CN111786550A

CN111786550A - Method for realizing soft start of bidirectional converter

Info

Publication number: CN111786550A
Application number: CN202010745794.XA
Authority: CN
Inventors: 李珣; 李健; 黄勇; 黄诚; 刘思佳; 代高强
Original assignee: Sichuan Changhong Electric Co Ltd
Current assignee: Sichuan Changhong Electric Co Ltd
Priority date: 2020-07-29
Filing date: 2020-07-29
Publication date: 2020-10-16
Anticipated expiration: 2040-07-29
Also published as: CN111786550B

Abstract

The invention discloses a method for realizing soft start of a bidirectional converter, which comprises the following steps: A. initializing a control module and parameters related to soft start; B. judging the working state of the current system, and when the battery pack index meets the charging condition, if the power grid state is normal, entering the step C, and if the power grid end is disconnected, entering the step D; C. the system works in a reverse charging mode, starts soft start in the reverse charging mode, and finishes a first control process by an interrupt program; D. the system works in a forward discharge mode, starts soft start in the forward discharge mode, and finishes a second control process by an interrupt program; E. the system finishes the soft start process and stably enters the working stage under the control of a fixed reference value PI. Compared with a single duty ratio adjusting mode, the method is safer and more reliable, the output voltage increasing rate and the starting time can be flexibly adjusted, an additional hardware circuit is not needed, important devices can be effectively protected, and the system reliability is improved.

Description

Method for realizing soft start of bidirectional converter

Technical Field

The invention relates to the technical field of new energy and power electronics, in particular to a method for realizing soft start of a bidirectional converter.

Background

When the bidirectional converter is powered on and started, strong impact current can be generated due to large pressure difference among the internal bus capacitor, the voltage of the energy storage battery pack and the input voltage of a power grid, the power device of the equipment is easily damaged, and the service life of the equipment is shortened.

In order to reduce the damage caused by excessive di/dt in the starting process, a hardware circuit composed of a power resistor, a contactor, a fuse and the like is generally added to limit and discharge the impact current. But adding soft start devices increases hardware cost and may extend the start-up time too much. In recent years, there is a software mode for gradually increasing the driving pulse width from 0 by controlling an inverter output tube, but the soft start process is a mode which is separated from PI control and saturation amplitude limiting protection, and it cannot be guaranteed that the last stage driving pulse width in the start stage is just suitable for the pulse width required by the PI control stage in normal operation, and once the last stage driving pulse width is not suitable for the PI control stage in normal operation, the first PI output over-excitation reaction in the normal operation stage is still difficult to avoid.

Disclosure of Invention

The invention aims to overcome the defects in the background art, provides a method for realizing the soft start of a bidirectional converter, and particularly provides a method for realizing the soft start of the bidirectional converter through software control, which is safer and more reliable than a single duty ratio regulation mode, can flexibly regulate the incremental rate of output voltage and the start duration, does not need to increase an additional hardware circuit, can effectively protect important devices, and improves the reliability of a system.

In order to achieve the technical effects, the invention adopts the following technical scheme:

a method for realizing soft start of a bidirectional converter comprises the following steps:

A. initializing a control module and parameters related to soft start;

B. judging the working state of the current system, and when the battery pack index meets the charging condition, if the power grid state is normal, entering the step C, and if the power grid end is disconnected, entering the step D;

C. the system works in a reverse charging mode, starts soft start in the reverse charging mode, and finishes a first control process by an interrupt program;

D. the system works in a forward discharge mode, starts soft start in the forward discharge mode, and finishes a second control process by an interrupt program;

E. the system finishes the soft start process and stably enters the working stage under the control of a fixed reference value PI.

Further, in the step B, the working state of the current system is specifically determined according to the receiving instruction and the sampling data of the system human-computer interaction unit.

Further, the control modules and parameters initialized in the step a include Boost control module, Buck control module, observer control module, and Rectifier module parameters.

