Space vector modulation method based on single-phase parallel current source type inverter
By classifying the current vector into three categories and selecting appropriate redundant switching states, the DC current imbalance problem of single-phase parallel current source inverters is solved, thereby improving the current waveform and enhancing system reliability.
Patent Information
- Application Number
- CN202511133281.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-13
- Publication Date
- 2025-12-23
AI Technical Summary
In the existing technology, single-phase parallel current source inverters lack DC current balancing methods, resulting in poor system reliability and current waveform quality.
By dividing the current vector into large current vector, small current vector and zero current vector, rationally selecting redundant switch states, and using the ampere-second balance principle to synthesize the reference current vector, the DC bridge arm current balance is achieved.
It achieves DC bridge arm current balancing, improves grid-connected current waveform quality, and enhances system reliability and harmonic performance of the current waveform.
Smart Images
Figure CN121193055A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of space vector modulation technology, and relates to a space vector modulation method, particularly a space vector modulation method based on a single-phase parallel current source inverter. Background Technology
[0002] With the rapid development of renewable energy sources such as photovoltaics and wind power, the requirements for inverters, the core of energy conversion, are becoming increasingly stringent. Traditional voltage source inverters suffer from drawbacks such as easy damage to DC capacitors and poor short-circuit withstand capability, significantly reducing system reliability. In contrast, current source inverters offer advantages such as simple topology and control, high-quality output current waveform, and strong short-circuit withstand capability, making them widely applicable to distributed grid-connected systems. As equipment power ratings continue to increase, single-phase parallel current source topologies are widely used for expanding current source systems due to their modular structure and flexible control. However, current research on single-phase parallel current source inverters is relatively limited, and many practical problems remain unresolved.
[0003] In recent years, single-phase current source inverters have attracted widespread attention both domestically and internationally due to their advantages such as simple control, high efficiency, small size, and low cost. Yang Xiaofeng improved the control strategy for parallel current source inverter systems by introducing virtual impedance to increase the equivalent impedance of the inverter system, thus achieving the goal of circulating current suppression. Yao Gang, for multi-level current source converters with lower cascade numbers, introduced a topology for single-phase multi-level current source converters based on a hybrid low-frequency and high-frequency modulation strategy, reducing switching losses and harmonic components. Zhu Xiaonan proposed a pulse width modulation method combining carrier stacking and phase shifting, effectively suppressing system leakage current.
[0004] However, to date, no literature has studied DC current balancing methods for parallel current source inverters.
[0005] A search revealed no publicly available literature of the same or similar prior art as this invention. Summary of the Invention
[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a space vector modulation method based on a single-phase parallel current source inverter. In the space vector modulation of the single-phase parallel current source inverter, the DC bridge arm current balance is achieved by reasonably selecting the redundant switch states, thereby improving the waveform quality of the grid-connected current.
[0007] The present invention solves its practical problem by adopting the following technical solution:
[0008] A space vector modulation method based on a single-phase parallel current source inverter, wherein the AC side is connected to the power grid through a CL filter, and the DC side is connected to a smoothing inductor and then connected in parallel to the DC bus, includes the following steps:
[0009] Step 1: Construct a single-phase parallel current source inverter circuit, based on the output current I. w The amplitudes are different, so all current vectors of the single-phase parallel current source inverter are divided;
[0010] Step 2: Analyze the impact of the small current vector redundant switch state on the DC current, and construct a small current vector switch state selection strategy;
[0011] Step 3: Analyze the impact of zero-current vector redundant switch states on DC current and construct a zero-current vector switch state selection strategy;
[0012] Step 4: Within each sampling period, the reference current vector I is synthesized from the two closest stationary current vectors according to the ampere-second balance principle. ref Simultaneously, the grid voltage u is collected. s The DC arm currents i1 to i4 are balanced by selecting redundant switch states according to the strategies in steps 2 and 3.
