Servo driver and its overshoot-free current loop circuit

Abstract

This invention provides a servo driver and its overshoot-free current loop circuit. The overshoot-free current loop circuit includes three current loops disposed within the servo driver and corresponding to the U-phase, V-phase, and W-phase of the servo motor, respectively. Each current loop includes an actual current feedback module, a command current conversion module, a current comparison module, and a MOSFET switching module. The actual current feedback module is connected to the current output terminal of the corresponding phase and the first input terminal of the current comparison module. The command current conversion module is connected to the upper controller of the servo motor and the second input terminal of the current comparison module. The current comparison module is connected to the first input terminal of the MOSFET switching module and the voltage input terminal of the corresponding phase of the servo motor. The servo driver of this invention uses a purely hardware-based current loop. Through the interconnection and signal transmission between the modules, the overshoot of the current step response can be reduced by several times, improving the speed and accuracy of current control.

Description

Technical Field

[0001] This invention relates to the field of servo driver technology, and in particular to a servo driver and its overshoot-free current loop circuit. Background Technology

[0002] Typically, a servo motor drive and control system includes a position loop, a speed loop, and a current loop. The current loop is the lowest-level closed loop, and the position and speed loops are entirely built upon it. The performance of the current loop is generally measured by two metrics: the rise time and overshoot of the current step response. The shorter the rise time and the smaller the overshoot, the higher the performance of the current loop.

[0003] Existing servo drive control systems generally use a PID (Proportional-Integral-Derivative) algorithm to form the current loop. The PID calculation is performed in the controller's system software, while current detection feedback and current command execution are handled in the driver hardware. The current detection feedback is implemented by the ADC (Analog-to-Digital Converter) module in the driver, and the current command execution is implemented by the IGBT (Insulated-Gate Bipolar Transistor) module in the driver.

[0004] The aforementioned prior art has the following drawbacks:

[0005] 1. The current loop is implemented through digital calculations in the software, which has high latency and insufficient real-time performance, resulting in a large overshoot in the current step response;

[0006] 2. Using IGBTs as switching devices results in high switching losses and makes it difficult to operate at switching frequencies above 20kHz, thus limiting the accuracy of current control and affecting the performance of the current loop. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the defects of the current loop in the prior art, which is implemented by digital quantity calculation in software, resulting in high latency, insufficient real-time performance, and large overshoot of current step response. The present invention provides a servo driver and its overshoot-free current loop circuit.

[0008] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0009] The present invention provides a non-overshoot current loop circuit for a servo driver. The non-overshoot current loop circuit includes three current loops disposed in the servo driver and corresponding to the U phase, V phase and W phase of the servo motor, respectively. The current loops include an actual current feedback module, a command current conversion module, a current comparison module and a MOSFET (metal-oxide-semiconductor field-effect transistor) switching module.

[0010] The input terminal of the actual current feedback module is connected to the current output terminal of the corresponding phase of the servo motor, and the output terminal is connected to the first input terminal of the current comparison module; the input terminal of the command current conversion module is connected to the upper controller of the servo motor, and the output terminal is connected to the second input terminal of the current comparison module; the output terminal of the current comparison module is connected to the first input terminal of the MOSFET switching module, and the output terminal of the MOSFET switching module is connected to the voltage input terminal of the corresponding phase of the servo motor.

[0011] The actual current feedback module is used to collect the current actual current analog quantity of the corresponding phase of the servo motor, modulate the current actual current analog quantity to obtain the actual current analog modulation quantity, and output the actual current analog modulation quantity to the first input terminal of the current comparison module.

[0012] The command current conversion module is used to receive the command current digital quantity from the upper controller, convert the command current digital quantity into the command current analog quantity, modulate the command current analog quantity to obtain the command current analog modulated quantity, and output the command current analog modulated quantity to the second input terminal of the current comparison module.

[0013] The current comparison module is used to receive the actual current analog modulation amount and the command current analog modulation amount, and after comparison, outputs a switch control digital quantity to the first input terminal of the MOSFET switching module.

[0014] The MOSFET switching module includes a control circuit and a MOSFET three-phase bridge. The control circuit receives the digital control signal of the switch, processes it to obtain the switching state of the three arms of the MOSFET three-phase bridge at the next moment, and outputs it to the MOSFET three-phase bridge. The MOSFET three-phase bridge outputs voltage to the voltage input terminal of the corresponding phase of the servo motor according to the switching state. The switching state is used to control the actual current analog modulation amount at the next moment to approach the command current analog modulation amount.

[0015] Preferably, the current loop further includes a protection module, the input terminal of which is connected to the current output terminal of the corresponding phase of the servo motor, and the output terminal is connected to the second input terminal of the MOSFET switching module;

[0016] The protection module is used to detect the current actual current analog quantity of the corresponding phase of the servo motor, and when the current actual current analog quantity exceeds the current threshold, it triggers and outputs a shutdown signal to the second input terminal of the MOSFET switching module.

[0017] The control circuit is used to receive the shutdown signal and, in response to the shutdown signal, turn off the MOSFET three-phase bridge.

[0018] Preferably, in the current loop corresponding to phase W of the servo motor, the input terminal of the actual current feedback module is connected to the current output terminals of phases U and V of the servo motor. The actual current feedback module is used to collect the current actual current analog quantity of phases U and V of the servo motor, calculate the actual current analog modulation quantity of phase W through the operational amplifier circuit, and output the actual current analog modulation quantity to the first input terminal of the current comparison module.

[0019] Preferably, the actual current feedback module uses an isolation operational amplifier or a current transformer as the data acquisition device.

[0020] Preferably, the actual current feedback module uses an operational amplifier circuit to modulate the current actual current analog quantity to obtain the actual current analog modulation quantity.

[0021] Preferably, the command current conversion module uses a DAC (digital-to-analog converter) device to convert the digital command current into an analog command current.

[0022] Preferably, the current comparison module includes a comparator operational amplifier circuit.

[0023] Preferably, the operating frequency of the MOSFET three-phase bridge is above 200kHz.

[0024] Preferably, the control circuit is composed of an FPGA (Field Programmable Gate Array).

[0025] The present invention also provides a servo driver, including an overshoot-free current loop circuit as described above disposed therein.

[0026] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0027] The positive and progressive effects of this invention are as follows: The servo driver of this invention adopts a pure hardware current loop. Through the interconnection and signal transmission between the actual current feedback module, the command current conversion module, the current comparison module and the MOSFET switching module, the overshoot of the current step response can be reduced by several times, thereby improving the speed and accuracy of current control. Attached Figure Description

[0028] Figure 1 This is a circuit diagram of the current loop in Embodiment 1 of the present invention.

[0029] Figure 2 This is a specific circuit diagram of Embodiment 1 of the present invention.

[0030] Figure 3 This is a circuit diagram of the W-phase current loop in Embodiment 2 of the present invention. Detailed Implementation

[0031] The present invention will be described more clearly and completely below with reference to a preferred embodiment and the accompanying drawings.

[0032] Example 1

[0033] This embodiment provides a non-overshoot current loop circuit for a servo driver. The non-overshoot current loop circuit includes three current loops disposed within the servo driver and corresponding to the U-phase, V-phase, and W-phase of the servo motor, respectively. Figure 1 As shown in the figure (the illustration takes the U-phase current loop as an example, and the V / W phase current loop is similar; the content in the dashed box represents the internal components of the non-driver), the current loop includes an actual current feedback module 101, a command current conversion module 102, a current comparison module 103, and a MOSFET switching module 104.

[0034] The input terminal of the actual current feedback module 101 is connected to the current output terminal of the corresponding phase of the servo motor 201, and the output terminal is connected to the first input terminal of the current comparison module 103; the input terminal of the command current conversion module 102 is connected to the host controller 202 of the servo motor 201, and the output terminal is connected to the second input terminal of the current comparison module 103; the output terminal of the current comparison module 103 is connected to the first input terminal of the MOSFET switching module 104, and the output terminal of the MOSFET switching module 104 is connected to the voltage input terminal of the corresponding phase of the servo motor 201.

[0035] The actual current feedback module 101 is used to collect the current actual current analog quantity of the corresponding phase of the servo motor 201 (the current actual current analog quantity of the U / V / W phase is denoted as Act_iu / Act_iv / Act_iw respectively), modulate the current actual current analog quantity to obtain the actual current analog modulation quantity (the actual current analog modulation quantity of the U / V / W phase is denoted as Act_iuu / Act_ivv / Act_iww respectively), and output the actual current analog modulation quantity to the first input terminal of the current comparison module 103.

[0036] The command current conversion module 102 is used to receive the command current digital quantity from the host controller 202, convert the command current digital quantity into a command current analog quantity, modulate the command current analog quantity to obtain the command current analog modulation quantity (the command current analog modulation quantities of the U / V / W phases are denoted as Cmd_iuu / Cmd_ivv / Cmd_iww respectively), and output the command current analog modulation quantity to the second input terminal of the current comparison module 103.

[0037] The current comparison module 103 is used to receive the actual current analog modulation amount and the command current analog modulation amount, and after comparison, outputs a switch control digital quantity to the first input terminal of the MOSFET switch module 104.

[0038] The MOSFET switching module 104 includes a control circuit and a MOSFET three-phase bridge. The control circuit receives the digital value of the switch control, processes it to obtain the switching state of the three bridge arms of the MOSFET three-phase bridge at the next moment, and outputs it to the MOSFET three-phase bridge. The MOSFET three-phase bridge outputs voltage to the voltage input terminal of the corresponding phase of the servo motor according to the switching state. The switching state is used to control the actual current analog modulation amount at the next moment to approach the command current analog modulation amount.

[0039] Figure 2 A specific circuit diagram of the overshoot-free current loop circuit of this embodiment is shown. The actual current feedback module 101 uses a current transformer as the acquisition device. In other embodiments, the actual current feedback module 101 can also use an isolated operational amplifier as the acquisition device. The actual current feedback module 101 further uses an operational amplifier circuit to modulate the current analog quantity of the actual current to obtain an actual current analog modulation quantity. The command current conversion module 102 uses a DAC device to convert the command current digital quantity into a command current analog quantity. The current comparison module 103 includes a comparator operational amplifier circuit. Specifically, the positive input terminal of the comparator operational amplifier circuit is Act_iuu, and the negative input terminal is Cmd_iuu. If Act_iuu > Cmd_iuu, the module outputs a digital quantity of 0; otherwise, it outputs 1. The other two are similar. The control circuit is composed of an FPGA. The FPGA drives the MOSFET driving module. When the upper MOSFET (T1-T6) of each phase is turned on / the lower MOSFET is turned off, the current of that phase increases; when the lower MOSFET is turned on / the upper MOSFET is turned off, the current of that phase decreases. The operating frequency of the MOSFET three-phase bridge is preferably above 200kHz. It should be noted that the specific circuit diagrams for the DAC, comparator, and operational amplifier can be designed according to different components. Figure 2 This is just a simplified illustration.

[0040] The above current loop completes one feedback cycle in just 1 to 2 microseconds (the exact time depends on the selection of each module's components). The current regulation frequency can reach over 200 kHz with minimal delay, thus improving the speed and accuracy of current control.

[0041] In an alternative embodiment, the current loop may further include a protection module 105, wherein the input terminal of the protection module 105 is connected to the current output terminal of the corresponding phase of the servo motor 201, and the output terminal is connected to the second input terminal of the MOSFET switching module 104.

[0042] The protection module 105 is used to detect the current actual current analog quantity of the corresponding phase of the servo motor, and when the current actual current analog quantity exceeds the current threshold, it triggers and outputs a shutdown signal to the second input terminal of the MOSFET switching module 104.

[0043] The control circuit is used to receive the shutdown signal and, in response to the shutdown signal, turn off the MOSFET three-phase bridge.

[0044] The protection module 105 can protect the MOSFET from damage caused by overcurrent and overheating. Since the current loop is composed entirely of hardware and automatically closes upon power-up, to prevent excessive current from burning out the MOSFET when the command current is uncertain, overcurrent detection is added. If overcurrent is detected, the MOSFET is automatically shut down.

[0045] Example 2

[0046] This embodiment is basically the same as Embodiment 1, except that, as Figure 3 As shown, in this embodiment, corresponding to the current loop of phase W of the servo motor, the input terminal of the actual current feedback module 101 is connected to the current output terminals of phases U and V of the servo motor 201. The actual current feedback module 102 is used to collect the current analog quantities Act_iu and Act_iv of phases U and V of the servo motor 201, calculate the actual current analog modulation quantity Act_iww of phase W through the operational amplifier circuit, and output the actual current analog modulation quantity to the first input terminal of the current comparison module. Wherein, Act_iww=-(Act_iuu+Act_ivv), Act_iuu is the actual current analog modulation quantity of phase U, and Act_ivv is the actual current analog modulation quantity of phase V.

[0047] Example 3

[0048] This embodiment provides a servo driver, including an overshoot-free current loop circuit as described in Embodiment 1 or 2, disposed within it. The servo driver employs a purely hardware current loop, and through the interconnection and signal transmission between the actual current feedback module, command current conversion module, current comparison module, MOSFET switching module, and protection module, it can reduce the overshoot of the current step response by several times, thereby improving the speed and accuracy of current control.

[0049] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A servo driver overshoot-free current loop circuit, characterized by, The non-overshoot current loop circuit comprises three current loops corresponding to U-phase, V-phase and W-phase of the servo motor respectively, and the current loop comprises an actual current feedback module, an instruction current conversion module, a current comparison module and a MOSFET switch module; The input end of the actual current feedback module is connected with the current output end of the corresponding phase of the servo motor, and the output end is connected with the first input end of the current comparison module; The input end of the instruction current conversion module is connected with the upper controller of the servo motor, and the output end is connected with the second input end of the current comparison module; the output end of the current comparison module is connected with the first input end of the MOSFET switch module, and the output end of the MOSFET switch module is connected with the voltage input end of the corresponding phase of the servo motor; The actual current feedback module is used for collecting the current actual current analog quantity of the corresponding phase of the servo motor, modulating the current actual current analog quantity to obtain an actual current analog modulation quantity, and outputting the actual current analog modulation quantity to the first input end of the current comparison module; The instruction current conversion module is used for receiving the instruction current digital quantity from the upper controller, converting the instruction current digital quantity into an instruction current analog quantity, modulating the instruction current analog quantity to obtain an instruction current analog modulation quantity, and outputting the instruction current analog modulation quantity to the second input end of the current comparison module; The current comparison module is used for receiving the actual current analog modulation quantity and the instruction current analog modulation quantity, and outputting a switch control digital quantity to the first input end of the MOSFET switch module after comparison; The MOSFET switch module comprises a control circuit and a MOSFET three-phase bridge, the control circuit is used for receiving the switch control digital quantity, processing the switch control digital quantity to obtain the switch state of the three bridge arms of the MOSFET three-phase bridge at the next moment and outputting the switch state to the MOSFET three-phase bridge, and the MOSFET three-phase bridge is used for outputting a voltage to the voltage input end of the corresponding phase of the servo motor according to the switch state, and the switch state is used for controlling the actual current analog modulation quantity to approach the instruction current analog modulation quantity at the next moment.

2. The no-overshoot current loop circuit of claim 1, wherein, The current loop further comprises a protection module, the input end of the protection module is connected with the current output end of the corresponding phase of the servo motor, and the output end is connected with the second input end of the MOSFET switch module; The protection module is used for detecting the current actual current analog quantity of the corresponding phase of the servo motor, and outputting a shutdown signal to the second input end of the MOSFET switch module when the current actual current analog quantity exceeds a current threshold value; The control circuit is used for receiving the shutdown signal and shutting down the MOSFET three-phase bridge in response to the shutdown signal.

3. The no-overshoot current loop circuit of claim 1 or 2, wherein, In the current loop corresponding to the W phase of the servo motor, the input end of the actual current feedback module is connected with the current output end of the U phase and V phase of the servo motor, the actual current feedback module is used to collect the current actual current analog quantity of the U phase and V phase of the servo motor, calculate the actual current analog modulation quantity of the W phase through an operational amplifier circuit, and output the actual current analog modulation quantity to the first input end of the current comparison module.

4. The no-overshoot current loop circuit of claim 1, wherein, The actual current feedback module uses an isolation operational amplifier or a current transformer as a collection device.

5. The no-overshoot current loop circuit of claim 1, wherein, The actual current feedback module uses an operational amplifier circuit to modulate the current actual current analog quantity to obtain an actual current analog modulation quantity.

6. The no-overshoot current loop circuit of claim 1, wherein, The instruction current conversion module uses a DAC device to convert the instruction current digital quantity into an instruction current analog quantity.

7. The no-overshoot current loop circuit of claim 1, wherein, The current comparison module includes a comparator operational amplifier circuit.

8. The no-overshoot current loop circuit of claim 1, wherein, The working frequency of the MOSFET three-phase bridge is above 200 kHz.

9. The no-overshoot current loop circuit of claim 1, wherein, The control circuit is composed of an FPGA.

10. A servo driver characterized by comprising: The current loop circuit without overshoot comprises the current loop circuit without overshoot according to any one of claims 1-9.

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