Power grid output control method and control device of power frequency inverter and power frequency inverter

Abstract

The invention provides a power grid output control method and device of a power frequency inverter and the power frequency inverter, and the method comprises the steps: controlling a power grid auxiliary power supply to supply power to a battery auxiliary power supply when the power grid input voltage of a power grid is detected, so as to enable the battery auxiliary power supply to supply power to the power frequency inverter; under the condition that the preset magnetic bias compensation condition is met, the main circuit is controlled to start magnetic bias automatic compensation; when the battery voltage is larger than or equal to a preset soft start voltage threshold value, the magnetic bias compensation amount needed by magnetic bias automatic compensation control is obtained; controlling a main circuit to carry out inversion soft start output according to the magnetic bias compensation amount; when the soft start voltage meets the preset voltage output condition, the power grid relay is controlled to be closed, so that bypass discharge loading is achieved. According to the embodiment of the invention, the problem of soft start failure under the condition of no battery or insufficient power supply of the battery is effectively solved, meanwhile, the problem that a power device is damaged when power grid output is switched is solved, and the service life of the device is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation, and in particular to a power grid output control method and control device of a power frequency inverter and a power frequency inverter. Background Art

[0002] In the prior art, when the power grid is normal, the power frequency inverter switches from no output to grid output by using battery soft start and then switching to grid output. However, when there is no battery or the battery power supply is insufficient, the probability of soft start failure increases and the reliability is low. Even if the design forces grid output, the transformer in the power frequency inverter will generate a huge excitation inrush current when the output starts, causing damage to the power device, thereby reducing the life of the device. Summary of the invention

[0003] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide a grid output control method, a control device and a grid inverter of an industrial frequency inverter, which effectively solve the problem of soft start failure in the absence of a battery or insufficient battery power supply, and at the same time solve the problem of damage to power devices when switching grid output, thereby improving the life of the devices.

[0004] In a first aspect, an embodiment of the present invention provides a grid output control method of a power frequency inverter, wherein the power frequency inverter comprises a main circuit, a grid auxiliary power supply, a battery auxiliary power supply and a relay circuit, wherein the main circuit is connected to the battery auxiliary power supply and the relay circuit respectively, the grid auxiliary power supply is connected to the battery auxiliary power supply and the grid, the relay circuit comprises an inverter relay and a grid relay, the inverter relay is connected to a load, the grid relay is connected to the grid and the inverter relay, the main circuit is also connected to a battery, and the grid output control method comprises:

[0005] When a grid input voltage of the grid is detected, controlling the grid auxiliary power supply to supply power to the battery auxiliary power supply, so that the battery auxiliary power supply supplies power to the power frequency inverter;

[0006] When a preset bias magnetic compensation condition is met, the main circuit is controlled to start automatic bias magnetic compensation, wherein the preset bias magnetic compensation condition includes that the battery does not meet the soft start trigger condition, the power grid is in a normal state, and the power frequency inverter meets the bypass output condition;

[0007] Determining whether the battery voltage connected to the battery terminal of the main circuit is greater than or equal to a preset soft start voltage threshold;

[0008] When the battery voltage is greater than or equal to a preset soft-start voltage threshold, obtaining a bias magnetic compensation amount required for automatic bias magnetic compensation;

[0009] Controlling the main circuit to perform inverter soft start output according to the bias magnetic compensation amount;

[0010] Determining whether the soft-start voltage output by the main circuit meets a preset voltage output condition;

[0011] When the soft-start voltage meets the preset voltage output condition, the grid relay is controlled to close to achieve bypass discharge and load.

[0012] The grid output control method of the power frequency inverter provided in the embodiment of the present invention has at least the following beneficial effects: when the grid input voltage of the grid is detected, the grid auxiliary power supply is controlled to supply power to the battery auxiliary power supply, so that the battery auxiliary power supply supplies power to the power frequency inverter; when the preset bias magnetic compensation condition is met, the bias magnetic automatic compensation is started by controlling the main circuit, and it is judged whether the battery voltage connected to the battery end of the main circuit is greater than or equal to the preset soft start voltage threshold. When the battery voltage is greater than or equal to the preset soft start voltage threshold, the bias magnetic compensation amount required for the bias magnetic automatic compensation is obtained, and then the main circuit is controlled to perform inverter soft start output according to the bias magnetic compensation amount; then, it is judged whether the soft start voltage output by the main circuit meets the preset voltage output condition. When the soft start voltage meets the preset voltage output condition, the grid relay is controlled to close to realize bypass discharge load, thereby realizing no excitation inrush current, stable and fast switching of grid output, and realizing charging wake-up of low-voltage battery, effectively solving the problem of soft start failure in the case of no battery or insufficient battery power supply, and at the same time solving the problem of damage to power devices when switching grid output, thereby improving the life of the devices.

[0013] In the above-mentioned power grid output control method, when the preset bias magnetic compensation condition is not met, the main circuit is prohibited from starting the automatic bias magnetic compensation;

[0014] The power frequency inverter is controlled to enter a standby state and output an alarm signal.