[0013] Moreover, the single-phase parallel current source inverter circuit includes: current source #1 and current source #2 are two single-phase full-bridge circuits composed of symmetrical gate commutation thyristors SGCT. After being connected in parallel on the AC side, they share a capacitor-inductor CL filter and are connected to the grid. On the DC side, they are respectively connected to smoothing inductors and then connected in parallel to the DC bus.
[0014] Wherein, the grid voltage is u s The grid current is i s The output PWM current is i w The filter capacitor current is i c The AC filter capacitor is C, the AC filter inductor is L, the upper and lower bridge arm smoothing inductors of current source #1 are L1 and L2 respectively, and the corresponding bridge arm currents are i1 and i2 respectively. The upper and lower bridge arm smoothing inductors of current source #2 are L3 and L4 respectively, and the corresponding bridge arm currents are i3 and i4 respectively. The DC bus current is i d .
[0015] Furthermore, step 1 is based on the output current I w The specific method for dividing all current vectors of a single-phase parallel current source inverter, based on their different amplitudes, is as follows:
[0016] They are divided into three categories: large current vectors (I1, I2), small current vectors (I3, I4), and zero current vectors (I0);
[0017] Furthermore, the selection strategy for the small current vector redundant switch state in step 2 is as follows:
[0018] Small current vector redundant switch state selection: When the small current vector is used for modulation, it is based on the current grid voltage u. s The DC current i1~i4 selects the small current vector redundant switching state to balance the DC side upper or lower bridge arm current.
[0019] Furthermore, the selection strategy for the small current vector redundant switch state in step 3 is as follows:
[0020] Zero-current vector redundant switch state selection: When zero-current vector is used for modulation, it is based on the current grid voltage u. s The DC current i1 to i4 select the zero-current vector redundant switching state to balance the DC side upper and lower bridge arm currents.
[0021] Furthermore, within each sampling period of step 4, a reference current vector I is synthesized from the two closest stationary current vectors according to the ampere-second balance principle. ref The specific method is as follows:
[0022] When the reference current vector I ref When it falls in regions 1 and 4, it is synthesized by the large current vector and the small current vector; when the reference current vector I... ref When falling within regions 2 and 3, the vectors are synthesized from small current vectors and zero current vectors; simultaneously, the grid voltage u is collected. s Based on the strategies in steps 2 and 3, redundant switch states are selected to achieve DC bridge arm current balancing, along with DC currents i1 to i4.
[0023] Furthermore, the following steps are included after step 4:
[0024] Step 5: Build a simulation model of a 10kW single-phase parallel current source inverter to verify the above method.
[0025] Furthermore, the specific method for step 5 is as follows:
[0026] Increase the deviation of the DC bus inductance of current source #1 and current source #2 by 20%; first, adjust the DC current i dc and reference value i dc * The difference is used as the input to the PI controller to obtain the grid current amplitude I. s Secondly, the phase angle θ of the grid voltage is obtained through the PLL, and I... s Combined with θ, we obtain the sinusoidal reference grid current i. s * Then, the grid current i s with is * The difference is used by the PR controller to obtain the final reference current vector I. ref Finally, based on the ampere-second balance principle, the action time of each vector is determined, and appropriate redundant switch states are selected according to the strategies in steps 2 and 3 to generate gate drive signals.
[0027] Advantages and beneficial effects of the present invention:
[0028] This invention proposes a space vector modulation method based on a single-phase parallel current source inverter. The current vectors are categorized into three types: large current vectors, small current vectors, and zero current vectors. Large current vectors have no redundancy, while the redundancy of small current vectors can affect either the upper or lower bridge arm current. The redundancy of zero current vectors can simultaneously affect the currents of all four DC bridge arms. By rationally selecting the redundant switching states of the small and zero current vectors, DC bridge arm current balancing can be achieved. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the circuit topology of a single-phase parallel current source inverter in an embodiment of the present invention;
[0030] Figure 2 This is a current vector diagram of a single-phase parallel current source inverter in an embodiment of the present invention;
[0031] Figure 3 This is the current loop diagram in the switching state 14:12 in this embodiment of the invention;
[0032] Figure 4 This is a schematic diagram of the parallel current source inverter circuit topology and modulation method in an embodiment of the present invention;
[0033] Figure 5 The image shows a comparison of the steady-state simulation waveforms of DC current using the method proposed in this invention and the traditional method.
