CN104852621A - Switch driving method eliminating dead zone influence of neutral-point-clamped three-level topology switch - Google Patents

Abstract

The invention relates to a switch driving method eliminating dead zone influence of a neutral-point-clamped three-level topology switch. Each phase of bridge arm of three-level topology includes four switching tubes, the switch driving method includes the steps of: 1) detecting a current direction of current of each phase; 2) judging whether the direction of current of each phase is a set forward direction, if yes, executing step 3), and if no, executing step 4); 3) switching off in advance and switching on in a delayed manner the third and the fourth switching tubes of the corresponding phase in advance; and 4) switching off in advance and switching on in a delayed manner the first and the second switching tubes of the corresponding phase. Compared with the prior art, the switch driving method provided by the invention has the advantages of being high in control precision, effectively saving computing resources of a processor, etc.

Description

A switch driving method to eliminate the influence of dead zone of neutral-point-clamped three-level topology switch

technical field

The invention relates to a driving method for an IGBT of a three-level (neutral-point clamped) converter, in particular to a switch driving method for eliminating the influence of a dead zone of a neutral-point clamped three-level topology switch.

Background technique

Compared with the traditional two-level full-bridge topology, the three-level NPC (neutral point clamped) topology has a series of advantages: 1) small switching loss and high efficiency; 2) small dv/dt during switching , the electromagnetic interference (EMI) caused is small; 3) The output voltage waveform is three-level, the harmonic content is small, and the required filter inductance is small, which is beneficial to reduce system cost and power loss. It is precisely because of the above advantages that the three-level NPC topology has been widely used in medium voltage and high power, and has achieved good application results. In the three-level NPC topology, in order to prevent a certain bridge arm from passing through, it is necessary to add dead time between the first tube and the third tube, the second tube and the fourth tube of the bridge arm, so that the output voltage waveform will have a certain distortion.

In order to eliminate the voltage distortion caused by the dead time, the present invention proposes a dead time elimination method based on this topology. By detecting the flow direction of the three-phase current, the switching action is reasonably arranged to eliminate the influence of the dead time on the output voltage.

Contents of the invention

The object of the present invention is to provide a switch driving method with high control precision and saving computing resources to eliminate the influence of the dead zone of the neutral-point clamped three-level topology switch in order to overcome the above-mentioned defects in the prior art.

The purpose of the present invention can be achieved through the following technical solutions:

A switch driving method for eliminating the influence of the dead zone of a neutral-point clamped three-level topology switch. Each phase bridge arm of the three-level switch includes four switching tubes. The switch driving method includes the following steps:

1) Detect the current current direction of each phase;

2) Determine whether the current direction of each phase is the set positive direction, if so, then perform step 3), if not, then perform step 4);

3) Turn off the third and fourth switching tubes of the corresponding phases in advance and turn them on with a delay;

4) The first and second switching tubes corresponding to the phase are turned off in advance and turned on with a delay.

In said step 3) and step 4), the advance time of early shutdown is equal to the delay time of delayed turn-on.

The advance time of the early shutdown and the delay time of the delayed turn-on are both T _D :

T _D ＝1.2*(T _offmax -T _onmin )

Among them, T _offmax is the maximum time of IGBT turn-off delay, and T _onmin is the minimum time of IGBT turn-on delay.

The switch driving method is implemented by a digital integrated circuit.

The digital integrated circuit is CPLD.

Compared with the prior art, the present invention has the following advantages:

1. The present invention detects the flow direction of the three-phase current and reasonably arranges the switching action to eliminate the influence of the dead zone on the output voltage. It is not necessary to calculate how much the dead zone affects the output voltage, which improves the control accuracy and saves control The computing resources of the chip.

2. The dead zone control strategy of the present invention can be completely realized by CPLD, which has nothing to do with the modulation method, and has high versatility and is easy to realize.