Further, the control module and parameters initialized in the step a include a proportional integral coefficient, a reference value and a feedback value of a Boost control voltage loop PI _ Vb _ Boost and a current loop PI _ Iin; a soft start step value Vb _ boost _ Ref _ ss _ step of PI _ Vb _ boost;

the proportional-integral coefficient, the reference value and the feedback value of the Inverter control voltage loop PI _ vacrms (the effective voltage value is adopted for control) and the current loop PI _ iac; the soft start step value of PI _ vacrms _ Ref _ ss _ step;

proportional integral parameters, reference values and feedback values of the Buck control voltage loop PI _ Vbatt _ Buck and the current loop PI _ Ichar _ Buck; soft start step value Ichar _ Ref _ ss _ step of PI _ Ichar _ buck;

the Rectifier controls a proportional integral parameter, a reference value and a feedback value of the voltage loop PI _ Vb _ buck and the current loop PI _ iac; the soft start step value of PI _ Vb _ buck is Vb _ buck _ Ref _ ss _ step.

Further, the first control process includes:

s1.1, gradually increasing the reference value Vb _ BUCK _ Ref of the PI _ Vb _ BUCK from 0, and gradually increasing Vb _ BUCK _ Ref _ ss _ step each time until Vb _ BUCK _ Ref reaches a per unit value VB _ BUCK _ REF corresponding to the target voltage of the bus voltage;

s1.2, sending a grid current iac, a grid voltage vac and a bus voltage Vb sampling value into a phase-locked loop module, a PI _ Vb _ buck and a PI _ iac, and generating a drive wave output of a power switching tube of a charging control rectification circuit after double-loop proportional integral calculation and saturation amplitude limiting;

s1.3, gradually increasing the reference value Ichar _ BUCK _ Ref of the PI _ Ichar _ BUCK from 0, and increasing Ichar _ Ref _ ss _ step each time until the Ichar _ BUCK _ Ref reaches a per unit value ICHAR _ BUCK _ REF corresponding to the target voltage of the battery pack voltage;

s1.4, sending the voltage Vbatt of the battery pack, the charging current Ichar and the sampled value of the voltage Vb of the bus into PI _ Vbatt _ Buck and PI _ Ichar, and generating the driving wave output of the power switching tube of the Buck circuit after double-loop proportional integral calculation and saturation amplitude limiting.

Further, the second control process includes:

s2.1, gradually increasing the reference value Vb _ BOOST _ Ref of the PI _ Vb _ BOOST from 0, and gradually increasing the Vb _ BOOST _ Ref _ ss _ step each time until the Vb _ BOOST _ Ref reaches a per unit value VB _ BOOST _ REF corresponding to the target voltage of the bus voltage;

s2.2, sending the battery pack discharge current Iin and the bus voltage Vb sampling value into PI _ Vb _ Boost and PI _ Iin, and generating Boost switching tube driving wave output of a Boost circuit after double-ring proportional integral calculation and saturation amplitude limiting;

s2.3, gradually increasing the reference value of PI _ varms _ Ref from 0, and gradually increasing the reference value of PI _ varms _ Ref from 0 to increment by each time until the reference value of the PI _ varms _ Ref is not less than the per unit value of the target effective value of the output alternating voltage VACRMS _ REF;

s2.4, the output alternating voltage vac and the output current iac sampling values are sent to PI _ vacrms and PI _ iac, and after double-loop proportional integral calculation and saturation amplitude limiting, power switch tube driving wave output of the inverter circuit is generated.

Compared with the prior art, the invention has the following beneficial effects:

the invention discloses a soft start realization method of a bidirectional converter, which is characterized in that in the starting process, flexible step length control is carried out on reference values of a Boost (Boost) control module and an inversion (Inverter) control module in a discharging stage and a rectification (Rectifier) control module and a Buck (Buck) control module in a charging stage, and stable step-up output under PI control and saturation amplitude limiting protection is realized in a timing interruption mode. No matter in a discharging or charging mode, no matter in a starting or normal working stage, the system can be ensured to be under PI and saturation amplitude limiting control, so that the optimal starting effect of being safer and more flexible and smoother in stage switching is achieved. Compared with the single duty ratio adjusting mode in the prior art, the technical scheme of the application is safer and more reliable, the output voltage increasing rate and the starting time can be flexibly adjusted, and an additional hardware circuit is not needed to be added, so that important devices are effectively protected, and the system reliability is improved.

Drawings

FIG. 1 is a system block diagram of one embodiment of the present invention.

Fig. 2 is a control flow diagram of an embodiment of the present invention.

Detailed Description

The invention will be further elucidated and described with reference to the embodiments of the invention described hereinafter.

Example (b):

the first embodiment is as follows:

the invention provides a software implementation method for soft start of a bidirectional converter, which comprises the steps of flexibly controlling a voltage boosting module and an inversion module in a discharging mode and a rectification module and a voltage reduction module in a charging mode in a starting process, realizing stable incremental output under PI control and saturation amplitude limiting protection in a timing interruption mode, obtaining the optimal starting effect and ensuring that the starting current can be controlled within a safe value range. The process flow of the present invention will be specifically described in one embodiment below:

as shown in fig. 1, which is a system block diagram of an application embodiment of the present invention, for a certain single-phase energy storage bidirectional converter, in this embodiment, a reference value of a battery pack terminal voltage of an energy storage unit is set to 192V, a reference value of a rated dc side bus voltage Vbus is set to 370V, a control cycle of a Boost/Buck and Inverter/Rectifier circuit is 50us, a reference value of an ac side voltage effective value, namely, vacrms is set to 220V, a reference value of a constant current charging current is set to 5A, and a main control chip adopts a certain brand 32-bit microcontroller.

Specifically, as shown in fig. 2, the method for implementing soft start of the bidirectional converter in this embodiment includes the following specific operation steps:

step 1, initializing a control module and parameters related to soft start.

The method specifically comprises initializing parameters of a Boost control module, a Buck control module, an Inverter control module and a Rectifier module related to soft start, wherein the initialized control module and the parameters comprise proportional integral coefficients, reference values and feedback values of a Boost control voltage loop PI _ Vb _ Boost and a current loop PI _ Iin; a soft start step value Vb _ boost _ Ref _ ss _ step of PI _ Vb _ boost; the proportional-integral coefficient, the reference value and the feedback value of the Inverter control voltage loop PI _ vacrms (the effective voltage value is adopted for control) and the current loop PI _ iac; the soft start step value of PI _ vacrms _ Ref _ ss _ step; proportional integral parameters, reference values and feedback values of the Buck control voltage loop PI _ Vbatt _ Buck and the current loop PI _ Ichar _ Buck; soft start step value Ichar _ Ref _ ss _ step of PI _ Ichar _ buck; the Rectifier controls a proportional integral parameter, a reference value and a feedback value of the voltage loop PI _ Vb _ buck and the current loop PI _ iac; the soft start step value of PI _ Vb _ buck is Vb _ buck _ Ref _ ss _ step.

Specifically, in this embodiment, the reference value of the rated dc-side bus voltage Vbus of PI _ Vb _ boost is set to 370V, and Vb _ boost _ Ref _ ss _ step is set to 0.000008; the reference value of the effective voltage value vacrms of the Inverter control voltage ring PI _ vacrms is set to be 220V, and vacrms _ Ref _ ss _ step is set to be 0.000004; the reference value of the Buck control voltage loop PI _ Ichar _ Buck is set to be 5A, and Ichar _ Ref _ ss _ step is set to be 0.00001; the reference value of the Rectifier control voltage loop PI _ Vb _ buck is set to 370V and Vb _ buck _ Ref _ ss _ step is set to 0.000005.

Step 2, judging the working state of the current system according to the receiving instruction and the sampling data of the human-computer interaction unit of the system, and entering step 3 if the power grid state is normal and the battery pack index meets the charging condition; and if the power grid end is disconnected and the indexes of the battery pack meet the discharging condition, entering the step 4.

And 3, starting soft start of the system in a reverse charging state, and finishing the following control process by an interrupt program:

s1, gradually increasing the reference value Vb _ BUCK _ Ref of the PI _ Vb _ BUCK from 0, and increasing Vb _ BUCK _ Ref _ ss _ step each time until Vb _ BUCK _ Ref reaches a per unit value VB _ BUCK _ REF corresponding to the target voltage of the bus voltage, namely, 0.000005 each time in the embodiment, until Vb _ BUCK _ Ref is larger than or equal to a per unit value 0.5111 corresponding to the target value 370V of the direct-current bus voltage.

And S2, sending the power grid current iac, the power grid voltage vac and the bus voltage Vb sampling value into a phase-locked loop module, a PI _ Vb _ buck and a PI _ iac, and generating the drive wave output of the power switching tube of the rectifier circuit for charge control after double-loop proportional integral calculation and saturation amplitude limiting.

