A switching loss equalization control system and method based on level hybrid modulation and a storage medium

Abstract

The application discloses the technical field of level modulation, and relates to a switching loss equalization control system and method based on level hybrid modulation, and a storage medium, which comprises the following modules: a signal processing module, which is used to acquire a three-level modulation voltage; a mode switching decision module, which is used to acquire the difference between the internal and external tube losses, and update a modulation mode flag bit by comparing a hysteresis threshold value; and a level hybrid modulation module, which is used to read the three-level modulation voltage and the modulation mode flag bit, and execute three-level modulation or equivalent two-level modulation to output a final modulation wave for controlling the state of a switching tube. The mode switching decision module of the application takes the three-level modulation voltage as the final modulation wave when three-level modulation is performed, and allocates the duty cycle of the intermediate level of the three-level modulation voltage to the high and low levels to obtain a two-level modulation voltage and acquire the final modulation wave when equivalent two-level modulation is performed, so that the dynamic equalization distribution of the internal and external tube losses is realized, and the thermal stability and reliability of the system are improved.

Description

Technical Field

[0001] This invention relates to the field of level modulation, and more specifically to a switching loss equalization control system, method, and storage medium based on level hybrid modulation. Background Technology

[0002] In motor drive systems, the T-type three-level topology, as an advanced power conversion topology, has been widely used in medium- and high-power motor drives due to its unique technical advantages. The T-type three-level topology consists of two outer transistors and two inner transistors forming a single-phase bridge arm. The outer transistors are the main switches, and the inner transistors are clamping switches. The DC side uses two series capacitors for voltage division, and the midpoint is clamped by the inner transistors to achieve three output levels. Compared to the NPC (neutral point clamped) three-level topology, the inner transistors in the T-type three-level topology only conduct when the output is at 0 level, resulting in lower switching losses and lower harmonic distortion (THD) of the output voltage. Therefore, it is more suitable for motor drive scenarios with high requirements for efficiency and waveform quality.

[0003] However, the existing modulation strategies of T-type three-level motor controllers still have the following shortcomings:

[0004] Low-modulation control leads to severe overheating of the internal transistor: Traditional SPWM (Sinusoidal Pulse Width Modulation) and SVPWM (Space Vector Pulse Width Modulation) strategies, when using low modulation, significantly increase the duty cycle of the zero-level output of each phase bridge arm, causing the internal transistor to conduct for extended periods. Since the on-resistance of the internal transistor is typically greater than that of the external transistor, and the current flowing through the internal transistor is comparable to that of the external transistor, the conduction loss of the internal transistor increases dramatically, resulting in significant overheating. For example, in low-speed, high-torque conditions such as starting and climbing in new energy vehicles, low motor controller modulation over long periods can accelerate the aging of the internal transistor and even lead to thermal breakdown.

[0005] Midpoint potential is prone to imbalance: The stability of the midpoint potential in a T-type three-level topology depends on the charging and discharging balance of the two capacitors on the DC side and the symmetry of the three-phase current. In practical applications, factors such as unbalanced three-phase loads, differences in the on-state voltage drop of switching transistors, inconsistent capacitor parameters, and sampling errors can cause the midpoint current to be non-zero, leading to midpoint potential deviation. Midpoint potential deviation will cause asymmetry in the positive and negative half-cycles of the output voltage, increase harmonic content, and also cause uneven voltage stress on the switching transistors. Existing midpoint potential control methods mostly use zero-sequence voltage injection or vector action time adjustment, but these methods have poor control effects under low-level conditions and are prone to conflict with modulation strategies, resulting in a decrease in output performance.

[0006] To address these issues, researchers in related fields have made numerous attempts. For example, an adaptive SVPWM strategy can be used to reduce the on-time of the inner transistor by adjusting the vector combination method. However, this method increases algorithm complexity and has limited effectiveness in controlling the midpoint potential. Alternatively, a two-level modulation strategy can be used to completely replace the three-level modulation strategy to avoid inner transistor operation, but this method leads to increased harmonic content in the output voltage and cannot maintain performance under high modulation levels. Furthermore, in terms of midpoint potential control, existing methods are mostly designed for specific operating conditions and lack a full-range adaptive control mechanism, making it difficult to meet the needs of wide-range speed-regulating motor drive systems.

[0007] Therefore, there is an urgent need for a switching loss equalization control system and method that can simultaneously suppress internal tube heating under low-temperature conditions and balance the midpoint potential under all operating conditions, so as to improve the overall performance of the T-type three-level motor controller and promote its application in more high-performance motor drive scenarios. Summary of the Invention

[0008] The purpose of this invention is to provide a switching loss equalization control system, method, and storage medium based on level hybrid modulation, which solves the problems of insufficient internal tube heating suppression capability and point potential balance capability under all operating conditions in the prior art when using level hybrid modulation.

[0009] The present invention achieves the above objectives through the following technical solutions:

[0010] A switching loss sharing control system based on level hybrid modulation, applied to a T-type three-level motor controller; comprising:

[0011] The signal processing module is used to acquire the three-phase reference modulation voltage in real time using the FOC control strategy, and normalize it to obtain the three-level modulation voltage.