[0034] Figure 6 The image shows a comparison of the steady-state simulation waveforms of the output PWM current and grid current using the method proposed in this invention and the traditional method. Detailed Implementation
[0035] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings:
[0036] A space vector modulation method based on a single-phase parallel current source inverter, wherein the AC side is connected to the power grid through a CL filter, and the DC side is connected to a smoothing inductor and then connected in parallel to the DC bus, includes the following steps:
[0037] Step 1: Construct a single-phase parallel current source inverter circuit, based on the output current I.w The amplitudes are different, so all current vectors of the single-phase parallel current source inverter are divided;
[0038] The single-phase parallel current source inverter circuit includes: current source #1 and current source #2 are two single-phase full-bridge circuits composed of symmetrical gate-commutated thyristors (SGCTs). They are connected in parallel on the AC side and share a capacitor-inductor (CL) filter connected to the grid. On the DC side, they are connected to smoothing inductors and then connected in parallel to the DC bus. The grid voltage is u. s The grid current is i s The output PWM current is i w The filter capacitor current is i c The AC filter capacitor is C, the AC filter inductor is L, the upper and lower bridge arm smoothing inductors of current source #1 are L1 and L2 respectively, and the corresponding bridge arm currents are i1 and i2 respectively. The upper and lower bridge arm smoothing inductors of current source #2 are L3 and L4 respectively, and the corresponding bridge arm currents are i3 and i4 respectively. The DC bus current is i d .
[0039] The step 1 is based on the output current I w The specific method for dividing all current vectors of a single-phase parallel current source inverter, based on their different amplitudes, is as follows:
[0040] They are divided into three categories: large current vectors (I1, I2), small current vectors (I3, I4), and zero current vectors (I0);
[0041] Step 2: Analyze the impact of the small current vector redundant switch state on the DC current, and construct a small current vector switch state selection strategy;
[0042] The selection strategy for the small current vector redundant switch state in step 2 is as follows:
[0043] Small current vector redundant switch state selection: When the small current vector is used for modulation, it is based on the current grid voltage u. s The DC current i1~i4 selects the small current vector redundant switching state to balance the DC side upper or lower bridge arm current.
[0044] Step 3: Analyze the impact of zero-current vector redundant switch states on DC current and construct a zero-current vector switch state selection strategy;
[0045] The selection strategy for the small current vector redundant switch state in step 3 is as follows:
[0046] Zero-current vector redundant switch state selection: When zero-current vector is used for modulation, it is based on the current grid voltage u. sThe DC current i1 to i4 select the zero-current vector redundant switching state to balance the DC side upper and lower bridge arm currents.
[0047] Step 4: Within each sampling period, the reference current vector I is synthesized from the two closest stationary current vectors according to the ampere-second balance principle. ref Simultaneously, the grid voltage u is collected. s The DC arm currents i1 to i4 are balanced by selecting redundant switch states according to the strategies in steps 2 and 3.
[0048] In each sampling period of step 4, the reference current vector I is synthesized from the two closest stationary current vectors according to the ampere-second balance principle. ref The specific method is as follows:
[0049] When the reference current vector I ref When it falls in regions 1 and 4, it is synthesized by the large current vector and the small current vector; when the reference current vector I... ref When falling within regions 2 and 3, the vectors are synthesized from small current vectors and zero current vectors; simultaneously, the grid voltage u is collected. s Based on the strategies in steps 2 and 3, redundant switch states are selected to achieve DC bridge arm current balancing, along with DC currents i1 to i4.
[0050] The following steps are included after step 4:
[0051] Step 5: Build a simulation model of a 10kW single-phase parallel current source inverter to verify the above method.
[0052] The specific method for step 5 is as follows:
[0053] Increase the deviation of the DC bus inductance of current source #1 and current source #2 by 20%; first, adjust the DC current i dc and reference value i dc * The difference is used as the input to the PI controller to obtain the grid current amplitude I. s Secondly, the phase angle θ of the grid voltage is obtained through the PLL, and I... s Combined with θ, we obtain the sinusoidal reference grid current i. s * Then, the grid current i s with i s * The difference is used by the PR controller to obtain the final reference current vector I. ref Finally, based on the ampere-second balance principle, the action time of each vector is determined, and appropriate redundant switch states are selected according to the strategies in steps 2 and 3 to generate gate drive signals.
[0054] In this embodiment, Figure 1 This is a circuit topology diagram of a specific embodiment of the present invention. The parallel current source inverter adopts two parallel full-bridge topologies. Each full bridge consists of four SGCTs (Symmetrical Gate-Commutated Thyristors) with reverse current blocking capability. The AC side is connected to the power grid through a CL filter, and the DC side is connected to the DC bus after being connected to smoothing inductors.
[0055] A space vector modulation method based on a single-phase parallel current source inverter includes the following steps:
[0056] Step 1: According to the constraints of the current source converter: at any given time, each full bridge has exactly two devices on, one in the upper half-bridge and the other in the lower half-bridge. Under this constraint, a single-phase parallel current source has 5 static PWM current vectors and 16 switching states.
[0057] Based on the output current I w Based on their different amplitudes, these current vectors can be divided into three categories: large current vectors (I1, I2), small current vectors (I3, I4), and zero current vectors (I0).
[0058] Current vector diagram as shown Figure 2 As shown in Table 1, the PWM current vector classification and corresponding output current and switching states are represented by four digits separated by colons. The first two digits represent the two on-switch device numbers in current source #1, and the last two digits represent the two on-switch device numbers in current source #2. Table 1 shows that large current vectors do not have redundant switching states, while small current vectors and zero current vectors do.
[0059] Table 1. Current vector classification of single-phase parallel current source inverters and corresponding output current and switching states.
[0060]
[0061]
[0062] Step 2: Analyze the impact of small current vector redundant switch states on DC current, and construct a small current vector switch state selection strategy.
[0063] The analysis will be based on the switching state 14:12 of the small current vector I3. Figure 3 The diagram shows the current loop of a single-phase parallel current source inverter in switching state 14:12, where u is the current loop. p1 and u n1 These are the upper and lower bridge arm voltages on the DC side of current source #1, u p2 and u n2These are the upper and lower bridge arm voltages on the DC side of current source #2, respectively.
[0064] Depend on Figure 3 It can be seen that at this time u p1 and u p2 The voltage difference between them is 0, while u n1 and u n2 The voltage difference between them is -u s When the grid voltage u s When the voltage is greater than 0, switch state 14:12 can increase current i4 and decrease current i2; when the grid voltage u s When <0, the effect is opposite. Therefore, based on the current grid voltage u s By understanding the relationship between the positive and negative values of the switch and the magnitudes of the bridge arm currents i1 to i4, and selecting appropriate switching states, balanced control of the bridge arm currents i1 to i4 can be achieved. For example, when u s When i2 > i4 and i2 > i4, selecting switch state 14:12 is beneficial for balancing currents i2 and i4. The switch state selection logic for the small current vector I3 is shown in Table 2, where 1 indicates that the condition is true, 0 indicates that the condition is false, and X indicates that the condition is not considered. Similarly, the influence of redundant switch states of current vector I4 on the bridge arm current can be analyzed. The analysis shows that each switch state can only affect one pair of bridge arm currents.
[0065] Table 2. Logic Table for Selecting the Switch State of Small Current Vector I3
[0066]
[0067] Step 3: Analyze the impact of zero-current vector redundant switch states on DC current and construct a zero-current vector switch state selection strategy.
