CN115882442A

CN115882442A - Power parallel system and direct current bus voltage control method thereof

Info

Publication number: CN115882442A
Application number: CN202310135203.0A
Authority: CN
Inventors: 王成悦; 江才; 汪习成
Original assignee: Sunshine Hydrogen Energy Technology Co Ltd
Current assignee: Sunshine Hydrogen Energy Technology Co Ltd
Priority date: 2023-02-09
Filing date: 2023-02-09
Publication date: 2023-03-31

Abstract

The application provides a power supply parallel system and a direct current bus voltage control method thereof, wherein the method comprises the steps of judging whether the direct current bus voltage of the power supply parallel system is in a first preset range through a host in each power supply; if the direct current bus voltage is outside the first preset range, the host controls the direct current bus voltage outer ring of the host to be switched into an I control mode from a PI control mode, so that the active current given value can be changed rapidly, the direct current bus voltage is controlled, the dynamic response performance of the power parallel system is improved, the switching tube drive of the AC/DC converter can be closed when the direct current bus voltage is too high, and the influence on the operation reliability of the power parallel system and the performance and the service life of a load due to the mismatching of input and output energy is avoided. In addition, when the host fails, the slave can be timely informed to be switched to the host, fault-tolerant control and uninterrupted power supply to a load are realized, and the operation reliability of the system is effectively improved.

Description

Power parallel system and direct current bus voltage control method thereof

Technical Field

The application relates to the technical field of power electronics, in particular to a power supply parallel system and a direct current bus voltage control method thereof.

Background

At present, for a scene with large required power, loads such as an electrolytic cell of a hydrogen production system, a battery of a power station energy storage system, or a power battery of an electric vehicle and the like are generally realized in a multi-machine parallel connection mode.

Taking a PWM (pulse width modulation) hydrogen production power supply parallel system as an example, most of hydrogen production power supplies inside the system adopt a two-stage circuit topology structure of rectification (AC/DC) and direct current voltage reduction (DC/DC), when the system operates in parallel, all hydrogen production power supplies share the same source, an output end is connected to the same electrolytic cell, in order to suppress parallel high-frequency circulating current, carrier synchronization is performed between units of the power supply parallel system, and a positive pole and a negative pole of a direct current bus are also connected together, so in the prior art, master-slave current sharing control based on PI (proportional integral) is generally adopted, that is, one hydrogen production power supply serves as a master and operates in a voltage mode, and the rest N-1 hydrogen production power supplies serve as slaves and operate in a current mode.

However, the control loop bandwidth in the control scheme cannot be increased without limit, so that the dynamic performance of the corresponding power supply parallel system is poor, input power and output power are not matched easily when the power of a source end or a load end changes rapidly, and the phenomenon of sudden rise or sudden fall of the voltage of a direct-current bus occurs, so that the operation reliability of the power supply parallel system, the performance of the load and the service life of the load are influenced; therefore, how to control the voltage stabilization of the dc bus in the power parallel system is an urgent problem to be solved.

Disclosure of Invention

In view of this, the present application provides a power parallel system and a dc bus voltage control method thereof, so as to control a dc bus voltage and improve a dynamic response performance of the power parallel system.

In order to achieve the above purpose, the present application provides the following technical solutions:

the first aspect of the application provides a direct current bus voltage control method of a power parallel system, wherein the power parallel system comprises a power supply with at least two direct current buses connected in parallel; the direct current bus voltage control method comprises the following steps:

the host in each power supply judges whether the voltage of the direct current bus of the power supply parallel system is in a first preset range;

and if the direct current bus voltage is out of the first preset range, the host controls the direct current bus voltage outer ring of the host to be switched from a PI control mode to an I control mode.

Optionally, the host controls the dc bus voltage outer ring to be switched from the PI control mode to the I control mode, including:

if the direct current bus voltage is smaller than the lower limit value of the first preset range, the host controls the given value of the active current to be increased on the basis of the output quantity of the controller of the direct current bus voltage outer ring;

and if the direct current bus voltage is larger than the upper limit value of the first preset range, the host controls the given value of the active current to be decreased progressively on the basis of the controller output quantity of the direct current bus voltage outer ring.

Optionally, the step length of the host controlling the increase or decrease of the given value of the active current is as follows: the product of the rated current of the input side of the power supply parallel system and a preset proportion;

the preset proportion is as follows: the ratio of the control period of the power supply parallel system to the response time of the input side current of the power supply parallel system from zero to the rated current.

Optionally, before the host in each of the power supplies determines whether the dc bus voltage of the power supply parallel system is within a first preset range, the method further includes:

the host machine judges whether the voltage of the direct current bus is in a second preset range or not; the first preset range belongs to the second preset range;

if the direct current bus voltage is within the second preset range, the host executes a step of judging whether the direct current bus voltage of the power supply parallel system is within a first preset range;

and if the voltage of the direct current bus is out of the second preset range, switching the voltage mode of the host machine into a switching tube drive prohibition mode, and enabling the rectifying circuit of the host machine to operate in an uncontrolled rectifying state.

Optionally, after the host is switched from the voltage mode to the switching tube driving prohibition mode, the method further includes:

the host machine judges whether the voltage of the direct current bus is smaller than the lower limit value of a third preset range; the third preset range belongs to the first preset range;

and if the direct-current bus voltage is smaller than the lower limit value of the third preset range, the host is switched to the voltage mode from the switching tube drive prohibition mode.

Optionally, the switching tube driving prohibition mode of the host is switched to the voltage mode, and the switching tube driving prohibition mode includes:

the host assigns the current active current instantaneous feedback value to the integral output of the direct current bus voltage outer loop controller;

the host clears the integral output of the active current inner loop controller of the host;

and the host machine controls the given value of the outer ring of the direct current bus voltage to be changed from the current value of the direct current bus voltage to the rated voltage of the direct current bus in a gradient manner.

Optionally, after determining whether the dc bus voltage of the power parallel system is within a first preset range, the method further includes:

if the direct current bus voltage is within the first preset range, the host judges whether the direct current bus voltage is within a third preset range; the third preset range belongs to the first preset range;

if the direct current bus voltage is within the third preset range, the host determines the current control mode of the direct current bus voltage outer ring;

if the current control mode of the outer ring of the direct-current bus voltage is a PI control mode, the host maintains the current control mode;

and if the current control mode of the direct current bus voltage outer ring is an I control mode, the host controls the direct current bus voltage outer ring to be switched into a PI control mode.

Optionally, the host controls the dc bus voltage outer loop to switch to a PI control mode, including:

the host assigns the current active current given value to the integral output of the direct current bus voltage outer loop controller;

Optionally, the method further includes:

and the host issues the given active value to each slave in each power supply through communication.

the master machine controls the slave machines in the power supplies through communication, and switches from a current mode to a switching tube drive prohibition mode.

Optionally, if the dc bus voltage is smaller than the lower limit of the third preset range, the method further includes:

the master machine controls the slave machines in the power supplies and switches from the switching tube drive prohibition mode to the current mode.

Optionally, the master controls a slave in each of the power supplies, and switches from the switching tube drive prohibition mode to the current mode, including:

the master sends switch tube drive prohibition marks to the slaves through communication;

each slave machine clears the integral output of the active current inner loop controller of the slave machine according to the switch tube drive prohibition mark;

and each slave machine operates in the current mode according to the active given value issued by the host machine.

Optionally, before the host determines the dc bus voltage, the method further includes:

each power supply completes the setting of a master machine and a slave machine; the master operates in voltage mode and the slaves operate in current mode.

Optionally, at any time after the power supplies complete the setting of the master and the slave, the method further includes:

when the main machine has a fault, any slave machine is controlled to be switched into the main machine through communication, so that the main machine is switched from a current mode to a voltage mode.

Optionally, the process of switching from the current mode to the voltage mode includes:

assigning the current active current instantaneous feedback value to the integral output of the direct current bus voltage outer loop controller;

and controlling a given value of an outer ring of the self direct current bus voltage to be changed from the current value of the direct current bus voltage to the rated voltage of the direct current bus in a gradient manner.

and the host machine determines the upper limit value and the lower limit value of each preset range.

A second aspect of the present application provides a power parallel system, comprising at least two power sources connected in parallel with a dc bus, each of the power sources being communicatively connected for performing the dc bus voltage control method of the power parallel system according to any one of the first aspect.

Optionally, the input side of each power supply is connected in parallel to the input side of the power supply parallel system through a corresponding input switch;

and the output side of each power supply is connected in parallel to the output side of the power supply parallel system through a corresponding direct current load switch.

Optionally, the power supply includes: an AC/DC converter;

the alternating current side of the AC/DC converter is connected with the input side of the power supply;

and the direct current side of the AC/DC converter is connected with the direct current bus and the output side of the power supply.

Optionally, the power supply further includes: a DC/DC converter;

the DC/DC converter is provided between the DC bus and an output side of the power supply.

Optionally, the input side of the power parallel system is connected to a renewable energy power generation system or a power grid, and the output side of the power parallel system is connected to an electrolytic cell or a rechargeable battery.

According to the direct current bus voltage control method of the power parallel system, whether the direct current bus voltage of the power parallel system is within a first preset range or not is judged through a host in each power supply; if the direct current bus voltage is outside the first preset range, the host controls the direct current bus voltage outer ring of the host to be switched to an I control mode from a PI control mode, so that the active current given value can be changed rapidly, the direct current bus voltage is controlled, the dynamic response performance of the power parallel system is improved, and the influence on the operation reliability of the power parallel system, the performance of a load and the service life of the load due to the mismatching of input and output energy is avoided.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

Fig. 1 is a control block diagram of a master-slave three-phase PWM rectifier parallel system according to an embodiment of the present disclosure;

fig. 2 is a schematic structural diagram of a power parallel system according to an embodiment of the present disclosure;

fig. 3 is a flowchart of a dc bus voltage control method of a power parallel system according to an embodiment of the present disclosure;

fig. 4 is another flowchart of a dc bus voltage control method of a power parallel system according to an embodiment of the present disclosure;

fig. 5 is another flowchart of a dc bus voltage control method of a power parallel system according to an embodiment of the present disclosure;

fig. 6 is another flowchart of a dc bus voltage control method of a power parallel system according to an embodiment of the present disclosure;

fig. 7 is another flowchart of a dc bus voltage control method of a power parallel system according to an embodiment of the present disclosure;

fig. 8 is another flowchart of a dc bus voltage control method of a power parallel system according to an embodiment of the present disclosure.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In this application, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising a … …" does not exclude the presence of another identical element in a process, method, article, or apparatus that comprises the element.