[0012] The mode switching decision module is used to obtain the loss difference between the inner and outer tubes of each phase of the motor controller in real time according to the switching tube loss model, and compare the loss difference with the preset hysteresis threshold to update the modulation mode flag bit.

[0013] The level-mixed modulation module is used to read the three-level modulation voltage and the modulation mode flag of each phase, and select to perform three-level modulation or equivalent two-level modulation according to the modulation mode flag, and output the final modulation wave of each phase to control the state of the switching transistor.

[0014] In three-level modulation, the three-level modulation voltage is used as the final modulation wave;

[0015] In equivalent two-level modulation, the duty cycle of the middle level of the three-level modulation voltage is evenly distributed to the high level and the low level to obtain a two-level modulation voltage. Based on the two-level modulation voltage, the final modulation wave is obtained.

[0016] As a further optimization of the invention, the mode switching decision module independently generates a modulation mode flag bit for each phase arm of the motor; the hysteresis threshold is configured such that when the system is running in steady state, at least two phases of the three-phase bridge arm operate in three-level modulation mode, and at most one phase operates in equivalent two-level modulation mode.

[0017] As a further optimization of the invention, the mode switching decision module includes a hysteresis switching logic unit, which is configured as follows:

[0018] The hysteresis threshold is set, and the hysteresis threshold is divided into a first threshold and a second threshold;

[0019] When the difference between the inner and outer tube losses of a certain phase is greater than the first threshold, the modulation mode flag of that phase is switched to indicate the three-level modulation mode.

[0020] When the negative of the difference between the inner and outer tube losses of a certain phase is greater than the second threshold, the modulation mode flag of that phase is switched to indicate the equivalent two-level modulation mode.

[0021] As a further optimization of the invention, when the mode switching decision module obtains the difference between the inner and outer tube losses according to the switching tube loss model, it takes the sum of the inner tube's conduction loss and switching loss as the inner tube loss; takes the sum of the outer tube's conduction loss and switching loss as the outer tube loss; and takes the difference between the inner tube loss and the outer tube loss as the difference between the inner and outer tube losses.

[0022] As a further optimization of the invention, the level mixing modulation module includes:

[0023] A three-level PWM generator is used to enter a three-level modulation mode according to the modulation mode flag bit, use the three-level modulation voltage as the final modulation wave, and generate a PWM drive signal using the in-phase carrier stacking method.

[0024] A two-level PWM generator is used to enter an equivalent two-level modulation mode according to the modulation mode flag, perform duty cycle allocation to obtain a two-level modulation voltage, and obtain the final modulation wave based on the two-level modulation voltage. A bipolar modulation method is used to generate a PWM drive signal.

[0025] As a further optimization of the invention, it also includes a midpoint potential balance control module, which is used to obtain the common-mode voltage based on the voltage deviation of the upper and lower capacitors on the DC side, the current of each phase and the modulation mode flag, and inject the common-mode voltage into the two-level modulation voltage to form the final modulation wave, so as to adjust the midpoint current and suppress the DC side midpoint potential offset.

[0026] As a further optimization of the invention, in the process of obtaining the common-mode voltage based on the voltage deviation of the upper and lower capacitors on the DC side, the current of each phase, and the modulation mode flag:

[0027] Within the full modulation range, based on the voltage boundary constraints of the current modulation range, the common-mode voltage for the balance control of the midpoint potential is solved by simultaneously solving the equations for the modulation wave, duty cycle, and midpoint current. If the solution value exceeds the voltage boundary, the boundary voltage value is taken as the common-mode voltage.

[0028] A switching loss equalization control method based on level hybrid modulation includes the following steps:

[0029] The three-phase reference modulation voltage is acquired in real time using the FOC control strategy and then normalized to obtain the three-level modulation voltage.

[0030] The loss difference between the inner and outer tubes of each phase of the motor controller is obtained in real time according to the switching tube loss model, and the loss difference is compared with the preset hysteresis threshold to generate the modulation mode flag bit of each phase.

[0031] It receives the three-level modulation voltage and the modulation mode flag of each phase, and performs three-level modulation or equivalent two-level modulation according to the modulation mode flag, and outputs the final modulation wave of each phase to control the state of the switching transistor.

[0032] In three-level modulation, the three-level modulation voltage is used as the final modulation wave; in equivalent two-level modulation, the duty cycle of the middle level of the three-level modulation voltage is evenly distributed to the high level and the low level to obtain the two-level modulation voltage, and the final modulation wave is obtained based on the two-level modulation voltage.

[0033] As a further optimization of the invention, the following steps are also included:

[0034] Based on the voltage deviation of the upper and lower capacitors on the DC side, the current of each phase, and the modulation mode flag, a common-mode voltage is calculated and injected into the final modulation wave to adjust the midpoint current and suppress the DC side midpoint potential shift.

[0035] A storage medium having computer program instructions stored thereon, which implement the above method when executed by a processor.

