CN109802557B

CN109802557B - Soft start and power regulation method and device for variable frequency power supply

Info

Publication number: CN109802557B
Application number: CN201910014668.4A
Authority: CN
Inventors: 赵志刚; 王志勇; 俞建悦; 顾永德
Original assignee: Jama Technology Co ltd
Current assignee: MOSO POWER SUPPLY TECHNOLOGY Co.,Ltd.
Priority date: 2019-01-04
Filing date: 2019-01-04
Publication date: 2021-01-29
Anticipated expiration: 2039-01-04
Also published as: CN109802557A

Abstract

The embodiment of the invention discloses a method and a device for soft start and power regulation of a variable frequency power supply, wherein the method comprises the following steps: checking whether the variable frequency power supply has system fault; if not, executing a soft start process; the soft start process, comprising: adjusting the duty cycle of the PWM output to a first duty cycle for a first period of time and adjusting the PWM output frequency from a first frequency F1 to a second frequency F2; adjusting the PWM output frequency from F2 to a third frequency F3 or a fourth frequency F4 for a second time period; fixing the PWM output frequency in a third time period; adjusting the lower limit frequency of the PWM output frequency in a fourth time period; after the soft start process is executed, the duty ratio of the PWM output is fixed, and the upper limit and the lower limit of the PWM output frequency are adjusted to adjust the PWM output frequency. The embodiment of the invention can realize stable power-on of the variable frequency power supply and continuous adjustment of output power, and meet the requirements of different power outputs.

Description

Soft start and power regulation method and device for variable frequency power supply

Technical Field

The invention relates to the technical field of electronics, in particular to a method and a device for soft start and power regulation of a variable frequency power supply.

Background

After the variable frequency power supply is powered on, when an Insulated Gate Bipolar Transistor (IGBT) in the variable frequency power supply is switched on for the first time, a high output voltage is output from the secondary side of the transformer, the transformer is easy to ignite, the insulation of the transformer is damaged, the power supply is damaged, and the service life of the variable frequency power supply is shortened. In order to solve the above problems and prolong the service life of the variable frequency power supply and the magnetron, the prior art generally adopts a variable frequency power supply soft start technology, and the prior variable frequency power supply soft start technology generally realizes soft start by adjusting the duty ratio of Pulse Width Modulation (Pulse Width Modulation, abbreviated as PWM), however, the soft start mode of driving the IGBT with asymmetric duty ratio is easy to cause magnetic saturation of the transformer and generate larger impact current, thereby damaging the peripheral devices such as the IGBT and the drive control.

In addition, the magnetron is the heart of microwave application equipment, and needs a strong constant magnetic field when the magnetron normally works, so a power supply is needed to provide a negative direct-current high voltage for supplying power to the magnetron, when the magnetron starts oscillation, if the control PWM frequency or pulse width of the IGBT changes, the direct-current high voltage on the secondary side of the transformer also jumps, when the magnetron starts oscillation, the impact current is large, and peripheral devices such as the IGBT, the drive control and the like are easily damaged. At present, output power regulation through a digital power supply or a power tube duty ratio is discrete, the adjustable range of the output power is limited, the adjustable precision is low, and the output requirements of all powers cannot be met.

In summary, the soft start and power adjustment technology of the present variable frequency power supply cannot ensure stable power-up of the variable frequency power supply, and the adjustable range of the output power is limited and the adjustable precision is low.

Disclosure of Invention

The embodiment of the invention provides a method and a device for soft start and power regulation of a variable frequency power supply, which can realize stable power-on of the variable frequency power supply, improve the adjustable range and adjustable precision of output power and meet the requirements of different power outputs.

In a first aspect, an embodiment of the present invention provides a method for soft start and power regulation of a variable frequency power supply, where the method includes the following steps:

checking whether the variable frequency power supply has system fault;

if not, executing a soft start process;

the soft start process, comprising:

adjusting the duty cycle of the PWM output to a first duty cycle for a first period of time and adjusting the PWM output frequency from a first frequency F1 to a second frequency F2;

adjusting the PWM output frequency from F2 to a third frequency F3 in a second time period, and stopping adjustment if the output current is greater than a preset current threshold in the adjustment process of the PWM output frequency, wherein the PWM output frequency is F4;

fixing the PWM output frequency in a third time period, and setting the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency as the current PWM output frequency;

in a fourth time period, according to the output voltage and the output current feedback of the current variable frequency power supply, obtaining a PWM output frequency, and adjusting the lower limit frequency of the PWM output frequency;

after the soft start process is executed, fixing the duty ratio of PWM output, obtaining PWM output frequency according to the output voltage and output current feedback of the current variable frequency power supply, adjusting the upper limit frequency and the lower limit frequency of the PWM output frequency to adjust the PWM output frequency, if the PWM output frequency is higher than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and if the PWM output frequency is lower than the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency.

In the embodiment of the invention, whether the system fault occurs in the variable frequency power supply is checked, and if the system fault does not occur in the variable frequency power supply, the soft start process is executed, so that the safe start of the variable frequency power supply is ensured, and the damage to the variable frequency power supply caused by the soft start under the condition of the system fault is avoided. By executing the soft start process, the stable power-on of the variable frequency power supply is realized. The adjustable range and the adjustable precision of the output power are improved by fixing the duty ratio of the PWM output and adjusting the upper limit and the lower limit of the PWM output frequency so as to adjust the PWM output frequency, and the requirements of different power outputs are met.

Optionally, checking whether the variable frequency power supply has a system fault includes: checking whether the variable frequency power supply has system fault; if so, generating a state word, wherein the state word reflects the current state of the variable frequency power supply and comprises a system fault of the variable frequency power supply and the running state of the variable frequency power supply; based on the status word, a system fault is handled.

In the embodiment of the invention, the system fault is processed by checking whether the variable frequency power supply has the system fault or not, and if so, the safe starting and the reliable operation of the variable frequency power supply are ensured.

Optionally, the soft start process includes:

in a first time period, adjusting the duty ratio of the PWM output from a second duty ratio to a first duty ratio, adjusting the PWM output frequency from F1 to F2, wherein the adjustment step size is the difference between F1 and F2 divided by the value of the first time period, F1 is the initial value of the PWM output frequency, F1 is smaller than the maximum switching frequency of a power switching device of the variable-frequency power supply, and F1 is larger than or equal to F2;

in the embodiment of the invention, in the first time period, by adjusting the duty ratio and the PWM output frequency of the PWM output, the adjustment step length of the PWM output frequency is the value obtained by dividing the difference between F1 and F2 by the first time period, so that the generation of large impact current when the variable frequency power supply is conducted can be prevented, the damage of devices of the variable frequency power supply is prevented, and the stress requirement of switching devices of the variable frequency power supply is reduced.

