Method and system for calculating power loss of single-stage differential boost inverter

Abstract

The invention discloses a power loss calculation method and system for a single-stage differential boost inverter. The power loss calculation method comprises the following steps: S1, constructing a three-phase differential boost inverter circuit based on a SiC MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor); s2, analyzing an inductive current in the three-phase differential boost inverter circuit to obtain an expression of a current flowing through an MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor); and S3, obtaining the power loss of the three-phase DBI according to the expression of the current flowing through the MOSFET. By adopting the technical scheme of the invention, the loss of the power device in the circuit is effectively calculated.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC-AC inverters, and in particular relates to a power loss calculation method and system for a single-stage differential boost inverter. Background Art

[0002] With the widespread adoption of renewable energy systems, such as photovoltaics and fuel cells, the demand for efficient power conversion is increasing. As a key component in these systems, inverters must be compact and minimize passive components to reduce weight and size. Traditional two-stage inverters (combining a boost DC / DC converter and a full-bridge inverter) suffer from reduced efficiency and increased control complexity under varying load conditions due to the interdependence between the stages.

[0003] As a new topology, the differential boost inverter (DBI) has the advantages of reducing nonlinearity and independently controlling each phase module, making it suitable for practical power systems. However, the differential boost inverter (DBI) achieves both boost and inversion functions through a single-stage structure, simplifying the topology, but still faces the following problems: (1) Inaccurate loss calculation: Existing models ignore high-frequency pulsation waveforms and operational asymmetry, resulting in a large deviation between theoretical and actual losses; (2) Insufficient high-frequency performance: Traditional silicon-based devices (such as IGBTs) have high switching losses, which limits the increase in switching frequency and cannot fully realize the potential of miniaturization of passive components; (3) The contradiction between efficiency and volume: Existing DBIs have large efficiency fluctuations over a wide input voltage range, requiring large-capacity capacitors and inductors to suppress ripple, which increases the system volume. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for calculating the power loss of a single-stage differential boost inverter, which effectively calculates the loss of power devices in the circuit.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for calculating power loss of a single-stage differential boost inverter includes:

[0007] Step S1, constructing a three-phase differential boost inverter circuit based on SiC MOSFET;

[0008] Step S2: Analyze the inductor current in the three-phase differential boost inverter circuit to obtain an expression for the current flowing through the MOSFET;

[0009] Step S3: Obtain the power loss of the three-phase DBI according to the expression of the current flowing through the MOSFET.

[0010] Preferably, a three-phase differential boost inverter circuit based on SiC MOSFET is composed of three identical bidirectional DC / AC boost inverters; each phase bridge arm contains two MOSFET devices; the three-phase differential boost inverter circuit outputs a sinusoidal voltage with a DC bias.

[0011] As a preference, the two modes of operation of the device when the three-phase differential boost inverter circuit is running are as follows:

[0012] (a) includes two situations: when the lower tube is turned on and the upper tube is turned off, the inductor current flows back from the lower tube to the negative pole of the power supply or flows through the anti-parallel diode of the lower tube; when it is in the dead zone, at the moment before the dead zone begins, I La <0; at this time, the inductor current flows through the anti-parallel diode of the lower tube;

[0013] (b) There are two cases: when the upper tube is turned on and the lower tube is turned off, the inductor current supplies power to the load and capacitor through the anti-parallel diode of the upper tube, or flows back through the upper tube and feeds back to the DC side; when it is in the dead zone, at the moment before the dead zone begins, I La >0; at this time, the inductor current flows through the anti-parallel diode of the upper tube.

[0014] The present invention also provides a power loss calculation system for a single-stage differential boost inverter, comprising:

[0015] The first processing module is used to construct a three-phase differential boost inverter circuit based on SiC MOSFET;

[0016] The second processing module is used to analyze the inductor current in the three-phase differential boost inverter circuit to obtain an expression for the current flowing through the MOSFET;

[0017] The third processing module is used to obtain the power loss of the three-phase DBI according to the expression of the current flowing through the MOSFET.

[0018] Preferably, a three-phase differential boost inverter circuit based on SiC MOSFET is composed of three identical bidirectional DC / AC boost inverters; each phase bridge arm contains two MOSFET devices; the three-phase differential boost inverter circuit outputs a sinusoidal voltage with a DC bias.

