A Loss Calculation Method for a Three-Phase Full-Bridge Uncontrolled Rectifier Circuit

Abstract

The present invention relates to the technical field of power device loss calculation, and particularly to a method for calculating the loss of a three-phase full-bridge uncontrolled rectifier circuit, which solves the technical defect that the method for calculating the power loss of a three-phase full-bridge uncontrolled rectifier circuit in the prior art is not simple enough. The invention gives an analytical expression for the periodic average conduction loss of the diodes in the three-phase full-bridge uncontrolled rectifier circuit, and an analytical expression for the periodic average switching loss of the diodes in the three-phase full-bridge uncontrolled rectifier circuit. The present invention provides a simple method for calculating the conduction loss and switching loss, which does not require high-frequency real-time data acquisition and calculation depending on hardware, and can be applied to the selection design of power devices and the design of cooling systems.

Description

Technical Field

[0001] The present invention relates to the technical field of power device loss calculation, and particularly to a loss calculation method for a three-phase full-bridge uncontrolled rectifier circuit. Background Art

[0002] The topology of a three-phase full-bridge uncontrolled rectifier circuit is a very simple circuit topology. As Figure 1 shown, it is composed of three diodes (D1, D3, D5) with a common cathode and three diodes (D2, D4, D6) with a common anode. The characteristic of a diode is that it conducts when the anode voltage is greater than the cathode voltage. Then, for the three diodes in the common cathode group, the one with the largest AC voltage connected to the anode conducts; while for the three diodes in the common anode group, the one with the smallest AC voltage connected to the cathode conducts. The topology of the three-phase full-bridge uncontrolled rectifier circuit is widely used in high-power variable current systems such as industrial frequency conversion, diesel generators, and diesel locomotives. In high-power frequency conversion systems, the heating of power devices usually needs to be considered key points in the design stage. Accurately calculating the loss of power devices and then configuring reasonable cooling equipment is crucial for the reliable operation of the entire system. However, at present, there is no simple method to calculate the power loss of a three-phase full-bridge uncontrolled rectifier circuit.

[0003] The published document with the application number 201610546731.5 discloses a power unit loss calculation method, and designs a loss calculation method and device for a diode three-phase full-bridge uncontrolled rectifier circuit. This method gives a loss calculation method for a diode uncontrolled rectifier circuit based on the mechanism. However, this calculation method relies on high-frequency real-time data acquisition and calculation of hardware, and does not give a simple average loss calculation method, and cannot be applied to product design. Summary of the Invention

[0004] To overcome the technical defect that the method for calculating the power loss of a three-phase full-bridge uncontrolled rectifier circuit in the prior art is not simple enough, the present invention provides a loss calculation method for a three-phase full-bridge uncontrolled rectifier circuit.

[0005] The present invention provides a loss calculation method for a three-phase full-bridge uncontrolled rectifier circuit, wherein the power supply of the three-phase full-bridge uncontrolled rectifier circuit is a three-phase AC sine wave, and the conduction interval of each diode in a sine wave cycle is 2π / 3. Taking phase A as an example, the conduction interval of diode D1 is Since the working current of each diode is the same in one cycle, when calculating the loss, only one of them needs to be calculated; the calculation method is as follows:

[0006] First, model the three-phase full-bridge uncontrolled rectifier circuit. Denote the initial phase angle of the phase A voltage sine wave as 0 and the amplitude as U m , then the expression of the phase A voltage is:

[0007] U a = U m sin(ωt)(1);

[0008] It is noted that there is a phase difference between the voltage and the current The amplitude of the current in phase A is I m , and the expression for the current in phase A is:

[0009]

[0010] Therefore, according to the expression for the on-state loss power of the diode P Dsal = I f (r f I f + V f0 ), the on-state loss of the diode D1 in the sine wave period is obtained as:

[0011]

[0012] Among them, in formula (3), r f and V f0 are obtained by first-order fitting of the typical curve data of the on-state voltage drop and on-state current of the diode;

