A novel dead-time adaptive control method and device for bridge arm topology

Abstract

The application provides a novel dead-time adaptive control method and device for a bridge arm topology. When complementary driving, the first dead-time is shortened as much as possible to reduce the dead-time freewheeling loss and effectively reduce a large number of harmonics caused by the dead-time insertion under the premise of avoiding bridge arm shoot-through, thereby improving the operation stability of an electrical system. Meanwhile, the second dead-time is dynamically adjusted according to the load current change to ensure that the second dead-time value can eliminate the output capacitor loss and reduce the dead-time freewheeling loss in the full power range, thereby improving the efficiency. Moreover, the second dead-time is too large to affect the output waveform quality of the circuit, and therefore, the second dead-time harmonic restriction is added to relieve the contradiction between the efficiency and the reliability.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and specifically to a novel dead-zone adaptive control method and device for bridge arm topologies. Background Technology

[0002] In the basic bridge arm topologies of commonly used electrical systems such as inverters and motor drives, bridge arm shoot-through is one of the most common and serious problems. Although adding dead time can minimize bridge arm shoot-through, improper dead time settings can also have significant negative impacts on the electrical system.

[0003] On the one hand, dead time causes distortion in the output voltage and current of the bridge arm circuit, increases the total harmonic distortion (THD), and reduces the quality of power conversion. This is especially true at high switching frequencies, where it can accumulate significant output errors and affect the stability of the motor system. On the other hand, the reverse conduction loss of the power transistor is high within the dead time, and the insertion of dead time significantly impacts system efficiency. Furthermore, the turn-off time of the power transistor varies considerably with the output load current of the bridge arm circuit. When the dead time is too short, unreleased energy from the output capacitor will be released through the power transistor's channel, causing channel current spikes and losses. These output capacitor losses are particularly severe under light loads and high switching frequencies. Therefore, both excessively long and excessively short dead times result in additional power losses, hindering system efficiency. An effective dead time optimization method is urgently needed to achieve a balance between high efficiency and high reliability. Summary of the Invention

[0004] An unreasonable dead-time setting can significantly affect the reliability and efficiency of bridge arm circuits. Current dead-time optimization methods still suffer from problems such as not fully exploring the relationship between dead time and load, and increasing system size and cost. This invention proposes a novel dead-time adaptive control method and device for bridge arm topologies. Based on the relationship between the optimal values ​​of the first and second dead times and the load current, an adaptive control strategy is used, and harmonic limiting measures are introduced to minimize bridge arm circuit losses and improve electrical system efficiency while ensuring reliability.

[0005] The technical solution of the present invention is as follows:

[0006] A novel dead-time adaptive control method for bridge arm topology includes a bridge arm topology structure, a first power transistor and a second power transistor that cooperate with each other, characterized in that the dead time before the lower power transistor of the bridge arm is turned on is the first dead time, and the dead time after the lower power transistor of the bridge arm is turned off is the second dead time.

[0007] Step 1, determine the location of the dead time based on the current flow direction: determine the optimal value of the first dead time based on the rise time of the gate-source voltage of the first power transistor and the fall time of the gate-source voltage of the second power transistor; determine the optimal value of the second dead time based on the rise time of the gate-source voltage of the second power transistor and the fall time of the drain-source voltage of the second power transistor.

[0008] Step 2: Within the full power range, fix the first dead time as the optimal value T for the first dead time. D1_opt Based on the optimal values ​​of load current and second dead time under different load conditions, the value of the second dead time is optimized to obtain the optimized second dead time T. D2_opt ;

[0009] Step 3, define the dead time before the second power transistor is turned on as t. d_on The dead time after shutdown is denoted as t. d_off Determine the magnitude of the load current. When the load current is greater than 0, let t... d_on =T D1_opt , t d_off =T D2_opt Otherwise, let t d_on =T D2_opt , t d_off =T D1_opt This enables adaptive control of the dead zone and minimizes the total loss of the bridge arm circuit.

