A circuit for reducing the thermal damage of a switching transistor of a pulse power generating unit

Abstract

The application provides a circuit for reducing the heat loss of a switching transistor of a pulse power generating unit, one side of an energy storage transformer is connected with a parallel input capacitor, the other side is connected with a parallel output capacitor, a storage inductor is arranged on the primary side of the energy storage pulse transformer and is connected with the switching transistor through a leakage inductor, an RDD branch is connected in parallel with the capacitor of the energy storage pulse transformer, and an RCD branch is connected in parallel on the series connection of the storage inductor and the leakage inductor of the primary side, the leakage energy of the energy storage pulse transformer is partially converted into RCD heat energy absorption, and the other part is resonated and consumed by using the parasitic capacitor of the transformer and the DBD load, the heat loss problem of the switching transistor is eliminated, an additional large-size radiator is not needed, and an additional power radiator design for the RCD branch is not needed, the volume of the whole MPPM is greatly reduced, and the reliability of the operation of the MPPM system is improved.

Description

Technical Field

[0001] This invention relates to the field of pulse power generation units, specifically a circuit for reducing the heat loss of the switching transistors in a pulse power generation unit. Background Technology

[0002] The power supply topology of the pulse power generation unit mainly consists of an energy storage pulse transformer T, an IGBT power switching unit Q, and a resistor-diode-diode (RDD) branch for the output pulse voltage shaping circuit. The electrode load of the DBD is equivalent to a capacitive load. The equivalent circuit of the energy storage pulse transformer T is generally as follows: the primary side consists of an ideal energy storage inductor, the number of primary turns, the number of secondary turns, and the primary leakage inductance. The primary side current can be divided into the current flowing through the energy storage inductor and the excitation current. The secondary side current of the transformer is the current of the DBD discharge electrode load.

[0003] Reducing the heat loss of switching transistors is a challenge in existing technologies. In practical engineering circuits, the parasitic capacitance between the collector and emitter of an IGBT is typically on the order of picofarads, and the primary leakage inductance of an energy storage pulse transformer is typically on the order of microhenries. Therefore, the unit of peak voltage is kilovolt. The heat loss on the switching transistor Q is considerable and increases exponentially with the increase of MPPM pulse power frequency. In practical engineering applications, to ensure the reliability of MPPM operation, it is necessary to add an additional large-volume heat sink and provide additional power cooling design for the RCD branch, which greatly reduces the overall size of the MPPM and improves the reliability of the MPPM system. Summary of the Invention

[0004] 1. The technical problem to be solved:

[0005] How to reduce the thermal loss of the switching transistor in the pulse power generation unit.

[0006] 2. Technical Solution:

[0007] To address the above problems, this invention provides a circuit for reducing the thermal loss of the switching transistor in a pulse power generation unit, comprising an energy storage pulse transformer T, wherein an input capacitor C is connected in parallel to one side of the energy storage transformer T. out On the other side, a parallel output capacitor U load The primary side of the energy storage pulse transformer T is equipped with an energy storage inductor L. p Through a single side leakage sensation L pri_lk The capacitor U of the energy storage pulse transformer T is connected to the switching transistor Q. load An RDD branch is connected in parallel, the RDD branch including a first diode D1 and a second diode D2 connected in series, wherein the second diode D2 is connected in parallel with a first resistor R1 in series with an energy storage inductor L. p and primary side leakage inductance Lpri_lk The upper parallel RCD branch includes a third diode D connected in series. s Second capacitor C s The second capacitor C s A second resistor R is connected in parallel. s .

[0008] The energy storage inductor L p The energy storage process is as follows: Energy storage inductor L p The DC voltage U through the boost converter T out Stored energy flows through the energy storage inductor L p Current I pri_st Linear increase, small excitation current I pri_m Energy is transferred to the secondary side. At this time, the high-voltage secondary side current I of the energy storage transformer is... sec The current is negative, flowing through the first resistor R1 and the first diode D1 of the RDD branch.

[0009] When the switching transistor Q is turned off, the third diode D in the RCD branch transistor... s Quickly enters the conduction state, one-time side leakage L pri_lk The current flows into the RCD branch and onto the third diode C. s Charging causes the second capacitor C to... s Go to U cs As the current gradually increases, the switching transistor Q is turned off with zero current.