And S3, gradually increasing the reference value Ichar _ BUCK _ Ref of the PI _ Ichar _ BUCK from 0, and increasing Ichar _ Ref _ ss _ step each time until Ichar _ BUCK _ Ref reaches the per unit value ICHAR _ BUCK _ REF corresponding to the target voltage of the battery pack voltage, namely, 0.00001 each time in the embodiment until the value Ichar _ BUCK _ Ref is greater than or equal to the per unit value 0.2652 corresponding to the target current value 5A of the constant-current charging current.

And S4, sending the voltage Vbatt of the battery pack, the charging current Ichar and the sampled value of the voltage Vb of the bus into PI _ Vbatt _ Buck and PI _ Ichar, and generating the driving wave output of the power switching tube of the Buck circuit after double-loop proportional integral calculation and saturation amplitude limiting.

And completing the soft start process of the charging mode after the system is electrified for about 7 seconds, and then starting to carry out the normal working process of charging the energy storage unit from the power supply of the power grid under the control of the direct-current side double loop and the alternating-current side double loop.

And 4, when the system receives a discharge instruction to the load after being electrified, completing soft start according to the following steps:

s1, gradually increasing the reference value Vb _ BOOST _ Ref of the PI _ Vb _ BOOST from 0, and gradually increasing the Vb _ BOOST _ Ref _ ss _ step each time until the Vb _ BOOST _ Ref reaches the per unit value VB _ BOOST _ REF corresponding to the target voltage of the bus voltage. In this embodiment, the bus voltage is incremented by 0.000008 each time until Vb _ boost _ Ref reaches the per unit value 0.5111 corresponding to the target voltage 370V of the bus voltage.

And S2, sending the discharge current Iin of the battery pack and the sampled value of the bus voltage Vb into PI _ Vb _ Boost and PI _ Iin, and generating Boost switching tube driving wave output of the Boost circuit after double-loop proportional integral calculation and saturation amplitude limiting.

3) And gradually increasing the reference value VACRMS _ Ref of the PI _ VACRMS from 0, and increasing the reference value VACRMS _ Ref _ ss _ step each time until the reference value VACRMS _ Ref is not less than the corresponding per unit value VACRMS _ REF of the target effective value of the output alternating voltage. In this embodiment, the voltage is incremented by 0.000004 each time until vacrms _ Ref reaches the per unit value 0.5625 corresponding to the target effective value 220V of the output ac voltage.

And S3, sending sampling values of the output alternating voltage vac and the output current iac into PI _ vacrms and PI _ iac, and generating power switch tube driving wave output of the inverter circuit after double-loop proportional integral calculation and saturation amplitude limiting.

And after the soft starting process of the discharging mode is finished for about 8s, the system stably enters a normal working stage with fixed reference value PI control.

It was found that by the above soft-start processing, the dc side boost IGBT current spike was reduced from 18A to 2.5A, and the ac inverter bridge IGBT current spike was reduced from 2A to 0.5A. The whole starting process is more stable, safer and more reliable, and the impact on important devices is greatly reduced.

It will be understood that the above embodiments are merely exemplary embodiments taken to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.

Claims

1. A method for realizing soft start of a bidirectional converter is characterized by comprising the following steps:

A. initializing a control module and parameters related to soft start;

2. The method for realizing soft start of the bidirectional converter according to claim 1, wherein in step B, the current system operating state is determined according to a received command and sampled data of a system human-computer interaction unit.

3. The method for realizing soft start of the bidirectional converter according to claim 1 or 2, wherein the control modules and parameters initialized in the step a include parameters of a Boost control module, a Buck control module, an Inverter control module and a Rectifier module.

4. The method for realizing the soft start of the bidirectional converter according to claim 3, wherein the control module and the parameters initialized in the step A comprise a proportional integral coefficient, a reference value and a feedback value of a Boost control voltage loop PI _ Vb _ Boost and a current loop PI _ Iin; a soft start step value Vb _ boost _ Ref _ ss _ step of PI _ Vb _ boost;

proportional integral coefficients, reference values and feedback values of the voltage loop PI _ vacrms and the current loop PI _ iac are controlled by the Inverter; the soft start step value of PI _ vacrms _ Ref _ ss _ step;

5. The method of claim 4, wherein the first control procedure comprises:

6. The method of claim 4, wherein the second control procedure comprises: