Bidirectional AC-DC converter capable of realizing active power decoupling

Abstract

The invention discloses a bidirectional AC-DC converter capable of realizing active power decoupling, and belongs to the technical field of power electronic converters. The circuit comprises a main loop and a control unit, the main circuit unit is provided with a single-phase full-bridge power unit and an active power decoupling unit, and the active power decoupling unit is composed of two switching tubes, a decoupling inductor and two split capacitors. During rectification, a voltage outer loop and a current inner loop double closed loop are used for controlling an input power factor, stabilizing an output voltage and tracking a power grid voltage; inverting adopts double closed loops of a capacitive current inner loop and a grid-connected current outer loop and power grid voltage proportion feedforward control, and it is guaranteed that the grid-connected current rapidly follows the power grid voltage. Frequency doubled power is generated by controlling capacitance voltage fundamental frequency fluctuation of the split type power decoupling circuit, and the power difference between the alternating current side and the direct current side is compensated. Parameters are calculated according to a theoretical formula, a switching tube tracks a reference to realize frequency doubling power balance, a thin-film capacitor can be used for replacing an electrolytic capacitor, the cost is reduced, the power density is improved, and the performance is excellent and the application prospect is wide through verification of various oscillogram.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic converters, and in particular relates to a bidirectional AC-DC converter with an active power decoupling function and a control method thereof. Background Art

[0002] In industrial production, the energy consumption generated by motors accounts for the majority of total energy consumption. With the continuous development of frequency conversion technology, it has brought hope to the energy-saving goals in the industrial field. In some special motor speed control systems, frequent braking is required, and the energy of these general frequency converters cannot be recovered, which causes the capacitor on the DC bus to generate a pumped voltage due to the reverse flow of energy. The motor feedback energy will cause the bus capacitor voltage to pump up. The energy feedback function in the motor speed control system can be realized through a bidirectional AC-DC converter.

[0003] Since the DC side of the bidirectional AC-DC converter will generate twice the power frequency ripple power, the traditional way is to connect a large-capacity electrolytic capacitor in parallel on the DC side to absorb the ripple power. However, electrolytic capacitors have a short life, poor safety performance, and a high device failure rate. They not only occupy a large volume of the converter, but also affect the dynamic performance of the system. In comparison, film capacitors have a long life and high reliability, but are limited by the manufacturing process and their capacitance is generally small. Therefore, it is necessary to design an active power decoupling circuit to absorb the twice power frequency voltage ripple on the DC bus, thereby reducing the DC bus capacitance value, and using film capacitors instead of electrolytic capacitors.

[0004] The commonly used topologies for active power decoupling are mainly divided into Buck type, Boost type and other decoupling circuits. However, for the Buck type decoupling circuit, the capacitor voltage of the decoupling circuit in this topology must be lower than the DC bus voltage and the capacitor value is relatively large. In addition, the device current stress is large and the system efficiency is low; while in the Boost type decoupling circuit, the capacitor voltage of the decoupling circuit must be higher than the DC bus voltage. In the system with a large bus voltage, this undoubtedly increases the voltage stress of the capacitor and power device. In contrast, this paper adopts a capacitor split power decoupling circuit. The split capacitors C1 and C2 have the dual functions of reducing the double frequency ripple power and filtering the switching frequency ripple, further eliminating the DC bus filter capacitor. The ripple power is buffered by the split capacitors C1 and C2, and the capacitor voltage waveform is adjusted by controlling switches Q5 and Q6. The control method is relatively easy to implement. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] In the first aspect, an embodiment of the present invention provides a grid-connected inverter power decoupling control system based on active damping, which includes a device housing, in which a circuit board is arranged, and the circuit board includes a control unit and a main circuit unit; the main circuit unit includes a single-phase full-bridge power inverter unit and a power decoupling unit; the parallel decoupling unit is composed of two switching tubes, a decoupling inductor and a decoupling capacitor, and is connected in parallel to the input DC voltage source Vbus side through the two switching tubes.

[0007] As a preferred solution of the bidirectional AC-DC converter capable of realizing active power decoupling described in the present invention, the control implementation method of the bidirectional AC-DC converter is as follows: the rectification mode uses a voltage outer loop and a current inner loop dual closed-loop control to realize the correction of the input power factor. The voltage outer loop controls the output voltage to ensure that the voltage on the output DC bus is stable near the set value. The current inner loop controls the input current to ensure that the input current tracks the grid voltage. While the inverter mode uses the current double closed loop of the capacitor current inner loop and the grid-connected current outer loop, the grid voltage proportional feedforward control is used to suppress the influence of the grid voltage on the grid current, so that the grid-connected current can quickly follow the grid voltage.

[0008] As a preferred solution of the bidirectional AC-DC converter capable of realizing active power decoupling described in the present invention, the active power decoupling method generates base frequency fluctuations by controlling the capacitor voltage in the capacitor splitting power decoupling circuit, thereby generating double frequency power to compensate for the difference power between the average power on the DC side and the instantaneous power on the AC side. Taking the rectification direction as an example, the formula for the double frequency pulsating power that needs to be suppressed is as follows:

[0009]

[0010] Among them, v g 、i g are the AC input voltage and current, V g ,I g are the amplitudes of the AC input voltage and current, the AC angular frequency ω=100π, and the phase difference satisfy AC input power p g The expression is:

[0011]

[0012] For the power frequency component in the circuit, assume the filter inductor L f =L1+L g , filter inductor L f And filter capacitor C f The expressions of instantaneous power on are:

[0013]

[0014] The input power expressions of the full-bridge side of the single-phase AC / DC converter are:

[0015]

[0016] Among them, DC output power is a constant power, corresponding to the instantaneous power p of twice the power frequency ripple r The expression is:

[0017]

[0018] Among them, the instantaneous power amplitude of the double power frequency ripple is P r The expression of the phase ψ is:

[0019]

[0020] As a preferred solution of the bidirectional AC-DC converter capable of realizing active power decoupling described in the present invention, the voltage of the split capacitors C1 and C2 needs to present fundamental frequency fluctuation.

[0021] The voltage expression of split capacitors C1 and C2 is:

[0022]

[0023] Among them, V bus is the DC bus voltage, V C is the amplitude of the voltage fundamental frequency component, θ is the phase of the voltage fundamental frequency component, at this time, the current flowing into the decoupling inductor L d The current expression is:

[0024]

[0025] Among them, i C1 、i C2 are the currents flowing into the split capacitors C1 and C2 respectively. Both the split capacitors and the decoupling inductors generate double frequency power. The corresponding power expression is:

[0026]

[0027] In order to suppress the double frequency power fluctuation on the DC side, it is necessary to achieve the balance between the active power decoupling circuit and the double frequency power output on the AC side, that is, to satisfy the expression p r =p Cd +p Ld ,Right now:

[0028]

[0029] By solving the equation, we can get V CThe switches Q1 and Q2 control the capacitor voltage and the decoupling inductor current to track this reference, achieving double frequency power balance, that is, the amplitude of the voltage fundamental frequency component V C The phase θ of the voltage fundamental frequency component satisfies the expression:

[0030]

[0031] Among them, the expressions corresponding to A and B are:

[0032]

[0033] Therefore, as long as the theoretical value of the decoupling current in the decoupling inductor can be tracked, the twice power frequency ripple power of the bidirectional AC-DC converter can be transferred to the split capacitors C1 and C2, and the problem of instantaneous power imbalance between the AC and DC sides of the bidirectional AC-DC converter can be solved, effectively suppressing the secondary ripple voltage on the DC side.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a circuit topology diagram of an embodiment of a bidirectional AC-DC converter capable of realizing active power decoupling according to the present invention in Embodiment 1.

[0036] Figure 2 1 is a transfer function diagram of the rectification mode of the bidirectional AC-DC converter embodiment capable of realizing active power decoupling of the present invention in Embodiment 1.

[0037] Figure 3 1 is a transfer function diagram of the inverter mode of the bidirectional AC-DC converter embodiment capable of realizing active power decoupling of the present invention in Embodiment 1.

[0038] Figure 4 This is the PSIM waveform diagram a of the rectification mode in Example 1.

[0039] Figure 5 This is the PSIM waveform diagram b of the rectification mode in Example 1.

[0040] Figure 6 This is the PSIM waveform diagram a of the inverter mode in Example 1.

[0041] Figure 7 This is the PSIM waveform diagram b of the inverter mode in Example 1.

[0042] Figure 8 This is working mode a of the active power decoupling part in Example 1.

[0043] Fig. 9This is the working mode b of the active power decoupling part in Example 1.

[0044] Fig.10 FIG. 4 is a transfer function diagram of the active power decoupling part control method in Example 1.

[0045] Fig.11 This is the PSIM waveform diagram of the active power decoupling part in Example 1. DETAILED DESCRIPTION

[0046] Reference Figure 1 to Figure 3 , which is the first embodiment of the present invention, provides a bidirectional AC-DC converter capable of realizing active power decoupling, including a main circuit unit and a control unit; the main circuit unit includes a single-phase full-bridge power unit and an active power decoupling unit; the active power decoupling unit is composed of two switching tubes, a decoupling inductor and two split capacitors.

[0047] Furthermore, the active power decoupling unit includes a MOS tube S5 and a MOS tube S6, and the two MOS tubes are connected in parallel on one side of the DC bus voltage; the MOS tube S5 and the MOS tube S6 form a half-bridge bridge arm; the active power decoupling unit includes split capacitors C1 and C2, and the two capacitors are connected in parallel on one side of the DC bus voltage; the midpoint of the bridge arm and the midpoint of the split capacitor are connected through a decoupling inductor Ld; the single-phase full-bridge power unit includes an AC power supply and four fully-controlled switching devices S1-S4, and an LCL filter.

[0048] like Figure 1 As shown, the power unit is connected to the grid Vg through a grid-connected LCL filter to form a single-phase full bridge.

[0049] Preferably, the rectification mode of the bidirectional AC-DC converter utilizes dual closed-loop control of a voltage outer loop and a current inner loop to realize input power factor correction. The voltage outer loop controls the output voltage to ensure that the voltage on the output DC bus is stable near the set value, and the current inner loop controls the input current to ensure that the input current tracks the grid voltage. The inverter mode utilizes a current double closed-loop of a capacitor current inner loop and a grid-connected current outer loop, while utilizing grid voltage proportional feedforward control to suppress the influence of the grid voltage on the grid current, so that the grid-connected current can quickly follow the grid voltage.

[0050] Further, from Figure 2It can be seen from the current inner loop control block diagram of the rectification mode that the current loop reference current amplitude Iref is multiplied by the phase-locked loop output to obtain the reference current of the current loop. The grid-side inductor current ig sampling value is compared with the current loop reference current iref to obtain the error value, and the drive signal of the switch tube is obtained through PWM modulation. The output voltage of the voltage outer loop is multiplied by the grid voltage sampling value as the reference value of the current inner loop, which affects the content of grid-connected current harmonics. A notch filter with a center frequency of twice the power frequency is added to filter out the secondary power frequency component of the DC bus voltage, and the voltage loop bandwidth is set to 1 / 10 to 1 / 5 times the ripple frequency. The sampled DC bus voltage Vbus is compared with the given reference voltage Vref. After PI calculation, the result is used to eliminate the double frequency ripple caused by the DC bus with a notch filter to obtain the reference current amplitude Iref of the current loop, and then the voltage loop is closed through the transfer function from the grid-side current amplitude to the output voltage.

[0051] Further, from Figure 3 It can be seen from the control block diagram of the rectification mode that the double closed loop of capacitor current inner loop and grid-connected current outer loop is adopted. At the same time, the frequency characteristics of the LCL filter are changed through the active damping control algorithm to achieve resonance suppression, and the grid voltage proportional feedforward control is used to suppress the influence of the grid voltage on the grid current, so that the grid-connected current can quickly follow the grid voltage.

[0052] like Figure 4 and Figure 5 The steady-state and dynamic PSIM waveforms under rectification mode are shown. It can be seen that the input power factor and output voltage dynamic characteristics can be well met.

[0053] like Figure 6 and Figure 7 The PSIM waveform diagram of steady-state characteristics and dynamic characteristics under rectification mode is shown. It can be seen that it can well meet the grid-connected power quality and grid-connected current dynamic characteristics.

[0054] Preferably, the active power decoupling method generates fundamental frequency fluctuations by controlling the capacitor voltage in the capacitor splitting power decoupling circuit, thereby generating double frequency power to compensate for the difference power between the average power on the DC side and the instantaneous power on the AC side. Taking the rectification direction as an example, the formula for the double frequency pulsating power that needs to be suppressed is as follows:

[0055]

[0056] Among them, v g 、i g are the AC input voltage and current, V g ,I g are the amplitudes of the AC input voltage and current, the AC angular frequency ω=100π, and the phase difference satisfy AC input power p g The expression is:

[0057]

[0058] For the power frequency component in the circuit, assume the filter inductor L f =L1+L g , filter inductor L f And filter capacitor C f The expressions of instantaneous power on are:

[0059]

[0060] The input power expressions of the full-bridge side of the single-phase AC / DC converter are:

[0061]

[0062] Among them, DC output power is a constant power, corresponding to the instantaneous power p of twice the power frequency ripple r The expression is:

[0063]

[0064] Among them, the instantaneous power amplitude of the double power frequency ripple is P r The expression of the phase ψ is:

[0065]

[0066] As a preferred solution of the bidirectional AC-DC converter capable of realizing active power decoupling described in the present invention, the voltage of the split capacitors C1 and C2 needs to present fundamental frequency fluctuation.

[0067] The voltage expression of split capacitors C1 and C2 is:

[0068]

[0069] Among them, V bus is the DC bus voltage, V C is the amplitude of the voltage fundamental frequency component, θ is the phase of the voltage fundamental frequency component, at this time, the current flowing into the decoupling inductor L d The current expression is:

[0070]

[0071] Among them, i C1 、i C2 are the currents flowing into the split capacitors C1 and C2 respectively. Both the split capacitors and the decoupling inductors generate double frequency power. The corresponding power expression is:

[0072]

[0073] In order to suppress the double frequency power fluctuation on the DC side, it is necessary to achieve the balance between the active power decoupling circuit and the double frequency power output on the AC side, that is, to satisfy the expression p r =p Cd +p Ld ,Right now:

[0074]

[0075] By solving the equation, we can get V C The switches Q1 and Q2 control the capacitor voltage and the decoupling inductor current to track this reference, achieving double frequency power balance, that is, the amplitude of the voltage fundamental frequency component V C The phase θ of the voltage fundamental frequency component satisfies the expression:

[0076]

[0077] Among them, the expressions corresponding to A and B are:

[0078]

[0079] like Figure 8 and Fig. 9 As shown, when S5 is turned on and S6 is turned off, the decoupling inductor Ld is connected in parallel with the split capacitor C1, and the decoupling inductor current increases. When S5 is turned off and S6 is turned on, the decoupling inductor Ld is connected in parallel with the split capacitor C2, and the decoupling inductor current decreases.

[0080] like Fig.10 As shown, the current loop reference current amplitude Idref is multiplied by the phase-locked loop output to obtain the reference current of the current loop. The decoupled inductor current id sampling value is compared with the current loop reference current iref to obtain the error value, which is compared with the voltage v1 across the split capacitor C1 after the PI link to obtain the error value, and then added to the PWM modulation to obtain the drive signal of the switch tubes S5 and S6.

[0081] like Fig.11 The active power decoupling shown can effectively reduce the double ripple voltage on the DC side, and the capacitor value used is small. Film capacitors can be used to replace electrolytic capacitors to improve power density.

[0082] In summary, the bidirectional AC-DC converter capable of realizing active power decoupling described in the present invention uses a voltage outer loop and a current inner loop double closed loop to control the input power factor during rectification, stabilize the output voltage, and track the grid voltage; the inverter uses a capacitor current inner loop and a grid current outer loop double closed loop and grid voltage proportional feedforward control to ensure that the grid current quickly follows the grid voltage. By controlling the fundamental frequency fluctuation of the capacitor voltage in the split-type power decoupling circuit, double frequency power is generated to compensate for the power difference between the AC and DC sides. According to the theoretical formula to calculate the parameters, the switch tube tracks the benchmark to achieve double frequency power balance and suppress the DC secondary ripple voltage. Film capacitors can be used instead of electrolytic capacitors to reduce costs and increase power density. The performance is excellent as verified by a variety of waveform diagrams, and the application prospects are broad.

[0083] The above specific implementation methods or examples are only used to explain the technical solutions of the present invention, and are not intended to limit the present application. The detailed description parts are regarded as conventional technical means or common knowledge in the field. Ordinary technicians in this field should understand that based on the design concept of the present application, the technical solutions recorded in the aforementioned implementation methods should be adaptively modified, or some or all of the technical features therein should be replaced by equivalents. These modifications and replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

[0084] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A bidirectional AC-DC converter capable of realizing active power decoupling, characterized in that: The circuit includes a main circuit unit and a control unit; the main circuit unit includes a single-phase full-bridge power unit and an active power decoupling unit; the active power decoupling unit is composed of two switching tubes, a decoupling inductor and two split capacitors.

2. The bidirectional AC-DC converter capable of realizing active power decoupling according to claim 1, characterized in that: The active power decoupling unit comprises a MOS tube S5 and a MOS tube S6, and the two MOS tubes are connected in parallel on one side of the DC bus voltage; the MOS tube S5 and the MOS tube S6 form a half-bridge arm; the active power decoupling unit comprises split capacitors C1 and C2, and the two capacitors are connected in parallel on one side of the DC bus voltage; a decoupling inductor L is connected between the midpoint of the bridge arm and the midpoint of the split capacitor d Connection; the single-phase full-bridge power unit includes an AC power supply and four fully controlled switching devices S1-S4, and an LCL filter.

3. The bidirectional AC-DC converter capable of realizing active power decoupling as claimed in claim 2, characterized in that: The rectifier mode uses a dual closed-loop control of voltage outer loop and current inner loop to correct the input power factor. The voltage outer loop controls the output voltage to ensure that the voltage on the output DC bus is stable near the set value, and the current inner loop controls the input current to ensure that the input current tracks the grid voltage. The inverter mode uses a dual closed-loop current of capacitor current inner loop and grid-connected current outer loop, while using grid voltage proportional feedforward control to suppress the influence of grid voltage on grid current, so that the grid-connected current can quickly follow the grid voltage.

4. The bidirectional AC-DC converter capable of realizing active power decoupling as claimed in claim 3, characterized in that: The active power decoupling method generates fundamental frequency fluctuations by controlling the capacitor voltage in the capacitor splitting power decoupling circuit, thereby generating double frequency power to compensate for the difference power between the average power on the DC side and the instantaneous power on the AC side. By only tracking the theoretical value of the decoupling current in the decoupling inductor, the double power frequency ripple power of the bidirectional AC-DC converter can be transferred to the split capacitors C1 and C2, solving the problem of instantaneous power imbalance between the AC and DC sides of the bidirectional AC-DC converter and effectively suppressing the secondary ripple voltage on the DC side.

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