoint voltage of the bridge arm of phase A is shown. When the drive signal is high, the corresponding power tube is turned on, and when the drive signal is low, the corresponding power tube is turned off. When the fixed dead time △t1=t2-t0=t6-t4 is set according to the existing method, the waveform of the drive signal of the upper tube and the lower tube is as follows: Figure 2 As shown in (b) of the figure. As shown in (b), the upper tube and the lower tube are both turned off during the time periods t0-t2 and t4-t6. When considering the switching delay of the power tube, such as the typical switching delay of SiCMOSFET, the gate-source voltage V gsH and the gate-source voltage V gsL The waveform diagram is as follows Figure 2 As shown in (c), the delay of turning on the power tube is t3-t2, and the delay of turning off the power tube is t1-t0.

[0038] The direction in which the load current flows from the midpoint of the bridge arm to the load is the positive direction. Figure 2 It can be seen that when the load current flowing through the load connected to the bridge arm is in the positive direction, such as Figure 2 I shown in (c) A > V at 0 an Waveform, the actual bridge arm midpoint voltage waveform V when the upper tube in the bridge arm is turned off an It is consistent with the ideal waveform in (a) and has no dead zone effect. When the lower tube is turned off, the reverse-connected freewheeling diode at both ends of the lower tube is turned on for freewheeling. Therefore, the actual bridge arm midpoint voltage waveform differs from the ideal waveform by a width of t3-t1, resulting in phase voltage loss. When the load current flowing through the load connected to the bridge arm is in the negative direction, such as Figure 2 I shown in (c) A V when <0 an Waveform, actual bridge arm midpoint voltage waveform V when the lower tube in the bridge arm is turned off an It is consistent with the ideal waveform in (a) and has no dead zone effect. When the upper tube is turned off, the freewheeling diodes connected in reverse at both ends of the upper tube are turned on for freewheeling. Therefore, the actual bridge arm midpoint voltage waveform differs from the ideal waveform by a width of t7–t5, resulting in phase voltage redundancy.

[0039] Based on the above analysis, the inverter circuit control method includes for any bridge arm in the inverter circuit, please combine Figure 3 The control method flow chart shown:

[0040] First, the magnitude and direction of the load current flowing through the load connected to the bridge arm are collected. The magnitude of the collected load current is the instantaneous value of the current, and the direction of the collected load current is the positive direction or the negative direction. The load current can be collected using the current sensor provided by the inverter circuit, so this method does not require the addition of additional hardware structure.

[0041] Then, according to the direction of the load current, the modulation wave of one power tube in the bridge arm is determined as the reference waveform, and the modulation wave of the other power tube is the waveform after adjusting the offset voltage of the reference waveform. There are two cases:

[0042] (1) When the load current is in the positive direction, the modulation wave of the upper tube in the bridge arm is determined to be the reference waveform, and the modulation wave of the lower tube is the waveform after adding the offset voltage △u to the reference waveform.

[0043] (2) When the load current is in the negative direction, the modulation wave of the lower tube in the bridge arm is determined to be the reference waveform, and the modulation wave of the upper tube is the waveform obtained by reducing the offset voltage △u from the reference waveform.

[0044] Please refer to Figure 4 As shown in the schematic diagram, the load current I L When it is greater than 0, it is in the positive direction and the load current I L When it is less than 0, it is in the negative direction. Figure 4 The rectangular modulation wave in the form of a solid line is the modulation wave of the upper tube, the rectangular modulation wave in the form of a dotted line is the modulation wave of the lower tube, and the triangular wave in the form of a solid line is the carrier used.

[0045] The switching speed of SiC MOSFET is also related to the load current. When the load current is large, the turn-off time of SiC MOSFET will be shorter, and when the load current is small, the turn-off time of SiC MOSFET will be longer. Therefore, the offset voltage △u adjusted here is not a fixed value, but is related to the load current.

[0046] In one embodiment, determining the offset voltage Δu according to the magnitude of the load current includes:

[0047] First, determine the instantaneous value of the dead time T based on the load current d , including: determining the on-time T corresponding to the load current according to the on-time curve of the power tube used in the inverter circuit on The on-time curve is a pre-fitted curve and reflects the change of the on-time of the power tube with the load current. And the off-time T corresponding to the load current is determined according to the off-time curve of the power tube used in the inverter circuit. off The turn-off time curve is a pre-fitted curve and reflects the change of the turn-off time of the power tube with the load current. Then according to the turn-on time Ton and the off time T off Determine the instantaneous value of the dead time T d Generally, the instantaneous value of the dead time is set to T d =n*(T off -T on ), n is a margin parameter to prevent the bridge arm from being directly connected, for example, n=2.

[0048] The above-mentioned turn-on time curve and turn-off time curve are pre-fitted and determined. The method also includes the step of fitting the two curves before application, including performing a double pulse test on the power tube used in the inverter circuit to obtain test data, and the test data includes the turn-on time and turn-off time of the power tube under different load currents. Then, based on the test data, a quadratic function is fitted to the relationship between the turn-on time of the power tube and the load current to obtain the turn-on time curve, and based on the test data, an exponential function is fitted to the relationship between the turn-off time of the power tube and the load current to obtain the turn-off time curve. The turn-on time curve can be expressed as T on =ai 2 +bi+c, the turn-off time curve can be expressed as T off =Ai B , a, b, c, A, B are all parameters and B is a negative number, i is the magnitude of the load current, and the values ​​of the specific parameters are determined according to the actual fitting situation.

[0049] Determine the instantaneous value of the dead time T based on the load current d After that, the offset voltage △u=T d *k, k is the slope of the carrier used.

[0050] Then, the upper tube drive signal V can be generated based on the carrier and the modulation wave of the upper tube. PWMH , based on the carrier and the modulation wave of the lower tube, the lower tube drive signal V is generated PWML . Including: when the carrier is less than the modulation wave of the upper tube, the upper tube drive signal is high level; when the carrier is greater than the modulation wave of the upper tube, the upper tube drive signal is low level, thereby generating the upper tube drive signal. When the carrier is less than the modulation wave of the lower tube, the lower tube drive signal is low level; when the carrier is greater than the modulation wave of the upper tube, the lower tube drive signal is high level, thereby generating the lower tube drive signal. Please refer to Figure 4 In the schematic diagram shown, the dead time is represented by shaded fill.

[0051] Then, the upper tube of the bridge arm is controlled according to the upper tube drive signal, and the lower tube of the bridge arm is controlled according to the lower tube drive signal, so as to realize the adaptive optimization of the dead time. In addition, some existing practices use the upper tube of the bridge arm as the active tube and the lower tube as the passive tube. By blocking the drive signal of the passive tube, the inverter topology is naturally free of dead zones without changing it, thus avoiding the dead zone effect from the source and improving the quality of the inverter output current. However, the diode freewheeling loss caused by it will also reduce the inverter efficiency. However, the present application is different from the existing dead zone elimination method. The present application does not block the pulse signal of the passive tube, but only moves the rising edge of the passive tube forward and the falling edge backward, which will not increase the loss of the freewheeling diode.

[0052] The above is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. An inverter circuit control method for realizing adaptive dead time optimization, characterized in that: The inverter circuit control method does not block the pulse signal of the passive tube, so that the rising edge of the passive tube moves forward and the falling edge moves backward, thereby reducing the diode freewheeling loss and output capacitor loss; the inverter circuit control method includes for any bridge arm in the inverter circuit: Collecting the magnitude and direction of the load current flowing through the load connected to the bridge arm, with the direction of the load current flowing from the midpoint of the bridge arm to the load being the positive direction; According to the direction of the load current, the modulation wave of one power tube in the bridge arm is determined to be the reference waveform, and the modulation wave of the other power tube is the waveform after the reference waveform is adjusted with an offset voltage, and the offset voltage is related to the magnitude of the load current: The method for determining the offset voltage includes: determining the instantaneous value of the dead time T based on the magnitude of the load current d ; Determine the offset voltage △u=T d *k, k is the slope of the carrier; The instantaneous value T of the dead time is determined based on the magnitude of the load current. d The method comprises: determining an on-time T corresponding to the load current according to an on-time curve of a power tube used in the inverter circuit; on The turn-on time curve is a pre-fitted curve and reflects the change of the turn-on time of the power tube with the magnitude of the load current; the turn-off time T corresponding to the magnitude of the load current is determined according to the turn-off time curve of the power tube used in the inverter circuit. off The turn-off time curve is a pre-fitted curve and reflects the change of the turn-off time of the power tube with the load current; according to the turn-on time T on and the off time T off Determine the instantaneous value of the dead time T d =n*(T off -T on ), n is the margin parameter; Methods for pre-fitting the turn-on time curve and the turn-off time curve include: Performing a double pulse test on the power tube used in the inverter circuit to obtain test data, the test data including the on time and off time of the power tube under load currents of different magnitudes; Based on the test data, a quadratic function is fitted to the relationship between the turn-on time of the power tube and the load current to obtain a turn-on time curve. Based on the test data, an exponential function is fitted to the relationship between the turn-off time of the power tube and the load current to obtain a turn-off time curve. The turn-on time curve can be expressed as: , the turn-off time curve can be expressed as , , , , , are parameters and is a negative number, is the magnitude of the load current; An upper tube driving signal is generated based on the carrier and the modulation wave of the upper tube, and a lower tube driving signal is generated based on the carrier and the modulation wave of the lower tube. The upper tube of the bridge arm is controlled according to the upper tube driving signal, and the lower tube of the bridge arm is controlled according to the lower tube driving signal.

2. The inverter circuit control method according to claim 1, characterized in that: The method of determining, according to the direction of the load current, that the modulation wave of one power tube in the bridge arm is a reference waveform and the modulation wave of another power tube is a waveform obtained by adjusting the offset voltage of the reference waveform comprises: When the load current is in a positive direction, determining that the modulation wave of the upper tube in the bridge arm is a reference waveform, and the modulation wave of the lower tube is a waveform obtained by adding the offset voltage to the reference waveform; When the load current is in a negative direction, it is determined that the modulation wave of the lower tube in the bridge arm is a reference waveform, and the modulation wave of the upper tube is a waveform obtained by reducing the offset voltage from the reference waveform.

3. The inverter circuit control method according to claim 1, characterized in that: Generating the upper tube drive signal and the lower tube drive signal includes: When the carrier wave is smaller than the modulation wave of the upper tube, the upper tube drive signal is at a high level; when the carrier wave is larger than the modulation wave of the upper tube, the upper tube drive signal is at a low level, thereby generating an upper tube drive signal; When the carrier wave is smaller than the modulation wave of the lower tube, the lower tube drive signal is at a low level; when the carrier wave is larger than the modulation wave of the upper tube, the lower tube drive signal is at a high level, thereby generating a lower tube drive signal.

4. The inverter circuit control method according to claim 1, characterized in that: The power tube used in the inverter circuit is SiC MOSFET.

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