As new energy and energy storage technologies advance rapidly, the control methods for Power Conversion System (PCS) have become more critical than ever. Acting as the core link between storage batteries and the power grid, these methods directly shape the system’s stability, power response, and grid compatibility.

Different control strategies lead to fundamentally different interactions between the converter and the grid. Today, the industry mainly adopts three technical approaches: PQ control, V/F control, and Virtual Synchronous Generator (VSG) control. Understanding their core differences, strengths, weaknesses, and applications is essential for designing and operating modern power systems. This article starts by introducing a fundamental classification—grid-forming versus grid-following—before diving into a detailed comparison of these strategies.

1. Two Core Control Modes: Grid-Forming vs. Grid-Following

To make sense of different control strategies, we can use a simple but powerful framework that sorts them into two main roles: the “leader” and the “follower”. This division helps clarify how inverters interact with the power grid.

1.1 Grid-Following Control: The Grid’s “Loyal Follower

Think of grid-following control as a “loyal follower” or a “controlled current source.” Its main job is to adapt to and follow an existing stable grid.

Using its internal Phase-Locked Loop (PLL) circuit, it precisely detects and locks onto the grid’s voltage waveform—much like a radar tracking a signal. This allows it to synchronize its own frequency and phase with the grid. Once synchronized, it injects or absorbs specific amounts of active power (P) and reactive power (Q) based on commands from a central dispatch system or preset values.

1.2 Grid-Forming Control: The Grid’s “Active Builder”

In contrast, grid-forming control acts as an “active builder” or a “controlled voltage source.” Instead of passively following the grid, a grid-forming inverter can actively establish and maintain its own stable AC grid.

It doesn’t rely on the external power grid. Instead, it independently generates a stable voltage waveform, setting the system’s voltage amplitude and frequency. This allows it to operate autonomously without support from a main grid—making it ideal for islanded systems, microgrids, or black-start recovery scenarios.

2. In-Depth Comparison: Three Mainstream Control Strategies

Now that we understand the core concepts, let’s examine how the three main control strategies stack up in practice.

2.1 PQ Control: The Precision Follower

PQ control represents the most straightforward grid-following approach. Its primary mission is precise power delivery according to dispatch commands.

The strength of PQ control lies in its simplicity and fast dynamic response. However, this comes with significant limitations. Since it depends entirely on a stable grid reference, it tends to struggle in weak grid environments where system strength is limited. During grid faults, PQ-controlled converters typically disconnect rather than providing support.

2.2 V/F Control: The Independent Operator

V/F control serves as the fundamental grid-forming approach, focusing on maintaining stable voltage and frequency regardless of load conditions.

This strategy excels in islanded operation where it can establish and maintain a stable microgrid. The trade-off comes in grid-connected operation, where V/F controllers show limited flexibility in managing power flow between sources.

2.3 VSG Control: The Intelligent Emulator

Virtual Synchronous Generator control represents the advanced evolution of grid-forming technology. By emulating the physical characteristics of traditional synchronous generators, VSG controllers provide both voltage formation and crucial inertial response.

The key advantage here is inertial support – VSG controllers naturally resist frequency changes, just like rotating masses in conventional generators. This makes them particularly valuable in grids with high renewable penetration. While more complex to implement, VSG technology addresses the inertia gap that pure power-electronics-based systems create.

3. Practical Applications and Future Trends

Making the Right Choice

Each control strategy serves distinct purposes:

• Choose PQ control when you need precise power tracking in strong grid conditions
• Select V/F control for independent microgrid operation and black-start capability
• Implement VSG control when you need to strengthen weak grids and provide inertial support

The Industry Shift

We’re witnessing a significant transition in power system design. As inverter-based resources replace conventional generators, the natural inertia that traditionally stabilized our grids is disappearing.

This creates a growing need for grid-forming capabilities – particularly advanced approaches like VSG that can replicate the stabilizing effects of rotating masses. Looking ahead, we expect grid-forming technology to evolve from a specialized solution to a standard requirement for new energy storage projects.

Conclusion: Building More Resilient Power Systems

The choice between grid-following and grid-forming strategies is no longer just a technical detail – it’s becoming a strategic decision that affects overall system reliability. While grid-following solutions like PQ control will continue to serve specific applications, the industry’s clear direction points toward wider adoption of grid-forming technologies.

For system designers and operators, understanding these differences is crucial for building the resilient, renewable-powered grids of the future.