Current control method and system for inverters

Abstract

The application discloses a current control method and system of an inverter, and the current control method comprises the following steps: determining the deviation between a given current and a single-phase output current; taking the deviation between the given current and the single-phase output current as a static coordinate system alpha-axis input quantity, and setting a static coordinate system beta-axis input quantity as 0; after transformation from the static coordinate system to a rotating coordinate system, obtaining a dq-axis current deviation in the rotating coordinate system, so as to control the single-phase inverter after adjustment by a PI current controller. When the PI current controller is used for control in the case that the power grid is weak, no static error can be followed between the given current and the feedback current, and the dynamic performance is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of control, in particular to a current control method and system of an inverter. BACKGROUND

[0002] Single-phase inverters are widely used in photovoltaic power generation, electromagnetic stirring, vehicle charging and other fields due to their simple structure, flexible modulation strategy and bidirectional energy flow.

[0003] At present, the control method of the single-phase inverter is mainly implemented in the stationary coordinate system, and the given and feedback are sinusoidal, and the PI controller selected for the sinusoidal given has a steady-state error. For some electromagnetic stirrers and other occasions, two-phase currents are required to be output, and the phases of the two-phase currents are 90° apart. If the two-phase currents are controlled separately in the stationary coordinate system, there will still be a steady-state error between the actual current and the given current, which will affect the current control effect.

[0004] Three-phase inverters that are controlled in the rotating coordinate system have been widely used. Since the given and feedback are direct current components, the PI controller can be used to follow without steady-state error. However, when the single-phase sinusoidal quantity is converted to the rotating coordinate system, there is still an alternating current on the dq axis. The common method is to virtually generate another orthogonal alternating current by delaying 90°, but the delay method has poor dynamic performance. If the given signal is virtually generated by a generalized second-order integral, the implementation is more complex. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a current control method and system of an inverter to solve the problem of steady-state error when the existing single-phase inverter and two-phase orthogonal inverter are controlled in the stationary coordinate system.

[0006] The technical solution adopted by the present application to solve the above technical problems is as follows:

[0007] According to one aspect of the present application, a current control method of a single-phase inverter is provided, the method comprising:

[0008] determining the deviation between the given current and the single-phase output current;

[0009] the deviation between the given current and the single-phase output current is used as the stationary coordinate system α-axis input quantity, and the stationary coordinate system β-axis input quantity is set to 0;

[0010] After the transformation from the stationary coordinate system to the rotating coordinate system, the dq-axis current deviation in the rotating coordinate system is obtained, and the single-phase inverter is controlled after being adjusted by the PI current controller.

[0011] According to an aspect of the present application, a current control system of a single-phase inverter is provided, comprising a first coordinate transformation module, a PI current controller, a second coordinate transformation module, a PWM modulation module and a sampling module;

[0012] The first coordinate transformation module is configured to output a dq-axis current deviation in a rotating coordinate system; wherein an α-axis input of the first coordinate transformation module is a deviation between a given current and a single-phase output current, and a β-axis input is set to 0;

[0013] The PI current controller is configured to adjust the dq-axis current deviation to control the single-phase inverter;

[0014] The second coordinate transformation module is configured to obtain αβ-axis command voltages in a stationary coordinate system by transforming the dq-axis command voltages output by the PI current controller from the rotating coordinate system to the stationary coordinate system;

[0015] The PWM modulation module is configured to determine a duty cycle of a switch tube in the single-phase inverter according to the α-axis command voltage;

[0016] The sampling module is configured to sample the single-phase output current of the single-phase inverter.

[0017] According to an aspect of the present application, a current control method of a two-phase orthogonal inverter is provided, comprising:

[0018] The two-phase output currents are respectively taken as α-axis and β-axis inputs in a stationary coordinate system;

[0019] After transformation from the stationary coordinate system to a rotating coordinate system, a dq-axis current deviation in the rotating coordinate system is determined according to given current components, and the two-phase orthogonal inverter is controlled after adjustment by a PI current control unit.