[0015] In the above-mentioned power grid output control method, the step of judging whether the battery voltage connected to the battery terminal of the main circuit is greater than or equal to a preset soft-start voltage threshold comprises:

[0016] determining whether the battery voltage at the battery terminal increases;

[0017] If so, if the grid voltage satisfies the preset soft-start condition, determining whether the battery voltage is greater than or equal to a preset soft-start voltage threshold;

[0018] If not, it is determined that the battery terminal is abnormal and an alarm signal is output.

[0019] In the above-mentioned power grid output control method, the main circuit includes a DC bus and an inverter connected in sequence, and the step of obtaining the bias magnetic compensation amount required for automatic bias magnetic compensation includes:

[0020] Obtaining an inverter voltage and a grid voltage of the inverter;

[0021] The required bias magnetic compensation amount is determined according to the inverter voltage and the grid voltage.

[0022] In the above-mentioned power grid output control method, the DC bus is provided with a bus capacitor, and the main circuit is controlled to perform inverter soft start output according to the bias magnetic compensation amount, including:

[0023] Determining the inverter voltage required to be output by the inverter according to the bias compensation amount and the bus voltage of the bus capacitor;

[0024] Controlling a PWM signal output to the inverter according to the inverter voltage to control a soft start output of the inverter;

[0025] The output step size of the inverter is adjusted according to the PWM signal, and the positive and negative half-cycle voltage difference output by the inverter during the soft start process is adjusted.

[0026] In the above-mentioned power grid output control method, it also includes:

[0027] When it is determined that the number of times that the soft-start voltage does not meet the preset voltage output condition is greater than or equal to the preset number of times, it is determined that the battery terminal is abnormal and an alarm signal is output.

[0028] In the above-mentioned power grid output control method, after the power grid relay is controlled to be closed when the soft-start voltage meets the preset voltage output condition, the power grid output control method further includes:

[0029] When the battery meets the soft start trigger condition, the main circuit is controlled to receive the voltage from the battery, and the main circuit is controlled to enter the grid-connected mode to achieve grid-connected charging and loading.

[0030] In a second aspect, an embodiment of the present invention provides a control device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the power grid output control method as described in the embodiment of the first aspect above is implemented.

[0031] In a third aspect, an embodiment of the present invention provides an industrial frequency inverter, comprising a control device, a main circuit, a grid auxiliary power supply, a battery auxiliary power supply and a relay circuit as described in the embodiment of the second aspect above, wherein the control device is connected to the main circuit, the battery auxiliary power supply and the relay circuit respectively, the main circuit is connected to the battery auxiliary power supply and the relay circuit respectively, the grid auxiliary power supply is connected to the battery auxiliary power supply and the grid, the relay circuit comprises an inverter relay and a grid relay, the inverter relay is connected to a load, the grid relay is connected to the grid and the inverter relay, and the main circuit is also connected to a battery.

[0032] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer-executable instructions, and the computer-executable instructions are used to enable a computer to execute the power grid output control method as described in the embodiment of the first aspect above.

[0033] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention is further described below in conjunction with the accompanying drawings and embodiments;

[0035] Figure 1 is a schematic diagram of an industrial frequency inverter provided by an embodiment of the present invention;

[0036] Figure 2 It is a flow chart of a power grid output control method of a power frequency inverter provided by an embodiment of the present invention;

[0037] Figure 3 is a flow chart of another power grid output control method of an industrial frequency inverter provided by an embodiment of the present invention;

[0038] Figure 4 It is a schematic diagram of the structure of a control device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0040] It should be understood that in the description of the embodiments of the present invention, if there is a description of "first", "second", etc., it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features. "At least one" means one or more, "more than" means more than two, greater than, less than, exceeding, etc. are understood to not include the number itself, above, below, within, etc. are understood to include the number itself, and "several" means one or more, unless otherwise clearly and specifically limited. "And / or" describes the association relationship of associated objects, indicating that three relationships can exist. It can be understood that A and / or B can represent the situation where A exists alone, A and B exist at the same time, or B exists alone. Among them, A and B can be singular or plural.

[0041] In addition, unless otherwise clearly specified and limited, the term "connected / connected" should be understood in a broad sense, for example, it can be a fixed connection or a movable connection, a detachable connection or a non-detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be directly connected or indirectly connected through an intermediate medium. It should be noted that although the logical order is shown in the flowchart, in some cases, the steps shown or described can be performed in a different order from that in the flowchart. It should be noted that the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] It is worth noting that in the related technology, when the power grid is normal, the power frequency inverter will switch to the grid output after battery soft start. However, in the case of no battery or insufficient battery power, the probability of soft start failure will increase and the reliability will be low. Even if the design forces grid output, the transformer in the power frequency inverter will generate a huge excitation surge current when the output starts, which will reduce the life of the device or even damage and burn it.