[0068] The two switching states 12:12 and 34:34 with zero current vector do not have current sharing capability, while the other four switching states do. Taking switching state 14:23 as an example for analysis, when the grid voltage u... s When the voltage is greater than 0, switch state 14:23 can increase currents i3 and i4, and decrease currents i1 and i2; when the grid voltage u s When <0, the situation is reversed. Therefore, it still depends on u. s The appropriate switching state is selected based on the bridge arm currents i1 to i4. The switching state selection logic for the zero current vector I0 is shown in Table 3. Analysis revealed that all four switching states can affect the two pairs of bridge arm currents.
[0069] Table 3 Zero Current Vector I0 Switch State Selection Logic Table
[0070]
[0071] Step 4: Determine the reference current vector I refThen, from the distance reference current vector I ref The two most recent static current vectors were synthesized based on the ampere-second balance principle.
[0072] The specific synthesis method is as follows: when the reference current vector I... ref Falling as Figure 2 Regions 1 and 4 are synthesized from large current vectors and small current vectors; when the reference current vector I... ref Falling as Figure 2 Regions 2 and 3 are shown as synthesized from small current vectors and zero current vectors. Simultaneously, the grid voltage u is collected. s The DC arm currents i1 to i4 are balanced by selecting redundant switch states according to the strategies in Tables 2 and 3.
[0073] Step 5: Build a simulation model of a 10kW single-phase parallel current source inverter to verify the above method. To verify the effectiveness of the single-phase parallel current source inverter under DC current imbalance conditions, increase the DC bus inductance deviation of current source #1 and current source #2 by 20%. Figure 4 For the specific control and modulation block diagram, firstly, the DC current i dc and reference value i dc * The difference is used as the input to the PI controller to obtain the grid current amplitude I. s Secondly, the phase angle θ of the grid voltage is obtained through the PLL, and I... s Combined with θ, we obtain the sinusoidal reference grid current i. s * Then, the grid current i s with i s * The difference is used by the PR controller to obtain the final reference current vector I. ref Finally, based on the ampere-second balance principle, the action time of each vector is determined, and appropriate redundant switch states are selected according to the strategies in Tables 2 and 3 to generate gate drive signals.
[0074] Figure 5 The figures show the steady-state DC current simulation waveforms of the modulation method proposed in this invention and the traditional method, with the total DC current controlled at 80A. Due to the inductance discrepancy between the two current source inverters, i1 and i3 are 46A and 34A respectively under the traditional method. Therefore, the traditional modulation method cannot guarantee DC arm current balance when the circuit parameters of the single-phase parallel current source inverters are inconsistent. After adopting the proposed method, the currents of the upper and lower arms are basically balanced, both around 40A.
[0075] Figure 6This diagram compares the steady-state simulation waveforms of the output current and grid current using the modulation method proposed in this invention and the conventional method. The conventional method produces a three-level output current with a THD as high as 79.47%, while the grid current THD is 3.6%. Using the proposed method, the output current becomes a five-level output current with a THD of only 38.76%, while the grid current THD decreases to 2.58%.
[0076] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.
Claims
1. A space vector modulation method based on a single-phase parallel current source inverter, characterized in that: Based on the single-phase parallel current source inverter topology, the AC side is connected to the grid through a CL filter, and the DC side is connected to the DC bus after being connected to smoothing inductors. The process includes the following steps: Step 1: Construct a single-phase parallel current source inverter circuit, based on the output current I. w The amplitudes are different, so all current vectors of the single-phase parallel current source inverter are divided; Step 2: Analyze the impact of the small current vector redundant switch state on the DC current, and construct a small current vector switch state selection strategy; Step 3: Analyze the impact of zero-current vector redundant switch states on DC current and construct a zero-current vector switch state selection strategy; Step 4: Within each sampling period, the reference current vector I is synthesized from the two closest stationary current vectors according to the ampere-second balance principle. ref Simultaneously, the grid voltage u is collected. s The DC arm currents i1 to i4 are balanced by selecting redundant switch states according to the strategies in steps 2 and 3.
