A control method of a current source type converter based on bidirectional switch

Abstract

The application discloses a control method of a current source type converter based on a bidirectional switch, which comprises the following steps: firstly, obtaining a current sector where a three-phase current space vector is located; secondly, sampling three-phase voltages of the current source type converter by using a voltage detection circuit; thirdly, dividing the whole working interval into a main interval and a transition interval according to the three-phase voltage values; fourthly, using the same vector distribution table in the main interval and the transition interval; fifthly, not limiting the type of zero vector in each current sector; sixthly, adopting a two-step commutation mode in the main interval; seventhly, adopting a four-step commutation mode when commutation is performed between two phases with relatively close voltage values in the transition interval; and eighthly, adopting the two-step commutation mode in other cases. The control method can reduce the commutation time of the current source type converter, reduce the common-mode voltage in the transition interval of the converter, and reduce harmonic distortion, so as to guarantee the efficient and reliable operation of the current source type converter system.

Description

Technical Field

[0001] This invention relates to the field of commutation technology between bidirectional switches in converters, and specifically to a control method for a current source converter based on bidirectional switches. Background Technology

[0002] There are generally two topologies for power conversion circuits between DC and AC: voltage source converters and current source converters. Voltage source converters, compared to current source converters, have lower conduction losses due to the absence of series diodes, and are therefore widely used and researched. However, as the switching frequency of converters gradually increases, voltage source converters face the risk of bridge arm shoot-through and generate significant electromagnetic interference. Current source converters, on the other hand, have self-limiting current characteristics, do not have the risk of bridge arm shoot-through at high frequencies, and have lower electromagnetic interference, thus gaining increasing attention. Furthermore, due to the development of semiconductor devices in recent years, bidirectional switches have been developed. These switches have low conduction losses, four-quadrant operation characteristics, and inherent reverse blocking characteristics required by current source converters, as shown in the attached diagram. Figure 2 The four operating modes shown indicate that the bidirectional switch can eliminate the need for the diodes connected in series in the current source converter, thus overcoming the high conduction loss of the current source converter. This creates conditions for the current source converter to replace the voltage source converter at high frequencies.

[0003] However, current source converters based on bidirectional switches encounter new problems in commutation between two phases. Since normal operation of a current source converter requires no short circuits between capacitors and no open circuits in the circuit, overlapping commutation and dead-time commutation cannot be used. Therefore, diode mode must be introduced during commutation to ensure normal operation of the converter. The topology is shown in the attached figure. Figure 1 As shown. Since a two-phase bidirectional switch is actually four switches, the operating sequence of the four switches during the commutation process needs to be considered. The current four-step commutation method applied to this topology, which sequentially turns the four switches on or off, requires four steps, resulting in a long commutation process, affecting the output waveform quality, and increasing additional switching losses. A similar bidirectional switch commutation method exists in matrix converters, with one-step and two-step commutation methods having shorter commutation processes. The one-step commutation method has the shortest commutation process, but it requires the bidirectional switches to operate in diode mode even when current is flowing, resulting in high conduction losses and negating the significance of using bidirectional switches in current-source converters. The two-step commutation method, where the bidirectional switches are simultaneously open during current flow (as disclosed in Chinese Patent ZL200710168370.6, a control method and device for matrix converters), enhances the reliability of commutation in the transition region, but suffers from a large common-mode voltage in the transition region. Furthermore, the different vector distribution methods at the boundary between the main and transition regions lead to significant harmonic distortion, thus requiring further improvement. Summary of the Invention

[0004] The present application aims at the deficiency in the prior art, and provides a control method of a current source type converter based on bidirectional switches, which can reduce the commutation time of the current source type converter, reduce the common-mode voltage in the transition interval of the converter, and reduce the harmonic distortion, so as to ensure the efficient and reliable operation of the current source type converter system.

[0005] The present application provides a novel commutation method of a current source type converter based on bidirectional switches, which can reduce the commutation process, reduce the switching loss in the commutation, reduce the common-mode voltage in the transition interval of the converter, reduce the harmonic distortion, widen the range of the transition interval, and ensure the efficient and reliable operation of the converter system.

