Zero vector period switching and junction temperature balance control method of single-phase PWM rectifier

Abstract

The invention belongs to the field of power electronics and power transmission, and discloses a zero vector period switching and junction temperature balance control method of a single-phase PWM rectifier. The zero vector period switching method is based on a model predictive control algorithm, a fundamental wave period is adopted as a zero vector switching period, and different zero vectors and an optimal non-zero vector are alternately used in adjacent fundamental wave periods to form an optimal switching sequence. According to the junction temperature balance control method, the conduction time and the switching frequency of the devices are controlled according to the optimal switching sequence, so that junction temperature balance of all the switching devices of the rectifier is achieved, device reliability reduction caused by local overheating is avoided, meanwhile, additional hardware cost does not need to be increased, the basic electrical performance of a rectification system is not affected, and the reliability of the rectifier is improved. And the thermal stability and reliability of the rectification system are improved.

Description

Technical Field

[0001] The present invention relates to the fields of power electronics and electric transmission, and in particular to a zero vector periodic switching and junction temperature balance control method for a single-phase PWM rectifier. Background Art

[0002] Single-phase PWM rectifiers have important application value in industrial scenarios such as high-power rail traction power supply systems and high-reliability uninterruptible power supplies due to their technical advantages such as supporting bidirectional energy transmission, maintaining unity power factor characteristics of grid-side voltage and current, and ensuring DC bus voltage stability.

[0003] However, during the operation of single-phase PWM rectifiers, a large amount of industrial operation data and failure mechanism analysis have shown that the junction temperature of the core component, the power semiconductor switching device, seriously affects the system reliability. Specifically, an increase in the average junction temperature and the fluctuation amplitude will significantly accelerate the aging and failure process of the device. In a rectifier system containing multiple power switching devices, the overall reliability index is often determined by the individual device that experiences the highest average junction temperature and the largest junction temperature fluctuation. Therefore, achieving the balance and suppression of the junction temperature of each power device has become the key to improving the operational reliability and service life of power electronic devices.

[0004] Currently, balancing and suppressing the junction temperature of power devices is primarily achieved through active thermal management technology systems, which are broadly categorized into external thermal control and internal thermal control. External thermal control primarily achieves temperature control by improving the device's peripheral heat dissipation. However, external thermal control suffers from the limitation of lag in dynamic temperature control response, making it difficult to promptly address the rapid heating of the device during transient conditions. Internal thermal control, on the other hand, achieves rapid junction temperature regulation through real-time adjustments to electrical parameters directly related to device power consumption. However, this internal thermal control approach increases both control system complexity and economic costs. On the one hand, more complex control algorithms and circuit designs are required to precisely adjust these electrical parameters. On the other hand, to ensure system stability and reliability, sensors and monitoring equipment are required to monitor device parameters such as temperature and power consumption in real time, significantly increasing system costs.

[0005] Therefore, in the field of converter control, Model Predictive Control (MPC) algorithms have become a hot research topic due to their excellent dynamic response characteristics and multi-constraint optimization capabilities. MPC algorithms can quickly calculate the optimal control input based on the current state of the system and the prediction model, thereby achieving precise control of the system.

[0006] However, existing fixed-frequency MPC algorithms primarily focus on optimizing voltage vectors and streamlining calculations, lacking systematic consideration of the thermal effects of switching sequences. Theoretical analysis and experimental verification have shown that switching sequences composed of multiple redundant voltage vectors for the same output level have varying impacts on the junction temperature of each device. Excessive use of any one redundant voltage vector can lead to uneven junction temperatures across the device, and this imbalance worsens with increasing load power, severely impacting system reliability and lifespan. Summary of the Invention

[0007] The object of the present invention is to provide a zero vector periodic switching and junction temperature balance control method for a single-phase PWM rectifier, so that each power device can achieve junction temperature balance.

[0008] To solve the above technical problems, the present invention proposes a zero-vector periodic switching method for a single-phase PWM rectifier, including designing an optimal switching sequence. The optimal switching sequence uses a fundamental wave period as a zero-vector switching period, and alternately uses different zero vectors and an optimal non-zero vector between adjacent fundamental wave periods to form an optimal switching sequence. Specifically, the method includes:

[0009] In the kth fundamental wave cycle, the first zero vector and the optimal non-zero vector are used to form a first optimal switching sequence;

[0010] In the k+1th fundamental wave cycle, the second zero vector and the optimal non-zero vector are used to form a second optimal switching sequence;

[0011] In the k+2th fundamental wave cycle, the first zero vector and the optimal non-zero vector are used to form the first optimal switching sequence, and the sequence is repeated;

[0012] Here, according to the input voltage of the single-phase PWM rectifier, the voltage between points a and b of the bridge arm is measured, and the optimal non-zero vector is selected according to the polarity of the voltage:

[0013] When the voltage is ≥0, selecting a first non-zero vector as the optimal non-zero vector, wherein the first non-zero vector represents the switching state of the device when a forward voltage is applied between points ab;

[0014] When the voltage is less than 0, a second non-zero vector is selected as the optimal non-zero vector, and the second non-zero vector represents the switching state of the device when a negative voltage is applied between points ab.

[0015] Furthermore, the method further includes obtaining a current reference value of the kth fundamental wave period by using a second-order generalized integration algorithm through an outer-loop voltage PI controller and a phase-locked loop, specifically including:

[0016] Obtain the DC side voltage reference value and actual DC side voltage of the kth fundamental wave cycle;

[0017] The DC side voltage of the kth fundamental wave cycle is tracked by the outer loop voltage PI controller to obtain and output a current reference value of the kth fundamental wave cycle;

[0018] The grid voltage is coupled with the current reference value of the kth fundamental wave period through the phase-locked loop and a second-order generalized integration algorithm to output a current reference value of the kth fundamental wave period.