Description of drawings

FIG. 1 is a schematic diagram of a topology structure of a three-level NPC;

Fig. 2 is a schematic diagram of the switching state of each bridge arm;

Among them, (2a) is a schematic diagram of [1] state, (2b) is a schematic diagram of [0] state, and (2c) is a schematic diagram of [-1] state;

Fig. 3 is a schematic diagram of the current flow circuit when the current direction is positive under the three switching states of each bridge arm;

Among them, (3a) is the current flow loop in the [1] state, (3b) is the current flow loop in the [0] state, and (3c) is the current flow loop in the [-1] state;

4 is a schematic diagram of the current flow circuit when the current direction is negative under the three switching states of each bridge arm;

Among them, (4a) is the current flow loop in the [1] state, (4b) is the current flow loop in the [0] state, and (4c) is the current flow loop in the [-1] state;

5 is a schematic diagram of waveforms of ideal drive signals and drive signals with dead zones added in different situations in the prior art;

Wherein, (5a) is the schematic diagram of the waveform when the current direction is positive, and (5b) is the schematic diagram of the waveform when the current direction is positive;

Fig. 6 is the waveform schematic diagram of the ideal drive signal and the drive signal with dead zone added in different situations by adopting the method of the present invention;

Among them, (6a) is a schematic diagram of the waveform when the current direction is positive, and (6b) is a schematic diagram of the waveform when the current direction is positive.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is carried out on the premise of the technical solution of the present invention, and detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

The topological structure of the three-level NPC is shown in Fig. 1, S ₁ , S ₂ , ..., S ₁₂ are IGBT switch tubes. Taking the first phase bridge arm as an example, as shown in Figure 2, each bridge arm of the three-level NPC has three states [1,0,-1], and it can only be two adjacent states in each switching cycle Switch between, that is, switch between 0 state and 1 state or switch between 0 state and -1 state.

Assume that the direction of the current shown in Figure 2 is positive, and the opposite is negative. When the current is positive, the current flow circuits in the three switching states are shown in Figure 3. It can be seen from Figure 3 that when _ia >0, no matter which state the bridge arm is in [1,0,-1], the switches S ₃ and S ₄ do not flow current, that is to say, no matter the What kind of driving signals S ₃ and S ₄ are in the off state will not affect the output voltage. In the case that the current direction can be accurately measured, we can make S ₃ and S ₄ in the off state when _ia >0, However, S ₁ and S ₂ are turned on and off according to the ideal switching time, thus eliminating the influence of the dead time on the output voltage waveform.

When the current is negative, the current flow circuit in the three switch states is shown in Figure 4. When _ia <0, no matter which state the bridge arm is in [1,0,-1], the switch tube S ₁ and S ₂ do not flow current, that is to say, no matter whether they are turned on or off, the output voltage will not be affected. In the case that the current direction can be accurately measured, we can make S ₁ and S ₂ in the off state when _ia >0 , while S ₃ and S ₄ are turned on and off according to the ideal switching time, thus eliminating the influence of the dead time on the output voltage waveform.

From the modulation method of the three-level topology, it can be known that each bridge arm can only switch between adjacent states in each switching cycle, as shown in Figure 5, the ideal driving signal and the driving signal with dead zone added in different situations For the influence of the dead zone, there is an error voltage between the actual output voltage U _AN and the ideal voltage U _ANO , let this voltage be ΔU _AN , then ΔU _AN can be expressed as follows:

${\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; AN</span>}}<span\; class="notranslate">\; =</span>\left\{\begin{array}{c}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; PWM</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>\\ \frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; PWM</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the above formula, T _d =t _d +t _on -t _off , t _d is the dead time, t _on is the turn-on delay of IGBT, t _off is the turn-off delay of IGBT; f _c =1/T _PWM —— Carrier frequency, T _PWM is the carrier period.

Through the above analysis, we can know that the actual output voltage after adding the dead zone can be expressed as:

U _AN ＝U _ANO +ΔU _AN

From the above analysis, it can be concluded that the output voltage deviation caused by the dead zone is related to the direction of the current flowing through the bridge arm and the dead zone time, so the accurate detection of the current direction is very important. If the detection of the current direction is wrong, the dead zone compensation will Backfired. According to the above analysis, it can be known that in the case of determining the direction of the current, the switch tube with no current flowing can be turned off all the time, but this requires that the direction of each phase current must be accurately detected. At the current zero crossing point, the error of the sensor will cause the current The direction detection will jump back and forth between positive and negative to affect the dead zone compensation, so here we don’t keep the tubes with no current flowing always off, but turn on a dead time in advance and delay a dead time to turn off, so that even in the current direction When the detection is inaccurate, there will not be too much output voltage error. The specific waveform diagram is shown in Figure 6.