[0006] The present application adopts the technical scheme that:

[0007] A control method of a current source type converter based on bidirectional switches, which first obtains a current sector of a three-phase current space vector, then samples the three-phase voltage of the current source type converter by using a voltage detection circuit, divides the whole working interval into a main interval and a transition interval according to the three-phase voltage value, uses the same vector allocation table in the main interval and the transition interval, does not limit the type of zero vector in each current sector, adopts a two-step commutation mode in the main interval, adopts a four-step commutation mode when commutation is performed between two phases with similar voltage in the transition interval, and adopts a two-step commutation mode in other cases.

[0008] The commutation process in the transition interval is as follows:

[0009] It is judged whether the transition interval is u P ≈u M The transition interval, if yes, the two phases with similar voltage are P phase and M phase, in the transition interval, two-step commutation is adopted between P phase and N phase and between M phase and N phase, and four-step commutation is adopted between P phase and M phase. P ≈u M The transition interval is u M ≈u N The transition interval, at this time, the two phases with similar voltage are M phase and N phase, in the transition interval, two-step commutation is adopted between P phase and N phase and between P phase and M phase, and four-step commutation is adopted between M phase and N phase.

[0010] The switches with the same current direction are defined as forward pipes, and the switches with opposite current direction are defined as reverse pipes.

[0011] The four-step commutation between P phase and M phase passes through the following states in turn:

[0012] In PM1 state, the two semiconductor switches of M phase are all off, the forward tube of P phase is open as the current output channel, and the forward tube of N phase is open as auxiliary commutation;

[0013] In PM2 state, the forward tubes of P phase and M phase are open as possible current output channels, and the forward tube of N phase is open as auxiliary commutation;

[0014] In PM3 state, the two semiconductor switches of P phase are all off, the forward tube of M phase is open as the current output channel, and the forward tube of N phase is open as auxiliary commutation;

[0015] The four-step commutation between M phase and N phase successively passes through the following states:

[0016] In MN1 state, the two semiconductor switches of N phase are all off, the forward tube of M phase is open as the current output channel, and the reverse tube of P phase is open as auxiliary commutation;

[0017] In MN2 state, the forward tubes of M phase and N phase are open as possible current output channels, and the reverse tube of P phase is open as auxiliary commutation;

[0018] In MN3 state, the two semiconductor switches of M phase are all off, the forward tube of N phase is open as the current output channel, and the reverse tube of P phase is open as auxiliary commutation.

[0019] Compared with the prior art, the present application has the following advantages:

[0020] (1) Different commutation modes are adopted in the main interval and the transition interval of the present application, and four-step commutation is adopted when the voltage of two phases is close in the transition interval, and two-step commutation is adopted in other cases. Since four-step commutation is only performed when the voltage of two phases is close in the transition interval, and not in the transition interval, the reliability of commutation is ensured while the commutation time and switching loss are reduced as much as possible, and the output harmonics are reduced while the commutation process is reduced to the greatest extent.

[0021] (2) The same vector distribution mode is used in the main interval and the transition interval of the present application, and no specific zero vector is inserted, which reduces the common-mode voltage of the current source converter, and the harmonic distortion caused at the junction of the main interval and the transition interval is smaller, and the vector distribution mode can be flexibly changed according to the needs of application, and is no longer limited to one mode.

[0022] (3) The same vector distribution mode is used in the two intervals of the present application, and the two phases close to the transition interval are directly commutated through four steps. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a schematic diagram of the topology structure of the current source converter based on bidirectional switches.

[0024] Figure 2 The schematic diagram of four working modes of bidirectional switch.

[0025] Figure 3 The schematic diagram of control method of the application.

[0026] Figure 4 The schematic diagram of three-phase output voltage interval division.

[0027] Figure 5 The strategy diagram of traditional two-step commutation mode.

[0028] Figure 6 The commutation strategy diagram of transition interval of the control method of the application in u P ≈u M The commutation strategy diagram of transition interval of the control method of the application in u

[0029] Figure 7 The commutation strategy diagram of transition interval of the control method of the application in u M ≈u N The commutation strategy diagram of transition interval of the control method of the application in u DETAILED DESCRIPTION

[0030] The application will be further explained in detail in combination with the drawings and embodiments as follows:

[0031] The steps of the control method of the current source type converter based on bidirectional switch are as follows:

[0032] The first step: according to the space vector modulation principle, the sector where the three-phase current space vector is located is calculated through the three-phase reference current, the basic current vector is determined and the action time T1, T2, T0 of each vector is obtained, the modulation principle is referred to the published paper "Research on Space Vector Pulse Width Modulation Method", (China Electrical Engineering Journal, 2001, No. 5), considering the reduction of common mode voltage and the reduction of harmonic distortion caused by different vector distribution sequence at the junction of main interval and transition interval, the application does not use the way of inserting a specific zero vector (the specific zero vector will cause the maximum common mode voltage in the interval) in the transition interval but uses the same vector distribution way in the whole interval, that is, the same vector distribution table is used in the transition interval and the main interval, and the type of zero vector in the vector distribution way can be flexibly adjusted according to the needs of application, the specific vector distribution table in the embodiment is shown in Table 1, and commutation between two phases with similar voltage values is allowed in the distribution vector.

[0033] Table 1 vector distribution table

[0034]

[0035] Among them, I7 zero vector turns on the switch of a phase, I8 zero vector turns on the switch of b phase, and I9 zero vector turns on the switch of c phase.

[0036] In addition, the positions of the I7 zero vector, the I8 zero vector and the I9 zero vector in the vector distribution table can be replaced by other zero vectors except themselves to form a new vector distribution table.

[0037] Second step: divide each phase voltage cycle into 6 main intervals and 6 transition intervals in the following way, the division rule is as shown in Figure 4 u a u b u c a, b, c are the phase voltages at the three-phase capacitor, u P u M u N u

[0038] Main interval I: u a u c u b u P u a u M u c u N u b ;

[0039] Main interval II: u a u b u c u P u a u M u b u N u c ;

[0040] Main interval III: u b u a u c u P u b u M u a u N u c ;

[0041] Main interval IV: u b u c u a u P u b u M u c u N u a ;

[0042] Main interval V: u c u b>u a , u P = u c , u M = u b , u N = u a ;

[0043] Main interval VI: u c > u a > u b , u P = u c , u M = u a , u N = u b ;

[0044] The setting of the transition interval is to ensure that no short circuit occurs when the main interval commutation strategy is used due to the voltage sensor accuracy limit and the influence of the capacitor ripple, therefore, in the embodiment, the interval in which the absolute value of the difference of the two phases is less than 0.32 times the phase voltage amplitude is defined as the transition interval, corresponding to the above difference, the time width of the transition interval is calculated as 1.2 ms (the phase voltage period is 20 ms) through a sine function, and the 1.2 ms here is determined by the capacitor ripple and the voltage detection accuracy and the like, and can be appropriately adjusted without causing short circuit. The common-mode voltage of the present application is smaller under the same transition interval time width, and the width range of the transition interval is widened relative to the prior control method, so that the circuit is more reliable, and the present application still has a smaller common-mode voltage under a transition interval time width of 3.3 ms, and the circuit is relatively more reliable.

[0045] I-II transition interval: u P = u a , u M = u c , u N = u b ;

[0046] II-III transition interval: u P = u a , u M = u b , u N = u c ;

[0047] III-IV transition interval: u P = u b , u M = u a , u N = u c ;

[0048] IV-V transition interval: u P = u bu M =u c u N =u a ;

[0049] Transition interval from V to VI: u P =u c u M =u b u N =u a ;

[0050] VI-Ⅰ Transitional range: u P =u c u M =u a u N =u b ;

[0051] In the three transition intervals II-III, IV-V, and VI-I, u P and u M Approaching, denoted as u P ≈u M Transition intervals, in the other three transition intervals, u M and u N Approaching, denoted as u M ≈u N Transitional range.

[0052] The three-phase voltage at the capacitor of the current source converter is sampled to obtain the relative relationship of the three-phase voltage, and the current operating range of the converter is determined by the interval allocation method above.

[0053] Step 3: Based on the current vector and operating range at this time, obtain the main output state at this time, i.e. P, M, N in the state diagram;

[0054] Step 4: Determine if the working area is located within the main area. If yes, proceed to Step 5; otherwise, proceed to Step 6.

[0055] Step 5: Based on the current output state and the output state of the previous sampling cycle, the traditional two-step commutation method is used to control the bidirectional switch. The traditional two-step commutation strategy is as follows: Figure 5 As shown, proceed to step nine;

[0056] For example, if the output state of the previous sampling period was P and the current output state is M, then the switch state corresponding to the PM state will be executed first as a transition, and then the switch state corresponding to the M state will be executed.

[0057] Step 6: Determine if the transition interval is u P ≈u M If it is a transition interval, proceed to step seven; otherwise, it is u.M ≈u N Transition interval, into the eighth step;

[0058] Seventh step: according to the output state at this time and the output state of the last sampling period, control the bidirectional switch according to the transition interval commutation method as follows, u P ≈u M The commutation method of the transition interval is as shown in Figure 6 , wherein the switch in the same direction of the current is defined as the forward tube, and the switch in the opposite direction of the current is defined as the reverse tube, and then into the ninth step;

[0059] Since the first step vector distribution method allows commutation between two phases with similar voltages in the whole interval, it also requires commutation between two phases with similar voltages in the transition interval. Due to the close voltage between P phase and M phase, as well as the influence of voltage ripple, sensor accuracy and sampling delay, the voltage size relationship may be detected incorrectly, resulting in a short circuit during commutation. In order to ensure the safe commutation of P and M two phases, three intermediate states PM1, PM2 and PM3 are inserted between P and M two phases. The three intermediate states ensure that even if the voltage detection is incorrect, a short circuit will not occur during commutation, ensuring the reliability of the commutation. When commutation between other two phases (P and N, M and N) in the same interval, since the voltage difference is large, the voltage relationship detection error will not occur, so the two-step commutation with high efficiency is still used.

[0060] In the state of R, the two semiconductor switches of the P phase are opened as the current channel, the two semiconductor switches of the M phase are fully turned off, and the forward tube of the N phase is opened as the auxiliary commutation;

[0061] In the state of M, the two semiconductor switches of the P phase are fully turned off, the two semiconductor switches of the M phase are opened as the current channel, and the forward tube of the N phase is opened as the auxiliary commutation;

[0062] In the state of N, the reverse tubes of the P phase and the M phase are opened as the auxiliary commutation, and the two semiconductor switches of the N phase are opened as the current channel, which is the same as the state of N in the main interval;

[0063] In the state of MN, the two semiconductor switches of the P phase are fully turned off, the reverse tube of the M phase and the forward tube of the N phase are opened as the auxiliary commutation;

[0064] In the state of NP, the two semiconductor switches of the M phase are fully turned off, the reverse tube of the P phase and the forward tube of the N phase are opened as the auxiliary commutation, which is the same as the state of NP in the main interval;

[0065] In the state of PM1, the two semiconductor switches of the M phase are fully turned off, the forward tube of the P phase is opened as the current output channel, and the forward tube of the N phase is opened as the auxiliary commutation;

[0066] In PM2 state, the forward tubes of P phase and M phase are opened as possible current output channels, and the forward tube of N phase is opened as auxiliary commutation;

[0067] In PM3 state, the two semiconductor switches of P phase are fully turned off, the forward tube of M phase is opened as current output channel, and the forward tube of N phase is opened as auxiliary commutation;

[0068] The commutation from P phase to N phase and the commutation from N phase to P phase both need to pass through NP state first, belonging to two-step commutation.

[0069] The commutation from M phase to N phase and the commutation from N phase to M phase both need to pass through MN state first, belonging to two-step commutation.