And in the second time period, fixing the duty ratio of the PWM output as the first duty ratio, adjusting the PWM output frequency from F2 to F3, wherein the adjustment step is the value obtained by dividing the difference between F2 and F3 by the second time period, and stopping the adjustment of the PWM output frequency if the output current is greater than a preset current threshold value in the adjustment process of the PWM output frequency, wherein the PWM output frequency is F4, F2 is greater than or equal to F4, and F4 is greater than or equal to F3.

In the embodiment of the invention, in the second time period, the PWM output frequency is adjusted, the adjustment step length is a value obtained by dividing the difference between F2 and F3 by the second time period, and if the output current is greater than the preset current threshold value in the adjustment process, the adjustment of the PWM output frequency is stopped, so that the operation of the variable frequency power supply can be prepared, and the safe start of the variable frequency power supply is ensured.

In the third time period, the duty ratio of the fixed PWM output is the first duty ratio, the fixed PWM output frequency is the PWM output frequency at the end time of the second time period, and the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency are set as the current PWM output frequency.

In the embodiment of the invention, in the third time period, the stability of the output voltage can be ensured by fixing the duty ratio and the PWM output frequency of the PWM output, so that the subsequent stable switching of the output power of the variable frequency power supply is ensured.

In a fourth time period, fixing the duty ratio of the PWM output as the first duty ratio, obtaining the PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, adjusting the lower limit frequency of the PWM output frequency to the minimum upper limit value F7 of the PWM output frequency, and completing the soft start of the variable frequency power supply, wherein F7 is the resonant frequency of the variable frequency power supply.

Optionally, the PWM output frequency is obtained according to the output voltage and the output current feedback at the present moment, the lower limit frequency of the PWM output frequency is adjusted to the minimum upper limit F7 of the PWM output frequency, and the soft start of the variable frequency power supply is completed, which specifically includes:

obtaining PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, adjusting the lower limit frequency of the PWM output frequency by taking a first step size Delta S1 as a step size, finishing the soft start of the variable frequency power supply when the lower limit frequency of the PWM output frequency is adjusted to F7 from the initial value of the lower limit frequency of the PWM output frequency, wherein F7 is smaller than F3, if the PWM output frequency is smaller than the lower limit frequency of the PWM output frequency in the adjustment process of the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency, if the PWM output frequency is larger than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and F7 is the resonant frequency of the.

In the embodiment of the invention, in the fourth time period, the fixed PWM output power is converted into the PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, so that preparation is made for the variable frequency power regulation of the next stage.

Optionally, obtaining a PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, adjusting an upper limit frequency and a lower limit frequency of the PWM output frequency to adjust the PWM output frequency, if the PWM output frequency is higher than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and if the PWM output frequency is lower than the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency, including:

obtaining a target primary side current corresponding to the target output power according to the number of turns of the primary side of the variable frequency power supply, the number of turns of the secondary side of the variable frequency power supply, the output voltage of the secondary side and the preset target output power of the variable frequency power supply;

executing the following process I and process II until the real-time primary current obtained by sampling the primary current of the variable frequency power supply is equal to the target primary current, wherein

The first process comprises the following steps:

if the real-time primary side current is larger than the target primary side current, increasing the upper limit frequency of the PWM output frequency by taking a second step size delta S2 as a step size, comparing the upper limit frequency of the PWM output frequency with the maximum upper limit value F0 of the PWM output frequency, if the upper limit frequency of the PWM output frequency is smaller than F0, switching the variable frequency power supply to a process II, if the upper limit frequency of the PWM output frequency is larger than F0, the upper limit frequency of the PWM output frequency is equal to F0, increasing the lower limit frequency of the PWM output frequency by taking the step size delta S2 as a step size, if the lower limit frequency of the PWM output frequency is larger than or equal to F0, checking whether the variable frequency power supply has a system fault, if the lower limit frequency of the PWM output frequency is smaller than F0, switching the variable frequency power supply to the process II, F0 is smaller than the maximum switching frequency of a;

if the real-time primary side current is smaller than the target primary side current, reducing the lower limit frequency of the PWM output frequency by taking Delta S2 as a step length, comparing the lower limit frequency of the PWM output frequency with F7, if the lower limit frequency of the PWM output frequency is larger than F7, switching to a second process by the variable frequency power supply, if the lower limit frequency of the PWM output frequency is smaller than or equal to F7, the lower limit frequency of the PWM output frequency is equal to F7, and reducing the upper limit frequency of the PWM output frequency by taking Delta S2 as a step length, at the moment, if the upper limit frequency of the PWM output frequency is smaller than or equal to F7, checking whether the variable frequency power supply has a system fault, and if the upper limit frequency of the PWM output frequency is larger than F7, switching;

the second process comprises the following steps:

and obtaining PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, if the PWM output frequency is smaller than the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency, if the PWM output frequency is larger than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and if the PWM output frequency is larger than or equal to the lower limit frequency of the PWM output frequency and is smaller than or equal to the upper limit frequency of the PWM output frequency, the first execution process is returned.

In the embodiment of the invention, the target primary side current corresponding to the target output power is calculated, the PWM output frequency is adjusted by adjusting the upper limit frequency and the lower limit frequency of the PWM output frequency, and then the output power is adjusted until the real-time primary side current obtained by sampling the primary side current of the variable frequency power supply is equal to the target primary side current, so that the adjustable range and the adjustable precision of the power are improved, and the continuous adjustment of the output power is realized.

In a third aspect, an embodiment of the present invention further provides a device for soft start and power adjustment of a variable frequency power supply, where the device can achieve the beneficial effects of the method for soft start and power adjustment of a variable frequency power supply described in the first aspect. The functions of the device can be realized by hardware, and can also be realized by hardware executing corresponding software. The hardware or software includes at least one module corresponding to the above functions.

Optionally, the apparatus comprises a first checking unit, a soft start unit and an adjusting unit.

And the first checking unit is used for checking whether the variable frequency power supply has a system fault.

And the soft start unit is used for executing a soft start process including the following steps if the system fault does not occur in the variable frequency power supply.

A first starting unit: the method includes adjusting a duty cycle of the PWM output to a first duty cycle during a first time period, and adjusting a PWM output frequency from a first frequency F1 to a second frequency F2.

A second starting unit: and the PWM output frequency is adjusted from F2 to a third frequency F3 in the second time period, and if the output current is greater than a preset current threshold in the adjustment process of the PWM output frequency, the adjustment is stopped, and the PWM output frequency is F4.

A third starting unit: and the PWM frequency setting module is used for fixing the PWM output frequency in the third time period and setting the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency as the current PWM output frequency.

A fourth starting unit: and the PWM frequency control circuit is used for obtaining PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply in the fourth time period and adjusting the lower limit frequency of the PWM output frequency.

And the adjusting unit is used for fixing the duty ratio of the PWM output after the soft start process is executed, obtaining the PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, and adjusting the upper limit frequency and the lower limit frequency of the PWM output frequency to adjust the PWM output frequency, wherein if the PWM output frequency is higher than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and if the PWM output frequency is lower than the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency.