[0020] According to another aspect of the present application, a current control system of a two-phase orthogonal inverter is provided, comprising a first coordinate transformation unit, a determination unit, a PI current control unit, a second coordinate transformation unit, a PWM modulation unit, a first sampling unit and a second sampling unit;

[0021] The first coordinate transformation unit is configured to output dq-axis current components in a rotating coordinate system; wherein an α-axis input of the first coordinate transformation unit is a first-phase output current, and a β-axis input is a second-phase output current;

[0022] The determination unit is configured to determine a dq-axis current deviation in the rotating coordinate system according to the dq-axis current components in the rotating coordinate system and given current components;

[0023] The PI current control unit is configured to adjust a dq-axis current deviation to control the two-phase orthogonal inverter.

[0024] The second coordinate transformation unit is configured to obtain αβ-axis command voltages in a stationary coordinate system by transforming the dq-axis command voltages output by the PI current control unit from a rotating coordinate system to the stationary coordinate system.

[0025] The PWM modulation unit is configured to determine duty cycles of the switching tubes in the two-phase orthogonal inverter according to the αβ-axis command voltages.

[0026] The first sampling unit is configured to sample a first-phase output current of the two-phase orthogonal inverter.

[0027] The second sampling unit is configured to sample a second-phase output current of the two-phase orthogonal inverter.

[0028] The current control method and system of the inverter provided by the embodiments of the present application can realize no static error following between a given current and a feedback current and good dynamic performance when a PI current controller is used for control. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The current control method of the single-phase inverter provided by the embodiments of the present application is shown in the figure.

[0030] Figure 2 The current control system block diagram of the single-phase inverter provided by the embodiments of the present application is shown in the figure.

[0031] Figure 3 The current control method of the two-phase orthogonal inverter provided by the embodiments of the present application is shown in the figure.

[0032] Figure 4 The current control system block diagram of the two-phase orthogonal inverter provided by the embodiments of the present application is shown in the figure.

[0033] Figure 5 The bridge arm driving signal generation diagram provided by the embodiments of the present application is shown in the figure.

[0034] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0035] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear, explicit and understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0036] Embodiment 1:

[0037] The variables and their definitions involved in the embodiments of the present application are shown as follows:

[0038] Amplitude of the given current;

[0039] ω: Frequency of the given current;

[0040] θ: Angle for coordinate transformation;

[0041] Instantaneous value of the given current;

[0042] i L : Single-phase output current value;

[0043] Δi L : Deviation of the given current from the single-phase output current;

[0044] Δi d : Deviation of the given current from the single-phase output current transformed to the current deviation on the d-axis;

[0045] Δi q : Deviation of the given current from the single-phase output current transformed to the current deviation on the q-axis;

[0046] K p : PI current controller proportional parameter on the dq-axis;

[0047] K i : PI current controller integral parameter on the dq-axis;

[0048] V d_PI : d-axis PI current controller output;

[0049] V q_PI : q-axis PI current controller output;

[0050] V d_ffd : d-axis feedforward voltage;

[0051] V q_ffd : q-axis feedforward voltage;

[0052] d-axis command voltage;

[0053] q-axis command voltage;

[0054] α-axis command voltage;

[0055] β-axis command voltage;

[0056] d a : Duty cycle of the upper switch tube of the first bridge arm in the H-bridge;

[0057] d b : duty cycle of the upper switch of the second bridge arm in the H-bridge.

[0058] A current control method of a single-phase inverter, wherein the single-phase inverter comprises an H-bridge circuit, and an output end of the H-bridge circuit is provided with a filter inductor L, and RL is an equivalent resistance of the filter inductor L. The current control method comprises the following steps:

[0059] In step S11, a deviation between a given current and a single-phase output current is determined.

[0060] Specifically, the determination of the deviation between the given current and the single-phase output current comprises:

[0061] An angle for coordinate transformation is determined.

[0062] According to the angle for coordinate transformation, the deviation between the given current and the single-phase output current is obtained.

[0063] The angle for coordinate transformation θ can be obtained by integrating the frequency ω of the given current, or the angle for coordinate transformation θ can be obtained by a grid phase-locked loop when the single-phase inverter output is connected to the grid through the inductor.

[0064] The instantaneous value of the given current is The deviation between the given current and the single-phase output current is Wherein, is a bias angle, which can be set to any angle; the single-phase output current i L The single-phase output current i

[0065] In step S12, the deviation between the given current and the single-phase output current is taken as an α-axis input quantity in a stationary coordinate system, and a β-axis input quantity in the stationary coordinate system is set to 0.

[0066] In step S13, after transformation from the stationary coordinate system to a rotating coordinate system, a dq-axis current deviation in the rotating coordinate system is obtained, and the single-phase inverter is controlled after adjustment by a PI current controller.

[0067] Wherein, the transformation formula is Wherein, Δi d , Δi q is the dq-axis current deviation in the rotating coordinate system.

[0068] After adjustment by the PI current controller, the dq-axis current deviation Δi d , Δi q is obtained. Wherein, the dq-axis component Δi d , Δi qAfter the PI current controller adjustment, the output is wherein K p , K i are the proportional, integral coefficients of the current loop respectively.

[0069] The dq-axis command voltage After the transformation from the rotating coordinate system to the stationary coordinate system, the αβ-axis command voltage in the stationary coordinate system is obtained wherein the transformation formula is

[0070] According to the α-axis command voltage The duty cycle of the switch tube in the single-phase inverter is determined. Wherein, the β-axis command voltage is discarded.

[0071] The upper switch tube duty cycle d a , d b of the first bridge arm and the second bridge arm of the H-bridge circuit is as follows: The lower switch tube duty cycle is complementary to the upper tube.

[0072] The following describes the current control system block diagram of the single-phase inverter shown in Figure 2 .

[0073] As shown in Figure 2 , I is the amplitude of the given current, ω is the frequency of the given current, and θ is the angle for coordinate transformation. Wherein: The instantaneous value of the given current

[0074] is:

[0075] The deviation between the given current and the single-phase output current is: The single-phase output current i L can be obtained by sampling through a sampling module, such as a current sensor.

[0076] The deviation between the given current and the single-phase output current is taken as the stationary coordinate system α-axis input, and the stationary coordinate system β-axis input is set to 0; through the first coordinate transformation module (shown as αβ / dq in the figure), after the transformation from the stationary coordinate system to the rotating coordinate system, the obtained dq-axis current deviation is:

[0077]

[0078] That is

[0079] The dq-axis current deviation Δi d , Δi q is adjusted through the PI current controller, and the PI current controller output is: V​d_PI = K p (Δi d )+ K i ∫(Δi d )dt, V q_PI = K p (Δi q )+ K i ∫(Δi q )dt.

[0080] The dq-axis instruction voltage is: wherein, V d_ffd and V q_ffd are feedforward voltages, for the case that the single-phase inverter output is connected to the inductance only, V d_ffd and V q_ffd are both 0. If the single-phase inverter output is connected to the inductance and then to the power grid, V d_ffd and V q_ffd are the dq-axis components obtained by coordinate transformation of the power grid voltage. The advantage of using the feedforward voltage is that the output of the PI current controller can be kept around 0, and the main component of the given voltage in the dq-axis is provided by the feedforward voltage, which improves the dynamic performance of the current control.

[0081] The dq-axis instruction voltage is transformed from the rotating coordinate system to the stationary coordinate system through the second coordinate transformation module (shown as dq / αβ in the figure), and the αβ-axis instruction voltage obtained is wherein, the β-axis instruction voltage is discarded, and only the α-axis instruction voltage

[0082] The PWM modulation module is used to determine the duty cycle of the switch tube in the single-phase inverter according to the α-axis instruction voltage.

[0083] The upper switch tube duty cycle of the first bridge arm and the second bridge arm of the H-bridge circuit is: The lower switch tube duty cycle is complementary to the upper switch tube duty cycle.

[0084] When the PWM is generated, the modulation signal is proportional to the duty cycle, and the ratio is the peak value of the triangular carrier. For the generation of the PWM signal of a certain bridge arm, reference can be made to Figure 5 .

[0085] Embodiment 2:

[0086] The variables involved in the embodiments of the application and their definitions are shown as follows:

[0087] ω: frequency of the given current;

[0088] θ: angle for coordinate transformation;

[0089] d-axis given current

[0090] q-axis given current

[0091] i α : A-phase output current value

[0092] i β : B-phase output current value

[0093] i d : output current i α , i β d-axis component transformed into a rotating coordinate system

[0094] i q : output current i α , i β q-axis component transformed into a rotating coordinate system

[0095] Δi d : d-axis current deviation

[0096] Δi q : q-axis current deviation

[0097] K p : PI current control unit proportional parameter

[0098] K i : PI current control unit integral parameter

[0099] d-axis command voltage

[0100] q-axis command voltage

[0101] α-axis command voltage

[0102] β-axis command voltage

[0103] d a : first bridge arm upper tube duty ratio

[0104] d b : second bridge arm upper tube duty ratio

[0105] d c : third bridge arm upper tube duty ratio

[0106] A current control method of a two-phase orthogonal inverter, wherein the two-phase current output by the two-phase orthogonal inverter is a sine wave, and the phase difference is 90°; the two-phase orthogonal inverter includes a two-phase three-bridge-arm inverter circuit, and the output end has a filter inductor L, R LThe equivalent resistance of the filter inductor L. It should be noted that the two-phase orthogonal inverter is not limited to the two-phase three-bridge arm inverter circuit.

[0107] The current control method comprises:

[0108] In step S21, the two-phase output currents are taken as the α-axis input and the β-axis input of the stationary coordinate system respectively.

[0109] Specifically, the two-phase output currents can be sampled by a current sensor.

[0110] In step S22, after the transformation from the stationary coordinate system to the rotating coordinate system, the dq-axis current deviation in the rotating coordinate system is determined according to the given current components, and the two-phase orthogonal inverter is controlled after being adjusted by a PI current control unit.

[0111] The angle θ for coordinate transformation is determined; and similarly to the foregoing, the angle θ for coordinate transformation can be obtained by integrating the frequency ω of the given current.

[0112] According to the angle θ for coordinate transformation, the dq-axis components in the rotating coordinate system are obtained by the following transformation formula: d , i q ;

[0113] wherein i α , i β are the αβ-axis inputs of the stationary coordinate system.

[0114] According to the dq-axis given current and the dq-axis components i d , i q , the dq-axis current deviation Δi d , Δi q is obtained.

[0115] After the dq-axis current deviation Δi d , Δi q is adjusted by a PI current control unit, the dq-axis command voltage

[0116] The output of the PI current control unit is wherein K p , K i are the proportional and integral coefficients of the current loop respectively.

[0117] After the dq-axis command voltage is transformed from the rotating coordinate system to the stationary coordinate system, the αβ-axis command voltage in the stationary coordinate system is obtained.

[0118] wherein the transformation formula is

[0119] According to the αβ axis instruction voltage The duty cycles of the switching tubes in the two-phase orthogonal inverter are determined.

[0120] Wherein, the duty cycles d a , d b , d c of the switching tubes in the first bridge arm, the second bridge arm and the third bridge arm of the two-phase orthogonal inverter (assuming a two-phase three-bridge-arm inverter circuit) are determined. d q The driving signal of the lower switching tube is complementary to that of the upper switching tube.

[0121] When the PWM signal is generated, the modulation signal is proportional to the duty cycle, and the ratio is the peak value of the triangular carrier. For a certain bridge arm PWM signal generation, see Figure 5 .

[0122] The following is described in conjunction with the current control system block diagram of the two-phase orthogonal inverter shown in Figure 4 :

[0123] The output current of the two-phase orthogonal inverter is sampled by the first sampling unit and the second sampling unit, such as a current sensor; the two-phase output current is taken as the α-axis input and the β-axis input of the stationary coordinate system, respectively.

[0124] According to the angle θ for coordinate transformation, the dq-axis components i α , i β in the rotating coordinate system are obtained through the first coordinate transformation unit (αβ / dq shown in the figure) from the stationary coordinate system to the rotating coordinate system.

[0125] Wherein, i α , i β are the αβ-axis inputs of the stationary coordinate system.

[0126] Then, the dq-axis current deviations Δi d , Δi q in the rotating coordinate system are determined by the determination unit according to the dq-axis current components i α , i β in the rotating coordinate system and the given current components . d q

[0127] After the dq-axis current deviations Δi d , Δi q are adjusted by the PI current control unit, the dq-axis instruction voltages

[0128] The output of the PI current control unit is Wherein, K p , K iThe proportional and integral coefficients of the current loop, respectively.