2. The space vector modulation method based on a single-phase parallel current source inverter according to claim 1, characterized in that: The single-phase parallel current source inverter circuit includes: current source #1 and current source #2 are two single-phase full-bridge circuits composed of symmetrical gate commutated thyristors SGCT. After being connected in parallel on the AC side, they share a capacitor-inductor CL filter and are connected to the grid. On the DC side, they are respectively connected to smoothing inductors and then connected in parallel to the DC bus. Wherein, the grid voltage is u s The grid current is i s The output PWM current is i w The filter capacitor current is i c The AC filter capacitor is C, the AC filter inductor is L, the upper and lower bridge arm smoothing inductors of current source #1 are L1 and L2 respectively, and the corresponding bridge arm currents are i1 and i2 respectively. The upper and lower bridge arm smoothing inductors of current source #2 are L3 and L4 respectively, and the corresponding bridge arm currents are i3 and i4 respectively. The DC bus current is i d .
3. The space vector modulation method based on a single-phase parallel current source inverter according to claim 1, characterized in that: The step 1 is based on the output current I w The specific method for dividing all current vectors of a single-phase parallel current source inverter, based on their different amplitudes, is as follows: They are divided into three categories: large current vectors (I1, I2), small current vectors (I3, I4), and zero current vectors (I0).
4. The space vector modulation method based on a single-phase parallel current source inverter according to claim 1, characterized in that: The selection strategy for the small current vector redundant switch state in step 2 is as follows: Small current vector redundant switch state selection: When the small current vector is used for modulation, it is based on the current grid voltage u. s The DC current i1 to i4 selects the small current vector redundant switch state to balance the DC side upper or lower bridge arm current.
5. The space vector modulation method based on a single-phase parallel current source inverter according to claim 1, characterized in that: The selection strategy for the small current vector redundant switch state in step 3 is as follows: Zero-current vector redundant switch state selection: When zero-current vector is used for modulation, it is based on the current grid voltage u. s The DC current i1 to i4 select the zero-current vector redundant switching state to balance the DC side upper and lower bridge arm currents.
6. The space vector modulation method based on a single-phase parallel current source inverter according to claim 1, characterized in that: In each sampling period of step 4, the reference current vector I is synthesized from the two closest stationary current vectors according to the ampere-second balance principle. ref The specific method is as follows: When the reference current vector I ref When falling in regions 1 and 4, it is composed of the large current vector and the small current vector; When the reference current vector I ref When falling within regions 2 and 3, the vectors are synthesized from small current vectors and zero current vectors; simultaneously, the grid voltage u is collected. s Based on the strategies in steps 2 and 3, redundant switch states are selected to achieve DC bridge arm current balancing, along with DC currents i1 to i4.
7. The space vector modulation method based on a single-phase parallel current source inverter according to claim 1, characterized in that: The following steps are included after step 4: Step 5: Build a simulation model of a 10kW single-phase parallel current source inverter to verify the above method.
8. The space vector modulation method based on a single-phase parallel current source inverter according to claim 1, characterized in that: The specific method for step 5 is as follows: Increase the deviation of the DC bus inductance of current source #1 and current source #2 by 20%; first, adjust the DC current i dc and reference value i dc * The difference is used as the input to the PI controller to obtain the grid current amplitude I. s Secondly, the phase angle θ of the grid voltage is obtained through the PLL, and I... s Combined with θ, a sinusoidal reference grid current i is obtained. s * ; Then, the grid current i s with i s * The difference is used by the PR controller to obtain the final reference current vector I. ref Finally, based on the ampere-second balance principle, the action time of each vector is determined, and appropriate redundant switch states are selected according to the strategies in steps 2 and 3 to generate gate drive signals.