Optionally, the first checking unit includes: a second checking unit, a generating unit and a processing unit. And the second checking unit is used for checking whether the variable frequency power supply has a system fault. And the generating unit is used for generating a state word if the variable frequency power supply has a system fault, wherein the state word reflects the current state of the variable frequency power supply and comprises the system fault of the variable frequency power supply and the running state of the variable frequency power supply. And the processing unit is used for processing the system fault according to the status word.

Optionally, the soft start unit includes: the device comprises a first starting unit, a second starting unit, a third starting unit and a fourth starting unit.

The first starting unit is used for adjusting the duty ratio of the PWM output from the second duty ratio to the first duty ratio and adjusting the PWM output frequency from F1 to F2 within a first time period, the adjustment step is the difference between F1 and F2 divided by the value of the first time period, F1 is the initial value of the PWM output frequency, F1 is smaller than the maximum switching frequency of a power switching device of the variable-frequency power supply, and F1 is larger than or equal to F2.

And the second starting unit is used for fixing the duty ratio of the PWM output as the first duty ratio in the second time period, adjusting the PWM output frequency from F2 to F3, wherein the adjustment step is the value obtained by dividing the difference between F2 and F3 by the second time period, and stopping the adjustment of the PWM output frequency if the output current is greater than a preset current threshold value in the adjustment process of the PWM output frequency, wherein the PWM output frequency is F4, F2 is greater than or equal to F4, and F4 is greater than or equal to F3.

And the third starting unit is used for fixing the duty ratio of the PWM output as the first duty ratio, fixing the PWM output frequency as the PWM output frequency at the end time of the second time period, and setting the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency as the current PWM output frequency in a third time period.

And the fourth starting unit is used for fixing the duty ratio of the PWM output as the first duty ratio in a fourth time period, obtaining the PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, adjusting the lower limit frequency of the PWM output frequency to the minimum upper limit value F7 of the PWM output frequency, and finishing the soft start of the variable frequency power supply, wherein F7 is the resonant frequency of the variable frequency power supply.

Optionally, the fourth starting unit is specifically configured to: in a fourth time period, fixing the duty ratio of the PWM output as a first duty ratio, obtaining a PWM output frequency according to the output voltage and output current feedback of the current variable frequency power supply, adjusting the lower limit frequency of the PWM output frequency by taking the first step size delta S1 as a step size, finishing the soft start of the variable frequency power supply when the lower limit frequency is adjusted to F7 from the initial value of the lower limit frequency of the PWM output frequency, wherein F7 is smaller than F3, if the PWM output frequency is smaller than the lower limit frequency of the PWM output frequency in the adjustment process of the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency, if the PWM output frequency is larger than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and F7 is the resonant frequency.

Optionally, the adjusting unit includes: a conversion unit and an execution unit.

And the conversion unit is used for obtaining a target primary side current corresponding to the target output power according to the number of turns of the primary side of the variable frequency power supply, the number of turns of the secondary side of the variable frequency power supply, the output voltage of the secondary side and the preset target output power of the variable frequency power supply.

An execution unit for executing a first process and a second process until a real-time primary current obtained by sampling a primary current of a variable frequency power supply is equal to a target primary current, wherein,

the first process comprises the following steps:

if the real-time primary side current is larger than the target primary side current, increasing the upper limit frequency of the PWM output frequency by taking a second step size delta S2 as a step size, comparing the upper limit frequency of the PWM output frequency with the maximum upper limit value F0 of the PWM output frequency, if the upper limit frequency of the PWM output frequency is smaller than F0, switching the variable frequency power supply to a process II, if the upper limit frequency of the PWM output frequency is larger than F0, enabling the upper limit frequency of the PWM output frequency to be equal to F0, increasing the lower limit frequency of the PWM output frequency by taking delta S2 as a step size, if the lower limit frequency of the PWM output frequency is larger than or equal to F0, checking whether the variable frequency power supply has a system fault, if the lower limit frequency of the PWM output frequency is smaller than F0, switching the variable frequency power supply to the process II, wherein F0 is smaller than the maximum switching frequency of a power;

if the real-time primary side current is smaller than the target primary side current, reducing the lower limit frequency of the PWM output frequency by taking Delta S2 as a step length, comparing the lower limit frequency of the PWM output frequency with F7, if the lower limit frequency of the PWM output frequency is larger than F7, switching to a process II, if the lower limit frequency of the PWM output frequency is smaller than or equal to F7, making the lower limit frequency of the PWM output frequency equal to F7, and reducing the upper limit frequency of the PWM output frequency by taking Delta S2 as a step length, at the moment, if the upper limit frequency of the PWM output frequency is smaller than or equal to F7, checking whether the variable frequency power has a system fault, and if the upper limit frequency of the PWM output frequency is larger than F7, switching to the process II;

the second process comprises the following steps:

In a third aspect, an embodiment of the present invention further provides a variable frequency power supply, where the variable frequency power supply can achieve the beneficial effects of the method for soft start and power adjustment of the variable frequency power supply described in the first aspect. The function of the variable frequency power supply can be realized by hardware, and can also be realized by executing corresponding software by hardware. The hardware or software includes at least one module corresponding to the above functions. The variable frequency power supply comprises a memory, a voltage and current checking circuit, a microprocessor and a communication circuit, wherein the memory is used for storing relevant data of the variable frequency power supply, the voltage and current checking circuit is used for acquiring the relevant data of the variable frequency power supply, the processor is used for controlling and managing the action of the variable frequency power supply according to a program instruction, and the communication circuit is used for supporting the communication between the variable frequency power supply and other communication equipment.

In a fourth aspect, embodiments of the present invention provide a computer program product containing instructions that, when run on a microprocessor, cause the microprocessor to perform the method for soft start and power regulation of a variable frequency power supply described in the first aspect above.

Drawings

Reference will now be made in brief to the drawings that are needed in describing embodiments or prior art.

Fig. 1 is a schematic structural diagram of a variable frequency power supply according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a system architecture of a soft start and power regulation system of a variable frequency power supply according to an embodiment of the present invention;

fig. 3 is a schematic flowchart of a method for soft start and power regulation of a variable frequency power supply according to an embodiment of the present invention;

fig. 4 is a schematic flow chart of a variable frequency power adjustment according to an embodiment of the present invention;

FIG. 5 is a schematic flow chart of another variable frequency power adjustment provided by the embodiment of the present invention;

fig. 6 is a schematic structural diagram of a soft start and power regulation apparatus of a variable frequency power supply according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described below with reference to the drawings in the embodiments of the present invention. It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Furthermore, the terms "first," "second," and "third," etc. are used to distinguish between different objects and are not used to describe a particular order.