[0010] When the input voltage U pulse The generated reflected voltage U pri Greater than transistor voltage U cs At that time, the diode D of the RCD branch s Cut off, U cs Peak voltage U cs_peak for:

[0011]

[0012] Therefore, the heat loss W of the RCD branch during a single pulse cycle can be derived. RCD_dis for:

[0013]

[0014] One side leakage sensation L pri_lk A portion of the energy is consumed in the RCD branch, and the remaining energy is utilized by the input voltage U at the output terminal of the pulse transformer secondary side. pulse High reflection voltage value U pri Resonance dissipation occurs, resulting in primary side leakage L. pri_lk During the resonant energy dissipation phase, the resonant circuit is controlled by the fourth diode D of the switching transistor Q. QOne side leakage sensation L pri_lk Energy storage inductor L p It is composed of the RCD branch, and at this time the current flowing through the switching transistor Q is always zero.

[0015] 3. Beneficial effects:

[0016] This invention converts part of the leakage inductance energy of the energy storage pulse transformer into RCD heat dissipation energy absorption, and the other part is dissipated by resonance using the parasitic capacitance of the transformer and DBD load. This not only eliminates the heat loss problem of the switching transistor, but also eliminates the need to add an additional large heat sink, and also eliminates the need to provide additional power heat dissipation design for the RCD branch, greatly reducing the overall size of the MPPM and improving the reliability of the MPPM system. Attached Figure Description

[0017] Figure 1 This is a circuit diagram of the present invention.

[0018] Figure 2 This is a waveform analysis diagram with RCD branch.

[0019] Figure 3 This is a waveform diagram of a power switching unit without an RCD branch.

[0020] Figure 4 This is a waveform diagram of the power switching unit with RCD branch.

[0021] Figure 5 This is a thermal image of the power switching transistor Q without RCD running for 5 minutes when the power switching frequency is 1.4kHz.

[0022] Figure 6 This is a thermal image of the RCD power switching transistor Q after 5 minutes of operation when the power switching frequency is 1.4kHz.

[0023] Figure 7 This is a thermal image of the power switching transistor Q without RCD running for 5 minutes when the power switching frequency is 2kHz.

[0024] Figure 8 This is a thermal image of the RCD power switching transistor Q after 5 minutes of operation when the power switching frequency is 2kHz. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings.

[0026] To address the heat loss problem of the power switching transistor Q in the pulse power generation unit, a circuit for reducing the heat loss of the switching transistor in the pulse power generation unit is proposed, such as... Figure 4 As shown, it includes an energy storage pulse transformer T, with an input capacitor C connected in parallel to one side of the energy storage simulcast transformer T. outOn the other side, a parallel output capacitor U load The primary side of the energy storage pulse transformer T is equipped with an energy storage inductor L. p Through a single side leakage sensation L pri_lk The capacitor U of the energy storage pulse transformer T is connected to the switching transistor Q. load An RDD branch is connected in parallel, wherein the RDD branch includes a first diode D1 and a second diode D2 connected in series, and the second diode D2 is connected in parallel with a first resistor R. 1， In the series-connected energy storage inductor L p and primary side leakage inductance L pri_lk The upper parallel RCD branch includes a third diode D connected in series. s Second capacitor C s The second capacitor C s A second resistor R is connected in parallel. s .

[0027] Although the proposed RCD branch circuit structure is similar to the traditional RCD snubber circuit in flyback topology, the operating mode of the applied circuit is different. The leakage inductance L on the primary side of the transformer... pri_lk Only a portion of the energy is consumed in the RCD branch. pri_lk The remaining energy is utilized by the high pulse voltage U at the secondary output of the pulse transformer. pulse High reflection voltage value U pri Resonant dissipation is achieved, eliminating the need for additional heat dissipation design for the RCD branch.

[0028] After adding the RCD branch, the energy storage inductor L p The energy storage is the same as when there is no RCD branch, and the specific process is as follows: Figure 2 As shown, the energy storage inductor L p The DC voltage U through the boost converter T out Stored energy flows through the energy storage inductor L p Current I pri_st Linear increase, small excitation current I pri_m Energy is transferred to the secondary side. At this time, the high-voltage secondary side current I of the energy storage transformer is... sec The current is negative, flowing through the first resistor R1 and the first diode D1 of the RDD branch.

