Active thermal management control method for single-phase photovoltaic inverter with optimized electrical characteristics

Abstract

The application discloses a kind of single-phase photovoltaic inverter active thermal management control methods containing electrical characteristic optimization, the method includes the following steps: the parameter of photovoltaic array link, DAB direct current conversion link, H bridge inverter grid-connected link and power grid link is measured, the real-time switch frequency of gallium nitride device and the phase shift parameter D between DAB direct current conversion link primary and secondary edge overall drive signal are adjusted in real time a , primary side drive signal internal phase shift parameter D b , secondary side drive signal internal phase shift parameter D c The application introduces active thermal management control method on the basis of conventional single-phase photovoltaic inverter, realizes the inhibition of power semiconductor device junction temperature and overall reliability promotion, uses DAB converter for the DC / DC link of conventional single-phase photovoltaic inverter and combines triple shift control and active thermal management control method to eliminate local pseudo maximum power point, realizes photovoltaic array output electrical characteristic optimization.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics and power electronics technology, and relates to an active thermal management control method for a single-phase photovoltaic inverter, specifically an active thermal management control method for a single-phase photovoltaic inverter with electrical characteristic optimization. Background Technology

[0002] Energy is the foundation and driving force of human civilization, and it is crucial for promoting economic and social development and improving people's well-being. In the continuous increase of installed capacity of renewable energy power generation in the new era, photovoltaic (PV) power generation has consistently held a leading position among different forms of renewable energy generation. Although many regions in China have successively formulated relevant incentive policies for PV power generation, the cost of PV power generation remains higher than that of traditional thermal power. Therefore, developing unidirectional PV inverters with better electrical characteristics and higher reliability is of significant strategic importance for reducing the maintenance costs of PV power generation and increasing its adoption rate.

[0003] A single-phase photovoltaic (PV) inverter consists of a PV array, a DC / DC converter, and a DC / AC converter. The PV array converts solar energy into DC voltage output, which is also the source of power input for the single-phase PV inverter. Due to the randomness of solar irradiance, a DC / DC converter is needed for voltage regulation. After regulation, the voltage is input to the DC / AC converter and then connected to the grid for user supply.

[0004] DC / DC converters can be applied in photovoltaic microgrids to stabilize the output voltage of the photovoltaic array and improve the stability of the system's photoelectric conversion. However, traditional single-phase photovoltaic inverters use non-isolated DC / DC converters, which exhibit local pseudo-maximum power points when achieving maximum power point control, hindering the full realization of the photovoltaic array's output power potential. Furthermore, the feedback control does not address junction temperature fluctuations in power semiconductor devices, which is detrimental to suppressing junction temperature and extending the lifespan of these devices.

[0005] The lifespan of power devices directly affects the reliability of inverters; inverter failures due to power device losses can account for up to 34%. Introducing active thermal management control into single-phase photovoltaic inverters can improve the lifespan of power devices and the overall reliability of the inverter, while also accurately predicting the service life based on the actual operating conditions of single-phase photovoltaic inverters. Summary of the Invention

[0006] To address the aforementioned problems in the background technology, this invention provides an active thermal management control method for single-phase photovoltaic inverters with optimized electrical characteristics. This invention introduces an active thermal management control method into the traditional single-phase photovoltaic inverter, achieving suppression of junction temperature in power semiconductor devices and improving overall reliability. It utilizes a DAB converter in the DC / DC stage of a traditional single-phase photovoltaic inverter and combines triple shift control with active thermal management control to eliminate local pseudo-maximum power points, thereby optimizing the electrical characteristics of the photovoltaic array output.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A single-phase photovoltaic inverter includes a photovoltaic array stage, a DAB DC-DC converter stage, and an H-bridge inverter grid-connected stage, wherein:

[0009] The photovoltaic array consists of three photovoltaic units G a G b G c It is composed of series connections and each unit is connected in parallel with a diode D. a D b D c A voltage regulator capacitor C is connected in parallel to the output port. i ;

[0010] The DAB DC-DC converter stage consists of a primary-side H-bridge and a secondary-side H-bridge. The primary-side H-bridge includes high-frequency gallium nitride devices S1, S2, S3, and S4, and their respective parallel-connected body diodes D1, D2, D3, and D4. The secondary-side H-bridge includes high-frequency gallium nitride devices S5, S6, S7, and S8, and their respective parallel-connected body diodes D5, D6, D7, and D8. The primary-side H-bridge is connected to the secondary-side H-bridge via a high-frequency isolation transformer. A DC-DC stabilizing capacitor C1 is connected in parallel at the DC-DC converter output terminal of the DAB stage, and an H-bridge inverter grid-connected stage is connected in parallel at the output port of the secondary-side H-bridge. After rectification, grid connection is performed.

[0011] The H-bridge inverter grid connection stage includes S9, S... 10 S 11 S 12 High-frequency gallium nitride devices and their respective parallel body diodes D9 and D 10 D 11 D 12 .

[0012] An active thermal management control method for the above-mentioned single-phase photovoltaic inverter includes the following steps:

[0013] (1) Monitor the photovoltaic array voltage value V and photovoltaic array current value I in real time, and then import them into the MPPT control program;

[0014] (2) The output value after MPPT retrieval is accumulated with V, and then a PI circuit is introduced and connected with the diode current i. d The difference is calculated and finally introduced into the PI stage in step (3);

[0015] (3) Real-time voltage U at the grid terminal g With the ideal set voltage U at the grid end s The difference is calculated, and the value after the difference is passed through a zero-order hold and then fed into a PI circuit. The difference is then calculated with the value in step (2) to finally obtain the required real-time phase value.

[0016] (4) Sampling gallium nitride device reference junction temperature T ref , will T ref The measured value T of gallium nitride device mes After subtraction, import the results into the periodic averaging module and the PI module respectively, and finally subtract the results to obtain the real-time duty cycle value.

[0017] (5) The final PWM signal is input into the corresponding gallium nitride device driver to complete the active thermal management control method.

[0018] A method for predicting the lifetime of the above-mentioned single-phase photovoltaic inverter includes the following steps:

[0019] (1) Set the sensor's first discrete sampling time, collect the junction temperature value of the gallium nitride power device in real time, and perform a second discrete filtering on the junction temperature value to filter out the peak and valley spikes in the temperature cycle.

[0020] (2) Traverse the array obtained by discretization filtering in step (1) one by one. Starting from the first data point, determine the product of the difference between the next data point and the previous data point and the difference between the next data point and the next data point. Determine the peak and valley point type based on the sign of the product.

[0021] (3) Use the rainflow counting method to extract the effective load cycle, and obtain the junction temperature effective load average value, cycle range and cycle number;

[0022] (4) The damage of gallium nitride devices in a single thermal cycle was calculated using the accurate damage model of gallium nitride devices. The accurate damage model of gallium nitride devices is as follows:

[0023]

[0024] Where a is the slope of the accelerated aging test curve of gallium nitride device, b is the intersection point of the accelerated aging test curve of gallium nitride power device with the vertical axis, b2-b6 are the material constants, and ΔT j T represents the amplitude of a single junction temperature fluctuation. jmax T represents the maximum junction temperature. onWhere I is the heating time, V is the load current, V is the blocking voltage, and D is the bonding wire diameter.

[0025] (5) The number of cycles that a gallium nitride power device can withstand under thermal cycling stress is n. i In this case, the number of cycles that cause the device to fail is N. i The single-use damage value of gallium nitride power devices is:

[0026]

[0027] Throughout the entire operating process, the gallium nitride power device is subjected to m different amplitudes of thermal cycling stress, and the overall cumulative damage value is:

[0028]

[0029] Gallium nitride power devices fail when the overall cumulative damage F reaches 1.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. This invention, based on the application scenario of single-phase photovoltaic inverters, divides the photovoltaic power generation process into a photovoltaic array port, a DAB (Digital-to-Analog Converter) stage, and an H-bridge inverter grid-connected stage. A maximum power point control (MPP) stage is added to the photovoltaic array port to maintain the maximum power output of the photovoltaic array and reduce power degradation caused by environmental factors such as cloud cover and damage to the photovoltaic panel's surface. Triple phase-shift control and active thermal management control are added to the DAB DC-DC converter stage and the H-bridge inverter grid-connected stage to maintain the stability of the DAB DC-DC converter output and improve the lifespan of the power devices in this stage.