It is to be understood that the terminology used in the embodiments of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the examples of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

The variable frequency power supply in the embodiment of the invention can be widely applied to the household appliance manufacturing industry, the motor industry, the electronic manufacturing industry, the laboratory and the like. The variable frequency power supply in the embodiment of the invention is applied to equipment adopting a flyback, half-bridge or full-bridge power supply topological structure, and the applied equipment comprises products such as an air conditioner, a washing machine, a microwave oven, a refrigerator, an exchange type power supply, a transformer and the like. The embodiment of the present invention is not particularly limited thereto.

Referring to fig. 1, fig. 1 is a schematic diagram of a hardware structure of a variable frequency power supply 100 according to an embodiment of the present invention, where the variable frequency power supply 100 includes: a memory 101, a communication circuit 102, a voltage current detection circuit 103 and a microprocessor 104. The memory 101 is used for storing related data of the variable frequency power supply, such as abnormal data, the communication circuit 102 is used for communicating with other equipment under the control of the microprocessor 104, the voltage and current detection circuit 103 is used for collecting related data of the variable frequency power supply, and the microprocessor 104 is used for executing program instructions. The microprocessor 104, when executing instructions, may perform the method of soft-starting and power regulation of the variable frequency power supply according to the program instructions.

Optionally, the variable frequency power supply 100 may also include a bus 105. The memory 101, the communication circuit 102, the voltage/current detection circuit 103, and the microprocessor 104 may be connected to each other via a bus 105. For ease of illustration, only one thick line is shown in FIG. 2, but it is not intended that there be only one bus or one type of bus.

In addition to the memory 101, the communication circuit 102, the voltage-current detection circuit 103, the microprocessor 104 and the bus 105 shown in fig. 2, the variable frequency power supply 100 in the embodiment may also include other hardware according to the actual function of the terminal, which is not described again.

Fig. 2 is a system architecture diagram of a soft start and power conditioning system 200 for a variable frequency power supply according to the present application. As shown in fig. 2, the system 200 for soft start and power regulation of a variable frequency power supply is composed of a signal acquisition module 201, a fault detection module 202, a protection processing module 203, a soft start module 204, and a variable frequency power regulation module 205, where the signal acquisition module 201 is configured to acquire signals such as voltage, current, and temperature. The fault detection module 202 is configured to determine whether the variable frequency power supply is working normally, whether a system fault occurs, and generate a status word, where the status word reflects a current status of the variable frequency power supply, including a system fault of the variable frequency power supply and an operating status of the variable frequency power supply, and when detecting that the variable frequency power supply is working abnormally, the power supply output can be turned off in time, so as to prevent the power supply from being damaged. The protection processing module 203 is configured to take different protection measures for different faults according to the status word, so as to ensure safe and reliable operation of the power supply. The soft start module 204 is used for ensuring stable power-on of the variable frequency power supply, and prolonging the service life of the variable frequency power supply. The variable frequency power adjusting module 205 is used to improve the adjustable range and precision of power and realize continuous adjustment of power.

Under the operating environment, the embodiment of the invention provides a soft start and power regulation method of the variable frequency power supply as shown in fig. 3. Referring to fig. 3, the method for soft start and power regulation of the variable frequency power supply includes:

s301, checking whether the variable frequency power supply has a system fault, and if not, executing the step S302.

Optionally, before the variable frequency power supply is started, whether the variable frequency power supply has a system fault is checked.

Optionally, during the operation of the variable frequency power supply, whether the variable frequency power supply has a system fault is periodically checked.

Optionally, whether a system fault occurs in the variable frequency power supply is checked, including whether the access voltage of the variable frequency power supply is normal, whether the resistance value of a negative thermistor of the variable frequency power supply is normal, and whether the current of the variable frequency power supply is normal, where the negative thermistor is used to monitor the temperature of components of the variable frequency power supply.

It can be understood that the access voltage of the variable frequency power supply should satisfy the preset voltage range, if the access voltage is too low, the output power is insufficient, if the access voltage is too high, the output power is too high, and the voltage-resistant range of partial components of the variable frequency power supply is possibly exceeded, so that the damage of the components is caused, and the service life of the variable frequency power supply is influenced. The negative thermistor is used for monitoring the temperature of components of the variable frequency power supply, the higher the temperature of the components of the variable frequency power supply is, the smaller the resistance value of the negative thermistor is, and the components of the variable frequency power supply can be a transformer, a power switch device and the like. If the system fault of the variable frequency power supply is detected before the variable frequency power supply is started, whether the output current of the variable frequency power supply is smaller than a preset value a1 can be detected, for example, a1 is zero. If the system fault of the variable frequency power supply is detected during the operation of the variable frequency power supply, whether the output current of the variable frequency power supply is in a preset range A1 can be detected, and the preset range A1 is determined by the output voltage and the output power of the current variable frequency power supply.

Optionally, whether the system fault occurs in the variable frequency power supply is checked, if the system fault occurs in the variable frequency power supply, a state word is generated, and the state word reflects the current state of the variable frequency power supply, including the system fault of the variable frequency power supply and the running state of the variable frequency power supply. Then, a system fault is determined according to the status word, and the system fault is processed. After the system failure is processed, step S301 is executed.

S302, adjusting the duty ratio of the PWM output to a first duty ratio in a first time period, and adjusting the PWM output frequency from a first frequency F1 to a second frequency F2.

Optionally, in the first time period, the duty ratio of the PWM output is adjusted from the second duty ratio to the first duty ratio, that is, the duty ratio of the PWM output driving the power switching device turned on at the high level is adjusted from 0% to the first duty ratio, and the duty ratio of the PWM output driving the power switching device turned on at the low level is adjusted from 100% to the first duty ratio. And configuring the PWM output frequency, adjusting the PWM output frequency from F1 to F2, wherein the adjustment step is the value obtained by dividing the difference between F1 and F2 by the first time period, F1 is the initial value of the PWM output frequency, F1 is smaller than the maximum switching frequency of a power switching device of the variable-frequency power supply, and F1 is larger than or equal to F2.

It will be appreciated that the PWM output is configured to a PWM register for driving the power switching devices.

Optionally, the first time period is greater than 50ms and less than 1s, for example, the first time period is 100 ms.

It can be understood that the value of the first duty cycle is determined according to the actual requirement of the variable frequency power supply, and the values of the first duty cycles of the variable frequency power supplies of different variable frequency devices may be different, for example, the value of the first duty cycle is 50%, which is not limited in the present invention. F1 is the initial value of PWM output frequency, and F1 is less than the maximum switching frequency of the power switching device of the variable frequency power supply, and the value of F1 is decided according to the actual demand of the variable frequency power supply. For example, F1 is 60% of the maximum switching frequency of the power switch device of the variable frequency power supply, which is not limited in the present invention.

For example, a system check is performed on the variable frequency power supply of the variable frequency microwave oven, and if the variable frequency power supply of the variable frequency microwave oven has no system fault, a soft start process is executed. Firstly, the duty ratio of the PWM output of the upper tube of the power switch tube is adjusted from 0% to 50% within 100ms, the duty ratio of the PWM output of the lower tube of the power switch tube is adjusted from 100% to a first duty ratio, the initial value of the PWM output frequency is set to be 60KHZ, the PWM output frequency is adjusted from 60KHZ to 50KHZ, and the step length is adjusted to be 100 HZ/ms.

And S303, adjusting the PWM output frequency from F2 to a third frequency F3 in a second time period, and stopping adjustment if the output current is greater than a preset current threshold in the adjustment process of the PWM output frequency, wherein the PWM output frequency is F4.

Optionally, in the second time period, the duty ratio of the PWM output is fixed to be the first duty ratio, the PWM output frequency is adjusted from F2 to F3, the adjustment step size is a value obtained by dividing the difference between F2 and F3 by the second time period, if the output current is greater than a preset current threshold value during the adjustment of the PWM output frequency, the adjustment of the PWM output frequency is stopped, at this time, the PWM output frequency is F4, F2 is greater than or equal to F4, and F4 is greater than or equal to F3.

Optionally, the second time period is greater than 1s and less than 10s, for example, the second time period is 4 s.

It can be understood that, during the second time period, the PWM output frequency is adjusted from F2 to F3, and if the output currents of the variable frequency power supplies are all smaller than the preset current threshold during the adjustment of the PWM output frequency, at the end time of the second time period, the PWM output frequency is F3. If the output current of the variable frequency power supply is greater than the preset current threshold value at the time t in the adjustment process of the PWM output frequency, at this time, the PWM output frequency is F4, and the PWM output frequency is fixed to be F4 from the time t to the end time of the second time period. The preset current threshold is determined according to the actual demand of the variable frequency power supply, and the value of the preset current threshold is generally 1A, which is not limited in the present invention.

For example, a soft start process is performed on a variable frequency power supply of a variable frequency microwave oven. The duty cycle of the PWM output is adjusted to 50% within 100ms, and the PWM output frequency is adjusted from 60KHZ to a second frequency of 50 KHZ. And fixing the duty ratio of the PWM output as a first duty ratio in 4S, adjusting the PWM output frequency from 50KHZ to 36KHZ, wherein the adjustment step length is 3.5Hz/ms, and if the output current of the variable frequency power supply is less than 1A in the adjustment process, the PWM output frequency is 36KHZ at the end time of the 4S. If the output current value of the variable frequency power supply is greater than 1A at the intermediate time in the adjustment process of the PWM output frequency, the PWM output frequency is 43KHZ from the intermediate time to the end time. For the frequency conversion microwave oven, the preheating requirement of the magnetron of the frequency conversion microwave oven can be met by the PWM output frequency adjustment in the 4S.

And S304, fixing the PWM output frequency in a third time period, and setting the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency as the current PWM output frequency.

Optionally, in a third time period, the duty ratio of the fixed PWM output is the first duty ratio, the fixed PWM output frequency is the PWM output frequency at the end time of the second time period, and the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency are set as the current PWM output frequency.

Optionally, the third time period is greater than 50ms and less than 1s, for example, the third time period is 100 ms.

It can be understood that the stability of the output voltage of the variable frequency power supply can be ensured by fixing the duty ratio and the PWM output frequency of the PWM output, and then the stable switching of the subsequent variable frequency power is ensured.

For example, within 10ms, the duty ratio of the fixed PWM output is 50%, the PWM output frequency is 36KHZ, and the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency are set to 36 KHZ.

S305, in a fourth time period, according to the output voltage and the output current feedback of the current variable frequency power supply, obtaining a PWM output frequency, and adjusting the lower limit frequency of the PWM output frequency.

Optionally, in a fourth time period, the duty ratio of the PWM output is fixed to the first duty ratio, and the PWM output frequency is obtained according to the output voltage and the output current feedback of the current variable frequency power supply. The calculation expression of the PWM output frequency is F7+ K1 XIadc + K2 XUadc, wherein K1 and K2 are constants, Iadc is the output value of the analog-to-digital converter (ADC) of the instantaneous current of the variable frequency power supply, and Uadc is the output value of the ADC of the instantaneous output voltage of the variable frequency power supply. And adjusting the lower limit frequency of the PWM output frequency by taking the first step size delta S1 as a step size, finishing the soft start of the variable frequency power supply when the lower limit frequency of the PWM output frequency is adjusted to the minimum lower limit value F7 of the PWM output frequency from the initial value of the lower limit frequency of the PWM output frequency, wherein F7 is smaller than F3, and F7 is the resonant frequency of the variable frequency power supply. Δ S1 takes the value of the difference between the PWM output frequency at the end of the second time period and F7 divided by the value of the fourth time period. If the PWM output frequency is less than the lower limit frequency of the PWM output frequency during the adjustment of Fd, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency, and if the PWM output frequency is greater than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency.

Optionally, the fourth time period is greater than 1s and less than 10s, for example, the fourth time period is equal to 2 s.

It can be understood that if the PWM output frequency at the end of the second time period is F3, the initial values of Fu and Fd are both F3, and Δ S1 is the difference between F3 and F7 divided by the fourth time period. And adjusting the lower limit frequency of the PWM output frequency by taking the delta S1 as a step, and completing the soft start of the variable frequency power supply when the lower limit frequency of the PWM output frequency is adjusted from F3 to F7.

S306, after the soft start process is executed, fixing the duty ratio of PWM output, obtaining PWM output frequency according to the output voltage and output current feedback of the current variable frequency power supply, adjusting the upper limit frequency and the lower limit frequency of the PWM output frequency to adjust the PWM output frequency, if the PWM output frequency is higher than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and if the PWM output frequency is lower than the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency.

Optionally, the method includes the steps of obtaining a PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, adjusting an upper limit frequency and a lower limit frequency of the PWM output frequency to adjust the PWM output frequency, if the PWM output frequency is higher than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and if the PWM output frequency is lower than the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency, and specifically includes the following steps:

and configuring the PWM output frequency according to the output voltage and the output current feedback of the current variable-frequency power supply, wherein the PWM output frequency is represented by Fout, and Fout is F7+ K1 × Iadc + K2 × Uadc.

According to the number of turns N1 of the primary side of the variable frequency power supply, the number of turns N2 of the secondary side of the variable frequency power supply and the output voltage V of the secondary side_outAnd the preset target output power P of the variable frequency power supply_setTo obtain P_setCorresponding target primary side current I_set，I_setThe calculation of (d) can be expressed as follows:

k3 is a correction coefficient, and when the power is output fixedly, the target primary side current and the real-time primary side current obtained by samplingThe ratio of the flows is K3.

And executing the following first process and second process until the real-time primary current obtained by sampling the primary current of the variable-frequency power supply is equal to the target primary current, wherein Fd represents the lower limit frequency of Fout, and Fu represents the upper limit frequency of Fout.

As shown in fig. 4, the first process includes:

s401, sampling to obtain real-time primary side current I_act。

Optionally, from the current time, sampling the primary current of the variable frequency power supply in a first sampling time period with a first sampling period Δ T as a period, and averaging the sampled primary current of the variable frequency power supply in the first sampling time period, where the average is the real-time primary current I_act。

S402, comparison I_actAnd I_setIf I is_actIs greater than I_setStep S403 is executed, if I_actIs less than I_setStep S407 is executed.

And S403, increasing Fu by taking the second step length deltaS 2 as a step.

It is understood that the value of Δ S2 is determined according to the actual requirement of the variable frequency power source, for example, the value of Δ S2 is 100HZ, which is not limited in the present invention.

S404, judging whether Fu is larger than or equal to the maximum upper limit value F0 of Fout, if yes, executing the step S405, and if not, switching the variable frequency power supply to the process II, wherein F0 is larger than or equal to F1.

It can be understood that F0 is equal to or greater than F1, F0 is less than the maximum switching frequency of the power switching device of the variable frequency power supply, and the value of F0 is determined according to the actual requirement of the variable frequency power supply, for example, the value of F0 is 60% of the maximum switching frequency of the power switching device of the variable frequency power supply, which is not limited in the present invention.

S405, Fu equals F0, and increases Fd in steps as Δ S2.

S406, judging whether Fd is larger than or equal to F0, if so, executing the step S301, otherwise, switching the variable frequency power supply to the process II.

And S407, reducing Fd by using the step of delta S2.

And S408, judging whether the Fd is less than or equal to F7, if not, switching the variable frequency power supply to the process II, and if so, executing the step S409.

S409, make Fd equal to F7, and decrease Fu by step Δ S2.

S410, judging whether Fu is less than or equal to F7, if yes, executing the step S301, and if not, switching the variable frequency power supply to the process II;

as shown in fig. 5, the second process includes:

and S411, obtaining Fout according to the output voltage and the output current feedback of the current variable frequency power supply.

S412, determine whether Fout is smaller than Fd, if yes, go to step S413, otherwise go to step S414.

S413, Fout equals Fd, and then proceed to process one above.

And S414, judging whether Fout is larger than Fu, if so, executing the step S415, otherwise, turning to the first process.

S415, Fout equals Fu, and then proceeds to process one above.

The scheme provided by the embodiment of the invention realizes the stable power-on of the variable frequency power supply, improves the adjustable range and the adjustable precision of the output power and meets the requirements of different power outputs. In the embodiment of the invention, whether the system fault occurs in the variable frequency power supply is checked, and if the system fault does not occur in the variable frequency power supply, the soft start process is executed, so that the safe start of the variable frequency power supply is ensured, and the damage to the variable frequency power supply caused by the soft start under the condition of the system fault is avoided. The system fault of the variable frequency power supply is checked and processed during the operation of the variable frequency power supply, so that the reliable operation of the variable frequency power supply is guaranteed. In the first time period, the duty ratio and the PWM output frequency of the PWM output are adjusted, so that the generation of large impact current when the variable frequency power supply is firstly conducted can be avoided, the device damage of the variable frequency power supply is prevented, and the stress requirement of a power switch device is reduced. In the second time period, the PWM output frequency is adjusted, so that preparation can be made for the operation of the variable frequency power supply, and the safe starting of the variable frequency power supply is guaranteed. In the third time period, the stability of the output voltage can be guaranteed by fixing the duty ratio and the PWM output frequency of the PWM output, and the stable switching of the output power of the subsequent variable frequency power supply is further guaranteed. In the fourth time period, the fixed PWM output power is converted into the PWM output frequency according to the output voltage and the output current feedback of the current variable-frequency power supply, so that preparation is made for the variable-frequency power regulation of the next stage, and the stable switching from the current output power to the target output power is guaranteed. According to the frequency conversion power adjusting method provided by the embodiment of the invention, the PWM output frequency is adjusted by adjusting the upper limit and the lower limit of the PWM output frequency, so that the power is adjusted, the adjustable range and the adjustable precision of the power are improved, and the user experience is effectively improved.

The embodiment of the invention also provides a soft start and power regulation device of the variable frequency power supply, and the device can realize the beneficial effects of the soft start and power regulation method of the variable frequency power supply. The functions of the device can be realized by hardware, and can also be realized by hardware executing corresponding software. The hardware or software includes at least one module corresponding to the above functions.

Referring to fig. 6, fig. 6 is a block diagram of a soft start and power regulation apparatus for a variable frequency power supply according to an embodiment of the present invention, where the apparatus includes: a first checking unit 601, a soft start unit 602 and an adjusting unit 603.

The first checking unit 601 is configured to check whether a system fault occurs in the variable frequency power supply.

A soft start unit 602, configured to execute a soft start process if the variable frequency power supply has no system fault, where the soft start process includes:

a first starting unit: for adjusting the duty cycle of the PWM output to a first duty cycle and the PWM output frequency from a first frequency F1 to a second frequency F2 during a first time period;

a second starting unit: the PWM output frequency is adjusted from F2 to a third frequency F3 in a second time period, if the output current is greater than a preset current threshold value in the adjustment process of the PWM output frequency, the adjustment is stopped, and the PWM output frequency is F4;

a third starting unit: the PWM frequency setting device is used for fixing the PWM output frequency in a third time period and setting the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency as the current PWM output frequency;

a fourth starting unit: and the PWM output frequency is obtained according to the output voltage and the output current feedback of the current variable frequency power supply in the fourth time period, and the PWM output frequency is adjusted by adjusting the lower limit frequency of the PWM output frequency.

An adjusting unit 603, configured to fix a duty ratio of the PWM output after the soft start process is performed, obtain a PWM output frequency according to an output voltage and an output current feedback of the current variable frequency power supply, and adjust an upper limit frequency and a lower limit frequency of the PWM output frequency to adjust the PWM output frequency, where the PWM output frequency is equal to the upper limit frequency of the PWM output frequency if the PWM output frequency is higher than the upper limit frequency of the PWM output frequency, and the PWM output frequency is equal to the lower limit frequency of the PWM output frequency if the PWM output frequency is lower than the lower limit frequency of the PWM output frequency.

Optionally, the first checking unit 601 includes: a second checking unit, a generating unit and a processing unit. And the second checking unit is used for checking whether the variable frequency power supply has a system fault. And the generating unit is used for generating a state word if the variable frequency power supply has a system fault, wherein the state word reflects the current state of the variable frequency power supply and comprises the system fault of the variable frequency power supply and the running state of the variable frequency power supply. And the processing unit is used for processing the system fault according to the status word.