[0029] like Figure 2 As shown, the switching transistor Q at t 2-1 When the circuit is turned off, diode D in the RCD branch is... s It quickly enters the conduction state, leakage inductance L pri_lk The current flows into the RCD branch to C s Charging makes the voltage U csAs the current gradually increases, the switching transistor Q is turned off with zero current, and the heat dissipation W... Q_dis Almost zero. RCD branch with U pri The relationship equation is as follows:

[0030]

[0031] exist Figure 2 Chinese 2-2 When U pulse The generated reflected voltage U pri For (N) p / N s )*U pulse_re Greater than U cs At that time, the diode D of the RCD branch s Cut off, U cs Peak voltage U cs_peak for:

[0032]

[0033] Therefore, the heat loss W of the RCD branch during a single pulse cycle can be derived. RCD_dis for:

[0034]

[0035] In t 2-2 to t 2-3 Between: is the primary side leakage inductance L pri_lk The resonant energy dissipation stage. The resonant circuit mainly consists of the fourth diode D of the switching transistor Q. Q Primary leakage inductance L pri_lk Energy storage inductor L p It consists of the RCD branch. At this time, the current flowing through the switching transistor Q is always zero, and there is almost no heat loss. Therefore, the heat loss problem of Q is solved from the perspective of circuit theory.

[0036] To address the issue of localized overheating at the DBD electrode load, a capacitive load C is used. load The key waveform of the power switching unit at 100pF is as follows: Figure 3 and Figure 4 As shown. Figure 3 For waveforms without RCD branches, I pri U is the current waveform flowing through the switching transistor Q. ce This is the voltage waveform between the collector and emitter of the IGBT, used to evaluate the switching losses of the switching transistor Q. Figure 4 The waveform is for the RCD branch.

[0037] from Figure 3It can be seen that when a turn-off signal is given to Q, due to the leakage inductance on the primary side of the pulse transformer, the current I flowing through transistor Q increases. pri It slowly declines from the peak at 4A. ce The voltage gradually increases, reaching a peak at 1.2 kV, forming the first loss overlap region ①, lasting for 0.5 μs, resulting in a heat loss of W. Q_dis1 Subsequently, U ce The current begins to decline from its peak, then reverses course and is no longer 0A, forming a loss overlap region ②, which lasts for 0.8μs. The resulting heat loss is W. Q_dis2 Then, resonant losses occur within the parasitic capacitance of the IGBT, resulting in a heat loss of W. Q_dis3 -W Q_dis6 .

[0038] After the primary side of the pulse transformer is connected in parallel with the RCD branch, U ce and I pri Waveform as Figure 4 As shown. When the PWM control signal is off, I pri From 4A, it dropped rapidly, U ce The voltage only rises to 100V, forming the first loss overlap region①, which lasts for 80ns, resulting in very little heat loss W. Q_dis1 It is evident that the proposed RCD branch can effectively address the heat loss problem of the switching transistor Q in the pulse power generation unit.

[0039] To more intuitively evaluate the effectiveness of the proposed RCD branch heat loss reduction method, Figures 5-8 The following are given: power switching transistor Q at different pulse power frequencies f PWM Comparison of thermal images after running for 5 minutes. Figure 5 and Figure 6 f was displayed PWM The effect of the proposed RCD branch at 1.4kHz is shown.

[0040] Then f PWM Slightly increasing the frequency to 2kHz, the thermal imaging comparison image is as follows. Figure 6 and Figure 7 As shown. The thermal equilibrium temperatures of the switching transistor Q are 83.7℃ and 115.3℃, respectively. Figure 5 and Figure 8 As shown, using the proposed RCD heat loss reduction method, the thermal equilibrium temperatures of the switching transistor Q were reduced to 43.3℃ and 52℃, respectively.

[0041] This invention utilizes the combined effect of the RCD-RDD dual branches. The RCD branch solves the heat loss problem of the switching transistor inside the power supply, while the RDD branch solves the heat generation problem of the DBD electrode load. This ensures the optimized size design of the MPPM system and the normal stable discharge operation of the DBD electrode load, and also enables safe and reliable contact with the human body.