[0013] Substituting formula (2) into formula (3), the on-state loss of the diode D1 can be obtained as:

[0014]

[0015] Secondly, for the reverse recovery loss power of the diode D1, first obtain the current at the turn-off moment as:

[0016]

[0017] Since a diode conducts only once in a sine wave period with a frequency of f, then, according to the expression for the average loss power in one working cycle T It is deduced that the reverse recovery loss power of the diode D1 in a sine wave period is:

[0018]

[0019] In formula (6), E rec (I f_rec ) is the functional representation of the diode power loss E rec and the current, U DC is the DC bus voltage actually used in specific applications, and U DC_test is the DC bus voltage used to measure the switching energy in the power device manual.

[0020] The technical solution provided by the present invention has the following advantages compared with the prior art: The present invention provides a simple calculation method for conduction loss and switching loss, which does not rely on high-frequency real-time data acquisition and calculation of hardware and can be applied to the selection design of power devices and the design of cooling systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings herein are incorporated into and constitute a part of this specification, showing embodiments consistent with the present invention and, together with the specification, are used to explain the principles of the present invention.

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 is the three-phase full-bridge uncontrolled rectifier circuit topology described in the embodiments of the present invention;

[0024] Figure 2 is the voltage V f borne by the diode of the present invention f versus the current I

[0025] Figure 3 is the power loss E rec of the diode of the present invention f versus the current I DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] In order to more clearly understand the above objects, features and advantages of the present invention, the following will further describe the solution of the present invention. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0027] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0028] The losses of the diode mainly include conduction loss P Dsal , turn-on loss, reverse recovery loss P Dsw and cut-off loss. Among them, the cut-off loss and turn-on loss of the diode are very small and can be ignored.

[0029] The conduction loss power of the diode refers to the product of the conduction voltage drop of the diode and the conduction current when the diode is in the conduction state, that is, P Dsal =V f If ;

[0030] The on-state voltage drop of the diode can generally be found in the data sheet provided by the manufacturer. Figure 2 The diode forward voltage drop V f and forward current I f For such a curve, the first-order linear approximation can be used to convert the on-state voltage drop V f Represented as V f =r f I f +V f0 , where r f and V f0 It can be obtained by first-order fitting of the above curve data.

[0031] Therefore, the formula V f =r f I f +V f0 Substitution formula P Dsal =V f I f , the diode conduction power loss expression can be obtained as: P Dsal =I f (r f I f +V f0 ).

[0032] The reverse recovery process of a diode is a very short process, which is basically no more than 1us. For such a short process, it is very difficult to calculate its loss using the integral method. However, according to the device manual provided by the manufacturer, it can be found that the reverse recovery loss is related to the current at the turn-off time (such as Figure 3 ). Therefore, in engineering calculations, the reverse recovery loss of the diode directly refers to the current-related characteristic curve published by the manufacturer, and its average power loss expression in one working cycle is: Among them, E rec (I f )for Figure 3 The function of the curve in the middle represents that I f is the current at the turn-off moment, T is the diode working cycle, V DC is the DC bus voltage actually used in the specific application, V DC _ test This is the DC bus voltage used in measuring switching energy in the power device manual. The ratio of these two voltages is used as a correction factor for the difference between the DC bus voltage actually used in reverse loss calculation and the voltage measured by the manual curve.

[0033] On this basis, in a certain embodiment of the present invention, a method for calculating the losses of a three-phase full-bridge uncontrolled rectifier circuit is provided, where the power supply of the three-phase full-bridge uncontrolled rectifier circuit is a three-phase AC sine wave. Figure 1 The analysis of the operating characteristics of each device in the circuit topology is shown in Table 1.