Optionally, the soft start unit 602 includes: the device comprises a first starting unit, a second starting unit, a third starting unit and a fourth starting unit.

Optionally, the adjusting unit 603 includes: a conversion unit and an execution unit.

the first process comprises the following steps:

the second process comprises the following steps:

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied as hardware or software instructions executed by a microprocessor. The software instructions may be composed of corresponding software modules, and the software modules may be stored in a Random Access Memory (RAM), a flash memory, a Read Only Memory (ROM), an Erasable Programmable Read Only Memory (EPROM), an Electrically Erasable Programmable Read Only Memory (EEPROM), a register, a hard disk, a removable hard disk, a compact disc read only memory (CD-ROM), or any other form of storage medium known in the art. An exemplary storage medium is coupled to the microprocessor such that the microprocessor can read information from, and write information to, the storage medium. Of course, the storage medium may also be integral to the microprocessor.

Those skilled in the art will recognize that, in one or more of the examples described above, the functions described in connection with the embodiments of the invention may be implemented in hardware, software, firmware, or any combination thereof. When implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the embodiments of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the scope of the embodiments of the present invention.

Claims

1. A method for soft start and power regulation of a variable frequency power supply, the method comprising:

checking whether the variable frequency power supply has system fault;

if not, executing a soft start process;

the soft start process, comprising:

adjusting the duty cycle of the Pulse Width Modulation (PWM) output to a first duty cycle for a first time period and adjusting the PWM output frequency from a first frequency F1 to a second frequency F2;

adjusting the PWM output frequency from the F2 to a third frequency F3 in a second time period, and stopping adjustment if the current is greater than a preset current threshold in the adjustment process of the PWM output frequency, wherein the PWM output frequency is F4;

fixing the PWM output frequency in a third time period, and setting initial values of an upper limit frequency and a lower limit frequency of the PWM output frequency as the current PWM output frequency, wherein the upper limit frequency and the lower limit frequency of the PWM output frequency are used for adjusting the PWM output frequency;

in a fourth time period, according to the output voltage and the output current feedback of the current variable frequency power supply, obtaining the PWM output frequency, and adjusting the lower limit frequency of the PWM output frequency;

after the soft start process is executed, fixing the duty ratio of the PWM output, obtaining the PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, and adjusting the upper limit frequency and the lower limit frequency of the PWM output frequency to adjust the PWM output frequency, wherein if the PWM output frequency is higher than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and if the PWM output frequency is lower than the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency.

2. The method of claim 1, wherein the checking whether the variable frequency power supply has a system fault comprises:

checking whether the variable frequency power supply has a system fault;

if so, generating a state word, wherein the state word reflects the current state of the variable frequency power supply and comprises a system fault of the variable frequency power supply and the running state of the variable frequency power supply;

and processing the system fault according to the status word.

3. The method of claim 2, wherein the soft start process comprises:

during the first time period, adjusting the duty ratio of the PWM output from a second duty ratio to a first duty ratio, adjusting the PWM output frequency from the F1 to the F2 by a step size which is the difference between the F1 and the F2 divided by the value of the first time period, wherein the F1 is the initial value of the PWM output frequency, the F1 is less than the maximum switching frequency of a power switching device of the variable-frequency power supply, and the F1 is greater than or equal to the F2;

in the second time period, fixing the duty ratio of the PWM output as a first duty ratio, adjusting the PWM output frequency from F2 to F3 by a step size obtained by dividing the difference between F2 and F3 by the second time period, and stopping the adjustment of the PWM output frequency if the output current is greater than a preset current threshold value during the adjustment of the PWM output frequency, where the PWM output frequency is F4, the F2 is greater than or equal to F4, and the F4 is greater than or equal to F3;

in the third time period, fixing the duty ratio of the PWM output as a first duty ratio, fixing the PWM output frequency as the PWM output frequency at the end time of the second time period, and setting the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency as the current PWM output frequency;

in the fourth time period, fixing the duty ratio of the PWM output as a first duty ratio, obtaining the PWM output frequency according to the current output voltage and output current feedback of the variable frequency power supply, adjusting the lower limit frequency of the PWM output frequency to the minimum lower limit F7 of the PWM output frequency, and completing the soft start of the variable frequency power supply, where F7 is the resonant frequency of the variable frequency power supply.

4. The method according to claim 3, wherein the obtaining the PWM output frequency according to the current output voltage and output current feedback of the variable frequency power supply, adjusting a lower limit frequency of the PWM output frequency to a minimum lower limit F7 of the PWM output frequency, and completing the soft start of the variable frequency power supply specifically comprises:

obtaining the PWM output frequency according to the current output voltage and output current feedback of the variable frequency power supply, adjusting the lower limit frequency of the PWM output frequency by taking a first step size Delta S1 as a step size, finishing the soft start of the variable frequency power supply when the lower limit frequency of the PWM output frequency is adjusted to F7 from the initial value of the lower limit frequency of the PWM output frequency, wherein F7 is smaller than F3, if the PWM output frequency is smaller than the lower limit frequency of the PWM output frequency in the adjustment process of the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency, and if the PWM output frequency is larger than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency.

5. The method of claim 4, wherein the obtaining the PWM output frequency according to the output voltage and the output current feedback of the present variable frequency power supply, adjusting an upper limit frequency and a lower limit frequency of the PWM output frequency to adjust the PWM output frequency, wherein the PWM output frequency is equal to the upper limit frequency of the PWM output frequency if the PWM output frequency is higher than the upper limit frequency of the PWM output frequency, and wherein the PWM output frequency is equal to the lower limit frequency of the PWM output frequency if the PWM output frequency is lower than the lower limit frequency of the PWM output frequency comprises:

executing the following process I and process II until the real-time primary current obtained by sampling the primary current of the variable frequency power supply is equal to the target primary current, wherein the process I and the process II are carried out until the real-time primary current obtained by sampling the primary current of the variable frequency power supply is equal to the target primary current

