KR100823725B1 - Feed-forward compensation method and apparatus for pwm converter in a cascaded multilevel inverter - Google Patents

Abstract

An apparatus and a method for controlling a PWM(Pulse Width Modulation) converter of a cascaded multilevel topology are provided to prevent an over-voltage or a low voltage by uniformly maintaining a DC link voltage of each module. An apparatus for controlling a PWM(Pulse Width Modulation) converter of a cascaded multilevel topology includes a PWM converter, a PWM converter controller, an inverter module, and a DC link. The PWM converter converts an AC input power into a DC power by a PWM. The PWM converter controller controls the PWM converter, and is sequentially coupled to a voltage controller(34), a current controller(36), and a PWM generator(38). The inverter module inverts the DC power outputted from the PWM converter to an AC power, and drives an induction motor. The DC link is located between the PWM converter and the inverter module. The voltage of the DC link is compared with a reference voltage value, and is feed-backed to an input of the voltage controller. A current command value calculated from an output power of the inverter module is feed-forwarded to an input of the current controller with an output of the voltage controller.

Description

Feed-forward compensation method and apparatus for PWM converter in a cascaded multilevel inverter}

1 is a block diagram of a basic induction motor control system.

2 is a waveform diagram for explaining a problem caused by the difference in responsiveness between the PWM feedback value 8 and the inverter feedback value 9;

3 is an exemplary configuration of a general induction motor control system, illustrating the H-Bridge cascaded 3300 [V], 2 [MVA] 7-level PWM converter / inverter system.

4 is a detailed circuit diagram of the power unit of FIG. 3.

5 is a view for explaining CAN communication between the main control unit and the module control unit.

6 is a block diagram of a PWM converter controller having a forward compensation term according to the present invention.

<Description of reference numerals not indicated>

DC link (3), DC link capacitor (6), reference value (7), PWM feedback value (8), inverter feedback value (9), power circuit section (10), input power supply (11), input transformer (12) , Secondary side output (13), cell module (14), induction motor (15), pulse generator (16), three-phase step-up PWM converter (17), single-phase inverter (18), controller (20), module controller ( 22), voltage feedback value (39), forward compensation value (40)

The present invention relates to a method of increasing the responsiveness and reducing the voltage variation of an input PWM converter used in a cascaded multilevel topology for induction motor control.

The direct multi-level inverter circuit is easy to modularize and can be used in series as a high voltage inverter for induction motor control because the output voltage can be gradually increased by connecting modules in series. In this case, the inverter performs vector control for instantaneous torque control of the induction motor, returns the regenerative energy or regenerative power of the load facility to the power supply side when decelerating the motor, and uses a PWM converter to increase the facility utilization and efficiency by unit input power factor control. do.

1 shows a control circuit of an inverter driven induction motor including a general PWM converter. It includes a PWM converter (~ / =) (1) for converting AC power into DC but converting to PWM method and an inverter (= / ~) (2) for inverting DC into AC to drive the induction motor 15. , They are connected by a DC link 3. The PWM converter 1 and the inverter 2 are controlled by the PWM converter controller 4 and the inverter controller 5, respectively. The PWM converter controller 4 is composed of a voltage controller, a current controller, and a PWM unit, and feeds the DC link voltage back to the feedback input unit to compare the reference value with the reference value to make the voltage of the DC link 3 constant. The inverter controller 5 also controls the inverter 2 by feeding back a signal (PLG signal) output from the induction motor 15 to perform the speed control of the induction motor 15.

2 illustrates to compare the waveform of the reference value 7 with the PWM feedback value 8 and the inverter feedback value 9. The reference value 7 is given in the form of a square wave with distinct edges, but the PWM feedback value 8 and the inverter feedback value 9 follow a curve as shown in FIG. 2 depending on the response performance. Here, since the responsiveness of the PWM feedback value 8 and the inverter feedback value 9 is different, a waveform difference occurs between them, which degrades the performance of the control system as a whole.

In addition, when rapid acceleration and deceleration of the induction motor is required, in order to supply a constant DC power supply to the DC link 3, the gain of the PWM converter 1 must be increased and a large DC link capacitor 6 is required. This requires faster control cycles and higher switching frequencies, which adds to the burden on the control system, increases system losses, reduces efficiency, and increases prices.

To overcome this problem, we propose a controller structure that calculates the PWM converter current command value in advance from the voltage and current command value of the inverter controlling the motor so as to supply a constant DC power even in the case of load changes and directly inputs it to the current controller of the converter. .

It is therefore an object of the present invention to provide a PWM converter control device and method for a multilevel inverter system that improves responsiveness by reducing the variation of the DC link voltage by forward compensating power generated in the inverter module to the PWM converter.

The apparatus and method for PWM converter control of a multilevel inverter system according to the present invention basically include a PWM converter for converting AC input power by PWM to a PWM converter, a PWM converter controller for controlling the same, and a DC output from the PWM converter to an AC. An inverter module for driving an induction motor by inverse conversion, and a multilevel inverter system comprising a DC link between these PWM converter and the inverter.

According to the present invention, the PWM converter controller is a voltage controller, a current controller, a PWM generator is sequentially connected, the voltage of the DC link is fed back to the input of the voltage controller compared to the reference voltage value, the output of the inverter module The current command value calculated from the electric power is fed to the input of the current controller together with the output of the voltage controller.

로부터

에 의해 계산될 수 있다. 상기 인버터 모듈의 출력은 전원의 각 상별로 계산된다. 또한, 상기 전류제어기는 PI 제어기로 구성된다. 그리고 상기 PWM 컨버터의 제어 주기는 인버터의 제어 주기와 동일한 것을 특징으로 한다. The forward compensation current command value i _{qe_ff} of the PWM converter is the output power P _{xs_ff} of the inverter module and the input power supply voltage on the synchronous coordinate system.

from

Can be calculated by The output of the inverter module is calculated for each phase of the power source. In addition, the current controller is composed of a PI controller. And the control period of the PWM converter is characterized in that the same as the control period of the inverter.

Hereinafter, with reference to the accompanying drawings will be described in detail the invention.

Figure 3 shows the configuration of the 3300 [V], 2 [MVA] 7-level PWM converter and inverter system for implementing the spirit of the present invention.

The power circuit unit 10 includes an input transformer 12 and a power cell module 14. The input transformer 12 has nine secondary outputs 13 for supplying independent power supplies isolated from the input power supply 11 to each cell module 14. The power cell module 14 has three modules connected in series to form a phase. Referring to FIG. 4, the primary side of the input transformer 12 has a Y connection and the secondary side has a delta connection, and the cell module 14 at the three phase output of the secondary side constitutes a PWM converter. More specifically, the input terminal of the cell module 14 constitutes a three-phase boost type PWM converter 17 and the output stage has a structure of a single phase inverter 18, which shares a DC link capacitor (C in FIG. 4). Doing. The switching elements of each cell module 14 were all composed of 1700 [V] class Insulated Gate Bipolar Transistor (IGBT).

The control unit 20 includes a main control unit MAIN B / D 21, a module control unit CELL MAIN B / D 22, a sensing unit SINTF B / D 23, and an interface unit VFINTF B / D. It consists of 24. The main control unit 21 performs calculation (computing) for controlling the induction motor IM. The main controller 21 operates in conjunction with the MMI system 31, the host controller 32, and the web-based monitor system 33. The module controller 22 controls the PWM converter and the inverter. The module controller 22 receives the voltage command from the main controller 21 to perform PWM and outputs a gate signal for performing control of each cell module 14. The sensing unit 23 detects magnitudes of voltage and current from the input power source 11 and converts the magnitudes of the voltages and currents into digital signals through the AD converters (ADC B / D) 25. Send sensing data. The exchange of information between the main control unit 21 and the module control unit 22 employs CAN communication by the CAN communication unit 26, and the interface unit 24 provides high-speed digital communication that is robust against noise by achieving electrical isolation between the controllers. Is trying to.

In addition, the current applied to the induction motor 15 and the heating temperature of the motor is converted into digital in the AD converter 25 is transmitted to the main control unit 21 as sensing data, and detects the rotational speed of the motor 15 The output of the pulse generator (PLG) 16 (PLG signal) is also fed back and used for vector control of the induction motor 15.

5 is a configuration diagram for describing CAN communication between the main controller 21 and the module controller 22. The main control unit 21 and the module control unit 22 may perform bidirectional communication using CAN communication, and exchange command values and status information at a maximum speed of 1 [Mbps]. CAN communication connects various control units in parallel so that each controller can exchange information with each other smoothly and processes them in the order of priority. The advantage is that you can control it.

In FIG. 5, the main controller 21 performs speed control and current control for controlling the motor, and controls each single-phase inverter module controller INVERTER XY through the first CAN controller 26a, where X = A, B, C, Y =. The output voltage command value is transmitted to 1,2,3) every control cycle. At the same time, the main controller 21 transmits the output power of the motor to the PWM converter module controller CONVERTER XY, where X = A, B, C, Y = 1,2,3 through the second CAN controller 26b. The inverter module controller receives the voltage command value of the main controller, detects the DC link voltage, generates a driving signal of the switching element IGBT, and sends the module state information to the main controller 21. The PWM converter module controller receives a DC link command value from the main controller, detects an input voltage and a current, performs a unit power factor control algorithm, and transmits state information to the main controller.

6 is a block diagram of a PWM converter controller included in a module controller 22 having a feed forward compensation term according to the present invention. Conventionally, the voltage of the DC link v _dc is fed back to the front of the voltage controller 34 to control the PWM by the PWM converter 39 in comparison with the voltage reference value v _{dc_ref.} Similarly, in order to match the response curves of the PWM feedback value 8 and the inverter feedback value 9 in FIG. 2 to improve the response, the current command value i _{qe_ff} is _fed to the input of the current controller 36 of the PWM converter controller. feed forward). Matching the response curves of the PWM feedback value 8 and the inverter feedback value 9 means that the variation of the DC link voltage is eliminated. For this purpose (response improvement), the current forward compensation value 40 is input between the output of the voltage controller 34 and the input of the current controller 36, unlike the feedback of the voltage reference value.

Here, since PWM conversion is performed by reflecting the current command value, i.e., the forward compensation value 40 i _{qe_ff} calculated as in Equation 3, the DC link voltage can be reduced, thereby reducing the capacity of the DC link capacitor. . That is, the capacitance value required for the same DC link voltage variation can be reduced.

The current controller 36 was constructed using a PI controller to have the same transfer function as the first order lowpass filter. In addition, the control period of the converter was selected to be the same as the control period of the inverter, and the cutoff frequency of the current controller was set to be the same. That is, the controller is designed to have the same responsiveness to the same current command value.

The principle of FIG. 6 is described theoretically as follows. _Converts the speed controller output (i _{dqse_ref} ) of the inverter on the synchronous coordinate system having the d-axis and the q-axis and the current controller output (v _{dqse_ref} ) of the inverter into command values for each phase of the stationary coordinate system (Equation 1). In Equation 1, a, b, and c refer to each phase.

Multiplying the voltage and current command value converted from the above equation to the stationary coordinate system calculates the inverter module output power as shown in Equation 2.

로부터 수학식 3과 같이 구할 수 있다. 여기서

는 컨버터의 3상 입력 상전압의 최대값을 의미한다. Therefore, the current compensation value i _{qe_ff} of the PWM converter is the output power P _{xs_ff} of the inverter module obtained from Equation 2 and the input power supply voltage on the synchronous coordinate system.

It can be obtained from Eq. here

Is the maximum value of the three-phase input phase voltage of the converter.

In addition, the size of the DC link capacitor can be reduced by forward compensating the current compensation value of the PWM converter calculated from the output power of the inverter module to the PWM converter controller. There is an effect of reducing the capacitance required for the same DC link voltage variation.

The best embodiments have been disclosed in the drawings and specification above. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

According to the present invention, as the PWM converter monitors the operation state of the induction motor driving inverter, it can provide fast response that cannot be realized by the voltage controller of the conventional PWM converter. That is, even in a transient state such as acceleration and deceleration of the motor, the DC link voltage of each module can be kept constant to prevent overvoltage or undervoltage. In addition, DC link capacitors can be reduced by forward compensating the power generated by the inverter module to the PWM converter. There is an effect of reducing the capacitance required for the same DC link voltage variation.

Claims (6)

PWM converter for converting AC input power to DC by PWM, PWM converter for controlling the PWM converter, the voltage controller, current controller, and PWM generator sequentially connected, and direct current output from the PWM converter to AC An inverter module for driving an induction motor by inverse conversion, and a multilevel inverter system comprising a DC link between the PWM converter and the inverter module. The voltage of the DC link is compared with a reference voltage value and fed back to the input of the voltage controller, And a current command value calculated from the output power of the inverter module is fed forward to the input of the current controller together with the output of the voltage controller. The current command value i _{qe_ff} fed forward to the input of the current controller is the output power P _{xs_ff} of the inverter module and the input power supply voltage on the synchronous coordinate system.

from

The PWM converter control device of the multi-level inverter system, characterized in that calculated by. The apparatus of claim 1, wherein the control period of the PWM converter is the same as the control period of the inverter module. PWM converter for converting AC input power to DC by PWM, PWM converter for controlling the PWM converter, the voltage controller, current controller, and PWM generator sequentially connected, and direct current output from the PWM converter to AC A control method in a multilevel inverter system comprising an inverter module for driving an induction motor by reverse conversion and a DC link between the PWM converter and the inverter module, Comparing the voltage of the DC link with a reference voltage value and feeding back to the input of the voltage controller, And a current command value calculated from the output power of the inverter module is added to the output of the voltage controller to feed forward to the input of the current controller. The current command value i _{qe_ff} fed forward to the input of the current controller is the output power P _{xs_ff} of the inverter module and the input power supply voltage on the synchronous coordinate system.

from

The PWM converter control method of a multilevel inverter system, characterized in that calculated by. The method of claim 4, wherein the control period of the PWM converter is the same as the control period of the inverter.

Images