[0043] Based on this, the embodiment of the present application proposes a grid output control method, a control device and a power frequency inverter of an industrial frequency inverter. When the grid input voltage of the grid is detected, the grid auxiliary power supply is controlled to supply power to the battery auxiliary power supply so that the battery auxiliary power supply supplies power to the industrial frequency inverter; when the preset bias magnetic compensation condition is met, the bias magnetic automatic compensation is turned on by controlling the main circuit, and it is judged whether the battery voltage connected to the battery end of the main circuit is greater than or equal to the preset soft start voltage threshold. When the battery voltage is greater than or equal to the preset soft start voltage threshold, the bias magnetic compensation amount required for the bias magnetic automatic compensation is obtained, and then the main circuit is controlled to perform inverter soft start output according to the bias magnetic compensation amount; then, it is judged whether the soft start voltage output by the main circuit meets the preset voltage output condition. When the soft start voltage meets the preset voltage output condition, the grid relay is controlled to close to realize bypass discharge load, thereby realizing no excitation inrush current, stable and fast switching of grid output, and can also realize charging wake-up of low-voltage batteries, effectively solving the problem of soft start failure in the case of no battery or insufficient battery power supply, and at the same time solving the problem of damage to power devices when switching grid output, thereby improving the life of the devices.

[0044] The embodiments of the present invention are further described below in conjunction with the accompanying drawings.

[0045] like Figure 1 As shown, an embodiment of the present invention provides a structural schematic diagram of an industrial frequency inverter, the industrial frequency inverter includes a main circuit, a grid auxiliary power supply, a battery auxiliary power supply and a relay circuit, the main circuit is connected to the battery auxiliary power supply and the relay circuit respectively, the grid auxiliary power supply is connected to the battery auxiliary power supply and the grid, the relay circuit includes an inverter relay and a grid relay, the inverter relay is connected to the load, the grid relay is connected to the grid and the inverter relay, and the main circuit is also connected to the battery.

[0046] The battery auxiliary power supply can supply power to the control device and each module circuit in the power frequency inverter.

[0047] The main circuit includes a DC bus, an inverter (also known as a DC / AC converter), and a line filter, which work together to achieve effective conversion and distribution of electrical energy. In addition, the main circuit may also include a DC / DC converter (not shown in the figure) and a transformer (not shown in the figure), and the transformer may be connected to the output end of the line filter.

[0048] The inverter relay (i.e. INV Relay) is used to control the connection between the inverter and the load. Its main function is to connect the inverter to the load when the system starts, and to disconnect when the system is shut down or a fault occurs. The status detection of INV Relay is a key step to ensure the safe operation of the power frequency inverter. By detecting the voltage on the inverter side, it can be determined whether the relay is working properly.

[0049] The grid relay (GRID Relay) is used to control the connection between the inverter and the AC grid. It ensures that the inverter can be connected to the grid under safe conditions and disconnects in time when the grid fails or requires maintenance. The status detection of GRID Relay involves monitoring parameters such as grid voltage, frequency, and phase sequence to ensure that the output of the inverter meets the grid connection requirements.

[0050] In one embodiment, the battery may be a 51.2V lithium battery.

[0051] The power frequency inverter is a device that converts DC power into AC power. It achieves the conversion from DC to AC by changing the direction and magnitude of the current. The power frequency inverter may encounter DC bias problems during operation, which is mainly caused by factors such as the DC component generated by the control system, zero drift, inconsistent switch characteristics, and system dynamic response. DC bias will have adverse effects on the inverter, output transformer, and AC load, seriously threatening the reliable operation of the power frequency inverter.

[0052] The inverter may be a DC / AC converter.

[0053] It should be noted that the entire industrial frequency inverter is controlled by a control device, which automatically compensates for the bias magnetism to achieve impact-free soft start and AC power output to meet load operation requirements. After the battery is connected, communication can be established through the RS485 hardware interface, and the main circuit and relay circuit can be further controlled to realize the charging and discharging of the lithium battery.

[0054] Figure 2 is a flow chart of a method for controlling the power grid output of a power frequency inverter provided by an embodiment of the present invention. The method for controlling the power grid output of a power frequency inverter can be applied to Figure 1 In the industrial frequency inverter in the illustrated embodiment, the grid output control method may include but is not limited to steps S110 to S170.

[0055] Step S110: when the grid input voltage of the grid is detected, the grid auxiliary power supply is controlled to supply power to the battery auxiliary power supply, so that the battery auxiliary power supply supplies power to the power frequency inverter.

[0056] In this step, when the grid input voltage of the power grid is detected, the grid auxiliary power supply is controlled to supply power to the battery auxiliary power supply, so that the battery auxiliary power supply supplies power to each module in the industrial frequency inverter. When the battery quality is poor, it can give priority to meeting the customer's load usage needs and use the mains power to perform more comprehensive activation and charging management of the battery.

[0057] Step S120: When the preset bias magnetic compensation conditions are met, the main circuit is controlled to start automatic bias magnetic compensation.

[0058] Among them, the preset bias magnetic compensation conditions include that the battery does not meet the soft start trigger condition, the power grid is in a normal state and the power frequency inverter meets the bypass output condition, and the battery does not meet the soft start trigger condition, that is, there is no battery or the battery power supply is insufficient. The power grid is in a normal state for the voltage fluctuation to be within a certain range. It can be understood that the stability of the grid voltage is crucial to the success of the soft start. Soft start technology can reduce the impact on the power grid. During the soft start process, the grid voltage needs to be maintained within a relatively stable range to ensure the normal operation of other equipment. In this embodiment, meeting the bypass output condition can be understood as the power grid is in an available state, can provide sufficient power to support the load demand, and the bypass output voltage and frequency match the grid voltage and frequency to ensure that the load can be smoothly switched to the bypass power supply.