The first process comprises the following steps:

if the real-time primary side current is larger than the target primary side current, increasing the upper limit frequency of the PWM output frequency by taking a second step size Delta S2 as a step size, comparing the upper limit frequency of the PWM output frequency with the maximum upper limit value F0 of the PWM output frequency, if the upper limit frequency of the PWM output frequency is smaller than F0, switching the variable frequency power supply to the process II, if the upper limit frequency of the PWM output frequency is larger than F0, the upper limit frequency of the PWM output frequency is equal to F0, increasing the lower limit frequency of the PWM output frequency by taking Delta S2 as a step size, if the lower limit frequency of the PWM output frequency is larger than or equal to F0, checking whether the variable frequency power supply has a system fault, if the lower limit frequency of the PWM output frequency is smaller than F0, switching the variable frequency power supply to the process II, wherein F0 is smaller than the maximum switching frequency of a power switching device of the variable frequency power supply, the F0 is equal to or greater than the F1;

if the real-time primary side current is smaller than the target primary side current, reducing the lower limit frequency of the PWM output frequency by taking the delta S2 as a step length, comparing the lower limit frequency of the PWM output frequency with the F7, if the lower limit frequency of the PWM output frequency is larger than the F7, switching the variable frequency power supply to the second process, if the lower limit frequency of the PWM output frequency is smaller than or equal to the F7, making the lower limit frequency of the PWM output frequency equal to the F7, and reducing the upper limit frequency of the PWM output frequency by taking the delta S2 as a step length, at the moment, if the upper limit frequency of the PWM output frequency is smaller than or equal to the F7, checking whether the variable frequency power supply has a system fault, and if the upper limit frequency of the PWM output frequency is larger than the F7, switching the variable frequency power supply to the second process;

the second process comprises the following steps:

and obtaining the PWM output frequency according to the current output voltage and output current feedback of the variable frequency power supply, if the PWM output frequency is smaller than the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency, if the PWM output frequency is larger than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and if the PWM output frequency is larger than or equal to the lower limit frequency of the PWM output frequency and is smaller than or equal to the upper limit frequency of the PWM output frequency, the process I is executed in a returning mode.

6. A soft start and power regulation apparatus for a variable frequency power supply, the apparatus comprising:

the first checking unit is used for checking whether the variable frequency power supply has system faults or not;

a soft start unit, configured to execute a soft start process if the variable frequency power supply has no system fault, including:

a second starting unit: the PWM output frequency is adjusted from the F2 to a third frequency F3 in a second time period, if the output current is greater than a preset current threshold value in the adjustment process of the PWM output frequency, the adjustment is stopped, and the PWM output frequency is F4;

a third starting unit: the PWM frequency control circuit is used for fixing the PWM output frequency in a third time period and setting the initial values of the upper limit frequency and the lower limit frequency of the PWM output frequency as the current PWM output frequency, wherein the upper limit frequency and the lower limit frequency of the PWM output frequency are used for adjusting the PWM output frequency;

a fourth starting unit: the PWM output frequency is obtained according to the current output voltage and output current feedback of the variable frequency power supply in a fourth time period, and the lower limit frequency of the PWM output frequency is adjusted;

and the adjusting unit is used for fixing the duty ratio of the PWM output after the soft start process is executed, obtaining the PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, adjusting the upper limit frequency and the lower limit frequency of the PWM output frequency to adjust the PWM output frequency, if the PWM output frequency is higher than the upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and if the PWM output frequency is lower than the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to the lower limit frequency of the PWM output frequency.

7. The apparatus of claim 6, wherein the first checking unit comprises:

the second checking unit is used for checking whether the variable frequency power supply has system faults or not;

the generating unit is used for generating a state word if the variable frequency power supply has a system fault, wherein the state word reflects the current state of the variable frequency power supply and comprises the system fault of the variable frequency power supply and the running state of the variable frequency power supply;

and the processing unit is used for processing the system fault according to the state word.

8. The apparatus of claim 7, wherein the soft start unit comprises:

a first starting unit, configured to adjust, in the first time period, a duty ratio of the PWM output from a second duty ratio to a first duty ratio, and adjust the PWM output frequency from F1 to F2, where the adjustment step size is a value obtained by dividing a difference between F1 and F2 by the first time period, the F1 is an initial value of the PWM output frequency, the F1 is smaller than a maximum switching frequency of a power switching device of the variable frequency power supply, and the F1 is greater than or equal to the F2;

a second starting unit, configured to fix the duty ratio of the PWM output as a first duty ratio in the second time period, adjust the PWM output frequency from F2 to F3 by a step size that is a value obtained by dividing a difference between F2 and F3 by the second time period, and stop adjusting the PWM output frequency if the output current is greater than a preset current threshold during adjustment of the PWM output frequency, where the PWM output frequency is F4, the F2 is greater than or equal to F4, and the F4 is greater than or equal to F3;

a third starting unit, configured to fix, in the third time period, a duty ratio of the PWM output as a first duty ratio, fix the PWM output frequency as a PWM output frequency at an end time of the second time period, and set initial values of an upper limit frequency and a lower limit frequency of the PWM output frequency as the current PWM output frequency;

and a fourth starting unit, configured to fix the duty ratio of the PWM output as the first duty ratio in the fourth time period, obtain the PWM output frequency according to the current output voltage and output current feedback of the variable frequency power supply, adjust a lower limit frequency of the PWM output frequency to a minimum lower limit F7 of the PWM output frequency, and complete soft start of the variable frequency power supply, where F7 is a resonant frequency of the variable frequency power supply.

9. The apparatus according to claim 8, wherein the fourth starting unit is specifically configured to:

in the fourth time period, fixing the duty ratio of the PWM output as a first duty ratio, obtaining the PWM output frequency according to the output voltage and the output current feedback of the current variable frequency power supply, adjusting the lower limit frequency of the PWM output frequency by taking a first step size Delta S1 as a step size, when the lower limit frequency of the PWM output frequency is adjusted to F7 from the initial value of the lower limit frequency of the PWM output frequency, completing the soft start of the variable frequency power supply, the F7 is less than the F3, if the PWM output frequency is less than the lower limit frequency of the PWM output frequency during the adjustment of the lower limit frequency of the PWM output frequency, the PWM output frequency is equal to a lower limit frequency of the PWM output frequency, and if the PWM output frequency is greater than an upper limit frequency of the PWM output frequency, the PWM output frequency is equal to the upper limit frequency of the PWM output frequency, and F7 is the resonant frequency of the variable frequency power supply.

10. The apparatus of claim 9, wherein the adjustment unit comprises:

the conversion unit is used for obtaining a target primary side current corresponding to the target output power according to the number of turns of the primary side of the variable frequency power supply, the number of turns of the secondary side of the variable frequency power supply, the output voltage of the secondary side and the preset target output power of the variable frequency power supply;

an execution unit, configured to execute a first process and a second process until a real-time primary current obtained by sampling a primary current of the variable frequency power supply is equal to the target primary current, wherein,

the first process comprises the following steps:

if the real-time primary side current is smaller than the target primary side current, reducing the lower limit frequency of the PWM output frequency by taking the delta S2 as a step length, comparing the lower limit frequency of the PWM output frequency with the F7, if the lower limit frequency of the PWM output frequency is larger than the F7, switching the variable frequency power supply to the process II, if the lower limit frequency of the PWM output frequency is smaller than or equal to the F7, the lower limit frequency of the PWM output frequency is equal to the F7, and reducing the upper limit frequency of the PWM output frequency by taking the delta S2 as a step length, at the moment, if the upper limit frequency of the PWM output frequency is smaller than or equal to the F7, checking whether the variable frequency power supply has a system fault, and if the upper limit frequency of the PWM output frequency is larger than the F7, switching the variable frequency power supply to the process II;

the second process comprises the following steps: