阅读说明：本技术 一种双向变换器及其调制方法 (Bidirectional converter and modulation method thereof ) 是由 刘亮 申智 程林 陈方林 陈强云 方伟 董浩 于 2020-11-27 设计创作，主要内容包括：本发明提供一种双向变换器及其调制方法,该方法包括：依据检测到的双向变换器两侧的总母线电压,判断双向变换器是否满足单双级调制切换条件；在满足单双级调制切换条件时,控制双向变换器切换调制,并在切换调制时加入电流前馈和电压前馈；在完成切换调制之后,切除电流前馈；从而在现有控制策略的基础上,在切换调制模式的瞬间增加输出电流和输出电压的占空比前馈,可保证输出电流和输出电压的稳定。并且,采用的是软件控制方式,避免了采用硬件电路增加的成本的问题,控制简单、易实现,提高系统稳定性。(The invention provides a bidirectional converter and a modulation method thereof, wherein the method comprises the following steps: judging whether the bidirectional converter meets a single-stage and double-stage modulation switching condition or not according to the detected total bus voltage on two sides of the bidirectional converter; when the single-stage modulation and double-stage modulation switching conditions are met, the bidirectional converter is controlled to switch and modulate, and current feedforward and voltage feedforward are added during switching and modulating; after the switching modulation is completed, cutting off the current feed-forward; therefore, on the basis of the existing control strategy, duty ratio feedforward of output current and output voltage is increased at the moment of switching the modulation mode, and the stability of the output current and the output voltage can be ensured. In addition, a software control mode is adopted, the problem of cost increase caused by the adoption of a hardware circuit is solved, the control is simple and easy to realize, and the system stability is improved.)

1. A modulation method for a bidirectional converter, comprising:

respectively detecting the total voltage on two sides of the bidirectional converter;

judging whether the bidirectional converter meets a single-stage and double-stage modulation switching condition or not according to the total voltage on the two sides;

when the bidirectional converter meets the switching condition of single-stage and double-stage modulation, the bidirectional converter is controlled to switch the modulation mode, and current feedforward and voltage feedforward are added when the modulation mode is switched;

and cutting off the current feed-forward after the modulation mode switching is completed.

2. The modulation method of the bidirectional converter according to claim 1, wherein adding current feed forward when switching the modulation mode comprises:

replacing an integral of a current loop regulator of the bidirectional converter with the current feed forward.

3. The method of modulating a bi-directional converter as claimed in claim 2, further comprising, prior to said adding current feed forward:

determining the current feed forward.

4. The method of modulating a bi-directional converter as recited in claim 3, wherein determining said current feed forward comprises:

determining switching parameters of the bidirectional converter according to bridge arm inductance values of the bidirectional converter, switching time and the total voltage on two sides;

and obtaining the current feedforward according to the actual current value of the bidirectional converter and the switching parameter.

5. The modulation method of the bidirectional converter according to claim 4, wherein obtaining the current feed-forward according to the actual current value of the bidirectional converter and the switching parameter comprises:

and taking the product of the actual current value of the bidirectional converter and the switching parameter as the current feedforward.

6. Method for modulating a bidirectional converter according to claim 4, characterized in that the formula used for determining said switching parameters is:

wherein K is the switching parameter, L is the bridge arm inductance value, Δ t is the switching time, U₁Is the total voltage of the first side of the bidirectional converter, U₂Is the total voltage on the second side of the bidirectional converter.

7. The modulation method of a bidirectional converter according to claim 2, wherein the current feed-forward is applied for only one carrier cycle at the instant of switching the modulation scheme.

8. The modulation method of the bidirectional converter according to claim 1, wherein the voltage feed forward is added when the modulation mode is switched, and the method comprises the following steps:

and superposing the output quantity of a current loop regulator of the bidirectional converter by the voltage feedforward.

9. The modulation method of the bidirectional converter according to claim 8, wherein the voltage feed-forward is a real-time calculation value or an instantaneous calculation value when the modulation mode is switched.

10. The modulation method of a bidirectional converter according to claim 9, wherein said real-time calculated value and said instantaneous calculated value are:

at the moment of calculation, the ratio between the smaller and the larger of said total voltage across said bidirectional converter.

11. The modulation method of a bidirectional converter according to claim 10,

if the total voltage on both sides of the bidirectional converter satisfies U₁≤U₂Then the calculation formula adopted by the voltage feedforward is

If the total voltage on both sides of the bidirectional converter satisfies U₁>U₂Then the calculation formula adopted by the voltage feedforward is

Wherein, U₁Is said total voltage, U, of said first side of said bidirectional converter₂Is said total voltage, U, of said second side of said bidirectional converter_dutyFeeding forward the voltage.

12. The modulation method of the bidirectional converter according to any one of claims 1 to 11, further comprising, after completion of the modulation scheme switching:

the voltage feed forward applied to the bidirectional converter is matched to the current modulation mode of the bidirectional converter.

13. The method of claim 12, wherein the voltage feed-forward is a predetermined value when the bi-directional converter is in a dual stage modulation mode.

14. The modulation method of the bidirectional converter according to claim 13, wherein the preset value is in a range of 0.85 to 0.95.

15. The method of claim 12, wherein the voltage feed forward is a real-time calculated value or an instantaneous calculated value when entering a single-stage modulation mode when the bidirectional converter is in the single-stage modulation mode.

16. The modulation method of the bidirectional converter according to any one of claims 1 to 11, wherein the control strategy of the bidirectional converter is a current closed loop or a voltage-current double closed loop when the bidirectional converter is in a single-stage modulation mode or a double-stage modulation mode.

17. A bidirectional converter, comprising: the device comprises a controller, a detection module and a main circuit; wherein:

two sides of the main circuit are respectively used as a first side and a second side of the bidirectional converter, and the first side and the second side are respectively provided with corresponding total bus capacitors;

the controller is connected to the control terminal of the main circuit and the output terminal of the detection module, respectively, and is configured to perform the modulation method of the bidirectional converter according to any one of claims 1 to 16.

18. The bidirectional converter of claim 17, wherein the main circuit comprises: the circuit comprises a first inductor, a second inductor, a first side branch and a second side branch;

the first side branch and the second side branch each include: the circuit comprises an upper bridge arm, a lower bridge arm, a positive half bus capacitor, a negative half bus capacitor, a positive relay and a negative relay;

the upper bridge arm is connected with the positive half bus capacitor in parallel, and the lower bridge arm is connected with the negative half bus capacitor in parallel;

the upper bridge arm and the lower bridge arm respectively comprise two inner pipes and two outer pipes which are connected in series, the connection point of the inner pipes and the outer pipes is used as the midpoint of the corresponding bridge arm, and the upper bridge arm and the lower bridge arm are connected in series through the inner pipes;

the middle points of the upper bridge arms are connected through the first inductors, and the middle points of the lower bridge arms are connected through the second inductors;

the positive relay is arranged on a positive bus between the corresponding bus capacitor and the positive half bus capacitor;

the negative relay is arranged on a negative bus between the corresponding bus capacitor and the negative half-bus capacitor.

19. The bidirectional converter according to claim 18, wherein the positive relay and the negative relay are each connected in parallel with a resistor and a diode connected in series;

the direction of the diode is the same as the current direction charged by the positive and negative half bus capacitors on the corresponding side.

Technical Field

The invention belongs to the technical field of bidirectional converters, and particularly relates to a bidirectional converter and a modulation method thereof.

Background

The bidirectional DC/DC converter topology is shown in fig. 1, where the total voltage across it is usually different; when the current flows from the high-voltage side to the low-voltage side, the high-voltage side and the low-voltage side are operated in buck modes; operating in boost mode when current flows from the low voltage side to the high voltage side; buck mode and boost mode are free to switch, but when the total voltage on both sides is close or equal, both modes switch frequently and the output ripple is large.

The prior art provides a smooth switching control method, which divides a working mode into a buck mode, a boost mode and a buck-boost mode through an external hardware circuit, wherein the buck mode, the boost mode and the boost mode are operated in the buck-boost mode when 0.8Vo < Vin <1.25Vo, the buck mode and the boost mode are alternately executed in a carrier control period, and Vin is input voltage and Vo is output voltage; although the scheme can realize smooth switching between the buck mode and the boost mode, the hardware circuit and the cost are increased, and the control is complex.

The other scheme provides that a two-stage modulation strategy is adopted to replace a buck-boost mode in software control, and the method is different from the conventional single-stage modulation mode in which only the high-voltage side performs chopping control, and switching tubes on two sides of the two-stage modulation mode perform chopping control; although the scheme can avoid frequent switching between the buck mode and the boost mode, the large fluctuation of the output current and the output voltage can be caused during switching of single-stage and double-stage modulation, and the stable operation of the system is influenced.

Disclosure of Invention

In view of this, an object of the present invention is to provide a bidirectional converter and a modulation method thereof, which are used to ensure the stability of output current and output voltage at the moment of switching modulation modes, and are simple and easy to control, and improve the system stability.

The invention discloses a modulation method of a bidirectional converter in a first aspect, which comprises the following steps:

respectively detecting the total voltage on two sides of the bidirectional converter;

judging whether the bidirectional converter meets a single-stage and double-stage modulation switching condition or not according to the total voltage on the two sides;

when the bidirectional converter meets the switching condition of single-stage and double-stage modulation, the bidirectional converter is controlled to switch the modulation mode, and current feedforward and voltage feedforward are added when the modulation mode is switched;

and cutting off the current feed-forward after the modulation mode switching is completed.

Optionally, adding current feed-forward when switching the modulation mode includes:

replacing an integral of a current loop regulator of the bidirectional converter with the current feed forward.

Optionally, before the adding the current feed-forward, the method further includes:

determining the current feed forward.

Optionally, determining the current feed forward comprises:

determining switching parameters of the bidirectional converter according to bridge arm inductance values of the bidirectional converter, switching time and the total voltage on two sides;

and obtaining the current feedforward according to the actual current value of the bidirectional converter and the switching parameter.

Optionally, obtaining the current feed-forward according to the actual current value of the bidirectional converter and the switching parameter includes:

and taking the product of the actual current value of the bidirectional converter and the switching parameter as the current feedforward.

Optionally, the formula for determining the handover parameter is as follows:

wherein K is the switching parameter, L is the bridge arm inductance value, Δ t is the switching time, U₁Is the total voltage of the first side of the bidirectional converter, U₂Is the total voltage on the second side of the bidirectional converter.

Optionally, the current feed-forward only acts for one carrier period at the instant of switching the modulation mode.

Optionally, adding voltage feedforward when switching the modulation mode includes:

and superposing the output quantity of a current loop regulator of the bidirectional converter by the voltage feedforward.

Optionally, the voltage feedforward is a real-time calculation value or an instantaneous calculation value when the modulation mode is switched.

Optionally, the real-time calculated value and the instantaneous calculated value are:

at the moment of calculation, the ratio between the smaller and the larger of said total voltage across said bidirectional converter.

Alternatively to this, the first and second parts may,

if the total voltage on both sides of the bidirectional converter satisfies U₁≤U₂Then the calculation formula adopted by the voltage feedforward is

If the total voltage on both sides of the bidirectional converter satisfies U₁>U₂Then the calculation formula adopted by the voltage feedforward is

Wherein, U₁Is said total voltage, U, of said first side of said bidirectional converter₂Is said total voltage, U, of said second side of said bidirectional converter_dutyFeeding forward the voltage.

Optionally, after the switching of the modulation scheme is completed, the method further includes:

the voltage feed forward applied to the bidirectional converter is matched to the current modulation mode of the bidirectional converter.

Optionally, when the bidirectional converter is in a two-stage modulation mode, the voltage feedforward is a preset value.

Optionally, the preset value is within a range of 0.85-0.95.

Optionally, when the bidirectional converter is in a single-stage modulation mode, the voltage feedforward is a real-time calculation value or an instantaneous calculation value when the bidirectional converter enters the single-stage modulation mode.

Optionally, the real-time calculated value is:

the ratio between the smaller and the larger of said total voltage across said bidirectional converter.

Optionally, if the total voltage on both sides of the bidirectional converter satisfies U₁≤U₂Then the calculation formula adopted by the voltage feedforward is

If the total voltage on both sides of the bidirectional converter satisfies U₁>U₂Then the calculation formula adopted by the voltage feedforward is

Wherein, U₁Is said total voltage, U, of said first side of said bidirectional converter₂Is said total voltage, U, of said second side of said bidirectional converter_dutyFeeding forward the voltage.

Optionally, when the bidirectional converter is in a single-stage modulation mode or a dual-stage modulation mode, the control strategy is a current closed loop or a voltage-current dual closed loop.

A second aspect of the present invention discloses a bidirectional converter, including: the device comprises a controller, a detection module and a main circuit; wherein:

two sides of the main circuit are respectively used as a first side and a second side of the bidirectional converter, and the first side and the second side are respectively provided with corresponding total bus capacitors;

the controller is connected to the control end of the main circuit and the output end of the detection module, respectively, and is configured to execute the modulation method of the bidirectional converter according to any one of the first aspect of the present invention.

Optionally, the main circuit includes: the circuit comprises a first inductor, a second inductor, a first side branch and a second side branch;

the first side branch and the second side branch each include: the circuit comprises an upper bridge arm, a lower bridge arm, a positive half bus capacitor, a negative half bus capacitor, a positive relay and a negative relay;

the upper bridge arm is connected with the positive half bus capacitor in parallel, and the lower bridge arm is connected with the negative half bus capacitor in parallel;

the upper bridge arm and the lower bridge arm respectively comprise two inner pipes and two outer pipes which are connected in series, the connection point of the inner pipes and the outer pipes is used as the midpoint of the corresponding bridge arm, and the upper bridge arm and the lower bridge arm are connected in series through the inner pipes;

the middle points of the upper bridge arms are connected through the first inductors, and the middle points of the lower bridge arms are connected through the second inductors;

the positive relay is arranged on a positive bus between the corresponding bus capacitor and the positive half bus capacitor;

the negative relay is arranged on a negative bus between the corresponding bus capacitor and the negative half-bus capacitor.

Optionally, the positive relay and the negative relay are connected in parallel with a resistor and a diode which are connected in series;

the direction of the diode is the same as the current direction charged by the positive and negative half bus capacitors on the corresponding side.

As can be seen from the above technical solutions, a modulation method for a bidirectional converter according to the present invention includes: respectively detecting the total bus voltage at two sides of the bidirectional converter; judging whether the bidirectional converter meets the single-stage and double-stage modulation switching condition or not according to the total bus voltage on the two sides; when the bidirectional converter meets the switching condition of single-stage and double-stage modulation, the bidirectional converter is controlled to switch and modulate, and current feedforward and voltage feedforward are added during switching and modulating; after the switching modulation is completed, cutting off the current feed-forward; therefore, on the basis of the existing control strategy, duty ratio feedforward of output current and output voltage is increased at the moment of switching the modulation mode, and the stability of the output current and the output voltage can be ensured. In addition, a software control mode is adopted, the problem of cost increase caused by the adoption of a hardware circuit is solved, the control is simple and easy to realize, and the system stability is improved.

Drawings

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

FIG. 1 is a schematic diagram of a bi-directional DC/DC converter provided by an embodiment of the present invention;

fig. 2 is a flowchart of a modulation method of a bidirectional converter according to an embodiment of the present invention;

fig. 3 is a control block diagram of a modulation method of a bidirectional converter provided in the prior art;

fig. 4 is a control block diagram of a modulation method of a bidirectional converter according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, 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 some, but not all, embodiments of the present invention. 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 an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The embodiment of the invention provides a modulation method of a bidirectional converter, which is used for solving the problem that the stable operation of a system is influenced by the large fluctuation of output current and output voltage caused by single-stage and double-stage modulation switching in the prior art.

The modulation method of the bidirectional converter, see fig. 2, includes:

and S101, respectively detecting the total voltage on two sides of the bidirectional converter.

Specifically, a total voltage on a first side of the bidirectional converter is detected, and a total voltage on a second side of the bidirectional converter is detected.

The total voltage at two sides of the bidirectional converter can be respectively detected through the two voltage acquisition units; the specific detection process is not described herein any more, and is all within the scope of the application.

The bidirectional converter may be a bidirectional DC/DC converter as shown in fig. 1, and when the bidirectional converter is applied to an energy storage system, the total voltages on both sides thereof are a battery-side total voltage (a voltage between Vbat + and Vbat-as shown in fig. 1) and a bus-side total voltage (a voltage between Vbus + and Vbus-as shown in fig. 1), respectively.

And S102, judging whether the bidirectional converter meets the single-stage and double-stage modulation switching condition or not according to the total voltage on two sides of the bidirectional converter.

Specifically, the total voltages at two sides of the bidirectional converter can be compared, and when the ratio of the total voltages at two sides exceeds a preset range, the condition of switching from double-stage modulation to single-stage modulation can be met; when the ratio of the total voltages at the two sides is in a preset range, the condition of switching from single-stage modulation to double-stage modulation can be met; the preset range may refer to a range of about 1, such as [0.8, 1.25], or [0.9, 1.1], which is not specifically limited herein, and is within the protection scope of the present application as the case may be.

The above description is only an example, and the specific process of step S102 is not limited specifically here, and is within the scope of the present application as the case may be.

S103, when the bidirectional converter meets the single-stage and double-stage modulation switching condition, controlling the bidirectional converter to switch the modulation mode, and adding current feedforward and voltage feedforward when switching the modulation mode.

The bidirectional converter has two modulation modes, namely a single-stage modulation mode and a two-stage modulation mode; for example, the two-stage modulation mode is operated when the Vo is less than 0.9 and the Vin is less than 1.1, and the single-stage modulation mode is operated in other ranges; vin is the input voltage and Vo is the output voltage. During a two-stage modulation mode, the switching tubes on two sides of the bidirectional converter are subjected to chopping control: in the single-stage modulation mode, only the switching tube on one side of the bidirectional converter performs chopping control, for example, the switching tube on the high-voltage side performs chopping control.

In a single-stage modulation mode, when the difference between the total voltages at two sides of the bidirectional converter is small, the duty ratio is lost, so that the problem of large fluctuation of the output current and voltage is caused; when the mixed modulation strategy is switched in single-stage modulation and double-stage modulation, the output current and voltage fluctuation is large. Because the voltage stability is the premise of current stability, current feedforward and voltage feedforward are added at the moment of switching the modulation mode to supplement the duty ratio required by the current, so that the current and the voltage of the bidirectional converter are stable at the moment of switching the modulation mode.

And S104, cutting off current feedforward after the modulation mode is switched.