[0010] The present invention also discloses a novel dead-time adaptive control device for a bridge arm topology, comprising a main power circuit consisting of at least one pair of complementary driven power transistors; and a drive circuit for driving the power transistors in the main power circuit.

[0011] A controller is used to execute the novel dead-zone adaptive control method described above.

[0012] Furthermore, the current polarity determination module is used to determine whether the current is flowing into or out of the bridge arm midpoint, thereby distinguishing between the first dead time and the second dead time; when the current is determined to be flowing out of the bridge arm midpoint, the current is determined to be in the positive direction, and the current turning module is greater than zero; when the current is determined to be flowing into the bridge arm midpoint, the current is determined to be in the negative direction, and the current turning module is less than zero.

[0013] Furthermore, in the current greater than zero module, the first dead time is the dead time before the upper tube of the bridge arm is turned on, and the second dead time is the dead time after the upper tube of the bridge arm is turned off. After determining the dead time position, the first dead time is set to a fixed value according to the optimization method, and the second dead time is dynamically adjusted with the load current.

[0014] Furthermore, in the current less than zero module, the first dead time is the dead time before the lower tube of the bridge arm is turned on, and the second dead time is the dead time after the lower tube of the bridge arm is turned off. After determining the dead time position, the first dead time is set to a fixed value according to the optimization method, and the second dead time is dynamically adjusted with the load current.

[0015] Beneficial effects

[0016] (1) The present invention introduces harmonic suppression measures in dead time control, which suppresses a large number of odd harmonics during dead time, thereby improving the stability and reliability of the system and improving the efficiency of the electrical system.

[0017] (2) This invention takes different measures to address the different effects of the first dead time and the second dead time on the efficiency of the electrical system: the shorter the first dead time is, the better it is to reduce dead-time follow current loss, while the output capacitor loss needs to be considered when setting the second dead time; therefore, the optimal value of the first dead time can be set to a fixed value, and the optimal value of the second dead time is related to the load current and needs to be changed with the load current. This approach is more targeted and improves the efficiency of the electrical system.

[0018] The novel dead-time adaptive control method and device provided by this invention not only enable the dead time to be dynamically adjusted according to the load conditions, but also introduce harmonic suppression measures, thereby improving the efficiency of the electrical system while suppressing harmonics. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a three-phase inverter circuit provided in an embodiment of the present invention;

[0020] Figure 2 This is a dead time setting diagram for a phase bridge arm provided in an embodiment of the present invention;

[0021] Figure 3 This is a first dead time curve that minimizes the total loss of the bridge arm under different load conditions, provided by an embodiment of the present invention.

[0022] Figure 4 This is a second dead time curve that minimizes the total loss of the bridge arm under different load conditions, provided by an embodiment of the present invention.

[0023] Figure 5 This is a diagram defining the positions of the first dead time and the second dead time according to an embodiment of the present invention;

[0024] Figure 6 This is a flowchart of a novel dead-zone adaptive control method for a single-phase bridge arm provided in an embodiment of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Figure 1 A schematic diagram of a three-phase inverter circuit according to an embodiment of the present invention is shown. Each bridge arm that is mutually driven needs to be inserted with a dead time to avoid bridge arm shoot-through, but an inappropriate dead time setting will reduce the stability and efficiency of the electrical system.

[0027] Figure 2 This diagram illustrates the dead time setting for a single-phase bridge arm according to an embodiment of the present invention. The dead time in the bridge arm circuit can be divided into two categories: signal dead time and drive signal dead time. Signal dead time refers to the time during which the PWM control signals of the upper and lower transistors of the bridge arm are simultaneously turned off, i.e., T... M1 and T M2 The dead time of the drive signal refers to the time between the start of the rise of the gate-source voltage of a power transistor in the bridge arm circuit and the start of the fall of the gate-source voltage of its complementary transistor, i.e., the first dead time T. D1 Second dead zone time T D2 Among them, T D1 T is the dead time before the forward-conducting active power transistor turns on. D2 This is the dead time after the forward-conducting active power transistor is turned off.

[0028] In practical circuits, the signal dead time T can be directly controlled by controlling the output of the digital controller. M The dead time of the drive signal is determined by its magnitude, but it cannot be directly controlled by the designer; it is highly dependent on the specific parameters of the components and power devices in the drive circuit. The dead time of the drive signal is jointly determined by the signal dead time and the drive circuit delay, satisfying the following relationship:

[0029] T D =T M -t PDL +t PDH (7)

[0030] Among them, t PDL t is the propagation delay from the start of the PWM signal decreasing to the start of the gate-source voltage decreasing. PDH This refers to the propagation delay from the start of the PWM signal's rise to the start of the gate-source voltage's rise. By determining the optimized drive signal dead time and propagation delay time, an adjustable optimized signal dead time can be obtained.

[0031] This invention proposes an adaptive control method for the dead time of this drive signal.

[0032] Step 1: Determine the location of the dead time based on the current flow direction. For example... Figure 5 The diagram shown illustrates the definition of the first and second dead times according to an embodiment of the present invention. Current flowing out from the midpoint of the bridge arm is considered positive, while current flowing in from the midpoint is considered negative. When i > 0, Q2 is the active power transistor, and the dead time before Q2 is turned on is T. D1 The dead time after Q2 is turned off is T. D2 When i < 0, Q1 is the active power transistor, and the dead time before Q1 is turned on is T. D1 The dead time after Q1 is turned off is T. D2 .

[0033] The optimal value of the first dead time is determined based on the rise time of the gate-source voltage of the first power transistor and the fall time of the gate-source voltage of the second power transistor.

[0034] T D1_opt =t2-t1 (1)

[0035] Where t2 is the time from when the gate-source voltage of the second power transistor starts to decrease until it decreases to the threshold voltage, and t2 is the time from when the gate-source voltage of the first power transistor starts to rise until it rises to the threshold voltage.

[0036] The optimal value for the first dead time ensures that the upper channel is shut off just as the lower channel is opened, thus avoiding reverse conduction losses during the first dead time.

[0037] The optimal value of the second dead time is determined based on the rise time of the gate-source voltage and the fall time of the drain-source voltage of the second power transistor.

[0038] T D2_opt * =t4-t3 (2)

[0039] Where t4 is the time from when the gate-source voltage of the first power transistor begins to decrease until the drain-source voltage of the second power transistor decreases to 0, and t3 is the time from when the gate-source voltage of the second power transistor begins to rise until it rises to the threshold voltage; where t4–t3 decreases as the load current increases, the optimal value of the second dead time T is found across the full power range. D2_opt * Dynamically adjusts as the load current changes.

[0040] Step 2: Optimize the first dead time and the second dead time within the full power range: Based on the load current under different load conditions, obtain the relationship curves between the load current and the optimal values ​​of the first dead time and the second dead time, respectively. Obtain the corresponding dead time through these relationship curves to achieve adaptive control of the dead time and minimize the total loss of the bridge arm circuit.

[0041] Optimize first dead zone time:

[0042] Figure 3 The diagram illustrates the first dead-time curves that minimize the total arm loss under different load conditions according to an embodiment of the present invention. As can be seen from the diagram, the values ​​of t2 and t1 remain essentially constant as the load current changes; therefore, T... D1_opt The value of t2–t1 remains basically unchanged, consistent with the analysis in equation (4). t2–t1 is only related to the inherent parameters of the power transistor and its driving circuit, and will not change due to changes in load conditions. Therefore, within the full power range, the first dead time T D1_opt It can be set to a fixed value.

[0043] The optimal value for a fixed first dead time is:

[0044]

[0045] Among them, R G For the driving resistor, C ISS For the input capacitance, U GS(off) To drive the turn-off voltage, U GS(on) To drive the turn-on voltage, U GS(th) This is the threshold voltage.

[0046] Optimize the second dead zone time:

[0047] Expanding the optimal value of the second dead time equation (2), it is as follows:

[0048]

[0049] Among them, Q OSS (U DC When the drain-source voltage of the power transistor is U DC At that time, the amount of charge stored in the output capacitor of the power transistor.

[0050] As can be seen from equation (5), since the load current is very small, T D2_opt * This will be significant, thus increasing the harmonics of the bridge arm circuit's output waveform. Therefore, harmonic limiting measures need to be added. This can be achieved by reducing the harmonics of T when the load current is less than a certain value. D2_opt Set to a fixed, relatively large value, namely the first dead zone threshold value T. max When the load current is large, T D2_opt* It hardly changes with the load current, but when the load current exceeds a certain value, T can be adjusted. D2_opt * Set to a fixed, relatively small value, namely the second dead zone threshold value T. min Within the middle range, the second dead zone time is set according to the rule shown in formula (2).

[0051] The first dead zone threshold is to prevent excessive dead time from causing severe distortion of the bridge arm circuit output waveform, while the second dead zone threshold is to reduce the complexity of the control program.

[0052] Figure 4 The figure shows the second dead-time curves that minimize the total loss of the bridge arm under different load conditions according to an embodiment of the present invention. From the figure, it can be seen that T... D2_opt * It will decrease as the load current increases, consistent with the analysis in equation (5). This is because T D2 When the voltage is low, the channel of the freewheeling diode in the bridge arm begins to conduct before the drain-source voltage drops to 0V. At this time, the energy that has not yet been converted in the output capacitor will be released through the channel of the freewheeling diode. At the same time, the DC bus power supply will also discharge through the channel, further increasing the current spike in the channel. This poses a risk of exceeding the current range of the power transistor and greatly increases the losses. D2 When the second dead time is large, it will increase the reverse conduction loss within the dead zone. Therefore, the optimal second dead time needs to avoid output capacitor losses and eliminate excess reverse conduction losses, i.e., the channel turns on when the drain-source voltage of the freewheeling diode drops to 0. Since the drain-source voltage drop time of the freewheeling diode decreases with the increase of load current, T... D2_opt * It will decrease as the load current increases.

[0053] When the load current is very small, T D2_opt * This will be significant, thus affecting the output waveform quality of the bridge arm circuit. Therefore, harmonic limiting measures need to be added. This can be achieved by reducing T when the load current is less than the first current threshold. D2_opt * Set a fixed first dead zone threshold value; when the load current is large, T D2_opt It hardly changes with the load current, but can adjust T when the load current exceeds the second current threshold. D2_opt Set a fixed second dead zone threshold value; within the middle range, set the second dead zone time according to the rule shown in equation (5).

[0054] The optimized second dead time is:

[0055]

[0056] When the load current is less than the first current threshold, the second dead time is maintained at the first dead time threshold; when the load current is greater than the second current threshold, the second dead time is maintained at the second dead time threshold; when the load current is within the first current threshold and the second current threshold, the second dead time decreases as the load current increases according to equation (5).

[0057] Step 3: Implement adaptive control of the first dead time and the second dead time. For example... Figure 6 The diagram shown is a flowchart of a novel dead-time adaptive control method for a single-phase bridge arm according to an embodiment of the present invention. Without considering current polarity, the dead time before Q2 is turned on is defined as t. d_on The dead time after Q2 is turned off is denoted as t. d_off If the load current is greater than 0, then t d_on For the first dead zone time, t d_off This is the second dead time; if the load current is less than or equal to 0, then t d_off For the first dead zone time, t d_on The second dead zone time is set according to the optimization setting principles.