[0070] The commutation from P phase to M phase needs to pass through PM1, PM2, PM3 state first, and the commutation from M phase to P phase needs to pass through PM3, PM2, PM1 state first, belonging to four-step commutation.

[0071] In the eighth step, the bidirectional switches are controlled according to the output state at this time and the output state in the last sampling period according to the transition interval commutation mode as shown in the following table: M ≈u N The commutation mode in the transition interval is shown in the following table: Figure 7 The switches with the same direction as the current direction are defined as forward tubes, and the switches with the opposite direction as the current direction are defined as reverse tubes, and then the ninth step is entered.

[0072] Since the first step of the vector allocation mode allows the commutation between two phases with similar voltages in the whole interval, the commutation between two phases with similar voltages in the transition interval is also required. Due to the close voltage between M phase and N phase, the voltage ripple, sensor accuracy, and sampling delay, etc., the voltage size relationship detection may be wrong, which may cause a short circuit during commutation. In order to ensure the safe commutation of M and N phases, three intermediate states MN1, MN2, and MN3 are inserted between M and N phases. The three intermediate states ensure that even if the voltage detection is wrong, a short circuit will not occur during commutation, ensuring the reliability of the commutation. During the commutation between the other two phases (P and M, P and N) in the same interval, since the voltage difference is large, the voltage relationship detection error will not occur, so the two-step commutation with high efficiency is still used.

[0073] In P state, the two semiconductor switches of P phase are opened as current channels, and the forward tubes of M phase and N phase are opened as auxiliary commutation, which is the same as the main interval P state;

[0074] In M state, the reverse tube of P phase is opened as auxiliary commutation, the two semiconductor switches of M phase are opened as current channels, and the two semiconductor switches of N phase are fully turned off;

[0075] In the N state, the reverse tube of the phase R is turned on as auxiliary commutation, the two semiconductor switches of the phase M are all turned off, and the two semiconductor switches of the phase N are turned on as current passage in both directions;

[0076] In the PM state, the reverse tube of the phase R and the forward tube of the phase M are turned on as auxiliary commutation, and the two semiconductor switches of the phase N are all turned off;

[0077] In the NP state, the two semiconductor switches of the phase M are all turned off, and the reverse tube of the phase R and the forward tube of the phase N are turned on as auxiliary commutation, which is the same as the NP state of the main interval;

[0078] In the MN1 state, the two semiconductor switches of the phase N are all turned off, the forward tube of the phase M is turned on as current output passage, and the reverse tube of the phase R is turned on as auxiliary commutation;

[0079] In the MN2 state, the forward tubes of the phases M and N are turned on as possible current output passages, and the reverse tube of the phase P is turned on as auxiliary commutation;

[0080] In the MN3 state, the two semiconductor switches of the phase M are all turned off, the forward tube of the phase N is turned on as current output passage, and the reverse tube of the phase P is turned on as auxiliary commutation;

[0081] The commutation from the phase P to the phase M and the commutation from the phase M to the phase P both need to pass through the PM state first, belonging to two-step commutation.

[0082] The commutation from the phase P to the phase N and the commutation from the phase N to the phase P both need to pass through the NP state first, belonging to two-step commutation.

[0083] The commutation from the phase M to the phase N needs to pass through the MN1, MN2 and MN3 states first, and the commutation from the phase N to the phase M needs to pass through the MN3, MN2 and MN1 states first, belonging to four-step commutation;

[0084] The ninth step is to save the output state as the output state of the last sampling period, wait for the next sampling period, and enter the first step.

[0085] The unmentioned parts of the present application are applicable to the prior art.