[0036] The beneficial effects of this invention are as follows:

[0037] 1) This invention calculates the loss difference between the inner and outer tubes of each phase in real time and makes independent decisions for each phase based on hysteresis switching logic, adopting a three-level or equivalent two-level modulation mode. Under low-level conditions, it can automatically transfer the current path from the high-loss inner tube to the outer tube, realize the dynamic balance distribution of the inner and outer tube losses, reduce the temperature rise of the inner tube when running at low speed, and improve the thermal stability and reliability of the system.

[0038] 2) This invention addresses the problems of altered midpoint current model and increased imbalance caused by hybrid modulation strategies. By injecting adaptive common-mode voltage for closed-loop control, it can solve for the optimal common-mode voltage in real time based on voltage boundary constraints under low, medium, and high modulation modes, quickly correcting the midpoint potential shift, ensuring the stability of the DC-side capacitor voltage under all operating conditions, guaranteeing the output power quality, and making the control system highly robust.

[0039] 3) The equivalent two-level modulation strategy adopted in this invention strictly ensures the consistency between its output fundamental voltage and three-level modulation, thus it will not introduce additional voltage harmonics or affect the accuracy of field-oriented control. The speed control performance, dynamic response and current waveform quality of the motor are maintained, achieving a balance between efficiency, reliability and performance.

[0040] 4) The control system of the present invention has a high degree of modularity and moderate algorithm computation, making it easy to integrate and promote in existing digital controllers. It can be widely used in medium and high power, wide speed regulation motor control scenarios using T-type three-level topology, such as electric drive of new energy vehicles, industrial servo, and rail transit traction, and has strong applicability. Attached Figure Description

[0041] Figure 1 This is a system block diagram of the first embodiment of the present invention;

[0042] Figure 2 This is the main circuit diagram of the motor controller of the present invention;

[0043] Figure 3 This is a control block diagram of the control system of the present invention;

[0044] Figure 4 This is a schematic diagram illustrating the dynamic switching principle of the modulation strategy for equalizing loss in this invention.

[0045] Figure 5 This is a flowchart of the hysteresis control for balancing the heating of the inner and outer tubes in this invention.

[0046] Figure 6 This is a schematic diagram of the level modulation of the present invention;

[0047] Figure 7 This is a system block diagram of the second embodiment of the present invention;

[0048] Figure 8 This is a diagram showing the midpoint current path at the midpoint of the DC side of the present invention.

[0049] Figure 9 This is a flowchart of the control method according to the third embodiment of the present invention;

[0050] Figure 10 This is a flowchart of the control method according to the fourth embodiment of the present invention. Detailed Implementation

[0051] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0052] First Embodiment

[0053] like Figures 1-4 As shown, this embodiment relates to a switching loss equalization control system based on level hybrid modulation, which includes the following modules:

[0054] The signal processing module is used to acquire the three-phase reference modulation voltage in real time using a rotor magnetic field oriented vector control strategy (hereinafter referred to as FOC control strategy), and normalize it to obtain a three-level modulation voltage;

[0055] The mode switching decision module is used to obtain the loss difference between the inner and outer tubes of each phase of the motor controller in real time according to the switching tube loss model, and compare the loss difference with the preset hysteresis threshold to update the modulation mode flag bit.

[0056] The level-mixed modulation module is used to read the three-level modulation voltage and the modulation mode flag of each phase, and select to perform three-level modulation or equivalent two-level modulation according to the modulation mode flag, and output the final modulation wave of each phase to control the state of the switching transistor.

[0057] In three-level modulation, the three-level modulation voltage is used as the final modulation wave. In equivalent two-level modulation, the duty cycle of the middle level of the three-level modulation voltage is evenly distributed between the high and low levels to obtain a two-level modulation voltage. The final modulation wave is then obtained based on this two-level modulation voltage. Here, the low level is -1, the middle level is 0, and the high level is 1.

[0058] The control system is suitable for T-type three-level motor controllers. This control system employs a dual closed-loop speed control strategy for the T-type three-level motor controller. This strategy is responsible for converting the given speed into precise voltage modulation commands, as well as dynamically switching the modulation strategy and balancing losses. Under low-voltage conditions, the control system dynamically switches between three-level modulation and equivalent two-level modulation based on the difference in losses between the inner and outer tubes to optimize heat dissipation and reduce thermal stress on the inner tube.

[0059] Figure 2This is the main circuit diagram of the motor controller provided in this embodiment, showing the main circuit of the motor controller based on a T-type three-level topology. The main circuit mainly includes a permanent magnet synchronous motor, a DC-side power supply, a DC-side electrolytic capacitor, and a T-type three-level IGBT module. The T-type three-level IGBT module includes multiple IGBT switching transistors, which are insulated-gate bipolar transistors. The IGBT switching transistors are divided into four transistors for phase A (A1, A2, A3, A4), four transistors for phase B (B1, B2, B3, B4), and four transistors for phase C (C1, C2, C3, C4). The DC-side electrolytic capacitor is divided into upper and lower capacitors. , The total voltage on the DC side is , Figure 2 The image on the right shows a permanent magnet synchronous motor. The permanent magnets of the motor have north and south poles (S and N), and the motor has three-phase winding terminals (A, B, and C). Tm in the diagram represents the motor torque. Specific parameters of the main circuit are shown in Table 1.

[0060] Table 1 Main Circuit Parameter Table

[0061] ;

[0062] See Figure 3 The system control block diagram provided in this embodiment includes the following units in the signal processing module:

[0063] The motor operating parameter sampling unit is used to acquire the motor's mechanical speed via an encoder. With mechanical angle The three-phase stator current is collected by a Hall current sensor. It is equipped with a voltage sensor to collect the DC bus voltage and the upper and lower capacitor voltage in real time. The sampling frequency is set to 10kHz to ensure the real-time performance and accuracy of the control.

[0064] The coordinate transformation unit is used to transform the acquired three-phase stator current. Perform Clarke and Park transformations to convert it into current components in a two-phase rotating coordinate system (dq axis) that rotates synchronously with the rotor magnetic field. The angle required for Park's transformation is determined by mechanical angle. The electrical angle is calculated based on the number of motor pole pairs. The conversion relationship is shown in the following formula:

[0065] ;

[0066] Let be the mechanical angular velocity of the motor. It is electric angular velocity, and its unit is: ; The mechanical speed of the motor, in units of: ; For the mechanical angle of the motor, The electrical angle of the motor is expressed in degrees, with the unit being: , This represents the number of pole pairs of the motor. .

[0067] The speed outer loop control unit is used to employ a speed outer loop PI regulator based on a given speed. With actual mechanical speed The error is used to calculate the q-axis current setpoint required to maintain the target rotational speed. Its control law is:

[0068] ;

[0069] in, These are the proportional and integral gains of the outer speed loop, respectively; This is the output signal of the outer loop PI regulator for the speed. Zero, As the reference signal for the inner current loop, where, This reference signal is the q-axis current setpoint; The given speed of the motor, This refers to the mechanical speed of the motor. and All units are: .

[0070] in, It can be obtained by tuning the following formula:

[0071] ;

[0072] in: Let be the moment of inertia of the motor. The desired bandwidth of the speed loop, This represents the number of pole pairs of the motor. Represents permanent magnet flux linkage.

[0073] The inner current loop control unit also employs PI control, incorporating a feedforward decoupling term to eliminate coupling effects between the d and q axes. The d-axis and q-axis modulation voltages are calculated in a two-phase rotating coordinate system. They are respectively:

[0074] ;

[0075] in, This is the PI proportional gain of the inner current loop. The integral gain of the PI controller. It is electric angular velocity. They are Shaft inductance component; Represents permanent magnet flux linkage. For the Laplace operator.

[0076] Inverse coordinate transformation unit. The calculated modulated voltage in the rotating coordinate system... After inverse Park transform and inverse Clarke transform, the reference modulation voltage in the three-phase stationary coordinate system is obtained. , Figure 3 In That is, the reference modulation voltage Reference modulation voltage The three-level modulation voltage was obtained after normalization. , That is, a three-level modulated voltage. , That is, the three-phase stator current. , Common-mode voltage, This is the modulation mode flag. Options A, B, and C can be selected. These voltage commands will be sent to the subsequent modulation strategy module. The modulation strategy module includes a mode switching decision module, a level mixing modulation module, and a PWM drive signal generation module.

[0077] The modulation strategy module determines whether each phase in the main circuit needs to switch modulation modes through the mode switching decision module. After the modulation mode is determined, the level mixing modulation module generates the final modulation wave. Finally, the PWM drive signal generation module generates a PWM drive signal based on the final modulation wave and the modulation mode to control the state of each switch in the main circuit, thus ensuring that switching losses are evenly distributed. The following sections will introduce each module of the modulation strategy module in turn.

[0078] See Figure 4 Taking phase A of the main circuit as an example, Figure 4 This diagram illustrates the dynamic switching principle of the modulation strategy for equalizing losses in the mode switching decision module. The mode switching decision module includes an IGBT loss model establishment unit, a loss difference monitoring unit, and a hysteresis switching logic control unit.

[0079] The IGBT loss model establishment unit uses a general loss model to calculate the heat generation of each IGBT switch. : This general loss model is the switching transistor loss model. The IGBT loss model building unit establishes the switching transistor loss model based on the above heat generation calculation formula. The heat generation calculated by the switching transistor loss model is... Total losses of switching transistor A1 Total losses of switching transistor A2 Total losses of switching transistor A3 Total losses of switching transistor A4 Total losses of switching transistor B1 Total losses of switching transistor B2 Total losses of switching transistor B3 Total losses of switching transistor B4 Total losses of switching transistor C1 Total losses of switching transistor C2 Total losses of switching transistor C3 Total losses of switching transistor C4 .

[0080] The conduction loss is: ,in Threshold voltage, For on-resistance, This represents the current flowing through the IGBT switching transistor.

[0081] Switching loss is , The switching energy curves provided in the device datasheet were consulted, and the results were calculated after fitting and compensation based on the DC bus voltage and junction temperature.

[0082] The loss difference monitoring unit is used to calculate the difference in losses between the internal and external transistors in each phase arm of the main circuit. For each phase (e.g., phase A), the total external transistor loss is calculated separately. and total loss of inner tube This allows for real-time monitoring of the difference in losses between the inner and outer tubes. The calculation method for the difference in losses between the inner and outer tubes in phases B and C is the same as that in phase A, and will not be elaborated further.