[0058] This invention also proposes a novel dead-time adaptive control method and device for bridge arm topologies. While ensuring reliability, the dead time is dynamically adjusted according to load conditions based on the principle of minimizing bridge arm losses, and harmonic suppression measures are introduced to improve electrical system efficiency while suppressing harmonics. The device specifically includes: a main power circuit, composed of at least one pair of complementary driven power transistors; a drive circuit for driving the power transistors in the main power circuit; and a controller for executing the novel dead-time adaptive control method for bridge arm topologies.

[0059] The controller includes a current polarity determination module, which determines whether the current flows into or out of the bridge arm midpoint, thereby distinguishing between the first dead time and the second dead time. Specifically, when the current is determined to flow out of the bridge arm midpoint, the current is determined to be in the positive direction, and the current direction is greater than zero. When the current is determined to flow into the bridge arm midpoint, the current is determined to be in the negative direction, and the current direction is less than zero.

[0060] The current-to-zero module controls the first dead time to a fixed optimal value based on the current flow direction, and controls the second dead time to dynamically change with the load current, subject to the threshold values ​​of both the first and second dead times. The first dead time is the dead time before the upper bridge arm power transistor is turned on, and the second dead time is the dead time after the upper bridge arm power transistor is turned off. When i>0, the upper bridge arm power transistor Q2 is the active power transistor, and the dead time before Q2 is turned on is T. D1The dead time after the upper arm power transistor Q2 is turned off is T. D2 After determining the dead time location, the first dead time is set to a fixed value according to the optimization method. The second dead time is dynamically adjusted according to the load current.

[0061] The current-to-zero module controls the first dead time to a fixed optimal value based on the current flow direction, and controls the second dead time to dynamically change with the load current, subject to the threshold values ​​of both the first and second dead times. The first dead time is the dead time before the lower bridge arm power transistor turns on, and the second dead time is the dead time after the lower bridge arm power transistor turns off. When i < 0, the lower bridge arm power transistor Q1 is the active power transistor, and the dead time before Q1 turns on is T. D1 The dead time after the lower bridge arm power transistor Q1 is turned off is T. D2 After determining the dead time position, the first dead time is set to a fixed value according to the optimization method, while the second dead time is dynamically adjusted according to the load current. The first dead time threshold is set to prevent excessive dead time from causing severe distortion of the bridge arm circuit output waveform, while the second dead time threshold is set to reduce the complexity of the control program.

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A novel dead-time adaptive control method for a bridge arm topology, comprising a bridge arm topology structure, a first power transistor and a second power transistor cooperating with each other, characterized in that, The dead time before the lower pipe of the bridge arm is turned on is the first dead time, and the dead time after the lower pipe of the bridge arm is turned off is the second dead time. Step 1, determine the location of the dead time based on the current flow direction: determine the optimal value of the first dead time based on the rise time of the gate-source voltage of the first power transistor and the fall time of the gate-source voltage of the second power transistor; determine the optimal value of the second dead time based on the rise time of the gate-source voltage of the second power transistor and the fall time of the drain-source voltage of the second power transistor. Step 2: Within the full power range, fix the first dead time as the optimal value for the first dead time. ; Based on the optimal values ​​of load current and second dead time under different load conditions, the value of the second dead time is optimized to obtain the optimized second dead time. ; The optimal value of the second dead time is subject to the dynamic adjustment of the load current and is limited by the first dead time threshold and the second dead time threshold. The second dead time is optimized and adjusted as follows: when the load current is less than the first current threshold, the second dead time is maintained at the first dead time threshold. When the load current is greater than the second current threshold value, the second dead time is maintained at the second dead time threshold value. When the load current is within the first current threshold and the second current threshold, the second dead time is determined according to the formula. It decreases as the load current increases, where Q is in the formula. OSS (U DC When the drain-source voltage of the power transistor is U DC At that time, the amount of charge stored in the output capacitor of the power transistor, R G For the driving resistor, C ISS For the input capacitance, U GS(off) To drive the turn-off voltage, U GS(on) To drive the turn-on voltage, U GS(th) Threshold voltage, This is the load current; Step 3, define the dead time before the second power transistor is turned on as t. d_on The dead time after shutdown is denoted as t. d_off Determine the magnitude of the load current. When the load current is greater than 0, let t... d_on = , t d_off = Otherwise, let t d_on = , t d_off = This enables adaptive control of the dead zone and minimizes the total loss of the bridge arm circuit.