Claims

1. A control method of a bidirectional switch-based current-source type converter, characterized by, The control method firstly obtains a current sector where a three-phase current space vector is located, then samples three-phase voltages of the power converter by using a voltage detection circuit, divides the whole working interval into a main interval and a transition interval according to the three-phase voltage values, uses the same vector distribution table in the main interval and the transition interval, does not limit the type of zero vector in each current sector, adopts two-step commutation in the main interval, adopts four-step commutation when commutation between two phases with closer voltage values in the transition interval, and adopts two-step commutation in other cases; The commutation process of the transition interval is as follows: whether the transition interval is u P ≈u M the transition interval is u P ≈u M the transition interval is u M ≈u N the transition interval is u Switches in the same direction as the current are defined as forward pipes, and switches in the opposite direction of the current are defined as reverse pipes; The four-step commutation between the P phase and the M phase successively passes through the following states: In the PM1 state, two semiconductor switches of the M phase are all turned off, the forward pipe of the P phase is turned on as a current output channel, and the forward pipe of the N phase is turned on as auxiliary commutation; In the PM2 state, the forward pipes of the P phase and the M phase are turned on as possible current output channels, and the forward pipe of the N phase is turned on as auxiliary commutation; In the PM3 state, two semiconductor switches of the P phase are all turned off, the forward pipe of the M phase is turned on as a current output channel, and the forward pipe of the N phase is turned on as auxiliary commutation; The four-step commutation between the M phase and the N phase successively passes through the following states: In the MN1 state, two semiconductor switches of the N phase are all turned off, the forward pipe of the M phase is turned on as a current output channel, and the reverse pipe of the P phase is turned on as auxiliary commutation; In the MN2 state, the forward pipes of the M phase and the N phase are turned on as possible current output channels, and the reverse pipe of the P phase is turned on as auxiliary commutation; In the MN3 state, two semiconductor switches of the M phase are all turned off, the forward pipe of the N phase is turned on as a current output channel, and the reverse pipe of the P phase is turned on as auxiliary commutation.

2. The control method of the bidirectional switch-based current-source type converter according to claim 1, characterized in that, The vector distribution table is as follows: In the vector distribution table, the I7 zero vector turns on the switch of the bridge arm corresponding to the a phase, the I8 zero vector turns on the switch of the bridge arm corresponding to the b phase, and the I9 zero vector turns on the switch of the bridge arm corresponding to the c phase. In addition, the positions of the I7 zero vector, the I8 zero vector and the I9 zero vector in the vector distribution table can be replaced by other zero vectors except themselves to form a new vector distribution table.

3. The control method of the bidirectional switch-based current-source-type converter according to claim 1, characterized by, The division mode of the main interval and the transition interval is that each phase voltage period is divided into six main intervals and six transition intervals, and the division rule is as follows: Main interval I: u a > u c > u b , u P = u a , u M = u c , u N = u b ; Main interval II: u a > u b > u c , u P = u a , u M = u b , u N = u c ; Main interval III: u b > u a > u c , u P = u b , u M = u a , u N = u c ; Main interval IV: u b > u c > u a , u P = u b , u M = u c , u N = u a ; Main interval V: u c > u b > u a , u P = u c , u M = u b , u N = u a ; Main interval VI: u c > u a > u b , u P = u c , u M = u a , u N = u b ; wherein u a ,u b ,u c are the phase voltages at the three-phase capacitor a, b, c; u P ,u M ,u N denote the maximum, intermediate and minimum voltage of the three-phase voltage, respectively: I-II transition zone: u P = u a , u M = u c , u N = u b ; II-III transition region: u P = u a , u M = u b , u N = u c ; III-IV transition region: u P = u b , u M = u a , u N = u c ; IV-V transition region: u P = u b , u M = u c , u N = u a ; V - VI transition region: u P = u c , u M = u b , u N = u a ; VI - I transition region: u P = u c , u M = u a , u N = u b ; In the three transition intervals II-III, IV-V, VI-I, u P and u M is close to, denoted as u P ≈u M is close to, denoted as u M and u N is close to, denoted as u M ≈u N is close to, denoted as u 4. The control method of the bidirectional switch-based current-source-type converter according to claim 1, characterized by, The control method has smaller common-mode voltage under the same time width of the transition interval, and widens the time width range of the transition interval.

5. The control method of the bidirectional switch-based current-source-type converter according to claim 1, characterized by, The interval where the absolute value of the difference between two phases is less than 0.32 times the phase voltage amplitude is defined as the transition interval, the time width of the transition interval is 1.2 ms, and the phase voltage period is 20 ms.

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