[0019] Furthermore, the method further includes selecting an optimal non-zero voltage vector of the kth fundamental wave period according to a model predictive control algorithm; the selecting the optimal non-zero voltage vector of the kth fundamental wave period includes:

[0020] Obtaining the first non-zero vector V1 of the kth fundamental wave period of the single-phase PWM rectifier, the second non-zero vector V2 of the kth fundamental wave period, the current flowing through the inductor of the kth fundamental wave period, and a current reference value;

[0021] According to the polarity of the voltage in the kth fundamental wave period, an optimal non-zero vector in the kth fundamental wave period is selected.

[0022] Furthermore, the method further includes calculating the vector action time of the kth fundamental wave period, wherein the calculating the vector action time of the kth fundamental wave period includes:

[0023] According to the optimal non-zero vector of the kth fundamental wave period and the volt-second balance principle, the optimal non-zero vector action time and the first zero vector action time of the kth fundamental wave period are calculated, and the optimal non-zero vector action time and the first zero vector action time satisfy:

[0024] T=t0(k)+t opt (k), where T is the switching period, t opt (k) is the action time of the optimal non-zero vector, and t0(k) is the action time of the zero vector.

[0025] Furthermore, the method further includes switching to a zero vector, wherein the switching to a zero vector includes:

[0026] Obtain the first zero vector of the kth fundamental wave period and the second zero vector of the k+1th fundamental wave period, or obtain the second zero vector of the kth fundamental wave period and the first zero vector of the k+1th fundamental wave period;

[0027] The first zero vector and the second zero vector having different periods are received and switched to the optimal switching sequence.

[0028] A method for controlling junction temperature balance of a single-phase PWM rectifier is based on the aforementioned zero-vector periodic switching method. An optimal switching sequence is obtained through the zero-vector periodic switching method. A bridge arm switching signal is generated according to the optimal switching sequence. The device conduction time and switching times are controlled to obtain the loss distribution, junction temperature mean, and fluctuation amplitude of multiple switches and multiple diodes of the single-phase PWM rectifier. The method comprises the following steps:

[0029] Dividing a fundamental wave cycle of the single-phase PWM rectifier into four regions according to the phase between the current of the single-phase PWM rectifier and the voltage between points a and b, the four regions including a first working region, a second working region, a third working region and a fourth working region;

[0030] Selecting optimal non-zero vectors corresponding to the four regions according to the polarity of the voltage, and determining a switching sequence consisting of the optimal non-zero vectors and the zero vector used in the four regions;

[0031] Calculate the average losses of multiple switches and diodes based on their conduction time and switching times under different switching sequences.

[0032] Based on the electrothermal analogy theory and the average losses of multiple switching tubes and multiple diodes under different switching sequences, the mean junction temperature and maximum junction temperature fluctuation of each switching tube and each diode are constructed.

[0033] Furthermore, selecting the optimal non-zero vectors in the four regions according to the polarity of the voltage and determining a switching sequence consisting of the optimal non-zero vectors and the zero vector used in the four regions includes:

[0034] When the first zero vector is used in the kth fundamental wave period: the first working area selects the second non-zero vector as the first optimal non-zero vector to form the first switching sequence; the second working area selects the first non-zero vector as the first optimal non-zero vector to form the first switching sequence; the third working area selects the first non-zero vector as the first optimal non-zero vector to form the first switching sequence; and the fourth working area selects the second non-zero vector as the first optimal non-zero vector to form the first switching sequence.

[0035] When the second zero vector is used in the k+1th fundamental wave period: the first working area selects the second non-zero vector as the second optimal non-zero vector to form the second switching sequence; the second working area selects the first non-zero vector as the second optimal non-zero vector to form the second switching sequence; the third working area selects the first non-zero vector as the second optimal non-zero vector to form the second switching sequence; and the fourth working area selects the second non-zero vector as the second optimal non-zero vector to form the second switching sequence.

[0036] Furthermore, the calculation of average losses of the multiple switching tubes and the multiple diodes according to the conduction time and the number of switches under different switching sequences specifically includes:

[0037] respectively calculating average losses of a plurality of switching tubes and a plurality of diodes in one fundamental wave cycle under the first switching sequence and the second switching sequence;

[0038] Based on the average losses of multiple switching tubes and multiple diodes in one fundamental wave cycle, the average fundamental wave cycle losses of multiple switching tubes and the average fundamental wave cycle losses of multiple diodes in two adjacent fundamental wave cycles are calculated, which can be expressed as:

[0039]

[0040] According to formula (1), we can get:

[0041]

[0042] Among them, PTi_ave is the average loss of multiple switching tubes in the fundamental cycle, PDi_ave is the average loss of multiple diodes in the fundamental cycle, PSS1 Ti_ave is the average loss of multiple switching tubes in the first switching sequence SS1 state, PSS2 Ti_ave is the average loss of multiple switching tubes in the second switching sequence SS2 state, PSS1Di_ave is the average loss of multiple diodes in the fundamental cycle in the first switching sequence SS1 state, and PSS2 Di_ave is the average loss of multiple diodes in the second switching sequence SS2 state.

[0043] Furthermore, based on the electrothermal analogy theory and the average losses of multiple switching tubes and multiple diodes under different switching sequences, the average junction temperature of each switching tube and each diode is constructed, which is expressed as:

[0044]

[0045] Among them, T jTi_ave is the average junction temperature of each switching tube during the fundamental cycle, TjDi_ave is the average junction temperature of each diode during the fundamental cycle, T jT0 and T jD0 are the initial junction temperatures of the switch tube and diode respectively; R djcm and R tjcm They are the thermal resistances from the switch tube and diode to the casing respectively.

[0046] Furthermore, based on the electrothermal analogy theory and combined with the average losses of multiple switching tubes and multiple diodes under different switching sequences, the maximum junction temperature fluctuation of each switching tube and each diode is constructed and expressed as:

[0047]

[0048] Where, ΔT jTi_max is the maximum junction temperature fluctuation within the fundamental cycle of each switching tube, ΔTjDi_max is the maximum junction temperature fluctuation within the fundamental cycle of each diode; PSSx Ti_ave is the larger value of PSS1 Ti_ave and PSS2Ti_ave, and PSSy Ti_ave is the smaller value of PSS1 Ti_ave and PSS2 Ti_ave; PSSx Di_ave is the larger value of PSS1 Di_ave and PSS2 Di_ave, and PSSy Di_ave is the smaller value of PSS1Di_ave and PSS2 Di_ave; f0 is the fundamental frequency.

[0049] Compared with the prior art, the present invention has at least the following beneficial effects:

[0050] The present invention achieves a balanced junction temperature distribution among the switching devices in a single-phase PWM rectifier by sequentially switching the zero vector selection mode between adjacent fundamental wave cycles while maintaining the principle of selecting the non-zero vector according to the polarity of the input voltage. This avoids the degradation of device reliability due to local overheating. At the same time, the invention improves the thermal stability and reliability of the rectifier system without increasing additional hardware costs and without affecting the basic electrical performance of the rectifier system. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A topological diagram of a single-phase two-level PWM rectifier in one embodiment of the present invention;

[0052] Figure 2 This is a structural block diagram of a model predictive control algorithm in one embodiment of the present invention;

[0053] Figure 3 Schematic diagram of fundamental wave period area division in one embodiment of the present invention;

[0054] Figure 4 Schematic diagram of zero vector switching principle in one embodiment of the present invention;

[0055] Figure 5 Schematic diagram of grid-side voltage and current simulation waveforms based on zero vector switching in one embodiment of the present invention;

[0056] Figure 6 1 is a waveform diagram of a bridge arm switch signal based on zero vector switching in one embodiment of the present invention;

[0057] Figure 7 This is a simulated waveform of the junction temperature of a switch tube based on zero vector switching in one embodiment of the present invention;

[0058] Figure 8 : This is a diode junction temperature simulation waveform based on zero vector switching in one embodiment of the present invention;

[0059] Figure 9 This is a waveform of a switch tube junction temperature experiment based on zero vector switching in one embodiment of the present invention;

[0060] Figure 10 FIG. 1 is a diode junction temperature experimental waveform based on zero vector switching in one embodiment of the present invention.

[0061] Figure numbers: 1. Select the optimal non-zero voltage vector for the kth fundamental wave period; 2. Calculate the vector action time for the kth fundamental wave period; 3. Design the optimal switching sequence; 4. Switch to zero vector; 5. Outer loop voltage PI controller; 6. Phase-locked loop. DETAILED DESCRIPTION

[0062] The following, in conjunction with a schematic diagram, provides a more detailed description of a zero-vector periodic switching and junction temperature balancing control method for a single-phase PWM rectifier according to the present invention. This diagram illustrates a preferred embodiment of the present invention. It should be understood that those skilled in the art may modify the present invention described herein while still achieving the beneficial effects of the present invention. Therefore, the following description should be understood as a general guideline for those skilled in the art and is not intended to limit the present invention.

[0063] The following paragraphs describe the present invention in more detail by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are greatly simplified and not to exact scale, and are provided solely for the purpose of assisting in the description of the embodiments of the present invention.

[0064] like Figure 1 The figure shows a single-phase, two-level PWM rectifier topology. In the figure, an AC power source us, an inductor L, and a resistor R are connected in series to connection points a and b of a rectifier bridge. The rectifier bridge is also connected in parallel to a filter capacitor C and a load resistor RL, respectively. Here, is refers to the input current, uab refers to the bridge arm voltage between points a and b, and ubc refers to the rectifier's DC output voltage.

[0065] The rectifier bridge consists of four IGBT switching tubes and a diode anti-parallel to each IGBT switching tube. Among them, the first switching tube T1 and the first diode D1 are located in the upper left bridge arm, the second switching tube T2 and the second diode D2 are located in the lower left bridge arm, the third switching tube T3 and the third diode D3 are located in the upper right bridge arm, and the fourth switching tube T4 and the first quadrupole D4 are located in the lower right bridge arm. The midpoints of the left bridge arm and the right bridge arm are marked as point a and point b, respectively.

[0066] Example 1

[0067] This embodiment is based on the above Figure 1 , proposed a zero-vector periodic switching method for single-phase PWM rectifier, such as Figure 2 The zero-vector periodic switching method, based on a model predictive control algorithm, includes designing an optimal switching sequence 3. This optimal switching sequence 3 uses the fundamental wave period as the zero-vector switching period. Different zero vectors are alternately used with the optimal non-zero vector between adjacent fundamental wave periods to form an optimal switching sequence. This prevents some components from being exposed to high temperatures for extended periods, thereby extending the service life of the entire rectifier system. Furthermore, because this method is implemented at the control algorithm level, it does not require additional hardware and does not significantly increase the complexity and cost of the rectifier system.

[0068] In this embodiment, the design of the optimal switching sequence 3 specifically includes:

[0069] In the kth fundamental wave cycle, the first zero vector V0 and the optimal non-zero vector Vopt are used to form the first optimal switching sequence {V0, Vopt, V0}; in the k+1th fundamental wave cycle, the second zero vector V3 and the optimal non-zero vector Vopt are used to form the second optimal switching sequence {V3, Vopt, V3}; in the k+2th fundamental wave cycle, the first zero vector V0 and the optimal non-zero vector Vopt are used to form the first optimal switching sequence {V0, Vopt, V0}, and the cycle continues.

[0070] The optimal non-zero vector is selected based on the input voltage of the single-phase PWM rectifier, the voltage between points a and b in the bridge arm is measured, and the optimal non-zero vector is selected based on the polarity of the voltage. When the voltage is ≥ 0, the first non-zero vector V1 is selected as the optimal non-zero vector. The first non-zero vector V1 represents the switching state of the device when a positive voltage is applied between points a and b. When the voltage is < 0, the second non-zero vector V2 is selected as the optimal non-zero vector. The second non-zero vector V2 represents the switching state of the device when a negative voltage is applied between points a and b.

[0071] In this embodiment, the zero-vector period switching method further comprises obtaining a current reference value for the kth fundamental cycle using a second-order generalized integrator (SOGI) algorithm via an outer-loop voltage PI controller 5 and a phase-locked loop 6. The outer-loop voltage PI controller 5 enables precise tracking of the DC side voltage, the phase-locked loop 6 provides accurate phase information, and the second-order generalized integrator algorithm effectively processes AC signals, improving the system's anti-interference capability.

[0072] Specifically, the current reference value of the kth fundamental wave period is obtained by using the second-order generalized integration algorithm through the outer loop voltage PI controller 5 and the phase-locked loop 6, including:

[0073] First, the DC link voltage reference value U*dc(k) and the actual DC link voltage udc(k) of the kth fundamental wave cycle are obtained.

[0074] Then, the DC side voltage tracking of the kth fundamental wave period is achieved through the outer loop voltage PI controller 5, and the current reference value I*gm(k) of the kth fundamental wave period is obtained and output.

[0075] Then, the grid voltage ug(k) is integrated with the current reference value I*gm(k) of the kth fundamental wave period through the phase-locked loop 6 and a second-order generalized integration algorithm to output the current reference value i*g(k) of the kth fundamental wave period.

[0076] In this embodiment, the zero vector period switching method further includes selecting the optimal non-zero voltage vector 1 of the kth fundamental wave period according to the model predictive control algorithm, wherein selecting the optimal non-zero voltage vector 1 of the kth fundamental wave period includes:

[0077] The first non-zero vector V1 of the kth fundamental wave period of the single-phase PWM rectifier, the second non-zero vector V2 of the kth fundamental wave period, the current flowing through the inductor of the kth fundamental wave period, and the current reference value i*g(k) are obtained.

[0078] According to the polarity of the voltage uab in the kth fundamental wave period, the optimal non-zero vector Vopt(k) of the kth fundamental wave period is selected.

[0079] In this embodiment, the zero-vector periodic switching method further includes calculating the vector action time 2 of the k-th fundamental wave period. The calculation of the vector action time 2 of the k-th fundamental wave period is based on the volt-second balance principle and can accurately determine the action time of each vector, thereby achieving precise control of the single-phase PWM rectifier. By reasonably allocating the action time of the zero vector and the non-zero vector, the loss distribution of each switching tube can be effectively balanced, thereby achieving balanced control of the junction temperature.

[0080] Specifically, the calculation of the vector action time 2 of the kth fundamental wave period includes:

[0081] According to the optimal non-zero vector Vopt(k) of the kth fundamental wave period and the volt-second balance principle, the optimal non-zero vector action time and the first zero vector action time of the kth fundamental wave period are calculated, and the optimal non-zero vector action time and the first zero vector action time satisfy T=t0(k)+topt(k), where T is the switching period, topt(k) is the action time of the optimal non-zero vector, and t0(k) is the action time of the zero vector.

[0082] In this embodiment, the zero vector periodic switching method further includes switching the input zero vector 4, and the switching input zero vector 4 includes:

[0083] Obtain the first zero vector V0(k) of the kth fundamental wave period and the second zero vector V3(k+l) of the k+lth fundamental wave period, or obtain the second zero vector V3(k) of the kth fundamental wave period and the first zero vector V0(k+l) of the k+lth fundamental wave period.

[0084] The first zero vector and the second zero vector received with different fundamental wave periods are switched and transmitted to the optimally designed switching sequence 3.

[0085] Example 2

[0086] This embodiment, based on Example 1, proposes a junction temperature balance control method for a single-phase PWM rectifier. The junction temperature balance control method obtains an optimal switching sequence through the zero vector periodic switching method, generates a bridge arm switching signal based on the optimal switching sequence, controls the device conduction time and switching times, and obtains the loss distribution, junction temperature mean, and fluctuation amplitude of multiple switching tubes and multiple diodes of the single-phase PWM rectifier. The junction temperature balance control method includes the following steps:

[0087] A fundamental wave cycle of the single-phase PWM rectifier is divided into four regions according to the phase between the current of the single-phase PWM rectifier and the voltage between points a and b. The four regions include a first working region, a second working region, a third working region and a fourth working region.

[0088] According to the polarity of the voltage, optimal non-zero vectors are correspondingly selected in the four regions, and a switching sequence consisting of the optimal non-zero vectors and the zero vector used in the four regions is determined.

[0089] Calculate the average losses of multiple switching tubes and multiple diodes based on their conduction time and switching times under different switching sequences.

[0090] Based on the electrothermal analogy theory and the average losses of multiple switching tubes and multiple diodes under different switching sequences, the mean junction temperature and maximum junction temperature fluctuation of each switching tube and each diode are constructed.

[0091] Specifically, such as Figure 3 As shown, according to the polarity relationship between the grid current ig and the voltage uab, one fundamental wave cycle of the rectifier is divided into four working areas, namely the first working area A1, the second working area A2, the third working area A3 and the fourth working area A4, where φ is the phase angle of the voltage uab lagging the grid current ig.

[0092] In this embodiment, selecting the optimal non-zero vectors corresponding to the four regions according to the polarity of the voltage uab and determining the switching sequence consisting of the optimal non-zero vectors and the zero vector used in the four regions includes:

[0093] Specifically, such as Figure 4 As shown, when the first zero vector V0 is used in the kth fundamental wave period:

[0094] In the first working area A1, ig≥0 and uab<0, the second non-zero vector V2 is selected as the first optimal non-zero vector to form the first switching sequence {V0, V2, V0}.

[0095] In the second working area A2, ig≥0 and uab≥0, the first non-zero vector V1 is selected as the first optimal non-zero vector to form the first switching sequence {V0, V1, V0}.

[0096] In the third working area A3, ig<0 and uab≥0, the first non-zero vector V1 is selected as the first optimal non-zero vector to form the first switching sequence {V0, V1, V0}.

[0097] In the fourth working area A4, ig<0 and uab<0, the second non-zero vector V2 is selected as the first optimal non-zero vector to form the first switching sequence {V0, V2, V0}.

[0098] Similarly, when the second zero vector is used in the k+1th fundamental wave period:

[0099] In the first working area A1, ig≥0 and uab<0, the second non-zero vector V2 is selected as the second optimal non-zero vector to form the second switching sequence {V3, V2, V3}.

[0100] In the second working area A2, ig≥0 and uab≥0, the first non-zero vector V1 is selected as the second optimal non-zero vector to form the second switching sequence {V3, V1, V3}.

[0101] In the third working area A3, ig<0 and uab≥0, the first non-zero vector V1 is selected as the second optimal non-zero vector to form the second switching sequence {V3, V1, V3}.

[0102] In the fourth working area A4, ig<0 and uab<0, the second non-zero vector V2 is selected as the second optimal non-zero vector to form the second switching sequence {V3, V2, V3}.

[0103] In this embodiment, the calculation of the average losses of the multiple switching tubes and the multiple diodes according to the conduction time and the number of switching times of the multiple switching tubes and the multiple diodes under different switching sequences specifically includes:

[0104] The average losses of multiple switching tubes and multiple diodes in one fundamental wave cycle in the first switching sequence and the second switching sequence are calculated respectively.

[0105] Based on the average losses of multiple switching tubes and multiple diodes in one fundamental wave cycle, the fundamental wave cycle average loss PTi_ave of multiple switching tubes and the fundamental wave cycle average loss PDi_ave of multiple diodes in two adjacent fundamental wave cycles are calculated, which can be expressed as:

[0106]

[0107] According to formula (1), we can get:

[0108]

[0109] Among them, PSS1Ti_ave is the fundamental-wave cycle average loss of multiple switching tubes in the first switching sequence SS1 state, PSS2Ti_ave is the fundamental-wave cycle average loss of multiple switching tubes in the second switching sequence SS2 state, PSS1Di_ave is the fundamental-wave cycle average loss of multiple diodes in the first switching sequence SS1 state, and PSS2Di_ave is the fundamental-wave cycle average loss of multiple diodes in the second switching sequence SS2 state.

[0110] In this embodiment, based on the electrothermal analogy theory and combined with the average losses of multiple switching tubes and multiple diodes under different switching sequences, the average junction temperature of each switching tube and each diode is constructed, which is expressed as:

[0111]

[0112] Wherein, TjTi_ave is the average junction temperature of each switch tube during the fundamental cycle, TjDi_ave is the average junction temperature of each diode during the fundamental cycle, TjT0 and TjD0 are the initial junction temperatures of the switch tube and diode, respectively; Rdjcm and Rtjcm are the thermal resistances from the switch tube and diode to the case, respectively.

[0113] In this embodiment, based on the electrothermal analogy theory and combined with the average losses of multiple switching tubes and multiple diodes under different switching sequences, the maximum junction temperature fluctuation of each switching tube and each diode is constructed, which is expressed as:

[0114]

[0115] Among them, ΔTjTi_max is the maximum junction temperature fluctuation within the fundamental cycle of each switching tube, ΔTjDi_max is the maximum junction temperature fluctuation within the fundamental cycle of each diode; PSSx Ti_ave is the larger value of PSS1 Ti_ave and PSS2Ti_ave, PSSyTi_ave is the smaller value of PSS1 Ti_ave and PSS2 Ti_ave; PSSx Di_ave is the larger value of PSS1 Di_ave and PSS2 Di_ave, PSSy Di_ave is the smaller value of PSS1Di_ave and PSS2 Di_ave; f0 is the fundamental frequency.

[0116] In summary, in this embodiment, the fundamental wave period is used as the zero vector switching period, and the optimal non-zero vector Vopt is selected based on the polarity of the voltage uab in different regions of the fundamental wave period. Specifically, in the first fundamental wave period, the first zero vector V0 is used to form the switching sequence {V0, Vopt, V0} (denoted as switching sequence SS1); in the l+1 fundamental wave period, the second zero vector V3 is used to form the switching sequence {V3, Vopt, V3} (denoted as switching sequence SS2); in the l+2 fundamental wave period, the first zero vector V0 is again used to form the switching sequence SS1, and in the l+3 fundamental wave period, the second zero vector V3 is again used to form the switching sequence SS2. The zero vector selection for subsequent fundamental wave periods is alternately switched according to the above rule. The bridge arm control signal generated thereby can strictly control the device's on-time and switching times, thereby achieving junction temperature balance between two adjacent fundamental wave periods. This effectively solves the problem of uneven junction temperature within a fundamental wave period caused by the traditional MPC algorithm using only one zero vector, significantly improving the reliability and service life of the system.

[0117] Example 3

[0118] This embodiment is a specific experimental operation based on Examples 1 and 2. A low-power experimental platform is built using Infineon modules. A sampling circuit collects the rectifier system's DC side voltage reference value U*dc(k), current reference value I*gm(k), and actual DC side voltage udc(k) data in real time. An outer-loop voltage PI controller 5 and a phase-locked loop 6 are used with a second-order generalized integration algorithm to accurately track the DC side voltage and, based on this, obtain the current reference value i*g(k). Based on the model predictive control algorithm, the optimal non-zero vector is determined. The action time of the optimal non-zero vector is further calculated based on the volt-second balance principle and combined with the zero-vector switching module to form an optimal switching sequence, ultimately generating a bridge arm control signal to drive the rectifier. Simultaneously, an infrared thermometer is used to detect changes in the junction temperature of the switching device in real time, providing data support for system optimization.

[0119] Specifically, such as Figure 5 As shown in the figure, the waveform of the three key electrical parameters of the single-phase PWM rectifier changing with time is shown. The horizontal axis in the figure represents time t, with a unit of 10ms / grid, and the left side of the vertical axis is the voltage unit V, and the right side is the current unit A. Figure 5 It contains three curves of different colors: the blue curve is the grid voltage ug, which changes in a sinusoidal periodic waveform with an amplitude of approximately ±150V; the red curve is the grid current ig, which also changes in a sinusoidal periodic waveform with an amplitude of approximately ±50A. The grid current ig and the grid voltage ug have the same frequency but a certain phase difference; the green curve is the DC side voltage udc, which is about 200V, but has slight fluctuations.

[0120] Figure 5 Figure 1 shows the electrical characteristics of a single-phase PWM rectifier in steady-state operation. The DC voltage (udc) remains relatively stable, while the AC grid voltage (ug) and current (ig) exhibit periodic variations. These waveforms demonstrate the rectifier system's excellent control over power conversion.

[0121] exist Figure 5 On the basis of Figure 6 The bridge arm switching signal waveform is shown, that is, the switching sequence diagram of the single-phase PWM rectifier in two adjacent fundamental wave cycles, which clearly shows the application of the zero-vector periodic switching method.

[0122] Figure 6 It contains two different switching signals Sa and Sb, represented by blue and red respectively. The horizontal axis in the figure represents time t, with a unit of 10ms / grid; the vertical axis represents the switch state. When the value of the switch signal is 1, it indicates that the switch is on, and when the value of the switch signal is 0, it indicates that the switch is off.

[0123] Further, Figure 6Figure 1 shows the switching sequence SS1 and switching sequence SS2 regions included in the switching signals Sa and Sb. In switching sequence SS1, when the switching signal Sa remains in the on state (i.e., the value is 1), the switching signal Sb is in the off state (i.e., the value is 0). When the switching signal Sa switches to the off state (i.e., the value is 0), the switching signal Sb switches to the on state (i.e., the value is 1). The on time of the switching signal Sa corresponds to the off time of the switching signal Sa.

[0124] In the switching sequence SS2 , the states of the switching signal Sa and the switching signal Sb are opposite to those of the switching sequence SS1 .

[0125] pass Figure 6 The bridge arm switching signal waveform is displayed, intuitively illustrating the change pattern of the switching signal within two adjacent fundamental wave cycles when implementing the zero-vector periodic switching control method. In this way, balanced control of the junction temperature of each switching device in the single-phase PWM rectifier is achieved.

[0126] In this embodiment, the junction temperature of the diode and switch tube of the single-phase PWM rectifier is simulated, and the simulation results are as follows: Figure 7 and Figure 8 shown. Figure 7 The junction temperature simulation waveforms of the four switching tubes in the single-phase PWM rectifier are shown in the figure. Figure 8 The figure shows the junction temperature simulation waveforms of four diodes in a single-phase PWM rectifier.

[0127] exist Figure 7 In the figure, the vertical axis represents the junction temperature of the switch, TjT, in degrees Celsius, ranging from 48°C to 60°C; the horizontal axis represents time, t, in 200ms / division. The blue curve in the figure represents the first switch, TjT1; the red curve represents the second switch, TjT2; the green curve represents the third switch, TjT3; and the yellow curve represents the fourth switch, TjT4.

[0128] As can be seen from the simulated junction temperature waveforms of the switching tubes, the simulated curves of the four switching tubes all show a rapid upward trend from the initial stage, then tend to stabilize, and show periodic small fluctuations in the stable state. The enlarged illustration in the upper right corner shows the details of the junction temperature fluctuations in the stable stage, with the temperature range between 52°C and 56°C.

[0129] exist Figure 8 In the figure, the ordinate represents the diode junction temperature, TjD, in °C, ranging from 45°C to 65°C; the abscissa represents time, t, in 200ms / division. The blue curve represents the junction temperature, TjD1, of the first diode; the red curve represents the junction temperature, TjD2, of the second diode; the green curve represents the junction temperature, TjD3, of the third diode; and the yellow curve represents the junction temperature, TjD4, of the fourth diode.

[0130] As can be seen from the diode junction temperature simulation waveforms, the simulated curves of the four diodes all show an initial rapid rise followed by stabilization, with periodic fluctuations occurring within the stable state. The enlarged illustration in the lower right corner shows the details of the junction temperature fluctuations during the stable phase, ranging from 58°C to 62°C.

[0131] according to Figure 7 and Figure 8 The simulation results show that when the zero-vector periodic switching control method is adopted, the junction temperatures between all switching tubes and all diodes tend to be balanced, and their respective fluctuation ranges are similar, with only differences in the fluctuation phase. This verifies that the junction temperature balance control method can effectively achieve the goal of junction temperature balance control.

[0132] Based on the above Figure 7 and Figure 8 The simulation results are verified experimentally. The experimental verification results are as follows Figure 9 and Figure 10 shown. Figure 9 The paper shows the Figure 7 Simulation principle, experimental waveforms of junction temperature of four switching tubes in single-phase PWM rectifier, Figure 10 Demonstrated based on Figure 8 Simulation principle, experimental waveforms of junction temperature of four diodes in single-phase PWM rectifier.

[0133] exist Figure 9 In the figure, the ordinate represents the junction temperature TjT of the switch, in degrees Celsius, ranging from 36°C to 40°C; the abscissa represents time t, in 5s / division. The four curves in the figure, each colored differently, represent the junction temperatures of the four switch tubes. The blue curve represents the first switch tube, TjT1, with an average junction temperature of 37.6°C; the red curve represents the second switch tube, TjT2, with an average junction temperature of 37.3°C; the green curve represents the third switch tube, TjT3, with an average junction temperature of 37.2°C; and the yellow curve represents the fourth switch tube, TjT4, with an average junction temperature of 37.4°C.

[0134] From the experimental waveforms of the switch tube junction temperature, we can see that the waveforms of the four switch tubes all show slight fluctuations, but overall they remain within a very close temperature range.

[0135] exist Figure 10In the graph, the ordinate represents the diode junction temperature, TjD, in degrees Celsius, ranging from 38°C to 42°C; the abscissa represents time, t, in 5 seconds per grid. The four color-coded curves in the figure represent the junction temperatures of the four diodes. The blue curve represents the junction temperature, TjD1, of the first diode, with an average junction temperature of 39.7°C; the red curve represents the junction temperature, TjD2, of the second diode, with an average junction temperature of 39.9°C; the green curve represents the junction temperature, TjD3, of the third diode, with an average junction temperature of 39.8°C; and the yellow curve represents the junction temperature, TjD4, of the fourth diode, with an average junction temperature of 40.1°C.

[0136] Similarly, from the diode junction temperature experimental waveform, it can be obtained that the junction temperatures of the four diodes are also kept in a very close temperature range.

[0137] According to the experimental results, the maximum junction temperature difference between all switching tubes is only 0.4°C, and the maximum junction temperature difference between all diodes is only 0.4°C. This intuitively proves that the zero-vector periodic switching control method described in this application can effectively achieve junction temperature balance between switching devices, fully verifying the effectiveness of this control method in practical applications.

[0138] In summary, from Figure 7 and Figure 8 The simulation results and Figure 9 and Figure 10 Experimental results show that the proposed zero-vector periodic switching control method not only demonstrates good junction temperature balancing in theoretical simulations but also achieves satisfactory results in practical applications. By alternating between different zero-vector control strategies between adjacent fundamental cycles, the proposed method successfully achieves junction temperature balancing for each switching device in a single-phase PWM rectifier, effectively avoiding device reliability issues caused by uneven junction temperature. This is of great significance for improving overall system reliability and service life.

[0139] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A zero vector periodic switching method for a single-phase PWM rectifier based on a model predictive control algorithm, characterized in that: The method includes designing an optimal switching sequence, wherein the optimal switching sequence uses a fundamental wave period as a zero vector switching period, and alternately uses different zero vectors and an optimal non-zero vector between adjacent fundamental wave periods to form an optimal switching sequence, specifically including: In the kth fundamental wave cycle, the first zero vector and the optimal non-zero vector are used to form a first optimal switching sequence; In the k+1th fundamental wave cycle, the second zero vector and the optimal non-zero vector are used to form a second optimal switching sequence; In the k+2th fundamental wave cycle, the first zero vector and the optimal non-zero vector are used to form the first optimal switching sequence, and the sequence is repeated; Here, according to the input voltage of the single-phase PWM rectifier, the voltage between points a and b of the bridge arm is measured, and the optimal non-zero vector is selected according to the polarity of the voltage: When the voltage is ≥0, selecting a first non-zero vector as the optimal non-zero vector, wherein the first non-zero vector represents the switching state of the device when a forward voltage is applied between points ab; When the voltage is less than 0, a second non-zero vector is selected as the optimal non-zero vector, and the second non-zero vector represents the switching state of the device when a negative voltage is applied between points ab.

2. The zero vector periodic switching method according to claim 1, wherein: The method also includes obtaining the current reference value of the kth fundamental wave cycle by using a second-order generalized integration algorithm through an outer loop voltage PI controller and a phase-locked loop, specifically including: Obtain the DC side voltage reference value and actual DC side voltage of the kth fundamental wave cycle; The DC side voltage of the kth fundamental wave cycle is tracked by the outer loop voltage PI controller to obtain and output a current reference value of the kth fundamental wave cycle; The grid voltage is coupled with the current reference value of the kth fundamental wave period through the phase-locked loop and a second-order generalized integration algorithm to output a current reference value of the kth fundamental wave period.

3. The zero vector periodic switching method according to claim 1, wherein: The method further includes selecting an optimal non-zero voltage vector of the kth fundamental wave period according to a model predictive control algorithm; the selecting the optimal non-zero voltage vector of the kth fundamental wave period includes: Obtaining the first non-zero vector V1 of the kth fundamental wave period of the single-phase PWM rectifier, the second non-zero vector V2 of the kth fundamental wave period, the current flowing through the inductor of the kth fundamental wave period, and a current reference value; According to the polarity of the voltage in the kth fundamental wave period, an optimal non-zero vector in the kth fundamental wave period is selected.

4. The zero vector periodic switching method according to claim 1, wherein: The method further includes calculating the vector action time of the kth fundamental wave period, wherein the calculating the vector action time of the kth fundamental wave period includes: According to the optimal non-zero vector of the kth fundamental wave period and the volt-second balance principle, the optimal non-zero vector action time and the first zero vector action time of the kth fundamental wave period are calculated, and the optimal non-zero vector action time and the first zero vector action time satisfy: T=t0(k)+t opt (k), where T is the switching period, t opt (k) is the action time of the optimal non-zero vector, and t0(k) is the action time of the zero vector.

5. The zero vector period switching method according to claim 1, wherein: The invention also includes switching to a zero vector, wherein the switching to a zero vector includes: Obtain the first zero vector of the kth fundamental wave period and the second zero vector of the k+1th fundamental wave period, or obtain the second zero vector of the kth fundamental wave period and the first zero vector of the k+1th fundamental wave period; The first zero vector and the second zero vector having different periods are received and switched to the optimal switching sequence.

6. A junction temperature balance control method for a single-phase PWM rectifier, based on the zero-vector periodic switching method according to any one of claims 1 to 5, characterized in that: The method of periodic switching of the zero vector is used to obtain an optimal switching sequence, generate a bridge arm switching signal according to the optimal switching sequence, control the device conduction time and the number of switches, and obtain the loss distribution, junction temperature average and fluctuation amplitude of multiple switch tubes and multiple diodes of the single-phase PWM rectifier, including the following steps: Dividing a fundamental wave cycle of the single-phase PWM rectifier into four regions according to the phase between the current of the single-phase PWM rectifier and the voltage between points a and b, the four regions including a first working region, a second working region, a third working region and a fourth working region; Selecting optimal non-zero vectors corresponding to the four regions according to the polarity of the voltage, and determining a switching sequence consisting of the optimal non-zero vectors and the zero vector used in the four regions; Calculate the average losses of multiple switches and diodes based on their conduction time and switching times under different switching sequences. Based on the electrothermal analogy theory and the average losses of multiple switching tubes and multiple diodes under different switching sequences, the mean junction temperature and maximum junction temperature fluctuation of each switching tube and each diode are constructed.

7. The junction temperature balance control method according to claim 6, wherein: The selecting of the optimal non-zero vectors in the four regions according to the polarity of the voltage and determining a switching sequence consisting of the optimal non-zero vectors and the zero vector used in the four regions includes: When the first zero vector is used in the kth fundamental wave period: the first working area selects the second non-zero vector as the first optimal non-zero vector to form the first switching sequence; the second working area selects the first non-zero vector as the first optimal non-zero vector to form the first switching sequence; the third working area selects the first non-zero vector as the first optimal non-zero vector to form the first switching sequence; and the fourth working area selects the second non-zero vector as the first optimal non-zero vector to form the first switching sequence. When the second zero vector is used in the k+1th fundamental wave period: the first working area selects the second non-zero vector as the second optimal non-zero vector to form the second switching sequence; the second working area selects the first non-zero vector as the second optimal non-zero vector to form the second switching sequence; the third working area selects the first non-zero vector as the second optimal non-zero vector to form the second switching sequence; and the fourth working area selects the second non-zero vector as the second optimal non-zero vector to form the second switching sequence.

8. The junction temperature balance control method according to claim 6, wherein: Calculating the average losses of the multiple switching tubes and the multiple diodes according to the conduction time and the number of switches under different switching sequences specifically includes: respectively calculating average losses of a plurality of switching tubes and a plurality of diodes in one fundamental wave cycle under the first switching sequence and the second switching sequence; Based on the average losses of multiple switching tubes and multiple diodes in one fundamental wave cycle, the average fundamental wave cycle losses of multiple switching tubes and the average fundamental wave cycle losses of multiple diodes in two adjacent fundamental wave cycles are calculated, which can be expressed as: According to formula (1), we can get: Among them, PTi_ave is the average loss of multiple switching tubes in the fundamental cycle, PDi_ave is the average loss of multiple diodes in the fundamental cycle, PSS1 Ti_ave is the average loss of multiple switching tubes in the first switching sequence SS1 state, PSS2 Ti_ave is the average loss of multiple switching tubes in the fundamental cycle in the second switching sequence SS2 state, PSS1 Di_ave is the average loss of multiple diodes in the fundamental cycle in the first switching sequence SS1 state, and PSS2 Di_ave is the average loss of multiple diodes in the fundamental cycle in the second switching sequence SS2 state.

9. The junction temperature balance control method according to claim 6, wherein: According to the electrothermal analogy theory, combined with the average losses of multiple switching tubes and multiple diodes under different switching sequences, the average junction temperature of each switching tube and each diode is constructed and expressed as: Among them, T jTi_ave is the average junction temperature of each switching tube during the fundamental cycle, T jDi_ave is the average junction temperature of each diode during the fundamental cycle, TjT0 and TjD0 are the initial junction temperatures of the switch tube and diode respectively; Rdjcm and Rtjcm are the thermal resistances from the switch tube and diode to the case respectively.

10. The junction temperature balance control method according to claim 6, wherein: According to the electrothermal analogy theory, combined with the average losses of multiple switching tubes and multiple diodes under different switching sequences, the maximum junction temperature fluctuation of each switching tube and each diode is constructed and expressed as: Among them, ΔTjTi_max is the maximum junction temperature fluctuation within the fundamental cycle of each switching tube, ΔTjDi_max is the maximum junction temperature fluctuation within the fundamental cycle of each diode; PSSx Ti_ave is the larger value of PSS1 Ti_ave and PSS2Ti_ave, and PSSy Ti_ave is the smaller value of PSS1 Ti_ave and PSS2 Ti_ave; PSSx Di_ave is the larger value of PSS1 Di_ave and PSS2 Di_ave, and PSSy Di_ave is the smaller value of PSS1Di_ave and PSS2 Di_ave; f0 is the fundamental frequency.

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