[0129] The dq-axis command voltage Through the second coordinate transformation unit (shown as dq / αβ in the figure), after the transformation from the rotating coordinate system to the stationary coordinate system, the αβ-axis command voltage in the stationary coordinate system is obtained

[0130] The transformation formula is

[0131] The PWM modulation unit determines the duty ratios of the switching tubes in the two-phase orthogonal inverter according to the αβ-axis command voltage

[0132] The switching tube duty ratios d a , d b , and d c of the first bridge arm, the second bridge arm, and the third bridge arm in the two-phase orthogonal inverter (assuming a two-phase three-bridge-arm inverter circuit) are determined according to the αβ-axis command voltage The drive signal of the lower switching tube is complementary to that of the upper tube.

[0133] The preferred embodiments of the present application are described above with reference to the accompanying drawings, and the scope of the right of the present application is not limited by this. Any modification, equivalent replacement, and improvement made by those skilled in the art without departing from the scope and essence of the present application shall be within the scope of the right of the present application.​

Claims

1. A current control method for a single-phase inverter, characterized in that, The method includes: Determine the deviation between the given current and the single-phase output current; The deviation between the given current and the single-phase output current is used as the input quantity of the α-axis of the stationary coordinate system, while the input quantity of the β-axis of the stationary coordinate system is set to 0. After the transformation from the stationary coordinate system to the rotating coordinate system, the dq axis current deviation in the rotating coordinate system is obtained, which is then adjusted by the PI current controller to control the single-phase inverter. Determining the deviation between the given current and the single-phase output current includes: Determine the angles used for coordinate transformation; The deviation between the given current and the single-phase output current is obtained based on the angle used for coordinate transformation; The deviation between the given current and the single-phase output current is determined by the following formula: Where, Δi L The deviation between the given current and the single-phase output current. Let θ be the instantaneous value of the given current, and θ be the angle used for coordinate transformation. The offset angle, For a given current amplitude, i L This is the single-phase output current value.

2. The method according to claim 1, characterized in that, Determining the angle used for coordinate transformation includes: The angle used for coordinate transformation is obtained by integrating the frequency of the given current; or, the angle used for coordinate transformation is obtained from the phase-locked loop of the power grid.

3. The method according to claim 1, characterized in that, The transformation formula from the stationary coordinate system to the rotating coordinate system is: Where, Δi L The deviation between the given current and the single-phase output current, θ is the angle used for coordinate transformation, and Δi d For the d-axis current deviation in the rotating coordinate system, Δi q This represents the q-axis current deviation in the rotating coordinate system.

4. The method according to claim 1, characterized in that, The control of the single-phase inverter after adjustment by the PI current controller includes: The dq-axis current deviation in the rotating coordinate system is adjusted by a PI current controller to obtain the dq-axis command voltage. The command voltage of the dq axis is transformed from the rotating coordinate system to the stationary coordinate system to obtain the command voltage of the αβ axis in the stationary coordinate system. The duty cycle of the switching transistors in the single-phase inverter is determined based on the α-axis command voltage.

5. A current control system for a single-phase inverter, characterized in that, It includes a first coordinate transformation module, a PI current controller, a second coordinate transformation module, a PWM modulation module, and a sampling module; The first coordinate transformation module is used to output the dq-axis current deviation in the rotating coordinate system; wherein, the α-axis input of the first coordinate transformation module is the deviation between the given current and the single-phase output current, and the β-axis input is set to 0; determining the deviation between the given current and the single-phase output current includes: determining the angle used for coordinate transformation; obtaining the deviation between the given current and the single-phase output current based on the angle used for coordinate transformation; the deviation between the given current and the single-phase output current is determined by the following formula: Where, Δi L The deviation between the given current and the single-phase output current. Let θ be the instantaneous value of the given current, and θ be the angle used for coordinate transformation. The offset angle, For a given current amplitude, i L This is the single-phase output current value; The PI current controller is used to adjust the dq axis current deviation in order to control the single-phase inverter. The second coordinate transformation module is used to transform the dq-axis command voltage output by the PI current controller from the rotating coordinate system to the stationary coordinate system to obtain the αβ-axis command voltage in the stationary coordinate system. The PWM modulation module is used to determine the duty cycle of the switching transistors in the single-phase inverter based on the α-axis command voltage. The sampling module is used to sample the single-phase output current of the single-phase inverter.

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