[0019] As a preference, the two modes of operation of the device when the three-phase differential boost inverter circuit is running are as follows:

[0020] (a) includes two situations: when the lower tube is turned on and the upper tube is turned off, the inductor current flows back from the lower tube to the negative pole of the power supply or flows through the anti-parallel diode of the lower tube; when it is in the dead zone, at the moment before the dead zone begins, I La <0; at this time, the inductor current flows through the anti-parallel diode of the lower tube;

[0021] (b) There are two cases: when the upper tube is turned on and the lower tube is turned off, the inductor current supplies power to the load and capacitor through the anti-parallel diode of the upper tube, or flows back through the upper tube and feeds back to the DC side; when it is in the dead zone, at the moment before the dead zone begins, I La >0; at this time, the inductor current flows through the anti-parallel diode of the upper tube.

[0022] This paper establishes a direct link between modulation parameters and circuit efficiency by introducing multi-frequency waveform analysis and considering operational asymmetry. Furthermore, SiC MOSFETs are used in actual circuits to expand the switching frequency range and reduce device losses. Furthermore, by combining circuit simulation with theoretical calculations, the switching frequencies at minimum error and maximum efficiency are found, providing design engineers with a practical tool that balances calculation accuracy and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0024] Figure 1 This is a flow chart of a method for calculating power loss of a single-stage differential boost inverter according to an embodiment of the present invention;

[0025] Figure 2 It is a three-phase differential boost inverter circuit;

[0026] Figure 3 is the modulation function of the three-phase DBI circuit and the MOSFET device switching signal;

[0027] Figure 4 Schematic diagram of the derived waveform and the actual waveform;

[0028] Figure 5 There are two modes of device operation; (a) and (b) are mode 1, where the current flows through the lower tube S a2 Schematic diagram of two paths, (c) and (d) are mode 2, that is, the current flows through the upper tube S a1 Schematic diagram of two paths;

[0029] Figure 6 is the relationship between the total conduction loss and switching loss and the switching frequency;

[0030] Figure 7 The simulation results of the three-phase DBI circuit proposed in this invention are shown in Figure 1. (a) is the three-phase inductor current, (b) is the capacitor voltage, and (c) is the output current.

[0031] Figure 8 Comparison of the simulation results and theoretical calculation results of the loss calculation method proposed in this invention at different frequencies;

[0032] Figure 9 The simulation results and theoretical calculation results of the loss calculation method proposed in this invention are compared under different input voltages. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1:

[0036] like Figure 1 As shown, an embodiment of the present invention provides a method for calculating power loss of a single-stage differential boost inverter, including:

[0037] Step S1, constructing a three-phase differential boost inverter circuit based on SiC MOSFET;

[0038] Step S2: Analyze the inductor current in the three-phase differential boost inverter circuit to obtain an expression for the current flowing through the MOSFET;

[0039] Step S3: Obtain the power loss of the three-phase DBI according to the expression of the current flowing through the MOSFET.

[0040] As an implementation method of the embodiment of the present invention, in step S1, Figure 2 As shown in Figure 1, the SiC MOSFET-based three-phase differential boost inverter circuit consists of three identical bidirectional DC / AC boost inverters, with each phase containing two SiC MOSFET power devices, an inductor, and a capacitor. Each phase capacitor is connected to a common point, which is shared with the other two phase capacitors and connected to the negative terminal of the DC power supply. The output of each phase inverter bridge is connected to one end of the load, and the other ends of the three phase loads are connected together to form a star connection. Figure 2 Medium V in is the DC power supply voltage, R La 、R Lb and R Lc is the inductance, L a , L b and Lc is the equivalent internal resistance, C a 、C b and C c is the output parallel capacitor, and its relationship is R La =R Lb =R Lc , L a =L b =L c , C a =C b =C c Each phase bridge arm contains two MOSFET devices S x1 , S x2 , x∈{a, b, c}, the circuit outputs a sinusoidal voltage with a DC bias, that is,

[0041]

[0042] Among them, V an ,V bn ,V cn They are the three-phase inverter output phase voltage, that is, the load voltage, V m is the output voltage amplitude, ω is the fundamental angular frequency, for three-phase DBI, when it is in boost mode, assuming the boost ratio is,

[0043] B = V m / V in (2)

[0044] Among them, V in is the DC voltage on the input side, which means that the sinusoidal amplitude of the output voltage is determined by the input voltage. At the same time, it is assumed that

[0045] K = V dc / V in (3)

[0046] Among them, V dc is the DC bias on the output side. The above formula shows that the bias voltage is also determined by the input voltage. The three-phase DBI circuit of the present invention adopts PWM modulation method, and the output side voltage can be obtained by the boost ratio of the ideal boost converter. The boost ratio is defined as follows:

[0047]

[0048] Among them, V oa ,V ob ,V oc is the voltage of the inverter output to the negative pole of the DC bus, d a ,d b ,d c is the duty cycle function of the three phases.