Claims

1. A circuit for reducing the heat loss of a switching transistor in a pulse power generation unit, comprising an energy storage pulse transformer T, wherein the energy storage pulse transformer T has a primary winding Np and a secondary winding Ns, the primary winding Np having a parasitic primary leakage inductance Lpri_lk, and the secondary winding Ns having a parasitic secondary leakage inductance Lsec_lk; an input capacitor Cout is provided at the circuit input terminal, the primary circuit of the energy storage pulse transformer T is connected in parallel across the input capacitor Cout, and an output capacitor Cload is connected in parallel across the secondary circuit of the energy storage pulse transformer T; the primary circuit includes an energy storage inductor Lp and a switching transistor Q, the switching transistor Q having a built-in body diode DQ, and the switching transistor... The gate of Q is connected to a PWM control signal to control its on / off state for flyback energy storage and release; the positive terminal of the input capacitor Cout is connected to the first terminal of the energy storage inductor Lp and the first terminal of the RCD branch; the first terminal of the energy storage inductor Lp is connected to the non-same-name terminal of the primary coil Np of the energy storage pulse transformer, and the second terminal of the energy storage inductor Lp is connected to the same-name terminal of the primary coil Np of the energy storage pulse transformer. The same-name terminal of the primary coil Np is connected to the drain of the switching transistor Q through the parasitic primary leakage inductance Lpri_lk. The source of the switching transistor Q and the anode of the body diode DQ are connected to the negative terminal of the input capacitor Cout; the RCD branch is connected in parallel in the series connection of the energy storage inductor Lp, the primary coil Np, and the primary leakage inductance Lpri_lk. At both ends of the connecting branch, the RCD branch includes a third diode Ds, a second capacitor Cs, and a second resistor Rs; the cathode of the third diode Ds is connected to the positive terminal of the input capacitor Cout, and the anode of the third diode Ds is simultaneously connected to the positive terminal of the second capacitor Cs and one end of the second resistor Rs; the negative terminal of the second capacitor Cs and the other end of the second resistor Rs are connected to the connection node between the primary side leakage inductance Lpri_lk and the drain of the switching transistor; the two ends of the secondary side coil Ns of the energy storage pulse transformer T are connected in parallel with the RDD branch and the output capacitor Cload; the RDD branch includes a first diode D1, a second diode D2, and a first resistor R1; the corresponding terminal of the secondary side coil Ns is connected via the parasitic secondary side leakage inductance Lsec_l k connects to the cathode of the first diode D1; the anode of the first diode D1 is simultaneously connected to the anode of the second diode D2 and one end of the first resistor R1; the cathode of the second diode D2 and the other end of the first resistor R1 are connected to the non-identical terminals of the secondary coil Ns; the output capacitor Cload is connected in parallel across the two ends of the RDD branch; the energy storage process of the energy storage inductor Lp is as follows: the energy storage inductor Lp stores energy through the DC voltage Uout of the input capacitor Cout; the current Ipri_st flowing through the energy storage inductor Lp increases linearly; the small excitation current Ipri_m transfers the energy to the secondary side; at this time, the high-voltage secondary side current Isec of the energy storage transformer is negative; and the current flows through the first resistor R1 and the first diode D1 of the RDD branch.When the switching transistor Q is turned off, the third diode Ds in the RCD branch quickly enters the conducting state. The current in the primary leakage inductance Lpri_lk flows into the RCD branch, charging the second capacitor Cs and causing the voltage Ucs on Cs to gradually increase. At this time, the switching transistor Q is turned off with zero current.

2. The circuit for reducing the thermal loss of the switching transistor in the pulse power generation unit as described in claim 1, characterized in that: When the input voltage U pulse The generated reflected voltage U pri Greater than transistor voltage U cs At that time, the diode D of the RCD branch s Cut off, U cs Peak voltage U cs_peak for: Therefore, the heat loss W of the RCD branch during a single pulse cycle can be derived. RCD_dis for: 。 3. The circuit for reducing the thermal loss of the switching transistor in the pulse power generation unit as described in claim 1, characterized in that: One side leakage sensation L pri_lk A portion of the energy is consumed in the RCD branch, and the remaining energy is utilized by the input voltage U at the output terminal of the pulse transformer secondary side. pulse High reflection voltage value U pri Resonance dissipation occurs, resulting in primary side leakage L. pri_lk During the resonant energy dissipation phase, the resonant circuit is controlled by the fourth diode D of the switching transistor Q. Q One side leakage sensation L pri_lk Energy storage inductor L p It is composed of the RCD branch, and at this time the current flowing through the switching transistor Q is always zero.

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