CN113659859A - Analog sine wave modulation method of off-grid inverter and storage medium - Google Patents

Abstract

The invention relates to the technical field of inverters, and provides an analog sine wave modulation method and a storage medium for off-grid inverters. Get the target radian, and then output the corresponding target sine carrier according to the target radian, control the inverter circuit to perform pulse width modulation, and convert the connected DC power into the corresponding sine wave AC. The algorithm is simple, the amount of calculation is small, and the operation efficiency is high. Therefore, The low-cost, high-efficiency inverter AC output can be achieved by using a processing chip with a smaller program space.

Description

An analog sine wave modulation method and storage medium of an off-grid inverter

technical field

The invention relates to the technical field of inverters, in particular to an analog sine wave modulation method and a storage medium of an off-grid inverter.

Background technique

The function of the inverter is a device that converts DC power (battery, storage battery) into AC power (usually 220v50HZ sine or square wave). In layman's terms, an inverter is a device that converts direct current (DC) into alternating current (AC). It consists of inverter bridge, control logic and filter circuit.

Classified according to the nature of the wave, inverters include sine wave inverters and square wave inverters. The output of a sine wave inverter is a sine wave alternating current. In the sine wave inverter system, it is necessary to convert the input DC power into AC power after sinusoidal modulation. The inverter in the prior art mainly adopts the table look-up method and Taylor series expansion to calculate the sine value, and then performs pulse width modulation according to the sine value, and the output is alternating current.

The advantages and disadvantages of the above two methods are as follows;

1. The advantage of the table lookup method is that the speed is fast, the amount of calculation is small, and it takes up a lot of program space;

2. Taylor series expansion, the advantage is that it takes up less space than the look-up table, and the disadvantage is that the amount of calculation is large, which requires the computing power of the chip.

At present, the price of chips on the market is generally too high, so it is limited to production costs. Customers cannot obtain chip costs with high computing power and large space, so they cannot improve the working efficiency of inverters.

SUMMARY OF THE INVENTION

The invention provides an analog sine wave modulation method and a storage medium for an off-grid inverter, which solves the problem that the existing inverter processing chip is too expensive, resulting in incompatibility between production cost and work efficiency (ie, computing power). question.

In order to solve the above technical problems, the present invention provides an analog sine wave modulation method for an off-grid inverter, comprising an MCU and an inverter circuit connected thereto, and an input end of the inverter circuit is connected to a DC power supply;

The MCU is configured to calculate a target radian according to a preset modulation algorithm, and then output a corresponding target sinusoidal carrier according to the target radian;

The inverter circuit is used to perform pulse width modulation according to the target sine carrier wave, and convert the connected DC power supply into a corresponding sine wave AC power;

The calculation formula of the preset modulation algorithm is as follows:

Among them, V _ac is the voltage value of the sine wave alternating current, V _dc is the voltage value of the DC power supply, and θ is the target radian of the inverter circuit.

Based on the compatibility needs of the existing inverter cost and computing power, this basic scheme designs a preset modulation algorithm to calculate the target radian, and then outputs the corresponding target sine carrier according to the target radian, and controls the inverter circuit to perform pulse width modulation. , convert the connected DC power into the corresponding sine wave AC. The algorithm is simple, the calculation amount is small, and the operation efficiency is high. Therefore, the low-cost and high-efficiency inverter AC output can be achieved by using a processing chip with a small program space.

In a further embodiment, the calculation of the target radian according to the preset modulation algorithm is specifically:

A. According to the carrier frequency and the inverter frequency of the inverter circuit, determine the total number of carriers in each inverter cycle;

B. Divide the target angle variable of each carrier according to the total number of carriers;

C. According to the target angle variable, determine the variation law of the radian value of the inverter circuit in each inverter cycle;

D. Calculate the target radian according to the change rule and the current time stage.

In further embodiments, the step C comprises:

C1. According to the total number of carriers, each inversion cycle is equally divided into a plurality of time stages;

C2. Calculate the first functional relationship formula between each of the time stages and the target angle variable;

C3. Substitute the first functional relationship formula into the sine formula, obtain the radian value of each time period in each cycle, and establish a second functional relationship formula.

This scheme starts with the periodic change of the radian value in the pulse width modulation, and calculates the radian value of the inverter in each time period of each cycle in reverse, shortening the calculation time, so that the sine wave alternating current can be output quickly.

In a further implementation, in the step C2, when each carrier corresponds to a time period, the first functional relationship formula is as follows:

Among them, X is a variable representing the current time period, and n is the total number of carriers.

This scheme sets each carrier to correspond to a time period, and performs radian distribution and radian value calculation, which can reduce the calculation difficulty of the radian value and improve the calculation efficiency.

In a further embodiment, in the step C2, the second functional relationship formula is as follows:

则，When the time period is the positive half of the inversion period, that is

but,

则，When the time period is the negative half of the inversion period, that is,

but,

Among them, X is a variable representing the current time period, X∈N, and n is the total number of carriers.

The present invention also provides a storage medium on which a computer program is stored, and the computer program is used to implement the above-mentioned method for simulating sine wave modulation of an off-grid inverter. The storage medium may be a magnetic disk, an optical disk, a read only memory (Read Only Memory, ROM), or a random access device (Random Access Memory, RAM), or the like.

Description of drawings

1 is a schematic diagram of the output of a sine wave alternating current in an analog sine wave modulation method for an off-grid inverter provided by an embodiment of the present invention;

Among them: MCU1, inverter circuit 2.

Detailed ways

The embodiments of the present invention will be explained in detail below in conjunction with the accompanying drawings. The examples are given only for the purpose of illustration and should not be construed as a limitation of the present invention. The accompanying drawings are only used for reference and description, and do not constitute a limitation on the protection scope of the patent of the present invention. limitation, since many changes may be made in the present invention without departing from the spirit and scope of the invention.

Example 1

An embodiment of the present invention provides an analog sine wave modulation method for an off-grid inverter, as shown in FIG. 1 , in this embodiment, it includes an MCU1 and an inverter circuit 2 connected thereto, and an input of the inverter circuit 2 is included. The terminal is connected to the DC power supply;

MCU1 is used to calculate the target radian according to the preset modulation algorithm, and then output the corresponding target sinusoidal carrier according to the target radian;

The inverter circuit 2 is used to perform pulse width modulation according to the target sine carrier wave, and convert the connected DC power supply into the corresponding sine wave AC power. The inverter circuit 2 in this embodiment is a conventional inverter bridge circuit, and thus will not be repeated in this embodiment of the present invention.

The calculation formula of the preset modulation algorithm is as follows:

Among them, V _ac is the voltage value of the sine wave alternating current, V _dc is the voltage value of the DC power supply, θ is the target radian of the inverter circuit 2, 0≤θ<2π.

In this embodiment, calculating the target radian according to the preset modulation algorithm is specifically:

A. According to the carrier frequency and the inverter frequency of the inverter circuit 2, determine the total number of carriers in each inverter cycle.

即每个载波，逆变器输出旋转

个弧度，n个载波刚好旋转一周(圈)。In this embodiment, let the inverter frequency be Fb (fundamental frequency) and the carrier frequency be Fc, then the number of carriers in the whole cycle can be defined

i.e. for each carrier, the inverter output rotates

radians, the n carriers make exactly one revolution (circle).

B. Divide the target angle variable of each carrier according to the total number of carriers;

C. Determine the variation law of the radian value of the inverter circuit 2 in each inverter cycle according to the target angle variable, including steps C1 to C2:

C1. According to the total number of carriers, each inverter cycle is equally divided into multiple time stages;

C2. Calculate the first functional relationship formula between each time stage and the target angle variable.

In this embodiment, when each carrier corresponds to a time period, the first functional relationship formula is as follows:

Among them, X is a variable representing the current time period, and n is the total number of carriers.

In this embodiment, each carrier is set to correspond to a time period, and radian distribution and radian value calculation are performed, which can reduce the calculation difficulty of the radian value and improve the calculation efficiency.

C3. Substitute the first functional relationship formula into the sine formula, obtain the radian value of each time period in each cycle, and establish the second functional relationship formula.

In this embodiment, the second functional relationship formula is as follows:

则，When the time period is the positive half cycle of the inverter cycle, that is

but,

则，When the time period is the negative half cycle of the inverter cycle, that is

but,

Among them, X is a variable representing the current time period, X∈N (N is an integer), and n is the total number of carriers.

This embodiment starts with the cycle change of the radian value in the pulse width modulation, and calculates the radian value of the inverter in each time period of each cycle in reverse, shortens the calculation time, and can quickly output the sine wave alternating current.

D. Calculate the target radian according to the change rule and the current time stage.

In this embodiment, the specific output process of the sine wave alternating current is as follows:

Taking the initial phase of the sine wave alternating current as 0 as an example, at this time the initial value of X is 0, MCU1 will directly calculate the target radian according to formula (3), and X+1 after each time period, and then output according to formula (1) Corresponding target sinusoidal carrier;

For example, when θ=0, then X=0, sin(θ)=0;

则

sin(θ)＝1；when

but

sin(θ)=1;

则

sin(θ)＝-1。when

but

sin(θ)=-1.

The inverter circuit 2 is used to perform pulse width modulation according to the target sine carrier wave, and convert the connected DC power supply into the corresponding sine wave AC power.

When the inverter cycle enters the negative half cycle, MCU1 will directly calculate the target radian according to formula (4). Similarly, X+1 will be generated every time period passes, and then the corresponding target sinusoidal carrier will be output according to formula (1).

The embodiment of the present invention designs a preset modulation algorithm to calculate the target radian based on the compatibility requirements of the existing inverter cost and computing capability, and then outputs the corresponding target sine carrier according to the target radian, and controls the inverter circuit 2 to perform pulse width modulation , convert the connected DC power into the corresponding sine wave AC. The algorithm is simple, the calculation amount is small, and the operation efficiency is high. Therefore, the low-cost and high-efficiency inverter AC output can be achieved by using a processing chip with a small program space.

Example 2

An embodiment of the present invention further provides a storage medium on which a computer program is stored, where the computer program is used to implement the analog sine wave modulation method for an off-grid inverter provided in the above-mentioned Embodiment 1. The storage medium may be a magnetic disk, an optical disk, a read only memory (Read Only Memory, ROM), or a random access device (Random Access Memory, RAM) or the like.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (6)

1. A simulation sine wave modulation method of an off-grid inverter is characterized by comprising the following steps: the inverter comprises an MCU and an inverter circuit connected with the MCU, wherein the input end of the inverter circuit is connected with a direct-current power supply;

the MCU is used for calculating a target radian according to a preset modulation algorithm and further outputting a corresponding target sinusoidal carrier according to the target radian;

the inverter circuit is used for carrying out pulse width modulation according to the target sine carrier and converting an accessed direct-current power supply into corresponding sine-wave alternating current;

the preset modulation algorithm has the following calculation formula:

wherein, V_acIs the voltage value of sine-wave alternating current, V_dcAnd theta is the voltage value of the direct-current power supply, and theta is the target radian of the inverter circuit.

2. The method according to claim 1, wherein the calculating the target radian according to the preset modulation algorithm specifically comprises:

A. determining the total number of carriers in each inversion period according to the carrier frequency and the inversion frequency of the inversion circuit;

B. dividing a target angle variable of each carrier according to the total number of the carriers;

C. determining the change rule of the radian value of the inverter circuit in each inversion period according to the target angle variable;

D. and calculating the target radian according to the change rule and the current time stage.

3. The method as claimed in claim 2, wherein the step C comprises:

c1, equally dividing each inversion period into a plurality of time stages according to the total number of the carriers;

c2, calculating a first functional relation formula of each time phase and the target angle variable;

and C3, substituting the first functional relation formula into a sine formula to obtain an arc value of each time stage in each period, and establishing a second functional relation formula.

4. The method as claimed in claim 3, wherein in the step C2, when each carrier wave corresponds to a time period, the first functional relationship formula is as follows:

wherein, X is a variable representing the current time phase, and n is the total number of carriers.

5. The method as claimed in claim 4, wherein in step C2, the second functional relationship formula is as follows:

when the time period is the positive half of the inversion cycle, i.e.

Then the process of the first step is carried out,

when the time period is the negative half of the inversion cycle, i.e.

Then the process of the first step is carried out,

wherein, X is a variable representing the current time phase, X belongs to N, and N is the total number of carriers.

6. A storage medium having a computer program stored thereon, characterized in that: the computer program is for implementing an off-grid inverter analog sine wave modulation method as claimed in claims 1-5.

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