[0083] The hysteresis switching logic control unit is used to set the hysteresis threshold, which is a positive value, and the hysteresis threshold is divided into a first threshold. Second threshold The hysteresis switching logic control unit compares the difference in losses between the internal and external transistors with two hysteresis thresholds. and Comparative analysis is performed to obtain the modulation mode flag. , We can choose A, B, or C. When At that time, the modulation mode is a three-level modulation mode. At this time, the modulation mode is an equivalent two-level modulation mode. The specific analysis is as follows:

[0084] If any one of the bridge arms ( (A, B, C can be chosen), indicating that the outer tube is overheated. This switches the level mixing modulation module to three-level modulation mode for three-level modulation. In three-level modulation mode, the internal and external transistors share the losses, and under low-level conditions, the internal transistor heats up rapidly while the external transistor heats up slowly, resulting in a more even temperature rise.

[0085] If any one of the bridge arms ( (A, B, C can be chosen), indicating that the inner tube is overheated. This switches the level mixing modulation module to the equivalent two-level modulation mode for equivalent two-level modulation. In the equivalent two-level modulation mode, the inner tube does not operate, and its losses are transferred to the outer tube, thereby reducing the temperature of the inner tube.

[0086] In addition, based on the above analysis, there are two hysteresis thresholds. and Boundary values ​​exist, including minimum and maximum values. The boundary values ​​are obtained as follows:

[0087] Minimum value: Set both hysteresis threshold boundary values ​​to zero, so that a switching occurs almost once per switching cycle. The high-frequency switching ensures that the difference in loss is basically zero.

[0088] Maximum value: This maximum value must ensure that the losses of the outer tube and the inner tube are the same within one power frequency cycle. That is, monitoring the losses of the inner and outer tubes, the switching point is defined as the condition where the loss of the inner tube in three-level modulation equals the sum of the losses of the outer tube in three-level modulation and two-level modulation within each power frequency cycle of each phase. The difference between the inner and outer tube losses at this switching point is taken as the maximum value. Hysteresis threshold. and You can take any value within these two boundary values.

[0089] The level mixing modulation module will be introduced in detail next:

[0090] See Figure 5 Taking phase A of the main circuit as an example again, Figure 5 The flowchart illustrates the hysteresis control process for balancing the heating of the inner and outer tubes. The level-mixing modulation module generates the final modulation wave according to the hysteresis control process. Under low-level conditions, the conduction loss of the inner tube in the T-type topology increases significantly. To balance the device temperature rise, this embodiment proposes a hysteresis switching strategy based on real-time loss calculation.

[0091] See Figure 6 , Figure 6 This diagram illustrates the equivalent implementation of two-level and three-level modulation. To achieve equivalent operation to the three-level modulation strategy, an equivalent two-level modulation wave is obtained through a level mixing modulation module, which then controls the switching state of the main circuit's motor controller.

[0092] The level-mixing modulation module includes a three-level PWM generator and a two-level PWM generator.

[0093] The three-level PWM generator enters the three-level modulation mode according to the modulation mode flag, uses the three-level modulation voltage as the final modulation wave, and generates the PWM drive signal by using the in-phase carrier stacking method.

[0094] Specifically, in three-level modulation, the three-level modulation voltage is used as the final modulation wave. The triangular carrier is divided into upper and lower parts, which are compared with the final modulation waves of each phase to generate the driving logic of the inner and outer transistors. This generates the PWM driving signal of the T-type three-level bridge arm to control the state of the switching transistor.

[0095] The two-level PWM generator enters the equivalent two-level modulation mode according to the modulation mode flag, performs duty cycle allocation to obtain the two-level modulation voltage, and obtains the final modulation wave based on the two-level modulation voltage. It then uses bipolar modulation to generate the PWM drive signal.

[0096] Specifically, in equivalent two-level modulation, the duty cycle of the middle level of the three-level modulation voltage is evenly distributed to the high level and the low level to obtain a two-level modulation voltage. Based on the two-level modulation voltage, the final modulation wave is obtained. A centrally symmetrical triangular carrier wave is used to compare with the modulation waves of each phase, thereby generating the PWM drive signal of the T-type three-level bridge arm to control the state of the switching transistor.

[0097] It should be noted that the derivation process of the relationship between the three-level modulation wave and the duty cycle is as follows:

[0098] Three-phase reference modulation voltage Normalized to the range [-1, 1], the three-level modulation voltage is obtained. For any phase, the duty cycles for its output -1, 0, and 1 levels are respectively... And satisfy Without injecting common-mode voltage, the three-level modulated voltage... The relationship with duty cycle is: The maximum phase is obtained by sorting the three-level modulated voltages. intermediate phase Minimum phase By combining the positive and negative values ​​of the three-level modulation voltage, three duty cycle conditions can be obtained. Thus, the corresponding duty cycles of each level can be solved from the nine equations.

[0099] ;

[0100] Solving for:

[0101] ;

[0102] The above formula represents the relationship between the duty cycle and the modulation voltage in three-level modulation without common-mode voltage injection. Where, These represent the duty cycles of the three maximum phase levels. These represent the duty cycles of the three levels in the intermediate phase. These represent the duty cycles of the three minimum phase levels.

[0103] The final modulated wave generation process corresponding to the two-level modulated voltage is as follows: There is no 0 level in two-level modulation. To obtain an equivalent two-level modulated wave, the 0-level duty cycle of each phase in three-level modulation is evenly distributed between the 1-level and -1-level. That is, the new two-level duty cycle satisfies:

[0104] = ;

[0105] = ;

[0106] in, In two-level modulation, this refers to the duty cycle of the -1 level and the 1 level.

[0107] Substituting the three-level duty cycle formula into the above equation, we can obtain the two-level duty cycle formula:

[0108] ;

[0109] Based on this, the equivalent two-level normalized modulation voltage can be derived. for:

[0110] = ;

[0111] This means that, without changing the line voltage output, a completely equivalent two-level modulation instruction can be obtained from the three-level modulation logic simply by redistributing the duty cycle.

[0112] Through the above mathematical relationship, it can be ensured that when the same three-level modulation voltage command is input, the fundamental components of the three-phase line voltages output by the two modulation strategies are completely consistent.

[0113] Second Embodiment

[0114] Please see Figure 7 This embodiment relates to a switching loss equalization control system based on level hybrid modulation. The control system includes a signal processing module, a mode switching decision module, a level hybrid modulation module, and a PWM drive signal generation module, as described in the first embodiment. In addition to the above modules, this embodiment also includes a potential balance control module.

[0115] It should be noted that since the modulation strategy switching in the first embodiment will affect the midpoint current, this embodiment sets up a potential balance control module based on the requirement of strong robustness across the full modulation range, and achieves balance control of the midpoint potential through the potential balance control module.

[0116] In this embodiment, the dual closed-loop speed control strategy of the T-type three-level motor controller in the control system also has the following functions: to address the impact of the hybrid modulation strategy on the midpoint potential, midpoint potential balance control is performed, and the optimal common-mode voltage is calculated and injected in real time to suppress DC-side midpoint voltage offset. The potential balance control module includes an intermediate current modeling unit, a balance control unit, and a common-mode voltage calculation unit.

[0117] The intermediate current modeling unit is used to build the intermediate current model. Specifically, such as... Figure 8 As shown, during one switching cycle, assuming the three-phase current... The current is constant, but because one phase of the main circuit is under two-level modulation and another phase is under three-level modulation, the phase under two-level modulation has no current flowing to the midpoint and therefore no midpoint current is generated. Combined with the modulation switching flag, the midpoint current can be obtained. The model is:

[0118] ;

[0119] in, These are the currents of the maximum phase, intermediate phase, and minimum phase, respectively.

[0120] The balance control unit is used to inject common-mode voltage into the modulation wave generation unit. This is to achieve balanced control of the midpoint potential. That is, in this embodiment, during equivalent two-level modulation, the midpoint potential is... As the final modulated wave, (n=A,B,C). Injection It will change the duty cycle of the 0 level in each phase, thereby controlling the neutral point current. .

[0121] Balance objective: When the capacitor voltages are balanced, the balance control objective is to make the average midpoint current zero, i.e. .

[0122] Adjustment target: such as Figure 8 As shown, when a voltage deviation between the upper and lower capacitors is detected... At that time, the current flowing into the midpoint is: The goal of balance control is to generate a desired current so that the capacitor voltage can return to balance within one switching cycle, i.e., the capacitor voltage returns to its normal value. Therefore, we have: , Its desired current value is designed as ;

[0123] in: This is the total capacitor voltage on the DC side. These are the voltages of the upper and lower capacitors on the DC side, respectively. This refers to the current in the upper and lower capacitors on the DC side. For the desired current to flow through the midpoint, Let the current flowing through the midpoint be... The capacitance value is... In the calculation formula, for The capacitance value, in In the calculation formula, for The capacitance value, in this embodiment and The capacitance values ​​are equal. The switching cycle.

[0124] The common-mode voltage calculation unit is used for solving and limiting the common-mode voltage across the entire modulation range. By simultaneously solving the modulation wave constraint equation, duty cycle equation, and midpoint current equation, the common-mode voltage calculation unit can find the optimal common-mode voltage that achieves the aforementioned balance or regulation objectives across the entire modulation range. When solving this problem, the modulation index must be considered, as it determines the injected common-mode voltage. Then, by determining the range within which the three-phase modulation voltage can be located, the final three duty cycle constraint equations can be determined.

[0125] By simultaneously solving the modulation wave constraint equation, the duty cycle equation, and the midpoint current equation, six equations can be obtained:

[0126] ;

[0127] Nine of the duty cycles are unknowns, and three equations are still missing to solve for them. The modulation index must be considered when solving these equations, as it determines the injected common-mode voltage. Then, by determining the range within which the three-phase modulation voltage can be, the final three duty cycle constraint equations can be established:

[0128] Low-profile system region: Three-phase modulated wave injection After that, the positive and negative signs of the three-phase modulation voltage can be changed.

[0129] Mid-modulation region: Only intermediate phase modulation wave injection Afterwards, the positive and negative situations can be changed.

[0130] High-intensity region: Three-phase modulated wave injection After that, the signs will not change, and the classification will be based on the positive or negative sign of the intermediate phase voltage.

[0131] Converted into a mathematical equation, as shown below:

[0132] ;

[0133] in, These are the voltages of the maximum phase, intermediate phase, and minimum phase, respectively.

[0134] The solutions for the above three ranges are shown in Table 2:

[0135] Table 2 Voltage Boundary Range Table

[0136] ;

[0137] The duty cycle after common-mode voltage injection during low-frequency operation is shown in Table 3:

[0138] Table 3. Duty Cycle Allocation Table for Low-Key System

[0139] ;

[0140] During the common-mode regulation, the duty cycle after common-mode voltage injection is shown in Table 4:

[0141] Table 4. Duty Cycle Allocation Table for Central Adjustment System

[0142] ;

[0143] The duty cycle after common-mode voltage injection during high-modulation operation is shown in Table 5:

[0144] Table 5. High-profile system duty cycle allocation table

[0145] ;

[0146] Therefore, based on the six equations mentioned above, combined with the three duty cycle conditions after injecting the common-mode voltage, and solving nine equations for nine unknowns, the optimal common-mode voltage that can achieve the above balance or regulation target can be found across the entire modulation range. .

[0147] When the calculated common-mode voltage exceeds the defined voltage range, the boundary voltage value is taken as the common-mode voltage for injection, which can balance the midpoint potential at the maximum rate.

[0148] Based on the current modulation mode (three-level modulation mode / equivalent two-level modulation mode), the final three-phase modulation voltage is compared with the corresponding carrier to generate the PWM drive signal for the IGBT switching transistor, thereby controlling the on / off state of the bridge arm.

[0149] The control system in this embodiment has the following advantages:

[0150] Without affecting motor control performance: The equivalent two-level modulation strategy ensures that the relationship between space vector voltage, phase voltage and line voltage remains unchanged under the hybrid modulation mode. Combined with the precise adjustment of the FOC control strategy, the speed control accuracy and dynamic response speed of the motor are not affected, meeting the requirements of high-performance motor drive.

[0151] The system is easy to implement: the control algorithm structure of the control system is clear, the amount of computation is moderate, it can be implemented based on the DSP controller, and it is easy to promote and apply on a large scale.

[0152] Wide range of applications: The control system can be applied to various motor control scenarios using T-type three-level topology, such as new energy vehicle drive systems, industrial servo motors, rail transit traction systems, and ship propulsion systems. It is especially suitable for applications requiring wide speed range, low loss, and high reliability, and has strong practicality and engineering value.

[0153] In addition, some other embodiments include the following modules:

[0154] The real-time feedback monitoring module is used to continuously collect parameters such as motor speed, current, midpoint potential, and IGBT switch junction temperature, and dynamically adjust the PI regulator output, modulation mode, and common-mode voltage injection value to ensure stable system operation.

[0155] The fault protection module is used to immediately cut off the PWM drive signal and stop the motor from running when abnormalities such as overcurrent, overvoltage, or IGBT switching transistor overheating are detected, so as to avoid equipment damage.

[0156] Third Embodiment

[0157] like Figure 9 As shown, this embodiment relates to a switching loss equalization control method based on level hybrid modulation. The switching loss equalization control method is applicable to the control system of the first embodiment, and the method includes the following steps:

[0158] Step S1: Use the FOC control strategy to acquire the three-phase reference modulation voltage in real time, and normalize it to obtain the three-level modulation voltage.

[0159] Step S2: Obtain the loss difference between the inner and outer tubes of each phase of the motor controller in real time according to the switching tube loss model, and compare the loss difference with the preset hysteresis threshold to generate the modulation mode flag bit of each phase.

[0160] Step S3: Receive the three-level modulation voltage and the modulation mode flag of each phase, and perform three-level modulation or equivalent two-level modulation according to the modulation mode flag, and output the final modulation wave of each phase to control the state of the switching transistor.

[0161] In step S3, during three-level modulation, the three-level modulation voltage is used as the final modulation wave; during equivalent two-level modulation, the duty cycle of the middle level of the three-level modulation voltage is evenly distributed to the high level and the low level to obtain the two-level modulation voltage, and the final modulation wave is obtained based on the two-level modulation voltage.

[0162] Fourth embodiment

[0163] like Figure 10 As shown, this embodiment relates to a switching loss equalization control method based on level hybrid modulation. The switching loss equalization control method is applicable to the control system of the second embodiment. The method includes the following steps:

[0164] Step S4: Calculate a common-mode voltage based on the voltage deviation of the upper and lower capacitors on the DC side, the current of each phase, and the modulation mode flag. Inject the common-mode voltage into the final modulation wave in step S3 to adjust the midpoint current and suppress the DC side midpoint potential shift.

[0165] Fifth embodiment

[0166] This embodiment relates to a storage medium storing computer program instructions, which, when executed by a processor, can implement the control method disclosed in the third or fourth embodiment.

