A pre-stage circuit of a current source inverter for motor driving

Abstract

The present invention relates to a pre-stage circuit of a current source inverter for motor driving, comprising inductors L1 and L2, diodes D1 and D2, IGBT switch devices S1 and S2, and capacitor C1; one end of the inductor L1 is connected to the positive terminal of a DC power grid, the other end of the inductor L1 is connected to one end of the inductor L2 via the switch device S1, the other end of the inductor L2 is connected to the current source inverter, one end of the diode D1 is connected between the inductor L1 and the switch device S1, the other end of the diode D1 is simultaneously connected to one end of the switch device S2 and one end of the capacitor C1, the other end of the switch device S2 is connected between the switch device S1 and the inductor L2, and is simultaneously connected to one end of the diode D2, the other end of the capacitor C1 is simultaneously connected to the negative terminal of the DC power grid, the other end of D2 and the current source inverter. The pre-stage circuit can not only generate current on the current source inverter side, but also control the magnitude of the current on the DC power grid side, and has lower power consumption.

Description

Technical Field

[0001] The invention belongs to the field of current source inverters, and in particular relates to a front-stage circuit of a current source inverter for motor driving. Background Art

[0002] The current source inverter (CSI) used for motor drive has the advantages of small voltage and current harmonics, high efficiency at high power, and boost drive. It is a possible inverter structure to be used in high-power drive situations.

[0003] The current source inverter can modulate DC current into AC current. It can control the current size on the AC side, but cannot control the current on the DC side. Therefore, the current source inverter drive system is often a two-stage structure. The inverter itself is the first stage, and the DC current generating circuit connected between the inverter and the power grid is the first stage, that is, the front stage circuit. When connected to an AC grid, the front stage circuit can use a current source rectifier (CSR), and when connected to a DC grid, a DC / DC circuit can be used. For example, when connecting to a DC grid, a common method is to use a Buck circuit to generate the required DC current, such as Figure 2 As shown, this will generate a large pulsating current on the DC side. If a cascaded Buck circuit structure is used, it will cause a large device power loss. The above problems limit the application of current source inverters in ordinary DC power grids. Summary of the invention

[0004] The object of the present invention is to provide a front-stage circuit of a current source inverter for motor driving, which can not only generate current on the current source inverter side, but also control the magnitude of the current on the DC grid side and has lower power consumption.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a front-stage circuit of a current source inverter for motor driving, comprising inductors L1 and L2, diodes D1 and D2, IGBT switching devices S1 and S2, and capacitor C1; one end of the inductor L1 is connected to the positive terminal of the DC power grid, the other end of the inductor L1 is connected to one end of the inductor L2 via the switching device S1, the other end of the inductor L2 is connected to the current source inverter, one end of the diode D1 is connected between the inductor L1 and the switching device S1, the other end of the diode D1 is simultaneously connected to one end of the switching device S2 and one end of the capacitor C1, the other end of the switching device S2 is connected between the switching device S1 and the inductor L2, and is simultaneously connected to one end of the diode D2, and the other end of the capacitor C1 is simultaneously connected to the negative terminal of the DC power grid, the other end of D2, and the current source inverter.

[0006] Furthermore, the front-stage circuit can control the current on the DC side and the current source side simultaneously to generate the required current.

[0007] Furthermore, the voltage of capacitor C1 is higher than the voltage of the DC grid.

[0008] Furthermore, when the switch device S1 is turned on, the current of the inductor L1 i 1 flows through the switch device S1 to the inductor L2. At this time, the inductor L2 current i 6= i 2+ i 4, among which i 4 from i 3 or i 5. Depends on whether the switch device S2 is turned on;

[0009] When the switch device S1 is turned off, the inductor L1 current i 1 charges capacitor C1, causing the voltage of capacitor C1 to increase; at this time, the current of inductor L2 i 6 All from i 4. According to the conduction state of the switch device S2, i 4 from i 3 or i 5;

[0010] Capacitor C1 acts as a buffer and energy storage. When the capacitor voltage exceeds the set value (the set value should be higher than the DC grid voltage), the switch device S2 is turned on. At this time, capacitor C1 discharges and flows to the load through inductor L2.

[0011] When the switch device S1 is turned on and the switch device S2 is turned off, the DC grid voltage passes through the inductor L1. i 1= i 2 < i 6, so the diode D2 is turned on, the voltage at the connection point between the switch device S1 and the inductor L2 is approximately the negative terminal voltage of the DC grid, so the inductor L1 current i 1 Increase;

[0012] When the switch device S1 is turned off and the diode D1 is turned on, or when the switch device S1 is turned on and the switch device S2 is also turned on, one end of the inductor L1 is connected to the DC grid and the other end is connected to the positive electrode of the capacitor C1; since the voltage of the capacitor C1 is higher than the voltage of the DC grid, the current of the inductor L1 decreases at this time.

[0013] Furthermore, the control process of the switch device S1 is as follows: Assuming that the DC current to be sent to the current source inverter is I MRef In actual operation, the current is i 6. I MRef and i 6 is sent to the first subtractor for difference, and the difference is sent to the first PI controller to obtain the input current on the DC grid side I GRef ;WillI GRef As a reference current value and actual input current value i 1 Make a difference in the second subtractor, and send the difference to the second PI controller to get the control quantity u ctrl1 ; Modulation is performed in this way, that is, the carrier generated by the first carrier generator is compared with the first comparator, and the driving signal of the switching device S1 is obtained. G 1.

[0014] Furthermore, the control process of the switch device S2 is as follows: Assuming that the reference voltage of the capacitor C1 is U CRef , the actual working voltage of capacitor C1 is U C1 , send the two to the third subtractor for difference, and send the difference to the third PI controller to get the control quantity u ctrl2 ; Modulate it, that is, compare it with the carrier generated by the second carrier generator through the second comparator, and obtain the driving signal of the switching device S2 G 2.

[0015] Compared with the prior art, the present invention has the following beneficial effects: in the present invention, a part of the energy from the DC grid to the driving load passes through the diode D1 and the switch device S2, while the other part only passes through the switch device S1. In particular, when the motor speed is high, the current sent to the load is i 6 Close to DC side current i 1. Most of the energy reaches the load only through the switch device S1, which helps to reduce the loss of the device. i 1 and i 6 are continuous rather than pulse currents. The former is beneficial to reducing the impact on the power grid, thus eliminating the need for additional large-capacity capacitors for filtering, while the latter meets the needs of the CSI circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 1 is a front-stage circuit diagram of an embodiment of the present invention.

[0017] Figure 2 This is a conventional front-stage circuit diagram that can generate direct current in an embodiment of the present invention.

[0018] Figure 3 1 is a structural diagram of a current source inverter in an embodiment of the present invention.

[0019] Figure 4 is a control circuit diagram of the switch device S1 in an embodiment of the present invention.

[0020] Figure 5 is a control circuit diagram of the switch device S2 in an embodiment of the present invention.

[0021] Figure 6 1 is a current waveform diagram of multiple branches in the front-stage circuit in an embodiment of the present invention.

[0022] Figure 7 1 is a waveform diagram of motor drive related parameters of a current source inverter using the front-stage circuit in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0024] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] Conventional current source inverter (CSI) such as Figure 3 As shown, by controlling the switching devices of each phase, the DC current is connected to different circuits during the conduction time, that is, the current is modulated, and after filtering by the capacitor, the motor can obtain a sinusoidal drive current.

[0027] like Figure 1 As shown, this embodiment provides a front-stage circuit of a current source inverter for motor driving, which is connected in series between a conventional CSI and a DC power grid, and includes inductors L1 and L2, diodes D1 and D2, IGBT switching devices S1 and S2, and capacitor C1; one end of the inductor L1 is connected to the positive terminal of the DC power grid, the other end of the inductor L1 is connected to one end of the inductor L2 via the switching device S1, the other end of the inductor L2 is connected to the current source inverter, one end of the diode D1 is connected between the inductor L1 and the switching device S1, the other end of the diode D1 is simultaneously connected to one end of the switching device S2 and one end of the capacitor C1, the other end of the switching device S2 is connected between the switching device S1 and the inductor L2, and is simultaneously connected to one end of the diode D2, and the other end of the capacitor C1 is simultaneously connected to the negative terminal of the DC power grid, the other end of D2, and the current source inverter.

[0028] The front-stage circuit of the above-mentioned motor driving current source inverter can control the current on the DC side and the current source side at the same time to generate the required current. Its working principle is:

[0029] (1) When the switch device S1 is turned on, the current of the inductor L1 i 1 flows through the switch device S1 to the inductor L2. At this time, the inductor L2 current i 6= i 2+ i 4, among which i 4 may come from i 3. It may also come from i 5. Depends on whether the switch device S2 is turned on.

[0030] (2) When the switch device S1 is turned off, the current of the inductor L1 i 1 charges capacitor C1, causing the voltage of capacitor C1 to increase; at this time, the current of inductor L2 i 6 All from i 4. According to the conduction state of the switch device S2, i 4 may come from i 3. It may also come from i 5.

[0031] (3) Capacitor C1 acts as a buffer and energy storage. When the capacitor voltage exceeds the set value (the set value should be higher than the DC grid voltage), the switch device S2 opens. At this time, capacitor C1 discharges and flows to the load through inductor L2.

[0032] (4) When the switch device S1 is turned on and the switch device S2 is turned off, the DC grid voltage passes through the inductor L1. i 1= i 2< i 6, so the diode D2 is turned on, the voltage at the connection point between the switch device S1 and the inductor L2 is approximately the negative terminal voltage of the DC grid, so the inductor L1 current i 1 Increase.

[0033] (5) When the switch S1 is turned off and the diode D1 is turned on, or when the switch S1 is turned on and the switch S2 is also turned on, one end of the inductor L1 is connected to the DC grid and the other end is connected to the positive electrode of the capacitor C1; since the voltage of the capacitor C1 is higher than the voltage of the DC grid, the current of the inductor L1 decreases at this time.

[0034] From the above analysis, we can see that (1) if S1 is turned on, the DC grid voltage will directly act on the CSI circuit through the inductor. When the drive motor speed is low, the back electromotive force is small and cannot balance the DC grid voltage, which will cause the current to continue to increase. When S1 is turned off, the DC grid side is connected to capacitor C1 through inductor L1. Since the voltage of C1 is higher than the DC grid voltage U g1 , will makei 1 current decreases. Therefore, by controlling the S1 switch, the DC grid side current can be controlled i 1. (2) Capacitor C1 acts as an energy buffer or current converter, absorbing part of i 1 current and convert it into i 3 Current, the current that is ultimately output to the CSI circuit i 6 Current from the grid side i 2 and from the energy buffer circuit i 4. The buffer circuit based on capacitor C1 cannot control its output current, but depends on the input current i 1. Current i The larger the 1 is, the more energy is input. After the buffer circuit is converted, the output current i 4 is also larger. (3) From the perspective of energy balance, assuming that the CSI output load current remains unchanged, when the drive motor speed is low, the back electromotive force is low, the load energy consumption is small, and the current i 6 Much larger than the current i 1. At this time, S1 is in the off state for most of the switching cycle, so most of the energy is buffered by capacitor C1 and then sent to i 6. When the motor speed increases, the back electromotive force increases, the load energy consumption increases, and the current i 6 Approaching i 1. At this time, S1 is in the on state most of the time during the switching cycle, and most of the current flows directly from the DC grid to the load through S1.

[0035] The control method of the switch device S1 in the front stage circuit is as follows: Figure 4 Assume that the DC current to be sent to the current source inverter is I MRef (Its value is related to the motor control algorithm and is not within the scope of the present invention). This is the CSI DC current reference value required in the drive motor control algorithm. In actual operation, this current is i 6. I MRef and i 6 is sent to subtractor 1 for difference, and the difference is sent to PI controller 1 to obtain the input current of the DC grid side I GRef ;Will I GRef As a reference current value and actual input current value i 1 Make a difference in subtractor 2, and send the difference to PI controller 2 to get the control quantity u ctrl1 ; Modulation is performed by comparing the carrier generated by the carrier generator 1 with the comparator 1 to obtain the driving signal of the switching device S1 G 1.

[0036] The control method of the switch device S2 is as follows: Figure 5 Assume that the reference voltage of capacitor C1 is U CRef (higher than the DC bus voltage), the actual working voltage of capacitor C1 is U C1 , send the two to subtractor 3 for difference, and send the difference to PI controller 3 to get the control quantity u ctrl2 ; Modulation is performed by comparing the carrier generated by the carrier generator 2 with the comparator 2 to obtain the driving signal of the switching device S2 G 2.

