Control method of bidirectional ac / dc converter compatible with single / three-phase operation in single-phase inversion mode

Abstract

The application discloses a control method of a single / three-phase compatible bidirectional AC / DC converter in a single-phase inverter mode, which comprises the following steps: 1, a topological structure is a three-phase four-wire converter with split capacitors, comprising a three-phase active bridge arm composed of power devices and an N-phase passive bridge arm composed of split capacitors; 2, in the single-phase inverter mode, the A phase and the B phase are connected in parallel through relays, and the C phase and the N phase are also connected in parallel through relays to form a single-phase inverter output; 3, the A phase and the B phase are controlled by adopting a voltage effective value outer ring, a voltage instantaneous value inner ring and a current instantaneous value inner ring three-loop control, the AC output voltage is adjusted, and the C phase is controlled by adopting an independent current loop control, and the C and N phase current stress is adjusted. The application realizes mixed control of the inverter single-phase AC output voltage and the C and N phase current, can increase the single-phase output power to 1 / 2 of the three-phase rated power without increasing additional power devices and element overdesign.

Description

Technical Field

[0001] This invention belongs to the field of control of three-phase four-wire inverter systems, specifically relating to a control method for a bidirectional AC / DC converter compatible with single / three-phase operation in single-phase inverter mode. Background Technology

[0002] On-board chargers (OBCs) provide the ability to charge electric vehicle batteries directly from the AC grid, typically operating in grid-to-vehicle (G2V) mode. Additionally, OBCs can operate in vehicle-to-home (V2H) or vehicle-to-load (V2L) modes, acting as an inverter to provide power. With the increasing popularity of electric vehicles and growing interest in V2X (V2G, V2L, V2H, or V2V) operation, bidirectional power transfer capabilities are becoming increasingly important for OBCs.

[0003] OBCs (On-Board Converters) are generally available in two-stage and single-stage configurations, with industrial electric vehicles mostly employing a two-stage configuration. A two-stage OBC consists of a bidirectional AC / DC converter and an isolated DC / DC converter. With the increasing demand for fast charging and V2X services, higher-power bidirectional AC / DC converters are crucial for OBCs. Three-phase (3-ph) bridge converters are widely used as potential candidates due to their simple structure and mature control schemes. To facilitate interconnection with various power grids and load conditions, the AC / DC converter also needs to operate in single-phase (1-ph) mode. Therefore, bidirectional AC / DC converters capable of operating in both 3-ph and 1-ph modes are becoming the preferred choice for OBCs.

[0004] Typically, a 3-ph bidirectional AC / DC converter can easily achieve single-phase operation using only a portion of its branches. However, because the converter-stage components for each phase are designed for their three-phase rated power, the output power of the 1-ph is limited to one-third of the three-phase rated power. To address this issue, many academic papers have proposed different solutions. For example, in "Three-phase 11kW on-board charger with single-phase reverse function," Mun, Choi SW, Hong DY, et al., Journal of Power Electronics 22.8(2022):1255-1264, a method is proposed to increase the single-phase output power to half of the three-phase rated power by over-designing the converter-stage components. However, this increases the size and cost of the on-board charger. Other papers propose adding an additional bridge arm to form a three-phase four-wire four-bridge-arm converter to increase the rated power of the single-phase output, but this also increases cost. Summary of the Invention

[0005] To overcome the limitations of the above-mentioned technical solutions, this invention proposes a control method for a bidirectional AC / DC converter compatible with single / three-phase operation in single-phase inverter mode, based on a split capacitor three-phase four-wire inverter. The aim is to increase the single-phase output power to 1 / 2 of the three-phase rated power without adding extra components or over-designing, thereby improving the single-phase output power level while ensuring AC voltage stability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The present invention provides a control method for a bidirectional AC / DC converter compatible with single / three-phase operation in single-phase inverter mode, characterized by the following steps:

[0008] Step 1: In single-phase inverter mode, connect phases A and B in parallel, and phases C and N in parallel in the topology of the bidirectional AC / DC converter;

[0009] Step 2: Use a three-loop control strategy based on the effective value of voltage, instantaneous value of voltage, and instantaneous value of current to adjust the AC output voltage of phase A and phase B of the bidirectional AC / DC inverter to obtain the control signals of phase A and phase B;

[0010] Step 3: Use an independent AC current loop control strategy to adjust the current stress between the C phase and N phase of the bidirectional AC / DC converter to obtain the C phase control signal;

[0011] Step 4: Input the control signals of phase A, phase B, and phase C into the pulse width modulator to generate PWM pulse signals for controlling the power devices in the bidirectional AC / DC converter to turn on and off, thereby realizing the control of the output AC voltage of the bidirectional AC / DC converter and the current stress between phase C and phase N.

[0012] The single-phase control method for a three-phase four-wire inverter described in this invention is also characterized in that, in step 2, the output AC voltages of phase A and phase B are adjusted according to the following process:

[0013] Step 2.1: Acquire the A-phase voltage of the filter capacitor C on the AC side of the bidirectional AC / DC converter.

[0014] Step 2.2: Measure the A-phase voltage of the filter capacitor C on the AC side. The effective value (RMS) of the phase A voltage of the AC side filter capacitor C is obtained by performing an effective value (RMS) calculation.

[0015] Step 2.3: Set the effective value of the target voltage of phase A as a reference value. With the effective value of phase A voltage After subtraction, the error value of phase A is obtained. Then, proportional-integral control is applied to the error value of phase A to obtain the reference value of the output voltage amplitude of phase A.

[0016] Step 2.4: Multiply the reference value of the output voltage amplitude of phase A by sin(ωt) to obtain the inner loop reference value of the instantaneous value of phase A voltage. The inner loop reference value of the instantaneous value of phase A voltage. Feedback value of phase A voltage instantaneous After subtraction, the voltage difference of phase A is obtained. Then, proportional resonance control is applied to the voltage difference of phase A to obtain the reference value of the inductor current of phase A. Here, ω represents the angular frequency of the controlled output voltage, ω=2πf, and f represents the frequency of the controlled output voltage.

[0017] Step 2.5: Compare the reference value of phase A inductor current with the instantaneous value of phase A inductor current. After subtraction, the resulting difference is then subjected to proportional resonance control to obtain the A-phase modulation signal;

[0018] Step 2.6: The A-phase modulation signal is input into the PWM modulator to obtain the inverter A-phase control signal using equation (1). The phase A voltage used for the filter capacitor C on the AC side. To take control:

[0019]

[0020] In equation (1), s is the Laplace operator, and G DVC (s) is a voltage RMS PI controller, and in, This is the adjustment coefficient for the proportion P. G is the adjustment coefficient for integral I. AVC (s) represents the inner-loop PR controller for the instantaneous voltage value, and in, This is the adjustment coefficient for the voltage inner loop proportional gain P. ω is the adjustment coefficient of the inner loop resonance R for the instantaneous voltage value. g G is the rated angular frequency of the mains voltage; ACC (s) is a current loop PR controller, and in, This is the adjustment coefficient for the current loop proportional gain P. This is the adjustment coefficient of the current loop resonance R.

[0021] The AC current loop control strategy in step 3 is performed as follows:

[0022] Step 3.1: Collect the A-phase, B-phase, and C-phase inductor currents of the side inductor L in the bidirectional AC / DC converter.

[0023] Step 3.2: Analyze the inductor currents of phases A and B. After adding and inverting the values, multiply by the current distribution coefficient k to obtain the C-phase inductor current. Reference value

[0024] Step 3.3: Convert the C-phase inductor current Reference value Instantaneous feedback value of C-phase inductor current After subtraction, the obtained C-phase error value is then subjected to proportional resonance control, thereby obtaining the C-phase control signal in the bidirectional AC / DC inverter using equation (2).

[0025]

[0026] In equation (2), s is the Laplace operator, G' ACC (s) is the C-phase current loop PR controller, and in, The adjustment coefficient of the C-phase current loop proportional P is given. The adjustment coefficient R is the resonant coefficient of the C-phase current loop. This is the rated angular frequency of the grid voltage.

[0027] The present invention provides an electronic device, including a memory and a processor, wherein the memory is used to store a program that supports the processor in executing the control method, and the processor is configured to execute the program stored in the memory.

[0028] The present invention discloses a computer-readable storage medium on which a computer program is stored, wherein the computer program is executed by a processor to perform the steps of the control method.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. The control method proposed in this invention can flexibly allocate the magnitude of C-phase current and N-phase current by setting the corresponding current distribution coefficient, so that the split capacitor acts as the fourth bridge arm. In single-phase mode, it can realize the parallel output of every two bridge arms, thereby increasing the single-phase output power to 1 / 2 of the three-phase rated power without increasing the cost of additional components. Compared with the corresponding three-phase four-bridge arm inverter, the split capacitor three-phase four-wire inverter has a lower cost advantage.

[0031] 2. This invention addresses the single-phase control problem of split capacitor three-phase four-wire inverters. Unlike existing pure voltage loop control, it uses a three-loop control system (effective voltage value, instantaneous voltage value, and instantaneous current value) to control the switching devices of phases A and B, and uses an instantaneous current loop to control the switching devices of phase C. This allows for the adjustment of the current stress between phase C and phase N while regulating the AC output voltage. Attached Figure Description

[0032] Figure 1 This is a topology diagram of the three-phase four-wire inverter used in the implementation of this invention during single-phase operation;

[0033] Figure 2 The control structure block diagram of the three-phase four-wire inverter used in the implementation of this invention during single-phase operation;

[0034] Figure 3 To employ the control method of this invention, a three-phase four-wire inverter at power level S n Voltage and current waveforms when the power is 6.6 kW and k = 1 / 2.

[0035] Figure 4 To employ the control method of this invention, a three-phase four-wire inverter at power level S n =6.6kW, k=1 / 3 voltage and current waveforms. Detailed Implementation

[0036] The specific embodiments and working principles of the present invention will be further described in detail below with reference to the accompanying drawings.

[0037] In this embodiment, a control method for a bidirectional AC / DC converter compatible with single / three-phase operation in single-phase inverter mode is based on the fact that the bidirectional on-board charger operates in V2L mode. The on-board charger (OBC) of the front stage is a split capacitor three-phase four-wire inverter, which can not only act as a three-phase 380V grid to supply power to the load, but also as a single-phase 220V grid to supply power to the load. At the same time, the current sharing problem between the C-phase active bridge arm and the N-phase capacitor passive bridge arm is also considered.

[0038] The topology used in this embodiment is as follows: Figure 1 As shown, this topology is a three-phase four-wire inverter with split capacitors, and includes a three-phase full-bridge inverter, an AC-side inductor L, and an AC-side filter capacitor C. In this embodiment, L = 300uH and C = 10uF.

[0039] The single-phase control method of this three-phase four-wire inverter is based on the topology of a split capacitor three-phase four-wire inverter, which connects phases A and B in parallel and phases C and N in parallel to form a single-phase output. Phases A and B are controlled by a three-loop control system, which uses the effective value of voltage, instantaneous value of voltage, and instantaneous value of current to regulate the AC voltage. Phase C is controlled by an AC current loop to regulate the current between phase C and phase N. The three-phase control signals are then input to a pulse width modulator to generate PWM switching signals for controlling the power devices in the inverter to turn on and off, thereby achieving single-phase control of the inverter.

[0040] In specific implementation, the control structure block diagram of this control method is as follows: Figure 2 As shown, the specific control process is as follows:

[0041] Step 1: In single-phase inverter mode, connect phases A and B in parallel, and phases C and N in parallel in the topology of the bidirectional AC / DC converter;

[0042] Step 2: Use a three-loop control strategy based on the effective value of voltage, instantaneous value of voltage, and instantaneous value of current to adjust the AC output voltage of phase A and phase B of the bidirectional AC / DC inverter to obtain the control signals of phase A and phase B;

[0043] Step 2.1: Acquire the A-phase voltage of the filter capacitor C on the AC side of the bidirectional AC / DC converter.

[0044] Step 2.2: Measure the A-phase voltage of the filter capacitor C on the AC side. The effective value (RMS) of the phase A voltage of the AC side filter capacitor C is obtained by performing an effective value (RMS) calculation.

[0045] Step 2.3: Set the effective value of the target voltage of phase A as a reference value. With the effective value of phase A voltage After subtraction, the error value of phase A is obtained. Then, proportional-integral control is applied to the error value of phase A to obtain the reference value of the output voltage amplitude of phase A.

[0046] Step 2.4: Multiply the reference value of the output voltage amplitude of phase A by sin(ωt) to obtain the inner loop reference value of the instantaneous value of phase A voltage. The inner loop reference value of the instantaneous value of phase A voltage. Feedback value of phase A voltage instantaneous After subtraction, the voltage difference of phase A is obtained. Then, proportional resonance control is applied to the voltage difference of phase A to obtain the reference value of the inductor current of phase A. Here, ω represents the angular frequency of the controlled output voltage, ω=2πf, and f represents the frequency of the controlled output voltage.

[0047] Step 2.5: Compare the reference value of phase A inductor current with the instantaneous value of phase A inductor current. After subtraction, the resulting difference is then subjected to proportional resonance control to obtain the A-phase modulation signal;

[0048] Step 2.6: The A-phase modulation signal is input into the PWM modulator to obtain the inverter A-phase control signal using equation (1). The phase A voltage used for the filter capacitor C on the AC side. To take control:

[0049]

[0050] In equation (1), s is the Laplace operator, and G DVC (s) is a voltage RMS PI controller, and in, This is the adjustment coefficient for the proportion P. G is the adjustment coefficient for integral I. AVC (s) represents the inner-loop PR controller for the instantaneous voltage value, and in, This is the adjustment coefficient for the voltage inner loop proportional gain P. ω is the adjustment coefficient of the inner loop resonance R for the instantaneous voltage value. g G is the rated angular frequency of the mains voltage; ACC (s) is a current loop PR controller, and in, This is the adjustment coefficient for the current loop proportional gain P. This is the adjustment coefficient of the current loop resonance R.

[0051] Step 3: Use an independent AC current loop control strategy to adjust the current stress between the C phase and N phase of the bidirectional AC / DC converter to obtain the C phase control signal;

[0052] Step 3.1: Collect the A-phase, B-phase, and C-phase inductor currents of the side inductor L in the bidirectional AC / DC converter.

[0053] Step 3.2: Analyze the inductor currents of phases A and B. After adding and inverting the values, multiply by the current distribution coefficient k to obtain the C-phase inductor current. Reference value

[0054] Step 3.3: Convert the C-phase inductor current Reference value Instantaneous feedback value of C-phase inductor current After subtraction, the obtained C-phase error value is then subjected to proportional resonance control, thereby obtaining the C-phase control signal in the bidirectional AC / DC inverter using equation (2).

[0055]

[0056] In equation (2), s is the Laplace operator, G′ ACC (s) is the C-phase current loop PR controller, and in, The adjustment coefficient of the C-phase current loop proportional P is given. The adjustment coefficient R is the resonant coefficient of the C-phase current loop. This is the rated angular frequency of the grid voltage.

[0057] In practice, the control parameters of the AC voltage RMS outer loop PI controller, the AC voltage instantaneous value PR controller, and the AC current loop PR controller are based on the inverter's system parameters and rated capacity S. n The settings. In this embodiment, S n =6.6kw.

[0058] Step 4: Input the control signals of phase A, phase B, and phase C into the pulse width modulator to generate PWM pulse signals for controlling the power devices in the bidirectional AC / DC converter to turn on and off, thereby realizing the control of the output AC voltage of the bidirectional AC / DC converter and the current stress between phase C and phase N.

[0059] To verify the effectiveness of the control method of this invention, a corresponding simulation model was built using the power electronics simulation software PLECS, and the simulation results are as follows. Figure 3 , Figure 4 As shown.

[0060] Figure 3 To employ the control method of this invention, a three-phase four-wire inverter at power level S n =6.6kW, output voltage when current distribution coefficient k=1 / 2 C-phase current i c N-phase current i n Waveform diagram. (From...) Figure 3 As shown: Using the control method of this invention, the output voltage With target voltage Consistent, C-phase current i c N-phase current i n It can achieve flow sharing control, i c =i n ≈15A, which complies with the national standard "GB / T 40432-2021 Conductive On-board Charger for Electric Vehicles", thereby increasing the single-phase output power to 1 / 2 of the three-phase rated power without increasing additional component costs or over-design of components.

[0061] To further verify the universality of the control method of the present invention, consider the current distribution coefficient k = 1 / 3, i.e., i n =2i c The situation at that time.

[0062] Figure 4 To employ the control method of this invention, a three-phase four-wire inverter at power level S n =6.6kW, output voltage when current distribution factor k=1 / 3 C-phase current i c N-phase current i n Waveform diagram. (From...) Figure 4 As shown: Using the control method of this invention, the output voltage With target voltage Consistent, N-phase current i n It is the C-phase current i c Twice as much.

[0063] In this embodiment, an electronic device includes a memory and a processor. The memory stores a program that supports the processor in executing the single-phase control method described above, and the processor is configured to execute the program stored in the memory.

[0064] In this embodiment, a computer-readable storage medium stores a computer program, which is executed by a processor to perform the steps of the single-phase control method described above.