Due to the symmetry of the bridge arm circuit, the waveform diagram in the case of N-O-N will not be specifically analyzed here. The influence of the optimized drive signal on the output voltage is analyzed below:

From the above analysis, we can know that there is an error voltage between the actual output voltage U _AN and the ideal voltage U _ANO , let this voltage be ΔU _AN , then ΔU _AN under the new dead strategy can be expressed as follows:

${\mathrm{<span\; class="notranslate">\; \&Delta;\; U</span>}}_{\mathrm{<span\; class="notranslate">\; AN</span>}}<span\; class="notranslate">\; =</span>\left\{\begin{array}{c}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; *</span>}}{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; PWM</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>\\ \frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; *</span>}}{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; PWM</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the above formula f _c =1/T _PWM - Carrier frequency.

Comparing formula (1), we can see that under this dead zone strategy, we reduce the error voltage by ±t _d *U _dc /T _PWM , which greatly reduces the influence of the dead zone time on the output voltage waveform.

According to the previous analysis, the switch driving method of this embodiment to eliminate the influence of the dead zone of the neutral-point clamped three-level topology switch can be implemented by digital integrated circuits such as CPLD, including the following steps:

1) Detect the current current direction of each phase;

2) Determine whether the current direction of each phase is the set positive direction, if so, then perform step 3), if not, then perform step 4);

3) Turn off the third and fourth switching tubes of the corresponding phases in advance and turn them on with a delay;

4) The first and second switching tubes corresponding to the phase are turned off in advance and turned on with a delay.

In step 3) and step 4), the advance time of early shutdown and the delay time of delayed turn-on are both T _D :

T _D ＝1.2*(T _offmax -T _onmin )

Among them, T _offmax is the maximum time of IGBT turn-off delay, and T _onmin is the minimum time of IGBT turn-on delay.

As shown in Figure 1, according to the above steps, the dead zone control strategy of this embodiment is as follows: when _ia >0, S ₃ and S ₄ are turned off in advance and delayed to turn on; when _ia <0, S ₁ , S 4 ₂ Early turn-off delay and turn on; when i _b >0, S ₇ and S ₈ turn on early turn-off delay; when i _b <0, S ₅ and S ₆ turn on early turn-off and delay; when _ic > 0, S ₁₁ and S ₁₂ are turned off in advance and delayed to turn on, and when _ic <0, S ₉ and S ₁₀ are turned off in advance and turned on with a delay.

Claims (5)

1. A switch driving method that eliminates the influence of the dead zone of the neutral-point clamped three-level topology switch, each phase bridge arm of the three-level switch comprises four switching tubes, it is characterized in that the switch driving method comprises the following steps : 1) Detect the current current direction of each phase; 2) Determine whether the current direction of each phase is the set positive direction, if so, then perform step 3), if not, then perform step 4); 3) Turn off the third and fourth switching tubes of the corresponding phases in advance and turn them on with a delay; 4) The first and second switching tubes corresponding to the phase are turned off in advance and turned on with a delay. 2. the switch drive method that eliminates the dead zone influence of neutral point clamp type three-level topology switch according to claim 1, is characterized in that, in described step 3) and step 4), the advance time of shutting off in advance and The delay time of delay opening is equal. 3. the switch drive method for eliminating the influence of the dead zone of the neutral-point clamped three-level topology switch according to claim 2, characterized in that the advance time of the early shutdown and the delay time of the delayed turn-on are both T _D : T _D ＝1.2*(T _offmax -T _onmin ) Among them, T _offmax is the maximum time of IGBT turn-off delay, and T _onmin is the minimum time of IGBT turn-on delay. 4. The switch driving method for eliminating the influence of the dead zone of the neutral-point clamped three-level topology switch according to claim 1, characterized in that, the switch driving method is implemented by a digital integrated circuit. 5. The switch driving method for eliminating the influence of the dead zone of the neutral-point clamped three-level topology switch according to claim 4, wherein the digital integrated circuit is a CPLD.