[0167] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A switching loss sharing control system based on level hybrid modulation, applied to a T-type three-level motor controller; characterized in that, include: The signal processing module is used to acquire the three-phase reference modulation voltage in real time using the FOC control strategy, and normalize it to obtain the three-level modulation voltage. The mode switching decision module is used to obtain the loss difference between the inner and outer tubes of each phase of the motor controller in real time according to the switching tube loss model, and compare the loss difference with the preset hysteresis threshold to update the modulation mode flag bit. The level-mixed modulation module is used to read the three-level modulation voltage and the modulation mode flag of each phase, and select to perform three-level modulation or equivalent two-level modulation according to the modulation mode flag, and output the final modulation wave of each phase to control the state of the switching transistor. In three-level modulation, the three-level modulation voltage is used as the final modulation wave; In equivalent two-level modulation, the duty cycle of the middle level of the three-level modulation voltage is evenly distributed to the high level and the low level to obtain a two-level modulation voltage. Based on the two-level modulation voltage, the final modulation wave is obtained. The mode switching decision module includes a hysteresis switching logic unit, which is configured as follows: The hysteresis threshold is set, and the hysteresis threshold is divided into a first threshold and a second threshold; When the difference between the inner and outer tube losses of a certain phase is greater than the first threshold, the modulation mode flag of that phase is switched to indicate the three-level modulation mode. When the negative of the difference between the inner and outer tube losses of a certain phase is greater than the second threshold, the modulation mode flag of that phase is switched to indicate the equivalent two-level modulation mode.

2. The switching loss sharing control system according to claim 1, characterized in that: The mode switching decision module generates a modulation mode flag bit independently for each phase arm of the motor; the hysteresis threshold is configured such that when the system is running in steady state, at least two phases of the three-phase bridge arm operate in three-level modulation mode and at most one phase operates in equivalent two-level modulation mode.

3. The switching loss sharing control system according to claim 1, characterized in that: When the mode switching decision module obtains the difference between the inner and outer tube losses based on the switching tube loss model, it takes the sum of the inner tube's conduction loss and switching loss as the inner tube loss; takes the sum of the outer tube's conduction loss and switching loss as the outer tube loss; and takes the difference between the inner tube loss and the outer tube loss as the difference between the inner and outer tube losses.

4. The switching loss sharing control system according to claim 1, characterized in that, The level mixing modulation module includes: A three-level PWM generator is used to enter a three-level modulation mode according to the modulation mode flag bit, use the three-level modulation voltage as the final modulation wave, and generate a PWM drive signal using the in-phase carrier stacking method. A two-level PWM generator is used to enter an equivalent two-level modulation mode according to the modulation mode flag, perform duty cycle allocation to obtain a two-level modulation voltage, and obtain the final modulation wave based on the two-level modulation voltage. A bipolar modulation method is used to generate a PWM drive signal.

5. The switching loss sharing control system according to any one of claims 1-4, characterized in that, Also includes: The midpoint potential balance control module is used to obtain the common-mode voltage based on the voltage deviation of the upper and lower capacitors on the DC side, the current of each phase, and the modulation mode flag, and inject the common-mode voltage into the two-level modulation voltage to form the final modulation wave, so as to adjust the midpoint current and suppress the DC side midpoint potential offset.

6. The switching loss sharing control system according to claim 5, characterized in that, In the process of obtaining the common-mode voltage based on the voltage deviation of the upper and lower capacitors on the DC side, the current of each phase, and the modulation mode flag: Within the full modulation range, based on the voltage boundary constraints of the current modulation range, the common-mode voltage for the balance control of the midpoint potential is solved by simultaneously solving the equations for the modulation wave, duty cycle, and midpoint current. If the solution value exceeds the voltage boundary, the boundary voltage value is taken as the common-mode voltage.

7. A switching loss sharing control method based on level hybrid modulation, characterized in that, The control system according to any one of claims 1-6 includes the following steps: The three-phase reference modulation voltage is acquired in real time using the FOC control strategy and then normalized to obtain the three-level modulation voltage. The loss difference between the inner and outer tubes of each phase of the motor controller is obtained in real time according to the switching tube loss model, and the loss difference is compared with the preset hysteresis threshold to generate the modulation mode flag bit of each phase. It receives the three-level modulation voltage and the modulation mode flag of each phase, and performs three-level modulation or equivalent two-level modulation according to the modulation mode flag, and outputs the final modulation wave of each phase to control the state of the switching transistor. In three-level modulation, the three-level modulation voltage is used as the final modulation wave; in equivalent two-level modulation, the duty cycle of the middle level of the three-level modulation voltage is evenly distributed to the high level and the low level to obtain the two-level modulation voltage, and the final modulation wave is obtained based on the two-level modulation voltage.

8. The switching loss sharing control method according to claim 7, characterized in that, It also includes the following steps: Based on the voltage deviation of the upper and lower capacitors on the DC side, the current of each phase, and the modulation mode flag, a common-mode voltage is calculated and injected into the final modulation wave to adjust the midpoint current and suppress the DC side midpoint potential shift.

9. A storage medium storing computer program instructions thereon, characterized in that, The method described in claim 7 or 8 is implemented when the computer program instructions are executed by the processor.

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