[0037] The control effect of the front stage circuit of the present invention is as follows: Figure 6 As shown, it can be seen that although i 2 and i 4 There are pulse currents in both cases, but the DC grid side current i 1 and CSI side current i 6 is relatively stable and only contains switching harmonics. The effect of using this type of CSI inverter to drive the motor is as follows Figure 7 As shown, it can be seen that the motor can obtain a smooth sinusoidal current and achieve speed regulation operation.

[0038] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A front-stage circuit of a current source inverter for motor driving, characterized in that: It includes inductors L1 and L2, diodes D1 and D2, IGBT switching devices S1 and S2, and capacitor C1; one end of the inductor L1 is connected to the positive terminal of the DC power grid, the other end of the inductor L1 is connected to one end of the inductor L2 via the switching device S1, the other end of the inductor L2 is connected to the current source inverter, one end of the diode D1 is connected between the inductor L1 and the switching device S1, the other end of the diode D1 is simultaneously connected to one end of the switching device S2 and one end of the capacitor C1, the other end of the switching device S2 is connected between the switching device S1 and the inductor L2, and is simultaneously connected to one end of the diode D2, and the other end of the capacitor C1 is simultaneously connected to the negative terminal of the DC power grid, the other end of D2, and the current source inverter; When the switch device S1 is turned on, the inductor L1 current i 1 flows through the switch device S1 to the inductor L2. At this time, the inductor L2 current i 6= i 2+ i 4, among which i 4 from i 3 or i 5. Depends on whether the switch device S2 is turned on; When the switch device S1 is turned off, the inductor L1 current i 1 charges capacitor C1, causing the voltage of capacitor C1 to increase; at this time, the current of inductor L2 i 6 All from i 4. According to the conduction state of the switch device S2, i 4 from i 3 or i 5; Capacitor C1 acts as a buffer and energy storage. When the capacitor voltage exceeds the set value, the switch device S2 opens, and capacitor C1 discharges and flows to the load through inductor L2. When the switch device S1 is turned on and the switch device S2 is turned off, the DC grid voltage passes through the inductor L1. i 1= i 2 < i 6, so the diode D2 is turned on, the voltage at the connection point between the switch device S1 and the inductor L2 is approximately the negative terminal voltage of the DC grid, so the inductor L1 current i 1 Increase; When the switch device S1 is turned off and the diode D1 is turned on, or when the switch device S1 is turned on and the switch device S2 is also turned on, one end of the inductor L1 is connected to the DC grid and the other end is connected to the positive electrode of the capacitor C1; since the voltage of the capacitor C1 is higher than the voltage of the DC grid, the current of the inductor L1 decreases at this time.

2. The front stage circuit of a current source inverter for motor driving according to claim 1, characterized in that: The front-stage circuit can control the current on the DC side and the current source side at the same time to generate the required current.

3. The front stage circuit of a current source inverter for driving a motor according to claim 1, characterized in that: The voltage of capacitor C1 is higher than the DC grid voltage.

4. A front-stage circuit of a current source inverter for driving a motor according to any one of claims 1 to 3, characterized in that: The control process of the switch device S1 is: Assuming that the DC current to be sent to the current source inverter is I MRef In actual operation, the current is i 6. I MRef and i 6 is sent to the first subtractor for difference, and the difference is sent to the first PI controller to obtain the input current on the DC grid side I GRef ;Will I GRef As a reference current value and the actual input current value i 1 Make a difference in the second subtractor, and send the difference to the second PI controller to get the control quantity u ctrl1 ; Modulation is performed in this way, that is, the carrier generated by the first carrier generator is compared with the first comparator, and the driving signal of the switching device S1 is obtained. G 1.

5. The front stage circuit of a current source inverter for driving a motor according to any one of claims 1 to 3, characterized in that: The control process of the switch device S2 is as follows: Assuming that the reference voltage of the capacitor C1 is U CRef , the actual working voltage of capacitor C1 is U C1 , send the two to the third subtractor for difference, and send the difference to the third PI controller to get the control quantity u ctrl2 ; Modulate it, that is, compare it with the carrier generated by the second carrier generator through the second comparator, and obtain the driving signal of the switching device S2 G 2.

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