[0032] 2. This invention applies the DAB (Direct Current Converter) stage to a single-phase photovoltaic inverter, overcoming the problem of local pseudo-maximum power point in traditional single-phase photovoltaic inverters. It can also improve the search rate and accuracy of the maximum power point, thereby improving the photoelectric conversion efficiency of the photovoltaic array and the full utilization of light energy.

[0033] 3. The active thermal management control method proposed in this invention uses real-time adjustment of the real-time phase and real-time duty cycle of the drive signals of the DAB DC-DC converter and the H-bridge inverter to reduce the junction temperature fluctuation and average junction temperature of the power devices, thereby improving the service life of the power devices and the overall reliability of the single-phase photovoltaic inverter.

[0034] 4. The life prediction method for single-phase photovoltaic inverters proposed in this invention collects historical load damage and current junction temperature fluctuations of power devices in each stage of the single-phase photovoltaic inverter in real time to perform life prediction assessment. The extracted junction temperature sequence can completely reflect the damage of power devices and accurately predict the life of each stage. Attached Figure Description

[0035] Figure 1 It is a single-phase photovoltaic inverter topology;

[0036] Figure 2 This is a schematic diagram of an active thermal management control strategy;

[0037] Figure 3 This is a schematic diagram of the active thermal management control variable feedback;

[0038] Figure 4 This is a comparison chart of the discretized and filtered junction temperature curve with the original waveform.

[0039] Figure 5 This is the relationship between the output power and output voltage of the photovoltaic array in the first set of state modes;

[0040] Figure 6 This is the relationship between the output power and output voltage of the photovoltaic array under the second set of state modes;

[0041] Figure 7 This is the junction temperature fluctuation curve of the S1 GaN HEMT device under the second state mode;

[0042] Figure 8 This is the junction temperature fluctuation curve of the S1 GaN HEMT device under the third state mode. Detailed Implementation

[0043] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0044] Specific Implementation Method 1: This implementation method provides a single-phase photovoltaic inverter, such as... Figure 1 As shown, the main topology of the single-phase photovoltaic inverter can be divided into three parts: a photovoltaic array stage, a DAB DC-DC conversion stage, and an H-bridge inverter grid-connected stage, wherein:

[0045] The photovoltaic array consists of three photovoltaic units G a G b G c It is composed of series connections and each unit is connected in parallel with a diode D. a D b D c The output port is connected to a voltage regulator capacitor C. i Through DC voltage regulator capacitor C i Voltage regulation; the photovoltaic array port is connected to the primary-side H-bridge of the DAB converter.

[0046] The DAB (Direct-to-Browser) converter stage consists of a primary-side H-bridge and a secondary-side H-bridge. The primary-side H-bridge includes high-frequency gallium nitride (GaN) devices S1, S2, S3, and S4, each with its parallel body diodes D1, D2, D3, and D4. The secondary-side H-bridge includes high-frequency GaN devices S5, S6, S7, and S8, each with its parallel body diodes D5, D6, D7, and D8. The primary-side H-bridge is connected to the secondary-side H-bridge via a high-frequency isolation transformer, the leakage inductance of which is L. k The voltage ratio of the high-frequency isolation transformer port windings is 1:n, and the voltage at port CD, after being referred to port AB, is V. cd / n, phase shift parameter The power transmission direction of the DAB DC-DC converter is determined, and the phase shift parameters are set. This allows power to flow from the photovoltaic array to the secondary side of the DAB DC-DC converter stage. The output of the DAB stage is connected in parallel with a DC-DC stabilizing capacitor C1. The secondary H-bridge is stabilized by the DC-DC stabilizing capacitor C1. The output port of the secondary H-bridge is connected in parallel with the H-bridge inverter grid-connected stage. After rectification, the system is connected to the grid. The grid inductance is L2 and the grid capacitor is C2.

[0047] The H-bridge inverter grid connection stage includes S9, S... 10 S 11 S 12 High-frequency gallium nitride devices and their respective parallel body diodes D9 and D 10 D 11 D 12 Ports E and F are used for grid-connected output, and L2 and R2 are connected in series to characterize the equivalent inductance and resistance of the power grid.

[0048] In this embodiment, the power input stage of the single-phase photovoltaic inverter is the photovoltaic array stage, and the equation relating the output current and voltage is as follows:

[0049]

[0050] Among them, I s I0 is the photocurrent value; I0 is the diode reverse saturation current; n is the diode factor constant; k is the Boltzmann constant; T is the battery temperature; N0 c V represents the number of photovoltaic cells connected in series; q represents the charge; V out I is the output voltage of the photovoltaic cell. out For the output current of the photovoltaic cell; R a R is the parallel resistance of a single photovoltaic unit. b This is the series resistor for the photovoltaic array bus.

[0051] In this embodiment, the maximum output power of the photovoltaic array can be expressed as:

[0052]

[0053] Among them, V max I represents the maximum output voltage of the entire photovoltaic array. max V represents the maximum output current of the entire photovoltaic array. m I represents the maximum output voltage of a single photovoltaic unit. m This represents the maximum output voltage of a single photovoltaic unit.

[0054] In this embodiment, the multi-phase shift control is based on the transformer primary input voltage U. in The rising edge position and the configuration of the region enclosed by the phase shift control coordinates in three-dimensional space are confirmed to determine the working mode and the triple phase shift angles D1, D2, and D3. The switching period is T. s The per-unit transmission power of the DAB DC-DC converter stage is:

[0055] P A =2(D1-2D2-D3+2)(1-D3).

[0056] In this embodiment, the per-unit power transmission value of the DAB DC-DC converter stage is:

[0057]

[0058] Where N is the turns ratio of the primary and secondary sides of the transformer in the DAB stage; f s U is the switching frequency of the DAB stage; L is the sum of the external inductance of the DAB stage and the leakage inductance of the transformer; U in U is the primary input voltage of the DAB circuit; out This is the secondary output voltage of the DAB stage.

[0059] In this embodiment, the output power of the H-bridge inverter grid-connected stage maintains a dynamic balance with the grid load power:

[0060]

[0061] Where, ω g L is the voltage angular frequency of the power grid link; r C is the output inductance of the power grid link; r The equivalent capacitance output for the power grid link; U g Q represents the effective value of the output voltage of the power grid link; out Q represents the reactive power output of the H-bridge inverter grid-connected stage. g This refers to the reactive power output from the H-bridge inverter grid connection stage to the power grid stage.

[0062] In this embodiment, the conduction loss and switching loss of the high-frequency gallium nitride devices (GaNHEMT devices) contained in the DAB DC-DC converter stage and the H-bridge inverter grid-connected stage can be obtained through simulation and testing.

[0063] In this embodiment, all GaN HEMT devices have the same switching cycle. The power devices in the primary and secondary H-bridges of the DAB DC-DC converter are symmetrically turned on. Adjusting the phase difference between the two sets of drive signals enables power transfer between the primary and secondary sides. The phase-shift control method utilizes this principle, adjusting the phase shift value... This is used to control the phase difference of the voltage signals at the primary and secondary terminals, thereby adjusting the direction of power flow and the output voltage amplitude. The single-phase shift control method only requires adjusting one parameter variable. When forward power transmission is required When reverse power transfer is required

[0064] Specific Implementation Method Two: This implementation method provides an active thermal management control method for a single-phase photovoltaic inverter as described in Specific Implementation Method One. The method includes the following steps: measuring the parameters of the photovoltaic array stage, the DAB DC-DC converter stage, the H-bridge inverter grid-connected stage, and the grid stage; and adjusting the real-time switching frequency of the gallium nitride device and the phase shift parameter D between the primary and secondary drive signals of the DAB DC-DC converter stage in real time. a The internal phase shift parameter D of the primary-side drive signal b The internal phase shift parameter D of the secondary drive signal c The specific input quantities measured by the controller include: the output voltage and current of the photovoltaic array, the primary and secondary voltages at the DAB converter, the junction temperature of the DAB converter output, and grid voltage feedback. The control block diagram is shown below. Figure 3 As shown, the specific implementation steps are as follows:

[0065] (1) Monitor the photovoltaic array voltage value V and photovoltaic array current value I in real time, and then import them into the MPPT control program.

[0066] (2) The output value after MPPT retrieval is accumulated with V, and then a PI circuit is introduced and connected with D. a D b D c Current i d The difference is calculated, and finally introduced into the PI stage of step (3).

[0067] (3) Real-time voltage U at the grid terminal g With the ideal set voltage U at the grid end s The difference is calculated, and the value after the difference is passed through a zero-order hold circuit and then fed into a PI circuit. The difference is then calculated with the value in step (2) to finally obtain the required real-time phase value.

[0068] (4) Sample the reference junction temperature T of all high-frequency gallium nitride devices in the DAB DC-DC converter stage and the H-bridge inverter grid-connected stage. ref , will T refThe measured value T of gallium nitride device mes After subtracting the values, import them into the periodic averaging module and the PI module respectively. Finally, subtract the results to obtain the real-time duty cycle value.

[0069] (5) The final PWM signal is input into the corresponding gallium nitride device driver to complete the active thermal management control method.

[0070] In this embodiment, the output voltage V and bus current I of the photovoltaic array port are sampled in real time and imported into the MPPT control program to achieve maximum power point control of the photovoltaic array port. The DC-DC conversion stage uses a DAB converter to eliminate local pseudo-maximum power points, improve the search speed for the maximum power point, and avoid interference from local pseudo-maximum power points. The output voltage V of the photovoltaic array, the bus current I, and the real-time feedback voltage U from the grid are all measured. g , grid set voltage U s Four parameters together determine the real-time phase difference of the PWM control signals on the primary and secondary sides of the DAB DC-DC converter stage; the measured and set junction temperatures of the power devices in the DAB DC-DC converter stage and the H-bridge inverter stage together determine the real-time duty cycle of the DAB DC-DC converter stage and the H-bridge inverter stage; by adjusting the phase and duty cycle of the final control signals of the DAB DC-DC converter stage and the H-bridge inverter stage in real time, junction temperature regulation is achieved, thus achieving the effect of active thermal management.

[0071] In this embodiment, a schematic diagram of the active thermal management control strategy is shown below. Figure 2 As shown. The circuit controller design should ensure that the sensors accurately extract the corresponding feedback parameters, guaranteeing real-time phase and duty cycle control to achieve active thermal management. The photovoltaic array bus voltage measurement location is at the stabilizing capacitor C. i The voltage at both ends, the photovoltaic array bus current measurement location is the current value on the path between the photovoltaic array and the DAB DC-DC conversion link, the grid-side real-time voltage measurement location is the bus voltage after grid connection, and the power device junction temperature measurement value is the junction temperature of each GaN HEMT power device.

[0072] In this embodiment, the active thermal management control variable feedback diagram is as follows: Figure 3 As shown. According to the type of controlled object, the control variable feedback can be divided into two parts. The first part is the electrical strategy part, which is used to achieve maximum power point control and grid voltage stability. Specifically, it adjusts the bus current and voltage values ​​in real time through photovoltaic array current and voltage feedback to achieve maximum power point control. It also collects the grid voltage value in real time at the grid output terminal and compares it with the reference voltage to achieve grid-side voltage stabilization. Furthermore, the intermediate link in the electrical strategy part is the DAB (Digital-to-Bio) converter, and the specific control and optimization strategies for this part are as follows:

[0073] (1) Determine the independent phase-shifting control parameters.

[0074] Introducing triple phase-shift control parameter D a D b D c The primary voltage U of the high-frequency isolation transformer in the DAB DC-DC converter stage in Only with D a D1 is related to the secondary voltage U. out Only with D b D c Relatedly, a standard square wave auxiliary function S(t) is introduced for mode classification, and the current flows through inductor L k The current is:

[0075]

[0076] Current i L Valid values ​​are:

[0077]

[0078] Where Sr1(t) = Sr(t), Sr2(t) = Sr(t-D1T), Sr3(t) = Sr(t-D0T), and Sr4(t) = Sr(t-D0T-D2T). Sr(t) is the integral of a standard two-level square wave function. The relationship between the effective value of the inductor current and the phase shift parameter is thus established.

[0079] (2) The per-unit power transmission capacity of the high-frequency isolation transformer is:

[0080] P A = 2(D1-2D2-D3+2)(1-D3)

[0081] The per-unit value of the high-frequency isolation transformer's transmitted power is calculated in real time, and its compliance with the power transmission requirements of the intermediate stage of the single-phase photovoltaic inverter is monitored in real time. The per-unit value of the transmitted power is affected only by three phase-shifting parameters and is unaffected by other electrical parameters such as inductor current, transformer primary voltage, and transformer secondary voltage. The root-mean-square value I of the inductor current... rms The square of the root mean square value I rms 2 Since they are directly proportional and have the same monotonicity, and both reach their maximum or minimum values ​​at the same location, the per-unit value is directly calculated by squared. Therefore, the per-unit value of the transformer's transmitted power is:

[0082]

[0083] Specific Implementation Method Three: This implementation method provides a lifespan prediction method for a single-phase photovoltaic inverter as described in Specific Implementation Method One. The method extracts the junction temperature fluctuation values ​​of each power device in the single-phase photovoltaic inverter in real time, accumulates them to a certain point, and then performs a lifespan prediction assessment, taking the minimum lifespan value as the expected lifespan value of the single-phase photovoltaic inverter. The specific implementation steps are as follows:

[0084] (1) Set the sensor's first discrete sampling time, collect the junction temperature values ​​of all high-frequency gallium nitride devices contained in the DAB DC-DC converter and H-bridge inverter grid-connected circuit in real time, and perform secondary discrete filtering on the junction temperature values ​​to filter out peaks and valleys and spikes in the temperature cycle.

[0085] (2) Traverse the array obtained by discretization filtering in step (1) one by one. Starting from the first data point, determine the product of the difference between the next data point and the previous data point and the difference between the next data point and the next data point. Determine the peak and valley point type based on the sign of the product.

[0086] (3) Use the rainflow counting method to extract the effective load cycle, and obtain the junction temperature effective load average value, cycle range and cycle number.

[0087] (4) The damage of gallium nitride devices in a single thermal cycle is accurately calculated using the accurate damage model of gallium nitride devices. The accurate damage model of gallium nitride devices is as follows:

[0088]

[0089] Where a is the slope of the accelerated aging test curve of gallium nitride device, b is the intersection point of the accelerated aging test curve of gallium nitride power device with the vertical axis, b2-b6 are the material constants, and ΔT j T represents the amplitude of a single junction temperature fluctuation. jmax T represents the maximum junction temperature. on Where I is the heating time, V is the load current, D is the blocking voltage, and D is the bonding wire diameter. This model is used to accurately calculate the damage of gallium nitride devices in a single thermal cycle.

[0090] (5) The number of cycles that a gallium nitride power device can withstand under thermal cycling stress is n. i In this case, the number of cycles that cause the device to fail is N. i The single-type damage value of gallium nitride power devices is:

[0091]

[0092] Throughout the entire operating process, the gallium nitride power device is subjected to m different amplitudes of thermal cycling stress, and the overall cumulative damage value is:

[0093]

[0094] Gallium nitride power devices fail when the overall cumulative damage F reaches 1.

[0095] In this embodiment, the supporting algorithm predicts the overall service life of a single-phase photovoltaic inverter based on the current operating conditions of the power devices and historical accumulated damage. The single-phase photovoltaic inverter topology is divided into three parts for centralized collection of junction temperatures and lifetime prediction. The first part is the junction temperature fluctuation data of the primary-side gallium nitride power devices and diodes in the DAB DC-DC converter stage, that is, effective damage load extraction and minimum lifetime extraction are performed by calculating the junction temperature fluctuation of the components. The second and third parts are the junction temperature data of the secondary-side gallium nitride power devices and diodes in the DAB converter DC-DC converter stage and the junction temperature data of the gallium nitride power devices and diodes in the H-bridge inverter stage, respectively. Then, the effective damage load extraction and minimum lifetime extraction method in the first part is repeated to perform lifetime assessment. Through the above steps, the lifetime prediction of the single-phase photovoltaic inverter can be completed.

[0096] Figure 4 The diagram illustrates discretization filtering for power semiconductor devices. The purpose of filtering is to eliminate extremely small peaks and troughs in the cyclic curves of the temperature load curve, while retaining effective peak and trough values. The advantage of discretization filtering is that it eliminates the step of isopleth filtering during the later peak and trough point extraction process. In practical applications, large peaks and troughs contain several small peak and trough spikes; therefore, this invention sets an appropriate discretization filtering time to filter out these peaks and troughs with very small amplitudes. This discretization filtering technique can effectively remove noise signals.

[0097] Example:

[0098] This embodiment sets up three control groups. The first group uses a Boost converter in the photovoltaic DC / DC stage, and the active thermal management control method proposed in this invention is selected as the control strategy. The second group uses a DAB converter in the photovoltaic DC / DC stage, and the active thermal management control method proposed in this invention is selected as the control strategy. The third group uses a DAB converter in the photovoltaic DC / DC stage, and the conventional maximum power point control is selected as the control strategy.

[0099] The first and second groups of comparisons are used to determine the optimization of the electrical characteristics of single-phase photovoltaic inverters after using a DAB converter in the photovoltaic DC / DC stage. The second and third groups of comparisons are used to determine the performance of the active thermal management control method proposed in this invention in improving the lifespan of power semiconductor devices.

[0100] The operating steps for each configuration in lifetime prediction are as follows: Using a hardware-in-the-loop test system, inductive and resistive loads are configured at the end of the photovoltaic inverter to simulate the power consumption conditions after grid connection, and the operating time T is set. sim Extracting power semiconductor devices from 0 to T simReal-time junction temperature values ​​within the specified range are extracted, discretized, filtered, and then imported into the rainflow counting method to complete the power semiconductor device lifetime assessment. For each configuration, in the electrical characteristic assessment, the bus voltage and bus current trajectories at the photovoltaic array terminal are extracted in real time to determine whether the photovoltaic array has reached its maximum power point.

[0101] Figure 5 The diagram shows the output power (PU) relationship of the photovoltaic array under the first configuration. Since only a boost converter is used in the DC / DC stage of the topology, there is a local pseudo-maximum power point. The system may be at the local pseudo-maximum power point for a long time during operation, which is not conducive to the exploration of system performance.

[0102] Figure 6 The diagram shows the output power (PU) relationship of the photovoltaic array under the second configuration. Because a DAB converter is used in the DC / DC stage of the single-phase photovoltaic inverter, local pseudo-maximum power points are eliminated. No local pseudo-maximum power points exist during system operation, thus achieving optimized electrical characteristics.

[0103] Figure 7 The junction temperature fluctuation curves of the S1 GaN HEMT device under the second configuration. Figure 8 For the junction temperature fluctuation curve of the S1 GaNHEMT device under the third configuration, according to the lifetime prediction operation steps described in this invention, the expected lifetime of the second group is 13.36 years and the expected lifetime of the third group is 11.23 years. The active thermal management control method proposed in this invention has an improvement rate of 18.97% under the operating conditions specified in this invention.

Claims

1. A single-phase photovoltaic inverter, characterized in that... The single-phase photovoltaic inverter includes a photovoltaic array stage, a DAB DC-DC conversion stage, and an H-bridge inverter grid-connected stage, wherein: The photovoltaic array consists of three photovoltaic units G a G b G c It is composed of series connections and each unit is connected in parallel with a diode D. a D b D c A voltage regulator capacitor C is connected in parallel to the output port. i ; The DAB DC-DC converter stage consists of a primary-side H-bridge and a secondary-side H-bridge. The primary-side H-bridge includes high-frequency gallium nitride devices S1, S2, S3, and S4, and their respective parallel-connected body diodes D1, D2, D3, and D4. The secondary-side H-bridge includes high-frequency gallium nitride devices S5, S6, S7, and S8, and their respective parallel-connected body diodes D5, D6, D7, and D8. The primary-side H-bridge is connected to the secondary-side H-bridge via a high-frequency isolation transformer. A DC-DC stabilizing capacitor C1 is connected in parallel at the DC-DC converter output terminal of the DAB stage, and an H-bridge inverter grid-connected stage is connected in parallel at the output port of the secondary-side H-bridge. After rectification, grid connection is performed. The H-bridge inverter grid connection stage includes S9, S... 10 S 11 S 12 High-frequency gallium nitride devices and their respective parallel body diodes D9 and D 10 D 11 D 12 ; The equation relating the output current and voltage of the photovoltaic array is as follows: Among them, I s I0 is the photocurrent value; I0 is the diode reverse saturation current; n is the diode factor constant; k is the Boltzmann constant; T is the battery temperature; N0 c V represents the number of photovoltaic cells connected in series; q represents the charge; V out I is the output voltage of the photovoltaic cell. out For the output current of the photovoltaic cell; R a R is the parallel resistance of a single photovoltaic unit. b For the series resistance of the photovoltaic array bus; The maximum output power of the photovoltaic array is expressed as: Among them, V max I represents the maximum output voltage of the entire photovoltaic array. max V represents the maximum output current of the entire photovoltaic array. m I represents the maximum output voltage of a single photovoltaic unit. m This represents the maximum output voltage of a single photovoltaic unit. The per-unit transmission power of the DAB DC-DC converter is: in, , , It is a triple phase shift angle; The per-unit power transfer value of the DAB DC-DC converter stage is: Where N is the turns ratio of the primary and secondary sides of the transformer in the DAB stage; f s U is the switching frequency of the DAB stage; L is the sum of the external inductance of the DAB stage and the leakage inductance of the transformer; U in U is the primary input voltage of the DAB circuit; out This refers to the secondary-side output voltage of the DAB circuit. The output power of the H-bridge inverter grid-connected stage maintains a dynamic balance with the grid load power: Where, ω g L is the voltage angular frequency of the power grid link; r C is the output inductance of the power grid link; r The equivalent capacitance output for the power grid link; U g Q represents the effective value of the output voltage of the power grid link; out Q represents the reactive power output of the H-bridge inverter grid-connected stage. g This refers to the reactive power output from the H-bridge inverter grid connection stage to the power grid stage.

2. The single-phase photovoltaic inverter according to claim 1, characterized in that... The switching cycles of the high-frequency gallium nitride devices are all the same, and the power devices of the primary and secondary H-bridges in the DAB DC-DC converter are symmetrically turned on.

3. An active thermal management control method for a single-phase photovoltaic inverter according to any one of claims 1-2, characterized in that... The method includes the following steps: (1) Monitor the photovoltaic array voltage value V and photovoltaic array current value I in real time, and then import them into the MPPT control program; (2) The output value after MPPT retrieval is accumulated with V, and then introduced into a PI circuit and the phase shift parameter D between the primary and secondary drive signals of the DAB DC-DC converter circuit is added. a The internal phase shift parameter D of the primary-side drive signal b The internal phase shift parameter D of the secondary drive signal c Current i d The difference is calculated and finally introduced into the PI stage in step (3); (3) Real-time voltage U at the grid terminal g With the ideal set voltage U at the grid end s The difference is calculated, and the value after the difference is passed through a zero-order hold and then fed into a PI circuit. The difference is then calculated with the value in step (2) to finally obtain the required real-time phase value. (4) Sampling the reference junction temperature T of the gallium nitride device ref , will T ref The measured value T of gallium nitride device mes After subtraction, import the results into the periodic averaging module and the PI module respectively, and finally subtract the results to obtain the real-time duty cycle value. (5) Input the final obtained PWM signal into the corresponding gallium nitride device driver to complete the active thermal management control method.

4. A method for predicting the lifetime of a single-phase photovoltaic inverter according to any one of claims 1-2, characterized in that... The method includes the following steps: (1) Set the sensor's first discrete sampling time, collect the junction temperature value of the gallium nitride power device in real time, and perform secondary discrete filtering on the junction temperature value to filter out the peak and valley spikes in the temperature cycle. (2) Traverse the array obtained by discretization filtering in step (1) one by one, starting from the first data point, determine the product of the difference between the next data point and the previous data point and the difference between the next data point and the next data point, and determine the peak and valley point type according to the sign of the product; (3) Use the rainflow counting method to extract the effective load cycle, and obtain the junction temperature effective load average value, cycle range, and number of cycles; (4) The damage of a gallium nitride device in a single thermal cycle is calculated using a precise damage model for gallium nitride devices. The precise damage model for gallium nitride devices is as follows: Where a is the slope of the accelerated aging test curve of gallium nitride device, b is the intersection of the accelerated aging test curve of gallium nitride power device with the vertical axis, b2-b6 are material constants, and ΔT j T represents the amplitude of a single junction temperature fluctuation. jmax The maximum junction temperature, t on I is the heating time, V is the photovoltaic array current, D is the photovoltaic array voltage, and D is the bonding wire diameter. (5) The number of cycles that a gallium nitride power device can withstand under thermal cycling stress is n. i The number of cycles at which the device fails under thermal cycling stress is N. i The single-use damage value of gallium nitride power devices is: Throughout the entire operating process, the gallium nitride power device is subjected to m different amplitudes of thermal cycling stress, and the overall cumulative damage value is: Gallium nitride power devices fail when the overall cumulative damage F reaches 1.

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