[0034] Table 1 Conduction status of each device

[0035]

[0036] As can be seen from Table 1, within a sine wave cycle, the conduction interval of each diode is 2π / 3. Taking phase A as an example, the conduction interval of diode D1 is Since the operating current of each diode is the same within one cycle, when calculating the losses, it is only necessary to calculate one of them; the calculation method is as follows:

[0037] First, model the three-phase full-bridge uncontrolled rectifier circuit. Denote the initial phase angle of the sine wave voltage of phase A as 0 and the amplitude as U m , then the expression of the voltage of phase A is:

[0038] U a = U m sin(wt) (1);

[0039] Denote the phase difference between the voltage and the current as The amplitude of the current of phase A is I m , and the expression of the current of phase A is:

[0040]

[0041] Therefore, according to the expression of the on-state loss power of the diode P Dsal = I f (r f I f + V f0 ), the on-state loss of diode D1 within the sine wave cycle is obtained as:

[0042]

[0043] Among them, in formula (3), r f and V f0 are obtained through the first-order fitting of the typical curve data of the on-state voltage drop and on-state current of the diode;

[0044] Substitute formula (2) into formula (3), and the on-state loss of diode D1 can be obtained as:

[0045]

[0046] Secondly, for the reverse recovery loss power of diode D1, first obtain the current at the turn-off moment as:

[0047]

[0048] Since a diode conducts only once within a sine wave period of frequency f, then, according to the expression for the average loss power within one working cycle T It is deduced that the reverse recovery loss power of diode D1 within one sine wave period is:

[0049]

[0050] In formula (6), E rec (I f_rec ) represents the functional relationship between the diode power loss E rec and the current, U DC is the DC bus voltage actually used in specific applications, and U DC_test is the DC bus voltage adopted when measuring the switching energy in the power device manual.

[0051] In this embodiment, the DIODE diode model is Infineon DD800S330305.

[0052] Diode saturation conduction voltage drop (first-order approximation): V d = r d I d + V d0 = 0.00195I d + 1.1295, diode reverse recovery loss energy E rec_d :

[0053] E rec_d (I f ) = 2.3005e-10I f 3 - 9.6426e-7I f 2 + 1.6075e-3I f + 0.247,

[0054] U dc_test = 1800V.

[0055] Parameter input is:

[0056] Power factor 0.95;

[0057] Phase current amplitude I: 1200;

[0058] Sine wave frequency f: 50Hz;

[0059] Bus voltage U dc : 1800V.

[0060] Loss calculation:

[0061]

[0062]

[0063]

[0064] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments described herein, but rather to the broadest scope consistent with the principles and novel features invented herein.

Claims

1. A method for calculating the losses of a three-phase full-bridge uncontrolled rectifier circuit. The power supply of the three-phase full-bridge uncontrolled rectifier circuit is a three-phase AC sine wave. In a sine wave cycle, the conduction interval of each diode is 2π / 3. Taking phase A as an example, the conduction interval of diode D1 is Since the operating current of each diode is the same in one cycle, when calculating the losses, it is only necessary to calculate one of them; it is characterized in that The calculation method is as follows: First, model the three-phase full-bridge uncontrolled rectifier circuit. Denote the initial phase angle of the sine wave of phase A voltage as 0 and the amplitude as U m , then the expression of phase A voltage is: U a = U m sin(wt)(1); It is noted that there is a phase difference between voltage and current The amplitude of the phase A current is I m , and the expression for the phase A current is as follows: Therefore, according to the diode conduction loss power expression P Dsal = I f (r f I f + V f0 ), the conduction loss of diode D1 within the sine wave period is obtained as follows: Among them, in formula (3), r f and V f0 are obtained by first-order fitting of the typical curve data of the diode forward voltage drop and forward current. Substituting formula (2) into formula (3), the conduction loss of diode D1 can be obtained as follows: Secondly, for the reverse recovery loss power of diode D1, first obtain the current at the turn-off moment as follows: Since a diode conducts only once within a sine-wave period of frequency f, then, according to the expression for the average power loss within one operating cycle T it is derived that the reverse recovery power loss of diode D1 within one sine-wave period is: In Equation (6), E rec (I f_rec ) represents the diode power loss E rec as a function of current, U DC is the DC bus voltage actually used in a specific application, and U DC_test is the DC bus voltage used to measure the switching energy in the power device manual.

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