[0065] In summary, the above control method can not only stabilize the output voltage, but also flexibly allocate the C-phase and N-phase current by setting the current distribution coefficient, thus avoiding overcurrent. When the current distribution coefficient k is 1 / 2, the single-phase output power can be increased to 1 / 2 of the three-phase output rated power without adding extra devices and components.

Claims

1. A control method for a bidirectional AC / DC converter compatible with single / three-phase operation in single-phase inverter mode, characterized in that, Includes the following steps: Step 1: In single-phase inverter mode, connect phases A and B in parallel, and phases C and N in parallel in the topology of the bidirectional AC / DC converter; Step 2: Use a three-loop control strategy based on the effective value of voltage, instantaneous value of voltage, and instantaneous value of current to adjust the AC output voltage of phase A and phase B of the bidirectional AC / DC inverter to obtain the control signals of phase A and phase B; Step 2.1: Collect the filter capacitor on the AC side of the bidirectional AC / DC converter. Phase A voltage ; Step 2.2: Measure the A-phase voltage of the filter capacitor C on the AC side. The effective value (RMS) of the phase A voltage of the AC side filter capacitor C is obtained by performing an effective value (RMS) calculation. ; Step 2.3: Set the effective value of the target voltage of phase A as a reference value. With the effective value of phase A voltage After subtraction, the error value of phase A is obtained. Then, proportional-integral control is applied to the error value of phase A to obtain the reference value of the output voltage amplitude of phase A. Step 2.4: Compare the reference value of the output voltage amplitude of phase A with... After multiplication, the inner loop reference value of the instantaneous phase A voltage is obtained. The inner loop reference value of the instantaneous value of phase A voltage. Feedback value of phase A voltage instantaneous After subtraction, the voltage difference of phase A is obtained. Then, proportional resonance control is applied to the voltage difference of phase A to obtain the reference value of the inductor current of phase A. Indicates the angular frequency of the controlled output voltage. , Indicates the frequency of the controlled output voltage; Step 2.5: Compare the reference value of phase A inductor current with the instantaneous value of phase A inductor current. After subtraction, the resulting difference is then subjected to proportional resonance control to obtain the A-phase modulation signal; Step 2.6: The A-phase modulation signal is input into the PWM modulator to obtain the inverter A-phase control signal using equation (1). Used to measure the A-phase voltage of the filter capacitor C on the AC side. To take control: (1) In equation (1), For the Laplace operator, It is a voltage RMS PI controller, and ,in, This is the adjustment coefficient for the proportion P. This is the adjustment coefficient for integral I. The inner-loop PR controller represents the instantaneous voltage value, and ,in, This is the adjustment coefficient for the voltage inner loop proportional gain P. The adjustment coefficient of the inner loop resonance R is the instantaneous voltage value. The rated angular frequency of the grid voltage; It is a current loop PR controller, and ,in, This is the adjustment coefficient for the current loop proportional gain P. This is the adjustment coefficient of the current loop resonance R; Step 3: Use an independent AC current loop control strategy to adjust the current stress between the C phase and N phase of the bidirectional AC / DC converter to obtain the C phase control signal; Step 3.1: Acquire the mid-side inductance of the bidirectional AC / DC converter The inductor currents of phases A, B, and C , , ; Step 3.2: Analyze the inductor currents of phases A and B. , After adding and inverting, multiply by the current distribution factor. The current of phase C inductor is obtained. Reference value ; Step 3.3: Convert the C-phase inductor current Reference value Instantaneous feedback value of C-phase inductor current After subtraction, the obtained C-phase error value is then subjected to proportional resonance control, thereby obtaining the C-phase control signal in the bidirectional AC / DC inverter using equation (2). : (2) In equation (2), For the Laplace operator, It is a C-phase current loop PR controller, and ,in, The adjustment coefficient of the C-phase current loop proportional P is given. The adjustment coefficient R is the resonant coefficient of the C-phase current loop. The rated angular frequency of the grid voltage; Step 4: Input the control signals of phase A, phase B, and phase C into the pulse width modulator to generate PWM pulse signals for controlling the power devices in the bidirectional AC / DC converter to turn on and off, thereby realizing the control of the output AC voltage of the bidirectional AC / DC converter and the current stress between phase C and phase N.

2. An electronic device, comprising a memory and a processor, characterized in that, The memory is used to store a program that supports the processor in executing the control method of claim 1, and the processor is configured to execute the program stored in the memory.

3. A computer-readable storage medium storing a computer program, characterized in that, The computer program is executed by the processor to perform the steps of the control method of claim 1.

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