[0059] In this step, when the preset bias magnetic compensation conditions are met, the main circuit is controlled to start automatic bias magnetic compensation, which can ensure the smooth output of the non-excitation current and impact of the city power without a battery, more reliable grid output, more stable system operation, and reduce the failure rate of the main circuit functional modules; in addition, after the battery is connected, external communication can be achieved through RS232 hardware to let the outside world know the machine status, such as synchronizing battery voltage, current, capacity, fault and other information, reminding the user to solve the battery disconnection problem in time, making charging and discharging more intelligent and reliable.

[0060] Step S130: determining whether the battery voltage connected to the battery terminal of the main circuit is greater than or equal to a preset soft-start voltage threshold.

[0061] Among them, when the battery does not meet the soft start triggering condition, the battery voltage connected to the battery terminal of the main circuit comes from the battery auxiliary power supply.

[0062] Step S140: when the battery voltage is greater than or equal to the preset soft-start voltage threshold, obtaining the bias magnetic compensation amount required for automatic bias magnetic compensation;

[0063] Step S150: Control the main circuit to perform inverter soft start output according to the bias magnetic compensation amount.

[0064] In step S140 and step S150, by obtaining the bias compensation amount required for automatic bias compensation and controlling the main circuit to perform inverter soft start output according to the bias compensation amount, it is possible to achieve a function of switching the grid output without excitation surge current and stably and quickly, making the operation of the industrial frequency inverter more stable.

[0065] Step S160: determining whether the soft-start voltage output by the main circuit meets a preset voltage output condition.

[0066] Step S170: When the soft-start voltage meets the preset voltage output condition, the grid relay is controlled to close to achieve bypass discharge with load.

[0067] Among them, the soft-start voltage can refer to the output voltage of the inverter. In the case of a wired filter, the soft-start voltage can also refer to the output voltage after filtering by the wired filter. The soft-start voltage meets the preset voltage output condition, that is, the soft-start voltage is within a certain range. In addition, bypass discharge load refers to the process of continuing to provide power to the load through the bypass path in the power frequency inverter when the main power path (such as the charging path of the battery in this embodiment) cannot be used due to maintenance, failure or other reasons. In this solution, when the battery does not meet the soft-start trigger condition, the battery auxiliary power supply is used to power each module of the power frequency inverter, and then the grid input voltage can be transmitted to the load through the grid relay and the inverter relay in turn to realize the switching grid output function.

[0068] It should be noted that the inverter output and bypass discharge load need to be synchronized to ensure that the frequency, phase and voltage amplitude are the same. In the case of synchronization, the switching between the inverter output and the bypass power supply can be achieved by uninterrupted switching.

[0069] In one embodiment, when the soft-start voltage does not meet the preset voltage output condition, it is determined whether the number of times the soft-start voltage does not meet the preset voltage output condition is greater than or equal to the preset number of times. If the number of times the soft-start voltage does not meet the preset voltage output condition is greater than or equal to the preset number of times, it is determined that the battery terminal is abnormal, and an alarm signal is output. If the number of times the soft-start voltage does not meet the preset voltage output condition is less than the preset number of times, it is determined whether the battery voltage connected to the battery terminal of the main circuit is greater than or equal to the preset soft-start voltage threshold, and so on, which will not be repeated here.

[0070] In an embodiment of the present application, when the grid input voltage of the grid is detected, the grid auxiliary power supply is controlled to supply power to the battery auxiliary power supply so that the battery auxiliary power supply supplies power to the industrial frequency inverter; when the preset bias compensation conditions are met, the bias automatic compensation is turned on by controlling the main circuit, and it is determined whether the battery voltage connected to the battery end of the main circuit is greater than or equal to the preset soft start voltage threshold. When the battery voltage is greater than or equal to the preset soft start voltage threshold, the bias compensation amount required for the bias automatic compensation is obtained, and then the main circuit is controlled to perform inverter soft start output according to the bias compensation amount; then, it is determined whether the soft start voltage output by the main circuit meets the preset voltage output conditions. When the soft start voltage meets the preset voltage output conditions, the grid relay is controlled to close to realize bypass discharge with load, thereby realizing no excitation inrush current, stable and fast switching of grid output, and can also realize charging wake-up of low-voltage batteries, effectively solving the problem of soft start failure in the absence of battery or insufficient battery power supply, and at the same time solving the problem of damage to power devices when switching grid output, thereby improving the life of the devices.

[0071] In some embodiments, the grid output control method may further include but is not limited to steps S210 to S220.

[0072] Step S210: when the preset bias magnetic compensation condition is not met, prohibiting the main circuit from starting the automatic bias magnetic compensation;

[0073] Step S220: Control the industrial frequency inverter to enter a standby state and output an alarm signal.

[0074] In an embodiment of the present application, by prohibiting the main circuit from starting automatic bias compensation when the preset bias compensation conditions are not met, controlling the industrial frequency inverter to enter standby mode and outputting an alarm signal, the failure rate of the main circuit functional module can be reduced, effectively solving the problem of excitation surge current easily damaging the machine, and extending the service life of the machine.

[0075] In some embodiments, step S130 may include but is not limited to steps S310 to S330.

[0076] Step S310: Determine whether the battery voltage at the battery terminal increases.

[0077] Among them, judging whether the battery voltage at the battery terminal increases may specifically be judging whether the battery voltage at the battery terminal is greater than a battery terminal voltage threshold. The battery terminal voltage threshold may be set according to actual conditions and is not specifically limited herein.

[0078] Step S320: If yes, then when the grid voltage meets the preset soft-start condition, determine whether the battery voltage is greater than or equal to the preset soft-start voltage threshold.

[0079] Among them, the preset soft-start voltage threshold can be set according to actual conditions, and no specific restrictions are made here. In addition, the judgment of the preset soft-start voltage threshold needs to consider the matching of the battery and grid voltage. During the startup process, if the battery voltage is lower than the preset soft-start voltage threshold, it may be necessary to delay the startup or take other measures to protect the battery and equipment. At the same time, if the grid voltage fluctuates too much, it may also be necessary to adjust the startup strategy to avoid causing excessive impact on the grid. Therefore, it is possible to determine whether the grid voltage meets the preset soft-start conditions by judging the fluctuation of the grid voltage. When the fluctuation amplitude of the grid voltage is within a certain range, it is determined that the grid voltage meets the preset soft-start conditions.

[0080] Furthermore, in one embodiment, if the battery voltage is greater than or equal to a preset soft-start voltage threshold, the bias compensation amount required for automatic bias compensation is calculated, and the inverter voltage required to be output by the inverter is determined based on the bias compensation amount and the bus voltage of the bus capacitor C1. Then, the PWM signal output to the inverter is controlled based on the inverter voltage to control the soft-start output of the inverter, and then the output step of the inverter is adjusted based on the PWM signal, as well as the positive and negative half-cycle voltage difference output by the inverter during the soft-start process.

[0081] In the control strategy of the inverter, a digital PI controller may be used to calculate the bias compensation amount. The actual bias compensation amount calculation may need to be adjusted according to the specific application scenario and system parameters. When designing the compensation strategy, it is usually necessary to perform dynamic simulation and experimental verification of the system to ensure that the compensation effect meets the actual requirements.

[0082] It should be noted that the inverter may generate DC bias magnetism during operation, which will cause the transformer core to saturate and affect system performance. In order to compensate for this bias magnetism, in some embodiments, a closed-loop control strategy can be adopted to detect the DC component on the primary side of the transformer, feed it back to the controller for error amplification, and then adjust the pulse width modulation (PWM) signal to eliminate the DC component and achieve bias magnetism compensation. This method can adjust the width of SPWM in real time so that the positive and negative pulse volt-second products of the transformer are the same, thereby achieving the purpose of eliminating the DC component.

[0083] The soft start output of the inverter can be achieved by gradually increasing the output voltage and frequency, thereby reducing the current shock and mechanical shock at startup. This can be achieved by controlling the duty cycle of the PWM signal so that the output voltage gradually increases according to a predetermined ramp.

[0084] Adjusting the output step size of the inverter involves precise control of the inverter output voltage. Adjusting the output step size usually involves modulation of the PWM signal. By changing the duty cycle of the PWM signal, the amplitude of the inverter output voltage can be adjusted. During the soft start process, the duty cycle of the PWM signal can be gradually increased to achieve smooth voltage changes.

[0085] During the soft start process, the voltage fluctuation can be reduced by adjusting the positive and negative half-cycle voltage difference output by the inverter during the soft start process, that is, reducing the difference between the positive and negative half-cycle voltage differences. Among them, the adjustment of the positive and negative half-cycle voltage difference output by the inverter during the soft start process can be achieved by adjusting the phase and duty cycle of the PWM signal. For example, by adding dead time to the PWM signal, the dead zone effect of the switching device can be compensated, thereby reducing voltage fluctuations. For example, in a PWM full-bridge inverter, the driving signals of the positive and negative outputs can be controlled so that in one cycle, the high level time of the positive output is longer than the high level time of the negative output, so that the output voltage will have a positive DC component, and a corresponding negative level is output through the voltage follower, and the modulation wave is negatively offset, so that the DC component caused by the control system, etc. can be adaptively offset.

[0086] Furthermore, in one embodiment, if the battery voltage is less than a preset soft-start voltage threshold, the main circuit is re-controlled to start automatic bias magnetic compensation, waiting for the battery voltage connected to the battery terminal of the main circuit to rise to the preset soft-start voltage threshold, and so on, which will not be repeated here.

[0087] Step S330: If not, determine that the battery terminal is abnormal and output an alarm signal.

[0088] The battery terminal abnormality may be a battery terminal failure or other abnormal conditions.

[0089] In an embodiment of the present application, it is determined whether the battery voltage at the battery end increases. If the battery voltage at the battery end increases, then when the grid voltage meets the preset soft-start conditions, it is determined whether the battery voltage is greater than or equal to the preset soft-start voltage threshold; conversely, if the battery voltage at the battery end does not increase, it is determined that the battery end is abnormal, and the soft start is stopped and an alarm signal is output to remind relevant personnel to make repairs in time.

[0090] In some embodiments, when the main circuit includes a DC bus and an inverter connected in sequence, step S140 may include but is not limited to the following steps:

[0091] Step S410: Obtain the inverter voltage of the inverter and the grid voltage.

[0092] Exemplarily, the inverter voltage of the inverter and the grid voltage may be detected in real time by a voltage sensor.

[0093] Step S420: Determine the required bias magnetic compensation amount according to the inverter voltage and the grid voltage.

[0094] In an embodiment of the present application, after the bias magnetic amount that needs to be compensated for the transformer is calculated by converting the voltage difference between the inverter voltage and the grid voltage, the inverter soft start is controlled to output a suitable voltage to compensate for the bias magnetic amount.

[0095] In some embodiments, when the DC bus is provided with a bus capacitor, step S150 may include but is not limited to the following steps:

[0096] Step S510: determining the inverter voltage required to be output by the inverter according to the bias compensation amount and the bus voltage of the bus capacitor.

[0097] Among them, the bus voltage of the bus capacitor C1 is detected, and specifically, the voltage on the DC bus can be detected in real time by a voltage sensor. This voltage gradually increases during the soft start of the inverter. In addition, the control device calculates the required inverter voltage based on the bus voltage of the detected bus capacitor. After the required inverter voltage is calculated, a corresponding PWM signal can be generated to facilitate closed-loop control of the inverter output voltage. In some embodiments, the inverter voltage can be achieved by adjusting the duty cycle of the PWM signal. The inverter voltage can be determined based on the difference between the bus voltage and a preset modulation index (for example, the product between the difference between the bus voltage and the modulation index), and the modulation index (or duty cycle) is the ratio of the high level duration in the PWM signal to the entire cycle time. The embodiments of the present invention are not specifically limited.

[0098] In addition, the grid auxiliary power supply can supply power to the bus capacitor.

[0099] Step S520: controlling the PWM signal output to the inverter according to the inverter voltage to control the soft start output of the inverter.

[0100] It should be noted that the inverter may generate DC bias during operation, which will cause the transformer core to saturate and affect system performance. In order to compensate for this bias, a closed-loop control strategy can be used to detect the DC component on the primary side of the transformer, feed it back to the controller for error amplification, and then adjust the pulse width modulation (PWM) signal to eliminate the DC component and achieve bias compensation. This method can adjust the width of SPWM in real time so that the positive and negative pulse volt-second products of the transformer are the same, thereby achieving the purpose of eliminating the DC component.

[0101] The soft start output of the inverter can be achieved by gradually increasing the output voltage and frequency, thereby reducing the current shock and mechanical shock at startup. This can be achieved by controlling the duty cycle of the PWM signal so that the output voltage gradually increases according to a predetermined ramp.

[0102] Step S530: adjusting the output step size of the inverter according to the PWM signal, and adjusting the positive and negative half-cycle voltage difference output by the inverter during the soft start process.

[0103] Adjusting the output step size of the inverter involves precise control of the inverter output voltage. Adjusting the output step size usually involves modulation of the PWM signal. By changing the duty cycle of the PWM signal, the amplitude of the inverter output voltage can be adjusted. During the soft start process, the duty cycle of the PWM signal can be gradually increased to achieve smooth voltage changes.

[0104] In an embodiment of the present application, the inverter voltage required to be output by the inverter is determined by the bias compensation amount and the bus voltage of the bus capacitor, and the PWM signal output to the inverter is controlled according to the inverter voltage to control the soft start output of the inverter. The output step of the inverter can be adjusted according to the PWM signal, and the positive and negative half-cycle voltage difference output by the inverter during the soft start process can be adjusted to achieve soft start of the main circuit and compensate for the bias, thereby safely and effectively avoiding the huge excitation current of the transformer, and at the same time reducing the risk of device damage. In addition, the use scenarios of the machine can be expanded, and the impact on the user's load and equipment such as air switches can be reduced, bringing economic benefits to the user.

[0105] In some embodiments, when it is determined that the soft-start voltage does not meet the preset voltage output condition for a number of times greater than or equal to a preset number of times, it is determined that the battery terminal is abnormal and an alarm signal is output.

[0106] The preset number of times may be 2 times, 3 times or other values, and may be set according to actual conditions, and is not specifically limited here. In addition, the battery terminal abnormality may be a battery terminal failure or other abnormal conditions.

[0107] In some embodiments, when the soft-start voltage meets the preset voltage output condition and controls the grid relay to close, when the battery meets the soft-start trigger condition, the main circuit is controlled to receive the voltage from the battery and the main circuit is controlled to enter the grid-connected mode to achieve grid-connected charging with load.

[0108] After the soft start output is completed, it is determined whether the battery is connected or the battery is restored. If so, the battery charging mode is turned on, and the control device controls the main circuit to enter the grid-connected mode to achieve grid-connected charging and loading, otherwise the bypass discharge and loading is maintained.

[0109] like Figure 3As shown, in one embodiment, at the beginning, the grid input voltage of the power grid is detected. When the grid input voltage of the power grid is detected, the grid auxiliary power supply is controlled to supply power to the battery auxiliary power supply, so that the battery auxiliary power supply supplies power to the power frequency inverter. Then, when the preset bias magnetic compensation condition is met, the control device determines whether the preset bias magnetic compensation condition is met. If the preset bias magnetic compensation condition is not met, the main circuit is prohibited from starting the automatic bias magnetic compensation, and the power frequency inverter is controlled to enter the standby state and output an alarm signal; if the preset bias magnetic compensation condition is met, the main circuit is controlled to start the automatic bias magnetic compensation, and then, it is determined whether the battery voltage at the battery end increases. If not, that is, the battery voltage at the battery end does not increase, it is determined that the battery end is abnormal, the soft start is stopped, and an alarm signal is output; if so, that is, the battery voltage at the battery end increases, combined with the grid voltage, it is determined whether the preset soft start voltage threshold is met, that is, when the grid voltage meets the preset soft start condition, it is determined whether the battery voltage is greater than or equal to the preset soft start voltage threshold. If not, That is, if the battery voltage is less than the preset soft-start voltage threshold, the main circuit continues to keep the automatic bias compensation turned on, waiting for the battery voltage connected to the battery end of the main circuit to rise to the preset soft-start voltage threshold, and so on, which will not be repeated here; if it is, that is, the battery voltage is greater than or equal to the preset soft-start voltage threshold, the bias compensation amount is calculated, the inverter soft-start output is adjusted, the output step is adjusted, and the voltage difference of the half cycle in the soft start is adjusted, that is, the inverter voltage and the grid voltage of the inverter are obtained, and the inverter voltage required to be output by the inverter is determined according to the bias compensation amount and the bus voltage of the bus capacitor, and the PWM signal output to the inverter is controlled according to the inverter voltage to control the soft-start output of the inverter, and the output step of the inverter is adjusted according to the PWM signal, as well as the positive and negative half-cycle voltage difference output by the inverter during the soft start process.

[0110] Further, determine whether the soft-start voltage meets the preset voltage output conditions. If not, that is, the soft-start voltage does not meet the preset voltage output conditions, then determine whether the number of failures is greater than or equal to the preset number of times, that is, determine whether the number of times the soft-start voltage does not meet the preset voltage output conditions is greater than or equal to the preset number of times. When it is determined that the number of times the soft-start voltage does not meet the preset voltage output conditions is greater than or equal to the preset number of times, it is determined that the battery terminal is abnormal. At this time, the soft start is stopped and an alarm signal is output; if not, that is, the number of times the soft-start voltage does not meet the preset voltage output conditions is less than the preset number of times, combined with the grid voltage, determine whether the preset soft-start voltage threshold is met, and so on. It will not be repeated here.

[0111] If so, that is, the soft-start voltage meets the preset voltage output condition, the grid relay is controlled to close, and then the inverter relay is closed to achieve bypass discharge load. Then, after the soft-start output is completed, it is determined whether the battery is connected or whether the battery is restored. If so, the battery charging mode is turned on, and the control device controls the inverter to enter the grid-connected mode to achieve grid-connected charging load, otherwise the bypass discharge load is maintained. It should be noted that the closing angle selection of the grid relay can usually be based on the phase angle of the grid voltage. By selecting a suitable phase angle to close the relay, the current shock and voltage fluctuation during closing can be reduced.

[0112] like Figure 4 As shown, an embodiment of the present invention provides a control device 1000, including a memory 1010, a processor 1020, and a computer program stored in the memory 1010 and executable on the processor 1020, wherein the processor 1020 and the memory 1010 may be connected via a bus or other means. Figure 4 An example of a bus connection is shown, and when the processor executes the computer program, the power grid output control method of the first aspect embodiment is implemented as described above.

[0113] An embodiment of the present invention provides an industrial frequency inverter, comprising a control device, a main circuit, a grid auxiliary power supply, a battery auxiliary power supply and a relay circuit as described above in the second aspect of the embodiment, the control device is respectively connected to the main circuit, the battery auxiliary power supply and the relay circuit, the main circuit is respectively connected to the battery auxiliary power supply and the relay circuit, the grid auxiliary power supply is connected to the battery auxiliary power supply and the grid, the relay circuit comprises an inverter relay and a grid relay, the inverter relay is connected to the load, the grid relay is connected to the grid and the inverter relay, and the main circuit is also connected to the battery.

[0114] An embodiment of the present invention provides a computer-readable storage medium, which stores computer-executable instructions. The computer-executable instructions can be used to enable a computer to execute the power grid output control method of the first embodiment as described above.

[0115] It will be appreciated by those skilled in the art that all or some of the steps and systems in the disclosed methods above may be implemented as software, firmware, hardware and appropriate combinations thereof. Some physical components or all physical components may be implemented as software executed by a processor, such as a central processing unit, a digital signal processor or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application specific integrated circuit. Such software may be distributed on a computer-readable medium, which may include a computer storage medium or a non-transitory medium and a communication medium or a temporary medium. As known to those skilled in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information such as computer-readable instructions, data structures, program modules or other data. Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disk DVD or other optical disk storage, magnetic cassettes, magnetic tapes, disk storage or other magnetic storage devices, or any other medium that may be used to store desired information and may be accessed by a computer. Furthermore, it is well known to those skilled in the art that communication media typically embodies computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and may include any information delivery media.

[0116] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. A method for controlling power grid output of an industrial frequency inverter, characterized in that: The power frequency inverter comprises a main circuit, a grid auxiliary power supply, a battery auxiliary power supply and a relay circuit, wherein the main circuit is connected to the battery auxiliary power supply and the relay circuit respectively, the grid auxiliary power supply is connected to the battery auxiliary power supply and the grid, the relay circuit comprises an inverter relay and a grid relay, the inverter relay is connected to a load, the grid relay is connected to the grid and the inverter relay, the main circuit is also connected to a battery, and the grid output control method comprises: When a grid input voltage of the grid is detected, controlling the grid auxiliary power supply to supply power to the battery auxiliary power supply, so that the battery auxiliary power supply supplies power to the power frequency inverter; When a preset bias magnetic compensation condition is met, the main circuit is controlled to start automatic bias magnetic compensation, wherein the preset bias magnetic compensation condition includes that the battery does not meet the soft start trigger condition, the power grid is in a normal state, and the power frequency inverter meets the bypass output condition; Determining whether the battery voltage connected to the battery terminal of the main circuit is greater than or equal to a preset soft start voltage threshold; When the battery voltage is greater than or equal to a preset soft-start voltage threshold, obtaining a bias magnetic compensation amount required for automatic bias magnetic compensation; Controlling the main circuit to perform inverter soft start output according to the bias magnetic compensation amount; Determining whether the soft-start voltage output by the main circuit meets a preset voltage output condition; When the soft-start voltage meets the preset voltage output condition, the grid relay is controlled to close to achieve bypass discharge and load.

2. The power grid output control method according to claim 1, characterized in that: Also includes: When the preset bias magnetic compensation conditions are not met, the main circuit is prohibited from starting automatic bias magnetic compensation; The power frequency inverter is controlled to enter a standby state and output an alarm signal.

3. The power grid output control method according to claim 1, characterized in that: The determining whether the battery voltage connected to the battery terminal of the main circuit is greater than or equal to a preset soft start voltage threshold comprises: determining whether the battery voltage at the battery terminal increases; If so, if the grid voltage satisfies the preset soft-start condition, determining whether the battery voltage is greater than or equal to a preset soft-start voltage threshold; If not, it is determined that the battery terminal is abnormal and an alarm signal is output.

4. The power grid output control method according to claim 1, characterized in that: The main circuit includes a DC bus and an inverter connected in sequence, and the method of obtaining the bias magnetic compensation amount required for automatic bias magnetic compensation includes: Obtaining an inverter voltage and a grid voltage of the inverter; The required bias magnetic compensation amount is determined according to the inverter voltage and the grid voltage.

5. The power grid output control method according to claim 4, characterized in that: The DC bus is provided with a bus capacitor, and the main circuit is controlled to perform inverter soft start output according to the bias magnetic compensation amount, including: Determining the inverter voltage required to be output by the inverter according to the bias compensation amount and the bus voltage of the bus capacitor; Controlling a PWM signal output to the inverter according to the inverter voltage to control a soft start output of the inverter; The output step size of the inverter is adjusted according to the PWM signal, and the positive and negative half-cycle voltage difference output by the inverter during the soft start process is adjusted.

6. The power grid output control method according to claim 1, characterized in that: Also includes: When it is determined that the number of times that the soft-start voltage does not meet the preset voltage output condition is greater than or equal to the preset number of times, it is determined that the battery terminal is abnormal and an alarm signal is output.

7. The power grid output control method according to claim 1, characterized in that: After the grid relay is controlled to be closed when the soft-start voltage meets the preset voltage output condition, the grid output control method further includes: When the battery meets the soft start trigger condition, the main circuit is controlled to receive the voltage from the battery, and the main circuit is controlled to enter the grid-connected mode to achieve grid-connected charging and loading.

8. A control device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the power grid output control method according to any one of claims 1 to 7 when executing the computer program.

9. An industrial frequency inverter, characterized in that: It includes the control device as claimed in claim 8, a main circuit, a grid auxiliary power supply, a battery auxiliary power supply and a relay circuit, the control device is connected to the main circuit, the battery auxiliary power supply and the relay circuit respectively, the main circuit is connected to the battery auxiliary power supply and the relay circuit respectively, the grid auxiliary power supply is connected to the battery auxiliary power supply and the grid, the relay circuit includes an inverter relay and a grid relay, the inverter relay is connected to a load, the grid relay is connected to the grid and the inverter relay, and the main circuit is also connected to a battery.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer-executable instructions, and the computer-executable instructions are used to enable a computer to execute the power grid output control method according to any one of claims 1 to 7.

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