FIG. 1 is a control block diagram of a master-slave three-phase PWM rectifier (AC/DC) parallel system with a host (the upper one shown in FIG. 1) operating in voltage mode, in which the grid-connected active power is controlled by a double closed loop of a DC bus voltage outer loop and an active current inner loop to give a DC bus voltage U _{dc_ref} Instantaneous feedback value U of DC bus voltage _dc Comparing, passing the generated error signal through DC bus voltage outer loop controller G _v Is output as a set value I of the d-axis current (i.e. the active current) _{d_ref1} ，I _{d_ref1} D-axis component instantaneous feedback value I of three-phase inductive current _d1 Making a difference, controlled by an active current inner loopDevice G _{i_d} Modulating and outputting active power modulation signal U _{_d1} (ii) a The grid-connected reactive power can be controlled by adopting a single closed loop of a reactive current inner loop, and a given value I of q-axis current (namely reactive current) can be obtained from a set reactive power value _{q_ref1} ，I _{q_ref1} Q-axis component instantaneous feedback value I of three-phase inductive current _q1 Making difference, passing through reactive current inner loop controller G _{i_q} Modulating and outputting reactive power modulating signal U _{_q1} . Active and reactive power modulation signal U _{_d1} 、U _{_q1} Respectively with the feed-forward component U of the network voltage _{g_d} 、U _{g_q} And (4) superposing to obtain a total modulation signal of a system control link. Host DC bus voltage outer ring controller G _v Active and reactive current inner loop controller G _{i_d} 、G _{i_q} A PI regulator is used. The other slave machines (the lower one shown in fig. 1, and only one is shown in the figure as an example) work in a current mode, and after the master machine is started, the slave machines obtain d-axis and q-axis current given values I according to received master machine active and reactive current information _{d_ref2} 、I _{q_ref2} Given value of current I _{d_ref2} 、I _{q_ref2} Instantaneous feedback values I of d-axis and q-axis components of three-phase inductive currents of slave _d2 、I _q2 Making difference, passing through active and reactive current inner loop controller G _{i_d} 、G _{i_q} Modulating, outputting active and reactive power modulating signal U _{_d2} 、U _{_q2} Respectively with the grid voltage feedforward component U _{g_d} 、U _{g_q} And (4) superposing to obtain a total modulation signal of a system control link. Active and reactive current inner loop controller G of slave machine _{i_d} 、G _{i_q} A proportional-integral PI regulator is used. Other links shown in fig. 1 are the same as those in the prior art, and are not described in detail here.

At present, research contents of a plurality of domestic and foreign documents focus on parallel steady-state current sharing control and circulation suppression, but most of the research contents do not relate to the problem of dynamic response of multi-machine parallel operation. The dynamic response time of the system is limited by the loop bandwidth of the controller, and the input and output energy mismatch can cause sudden rise or sudden fall of the direct current bus voltage, wherein the sudden rise of the direct current bus voltage can threaten the service life of a power switching tube device in the converter; the sudden drop of the dc bus voltage may cause a large drop of the load voltage, which not only seriously affects the life and performance of the load, but also may cause the power parallel system to be in a runaway state. The PI regulator adopted by the PWM rectification power supply control system belongs to phase lag correction regulation, can improve the steady-state precision of a system and improve the stability of the system, but the PI regulator trades the stability of the system by sacrificing rapidity, and can improve the bandwidth of a system loop by setting the control parameters of the PI regulator in engineering, particularly increasing a proportionality coefficient, but the bandwidth of the loop is limited by switching frequency (can not exceed half of the switching frequency), while the phase margin is limited by loop control and sampling delay, so that the bandwidth of the control system loop can not be improved unlimitedly, the rapid response capability of the PWM power supply controller to the output load power is limited by bottleneck, and particularly when the output load is switched between no-load and rated power, the larger fluctuation of direct-current bus voltage and output voltage is difficult to be effectively inhibited through conventional PI regulation.

Therefore, the application provides a direct current bus voltage control method of a power parallel system, so as to control the direct current bus voltage and improve the dynamic response performance of the power parallel system.

The power supply parallel system is a master-slave type PWM power supply parallel system, and comprises a plurality of power supplies as shown in figure 2; the input side of each power supply is connected to the input side of the power supply parallel system through corresponding input switches, and further connected with the same input source, such as renewable energy or a power grid; the positive pole and the negative pole of the direct current bus of each power supply are respectively connected in parallel; the output side of each power supply is connected in parallel with the output side of the power supply parallel system through a corresponding direct current load switch respectively, and then connected with the same load, such as an electrolytic cell or a rechargeable battery; each power supply is communicatively interconnected via a bus, such as a CAN bus (described below as an example) or a Modbus, and may be specifically interconnected via a respective communication port (e.g., a CAN communication interface shown in fig. 2). Each power supply may include a corresponding AC/DC converter (such as AC/DC PWM rectification shown in fig. 2) and a DC/DC converter (such as DC/DC buck shown in fig. 2), or may only have a corresponding AC/DC converter, depending on the specific application environment.

Referring to fig. 3, the method for controlling the dc bus voltage of the power parallel system includes:

s101, the host in each power supply judges whether the direct-current bus voltage of the power supply parallel system is in a first preset range.

The upper and lower limits of the first preset range may be determined by the host computer before executing S101; furthermore, the host may set multiple thresholds for the comparison of the dc bus voltage simultaneously, such as: a first high pressure threshold, a second high pressure threshold, a third high pressure threshold, a first low pressure threshold, and a second low pressure threshold; wherein the third high pressure threshold value>Second high voltage threshold>First high voltage threshold>First low voltage threshold>A second low pressure threshold; in practical application, the host can be based on the rated voltage U of the DC bus _{dc_ed} To determine the above thresholds, for example, a first high voltage threshold of 1.025 u may be set _{dc_ed} The second high pressure threshold is 1.05 × U _{dc_ed} The third high voltage threshold is 1.1 × U _{dc_ed} (ii) a The second low-voltage threshold value can be comprehensively set according to the input voltage peak value and the output rated voltage of the DC/DC converter, and the maximum value of the input voltage peak value and the output rated voltage of the DC/DC converter is taken; the first low voltage threshold may be set to be 1.05 times of the second low voltage threshold, but is not limited thereto, and the setting of the first low voltage threshold mainly refers to the normal fluctuation range of the dc bus voltage. Of course, this is merely an example, and in practical applications, the voltage may be set according to the rated voltage and the maximum withstand voltage of the switching device, and the present invention is not limited to this.

The first high-voltage threshold and the first low-voltage threshold form a normal working range of the direct-current bus of the PWM power supply, and the normal working range can be called as a third preset range; the second high pressure threshold and the second low pressure threshold are upper and lower limits of the first preset range; below the third high pressure threshold, this may be referred to as a second predetermined range.

The host computer detects the dc bus voltage in real time and only compares it with the corresponding threshold, and if the dc bus voltage is outside the first preset range, S102 is executed.

S102, the host controls the direct current bus voltage outer ring to be switched from a PI control mode to an I control mode.

The PWM power supply host works in a voltage mode, and when the direct-current bus voltage is between a first high-voltage threshold value and a first low-voltage threshold value, the direct-current bus voltage outer ring of the power supply host adopts a PI control mode; and when the direct current bus voltage is greater than a second high-voltage threshold value or less than a second low-voltage threshold value, the direct current bus voltage outer ring of the main machine is switched to an I control mode, so that the given value of the active current is rapidly increased or decreased.

According to the direct-current bus voltage control method of the power supply parallel system, when the direct-current bus voltage is beyond a first preset range, the host controls the direct-current bus voltage outer ring of the host to be switched to an I control mode from a PI control mode, so that the active current given value can be changed rapidly, the direct-current bus voltage is controlled, the dynamic response performance of the power supply parallel system is improved, and the influence on the operation reliability of the power supply parallel system and the working performance and service life of a load due to the mismatching of input and output energy is avoided.

Based on the above embodiment, in the method for controlling dc bus voltage, S102 may specifically include: if the direct current bus voltage is smaller than the lower limit value of the first preset range, the host controls the given value of the active current to be increased on the basis of the output quantity of the controller of the direct current bus voltage outer ring; if the direct current bus voltage is larger than the upper limit value of the first preset range, the host machine controls the active current set value to be decreased gradually on the basis of the controller output quantity of the direct current bus voltage outer ring.

And the step length of the host machine for controlling the increment or decrement of the given value of the active current is as follows: the product of the rated current of the input side of the power supply parallel system and a preset proportion; the preset proportion is as follows: control period T of power supply parallel system _s For which the input side current is from zero to the rated current I _ed I.e. the step size Δ I is calculated as:

specifically, the S102 may include:

(1) Assigning the control quantity output by the PI controller of the current direct current bus voltage outer ring to an active current given value I _{d_ref1} 。

(2) If the direct current bus voltage is less than the second low-voltage threshold value, the active current given value I _{d_ref1} In each control period T _s Integral addition is performed by a step size Δ I, namely: I.C. A _{d_ref1} ＝I _{d_ref1} +ΔI。

(3) If the direct current bus voltage is greater than the second high-voltage threshold value, the active current given value I _{d_ref1} In each control period T _s The integral decrement is carried out by a step size Δ I, namely: i is _{d_ref1} ＝I _{d_ref1} -ΔI。

Moreover, at any time (shown after S102 in the figure), the method for controlling the dc bus voltage may further include the steps shown in fig. 4:

and S201, the host issues the active given value to each slave in each power supply through communication.

The active given value may be an active current given value or an active power given value, which depends on the specific application environment, and is not limited herein. In practical application, the master machine CAN send the given value of the active current to each slave machine through a high-speed CAN communication bus, and control each slave machine and the master machine to synchronously increase or decrease the active current, so as to realize synchronous control of each slave machine.

Based on the above embodiments, further, when the DC bus voltage is greater than the third high voltage threshold, the main unit may switch to the switching tube driving disable mode, and turn off the switching tube driving of the AC/DC converter, so that the switching tube driving is switched from the controllable rectification to the uncontrolled rectification.

Referring to fig. 5 (which is illustrated on the basis of fig. 3 as an example), in this case, before S101, the method for controlling the dc bus voltage further includes:

s301, the host machine judges whether the voltage of the direct current bus is in a second preset range.

The second preset range is below the third high-voltage threshold, that is, the first preset range belongs to the second preset range; if the dc bus voltage is outside the second preset range, it indicates that the dc bus voltage is too high, and then S302 is performed. If the dc bus voltage is within the second preset range, S101 is executed.

S302, the host is switched to a switching tube drive forbidding mode from a voltage mode, so that the rectifying circuit of the host runs in an uncontrolled rectifying state.

Moreover, when the voltage of the direct current bus is reduced to the first low voltage threshold value, the direct current bus can be switched back to the voltage mode again; that is, after S302, the dc bus voltage control method may further include:

and S303, the host machine judges whether the voltage of the direct current bus is smaller than the lower limit value of a third preset range.

The upper limit value of the third preset range is the first high-pressure threshold value, and the lower limit value of the third preset range is the first low-pressure threshold value, so that the third preset range belongs to the first preset range.

If the dc bus voltage is smaller than the lower limit of the third preset range, S304 is executed.

S304, the host is switched from the switching tube drive forbidding mode to the voltage mode.

The process of S304 specifically includes:

(1) The host machine feeds back the current active current instantaneous feedback value I of the host machine _d1 And assigning the integral output to the direct current bus voltage outer loop controller.

(2) And the host clears the integral output of the active current inner loop controller.

(3) The host computer sends the current value (namely the instantaneous feedback value of the DC bus voltage) U of the DC bus voltage _dc Assigning a given value (i.e. the DC bus voltage given) U to the outer ring of the DC bus voltage _dcref 。

(4) Given value U of external ring of host computer controlled DC bus voltage _{dc_ref} Adding the control signals by step size delta U in each control period, namely; u shape _{dc_ref} ＝U _{dc_ref} + Δ U, up to U _{dc_ref} ＝U _{dc_ed} . Wherein, U _{dc_ed} For the rated voltage of the dc bus, the step size Δ U may be set to a small value, such as 0.001 × U _{dc_ed} But is not limited thereto.

In addition, by means of the communication interconnection between the master and the slave, after S302, the dc bus voltage control method may further include the steps shown in fig. 6 (shown in conjunction with fig. 4 and 5):

s202, the master machine controls the slave machines in the power supplies through communication, and the current mode is switched to the switch tube driving prohibition mode.

Similarly, if the dc bus voltage is smaller than the lower limit of the third preset range, the method for controlling the dc bus voltage further includes the steps shown in fig. 6:

and S203, the master machine controls the slave machines in the power supplies and switches from the switch tube drive forbidding mode to the current mode.

In practical application, the host may implement S202 and S203 by driving the prohibition flag through the switching tube, specifically: when S302 is executed, the master may set the switch tube drive prohibition flag to 1 at the same time, and then send it to each slave through communication, thereby implementing S202; and when S304 is executed, the master may simultaneously clear the switch tube driving prohibition flag to 0, and send it to each slave through communication, so as to implement S203.

Preferably, the master machine CAN send the active current set value and the switch tube drive prohibition mark to each slave machine through a high-speed CAN communication bus, and control the slave machine and the master machine to synchronously increase or decrease the active current or close the switch tube drive of the AC/DC converter.

Moreover, the S203 may specifically include: the host sends switch tube drive prohibition marks to all slaves through communication; each slave machine clears the integral output of the active current inner loop controller of the slave machine according to the switch tube drive prohibition mark; and then, each slave machine operates in a current mode according to the active given value issued by the host machine.

On the basis of the above embodiment, preferably, the dc bus voltage control method, referring to fig. 7 (shown as an example on the basis of fig. 5), further includes, after S101: if the dc bus voltage is within the first preset range, S103 is executed.

S103, the host machine judges whether the voltage of the direct current bus is in the third preset range.

The third preset range belongs to the first preset range; if the dc bus voltage is within the third predetermined range, step S104 is executed.

And S104, the host determines the current control mode of the outer ring of the direct-current bus voltage.

And if the current control mode of the outer ring of the direct-current bus voltage is the PI control mode, the host machine maintains the current control mode. If the current control mode of the outer ring of the dc bus voltage is the I control mode, S105 is executed.

And S105, the host machine controls the direct current bus voltage outer ring to be switched into a PI control mode.

The S105 specifically may include:

(1) The host computer gives a current active current given value I _{d_ref1} And assigning the integral output to the direct current bus voltage outer loop controller.

(2) The host computer converts the current value U of the DC bus voltage _dc Assigned to the given value U of the outer loop of the DC bus voltage _{dc_ref} 。

(3) If the given value U of the outer ring of the DC bus voltage _{dc_ref} Greater than the rated voltage U of the direct current bus _{dc_ed} Then controlling the given value U of the outer ring of the DC bus voltage _{dc_ref} Decreasing by a step size Δ U in each control period, i.e., decreasing; u shape _{dc_ref} ＝U _{dc_ref} Δ U, up to U _{dc_ref} ＝U _{dc_ed} 。

(4) If the given value U of the outer ring of the DC bus voltage _{dc_ref} Less than rated voltage U of DC bus _{dc_ed} Then controlling the given value U of the outer ring of the DC bus voltage _{dc_ref} Adding by step size delta U in each control period, namely; u shape _{dc_ref} ＝U _{dc_ref} + Δ U, up to U _{dc_ref} ＝U _{dc_ed} 。

Due to the current dc bus voltage (i.e. the current value of the dc bus voltage) U _dc Has been in the normal range between the first high pressure threshold and the first low pressure thresholdWithin the enclosure, to avoid triggering again an abnormal condition greater than the second high pressure threshold or less than the second low pressure threshold, the step Δ U may be set to a smaller value, such as 0.001 × U _{dc_ed} But is not limited thereto.

In addition to the above embodiments, before the host determines the dc bus voltage, the dc bus voltage control method preferably further includes the steps shown in fig. 8 (which is shown as an example on the basis of fig. 7):

and S100, completing the setting of the master and the slave by each power supply.

In practical application, the power supply with the minimum number can be used as a master and other power supplies can be used as slaves according to the number of each power supply in the PWM power supply parallel system, so that the master and slave setting is completed.

Specifically, each power supply CAN send running state information containing the number N of the power supply through the CAN communication bus, receive and identify the numbers of other power supplies of the power supply parallel system, and compare the numbers with the numbers of the other power supplies, wherein N =1, …, and N is the total number of the power supplies running in parallel in the system; in practical application, the power supply with the minimum number can be set as a master of the master-slave mode PWM power supply parallel system, and other power supplies are used as slaves of the master-slave mode PWM power supply parallel system; or, other power supplies, such as the power supply with the largest number, may be set as the master, and the other power supplies may be set as slaves; depending on the specific application environment, it is not limited herein.

Then, the host closes the input switch and the direct current load switch connected with the host, operates in a voltage mode, adopts double closed-loop control of a direct current bus voltage outer ring and an active current inner ring, establishes voltage on a common direct current bus, works in a sending mode in a CAN communication mailbox, and shares related information to each slave machine in real time through a data frame through a high-speed CAN communication bus.

The data frame sent by the host computer to each slave computer through the high-speed CAN communication bus specifically comprises the following information: (1) The active current set value output by the direct current bus voltage outer ring; (2) a switch tube drive prohibition flag; and (3) fault marking.

And each slave machine respectively closes the input switch and the direct current load switch to operate in a current mode, and the CAN communication mailbox of each slave machine works in a receiving mode.

It should be noted that, if the master fails, in order to ensure that the entire system CAN continue to operate, the master may send a failure flag to all slaves via the high-speed CAN communication bus, and then select any slave according to a preset rule, for example, a slave adjacent to the original master, so that the slave is automatically switched to a new master, and the control mode of the slave is switched from the current mode to the voltage mode.

That is, the dc bus voltage control method may further include, at any time after S100, the following steps shown in fig. 8 (shown in fig. 6 and 7 in combination):

and S105, when the master fails, controlling any slave to be switched to the master through communication, and switching the current mode of the slave to the voltage mode.

Moreover, the process of switching from the current mode to the voltage mode after the slave is switched to the host may specifically include:

(1) The current active current instantaneous feedback value I of the current converter is measured _dn (n is the slave machine number switched to the master machine), and is assigned to the integral output of the external ring controller of the direct current bus voltage.

(2) The current value U of the DC bus voltage _dc And assigning a given value U to the outer ring of the self direct current bus voltage _{dc_ref} 。

(3) If the given value U of the outer ring of the DC bus voltage _{dc_ref} Is greater than the rated voltage U of the direct current bus _{dc_ed} Then the given value U of the outer ring of the DC bus voltage is controlled _{dc_ref} Decreasing by a step size Δ U in each control period, i.e., decreasing; u shape _{dc_ref} ＝U _{dc_ref} Δ U, up to U _{dc_ref} ＝U _{dc_ed} 。

(4) If the external ring set value U of the DC bus voltage _{dc_ref} Less than rated voltage U of DC bus _{dc_ed} Then the given value U of the outer ring of the DC bus voltage is controlled _{dc_ref} Adding by step size delta U in each control period, namely; u shape _{dc_ref} ＝U _{dc_ref} + Δ U until U _{dc_ref} ＝U _{dc_ed} 。

The step size Δ U may be set to a smaller value, such as 0.001 × U _{dc_ed} But is not limited thereto.

In the embodiment, when the power supply host fails, the fault flag is immediately notified to all the power supply slave machines through high-speed CAN communication, any power supply slave machine, such as an adjacent power supply slave machine, is selected according to a preset rule to be automatically switched to the host machine, the control mode of the power supply slave machine is switched from a current mode to a voltage mode, and the CAN communication mailbox is correspondingly switched from a receiving mode to a sending mode, so that the fault-tolerant control of a power supply parallel system and the uninterrupted power supply to a load are realized, and the operation reliability of the system is effectively improved.

An example of a complete process is given below for the dc bus voltage control method of the master-slave PWM power supply parallel system, which specifically includes the following steps:

step 1: the specific process of completing the setting of the master and the slave by each power supply can be referred to the introduction of S100, which is not described herein again; then the master computer continues to step 2, and other slave computers jump to execute step 3.

And 2, step: the host machine closes the input switch and the direct current load switch, operates in a voltage mode, adopts double closed-loop control of a direct current bus voltage outer ring and an active current inner ring, establishes voltage on a public direct current bus, works in a sending mode through a CAN communication mailbox, shares relevant information to each slave machine in real time through a data frame through a high-speed CAN communication bus, and then jumps to execute the step 4. The data frame contains information: (1) The active current set value output by the direct current bus voltage outer ring; (2) a switch tube drive prohibition flag; and (3) fault marking.

And step 3: and (3) respectively closing the input switch and the direct current load switch of each slave, operating in a current mode, operating the CAN communication mailbox in a receiving mode, and then jumping to execute the step 15.

And 4, step 4: the host machine detects the voltage of the direct current bus in real time and according to the rated voltage U of the direct current bus _{dc_ed} And determining a first high voltage threshold, a second high voltage threshold and a third high voltage threshold of the direct current bus voltage, and a first low voltage threshold and a second low voltage threshold of the direct current bus voltage. Of each thresholdFor specific settings, reference may be made to the above embodiments, which are not described herein again.

And 5: and (4) judging whether the voltage of the direct-current bus is greater than a third high-voltage threshold value by the host, if so, skipping to execute the step 11, otherwise, continuing to execute the step 6.

Step 6: and (4) judging whether the voltage of the direct-current bus is greater than a second high-voltage threshold value by the host, if so, skipping to execute the step (8), and otherwise, continuing to execute the step (7).

And 7: and the host machine judges whether the voltage of the direct-current bus is smaller than a second low-voltage threshold value, if so, the step 8 is continuously executed, and otherwise, the step 9 is executed in a skipping way.

And 8: and the outer ring of the direct current bus voltage of the host is switched to an I control mode from a PI control mode. The specific process of this step may be as in the above embodiments, and is not described herein again.

And step 9: the host computer judges whether the voltage of the direct current bus is between the first high voltage threshold value and the first low voltage threshold value, if the conditions are met, the step 10 is continuously executed.

Step 10: judging the control mode of the voltage outer ring of the direct current bus of the host, and if the control mode is the PI control mode, skipping to execute the step 14; if the control mode is I control mode, the control mode is switched to PI control mode from I control mode, and then the step 14 is executed in a skipping mode. For a specific process of switching the external ring of the dc bus voltage of the host from the I control mode to the PI control mode, reference may be made to the above embodiments, which are not described herein again.

Step 11: the host machine is switched from a voltage mode to a switching tube drive prohibition mode, the switching tube drive of the AC/DC converter is closed, controllable rectification is converted into uncontrollable rectification, and meanwhile, the high-speed CAN communication bus is sent to a switching tube drive prohibition flag 1 contained in each slave machine data frame.

Step 12: the host computer judges whether the direct current bus voltage is smaller than a first low voltage threshold value, if the conditions are met, the step 13 is continuously executed.

Step 13: the host is switched to a voltage mode from a switching tube drive prohibition mode, and simultaneously sends the high-speed CAN communication bus to a switching tube drive prohibition flag clear 0 contained in each slave data frame. The specific process of switching the host from the switch tube driving prohibition mode to the voltage mode may be as described in the above embodiments, and details are not repeated here.

Step 14: the host judges whether the host has a fault in real time, if the host has the fault, the host stops and disconnects the input and output switches, and meanwhile, the high-speed CAN communication bus is sent to a fault mark 1 contained in each slave machine data frame.

Step 15: the slave machine receives an active current given signal from the host machine through the CAN communication bus, adopts the active current inner loop PI controller to realize closed loop tracking of the signal, judges whether a switch tube drive prohibition flag received through the CAN communication bus is 1 or not in real time, continues to execute the step 16 if the flag is 1, and otherwise jumps to execute the step 18.

Step 16: and switching the slave from the current mode to the switching tube drive prohibition mode, closing the switching tube drive of the AC/DC converter, and converting the controllable rectification into the uncontrollable rectification.

And step 17: the slave machine judges whether the switch tube drive prohibition flag received through the CAN communication bus is 0 in real time, and if the switch tube drive prohibition flag is 0, the slave machine continues to execute the step 18.

Step 18: judging the working mode of the slave, if the working mode is the current mode, continuing to execute the step 19; if the mode is the switching tube drive inhibition mode, the integral output of the active current inner loop PI controller is cleared by 0, and then the switching tube drive inhibition mode is switched to the current mode.

Step 19: each slave machine judges whether the host machine fault mark received through the CAN communication bus is 1 in real time, if so, any slave machine, such as the slave machine with the number determined in the step 1 and adjacent to the host machine, is switched to the host machine, the working mode of the slave machine is switched to a voltage mode from a current mode, and the CAN communication mailbox is switched to a sending mode from a receiving mode.

The direct current bus voltage control method can detect the direct current bus voltage through a host computer, and set a first high voltage threshold, a second high voltage threshold and a third high voltage threshold, and a first low voltage threshold and a second low voltage threshold, then according to the above thresholds, the direct current bus voltage outer ring is switched between a PI control mode and an I control mode, and in the I control mode, the active current given value is rapidly increased or decreased, especially when the direct current bus voltage is larger than the third high voltage threshold, the host computer is switched to a switching tube drive forbidding mode, and the increase of the direct current bus voltage is restrained by closing the switching tube drive of an AC/DC converter; meanwhile, the host machine sends the active given value and the switch tube drive prohibition mark to each slave machine through a high-speed CAN communication bus, and controls the slave machines and the host machine to synchronously increase or decrease the active current or close the switch tube drive of the AC/DC converter, so that the problem of sudden rise or sudden drop of the voltage of the direct current bus caused by mismatching of input and load power is solved, and the dynamic response performance of the PWM power supply parallel system for responding to the rapid change of the input or output power is effectively improved.

In addition, through the switching process of the master machine between the PI control mode and the I control mode, the switching tube drive forbidding mode and the voltage mode and the switching process of the slave machine between the current mode and the voltage mode, the smooth switching and transition of the master machine and the slave machine of the power supply between various control modes can be realized, and the impact of input and output currents and the large fluctuation of the voltage of a direct current bus are effectively avoided.

In addition, under the condition that the host machine has a fault, the direct-current bus voltage control method CAN inform the slave machine of the fault mark in time through high-speed CAN communication, so that the slave machine is automatically switched to the host machine, the control mode of the slave machine is switched from a current mode to a voltage mode, and the CAN communication mailbox is correspondingly switched from a receiving mode to a sending mode, thereby realizing fault-tolerant control of a power parallel system and uninterrupted power supply to a load and effectively improving the running reliability of the system.

Another embodiment of the present application further provides a power parallel system, as shown in fig. 2, including at least two power supplies (e.g., power supply 1 to power supply N shown in fig. 2) with dc buses connected in parallel, where each power supply is connected in communication, and is configured to execute the dc bus voltage control method of the power parallel system according to any of the above embodiments; the specific process and principle of the dc bus voltage control method may be referred to the above embodiments, and details are not repeated here.

In practical application, the output side of each power supply is connected in parallel to the output side of the power supply parallel system through a corresponding direct current load switch. The input side of each power supply is connected in parallel to the input side of the power parallel system through a corresponding input switch (such as an ac input switch shown in fig. 2).

The power supply parallel system can be applied to the field of hydrogen production and is used as a hydrogen production power supply parallel system, at the moment, the input side of the power supply parallel system can be connected with a power grid, such as an alternating current power grid, and can also be connected to the output end of a renewable energy power generation system, and the load connected with the output side of the power supply parallel system is an electrolytic cell; the power supply parallel system can also be applied to the field of charging, and can be used as a charging power supply parallel system, at the moment, the input side of the charging power supply parallel system can be connected with a power grid or connected to the output end of a renewable energy power generation system, and the load connected with the output side of the charging power supply parallel system can be a battery of an energy storage system, a power battery of an electric automobile or other chargeable and dischargeable batteries; the application does not limit the source connected with the input side and the load connected with the output side, and the application is determined according to the specific application environment and is within the protection scope of the application. That is, the direct current bus voltage control method can be suitable for the situation of direct current bus voltage runaway caused by input and output energy mismatch in a power supply parallel system, hydrogen production by renewable energy is only one situation, and when hydrogen production by a power grid is adopted, the problem of direct current bus voltage runaway can also exist due to sudden change of electrolytic cell load, so that the method can also be suitable for the situation; charging and other fields are similar and will not be described in detail.

As shown in fig. 2, the power supply may include: an AC/DC converter (AC/DC PWM rectification as shown in the figure) and a DC/DC converter (DC/DC buck as shown in the figure); wherein, the AC side of the AC/DC converter is used as the input side of the power supply; the direct current side of the AC/DC converter is connected with one side of the DC/DC converter through a direct current bus; one side of the DC/DC converter serves as an output side of the power supply.

Alternatively, the power supply may comprise only an AC/DC converter, i.e. only the AC/DC PWM rectification shown in fig. 2, while the DC/DC buck shown in fig. 2 is omitted; in this case, the AC side of the AC/DC converter is an input side of the power supply, and the DC side of the AC/DC converter is an output side of the power supply, and is connected in parallel via a DC bus.

When the input side of each power supply is connected to the output end of the renewable energy power generation system in parallel, each power supply may also adopt other forms of conversion structures as long as power conversion between the input side and the output side can be achieved, and the conversion structures are not limited herein.

The same and similar parts among the various embodiments in this specification can be referred to each other, and each embodiment focuses on differences from other embodiments. In particular, the system or system embodiments are substantially similar to the method embodiments and therefore are described in a relatively simple manner, and reference may be made to some of the descriptions of the method embodiments for related points. The above-described system and system embodiments are only illustrative, wherein the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

In the above description of the disclosed embodiments, the features described in the embodiments in this specification may be replaced or combined with each other to enable those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The direct current bus voltage control method of the power parallel system is characterized in that the power parallel system comprises a power supply with at least two direct current buses connected in parallel; the direct-current bus voltage control method comprises the following steps:

and if the direct current bus voltage is out of the first preset range, the host controls the direct current bus voltage outer ring of the host to be switched from a proportional-integral PI control mode to a pure integral I control mode.

2. The method according to claim 1, wherein the host controls the external dc bus voltage loop to switch from the PI control mode to the I control mode, and includes:

if the direct-current bus voltage is smaller than the lower limit value of the first preset range, the host controls the active current set value to be increased on the basis of the controller output quantity of the direct-current bus voltage outer ring;

3. The method for controlling the voltage of the direct current bus of the power parallel system according to claim 2, wherein the step length of the host machine for controlling the increment or decrement of the given value of the active current is as follows: the product of the rated current of the input side of the power supply parallel system and a preset proportion;

the preset proportion is as follows: a ratio of a control period of the power parallel system to a response time of an input side current thereof from zero to the rated current.

4. The method according to claim 1, wherein before the host in each of the power supplies determines whether the dc bus voltage of the power parallel system is within a first preset range, the method further comprises:

the host machine judges whether the voltage of the direct current bus is within a second preset range; the first preset range belongs to the second preset range;

if the direct-current bus voltage is out of the second preset range, the host is switched from a voltage mode to a switching tube drive prohibition mode, and the rectifying circuit of the host is operated in an uncontrolled rectifying state.

5. The dc bus voltage control method of claim 4, further comprising, after the host switches from the voltage mode to the switch tube drive disable mode:

and if the voltage of the direct current bus is smaller than the lower limit value of the third preset range, the host is switched from the switching tube drive prohibition mode to the voltage mode.

6. The dc bus voltage control method of claim 5, wherein switching the host from the switching tube drive disable mode to the voltage mode comprises:

the host clears the integral output of the active current inner loop controller;

7. The method for controlling the dc bus voltage of the power parallel system according to claim 1, further comprising, after determining whether the dc bus voltage of the power parallel system is within a first preset range:

if the direct-current bus voltage is within the first preset range, the host machine judges whether the direct-current bus voltage is within a third preset range; the third preset range belongs to the first preset range;

8. The method of claim 7, wherein the controlling the external loop of the DC bus voltage to switch to the PI control mode by the host comprises:

the host assigns the current active current given value to the integral output of the direct current bus voltage outer ring controller;

9. The dc bus voltage control method of the power parallel system according to any one of claims 1 to 8, further comprising:

10. The dc bus voltage control method of any of claims 4 to 6, further comprising, after the host switches from the voltage mode to the switching tube drive disable mode:

11. The method according to claim 5 or 6, further comprising, if the dc bus voltage is smaller than the lower limit of the third preset range:

12. The dc bus voltage control method of claim 11, wherein the master controlling the slave in each of the power supplies to switch from the switching tube drive disable mode to the current mode comprises:

13. The dc bus voltage control method of the power parallel system according to any one of claims 1 to 8, further comprising, before the host determines the dc bus voltage:

14. The dc bus voltage control method of claim 13, further comprising, at any time after each of the power supplies completes the master-slave setting:

15. The method of claim 14, wherein switching from current mode to voltage mode comprises:

16. The dc bus voltage control method of the power parallel system according to any one of claims 1 to 8, further comprising, before the host determines the dc bus voltage:

17. A power parallel system comprising at least two power sources connected in parallel with a dc bus, each of said power sources communicatively connected for performing the dc bus voltage control method of the power parallel system as claimed in any one of claims 1 to 16.

18. The electrical power parallel system of claim 17, wherein an input side of each of the electrical power sources is connected in parallel to an input side of the electrical power parallel system through a corresponding input switch;

19. The power parallel system of claim 18, wherein the power supply comprises: an AC/DC converter;

the DC side of the AC/DC converter is connected with the DC bus and the output side of the power supply.

20. The power parallel system of claim 19, wherein the power supply further comprises: a DC/DC converter;

21. The power parallel system according to any one of claims 17 to 20, wherein an input side of the power parallel system is connected with a renewable energy power generation system or a power grid, and an output side of the power parallel system is connected with an electrolytic cell or a rechargeable battery.