2. The novel dead-zone adaptive control method for bridge arm topology as described in claim 1, characterized in that, The optimal value for the first dead time is: ， Where t2 is the time from when the gate-source voltage of the second power transistor starts to decrease until it decreases to the threshold voltage, and t2 is the time from when the gate-source voltage of the first power transistor starts to rise until it rises to the threshold voltage.

3. The novel dead-zone adaptive control method for bridge arm topology as described in claim 2, characterized in that, The optimal value for the second dead time is: ， Where t4 is the time from when the gate-source voltage of the first power transistor starts to drop to when the drain-source voltage of the second power transistor drops to 0, and t3 is the time from when the gate-source voltage of the second power transistor starts to rise to when it rises to the threshold voltage.

4. The novel dead-zone adaptive control method for bridge arm topology as described in claim 1 or 3, characterized in that, Optimized second dead time T D2_opt Specifically: ， in, For the load current, |I min |To limit the threshold value of the first dead zone The first current threshold value, |I max |To limit the threshold value of the second dead zone The second current threshold value, Q OSS (U DC When the drain-source voltage of the power transistor is U DC At that time, the amount of charge stored in the output capacitor of the power transistor, R G For the driving resistor, C ISS For the input capacitance, U GS(off) To drive the turn-off voltage, U GS(on) To drive the turn-on voltage, U GS(th) This is the threshold voltage.

5. A novel dead-zone adaptive control system for bridge arm topology, characterized in that, The system implementing the novel dead-zone adaptive control method for bridge arm topology as described in claim 1 or 4, the system comprising: The main power circuit consists of at least one pair of complementary driven power transistors; The drive circuit is used to drive the power transistors in the main power circuit. A controller is used to execute the novel dead-zone adaptive control method for the bridge arm topology.

6. The novel dead-zone adaptive control system for bridge arm topology as described in claim 5, characterized in that, The controller includes a current polarity determination module, used to determine whether the current flows into or out of the bridge arm midpoint, thereby distinguishing between the first dead time and the second dead time; when it is determined that the current flows out of the bridge arm midpoint, the current is determined to be in the positive direction and the turning current is greater than zero module; when it is determined that the current flows into the bridge arm midpoint, the current is determined to be in the negative direction and the turning current is less than zero module.

7. The novel dead-zone adaptive control system for bridge arm topology as described in claim 6, characterized in that, The upper arm power transistor and the lower arm power transistor are connected in series to form the bridge arm structure. In the current greater than zero module, the upper bridge arm power transistor is an active power transistor. The dead time position before the upper bridge arm power transistor is turned on is determined as the first dead time position, and the dead time position after the upper bridge arm power transistor is turned off is determined as the second dead time position. At the same time, the first dead time is controlled to be a fixed optimal value, and the second dead time is controlled to change dynamically with the load current and is limited by the first dead time threshold value and the second dead time threshold value. In the current-less-zero module, the lower bridge arm power transistor is an active power transistor. The dead time position before the lower bridge arm power transistor is turned on is determined as the first dead time position, and the dead time position after the lower bridge arm power transistor is turned off is determined as the second dead time position. At the same time, the first dead time is controlled to be a fixed optimal value, and the second dead time is controlled to change dynamically with the load current and is limited by the first dead time threshold value and the second dead time threshold value. The first dead zone threshold is to prevent excessive dead time from causing severe distortion of the bridge arm circuit output waveform, while the second dead zone threshold is to reduce the complexity of the control program.

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