[0049] From the above formula, the duty cycle function of the circuit is

[0050]

[0051] Figure 3 The duty cycle function diagram of formula (5) is shown. By changing the values ​​of B and K, the duty cycle function expression is changed, thereby changing the working modes of the three DBIs.

[0052] As one implementation of an embodiment of the present invention, in step S2, the primary source of loss in the three-phase DBI circuit is the MOSFET. The first step in analyzing MOSFET losses is to determine the current flowing through the device. Because the circuit is three-phase symmetrical, the following work uses phase A as an example. In steady-state conditions, the relationship between the inductor current and the load current is:

[0053]

[0054] Among them, I a is the output current of phase A, I La_steady Phase A inductance L in steady state a The current, R L is the equivalent internal resistance of the inductor.

[0055] In practical applications, there is V in Much larger than R L I La Although the output capacitor exhibits zero net power loss in long-term steady-state operation, the above derivation method ignores its non-negligible periodic charging and discharging dynamic characteristics within a single switching cycle. By accurately quantifying the capacitor energy transfer within the cycle (i.e., equivalently treating it as the instantaneous output power component), and by incorporating the capacitor power term into equation (6), the inductor current can be expressed as follows:

[0056]

[0057] Among them, I La_cal This is the expression of the phase A inductor current after considering the capacitance proposed by the present invention, where C is the capacitance value of phase A.

[0058] Figure 4 The comparison between the current waveform derived from equations (6) and (7) and the actual waveform is shown. It can be noticed that the actual current waveform has high-frequency pulsation due to the charging and discharging of the inductor within one switching cycle.

[0059] Figure 5 The two modes of device operation are shown. Mode 1 includes two situations: the lower tube S a2 On, upper tube S a1 When turned off, the inductor current I La From the down tube Sa2 The channel flows back to the negative power supply or through the lower tube S a2 The anti-parallel diode is connected to the dead zone; when it is in the dead zone, before the start of the dead zone, I La <0. At this time, the inductor current I La From the down tube S a2 The anti-parallel diode is connected to the circuit for freewheeling. Figure 5 (a) indicates the current flowing through the lower tube S a2 Diode freewheeling, Figure 5 (b) indicates the current flowing through the lower tube S a2 Channel. Mode 2 includes two cases: upper tube S a1 Conducting, lower tube S a2 When turned off, the inductor current I La S a1 The anti-parallel diode to the load and capacitor C a Power supply, or through the upper tube S a1 Channel reflux, feedback to the DC side; when in the dead zone, before the start of the dead zone, I La >0. At this time, the inductor current I La From the upper tube S a1 The anti-parallel diode is connected to the circuit for freewheeling. Figure 5 (c) indicates the current flowing through the upper tube S a1 Diode freewheeling, Figure 5 (d) indicates the current flowing through the upper tube S a1 Channel. The mathematical models under different modes are: Mode 1:

[0060]

[0061] Mode 2:

[0062]

[0063] In the above formulas (8) and (9), I a Output AC current for phase A.

[0064] Based on equations (8) and (9), the high-frequency pulsating current of the inductor can be obtained as

[0065]

[0066] Among them, Δi La is the high frequency component flowing through the inductor of phase A, f sw is the sampling frequency.

[0067] As an implementation of an embodiment of the present invention, in step S3,

[0068] The formula for MOSFET conduction loss is as follows

[0069]

[0070] Among them, P C,M is the conduction loss of the MOS tube channel, P C,D is the conduction loss of the MOS tube body diode, T is the switching period, R DS,on is the drain-source resistance in the on state, I D is the drain current. V F0 is the forward voltage drop of the body diode, R F is the on-state resistance of the body diode, I F is the current flowing through the body diode.

[0071] For the three-phase DBI current in circuit analysis, its expression in one switching cycle can be given as

[0072]

[0073] Among them, I sa is the expression of the current flowing through the SiC MOSFET, Δi is the change in current flowing through the SiC MOSFET during one switching cycle, D is the duty cycle during one switching cycle, T sw is the sampling period.

[0074] It should be noted that although the duty cycle D in (12) is considered a constant, in actual circuits, it is a function that varies with time. a (t). Since the switching period T sw It is much smaller than the fundamental period, so the duty cycle can be approximated by taking the value of the duty cycle at the midpoint of the kth switching period:

[0075]

[0076] Among them, D k is the approximate duty cycle during the kth switching cycle.

[0077] According to formula (12) (13), we can get I sa The root mean square current expression and the simplified conduction loss calculation formula

[0078]

[0079] In the above formulas (14) and (15), I sa,rms is the RMS expression of the current flowing through the A-phase SiC MOSFET, t k is the starting time of the kth switching cycle, Δi is the change in current flowing through the SiC MOSFET during one switching cycle, I La is the inductor current flowing through phase A, Δi La is the high frequency component flowing through the inductor of phase A.

[0080] The following formula gives a widely used formula for calculating switching loss:

[0081]

[0082] For phase A, the upper tube S a1 and down tube S a2 The sum of the conduction time of each body diode in each cycle is one complete cycle. Therefore, Equation (16) can be written as:

[0083]

[0084] In the above formulas (16) and (17), P S,M is the switching loss of the MOS tube channel, E ON 、E OFF and E rec They are the turn-on energy loss, turn-off energy loss and reverse recovery loss of the anti-parallel diode for each pulse of MOSFET, V ref and I ref They are the switching voltage reference value and current reference value respectively.

[0085] The rated power of this invention is 2.5kW. The DC source voltage range is 100 to 300V, and the AC load voltage is 311V / 50Hz. The inductor and output capacitor are 150μH and 80μF, respectively. The SiC MOSFET model used in the circuit is IMW120R040M1H.

[0086] The power loss analysis and selected SiC devices proposed in this invention, Figure 6 Figure 1 shows the relationship between the total conduction and switching losses of a SiC-based three-phase DBI and the switching frequency. It can be seen that the circuit efficiency is highest at a switching frequency of 20kHz, so subsequent studies will use 20kHz as the switching frequency. Table 1 shows the device parameters of the three-phase DBI circuit analyzed in this paper.

[0087] Table 1

[0088] Parameter Values <![CDATA[Rated power, P m > 2.5kW <![CDATA[DC input voltage, V in > 100～300V <![CDATA[AC load voltage amplitude, V m > 150V <![CDATA[AC load voltage frequency, f o > 50Hz <![CDATA[Sampling frequency, f s > 100kHz <![CDATA[Switching frequency, f sw > 20kHz Inductance, L 150μH <![CDATA[Resistance value, R L > 2mΩ Output capacitance value, C 80μF

[0089] Based on the traditional loss calculation formula, the present invention improves the current expression on the basis of circuit analysis. Combined with the actual operating characteristics of MOSFET, it realizes loss calculation applicable to three-phase DBI circuit. Simulation is carried out in the actual circuit to verify the effectiveness of the proposed loss calculation method and give the optimal efficiency operating condition.

[0090] The proposed three-phase DBI circuit diagram was simulated in PLECS software at 20 kHz. Using the proposed loss calculation method, the inductor and capacitor values ​​in the simulation were 150 μH and 80 μF, respectively. The simulation was performed under an input voltage of 100-300 V. Figure 7 This is the simulation result of three-phase DBI circuit. Figure 8 、 Figure 9 The theoretical calculation and simulation results comparison of circuit efficiency under different switching frequencies and input voltages are given respectively.

[0091] Depend on Figure 8 It can be seen that when the switching frequency is 20kHz, the error of the loss calculation method of the present invention is the smallest, which is 0.43%. Figure 9 It can be seen that when the input voltage is 160V, the error between the loss calculation method proposed and the simulation experiment is the smallest, which is 0.1%. The two figures prove the effectiveness of the method of the present invention.

[0092] The present invention has the following advantages:

[0093] 1. The three-phase DBI circuit was analyzed, the inductor current was effectively fitted and an expression was given, which will help to deepen the subsequent research on the circuit.

[0094] 2. Perform modal analysis on the power devices in the circuit, explain their conduction conditions during circuit operation, and provide basic knowledge for device selection and loss calculation.

[0095] 3. By analyzing the power device losses at different frequencies and input voltages, the changing trend of circuit efficiency is obtained, which helps to select the appropriate operating conditions.

[0096] Example 2:

[0097] An embodiment of the present invention further provides a power loss calculation system for a single-stage differential boost inverter, comprising:

[0098] The first processing module is used to construct a three-phase differential boost inverter circuit based on SiC MOSFET;

[0099] The second processing module is used to analyze the inductor current in the three-phase differential boost inverter circuit to obtain an expression for the current flowing through the MOSFET;

[0100] The third processing module is used to obtain the power loss of the three-phase DBI according to the expression of the current flowing through the MOSFET.

[0101] As an implementation method of an embodiment of the present invention, a three-phase differential boost inverter circuit based on SiC MOSFETs is composed of three identical bidirectional DC / AC boost inverters; each phase bridge arm includes two MOSFET devices; the three-phase differential boost inverter circuit outputs a sinusoidal voltage with a DC bias.

[0102] As an implementation method of an embodiment of the present invention, the two modes of operation of the device when the three-phase differential boost inverter circuit is running are as follows:

[0103] Mode 1 includes two situations: when the lower tube is turned on and the upper tube is turned off, the inductor current flows back from the lower tube channel to the negative pole of the power supply or flows through the anti-parallel diode of the lower tube; when it is in the dead zone, at the moment before the dead zone begins, I La <0; at this time, the inductor current flows through the anti-parallel diode of the lower tube;

[0104] Mode 2 includes two situations: when the upper tube is turned on and the lower tube is turned off, the inductor current supplies power to the load and capacitor through the anti-parallel diode of the upper tube, or flows back through the upper tube channel and feeds back to the DC side; when it is in the dead zone, at the moment before the dead zone begins, I La >0; at this time, the inductor current flows through the anti-parallel diode of the upper tube.

[0105] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for calculating power loss of a single-stage differential boost inverter, characterized in that: include: Step S1, constructing a three-phase differential boost inverter circuit based on SiC MOSFET; Step S2: Analyze the inductor current in the three-phase differential boost inverter circuit to obtain an expression for the current flowing through the MOSFET; Step S3: Obtain the power loss of the three-phase DBI according to the expression of the current flowing through the MOSFET.

2. The method for calculating power loss of a single-stage differential boost inverter according to claim 1, wherein: The SiC MOSFET-based three-phase differential boost inverter circuit consists of three identical bidirectional DC / AC boost inverters; each phase contains two MOSFET devices; the three-phase differential boost inverter circuit outputs a sinusoidal voltage with a DC bias.

3. The method for calculating power loss of a single-stage differential boost inverter according to claim 1 is characterized in that the two modes of operation of the device when the three-phase differential boost inverter circuit is running are as follows: (a) includes two situations: when the lower tube is turned on and the upper tube is turned off, the inductor current flows back from the lower tube to the negative pole of the power supply or flows through the anti-parallel diode of the lower tube; when it is in the dead zone, at the moment before the dead zone begins, I La <0; at this time, the inductor current flows through the anti-parallel diode of the lower tube; (b) There are two cases: when the upper tube is turned on and the lower tube is turned off, the inductor current supplies power to the load and capacitor through the anti-parallel diode of the upper tube, or flows back through the upper tube and feeds back to the DC side; when it is in the dead zone, at the moment before the dead zone begins, I La >0; at this time, the inductor current flows through the anti-parallel diode of the upper tube.

4. A power loss calculation system for a single-stage differential boost inverter, characterized in that: include: The first processing module is used to construct a three-phase differential boost inverter circuit based on SiC MOSFET; The second processing module is used to analyze the inductor current in the three-phase differential boost inverter circuit to obtain an expression for the current flowing through the MOSFET; The third processing module is used to obtain the power loss of the three-phase DBI according to the expression of the current flowing through the MOSFET.

5. The power loss calculation system for a single-stage differential boost inverter according to claim 4, wherein: The SiC MOSFET-based three-phase differential boost inverter circuit consists of three identical bidirectional DC / AC boost inverters; each phase contains two MOSFET devices; the three-phase differential boost inverter circuit outputs a sinusoidal voltage with a DC bias.

6. The power loss calculation system for a single-stage differential boost inverter according to claim 5, wherein: The two modes of operation of the device when the three-phase differential boost inverter circuit is running are as follows: (a) includes two situations: when the lower tube is turned on and the upper tube is turned off, the inductor current flows back from the lower tube to the negative pole of the power supply or flows through the anti-parallel diode of the lower tube; when it is in the dead zone, at the moment before the dead zone begins, I La <0; At this time, the inductor current flows through the anti-parallel diode of the lower tube; (b) There are two cases: when the upper tube is turned on and the lower tube is turned off, the inductor current supplies power to the load and capacitor through the anti-parallel diode of the upper tube, or flows back through the upper tube and feeds back to the DC side; when it is in the dead zone, at the moment before the dead zone begins, I La >0; at this time, the inductor current flows through the anti-parallel diode of the upper tube.

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