At the moment of switching the modulation mode, the current fluctuation of the bidirectional converter is large, and after the modulation mode is switched, the current of the bidirectional converter tends to be stable, so that the current feedforward can be cut off after the modulation mode is switched.

In practical application, the current feedforward only acts on one carrier period at the moment of switching the modulation mode; that is, the process of switching the modulation mode can be completed only by one carrier period, the current feedforward acts on one carrier period, the current of the bidirectional converter can be stably converted, and the stability of the output current can be ensured; the current feedforward quantity is zero in normal operation so as to ensure the dynamic response capability of the current and realize smooth transition of the current.

According to the modulation method of the bidirectional converter provided by the embodiment, the problem of current and voltage mutation caused by abnormal duty ratio in the single-stage and double-stage modulation switching process can be solved, and the operation stability of a system is improved. In addition, a software control mode is adopted, the problem of cost increase caused by the adoption of a hardware circuit is solved, the control is simple and easy to realize, and the system stability is improved.

In the above embodiment, the current feed-forward is added when the modulation mode is switched, and the specific implementation form is as follows: replacing the integral quantity (Vr as shown in FIG. 4) of the current loop regulator of the bidirectional converter with the current feed-forward; that is, at the moment of switching the modulation scheme, the integral amount of the current loop regulator of the bidirectional converter is cleared, and superimposed by current feedforward as the output amount of the current loop regulator, and after the switching of the modulation scheme is completed, the current feedforward is cut off to recover the integral amount Vr of the current loop regulator.

In practical applications, before the adding of the current feed-forward in step S103, the method further includes: a current feed forward is determined.

The specific process for determining the current feed-forward is as follows:

(1) and determining the switching parameters of the bidirectional converter according to the bridge arm inductance value, the switching time and the total voltage on the two sides of the bidirectional converter.

In practical application, the formula for determining the handover parameter is as follows:

wherein K is a switching parameter, L is a bridge arm inductance value, Deltat is a switching time, and U₁Is the total voltage of the first side of the bidirectional converter, U₂Is the total voltage on the second side of the bi-directional converter. That is, the switching parameter is proportional to the bridge arm inductance and inversely proportional to the switching time, the total voltage on the second side, and the total voltage on the first side.

Also taking the bidirectional converter of the energy storage system as an example, the formula used for determining the switching parameter at this time is as follows:

wherein, V_batIs the total voltage, V, of the battery side of the bidirectional converter_busIs the total voltage on the bus side of the bi-directional converter.

The application scenario of the bidirectional converter is not specifically limited herein, and may be determined according to the actual situation, which is within the protection scope of the present application.

(2) And obtaining current feedforward according to the actual current value and the switching parameter of the bidirectional converter.

Specifically, the specific working process of obtaining the current feedforward is as follows: the product of the actual current value of the bidirectional converter and the switching parameter is used as current feedforward. The formula adopted for obtaining the current feedforward is as follows:

I_duty＝K*I_fed；

wherein, I_dutyIs current feed-forward, which is associated with a reference direction; k is a switching parameter; i is_fedIs the actual current value. That is, the current feed-forward is positively correlated with the switching parameter and the actual current value; taking an actual current value as an example, the larger the actual current value is, the larger the current feedforward is, and the smaller the actual current value is, the smaller the current feedforward is; the same process is applied to the handover parameters, and the details are not repeated here.

It should be noted that the starting operation moment of the bidirectional converter is a special switching moment, at which the actual current value I of the bidirectional converter is_fedZero and then will gradually increase; that is, the current feed-forward I of the bidirectional converter at the moment of the start-up operation_dutyAlso zero, and then gradually increases again.

In the above embodiment, the voltage feedforward is added when the modulation mode is switched, and the specific implementation form is as follows: feeding forward the output of the current loop regulator of the bi-directional converter with this voltage (shown as U in FIG. 4)_dutyThe other input signal of the applied adder) to be added; that is, after the modulation mode switching is completed, a voltage feedforward matching the current modulation mode of the bidirectional converter is superimposed on the output quantity of the current loop regulator of the bidirectional converter.

The voltage feedforward may be an instantaneous calculation value when the modulation scheme is switched, or may be a real-time calculation value with higher interference resistance.

Whether the calculation value is real time calculation value or instantaneous calculation value, the result obtained by calculation is: at the moment of calculation, the ratio between the smaller and the larger of the total voltage across the bidirectional converter.

If the total voltage on two sides of the bidirectional converter satisfies U₁≤U₂Then the voltage feedforward is calculated by the formula

If the total voltage on two sides of the bidirectional converter satisfies U₁>U₂Then the voltage feedforward is calculated by the formula

Wherein, U₁Is the total voltage of the first side of the bidirectional converter, U₂Is the total voltage, U, of the second side of the bidirectional converter_dutyIs a voltage feed forward.

It should be noted that when the bidirectional converter is applied to an energy storage system, the total voltage on both sides of the bidirectional converter may be the total voltage on the battery side and the total voltage on the bus side. If the total voltage on both sides of the bidirectional converter satisfies V_bat≤V_busThen the voltage feedforward is calculated by the formulaIf the total voltage on both sides of the bidirectional converter satisfies V_bat>V_busThen the voltage feedforward is calculated by the formulaWherein, V_batIs the total voltage, V, of the battery side of the bidirectional converter_busIs the total voltage on the bus side of the bi-directional converter.

In the voltage feedforward formula, the larger value of the total voltages on the two sides of the bidirectional converter is used as the denominator, and the smaller value of the total voltages on the two sides of the bidirectional converter is used as the numerator, that is, the value of the voltage feedforward is less than or equal to 1.

In order to avoid the problem of large voltage fluctuation caused by voltage mismatch between the single-stage modulation mode and the two-stage modulation mode, preferably, when the bidirectional converter is in the two-stage modulation mode, voltage feedforward is also applied, so that small voltage fluctuation of the bidirectional converter is ensured, and the voltage stability of the bidirectional converter is ensured. In addition, when the bidirectional converter is in a single-stage modulation mode, the voltage fluctuation is small, so that when the bidirectional converter is in the single-stage modulation mode, voltage feedforward can be applied, such as a real-time calculated value, or the voltage feedforward can not be applied, namely the voltage feedforward is kept to be an instantaneous calculated value when the bidirectional converter enters the single-stage modulation mode; of course, the anti-interference performance of the applied voltage feedforward is strong, and the stability of the voltage and the current of the bidirectional converter can be further ensured, so the method is more preferable; whether or not to apply voltage feed forward is not specifically limited herein, and may be determined as the case may be, and is within the scope of the present application.

That is, after the modulation scheme switching is completed, step S104 further includes: the voltage feed forward applied to the bi-directional converter is matched to the current modulation mode of the bi-directional converter.

Specifically, a voltage feedforward corresponding to the single-stage modulation mode can be applied when the bidirectional converter is in the single-stage modulation mode; applying voltage feedforward corresponding to the two-stage modulation mode when the bidirectional converter is in the two-stage modulation mode; therefore, the voltage feedforward which is applied and matched under different modulation modes can be used for restraining the influence caused by voltage fluctuation, and the stability of the output voltage can be ensured at the switching moment. Thus, the voltage feedforward is always applied to the bidirectional converter, and only after each modulation mode switching, the voltage feedforward applied to the bidirectional converter needs to be matched with the current modulation mode of the bidirectional converter to obtain a more stable output voltage.

The following describes the values of the voltage feedforward in the case where the bidirectional converter is in the single-stage modulation mode and the bidirectional converter is in the two-stage modulation mode.

(1) When the bidirectional converter is in a single-stage modulation mode, the voltage feedforward is a real-time calculation value or an instantaneous calculation value when the bidirectional converter enters the single-stage modulation mode.

The real-time calculated values and instantaneous calculated values may be: at the moment of calculation, the ratio between the smaller and the larger of the total voltage across the bidirectional converter.

Specifically, if the total voltage on both sides of the bidirectional converter satisfies U₁≤U₂Then the voltage feedforward is calculated by the formula

If the total voltage on both sides of the bidirectional converter satisfies V_bat>V_busThen the voltage feedforward is calculated by the formula

Wherein, U₁Is the total voltage of the first side of the bidirectional converter, U₂Is the total voltage, U, of the second side of the bidirectional converter_dutyIs a voltage feed forward.

It should be noted that when the bidirectional converter is applied to an energy storage system, the total voltage on both sides of the bidirectional converter may be the total voltage on the battery side and the total voltage on the bus side. If the total voltage on both sides of the bidirectional converter satisfies V_bat≤V_busThen the voltage feedforward is calculated by the formulaIf the total voltage on both sides of the bidirectional converter satisfies V_bat>V_busThen the voltage feedforward is calculated by the formulaWherein, V_batIs the total voltage, V, of the battery side of the bidirectional converter_busIs the total voltage on the bus side of the bi-directional converter.

In the voltage feedforward formula, the larger value of the total voltages on the two sides of the bidirectional converter is used as the denominator, and the smaller value of the total voltages on the two sides of the bidirectional converter is used as the numerator, that is, the value of the voltage feedforward is less than or equal to 1.

(2) When the bidirectional converter is in a two-stage modulation mode, the voltage feedforward is a preset value.

When the bidirectional converter is in a two-stage modulation mode, in order to improve the voltage utilization rate and avoid the influence of dead zones, the value of voltage feedforward is fixed; it need not vary as the total voltage of the first side and the total voltage of the second side vary. The preset value can be in the range of 0.85-0.95; that is, a value within the range of 0.85 to 0.95 is taken as a preset value. The value of the preset value is not specifically limited herein, and may be determined according to actual conditions, all of which are within the protection scope of the present application.

In the above embodiment, when the bidirectional converter is in the single-stage modulation mode or the dual-stage modulation mode, the control strategy is a current closed loop or a voltage-current double closed loop.

The voltage and current double closed loop is taken as an example for explanation:

in the prior art, a bidirectional converter control strategy is a conventional voltage-current double closed-loop control strategy (as shown in fig. 3), and the problem of large fluctuation of output voltage and current cannot be solved when a modulation mode is switched.

In the present embodiment, as shown in fig. 4, the voltage-current dual feedforward smooth switching control strategy is adopted. Will schedule voltage command U_refWith the actual voltage value U_fedTaking difference, and PI regulation and I_maxAnd I_minFor boundary amplitude limiting control, obtaining a scheduling current instruction I_ref(ii) a Then the current instruction I is scheduled_refAnd the actual current value I_fedCalculating the difference, and performing PI regulation to obtain integral quantity V of the current loop regulator_r(ii) a Then, at the moment of switching modulation mode, at the integral value V_rAlternative to current feed-forward I_duty(ii) a And after a carrier period, feeding the current forward I_dutyCutting, i.e. controlling, the switch back-hanging integral V_rAt least one of (1) and (b); that is, the output of the current loop regulator is an integral quantity V under a certain modulation mode_rAnd current feed-forward I at the moment of switching modulation mode_duty(ii) a In addition, the output of the current loop regulatorVoltage feedforward U with matched magnitude superposition_duty(ii) a Finally, the corresponding pulse modulation wave PWM is obtained, and then the switching tube control of the corresponding side of the main circuit of the self is carried out by the pulse modulation wave PWM. Wherein, I_maxTo clip maximum, I_minIs the clipping minimum.

It is worth to be noted that, in the prior art, buck mode and boost mode are freely switched by adopting power-down switching or shutdown switching, which is feasible when the bidirectional DC/DC converter only operates in a current loop control mode, but is not feasible when the bidirectional DC/DC converter operates in a voltage-current dual-loop control mode and controls an output voltage.

In the embodiment, the smooth switching of the modulation mode is realized only by applying current feedforward and voltage feedforward; therefore, the problem of single-stage and double-stage modulation power reduction or shutdown switching is solved, the on-line smooth switching function of mixed modulation during full-power operation is realized, and the hybrid modulation on-line smooth switching device has a wider application range and is more beneficial to being widely pushed and used.

An embodiment of the present invention provides a bidirectional converter, see fig. 1, including: a controller (not shown), a detection module (not shown), and a main circuit 10; wherein:

two sides of the main circuit 10 are respectively used as a first side and a second side of the bidirectional converter, and the first side and the second side are respectively provided with corresponding total bus capacitors (shown as C in FIG. 1)_bat、C_pv) (ii) a Specific total bus capacitance C_batArranged on the first side and having a total bus capacitance C_pvIs arranged on the second side.

Specifically, taking a bidirectional converter of the energy storage system as an example, the first side of the main circuit 10 is connected to the battery pack as a battery side, that is, the positive electrode Vbat + of the battery side is connected to the positive electrode of the battery pack, and the negative electrode Vbat-of the battery side is connected to the negative electrode of the battery pack; the second side of the main circuit is a bus side, the second side positive electrode of the main circuit is a bus side positive electrode Vbus +, and the second side negative electrode of the main circuit is a bus side Vbus-.

The controller is connected to the control end of the main circuit and the output end of the detection module, respectively, and is configured to execute the modulation method of the bidirectional converter provided in any of the embodiments.

For details of the working process and principle of the modulation method of the bidirectional converter, reference may be made to the above embodiments, and details are not repeated here.

In the above embodiment, the main circuit 10 includes: the inductor comprises a first inductor L1, a second inductor L2, a first side branch (comprising D1, D2, D3, D4, Q1, Q2, Q3, Q4, K1, K2, C1 and C2 shown in FIG. 1) and a second side branch (comprising D5, D6, D7, D8, Q5, Q6, Q7, Q8, K3, K4, C3 and C4 shown in FIG. 1).

First side branch road and second side branch road all include: the circuit comprises an upper bridge arm, a lower bridge arm, a positive half bus capacitor, a negative half bus capacitor, a positive relay and a negative relay; the upper bridge arm is connected with the positive half bus capacitor in parallel, and the lower bridge arm is connected with the negative half bus capacitor in parallel; the upper bridge arm and the lower bridge arm respectively comprise an inner pipe and an outer pipe which are connected in series, the connection point of the inner pipe and the outer pipe is used as the midpoint of the corresponding bridge arm, and the upper bridge arm and the lower bridge arm are connected in series through the inner pipe; the middle points of the upper bridge arms are connected through a first inductor, and the middle points of the lower bridge arms are connected through a second inductor; the positive relay is arranged on a positive bus between the corresponding total bus capacitor and the positive half bus capacitor; the negative relay is arranged on a negative bus between the corresponding total bus capacitor and the negative half bus capacitor.

Specifically, in the first side branch, an upper bridge arm (including D1, D2, Q1 and Q2 shown in fig. 1) is connected in parallel with a positive half bus capacitor C1, and a lower bridge arm (including D3, D4, Q3 and Q4 shown in fig. 1) is connected in parallel with a negative half bus capacitor C2; the middle pipe Q1 and the inner pipe Q2 of the upper bridge arm are connected in series, and the connection point is used as the midpoint of the upper bridge arm; the inner pipe Q3 and the outer pipe Q4 in the lower bridge arm are connected in series, the connection point is used as the midpoint of the lower bridge arm, and the inner pipe Q2 of the upper bridge arm and the inner pipe Q3 of the lower bridge arm are connected in series; the middle point of the upper bridge arm is connected with one end of a first inductor L1, and the middle point of the lower bridge arm is connected with one end of a second inductor L2; the positive relay K1 is arranged on the total bus capacitor C_batAnd the positive half bus capacitor C1; the negative relay K2 is arranged on the total bus capacitor C_batAnd negative half bus capacitance C2.

In the second side branch, an upper bridge arm (comprising D5, D6, Q5 and Q6 shown in FIG. 1) is connected in parallel with a positive half bus capacitor C3, and a lower bridge arm (comprising D7, D8, Q7 and Q8 shown in FIG. 1) is connected in parallel with a negative half bus capacitor C4; the middle pipe Q5 and the inner pipe Q6 of the upper bridge arm are connected in series, and the connection point is used as the midpoint of the upper bridge arm; the inner pipe Q7 and the outer pipe Q8 in the lower bridge arm are connected in series, the connection point is used as the midpoint of the lower bridge arm, and the inner pipe Q6 of the upper bridge arm and the inner pipe Q7 of the lower bridge arm are connected in series; the midpoint of the upper bridge arm is connected with the other end of the first inductor L1, and the midpoint of the lower bridge arm is connected with the other end of the second inductor L2; the positive relay K3 is arranged on the total bus capacitor C_pvAnd the positive half bus capacitor C3; the negative relay K2 is arranged on the total bus capacitor C_pvAnd negative half bus capacitance C4.

It should be noted that each diode is connected in parallel to a corresponding switch tube. Specifically, the diode D1 is connected in parallel with the switching tube Q1, the diode D2 is connected in parallel with the switching tube Q2, the diode D3 is connected in parallel with the switching tube Q3, the diode D4 is connected in parallel with the switching tube Q4, the diode D5 is connected in parallel with the switching tube Q5, the diode D6 is connected in parallel with the switching tube Q6, the diode D7 is connected in parallel with the switching tube Q7, and the diode D8 is connected in parallel with the switching tube Q8.

In practical application, the positive relay and the negative relay are connected in parallel with a resistor and a diode which are connected in series, so that a slow-start function with backflow prevention is realized; the direction of the diode is the same as the current direction charged by the positive and negative half bus capacitors on the corresponding side.

Specifically, one end of the positive relay K1 is connected to one end of the resistor R1 and one end of the positive half bus capacitor C1, and the other end of the positive relay K1 is connected to the anode of the diode KD1 and the total bus capacitor C_batIs connected to the other end of the diode KD1, the cathode of the diode KD1 being connected to one end of a resistor R1; one end of a negative relay K2 is respectively connected with one end of a resistor R2 and one end of a negative half bus capacitor C2, and the other end of the negative relay K2 is respectively connected with the cathode of a diode KD2 and a total bus capacitor C_batAnd the anode of diode KD2 is connected to one end of a resistor R2.

Positive relay KOne end of the positive relay K3 is connected with one end of a resistor R3 and a total bus capacitor C3, and the other end of the positive relay K3 is connected with the cathode of the diode KD3 and one end of a positive half bus capacitor C3 respectively_pvIs connected to the other end of the diode KD3, the anode of the diode KD3 being connected to one end of a resistor R3; one end of a negative relay K4 is respectively connected with the anode of the diode KD4 and one end of the negative half bus capacitor C4, and the other end of the negative relay K4 is respectively connected with one end of the resistor R4 and the total bus capacitor C_pvAnd the cathode of diode KD4 is connected to one end of a resistor R4.

Features described in the embodiments in the present specification may be replaced with or combined with each other, and the same and similar portions among the embodiments may be referred to each other, and each embodiment is described with emphasis 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 the present 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.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present 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.