A power converter, control method and related devices

Abstract

This application discloses a power converter, a control method, and related devices. The power converter includes a three-phase power conversion circuit and a controller. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit. The DC side of the three-phase power conversion circuit is suitable for connecting to a DC source, and the AC side of the three-phase power conversion circuit is suitable for connecting to a power grid, with the power grid using a star connection. The controller is used to obtain the current voltage of the DC source and the current temperature of the three-phase power conversion circuit, and selects a target modulation mode from multiple modulation modes based on the current voltage, current temperature, and the allowable loss threshold and target efficiency of the three-phase power conversion circuit to control the three-phase power conversion circuit. This scheme can flexibly switch the modulation mode according to the actual operating conditions, thereby improving the efficiency of the power converter.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, specifically to a power converter, control method, and related devices. Background Technology

[0002] Currently, in industrial and commercial sectors, voltage conversion generally employs a two-stage topology, consisting of a first-stage DC / DC circuit and a second-stage DC / AC circuit. The hardware structure of a two-stage topology is relatively complex, resulting in lower power density. Furthermore, control requires balancing the control objectives of both stages, leading to complex software control. Additionally, each stage of the two-stage topology incurs power conversion losses, thus resulting in lower efficiency. Summary of the Invention

[0003] In view of this, this application provides a power converter, control method and related apparatus, which have high power density and conversion efficiency, and can flexibly switch modulation modes.

[0004] This application provides a power converter, including: a three-phase power conversion circuit and a controller, each phase of the three-phase power conversion circuit including a four-switch Buck-Boost circuit, the DC side of the three-phase power conversion circuit being adapted to connect to a DC source, and the AC side of the three-phase power conversion circuit being adapted to connect to a power grid, wherein the power grid is star-connected;

[0005] The controller is used to obtain the current voltage of the DC source and the current temperature of the three-phase power conversion circuit, and to select a target modulation mode from multiple modulation modes based on the current voltage, the current temperature, the allowable loss threshold of the power switching transistors in the three-phase power conversion circuit and the target efficiency of the three-phase power conversion circuit, and to control the three-phase power conversion circuit.

[0006] Preferably, the controller is specifically configured to: obtain the maximum single-transistor loss of the power switch in the three-phase power conversion circuit and the efficiency of the three-phase power conversion circuit for each of the multiple modulation methods according to the current voltage and the current temperature, and select the modulation method whose maximum single-transistor loss is less than or equal to the allowable loss threshold and whose efficiency is greater than or equal to the target efficiency as the target modulation method.

[0007] Preferably, the controller is specifically configured to: obtain the target modulation scheme from a preset relationship table based on the current voltage, the current temperature, the allowable loss threshold, and the target efficiency.

[0008] Preferably, the controller is further configured to select the target modulation method according to a preset priority when there are multiple target modulation methods.

[0009] Preferably, the multiple modulation methods include sinusoidal pulse width modulation (SPWM) and discontinuous pulse width modulation (DPWM), and the priority of SPWM is higher than that of DPWM.

[0010] Preferably, the controller is further configured to control the three-phase power conversion circuit to operate at a reduced rate or shut down in the absence of the target modulation mode.

[0011] Preferably, the controller is specifically configured to: obtain the first maximum single-transistor loss of the power switching transistor in the three-phase power conversion circuit and the first efficiency of the three-phase power conversion circuit according to the current voltage and the current temperature, and use the SPWM as the target modulation mode when the first efficiency is greater than or equal to the target efficiency and the first maximum single-transistor loss is less than or equal to the allowable loss threshold;

[0012] If the first efficiency is less than the target efficiency or the first maximum single-transistor loss is greater than the allowable loss threshold, the second maximum single-transistor loss of the power switch in the three-phase power conversion circuit corresponding to the discontinuous pulse width modulation (DPWM) and the second efficiency of the three-phase power conversion circuit are obtained according to the current voltage and the current temperature. If the second efficiency is greater than or equal to the target efficiency and the second maximum single-transistor loss is less than or equal to the allowable loss threshold, the DPWM is used as the target modulation mode.

[0013] Preferably, the controller is further configured to: control the three-phase power conversion circuit to operate at a reduced rate or shut down when the second efficiency is less than the target efficiency or the second maximum single tube loss is greater than the allowable loss threshold.

[0014] Preferably, the controller is specifically configured to: obtain the second maximum single-transistor loss of the power switching transistor in the three-phase power conversion circuit and the second efficiency of the three-phase power conversion circuit according to the current voltage and the current temperature, and use the DPWM as the target modulation mode when the second efficiency is greater than or equal to the target efficiency and the second maximum single-transistor loss is less than or equal to the allowable loss threshold;

[0015] If the second efficiency is less than the target efficiency or the second maximum single-transistor loss is greater than the allowable loss threshold, the first maximum single-transistor loss of the power switch in the three-phase power conversion circuit and the first efficiency of the three-phase power conversion circuit are obtained according to the current voltage and the current temperature. If the first efficiency is greater than or equal to the target efficiency and the first maximum single-transistor loss is less than or equal to the allowable loss threshold, the SPWM is used as the target modulation mode.

[0016] Preferably, the controller is further configured to: control the three-phase power conversion circuit to operate at reduced capacity or shut down when the first efficiency is less than the target efficiency or the first maximum single tube loss is greater than the allowable loss threshold.

[0017] Preferably, the four-switch Buck-Boost circuit includes: a first switch, a second switch, a third switch, a fourth switch, an inductor, and an AC-side capacitor;

[0018] The first and second switching transistors are connected in series to form a first bridge arm, and the two ends of the first bridge arm are respectively connected to the positive and negative terminals of the DC source; the third and fourth switching transistors are connected in series to form a second bridge arm, the first end of the first inductor is connected to the midpoint of the first bridge arm, and the second end of the first inductor is connected to the midpoint of the second bridge arm; the first end of the second bridge arm serves as the output terminal of the three-phase power conversion circuit, the second end of the second bridge arm is connected to the negative terminal of the DC source, and the two ends of the AC side capacitor are respectively connected to the first end of the second bridge arm and the negative terminal of the DC source.

[0019] This application also provides a control method for a power converter, the power converter including a three-phase power conversion circuit, each phase of the three-phase power conversion circuit including a four-switch Buck-Boost circuit, the DC side of the three-phase power conversion circuit being adapted to connect to a DC source, the AC side of the three-phase power conversion circuit being adapted to connect to a power grid, the power grid being star-connected;

[0020] The control method includes:

[0021] Obtain the current voltage of the DC source and the current temperature of the power switching transistors in the three-phase power conversion circuit;

[0022] Based on the current voltage, the current temperature, the allowable loss threshold of the power switching transistors in the three-phase power conversion circuit, and the target efficiency of the three-phase power conversion circuit, a target modulation method is selected from multiple modulation methods;

[0023] The three-phase power conversion circuit is controlled according to the target modulation method.

[0024] Preferably, the step of selecting a target modulation scheme from multiple modulation schemes based on the current voltage, the current temperature, the allowable loss threshold of the power switches in the three-phase power conversion circuit, and the target efficiency of the three-phase power conversion circuit includes:

[0025] Based on the current voltage and the current temperature, obtain the maximum single-transistor loss of the power switch in the three-phase power conversion circuit corresponding to each of the multiple modulation methods and the efficiency of the three-phase power conversion circuit;

[0026] The modulation scheme in which the maximum single-tube loss is less than or equal to the allowable loss threshold and the efficiency is greater than or equal to the target efficiency is taken as the target modulation scheme.

[0027] Preferably, the step of selecting a target modulation scheme from multiple modulation schemes based on the current voltage, the current temperature, the allowable loss threshold of the power switches in the three-phase power conversion circuit, and the target efficiency of the three-phase power conversion circuit includes:

[0028] The target modulation scheme is obtained from a preset relationship table based on the current voltage, the current temperature, the allowable loss threshold, and the target efficiency.

[0029] Preferably, obtaining the target modulation scheme from a preset relationship table based on the current voltage, the current temperature, the allowable loss threshold, and the target efficiency includes:

[0030] Select the target relationship table based on the allowable loss threshold and the target efficiency;

[0031] The target modulation scheme is obtained from the target relationship table based on the current voltage and the current temperature.

[0032] Preferably, the control method further includes: when there are multiple target modulation methods, selecting the target modulation method according to a preset priority.

[0033] Preferably, the multiple modulation methods include sinusoidal pulse width modulation (SPWM) and discontinuous pulse width modulation (DPWM).

[0034] Preferably, the control method further includes:

[0035] In the absence of the target modulation mode, the three-phase power conversion circuit is controlled to operate at a reduced rate or shut down.

[0036] This application also provides a control device, including a processor and a memory, wherein the memory is used to store programs, instructions or code, and the processor is used to execute the programs, instructions or code in the memory to perform the control method described above.

[0037] This application also provides a computer-readable storage medium storing a computer program, which is loaded by a processor to execute the control method described above.

[0038] The power converter provided in this application embodiment, in grid-connected mode, can select a target modulation method from multiple modulation methods based on the current input voltage and current temperature, according to the target efficiency and allowable loss threshold for different application scenarios. This target modulation method is then used to control the three-phase power conversion circuit. Since the modulation method is selected based on the target efficiency, allowable loss threshold, and current voltage and temperature, an advantageous modulation method can be selected while meeting the target efficiency and allowable loss threshold, rather than a fixed one. This allows for flexible selection of a suitable modulation method based on operating conditions, leveraging the advantages of each modulation method. Simultaneously, the single-stage three-phase power conversion circuit based on a four-switch Buck-Boost circuit enables the power converter to achieve high power density and conversion efficiency. Attached Figure Description

[0039] Figure 1 A schematic diagram of a power converter provided in an embodiment of this application;

[0040] Figure 2 This is a schematic diagram of an SPWM modulation method for a power converter provided in an embodiment of this application;

[0041] Figure 3 This is a schematic diagram of a DPWM modulation method for a power converter provided in an embodiment of this application;

[0042] Figure 4 A schematic diagram of yet another power converter provided in the embodiments of this application;

[0043] Figure 5 This application provides a schematic diagram of a power converter modulation mode switching method.

[0044] Figure 6 A flowchart illustrating the modulation mode switching of a power converter provided in this application embodiment;

[0045] Figure 7 This application provides an efficiency diagram of DPWM for different input voltages and temperatures for embodiments of the application;

[0046] Figure 8 This application provides an efficiency diagram of SPWM for different input voltages and temperatures for embodiments of the application;

[0047] Figure 9This application provides a schematic diagram of the maximum single-transistor loss of DPWM under different input voltages and temperatures for embodiments of the present application;

[0048] Figure 10 This application provides a schematic diagram of the maximum single-transistor loss of SPWM under different input voltages and temperatures for embodiments of the present application;

[0049] Figure 11 A flowchart illustrating a control method for a power converter provided in an embodiment of this application;

[0050] Figure 12 This is a schematic diagram of a control device provided in an embodiment of this application. Detailed Implementation

[0051] Currently, in industrial and commercial sectors, voltage conversion generally employs a two-stage topology, consisting of a first-stage DC / DC circuit and a second-stage DC / AC circuit. The hardware structure of a two-stage topology is relatively complex, resulting in lower power density. Furthermore, control requires balancing the control objectives of both stages, leading to complex software control. Additionally, each stage of the two-stage topology incurs power conversion losses, thus resulting in lower efficiency.

[0052] Based on this, in the embodiments of this application, the power converter includes a single-stage three-phase power conversion circuit based on a four-switch Buck-Boost circuit, that is, the power converter is a single-stage power converter, which can improve power density, reduce power consumption and improve power conversion efficiency compared to a two-stage power converter.

[0053] To enable those skilled in the art to understand and implement the technical solutions provided in the embodiments of this application, the architecture of the power converter will be described below in conjunction with the accompanying drawings.

[0054] See Figure 1 The figure shows a schematic diagram of a power converter.

[0055] The power converter provided in this application includes a three-phase four-switch Buck-Boost circuit. This power converter is a single-stage DC / AC converter, which can improve power density compared to a two-stage power converter. Furthermore, because the power converter is single-stage, it can reduce power consumption and improve energy conversion efficiency compared to a two-stage power converter. Moreover, the power converter provided in this application can be applied to DC sources with a wide voltage range, such as photovoltaic panels or energy storage batteries. For example, in one possible implementation, the phase voltage amplitude is 311V, corresponding to an input voltage range of 280V-380V.

[0056] The first terminals of the three-phase four-switch Buck-Boost circuit are connected in parallel to a DC source. The second terminals of each circuit are independent and connected to the three AC phases of the power converter, respectively. The input voltage of the DC source is denoted by Uin. The AC side of the power converter is connected to the power grid via the second switch K2. The power grid is a three-phase grid, consisting of phases A, B, and C, with three-phase voltages ua, ub, and uc, where ua, ub, and uc represent the phase voltages of the grid. Specifically, the first terminal of the second switch K2 is connected to the second terminal of the filter inductor Lg, and the first terminal of the filter inductor Lg is connected to the output terminals of the Buck-Boost circuit, with the three phases corresponding to output terminals a, b, and c, respectively.

[0057] The first Buck-Boost circuit includes a first switch S1, a second switch S2, a first inductor L1, a third switch S3, and a fourth switch S4. The first switch S1 and the second switch S2 are connected in series to form the first bridge arm, and the third switch S3 and the fourth switch S4 are connected in series to form the second bridge arm. The first end of the first inductor L1 is connected to the midpoint of the first bridge arm, and the second end of the first inductor L1 is connected to the midpoint of the second bridge arm. The first end of the second bridge arm serves as the output terminal a of the three-phase power conversion circuit, and the second end of the second bridge arm is connected to the negative terminal m of the DC source. The two ends of the AC-side capacitor Cfa are connected to the first end of the second bridge arm and the negative terminal m of the DC source, respectively.

[0058] The second Buck-Boost circuit includes a fifth switch S5, a sixth switch S6, a second inductor L2, a seventh switch S7, and an eighth switch S8. Switches S5 and S6 are connected in series to form the third bridge arm, and switches S7 and S8 are connected in series to form the fourth bridge arm. The first end of the second inductor L2 is connected to the midpoint of the third bridge arm, and the second end of the second inductor L2 is connected to the midpoint of the fourth bridge arm. The first end of the fourth bridge arm serves as the output terminal b of the three-phase power conversion circuit, and the second end of the fourth bridge arm is connected to the negative terminal m of the DC source. The two ends of the AC-side capacitor Cfb are connected to the first end of the fourth bridge arm and the negative terminal m of the DC source, respectively.

[0059] The third Buck-Boost circuit includes a ninth switch S9, a tenth switch S10, a third inductor L3, an eleventh switch S11, and a twelfth switch S12. Switches S9 and S10 are connected in series to form the fifth bridge arm, and switches S11 and S12 are connected in series to form the sixth bridge arm. The first terminal of the third inductor L3 is connected to the midpoint of the fifth bridge arm, and the second terminal of the third inductor L3 is connected to the midpoint of the sixth bridge arm. The first terminal of the sixth bridge arm serves as the output terminal b of the three-phase power conversion circuit, and the second terminal of the sixth bridge arm is connected to the negative terminal m of the DC source. The two ends of the AC-side capacitor Cfc are connected to the first terminal of the sixth bridge arm and the negative terminal m of the DC source, respectively.

[0060] The three-phase output terminals a, b, and c are connected to the negative terminal m of the DC source via corresponding AC-side capacitors Cfa, Cfb, and Cfc, respectively.

[0061] In off-grid mode, the AC side of the three-phase power converter circuit is suitable for connecting a load Rd, which is connected in a star configuration. Specifically, the three-phase output terminals a, b, and c are connected to the first terminal of the first switch K1 via corresponding filter inductors Lg, and the second terminal of the first switch K1 is connected to the neutral point N via the load Rd. The load Rd represents the load connected when the power converter is off-grid. In grid-connected mode, the three-phase output terminals a, b, and c are connected to the first terminal of the second switch K2 via corresponding filter inductors Lg, and the second terminal of the second switch K2 is connected to the three-phase power grid.

[0062] In a three-phase three-wire system, the voltage of the three-phase power grid relative to the negative terminal m of the DC source is the DC bias voltage Uoff.

[0063] When the power converter is off-grid, K2 is open and K1 is closed, operating in a three-phase four-wire system.

[0064] When the power converter is connected to the grid, K2 is closed and K1 is open, operating in a three-phase three-wire system.

[0065] Currently, the commonly used modulation methods for grid-connected power converters include sinusoidal pulse width modulation (SPWM) and discontinuous pulse width modulation (DPWM).

[0066] See Figure 2 The figure is a schematic diagram of an SPWM modulation method for a power converter provided in an embodiment of this application.

[0067] Figure 2 In the diagram, the horizontal axis represents the phase, and the vertical axis represents the phase voltage. In SPWM modulation, the bias voltage uoff on the AC output capacitor of the power converter is a DC voltage, meaning uoff is a fixed voltage. The expression for uoff is as follows: This indicates the peak value of the output voltage.

[0068] See Figure 3 The figure is a schematic diagram of a DPWM modulation method for a power converter provided in an embodiment of this application.

[0069] Figure 3In the diagram, the horizontal axis represents phase, and the vertical axis represents phase voltage. In DPWM modulation, the bias voltage uoff on the AC output capacitor of the power converter is the negative of the minimum value of the three-phase voltage; that is, uoff is a positive wavy line, meaning Uoff is not a constant. The expression for uoff is as follows:

[0070] uoff(t) = -min[u ao (t),u bo (t),u co (t)].

[0071] u ao (t),u bo (t),u co (t) represents the voltage between the neutral point of the three-phase power grid and the negative terminal of the DC source, which can be a constant or a variable value.

[0072] The SPWM and DPWM modulation methods described above each have their own advantages and disadvantages. With SPWM modulation, the internal components of the power converter experience higher stress and lower efficiency, but the harmonic content is lower and the power quality is better. With DPWM modulation, the internal components of the power converter experience lower stress and higher efficiency, but the harmonic content is higher and the power quality is worse.

[0073] Therefore, SPWM modulation is suitable for scenarios with high power quality requirements but low requirements for operating efficiency and / or device stress, while DPWM is suitable for scenarios with high operating efficiency and / or device stress requirements but low requirements for power quality.

[0074] Power converters using a fixed modulation scheme cannot effectively utilize the advantages of SPWM and DPWM. Therefore, they cannot respond to the demands of the current operating state, potentially causing the power converter to operate continuously in a range of low efficiency or poor power quality. When the power converter is under high temperature conditions, the primary goal of reducing single-transistor losses is to ensure the long-term stable operation of the power devices. If SPWM is consistently used, the only options are power derating or shutdown. When the power converter has poor power quality, improving power quality is required. If DPWM is consistently used, the only options are increasing the DC-side voltage or shutdown.

[0075] In order to combine the advantages of SPWM and DPWM, this application provides a power converter that can select the modulation method according to the actual operating conditions, thereby ensuring power quality and efficiency while meeting the requirements, and thus balancing power loss, efficiency and power quality.

[0076] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0077] See Figure 4 This figure is a schematic diagram of another power converter provided in an embodiment of this application.

[0078] The power converter provided in this application includes a three-phase power conversion circuit and a controller 300. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit. The DC side of the three-phase power conversion circuit is suitable for connecting to a DC source, and the AC side of the three-phase power conversion circuit is suitable for connecting to a power grid, wherein the power grid is connected in a star configuration. The specific structure of the four-switch Buck-Boost circuit can be found in [reference needed]. Figure 1 The description will not be repeated here.

[0079] The controller 300 is used to obtain the current voltage of the DC source and the current temperature of the three-phase power conversion circuit, and, based on the current voltage, current temperature, the allowable loss threshold of the power switches in the three-phase power conversion circuit, and the target efficiency of the three-phase power conversion circuit, selects a target modulation method from multiple modulation methods to control the three-phase power conversion circuit. It should be understood that efficiency refers to the overall efficiency of the three-phase power conversion circuit. This application does not specifically limit the specific measurement method of the current temperature; for example, it could be the internal ambient temperature of the power converter, or the temperature of the circuit board where each power device in the power conversion circuit is located.

[0080] When the input voltage of a power converter is lower, the power converter's losses will increase, which in turn will reduce its efficiency.

[0081] Because power converters may operate under different conditions with varying input voltages and temperatures, and different applications have different requirements for the target efficiency and permissible loss thresholds of three-phase power conversion circuits, the power converter in grid-connected mode can flexibly and dynamically select the modulation method based on the current input voltage, current temperature T, target efficiency, and permissible loss thresholds. Maximum single-transistor loss refers to the maximum loss of a single switching transistor among all the switching transistors. For example, with three switching transistors, under the current voltage and temperature, if the first transistor loses 10W, the second transistor loses 20W, and the third transistor loses 30W, then the maximum single-transistor loss is 30W.

[0082] For ease of comparison, the allowable loss threshold can be the loss threshold allowed for a single switching transistor in a three-phase power conversion circuit. That is, the maximum single-transistor loss is compared with the allowable loss threshold.

[0083] Since the modulation method is selected based on the target efficiency, allowable loss threshold, current voltage, and current temperature, an advantageous modulation method can be selected under the premise of meeting the target efficiency and allowable loss threshold. It is not a fixed modulation method that is selected. This allows for flexible selection of a suitable modulation method according to the operating conditions, giving full play to the advantages of each modulation method.

[0084] This application does not specifically limit the specific types of various modulation methods; for example, it may include SPWM and DPWM. The modulation method can be selected based on the specific operating conditions of the power converter, thereby effectively utilizing the advantages of SPWM and DPWM. SPWM can improve power quality, while DPWM can reduce losses and improve efficiency, but its power quality is lower.

[0085] For example, one possible implementation involves a controller specifically configured to: calculate the maximum single-transistor loss and the efficiency of the three-phase power conversion circuit for each modulation mode under different temperatures and input voltages, based on test results of different modulation modes at different temperatures and input voltages, and pre-store these values ​​in the controller. When the converter is running in real-time, it looks up the maximum single-transistor loss and efficiency corresponding to each modulation mode in the multiple modulation modes based on the current voltage and temperature, and selects the modulation mode whose maximum single-transistor loss is less than or equal to the allowable loss threshold and whose efficiency is greater than or equal to the target efficiency as the target modulation mode. It should be understood that if multiple target modulation modes may meet the allowable loss threshold and target efficiency requirements, the target modulation mode can be selected according to a preset priority. For example, when multiple modulation modes include SPWM and DPWM, SPWM has a higher priority than DPWM.

[0086] Another implementation method reduces computational load. Based on test results of different modulation modes under varying temperatures and input voltages, a preset relationship table is obtained in advance. This table can be stored in the controller. The controller directly looks up the table based on the current voltage and temperature of the power converter to obtain the corresponding modulation mode. The preset relationship table refers to a table corresponding to each combination of allowable loss threshold and target efficiency, with each table including the modulation mode corresponding to voltage and temperature. Specifically, the controller is used to: obtain the target modulation mode from the preset relationship table based on the current voltage, current temperature, allowable loss threshold, and target efficiency.

[0087] The preset relationship table also applies to situations where there are multiple target modulation methods, and the controller selects the target modulation method according to the preset priority.

[0088] To protect the power converter and controller, it is also used to control the three-phase power conversion circuit to operate at a derating rate or shut down in the absence of a target modulation mode. Derating of a three-phase power conversion circuit refers to reducing the output power of the three-phase power conversion circuit.

[0089] To facilitate understanding of the power converter provided in the embodiments of this application, the relationship between the modulation method and the input voltage and temperature will be described in detail below with reference to the accompanying drawings.

[0090] See Figure 5 This figure is a schematic diagram of a power converter modulation mode switching provided in an embodiment of this application.

[0091] For ease of understanding, the power converter provided in this application converts both the input voltage and temperature into per-unit values. Figure 5 The horizontal axis represents the reciprocal of the per-unit input voltage value, 1 / U*, and the vertical axis represents the per-unit temperature value, T*.

[0092] The controller is specifically used to obtain all combinations of input voltage and temperature data when the maximum single-transistor loss of the power converter is the allowable loss threshold and the power converter efficiency is the target efficiency. Based on the current input voltage, the current device temperature, and all combinations of data, it selects either SPWM or DPWM.

[0093] Figure 5 In the context of input voltage and temperature, select SPWM when the input voltage and temperature are within the area enclosed by line segment M and the horizontal and vertical axes. Select DPWM when the input voltage and temperature are within the area enclosed by line segment M and the horizontal and vertical axes, the temperature per unit value of 1, and the reciprocal of the input voltage per unit value of 1.

[0094] Figure 5 Curve M represents the combination of the reciprocal of all input voltages and temperatures that satisfy the allowable loss threshold and target efficiency. That is, for any point on M, the input voltage and temperature can be modulated using any modulation scheme to achieve the target efficiency, with the maximum single-transistor loss not exceeding the allowable loss threshold. The controller specifically obtains the reciprocal of the current voltage per unit value and the current temperature per unit value. When the reciprocal of the current voltage per unit value and the current temperature per unit value are a combination of the reciprocals of the voltage per unit value and the temperature per unit value from all combined data, either SPWM or DPWM is selected. If the current input voltage and current temperature satisfy the values ​​on M, either SPWM or DPWM can be selected; for example, SPWM can be preferred.

[0095] The following describes a method for obtaining per-unit values ​​of input voltage and temperature.

[0096] The current voltage per-unit value is obtained based on the current input voltage, the maximum voltage and minimum voltage of the DC source; the current temperature per-unit value is obtained based on the current temperature, the highest temperature and the lowest temperature of the power device.

[0097] This application does not specifically limit the type of power device. For example, based on actual efficiency, power density and cost, a metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated-gate bipolar transistor (IGBT) with reverse conduction function can be selected.

[0098] Please refer to the following formula for details.

[0099] It can be based on the maximum value U of the input voltage max and minimum value U min The upper limit of the allowable temperature T for power devices max and lower limit T min Determine the normal operating range of the power converter. For ease of representation, the input voltage and temperature are normalized to the interval [0, 1] according to the following formula (1) to obtain the per-unit value, which facilitates the division of the SPWM and DPWM regions, where U* and T* are the normalized per-unit values ​​of the input voltage and temperature.

[0100]

[0101] Based on the operating requirements of the power converter, the target efficiency η* and the allowable loss threshold P* can be determined. The allowable loss threshold can be the loss threshold of a single power device. Through theoretical calculations, simulations, or experiments, the combination of temperature and input voltage that satisfies the conditions of efficiency η = η* and loss Ps = P* can be obtained, where temperature can be the temperature of the power device, mapped to... Figure 5 In this process, the switching boundary curves M for SPWM and DPWM are obtained.

[0102] In the SPWM region, the total harmonic distortion (THD) is low. THD represents power quality; the lower the THD, the better the power quality. When T*∈[0,1], dynamic switching between two modulation methods is adopted: when the temperature and input voltage fall within the region enclosed by M and the horizontal and vertical axes, SPWM is used; when the temperature and input voltage fall within the region enclosed by M and the horizontal and vertical axes, SPWM is used. When T* = 1, the region enclosed by the three curves is DPWM, and when... If T > 1, then power derating and other protective measures are taken. That is, the controller is also used to control the power converter to reduce the output power when the reciprocal of the current voltage per unit value is greater than 1 and the current temperature per unit value is greater than 1.

[0103] The above-described implementation method involves pre-obtaining the switching boundary M, then determining the region to be entered based on the current input voltage and temperature during real-time operation, and finally selecting SPWM or DPWM. Another implementation method is described below. The efficiency and losses corresponding to SPWM mode can be directly obtained based on the current input voltage and temperature to see if they meet the desired efficiency and loss requirements. If they do, SPWM is used. If not, the efficiency and maximum single-transistor loss corresponding to DPWM mode are obtained based on the current input voltage and temperature to see if they meet the requirements. If they do, DPWM is selected. If neither is met, the three-phase power conversion circuit is controlled to operate at a reduced rate or shut down. This application does not specifically limit the order in which SPWM and DPWM obtain the corresponding efficiency and loss; they can be obtained simultaneously or sequentially. Generally, to improve efficiency, it is advisable to first determine if SPWM meets the requirements; if not, then DPWM is considered. Therefore, power converters typically use SPWM modulation in most operating conditions.

[0104] The controller employs two methods: First, it determines the SPWM (Sinusoidal Pulse Width Modulation) efficiency, then the DPWM (Discontinuous Pulse Width Modulation) efficiency. Specifically, this involves: 1) determining the first efficiency and first maximum single-transistor loss of the SPWM based on the current voltage and temperature. The first maximum single-transistor loss refers to the maximum single-transistor loss corresponding to the SPWM at the current voltage and temperature. 2) determining the first efficiency, then the first maximum single-transistor loss. The first efficiency refers to the power converter's energy conversion efficiency when using SPWM at the current voltage and temperature. SPWM is used when the first efficiency is greater than or equal to the target efficiency and the first maximum single-transistor loss is less than or equal to the allowable loss threshold. 3) If the first efficiency is less than the target efficiency or the first maximum single-transistor loss is greater than the allowable loss threshold, the controller determines the second efficiency and second maximum single-transistor loss of the DPWM based on the current voltage and temperature. DPWM is used when the second efficiency is greater than or equal to the target efficiency and the second maximum single-transistor loss is less than or equal to the allowable loss threshold. The controller also employs a second method, determining the DPWM efficiency first, then the SPWM efficiency. Specifically, this involves obtaining the second efficiency and second maximum single-transistor loss of the DPWM based on the current input voltage and temperature. The second maximum single-transistor loss refers to the maximum single-transistor loss corresponding to the DPWM at the current input voltage and temperature. DPWM is used when the second efficiency is greater than or equal to the target efficiency and the second maximum single-transistor loss is less than or equal to the allowable loss threshold; when the second efficiency is less than the target efficiency or the second maximum single-transistor loss is greater than the allowable loss threshold, the first efficiency and the first maximum single-transistor loss of SPWM are obtained according to the current input voltage and the current temperature, and SPWM is used when the first efficiency is greater than or equal to the target efficiency and the first maximum single-transistor loss is less than or equal to the allowable loss threshold.

[0105] The following is combined Figure 6 This section describes the specific implementation process of first determining SPWM and then determining DPWM.

[0106] See Figure 6 The figure is a flowchart of the modulation mode switching of a power converter provided in an embodiment of this application.

[0107] S601: Obtain the current input voltage and current temperature of the power converter.

[0108] S602: Obtain the first efficiency η1 and the first maximum single-transistor loss P1 of the SPWM based on the current input voltage and the current temperature.

[0109] The first efficiency η1 and the first maximum single-tube loss P1 can be obtained through simulation or experimentation, such as current and voltage, and then the first efficiency and the first maximum single-tube loss can be calculated.

[0110] S603: If the first efficiency is greater than or equal to the target efficiency η* and the first maximum single tube loss is less than or equal to the allowable loss threshold P*, execute S604; otherwise, execute S605.

[0111] S604: Employs SPWM.

[0112] S605: Based on the current input voltage and current temperature, obtain the second efficiency η2 and the second maximum single-transistor loss P2 corresponding to the DPWM. The second efficiency η2 and the second maximum single-transistor loss P2 can be obtained through theoretical calculation, simulation, or experimental testing.

[0113] S606: If the second efficiency is greater than the target efficiency η* and the second maximum single tube loss is less than or equal to the allowable loss threshold P*, execute S607; otherwise, execute S608.

[0114] S607: Uses DPWM.

[0115] S608: Reduce output power or shut down.

[0116] The power converter provided in this application embodiment sets a target efficiency and an allowable loss threshold for a single power device. Based on the collected current input voltage and current temperature, if SPWM can achieve the target efficiency and the maximum single-tube loss does not exceed the allowable loss threshold, then SPWM modulation is used to ensure long-term good power quality. If DPWM mode can achieve the target efficiency and the maximum single-tube loss does not exceed the allowable loss threshold based on the current input voltage and current temperature, then DPWM mode is used to reduce losses, thereby reducing losses and improving efficiency, while ensuring no overheating occurs at the cost of power quality. If neither SPWM nor DPWM can guarantee the requirements, the controller is also specifically used to: control the three-phase power conversion circuit to operate at a reduced rate or shut down when the second efficiency is less than the target efficiency or the second maximum single-tube loss is greater than the allowable loss threshold, i.e., appropriate protection measures need to be taken.

[0117] The following diagram illustrates the efficiency and losses of SPWM and DPWM under different input voltages and temperatures.

[0118] See Figure 7 This figure is a schematic diagram of the efficiency of DPWM under different input voltages and temperatures provided in the embodiments of this application.

[0119] Figure 7 and Figure 5 The horizontal axis is similar to the vertical axis, so I will not repeat it here.

[0120] Figure 7 Taking the efficiency of DPWM as an example, there are three curves: η = 98.5%, η = 98%, and η = 97.5%. The region enclosed by the horizontal axis, vertical axis, and η = 98.5% represents η > 98.5%. The region enclosed by the horizontal axis, vertical axis, η = 98%, and η = 98.5% represents η = 98%–98.5%. The region enclosed by the horizontal axis, vertical axis, η = 98%, and η = 97.5% represents η = 97.5%–98%. The region enclosed by the horizontal axis, vertical axis, η = 97.5%, a temperature per unit value of 1, and the reciprocal of the input voltage per unit value is 1 represents η < 97.5%.

[0121] See Figure 8 This figure is a schematic diagram of the efficiency of SPWM under different input voltages and temperatures provided in the embodiments of this application.

[0122] Figure 8 and Figure 5 The horizontal axis is similar to the vertical axis, so I will not repeat it here.

[0123] Figure 8Taking the efficiency of SPWM as an example, there are three curves: η = 98.5%, η = 98%, and η = 97.5%. The region enclosed by the horizontal axis, vertical axis, and η = 98.5% represents η > 98.5%. The region enclosed by the horizontal axis, vertical axis, η = 98%, and η = 98.5% represents η = 98%–98.5%. The region enclosed by the horizontal axis, vertical axis, η = 98%, η = 97.5%, a temperature per-unit value of 1, and the reciprocal of the input voltage per-unit value represents η = 97.5%–98%. The region enclosed by η = 97.5%, a temperature per-unit value of 1, and the reciprocal of the input voltage per-unit value represents η < 97.5%.

[0124] See Figure 9 This figure is a schematic diagram of the maximum single-transistor loss of DPWM corresponding to different input voltages and temperatures provided in the embodiments of this application.

[0125] Figure 9 and Figure 5 The horizontal axis is similar to the vertical axis, so I will not repeat it here.

[0126] Figure 9 Taking the losses corresponding to DPWM as an example, there are three curves: Ps = 20W, Ps = 30W, and Ps = 40W. The region enclosed by the horizontal axis, vertical axis, and Ps = 20W represents Ps < 20W. The region enclosed by the horizontal axis, vertical axis, Ps = 20W, and Ps = 30W represents Ps = 20W to 30W. The region enclosed by the horizontal axis, vertical axis, Ps = 30W, and Ps = 40W represents Ps = 30W to 40W. The region enclosed by the horizontal axis, vertical axis, Ps = 40W, a temperature per unit value of 1, and the reciprocal of the input voltage per unit value is 1 represents Ps > 40W.

[0127] See Figure 10 This figure is a schematic diagram of the maximum single-transistor loss of SPWM corresponding to different input voltages and temperatures provided in the embodiments of this application.

[0128] Figure 10 and Figure 5 The horizontal axis is similar to the vertical axis, so I will not repeat it here.

[0129] Figure 10 Taking the losses corresponding to DPWM as an example, there are three curves: Ps = 20W, Ps = 30W, and Ps = 40W. The region enclosed by the horizontal and vertical axes and Ps = 20W represents Ps < 20W. The region enclosed by the horizontal and vertical axes, Ps = 20W, Ps = 30W, and a temperature per-unit value of 1 represents Ps = 20W to 30W. The region enclosed by the horizontal axis, Ps = 30W, Ps = 40W, a temperature per-unit value of 1, and the reciprocal of the input voltage per-unit value represents Ps = 30W to 40W. The region enclosed by Ps = 40W, a temperature per-unit value of 1, and the reciprocal of the input voltage per-unit value represents Ps > 40W.

[0130] The power converter provided in this application embodiment can dynamically switch to accommodate the performance differences of different modulation methods, thereby achieving a balance between efficiency and power quality.

[0131] Based on the power converter provided in the above embodiments, this application also provides a control method for the power converter, which will be described in detail below with reference to the accompanying drawings.

[0132] See Figure 11 The figure is a flowchart of a control method for a power converter provided in an embodiment of this application.

[0133] The power converter provided in this application includes a three-phase power conversion circuit. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit. The DC side of the three-phase power conversion circuit is adapted to be connected to a DC source, and the AC side of the three-phase power conversion circuit is adapted to be connected to the power grid. The power grid adopts a star connection. For details, please refer to the description of the above embodiments, which will not be repeated here.

[0134] The control method provided in this application includes:

[0135] S1001: Obtain the current voltage of the DC source and the current temperature of the three-phase power conversion circuit;

[0136] S1002: Select the target modulation method from multiple modulation methods based on the current voltage, current temperature, and the allowable loss threshold and target efficiency of the three-phase power conversion circuit; control the three-phase power conversion circuit according to the target modulation method.

[0137] One possible implementation involves selecting a target modulation scheme from multiple modulation schemes based on the current voltage, current temperature, and the allowable loss threshold and target efficiency of the three-phase power conversion circuit. This includes: obtaining the maximum single-tube loss and efficiency corresponding to each modulation scheme based on the current voltage and current temperature; and selecting the modulation scheme with a maximum single-tube loss less than or equal to the allowable loss threshold and an efficiency greater than or equal to the target efficiency as the target modulation scheme.

[0138] One possible implementation involves selecting a target modulation scheme from multiple modulation schemes based on the current voltage, current temperature, and the allowable loss threshold and target efficiency of the three-phase power conversion circuit. This includes obtaining the target modulation scheme from a preset relationship table based on the current voltage, current temperature, allowable loss threshold, and target efficiency.

[0139] One possible implementation involves obtaining the target modulation scheme from a preset relation table based on the current voltage, current temperature, allowable loss threshold, and target efficiency, including: selecting a target relation table based on the allowable loss threshold and target efficiency, and obtaining the target modulation scheme from the target relation table based on the current voltage and current temperature.

[0140] One possible implementation method, the control method further includes: when there are multiple target modulation methods, selecting the target modulation method according to a preset priority.

[0141] One possible implementation method, with multiple modulation methods including sinusoidal pulse width modulation (SPWM) and discontinuous pulse width modulation (DPWM).

[0142] One possible implementation method, the control method also includes: controlling the three-phase power conversion circuit to operate at a reduced rate or shut down in the absence of a target modulation mode.

[0143] In one possible implementation, see Figure 12 The figure is a schematic diagram of a control device provided in an embodiment of this application.

[0144] The control device may include a memory 1011 and a processor 1012. The processor 1012 may be connected to the power converter and can drive the switches in the various power conversion circuits of the power converter. For example... Figure 12 As shown, the memory can be random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (Electronic Programmable ROM), registers, hard disks, removable disks, etc.

[0145] The memory 1011 can store computer instructions. When the computer instructions stored in the memory 1011 are executed by the processor 1012, the processor 1012 can be used to execute the control methods described above. The memory 1011 can also store data, such as preset ranges, preset thresholds, and other information involved in the above embodiments.

[0146] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape) or a semiconductor medium (e.g., solid-state disk (SSD)).

[0147] This application also provides a readable storage medium for storing the methods provided in the above embodiments. Examples include random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (EPROM), registers, hard disks, removable disks, or any other form of storage medium in the art.

[0148] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the methods disclosed in the embodiments, since they correspond to the product embodiments disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the description of the product embodiments.

[0149] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A power converter, characterized in that, include: A three-phase power conversion circuit and controller, wherein each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit, the DC side of the three-phase power conversion circuit is adapted to connect to a DC source, and the AC side of the three-phase power conversion circuit is adapted to connect to a power grid, wherein the power grid is star-connected. The controller is used to obtain the current voltage of the DC source and the current temperature of the three-phase power conversion circuit, and to select a target modulation mode from multiple modulation modes based on the current voltage, the current temperature, the allowable loss threshold of the power switching transistors in the three-phase power conversion circuit and the target efficiency of the three-phase power conversion circuit, and to control the three-phase power conversion circuit.

2. The power converter according to claim 1, characterized in that, The controller is specifically configured to: obtain the maximum single-transistor loss of the power switch in the three-phase power conversion circuit and the efficiency of the three-phase power conversion circuit for each of the multiple modulation methods according to the current voltage and the current temperature, and select the modulation method whose maximum single-transistor loss is less than or equal to the allowable loss threshold and whose efficiency is greater than or equal to the target efficiency as the target modulation method.

3. The power converter according to claim 1, characterized in that, The controller is specifically configured to: obtain the target modulation scheme from a preset relationship table based on the current voltage, the current temperature, the allowable loss threshold, and the target efficiency.

4. The power converter according to any one of claims 1-3, characterized in that, The controller is further configured to select the target modulation method according to a preset priority when there are multiple target modulation methods.

5. The power converter according to claim 4, characterized in that, The various modulation methods include sinusoidal pulse width modulation (SPWM) and discontinuous pulse width modulation (DPWM), with SPWM having a higher priority than DPWM.

6. The power converter according to any one of claims 1-3, characterized in that, The controller is also used to control the three-phase power conversion circuit to operate at a reduced rate or shut down when the target modulation mode is not available.

7. The power converter according to claim 1, characterized in that, The controller is specifically configured to: obtain the first maximum single-transistor loss of the power switching transistor in the three-phase power conversion circuit and the first efficiency of the three-phase power conversion circuit according to the current voltage and the current temperature, and use the SPWM as the target modulation mode when the first efficiency is greater than or equal to the target efficiency and the first maximum single-transistor loss is less than or equal to the allowable loss threshold; If the first efficiency is less than the target efficiency or the first maximum single-transistor loss is greater than the allowable loss threshold, the second maximum single-transistor loss of the power switch in the three-phase power conversion circuit corresponding to the discontinuous pulse width modulation (DPWM) and the second efficiency of the three-phase power conversion circuit are obtained according to the current voltage and the current temperature. If the second efficiency is greater than or equal to the target efficiency and the second maximum single-transistor loss is less than or equal to the allowable loss threshold, the DPWM is used as the target modulation mode.

8. The power converter according to claim 7, characterized in that, The controller is also specifically used to: control the three-phase power conversion circuit to operate at reduced capacity or shut down when the second efficiency is less than the target efficiency or the second maximum single tube loss is greater than the allowable loss threshold.

9. The power converter according to claim 1, characterized in that, The controller is specifically configured to: obtain the second maximum single-transistor loss of the power switching transistor in the three-phase power conversion circuit and the second efficiency of the three-phase power conversion circuit according to the current voltage and the current temperature, and use the DPWM as the target modulation mode when the second efficiency is greater than or equal to the target efficiency and the second maximum single-transistor loss is less than or equal to the allowable loss threshold; If the second efficiency is less than the target efficiency or the second maximum single-transistor loss is greater than the allowable loss threshold, the first maximum single-transistor loss of the power switch in the three-phase power conversion circuit and the first efficiency of the three-phase power conversion circuit are obtained according to the current voltage and the current temperature. If the first efficiency is greater than or equal to the target efficiency and the first maximum single-transistor loss is less than or equal to the allowable loss threshold, the SPWM is used as the target modulation mode.

10. The power converter according to claim 9, characterized in that, The controller is further specifically used to: control the three-phase power conversion circuit to operate at reduced capacity or shut down when the first efficiency is less than the target efficiency or the first maximum single tube loss is greater than the allowable loss threshold.

11. The power converter according to any one of claims 1-10, characterized in that, The four-switch Buck-Boost circuit includes: a first switch, a second switch, a third switch, a fourth switch, an inductor, and an AC-side capacitor; The first and second switching transistors are connected in series to form a first bridge arm, and the two ends of the first bridge arm are respectively connected to the positive and negative terminals of the DC source; the third and fourth switching transistors are connected in series to form a second bridge arm, the first end of the first inductor is connected to the midpoint of the first bridge arm, and the second end of the first inductor is connected to the midpoint of the second bridge arm; the first end of the second bridge arm serves as the output terminal of the three-phase power conversion circuit, the second end of the second bridge arm is connected to the negative terminal of the DC source, and the two ends of the AC side capacitor are respectively connected to the first end of the second bridge arm and the negative terminal of the DC source.

12. A control method for a power converter, characterized in that, The power converter includes a three-phase power conversion circuit, each phase of which includes a four-switch Buck-Boost circuit. The DC side of the three-phase power conversion circuit is adapted to be connected to a DC source, and the AC side of the three-phase power conversion circuit is adapted to be connected to the power grid, wherein the power grid is connected in a star configuration. The control method includes: Obtain the current voltage of the DC source and the current temperature of the power switching transistors in the three-phase power conversion circuit; Based on the current voltage, the current temperature, the allowable loss threshold of the power switching transistors in the three-phase power conversion circuit, and the target efficiency of the three-phase power conversion circuit, a target modulation method is selected from multiple modulation methods; The three-phase power conversion circuit is controlled according to the target modulation method.

13. The control method according to claim 12, characterized in that, The step of selecting a target modulation scheme from multiple modulation schemes based on the current voltage, the current temperature, the allowable loss threshold of the power switches in the three-phase power conversion circuit, and the target efficiency of the three-phase power conversion circuit includes: Based on the current voltage and the current temperature, obtain the maximum single-transistor loss of the power switch in the three-phase power conversion circuit corresponding to each of the multiple modulation methods and the efficiency of the three-phase power conversion circuit; The modulation scheme in which the maximum single-tube loss is less than or equal to the allowable loss threshold and the efficiency is greater than or equal to the target efficiency is taken as the target modulation scheme.

14. The control method according to claim 12, characterized in that, The step of selecting a target modulation scheme from multiple modulation schemes based on the current voltage, the current temperature, the allowable loss threshold of the power switches in the three-phase power conversion circuit, and the target efficiency of the three-phase power conversion circuit includes: The target modulation scheme is obtained from a preset relationship table based on the current voltage, the current temperature, the allowable loss threshold, and the target efficiency.

15. The control method according to claim 14, characterized in that, The step of obtaining the target modulation scheme from a preset relationship table based on the current voltage, the current temperature, the allowable loss threshold, and the target efficiency includes: Select the target relationship table based on the allowable loss threshold and the target efficiency; The target modulation scheme is obtained from the target relationship table based on the current voltage and the current temperature.

16. The control method according to any one of claims 12-15, characterized in that, The control method further includes: When there are multiple target modulation methods, the target modulation method is selected according to a preset priority.

17. The control method according to claim 16, characterized in that, The various modulation methods include sinusoidal pulse width modulation (SPWM) and discontinuous pulse width modulation (DPWM).

18. The control method according to any one of claims 12-15, characterized in that, The control method further includes: In the absence of the target modulation mode, the three-phase power conversion circuit is controlled to operate at a reduced rate or shut down.

19. A control device, characterized in that, It includes a processor and a memory, the memory being used to store programs, instructions, or code, and the processor being used to execute the programs, instructions, or code in the memory to perform the control method as described in any one of claims 12-18.

20. A computer-readable storage medium, characterized in that, The system contains a computer program that is loaded by a processor to execute the control method as described in any one of claims 12-18.

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